rnac-20251231

UNITED STATES SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 10-K

For the fiscal year ended December 31, 2025

For the transition period from ____ to ____

Commission file number: 001-37798

Cartesian Therapeutics, Inc.

(Exact name of registrant as specified in its charter)

(Address of principal executive offices) (Zip Code)

(301) 348-8698

Registrant’s telephone number, including area code

Securities registered pursuant to Section 12(b) of the Act:

Title of each class Trading Symbol(s) Name of each exchange on which registered

Common Stock, $0.0001 par value per share RNAC The Nasdaq Stock Market LLC

Securities registered pursuant to Section 12(g) of the Act:

Title of each class

Contingent Value Rights

Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act. Yes o Noþ

Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or Section 15(d) of the Act. Yes o Noþ

Indicate by check mark whether the registrant: (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports); and (2) has been subject to such filing requirements for the past 90 days. Yesþ No o

Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit and post such files). Yesþ No o

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company, or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

Large accelerated filer ☐ Accelerated filer ☐

Non-accelerated filer þ Smaller reporting company þ

Emerging growth company ☐

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to section 13(a) of the Exchange Act. ☐

Indicate by check mark whether the registrant has filed a report on and attested to its management’s assessment of the effectiveness of its internal control over financial reporting under Section 404(b) of the Sarbanes-Oxley Act (15 U.S.C. 7262(b)) by the registered public accounting firm that prepared or issued its audit report. ☐

If securities are registered pursuant to Section 12(b) of the Act, indicate by check mark whether the financial statements of the registrant included in the filing reflect the correction of an error to previously issued financial statements. o

Indicate by check mark whether any of those error corrections are restatements that required a recovery analysis of incentive-based compensation received by any of the registrant’s executive officers during the relevant recovery period pursuant to §240.10D-1(b). o

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act). Yes ☐ No þ

The aggregate market value of common stock held by non-affiliates of the registrant based on the closing price of the registrant’s common stock as reported on the Nasdaq Stock Market on June 30, 2025, the last business day of the registrant’s most recently completed second quarter, was $108,739,558.

As of February 28, 2026, the registrant had 26,509,024 shares of common stock, par value $0.0001 per share, outstanding.

DOCUMENTS INCORPORATED BY REFERENCE

Portions of the registrant’s definitive Proxy Statement relating to its 2026 Annual Meeting of Stockholders to be filed with the Securities and Exchange Commission are incorporated by reference into Part III of this Annual Report on Form 10-K.

TABLE OF CONTENTS

Part I

Page

Item 1. Business 6

Item 1A. Risk Factors 29

Item 1B. Unresolved Staff Comments 57

Item 1C. Cybersecurity 57

Item 2. Properties 58

Item 3. Legal Proceedings 58

Item 4. Mine Safety Disclosures 58

Part II

Item 6. [Reserved] 59

Item 7A. Quantitative and Qualitative Disclosures About Market Risk 72

Item 8. Financial Statements and Supplementary Data 72

Item 9A. Controls and Procedures 72

Item 9B. Other Information 73

Item 9C. Disclosure Regarding Foreign Jurisdictions that Prevent Inspections 73

Part III

Item 10. Directors, Executive Officers and Corporate Governance 74

Item 11. Executive Compensation 74

Item 14. Principal Accountant Fees and Services 74

Part IV

Item 15. Exhibits and Financial Statement Schedules 75

Signatures 79

FORWARD-LOOKING STATEMENTS

This Annual Report on Form 10-K, or the Annual Report, contains forward-looking statements. We intend such forward-looking statements to be covered by the safe harbor provisions for forward-looking statements contained in Section 27A of the Securities Act of 1933, as amended, or the Securities Act, and Section 21E of the Securities Exchange Act of 1934, as amended, or the Exchange Act. All statements other than statements of historical facts contained in this Annual Report, including statements regarding our future results of operations and financial position, business strategy, prospective products, product approvals, research and development costs, timing and likelihood of success, the plans and objectives of management for future operations and future results of anticipated products, and the period over which we estimate our existing cash and cash equivalents will be sufficient to fund our future operating expenses and capital expenditure requirements are forward-looking statements. These statements involve known and unknown risks, uncertainties and other important factors that may cause our actual results, performance or achievements to be materially different from any future results, performance or achievements expressed or implied by the forward-looking statements.

In some cases, you can identify forward-looking statements by terms such as “may,” “will,” “should,” “expect,” “plan,” “anticipate,” “could,” “intend,” “target,” “project,” “contemplate,” “believe,” “estimate,” “predict,” “potential”, or “continue” or the negative of these terms or other similar expressions. The forward-looking statements in this Annual Report are only predictions. We have based these forward-looking statements largely on our current expectations and projections about future events and financial trends that we believe may affect our business, financial condition and results of operations. These forward-looking statements speak only as of the date of this Annual Report and are subject to a number of important factors that could cause actual results to differ materially from those in the forward-looking statements, including the factors described under the sections in this Annual Report titled “Risk Factors” and “Management’s Discussion and Analysis of Financial Condition and Results of Operations” as well as the following:

•our future results of operations and financial position, business strategy, and the length of time that we believe our existing cash resources will fund our operations;

•our market size and our potential growth opportunities;

•our preclinical and clinical development activities;

•our dependence on third-parties, including contract research organizations, or CROs, in the conduct of our pre-clinical studies and clinical trials;

•the efficacy and safety profile of our product candidates;

•the potential therapeutic benefits and economic value of our product candidates;

•the timing and results of preclinical studies and clinical trials;

•the potential impairment of our goodwill and indefinite lived intangible assets;

•the expected impact of macroeconomic conditions, including inflation, increasing interest rates and volatile market conditions, current or potential bank failures;

•the impact of global events, including the ongoing conflicts between Russia and Ukraine, the ongoing conflict in the Middle East and geopolitical tensions with China;

•the impact of political uncertainty on our product development;

•the receipt and timing of potential regulatory designations, approvals and commercialization of our product candidates;

•our ability to prevent or minimize the effects of litigation and other contingencies;

•our status as a development-stage company and our expectation to incur losses in the future, and the possibility that we never achieve or maintain profitability;

•uncertainties with respect to our ability to access future capital;

•our ability to maximize the value of our pipeline of product candidates;

•our unproven approach to therapeutic intervention;

•our ability to enroll patients in clinical trials, timely and successfully complete those trials and receive necessary regulatory approvals;

•our ability to continue to grow our manufacturing capabilities and resources;

•our ability to manufacture our product candidates, which in some cases are manufactured on a patient-by-patient basis;

•our ability to receive or manufacture sufficient quantities of our product candidates;

•our ability to maintain our existing or future collaborations or licenses and to seek new collaborations, licenses or partnerships;

•our ability to protect and enforce our intellectual property rights;

•federal, state, and foreign regulatory requirements, including U.S. Food and Drug Administration, or FDA, regulation of our product candidates;

•our ability to obtain and retain key executives and retain qualified personnel:

•developments relating to our competitors and our industry:

•any future payouts under the contingent value right, or CVR, issued to our holders of record as of the close of business on December 4, 2023; and

•our ability to monetize any of our legacy assets.

Moreover, we operate in an evolving environment. New risks and uncertainties may emerge from time to time, and it is not possible for management to predict all risk and uncertainties.

You should read this Annual Report and the documents that we reference in this Annual Report completely and with the understanding that our actual future results may be materially different from what we expect. We qualify all of our forward-looking statements by these cautionary statements. Except as required by applicable law, we do not plan to publicly update or revise any forward-looking statements contained herein, whether as a result of any new information, future events, changed circumstances or otherwise.

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PART I

Item 1. Business

Our Corporate History and Background

The Company (formerly known as Selecta Biosciences, Inc., or Selecta) was incorporated in Delaware on December 10, 2007, and is headquartered in Frederick, Maryland. On November 13, 2023, the Company and the Delaware corporation which, immediately prior to the Merger (as defined below), was known as Cartesian Therapeutics, Inc., or Old Cartesian, entered into an Agreement and Plan of Merger, or the Merger Agreement, by and among the Company, Sakura Merger Sub I, Inc., a Delaware corporation and a wholly owned subsidiary of the Company, or First Merger Sub, Sakura Merger Sub II, LLC, a Delaware limited liability company and wholly owned subsidiary of the Company, or Second Merger Sub, and Old Cartesian. Pursuant to the Merger Agreement, and simultaneously with execution thereof, (i) First Merger Sub merged with and into Old Cartesian, pursuant to which Old Cartesian was the surviving corporation, or the First Step Surviving Corporation, and became a wholly owned subsidiary of the Company, or the First Merger, and (ii) immediately following the First Merger, Old Cartesian (as the First Step Surviving Corporation) merged with and into Second Merger Sub, pursuant to which Second Merger Sub was the surviving company, or the Surviving Company, and continued under the name “Cartesian Bio, LLC”, or the Second Merger and, together with the First Merger, the Merger. In connection with the Merger and pursuant to the Merger Agreement, the Company (which was known as Selecta Biosciences, Inc. until immediately prior to the Merger) changed its corporate name to Cartesian Therapeutics, Inc.

Overview

We are a late clinical-stage biotechnology company pioneering cell therapy for the treatment of autoimmune diseases. We leverage our proprietary technology and manufacturing platform to introduce mRNA into cells to provide a therapeutic effect to patients suffering from a variety of autoimmune conditions. Unlike DNA, mRNA degrades naturally over time without integrating into the cell’s genetic material. Our cell therapies are designed to be dosed repeatedly like conventional drugs, administered in an outpatient setting and given without pre-treatment chemotherapy required with many conventional cell therapies.

Autoimmune diseases, where the immune system mistakenly attacks the body, are a family of more than 80 disorders. These diseases are typically treated with immunosuppressant medications, such as steroids, biologics and non-steroidal agents such as methotrexate, CD19 directed therapies and intravenous immunoglobulin. These treatments must be administered chronically and carry risks, including infection, osteoporosis and metabolic disease. The treatment landscape within generalized myasthenia gravis, or MG, offers agents that block the complement pathway or inhibit the neonatal Fc receptor, or FcRn, that typically must be administered chronically. Even with recent treatment advancements in the field of MG, we believe there remains a significant unmet need for outpatient treatments, administered over a short period of time, and can provide deep and durable clinical benefit.

Limitations of Current Biologic Treatments in Autoimmune Disease

Currently approved biologic therapies for MG, such as complement inhibitors and FcRn inhibitors have improved treatment options. However, these therapies are still limited by incomplete response, chronic dosing required to mitigate symptoms, immunosuppression risks, high treatment burden and lack of disease modification.

Not all patients with acetylcholine receptor autoantibody positive, or AChR+ MG, the subtype currently being pursued in our Phase 3 AURORA trial, respond adequately to currently approved biologics. We believe the variability in treatment response may be due to differences in underlying disease pathologies, with some patients having disease drivers beyond complement activation (for complement inhibitors) or immunoglobulin G, or IgG, reduction (for FcRn inhibitors). Additionally, some patients experience an initial improvement but later lose response, requiring adjustments in their treatment strategy.

Biologic therapies used for MG can increase the risk of infections. Complement inhibitors in particular, heighten susceptibility to Neisseria infections, necessitating vaccination and, in some cases, prophylactic antibiotic use. Patients receiving FcRn inhibitors may also experience an increased risk of infections due to immunoglobulin depletion. The long-term safety of these treatments remain an area of active study.

Currently approved biologic therapies require frequent infusions, which can be burdensome for patients. Efgartigimod (Vyvgart) and rozanolixizumab (Rystiggo) both require weekly infusions in repeated cycles, while zilucoplan (Zilbrysq) is administered daily, both nipocalimab-aahu (Imaavy) and eculizumab (Soliris) are administered every two weeks, ravulizumab (Ultomiris) every eight weeks for most body weights and inebilizumab-cdon (Uplizna) every six months following two initial doses. While ravulizumab and inebilizumab-cdon each reduce the frequency of infusions compared to eculizumab, both of these

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treatments require ongoing maintenance, which may impact patient quality of life. Access to infusion centers or home infusion services further adds to the logistical challenges.

The majority of approved biologic therapies for the treatment of MG focus on the management of symptoms rather than addressing the root cause of the disease. These treatments do not eliminate the underlying autoimmune process or autoreactive B and T cells, meaning patients typically require chronic lifelong therapy. While symptom control is critical, the need for continuous treatment highlights the unmet need for therapies that can induce long-term remission and a precision immune reset.

Limitations of Current DNA-Based Cell Therapy Treatments in Autoimmune Disease

Compared to biologic therapies, cell therapies have increased potential to provide a deep and durable clinical benefit; however, conventional DNA cell therapies have been associated with cytokine release syndrome, or CRS, neurological toxicities and Parkinsonism, infection, risk of secondary malignancy and death. The acute toxicities are from exponential amplification of the modified cell and the pre-treatment chemotherapy administered to enable cell amplification.

Conventional DNA-engineered chimeric antigen receptor, or CAR, T-cells are in clinical development for several autoimmune diseases. DNA CAR-T cells are typically administered to patients in a subtherapeutic dose, which means that the cells must proliferate to reach therapeutic numbers in the body. However, this proliferation is not controlled in magnitude nor duration, varies from patient to patient, and can be unpredictable. This proliferation occurs because the CAR gene is irreversibly integrated into the T-cell’s genome, causing a cascade in which every daughter cell carries the same CAR as the parent cells. The resulting unconstrained proliferation frequently exceeds the toxicity threshold, leading to serious adverse events, or SAEs.

The proliferation of DNA CAR-T cells typically requires pre-treatment chemotherapy, usually fludarabine and cyclophosphamide, administered for several days before CAR-T cell treatment. This chemotherapy is toxic, suppressing the immune system and increasing the risk of infection, anemia, and neurotoxicity.

Given these risks and requirements, conventional DNA cell therapies are administered under close monitoring in an inpatient setting, increasing their cost and limiting their reach to only the sickest patients.

Our Autoimmune Disease Solution

Descartes-08, our lead cell therapy product candidate, is an autologous CAR-T product targeting B-cell maturation antigen, or BCMA, in clinical development for the treatment of MG and myositis, specifically, moderate to severe multi-refractory dermatomyositis and antisynthetase syndrome. In contrast to conventional DNA-based CAR T-cell therapies, our CAR-T administration has been observed to provide deep and durable benefits through 12 months, is designed to not require preconditioning chemotherapy, to be administered in the outpatient setting and does not carry the risk of genomic integration associated with cancerous transformation. Descartes-08 has been granted Orphan Drug Designation and Regenerative Medicine Advanced Therapy, or RMAT, Designation by the FDA for the treatment of MG, and Rare Pediatric Disease Designation for the treatment of juvenile dermatomyositis, or JDM.

Based on efficacy and safety data observed in our clinical trials thus far, we believe our cell therapies have the potential to deliver deep and durable clinical benefit to a broad group of patients with autoimmune diseases after a single course of therapy. We aim to provide a personalized approach to treating patients that begins with the collection of a patient’s cells which we then use to manufacture our cell therapy product candidates. Once a patient’s cells have expanded in our process, we introduce mRNA to deliver a CAR into the cell. Once the manufacturing process is complete, we send the product candidate back to the treating physician where they administer six weekly infusions of our cell therapy to the patient. Descartes-08 is specifically designed to target and destroy the pathogenic, self-reactive cells that are the underlying cause of the autoimmune disease, with the goal of creating a precision immune reset for the patient.

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The table below summarizes key information about our development pipeline.

As of December 31, 2025, we have administered Descartes-08 to over 100 patients suffering from one of MG, multiple myeloma, and other diseases in open-label and randomized placebo-controlled trials on an outpatient basis. We have not observed product-related CRS, neurotoxicity or infection of any grade. The most common product-related adverse events, or AEs, observed, headache, nausea, and fever, were self-limited and resolved within 24 hours of onset.

Our Product Candidates

Descartes-08 for the Treatment of MG

Overview

Descartes-08 has been granted Orphan Drug Designation by the FDA for the treatment of MG. We chose MG as our lead indication because the pathogenesis for MG is common to many autoimmune diseases.

Background Information About MG

MG is a rare autoimmune disease that causes debilitating muscle weakness and fatigue. It is estimated to affect over 106,000 patients in the U.S. MG patients develop antibodies that lead to an immunological attack on critical signaling proteins at the junction between nerve and muscle cells, thereby inhibiting the ability of nerves to communicate properly with muscles. This results in muscle weakness in tissues throughout the body, potentially manifesting in partial paralysis of eye movements, problems in chewing and swallowing, respiratory problems, speech difficulties and weakness in skeletal muscles. As the disease progresses, symptom-free periods become less frequent and disease exacerbations can last for months. Disease symptoms reach their maximum levels within two to three years in approximately 80% of patients. Up to 20% of MG patients experience a respiratory crisis at least once in their lives. During the crisis phase, decline in respiratory function can become life-threatening. Patients in crisis often require intubation and mechanical ventilation.

There are no known cures for MG and the current standard of care consists of chronic use of steroids and other immunosuppressants. These treatments must be administered continually and carry risks such as infection, osteoporosis, and metabolic diseases. Newer agents, such as those that block the complement pathway or inhibit FcRn, are typically administered continually.

Clinical Development

To date, we have completed a Phase 1/2 trial of Descartes-08 in MG, which consisted of a Phase 1b portion, a Phase 2a portion, and a Phase 2b portion.

The primary objective of the Phase 1b portion of the trial was to determine the maximum tolerated dose of Descartes-08 for patients with MG. We observed Descartes-08 to be well-tolerated by the three patients who participated in this portion of the trial with no CRS or other serious product-related AEs observed.

The primary objective of the Phase 2a portion of the trial was to determine the optimal dosing schedule for patients with MG using the highest dose level tested in Phase 1b (52.5 x106 cells/kg). This portion of the trial was designed to assess the safety and preliminary efficacy of Descartes-08 when administered across three different treatment schedules (six doses given twice-weekly, once-weekly, or once-monthly). This portion of the trial evaluated 11 patients with particularly advanced disease

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as assessed by both patient and clinician-reported outcomes. 11 of the 14 patients included in the Phase 1b and Phase 2a portions of the trial were classified at screening to have Class III or IV disease, as defined by the Myasthenia Gravis Foundation of America, indicating they had moderate-to-severe weakness affecting their muscles.

The results of the Phase 2a portion of the trial, published in the Lancet Neurology in July 2023, indicated that after six weekly infusions of Descartes-08, the average improvement in all disease severity scores was three-to-five-fold greater than what is considered clinically meaningful by expert consensus. As shown in the figure below, clinical improvements persisted in all patients at Month 9, and in five of the seven remaining patients at a final, 12-month follow-up. Descartes-08 was observed to be well-tolerated with no reports of dose-limiting toxicities, CRS or neurotoxicity.

A–C: Mean change from Baseline (line) and standard error (bands) in Myasthenia Gravis Activities of Daily Living Score (MG-ADL, A), Quantitative Myasthenia Gravis Score (QMG, B), Myasthenia Gravis Composite Score (MGC, C) during 12 months of follow-up for MG-001 participants who received six once-weekly doses (n=7). MG-ADL is self-reported; MGC and QMG are neurologist-assessed.

All three participants with detectable anti-acetylcholine receptor antibody levels before treatment had an average 42% reduction in antibody levels by Month 6. These reductions deepened to 68% by Month 9 and persisted at Month 12. In summary, we observed continued clinical improvement and autoantibody reductions after BCMA directed mRNA CAR-T treatment for MG that persisted through the one-year follow-up period.

Follow-on results of the Phase 2b portion of the trial were presented in December 2024. The trial achieved its primary endpoint to assess the proportion of patients achieving a five-point or greater reduction in their MGC score at day 85. Patients received six weekly infusions at the dose established in Phase 1b (52.5 x106 cells/kg). The trial also involved a crossover component in which any patient originally assigned to placebo was given the opportunity to receive Descartes-08 after completing trial treatment.

In April, 2025, we reported updated, 12-month data from this trial and published this data in Nature Medicine in January 2026.

Deepening of responses was observed over time with participants included in the primary efficacy dataset who continued follow-up (n=12) experiencing an average MG-ADL reduction of 5.5 (±1.1) at Month 4 which was maintained through Month 12 (4.8±1.4). At Month 4, particularly deep responses were observed in participants without prior exposure to biologic therapies (n=7), including complement or neonatal fragment crystallizable receptor inhibitors, with an average MG-ADL reduction of 6.6 (±1.5). Responses amongst this patient population without prior exposure to biologic therapies were observed to deepen through Month 12 with an average MG-ADL reduction of 7.1 (±1.9). The deepest responses were observed as minimal symptom expression, or MSE, defined as an MG-ADL score of 0 or 1.

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The tables below set forth the results observed.

33% (4/12) of participants in the primary efficacy dataset and 57% (4/7) of participants with no prior exposure to biologic therapy were observed to achieve MSE by Month 6 and maintained it through Month 12. Responses were observed to be durable through Month 12, with 83% (10/12) of evaluable participants from the primary efficacy dataset maintaining a clinically meaningful response, defined as a reduction in MG-ADL score of at least 2 points. Of the seven participants with no prior exposure to biologic therapy that reached Month 12, 100% maintained at least a clinically meaningful response.

The safety profile observed in the follow-up portion of the Phase 2b trial was in line with what we reported at the time of our top line data readout as well as the Phase 2a portion of the trial. Of note, there was a Grade 2 upper respiratory infection reported in both the Descartes-08 and placebo groups. There were no other new AEs reported after Month 3 follow-up, including no hypogammaglobulinemia and other infections and there was no difference in vaccine titers between Descartes-08 and placebo.

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The table below summarizes the safety results observed.

We previously reported that there were three participants in the Phase 2a portion of the trial who were observed to have a response to Descartes-08, but then reverted to baseline, two patients one year after treatment and the other 1.5 years after treatment. As previously reported, there were two participants who were retreated and experienced rapid improvements in clinical scores and maintained minimum symptom expression for up to one year after receiving a second treatment cycle.

The tables below set forth key findings from these patients.

The time course and magnitude of treatment response upon retreatment were similar to those seen when the participants were first treated. Notably, in the one participant who completed their 12-month retreatment follow-up visit, the duration of response was observed to be longer than that patient’s initial response, and this patient had maintained minimum symptom expression at Month 12. The third retreated participant’s responses deepened from a 4-point MG-ADL reduction at Month 2 to a 9-point improvement in MG-ADL at Month 12 following retreatment.

In May 2025, we initiated our Phase 3 AURORA trial of Descartes-08 in patients with MG. The randomized, double-blind, placebo-controlled Phase 3 AURORA trial is designed to assess Descartes-08 versus placebo (1:1 randomization) administered as six weekly outpatient infusions without preconditioning chemotherapy in approximately 100 participants with AChR Ab+, MG. The primary endpoint will assess the proportion of Descartes-08 participants with an improvement in MG-ADL score of

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three points or more at Month 4 compared to placebo. Secondary endpoints will assess safety and tolerability and the proportion of participants with a reduction of four points or more in MG Composite, or MGC, score, as well as improvements in other validated MG severity scales, including QMG, and MG Quality of Life Revised Scale, or MG-QoL-15R. In January 2025, we received written agreement from the FDA under the Special Protocol Assessment, or SPA, process on the overall design of our planned AURORA trial. The SPA agreement indicates that the FDA has determined that the proposed trial design is acceptable to support a future Biologics License Application, or BLA, for Descartes-08 in MG, subject to the ultimate outcome of the trial.

The complete trial design for AURORA is set forth below.

Descartes-08 for the Treatment of Myositis

Background Information About Myositis

Myositis is a rare set of pathogenic autoantibody-driven diseases characterized by inflammation and muscle weakness. Myositis symptoms can range from mild to life-threatening and symptoms often include muscle weakness, joint or muscle pain, fatigue, swelling, trouble breathing or swallowing, and arrhythmia. Myositis impacts approximately 80,000 people in the United States.

Next Steps

Based on strong mechanistic alignment with our existing clinical data in MG and SLE as well as the significant unmet need that remains, in November 2025 we announced the expansion of our development of Descartes-08 into myositis, specifically dermatomyositis and antisynthetase syndrome, a significantly underserved market with high unmet need. The FDA accepted our investigational new drug application, or IND, in December 2025 for a clinical trial design which provides a potential opportunity for a single pivotal trial. We expect to commence this trial in the first half of 2026.

Our randomized, double-blind, placebo-controlled Phase 2 trial in myositis is designed to assess Descartes-08 versus placebo (1:1 randomization) administered as six weekly outpatient infusions without preconditioning chemotherapy in up to 50 patients with moderate to severe multi-refractory dermatomyositis and antisynthetase syndrome. The primary endpoint is expected to assess safety and efficacy of Descartes-08 compared to placebo added to standard of care in participants with myositis at Week 24. We currently intend to conduct a blinded interim analysis through the Data Safety Monitoring Board, or DSMB, after ten patients are enrolled and reach the primary endpoint, at which point we may revise sample size assumptions to what could be necessary to support the trial becoming pivotal, pending FDA review.

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The complete trial design for this trial is set forth below.

Descartes-08 for the Treatment of Juvenile Dermatomyositis

Background Information About Juvenile Dermatomyositis

Juvenile Dermatomyositis is a rare pediatric autoimmune disorder marked by pathognomonic skin rash and muscle inflammation affecting multiple organ systems including the joints, heart, lungs, kidneys, eyes, and gastrointestinal systems. The symptoms of JDM can range from mild to life-threatening and symptoms often include fatigue, joint pain, muscle weakness and fever. JDM impacts approximately 4,000 people in the United States.

Clinical Development

In December 2024, we filed an amendment to the IND for a pediatric basket trial including juvenile dermatomyositis, or JDM. The initiation of the Phase 2 pediatric basket trial was announced in January 2026. The FDA has also granted Descartes-08 Rare Pediatric Disease Designation for the treatment of JDM. The FDA grants Rare Pediatric Disease Designation for serious and life-threatening diseases that primarily affect children ages 18 years or younger and fewer than 200,000 people in the United States. Under the FDA’s recently renewed Rare Pediatric Disease Designation and priority review voucher programs, if Descartes-08 is approved for marketing in JDM, Cartesian may qualify for a priority review voucher that can be redeemed to receive priority review of a subsequent marketing application for a different product candidate.

Descartes-08 for the Treatment of Systemic Lupus Erythematosus

Overview

In November 2025, we announced topline data from our Phase 2 trial in SLE, a chronic autoimmune disease that causes systemic inflammation which affects multiple organ systems. We also announced a pause in further development of Descartes-08 in SLE, including further enrollment in the Phase 2 trial, in order to prioritize opportunities in MG and myositis. Shortly thereafter we made a further decision to no longer pursue development of Descartes-08 in SLE. The Phase 2 trial in SLE remains ongoing for follow-up only.

Background Information About Systemic Lupus Erythematosus

SLE is a chronic, immune-mediated connective tissue disease that can impact nearly all major organ systems. The most common manifestations of SLE are cutaneous and musculoskeletal symptoms, although neurological, gastrointestinal, hematological, and renal symptoms are regularly observed as well. Patients with SLE are at a substantially increased risk of infection and cardiovascular disease, contributing to estimated 10- and 15-year mortality rates of 9% and 15%, respectively. SLE is the most common form of lupus, representing approximately 70% of lupus patients, and approximately three million adults worldwide are estimated to have SLE.

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Clinical Development

The Phase 2 open-label trial was designed to evaluate outpatient administration of Descartes-08 without preconditioning chemotherapy or integrating vectors for the treatment of patients with moderate or severe SLE refractory to immunosuppressant therapy. The primary outcome measure assesses safety and tolerability, with secondary outcome measures assessing preliminary efficacy.

The complete trial design is set forth below.

The tables below set forth the results of the Phase 2 trial.

Initial data from the Phase 2 trial reported significant reduction in disease activity following initial Descartes-08 treatment with 100% of participants who reached Month 3 follow-up (n=3) achieving Lupus Low Disease Activity State, or LLDAS, response, defined by specific criteria that indicate low disease activity, improved patient outcomes, and sustained symptom improvement. Disease remission reported as DORIS response was seen in 2 out of 3 participants at Month 3. DORIS is defined as the Definition of Response in SLE indicating a clinical SLE Disease Activity Index, or SLEDAI-2K score of 0 and physician global assessment, or PGA, of less than 0.5. We believe these results suggest that Descartes-08 may have clinical effect in the field of autoimmune disease broadly.

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The tables below set forth the safety results from the Phase 2 trial.

In this trial, Descartes-08 continued to be observed as well-tolerated, supporting outpatient administration without the need for lymphodepleting chemotherapy. AEs reported were transient and mostly mild, with no AEs above Grade 2 or SAEs and notably, there were no cases of CRS and no cases of immune effector cell-associated neurotoxicity syndrome. Infusion-related fever and flu-like symptoms were the most common AEs, and all resolved within 24 hours. No hypogammaglobulinemia or decrease in vaccine titers were observed and immunoglobulin levels were consistent with measurements at baseline.

We believe observations of correlative biomarkers support application of Descartes-08 in multiple autoimmune diseases. In particular, we observed a statistically significant (p<0.01) decrease in proinflammatory cytokines associated with SLE pathogenesis (IL7, IL10, CCL20, ST1A1). Additionally, significant decreases were observed in plasmacytoid dendritic cells, or pDCs, three months after receiving Descartes-08 in both MG and SLE patients, which we believe supports the expansion into myositis, given myositis’ known pDC correlation.

Descartes-15

Descartes-15 is a next-generation, autologous anti-BCMA mRNA CAR-T. Using our proprietary technology and manufacturing platform, we designed Descartes-15 to be more resistant than Descartes-08 to recycling of the CAR upon multiple antigen exposures. We observed that Descartes-15 was 10-fold more potent than Descartes-08 in preclinical studies. In November 2025, we reported results from the Phase 1 dose escalation trial designed to assess safety and tolerability of outpatient administration of Descartes-15 in patients with multiple myeloma. In this trial, no significant AEs or dose-limiting

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toxicities were reported in any of the three participants. The only Descartes-15-related adverse event was a grade 2 hypotension occurring after the first two infusions. Despite favorable safety data observed in this trial, we have paused further development of Descartes-15 to prioritize opportunities for Descartes-08 in MG and myositis.

In-Vivo Development

Our current pipeline consists of autologous treatments for patients. However, there have been recent advancements within the in-vivo space. An in-vivo cell therapy treats disease by modifying a patient’s cells inside their body, rather than doing so via autologous means. In-vivo treatment options create an opportunity for more convenient dosing with less frequent procedures. As we advance our pipeline, we continue to evaluate the potential of enhanced delivery platforms for our cell therapies with multiple feasibility studies underway to explore the potential timing for optimizing in-vivo delivery of our assets currently in development.

Manufacturing

We have established wholly-owned internal manufacturing and research and development capabilities, designed to allow us to optimize processes rapidly in an iterative manner and maintain control over the critical components of the supply chain. Our main manufacturing facility is located in Frederick, Maryland, and operates under current good manufacturing practice, or cGMP. This facility has sufficient capacity to support current clinical needs and can potentially transition to support commercial manufacturing of our maturing pipeline of innovative cell therapies for the treatment of autoimmune diseases. We believe the Frederick facility has the potential to allow us to scale our wholly-owned, in-house cGMP manufacturing capabilities for late-stage clinical and commercial supply of our cell therapy product candidates, while continuing to maintain control over product quality and production.

We manufacture Descartes-08 in-house and are typically able to process and release lots for infusion within approximately three weeks. Our autologous cell therapy product candidates, including Descartes-08, are manufactured on a patient-by-patient basis. We have optimized our manufacturing processes through over 200 cGMP runs across all of our current and prior programs.

Intellectual Property

Our success depends in part on our ability to obtain, maintain, protect, defend and enforce proprietary rights for our product candidates and other discoveries, inventions, trade secrets and know-how that are critical to our business operations. Our success also depends in part on our ability to operate without infringing, misappropriating or otherwise violating the proprietary rights of others, and in part on our ability to prevent others from infringing, misappropriating or violating our proprietary rights. A discussion of risks relating to intellectual property is provided under the section titled “Risk Factors—Risks Related to Our Intellectual Property.”

We intend to continue developing intellectual property, and we intend to aggressively protect our position in key technologies. Our patents are focused on several key technologies, including the use of our mRNA CAR-T technology and other developments in our mRNA cell therapy pipeline. As of December 31, 2025, we had seven issued patents worldwide, including three patents issued in the United States (U.S. Patent Nos. 10,934,337, 11,220,535, and 11,999,773) and four patents issued outside the United States (Japanese Patent No. 7,379,654, Canadian Patent No. 3,158,025, Israeli Patent No. 285909, and Korean Patent No. 102588292). Our issued patents and any patents issuing from our pending applications are set to expire on various dates ranging from 2040 to 2044. Additionally, as of December 31, 2025, we had 24 patent applications pending worldwide, including seven U.S. applications and seventeen applications in ex-U.S. jurisdictions. A patent granted from U.S. Patent Application No. 18/654,279 will expire on March 13, 2040, a patent granted from U.S. Patent Application No. 17/919,092 will expire on April 15, 2041, a patent granted from U.S. Patent Application No. 18/292,670 will expire on July 28, 2042, a patent granted from U.S. Patent Application No. 19/166,014 will expire on March 15, 2044, and a patent granted from U.S. Patent Application No. 19/166,759 will expire on March 20, 2044, excluding any potential patent term adjustments, patent term extensions, or terminal disclaimers. These U.S. patent applications are directed to compositions of matter, methods of use, and methods of manufacture. In addition, a patent granted on any of foreign patent applications EP 20773688.5, AU 2020241428, CA 3199205, CN 202080020956.1, IN 202117036675, KR 2023-7034215, and MX/a/2021/011196 will expire March 2040, a patent granted on European patent application 21789568.9 will expire April 2041, and a patent granted on any of foreign patent application EP 24775468.2, AU 2024240255, BR112025019788-6, CA 3286127, CN 202480031788.4, JP 2025-554182, KR 10-2025-7034765, MX/a/2025/010878, and SG 11202506142T will expire March 2044. All of these patent applications are composition-of-matter, methods-of-use, and/or methods-of-manufacture applications. There are also two pending U.S. provisional applications, and any patent ultimately claiming priority to one of these provisional applications will expire in or around 2046. In addition, as of December 31, 2025, we had two registered marks protecting our brand and prospective products both domestically and internationally. With respect to the legacy Selecta assets, as of December 31, 2025, we had (i) 294 issued patents worldwide, including 14 patents issued in the United States and 280 issued outside the United

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States, set to expire on various dates in 2032 through 2040, (ii) 75 patent applications pending worldwide, including 13 U.S. applications and 62 applications outside the United States and (iii) two registered marks.

In addition to patent protection, we also rely on trade secrets, know-how, trademarks, confidential information, other proprietary information and continuing technological innovation to develop, strengthen and maintain our competitive position. We seek to protect and maintain the confidentiality of proprietary information to protect aspects of our business that are not amenable to, or that we do not consider appropriate for, patent protection. Although we take steps to protect our proprietary information and trade secrets, including through contractual means with our employees, consultants, contractors and collaborators, third-parties may independently develop substantially equivalent proprietary information and techniques or otherwise gain access to our trade secrets or disclose our technology. Thus, we may not be able to meaningfully protect our trade secrets. It is our policy to require our employees, consultants, outside scientific collaborators, sponsored researchers and other advisors to execute confidentiality and invention assignment agreements upon the commencement of employment or consulting relationships with us. However, such confidentiality agreements can be breached, and we may not have adequate remedies for any such breach. For more information regarding the risks related to our intellectual property, see the section titled “Risk factors—Risks Related to Our Intellectual Property.”

Key Agreements

Biogen License Agreement

On September 8, 2023, we entered into a non-exclusive, sublicensable, worldwide, perpetual license agreement, or the Biogen Agreement, with Biogen MA, Inc., or Biogen, to research, develop, make, use, offer, sell and import products or processes containing or using an engineering T-cell modified with an mRNA comprising, or encoding a protein comprising, certain sequences licensed under the Biogen Agreement for the prevention, treatment, palliation and management of autoimmune diseases and disorders, excluding cancers, neoplastic disorders, and paraneoplastic disorders. We are not obligated to pay Biogen any expenses, fees, or royalties.

We may terminate the Biogen Agreement for any reason or no reason, and Biogen may terminate the agreement after a notice-and-cure period of 30 days if we fail to pay a fee owed to Biogen or for any other material breach of the agreement. The Biogen Agreement will otherwise expire when all claims of all issued patents within the patents and patent applications licensed to us under the Biogen Agreement have expired or been finally rendered revoked, invalid or unenforceable by a decision of a court or government agency.

The Biogen Agreement encompasses patents and patent applications in the PCT/US2010/026825 patent family, which was filed March 10, 2010. In general, all patents that issue in this family have an expected expiration date of March 10, 2030, subject to potential patent term adjustments and/or extensions. For the U.S. patents and applications in this family, U.S. Patent 9,034,324 was awarded 677 days of patent term adjustment, which would extend the expiration date of this patent to January 16, 2032, absent any challenges to the patent term. The other issued patent in this family was not awarded any patent term adjustment, so its expected expiration date is March 10, 2030.

NCI License Agreement

Effective September 16, 2019, we entered into a non-exclusive, worldwide license agreement, or the NCI Agreement, with the U.S. Department of Health and Human Services, represented by the National Cancer Institute of the National Institutes of Health, or NCI.

Under the NCI Agreement, we were granted a license under certain NCI patents and patent applications designated in the agreement, to make, use, sell, offer and import products and processes within the scope of the patents and applications licensed under the NCI Agreement when developing and manufacturing anti-BCMA CAR-T cell products for the treatment of MG, pemphigus vulgaris, and immune thrombocytopenic purpura according to methods designated in the NCI Agreement.

In connection with our entry into the NCI Agreement, we paid to NCI a one-time $100,000 license royalty payment. Under the NCI Agreement, we are further required to pay NCI a low five-digit annual royalty. We must also pay earned royalties on net sales in a low single-digit percentage and pay up to $0.8 million in benchmark royalties upon our achievement of designated benchmarks that are based on the commercial development plan agreed between the parties.

Under the NCI Agreement, we must use reasonable commercial efforts to bring licensed products and licensed processes to the point of Practical Application (as defined in the NCI Agreement). Upon our first commercial sale, we must use reasonable commercial efforts to make licensed products and licensed processes reasonably accessible to the United States public. After our first commercial sale, we must make reasonable quantities of licensed products or materials produced via licensed processes available to patient assistance programs and develop educational materials detailing the licensed products. Unless we obtain a waiver from NCI, we must have licensed products and licensed processes manufactured substantially in the United States. Prior

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to the first commercial sale, upon NCI’s request, we are obligated to provide NCI with commercially reasonable quantities of licensed products made through licensed processes to be used for in vitro research.

Additionally, we must use reasonable commercial efforts to initiate a Phase 3 clinical trial of a licensed product by the fourth quarter of 2024, submit a BLA with respect to a licensed product by the fourth quarter of 2026, and make a first commercial sale of a licensed product by the fourth quarter of 2028.

The NCI Agreement terminates upon the expiration of the last to expire of the patent rights licensed thereunder, if not sooner terminated. The NCI License Agreement encompasses patents and patent applications in the PCT/US2013/032029 patent family, which was filed March 15, 2013. In general, all patents that issue in this family have an expected expiration of March 15, 2033, subject to potential patent term adjustments and/or extensions. For the U.S. patents and applications in this family, only two patents were awarded patent term adjustments. U.S. Patent 9,765,342 was awarded 297 days of patent term adjustment, which would extend the expiration date of this patent to January 6, 2034, absent any challenges to the patent term. The other patent, U.S. Patent 10,876,123, was awarded three days of patent term adjustment, but this patent is subject to terminal disclaimers filed against other family members, so this patent will not extend beyond the March 15, 2033 date. The other issued patents in this family were not awarded any patent term adjustment, so the expected expiration date for these patents also remains March 15, 2033. There is also a pending patent application which, if issued, will expire on March 15, 2033, but could also be subject to patent term adjustment and to any potential future terminal disclaimers. NCI has the right to terminate this agreement, after giving written notice and providing a cure period in accordance with its terms, if we are in default of a material obligation. We have the unilateral right to terminate the agreement in any country or territory by giving NCI 60 days’ written notice. We agreed to indemnify NCI against any liability arising out of our, sublicensees’ or third-parties’ use of the licensed patent rights and licensed products or licensed processes developed in connection with the licensed patent rights.

Sobi License Agreement

On June 11, 2020, we entered into a License and Development Agreement with Swedish Orphan Biovitrum AB (publ.), or Sobi, which was amended on October 31, 2023, or, as so amended, the Sobi License. Pursuant to the Sobi License, we granted Sobi an exclusive, worldwide (except as to Greater China) license to develop, manufacture and commercialize a drug candidate Nanoecapsulated Sirolimus plus Pegadricase, or NASP, formerly known as SEL-212, which is currently in development for the treatment of chronic refractory gout. Pursuant to the Sobi License, Sobi agreed to make milestone payments totaling up to $630.0 million to us upon the achievement of various development and regulatory milestones and, if commercialized, sales thresholds for annual net sales of NASP, and tiered royalty payments ranging from the low double digits on the lowest sales tier to the high teens on the highest sales tier. Any proceeds received from milestone payments or royalties relating to the Sobi License would be required to be distributed to holders of CVRs, net of certain deductions.

The transactions contemplated by the Sobi License were consummated on July 28, 2020. Sobi may terminate the Sobi License for any reason upon 180 days’ written notice, whereby all rights granted under the Sobi License would revert back to us. In addition, if Sobi were to terminate the Sobi License, we have the option to obtain a license to all patents and know-how necessary to exploit NASP in existence as of the termination date from Sobi in return for making an equitable royalty payment to Sobi.

Competition

The biotechnology and pharmaceutical industries are characterized by rapidly advancing technologies, intense competition, and a strong emphasis on proprietary products. We face potential competition from many different sources, including pharmaceutical and biotechnology companies, academic institutions, governmental agencies and public and private research institutions. Product candidates that we successfully develop and commercialize may compete with existing therapies and new therapies that may become available in the future. Our competitors may have significantly greater financial resources, established presence in the market, expertise in research and development, manufacturing, preclinical and clinical testing, obtaining regulatory approvals and reimbursement and marketing approved products than we do. These competitors also compete with us in recruiting and retaining qualified scientific, sales, marketing and management personnel, establishing clinical trial sites and patient registration for clinical trials, as well as in acquiring technologies complementary to, or necessary for, our programs. Smaller or early-stage companies may also prove to be significant competitors, particularly through collaborative arrangements with large and established companies.

The key competitive factors affecting the success of any other cell therapy product candidates that we develop, if approved, are likely to be their efficacy, durability of response, safety, convenience, price, the level of generic competition and the availability of reimbursement from government and other third-party payors.

Our commercial opportunity could be reduced or eliminated if our competitors develop and commercialize products that are more effective, have fewer or less severe side effects, are more convenient or are less expensive than any products that we

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may develop. Our competitors also may obtain FDA or other regulatory approval for their products more rapidly than we may obtain approval for ours. In addition, our ability to compete may be affected in many cases by insurers or other third-party payors seeking to encourage the use of generic or biosimilar products.

Descartes-08 may compete with products of other companies in the MG market, including Amgen, Argenx SE, UCB S.A., Johnson & Johnson through its Janssen Pharmaceuticals, Inc. subsidiary, AstraZeneca PLC through its Alexion Pharmaceuticals, Inc. subsidiary, Kyverna Therapeutics, Inc. and Cabaletta Bio, Inc.

Other companies developing CAR-T therapies include large, fully integrated pharmaceutical companies such as Novartis AG, Gilead Sciences, Inc., through its Kite Pharma, Inc. subsidiary, Bristol-Myers Squibb Company, and biopharmaceutical companies such as Kyverna Therapeutics, Inc. and Cabaletta Bio, Inc.

Government Regulation

Government authorities in the United States, at the federal, state and local level, and in other countries, extensively regulate, among other things, the research, development, testing, manufacturing, quality control, approval, labeling, packaging, storage, record-keeping, promotion, advertising, distribution, post-approval monitoring and reporting, marketing and export and import of products such as those we are developing.

We believe our cell therapy product candidates are subject to regulation in the United States as “biologics” or “biological products.” We expect to seek approval of Descartes-08 through a BLA reviewed by FDA’s Center for Biologics Evaluation and Research, or CBER.

Biological products are subject to regulation under the Federal Food, Drug, and Cosmetic Act, or the FD&C Act, and the Public Health Service Act, or the PHS Act, and other federal, state, local and foreign statutes and regulations. Descartes-08 and any other product candidates that we develop must be approved by the FDA before they may be legally marketed in the United States and by the appropriate foreign regulatory agency before they may be legally marketed in foreign countries.

We regard our mRNA-modified products as cell therapy products and not as genetic engineering or gene therapy products, because mRNA modifications are not embodied in DNA or incorporated into a genome. However, it is possible that in some jurisdictions, regulations on genetic engineering or genetic therapy may intentionally or unintentionally apply to our technology. This could create additional regulatory burden.

U.S. Biological Products Development Process

The process required by the FDA before a biologic, including a cell therapy, may be marketed in the United States is summarized below.

Biological product candidates are preclinically tested before any testing is done in humans. These tests, or non-clinical studies, include laboratory evaluations of product chemistry, toxicity and formulation, as well as animal studies to assess the potential safety and activity of the product candidate. The conduct of the preclinical tests must comply with federal requirements including good laboratory practices, or GLPs.

The clinical study sponsor must submit the results of the preclinical tests, together with manufacturing information, analytical data, any available clinical data or literature and a proposed clinical protocol, to the FDA as part of the IND which must become effective before human clinical trials may begin. The IND automatically becomes effective 30 days after receipt by the FDA, unless the FDA places the clinical study on a clinical hold within that 30-day time period. In such a case, the IND sponsor and the FDA must resolve any outstanding concerns before the clinical study can begin. The FDA may also impose clinical holds on a biological product candidate at any time before or during clinical trials due to safety concerns, non-compliance with regulatory requirements, or other issues. If the FDA imposes a clinical hold, trials may not recommence without FDA authorization and then only under terms authorized by the FDA. In addition to these requirements, biological product candidates may also require evaluation and assessment by an institutional biosafety committee, or IBC, that reviews and oversees research utilizing recombinant or synthetic nucleic acid molecules at an institution participating in a clinical trial.

Clinical trials are conducted under protocols detailing the objectives of the clinical study, dosing procedures, patient selection and exclusion criteria, and the parameters to be used to monitor patient safety. Each protocol and any amendments to the protocol must be submitted to the FDA as part of the IND. Clinical trials must be conducted and monitored in accordance with the FDA’s regulations, including with respect to good clinical practice, or GCP, requirements, including the requirement that all research subjects provide informed consent. Further, each clinical study must be reviewed and approved by an institutional review board, or IRB, at or servicing each institution at which the clinical study will be conducted. Human clinical trials are typically conducted in three sequential phases that may overlap or be combined:

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•Phase 1. The biological product candidate is evaluated in a limited population of patients or healthy volunteers to identify the maximum tolerated dose, recommended Phase 2 dose, possible adverse effects and safety risks. For the types of products and therapeutic areas we focus on, Phase 1 studies will generally be done in patients and not healthy volunteers.

•Phase 2. The biological product candidate is evaluated in a broader population to evaluate safety further and preliminarily evaluate the efficacy of the product for specific targeted diseases, and to determine the optimal dosing schedule.

•Phase 3. Clinical trials are undertaken to further evaluate dosage, clinical efficacy, potency, and safety in an expanded patient population at geographically dispersed clinical study sites. These clinical trials are intended to establish the overall risk/benefit ratio of the product candidate and provide an adequate basis for product labeling.

Cell and gene therapy products may differ from the traditional clinical trial phases. For example, clinical trials for cell and gene therapy products are often structured as a hybrid Phase 1/2 trial where a small group of participants with the disease are enrolled and both safety and efficacy tests are performed.

Through the SPA process, a sponsor may seek agreement from the FDA on critical features of a proposed protocol for their adequacy to support marketing approval. In response to a request for an SPA agreement, the FDA issues a letter to the sponsor indicating its agreement or non-agreement with elements of the proposed protocol. An SPA agreement documents the FDA’s concurrence with the adequacy and acceptability of specific critical elements of the protocol design, and the FDA may not change an SPA agreement once the trial is underway unless the sponsor or applicant agrees in writing or the FDA identifies a substantial scientific issue essential to determining the safety or effectiveness of the drug after the testing has begun. Even if the sponsor conducts the trial in accordance with an SPA agreement and the trial meets its endpoints with statistical significance, there is no guarantee that the FDA will accept or approve a marketing application. For example, the FDA could determine that the overall balance of risks and benefits for the product candidate is not adequate to support approval, or only justifies approval for a narrow set of clinical uses or approval with restricted distribution or other post-approval requirements or limitations. In January 2025, we received written agreement under the SPA process on overall design of the our planned Phase 3 AURORA trial for Descartes-08 in MG. The SPA agreement indicates that the FDA has determined that the proposed trial design is acceptable to support a future BLA for Descartes-08 in MG, subject to the ultimate outcome of the trial.

Post-approval clinical trials, sometimes referred to as Phase 4 clinical trials, may be conducted after initial marketing approval to gain additional experience from the treatment of patients in the intended therapeutic indication, particularly for long-term safety follow-up.

The FDA or the sponsor or a separate data safety monitoring board may suspend or terminate a clinical study at any time on various grounds. Similarly, an IRB can suspend or terminate approval of a clinical study at its institution if the clinical study is not being conducted in accordance with the IRB’s requirements or if the biological product candidate has been associated with unexpected serious harm to patients or otherwise in the interest of patient welfare.

Sponsors of clinical trials of FDA-regulated products, including biologics, are also required to register and disclose certain clinical trial information, which is publicly available at www.clinicaltrials.gov.

After the completion of clinical trials of a biological product candidate, FDA approval of a BLA must be obtained before commercial marketing of the biological product. The BLA must include results of product development, laboratory and animal trials, human trials, information on the manufacture and composition of the product, proposed labeling and other relevant information. In addition, under the Pediatric Research Equity Act, or PREA, a BLA or supplement to a BLA must contain a pediatric assessment unless the applicant has obtained a waiver or deferral. Pediatric assessment contains data gathered from pediatric studies using appropriate formulations for each age group for which the assessment is required and other data adequate to assess the safety and effectiveness of the biological product candidate for the claimed indications in all relevant pediatric subpopulations and to support dosing and administration for each pediatric subpopulation for which the product is safe and effective. Sponsors with an application for a new active ingredient, new indication, new dosage form, new dosing regimen, or new route of administration must submit an initial Pediatric Study Plan, or PSP, (or a deferral or waiver, as appropriate) within 60 days of an end-of-Phase 2 meeting or as may be agreed between the sponsor and FDA. Unless otherwise required by regulation, PREA does not apply to any biological product for an indication for which orphan designation has been granted.

Under the Prescription Drug Fee User Act, as amended, or PDUFA, each BLA must be accompanied by a substantial user fee. Fee waiver or reductions are available under certain circumstances, including for the first application filed by a small business. In addition, no user fees are assessed on BLAs on products designated as orphan drugs unless the product also includes a non-orphan indication.

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Within 60 days following submission of the application, the FDA conducts a preliminary review of a BLA to determine whether they are sufficiently complete to permit substantive review. The FDA may request additional information before deciding whether to accept a BLA for filing. The FDA may refuse to file any BLA that it deems incomplete or otherwise not reviewable and may request additional information. If the submission is accepted for filing, the FDA substantively reviews the BLA to determine, among other things, whether the proposed product is safe, pure and potent, and manufactured in accordance with appropriate procedures and controls to ensure product quality. The FDA may refer applications for novel biological products or biological products that present difficult questions of safety or efficacy to an advisory committee, typically a panel that includes clinicians and other experts, for review, evaluation and a non-binding recommendation on approval. The FDA may waive the review by an advisory committee and is not bound by the recommendation of an advisory committee, but it often follows such recommendations. During the biological product approval process, the FDA also will review proposed product labeling and will determine whether a Risk Evaluation and Mitigate Strategy, or REMS, is necessary to assure the safe use of the biological product candidate. If the FDA concludes a REMS is needed, the sponsor of the BLA must submit a proposed REMS; the FDA will not approve the BLA without a REMS, if required.

Before approving a BLA, the FDA will inspect the facilities in which the product is manufactured to determine whether the manufacturing processes and facilities are in compliance with cGMPs. The FDA may also audit the clinical investigation sites to determine that they have complied with GCPs.

Notwithstanding the submission of relevant data and information, the FDA may ultimately deny approval or seek additional information from the applicant. Data obtained from clinical trials are not always conclusive and the FDA may interpret data differently than the applicant interprets the same data. The FDA may also raise questions about product manufacturing and quality control. If the FDA denies approval of a BLA in its then-current form, the FDA will issue a complete response letter detailing deficiencies in the application. If a response letter is issued, the applicant may either resubmit the BLA, addressing all of the deficiencies identified in the letter, or withdraw the application.

One of the performance goals agreed to by the FDA under PDUFA is to review 90% of standard BLAs in 10 months from the filing date and 90% of priority BLAs in six months from the filing date, whereupon a review decision is to be made. The FDA does not always meet its PDUFA goal dates for standard and priority BLAs.

Orphan Designation

Prior to the submission of a BLA, the FDA may grant orphan designation to drugs or biologics intended to treat a rare disease or condition that affects fewer than 200,000 individuals in the United States, or if it affects more than 200,000 individuals in the United States, there is no reasonable expectation that the cost of developing and marketing the product for this type of disease or condition will be recovered from sales in the United States. After the FDA grants orphan designation, the identity of the therapeutic agent and its potential orphan use are disclosed publicly by the FDA. Orphan designation does not convey any advantage in or shorten the duration of the regulatory review and approval process.

In the United States, orphan designation entitles a party to financial incentives such as opportunities for grant funding towards clinical trial costs, tax advantages and user-fee waivers. In addition, if a product receives the first FDA approval for the indication for which it has orphan designation, the product is entitled to orphan exclusivity, which means the FDA may not approve any other application to market the “same drug” for the same indication for a period of seven years, except in limited circumstances, such as a showing of clinical superiority over the product with orphan exclusivity or where the manufacturer with orphan exclusivity is unable to assure sufficient quantities of the approved orphan product. Competitors, however, may receive approval of different products for the indication for which the orphan product has exclusivity or obtain approval for the same product but for a different indication for which the orphan product has exclusivity. Orphan product exclusivity also could block the approval of one of our products for seven years if a competitor obtains approval of the same biological product as defined by the FDA or if our product candidate is determined to be contained within the competitor’s product for the same indication or disease. The scope of any eventual orphan exclusivity relative to the orphan designation is the subject of ongoing litigation and as such is uncertain and may change. For example, under FDA regulations, a designated orphan product may not receive orphan exclusivity for a use that is broader than the indication for which it received orphan designation and FDA approval. However, in 2021, the U.S. Court of Appeals for the Eleventh Circuit in Catalyst Pharmaceuticals, Inc. v. Becerra adopted a broader interpretation of the scope of orphan exclusivity. The court in Catalyst held that orphan exclusivity blocks approval of another company’s application for the “same drug” for the “entire disease or condition” for which the drug is granted orphan designation, regardless of whether the product was approved only for a narrower use or indication. Similarly, in 2025, the U.S. District Court for the District of Columbia in Neurelis v. Brenner adopted the same reasoning as the court in Catalyst to reach the same conclusion. Although the FDA announced in January 2023 that it will not apply the Catalyst decision beyond the facts at issue in that case, neither a court of appeals nor FDA has addressed Neurelis and either Catalyst or Neurelis could serve as a precedent for future challenges to the FDA’s orphan product-related decisions.

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Orphan exclusivity may be lost if the FDA later determines that the orphan designation request was materially defective or if the manufacturer is unable to ensure the availability of sufficient quantities of the drug to meet the needs of patients with the rare disease or condition, or if the manufacturer chooses to provide consent to FDA approval of other applications.

Descartes-08 has been granted Orphan Drug Designation for the treatment of MG.

Expedited Development and Review Programs

The FDA offers various programs, including the Fast Track program, Breakthrough Therapy designation, RMAT designation and the National Priority Voucher, or CNPV, program that are intended to expedite or facilitate the process for reviewing new biological products that meet certain criteria. Specifically, new biological products are eligible for Fast Track designation if they are intended to treat a serious or life-threatening disease or condition and demonstrate the potential to address unmet medical needs for the disease or condition. Fast Track designation applies to the combination of the product and the specific indication for which it is being studied. The sponsor of a new biologic may request that the FDA designate the biologic as a Fast Track product at any time during the clinical development of the product.

Any product submitted to the FDA for marketing, including under a Fast Track program, may be eligible for other types of FDA programs intended to expedite development and review, such as priority review and accelerated approval. Any product is eligible for priority review if it treats a serious condition and, if approved, would provide a significant improvement in safety or effectiveness of treatment, diagnosis, or prevention compared to available therapies.

Additionally, a product may be eligible for accelerated approval. The FDA may approve a product for a serious or life-threatening disease or condition based on a determination that the product has an effect on a surrogate endpoint that is reasonably likely to predict clinical benefit, or on a clinical endpoint that can be measured earlier than irreversible morbidity or mortality, that is reasonably likely to predict an effect on irreversible morbidity or mortality or other clinical benefit, taking into account the severity, rarity, or prevalence of the condition and the availability or lack of alternative treatments. As a condition of approval, the FDA may require that a sponsor of a biological product subject to accelerated approval perform adequate and well-controlled post-marketing clinical studies to confirm such benefit. The Food and Drug Omnibus Reform Act of 2022, or FDORA, added the failure to conduct post-approval studies with due diligence or to submit timely progress reports on such studies to the list of prohibited acts under the FD&C Act, which means that any such failures, whether they result from a sponsor’s actions or the actions of third-parties, could provide the basis for withdrawal of the product on an expedited basis or other enforcement actions. In addition, the FDA currently requires as a condition for accelerated approval that promotional materials be submitted prior to use, which could adversely impact the timing of the commercial launch of the product.

In addition, under the provisions of The Food and Drug Safety and Innovation Act, or FDASIA, Congress and the FDA established a Breakthrough Therapy Designation which is intended to expedite the development and review of products that treat serious or life-threatening diseases or conditions. A breakthrough therapy is defined as a drug that is intended, alone or in combination with one or more other drugs, to treat a serious or life-threatening disease or condition, and preliminary clinical evidence indicates that the drug may demonstrate substantial improvement over existing therapies on one or more clinically significant endpoints, such as substantial treatment effects observed early in clinical development. The designation includes all of the features of Fast Track designation, as well as more intensive FDA interaction and guidance. Fast Track, priority review, accelerated approval, and breakthrough therapy designations do not change the standards for approval and may not necessarily expedite the development or approval process.

In 2016, the 21st Century Cures Act established what the FDA describes as RMAT designation. The RMAT designation program is intended to facilitate an efficient development program for, and expedite review of, any product that meets the following criteria: (i) the product qualifies as an RMAT, which is defined as a cell therapy, therapeutic tissue engineering product, human cell and tissue product, or any combination product using such therapies or products, with limited exceptions; (ii) the product is intended to treat, modify, reverse, or cure a serious or life-threatening disease or condition; and (iii) preliminary clinical evidence indicates that the product has the potential to address unmet medical needs for such a disease or condition. RMAT designation provides all the benefits of Breakthrough Therapy Designation, including early interactions to discuss any potential surrogate or intermediate endpoints to be used to support accelerated approval, eligibility for rolling review and potential eligibility for priority review. Product candidates granted RMAT designation may also be eligible for accelerated approval on the basis of a surrogate or intermediate endpoint reasonably likely to predict long-term clinical benefit, or reliance upon data obtained from a meaningful number of clinical trial sites, including through expansion of trials to additional sites, as appropriate.

Descartes-08 has been granted RMAT designation for the treatment of MG.

In 2025, the FDA also announced the opportunity for prescription drug and biological product companies to participate in the FDA Commissioner's CNPV pilot program. Companies selected for the CNPV program will be issued a voucher entitling

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the company to benefits including enhanced communications and rolling review to allow for a shortened review time. CNPV does not change the standards for approval and may not necessarily expedite the development or approval process.

Post-approval Requirements

Rigorous and extensive FDA regulation of biological products continues after approval. Manufacturers of our products are required to comply with applicable requirements in the cGMP regulations, including quality control and quality assurance and maintenance of records and documentation. Other post-approval requirements applicable to biological products include record-keeping requirements, reporting of adverse effects and reporting updated safety and efficacy information.

We also must comply with the FDA’s advertising and promotion requirements, such as the prohibition on promoting products for uses or in patient populations that are not described in the product’s approved labeling, known as “off-label use,” and the requirement to balance information provided about a product’s benefits with important safety information. Discovery of previously unknown problems or the failure to comply with the applicable regulatory requirements may result in restrictions on the marketing of a product or withdrawal of the product from the market as well as possible civil or criminal sanctions. Failure to comply may subject an applicant or manufacturer to administrative or judicial civil or criminal sanctions, expensive and onerous government investigations, and adverse publicity.

Conventional DNA-modified CAR-T cell products have been subject to extensive post-approval surveillance requirements. Because the mRNA of our products is temporary, we do not believe that our mRNA-modified products will be subject to requirements of this nature, although other post-approval requirements will apply.

Biosimilars and Exclusivity

The Patient Protection and Affordable Care Act, or ACA, includes a subtitle called the Biologics Price Competition and Innovation Act of 2009, or BPCIA, which created an abbreviated approval pathway for biological products that are biosimilar to or interchangeable with an FDA-licensed reference biological product.

Biosimilarity, which requires that there be no clinically meaningful differences between the biological product and the reference product in terms of safety, purity and potency, can be shown through analytical studies, animal studies and a clinical study or studies. The FDA has approved a number of products under these provisions.

To our knowledge, how the definition of “biosimilar” applies with regard to an mRNA-modified cell therapy has not been expressly stated in statute, regulation, or guidance, and has not been reviewed by a court. The regulatory pathway for a biosimilar to one of our products thus remains somewhat uncertain.

Under the BPCIA, an application for a biosimilar product may not be submitted to the FDA until four years following the date that the reference product was first licensed by the FDA. In addition, the approval of a biosimilar product may not be made effective by the FDA until 12 years from the date on which the reference product was first licensed. During this 12-year period of exclusivity, another company may still market a competing version of the reference product if the FDA approves a full BLA for the competing product containing the sponsor’s own preclinical data and data from adequate and well-controlled clinical trials to demonstrate the safety, purity and potency of their product. A biological product may also obtain pediatric exclusivity in the United States. For a biological product, pediatric exclusivity, if granted, adds six months to existing regulatory exclusivity periods. This six-month exclusivity, which runs from the end of other exclusivity protection, may be granted based on the voluntary completion of a pediatric study in accordance with an FDA-issued “Written Request” for such a study or studies.

The BPCIA is complex and continues to be interpreted and implemented by the FDA. As a result, the ultimate impact, implementation and meaning of the BPCIA is subject to significant uncertainty. For example, the FDA had previously required comparative clinical studies to support a demonstration of biosimilarity if there is residual uncertainty about whether there are clinically meaningful differences between the reference product and the proposed product. However, in October 2025, the FDA issued a new draft guidance document that largely permits biosimilar applications without comparative efficacy studies, thus potentially increasing the risk of sooner biosimilar entry.

Government Regulation Outside of the United States

Whether or not we obtain FDA approval for a product, we must obtain the requisite approvals from regulatory authorities in countries outside the United States prior to the commencement of clinical studies or marketing of the product in those countries.

The requirements and process governing the conduct of clinical studies, product licensing, pricing and reimbursement vary from country to country. In all cases, the clinical studies must be conducted in accordance with GCP and the applicable regulatory requirements and the ethical principles that have their origin in the Declaration of Helsinki.

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In the European Economic Area, or EEA, which is composed of the 27 member states of the European Union, or EU, plus Norway, Iceland and Liechtenstein, medicinal products can only be commercialized after obtaining a Marketing Authorization, or MA. To obtain an MA in the EEA, we must submit a marketing authorization application, which is similar to the U.S. BLA. There are two types of MAs.

The EU MA, which is issued by the European Commission through the Centralized Procedure, is based on the opinion of the Committee for Medicinal Products for Human Use, or CHMP, of the European Medicines Agency, or EMA, and is valid throughout the entire territory of the EEA. The Centralized Procedure is mandatory for certain types of products, such as biotechnology medicinal products, orphan medicinal products, advanced therapy medicinal products (comprising gene therapy, somatic cell therapy and tissue engineered products), among others. The Centralized Procedure is optional for other products containing a new active substance not yet authorized in the EEA, or for other products that constitute a significant therapeutic, scientific or technical innovation or which are in the interest of public health in the EU. Under the Centralized Procedure the maximum timeframe for the evaluation of a marketing authorization application is 210 days (excluding clock stops, when additional written or oral information is to be provided by the applicant in response to questions asked by the CHMP). Accelerated evaluation might be granted by the CHMP in exceptional cases. Under the accelerated procedure the standard 210 days review period is reduced to 150 days.

National MAs, which are issued by the competent authorities of the Member States of the EEA and only cover their respective territory, are available for products not falling within the mandatory scope of the Centralized Procedure. Where a product has already been authorized for marketing in a Member State of the EEA, this National MA can be recognized in another Member States through the Mutual Recognition Procedure. If the product has not received a National MA in any Member State at the time of application, it can be approved simultaneously in various Member States through the Decentralized Procedure.

EU law also provides opportunities for market exclusivity. Upon receiving MA, “new active substances” generally receive eight years of data exclusivity, which prevents regulatory authorities in the EU from referencing the innovator’s data to assess a generic or biosimilar application, and an additional two years of market exclusivity, during which no generic or biosimilar product can be marketed. The ten years of exclusivity will be extended to a maximum of eleven years if, during the first eight years of those ten years, the MA holder obtains an authorization for one or more new therapeutic indications which, during the scientific evaluation prior to their authorization, are held to bring a significant clinical benefit in comparison with existing therapies. However, there is no guarantee that a product will be considered by the EU’s regulatory authorities to be a new active substance which would be eligible for the relevant periods of data and market exclusivity.

The criteria for designating an “orphan medicinal product” in the EU are similar in principle to those in the United States. Under Article 3 of Regulation (EC) 141/2000, a medicinal product may be designated as orphan if (i) it is intended for the diagnosis, prevention or treatment of a life-threatening or chronically debilitating condition; (ii) either (a) such condition affects no more than five in 10,000 persons in the EU when the application is made, or (b) the product, without the benefits derived from orphan status, would not generate sufficient return in the EU to justify investment; and (iii) there exists no satisfactory method of diagnosis, prevention or treatment of such condition authorized for marketing in the EU, or if such a method exists, the product will be of significant benefit to those affected by the condition, as defined in Regulation (EC) 847/2000. Orphan medicinal products are eligible for certain financial and exclusivity incentives. In particular, orphan medicinal products in the EU can receive ten years of market exclusivity, during which time no MA application shall be accepted, and no MA shall be granted for a similar medicinal product for the same indication. The 10-year market exclusivity for orphan medicinal products may be reduced to six years if, at the end of the fifth year, it is established that the product no longer meets the criteria for orphan designation. Additionally, MA may be granted to a similar product during the 10-year period of market exclusivity for the same therapeutic indication at any time in certain circumstances, including if the second applicant can establish in its application that its product, although similar to the orphan medicinal product already authorized, is safer, more effective or otherwise clinically superior.

In the EU, for any new medicinal product that is protected by or eligible for a supplementary protection certificate, pediatric clinical trials must be conducted in accordance with a pediatric investigation plan, or PIP, that has been approved by the EMA. Normally, the pediatric clinical trials must be completed before the initial MA application for the relevant indication. However, the EMA may grant a deferral of the studies in order not to delay the approval of the product in adults and the EMA may waive the requirement to conduct studies in certain circumstances, such as if the relevant condition does not occur in children. If pediatric clinical trials are completed in accordance with an agreed PIP, the product will be entitled to a six-month extension of its supplementary protection certificate. However, if the product is authorized as an orphan medicinal product, it is entitled to a two-year extension of its 10 years of orphan exclusivity and not to an extension of the supplementary protection certificate.

For other countries outside of the EU, such as countries in Eastern Europe, Latin America or Asia, the requirements governing the conduct of clinical studies, product licensing, pricing and reimbursement vary from country to country. In all

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cases, again, the clinical studies must be conducted in accordance with GCP and the applicable regulatory requirements and the ethical principles that have their origin in the Declaration of Helsinki.

When conducting clinical trials in the EU, we must adhere to the provisions of the EU Clinical Trials Regulation (EU) No 536/2014. If the sponsor of the clinical trial is not established within the EU, it must appoint an entity within the EU to act as its legal representative, who shall be responsible for ensuring compliance with the sponsor’s obligations under the Regulation and be the addressee for all communications. The sponsor must take out a clinical trial insurance policy, and in most EU countries the sponsor is liable to provide ‘no fault’ compensation to any study subject injured in the clinical trial.

Prior to commencing a clinical trial in the EU, we must obtain a clinical trial authorization, or CTA, in each Member State in which the trial will be conducted. There is a centralized application procedure where one national authority leads the scientific review of the application, while each concerned member state complete an ethical review of any CTA. The application for a CTA must include, among other things, a copy of the trial protocol and an investigational medicinal product dossier containing information about the manufacture and quality of the medicinal product under investigation. Any substantial changes to the trial protocol or other information submitted with the CTAs must be notified to or approved by the relevant competent authorities.

We are also subject to data privacy and security laws in the jurisdictions outside of the U.S. in which we are established, run clinical trials or in which we sell or market our products once approved. For example, in Europe we are subject to Regulation (EU) 2016/679 (General Data Protection Regular, or GDPR) in relation to our collection, control, processing and other use of personal data (i.e., data relating to an identifiable living individual). We process personal data in relation to participants in our clinical trials in the EEA, including the health and medical information of these participants. The GDPR is directly applicable in each EU Member State, however, it provides that EU Member States may introduce further conditions, including limitations which could limit our ability to collect, use and share personal data (including health and medical information), or could cause our compliance costs to increase, ultimately having an adverse impact on our business. The GDPR imposes accountability and transparency obligations regarding personal data. We are also subject to EU rules with respect to cross-border transfers of personal data out of the EU and EEA. We are subject to the supervision of local data protection authorities in those EU jurisdictions where we are established or otherwise subject to the GDPR. A breach of the GDPR could result in significant fines, regulatory investigations, reputational damage, orders to cease/ change our use of data, enforcement notices, as well potential civil claims including class action type litigation where individuals suffer harm. Moreover, the United Kingdom leaving the EU could also lead to further legislative and regulatory changes. It remains unclear how the United Kingdom data protection laws or regulations will develop in the medium to longer term and how data transfer to the United Kingdom from the EU will be regulated. However, the United Kingdom has transposed the GDPR into domestic law with the Data Protection Act 2018, which remains in force following the United Kingdom’s departure from the EU.

Other Healthcare Laws

The federal Anti-Kickback Statute prohibits, among other things, any person or entity from knowingly (regardless of knowledge of this specific statute) and willfully offering, paying, soliciting, receiving or providing any remuneration, directly or indirectly, overtly or covertly, to induce or in return for purchasing, leasing, ordering, or arranging for or recommending the purchase, lease, or order of any item or service reimbursable, in whole or in part, under Medicare, Medicaid or other federal healthcare programs. The term “remuneration” has been broadly interpreted to include anything of value. The Anti-Kickback Statute has been interpreted to apply to arrangements between pharmaceutical manufacturers on the one hand and prescribers, purchasers, formulary managers, and other third-parties on the other. The majority of states also similar have anti-kickback laws, which in some cases apply to items and services reimbursed by private insurance.

The federal false claims and civil monetary penalties laws, including the civil False Claims Act, prohibit any person or entity from, among other things, knowingly presenting, or causing to be presented, a false, fictitious or fraudulent claim for payment to, or approval by, the federal government or knowingly making, using, or causing to be made or used a false record or statement material to a false or fraudulent claim to the federal government, or from knowingly making a false statement to avoid, decrease or conceal an obligation. A claim includes “any request or demand” for money or property presented to the U.S. government. Manufacturers can be held liable under false claims laws, even if they do not submit claims to the government, where they are found to have caused submission of false claims by, among other things, providing incorrect coding or billing advice about their products to customers that file claims, or by engaging or off-label promotion to customers that file claims. Violation of the federal Anti-Kickback Statute may also constitute a false or fraudulent claim for purposes of the federal civil False Claims Act. Actions under the civil False Claims Act may be brought by the Department of Justice or as a qui tam action by a private individual in the name of the government. Many states also have similar fraud and abuse statutes or regulations that apply to items and services reimbursed under Medicaid and other state programs, or, in several states, apply regardless of the payor.

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The federal Health Insurance Portability and Accountability Act of 1996, or HIPAA, prohibits, among other actions, knowingly and willfully executing, or attempting to execute, a scheme to defraud any healthcare benefit program, including private third-party payors, knowingly and willfully embezzling or stealing from a healthcare benefit program, willfully obstructing a criminal investigation of a healthcare offense, and knowingly and willfully falsifying, concealing or covering up a material fact or making any materially false, fictitious or fraudulent statement in connection with the delivery of or payment for healthcare benefits, items or services. A person or entity does not need to have actual knowledge of the statute or specific intent to violate it in order to have committed a violation.

In addition, the Physician Payments Sunshine Act requires applicable manufacturers to annually report certain payments and “transfers of value” provided to physicians (defined to include doctors, dentists, optometrists, podiatrists and chiropractors), certain other health care providers, as well as ownership and investment interests held by physicians and their immediate family members.

Sanctions under these federal and state fraud and abuse laws may include civil monetary penalties and criminal fines, exclusion from government healthcare programs, and imprisonment.

We may also be subject to data privacy and security regulation by both the federal government and the states in which we conduct our business. HIPAA, as amended by the Health Information Technology for Economic and Clinical Health act of 2009, or HITECH, and their respective implementing regulations, impose specified requirements relating to the privacy, security and transmission of individually identifiable health information held by covered entities and their business associates. Among other things, HITECH made HIPAA’s security standards directly applicable to, as well as imposed certain other privacy obligations on, “business associates,” defined as independent contractors or agents of covered entities that create, receive, maintain or transmit protected health information in connection with providing a service for or on behalf of a covered entity. HITECH also increased the civil and criminal penalties that may be imposed and gave state attorneys general new authority to file civil actions for damages or injunctions in federal courts to enforce the federal HIPAA laws and seek attorney’s fees and costs associated with pursuing federal civil actions. Even when HIPAA does not apply, according to the Federal Trade Commission, or FTC, failing to take appropriate steps to keep consumers’ personal information secure constitutes unfair acts or practices in or affecting commerce in violation of Section 5(a) of the Federal Trade Commission Act, 15 U.S.C § 45(a).

Coverage and Reimbursement

Significant uncertainty exists as to the coverage and reimbursement status of any pharmaceutical or biological products for which we obtain regulatory approval. In the United States and markets in other countries, patients who are prescribed treatments for their conditions and providers performing the prescribed services generally rely on third-party payors to reimburse all or part of the associated healthcare costs. Sales of any products for which we receive regulatory approval for commercial sale will therefore depend, in part, on the availability of coverage and adequate reimbursement from third-party payors. Third-party payors include government authorities, managed care plans, private health insurers and other organizations.

The process for determining whether a third-party payor will provide coverage for a pharmaceutical or biological product typically is separate from the process for setting the price of such product or for establishing the reimbursement rate that the payor will pay for the product once coverage is approved. Third-party payors may limit coverage to specific products on an approved list, also known as a formulary, which might not include all of the FDA-approved products for a particular indication.

A decision by a third-party payor not to cover our product candidates could reduce physician utilization of our products once approved and have a material adverse effect on our sales, results of operations and financial condition. Moreover, a third-party payor’s decision to provide coverage for a pharmaceutical or biological product does not imply that an adequate reimbursement rate will be approved. Adequate third-party reimbursement may not be available to enable us to maintain price levels sufficient to realize an appropriate return on our investment in product development.

In the EU, pricing and reimbursement schemes vary widely from country to country. Some countries provide that products may be marketed only after a reimbursement price has been agreed. Some countries may require the completion of additional studies that compare the cost effectiveness of a particular product candidate to currently available therapies (so called health technology assessments) in order to obtain reimbursement or pricing approval. The EU recently adopted Regulation (EU) 2021/2282 on health technology assessment, which provides a framework for Member States to cooperate on health technology assessments at the EU level. The regulation is directly applicable in all EU Member States which is in a phased period of applicability since January 12, 2025, although pricing will still be determined nationally. Moreover, at the national level, EU Member States may restrict the range of products for which their national health insurance systems provide reimbursement and to control the prices of medicinal products for human use. Member States may approve a specific price for a product or may instead adopt a system of direct or indirect controls on the profitability of the company placing the product on the market. Other Member States allow companies to fix their own prices for products, but monitor and control prescription volumes and issue guidance to physicians to limit prescriptions. Recently, many countries in the EU have increased the amount of discounts required on pharmaceuticals and these efforts could continue as countries attempt to manage healthcare expenditures, especially

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in light of the severe fiscal and debt crises experienced by many countries in the EU. The downward pressure on health care costs in general, particularly prescription products, has become intense. As a result, increasingly high barriers are being erected to the entry of new products in the marketplace. Political, economic and regulatory developments may further complicate pricing negotiations, and pricing negotiations may continue after reimbursement has been obtained. Reference pricing used by various EU Member States and parallel trade (arbitrage between low-priced and high-priced member states) can further reduce prices. Special pricing and reimbursement rules may apply to orphan drugs. Inclusion of orphan drugs in reimbursement systems tend to focus on the medical usefulness, need, quality and economic benefits to patients and the healthcare system as for any product. Acceptance of any medicinal product for reimbursement may come with cost, use and often volume restrictions, which again can vary by country. In addition, results-based rules of reimbursement may apply. There can be no assurance that any country that has price controls or reimbursement limitations for pharmaceutical products will allow favorable reimbursement and pricing arrangements for any of our products, if approved in those countries.

Healthcare Reform

A primary trend in the U.S. healthcare industry and elsewhere is cost containment. Government authorities and other third-party payors have attempted to control costs by limiting coverage and the amount of reimbursement for particular medical products.

Federal, state and local governments in the U.S. have established and continue to consider policies to limit the growth of healthcare costs, including the cost of prescription drugs. Recently there has also been heightened governmental scrutiny over the manner in which manufacturers set prices for their marketed products, which has resulted in several Congressional inquiries and proposed and enacted legislation designed to, among other things, bring more transparency to product pricing, review the relationship between pricing and manufacturer patient programs, and reform government program reimbursement methodologies for prescription drugs.

At the federal level, for example, the Inflation Reduction Act of 2022, or IRA, was signed into law. Key provisions of the IRA include the following, among others:

•The IRA requires manufacturers to pay rebates for Medicare Part B and Part D drugs whose price increases exceed inflation.

•The IRA eliminated the so-called “donut hole” under Medicare Part D by requiring manufacturers to subsidize, through a newly established manufacturer discount program, 10% of Part D enrollees’ prescription costs for brand drugs below the out-of-pocket maximum and 20% once the out-of-pocket maximum has been reached. The IRA also significantly lowered the beneficiary maximum out-of-pocket cost under Medicare Part D.

•The IRA delays the rebate rule that would require pass through of pharmacy benefit manager rebates to beneficiaries

•The IRA directs the Centers for Medicare and Medicaid Services, or CMS, to engage in price-capped negotiation for certain Medicare Part B and Part D products. Specifically, the IRA’s Price Negotiation Program applies to high-expenditure single-source drugs and biologics that have been approved for at least seven or 11 years, respectively, among other negotiation selection criteria, beginning with 10 high-cost drugs paid for by Medicare Part D starting in 2026, followed by 15 Part D drugs in 2027, 15 Part B or Part D drugs in 2028, and 20 Part B or Part D drugs in 2029 and beyond. The negotiated prices will be capped at a statutorily determined ceiling price. There are certain statutory exemptions from the IRA’s Price Negotiation Program, such as for a drug that has only orphan drug designations and is approved only for an indication or indications within the scope of such designation. The IRA’s Price Negotiation Program is currently the subject of legal challenges.

Manufacturers that fail to comply with the IRA may be subject to various penalties, including civil monetary penalties and a potential excise tax. The IRA permits the Secretary of Health and Human Services, or the HHS Secretary, to implement many of the IRA’s provisions through guidance, as opposed to regulation, for the initial years. The IRA is anticipated to have significant effects on the pharmaceutical industry and may reduce the prices pharmaceutical manufacturers can charge and reimbursement pharmaceutical manufacturers can receive for approved products, among other effects.

The Trump Administration has issued Executive Orders relating to prescription drug pricing and letters to pharmaceutical manufacturers that direct drug manufacturers to, among other things, offer most favored nation, or MFN, pricing in Medicaid, offer MFN pricing for all newly launched drugs; repatriate increased revenue from abroad to lower drug prices in the United States, and implement direct-to-consumer and direct-to-business distribution of their products at MFN pricing. The Administration has warned that manufacturers that fail to make “significant progress” toward MFN pricing will face enumerated regulatory and enforcement consequences. In September 2025, the Trump Administration began announcing deals with specific manufacturers to address its MFN goals.

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In addition, other legislative changes have been proposed and adopted in the United States. These include aggregate reductions of Medicare payments to providers of 2% per fiscal year, which went into effect on April 1, 2013, and, due to subsequent legislative amendments, will stay in effect through 2032 unless additional Congressional action is taken.

The Trump Administration has discussed several changes to the reach and oversight of the FDA, which could affect its relationship with the biotechnology and pharmaceutical industries, transparency in decision making and ultimately the cost and availability of prescription drugs. Drug pricing is an active area for regulatory reform at both the federal and state levels, and additional significant changes to current drug pricing and reimbursement structures in the U.S. could be forthcoming. It remains unclear how any new legislation or regulation might affect the prices we may obtain for any of our product candidates for which regulatory approval is obtained.

Employees and Human Capital Resources

We consider human capital to be an essential driver of our business and successful strategy creation and execution. Our people, driven by our collaborative, pioneering, and patient-focused culture, propel our business forward, strengthening us for long-term success.

As of December 31, 2025, we had 75 full-time employees, 62 of whom are primarily engaged in research and development activities and 13 of whom are primarily engaged in corporate functions. 60% of our employees have at least one of a Masters, PhD, or MD degree. All employees reside and work in the United States and our employees are not represented by a labor union. We consider our employee relations to be strong and in good standing.

Our goal is to continually engage our talented and diverse workforce to drive value creation both for our business and ultimately our patient populations. We believe in a proactive approach to talent management focusing on retention of key talent, critical role successor identification, and impactful employment development. Additional priority areas intended to drive engagement include successful recruitment of diverse talent, continual promotion of professional development at all levels, introduction, and evolution of business-friendly human resources solutions, coupled with an intentional culture dialog aimed to drive a high engagement, high performance, patient centric culture.

To further drive attraction and retention of our high-quality, experienced, and diverse workforce, we invest in the physical, emotional, and financial well-being of our employees. These investments include a competitive mix of compensation and generous insurance benefits. To assist employees with the rising cost of healthcare, we pay 100% of an employee’s deductible and co-insurance payments. All employees are eligible to participate in our equity compensation programs. All employees are awarded new hire equity and annual equity. Employees are also eligible to receive an annual cash bonus and to participate in a 401(k) retirement plan with an industry competitive company match.

Available Information

We file electronically with the SEC our annual reports on Form 10-K, quarterly reports on Form 10-Q, current reports on Form 8-K, proxy statements and other information. Our SEC filings are available to the public at the SEC’s website at http://www.sec.gov. We make available on our website at www.cartesiantherapeutics.com, free of charge, copies of these reports as soon as reasonably practicable after filing or furnishing these reports with the SEC. Additionally, our Code of Business Conduct and Ethics is available on our website. The hyperlink to our website is included as an inactive textual reference only, and the information on our website is not incorporated by reference in this Annual Report on Form 10-K or in any other filings we make with the SEC.

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RISK FACTORS SUMMARY

Investing in our common stock involves various risks. You should carefully read and consider the matters discussed in this Annual Report under the heading “Risk Factors,” which include the following risks:

•We are a development-stage company, and we expect to incur losses for the foreseeable future and may never achieve or maintain profitability.

•We will need substantial additional funding in order to complete development of our product candidates and commercialize our products, if approved. If we are unable to raise capital when needed and on terms favorable to us, we could be forced to delay, reduce or eliminate our product development programs or commercialization efforts.

•We develop our mRNA-based product candidates by leveraging our proprietary technology and our manufacturing platform, which is an unproven approach to the treatment of autoimmune disease. We are early in most of our clinical development efforts and may not be successful in our efforts to build a pipeline of product candidates and develop marketable drugs.

•Clinical drug development is inherently risky and involves a lengthy and expensive process, which is subject to a number of factors, many of which are outside of our control. We may incur additional costs or experience delays in completing, or ultimately be unable to complete, the development and commercialization of our product candidates.

•Interim, top-line and preliminary data from our clinical trials that we announce or publish from time to time may change as more patient data become available and are subject to audit and verification procedures that could result in material changes in the final data.

•Our product candidates may cause undesirable side effects or have other properties that could delay or prevent their regulatory approval, limit the commercial profile of an approved label, or result in significant negative consequences following marketing approval, if any.

•We have recorded a material amount of goodwill and indefinite-lived intangible assets in connection with the Merger. We have, and may in the future, record impairment charges, which would adversely impact our financial position and results of operations.

•We expect to continue to grow our manufacturing capabilities and resources and we must incur significant costs to develop this expertise and/or rely on third-parties to manufacture our products.

•We rely, and expect to continue to rely, on third-parties, including CROs, to conduct our clinical trials, and those third-parties may not perform satisfactorily, including by failing to meet deadlines for the completion of such trials.

•If we or our licensors are unable to adequately protect our proprietary technology, or obtain and maintain issued patents that are sufficient to protect our product candidates, others could compete against us more directly, which would negatively impact our business.

•We have been in the past and may in the future be subject to stockholder litigation.

Item 1A. Risk Factors

Investing in our common stock involves a high degree of risk. You should consider carefully the risks described below, together with the other information included or incorporated by reference in this Annual Report. If any of the following risks occur, our business, financial condition, results of operations and future growth prospects could be materially and adversely affected. In these circumstances, the market price of our common stock could decline. Other events that we do not currently anticipate or that we currently deem immaterial may also affect our business, prospects, financial condition and results of operations.

Risks Related to the Development of our Product Candidates

We develop our mRNA-based product candidates by leveraging our proprietary technology and our manufacturing platform, which is an unproven approach to the treatment of autoimmune disease. We may not be successful in our efforts to build a pipeline of product candidates and develop marketable drugs.

Our mRNA approach to develop product candidates for the treatment of autoimmune diseases is an unproven approach. Our most advanced product candidate, Descartes-08, is in Phase 3 clinical development. We have not demonstrated the ability to successfully complete any Phase 3 or other pivotal clinical trials, obtain regulatory approvals, manufacture a commercial product, or arrange for a third-party to do so on our behalf, or conduct other sales and marketing activities necessary for

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successful product commercialization. We may have problems identifying new product candidates and applying our technologies to other areas. Even if we are successful in identifying new product candidates, they may not be suitable for clinical development, including as a result of manufacturing difficulties, harmful side effects, limited efficacy or other characteristics that indicate that they are unlikely to be products that will receive marketing approval and achieve market acceptance. The success of our product candidates will depend on several factors, including the following:

•design, initiation and completion of preclinical studies and clinical trials with positive results;

•reliance on third-parties, including but not limited to collaborators, licensees, clinical research organizations and contract manufacturing organizations;

•receipt of marketing approvals from applicable regulatory authorities;

•obtaining and maintaining patent and trade secret protection and regulatory exclusivity for our product candidates and not infringing or violating patents or other intellectual property of third-parties;

•manufacturability, manufacturing, logistics, and stability of our cell therapies, including autologous cell therapies;

•growing our internal cGMP manufacturing capabilities to support commercial manufacturing or making arrangements with third-party manufacturers;

•launching commercial sales of our products, if and when approved, whether alone or in collaboration with others;

•acceptance of our products, if and when approved, by patients and the medical community;

•effectively competing with other therapies;

•obtaining and maintaining coverage and adequate reimbursement by third-party payors, including government payors, for our products, if approved;

•maintaining an acceptable safety profile of our products following approval; and

•maintaining and growing an organization of scientists and businesspeople who can develop and commercialize our product candidates and technology.

Our failure to successfully execute on of any of the foregoing for any reason would effectively prevent or delay approval of our lead and other product candidates.

Clinical drug development is inherently risky and involves a lengthy and expensive process which is subject to a number of factors, many of which are outside of our control. We may incur additional costs or experience delays in completing, or ultimately be unable to complete, the development and commercialization of our product candidates.

Clinical development is expensive, time consuming and involves significant risk. It is impossible to predict when or if any of our product candidates will prove effective and safe in humans or will receive regulatory approval, and the risk of failure through the development process is high. Before obtaining marketing approval from regulatory authorities for the sale of any product candidate, we must complete manufacturing and preclinical development and then conduct extensive clinical trials to demonstrate the safety and efficacy of our product candidates in humans. Manufacturing cell therapies, particularly those modified with mRNA, is a new field.

Preclinical development is costly and inherently uncertain. Early preclinical results may not be predictive of future results, however, if our technology proves to be ineffective or unsafe as a result of, among other things, adverse side effects, we may incur additional costs or experience delays in completing, or ultimately be unable to complete, the clinical development and commercialization of our product candidates.

Before obtaining marketing approval from regulatory authorities for the sale of our product candidates, we must conduct extensive clinical trials to demonstrate the safety and efficacy of the product candidate for its intended indications. Clinical testing is expensive, difficult to design and implement, can take many years to complete and its outcome is inherently uncertain. A failed clinical trial can occur at any stage of testing. Moreover, the outcome of preclinical testing and early clinical trials may not be predictive of the success of later clinical trials, and interim results of a clinical trial do not necessarily predict final results. Moreover, we may not be able to complete, or may be required to deviate from the current clinical trial protocol for a variety of reasons.

Many companies in the pharmaceutical and biotechnology industries have suffered significant setbacks in clinical trials after achieving positive results in preclinical development or early-stage clinical trials, and we cannot be certain that we will not

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face similar setbacks. Serious adverse events, or SAEs, caused by, or other unexpected properties of, any product candidates that we may choose to develop could cause us, an institutional review board or regulatory authority to interrupt, delay or halt clinical trials of one or more of such product candidates and could result in a more restrictive label or the delay or denial of marketing approval by the FDA or comparable non-U.S. regulatory authorities. If any product candidate that we may choose to develop is associated with SAEs or other unexpected properties, we may need to abandon development or limit development of that product candidate to certain uses or subpopulations in which those undesirable characteristics would be expected to be less prevalent, less severe or more tolerable from a risk-benefit perspective. Moreover, preclinical and clinical data is often susceptible to varying interpretations and analyses, and many companies that believed their product candidates performed satisfactorily in preclinical studies and clinical trials nonetheless failed to obtain FDA or other regulatory authority approval. If we fail to produce positive results in clinical trials of our product candidates, the development timeline and regulatory approval and commercialization prospects for our product candidates, and, correspondingly, our business and financial prospects, would be negatively impacted.

In addition, we cannot be certain as to what type and how many clinical trials the FDA will require us to conduct before we may gain regulatory approval to market any of our product candidates in the United States or other countries, if any. Prior to approving a new therapeutic product, the FDA generally requires that safety and efficacy be demonstrated in two adequate and well-controlled clinical trials. Although the FDA may provide comments regarding our development plan as part of an SPA agreement or otherwise, final determination for marketing application approval are made after a complete review of a marketing application and are based on the entirety of the data in the IND or BLA.

We may experience numerous unforeseen events during, or as a result of, clinical trials that could delay or prevent our ability to receive marketing approval for, or commercialize, our product candidates, including:

•clinical trials of our product candidates may produce unfavorable, incomplete or inconclusive results;

•we may be unable to manufacture our product candidates, which in some cases such as mRNA CAR-T, are manufactured on a patient-by-patient basis;

•regulators or institutional review boards may not authorize us or our investigators to commence a clinical trial or conduct a clinical trial at a prospective trial site or may place a clinical hold on existing clinical trials;

•we may experience delays in reaching, or fail to reach, agreement on acceptable terms with CROs or clinical trial sites;

•we may be unable to recruit suitable patients to participate in a clinical trial, the number of patients required for clinical trials of our product candidates may be larger than we expect, enrollment in these clinical trials may be slower than we expect or participants may drop out of these clinical trials at a higher rate than we expect, or enrollment could be affected by unforeseen geopolitical conflict;

•the number of clinical trial sites required for clinical trials of our product candidates may be larger than we expect;

•our third-party contractors may fail to comply with regulatory requirements or meet their contractual obligations to us in a timely manner, or at all;

•we may have to suspend or terminate clinical trials of our product candidates for various reasons, including a finding that the participants are being exposed to unacceptable health risks;

•investigators, regulators, data safety monitoring boards or institutional review boards may require that we or our investigators suspend or terminate clinical research, or we may decide to do so ourselves;

•investigators may deviate from the trial protocol, fail to conduct the trial in accordance with regulatory requirements or misreport study data;

•the cost of clinical trials of our product candidates may be greater than we expect or we may have insufficient resources to pursue or complete certain aspects of our clinical trial programs or to do so within the timeframe we planned;

•the supply or quality of raw materials or manufactured product candidates (whether provided by us or third-parties) or other materials necessary to conduct clinical trials of our product candidates may be insufficient, inadequate or not available at an acceptable cost, or in a timely manner, or we may experience interruptions in supply;

•laboratories that we rely upon to perform certain quality control tests may become unavailable, or their services could be delayed;

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•regulators may revise the requirements for approving our product candidates, or such requirements may not be as we expect;

•the FDA or comparable foreign regulatory authorities may disagree with our clinical trial design or our interpretation of data from preclinical studies and clinical trials, or may change the requirements for approval even after it has reviewed and commented on the design of our clinical trials;

•regarding trials managed by our existing or any future collaborators, our collaborators may face any of the above issues, and may conduct clinical trials in ways they view as advantageous to them but potentially suboptimal for us; and

•geopolitical events may affect international and overseas trial sites in ways beyond our control.

If we are required to conduct additional clinical trials or other testing of our product candidates beyond those that we currently contemplate, if we are unable to successfully complete clinical trials of our product candidates or other testing, if the results of these trials or tests are not positive or are only modestly positive or if there are safety concerns, or if we are forced to delay or abandon certain clinical trials or other testing in order to conserve capital resources, we may:

•be delayed in obtaining marketing approval for our product candidates, if at all;

•obtain marketing approval in some countries and not in others;

•obtain approval for indications or patient populations that are not as broad as intended or desired;

•obtain approval with labeling that includes significant use or distribution restrictions or safety warnings;

•be subject to additional post-marketing testing requirements; or

•have a product removed from the market after obtaining marketing approval.

We could also encounter delays if a clinical trial is suspended or terminated. Authorities may impose such a suspension or termination due to a number of factors, including failure to conduct the clinical trial in accordance with regulatory requirements or our clinical protocols, inspection of the clinical trial operations or trial site by the FDA or comparable foreign regulatory authorities resulting in the imposition of a clinical hold, unforeseen safety issues or adverse side effects, failure to demonstrate a benefit from using a drug, changes in governmental regulations or administrative actions or lack of adequate funding to continue the clinical trial. In addition, changes in regulatory requirements and policies may occur, and we may need to amend clinical trial protocols to comply with these changes. Amendments may require us to resubmit our clinical trial protocols to IRBs for reexamination, which may impact the costs, timing or successful completion of a clinical trial.

Our product development costs will increase if we experience delays in clinical testing or in obtaining marketing approvals. We do not know whether any of our preclinical studies or clinical trials will begin as planned, will need to be restructured or will be completed on schedule, or at all. Significant preclinical or clinical trial delays also could shorten any periods during which we may have the exclusive right to commercialize our product candidates or allow our competitors to bring products to market before we do, potentially impairing our ability to successfully commercialize our product candidates and harming our business and results of operations.

If we experience delays or difficulties in the enrollment of patients in clinical trials, our receipt of necessary regulatory approvals could be delayed or prevented.

We may not be able to initiate or continue clinical trials for our product candidates if we are unable to locate and enroll a sufficient number of eligible patients to participate in these trials as required by the FDA or similar regulatory authorities outside the United States. In addition, from time to time our competitors have ongoing clinical trials for product candidates that treat the same indications as our product candidates, and patients who would otherwise be eligible for our clinical trials may instead enroll in clinical trials of our competitors’ product candidates. Our inability to enroll a sufficient number of patients for our clinical trials would result in significant delays and could require us to abandon one or more clinical trials altogether. Enrollment delays in our clinical trials may result in increased development costs for our product candidates, which could cause the value of our common stock to decline and limit our ability to obtain additional financing.

We may conduct clinical trials for product candidates at sites outside the United States, and the FDA may not accept data from trials conducted in such locations or the complexity of regulatory burdens may otherwise adversely impact us.

Opening and conducting clinical trials at trial sites outside the United States may involve additional regulatory, administrative and financial burdens, including compliance with foreign and local requirements relating to regulatory submission and clinical trial practices. Although the FDA may accept data from clinical trials conducted outside the United

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States, acceptance of these data is subject to certain conditions imposed by the FDA. For example, the clinical trial must be well designed and conducted and performed by qualified investigators in accordance with GCPs and the FDA must be able to validate the data from the trial through an onsite inspection, if necessary. Generally, the patient population for any clinical trials conducted outside the United States must be representative of the population for which we intend to seek approval in the United States. In addition, while these clinical trials are subject to the applicable local laws, FDA acceptance of the data will be dependent upon its determination that the trials also complied with all applicable U.S. laws and regulations. Nonetheless, there can be no assurance that the FDA will accept data from trials conducted outside the United States. If the FDA does not accept the data from any trial that we conduct outside the United States, it would likely result in the need for additional clinical trials, which would be costly and time-consuming and delay or permanently halt our development of any applicable product candidates.

Additional risks inherent in conducting international clinical trials include:

•foreign regulatory requirements that could burden or limit our ability to conduct our clinical trials;

•increased costs and heightened supply constraints associated with the acquisition of standard of care drugs and/or combination or comparator agents for which we may bear responsibility in certain jurisdictions;

•administrative burdens of conducting clinical trials under multiple foreign regulatory schema;

•foreign exchange fluctuations;

•more burdensome manufacturing, customs, shipment and storage requirements;

•cultural differences in medical practice and clinical research;

•lack of consistency in standard of care from country to country;

•diminished protection of intellectual property in some countries;

•changes in country or regional regulatory requirements; and

•geopolitical instability or wars in regions outside of the United States where we conduct clinical trials may impact ongoing clinical trials.

We may not be able to qualify for or obtain various designations from regulators that would have the potential to expedite the review process of one or more of our product candidates and even if we do receive one or more such designations there is no guarantee that they will ultimately expedite the process, or aid in our obtaining marketing approval or provide market exclusivity.

There exist several designations that we can apply for from the FDA and other regulators that would provide us with various combinations of the potential for expedited regulatory review, certain financial incentives, aid in our obtaining marketing approval as well as the potential for post-approval exclusivity for a period of time. These designations include but are not limited to orphan drug designation, breakthrough therapy designation, accelerated approval, CNPV, fast track status and priority review for our product candidates. For example, Descartes-08 has been granted Orphan Drug Designation and RMAT Designation by the FDA for the treatment of MG. Descartes-08 received Rare Pediatric Disease Designation by the FDA for the treatment of JDM. We expect to seek one or more of these designations for our other current and future product candidates. There can be no assurance that any of our other product candidates will qualify for any of these designations. There can also be no assurance that any of our product candidates that do qualify for these designations will be granted such designations or that the FDA will not revoke a designation it grants at a later date, or that Congress will not change the law about a designation.

Further, there can be no assurance that any of our product candidates that are granted such designations, including Descartes-08, will ever benefit from such designations or that the FDA would not withdraw such designations once granted. Were we to receive a designation that promised a period of market exclusivity, such as orphan drug exclusivity, such exclusivity may not effectively protect the product from competition because different drugs can be approved for the same condition. In particular, the scope of exclusivity afforded for mRNA-modified cell therapy products may not be well defined and may change. Further with respect to orphan drug status, even after an orphan drug is approved, the FDA can subsequently approve the same drug for the same condition if the FDA concludes that the later drug is clinically superior if it is shown to be safer, more effective or makes a major contribution to patient care.

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Interim, top-line and preliminary data from our clinical trials that we announce or publish from time to time may change as more patient data become available and are subject to audit and verification procedures that could result in material changes in the final data.

From time to time, we may publish interim, top-line or preliminary data from our clinical studies, which is based on a preliminary analysis of then-available data, and the results and related findings and conclusions are subject to change following a full analysis of all data related to the particular trial. We also make assumptions, estimations, calculations and conclusions as part of our analyses of data, and we may not have received or had the opportunity to fully and carefully evaluate all data. As a result, the top-line results that we report may differ from future results of the same studies, or different conclusions or considerations may qualify such results, once additional data have been received and fully evaluated. Preliminary or top-line data also remain subject to audit and verification procedures that may result in the final data being materially different from the preliminary data we previously published. Interim data from clinical trials are subject to the risk that one or more of the clinical outcomes may materially change as patient enrollment continues and more patient data become available.

Interim, top-line or preliminary data may not be representative of final data. If final data is not as positive as earlier interim, top-line or preliminary we have released, our business prospects would be significantly harmed.

In addition, the information we choose to publicly disclose regarding a particular study or clinical trial is based on what is typically extensive information, and you or others may not agree with what we determine is the material or otherwise appropriate information to include in our disclosure. Any information we determine not to disclose may ultimately be deemed significant by you or others with respect to future decisions, conclusions, views, activities or otherwise regarding a particular product candidate or our business. As a result, preliminary and top-line data should not be relied upon in making an investment decision in our securities.

Our product candidates may cause undesirable side effects or have other properties that could delay or prevent their regulatory approval, limit the commercial profile of an approved label, or result in significant negative consequences following marketing approval, if any.

Undesirable side effects caused by our product candidates could cause us or regulatory authorities to interrupt, delay or halt clinical trials, could result in a more restrictive label or the delay or denial of regulatory approval by the FDA or other comparable foreign authorities and could result in decreased market acceptance of any of our product candidates, if approved. Results of our clinical trials could reveal a high and unacceptable severity and prevalence of side effects. In such an event, our trials could be suspended or terminated, and the FDA or comparable foreign regulatory authorities could order us to cease further development of or deny approval of our product candidates for any or all targeted indications.

In November 2023, the FDA issued a statement that it is investigating serious risk of T-cell malignancy following BCMA-directed or CD19-directed autologous CAR-T cell immunotherapies. While the FDA noted that it currently believes that the overall benefits of these products continue to outweigh their potential risks for their approved uses, the FDA stated that it is investigating the identified risk of T-cell malignancy with serious outcomes, including hospitalization and death, and is evaluating the need for regulatory action. Further, in January 2024, the FDA announced it would require a so-called “boxed warning” be added to the prescribing information for all six then-currently approved CAR-T therapies. A boxed warning is the strongest safety labeling the FDA may require. However, because all currently approved CAR T-cell immunotherapies are in oncology indications, there can be no assurance that FDA will reach the same risk-benefit analysis in other indications. In June 2025, the FDA eliminated the REMS for currently approved BCMA- and CD19-directed autologous chimeric antigen receptor CAR T cell immunotherapies, but maintained the boxed warning and stated that the products would continue to be subject to safety monitoring through AE reporting and any post-marketing commitments or requirements.

While we believe our mRNA-based CAR-T product candidates may have a differentiated toxicity profile than currently approved DNA-based CAR-T therapies, there can be no assurance that the FDA would not treat Descartes-08 or any of our other product candidates similar to approved DNA-based CAR-T therapies, or decide a REMS is necessary to assure safe use. The FDA’s investigation may impact the FDA’s review of product candidates that we are developing, or that we may seek to develop in the future, which may, among other things, result in additional regulatory scrutiny of our product candidates, delay the timing for receiving any regulatory approvals or impose additional post-approval requirements on any of our product candidates that receive regulatory approval.

Any drug-related side effects observed in our clinical trials could also affect patient enrollment in our clinical trials or the ability of any enrolled patients to complete such trials or result in potential product liability claims. Any of these occurrences may harm our business, financial condition and prospects significantly.

Additionally, if one or more of our product candidates receives marketing approval, and we or others later identify undesirable side effects caused by such products, a number of potentially significant negative consequences could result, including:

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•regulatory authorities may withdraw approvals of such product;

•regulatory authorities may require the addition of labeling statements, such as a boxed warning or a contraindication;

•regulatory authorities may impose additional restrictions on the marketing of, or the manufacturing processes for, the particular product;

•we may be required to create a medication guide outlining the risks of such side effects for distribution to patients;

•we could be sued and held liable for harm caused to patients, or become subject to fines, injunctions or the imposition of civil or criminal penalties;

•our reputation may suffer; and

•we could be required to develop a risk evaluation and mitigation strategies, or REMS, plan to prevent, monitor and/or manage a specific serious risk by informing, educating and/or reinforcing actions to reduce the frequency and/or severity of the event.

Any of these events could prevent us from achieving or maintaining market acceptance of a particular product candidate, if approved, and could significantly harm our business, results of operations and prospects.

Inadequate funding for the FDA and other government agencies and/or potentially shifting priorities under the new presidential administration could hinder the FDA’s and/or those other government agencies’ ability to hire and retain key leadership and other personnel, prevent new products and services from being developed or commercialized in a timely manner, or otherwise prevent those agencies from performing normal business functions on which the operation of our business may rely, which could negatively impact our business.

The ability of the FDA to review and approve new products, provide feedback on clinical trials and development programs, meet with sponsors and otherwise review regulatory submissions can be affected by a variety of factors, including government budget and funding levels; ability to hire and retain key personnel and accept the payment of user fees; and statutory, regulatory, and policy changes, among other factors. Average review times at the FDA may fluctuate as a result. In addition, government funding of other government agencies on which our operations may rely is subject to the political process, which is inherently fluid and unpredictable.

Disruptions at the FDA and other agencies may also increase the time necessary for new drugs to be reviewed and/or approved by necessary government agencies or to otherwise respond to regulatory submissions, which would adversely affect our business. For example, the Trump Administration has discussed several changes to the reach and oversight of the FDA, which could affect its relationship with the pharmaceutical industry, transparency in decision making and ultimately the cost and availability of prescription drugs. Additionally, over the last several years, the U.S. government has shut down multiple times and certain regulatory agencies, such as the FDA, have had to furlough or reduce the number of critical FDA and other government employees and stop critical activities. If funding for the FDA is reduced, FDA priorities change or a prolonged government shutdown occurs, it could significantly impact the ability of the FDA to timely review and process our regulatory submissions which could have a material adverse effect on our business.

Additionally, we have in the past received grant funding from the National Institutes of Health, or NIH, and under the terms of previously awarded grants we expect to continue to receive grant funding from the NIH. Although we do not consider any of these grants material to our business, a prolonged impact on the availability of grant funding from government agencies could adversely impact our business.

Risks Related to our Financial Position and Need for Additional Capital

We are a development-stage company, and we expect to incur losses for the foreseeable future and may never achieve or maintain profitability.

Except for the year ended December 31, 2022, we have incurred significant operating losses since our inception. We incurred a net loss of $130.3 million and $77.4 million for the years ended December 31, 2025, and 2024, respectively. As of December 31, 2025, we had an accumulated deficit of $822.4 million. To date, we have financed our operations primarily through public offerings and private placements of our securities, funding received from collaboration and license arrangements and a credit facility. We currently have no source of product revenue, and we do not expect to generate product revenue for the foreseeable future. We expect to devote substantially all of our financial resources and efforts to developing our mRNA-based therapies for the treatment of autoimmune diseases, identifying potential product candidates and conducting preclinical studies and our clinical trials. We are in the early stages of clinical development of most of our product candidates. We expect to

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continue to incur significant expenses and operating losses for the foreseeable future. We expect that our expenses will increase substantially as we:

•continue the research and development of our product candidates;

•increase and develop our manufacturing and distribution capacities;

•discover and develop additional product candidates;

•seek to maintain and enter into collaboration, licensing and other agreements, including, but not limited to research and development, and/or commercialization agreements;

•seek regulatory approvals for any product candidates that successfully complete clinical trials;

•potentially establish a sales, marketing and distribution infrastructure and scale up internal manufacturing capabilities to commercialize any products for which we may obtain regulatory approval;

•maintain, expand and protect our intellectual property portfolio, including through licensing arrangements;

•add clinical, scientific, operational, financial and management information systems and personnel, including personnel to support our product development and potential future commercialization efforts;

•experience any delays or encounter any issues with any of the above, including, but not limited to, failed studies, complex results, safety issues or other regulatory, manufacturing or scale-up challenges; and

•are exposed to broad macroeconomic conditions including inflation and supply chain tightness which could result in us paying more, or being unable, to access goods and services.

To become and remain profitable, we must succeed in developing and eventually commercializing products that generate significant revenue. This will require us to be successful in a range of challenging activities, including completing preclinical testing and clinical trials of our product candidates, discovering additional product candidates, obtaining regulatory approval and securing reimbursement for these product candidates, manufacturing, marketing and selling any products for which we may obtain regulatory approval, and establishing and managing our collaborations at various stages of a product candidate’s development. We are only in the preliminary stages of most of these activities. We may never succeed in these activities and, even if we do, may never generate revenues that are significant enough to achieve profitability.

Because of the numerous risks and uncertainties associated with pharmaceutical and biological product development, we are unable to accurately predict the timing or amount of increased expenses or when, or if, we will be able to achieve profitability. If we are required by the FDA or other regulatory authorities to perform studies in addition to those currently expected, or if there are any delays in completing our clinical trials or the development of any of our product candidates, our expenses could increase and product revenue could be further delayed.

We may not be able to sustain or increase profitability on a quarterly or annual basis. Our failure to remain profitable would depress our value and could impair our ability to raise capital, expand our business, maintain our research and development efforts, diversify our product offerings or continue our operations.

RNAC US Equity

RNAC · 10-K · period ended 2025-12-31

Item 1. Business

Item 1A. Risk Factors

RNAC US Equity☆

RNAC · 10-K · period ended 2025-12-31

Item 1. Business

Item 1A. Risk Factors

RNAC US Equity