Item 7. Management’s Discussion and Analysis of Financial Condition and Results of Operations

The following discussion and analysis of our financial condition and results of operations should be read in conjunction with our consolidated financial statements and related notes appearing elsewhere in this Annual Report. This discussion and other parts of this Annual Report contain forward-looking statements that involve risks and uncertainties, such as statements regarding our plans, objectives, expectations, intentions and projections. Our actual results could differ materially from those discussed in these forward-looking statements. Important factors that could cause or contribute to such differences include, but are not limited to, those discussed in Item 1A. “Risk Factors.” A discussion of the year ended December 31, 2022 compared to the year ended December 31, 2021 has been reported previously in our Annual Report on Form 10-K for the year ended December 31, 2022, filed with the SEC on March 2, 2023, under the heading “Management’s Discussion and Analysis of Financial Condition and Results of Operations.”

Overview

We are a clinical-stage biotechnology company developing mRNA cell therapies for the treatment of autoimmune diseases. We leverage our proprietary technology and manufacturing platform to introduce one or more mRNA molecules into cells to enhance their function. Unlike DNA, mRNA degrades naturally over time without integrating into the cell’s genetic material. Therefore, our mRNA cell therapies are distinguished by their capacity to be dosed repeatedly like conventional drugs, administered in an outpatient setting, and given without pre-treatment chemotherapy required with many conventional cell therapies. In an open-label Phase 2 clinical trial in patients with MG, a chronic autoimmune disease that causes disabling muscle weakness and fatigue, we observed that our lead product candidate, Descartes-08, generated a deep and durable clinical benefit.

We are leveraging our proprietary technology and manufacturing platform, RNA Armory®, to develop mRNA cell therapies for autoimmune diseases across three modalities. Our mRNA CAR-T modality is a personalized approach that collects a patient’s T-cells and uses mRNA to introduce a CAR into the cell. The CAR redirects the T-cells to target and destroy pathogenic self-reactive cells. Our mRNA MSC modality is an allogeneic approach that introduces one or more mRNAs into donor-sourced MSCs, enabling them to produce proteins that target key pathways involved in autoimmunity. These cells are banked and are designed to be administered off-the-shelf to any patient. Our mRNA in situ modality is designed to deliver mRNA into a patient’s lymph node to generate CAR-T cells and other proteins that target autoimmunity.

Merger

On November 13, 2023, the Company and Old Cartesian entered into the Merger Agreement. In connection with the Merger and pursuant to the Merger Agreement, the Company changed its corporate name to Cartesian Therapeutics, Inc., with Old Cartesian surviving as a wholly owned subsidiary of the Company, as summarized in Note 3 of the accompanying notes to the consolidated financial statements appearing elsewhere in this Annual Report.

Financial Operations

To date, we have financed our operations primarily through public offerings and private placements of our securities, funding received from research grants, collaboration and license arrangements and a credit facility. We do not have any products approved for sale and have not generated any product sales.

Except for the year ended December 31, 2022, we have incurred significant operating losses since our inception. We incurred a net loss of $219.7 million and had net income of $35.4 million for the years ended December 31, 2023 and 2022, respectively. As of December 31, 2023, we had an accumulated deficit of $614.6 million. We expect to continue to incur significant expenses and operating losses for the foreseeable future as we:

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•advance Descartes-08 for MG into Phase 3 development;

•continue to develop our preclinical and clinical-stage product candidates;

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

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

Until we can generate substantial product revenues, we expect to finance our cash needs through a combination of equity offerings, debt financings, and license and collaboration agreements. We may be unable to raise capital when needed or on reasonable terms, if at all, which would force us to delay, limit, reduce or terminate our product development or future commercialization efforts. We will need to generate significant revenues to achieve profitability, and we may never do so.

Concurrently with the closing of the Merger, we entered into a securities purchase agreement in which we agreed to issue 149,330.115 shares of Series A Preferred Stock, in exchange for aggregate gross proceeds of $60.25 million, or the November 2023 Private Placement. We granted customary registration rights to investors in connection with the November 2023 Private Placement.

We believe that our existing cash, cash equivalents, and restricted cash as of December 31, 2023, combined with net proceeds from the November 2023 Private Placement received subsequent to December 31, 2023 will enable us to fund our operating expenses and capital expenditure requirements into mid-2026. We have based this estimate on assumptions that may prove to be wrong, and we could use our capital resources sooner than we currently expect.

We intend to seek collaboration partners for the assets in the development programs that we are no longer actively advancing.

The consolidated financial information presented below includes the accounts of Cartesian Therapeutics, Inc. and our wholly owned subsidiaries, Selecta (RUS) LLC, a Russian limited liability company, or Selecta (RUS), and Selecta Biosciences Security Corporation, a Massachusetts securities corporation, and Cartesian Bio, LLC, a Delaware limited liability company, which is a variable interest entity for which we are the primary beneficiary. All intercompany accounts and transactions have been eliminated.

Collaboration and license revenue

To date, we have not generated any revenue from product sales. Our revenue consists primarily of collaboration and license revenue, which includes amounts recognized related to upfront and milestone payments for research and development funding under collaboration and license agreements. We expect that any revenue we generate will fluctuate from quarter to quarter because of the timing and amounts of fees, research and development reimbursements and other payments from collaborators. We do not expect to generate revenue from product sales for at least the next several years. If we or our collaborators fail to complete the development of our product candidates in a timely manner or fail to obtain regulatory approval as needed, our ability to generate future revenue will be harmed, and will affect the results of our operations and financial position. For further description of the agreements underlying our collaboration and license revenue, see Notes 2 and 14 to our consolidated financial statements included elsewhere in this Annual Report.

Research and development

Our research and development expenses consist of external research and development costs, which we track on a program-by-program basis and primarily include contract manufacturing organization related costs and fees paid to contract research organizations, and internal research and development costs, which are primarily compensation expenses for our research and development employees, lab supplies, analytical testing, allocated overhead costs and other related expenses. Our internal research and development costs are often devoted to expanding our programs and are not necessarily allocable to a specific target.

We expense research and development costs as incurred. Conducting a significant amount of research and development is central to our business model. Product candidates in clinical development generally have higher development costs than those in earlier stages of development, primarily due to the size, duration and cost of clinical trials. The successful development of our clinical and preclinical product candidates is highly uncertain. Clinical development timelines, the probability of success and development costs can differ materially from our expectations. For example, if the FDA or another regulatory authority were to require us to conduct clinical trials beyond those which we currently expect will be required for the completion of clinical development of a product candidate, or if we experience significant delays in enrollment in any of our clinical trials, we could be required to expend significant additional financial resources and time to complete any clinical development.

In June 2020, we and Swedish Orphan Biovitrum AB, or Sobi, entered into a License and Development Agreement, which was amended in October 2023, or, as so amended, the Sobi License. Pursuant to the Sobi License, clinical trial costs incurred to complete development of the product candidate SEL-212, including but not limited to costs incurred while conducting and completing the Phase 3 DISSOLVE trials for SEL-212, were reimbursed by Sobi. These costs, when reimbursed, were

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recognized as revenue consistent with the revenue recognition methodology disclosed in Note 14 to our consolidated financial statements included elsewhere in this Annual Report. The reimbursable costs exclude any costs of additional development activities required that were related to the ImmTOR platform and were unrelated to SEL-212.

In January 2023, we and Audentes Therapeutics, Inc., or Astellas, entered into a License and Development Agreement, or the Astellas Agreement. Pursuant to the Astellas Agreement, Astellas agreed to reimburse us for 25% of all budgeted costs incurred to complete the development of Xork, a bacterial IgG protease licensed from Genovis AB (publ.), or Genovis, for use in Pompe disease with an Astellas gene therapy investigational or authorized product. These costs, when reimbursed, will be recognized as revenue consistent with the revenue recognition methodology disclosed in Note 14 to our consolidated financial statements included elsewhere in this Annual Report.

General and administrative

General and administrative expenses consist primarily of salaries and related benefits, including stock-based compensation, related to our executive, finance, business development and support functions. Other general and administrative expenses include facility-related costs not otherwise allocated to research and development expenses, travel expenses for our general and administrative personnel and professional fees for auditing, tax and corporate legal services, including intellectual property-related legal services.

Investment income

Investment income consists primarily of interest income earned on our cash, cash equivalents and marketable securities.

Interest expense

Interest expense consists of interest expense on amounts borrowed under our credit facilities and loss on extinguishment of debt.

Other income, net

Other income, net consists primarily of sublease income.

Change in fair value of warrant liabilities

Common warrants classified as liabilities are remeasured quarterly at fair value, utilizing a Black-Scholes valuation methodology, with the change in fair value recognized as a component of earnings.

Change in fair value of contingent value right liability

The CVR liability is remeasured quarterly at fair value, utilizing a discounted cash flow valuation methodology, with the change in fair value recognized as a component of earnings.

Change in fair value of Series A Preferred Stock forward contract liabilities

The forward contract liability associated with the delayed issuance of the Series A Preferred Stock related to the Merger and November 2023 Private Placement is remeasured quarterly at fair value, utilizing the market price of our common stock, with the change in fair value recognized as a component of earnings.

Foreign currency transaction gain (loss)

The functional currency of Selecta (RUS) is the Russian ruble. In addition to holding cash denominated in Russian rubles, our Russian bank accounts also hold cash balances denominated in U.S. dollars to facilitate payments to be settled in U.S. dollars or other currencies. As of each of December 31, 2023 and 2022, we maintained cash of $0.2 million in Russian bank accounts in denominations of both Russian rubles and U.S. dollars. The amounts denominated in U.S. dollars and used in transacting the day-to-day operations of our Russian subsidiary are subject to transaction gains and losses, which are reported as incurred.

Results of Operations

Comparison of the Years Ended December 31, 2023 and 2022

Collaboration and license revenue

During the year ended December 31, 2023, we recognized $26.0 million of collaboration and license revenue, compared to $110.8 million for the year ended December 31, 2022, a decrease of $84.8 million, or 77%. The decrease was primarily due to a

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decrease of revenue recognized under the Sobi License resulting from both the shipment of clinical supply and the reimbursement of costs incurred for the Phase 3 DISSOLVE clinical program partially offset by an increase for revenue recognized under the Astellas Agreement.

Research and development expenses

For the year ended December 31, 2023, our research and development expenses were $71.8 million, compared to $72.4 million for the year ended December 31, 2022, a decrease of $0.6 million, or 1%. The decrease in cost was primarily the result of reductions in expenses incurred for preclinical and clinical programs due to the strategic reprioritization partially offset by expenses incurred for stock compensation and personnel expenses.

General and administrative expenses

During the year ended December 31, 2023, our general and administrative expenses were $40.6 million, compared to $23.9 million for the year ended December 31, 2022, an increase of $16.7 million, or 70%. The increase in costs was primarily the result of expenses incurred for stock compensation, personnel expenses, and professional fees incurred in connection with the Merger.

Investment income

Investment income for the year ended December 31, 2023 was $5.0 million, compared to $2.1 million for the year ended December 31, 2022, an increase of $2.9 million, or 138%. The increase in investment income was due to increased investment balances and higher interest rates.

Foreign currency transaction gain (loss)

We recognized de minimis foreign currency translation adjustments during each of the years ended December 31, 2023 and 2022.

Interest expense

Interest expense for the year ended December 31, 2023 was $2.8 million compared to $3.0 million for the year ended December 31, 2022, a decrease of $0.2 million, or 7%. Interest expense for the year ended December 31, 2023 comprised interest expense and amortization of the carrying costs of our credit facilities and loss on extinguishment of debt.

Change in fair value of warrant liabilities

For the year ended December 31, 2023, we recognized $12.7 million of income from the decrease in the fair value of warrant liabilities, compared to $20.9 million for the year ended December 31, 2022, a decrease of $8.2 million or 39.2%. Fair value of warrant liabilities was determined utilizing the Black-Scholes valuation methodology. The decrease in warrant value was primarily driven by a decrease in the per-share price of our common stock.

Change in fair value of contingent value right liability

For the year ended December 31, 2023 we recognized $18.3 million of expense associated with the increase in the fair value of CVR liability. The fair value of the CVR liability was determined utilizing a discounted cash flow valuation methodology. The increase in CVR value was primarily driven by the decrease in interest rates from the Merger to December 31, 2023 and the corresponding impact on the discount rate used in our discounted cash flow valuation. There was no CVR liability prior to the Merger and as such no CVR liability is reflected in our consolidated financial statements as of or for any period prior to the year ended December 31, 2023.

Change in fair value of Series A Preferred Stock forward contract liabilities

For the year ended December 31, 2023 we recognized $149.6 million of expense associated with the increase in the fair value of Series A Preferred Stock forward contract liabilities. The increase in Series A Preferred Stock value was primarily driven by an increase in the per-share price of our common stock since the date of the Merger and November 2023 Private Placement. A portion of the Series A Preferred Stock forward contract liability was settled during the year ended December 31, 2023 and there was no such forward contract liability prior to the Merger. There was no Series A Preferred Stock forward contract liability prior to the Merger and as such no Series A Preferred Stock forward contract liability is reflected in our consolidated financial statements as of or for any period prior to the year ended December 31, 2023.

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Other income, net

During the year ended December 31, 2023, we recognized other income, net of $0.7 million, compared to $0.3 million for the year ended December 31, 2022, an increase of $0.4 million, or 133%. The increase was primarily driven by sublease income.

Income taxes

During the year ended December 31, 2023, we recognized a current tax benefit of $19.0 million relating to the benefit of legacy Selecta tax attributes that reduced deferred tax liabilities during the year. For the year ended December 31, 2022, we recognized a $0.6 million benefit for penalty abatements received.

Net (loss) income

Net loss for the year ended December 31, 2023 was $219.7 million as compared to net income of $35.4 million for the year ended December 31, 2022, a decrease of $255.1 million, or 721%. The change was primarily due to decreased collaboration and license revenue and expenses associated with the change in fair value of the CVR liability and Series A Preferred Stock forward contract liability, and increased general and administrative expenses, partially offset by an increase in income tax benefit.

Liquidity and Capital Resources

Except for net income of $35.4 million for the year ended December 31, 2022, we have incurred recurring net losses since our inception. We expect that we will continue to incur losses and that such losses will increase for the foreseeable future. We expect that our research and development and general and administrative expenses will continue to increase and, as a result, we will need additional capital to fund our operations, which we may raise through a combination of equity offerings, debt financings, third-party funding, potential royalty and/or milestone monetization transactions and other collaborations and strategic alliances.

On a pro forma basis, giving effect to the receipt of $40.0 million of net proceeds from our November 2023 Private Placement received subsequent to December 31, 2023, our cash, cash equivalents, and restricted cash were $118.3 million as of December 31, 2023, of which $1.4 million was restricted cash related to lease commitments and $0.2 million was held by our Russian subsidiary designated solely for use in its operations.

In addition to our existing cash equivalents, we from time to time have received and may receive in the future research and development funding pursuant to our collaboration and license agreements. Currently, funding from payments under our collaboration agreements represent our only source of committed external funds.

Liability associated with the contingent value rights agreement, or CVR Agreement, entered into on December 6, 2023, will be settled solely through cash flow received under the Sobi License and any other Gross Proceeds (as such term is defined in the CVR Agreement) net of certain agreed deductions. Under the CVR Agreement, 100% of all milestone payments, royalties, and other amounts paid to us or our controlled entities under the Sobi License, and any other Gross Proceeds, in each case net of certain agreed deductions, will be distributed to holders of the CVRs. There is no contractual obligation for us to fund any amount related to the CVR liability.

Collaboration and License Agreements

In-licenses

In September 2023, we entered into the Biogen Agreement, a non-exclusive, sublicensable, worldwide, perpetual patent license agreement with 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. For further description of the Biogen Agreement, see Note 16 to our consolidated financial statements included elsewhere in this Annual Report.

Effective September 2019, we entered into the NCI Agreement, a nonexclusive, worldwide license agreement with 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 $0.1 million 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. For further description of the NCI Agreement, see Note 16 to our consolidated financial statements included elsewhere in this Annual Report.

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In October 2021, we and Ginkgo Bioworks Holdings, Inc., or Ginkgo, entered into a Collaboration and License Agreement, or the First Ginkgo Agreement, and paid Ginkgo a $0.5 million one-time upfront payment. In June 2022, we paid $0.5 million and issued 892,857 shares of our common stock then-valued at $1.0 million to Ginkgo for the achievement of certain preclinical milestones under the First Ginkgo Agreement. In January 2022, we entered into a Collaboration and License Agreement, or the Second Ginkgo Agreement, and paid Ginkgo a $1.5 million one-time upfront payment. In July 2023, we paid $1.0 million and issued 1,339,285 shares of our common stock then-valued at $1.5 million to Ginkgo for the achievement of certain preclinical milestones under the Second Ginkgo Agreement. For further description of the First Ginkgo Agreement and the Second Ginkgo Agreement, see Note 16 to our consolidated financial statements included elsewhere in this Annual Report.

Additionally, in October 2021, we entered into an Exclusive License Agreement with Genovis, or the Genovis Agreement, and paid Genovis a $4.0 million one-time upfront payment. In February 2023, as a result of the sublicense of Xork to Astellas, we made a $4.0 million payment to Genovis. For further description of the Genovis Agreement, see Note 16 to our consolidated financial statements included elsewhere in this Annual Report.

On September 7, 2021, we entered into a Collaboration and License Agreement, or the Cyrus Agreement, with Cyrus Biotechnology, Inc., or Cyrus, and purchased 2,326,934 shares of Cyrus’ Series B Preferred Stock, par value $0.0001 per share at a purchase price of $0.8595 per share for an aggregate purchase price of $2.0 million. In October 2023, we notified Cyrus of our termination of the Cyrus Agreement, effective December 29, 2023. For further description of the Cyrus Agreement, see Note 16 to our consolidated financial statements included elsewhere in this Annual Report.

Out-licenses

In January 2023, we entered into the Astellas Agreement with Astellas. Under this agreement, Astellas obtained the sole and exclusive right to commercialize Xork for use in Pompe disease in combination with an Astellas gene therapy investigational or authorized product, with a current focus on AT845. In connection with entry into this agreement, we received a $10 million upfront payment and are eligible to receive $340.0 million for certain additional development and commercial milestones plus royalties on any potential commercial sales where Xork is used as a pre-treatment for AT845. As a result of the sublicense of Xork to Astellas, we made a $4.0 million payment to Genovis in February 2023. For further description of the Astellas Agreement, see Note 14 to our consolidated financial statements included elsewhere in this Annual Report.

On October 1, 2021, we entered into a License Agreement, or the Takeda Agreement, with Takeda Pharmaceuticals USA, Inc. We received a $3.0 million upfront payment and were entitled to receive up to $1.124 billion in future additional payments over the course of the partnership that were contingent on the achievement of development or commercial milestones or Takeda’s election to continue its activities at specified development stages. The Takeda Agreement was terminated effective July 25, 2023. For further description of the Takeda Agreement, see Note 14 to our consolidated financial statements included elsewhere in this Annual Report.

In June 2020, we entered into the Sobi License. Sobi paid us a one-time, upfront payment of $75 million, and upon the closing of a private placement of our common stock to Sobi at a price of $4.6156 per share, we received an additional $25 million from Sobi. We are eligible to receive $630 million in milestone payments upon the achievement of various development and regulatory milestones and sales thresholds for annual net sales of SEL-212, and tiered royalty payments ranging from the low double digits on the lowest sales tier to the high teens on the highest sales tier. Sobi has agreed to fund the Phase 3 clinical program of SEL-212, which commenced in September 2020. In July 2022, we received $10.0 million for the completion of the enrollment of the DISSOLVE II trial. Proceeds from milestone payments and royalties on sales of SEL-212, if any, are required to be distributed, net of certain agreed deductions, to holders of the CVRs. For further description of the Sobi License, see Note 14 to our consolidated financial statements included elsewhere in this Annual Report.

Additionally, in June 2020, we and Sarepta Therapeutics, Inc., or Sarepta, entered into a Research License and Option Agreement, or the Sarepta Agreement. Sarepta paid us a $2.0 million upfront payment upon closing and $3.0 million for the achievement of certain pre-clinical milestones in June 2021. In August 2022, we received a payment of $2.0 million in exchange for a nine-month extension to Sarepta's options to both Duchenne muscular dystrophy and certain limb-girdle muscular dystrophies and a payment of $4.0 million for the achievement of certain non-clinical milestones. In March 2023, we were notified by Sarepta that Sarepta would not be exercising its exclusive option under the Sarepta Agreement. The Sarepta Agreement terminated upon the expiration of the option in March 2023. For further description of the Sarepta Agreement, see Note 14 to our consolidated financial statements included elsewhere in this Annual Report.

In December 2019, we and Asklepios BioPharmaceutical, Inc., or AskBio, entered into a license agreement, or the AskBio License Agreement. Pursuant to the AskBio License Agreement, AskBio previously exercised its option to exclusively license intellectual property rights covering ImmTOR to research, develop, and commercialize certain adeno-associated virus, or AAV, gene therapy products utilizing ImmTOR, and targeting the GAA gene, or derivatives thereof, to treat Pompe Disease. We received $7.0 million of upfront fees pursuant to the AskBio License Agreement. In November 2022, the AskBio License Agreement was mutually terminated. For further description of the AskBio License Agreement, see Note 14 to our consolidated financial statements included elsewhere in this Annual Report.

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Financings

On August 6, 2020, we entered into a sales agreement, or the 2020 Sales Agreement, with Jefferies LLC, as sales agent, pursuant to which we were permitted, from time to time, to issue and sell common stock with an aggregate value of up to $50.0 million in an “at-the-market” offering. On October 8, 2021, we delivered notice to Jefferies LLC that we were terminating the 2020 Sales Agreement, with effect as of October 19, 2021.

On October 25, 2021, we entered into a Sales Agreement, or the 2021 Sales Agreement, with Leerink Partners LLC, or Leerink Partners (and then known as SVB Leerink LLC), to sell shares of our common stock, from time to time, through an “at the market” equity offering program under which Leerink Partners will act as sales agent. The shares of common stock sold pursuant to the 2021 Sales Agreement, if any, would be issued and sold pursuant to a registration statement filed with the Securities and Exchange Commission, or SEC, for remaining aggregate gross sales proceeds of up to $51.0 million.

During the year ended December 31, 2023, we sold no shares of our common stock pursuant to the 2021 Sales Agreement. During the year ended December 31, 2022, we sold 774,544 shares of our common stock pursuant to the 2021 Sales Agreement for aggregate net proceeds of $2.1 million, after deducting commissions and other transaction costs. During the year ended December 31, 2021, we sold 13,767,511 shares of our common stock pursuant to the 2021 and 2020 Sales Agreements, as applicable, for aggregate net proceeds of $51.9 million, after deducting commissions and other transaction costs.

On April 11, 2022, we sold an aggregate of 27,428,572 shares of our common stock at a purchase price of $1.41 per share and warrants to purchase an aggregate of 20,571,429 shares of common stock at a purchase price of $1.55 per share underlying each common warrant for net proceeds of $36.9 million, after deducting commissions and other transaction costs.

On November 13, 2023, we entered into a securities purchase agreement with (i) Dr. Timothy A. Springer, a member of our Board of Directors; (ii) TAS Partners LLC, an affiliate of Dr. Springer, and (iii) Seven One Eight Three Four Irrevocable Trust, a trust associated with Dr. Murat Kalayoglu, a co-founder and the former chief executive officer of Old Cartesian, who joined our Board of Directors effective immediately after the effective time of the Merger, providing for the November 2023 Private Placement. In the November 2023 Private Placement, we issued and sold an aggregate of 149,330.115 shares of Series A Preferred Stock for an aggregate purchase price of $60.25 million, of which 50,189.789 shares of Series A Preferred Stock were issued and sold in the year ended December 31, 2023 for gross proceeds of $20.25 million, and 99,140.326 shares of Series A Preferred Stock were issued and sold subsequent to December 31, 2023 for gross proceeds of $40.0 million.

Indebtedness

We previously maintained a term loan of up to $35.0 million, of which $25.0 million was funded in August 2020. In September 2023, we entered into a payoff letter with Oxford Finance LLC and Silicon Valley Bank, a division of First-Citizens Bank & Trust Company (successor by purchase to the Federal Deposit Insurance Corporation as Receiver for SVBB (as successor to Silicon Valley Bank)), the lenders under the term loan, pursuant to which we paid all outstanding amounts under such term loan, together with accrued interest and a prepayment penalty, resulting in the full extinguishment of such term loan. The total payoff amount was $22.3 million, consisting of the remaining principal amount due of $19.8 million, the final payment fee of $2.3 million, the prepayment penalty of $0.2 million, and less than $0.1 million of accrued interest.

If in the future we seek debt financing, the terms of such debt could restrict our operating and financial flexibility by imposing liens on our assets and covenants on the operation of our business.

Future funding requirements

As of the date of this Annual Report, we have not generated any revenue from product sales. We do not know when, or if, we will generate revenue from product sales. We will not generate significant revenue from product sales unless and until we obtain regulatory approval and commercialize one of our current or future product candidates. Our primary uses of capital are, and we expect will continue to be, compensation and related expenses, third-party clinical research and development services, laboratory and related supplies, clinical costs, legal and other regulatory expenses, milestone and royalty payments for in-licenses, and general overhead costs. We expect that we will continue to generate losses for the foreseeable future, and we expect the losses to increase as we continue the development of, and seek regulatory approvals for, our product candidates, and begin to commercialize any approved products. We are subject to risks in the development of our products, and we may encounter unforeseen expenses, difficulties, complications, delays and other unknown factors that may adversely affect our business. We expect that we will need substantial additional funding to support our continuing operations.

The Certificate of Designation contains a provision granting each holder of the Series A Preferred Stock the option to require us to redeem any or all of such holder’s then-outstanding shares of Series A Preferred Stock beginning on the date that is 18 months following the Closing; provided, however, that no holder will have the right to seek redemption of any shares of Series A Preferred Stock to the extent that such holder would otherwise be unable to convert such shares of Series A Preferred Stock due to the common stock beneficial ownership limitation applicable to such holder. The per-share redemption price would be the average closing trading price of the common stock for the ten preceding trading days ending on, and including, the trading day immediately prior to the date a notice of conversion is delivered to us. We could be required to use a significant

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amount of our cash resources on hand to satisfy this redemption obligation, particularly if our stockholders do not ever approve the Conversion Proposal and no shares of Series A Preferred Stock are automatically converted into common stock, or generally if holders of Series A Preferred Stock exercise their redemption right with respect to a significant number of shares of Series A Preferred Stock or at a time when the trading price of our common stock is elevated. Further, in the event that we do not have sufficient cash on hand to satisfy our redemption obligations, we may need to raise additional capital to satisfy these potential obligations. Any redemption payments could materially limit the amount of cash we have available to fund our operations and the potential need to redeem shares of Series A Preferred Stock may limit the flexibility with which we seek to operate our business.

As of December 31, 2023, we had an accumulated deficit of $614.6 million. We anticipate operating losses to continue for the foreseeable future due to, among other things, costs related to research, development of our product candidates, conducting preclinical studies and clinical trials, and our administrative organization. We will require substantial additional financing to fund our operations and to continue to execute our strategy, and we will pursue a range of options to secure additional capital.

We regularly evaluate various potential sources of additional funding such as strategic collaborations, license agreements, debt issuance, potential royalty and/or milestone monetization transactions and the issuance of equity instruments to fund our operations. If we raise additional funds through strategic collaborations and alliances, which may include existing collaboration partners, we may have to relinquish valuable rights to our technologies or product candidates, or grant licenses on terms that are not favorable to us. To the extent that we raise additional capital through the sale of equity instruments, the ownership interest of our existing stockholders will be diluted, and other preferences may be necessary that adversely affect the rights of existing stockholders.

We believe that our existing cash, cash equivalents, and restricted cash as of December 31, 2023 combined with net proceeds from the November 2023 Private Placement received subsequent to December 31, 2023 will enable us to fund our operating expenses and capital expenditure requirements for at least the next 12 months. We may pursue additional cash resources through public or private equity or debt financings, by establishing collaborations with other companies or through the monetization of potential royalty and/or milestone payments pursuant to our existing collaboration and license arrangements. Management’s expectations with respect to our ability to fund current and long-term planned operations are based on estimates that are subject to risks and uncertainties. If actual results are different from management’s estimates, we may need to seek additional strategic or financing opportunities sooner than would otherwise be expected. However, there is no guarantee that any of these strategic or financing opportunities will be executed on favorable terms, and some could be dilutive to existing stockholders. If we are unable to obtain additional funding on a timely basis, we may be forced to significantly curtail, delay, or discontinue one or more of our planned research or development programs or be unable to expand our operations, meet long-term obligations or otherwise capitalize on our commercialization of our product candidates.

Our future capital requirements will depend on many factors, including:

•the timing for stockholder approval of the conversion of our Series A Preferred Stock into shares of our common stock and any redemptions of Series A Preferred Stock for cash;

•the scope, progress, results and costs of our clinical trials, preclinical development, manufacturing, laboratory testing and logistics;

•the number of product candidates that we pursue and the speed with which we pursue development;

•our headcount growth and associated costs;

•the costs, timing and outcome of regulatory review of our product candidates;

•the costs and timing of future commercialization activities, including manufacturing, marketing, sales and distribution, for any of our product candidates for which we receive marketing approval;

•the revenue, if any, from commercial sales of our product candidates for which we receive marketing approval;

•the costs and timing of preparing, filing and prosecuting patent applications, maintaining and enforcing our intellectual property rights and defending any intellectual property-related claims;

•the effect of competing technological and market developments; and

•the extent to which we acquire or invest in businesses, products and technologies, including entering into licensing or collaboration arrangements for product candidates.

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Summary of Cash Flows

Year Ended December 31,

Cash (used in) and provided by:

Effect of exchange rate changes on cash (53) 20 (3)

Operating activities

Net cash used in operating activities for the year ended December 31, 2023 was $51.2 million compared to $31.6 million in the same period in 2022. The increase in net cash used in operating activities of $19.6 million was primarily due to $56.2 million of net loss, adjusted for non-cash items, and $5.0 million of cash provided by changes in operating assets and liabilities, in each case during the year ended December 31, 2023.

Investing activities

Net cash provided by investing activities for the year ended December 31, 2023 was $34.6 million compared to net cash used in investing activities of $15.0 million in the same period in 2022, an increase of $49.6 million. The net cash provided by investing activities for the year ended December 31, 2023 was primarily proceeds from the maturities of marketable securities and cash assumed in the Merger offset by purchases of property and equipment. The net cash used in investing activities for the year ended December 31, 2022 was to purchase marketable securities and property and equipment, offset by proceeds from the maturities of marketable securities.

Financing activities

Net cash used in financing activities for the year ended December 31, 2023 was $13.1 million compared to net cash provided by financing activities of $39.2 million in the same period in 2022, a decrease of $52.3 million. The net cash used in financing activities for the year ended December 31, 2023 was primarily the result of repayments of principal on outstanding debt and settlement of equity awards in the Merger partially offset by proceeds from the November 2023 Private Placement. The net cash provided by financing activities for the year ended December 31, 2022 was primarily the result of net proceeds from issuance of common stock and warrants to purchase common stock and the issuance of common stock in the "at-the-market"offering contemplated by the 2021 Sales Agreement.

Recent Accounting Pronouncements

For a discussion of recently adopted or issued accounting pronouncements please see Note 2 to our consolidated financial statements included elsewhere in this Annual Report.

Off-Balance Sheet Arrangements

As of December 31, 2023, we did not have any off-balance sheet arrangements as defined in the rules and regulations of the SEC.

Critical Accounting Policies and Use of Estimates

Our management’s discussion and analysis of our financial condition and results of operations is based on our consolidated financial statements, which have been prepared in accordance with U.S. GAAP. The preparation of these consolidated financial statements requires us to make estimates and judgements that affect the reported amounts of assets, liabilities, revenues and expenses, and disclosure of contingent assets and liabilities in our consolidated financial statements. Actual results may differ from these estimates under different assumptions or conditions and could have a material impact on our reported results. While our significant accounting policies are more fully described in the notes to our consolidated financial statements included elsewhere in this Annual Report, we believe the following accounting policies to be the most critical in understanding the judgments and estimates we use in preparing our consolidated financial statements:

Revenue Recognition

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contract(s) with a customer; (ii) identify the performance obligations in the contract, including whether they are distinct in the context of the contract; (iii) determine the transaction price, including the constraint on variable consideration; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) we satisfy each performance obligation. We only apply the five-step model to contracts when it is probable that the entity will collect the consideration it is entitled to in exchange for the goods or services it transfers to the customer. At contract inception, once the contract is determined to be within the scope of ASC 606, we assess the goods or services promised within each contract and determine those that are performance obligations, and assess whether each promised good or service is distinct. If a promised good or service is not distinct, it is combined with other promised goods or services into a performance obligation. We then recognize as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. For example, certain performance obligations associated with the Astellas Agreement, (see Note 14) will be satisfied over time, and revenue will be recognized utilizing the input method.

Collaboration and License Revenue: We currently generate revenue through collaboration and license agreements with strategic collaborators for the development and commercialization of product candidates. Collaboration and license agreements with customers are generally accounted for in accordance with ASC 606. We analyze collaboration arrangements by first assessing whether they are within the scope of ASC Topic 808, Collaborative Arrangements (ASC 808), and evaluate whether such arrangements involve joint operating activities performed by parties that are both active participants in the activities and exposed to significant risks and rewards that are dependent on the commercial success of such activities. Collaboration agreements with customers that are not within the scope of ASC 808 are accounted for in accordance with ASC 606. To the extent the collaboration agreement is within the scope of ASC 808, we also assess whether any aspects of the agreement are within the scope of other accounting literature (specifically ASC 606). If we conclude that some or all aspects of the agreement are distinct and represent a transaction with a customer, we account for those aspects of the arrangement within the scope of ASC 606. We recognize the shared costs incurred that are not within the scope of other accounting literature as a component of the related expense in the period incurred by analogy to ASC Topic 730, Research and Development (ASC 730), and record reimbursements from counterparties as an offset to the related research and development costs. In determining the appropriate amount of revenue to be recognized as we fulfill our obligations under the agreements in accordance with ASC 606, we perform the five steps above. As part of the accounting for the arrangement, we must develop assumptions that require judgment to determine the stand-alone selling price for each performance obligation identified in the contract. We use key assumptions to determine the stand-alone selling price, which may include market conditions, reimbursement rates for personnel costs, development timelines and probabilities of regulatory success. The assumptions used to determine the stand-alone selling price and our satisfaction of performance obligations have a material effect on our collaboration and license revenue and may prove to be wrong.

The terms of our arrangements typically include one or more of the following: (i) upfront fees; (ii) milestone payments related to the achievement of development, regulatory, or commercial goals; (iii) royalties on net sales of licensed products; (iv) reimbursements or cost-sharing of research and development expenses; and (v) profit/loss sharing arising from co-promotion arrangements.

Licenses of Intellectual Property: If the license to our intellectual property is determined to be distinct from the other promised goods and services identified in the arrangement, we recognize revenues from non-refundable, upfront fees allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the license. If not distinct, the license is combined with other promised goods and services in the contract. For licenses that are combined with other promised goods and services, we assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue. We evaluate the measure of progress each reporting period and, if necessary, adjust the measure of performance and related revenue recognition. Optional licenses are evaluated to determine if they are issued at a discount, and therefore, represent material rights and should be accounted for as separate performance obligations.

Milestone Payments: At the inception of each arrangement that includes developmental and regulatory milestone payments, we evaluate whether the achievement of each milestone specifically relates to our efforts to satisfy a performance obligation or transfer a distinct good or service within a performance obligation. If the achievement of a milestone is considered a direct result of our efforts to satisfy a performance obligation or transfer a distinct good or service and the receipt of the payment is based upon the achievement of the milestone, the associated milestone value is allocated to that distinct good or service. If the milestone payment is not specifically related to our efforts to satisfy a performance obligation or transfer a distinct good or service, the amount is allocated to all performance obligations using the relative standalone selling price method. We also evaluate the milestone to determine whether they are considered probable of being reached and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price to be allocated, otherwise, such amounts are constrained and excluded from the transaction price. At the end of each subsequent reporting period, we re-evaluate the probability of achievement of such development milestones and any related constraint, and if necessary, adjust our estimate of the transaction price. Any such adjustments to the transaction price are allocated to the performance obligations on the same

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basis as at contract inception. Amounts allocated to a satisfied performance obligation shall be recognized as revenue, or as a reduction of revenue, in the period in which the transaction price changes.

Manufacturing Supply Services: Arrangements that include a promise for future supply of drug substance or drug product for either clinical development or commercial supply at the customer’s discretion are evaluated to determine if they are distinct and optional. For optional services that are distinct, we assess if they are priced at a discount, and therefore, provide a material right to the licensee to be accounted for as separate performance obligations.

Royalties: For arrangements that include sales-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, we will recognize revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied) in accordance with the royalty recognition constraint.

Clinical Trial Costs

Clinical trial expenses are a significant component of research and development expenses, and we outsource a significant portion of these costs to third parties. Third party clinical trial expenses include patient costs, clinical research organization costs and costs for data management. The accrual for site and patient costs includes inputs such as estimates of patient enrollment, patient cycles incurred, clinical site activations, and other pass-through costs. Payments for these activities are based on the terms of the individual arrangements, which may differ from the pattern of costs incurred, and are reflected on the consolidated balance sheets as a prepaid asset or accrued clinical trial cost. These third party agreements are generally cancellable, and related costs are recorded as research and development expenses as incurred. Non-refundable advance clinical payments for goods or services that will be used or rendered for future research and development activities are recorded as a prepaid asset and recognized as expense as the related goods are delivered or the related services are performed. We also record accruals for estimated ongoing clinical research and development costs. When evaluating the adequacy of the accrued liabilities, we analyze progress of the studies, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates may be made in determining the accrued balances at the end of any reporting period. Actual results could differ from the estimates made by us materially affecting our results of operations. The historical clinical accrual estimates made by us have not been materially different from the actual costs.

Warrant Liabilities

In December 2019, we issued common warrants in connection with a securities purchase agreement between us and a group of institutional investors and certain members of our Board of Directors, or the 2019 Warrants. Pursuant to the terms of the 2019 Warrants, we could be required to settle the common warrants in cash in the event of certain acquisitions of us and, as a result, the 2019 Warrants are required to be measured at fair value and reported as a liability on the balance sheet.

In April 2022, we issued warrants in connection with an underwritten offering of shares of common stock and warrants to purchase shares of common stock, or the 2022 Warrants. Pursuant to the terms of the 2022 Warrants, we could be required to settle the 2022 Warrants in cash in the event we are acquired under certain circumstances and, as a result, the 2022 Warrants are required to be measured at fair value and reported as a liability on the balance sheet.

We recorded the fair value of the 2019 Warrants and 2022 Warrants upon issuance using the Black-Scholes valuation model, and are required to revalue the common warrants at each reporting date with any changes in fair value recorded on our statement of operations. In December 2022, we amended the terms of the outstanding 2019 Warrants held by certain members of our Board of Directors to remove the cash settlement provision (as so amended, the Amended 2019 Warrants). As a result, the Amended 2019 Warrants were remeasured at fair value on December 20, 2022 and reclassified from a liability to equity on the balance sheet.

Inputs used to determine estimated fair value of the common warrant liabilities include the estimated fair value of the underlying stock at the valuation date, the estimated term of the warrants, risk-free interest rates, expected dividends and the expected volatility of the underlying stock. The estimates used to determine the fair value of these common warrants represent our best estimates, but may prove to be wrong. Therefore, the change in fair value of warrant liabilities could be materially different in the future.

Contingent Value Right Liability

The CVRs distributed pursuant to the terms of the CVR Agreement represent financial instruments that are accounted for under the fair value option election in ASC 825, Financial Instruments, or ASC 825. Under the fair value option election, the CVRs are initially measured at the aggregate estimated fair value of the CVRs and will be subsequently remeasured at estimated fair value on a recurring basis at each reporting period date. The estimated fair value of the CVR liability was determined using the discounted cash flow method to estimate future cash flows associated with the legacy assets, including the expected milestone and royalty payments under the Sobi License, net of deductions. Changes in fair value of the liability are presented within change in fair value of CVRs in the consolidated statements of operations and comprehensive income (loss). The liability value is based on significant inputs not observable in the market such as estimated cash flows, estimated

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probabilities of success, and risk-adjustment discount rates, which represent a Level 3 measurement within the fair value hierarchy.

Stock-Based Compensation

We account for all stock-based compensation granted to employees and non-employees using a fair value method. Stock-based compensation is measured at the grant date fair value and is recognized over the requisite service period of the awards, usually the vesting period, on a straight-line basis, net of estimated forfeitures. To the extent that actual forfeitures differ from our estimates, the differences are recorded as a cumulative adjustment in the period the estimates were adjusted. Stock-based compensation expense recognized in the consolidated financial statements is based on awards that ultimately vest.

The assumptions used in determining the fair value of stock-based awards represent our best estimates, but the estimates involve inherent uncertainties and the application of our judgment. As a result, if factors change and we use significantly different assumptions or estimates, our stock-based compensation expense could be materially different in the future.

Smaller Reporting Company

We qualify as a “smaller reporting company” under the rules of the Securities Act and the Exchange Act. As a result, we may choose to take advantage of certain scaled disclosure requirements available specifically to smaller reporting companies. We will remain a smaller reporting company until the last day of the fiscal year in which the aggregate market value of our common stock held by non-affiliated persons and entities, or our public float, is more than $700 million as of the last business day of our most recently completed second fiscal quarter, or until the fiscal year following the year in which we have at least $100 million in revenue and at least $250 million in public float as of the last business day of our most recently completed second fiscal quarter.

Item 7A. Quantitative and Qualitative Disclosures About Market Risk

The market risk inherent in our financial instruments and in our financial position represents the potential loss arising from adverse changes in interest rates. As of December 31, 2023 and 2022, we had cash, cash equivalents, restricted cash and marketable securities of $78.3 million and $136.2 million, respectively, consisting of non-interest and interest-bearing money market accounts, U.S. government agency securities and treasuries, corporate bonds and commercial paper. Our primary exposure to market risk is interest rate sensitivity, which is affected by changes in the general level of U.S. interest rates. Due to the short-term and the low risk profile of our money market accounts, an immediate 100 basis point change in interest rates would not have a material effect on the fair market value of our cash equivalents.

Item 8. Financial Statements and Supplementary Data

The consolidated financial statements together with the report of our independent registered public company accounting firm, required to be filed pursuant to this Item 8 are appended to this Annual Report. An index of those consolidated financial statements is found in Item 15.

Item 9. Changes in and Disagreements With Accountants on Accounting and Financial Disclosure

None.

Item 9A. Controls and Procedures

Evaluation of Disclosure Controls and Procedures

Our management, with the participation of our Chief Executive Officer and Chief Financial Officer, evaluated, as of the end of the period covered by this Annual Report, the effectiveness of our disclosure controls and procedures (as defined in Rules 13a-15(e) and 15d-15(e) under the Exchange Act). Based on that evaluation, our Chief Executive Officer and Chief Financial Officer concluded that our disclosure controls and procedures were not effective at the reasonable assurance level as of December 31, 2023 because of the material weakness in internal control over financial reporting discussed below.

Management’s Annual Report on Internal Control over Financial Reporting

Our management is responsible for establishing and maintaining adequate internal control over our financial reporting, as such term is defined in Rule 13a-15(f) and 15d-15(f) under the Exchange Act.

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Our management conducted an assessment of the effectiveness of our internal control over financial reporting based on the criteria set forth in “Internal Control - Integrated Framework (2013)” issued by the Committee of Sponsoring Organizations of the Treadway Commission.

Management’s assessment of and conclusion on the effectiveness of internal control over financial reporting did not include the internal controls of Old Cartesian, which is included in our consolidated financial statements as of and for the year ended December 31, 2023 and constituted 2% and 1% of total assets and total liabilities, respectively, as of December 31, 2023 and 0% and 1% of revenues and operating expenses, respectively, for the year then ended.

Based on this assessment, our management concluded that, as of December 31, 2023, our internal control over financial reporting was not effective.

As a result of its review, management identified a material weakness. A material weakness is a deficiency, or a combination of deficiencies, in internal control over financial reporting, such that a reasonable possibility exists that a material misstatement of our annual or interim financial statements would not be prevented or detected on a timely basis. There are no material accounting errors or omissions within the consolidated financial statements as a result of this material weakness. Management concluded that it did not design and implement effective internal controls specifically related to the documentation of the assumptions supporting the valuation of the in-process intangible assets in connection with the Old Cartesian material business combination and the initial and ongoing contingent value right obligation issued at the time to legacy Selecta stockholders. This includes a lack of sufficient documentation to provide evidence of the associated management review controls.

Remediation Plans for Material Weakness in Internal Control over Financial Reporting

We are committed to maintaining a strong internal control environment. In response to the identified material weakness above, we, with the oversight of the Audit Committee, intend to take comprehensive actions to remediate the material weakness in internal control over financial reporting. We expect to re-evaluate the scope and level of precision for conducting and documenting the reviews over significant acquisitions and contingent value rights including the review of prospective financial information used in valuation reports produced by third-party specialists supporting the accounting for business combinations and contingent value rights. The remediation efforts are intended both to address the identified material weakness and to enhance our overall financial control environment.

Inherent Limitations of Internal Controls

While we believe we have a robust and efficient system of internal and disclosure controls and procedures, our management, including our Chief Executive Officer and Chief Financial Officer, recognize that it is impossible for our disclosure controls and procedures or our internal controls to prevent all errors and all fraud. A control system, no matter how well conceived and operated, can provide only reasonable, not absolute, assurance that the objectives of the control system are met. Because of the inherent limitations in all control systems, no evaluation of controls can provide absolute assurance that all control issues and instances of fraud, if any, within our company have been detected. These inherent limitations include the realities that judgments in decision-making can be faulty, and that breakdowns can occur because of a simple error or mistake. Additionally, controls can be circumvented by the individual acts of some persons, by collusion of two or more people, or by management override of the control. The design of any system of controls also is based in part upon certain assumptions about the likelihood of future events, and there can be no assurance that any design will succeed in achieving its stated goals under all potential future conditions. Over time, controls may become inadequate because of changes in conditions, or the degree of compliance with the policies or procedures may deteriorate. Projections of any evaluation of effectiveness to future periods are subject to the risk that controls may become inadequate because of changes in conditions, or that the degree of compliance with the policies or procedures may deteriorate. Because of the inherent limitations in a cost-effective control system, misstatements due to error or fraud may occur and not be detected.

Changes in Internal Control over Financial Reporting

Except for our identification and assessment of the material weakness described above, there have been no changes in our internal control over financial reporting as defined in Rules 13a-15(f) and 15d-15(f) under the Exchange Act during the three months ended December 31, 2023 that have materially affected, or are reasonably likely to materially affect, our internal control over financial reporting.

Attestation Report of the Registered Public Accounting Firm

Ernst & Young LLP has independently assessed the effectiveness of our internal control over financial reporting as of December 31, 2023 and its report is included below.

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Report of Independent Registered Public Accounting Firm

To the Stockholders and the Board of Directors of Cartesian Therapeutics, Inc.

Opinion on Internal Control over Financial Reporting

We have audited Cartesian Therapeutics, Inc.’s internal control over financial reporting as of December 31, 2023, based on criteria established in Internal Control—Integrated Framework issued by the Committee of Sponsoring Organizations of the Treadway Commission (2013 framework) (the COSO criteria). In our opinion, because of the effect of the material weakness described below on the achievement of the objectives of the control criteria, Cartesian Therapeutics, Inc. (and subsidiaries) (the Company) has not maintained effective internal control over financial reporting as of December 31, 2023, based on the COSO criteria.

As indicated in the accompanying Management’s Annual Report on Internal Control Over Financial Reporting, management’s assessment of and conclusion on the effectiveness of internal control over financial reporting did not include the internal controls of Cartesian Bio, LLC, formerly known as Cartesian Therapeutics, Inc. (Old Cartesian), which is included in the 2023 consolidated financial statements of the Company and constituted 2% and 1% of total assets and total liabilities, respectively, as of December 31, 2023 and 0% and 1% of revenues and operating expenses, respectively, for the year then ended. Our audit of internal control over financial reporting of the Company also did not include an evaluation of the internal control over financial reporting of Old Cartesian.

A material weakness is a deficiency, or combination of deficiencies, in internal control over financial reporting, such that there is a reasonable possibility that a material misstatement of the company’s annual or interim financial statements will not be prevented or detected on a timely basis. The following material weakness has been identified and included in management’s assessment. Management has identified a material weakness in the design and operation of controls related to the valuation of the in-process intangible assets acquired as part of the Old Cartesian business combination and the Selecta Biosciences, Inc. contingent value right obligation.

We also have audited, in accordance with the standards of the Public Company Accounting Oversight Board (United States) (PCAOB), the consolidated balance sheet of the Company as of December 31, 2023 and 2022, the related consolidated statements of operations and comprehensive income (loss), changes in convertible preferred stock and stockholders’ equity (deficit) and cash flows for each of the three years in the period ended December 31, 2023, and the related notes and our report dated March 7, 2024 expressed an unqualified opinion thereon.

Basis for Opinion

The Company’s management is responsible for maintaining effective internal control over financial reporting and for its assessment of the effectiveness of internal control over financial reporting included in the accompanying Management’s Report on Internal Control over Financial Reporting. Our responsibility is to express an opinion on the Company’s internal control over financial reporting based on our audit. We are a public accounting firm registered with the PCAOB and are required to be independent with respect to the Company in accordance with the U.S. federal securities laws and the applicable rules and regulations of the Securities and Exchange Commission and the PCAOB.

We conducted our audit in accordance with the standards of the PCAOB. Those standards require that we plan and perform the audit to obtain reasonable assurance about whether effective internal control over financial reporting was maintained in all material respects.

Our audit included obtaining an understanding of internal control over financial reporting, assessing the risk that a material weakness exists, testing and evaluating the design and operating effectiveness of internal control based on the assessed risk, and performing such other procedures as we considered necessary in the circumstances. We believe that our audit provides a reasonable basis for our opinion.

Definition and Limitations of Internal Control Over Financial Reporting

A company’s internal control over financial reporting is a process designed to provide reasonable assurance regarding the reliability of financial reporting and the preparation of financial statements for external purposes in accordance with generally accepted accounting principles. A company’s internal control over financial reporting includes those policies and procedures that (1) pertain to the maintenance of records that, in reasonable detail, accurately and fairly reflect the transactions and dispositions of the assets of the company; (2) provide reasonable assurance that transactions are recorded as necessary to permit preparation of financial statements in accordance with generally accepted accounting principles, and that receipts and expenditures of the company are being made only in accordance with authorizations of management and directors of the company; and (3) provide reasonable assurance regarding prevention or timely detection of unauthorized acquisition, use, or disposition of the company’s assets that could have a material effect on the financial statements.

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Because of its inherent limitations, internal control over financial reporting may not prevent or detect misstatements. Also, projections of any evaluation of effectiveness to future periods are subject to the risk that controls may become inadequate because of changes in conditions, or that the degree of compliance with the policies or procedures may deteriorate.

/s/ Ernst & Young LLP

Boston, Massachusetts

March 7, 2024

Item 9B. Other Information

During the fiscal quarter ended December 31, 2023, none of our officers or directors, as defined in Rule 16a-1(f), informed us of the adoption, modification or termination of any "Rule 10b5-1 trading arrangement" or a "non-Rule 10b5-1 trading arrangement," as those terms are defined in Item 408 of Regulation S-K .

Item 9C. Disclosure Regarding Foreign Jurisdictions that Prevent Inspections

Not applicable.

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PART III

Item 10. Directors, Executive Officers and Corporate Governance

Incorporated by reference from the information in our Proxy Statement for our 2024 Annual Meeting of Stockholders, which we will file with the SEC within 120 days of the end of the fiscal year to which this Annual Report on Form 10-K relates.

Item 11. Executive Compensation

Item 12. Security Ownership of Certain Beneficial Owners and Management and Related Stockholder Matters

Item 13. Certain Relationships and Related Transactions, and Director Independence

Item 14. Principal Accountant Fees and Services

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PART IV

Item 15. Exhibits, Financial Statement Schedules

(a)(1) Financial Statements

See the “Index to Consolidated Financial Statements” on page F-1 below for the list of financial statements filed as part of this report.

(a)(2) Financial Statement Schedules

All financial schedules have been omitted because the required information is either presented in the consolidated financial statements filed as part of this Annual Report on Form 10-K or the notes thereto or is not required.

(a)(3) Exhibits

The following is a list of exhibits filed as part of this Annual Report on Form 10-K.

Incorporated by Reference

ExhibitNumber Exhibit Description Form File No. Exhibit FilingDate

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4.14 Description of Securities — — — Filed herewith

10.6# Non-Employee Director Compensation Program — — — Filed herewith

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21.1 Subsidiaries of Cartesian Therapeutics, Inc. — — — Filed herewith

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101.SCH Inline XBRL Taxonomy Extension Schema Document — — — Filed herewith

# Indicates management contract or compensatory plan.

Item 16. Form 10-K Summary

None.

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SIGNATURES

Pursuant to the requirements of Section 13 or 15(d) of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

CARTESIAN THERAPEUTICS, INC.

Date: March 7, 2024 By: /s/ Carsten Brunn, Ph.D.

Carsten Brunn, Ph.D.

President and Chief Executive Officer

Pursuant to the requirements of the Securities Exchange Act of 1934, this report has been signed by the following persons on behalf of the registrant in the capacities and on the dates indicated.

Signature Title Date

Carsten Brunn, Ph.D. (Principal Executive Officer)

/s/ Blaine Davis Chief Financial Officer March 7, 2024

Blaine Davis (Principal Financial and Accounting Officer)

/s/ Carrie S. Cox Director March 7, 2024

Carrie S. Cox

/s/ Timothy C. Barabe Director March 7, 2024

Timothy C. Barabe

/s/ Nishan de Silva, M.D. Director March 7, 2024

Nishan de Silva, M.D.

/s/ Murat Kalayoglu, M.D., Ph.D. Director March 7, 2024

Murat Kalayoglu, M.D., Ph.D.

/s/ Michael Singer, M.D., Ph.D. Director March 7, 2024

Michael Singer, M.D., Ph.D.

/s/ Timothy Springer, Ph.D. Director March 7, 2024

Timothy Springer, Ph.D.

/s/ Patrick Zenner Director March 7, 2024

Patrick Zenner

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Cartesian Therapeutics, Inc. and Subsidiaries

Index to Consolidated Financial Statements Pages

Report of Independent Registered Public Accounting Firm (PCAOB ID: 42) F-2

Consolidated Balance Sheets at December 31, 2023 and 2022 F-4

Notes to Consolidated Financial Statements F-8

F-1

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Report of Independent Registered Public Accounting Firm

To the Stockholders and the Board of Directors of Cartesian Therapeutics, Inc.

Opinion on the Financial Statements

We have audited the accompanying consolidated balance sheets of Cartesian Therapeutics, Inc. and subsidiaries (the Company) as of December 31, 2023 and 2022, the related consolidated statements of operations and comprehensive income (loss), changes in convertible preferred stock and stockholders’ equity (deficit) and cash flows for each of the three years in the period ended December 31, 2023, and the related notes (collectively referred to as the “consolidated financial statements”). In our opinion, the consolidated financial statements present fairly, in all material respects, the financial position of the Company at December 31, 2023 and 2022, and the results of its operations and its cash flows for the three years in the period ended December 31, 2023, in conformity with U.S. generally accepted accounting principles.

We also have audited, in accordance with the standards of the Public Company Accounting Oversight Board (United States) (PCAOB), the Company's internal control over financial reporting as of December 31, 2023, based on criteria established in Internal Control-Integrated Framework issued by the Committee of Sponsoring Organizations of the Treadway Commission (2013 framework), and our report dated March 7, 2024 expressed an adverse opinion thereon.

Basis for Opinion

These financial statements are the responsibility of the Company's management. Our responsibility is to express an opinion on the Company’s financial statements based on our audit. We are a public accounting firm registered with the PCAOB and are required to be independent with respect to the Company in accordance with the U.S. federal securities laws and the applicable rules and regulations of the Securities and Exchange Commission and the PCAOB.

We conducted our audit in accordance with the standards of the PCAOB. Those standards require that we plan and perform the audit to obtain reasonable assurance about whether the financial statements are free of material misstatement, whether due to error or fraud. Our audit included performing procedures to assess the risks of material misstatement of the financial statements, whether due to error or fraud, and performing procedures that respond to those risks. Such procedures included examining, on a test basis, evidence regarding the amounts and disclosures in the financial statements. Our audit also included evaluating the accounting principles used and significant estimates made by management, as well as evaluating the overall presentation of the financial statements. We believe that our audit provides a reasonable basis for our opinion.

Critical Audit Matter

The critical audit matter communicated below is a matter arising from the current period audit of the financial statements that was communicated or required to be communicated to the Audit Committee and that: (1) relates to accounts or disclosures that are material to the financial statements and (2) involved our especially challenging, subjective or complex judgments. The communication of the critical audit matter does not alter in any way our opinion on the consolidated financial statements, taken as a whole, and we are not, by communicating the critical audit matter below, providing a separate opinion on the critical audit matter or on the accounts or disclosures to which it relates.

F-2

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/s/ Ernst & Young LLP

We have served as the Company’s auditor since 2009.

Boston, Massachusetts

March 7, 2024

F-3

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Cartesian Therapeutics, Inc. and Subsidiaries

Consolidated Balance Sheets

(Amounts in thousands, except share data and par value)

December 31, December 31,

Assets

Current assets:

Marketable securities — 28,164

Prepaid expenses and other current assets 4,967 3,778

Non-current assets:

In-process research and development assets 150,600 —

Other assets — 26

Liabilities, convertible preferred stock, and stockholders’ (deficit) equity

Current liabilities:

Accrued expenses and other current liabilities 15,572 14,084

Warrant liabilities 720 —

Contingent value right liability 15,983 —

Forward contract liabilities 28,307 —

Non-current liabilities:

Loan payable, net of current portion — 17,786

Lease liability, net of current portion 8,789 10,055

Deferred revenue, net of current portion 3,538 —

Warrant liabilities, net of current portion 5,674 19,140

Contingent value right liability, net of current portion 342,617 —

Deferred tax liabilities, net 15,853 —

Commitments and contingencies (Note 19)

Options for Series A Preferred Stock 3,703 —

Stockholders’ (deficit) equity:

Accumulated other comprehensive loss (4,600) (4,558)

The accompanying notes are an integral part of these consolidated financial statements.

F-4

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Cartesian Therapeutics, Inc. and Subsidiaries

Consolidated Statements of Operations and Comprehensive Income (Loss)

(Amounts in thousands, except share and per share data)

Year Ended December 31,

Operating expenses:

Foreign currency transaction gain (loss), net 38 (22) —

Change in fair value of contingent value right liability (18,300) — —

Change in fair value of forward contract liabilities (149,600) — —

Other comprehensive (loss) income:

Foreign currency translation adjustment (53) 18 (2)

Unrealized gain (loss) on marketable securities 11 (10) (1)

Net (loss) income per share:

Weighted-average common shares outstanding:

The accompanying notes are an integral part of these consolidated financial statements.

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Cartesian Therapeutics, Inc. and Subsidiaries

Consolidated Statements of Changes in Convertible Preferred Stock and Stockholders’ Equity (Deficit)

(Amounts in thousands, except share data)

Options for Accumulated

Series A Series A Additional other Stockholders’

Shares Amount Amount Shares Amount capital deficit loss Equity

Issuance of common stock upon exercise of options — — — 447,492 — 778 — — 778

Issuance of vested restricted stock units — — — 201,250 — — — — —

Stock-based compensation expense — — — — — 7,720 — — 7,720

Currency translation adjustment — — — — — — — (2) (2)

Unrealized loss on marketable securities — — — — — — — (1) (1)

Issuance of common stock upon exercise of options — — — 71,190 — 156 — — 156

Issuance of vested restricted stock units — — — 131,430 — — — — —

Issuance of common stock, license agreement — — — 892,857 — 1,000 — — 1,000

Reclassification of warrant liabilities — — — — — 780 — — 780

Stock-based compensation expense — — — — — 10,194 — — 10,194

Currency translation adjustment — — — — — — — 18 18

Unrealized loss on marketable securities — — — — — — — (10) (10)

Issuance of vested restricted stock units — — — 636,418 — — — — —

Issuance of replacement options in Merger — — 3,643 — — 6,801 — — 6,801

Issuance of common stock, license agreement — — — 1,339,285 — 1,500 — — 1,500

Settlement of outstanding equity awards at Merger — — — — — (6,169) — — (6,169)

Distribution of contingent value rights — — — — — (340,300) — — (340,300)

Stock-based compensation expense — — 60 — — 20,964 — — 20,964

Currency translation adjustment — — — — — — — (53) (53)

Unrealized gain on marketable securities — — — — — — — 11 11

The accompanying notes are an integral part of these consolidated financial statements.

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Cartesian Therapeutics, Inc. and Subsidiaries

Consolidated Statements of Cash Flows

Year Ended December 31,

Cash flows from operating activities (Amounts in thousands)

Amortization of premiums and discounts on marketable securities (79) (375) 57

Impairment of Right of use asset 710 — —

Loss (gain) on disposal of property and equipment 477 (147) —

Contingent value right liability revaluation 18,300 — —

Forward contract liabilities revaluation 149,600 — —

Loss on extinguishment of debt 740 — —

Provision (benefit) for deferred taxes (19,000) — —

Changes in operating assets and liabilities:

Prepaid expenses, deposits and other assets (1,265) 2,471 (1,451)

Income taxes payable — (601) 601

Cash flows from investing activities

Cash assumed in acquisition of Old Cartesian 6,561 — —

Payment made for investments — — (2,000)

Purchases of marketable securities — (33,501) (30,455)

Purchases of property and equipment (206) (1,201) (1,085)

Net cash provided by (used in) investing activities 34,609 (15,002) (17,140)

Cash flows from financing activities

Debt amendment fee included in debt discount — (110) —

Net proceeds from issuance of common stock and common warrants — 36,859 —

Settlement of outstanding equity awards at Merger (6,169) — —

Proceeds from exercise of stock options — 156 778

Effect of exchange rate changes on cash (53) 20 (3)

Supplement cash flow information

Non-cash investing and financing activities

Cashless warrant exercise $ — $ — $ 5,624

Reclassification of warrant liability to equity $ — $ 780 $ —

Purchase of property and equipment not yet paid $ 128 $ 17 $ 224

The accompanying notes are an integral part of these consolidated financial statements.

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Cartesian Therapeutics, Inc. and Subsidiaries

Notes to Consolidated Financial Statements

1. Description of the Business

Cartesian Therapeutics, Inc., or the Company, (formerly known as Selecta Biosciences, Inc., or Selecta) was incorporated in Delaware on December 10, 2007, and is headquartered in Gaithersburg, Maryland. The Company is a clinical-stage biotechnology company developing mRNA cell therapies for the treatment of autoimmune diseases leveraging its proprietary technology and manufacturing platform to introduce one or more mRNA molecules into cells to enhance their function. The Company believes its mRNA cell therapies have the potential to deliver deep, durable clinical benefit to a broad group of patients with autoimmune diseases because they can be administered over a short period of time, in an outpatient setting, and without pre-treatment chemotherapy.

On November 13, 2023, the Company acquired, in accordance with the terms of the Agreement and Plan of Merger, or the Merger Agreement, the assets of the Delaware corporation which, immediately prior to the Merger (as defined below), was known as Cartesian Therapeutics, Inc., or Old Cartesian, as disclosed in Note 3. The transaction was structured as a stock-for-stock transaction pursuant to which all of Old Cartesian’s outstanding shares of capital stock were exchanged based on a fixed exchange ratio for consideration of 6,723,639 shares of the common stock, $0.0001 per share, of the Company and 384,930.724 shares of the newly designated Series A Non-Voting Convertible Preferred Stock, $0.0001 per share, or the Series A Preferred Stock. The Series A Preferred Stock is intended to have economic rights similar to the common stock, but with only limited voting rights. Additionally, the Company assumed all outstanding stock options of Old Cartesian. The common stock and Series A Preferred Stock related to the Merger were issued on December 5, 2023. For additional information, see Note 3.

In connection with the Merger, the Company entered into a definitive agreement, or the Securities Purchase Agreement, for a private investment in public equity transaction, or the November 2023 Private Placement, with the Investors (as defined below). The Securities Purchase Agreement provides for the issuance to the Investors of an aggregate of 149,330.115 shares of Series A Preferred Stock for an aggregate purchase price of approximately $60.25 million. For additional information, see Note 11.

In connection with the Merger, a contractual contingent value right, or CVR, was distributed to the holders of record of the Company's common stock and 2022 Warrants as of the close of business on December 4, 2023, but was not distributed to holders of shares of common stock or Series A Preferred Stock issued to stockholders of Old Cartesian or the Investors in the transactions. Holders of the CVRs will be entitled to receive certain payments from proceeds received by the Company, if any, related to the disposition or monetization of the Company's legacy assets following the issuance of the CVRs. For additional information, see Note 6.

The Company is subject to risks common to companies in the biotechnology industry including, but not limited to, new technological innovations, protection of proprietary technology, dependence on key personnel, compliance with government regulations and the need to obtain additional financing. Product candidates currently under development will require significant additional research and development efforts, including extensive preclinical and clinical testing and regulatory approval, prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel infrastructure and extensive compliance-reporting capabilities.

The Company’s product candidates are in pre-clinical and clinical development. There can be no assurance that the Company’s research and development will be successfully completed, that adequate protection for the Company’s intellectual property will be obtained, or maintained, that any products developed will obtain necessary government regulatory approval or that any approved products will be commercially viable. Even if the Company’s product development efforts are successful, it is uncertain when, if ever, the Company will generate significant revenue from product sales. The Company operates in an environment of rapid change in technology and substantial competition from pharmaceutical and biotechnology companies. In addition, the Company is dependent upon the services of its employees and consultants.

Liquidity and Management’s Plan

The future success of the Company is dependent on its ability to develop its product candidates and ultimately upon its ability to attain and sustain profitable operations. The Company is subject to a number of risks similar to other early-stage life science companies, including, but not limited to, successful development of its product candidates, raising additional capital with favorable terms, protection of proprietary technology and market acceptance of any approved future products. The successful development of product candidates requires substantial working capital, which may not be available to the Company on favorable terms or at all.

To date, the Company has financed its operations primarily through public offerings and private placements of its securities, funding received from research grants, collaboration and license arrangements and a credit facility. The Company currently has no source of product revenue, and it does not expect to generate product revenue for the foreseeable future. To

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date, the Company’s revenue has primarily been from collaboration agreements. The Company has devoted substantially all of its financial resources and efforts to developing its existing product candidates, identifying potential product candidates and conducting preclinical studies and clinical trials. The Company is in the early stages of development of its product candidates, and it has not completed development of any product candidates.

As of December 31, 2023, the Company’s cash, cash equivalents, and restricted cash were $78.3 million, of which $1.4 million was restricted cash related to lease commitments and $0.2 million was held by its Russian subsidiary designated solely for use in its operations. The Company believes the cash, cash equivalents and restricted cash as of December 31, 2023 combined with net proceeds of $40.0 million received subsequent to December 31, 2023 from the November 2023 Private Placement will enable it to fund its current planned operations for at least the next twelve months from the date of issuance of these financial statements, though it may pursue additional cash resources through public or private equity or debt financings or by establishing collaborations with other companies. Management’s expectations with respect to its ability to fund current and long term planned operations are based on estimates that are subject to risks and uncertainties. If actual results are different from management’s estimates, the Company may need to seek additional strategic or financing opportunities sooner than would otherwise be expected. However, there is no guarantee that any collaboration milestones will be achieved or that any of these strategic or financing opportunities will be executed on favorable terms, and some could be dilutive to existing stockholders. Further, the liability associated with the CVR Agreement (as defined below) will be settled solely through cash flow received under the Company's License and Development Agreement, or as so amended, the Sobi License, with Swedish Orphan Biovitrum AB (publ.), or Sobi, and any other Gross Proceeds (as defined in the CVR Agreement) net of certain agreed deductions. Under the CVR Agreement, 100% of all milestone payments, royalties and other amounts paid to the Company or controlled entities under the Sobi License, and any other Gross Proceeds will be distributed, net of specified deductions, to holders of the CVRs. There is no obligation to the Company to fund any amount related to the CVR liability. See Note 6.

The Certificate of Designation of Preferences, Rights, and Limitations of the Series A Non-Voting Convertible Preferred Stock, or the Certificate of Designation, contains a provision granting each holder of the Series A Preferred Stock the option to require the Company to redeem any or all of such holder’s then-outstanding shares of Series A Preferred Stock beginning on the date that is 18 months following the date of the closing of the Merger, November 13, 2023, at a price per share equal to the ten-day trailing average closing trading price of the common stock at such time; provided, however, that no holder will have the right to seek redemption of any shares of Series A Preferred Stock to the extent that such holder would otherwise be unable to convert such shares of Series A Preferred Stock due to the common stock beneficial ownership limitation applicable to such holder. The Company could be required to use a significant amount of its cash resources on hand to satisfy this redemption obligation, particularly if its stockholders do not ever approve a proposal to convert the Company’s Series A Preferred Stock into common stock, or generally if holders of Series A Preferred Stock exercise their redemption right with respect to a significant number of shares of Series A Preferred Stock or at a time when the trading price of the Company’s common stock is elevated. Further, in the event that the Company does not have sufficient cash on hand to satisfy its redemption obligations, the Company may need to raise additional capital to satisfy these potential obligations. Any redemption payments could materially limit the amount of cash the Company has available to fund our operations and the potential need to redeem shares of Series A Preferred Stock may limit the flexibility with which the Company seeks to operate its business.

If the Company is unable to obtain additional funding on a timely basis, it may be forced to significantly curtail, delay, or discontinue one or more of its planned research or development programs or be unable to expand its operations or otherwise capitalize on its commercialization of its product candidates. As of December 31, 2023, the Company had an accumulated deficit of $614.6 million. The Company anticipates operating losses to continue for the foreseeable future due to, among other things, costs related to research and development of its product candidates and its administrative organization.

Guarantees and Indemnifications

As permitted under Delaware law, the Company indemnifies its officers, directors, consultants and employees for certain events or occurrences that happen by reason of the relationship with, or position held at, the Company. Through December 31, 2023, the Company had not experienced any losses related to these indemnification obligations, and no claims were outstanding. The Company does not expect significant claims related to these indemnification obligations and, consequently, concluded that the fair value of these obligations is negligible, and no related reserves were established.

2. Summary of Significant Accounting Policies

Principles of Consolidation

The consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries, Selecta (RUS), LLC, or Selecta (RUS), a Russian limited liability corporation, and Selecta Biosciences Security Corporation, a Massachusetts securities corporation, and Cartesian Bio, LLC, a Delaware limited liability company, which is a variable interest entity for which the Company is the primary beneficiary. All significant intercompany accounts and transactions have been eliminated.

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Use of Estimates

The preparation of consolidated financial statements in conformity with U.S. GAAP requires the Company’s management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities as of the date of the consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. The Company’s management considers many factors in selecting appropriate financial accounting policies and controls, and bases its estimates on historical experience and other market-specific or other relevant assumptions that it believes to be reasonable under the circumstances. In preparing these consolidated financial statements, management used significant estimates in the following areas, among others: estimated fair value of the intangible assets acquired in connection with the Merger, estimated fair value of the CVRs, deferred income taxes, revenue recognition and estimating accrued research and development expenses. The Company assesses the above estimates on an ongoing basis; however, actual results could materially differ from those estimates.

Segment Information

The Company views its operations and manages its business in one operating segment, which prior to the Merger related to the research and development of nanoparticle immunomodulatory drugs for the treatment and prevention of human diseases and subsequent to the Merger relates to the research and development of cell therapy product candidates.

Cash Equivalents, Restricted Cash, Marketable Securities and Investments

Cash equivalents include all highly liquid investments maturing within 90 days from the date of purchase. Marketable securities consist of securities with remaining maturities greater than 90 days when purchased. The Company classifies these marketable securities as available-for-sale and records them at fair value in the accompanying consolidated balance sheets. Marketable securities with less than one year until maturity are classified as short term, while marketable securities with maturities greater than one year are classified as long term. Unrealized gains or losses are included in accumulated other comprehensive income (loss). Premiums or discounts from par value are amortized to investment income over the life of the underlying investment. Although available to be sold to meet operating needs or otherwise, securities are generally held through maturity. The cost of securities sold is determined based on the specific identification method for purposes of recording realized gains and losses.

The Company has also in the past invested in equity securities of a company whose securities are not publicly traded and where fair value is not readily available. This investment is recorded using cost minus impairment adjusted for changes in observable prices, depending on our ownership percentage and other factors that suggest we have significant influence. The Company monitors this investment to evaluate whether any increase or decline in its value has occurred, based on the implied value of recent company financings, public market prices of comparable companies and general market conditions. This investment is included in investments in the consolidated balance sheets.

Concentrations of Credit Risk and Off-Balance Sheet Risk

Financial instruments that potentially subject the Company to concentration of credit risk consist primarily of cash, cash equivalents, short-term deposits and marketable securities, investments, and accounts receivable. Cash and cash equivalents are deposited with federally insured financial institutions in the United States and may, at times, exceed federally insured limits. Management believes that the financial institutions that hold the Company’s deposits are financially creditworthy and, accordingly, minimal risk exists with respect to those balances. The Company also maintains cash in Russian bank accounts in denominations of both Russian rubles and U.S. dollars. As of December 31, 2023, the Company maintained approximately $0.2 million in Russian bank accounts in denominations of both Russian rubles and U.S. dollars.

Fair Value of Financial Instruments

The Company’s financial instruments consist mainly of cash equivalents, restricted cash, accounts payable, loans payable, marketable securities, investments, warrants to purchase common stock, forward contract liabilities, and contingent value rights. The carrying amounts of cash equivalents, restricted cash, accounts receivable, and accounts payable approximate their estimated fair value due to their short-term maturities.

Accounting standards define fair value as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. A three-level hierarchy is used to prioritize the inputs to valuation techniques used to measure fair value. The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (Level 1 measurements), and the lowest priority to unobservable inputs (Level 3 measurements). The three levels of the fair value hierarchy are described below:

Level 1—Level 1 inputs are quoted prices in active markets for identical assets or liabilities that the reporting entity has the ability to access at the measurement date.

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Level 2—Level 2 inputs are inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly. If the asset or liability has a specified (contractual) term, a Level 2 input must be observable for substantially the full term of the asset or liability.

Level 3—Level 3 inputs are unobservable inputs for the asset or liability in which there is little, if any, market activity for the asset or liability at the measurement date.

To the extent that a valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. The fair value of warrant liabilities and contingent value rights are determined using Level 3 inputs.

Fair value is a market-based measure considered from the perspective of a market participant rather than an entity-specific measure. Therefore, even when market assumptions are not readily available, the Company’s own assumptions are set to reflect those that market participants would use in pricing the asset or liability at the measurement date. The Company uses prices and inputs that are current as of the measurement date, including during periods of market dislocation. In periods of market dislocation, the observability of prices and inputs may change for many instruments. This condition could cause an instrument to be reclassified within levels in the fair value hierarchy.

The carrying amounts reflected in the consolidated balance sheet for investments approximate fair value and are assessed for impairment quarterly.

Property and Equipment

Property and equipment are recorded at cost and depreciated using the straight-line method over the estimated useful lives of the respective assets, generally seven years for furniture and fixtures, five years for laboratory equipment, software and office equipment and three years for computer equipment. Leasehold improvements are amortized over their useful life or the life of the lease, whichever is shorter. Major additions and betterments are capitalized. Maintenance and repairs, which do not improve or extend the life of the respective assets, are charged to operations as incurred. Costs incurred for construction in progress are recorded as assets and are not amortized until the construction is substantially complete and the assets are ready for their intended use.

Impairment of Long-Lived Assets

The Company reviews long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying value of an asset may not be recoverable. In order to determine if assets have been impaired, assets are tested at the lowest level for which identifiable independent cash flows are available. An impairment loss is recognized when the sum of projected undiscounted cash flows is less than the carrying value of the asset group. The measurement of the impairment loss to be recognized is based on the difference between the fair value and the carrying value of the asset group. The Company recognized a $0.7 million impairment charge on a right-of-use asset during the year ended December 31, 2023.

Debt Issuance Costs

Debt issuance costs and fees paid to lenders are recorded as a direct deduction from the face amount of the related debt. Debt issuance costs are amortized over the term of the related debt using the effective interest method and recorded as interest expense.

Accumulated Other Comprehensive Income (Loss)

Comprehensive income (loss) is defined as the change in the equity of a business entity during a period from transactions and other events and circumstances from non-owner sources. It includes all changes in equity during a period except those resulting from investments by owners and distributions to owners. Comprehensive income (loss) consists of: (i) all components of net income (loss) and (ii) all components of comprehensive income (loss) other than net income (loss), referred to as other comprehensive income (loss). Other comprehensive income (loss) is comprised of unrealized gains and losses on debt securities and foreign currency translation adjustments.

Revenue Recognition

Revenue is recognized when a customer obtains control of promised goods or services, in an amount that reflects the consideration which the entity expects to receive in exchange for those goods or services. Pursuant to ASC Topic 606, Revenue from Contracts with Customers (ASC 606), a customer is a party that has contracted with an entity to obtain goods or services that are an output of the entity’s ordinary activities in exchange for consideration. To determine revenue recognition for arrangements that an entity determines are within the scope of ASC 606, the Company performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract, including whether they are distinct in the context of the contract; (iii) determine the transaction price, including the constraint on variable consideration; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the

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Company satisfies each performance obligation. The Company only applies the five-step model to contracts when it is probable that the entity will collect the consideration it is entitled to in exchange for the goods or services it transfers to the customer. At contract inception, once the contract is determined to be within the scope of ASC 606, the Company assesses the goods or services promised within each contract and determines those that are performance obligations, and assesses whether each promised good or service is distinct. If a promised good or service is not distinct, it is combined with other promised goods or services into a performance obligation. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. For example, certain performance obligations associated with the License and Development Agreement, or Astellas Agreement, entered into with Audentes Therapeutics, Inc., or Astellas, (see Note 14) will be satisfied over time, and revenue will be recognized using the input method.

Collaboration and License Revenue: The Company currently generates its revenue through collaboration and license agreements with strategic collaborators for the development and commercialization of product candidates. Collaboration and license agreements with customers are generally accounted for in accordance with ASC 606. The Company analyzes collaboration arrangements by first assessing whether they are within the scope of ASC Topic 808, Collaborative Arrangements (ASC 808), and evaluates whether such arrangements involve joint operating activities performed by parties that are both active participants in the activities and exposed to significant risks and rewards that are dependent on the commercial success of such activities. Collaboration agreements with customers that are not within the scope of ASC 808 are accounted for in accordance with ASC 606. To the extent the collaboration agreement is within the scope of ASC 808, the Company also assesses whether any aspects of the agreement are within the scope of other accounting literature (specifically ASC 606). If the Company concludes that some or all aspects of the agreement are distinct and represent a transaction with a customer, the Company accounts for those aspects of the arrangement within the scope of ASC 606. The Company recognizes the shared costs incurred that are not within the scope of other accounting literature as a component of the related expense in the period incurred by analogy to ASC Topic 730, Research and Development (ASC 730), and records reimbursements from counterparties as an offset to the related research and development costs. In determining the appropriate amount of revenue to be recognized as it fulfills its obligations under the agreements in accordance with ASC 606, the Company performs the five steps above. As part of the accounting for the arrangement, the Company must develop assumptions that require judgment to determine the stand-alone selling price for each performance obligation identified in the contract. The Company uses key assumptions to determine the stand-alone selling price, which may include market conditions, reimbursement rates for personnel costs, development timelines and probabilities of regulatory success.

The terms of the Company’s arrangements typically include one or more of the following: (i) upfront fees; (ii) milestone payments related to the achievement of development, regulatory, or commercial goals; (iii) royalties on net sales of licensed products; (iv) reimbursements or cost-sharing of research and development expenses; and (v) profit/loss sharing arising from co-promotion arrangements.

Licenses of Intellectual Property: If the license to the Company’s intellectual property is determined to be distinct from the other promised goods and services identified in the arrangement, the Company recognizes revenues from non-refundable, upfront fees allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the license. If not distinct, the license is combined with other promised goods and services in the contract. For licenses that are combined with other promised goods and services, the Company assesses the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. Optional licenses are evaluated to determine if they are issued at a discount, and therefore, represent material rights and accounted for as separate performance obligations.

Milestone Payments: At the inception of each arrangement that includes developmental and regulatory milestone payments, the Company evaluates whether the achievement of each milestone specifically relates to the Company’s efforts to satisfy a performance obligation or transfer a distinct good or service within a performance obligation. If the achievement of a milestone is considered a direct result of the Company’s efforts to satisfy a performance obligation or transfer a distinct good or service and the receipt of the payment is based upon the achievement of the milestone, the associated milestone value is allocated to that distinct good or service. If the milestone payment is not specifically related to the Company’s effort to satisfy a performance obligation or transfer a distinct good or service, the amount is allocated to all performance obligations using the relative standalone selling price method. The Company also evaluates the milestone to determine whether they are considered probable of being reached and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price to be allocated, otherwise, such amounts are constrained and excluded from the transaction price. At the end of each subsequent reporting period, the Company re-evaluates the probability of achievement of such development milestones and any related constraint, and if necessary, adjusts its estimate of the transaction price. Any such adjustments to the transaction price are allocated to the performance obligations on the same basis as at contract inception. Amounts allocated to a satisfied

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performance obligation shall be recognized as revenue, or as a reduction of revenue, in the period in which the transaction price changes.

Manufacturing Supply Services: Arrangements that include a promise for future supply of drug substance or drug product for either clinical development or commercial supply at the customer’s discretion are evaluated to determine if they are distinct and optional. For optional services that are distinct, the Company assesses if they are priced at a discount, and therefore, provide a material right to the licensee to be accounted for as separate performance obligations.

Royalties: For arrangements that include sales-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company will recognize revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied) in accordance with the royalty recognition constraint.

Research and Development Costs

Costs incurred in the research and development of the Company’s products are expensed as incurred. Research and development expenses include costs incurred in performing research and development activities, including salaries and benefits, stock-based compensation expenses, facilities cost, overhead costs, contract services, supplies and other outside costs. Nonrefundable advance payments for goods and services that will be used in future research and development activities are expensed when the activity has been performed or when the goods have been received rather than when the payment is made.

Clinical Trial Costs

Clinical trial expenses are a significant component of research and development expenses, and the Company outsources a significant portion of these costs to third parties. Third party clinical trial expenses include patient costs, clinical research organization costs and costs for data management. The accrual for site and patient costs includes inputs such as estimates of patient enrollment, patient cycles incurred, clinical site activations, and other pass-through costs. Payments for these activities are based on the terms of the individual arrangements, which may differ from the pattern of costs incurred, and are reflected on the consolidated balance sheets as a prepaid asset or accrued clinical trial cost. These third party agreements are generally cancellable, and related costs are recorded as research and development expenses as incurred. Non-refundable advance clinical payments for goods or services that will be used or rendered for future research and development activities are recorded as a prepaid asset and recognized as expense as the related goods are delivered or the related services are performed. The Company also records accruals for estimated ongoing clinical research and development costs. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the studies, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates may be made in determining the accrued balances at the end of any reporting period. Actual results could differ from the estimates made by the Company. The historical clinical accrual estimates made by the Company have not been materially different from the actual costs.

In June 2020, the Company and Sobi entered into a License and Development Agreement, which was amended in October 2023. Pursuant to the Sobi License, clinical trial costs incurred to complete development of the SEL-212 product candidate, including but not limited to costs incurred while conducting and completing the Phase 3 DISSOLVE trials, were reimbursed by Sobi. These costs, when reimbursed, were recognized as revenue consistent with the revenue recognition methodology disclosed in Note 14. The reimbursable costs exclude any costs of additional development activities required that are related to the ImmTOR platform and that are unrelated to SEL-212.

In January 2023, the Company and Astellas entered into the Astellas Agreement. Pursuant to the Astellas Agreement, Astellas will reimburse the Company for 25% of all budgeted costs incurred to complete the development of Xork for use in Pompe disease with an Astellas gene therapy investigational or authorized product. These costs, when reimbursed, will be recognized as revenue consistent with the revenue recognition methodology disclosed in Note 14.

Income Taxes

The Company provides deferred tax assets and liabilities for the expected future tax consequences of temporary differences between the Company’s financial statement carrying amounts and the tax basis of assets and liabilities using enacted tax rates expected to be in effect in the years in which the differences are expected to reverse. A valuation allowance is provided to reduce the deferred tax assets to the amount that will more-likely-than-not be realized.

The Company determines whether it is more likely than not that a tax position will be sustained upon examination. If it is not more-likely-than-not that a position will be sustained, none of the benefit attributable to the position is recognized. The tax benefit to be recognized for any tax position that meets the more-likely-than-not recognition threshold is calculated as the largest amount that is more than 50% likely of being realized upon resolution of the contingency. The Company accounts for interest and penalties related to uncertain tax positions as part of its provision for income taxes. To date, the Company has not incurred interest and penalties related to uncertain tax positions.

Warrants

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The Company determines the accounting classification of warrants that are issued, as either liability or equity, by first assessing whether the warrants meet liability classification in accordance with ASC 480-10, Accounting for Certain Financial Instruments with Characteristics of both Liabilities and Equity, and then in accordance with ASC 815-40, Accounting for Derivative Financial Instruments Indexed to, and Potentially Settled in, a Company’s Own Stock. Under ASC 480, warrants are considered liability classified if the warrants are mandatorily redeemable, obligate the issuer to settle the warrants or the underlying shares by paying cash or other assets, or must or may require settlement by issuing variable number of shares.

If warrants do not meet liability classification under ASC 480-10, the Company assesses the requirements under ASC 815-40, which states that contracts that require or may require the issuer to settle the contract for cash are liabilities recorded at fair value, irrespective of the likelihood of the transaction occurring that triggers the net cash settlement feature. If the warrants do not require liability classification under ASC 815-40, in order to conclude equity classification, the Company assesses whether the warrants are indexed to its common stock and whether the warrants are classified as equity under ASC 815-40 or other applicable GAAP. After all relevant assessments are made, the Company concludes whether the warrants are classified as liability or equity. Liability classified warrants are required to be accounted for at fair value both on the date of issuance and on subsequent accounting period ending dates, with all changes in fair value after the issuance date recorded in the statements of operations as a gain or loss. Equity classified warrants are accounted for at fair value on the issuance date with no changes in fair value recognized after the issuance date.

Stock-Based Compensation

The Company accounts for all stock-based compensation granted to employees and non-employees using a fair value method. Stock-based compensation is measured at the grant date fair value and is recognized over the requisite service period of the awards, usually the vesting period, on a straight-line basis, net of estimated forfeitures. To the extent that actual forfeitures differ from the Company’s estimates, the differences are recorded as a cumulative adjustment in the period the estimates were adjusted. Stock-based compensation expense recognized in the consolidated financial statements is based on awards that ultimately vest.

Net (Loss) Income Per Share

The Company applies the two-class method to compute basic and diluted net (loss) income per share attributable to common stockholders when it has issued shares that meet the definition of participating securities. The two-class method determines net (loss) income per share for each class of common and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method requires (loss) income available to common stockholders for the period to be allocated between common and participating securities based upon their respective rights to share in the earnings as if all (loss) income for the period had been distributed. The Company's Series A Preferred Stock and 2022 Warrants participate in any dividends declared by the Company and are therefore considered to be participating securities. The participating securities are not required to participate in the losses of the Company, and therefore during periods of loss there is no allocation required under the two-class method.

Basic net (loss) income per share attributable to common stockholders is computed by dividing the net (loss) income attributable to common stockholders by the weighted average number of shares of common stock outstanding for the period. Diluted net (loss) income attributable to common stockholders is computed by adjusting net (loss) income per share attributable to common stockholders to reallocate undistributed earnings based on the potential impact of dilutive securities. Diluted net (loss) income per share attributable to common stockholders is computed by dividing the diluted net (loss) income attributable to common stockholders by the weighted average number of shares of common stock outstanding for the period, including potential dilutive common shares. For purpose of this calculation, outstanding options to purchase common stock and Series A Preferred Stock, forward contracts to issue Series A Preferred Stock, restricted stock units, warrants to purchase common stock, employee stock purchase plan stock, contingently issuable shares, and Series A Preferred Stock are considered potential dilutive common shares.

Contingent Liabilities

The Company accounts for its contingent liabilities in accordance with ASC No. 450, Contingencies. A provision is recorded when it is both probable that a liability has been incurred and the amount of the loss can be reasonably estimated. With respect to legal matters, provisions are reviewed and adjusted to reflect the impact of negotiations, estimated settlements, legal rulings, advice of legal counsel and other information and events pertaining to a particular matter.

Leases

The Company accounts for its leases in accordance with ASC Topic 842, Leases (ASC 842), and determines whether the arrangement is or contains a lease based on the unique facts and circumstances present. Most leases with a term greater than one year are recognized on the balance sheet as right-of-use assets, lease liabilities and, if applicable, long-term lease liabilities. The Company elected not to recognize leases with an original term less than one year on its balance sheet. Operating lease right-of-use assets and their corresponding lease liabilities are recorded based on the present value of lease payments over the expected remaining lease term. The interest rate implicit in lease contracts is typically not readily determinable. As a result, the Company

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utilizes its incremental borrowing rates, which are the rates incurred to borrow, on a collateralized basis over a similar term, an amount equal to the lease payments in a similar economic environment.

In accordance with the guidance in ASC 842, the fixed and in-substance fixed contract consideration must be allocated to lease and non-lease components based on their relative fair values. Non-components of a contract (e.g., administrative tasks that do not transfer a good or service to the Company, reimbursement or payment of a lessor’s cost, etc.) do not receive an allocation of the consideration in the contract. Although allocation of consideration of lease and non-lease components is required, the Company elected the practical expedient to not separate lease components (e.g. land, building, etc.) and non-lease components (e.g., common area maintenance, consumables, etc.). The lease component results in an operating right-of-use asset being recorded on the balance sheet and amortized on a straight-line basis as lease expense. Right-of-use assets and operating lease liabilities are remeasured upon certain modifications to leases using the present value of remaining lease payments and the estimated incremental borrowing rate upon lease modification.

The Company enters into lease agreements with terms generally ranging from two to eight years. Some of the Company’s lease agreements include Company options to either extend and/or early terminate the lease, the costs of which are included in its operating lease liabilities to the extent that such options are reasonably certain of being exercised. Leases with renewal options allow the Company to extend the lease term typically between one and five years. When determining the lease term, renewal options reasonably certain of being exercised are included in the lease term. When determining if a renewal option is reasonably certain of being exercised, the Company considers several economic factors, including but not limited to, the significance of leasehold improvements incurred on the property, whether the asset is difficult to replace, underlying contractual obligations, or specific characteristics unique to that particular lease that would make it reasonably certain that the Company would exercise such option. Renewal and termination options were generally not included in the lease term for the Company’s existing operating leases. Leases with an initial term of 12 months or less are not recorded on the balance sheet; the Company recognizes lease expense for these leases on a straight-line basis over the lease term.

Acquisitions

The Company evaluates acquisitions of assets and other similar transactions to assess whether or not the transaction should be accounted for as a business combination or asset acquisition by first applying a screen to determine if substantially all of the fair value of the gross assets acquired is concentrated in a single identifiable asset or group of similar identifiable assets. If the screen is met, the transaction is accounted for as an asset acquisition. If the screen is not met, further determination is required as to whether or not the Company has acquired inputs and processes that have the ability to create outputs, which would meet the requirements of a business. If determined to be a business combination, the Company accounts for the transaction under the acquisition method of accounting which requires the acquiring entity in a business combination to recognize the fair value of all assets acquired, liabilities assumed, and any non-controlling interest in the acquiree and establishes the acquisition date as the fair value measurement point. Accordingly, the Company recognizes assets acquired and liabilities assumed in business combinations based on the fair value estimates as of the date of acquisition. In accordance with ASC 805, Business Combinations, or ASC 805, the Company recognizes and measures goodwill as of the acquisition date, as the excess of the fair value of the consideration paid over the fair value of the identified net assets acquired.

Goodwill

Goodwill represents the amount of consideration paid in excess of the fair value of the identified net assets acquired as a result of the Company’s business acquisitions accounted for using the acquisition method of accounting. Goodwill is not amortized and is subject to impairment testing at a reporting unit level on an annual basis or when a triggering event occurs that may indicate the carrying value of the goodwill is impaired. An entity is permitted to first assess qualitative factors to determine if a quantitative impairment test is necessary. Such qualitative factors include macroeconomic conditions, industry and market considerations, cost factors, overall financial performance and other relevant events. Further testing is only required if the entity determines, based on the qualitative assessment, that it is more likely than not that the fair value of the reporting unit is less than its carrying amount.

The Company evaluates goodwill for impairment at least annually on October 1 and whenever facts and circumstances indicate that their carrying amounts may not be recoverable. For the year ended December 31, 2023, the Company determined that there was no impairment to goodwill.

Indefinite-Lived Intangible Assets

Indefinite-lived intangible assets consist of in-process research and development, or IPR&D. The fair values of IPR&D assets acquired in business combinations are capitalized. These assets are treated as indefinite-lived intangible assets until completion or abandonment of the projects, at which time the assets are amortized over the remaining useful life or written off, as appropriate.

Intangible assets with indefinite lives, including IPR&D, are tested for impairment if impairment indicators arise and, at a minimum, annually. However, an entity is permitted to first assess qualitative factors to determine if a quantitative impairment test is necessary. Further testing is only required if the entity determines, based on the qualitative assessment, that it is more

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likely than not that an indefinite-lived intangible asset’s fair value is less than its carrying amount. Otherwise, no further impairment testing is required. The indefinite-lived intangible asset impairment test consists of a one-step analysis that compares the fair value of the intangible asset with its carrying amount. If the carrying amount of an intangible asset exceeds its fair value, an impairment loss is recognized in an amount equal to that excess. The Company considers many factors in evaluating whether the value of its intangible assets with indefinite lives may not be recoverable, including, but not limited to, expected growth rates, the cost of equity and debt capital, general economic conditions, the Company’s outlook and market performance of the Company’s industry and recent and forecasted financial performance.

The Company evaluates indefinite-lived intangible assets for impairment at least annually on October 1 and whenever facts and circumstances indicate that their carrying amounts may not be recoverable. For the year ended December 31, 2023, the Company determined that there was no impairment to the IPR&D assets.

Series A Preferred Stock

The Company records the Series A Preferred Stock upon issuance at its fair value.The fair value includes the original issuance price, the settlement of any related forward contract, and is less issuance costs. The Company classifies its Series A Preferred Stock outside of stockholders’ equity as the redemption of such shares is outside the Company’s control. The Company does not adjust the carrying value of the Series A Preferred Stock to redemption value until it is probable of becoming redeemable, which the Company did not conclude was probable as of December 31, 2023.

Series A Preferred Stock Options

The Company classifies a portion of the fair value of the vested stock options for Series A Preferred Stock equal to the estimated redemption value on the measurement date outside of stockholders’ equity, as the redemption of the shares underlying the options are outside the Company’s control. Any fair value in excess of the estimated redemption value is recognized as additional paid-in capital. The estimated redemption value is based on the intrinsic value of the option. The Company does not adjust the carrying value of the stock options for Series A Preferred Stock until the underlying Series A Preferred Stock is probable of becoming redeemable. The Company concluded the redemption was not probable of occurring as of December 31, 2023. The Company records the stock options for Series A Preferred Stock based on the intrinsic value of the vested options.

Variable Interest Entities

The Company evaluates its variable interests in variable interest entities, or VIEs, and consolidates VIEs when the Company is the primary beneficiary. The Company determines whether it is the primary beneficiary of a VIE based on its assessment of whether the Company possesses both (i) the power to direct the activities that most significantly affect the VIE’s economic performance and (ii) the obligation to absorb losses that could be significant to the VIE or the right to receive benefits that could be significant to the VIE. The Company reevaluates the accounting for its VIEs upon the occurrence of events that could change the primary beneficiary conclusion.

Contingent Value Right Liability

The CVRs distributed by the Company pursuant to the terms of the CVR Agreement represent financial instruments that are accounted for under the fair value option election in ASC 825, Financial Instruments, or ASC 825. Under the fair value option election, the CVRs are initially measured at the aggregate estimated fair value of the CVRs and will be subsequently remeasured at estimated fair value on a recurring basis at each reporting period date. The estimated fair value of the CVR liability was determined using the discounted cash flow method to estimate future cash flows associated with the legacy assets, including the expected milestone and royalty payments under the Sobi License, net of deductions. Changes in fair value of the liability are presented within change in fair value of contingent value right liability in the consolidated statements of operations and comprehensive income (loss). The liability value is based on significant inputs not observable in the market such as estimated cash flows, estimated probabilities of success, and risk-adjustment discount rates, which represent a Level 3 measurement within the fair value hierarchy.

Forward Contract Liabilities

The Company accounts for contracts related to the future issuance of Series A Preferred Stock as a liability because the underlying shares of Series A Preferred Stock include a redemption feature that may require the Company to settle the instrument by transferring an asset. The forward contract liability is carried at fair value through the date the underlying Series A Preferred Stock are issued. The fair value of the forward contract liability was initially measured based on the fair value of the Series A Preferred Stock issued in the November 2023 Private Placement (see Note 11), less the purchase price, if any. Subsequent measurement of the fair value of the forward contract liability is based on the market price of the Company’s common stock, which represents the redemption and conversion value of the Series A Preferred Stock, less the purchase price, if any, on an as-converted basis. The remeasurement of the forward contract liability is based on Level 2 inputs within the fair value hierarchy as it’s based on observable market data. Changes in fair value of the liability are presented within change in fair value of forward contract liabilities in the consolidated statements of operations and comprehensive income (loss).

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Recent Accounting Pronouncements

Recently Adopted

In June 2016, the FASB issued ASU 2016-13, Financial Instruments-Credit Losses (Topic 326), Measurement of Credit Losses on Financial Instruments. Subsequently, in November 2018, the FASB issued ASU 2018-19, Codification Improvements to Topic 326, Financial Instruments-Credit Losses. ASU 2016-13 requires entities to measure all expected credit losses for most financial assets held at the reporting date based on an expected loss model which includes historical experience, current conditions, and reasonable and supportable forecasts. ASU 2016-13 also requires enhanced disclosures to help financial statement users better understand significant estimates and judgments used in estimating credit losses. This ASU is effective for smaller reporting companies for fiscal years beginning after December 15, 2022, with early adoption permitted. The Company adopted the new standard effective January 1, 2023, using a modified retrospective transition method, and there was no impact on its consolidated financial statements or results of operations upon adoption.

In January 2017, the FASB issued ASU 2017-04, Intangibles - Goodwill and Other (Topic 350), which eliminates Step 2 from the goodwill impairment test. Step 2 measures a goodwill impairment loss by comparing the implied fair value of a reporting unit’s goodwill with the carrying amount of that goodwill. Instead, entities will record an impairment charge based on the excess of a reporting unit’s carrying amount over its fair value (i.e., measure the charge based on today’s Step 1). This ASU is effective for annual and interim impairment tests performed in periods beginning after December 15, 2022. Early adoption of the standard is permitted. The Company adopted the new standard effective January 1, 2023 and there was no impact on its consolidated financial statements or results of operations upon adoption.

Not Yet Adopted

In November 2023, the FASB issued ASU 2023-07, Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures (ASU 2023-07), which requires an enhanced disclosure of significant segment expenses on an annual and interim basis. This guidance will be effective for the annual periods beginning the year ended December 31, 2024, and for interim periods beginning January 1, 2025. Early adoption is permitted. Upon adoption, the guidance should be applied retrospectively to all prior periods presented in the financial statements. The Company does not expect the adoption of this guidance to have a material impact on its consolidated financial statements.

In December 2023, the FASB issued ASU 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures (ASU 2023-09), which improves the transparency of income tax disclosures by requiring consistent categories and greater disaggregation of information in the effective tax rate reconciliation and income taxes paid disaggregated by jurisdiction. It also includes certain other amendments to improve the effectiveness of income tax disclosures. This guidance will be effective for the annual periods beginning the year ended December 31, 2025. Early adoption is permitted. Upon adoption, the guidance can be applied prospectively or retrospectively. The Company does not expect the adoption of this guidance to have a material impact on its consolidated financial statements.

3. Merger

On November 13, 2023, the Company merged with Old Cartesian in accordance with the terms of the Merger Agreement, by and among Selecta, Sakura Merger Sub I, Inc., a wholly owned subsidiary of Selecta, or First Merger Sub, Sakura Merger Sub II, LLC, a wholly owned subsidiary of Selecta, or Second Merger Sub, and Old Cartesian. Pursuant to the Merger Agreement, First Merger Sub merged with and into Old Cartesian, pursuant to which Old Cartesian was the surviving corporation and became a wholly owned subsidiary of Selecta, or the First Merger. Immediately following the First Merger, Old Cartesian merged with and into Second Merger Sub, pursuant to which Second Merger Sub was the surviving entity, or the Second Merger and, together with the First Merger, the Merger. In connection with the Second Merger, Old Cartesian changed its name to Cartesian Bio, LLC.

The Merger was intended to qualify as a tax-free reorganization for U.S. federal income tax purposes. As a result of the Merger, Selecta changed its corporate name to Cartesian Therapeutics, Inc. and its common stock began trading on the Nasdaq Global Market under the new trading symbol “RNAC” beginning on November 14, 2023.

The Merger Agreement was unanimously approved by the board of directors, or the Board of Directors, of Selecta and the board of directors of Old Cartesian. The Merger was consummated substantially concurrently with the entry into the Merger Agreement and was not subject to approval of the Company's stockholders.

Under the terms of the Merger Agreement, following the consummation of the Merger on November 13, 2023, or the Closing Date, in exchange for 100% of the outstanding shares of capital stock of Old Cartesian immediately prior to the effective time of the First Merger, the Company agreed to issue to the stockholders of Old Cartesian (i) 6,723,639 shares of the Company’s common stock and (ii) 384,930.724 shares of Series A Preferred Stock. The issuance of the shares of common stock and Series A Preferred Stock occurred on December 5, 2023 which was after the December 4, 2023 record date for the distribution of the CVRs (see Note 6); as such, the Old Cartesian stockholders did not have rights as holders of common stock or holders of Series A Preferred Stock until such issuance on December 5, 2023. In addition, all outstanding stock options to

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purchase Old Cartesian common stock were assumed by the Company and converted into stock options to purchase (i) shares of the Company’s common stock or (ii) shares of the Company’s Series A Preferred Stock on terms substantially identical to those in effect prior to Merger Agreement, except for adjustments to the underlying number of shares and the exercise price based on the Merger Agreement exchange ratio.

Pursuant to the Merger Agreement, the Company agreed to hold a stockholders’ meeting to submit the following proposals to a vote of its stockholders: (i) the approval of the conversion of shares of Series A Preferred Stock into shares of common stock, or the Conversion Proposal, and (ii) either or both of (A) the approval of an amendment to the Company’s restated certificate of incorporation, as amended, or the Charter, to increase the number of shares of common stock authorized under the Charter and (B) the approval of an amendment to the Charter to effect a reverse stock split of all outstanding shares of common stock, in either case (A) or (B) by a number of authorized shares or at a stock split ratio, as the case may be, sufficient to allow the conversion of all shares of Series A Preferred Stock issued in the Merger.

The Company concluded the acquisition resulted in the Company obtaining a controlling financial interest in a VIE in accordance with ASC 810, Consolidation. The Company determined that Old Cartesian was considered to be a VIE as it did not have sufficient equity to finance its activities without additional subordinated financial support. Prior to the Closing Date, the primary source of funding for Old Cartesian had been preferred stock financings. The Company acquired all of the outstanding shares of Old Cartesian and, therefore, is the sole equity holder and primary beneficiary. The Company has the obligation to the absorb losses and right to receive the benefits of Old Cartesian, and the power to direct the activities that most significantly affect the economic performance of Old Cartesian which the Company considers to be its development activities. Therefore, the Company is the primary beneficiary. Further, the Company concluded the VIE qualified as a business and accounted for the transaction as the acquisition of a business in accordance with ASC 805.As the primary beneficiary, the Company was the acquirer in the transaction.

The Company exchanged the right to receive shares of common stock and Series A Preferred Stock for all of the outstanding equity of Old Cartesian.The Company determined the rights to receive shares exchanged in the Merger represent a forward contract.The fair value of the forward contracts was determined based on the fair value of shares of common stock and Series A Preferred Stock underlying the forward contracts as of the acquisition date. The total purchase price consists of the fair value of the forward contracts in addition to a portion of the fair value of options exchanged in the transaction related to prior service. Under the acquisition method, the total purchase price of the acquisition was allocated to the net tangible and identifiable intangible assets acquired and liabilities assumed based on their estimated fair values as of the date of the acquisition.

The total fair value of the consideration of $168.5 million as of the Closing Date is summarized as follows (in thousands):

Forward contract to issue common stock $ 2,713

Forward contract to issue Series A Preferred Stock 155,308

Stock options allocated to consideration paid 10,444

The Company recorded the assets acquired and liabilities assumed as of the Closing Date based on the information available at that date. The following table presents the allocation of the purchase price to the estimated fair values of the assets acquired and liabilities assumed as of the Closing Date (in thousands):

Assets acquired: As of November 13, 2023

Cash and cash equivalents $ 6,561

Prepaid expenses and other current assets 309

Property and equipment, net 215

Right-of-use asset, net 915

In-process research and development assets 150,600

Liabilities assumed

Accrued expenses and other current liabilities $ 2,530

Lease liability $ 292

Lease liability, net of current portion $ 623

Deferred tax liability $ 34,853

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RNAC US Equity

RNAC · 10-K · period ended 2023-12-31

Item 7. Management’s Discussion and Analysis of Financial Condition and Results of Operations

Item 7A. Quantitative and Qualitative Disclosures About Market Risk

Item 8. Financial Statements and Supplementary Data

Item 9. Changes in and Disagreements With Accountants on Accounting and Financial Disclosure

Item 9A. Controls and Procedures

Item 9B. Other Information

Item 9C. Disclosure Regarding Foreign Jurisdictions that Prevent Inspections

Item 10. Directors, Executive Officers and Corporate Governance

Item 11. Executive Compensation

Item 12. Security Ownership of Certain Beneficial Owners and Management and Related Stockholder Matters

Item 13. Certain Relationships and Related Transactions, and Director Independence

Item 14. Principal Accountant Fees and Services

Item 15. Exhibits, Financial Statement Schedules

Item 16. Form 10-K Summary

RNAC US Equity☆

RNAC · 10-K · period ended 2023-12-31

Item 7. Management’s Discussion and Analysis of Financial Condition and Results of Operations

Item 7A. Quantitative and Qualitative Disclosures About Market Risk

Item 8. Financial Statements and Supplementary Data

Item 9. Changes in and Disagreements With Accountants on Accounting and Financial Disclosure

Item 9A. Controls and Procedures

Item 9B. Other Information

Item 9C. Disclosure Regarding Foreign Jurisdictions that Prevent Inspections

Item 10. Directors, Executive Officers and Corporate Governance

Item 11. Executive Compensation

Item 12. Security Ownership of Certain Beneficial Owners and Management and Related Stockholder Matters

Item 13. Certain Relationships and Related Transactions, and Director Independence

Item 14. Principal Accountant Fees and Services

Item 15. Exhibits, Financial Statement Schedules

Item 16. Form 10-K Summary

RNAC US Equity