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ITEM 7. MANAGEMENT’S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND RESULTS OF OPERATIONS

The purpose of this Management's Discussion and Analysis is to better allow our investors to understand and view our company from management's perspective. We are providing an overview of our business and strategy including a discussion of our financial condition and results of operations. You should read the following discussion in conjunction with the consolidated financial statements and the notes to the consolidated financial statements included elsewhere in this Annual Report on Form 10-K. This discussion contains forward-looking statements within the meaning of federal securities laws. Such forward-looking statements are subject to risks and uncertainties that could cause actual results to differ materially from those contained in such forward-looking statements, including those discussed in the section “Risk Factors” in Part I — Item 1A of this Annual Report on Form 10-K.

Overview

We are a late-stage clinical biopharmaceutical company focused on the development of novel therapeutics for a broad range of cancer indications. Our product candidates currently include galinpepimut-S, or GPS, a peptide immunotherapy directed against the Wilms tumor 1, or WT1, antigen, and SLS009 (formerly GFH009), a highly selective small molecule cyclin-dependent kinase 9, or CDK9, inhibitor.

Galinpepimut-S, or GPS: Highly Novel and Engineered Immunotherapy Targeting the WT1 Antigen

Our lead product candidate, GPS, is a cancer immunotherapeutic agent licensed from Memorial Sloan Kettering Cancer Center, or MSK, that targets the WT1 protein, which is present in 20 or more cancer types. Based on its mechanism of action as a directly immunizing agent, GPS has potential as a monotherapy or in combination with other immunotherapeutic agents to address a broad spectrum of hematologic, or blood, cancers and solid tumor indications.

In January 2020, we commenced in the United States an open label randomized Phase 3 clinical trial, the REGAL study, for GPS monotherapy in patients with acute myeloid leukemia, or AML, in the maintenance setting after achievement of second complete remission, or CR2, following successful completion of second-line antileukemic therapy. Patients are randomized (1:1) to receive either GPS or best available treatment, or BAT. We expect this study will be used as the basis for submission of a Biologics License Application, or BLA, subject to a statistically significant and clinically meaningful data outcome and agreement with the U.S. Food and Drug Administration, or the FDA. The primary endpoint of the REGAL study is overall survival. We planned to enroll approximately 125 to 140 patients at approximately 95 clinical sites in North America, Europe and Asia with a planned interim safety, efficacy and futility analysis after 60 events (deaths). In March 2024, we announced the completion of enrollment. Under our current assumptions with respect to enrollment and the estimated survival times for both the treated and control groups in the study, we believe, after discussions with our external statisticians and experts, that the planned interim analysis after 60 events (deaths) per the protocol will occur in the first half of 2024 and the final analysis after 80 events will occur by the end of 2024. Because these analyses are event driven, they are difficult to predict with any certainty and may occur at a different time than currently expected.

In December 2020, we entered into an exclusive license agreement, or 3D Medicines Agreement, with 3D Medicines Inc., or 3D Medicines, a China-based biopharmaceutical company developing next-generation immuno-oncology drugs, for the development and commercialization of GPS, as well as the Company’s next generation heptavalent immunotherapeutic GPS+, which is at preclinical stage, across all therapeutic and diagnostic uses in mainland China, Hong Kong, Macau and Taiwan, which we collectively refer to as Greater China, or the 3DMed Territory. We have retained sole rights to GPS and GPS+ outside of Greater China. In November 2022, we announced that we had agreed with 3D Medicines for 3D Medicines to participate in the REGAL study through the inclusion of approximately 20 patients from mainland China. Although the REGAL study has completed enrollment as announced in March 2024, in accordance with the predetermined statistical analysis plan, 3D Medicines may still enroll patients in mainland China. The timing of such participation and patient enrollment by 3D Medicines, if at all, cannot be predicted with certainty. As of December 31, 2023, we have received an aggregate of $10.5 million in upfront and milestone payments under the 3D Medicines Agreement and a total of $191.5 million in potential future development, regulatory and sales milestones, not including future royalties, remains under the license agreement, which milestones are variable in nature and not under our control. In December 2023, we commenced an arbitration proceeding against 3D Medicines regarding, among other things, the trigger and payment of $13.0 million in milestone payments due to us. See Item 3. Legal Proceedings.

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In December 2018, pursuant to a Clinical Trial Collaboration and Supply Agreement, we initiated a Phase 1/2 multi-arm "basket" type clinical study of GPS in combination with Merck & Co., Inc.’s anti-PD-1 therapy, pembrolizumab (Keytruda®). In 2020, we, together with Merck, determined to focus on ovarian cancer (second or third line). In November 2022, we reported topline clinical and initial immune response data from this study, which showed that treatment with the combination of GPS and pembrolizumab compared favorably to treatment with anti-PD-1 therapy alone in a similar patient population. In November 2023, additional immunobiological and clinical data from the study was presented at the International Gynecologic Cancer Society 2023 Annual Global Meeting which showed a correlation between immune response and PFS.

In February 2020, a Phase 1 open-label investigator-sponsored clinical trial of GPS, in combination with Bristol-Myers Squibb’s anti-PD-1 therapy, nivolumab (Opdivo®), in patients with malignant pleural mesothelioma, or MPM, who harbor relapsed or refractory disease after having received frontline standard of care multimodality therapy was commenced at MSK. Enrollment of a target total of 10 evaluable patients was completed at the end of 2022. We reported positive topline safety and efficacy data from this study in June 2023 and positive follow-up immune response and survival data in December 2023.

GPS was granted Orphan Drug Product Designations, or ODD, from the FDA, as well as orphan medicines designations from the European Medicines Agency, or EMA, for GPS in AML, MPM, and multiple myeloma, or MM, as well as Fast Track designation for AML, MPM, and MM from the FDA.

SLS009: Highly Selective Next Generation CDK9 Inhibitor

On March 31, 2022, we entered into an exclusive license agreement, or the GenFleet Agreement, with GenFleet Therapeutics (Shanghai), Inc., or GenFleet, a clinical-stage biotechnology company developing cutting-edge therapeutics in oncology and immunology, that grants rights to us for the development and commercialization of SLS009, a highly selective small molecule CDK9 inhibitor, across all therapeutic and diagnostic uses worldwide, except for Greater China.

CDK9 activity has been shown to correlate negatively with overall survival in a number of cancer types, including hematologic cancers, such as AML and lymphomas, as well as solid cancers, such as osteosarcoma, pediatric soft tissue sarcomas, melanoma, endometrial, lung, prostate, breast and ovarian. As demonstrated in preclinical and clinical data, to date, SLS009’s high selectivity has the potential to reduce toxicity as compared to older CDK9 inhibitors and other next-generation CDK9 inhibitors currently in clinical development and to potentially be more efficacious.

We completed a Phase 1 dose-escalating clinical trial in the United States and China for SLS009 in mid-2023 and reported positive safety and efficacy data for both patient cohorts, that is relapsed and/or refractory AML and refractory lymphoma. We also established in the trial a recommended Phase 2 dose, or RP2D, of 60 mg for AML and 100 mg for lymphomas.

In the second quarter of 2023, we commenced an open label, single arm, multi-center Phase 2a clinical trial with SLS009 in combination with venetoclax and azacitidine, or aza/ven, in patients with AML who failed or did not respond to treatment with venetoclax-based therapies. The trial is evaluating safety, tolerability, and efficacy at two dose levels of SLS009, 45 mg once weekly, and 60 mg once weekly or 30 mg twice a week, in combination with aza/ven. In addition to safety and tolerability of SLS009 in combination with aza/ven, the primary endpoints are complete response composite rate and duration of response. Additional endpoints include event free survival, overall survival, and pharmacokinetic and pharmacodynamic assessments. The trial includes several sites in the United States, will enroll a minimum of 20 patients and, based on initial results, may be expanded into a registrational trial.

In the fourth quarter of 2023, we completed enrollment in the 45 mg (safety) dose cohort in the Phase 2a study and reported positive initial topline data. We also commenced enrollment in the 60 mg dose cohort with patients randomized to one of two groups, 60 mg fixed dose once weekly or 30 mg fixed twice weekly. Each group will enroll five to 10 patients.

In March 2024, we announced positive topline data from the Phase 2a clinical trial of SLS009 in combination with aza/ven in r/r/ AML. A total of 21 patients were enrolled in the study as of March 15, 2024: 10 in the 45 mg safety cohort and 11 in the 60 mg cohort (30 mg twice a week or 60 mg once a week). Response rates observed in the three cohorts were 10% in the 45 mg once a week safety dose cohort (dose level below the RP2D),

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20% in the 60 mg once a week dose cohort, and 50% in the 30 mg twice a week dose cohort. Additionally, we observed strong anti-leukemic activity, which is defined as 50% or more bone marrow blast reduction in 67% of patients across all dose levels. Median OS has not been reached in any of the cohorts and the first patient enrolled in the study who achieved a CR continues on the study and remains leukemia-free 9 months after enrollment. During the trial, we identified potential biomarkers currently undergoing testing as predictive markers in the most recent portion of the study. Patients with the identified biomarkers exhibited significantly higher response rates: 100% response rate at the optimal dose level (30 mg twice a week) and 57% response rate across all dose levels. Furthermore, we have clarified the proposed biological basis and mechanism of action for SLS009 activity in patients with these biomarkers. The relevant biomarkers are present in multiple hematologic and solid cancer indications, with a substantial proportion of patients exhibiting them in additional indications, ranging up to ~50% of patients in some indications.

Additional topline data for the 60 mg dose cohort is expected in the second quarter of 2024.

In October 2023, we announced that our partner, GenFleet, dosed the first patient in a Phase Ib/II trial evaluating SLS009 in patients with relapsed/refractory, or r/r, peripheral T-cell lymphoma, or PTCL. The open-label, single-arm trial will enroll up to 95 patients to evaluate safety and efficacy and, based on the results, may serve as a registrational study. This initial PTCL study is fully funded by GenFleet and is being conducted in China. We expect to report initial topline data from the study in the second quarter of 2024.

In March 2024, GenFleet announced that it entered into a collaboration and supply agreement with BeiGene Switzerland GmbH to initiate a combination study of SLS009 and Brukinsa (zanubrutinib), a BTK inhibitor, in r/r diffused large B-cell lypmhoma, or DLBCL, and the first patient was dosed in the trial. The open-label, single-arm multi-center trial will be conducted in two parts. In the Phase 1b portion, 6-18 patients will be enrolled. In the Phase 2 portion, approximately 45 patients will be enrolled. This study is funded by GenFleet and is being conducted in China.

SLS009 is also currently being evaluated in pediatric solid tumors and leukemia models through the NCI Pediatric Preclinical in Vivo Testing, or PIVOT, program. Studies are supported through cooperative agreement grants from the NCI to the seven PIVOT research programs performing the PK and efficacy testing in pediatric tumors and a centralized coordinating center. We expect to report relevant data from the program in the second half of 2024.

For SLS009, the FDA granted Orphan Drug Product designations in AML and PTCL and Fast Track designations for r/r AML and r/r PTCL.

Components of Results of Operations

Licensing Revenue

Licensing revenue consists of revenue recognized pursuant to the 3D Medicines Agreement. In the future, we may generate revenue from a combination of regulatory, development, and sales milestone payments and royalties in connection with the 3D Medicines Agreement.

Cost of Licensing Revenue

Cost of licensing revenue consists of sublicensing fees incurred under our license from MSK in connection with the 3D Medicines Agreement.

Research and Development

Research and development expense consists of expenses incurred in connection with the discovery and development of our product candidates. We expense research and development costs as incurred. These expenses include:

•expenses incurred under agreements with clinical research organizations, or CROs, as well as investigative sites and consultants that conduct our preclinical studies and clinical trials;

•manufacturing and clinical drug supply expenses;

•outsourced professional scientific development services;

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•employee-related expenses, which include salaries, benefits and stock-based compensation;

•payments made under our license agreements, under which we acquired certain intellectual property;

•expenses relating to certain regulatory activities, including filing fees paid to regulatory agencies;

•laboratory materials and supplies used to support our research activities; and

•allocated expenses, utilities and other facility-related costs.

The successful development of our current and future product candidates is highly uncertain. At this time, we cannot reasonably estimate or know the nature, timing and costs of the efforts that will be necessary to complete the remainder of the development of, or when, if ever, material net cash inflows may commence from, any current or future product candidates. This uncertainty is due to the numerous risks and uncertainties associated with the duration and cost of our clinical trials, which vary significantly over the life of a project as a result of many factors, including:

•the number and geographical location of clinical sites included in the trials;

•the length of time required to enroll suitable patients;

•the number and geographical location of patients that ultimately participate in the trials;

•the number of doses patients receive;

•the duration of patient follow-up;

•the results of clinical trials;

•the expenses associated with manufacturing and clinical drug supply;

•the receipt of marketing approvals; and

•the commercialization of current and future product candidates.

Research and development activities are central to our business model. Oncology product candidates in the later stages of clinical development generally have higher development costs than those in the earlier stages of clinical development, primarily due to the increased size and duration of the later-stage clinical trials. We expect our research and development expenses to increase for the foreseeable future as we conduct and complete our ongoing early and late-stage clinical trials, initiate additional clinical trials, and expand regulatory activities associated with the preparation and submission of regulatory filings.

Our expenditures are subject to additional uncertainties, including the terms and timing of regulatory approvals. We may never succeed in achieving regulatory approval for any of our current or future product candidates. We may obtain unexpected results from our clinical trials. We may elect to discontinue, delay or modify clinical trials of some product candidates or target indications or focus on others. A change in the outcome of any of these variables with respect to the development of a product candidate could mean a significant change in the costs and timing associated with the development of that product candidate. For example, if the FDA or other regulatory authorities were to require us to conduct clinical trials beyond those that we currently anticipate, 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 on the completion of clinical development.

General and Administrative Expense

General and administrative expenses consist principally of salaries and related costs for personnel in executive, administrative, finance and legal functions, including stock-based compensation, travel expenses and recruiting expenses, fees for outside legal counsel, and director and officer insurance premiums. Other general and administrative expenses include facility related costs, patent filing and prosecution costs, professional fees for business development, accounting, consulting, legal and tax-related services associated with maintaining compliance with our Nasdaq listing and SEC reporting requirements, investor relations costs, and other expenses associated with being a public company.

If and when we believe that regulatory approval of a product candidate appears likely, we anticipate that an increase in general and administrative expenses will occur as a result of our preparation for commercial operations,

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particularly as it relates to the sales and marketing of such product candidate. Oncology product commercialization may take several years and millions of dollars in development costs.

Acquired In-Process Research and Development

Acquired in-process research and development consists of costs to acquire or license product candidates from third parties for development with no alternative future use as the technology and know-how acquired are not currently commercially viable.

Non-Operating Income

Non-operating income consists of changes in fair value of our warrant liability, changes in fair value of our contingent consideration, and interest income. Interest income primarily reflects the interest earned from our cash and cash equivalents.

Results of Operations for the Years Ended December 31, 2023 and 2022

The following table summarizes our results of operations for the years ended December 31, 2023 and 2022 (amounts in thousands):

Year ended December 31,

Operating expenses:

Cost of licensing revenue — 100 (100)

Acquired in-process research and development — 10,000 (10,000)

Further analysis of the changes and trends in our operating results are discussed below.

Licensing Revenue

There was no licensing revenue for the year ended December 31, 2023 and $1.0 million in licensing revenue for the year ended December 31, 2022 related to approval by China's National Medical Products Administration, or NMPA, of an Investigational New Drug, or IND, application filed by 3D Medicines for a small Phase 1 clinical trial investigating safety of GPS in China.

Cost of Licensing Revenue

There was no cost of licensing revenue recognized during the year ended December 31, 2023, and $0.1 million of sublicensing fees payable under our license from MSK in connection with the 3D Medicines Agreement during the year ended December 31, 2022.

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Research and Development

Research and development expenses were $24.0 million for the year ended December 31, 2023 compared to $20.3 million for the year ended December 31, 2022. As compared to the prior period, the $3.7 million increase in research and development expenses was primarily attributable to a $1.9 million increase in clinical trial expenses primarily related to our ongoing Phase 3 REGAL clinical trial of GPS in AML and our Phase 2a and Phase 1 clinical trials of SLS009, a $1.3 million increase in clinical and regulatory consulting expenses due to the advancement of our clinical programs, and a $1.1 million increase in personnel related expenses primarily due to increased headcount. These increases were partially offset by a $0.5 million decrease in manufacturing and clinical drug supply costs due to the timing of the manufacture of drug substance and drug product batches, and a $0.1 million decrease in licensing and other research and development costs. We anticipate that our research and development expenses will increase in the future as we continue to advance the development of GPS and SLS009, including our Phase 3 REGAL clinical trial of GPS in AML and the ongoing and planned clinical trials of SLS009.

General and Administrative

General and administrative expenses were $13.9 million for the year ended December 31, 2023 compared to $12.6 million for the year ended December 31, 2022. The $1.3 million increase was primarily driven by a $0.5 million increase in personnel related expenses primarily due to increased headcount, including a $0.3 million increase in non-cash stock-based compensation, a $0.6 million increase in intellectual property fees, a $0.1 million increase in outside services and public company costs, and a $0.1 million increase in other general and administrative costs.

Acquired In-Process Research and Development

There was no acquired in-process research and development expense during the year ended December 31, 2023. During the year ended December 31, 2022, we recognized $10.0 million for the acquisition of in-process research and development related to the in-licensing of SLS009.

Non-Operating Income

Non-operating income for the years ended December 31, 2023 and 2022 was as follows (in thousands):

Year ended December 31,

Change in fair value of warrant liability $ 4 $ 36 $ (32)

Change in fair value of contingent consideration — 296 (296)

Total non-operating income $ 529 $ 649 $ (120)

The decrease in our non-operating income during the year ended December 31, 2023 compared to the year ended December 31, 2022 was primarily due to a $0.3 million decrease in the change in fair value of contingent consideration in the prior period, partially offset by a $0.2 million increase in interest income earned from our cash and cash equivalents primarily due to higher interest rates.

The changes in fair value of warrant liability and changes in fair value of contingent consideration are all non-cash in nature.

Liquidity and Capital Resources

We did not generate any revenue from product sales in the years ended December 31, 2023 and 2022. Through December 31, 2023, we have only generated licensing revenue from the 3D Medicines Agreement. Since inception, we have incurred net losses, used net cash in our operations, and have funded substantially all of our operations through proceeds of the sale of equity securities and convertible notes.

Sources of Liquidity

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On March 19, 2024, we consummated a registered direct offering, or the March 2024 Registered Direct Offering, in which we entered into a Securities Purchase Agreement with two institutional investors pursuant to which we agreed to issue and sell 11,000,000 shares of our common stock and 2,029,316 pre-funded warrants exercisable for shares of common stock. Each share of common stock was sold together at a purchase price of $1.535 and each pre-funded warrant was sold at a purchase price of $1.5349. The gross proceeds to us from the March 2024 Registered Direct Offering were approximately $20.0 million, before deducting the placement agent's fees and related offering expenses. In a concurrent private placement, we agreed to issue to the two institutional investors exercisable for up to an aggregate of 13,029,316 shares of common stock warrants at an exercise price of $1.41 per share. Subsequent to the closing of the March 2024 Registered Direct Offering, 1,014,658 pre-funded warrants were exercised for shares of common stock.

On January 8, 2024, we consummated a public offering on a "reasonable best efforts" basis, or the January 2024 Offering, issuing 10,130,000 shares of common stock and an aggregate of 1,870,000 pre-funded warrants exercisable for shares of common stock, together with accompanying warrants to purchase an aggregate of 12,000,000 shares of common stock. Each share of common stock and accompanying common warrant were sold together at a combined offering price of $0.75, and each pre-funded warrant and accompanying common warrant were sold together at a combined offering price of $0.7499. The aggregate gross proceeds to us from the January 2024 Offering were approximately $9.0 million, before deducting the placement agent's fees and related offering expenses.

On November 2, 2023, we consummated a registered direct offering, or the November 2023 Registered Direct Offering, in which we entered into a Securities Purchase Agreement with a single institutional investor pursuant to which we agreed to issue and sell 3,100,000 shares of our common stock and 552,300 pre-funded warrants exercisable for shares of common stock, together with accompanying warrants to purchase an aggregate of 3,652,300 shares of common stock. Each share of common stock and accompanying warrant were sold together at a combined purchase price of $1.0952 and each pre-funded warrant and accompanying warrant were sold together at a combined purchase price of $1.0951. The net proceeds to us from the November 2023 Registered Direct Offering were approximately $3.5 million, after deducting the placement agent's fees and related offering expenses.

On February 28, 2023, we consummated an underwritten public offering, or the February 2023 Offering, issuing 7,220,217 shares of common stock and accompanying common stock warrants to purchase an aggregate of 7,220,217 shares of common stock. The shares of common stock and accompanying common stock warrants were sold at a combined price of $2.77 per share and accompanying common stock warrant. Each common stock warrant sold with the shares of common stock represents the right to purchase one share of our common stock at an exercise price of $2.77 per share. The common stock warrants are exercisable immediately and will expire on February 28, 2028, five years from the date of issuance. The net proceeds from the February 2023 Offering were approximately $18.5 million, after deducting underwriting discounts and commissions and estimated offering expenses, and excluding the exercise of any warrants.

On April 16, 2021, the Company entered into a Controlled Equity OfferingSM Sales Agreement, or the Sales Agreement, with Cantor Fitzgerald & Co., or the Agent. From time to time during the term of the Sales Agreement, subject to certain restrictions, we could offer and sell shares of common stock having an aggregate offering price up to a total of $50.0 million in gross proceeds. The Agent was entitled to collect a fee equal to 3% of the gross sales price of all shares of common stock sold. Shares of common stock sold under the Sales Agreement were offered and sold pursuant to our registration statement on Form S-3, which was filed with the SEC on April 16, 2021 and declared effective on April 29, 2021. During the year ended December 31, 2023, we sold a total of 92,882 shares of common stock pursuant to the Sales Agreement at an average price of $3.21 per share for aggregate net proceeds of approximately $0.3 million. On January 2, 2024, we mutually agreed with the Agent to terminate the Sales Agreement.

In December 2020, together with our wholly-owned subsidiary, SLSG Limited, LLC, we entered into the 3D Medicines Agreement pursuant to which we granted 3D Medicines a sublicensable royalty-bearing license under certain intellectual property owned or controlled by us, to develop, manufacture and have manufactured, and commercialize GPS and heptavalent GPS product candidates for all therapeutic and other diagnostic uses in the 3DMed Territory. As of December 31, 2023, we have received an aggregate of $10.5 million in upfront payments and certain technology transfer and regulatory milestone payments under our license agreement with 3D Medicines. A total of $191.5 million in potential future development, regulatory, and sales milestones, not including future

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royalties, remains under the 3D Medicines Agreement, which milestones are all variable in nature and not under our control.

Funding Requirements

As of December 31, 2023, we had an accumulated deficit of $217.2 million, cash and cash equivalents of $2.5 million and restricted cash and cash equivalents of $0.1 million. In addition, we had current liabilities of $13.7 million as of December 31, 2023. We expect that our cash and cash equivalents, together with the net proceeds from the January 2024 Offering and March 2024 Registered Direct Offering, will not be sufficient to fund our current planned operations for at least the next twelve months from the date of issuance of these financial statements. These conditions give rise to a substantial doubt over our ability to continue as a going concern. This going concern assumption is based on management’s assessment of the sufficiency of our current and future sources of liquidity and whether it is probable we will be able to meet our obligations as they become due for at least one year from the date our consolidated financial statements are available to be issued, and if not, whether our liquidation is imminent.

Our consolidated financial statements do not include any adjustments related to the recoverability and classification of recorded asset amounts or the amounts and classification of liabilities that might result from the outcome of this uncertainty. We anticipate incurring additional losses until such time, if ever, that we can generate significant sales of any current or future product candidates in development.

We will require substantial additional financing to develop any current or future product candidates. If we are unable to obtain additional funding on a timely basis, we will be required to scale back our plans and place certain activities on hold. We currently do not have any commitments to obtain additional funds. Our management continues to evaluate different strategies to obtain the required funding for future operations. These strategies may include public and private placements of equity and/or debt securities, as well as payments from potential strategic research and development collaborations or licensing and/or marketing arrangements with pharmaceutical companies. Additionally, we continue to pursue discussions with global and regional pharmaceutical companies for licensing and/or co-development rights to our product candidates. There can be no assurance that these future funding efforts will be successful.

Our future operations are highly dependent on a combination of factors, including (i) the timely and successful completion of any additional financings, (ii) our ability to complete revenue-generating partnerships with pharmaceutical and biotechnology companies, (iii) the success of our research and development activities, (iv) the development of competitive therapies by other biotechnology and pharmaceutical companies, and, ultimately, (v) regulatory approval and market acceptance of our product candidates.

Components of Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents

The following table provides a reconciliation of the components of cash, cash equivalents, restricted cash, and restricted cash equivalents reported in our consolidated balance sheets to the total of the amount presented in the consolidated statements of cash flows (in thousands):

December 31,

Restricted cash and cash equivalents 100 100

Restricted cash and cash equivalents of $0.1 million as of December 31, 2023 and 2022 relates to certificates of deposit maintained on hand with our financial institutions as collateral for our corporate credit cards.

Cash Flows

The following table summarizes our cash flows from operating, investing, and financing activities for the years ended December 31, 2023 and 2022 (in thousands):

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Year ended December 31,

Net cash (used in) provided by:

Net Cash Flow from Operating Activities

Net cash used in operating activities of $31.4 million during the year ended December 31, 2023 was primarily attributable to our net loss of $37.3 million, and partially offset by a change in our operating assets and liabilities of $3.3 million and various net non-cash charges of $2.6 million. The net change in our operating assets and liabilities is due to an increase in accounts payable of $2.3 million, an increase in accrued expenses and other current liabilities of $1.4 million, and a decrease in prepaid expenses and other assets of $0.1 million, which was partially offset by a decrease in operating lease liabilities of $0.5 million. Net non-cash charges were driven by $2.1 million in non-cash stock compensation expense and $0.5 million in non-cash lease expense.

Net cash used in operating activities of $23.8 million during the year ended December 31, 2022 was primarily attributable to our net loss of $41.3 million, and partially offset by various net non-cash charges of $11.9 million, and a change in our operating assets and liabilities of $5.6 million. Net non-cash charges were driven by $10.0 million in expense related to the acquired in-process research and development, $1.7 million in non-cash stock compensation expense, and $0.2 million in other net non-cash charges. The net change in our operating assets and liabilities is due to an increase in accrued expenses and other current liabilities of $3.6 million, an increase in accounts payable of $1.2 million and a decrease in prepaid expenses and other current assets of $1.3 million, which was partially offset by a decrease in operating lease liabilities of $0.5 million.

Net Cash Used in Investing Activities

Net cash used in investing activities of $5.5 million and $4.5 million during the years ended December 31, 2023 and 2022, respectively, was related to license payments made for the acquisition of in-process research and development under the GenFleet Agreement.

Net Cash Flow from Financing Activities

We generated $22.3 million of net cash from financing activities for the year ended December 31, 2023, which was due to $21.9 million in aggregate net proceeds received from the February 2023 Offering and the November 2023 Offering, $0.3 million in aggregate net proceeds received from the issuance of common stock under the Sales Agreement, and a $0.1 million in aggregate net proceeds received from the issuance of common stock under our employee stock purchase plan.

We generated $24.1 million of net cash from financing activities for the year ended December 31, 2022, which was due to $23.0 million in aggregate net proceeds received from our underwritten public offering, which closed in April 2022, $1.0 million in aggregate net proceeds received from the issuance of common stock under the Sales Agreement, and $0.1 million in aggregate net proceeds received from the issuance of common stock under our employee stock purchase plan.

Contractual Obligations and Other Commitments

Leases

Our lease commitments reflect payments due under our lease agreement for our office space in New York, New York that expires in September 2025. As of December 31, 2023, our contractual commitment for our lease was $1.0 million, which will be paid over the remaining term of the lease. For additional information on our leases and

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timing of future payments, please read Note 7, Leases, to the consolidated financial statements included in this Form 10-K.

Other Commitments

We acquire product candidates still in development and enter into research and development arrangements with third parties that often require milestone and royalty payments to the third-party contingent upon the occurrence of certain future events linked to the success of the product candidate in development. Milestone payments may be required, contingent upon the successful achievement of an important point in the development life-cycle of the pharmaceutical product (e.g., approval of the product for marketing by a regulatory agency). We also typically will need to make royalty payments based upon a percentage of the sales of the product candidate in the event that regulatory approval for marketing is obtained. Because of the contingent nature of these payments, they are not included in the table of contractual obligations.

These arrangements may be material individually and, in the event that multiple milestones are reached in the same period, the aggregate charge to expense could be material to the results of operations in any one period. In addition, these arrangements often give us the discretion to terminate development of the product candidate, which would allow us to avoid making the contingent payments; however, we are unlikely to cease development if the product candidate successfully achieves clinical testing objectives.

We enter into contracts in the normal course of business with various third parties for clinical trials, manufacturing, and other services and products for operating purposes. These contracts provide for termination upon notice. Payments due upon cancellation generally consist only of payments for services provided or expenses incurred, including non-cancellable obligations of our service providers, up to the date of cancellation. These payments have not been included separately within these contractual and other obligations disclosures.

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Critical Accounting Policies and Estimates

Our consolidated financial statements are prepared in accordance with U.S. generally accepted accounting principles. The preparation of our consolidated financial statements and related disclosures requires our management to make estimates and judgments that affect the reported amounts of assets and liabilities, disclosure of contingent assets and liabilities at the date of the consolidated financial statements, and the reported amounts of revenues and expenses during the reported period. We base such estimates on historical experience, known trends and events and various other factors that are believed to be reasonable under the circumstances, the results of which form the basis for making judgments about the carrying values of assets and liabilities that are not readily apparent from other sources. We evaluate our estimates and assumptions on an ongoing basis. Our actual results may differ from these estimates under different assumptions and conditions.

While our significant accounting policies are described in more detail in the notes to our audited consolidated financial statements appearing elsewhere in this Annual Report on Form 10-K, we believe that the following accounting policies are those most critical to the judgments and estimates used in the preparation of our consolidated financial statements.

Revenue Recognition

We record revenue in accordance with Accounting Standard Codification, or ASC, Topic 606, Revenue From Contracts with Customers. This standard applies to all contracts with customers, except for contracts that are within the scope of other standards, such as leases, insurance, collaboration arrangements and financial instruments. Under Topic 606, an entity recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration that the entity expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that an entity determines are within the scope of Topic 606, the entity performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the entity satisfies a performance obligation. We only apply the five-step model to contracts when it is probable that we will collect the consideration we are entitled to in exchange for the goods or services we transfer to the customer. At contract inception, once the contract is determined to be within the scope of Topic 606, we assess the goods or services promised within each contract and determine those that are performance obligations, and we assess whether each promised good or service is distinct. 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.

Development, Regulatory and Sales Milestones and Other Payments

At the inception of each arrangement that includes regulatory or development milestone payments, we evaluate whether the milestones are considered probable of being achieved and estimate 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. Milestone payments that are not within the control of us or the licensee, such as regulatory approvals, are not considered probable of being achieved until those approvals are received. We evaluate factors such as the scientific, clinical, regulatory, commercial, and other risks that must be overcome to achieve the particular milestone in making this assessment. There is considerable judgment involved in determining whether it is probable that a significant revenue reversal would not occur. At the end of each subsequent reporting period, we reevaluate the probability of achievement of all milestones subject to constraint and, if necessary, adjust our estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect revenues and earnings in the period of adjustment.

For arrangements that include sales-based royalties, including milestone payments upon first commercial sales and milestone payments based on a level of sales, which are the result of a customer-vendor relationship and for which the license is deemed to be the predominant item to which the royalties relate, we 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. To date, we have not recognized any royalty revenue resulting from any of our licensing arrangements.

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Goodwill

Goodwill is the excess of the cost of an acquired entity over the net amounts assigned to tangible and intangible assets acquired and liabilities assumed. Goodwill is not amortized but is subject to an annual impairment test. We have a single reporting unit and all goodwill relates to that reporting unit.

We perform our annual goodwill impairment test at the reporting unit level on October 1 of each fiscal year or more frequently if changes in circumstances or the occurrence of events suggest that an impairment exists. Goodwill is evaluated for impairment using the simplified test of goodwill impairment as defined by the Financial Accounting Standards Board, or FASB, Accounting Standards Update, or ASU, No. 2017-04. Under the guidance, goodwill impairment is measured by the amount by which the carrying value of a reporting unit exceeds its fair value, without exceeding the carrying amount of goodwill allocated to that reporting unit. If the fair value of the reporting unit is less than its carrying value, an impairment loss is recorded to the extent that the implied fair value of the reporting unit’s goodwill is less than the carrying value of the reporting unit’s goodwill.

Accrued Research and Development Expenses

As part of the process of preparing our consolidated financial statements, we are required to estimate our accrued research and development expenses. This process involves reviewing open contracts and purchase orders, communicating with applicable personnel to identify services that have been performed on our behalf and estimating the level of service performed and the associated cost incurred for the service when we have not yet been invoiced or otherwise notified of actual costs. The majority of our service providers require advance payments; however, some invoice us in arrears for services performed, on a pre-determined schedule or when contractual milestones are met. We make estimates of our accrued expenses as of each balance sheet date in the consolidated financial statements based on facts and circumstances known to us at that time. We periodically confirm the accuracy of the estimates with the service providers and make adjustments if necessary. Examples of estimated accrued research and development expenses include fees paid to:

•Vendors in connection with clinical development activities;

•the production of clinical trial materials;

•CROs in connection with clinical trials; and

•investigative sites in connection with clinical trials.

We base our expenses related to clinical trials on our estimates of the services received and efforts expended pursuant to quotes and contracts with multiple research institutions and CROs that conduct and manage preclinical studies and clinical trials on our behalf. The financial terms of these agreements are subject to negotiation, vary from contract to contract and may result in uneven payment flows. There may be instances in which payments made to our vendors will exceed the level of services provided and result in a prepayment of the expense. Payments under some of these contracts depend on factors such as the successful enrollment of patients and the completion of clinical trial milestones. In accruing service fees, we estimate the time period over which services will be performed and the level of effort to be expended in each period. If the actual timing of the performance of services or the level of effort varies from the estimate, we adjust the accrual or prepaid accordingly. Although we do not expect its estimates to be materially different from amounts actually incurred, our understanding of the status and timing of services performed relative to the actual status and timing of services performed may vary and may result in reporting amounts that are too high or too low in any particular period. To date, we have not made any material adjustments to our prior estimates of accrued research and development expenses.

Stock-Based Compensation

We account for stock-based compensation by estimating the fair value of each stock option on the date of grant using the Black-Scholes model. We recognize stock-based compensation expense on a straight-line basis over the vesting term. The Black-Scholes model requires us to make certain assumptions regarding: (i) the expected volatility in the market price of our shares; (ii) dividend yield; (iii) risk-free interest rates; and (iv) the period of time employees are expected to hold the award prior to exercise (referred to as the expected holding period). As a result, if we revise our assumptions and estimates, our stock-based compensation expense could change.

Given our limited history as a publicly traded company following the Merger on December 29, 2017, we did not have sufficient trading data to calculate volatility based on our own common stock, and the expected volatility was calculated as of each grant date based on our own implied volatility in combination with a peer group of publicly

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traded companies. The expected term of the stock options was determined based upon the simplified approach for employees and non-employee directors, allowed under SEC Staff Accounting Bulletin No. 110, which assumes that the stock options will be exercised evenly from vesting to expiration. As data associated with future exercises is obtained, the expected term of future grants will be adjusted accordingly.

We measure compensation for restricted stock units, or RSUs, based on the price of our shares at the grant date and we recognize the expense on a straight-line basis over the vesting period. The expense relating to RSUs that contain both a service and a performance condition is estimated and adjusted on a quarterly basis based upon our assessment of the probability that the performance condition would be met. As a result, if we revise such assessment, our stock-based compensation expense could change.

Recent Accounting Pronouncements

See Note 3 to our consolidated financial statements included elsewhere in this Annual Report on Form 10-K for a description of recent accounting pronouncements applicable to our consolidated financial statements.

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ITEM 7A. QUANTITATIVE AND QUALITATIVE DISCLOSURES ABOUT MARKET RISK

The primary objective of our investment activities is to preserve capital. We do not utilize hedging contracts or similar instruments.

We are exposed to certain market risks relating primarily to interest rate risk on our cash and cash equivalents and risks relating to the financial viability of the institutions which hold our capital and through which we have invested our funds. We manage such risks by investing primarily in money market mutual funds.

In addition, we are exposed to foreign currency exchange rate fluctuations relating to payments we make to certain vendors and suppliers and license partners using foreign currencies. We do not hedge against foreign currency risks. Consequently, changes in exchange rates could adversely affect our operating results and stock price. Such losses have not been significant to date.

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ITEM 8. FINANCIAL STATEMENTS AND SUPPLEMENTARY DATA

Page

Notes to Consolidated Financial Statements 138

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REPORT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

To the Stockholders and the Board of Directors of

SELLAS Life Sciences Group, Inc.

Opinion on the Financial Statements

We have audited the accompanying consolidated balance sheets of SELLAS Life Sciences Group, Inc. (the “Company”) as of December 31, 2023 and 2022, the related consolidated statements of operations, stockholders’ (deficit) equity and cash flows for the years then ended, 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 consolidated financial position of the Company as of December 31, 2023 and 2022, and the consolidated results of its operations and its cash flows for the years then ended, in conformity with accounting principles generally accepted in the United States of America.

Going Concern Uncertainty

The accompanying consolidated financial statements have been prepared assuming that the Company will continue as a going concern. As discussed in Note 2 to the consolidated financial statements, the Company has suffered recurring losses from operations and has a net capital deficiency that raise substantial doubt about its ability to continue as a going concern. Management’s plans in regard to these matters are also described in Note 2. The consolidated financial statements do not include any adjustments that might result from the outcome of this uncertainty.

Basis for Opinion

These consolidated financial statements are the responsibility of the Company’s management. Our responsibility is to express an opinion on the Company’s consolidated financial statements based on our audits. We are a public accounting firm registered with the Public Company Accounting Oversight Board (United States) (“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 audits 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 consolidated financial statements are free of material misstatement, whether due to error or fraud. The Company is not required to have, nor were we engaged to perform, an audit of its internal control over financial reporting. As part of our audits we are required to obtain an understanding of internal control over financial reporting but not for the purpose of expressing an opinion on the effectiveness of the Company’s internal control over financial reporting. Accordingly, we express no such opinion.

Our audits included performing procedures to assess the risks of material misstatement of the consolidatedfinancial statements, whether due to error or fraud, and performing procedures to respond to those risks. Such procedures included examining, on a test basis, evidence regarding the amounts and disclosures in the consolidatedfinancial statements. Our audits also included evaluating the accounting principles used and significant estimates made by management, as well as evaluating the overall presentation of the consolidated financial statements. We believe that our audits provide a reasonable basis for our opinion.

Critical Audit Matters

Critical audit matters are matters arising from the current period audit of the consolidated financial statements that were communicated or required to be communicated to the audit committee and that (1) relate to accounts or disclosures that are material to the consolidated financial statements and (2) involved our especially challenging, subjective, or complex judgments. We determined that there are no critical audit matters.

/s/ Moss Adams LLP

Campbell, California

March 28, 2024

We have served as the Company’s auditor since 2018.

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SELLAS LIFE SCIENCES GROUP, INC.

CONSOLIDATED BALANCE SHEETS

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

December 31,

ASSETS

Current assets:

Restricted cash and cash equivalents 100 100

Prepaid expenses and other current assets 542 531

Operating lease right-of-use assets 858 874

Deposits and other assets 275 399

LIABILITIES AND STOCKHOLDERS’ (DEFICIT) EQUITY

Current liabilities:

Accrued expenses and other current liabilities 7,650 6,286

Operating lease liabilities 446 372

Acquired in-process research and development payable — 5,500

Operating lease liabilities, non-current 460 573

Warrant liability — 4

Commitments and contingencies (Note 7)

Stockholders’ (deficit) equity:

Total stockholders’ (deficit) equity (7,976) 4,851

Total liabilities and stockholders’ (deficit) equity $ 6,219 $ 20,943

See accompanying notes to these consolidated financial statements.

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SELLAS LIFE SCIENCES GROUP, INC.

CONSOLIDATED STATEMENTS OF OPERATIONS

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

Year Ended December 31,

Licensing revenue $ — $ 1,000

Operating expenses:

Cost of licensing revenue — 100

Acquired in-process research and development — 10,000

Non-operating income:

Change in fair value of warrant liability 4 36

Change in fair value of contingent consideration — 296

Total non-operating income 529 649

Per share information:

Net loss per common share, basic and diluted $ (1.34) $ (2.13)

See accompanying notes to these consolidated financial statements.

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SELLAS LIFE SCIENCES GROUP, INC.

CONSOLIDATED STATEMENT OF STOCKHOLDERS' (DEFICIT) EQUITY

(Amounts in thousands, except share amounts)

Shares Amount

Issuance of common stock under employee stock purchase plan 25,089 — 85 — 85

Vesting of restricted stock units 40,044 — — — —

Stock-based compensation — — 1,726 — 1,726

Issuance of common stock, net of issuance costs 92,882 — 289 — 289

Issuance of common stock upon the exercise of warrants 14,000 — 14 — 14

Issuance of common stock under employee stock purchase plan 91,454 — 107 — 107

Vesting of restricted stock units 85,245 — — — —

Tax withholding on vesting of restricted stock units (28,613) — (31) — (31)

Stock-based compensation — — 2,094 — 2,094

See accompanying notes to these consolidated financial statements.

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SELLAS LIFE SCIENCES GROUP, INC.

CONSOLIDATED STATEMENTS OF CASH FLOWS

(Amounts in thousands)

Year ended December 31,

Cash flows from operating activities:

Adjustment to reconcile net loss to net cash used in operating activities:

Acquired in-process research and development charge — 10,000

Non-cash stock-based compensation 2,094 1,726

Change in fair value of contingent consideration — (296)

Change in fair value of common stock warrants (4) (36)

Changes in operating assets and liabilities:

Prepaid expenses and other assets 113 1,253

Accrued expenses and other current liabilities 1,449 3,646

Operating lease liabilities (518) (471)

Net cash used in operating activities (31,410) (23,809)

Cash flows from investing activities:

Cash paid for acquisition of in-process research and development (5,500) (4,500)

Net cash used in investing activities (5,500) (4,500)

Cash flows from financing activities:

Proceeds from issuance of common stock, net of issuance costs 289 1,048

Proceeds from the exercise of warrants 14 —

Proceeds from employee stock plan purchases 107 85

Tax withholding on vesting of restricted stock units (31) —

Net cash provided by financing activities 22,315 24,079

Supplemental disclosure of cash flow information:

Cash received during the year for interest $ 525 $ 317

Supplemental disclosures:

Payable for acquired in-process research and development $ — $ 5,500

Offering costs in accounts payable and accrued expenses $ 103 $ —

See accompanying notes to these consolidated financial statements.

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SELLAS LIFE SCIENCES GROUP, INC.

NOTES TO CONSOLIDATED FINANCIAL STATEMENTS

1. Organization and Description of Business

SELLAS Life Sciences Group, Inc. is a late-stage clinical biopharmaceutical company focused on novel therapeutics for a broad range of cancer indications. SELLAS’ lead product candidate, galinpepimut-S ("GPS"), is a cancer immunotherapeutic agent licensed from Memorial Sloan Kettering Cancer Center ("MSK") and targets the Wilms Tumor 1 ("WT1") protein, which is present in an array of tumor types. GPS has potential as a monotherapy or in combination with other immunotherapeutic agents to address a broad spectrum of hematologic, or blood, cancers and solid tumor indications. SELLAS' second product candidate is SLS009 (formerly GFH009), a small molecule, highly selective cyclin-dependent kinase 9 ("CDK9") inhibitor, which the Company licensed from GenFleet Therapeutics (Shanghai), Inc. ("GenFleet"), for all therapeutic and diagnostic uses in the world outside of mainland China, Hong Kong, Macau and Taiwan ("SLS009 Territory").

As used in this Annual Report on Form 10-K, the words the "Company," and "SELLAS" refer to SELLAS Life Sciences Group, Inc. and its consolidated subsidiaries.

2. Liquidity and Going Concern

The accompanying consolidated financial statements have been prepared on a going concern basis, which contemplates the realization of assets and the satisfaction of liabilities in the normal course of business. The accompanying consolidated financial statements do not reflect any adjustments relating to the recoverability and reclassifications of assets and liabilities that might be necessary if the Company is unable to continue as a going concern. The Company expects its costs and expenses to increase as it continues to develop its product candidates and progress its current and planned clinical programs.

Pursuant to the requirements of Accounting Standard Codification ("ASC") 205-40, Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern, management must evaluate whether there are conditions or events, considered in the aggregate, that raise substantial doubt about the Company’s ability to continue as a going concern within one year after the date that the consolidated financial statements are issued. This evaluation initially does not take into consideration the potential mitigating effect of management’s plans that have not been fully implemented as of the date these financial statements are issued, but will consider such plans if (1) it is probable that the plans will be effectively implemented within one year after the date the financial statements are issued, and (2) it is probable that the plans, when implemented, will mitigate the relevant condition or events that raise substantial doubt about the entity’s ability to continue as a going concern within one year after the date the consolidated financial statements are issued. Certain elements of the Company’s operating plan to alleviate the conditions that raise substantial doubt are outside of the Company’s control and cannot be included in management’s evaluation under the requirements of ASC 205-40.

Since inception, the Company has incurred recurring losses and negative cash flows from operations and has an accumulated deficit of $217.2 million as of December 31, 2023. During the year ended December 31, 2023, the Company incurred a net loss of $37.3 million and used $31.4 million of cash in operations. The Company continues to expect to generate operating losses and negative cash flows for the next few years and will need additional funding to support its planned operating activities through profitability. The transition to profitability is dependent upon the successful development, approval, and commercialization of the Company's product candidates and the achievement of a level of revenues adequate to support its cost structure. As of December 31, 2023, the Company had cash and cash equivalents of $2.5 million. The Company expects its cash and cash equivalents, together with the net proceeds from a public offering completed on January 8, 2024 (the "January 2024 Offering") and the registered direct offering completed on March 19, 2024 (the "March 2024 Registered Direct Offering"), will not be sufficient to fund its current planned operations for at least the next twelve months from the date of issuance of these financial statements. These conditions give rise to a substantial doubt over the Company’s ability to continue as a going concern. These consolidated financial statements do not include any adjustments related to the recoverability and classification of recorded asset amounts or the amounts and classification of liabilities that might result from the outcome of this uncertainty.

On March 19, 2024, the Company consummated the March 2024 Registered Direct Offering, in which we entered into a Securities Purchase Agreement with two institutional investors pursuant to which the Company

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SELLAS LIFE SCIENCES GROUP, INC.

NOTES TO CONSOLIDATED FINANCIAL STATEMENTS - Continued

agreed to issue and sell 11,000,000 shares of our common stock and 2,029,316 pre-funded warrants exercisable for shares of common stock. Each share of common stock was sold together at a purchase price of $1.535 and each pre-funded warrant was sold at a purchase price of $1.5349. The gross proceeds to the Company from the March 2024 Registered Direct Offering were approximately $20.0 million, before deducting the placement agent's fees and related offering expenses. In a concurrent private placement, the Company agreed to issue to the two institutional investors exercisable for up to an aggregate of 13,029,316 shares of common stock warrants at an exercise price of $1.41 per share. Subsequent to the closing of the March 2024 Registered Direct Offering, 1,014,658 pre-funded warrants were exercised for shares of common stock.

On January 8, 2024, the Company consummated the January 2024 Offering on a "reasonable best efforts" basis, issuing 10,130,000 shares of common stock and an aggregate of 1,870,000 pre-funded warrants exercisable for shares of common stock, together with accompanying warrants to purchase an aggregate of 12,000,000 shares of common stock. Each share of common stock and accompanying common warrant were sold together at a combined offering price of $0.75, and each pre-funded warrant and accompanying common warrant were sold together at a combined offering price of $0.7499. The aggregate gross proceeds to us from the January 2024 Offering were approximately $9.0 million, before deducting placement agents' fees and related offering expenses.

On November 2, 2023, the Company consummated a registered direct offering (the "November 2023 Registered Direct Offering"), pursuant to a Securities Purchase Agreement with a single institutional investor under which the Company agreed to issue and sell, 3,100,000 shares of its common stock and 552,300 pre-funded warrants exercisable for shares of common stock, together with accompanying warrants to purchase an aggregate of 3,652,300 shares of common stock. Each share of common stock and accompanying warrant were sold together at a combined purchase price of $1.0952 and each pre-funded warrant and accompanying warrant were sold together at a combined purchase price of $1.0951. The net proceeds to the Company from the November 2023 Registered Direct Offering were approximately $3.5 million, after deducting placement agents' fees and related offering expenses.

On February 28, 2023, the Company consummated an underwritten public offering (the "February 2023 Offering"), issuing 7,220,217 shares of common stock and accompanying common stock warrants to purchase an aggregate of 7,220,217 shares of common stock. The shares of common stock and accompanying common stock warrants were sold at a combined price of $2.77 per share and accompanying common stock warrant. Each common stock warrant sold with the shares of common stock represents the right to purchase one share of the Company’s common stock at an exercise price of $2.77 per share. The common stock warrants are exercisable immediately and will expire on February 28, 2028, five years from the date of issuance. The net proceeds to the Company from the February 2023 Offering were approximately $18.5 million, after deducting underwriting discounts and commissions and estimated offering expenses, and excluding the exercise of any warrants.

On April 16, 2021, the Company entered into a Controlled Equity OfferingSM Sales Agreement (the "Sales Agreement"), with Cantor Fitzgerald & Co. (the "Agent"). From time to time during the term of the Sales Agreement, the Company could offer and sell shares of common stock having an aggregate offering price up to a total of $50.0 million in gross proceeds. The Agent was entitled to collect a fee equal to 3% of the gross sales price of all shares of common stock sold. Shares of common stock sold under the Sales Agreement were offered and sold pursuant to the Company's registration statement on Form S-3, which was filed with the U.S. Securities and Exchange Commission ("SEC") on April 16, 2021 and declared effective on April 29, 2021. During the year ended December 31, 2023, the Company sold 92,882 shares of common stock pursuant to the Sales Agreement at an average price of $3.21 per share for aggregate net proceeds of approximately $0.3 million. On January 2, 2024, the Company mutually agreed with the Agent to terminate the Sales Agreement.

In December 2020, the Company, together with its wholly-owned subsidiary, SLSG Limited, LLC, entered into an Exclusive License Agreement (the “3D Medicines Agreement”) with 3D Medicines Inc. ("3D Medicines"), pursuant to which the Company granted 3D Medicines a sublicensable, royalty-bearing license, under certain intellectual property owned or controlled by the Company, to develop, manufacture and have manufactured, and commercialize GPS and heptavalent GPS product candidates for all therapeutic and other diagnostic uses in mainland China, Hong Kong, Macau and Taiwan ("3DMed Territory"). As of December 31, 2023, the Company has received an aggregate of $10.5 million in upfront payments and certain technology transfer and regulatory milestones. There is a total of $191.5 million in potential future development, regulatory, and sales milestones, not

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SELLAS LIFE SCIENCES GROUP, INC.

NOTES TO CONSOLIDATED FINANCIAL STATEMENTS - Continued

including future royalties, remains under the 3D Medicines Agreement, which milestones are all variable in nature and not under the Company's control.

The Company will require substantial additional financing to commercially develop any current or future product candidates. If the Company is unable to obtain additional funding on a timely basis, it will be required to scale back its plans and place certain activities on hold. The Company currently does not have any commitments to obtain additional funds. The Company's management continues to evaluate different strategies to obtain the required funding for future operations. These strategies may include public and private placements of equity and/or debt securities, as well as payments from potential strategic research and development collaborations or licensing and/or marketing arrangements with pharmaceutical companies. Additionally, the Company continues to pursue discussions with global and regional pharmaceutical companies for licensing and/or co-development rights to the Company's product candidates. There can be no assurance that these future funding efforts will be successful.

3. Basis of Presentation and Significant Accounting Policies

Basis of Presentation

The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States (“U.S. GAAP”). Any reference in these notes to applicable guidance is meant to refer to U.S. GAAP as found in the Accounting Standards Codification ("ASC") and Accounting Standards Updates (“ASU”) of the Financial Accounting Standards Board (“FASB”).

Principles of Consolidation

The consolidated financial statements include the financial statements of the Company and its wholly owned subsidiaries. All significant intercompany accounts and transactions have been eliminated upon consolidation. Unless the context otherwise indicates, reference in these notes to the "Company" refer to SELLAS Life Sciences Group, Inc., and its wholly owned subsidiaries, Private SELLAS, SLSG Limited, LLC, Sellas Life Sciences Limited, and Apthera, Inc. The functional currency of the Company's non-U.S. operations is the U.S. dollar.

Use of Estimates

The preparation of these consolidated financial statements in accordance with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting period.

On an ongoing basis, the Company evaluates its estimates using historical experience and other factors, including the current economic environment. Significant items subject to such estimates are assumptions used for purposes of determining stock-based compensation, carrying value of goodwill, and accounting for research and development activities. Management believes its estimates to be reasonable under the circumstances. Actual results could differ significantly from those estimates.

Segment Information

Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker, or decision-making group, in deciding how to allocate resources and in assessing performance. The Company views its operations and manages its business in one segment.

Fair Value of Financial Instruments

The Company measures certain financial assets and liabilities at fair value on a recurring basis. Fair value is an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be

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SELLAS LIFE SCIENCES GROUP, INC.

NOTES TO CONSOLIDATED FINANCIAL STATEMENTS - Continued

determined based on assumptions that market participants would use in pricing an asset or a liability. A three-tier fair value hierarchy is established as a basis for considering such assumptions and for inputs used in the valuation methodologies in measuring fair value:

Level 1—Quoted prices in active markets for identical assets or liabilities.

Level 2—Inputs other than quoted prices included within Level 1 that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities.

Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities.

As of December 31, 2023 and 2022, the carrying amounts of the Company’s financial instruments, including cash equivalents and accounts payable, approximate fair value due to the short-term nature of those instruments and were categorized as Level 1. As of December 31, 2022, the carrying amounts of the Company’s liability-classified warrants were recorded at their estimated fair value.The fair value of the warrants utilize certain unobservable inputs that fall within Level 3 of the fair value hierarchy. See Note 5 for additional information on the fair value of certain financial assets and liabilities.

Concentration of Credit Risk

Financial instruments that potentially expose the Company to concentrations of credit risk consist principally of cash on deposit with financial institutions, the balances of which frequently exceed federally insured limits.If any of the financial institutions with whom we do business were to be placed into receivership, we may be unable to access to the cash we have on deposit with such institutions.

Cash and Cash Equivalents

The Company considers any highly liquid investments, such as money market funds, with an original maturity of three months or less to be cash and cash equivalents.

Restricted Cash and Cash Equivalents

Restricted cash consists of certificates of deposit on hand with the Company’s financial institutions as collateral for its corporate credit cards.

The following table provides a reconciliation of the components of cash, cash equivalents, restricted cash, and restricted cash equivalents reported in the Company's consolidated balance sheets to the total amount presented in the consolidated statements of cash flows (in thousands):

December 31,

Restricted cash and cash equivalents 100 100

As of December 31, 2023 and 2022, the Company maintained $0.1 million on hand with the Company's financial institutions as collateral for its corporate credit cards.

Goodwill

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SELLAS LIFE SCIENCES GROUP, INC.

NOTES TO CONSOLIDATED FINANCIAL STATEMENTS - Continued

Goodwill is the excess of the cost of an acquired entity over the net amounts assigned to tangible and intangible assets acquired and liabilities assumed. Goodwill is not amortized but is subject to an annual impairment test. The Company has a single reporting unit and all goodwill relates to that reporting unit. The Company performs its annual goodwill impairment test on October 1 of each fiscal year, or more frequently if changes in circumstances or the occurrence of events suggest that an impairment exists.The Company continually evaluates financial performance, economic conditions and other relevant developments in assessing if an interim period impairment test is necessary.

The Company's goodwill balance at December 31, 2023 and 2022 was $1.9 million. The Company did not recognize any impairment of goodwill during the years ended December 31, 2023 and 2022. As of December 31, 2023 and 2022, there were no accumulated impairment losses related to goodwill.

Leases

The Company accounts for its leasing arrangements under ASU No. 2016-02, Leases (Topic 842) (“Topic 842”). Under Topic 842, all significant lease arrangements are generally recognized at lease commencement. Operating lease right-of-use ("ROU"), assets and lease liabilities are recognized at the commencement date. An ROU asset and corresponding lease liability is not recorded for leases with an initial term of 12 months or less (short term leases) and the Company recognizes lease expense for these leases as incurred over the lease term.

ROU assets represent the Company’s right to use an underlying asset during the reasonably certain lease terms and lease liabilities represent the Company’s obligation to make lease payments arising from the lease. The Company’s lease terms may include options to extend or terminate the lease when it is reasonably certain that the option will be exercised. Operating lease ROU assets and liabilities are recognized at commencement date based on the present value of lease payments over the lease term. The Company uses its incremental borrowing rate, based on the information available at commencement date, in determining the present value of lease payments. The operating lease ROU asset also includes any lease payments related to initial direct cost and prepayments, and excludes lease incentives. Lease expense is recognized on a straight-line basis over the lease term. The Company’s lease agreements contain lease and non-lease components, which are generally accounted for separately. See Note 7 for discussion of the Company’s facility leases.

Revenue Recognition

The Company records revenue in accordance with ASC Topic 606, Revenue From Contracts with Customers ("Topic 606"). This standard applies to all contracts with customers, except for contracts that are within the scope of other standards, such as leases, insurance, collaboration arrangements and financial instruments. Under Topic 606, an entity recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration that the entity expects to receive in exchange for those goods or services. To determine revenue recognition for arrangements that an entity determines are within the scope of Topic 606, the entity performs the following five-steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the entity satisfies a 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 Topic 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. The Company then allocates the transaction price to each distinct performance obligation based on its relative standalone selling price. The Company 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. See Note 10 for further discussion of the Company's revenue recognition associated with the 3D Medicines Agreement.

Development, Regulatory and Sales Milestones and Other Payments

At the inception of each arrangement that includes regulatory or development milestone payments, the Company evaluates whether the milestones are considered probable of being achieved and estimates the amount

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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. Milestone payments that are not within the control of the Company or the licensee, such as regulatory approvals, are not considered probable of being achieved until those approvals are received. The Company evaluates factors such as the scientific, clinical, regulatory, commercial, and other risks that must be overcome to achieve the particular milestone in making this assessment. There is considerable judgment involved in determining whether it is probable that a significant revenue reversal would not occur. At the end of each subsequent reporting period, the Company reevaluates the probability of achievement of all milestones subject to constraint and, if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect revenues and earnings in the period of adjustment.

For arrangements that include sales-based royalties, including milestone payments upon first commercial sales and milestone payments based on a level of sales, which are the result of a customer-vendor relationship and for which the license is deemed to be the predominant item to which the royalties relate, the Company recognizes 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. To date, the Company has not recognized any royalty revenue resulting from any of its licensing arrangements.

Acquired In-Process Research and Development

Costs incurred in obtaining technology licenses are immediately recognized as acquired in-process research and development expense, provided the technology licensed has no alternative future use as the technology and know-how acquired are not currently commercially viable. Payments related to contingent consideration such as development milestones, commercial milestones and royalties (Note 7) will be recognized when the contingency is probable and reasonably estimable in accordance with ASC 450, Contingencies.

Research and Development Expenses

Research and development costs are expensed as incurred. Research and development costs that are paid in advance of performance are capitalized as a prepaid expense and recognized as research and development expenses as the services are provided. Clinical study costs, a component of research and development expenses, are accrued over the service periods specified in the contracts and adjusted as necessary based on an ongoing review of the level of effort and costs actually incurred.

Research and development expenses consist primarily of development research performed by contract research organizations ("CROs"), personnel costs, including salaries, benefits and stock-based compensation, clinical drug supply, investigator grants, materials and supplies, consulting fees, licenses and fees, preclinical studies, and overhead allocations consisting of various support and facility-related costs.

Stock-based Compensation

The Company measures employee and non-employee director share-based awards at their grant-date fair value and records compensation expense on a straight-line basis over the vesting period of the awards.

Estimating the fair value of share-based awards requires the input of subjective assumptions, including the expected life of the options and stock price volatility. The Company accounts for forfeitures for stock option awards as they occur. The Company uses the Black-Scholes option pricing model to value its stock option awards. The assumptions used in estimating the fair value of share-based awards represent management’s estimate and involve inherent uncertainties and the application of management’s judgment. As a result, if factors change and management uses different assumptions, share-based compensation expense could be materially different for future awards.

The expected life of the stock options is estimated using the “simplified method,” as the Company has limited historical information from which to develop reasonable expectations about future exercise patterns and post-vesting employment termination behavior for its stock option grants. The simplified method is the midpoint between the vesting period and the contractual term of the option. The stock price volatility assumption is based on

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the historical volatility of the Company's publicly traded common stock. The risk-free rate is based on the U.S. Treasury yield curve commensurate with the expected life of the option.

Restricted Stock Units with Performance and Service Conditions

The Company's Board of Directors has granted restricted stock units ("RSUs") to employees that vest based on performance and service conditions. The fair values of the performance-based RSUs are measured on the date of grant and are based on the Company's closing stock price on such date. Compensation expense is recognized for the number of performance-based RSUs expected to be earned, provided the requisite service period has been rendered, after assessing the probability that certain performance criteria will be met. Cumulative adjustments are recorded each quarter to reflect the estimated outcome of the performance-related conditions until the date results are determined and settled. The Company accounts for forfeitures of performance-based RSUs when they occur. If performance criteria are not met or are not expected to be met, any compensation expense previously recognized to date associated with the performance-based RSUs will be reversed.

Restricted Stock Units with Service Conditions Only

The Board of Directors has granted RSUs to certain employees that vest based on continuous service. Time-vested RSUs awarded to employees vest one-fourth per year annually over four years, provided the employee remains employed with the Company. The fair values of the time-vested RSUs are measured on the date of grant and are based on the Company's closing stock price on such date. Compensation expense for time-vested RSUs with service conditions only are recognized straight-line over the applicable service period. The Company accounts for forfeitures of time-vested RSUs when they occur. Previously recognized compensation expense for forfeited RSUs are reversed in the period the time-vested RSUs are forfeited.

Income Taxes

The Company uses the asset and liability method of accounting for income taxes. Deferred tax assets and liabilities are recognized for the estimated future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases and operating loss and credit carryforwards. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. A valuation allowance is provided when it is more likely than not that some portion or all of a deferred tax asset will not be realized. The Company recognizes the benefit of an uncertain tax position that it has taken or expects to take on its income tax returns, if such a position is more likely than not to be sustained. Potential interest and penalties associated with unrecognized tax positions are recognized in income tax expense. No interest or penalties associated with unrecognized tax positions were recognized in either of the years ended December 31, 2023 or 2022.

The Company recognizes liabilities or assets for the deferred tax consequences of temporary differences between the tax basis of assets or liabilities and their reported amounts in the consolidated financial statements in accordance with FASB ASC 740-10, “Accounting for Income Taxes” (“ASC 740-10”). These temporary differences will result in taxable or deductible amounts in future years when the reported amounts of the assets or liabilities are recovered or settled. ASC 740-10requires that a valuation allowance be established when management determines that it is more likely than not that all or a portion of a deferred asset will not be realized. The Company evaluates the realizability of its net deferred income tax assets and valuation allowances as necessary, at least on an annual basis. During this evaluation, the Company reviews its forecasts of income in conjunction with other positive and negative evidence surrounding the realizability of its deferred income tax assets to determine if a valuation allowance is required. Adjustments to the valuation allowance will increase or decrease the Company’s income tax provision or benefit. The recognition and measurement of benefits related to the Company’s tax positions requires significant judgment, as uncertainties often exist with respect to new laws, new interpretations of existing laws, and rulings by taxing authorities. Differences between actual results and the Company’s assumptions or changes in the Company’s assumptions in future periods are recorded in the period they become known.

Net Loss Per Share

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Basic loss per share is computed by dividing net loss applicable to common stockholders by the weighted average number of shares of common stock outstanding during each period. Diluted loss per share includes the effect, if any, from the potential exercise or conversion of securities, such as warrants, stock options and unvested restricted stock that would result in the issuance of incremental shares of common stock. In computing the basic and diluted net loss per share, the weighted average number of shares remains the same for both calculations due to the fact that when a net loss exists, dilutive shares are not included in the calculation as the impact is anti-dilutive.

The following potentially dilutive securities outstanding have been excluded from the computation of diluted weighted average shares outstanding, as their impact would be anti-dilutive (in thousands):

December 31,

Recent Accounting Pronouncements Not Yet Adopted

In November 2023, the FASB issued ASU No. 2023-07, Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures, which provides updates to qualitative and quantitative reportable segment disclosure requirements, including enhanced disclosures about significant segment expenses and increased interim disclosure requirements, among others. ASU No. 2023-07 is effective for fiscal years beginning after December 15, 2023, and interim periods in fiscal years beginning after December 15, 2024. Early adoption is permitted, and the amendments should be applied retrospectively. The Company is currently evaluating the impact of the ASU on the consolidated financial statement disclosures but does not expect a material impact upon adoption.

In December 2023, the FASB issued ASU No. 2023-09, Improvements to Income Tax Disclosures, which amends the guidance in ASC 740, Income Taxes. The ASU is intended to improve the transparency of income tax disclosures by prescribing standard categories and greater disaggregation of information in the effective tax rate reconciliation, disclosure of income taxes paid disaggregated by jurisdiction, and modifies other income tax-related disclosures. ASU No. 2023-09 is effective for fiscal years beginning after December 15, 2024 and allows for adoption either prospectively or retrospectively. Early adoption is permitted. The Company is currently evaluating the impact of the ASU on the income tax disclosures within the consolidated financial statements but does not expect a material impact upon adoption.

4. Collaboration and In-License Agreements

As part of its business, the Company enters into in-licensing agreements with third parties that often require milestone and royalty payments based on the progress of the licensed asset through development and commercial stages. Milestone payments may be required, for example, upon approval of the product for marketing by a regulatory agency, and the Company may be required to make royalty payments based upon a percentage of net sales of the product. The expenditures required under these arrangements in any period may be material and are likely to fluctuate from period to period. These arrangements may permit the Company to unilaterally terminate development of the product and thereby avoid future contingent payments; however, the Company is unlikely to cease development if the compound successfully achieves clinical testing objectives.

Exclusive License Agreement with GenFleet Therapeutics (Shanghai) Inc.

On March 31, 2022, the Company entered into an exclusive license agreement with GenFleet pursuant to which GenFleet granted to the Company a sublicensable royalty-bearing license under certain of its intellectual property, to develop, manufacture, and commercialize SLS009 for the treatment, diagnosis or prevention of disease in humans and animals in the SLS009 Territory.

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In consideration for the exclusive license, the Company agreed to pay to GenFleet (i) an upfront and technology transfer fee of $10.0 million, all of which has been paid as of December 31, 2023, (ii) development and regulatory milestone payments for up to three indications totaling up to $48.0 million in the aggregate, and (iii) sales milestone payments totaling up to $92.0 million in the aggregate upon the achievement of certain net sales thresholds in a given calendar year. The Company also agreed to pay GenFleet single-digit tiered royalties based upon a percentage of annual net sales, with the royalty rate escalating based on the level of annual net sales of SLS009 in the SLS009 Territory ranging from the low to high single digits.

During the year ended December 31, 2022, the Company expensed $10.0 million related to the acquired technology as in-process research and development based on the assessment that the technology has no alternative future use as the technology and know-how acquired are not currently commercially viable. During the years ended December 31, 2023 and 2022, the Company made cash payments of $5.5 million and $4.5 million, respectively, pursuant to the exclusive license agreement.

Exclusive License Agreement with Memorial Sloan Kettering Cancer Center ("MSK")

On September 4, 2014, the Company entered into a license agreement (the “Original MSK License Agreement”) with MSK under which the Company was granted an exclusive license to develop and commercialize MSK’s WT1 peptide vaccine technology. The Original MSK License Agreement, unless terminated earlier in accordance with the terms of the Original MSK License Agreement, will continue on a country-by-country and licensed product-by-licensed product basis, until the later of: (i) expiration of the last valid claim embracing such licensed product; (ii) expiration of any market exclusivity period granted by law with respect to such licensed product; or (iii) ten (10) years from the first commercial sale in such country.

On May 25, 2017, the Company and MSK entered into an Amended and Restated Exclusive License Agreement (the “MSK A&R License Agreement”). Under the MSK A&R License Agreement, the Company expanded its license under the original MSK License Agreement, as amended, to include a license to commercially develop certain additional WT1 peptides through a program of exploiting certain patents and other rights covering such peptides. The MSK A&R License Agreement, among other changes, added certain milestone payments for each additional patent licensed product as defined in the MSK A&R License Agreement.

On October 11, 2017, the Company and MSK entered into a second Amended and Restated Exclusive License Agreement (the “Second MSK A&R License Agreement”). Under the Second MSK A&R License Agreement, the Company and MSK extended certain milestone dates for the Company in exchange for increased milestone payments.

The Company incurred $0.1 million of guaranteed minimum royalty payments under the Second MSK A&R License Agreement during the years ended December 31, 2023 and 2022. Such expenses have been included in research and development costs.

The Company incurred $0.1 million of sublicensing fees payable included in cost of licensing revenue under the Second MSK A&R License Agreement in connection with the 3D Medicines Agreement during the year ended December 31, 2022. There were no sublicensing fees incurred during the year ended December 31, 2023.

5. Fair Value Measurements

The following tables present information about the Company's assets and liabilities measured at fair value on a recurring basis in the consolidated balance sheets (in thousands):

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Assets:

Restricted cash equivalents 100 100 — —

Total assets measured and recorded at fair value $ 2,414 $ 2,414 $ — $ —

Liabilities:

Warrant liability $ — $ — $ — $ —

Total liabilities measured and recorded at fair value $ — $ — $ — $ —

Assets:

Restricted cash equivalents 100 100 — —

Total assets measured and recorded at fair value $ 16,709 $ 16,709 $ — $ —

Liabilities:

Warrant liability $ 4 $ — $ — $ 4

Total liabilities measured and recorded at fair value $ 4 $ — $ — $ 4

The Company did not transfer any financial instruments into or out of Level 3 classification during the years ended December 31, 2023 and 2022. See Note 9 for a reconciliation of the changes in the fair value of the warrant liability for the years ended December 31, 2023 and 2022.

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6. Balance Sheet Accounts

Prepaid expenses and other current assets consist of the following (in thousands):

December 31,

Clinical trial costs $ 399 $ 184

Professional fees 56 82

Prepaid expenses and other current assets $ 542 $ 531

Accrued expenses and other current liabilities consist of the following (in thousands):

December 31,

Compensation and related benefits 1,493 1,439

Accrued expenses and other current liabilities $ 7,650 $ 6,286

7. Legal Proceedings, Commitments and Contingencies

Legal Proceedings

From time to time, the Company is subject to various pending or threatened legal actions and proceedings, including those that arise in the ordinary course of its business, which may include employment matters, breach of contract disputes and stockholder litigation. Such actions and proceedings are subject to many uncertainties and to outcomes that are not predictable with assurance and that may not be known for extended periods of time. The Company records a liability in its consolidated financial statements for costs related to claims, including future legal costs, settlements and judgments, when the Company has assessed that a loss is probable and an amount can be reasonably estimated. If the reasonable estimate of a probable loss is a range, the Company records the most probable estimate of the loss or the minimum amount when no amount within the range is a better estimate than any other amount. The Company discloses a contingent liability even if the liability is not probable or the amount is not estimable, or both, if there is a reasonable possibility that a material loss may have been incurred.

On December 20, 2023, the Company commenced a binding arbitration proceeding against 3D Medicines, administered by the Hong Kong International Arbitration Centre and governed by New York State law in accordance with the dispute resolution provisions in the 3D Medicines Agreement. The arbitration proceeding involves, among other things, the trigger and payment of the relevant milestone payments due to the Company as well as 3D Medicines’ failure to use commercially reasonable best efforts to develop GPS in the 3DMed Territory, and particularly in mainland China. See Item 3. Legal Proceedings. Except for this arbitration proceeding, as of December 31, 2023, there was no other pending or threatened litigation.

Contingent Consideration related to Development, Regulatory and Commercial Milestone Payments

The Company acquires assets still in development and enters into research and development arrangements with third parties that often require milestone and royalty payments based on the progress of the asset through development stages. Milestone payments may be required, for example, upon approval of the product for marketing by a regulatory agency. In certain agreements, the Company is required to make royalty payments based upon a percentage of the sales.

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These arrangements may be material individually, and in the unlikely event that milestones for multiple products covered by these arrangements were reached in the same period, the aggregate charge to expense could be material to the results of operations. In addition, these arrangements often give the Company the discretion to unilaterally terminate development of the product, which would allow the Company to avoid making the contingent payments; however, the Company is unlikely to cease development if the compound successfully achieves clinical testing objectives. See Note 4 for additional information on the Company’s commitments under collaboration and license agreements.

Leases

The Company has a non-cancelable operating lease for certain executive, administrative, and general business office space for its headquarters in New York, New York, which commenced on June 5, 2020, was amended in February 2022 to add additional space, and had an initial lease term through December 30, 2024. The Company assessed the lease amendment for the additional space and determined it should be accounted for as a separate contract.

On December 11, 2023, the Company agreed to extend the expiration date for its office space through September 30, 2025. The Company assessed the amendment for the lease extension and determined it should be accounted for as a modification. Accordingly, on the effective modification date, the Company remeasured its operating lease liabilities and corresponding operating lease right-of-use assets at the present value of the remaining lease payments.

The weighted average discount rate used to account for the Company's operating lease under ASC 842, Leases, as of December 31, 2023 is approximately 13.0%. As of December 31, 2023, the leases have a remaining term of 1.75 years.

Rent expense related to the Company's operating lease was approximately $0.5 million for each of the years ended December 31, 2023 and 2022. The Company made cash payments related to operating leases of approximately $0.5 million during each of the years ended December 31, 2023 and 2022.

Future minimum rental payments under the Company's non-cancelable operating lease are as follows as of December 31, 2023 (in thousands):

Total minimum lease payments:

Total future minimum lease payments 1,010

Less: imputed interest (104)

Operating lease liabilities $ 906

8. Stockholders’ (Deficit) Equity

Preferred Stock

The Company has authorized up to 5,000,000 shares of preferred stock, $0.0001 par value per share, for issuance. There were no preferred shares outstanding as of December 31, 2023 and 2022.

Common Stock

The Company has authorized up to 350,000,000 shares of common stock, $0.0001 par value per share, for issuance.

Shares of common stock reserved for future issuance are as follows (in thousands):

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Warrants outstanding 15,854

Stock options outstanding 1,607

Restricted stock units outstanding 338

Shares reserved for future issuance under the Employee Stock Purchase Plans 183

Total shares of common stock reserved for future issuance 21,933

9. Warrants to Acquire Shares of Common Stock

The following is a summary of the Company's warrants to acquire shares of common stock activity for the year ended December 31, 2023 (in thousands, except per share data):

Warrants classified as equity:

Warrants classified as liability: 13 — — (13) — $ 7.5000

In connection with the closing of the January 2024 Offering at a combined offering price of $0.75, the Company agreed to (i) reduce the exercise price of an aggregate of 3,863,851 warrants that were issued to certain purchasers in an underwritten public offering that closed on April 5, 2022 (the "April 2022 Offering") to $0.75, (ii) reduce the exercise price of an aggregate of 3,652,300 warrants that were issued in the November 2023 Registered Direct Offering to $0.75, and (iii) extend the termination date of the April 2022 Offering warrants and the November 2023 Registered Direct Offering warrants to January 8, 2029. Concurrent with the closing of the January 2024 Offering, the exercise price of an aggregate of 7,220,217 warrants were also reduced to an exercise price of $0.75 per share.

Warrants to acquire shares of common stock primarily consist of equity-classified warrants. In addition, warrants to acquire shares of common stock that may require the Company to settle in cash are liability-classified warrants.

Warrants Classified as Equity

Equity-classified warrants consist of warrants to acquire common stock issued in connection with previous equity financings. During its evaluation of equity classification for warrants to acquire shares of common stock, the Company considered the conditions as prescribed within ASC 815-40, Derivatives and Hedging, Contracts in an

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Entity’s own Equity (“ASC 815-40”). The conditions within ASC 815-40 are not subject to a probability assessment. The warrants to acquire shares of common stock do not fall under the liability criteria within ASC 480, Distinguishing Liabilities from Equity, as they are not puttable and do not represent an instrument that has a redeemable underlying security. The warrants to acquire shares of common stock do meet the definition of a derivative instrument under ASC 815, but are eligible for the scope exception as they are indexed to the Company’s own stock and would be classified in permanent equity if freestanding.

On February 28, 2023, in connection with closing of the February 2023 Offering, the Company entered into amendments to an aggregate of 3,438,851 warrants, which had been previously issued by the Company in the April 2022 Offering, to reduce the exercise price of such warrants from $5.40 to $3.62, the average closing price of the Company’s common stock, as reported on the Nasdaq Capital Market, for the five trading days immediately preceding the pricing of the February 2023 Offering. The Company accounted for the amendment as a cost to issue equity with the incremental fair value of approximately $0.3 million recognized as an offset to the proceeds received. However, there was no net impact to the consolidated statements of stockholders' (deficit) equity because the warrants are equity classified.

On November 2, 2023, in connection with the closing of the November 2023 Registered Direct Offering, the Company entered into an amendment to reduce the exercise price of warrants to purchase up to 887,000 shares of the Company’s common stock which were issued in the April 2022 Offering and held by the purchaser in the November 2023 Registered Direct Offering to $0.9702, and amended the termination date of such warrants to November 2, 2028. Concurrent with the closing of the November 2023 Registered Direct Offering, an aggregate of 7,220,217 warrants issued in the February 2023 Offering were reduced to $0.9702 per share. The Company accounted for the change in exercise price as a cost to issue equity with the incremental fair value of approximately $0.4 million recognized as an offset to the proceeds received. However, there was no net impact to the consolidated statements of stockholders' (deficit) equity because the warrants are equity classified.

Warrants Classified as Liabilities

The liability-classified warrants consist of warrants to acquire common stock issued in connection with previous equity financings. These warrants may be settled in cash and were determined to not be indexed to the Company’s common stock. The Company's outstanding liability-classified warrants expired during the year ended December 31, 2023.

The estimated fair value of outstanding warrants accounted for as liabilities was determined at each balance sheet date through expiration. Any decrease or increase in the estimated fair value of the warrant liability as of each balance sheet date was recorded in the consolidated statement of operations as a change in fair value of warrant liability. The fair value of the warrants accounted for as liabilities is estimated using a Black-Scholes pricing model with the following inputs:

As of December 31,

Risk free interest rate n/a 4.75 %

Expected term (years) n/a 0.75

Expected dividend yield n/a — %

Strike price n/a $ 7.50

The changes in fair value of the warrant liability for the year ended December 31, 2023 and 2022 were as follows (in thousands):

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Warrant Liability

Warrant liability, January 1, 2022 $ 40

Change in fair value of warrants (36)

Warrant liability, December 31, 2022 4

Change in fair value of warrants (4)

Warrant liability, December 31, 2023 $ —

10. License Revenue with 3D Medicines, Inc.

Exclusive License Agreement with 3D Medicines, Inc.

In December 2020, the Company entered into the 3D Medicines Agreement pursuant to which the Company granted 3D Medicines a sublicensable royalty-bearing license under certain intellectual property owned or controlled by the Company, to develop, manufacture and have manufactured, and commercialize GPS and heptavalent GPS (referred to as GPS Plus) product candidates ("GPS Licensed Products") for all therapeutic and other diagnostic uses in the 3DMed Territory. In partial consideration for the rights granted by the Company, 3D Medicines agreed to pay the Company (i) a one-time upfront cash payment of $7.5 million, and (ii) milestone payments totaling up to $194.5 million in the aggregate upon the achievement of certain technology transfer, development and regulatory milestones, as well as sales milestones based on certain net sales thresholds of GPS Licensed Products in the 3DMed Territory in a given calendar year. 3D Medicines also agreed to pay tiered royalties based upon a percentage of annual net sales of GPS Licensed Products in the 3DMed Territory ranging from the high single digits to the low double digits.

Revenue Recognition

At inception, the Company evaluated the 3D Medicines Agreement under ASC 606 and recognized an initial transaction price of $9.5 million, which included the $7.5 million upfront fee as well as $2.0 million in development milestones that were assessed to be probable of being achieved, while the remaining milestones were variable consideration subject to constraint at inception. In the first quarter of 2022, an additional $1.0 million in licensing revenue was recognized upon approval by China’s National Medical Products Administration (“NMPA”) for a small Phase 1 clinical trial investigating safety of GPS in China.

There is $191.5 million in potential future development, regulatory, and sales milestones, not including future royalties, remaining under the 3D Medicines Agreement as of December 31, 2023, which milestones are variable in nature and not under the Company's control. At the end of each reporting period, the Company reevaluates the probability of achievement of the future development, regulatory, and sales milestones subject to constraint and, if necessary, will adjust its estimate of the overall transaction price. Any such adjustments will be recorded on a cumulative catch-up basis, which would affect revenues and earnings in the period of adjustment.

For the sales-based royalties, the Company will recognize revenue when the related sales occur. To date, the Company has not recognized any royalty revenue resulting from any of its licensing arrangements.

There was no licensing revenue recognized during the year ended December 31, 2023. Licensing revenue of $1.0 million recognized during the year ended December 31, 2022 related to the IND approval by the NMPA.

There was no cost of licensing revenue recognized during the year ended December 31, 2023. Cost of licensing revenue of $0.1 million was recognized during the year ended December 31, 2022 for sublicensing fees incurred under the Second MSK A&R License Agreement in connection with the 3D Medicines Agreement.

11. Stock-Based Compensation

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2017 Equity Incentive Plan

On December 29, 2017, the 2017 Equity Incentive Plan was approved by the stockholders of the Company, and currently allows for issuance of up to approximately 22,000 shares of common stock underlying stock options granted prior to September 10, 2019. The 2017 Equity Incentive Plan was terminated upon the approval of the 2019 Incentive Plan subject to outstanding stock options granted under the 2017 Equity Incentive Plan that remain exercisable through maturity for the Company's employees and directors.

2023 Amended and Restated Equity Incentive Plan

On September 10, 2019, the 2019 Equity Incentive Plan ("2019 Equity Plan") was approved by the stockholders of the Company, which currently allows for issuance of up to approximately 6,036,000 shares of common stock in connection with the grant of stock-based awards, including stock options, restricted stock, restricted stock units, stock appreciation rights and other types of awards as deemed appropriate.

The number of shares reserved for issuance under the 2019 Equity Plan automatically increased on January 1 of each year, for a period of four years, which commenced on January 1, 2020 and ended on (and including) January 1, 2023, by an amount equal to the lesser of (i) 5% of the total number of shares of common stock outstanding at the end of the prior fiscal year; and (ii) an amount determined by the Board of Directors or authorized committee.

On June 20, 2023, an amendment to the 2019 Equity Plan was approved by the stockholders of the Company, which amended and restated the 2019 Equity Plan (as amended and restated, the "2023 Amended and Restated Equity Incentive Plan") to increase the number of shares of common stock authorized for issuance under the 2019 Equity Plan by 3,000,000 shares.

As of December 31, 2023, approximately 3,951,000 shares of common stock were reserved for future grants under the 2019 Equity Incentive Plan.

The following table summarizes the components of stock-based compensation expense in the consolidated statements of operations for the years ended December 31, 2023 and 2022, respectively (in thousands):

Years Ended December 31,

Research and development $ 352 $ 270

Total stock-based compensation $ 2,094 $ 1,726

Options to Purchase Shares of Common Stock

The Company uses the Black-Scholes option-pricing model to estimate the fair value of stock-based awards and the following assumptions were used for stock options granted during the years ended December 31, 2023 and 2022, respectively:

Years Ended December 31,

Risk free interest rate 3.78 % 1.96 %

Expected lives (years) 6.20 6.18

Expected dividend yield — % — %

The weighted-average grant date fair value of options granted during the years ended December 31, 2023 and 2022 was $2.88 and $4.52, respectively.

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The Company’s expected common stock price volatility assumption is based upon the Company's own implied volatility in combination with the implied volatility of a basket of comparable companies. The expected life assumptions for employee grants were based upon the simplified method, which averages the contractual term of the Company’s options of 10 years with the average vesting term of four years for an average of six years. The expected life assumptions for non-employees were based upon the contractual term of the option. The dividend yield assumption is zero because the Company has never paid cash dividends and presently has no intention to do so. The risk-free interest rate used for each grant was also based upon prevailing short-term interest rates. The Company accounts for forfeitures as they occur, therefore, outstanding stock options equal vested and expected to vest stock options.

As of December 31, 2023, there was $2.9 million of unrecognized compensation cost related to outstanding stock options that is expected to be recognized as a component of the Company’s operating expenses over a weighted-average period of 2.34 years.

The following table summarizes stock option activity of the Company for the years ended December 31, 2023 and 2022, respectively:

The aggregate intrinsic values of outstanding and exercisable stock options at December 31, 2023 were calculated based on the closing price of the Company’s common stock as reported on the Nasdaq Capital Market on December 29, 2023 of $1.06 per share. The aggregate intrinsic value equals the positive difference between the closing fair market value of the Company’s common stock and the exercise price of the underlying stock options.

Time-Vested RSUs and RSUs with Performance Conditions

The Company granted RSUs pursuant to the Company's 2023 Amended and Restated Equity Incentive Plan that will settle in shares of common stock. As of December 31, 2023, there was $1.0 million of unrecognized compensation cost related to outstanding RSUs that is expected to be recognized as a component of the Company’s operating expenses over a weighted-average period of 2.09 years.

The following table summarizes RSU activity of the Company for the years ended December 31, 2023 and 2022, respectively:

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2021 Employee Stock Purchase Plan

On April 22, 2021, the Board of Directors adopted the 2021 Employee Stock Purchase Plan ("2021 ESPP") which was approved by the Company's stockholders on June 8, 2021. The 2021 ESPP allows employees to contribute up to 20% of their cash earnings, subject to a maximum of $25,000 per year under Internal Revenue Service rules, to be used to purchase shares of the Company's common stock on semi-annual purchase dates. The 2021 ESPP allows eligible employees to purchase shares of common stock at a price per share equal to 85% of the lower of the fair market value of the common stock at the beginning or end of each six-month offering period during the term of the 2021 ESPP.

During the years ended December 31, 2023 and 2022, 91,454 and 25,089 shares of common stock, respectively, were purchased by employees under the 2021 ESPP for proceeds of approximately $0.1 million. There are approximately 183,000 shares of common stock reserved for issuance under the 2021 ESPP as of December 31, 2023.

12. Income Taxes

The Company's loss before income taxes is as follows (in thousands):

As of December 31,

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The components of net deferred tax assets are as follows (in thousands):

As of December 31,

Stock-based compensation 613 229

Capitalized Section 174 research and development 1,755 765

Net deferred tax assets $ 184 $ 184

The components of gross deferred tax liabilities are as follows (in thousands):

As of December 31,

Right of use asset $ (184) $ (184)

Gross deferred tax liability $ (184) $ (184)

The net deferred tax liabilities are as follows (in thousands):

As of December 31,

Net deferred tax asset $ 184 $ 184

Gross deferred tax liability (184) (184)

Net deferred tax liability $ — $ —

The provision for income taxes differs from the provision computed by applying the federal statutory rate to net loss before income taxes as follows:

As of December 31,

U.S. federal statutory income tax rate (21.0) % (21.0) %

State and local taxes, net of federal benefit (0.4) % (0.1) %

Foreign rate differential 15.3 % 11.9 %

Valuation allowance 6.5 % 8.7 %

Permanent differences 0.4 % 0.2 %