ATRA 10-K & 10-Q changes, risk factors and insider trading

In January 2025, we announced that our board of directorsdirectors, hasworking with the company's financial and legal advisors, initiated a process to explore a range of strategic alternatives designed to maximize value for our stockholders. We previously engaged a well-known financial advisor to support the assessment of opportunities to advance and realize value from our CAR-T assets, for which we announced that we have since paused the CAR T programs and discontinued development operations in March 2025. The advisor’s scope was expanded to include a wider range of additional strategic alternatives,stockholders, which may include, but are not limited to, an acquisition, merger, reverse merger, other business combinations, sale of assets, licensing, or other strategic transactions. WeOur areboard activelyof indirectors discussionscontinues withto severalevaluate potential parties.strategic alternatives.

We have not set a definitive timetable for completion of this process, and there can be no assurance regarding the results or outcome of this process. It is possible that we may not pursue a strategic alternative as a result of this process, that a strategic alternative that has been pursued may not be attractive, or that a strategic alternative may not ultimately be consummated. As part of the process, our board of directors will consider a full range of strategic alternatives, including, but not limited to, those identified in range of strategic alternativealternatives described above.

We expect to devotecontinue devoting significant time and resources and to incur expenses in identifying and evaluating strategic alternatives for the company, which could have a material adverse effect on our business. A considerable portion of these expenses maywill be incurred regardless of whether a transaction is completed. Any such expenses will decrease the remaining cash available for use in our business. In addition, potential strategic transactions that require stockholder approval may not be approved by our stockholders or, if required, a counterparty’s stockholders. Further, any strategic transaction that is completed ultimately may not deliver the benefits we expect or enhance stockholder value.

There can be no assurance that the process to identify strategic alternatives for our business will result in a successfully consummated transaction. If we are unable to identify a viable strategic alternative or if such a transaction is not completed in a timely manner, or if we are unable to raise sufficientadditional capital sufficient to fund our operations, our board of directors may determine to pursue a liquidation and dissolution or other wind down of our business. In such an event, the amount of cash available for distribution to our stockholders, if any, will depend heavily on the timing of such decision and, ultimately, such liquidation, since the amount of cash available for distribution continues to decrease as we fund our operations while we evaluate our strategic options.

We have incurred substantial losses since our inception and anticipate that we will continue to incur substantial losses for the foreseeable future.

Investment in biopharmaceutical product development is highly speculative because it entails substantial upfront capital expenditures and significant risk that product candidates will fail to prove effective, gain regulatory approval or become commercially viable. We have one product, Ebvallo, which is approved in the EEA, the UK and Switzerland and have generated limited revenues from commercialization, and have incurred significant research, development and other expenses related to our ongoing operations and expect to continue to incur such expenses. As a result, we have incurred significant operating losses in every annual reporting period since our inception.inception, with the exception of the twelve months ending December 31, 2025. For the fiscal year ended December 31, 2024,2025, we reported a net lossincome of $85.4$32.7 million.million due to commercialization revenue combined with significant reductions in operating expenses.

We do not know when, or if, we will generate sufficient revenue from commercialization to offset our operating expenses. We expect to continue to incur significant expenses and operating losses for the foreseeable future as we continue to research, develop and seek regulatory approvals for our product candidatescandidate and any additional product candidates we may acquire, in-license or develop. We may encounter unforeseen expenses, difficulties, complications, delays and other unknown factors that may adversely affect our business. The size of our future net losses will depend, in part, on the rate of change of our expenses and our ability to generate revenues. If any of our product candidates fails in clinical studies or does not gain regulatory approval, or if approved, fails to achieve market acceptance, we may never become profitable. Even if we achieve profitability in the future, we may not be able to sustain profitability in subsequent periods. Our expenses may increase in the future as we continue to invest in research and development of our existing product candidates, investigate and potentially acquire new product candidates.

In addition, as a young business, weWe may encounter unforeseen expenses, difficulties, complications, delays and other known and unknown factors. We expect our financial condition and operating results to continue to fluctuate significantly from quarter to quarter and year to year due to a variety of factors, many of which are beyond our control. Accordingly, any of our quarterly or annual periods’ results are not indicative of future operating performance.

We have earned limited commercialization revenues to date. We may never achieve profitability.profitability or we may be unable to sustain profitability on a continuing basis.

To date, we have generated only limited revenues from commercialization. We have obtained regulatory approval for one product, Ebvallo, in the EEA, Switzerland and the UK. We have out-licensed the commercialization rights to tab-cel (Ebvallo in the EEA, Switzerland and the UK) to Pierre Fabre under the A&R Commercialization Agreement and we have sold certain royalty and milestone interests for the Initial Territory, subject to a specified cap, to HCRx pursuant to the HCRx Agreement. Our ability to generate revenues from commercialization and achieve profitability will be subject to the A&R Commercialization Agreement, the HCRx Agreement and depend on our commercialization partners’ ability to successfully commercialize products, including any of our current product and product candidates, and other product candidates that we may develop, in-license or acquire in the future. Our ability to generate revenues from the sale of products and achieve profitability will also depend on a number of additional factors, including our abilityability, or our commercialization partner's ability, to:

develop manufacturing and distribution processes for ourtab- novel T-cell immunotherapy product candidatescel;

develop commercial quantities of our products,tab-cel, including at acceptable cost levels;

establish and maintain adequate supply of our products,tab-cel, including cell lines with sufficient breadth to treat patients;

qualify our CMOs’ manufacturing facilities such that wePierre Fabre can maintain the supply of our products by ensuring adequate manufacturing of bulk drug substances and drug products in a manner that is compliant with global legal and regulatory requirements;

Our revenues from Ebvallo or any product candidate for which regulatory approval is obtained will be dependent, in part, upon the size of the markets in the territories for which we gain regulatory approval, the accepted price for the product, the ability to get reimbursement at any price, and the terms and conditions of our commercialization agreement with ourPierre partnerFabre for that territory. We do not retain any meaningful milestones or royalty payments from Pierre Fabre for Ebvallo in the Initial Territory until the applicable royalty cap under the HCRx Agreement is met, which could take many years, if at all. If the number of our addressable disease patients is not as significant as we estimate, the indication approved by regulatory authorities is narrower than we expect, or the reasonably accepted population for treatment is narrowed by competition, physician choice, treatment guidelines or a reduction in the incidence of the addressable disease, ourPierre partnersFabre may not successfully commercialize our products,tab-cel, even if approved. The timing and amount of any milestone and royalty payments we may receive from ourPierre partners,Fabre, as well as the commercial success of our productstab-cel will depend on, among other things, the efforts, allocation of resources, negotiation of pricing and reimbursement and successful commercialization of our products by ourPierre partners.Fabre. As a result, even if we generate product revenues, we may not become profitable and may need to obtain additional funding to continue operations. If we fail to become profitable or are unable to sustain profitability on a continuing basis, then we may be unable to continue our operations at planned levels and may be forced to reduce our operations.

We expect to expend substantial resources for the foreseeable future to continue the clinical development and manufacturing of our T-cell immunotherapy product candidates. We also expect to continue to expend resources for the development and manufacturing of our product and product candidates and the technology we have licensed or have an exclusive right to license from our partners. These expenditures will include costs associated with research and development, potentially acquiring or licensing new product candidates or technologies, conducting preclinical and clinical studies and potentially obtaining regulatory approvals and manufacturing products.operations. Under the terms of our license agreements with each of our in-license partners, we are obligated to make payments upon the achievement of certain development, regulatory and commercial milestones. In addition, other unanticipated costs may arise. Because the design and outcome of our ongoing, planned and anticipated clinical studies is highly uncertain, we cannot reasonably estimate the actual amounts necessary to successfully complete the development and commercialization of our product and product candidates.

the scope, progress, results and costs of researching and developing our product candidates,tab-cel, and conducting preclinical and clinical studies;

the timing of, and the costs involved in, obtaining regulatory approvals for our product candidates, if clinical studies are successful,tab-cel, including any costs from post-market requirements;

the timing, receipt and amount of sales of, or royalties on,on our product and future products, if anytab-cel; and the emergence of competing technologies or other adverse market developments.

As of December 31, 2024,2025, we had total cash,cash and cash equivalents and short-term investments of $42.5$8.5 million. Our existing cash, cash equivalents and short-term investments as of December 31, 20242025 will not be sufficient to fund our planned operations for at least the next twelve months from the date of issuance of these financial statements. These conditions raise substantial doubt about our ability to continue as a going concern for at least 12 months after the issuance of the accompanying consolidated financial statements.

To alleviate the conditions that raise substantial doubt about our ability to continue as a going concern, we plan to secure additional capital, potentially through a combination of public or private security offerings; use of our ATM facility; issuance of debt; and/or execution of strategic transactions. We may also need to raise additional funding as required based on the status of our development programsprogram and our projected cash flows. Although we have been successful in raising capital in the past, and expect to continue to raise capital as required, there is no assurance that we will be successful in obtaining sufficient funding on terms acceptable to us to fund continuing operations, if at all, or identify and enter into any strategic transactions that will provide the capital that we will require. In addition, as of the date of this Form 10-K, our public float was less than $75 million. As a result, we are subject to the limitations of General Instruction I.B.6 to Form S-3 until such time as our public float exceeds $75 million, which means we only have the capacity to sell shares up to one-third of our public float under shelf registration statements in any twelve-month period. We will remain constrained by the limitations of General Instruction I.B.6 to Form S-3 until such time as our public float exceeds $75 million, at which time the number of securities we may sell under a Form S-3 registration statement will no longer be limited by limitations of General Instruction I.B.6 to Form S-3. If we are unable to obtain sufficient funding on acceptable terms, we could be forced to delay, limit, reduce or terminate clinical studies or other developmentongoing activities for one or more of our product candidates,candidate, as well as our exploration of strategic alternatives, which could have a material adverse effect on our business, results of operations, and financial condition.

We have one approved product, Ebvallo, which is currently approved in the European Economic Area (EEA), the UK and Switzerland. In March 2025, we announced our decision to pause the development of our allogeneic CAR T programs and discontinue all CAR T development operations. All of our other product candidates are still in preclinical development. If we or our collaborators are unable to successfully develop, manufacture and commercialize our product or product candidatestab-cel or experience significant delays in doing so, our business may be materially harmed.

We have one approved product, Ebvallo, which is currently approved in the EEA, the UK and Switzerland. We have invested substantial resources in identifying and developing potential product candidates, conducting preclinical and clinical studies, manufacturing activities, and preparing for the commercial launch of our product and product candidates. Our ability to generate revenues from the sale of our product and product candidates,tab-cel, if approved, will depend heavily on the successful development and manufacture, and our partners' eventual commercialization of our product and product candidates.tab-cel.

The success of our product and product candidatestab-cel depends on many factors, including the following:

Our future success is dependent on the marketing authorization of our product candidates.tab-cel.

We only have one product, Ebvallo, that has gained marketing authorization, with approval currently in the EEA, the UK, and Switzerland. Our prioritized clinical-stage product candidates include tab-celTab-cel (tabelecleucel) is currently in Phase 3 development in the U.S. Our business is substantially dependent on our partner's ability to obtain regulatory approval for, and, if approved, to find a partner who can successfully commercialize our product candidatestab-cel in a timely manner.

Neither we nor our partnerspartner can commercialize product candidatestab-cel in the U.S. without first obtaining marketing authorization for the product candidatestab-cel from the FDA; similarly, neither we nor our partners can commercialize product candidatestab-cel outside of the U.S. without obtaining marketing authorization from comparable foreign regulatory authorities. Before obtaining regulatory approvals for the commercial sale of any product candidatetab-cel for a target indication, we must demonstrate with substantial evidence gathered in preclinical and clinical studies that the product candidatetab-cel is safe and effective for use for that target indication and that the manufacturing facilities, processes and controls are adequate with respect to such product candidate to assure stability, safety, purity,purity and potency.

The time required to obtain approval by the FDA and comparable foreign regulatory authorities is unpredictable but typically takes many years following the commencement of preclinical and clinical studies and depends upon numerous factors, including the substantial discretion of the regulatory authorities. The novel nature of our product candidatestab-cel may create further challenges in obtaining regulatory approval. For example, the FDA and comparable foreign regulatory authorities have limited experience with regulating the development and commercialization of T-cell immunotherapies, particularly allogeneic T-cell product candidates, and CAR T therapies, including assessing the comparability of different versions of such product candidates. In addition, approval policies, regulations, regulatory positions or the type and amount of clinical and other data necessary to gain approval may change during the course of a product candidate’s clinical development and throughout regulatory interactions, and may vary among jurisdictions, particularly for novel therapies. The EC has approved the MAA for Ebvallo as a monotherapy treatment for patients with EBV+ PTLD who have received at least one prior therapy under “exceptional circumstances,” which is a pathway under which marketing authorization is granted when “comprehensive data cannot be obtained even after authorization.” The MHRA and Swissmedic approved the marketing application for Ebvallo leveraging the EMA assessment. Under the exceptional circumstances marketing authorization, our commercial partner, Pierre Fabre, is subject to ongoing post-marketing obligations to continue confirmation of the benefits of Ebvallo, and if any of our other product candidates are approved under this pathway, we or our future commercial partners will be subject to this obligation.Ebvallo. Continuation of the Ebvallo marketing authorization is subject to annual re-assessment. The annual re-assessment will determine whether the Ebvallo marketing authorization should be maintained, changed, or suspended, based on Pierre Fabre’s fulfillment of post-marketing obligations and the risk/benefit profile of Ebvallo. If we, or ourPIerre commercial partners,Fabre, do not satisfy the ongoing post-marketing obligations or the risk/benefit profile of Ebvallo is determined not to be acceptable based on new clinical or post-marketing data, the EC, MHRA, or Swissmedic may change or suspend the marketing approval for Ebvallo. We have not obtained regulatory approval for any other product candidate, and itIt is possible Ebvallo (tabelecleucel) may not be approved in any other country other than those in which approval has been obtained and also possible that none of our other product candidates or any future product candidates will ever obtain regulatory approval.obtained.

Our product candidatesTab-cel could fail to receive regulatory approval from the FDA or a comparable foreign regulatory authority for many reasons, including:

failure to demonstrate the stability, safety, purity and potency of the product candidatetab-cel;

the insufficiency of data collected from clinical studies of our product candidatestab-cel to support the submission and filing of a BLA or other submission or to obtain regulatory approval;

inability to reach agreement with the FDA or comparable foreign regulatory authorities on the methodologies for, and assessment of, comparability of different versions of product candidatestab-cel used in non-pivotal studies, pivotal studies and for intended commercial use;

failure to obtain approval of our manufacturing processes or facilities of third party manufacturers with whom we contract for clinical and commercial supplies or our own manufacturing facility; or changes or inconsistencies in the requested or required methodologies, statistical analyses, specification criteria or regulatory submission requirements for a product candidate,tab-cel, including changes to, or inconsistencies with, applicable industry practice or precedent; or changes in the approval policies or regulations that render our preclinical and clinical data insufficient for approval or in positions, guidance or feedback communicated by the FDA or comparable foreign regulatory authorities that have a negative impact on the potential approval of a product candidate.tab-cel.

The FDA or a comparable foreign regulatory authority may require information beyond what we plan to provide in or expect to be required for a marketing application, including additional CMC information, preclinical or clinical data to support approval. These requirements may delay or prevent approval and our commercialization plans, or we may decide to abandon the development program. For example, at a Type B meeting in February 2022, we were not able to align with the FDA on comparability between tab-cel product versions used in the pivotal ALLELE study and the intended commercial product. The FDA initially recommended we conduct a new clinical trial with the commercial product to address the lack of alignment on comparability and to gain additional clinical experience with the intended commercial product. Throughout 2023, we held a number of meetings with the FDA on clinical and CMC aspects for a potential BLA submission for tab-cel. Ultimately, we reached agreement with the FDA on the comparability of tab-cel product manufactured using a different process version with the intended commercial product and subsequently held a pre-BLA meeting with the FDA that supported our plan to submit the tab-cel BLA in the second quarter of 2024. The BLA was submitted in May 2024, and the FDA accepted the BLA submission in July 2024 and granted priority review with a Prescription Drug User Fee Act target action date of January 15, 2025. Although the FDA designated tabelecleucel as a breakthrough therapy, a breakthrough designation (BTD) status is not considered in the FDA's decision to approve or not approve a product candidate. Designation as a breakthrough therapy is at the discretion of the FDA, and receipt of a BTD designation may not result in a faster development process, review or approval compared to drugs considered for approval under non-expedited FDA review procedures and does not assure ultimate approval by the FDA. In addition, the FDA may later decide that the product no longer meets the conditions for qualification and rescind the BTD designation or decide that the time period for FDA review or approval will not be shortened. Furthermore, our CMOs for tab-cel will undergo pre-approval inspection in connection with our tab-cel BLA, and we cannot be certain that we will be able to adequately support them through such inspection nor that they will successfully pass any such inspection. For example, we received thea second Complete Response Letter from the FDA in January 20252026 relating(Second solelyComplete Response Letter) claiming that the ALLELE trial, previously confirmed by the FDA as adequate to observationssupport duringthe pre-approvalBLA inspectionfiling, is no longer considered to be an adequate and well-controlled study due to deficiencies in study design, conduct and analysis, to provide substantial evidence of aeffectiveness third-party manufacturing facility in connection with ourof tab-cel BLA.to treat relapsed or refractory EBV+ PTLD. In addition, in January 2025, the FDA placed a clinical hold on Atara’s active Investigational New Drug (IND) applications. These INDs include the tab-cel program as monotherapy treatment for adult and pediatric patients two years of age and older with Epstein-Barr virus positive post-transplant lymphoproliferative disease (EBV+ PTLD) and ATA3219 for the treatment of non-Hodgkin’s lymphoma and systemic lupus erythematosus. SomeThe clinical siteshold thatis participateddirectly linked to inadequately addressed GMP compliance issues identified during the pre-approval inspection of a third party manufacturing facility referenced in tabelecleucelthe studiesResponse willLetter. alsoIn undergoJanuary inspection,2025, we notified investigators of the clinical holds for the tab-cel program. In February 2025, the third-party manufacturing facility referenced in the Response Letter was inspected and received an FDA Form 483. We worked with our partner, Pierre Fabre, to support this third-party manufacturer in addressing the compliance issues and in May 2025, the FDA confirmed the clinical hold issues were satisfactorily addressed and the FDA may also choose to inspect us aslifted the sponsorclinical ofholds thesefor studies.tab-cel Theand ATA3219 programs. In January 2026, the FDA ultimatelyconfirmed mayit notcompleted approvea thefollow-up BLA for anyinspection of the reasonsthird namedparty abovemanufacturing orfacility otherand reasons. Ifdetermined the FDAinspectional doesissues notat approvesuch facility have been adequately addressed and the BLA,deficiency this could result in a considerable delay to a subsequent BLA submission or could lead us not to pursue a BLA submission at all. For example, the FDA may not approve the BLA based on the data provided, including a concern that the current clinical dataset is insufficient. In this case, the conduct of an additional clinical trial or trialscomment in the leadResponse indicationLetter orhas completingbeen thesatisfactorily ongoing ALLELE study may be necessary to support a BLA approval for tab-cel. Conducting an additional clinical trial, if required, may prove too difficult or too expensive, and the process of designing a new clinical trial, enrolling enough patients, and completing treatment and data collection under the protocol could take a significant amount of time, effort, and resources. Even if we complete the clinical trial, the study may not meet its prespecified endpoints, and even if it does, the FDA may still disagree that the clinical trial is sufficient to support submission and approval of a BLA for tab-cel, or may consider that the data, while adequate for BLA approval, can support only a more limited indication than that for which we initially applied.resolved.

Our development activities and/or commercialization planning with our partners could be harmed or delayed by governmental or regulatory delays due to a variety of factors. These factors include limitations on the availability of governmental and regulatory agency personnel to review regulatory filings or engage with us (caused by global health concerns or otherwise); changes to governmental regulatory requirements, policies, guidelines or priorities, reallocation, or availability of government resources; or for other reasons, that may significantly delay the FDA’s, or other regulatory agencies', ability to review and process any submissions we have filed or may file or cause other regulatory delays. If global health or other concerns prevent the FDA or other regulatory authorities from conducting their regular inspections, or impact reviews or other regulatory activities, it could significantly impact the ability of the FDA or other regulatory authorities to review and process our regulatory submissions in a timely fashion, which could have a material adverse effect on our business.

If we do obtain approval for a product candidate marketing application, regulatory authorities may approve any of our product candidates for fewer or more limited indications than we request (including failing to approve the most commercially promising indications), may grant approval contingent on the performance of costly post-marketing clinical studies, or may approve a product candidate with a label that does not include the labeling claims necessary or desirable for the successful commercialization of that product candidate. In addition, the clinical study requirements of the FDA, EMA, MHRA, Swissmedic,Swissmedic and other regulatory agencies and the criteria these regulators use to determine the safety and efficacy of a product candidate are determined according to the type, complexity, novelty and intended use and market of the potential products. The regulatory approval process for novel product candidates, can be more complex and consequently more expensive and take longer than for other, better known or extensively studied pharmaceutical or other product candidates. Approvals by the EC and FDA of autologous CAR T therapies, such as Novartis’ Kymriah® and Gilead’s Yescarta®, may not be indicative of what these regulators may require for approval of our therapies. If an adverse safety issue or other adverse finding occurs in one or more of our clinical trials, including those that could result in a clinical hold, such events could adversely affect our other clinical trials of the same or related product candidates. Moreover, our product candidates may not perform successfully in clinical studies or may be associated with adverse events that distinguish them from those that have previously been approved, such as approved autologous CAR T therapies. For instance, exposure to allogeneic product candidates may result in adverse events not experienced with autologous products. Even if a product candidate is approved by the FDA and comparable foreign regulatory authorities, the approval might contain significant limitations related to use for specified age groups, warnings, precautions or contraindications, or may be subject to burdensome post-approval study or risk management requirements. If we are unable to obtain regulatory approval for one of our product candidates in one or more jurisdictions, or any approval contains significant limitations, we may not be able to obtain sufficient funding to continue the development of that product or generate revenues attributable to that product candidate. Also, any regulatory approval of our current or future product candidates, once obtained, may be withdrawn in a region or country by the respective regulatory agency.

We cannot be sure that the manufacturing processes used in connection with our T-cell immunotherapy product and product candidates will yield a sufficient supply of satisfactory products that are stable, safe, pure, and potent, or comparable to those T cells historically produced by our partnerspartners, or that processes will be scalable or profitable.

The results of preclinical studies or earlier clinical studies are not necessarily predictive of future results. Our existing product candidate in clinical studies, and any other product candidate we advance into clinical studies,candidates may not have favorable results in later clinical studies or receive regulatory approval.

Tab-cel has been predominantly evaluated in single-center studies under investigator-sponsored investigational new drug (IND) applications held by MSK and in our Expanded Access Programs, utilizing different response criteria and endpoints from those we have used or may utilize in later clinical studies. These Phase 2 clinical studies with tab-cel also enrolled a heterogeneous group of patients with a variety of EBV-driven malignancies, including EBV+ PTLD after HCT and EBV+ PTLD after SOT. These Phase 2 studies were not prospectively designed to evaluate the efficacy of tab-cel in the treatment of a single disease state for which we may later seek approval. Findings from early studies may not be reproducible in late phase studies we conduct. For instance, the current protocol for our ALLELE study in EBV+ PTLD is designed to rule out a 20% ORR as the null hypothesis. This means that if the lower bound of the 95% confidence interval on ORR among patients receiving at least one dose of tab-cel exceeds 20% at the end of the study, then the study would be expected to meet the primary endpoint for the treatment of PTLD. Assuming enrollment of 33 patients in a cohort of ALLELE, an observed ORR above approximately 37% would be expected to meet the primary endpoint for that cohort. In addition, our amended ALLELE study protocol includes an interim analysis as well as a final study analysis. We have previously received feedback from the FDA that an interim analysis of the ALLELE study may not be sufficient to support approval of a BLA. Moreover, final study results may not be consistent with interim study results. Furthermore, modifications to the total sample size of the ALLELE study and the statistical approach may be necessary in connection with the review of the BLA by the FDA. For example, in January 2026 we received the Second Complete Response Letter claiming that the ALLELE trial, previously confirmed by the FDA as adequate to support the BLA filing, is no longer considered to be an adequate and well-controlled study due to deficiencies in study design, conduct and analysis, to provide substantial evidence of effectiveness of tab-cel to treat relapsed or refractory EBV+ PTLD.

We may experience delays in our ongoing or future clinical studies and we do not know whether clinical studies will begin or enroll subjects on time, will need to be redesigned or will be completed on schedule, if at all. There can be no assurance that the FDA or comparable foreign regulatory authorities will not put clinical studies of any of our product candidates on clinical hold in the future. For example, inIn January 2025, we received the Response Letter from the FDA relating solely to observations during pre-approval inspection of a third party manufacturing facility in connection with our tab-cel BLA. The FDA placed a clinical hold on our INDsactive forIND applications which include the tab-cel asprogram well as ourand product candidate ATA3219. The clinical hold iswas directly linked to inadequately addressed GMP compliance issues identified during the pre-approval inspection of a third party manufacturing facility referenced in athe Response Letter we received in January 2025.Letter. Our ATA3219 product candidate is manufactured at a separate, fully compliant GMP-certified facility, the starting material used in its production are affected by the compliance issues at the same third-party facility referenced in the Response Letter. In addition,January 2025, we notified investigators of the newclinical EUholds Clinical Trials Regulation (EU) No 536/2014 (CTR) has amendedfor the systemtab-cel ofprogram. approvalIn forFebruary clinical2025, trialsthe third-party facility referenced in the EUResponse Letter was inspected and hasreceived establishedan aFDA newForm 483. We worked with our partner, Pierre Fabre, to support this third-party manufacturer in addressing the compliance issues and in May 2025, the FDA confirmed the clinical trialshold portalissues were satisfactorily addressed and database,the calledFDA lifted the Clinicalclinical Trials Information System (CTIS),holds for the submissiontab-cel and authorizationATA3219 programs. In January 2026, the FDA confirmed it completed a follow-up inspection of clinicalthe trialthird-party applications.manufacturing Clinicalfacility studiesand maydetermined the inspectional issues at such facility have been adequately addressed and the deficiency comment in the Response Letter has been satisfactorily resolved. In January 2026, we received the Second Complete Response Letter claiming that the ALLELE trial, previously confirmed by the FDA as adequate to support the BLA filing, is no longer considered to be delayed,an suspendedadequate and well-controlled study due to deficiencies in study design, conduct and analysis, to provide substantial evidence of effectiveness of tab-cel to treat relapsed or prematurelyrefractory terminatedEBV+ for a variety of reasons, such as:PTLD.

data that demonstrate an unacceptable benefit/risk profile, including a lack of efficacy, unforeseen safety issues or adverse side effects difficulties in manufacturing or obtaining from third parties sufficient quantities of clinical product and/or inability to supply a breadth of appropriate partially HLA matched cell lines from among the available T-cell lines to start or to use in clinical studies;

Atara Biotherapeutics is a leader in T-cell immunotherapy, leveraging its novel allogeneic Epstein-Barr virus (EBV) T-cell platform to develop transformative therapies for patients with cancer and autoimmune disease. Tab-cel (tabelecleucel), our lead program in Phase 3 clinical development in the U.S., has received marketing authorization approval (MAA) under the proprietary name Ebvallo™ for commercial sale in the European Economic Area (EEA) by the European Commission (EC), for commercial sale and use in the United Kingdom (UK) by the Medicines and Healthcare products Regulatory Agency (MHRA), and for commercial sale and use in Switzerland by Swissmedic. We are thepartnered mostwith advancedPierre allogeneicFabre T-cellMedicament immunotherapy(Pierre companyFabre) for commercialization in Europe and intendpotential tocommercialization, rapidlyif deliverapproved, off-the-shelfworldwide, treatmentsincluding toin the U.S. Tab-cel is currently in Phase 3 development in the U.S. for patients with highEBV- unmetassociated medicalpost-transplant need.lymphoproliferative Ourdisease platform(EBV+ leveragesPTLD) thewho uniquehave biologyfailed ofrituximab EBVor Trituximab cellsplus andchemotherapy, hasas thewell capabilityas to treat a wide range ofother EBV-driven diseases or other serious diseases through incorporation of engineered chimeric antigen receptors (CARs) or T-cell receptors (TCRs). Our strategic priority is:diseases.

In March 2025, we announced our decision to pause development of our allogeneic CAR T cell programs and to discontinue development operations for our CAR T programs, including all clinical trials evaluating ATA3219 and development operations for ATA3431. We expecthave tocompleted completenearly all wind-down activities for the CAR T programs by the end of the first quarter of 2025.programs. We have also stopped development on ATA188, an allogeneic T-cell immunotherapy targeting multiple sclerosis (MS).

Our T-cell immunotherapy platform is potentially applicable to a broad array of targets and diseases. Our off-the-shelf, allogeneic T-cell platform allows for rapid delivery of a T-cell immunotherapy product manufactured in advance of patient need and stored in inventory, with each manufactured lot of cells providing therapy for numerous potential patients. This differs from autologous treatments, in which each patient’s own cells must be extracted, genetically modified outside the body and then delivered back to the patient, requiring a complex logistics network. We select the appropriate set of cells for use based on a patient’s unique immune profile. One of our contract manufacturing organizations (CMOs) has completed commercial production qualification activities for tab-cel commercialization in the EEA and is in the process of completing commercial production qualification activities in the US. Another of our CMOs is currently in the process of completing commercial production qualification activities for tab-cel in the EEA. We continue to manufacture inventory according to Pierre Fabre’s commercial product supply strategy.

In October 2021, we entered into the Commercialization Agreement with Pierre Fabre (Pierre Fabre Commercialization Agreement), pursuant to which we granted to Pierre Fabre an exclusive, field-limited license to commercialize and distribute Ebvallo in Europe and select emerging markets in the Middle East, Africa, Eastern Europe and Central Asia (the Initial Territory) following regulatory approval. As contemplated by the Pierre Fabre Commercialization Agreement, we entered into (i) a Manufacturing and Supply Agreement (ii) a Pharmacovigilance Agreement (iii) and a Quality Agreement, in each case, with Pierre Fabre to further advance our partnership with Pierre Fabre. In September 2022, we amended the Pierre Fabre Commercialization Agreement and received an additional $30 million milestone payment from Pierre Fabre following EC approval of Ebvallo for EBV+ PTLD and subsequent filing of the MAA transfer to Pierre Fabre, in exchange for, among other things, a reduction in: (i) royalties we are eligible to receive as a percentage of net sales of Ebvallo in the Initial Territory, and (ii) the supply price mark up on tab-cel purchased by Pierre Fabre. Additionally, we agreed to extend the time period for provision of certain services to Pierre Fabre under the Pierre Fabre Commercialization Agreement. In December 2022, we entered into athe Purchase and Sale Agreement (HCRx Agreement) with HCR Molag Fund L.P. (HCRx,) a Delaware limited partnership. Pursuant to the terms of the HCRx Agreement, we received a total investment amount of $31.0$31 million in exchange for HCRx being entitled to receive a portion of the tiered, sales-based royalties for Ebvallo, in amounts ranging from the mid-single digits to significant double digits, as well as certain milestone payments, both related to the Initial Territory and otherwise payable to us by Pierre Fabre. The total royalties and milestones payable to HCRx related to the Initial Territory under the HCRx Agreement are capped between 185% and 250% of the total investment amount by HCRx, dependent upon the timing of such royalty and milestone payments to HCRx.

On October 31, 2023, we entered into an amended and restated Pierre Fabre Commercialization Agreement (A&R Commercialization Agreement), pursuant to which we expanded Pierre Fabre’s exclusive rights to research, develop, manufacture, commercialize and distribute tab-cel (Ebvallo) to include all other countries in the world (Additional Territory) in addition to the Initial Territory (together, the Territory), subject to our performance of certain obligations as described below. In December 2023, upon the effective date of the A&R Commercialization Agreement, we met the contractual right to receive an additional upfront cash payment of $20.0 million for the expanded exclusive license grant, for which the cash was received in January 2024. In March 2024, we met the contractual right to receive $20.0 million in milestone payments upon achieving a regulatory milestone, for which the cash was received in April 2024. In July 2024, we met the contractual right to receive an additional $20.0 million in milestone payments upon achieving acceptance of our biologics license application (BLA) for tab-cel by the United States Food and Drug Administration (FDA) and we received the cash in August 2024. WeIn willMarch 2025, we completed the transfer of all manufacturing responsibility to Pierre Fabre under the A&R Commercialization Agreement Amendment. Pierre Fabre is now responsible for manufacturing and supplying tabelecleucel for development and commercialization worldwide at its cost. Pursuant to the A&R Commercialization Agreement Amendment, Pierre Fabre has also beagreed to assume the costs related to remediation of the third-party manufacturing facility to address the FDA's requests to support resubmission of the BLA for tab-cel. In exchange for accelerating the transfer of all manufacturing responsibility and assumption of such remediation costs by Pierre Fabre, among other things, we agreed to reduce the amount of certain potential future regulatory and commercial milestone payments under the A&R Commercialization Agreement. In July 2025, we further amended the A&R Commercialization Agreement and completed the transfer of all clinical (including sponsorship of the ALLELE and tab-cel multi-cohort studies) and development responsibility to Pierre Fabre. Pierre Fabre is, at its cost, responsible for all clinical (including sponsorship of the ALLELE and tab-cel multi-cohort studies) and development activities (other than responsibility for regulatory activities) for tabelecleucel worldwide. In October 2025, we further amended the A&R Commercialization Agreement to transfer all regulatory activities (including sponsorship of the tab-cel BLA) to Pierre Fabre. Pierre Fabre is, at its cost, responsible for all regulatory activities (including sponsorship of the tab-cel BLA) for tab-cel worldwide, and Pierre Fabre is to use commercially reasonable efforts to obtain BLA approval as soon as possible. We will, at Pierre Fabre’s expense, continue to observe the regulatory activities and support Pierre Fabre in its efforts to obtain BLA approval. In December 2025, we amended the A&R Commercialization Agreement to, among other things, mitigate the impact of the cost of rebuilding commercial inventory in the United States. We agreed to reduce the milestone payment due upon BLA approval of tab-cel to $31 million in exchange for the right to receive an additional $15 million potential milestone payment upon achieving a certain commercial milestone. Under the terms of the A&R Commercialization Agreement, as amended by the A&R Commercialization Agreement Amendment, we are entitled to receive an aggregate of up to $580.0$308 million in remaining milestone payments upon achieving certain regulatory and commercial milestones relating to tab-cel in the Initial Territory, and an aggregate of up to $556 million in additional potential milestone payments upon achieving certain regulatory and commercial milestones relating to tab-cel in the Additional TerritoryTerritory, including up to $60.0$31.0 million in potential regulatory milestones in connection with the approval by the FDA of a BLA for tab-cel. We are in active discussions with Pierre Fabre on accelerating the transfer of all operational activities related to tab-cel, except the BLA sponsorship, to be completed as early as the end of the first quarter of 2025, as well as assumption by Pierre Fabre of certain costs related to the remediation of the third party manufacturing facility to address the FDA’s requests in order to lift the clinical hold and to support resubmission of the BLA for tab-cel. As part of these discussions, we expect to agree to reduce the amount of certain future potential regulatory and commercial milestone payments relating to tab-cel in the Additional Territory. We are also eligible to receive significant double-digit tiered royalties as a percentage of net sales of tab-cel (Ebvallo) in the Territory until the later of 12 years after the first commercial sale in each such country, the expiration of specified patent rights in each such country, or the expiration of all regulatory exclusivity for tab-cel in each such country. Royalty payments may be reduced in certain specified customary circumstances. Royalties and milestones from the commercialization of Ebvallo in the Initial Territory remain subject to the HCRx Agreement.

We have also entered into research collaborations with leading academic institutions such as Memorial Sloan Kettering Cancer Center (MSK) and the Council of the Queensland Institute of Medical Research (QIMR Berghofer) pursuant to which we acquired rights to novel and proprietary technologies and programs. In May 2025, we returned the rights to the ATA188 and EBV Vaccine programs to QIMR.

We and FUJIFILM Diosynth Biotechnologies California, Inc. (FDB) entered into a Master Services and Supply Agreement (Fujifilm MSA), which became effective in April 2022 and could extend for up to ten years. Pursuant to the Fujifilm MSA, FDB will supply us with specified quantities of our cell therapy products (if approved) and product candidates, manufactured in accordance with cGMP standards. The Fujifilm MSA does not obligate us to purchase products and product candidates exclusively from FDB. In March 2025, in connection with the transition of manufacturing responsibility for tab-cel to Pierre Fabre, we assigned and Pierre Fabre assumed, the Fujifilm MSA.

We have executed various strategic reductions in force over the past several years. In November 2023, we announced a reduction in force of approximately 30% of our workforce at that time. This workforce reduction resulted in total restructuring charges of $6.7 million, comprised primarily of severance payments and wages for the 60-day notice period in accordance with the California Worker Adjustment and Retraining Notification (WARN) Act. In most cases, the severance payments were paid as a lump sum in January 2024. As of December 31, 2024,2025, there are no remaining payments for the November 2023 reduction in force. All of the costs were cash expenditures and represent one-time termination benefits.

In January 2024, we announced a strategic reduction in workforceforce at that time of approximately 25%. The workforce reduction resulted in total restructuring charges of $5.1 million, comprised primarily of severance payments and wages for the 60-day notice period in accordance with the California WARN Act. In most cases, the severance payments were madepaid during in the first half of 2024. Certain of the notified employees had employment agreements that provided for separation benefits in the form of salary continuation, which were paid from February 2024 through January 2025. As of December 31, 2024,2025, approximately $0.1 million of further separation payments and benefitsthere are requiredno remaining payments for the January 2024 reduction in workforce.force. The majority of the associated costs arewere cash expenditures and primarily representrepresented one-time termination benefits.

In January 2025, we announced another strategic reduction in workforceforce at that time of approximately 50%. We expect to recognizerecognized approximately $7.5$7.2 million in total severance and related benefits as a result of this reduction in force, consisting primarily of severance payments and wages for the 60-day notice period in accordance with the California WARN Act. In most cases, the severance will bewas paid in the first half of 2025. Certain of the notified employees had employment agreements which provided for separation benefits in the form of salary continuation; these benefits will be paid from April 2025 throughby May 2026. The majorityAs of December 31, 2025, approximately $0.5 million of further separation payments and benefits are required for the January 2025 reduction in force. The associated costs represent cash expenditures.expenditures and primarily represent one-time termination benefits.

In March 2025, we announced a further strategic reduction in workforceforce at that time of approximately 50%,50%. retainingWe recognized approximately 35 employees essential to executing on our strategic priorities. We expect to recognize approximately $3.0$2.8 million in total severance and related benefits as a result of this reduction in force, consisting primarily of severance payments and wages for the 60-day notice period in accordance with the California WARN Act. In most cases, the severance will bewas paid in the first half of 2025. Certain of the notified employees had employment agreements which provided for separation benefits in the form of salary continuation; these benefits will be paid from May 2025 throughby May 2026. The majorityAs of December 31, 2025, approximately $0.1 million of further separation payments and benefits are required for the March 2025 reduction in force. The associated costs represent cash expenditures.expenditures and primarily represent one-time termination benefits.

Our net lossesincome were(loss) $85.4was $32.7 million and $276.1$(85.4) million for the years ended December 31, 20242025 and 2023,2024, respectively. As of December 31, 2024,2025, we had an accumulated deficit of $2.1$2.0 billion. Substantially all of our net losses have resulted from costs incurred in connection with our research and development programs and from general and administrative expenses associated with our operations. As of December 31, 2024,2025, our cash, cash equivalents and short-term investments totaled $42.5$8.5 million, which we intend to use to fund our operations.

We have generated limited commercialization revenues under the A&R Commercialization Agreement, following the December 2022 EC approval of Ebvallo. Our commercialization revenue recognized to date is derived from agreements with Pierre Fabre, primarily related to upfront license fees, milestone payments and amounts recognized from the sale of zero-cost inventories for which all performance obligations are complete, and is subject to the terms of the HCRx Agreement. We do not retain any meaningful milestone or royalty payments related to the Initial Territory under the A&R Commercialization Agreement until the applicable royalty cap under the HCRx Agreement is met, if at all.all, and milestone or royalty payments related to the Additional Territory under the A&R Commercialization Agreement isare subject to us obtaining regulatory approval in the US or for another market within the Additional Territory. Our license and collaboration revenue recognized to date is primarily derived from agreements with Bayer AG, which terminated as of July 31, 2022.

We expect that any revenue we generate from the A&R Commercialization Agreement, subject to the terms of the HCRx Agreement, will fluctuate from period to period as a result of the timing and number of inventory purchases by Pierre Fabre, potential milestone achievement,achievement and any potential regulatory approvals and the timing of manufacturing and cell selection technology transfer to Pierre Fabre.approvals.

Cost of commercialization revenue consists primarily of expenses associated with cell selection services performed for Pierre Fabre, in-license sales-related milestone costs, period manufacturing expenses and the lower of cost or net realizable value adjustments to inventories. Costs incurred to produce Ebvallo prior to regulatory approval, referred to as zero cost inventories, have been recorded as research and development expense in our consolidated statement of operations and comprehensive income (loss). Cost of commercialization revenue for Ebvallo produced after receiving regulatory approval and in a qualified manufacturing facility,facility also include direct and indirect costs related to the production of Ebvallo,Ebvallo. Such costs are recorded into cost of commercialization revenue as the related commercialization revenue is recognized on such Ebvallo shipments.recognized. Such costs include, but are not limited to, CMO costs, quality testing and validation, materials used in production, and an allocation of compensation, benefits and overhead costs associated with employees involved with production.

Our expenditures on current and future preclinical and clinical development programs are subject to numerous uncertainties in timing and cost to completion. The duration, costs, and timing of clinical studies and development of our product candidates will depend on a variety of factors, including:

the scope, rate of progress, and expenses of our ongoing clinical studies, potential additional clinical studies and other research and development activities;

General and administrative expenses consist primarily of compensation and benefits for legal, human resources, finance and other general and administrative employees, including stock-based compensation; professional services costs, including legal, patent, human resources, audit and accounting services; other outside services; and consulting costs; and information technology and overhead expenses.

Provision for income taxes consists primarily of income taxes in U.S. states and foreign jurisdictions. Our effective tax rate was 0.1% and 0% for the years ended December 31, 20242025 and 2023.2024, respectively.

Certain judgments affect the application of our revenue recognition policy. For example, we record short-term and long-term deferred revenue based on our best estimate of when such revenue will be recognized. Short-term deferred revenue consists of amounts that are expected to be recognized as revenue in the next 12 months, and long-term deferred revenue consists of amounts that we expect will be recognized after the next 12 months. ThisAs of December 31, 2025, this estimate is based on our forecasted patient demand, our currentregulatory operating plan,plan. andIf expectedthe datesduration or the scope of technologythe transfer,tab-cel andregulatory if these items shouldactivities change in the future, we may recognize a different amount of deferred revenue over the next 12-month period.

The fair value of our common stock is measured at the market price on the measurement date. For awards with performance-based vesting criteria, we assess the probability of the achievement of the performance conditions at the end of each reporting period and begin to recognize the share-based compensation costs when it becomes probable that the performance conditions will be met. For awards that are subject to both service and performance conditions, no expense is recognized until it is probable that performance conditions will be met. We do not believe there is a reasonable likelihood that there will be a material change in the future estimates or assumptions we use to determine stock-based compensation expense. However, if actual results are not consistent with our estimates or assumptions, we may be exposed to changes in stock-based compensation expense that could be material or the stock-based compensation expense reported in our financial statements may not be representative of the actual economic cost of the stock-based compensation.

We do not believe that there is a reasonable likelihood that there will be a material change in our liability for uncertain income tax positions or our effective income tax rate. However, if actual results are not consistent with our estimates or assumptions, we may be exposed to losses that could be material. We recorded a valuation allowance of approximately $368.4$355.0 million as of December 31, 20242025 related primarily to net operating loss carryforwards, and capitalized research expenses, and tax credit carryforwards.expenses.

Research and development expenses consisted of the following costs, by function, in the periods presented (certain items have been reclassified in prior periods for consistency in presentation):

MedicalTechnical operations and safetyquality expenseexpenses were $44.1$21.9 million in 20242025 as compared to $67.4$92.5 million in 2023.2024. The decrease in 20242025 iswas primarily due to lowerthe payrolltransition of tab-cel manufacturing activities to Pierre Fabre as of March 31, 2025, reduced headcount following the January, March and relatedMay costs, driven by the November 2023 and January 20242025 reductions in force and thepause closeof outresearch and development of the ATA188CAR PhaseT 2programs EMBOLDas studyof afterMarch it did not meet its primary endpoint.2025.

RegulatoryMedical and qualitysafety expenseexpenses were $29.9$9.8 million in 20242025 as compared to $34.4$44.1 million in 2023.2024. The decrease in 20242025 was primarily drivendue byto lowerreduced payrollheadcount following the January, March and relatedMay costs, driven by the November 2023 and January 20242025 reductions in force.force, Thisthe decreasetransition wasof partiallytab-cel offsetdevelopment by increased costs relatedactivities to activitiesPierre supportingFabre as of July 14, 2025 and termination of the tab-celATA3219 BLAphase submission.1 trials in NHL and lupus after the decision to pause research and development for CAR T assets in March 2025.

We have not set a definitive timetable for completion of this process, and there can be no assurance regarding the results or outcome of this process. It is possible that we may not pursue a strategic alternative as a result of this process, that a strategic alternative that has been pursued may not be attractive, or that a strategic alternative may not ultimately be consummated. As part of the process, our board of directors will consider a full range of strategic alternatives, including, but not limited to, those identified in the range of strategic alternatives described above.

Investment in biopharmaceutical product development is highly speculative because it entails substantial upfront capital expenditures and significant risk that product candidates will fail to prove effective, gain regulatory approval or become commercially viable. We have one product, Ebvallo, which is approved in the EEA, the UK and Switzerland and have generated limited revenues from commercialization, and have incurred significant research, development and other expenses related to our ongoing operations and expect to continue to incur such expenses. As a result, we have incurred significant operating losses in every annual reporting period since our inception, with the exception of the twelve months ended December 31, 2025. For the threesix months ended MarchJune 31,30, 2026, we reported a net loss of $4.1$9.0 million.

As of MarchJune 31,30, 2026, we had total cash andcash, cash equivalents and short-term investments of $8.4$9.9 million. Our existing cash, cash equivalents and short-term investments as of MarchJune 31,30, 2026 will not be sufficient to fund our planned operations for at least the next twelve months from the date of issuance of these financial statements. These conditions raise substantial doubt about our ability to continue as a going concern for at least 12 months after the issuance of the accompanying condensed consolidated financial statements.

To alleviate the conditions that raise substantial doubt about our ability to continue as a going concern, we plan to secure additional capital, potentially through a combination of public or private security offerings; use of our ATM facility; issuance of debt; and/or execution of strategic transactions. We may also need to raise additional funding as required based on the status of our development program and our projected cash flows. Although we have been successful in raising capital in the past, and expect to continue to raise capital as required, there is no assurance that we will be successful in obtaining sufficient funding on terms acceptable to us to fund continuing operations, if at all, or identify and enter into any strategic transactions that will provide the capital that we will require. In addition, as of the date of the filing of our Annual Report on Form 10-K for the year ended December 31, 2025, our public float was less than $75 million. As a result, we are subject to the limitations of General Instruction I.B.6 to Form S-3 until such time as our public float exceeds $75 million, which means we only have the capacity to sell shares up to one-third of our public float under shelf registration statements in any twelve-month period. We will remain constrained by the limitations of General Instruction I.B.6 to Form S-3 until such time as our public float exceeds $75 million, at which time the number of securities we may sell under a Form S-3 registration statement will no longer be limited by limitations of General Instruction I.B.6 to Form S-3. Further, our existing shelf registration statement on Form S-3 expires on November 11, 2026. If our public float remains below $75 million, any new or replacement registration statement on Form S-3 that we file will be subject to General Instruction I.B.6, which would limit the aggregate amount we may sell in primary offerings under that registration, including pursuant to the 2023 ATM Facility, in any 12-month period to one-third of our public float. If we are unable to obtain sufficient funding on acceptable terms, we could be forced to delay, limit, reduce or terminate ongoing activities of our product candidate, as well as our exploration of strategic alternatives, which could have a material adverse effect on our business, results of operations, and financial condition.

Generally, if a product with an orphan drug designation subsequently receives the first regulatory approval for the indication for which it has such designation, the product is entitled to a period of marketing exclusivity, which precludes the FDA, the EMA, and the MHRA from approving another marketing application for the same biologic for the same indication for that time period. The applicable period is seven years in the U.S. and ten years in the EU and the UK. The EU and UK exclusivity periods can be reduced to six years if a drug no longer meets the criteria for orphan drug designation or if the drug is sufficiently profitable so that market exclusivity is no longer justified. These periods may be reduced in the EU based on a new applicable legal framework, currentlywhich underwas reviewprovisionally agreed by the European ParliamentParliament, the Council and Council.the European Commission in December 2025 and remains subject to formal adoption. Orphan drug exclusivity may be lost if the FDA, EMA or MHRA determines that the request for designation was materially defective or if the manufacturer is unable to assure sufficient quantity of the drug to meet the needs of patients with the rare disease or condition. In the U.S., the FDA may still approve a later marketing application blocked by an ongoing period of orphan drug exclusivity in limited circumstances such as a demonstration of clinical superiority to the product with orphan drug exclusivity or if the FDA finds that the holder of the orphan drug exclusivity has not shown that it can assure the availability of sufficient quantities of the orphan drug to meet the needs of patients with the disease or condition for which the product was approved. As a result, even if one of our product candidates receives orphan exclusivity, the FDA can still approve or license other drugs or biological products that have a different active ingredient for use in treating the same indication or disease.

In the EU, the EMA may offer PRIME designation supportsto support the development and accelerated review by the EMA of new therapies that are expected to be of major public health interest to treat patients with unmet medical need.needs. With the new EU Pharmaceutical Regulation, applicable from the end of 2028, PRIME becomes subject to formal regulation. Despite thisPRIME designation and the associated opportunity for accelerated assessment, the EMA may decide that additional time is needed for the MAA review and convert the MAA to a standard review timeline. For example, the EMA converted the tab-cel MAA review timeline from accelerated to standard, despite tab-cel's PRIME designation.

Designation as a breakthrough therapy is at the discretion of the FDA, and access to PRIME is at the discretion of the EMA. Receipt of a BTD or PRIME designation for a product candidate may not result in a faster development process, review or approval compared to drugs considered for approval under non-expedited FDA or EMA review procedures and does not assure ultimate approval by either the FDA or EMA.in the EU. In addition, the FDA or EMA, respectively, may later decide that the product no longer meets the conditions for qualification and rescind the BTD or PRIME designation or decide that the time period for FDA or EMA, respectively, review or approval will not be shortened. For example, in June 2022, FDA published a draft guidance document outlining considerations for the FDA in rescinding BTD for products that no longer meet the requirements for that designation.

The proposed revision of the European legislation on pharmaceuticals, changes in governmental administration or changes in leadership at relevant agencies could lead to uncertainties over the regulatory framework that will be applicable to medicinal products in the EU and US, including orphan medicinal products.

For example, in AprilDecember 2023,2025, the EuropeanEU Commissionlegislators adoptedreached a wide-rangingpolitical proposalagreement foron a new EU Pharmaceutical Directive and aRegulation. This new Regulation. If made into law, this proposallegislation will reviseamend and/or replace and replacerepeal the existing general pharmaceutical legislation. This change will likely result in significant changes to the pharmaceutical industry. In particular, it is expected that the new Directive and Regulations will, if made into law,will affect the duration of the period of regulatory protection afforded to medicinal productsproducts, including regulatory data protectionprotection, (also called “datamarket exclusivity”), marketingand market exclusivity afforded to orphan medicinal products, as well as the conditions of eligibility to the orphan designation.

OnIn April 2, 2026, President Trump issued a proclamation pursuant to Section 232 of the Trade Expansion Act of 1962 (April 2026 Proclamation), which, among other things, directs the imposition of tariffs on specified imported pharmaceutical products and active pharmaceutical ingredients, subject to the exemptions set forth in Annex IV of the April 2026 Proclamation.AnnexProclamation. Annex IV includes, among other categories, products designated as orphan drugs by the FDA. While tab-cel has received FDA orphan drug designation for the treatment of EBV+ PTLD following hematopoietic cell transplant or solid organ transplant and Breakthrough Therapy Designation for the treatment of patients with EBV+ PTLD after hematopoietic cell transplant who have failed rituximab and we believe tab-cel is likely to qualify for the orphan drug exemption from Section 232 tariffs, we cannot assure you that the scope and application of the orphan drug carve-out will remain as currently drafted, or will not be narrowed, modified, or eliminated by subsequent executive, legislative, or administrative action; the carve-out will continue to apply if tab-cel is approved for any non-orphan indication or if tab-cel’s orphan drug designation or exclusivity is lost, narrowed, or not maintained; additional tariffs, import restrictions, or other trade measures will not be imposed on pharmaceutical products generally or on products imported from the European Union specifically, outside the framework of the April 2026 Proclamation, including through retaliatory measures imposed by the European Union or other jurisdictions; Pierre Fabre will be able to pass any incremental cost of tariffs through to payors, providers, or patients without adversely affecting the commercial viability of tab-cel in the United States or the pricing and reimbursement available for tab-cel; or tariffs or other trade measures, if imposed, will not cause delays, cost increases, or disruptions in Pierre Fabre’s supply chain or in the timing of a U.S. commercial launch of tab-cel, if approved.

AsWe ofcurrently Marchhave 31, 2026, we had 1310 employees. We may encounter difficulties in managing the size of our operations to support our continuing development activities and the commercialization of our product and potential commercialization of our product candidates by our partners. As our development and commercialization plans and strategies continue to evolve, or as a result of any future acquisitions, we must continue to improve our managerial, operational, financial and other procedures and processes to manage the size our of operations. Our management, personnel and systems currently in place may not be adequate to support any future growth. Future growth would impose significant added responsibilities on members of management, including:

Our stock price has fluctuated in the past and can be expected to be volatile in the future. On June 20, 2024, we effected a 1-for-25 reverse stock split of our common stock, which contributed to the fluctuation in our stock price. From January 1, 2025 through MarchJune 31,30, 2026, the reported sale price of our common stock has fluctuated between $3.92 and $19.15 per share. The stock market in general and the market for biotechnology companies in particular have experienced extreme volatility that has often been unrelated to the operating performance of particular companies. As a result of the general volatility of the biopharmaceutical market, investors may experience losses on their investment in our common stock. The market price of our common stock may be influenced by many factors, including the following:

We have beenin notifiedthe bypast Theand may in the future fail to meet the continued listing standards of the Nasdaq Stock Market LLC (Nasdaq), ofand ouras failurea to comply with one of its continued listing standards. If we continue to fail to meet the listing standards of Nasdaq,result, our common stock may be delisted, which could have a material adverse effect on the liquidity of our common stock.

While we have regained compliance with the MVLS Requirement, there is no guarantee that we will be able to maintain compliance with the MVLS Requirement, or other Nasdaq continued listing requirements, in the future. If we fail to maintain compliance with Nasdaq’s continued listing requirements, our common stock may be subject to delisting. If our common stock were to be delisted, the actual and potential liquidity of our common stock and our ability to raise future capital would be adversely affected and the market price of our common stock could decrease. If, for any reason, we arewould be unable to obtain listing on another national securities exchange or take action to restore our compliance with Nasdaq’s continued listing requirements, a reduction in some or all of the following may occur, each of which could have a material adverse effect on our stockholders:

the number of market markersmakers in our common stock;

We are highly dependent upon our executive officers and other key employees and the loss of the services of any of our executive officers or other key employees, including scientific, technical, accounting and finance or management personnel, could impede the achievement of our corporate objectives. In August 2022, we announced a reduction of our workforce by approximately 20% across all areas of our company, including members of management. In November 2023, we implemented a further reduction of our workforce by approximately 30%, and in January 2024, we conducted an additional reduction of our workforce by approximately 25%, including a member of management. In September 2024, Pascal Touchon, our President and Chief Executive Officer stepped down from his position and was appointed Chairperson of our board of directors, and AnhCo “Cokey” Nguyen, our Chief Scientific and Technical Officer, was appointed as our President and Chief Executive Officer. We implemented additional reductions in force in January, March, May and October 2025.2025, as well as June 2026. Losing members of management and other key personnel subjects us to a number of risks, including the failure to coordinate responsibilities and tasks, the necessity to create new management systems and processes, the impact on corporate culture, and the retention of historical knowledge. In addition, we may not be able to effectively transition members of our management into their new roles.

In August 2022, we reduced our workforce by approximately 20% across all areas of our company, including members of management. In November 2023, we further reduced our workforce by approximately 30%. In January 2024, we announced another reduction in force by approximately 25%. In January 2025, we announced another reduction in force by approximately 50%. In March 2025, we further reduced our workforce by approximately 50%. In May 2025, we completed an additional reduction in force of approximately 30% of total workforce.30%. In October 2025, we announced a further reduction in force of approximately 30%30%. In June 2026, we announced a further reduction in force of, at the time, approximately 23% of our total workforce, retaining approximately 1510 employees essential to advancing our strategic priorities. The reductions in force reflect a prioritization around key research and development programs and the reduction of our expense profile. We may not realize, in full or in part, the anticipated benefits, savings and improvements in our cost structure from our restructuring efforts due to unforeseen difficulties, delays or unexpected costs. If we are unable to realize the expected operational efficiencies and cost savings from restructuring, our operating results and financial condition would be adversely affected. We also cannot be certain that we will not have to undertake additional workforce reductions or restructuring activities in the future. Furthermore, our cost savings plan may be disruptive to our operations, which could affect our ability to generate product revenue. In addition, our workforce reductions could yield unanticipated consequences, such as attrition beyond planned staff reductions, or disruptions in our day-to-day operations. Our workforce reductions could also harm our ability to attract and retain qualified management, scientific, clinical, and manufacturing personnel who are critical to our business. Any failure to attract or retain qualified personnel could prevent us from successfully developing and commercializing our product candidates in the future, including tab-cel, if approved.

Numerous state laws are also designed to address privacy and information security issues, including but not limited to state medical privacy laws, state laws protecting personal information, state data breach notification laws, state genetic privacy laws, human subjects research laws and federal and state consumer protection laws. While some of these laws may include exemptions for HIPAA-covered data and clinical trial data, they add layers of complexity to compliance in the U.S. market, and could increase our compliance costs and adversely affect our business. For example, the California Consumer Protection Act (CCPA), which took effect on January 1, 2020, give California residents expanded rights to access and delete their personal information, opt out of certain personal information sharing, and receive detailed information about how their personal information is used. The CCPA provides for civil penalties for violations, as well as a private right of action when certain personal information is subject to unauthorized access and exfiltration, theft or disclosure due to a business' failure to implement and maintain reasonable security procedures, for data breaches which is expected to increase data breach litigation. The CCPA may increase our compliance costs and potential liability. The CCPA was substantially expanded on January 1, 2023, when the California Privacy Rights Act (CPRA) amendments to the CCPA became fully operative. The CPRA amendments, among other things, give California residents the ability to limit use of certain sensitive personal information, further restrict the use of cross-contextual advertising, establish restrictions on the retention of personal information, expand the types of data breaches subject to the CCPA’s private right of action, provide for increased penalties for CCPA violations concerning California residents under the age of 16, and establish a new California Privacy Protection Agency to implement and enforce the new law.

We, our partners, our CROs, our CMOs, and other business vendors on which we rely depend on information technology and telecommunication systems for significant elements of our operations, including, for example, systems handling human resources, financial reporting and controls, regulatory compliance and other infrastructure operations. Notwithstanding the implementation of security measures, given the size and complexity of our information technology systems and those of our third party vendors and other contractors and consultants, and the increasing amounts of proprietary, confidential and sensitive information that they maintain, such information technology systems have been subject to and remain vulnerable to breakdown, service interruptions, system malfunction, natural disasters, terrorism, war and telecommunication and electrical failures, as well as security breaches from inadvertent or intentional actions by our personnel, third party vendors, contractors, consultants, business partners, and/or other third parties, or from cyber-attacks by malicious third parties (including the deployment of harmful malware, ransomware, denial-of-service attacks, social engineering, and other means to affect service reliability and threaten the confidentiality, integrity, and availability of information), which may compromise our system infrastructure, or that of our third party vendors and other contractors and consultants, or lead to data leakage. The risk of a security breach or disruption, particularly through accidental actions or omissions by trusted insiders, cyber-attacks or cyber intrusions, including by computer hackers, viruses, foreign governments, and cyber terrorists, has generally increased as the number, intensity, and sophistication of attempted attacks and intrusions from around the world have increased. Although we take measures to protect sensitive data from unauthorized access, use or disclosure, we and our third party service providers frequently defend against and respond to cyber-attacks, and our information technology and infrastructure may be vulnerable to attacks by hackers or viruses or breached due to personnel error, malfeasance, or other malicious or inadvertent disruptions. Any such breach or interruption could compromise our networks and the information stored there could be accessed by unauthorized parties, manipulated, publicly disclosed, lost, or stolen.

As of MarchJune 31,30, 2026, we had significant U.S. federal and state NOLs due to prior period losses. Under the Tax Cuts and Jobs Act (the Tax Act), as modified by the CARES Act, federal NOLs generated in tax years beginning on or after January 1, 2018 may be carried forward indefinitely, but the utilization of such federal NOLs is limited to 80% of current year taxable income. It is uncertain if and to what extent states will conform to all or portions of the Tax Act and the CARES Act.

You should read the following discussion and analysis of our financial condition and results of operations together with our condensed consolidated financial statements and related notes included elsewhere in our Quarterly Report on Form 10-Q for the quarter ended MarchJune 31,30, 2026 and our Annual Report on Form 10-K for the year ended December 31, 2025. This discussion and other parts of this Quarterly Report contain forward-looking statements that involve risk and uncertainties, such as statements of our plans, objectives, expectations and intentions. As a result of many factors, including those factors set forth in the “Risk Factors” section of this Quarterly Report, our actual results could differ materially from the results described in or implied by the forward-looking statements contained in the following discussion and analysis.

We have executed various strategic reductions in force over the past several years. As of MarchJune 31,30, 2026 and December 31, 2025, we had approximately $0.1$0.8 million and $0.9 million, respectively, of further separation payments and benefits required for these reductions in force. In the three and six months ended MarchJune 31,30, 2026 expenses related to reductions in force were $0.$0.8 million, for each period. In the three and six months ended MarchJune 31,30, 2025 expenses related to reductions in force were approximately $9.8$1.5 million.million and $11.3 million, respectively.

Our net income (loss) was ($4.1$9.0) million and $38.0$40.4 million for the threesix months ended MarchJune 31,30, 2026 and 2025, respectively. As of MarchJune 31,30, 2026, we had an accumulated deficit of $2.0 billion. Substantially all of our net losses have resulted from costs incurred in connection with our research and development programs and from general and administrative expenses associated with our operations. As of MarchJune 31,30, 2026, our cash, cash equivalents and short-term investments totaled $8.4$9.9 million, which we intend to use to fund our operations.

The largest component of our total operating expenses since inception has been our investment in research and development activities, including the preclinical and clinical development of our product candidates. Research and development expenses consist primarily of compensation and benefits for research and development and regulatory support employees, including stock-based compensation; expenses incurred under agreements with contract research organizations and investigative sites that conduct preclinical and clinical studies; the costs of acquiring and manufacturing clinical study materials and other supplies, including expenses incurred under agreements with CMOs; payments under licensing and research and development agreements; other outside services and consulting costs; and facilities, information technology and overhead expenses. Research and development costs are expensed as incurred.

There have been no significant changes to our critical accounting policies and significant judgments and estimates during the threesix months ended MarchJune 31,30, 2026 from those disclosed in our management’s discussion and analysis of financial condition and results of operations included in our Annual Report on Form 10-K for the year ended December 31, 2025 filed with the SEC on March 16, 2026.

Comparison of the Three and Six Months Ended MarchJune 31,30, 2026 and 2025

Commercialization revenues were $0.5$0.6 million and $1.1 million for the three and six months ended MarchJune 31,30, 2026 as compared to $98.1$17.6 million and $115.7 million in the comparative 2025 period. The revenue in the prior-year period reflects the transfer of tab‑cel manufacturing responsibilities to Pierre Fabre on March 31, 2025, which resulted in a one‑time acceleration of revenue recognized upon satisfaction of substantially all commercialization and transition‑related performance obligations. In the current period, commercialization revenues relate solely to ongoing regulatory activities,activities and clinical vial sales, resulting in significantly lower revenue recognized during the three and six months ended MarchJune 31,30, 2026.

Cost of commercialization revenue was $0.1$0.2 million and $0.3 million for the three and six months ended MarchJune 31,30, 2026, as compared to $20.4$0.6 million and $21.0 million in the comparative 2025 period.periods. The decrease in the 2026 period is primarily due to the recognition of deferred cost of commercialization revenue in the prior-year period upon the transfer of manufacturing responsibilities to Pierre Fabre on March 31, 2025.

Technical operations and quality expenses were $1.0$0.9 million and $2.0 million in the three and six months ended MarchJune 31,30, 2026, as compared to $19.3$2.5 million and $21.8 million in the comparative 2025 period.periods. The decrease in 2026 was primarily due to the transition of tab-cel manufacturing activities to Pierre Fabre as of March 31, 2025 and reduced headcount following the 2025 reductions in force.

In the three months ended March 31, 2026 medicalMedical and safety expenses were approximately$0.1 million and ($1.3$1.2) million, which reflects a changemillion in estimate of final clinical related costs upon agreement being reached in this period. In the three and six months ended MarchJune 31,30, 2026, as compared to $3.6 million and $9.0 million in the comparative 2025 medical and safety expenses totaled $5.3 million.periods. The decrease in 2026 was primarily due to reduced headcount following the 2025 reductions in force, transition of tab-cel clinical trials to Pierre Fabre in July 2025, and termination of the ATA3219 phase 1 trials after decision to pause research and development for CAR T assets in March 2025. The decrease in the six month period was also due to a change in estimate of final clinical related costs upon agreement being reached as of March 31, 2026.

Regulatory expenses were $0.5$0.3 million and $0.8 million in the three and six months ended MarchJune 31,30, 2026, as compared to $2.8$1.1 million and $4.0 million in the comparative 2025 period.periods. The decrease in 2026 was primarily due to reduced headcount following the 2025 reductions in force.

General and administrative expenses were $3.6$3.8 million and $7.4 million in the three and six months ended MarchJune 31,30, 2026, as compared to $11.5$6.5 million and $18.0 million in the respective comparative 2025 period.periods. The decrease in 2026 was primarily due to reduced headcount following the 2025 reductions in force and lower general and administrative expenses.

Interest income was $54,000$0.1 million and $0.1 million in the three and six months ended MarchJune 31,30, 2026, as compared to $0.2$0.1 million and $0.4 million in the comparative 2025 period.periods. The decrease in the 2026 period was primarily due to lower average balances of cash, cash equivalents and available-for-sale securities.

Interest expense was $0.8$0.2 million and $1.0 million in the three and six months ended MarchJune 31,30, 2026, as compared to $1.0 million and $2.0 million in the comparative 2025 period,periods, primarily due to lower finance leasenon-cash interest expense.expense recognized on the liability related to the sale of future revenues under the HCRx Agreement in the 2026 periods.

In the past five years, we haveWe entered into two separatea sales agreementsagreement with Cowen and Company, LLC (Cowen): in November 2021 (2021 ATM Facility) and in November 2023 (2023 ATM Facility). EachThe ATM facility provides or provided for the sale, in our sole discretion, of shares of our common stock having an aggregate offering price of up to $100.0 million, through Cowen, as our sales agent. We filed a registration statement on Form S-3 registering the offer and sale of these shares under the Securities Act (2023 Registration Statement). Upon the effectiveness of the 2023 Registration Statement, the 2021 ATM Facility was terminated, and no further sales can be made under the 2021 ATM Facility. The issuance and sale of these shares by us pursuant to the ATM facilitiesfacility are deemed “at the market” offerings defined in Rule 415 under the Securities Act of 1933, as amended (Securities Act), and were registered under the Securities Act. Commissions of up to 3.0% are due on the gross sales proceeds of the common stock sold under eachthe ATM facility.

As of the date of the filing of our Annual Report on Form 10-K for the year ended December 31, 2025, our public float was less than $75 million. As a result, we are subject to the limitations of General Instruction I.B.6 to Form S-3 until such time as our public float exceeds $75 million, which means we only have the capacity to sell shares up to one-third of our public float under shelf registration statements in any twelve-month period. We will remain constrained by the limitations of General Instruction I.B.6 to Form S-3 until such time as our public float exceeds $75 million, at which time the number of securities we may sell under a Form S-3 registration statement will no longer be limited by limitations of General Instruction I.B.6 to FormS-3.Form S-3. Consistent with a recent SEC Corporation Finance Interpretation, the limitations of General Instruction I.B.6 of Form S-3 do not apply to the 2023 ATM Facility.Facility under our existing shelf registration statement on Form S-3. Further, our existing shelf registration statement on Form S-3 expires on November 11, 2026. If our public float remains below $75 million, any new or replacement registration statement on Form S-3 that we file will be subject to General Instruction I.B.6, which would limit the aggregate amount we may sell in primary offerings under that registration, including pursuant to the 2023 ATM Facility, in any 12-month period to one-third of our public float.

Our cash andcash, cash equivalents and short-term investments totaled $8.4$9.9 million and $8.5 million as of MarchJune 31,30, 2026 and December 31, 2025, respectively.

Comparison of the ThreeSix Months Ended MarchJune 31,30, 2026 and 2025

Net cash used in operating activities was $3.1$6.4 million in the threesix months ended MarchJune 31,30, 2026 as compared to $28.1$35.5 million in the comparative 2025 period. The decrease of $25.0$29.1 million was primarily due to lower compensation-related costs resulting from lower headcount driven by the 2025 reductions in force, as well as transition of tab-cel clinical trials and manufacturing activities to Pierre Fabre in 2025.

Net cash used in investing activities in the six months ended June 30, 2026 was $6.6 million, primarily reflecting purchases of short-term investments with no offsetting maturities, as compared to net cash provided by investing activities inof the three months ended March 31, 2026 was $0 as compared to $17.2$12.1 million in the comparative 2025 period, which primarily reflectingreflected proceeds from maturities and sales of available-for-sale securities.

Net cash provided by financing activities in the threesix months ended MarchJune 31,30, 2026 consisted of $3.0$7.8 million of net proceeds received from the 2023 ATM Facility. Net cash usedprovided inby financing activities in the comparativesix months ended June 30, 2025 period primarily consisted of $0.3$15.3 million in principalproceeds paymentsfrom onthe financeissuance leaseof obligations.pre-funded warrants and shares in an underwritten registered direct offering, net of discount.

Our existing cash, cash equivalents and short-term investments as of MarchJune 31,30, 2026 will not be sufficient to fund our planned operations for at least the next 12 months after the date of issuance of these financial statements. These conditions raise substantial doubt about our ability to continue as a going concern for at least 12 months after the issuance of the accompanying condensed consolidated financial statements.