ATRA

Productive Type A Meeting with FDA for tabelecleucel FDA guidance provided on resubmission of tabelecleucel BLA Year over Year costs and operating expenses reduction of 87% THOUSAND OAKS, Calif., August 12, 2026--(BUSINESS WIRE)--Atara Biotherapeutics, Inc. (Nasdaq: ATRA), 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 diseases, today reported financial results for the second quarter 2026 and business updates. "This was an important quarter for Atara. We and our partners, Pierre Fabre Pharmaceuticals (PFP), had a productive Type A meeting with the FDA where we confirmed the opportunity to resubmit the tabelecleucel BLA based on the existing Phase 3 single arm ALLELE trial. We are actively working with and supporting PFP in a resubmission that includes an updated dataset with additional patients and longer follow-up. Patients are still dying from EBV-driven PTLD, and we remain fully committed to ensuring that they have access to this new medicine," said Cokey Nguyen, President and Chief Executive Officer of Atara. "We continue to believe that tab-cel has significant commercial potential in the US, and we have taken steps to control expenses with the goal of protecting and maximizing shareholder value and enhancing our strategic flexibility." Tabelecleucel (tab-cel® or EBVALLO™) for Post-Transplant Lymphoproliferative Disease (PTLD) As previously communicated, PFP has indicated they intend to submit an updated dataset with additional patients and longer follow-up from the pivotal Phase 3 single arm ALLELE study as well as supportive data. Atara anticipates providing a further regulatory update later this quarter. Under its commercialization agreement with Pierre Fabre Laboratories, Atara is eligible to receive a $31 million milestone payment upon FDA approval of the tabelecleucel BLA, as well as significant double-digit tiered royalties as a percentage of net sales, and milestones related to commercial sales of EBVALLO. Second Quarter 2026 Financial Results: Cash, cash equivalents and short-term investments as of June 30, 2026, totaled $9.9 million, as compared to $8.4 million as of March 31, 2026. Net cash used in operating activities was $3.3 million for the second quarter 2026, as compared to $7.4 million in the same period in 2025. Total revenues were $0.6 million for the second quarter 2026, as compared to $17.6 million for the same period in 2025. Total revenues decreased by $17.0 million year-over-year, primarily due to the accelerated recognition of deferred revenue in 2025 following the transition of development activities to Pierre Fabre Laboratories. As a result, less deferred revenue remained available for recognition in the comparative period. Total costs and operating expenses include non-cash stock-based compensation, depreciation and amortization expenses of $0.4 million for the second quarter 2026, as compared to $3.0 million for the same period in 2025. Research and development expenses were $1.3 million for the second quarter 2026, as compared to $7.3 million for the same period in 2025. Research and development expenses include $0.1 million of non-cash stock-based compensation expenses for the second quarter 2026, as compared to $0.7 million for the same period in 2025. General and administrative expenses were $3.8 million for the second quarter 2026, as compared to $6.5 million for the same period in 2025. General and administrative expenses include $0.3 million of non-cash stock-based compensation expenses for the second quarter 2026, as compared to $2.1 million for the same period in 2025. Atara reported a net loss of $4.8 million, or ($0.32) basic and diluted loss per share, for the second quarter 2026, as compared to net income of $2.4 million, or $0.20 basic earnings per share and $0.19 diluted earnings per share, for the same period in 2025. 2026 Outlook and Cash Runway: Operating expenses are expected to decline significantly year-over-year, reflecting the full-year benefit of cost-reduction initiatives implemented in 2025 and first half of 2026. Atara expects its cash, cash equivalents, and short-term investments as of June 30, 2026, combined with operating efficiencies achieved in 2025 and first half of 2026, will be sufficient to fund planned operations into mid-2027. About Atara Biotherapeutics, Inc. Atara is harnessing the natural power of the immune system to develop off-the-shelf cell therapies for difficult-to-treat cancers and autoimmune conditions that can be rapidly delivered to patients from inventory. With cutting-edge science and differentiated approach, Atara is the first company in the world to receive regulatory approval of an allogeneic T-cell immunotherapy. Our advanced and versatile T-cell platform does not require T-cell receptor or HLA gene editing and forms the basis of a diverse portfolio of investigational therapies that target EBV, the root cause of certain diseases. Atara is headquartered in Southern California. For more information, visit atarabio.com and follow @Atarabio on X and LinkedIn. Forward-Looking Statements This press release contains or may imply "forward-looking statements" within the meaning of Section 27A of the Securities Act of 1933 and Section 21E of the Securities Exchange Act of 1934. For example, forward-looking statements include statements regarding: (1) the development, timing and progress of tab-cel, including the timing of PFP’s resubmission, the potential characteristics and benefits of tab-cel, and the results of, and prospects for bringing tab-cel to U.S. patients with EBV+ PTLD, the global partnership with Pierre Fabre Medicament involving tab-cel, and the potential financial benefits to Atara as a result of the global partnership with Pierre Fabre Medicament, including the receipt, timing and amount of any payments to be received by Atara thereunder; and (2) Atara’s cash runway, receipt of potential milestone payments, and estimated reduction in operating expenses, including Atara’s ability to fund its planned operations into mid-2027. Because such statements deal with future events and are based on Atara’s current expectations, they are subject to various risks and uncertainties and actual results, performance or achievements of Atara could differ materially from those described in or implied by the statements in this press release. These forward-looking statements are subject to risks and uncertainties, including, without limitation, risks and uncertainties associated with the costly and time-consuming pharmaceutical product development process and the uncertainty of clinical success; risks related to FDA’s review of tab-cel, including the risk that a resubmission of the tab-cel BLA may not address the deficiencies identified in the Complete Response Letter received on January 9, 2026 or other issues that may be raised by the FDA on review; the fact that PFP, and not Atara, holds the tab-cel BLA and controls the timing, content and strategy of any resubmission and related FDA interactions, and Atara's ability to influence the resubmission process is limited; Atara’s ability to access capital, and the sufficiency of Atara’s cash resources and access to additional capital on favorable terms or at all; and other risks and uncertainties affecting Atara, including those discussed in Atara’s filings with the Securities and Exchange Commission, including in the "Risk Factors" and "Management’s Discussion and Analysis of Financial Condition and Results of Operations" sections of Atara’s most recently filed periodic reports on Form 10-K and Form 10-Q and subsequent filings and in the documents incorporated by reference therein. Except as otherwise required by law, Atara disclaims any intention or obligation to update or revise any forward-looking statements, which speak only as of the date hereof, whether as a result of new information, future events or circumstances or otherwise. View source version on businesswire.com: https://www.businesswire.com/news/home/20260812726239/en/ Contacts Investor and Media Relations Amber DaughertySr. Director, Strategy and [email protected]

Productive meeting held with the FDA; planning for tabelecleucel BLA resubmission Operating efficiencies and ATM proceeds extend cash runway into mid-2027 THOUSAND OAKS, Calif., May 12, 2026--(BUSINESS WIRE)--Atara Biotherapeutics, Inc. (Nasdaq: ATRA), 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 diseases, today reported financial results for the first quarter 2026 and business updates. Tabelecleucel (tab-cel® or Ebvallo™) for Post-Transplant Lymphoproliferative Disease (PTLD) As previously communicated, Pierre Fabre Pharmaceuticals (PFP), with Atara’s support, had a productive meeting with the FDA and discussed a potential path forward to resubmitting the tab-cel Biologics License Application (BLA). The FDA agreed that a single arm study using an appropriate historical control applicable to the trial population, conducted in a pre-specified manner, could serve as an adequate and well controlled study and provide safety and efficacy data in support of a marketing application of tab-cel for the proposed indication. PFP has indicated they intend to submit an updated dataset with additional patients and longer follow-up from the pivotal Phase 3 single arm ALLELE study as well as supportive data, as a part of the resubmission plan being defined with the FDA. Atara anticipates providing a further regulatory update in the third quarter. First Quarter 2026 Financial Results Cash, cash equivalents and short-term investments as of March 31, 2026 totaled $8.4 million, as compared to $8.5 million as of December 31, 2025. Net cash used in operating activities was $3.1 million for the first quarter 2026, as compared to $28.1 million in the same period in 2025. Total revenues were $0.5 million for the first quarter 2026, as compared to $98.1 million for the same period in 2025. The prior‑year period reflects a one‑time acceleration of revenue recognized upon the transfer of tab‑cel manufacturing responsibilities to Pierre Fabre Laboratories on March 31, 2025. In the current period, commercialization revenue relates solely to ongoing regulatory activities Total costs and operating expenses include non-cash stock-based compensation, depreciation and amortization expenses of $0.8 million for the first quarter 2026, as compared to $6.0 million for the same period in 2025. Research and development expenses were $0.2 million for the first quarter 2026, as compared to $27.4 million for the same period in 2025. Research and development expenses also include $0.3 million of non-cash stock-based compensation expenses for the first quarter 2026, as compared to $1.6 million for the same period in 2025. General and administrative expenses were $3.6 million for the first quarter 2026, as compared to $11.5 million for the same period in 2025. General and administrative expenses include $0.5 million of non-cash stock-based compensation expenses for the first quarter 2026, as compared to $2.6 million for the same period in 2025. Atara reported a net loss of $4.1 million, or ($0.29) basic and diluted loss per share, for the first quarter 2026, as compared to net income of $38.0 million, or $3.53 basic earnings per share and $3.50 diluted earnings per share, for the same period in 2025. 2026 Outlook and Cash Runway: Operating expenses are expected to decline significantly year-over-year, reflecting the full-year benefit of cost-reduction initiatives implemented in 2025. Atara expects its cash, cash equivalents, and short-term investments as of March 31, 2026, combined with $4.8 million of ATM proceeds after quarter end and operating efficiencies achieved in 2025, will be sufficient to fund planned operations into mid-2027. About Atara Biotherapeutics, Inc. Atara is harnessing the natural power of the immune system to develop off-the-shelf cell therapies for difficult-to-treat cancers and autoimmune conditions that can be rapidly delivered to patients from inventory. With cutting-edge science and differentiated approach, Atara is the first company in the world to receive regulatory approval of an allogeneic T-cell immunotherapy. Our advanced and versatile T-cell platform does not require T-cell receptor or HLA gene editing and forms the basis of a diverse portfolio of investigational therapies that target EBV, the root cause of certain diseases. Atara is headquartered in Southern California. For more information, visit atarabio.com and follow @Atarabio on X and LinkedIn. Forward-Looking Statements This press release contains or may imply "forward-looking statements" within the meaning of Section 27A of the Securities Act of 1933 and Section 21E of the Securities Exchange Act of 1934. For example, forward-looking statements include statements regarding: (1) the development, timing and progress of tab-cel, including the timing of PFP’s resubmission, the potential characteristics and benefits of tab-cel, and the results of, and prospects for bringing tab-cel to U.S. patients with EBV+ PTLD, the global partnership with Pierre Fabre Medicament involving tab-cel, and the potential financial benefits to Atara as a result of the global partnership with Pierre Fabre Medicament, including the receipt, timing and amount of any payments to be received by Atara thereunder; and (2) Atara’s cash runway, receipt of potential milestone payments, and estimated reduction in operating expenses, including Atara’s ability to fund its planned operations into mid-2027. Because such statements deal with future events and are based on Atara’s current expectations, they are subject to various risks and uncertainties and actual results, performance or achievements of Atara could differ materially from those described in or implied by the statements in this press release. These forward-looking statements are subject to risks and uncertainties, including, without limitation, risks and uncertainties associated with the costly and time-consuming pharmaceutical product development process and the uncertainty of clinical success; risks related to FDA’s review of tab-cel, including the risk that a resubmission of the tab-cel BLA may not address the deficiencies identified in the Complete Response Letter received on January 9, 2026 or other issues that may be raised by the FDA on review; the fact that PFP, and not Atara, holds the tab-cel BLA and controls the timing, content and strategy of any resubmission and related FDA interactions, and Atara's ability to influence the resubmission process is limited; our ability to access capital, and the sufficiency of Atara’s cash resources and access to additional capital on favorable terms or at all; and other risks and uncertainties affecting Atara, including those discussed in Atara’s filings with the Securities and Exchange Commission, including in the "Risk Factors" and "Management’s Discussion and Analysis of Financial Condition and Results of Operations" sections of Atara’s most recently filed periodic reports on Form 10-K and Form 10-Q and subsequent filings and in the documents incorporated by reference therein. Except as otherwise required by law, Atara disclaims any intention or obligation to update or revise any forward-looking statements, which speak only as of the date hereof, whether as a result of new information, future events or circumstances or otherwise. Financials View source version on businesswire.com: https://www.businesswire.com/news/home/20260512257848/en/ Contacts Investor and Media Relations Amber Daugherty Sr. Director, Strategy and Operations [email protected]

Atara delivers significant operational efficiencies and extends cash runway through year-end 2026 A Type A meeting has been scheduled between Pierre Fabre Pharmaceuticals and the FDA THOUSAND OAKS, Calif., March 16, 2026--(BUSINESS WIRE)--Atara Biotherapeutics, Inc. (Nasdaq: ATRA), 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 diseases, today reported financial results for the fourth quarter and full year 2025 and business updates. "We continue to focus on streamlining our costs and liabilities, allowing us to be a nimbler, fit for purpose organization," said Cokey Nguyen Ph.D., President and Chief Executive Officer of Atara. "With the adjustments we have made we are able to focus on supporting our partner, Pierre Fabre Pharmaceuticals, as they work towards addressing the concerns in the latest Complete Response Letter with the agency. We strongly believe that tabelecleucel can bring substantial benefit to post-transplant lymphoproliferative disease patients and we are committed to supporting Pierre Fabre Pharmaceuticals as they get this life-saving drug to the finish line in the U.S." Tabelecleucel (tab-cel® or Ebvallo™) for Post-Transplant Lymphoproliferative Disease (PTLD) A Type A meeting with the U.S. Food and Drug Administration (FDA) has been scheduled for our partner Pierre Fabre Pharmaceuticals to discuss the issues raised by the FDA in the Complete Response Letter received in January 2026. We anticipate providing a regulatory update in the second quarter. Corporate Updates As previously communicated, Atara entered into an amendment (Amendment) to the Purchase and Sale Agreement dated as of December 20, 2022 with a fund managed by HealthCare Royalty ("HCRx"). Under the terms of the Amendment, HCRx agreed to amend the due date of the one-time $9.0 million cash payment associated with the achievement of a certain milestone from June 30, 2026 to January 1, 2028 in exchange for the issuance of a warrant to purchase up to 400,000 shares of Atara common stock. Financial Update: Fourth Quarter and Full Year 2025 Financial Results: Cash, cash equivalents and short-term investments as of December 31, 2025 totaled $8.5 million, as compared to $42.5 million as of December 31, 2024. Net cash used in operating activities was $5.7 million and $50.9 million for the fourth quarter and fiscal year 2025, as compared to $24.5 million and $68.7 million for the same periods in 2024. Atara reported a net loss of ($3.4) million, or ($0.25) per share, and a net income of $32.7 million, or $2.61 per share, for the fourth quarter and fiscal year 2025, respectively, as compared to a net loss of ($12.7) million, or ($1.19) per share, and ($85.4) million, or ($11.41) per share, for the same periods in 2024. Commercialization revenues were $120.8 million in 2025 as compared to $128.9 million in 2024. Total costs and operating expenses include non-cash stock-based compensation, depreciation and amortization expenses of $1.6 million and $11.9 million for the fourth quarter and fiscal year 2025, respectively, as compared to $6.9 million and $32.1 million for the same periods in 2024. Research and development expenses were ($0.2) million and $37.4 million for the fourth quarter and fiscal year 2025, respectively, compared to $28.7 million and $151.5 million for the same periods in 2024. The 2025 results include a $2.6 million non-cash gain from an ARC facility lease amendment, resulting in a fourth-quarter credit rather than an expense. Research and development expenses include $0.4 million and $2.9 million of non-cash stock-based compensation expenses for the fourth quarter and fiscal year 2025, respectively, compared to $2.6 million and $13.5 million for the same periods in 2024. General and administrative expenses were $4.3 million and $26.3 million for the fourth quarter and fiscal year 2025, respectively, as compared to $9.4 million and $39.9 million for the same periods in 2024. General and administrative expenses include $1.1 million and $6.9 million of non-cash stock-based compensation expenses for the fourth quarter and fiscal year 2025, respectively, compared to $3.3 million and $13.5 million for the same periods in 2024. 2026 Outlook and Cash Runway: Operating expenses are expected to continue to decline significantly year-over-year as a result of the comprehensive cost-reduction initiatives completed in 2025. Atara expects that cash, cash equivalents and short-term investments as of December 31, 2025, combined with recent ATM proceeds of $3.0 million and the operating efficiencies realized in 2025, will be sufficient to fund planned operations through year-end 2026. About Atara Biotherapeutics, Inc. Atara is harnessing the natural power of the immune system to develop off-the-shelf cell therapies for difficult-to-treat cancers and autoimmune conditions that can be rapidly delivered to patients from inventory. With cutting-edge science and differentiated approach, Atara is the first company in the world to receive regulatory approval of an allogeneic T-cell immunotherapy. Our advanced and versatile T-cell platform does not require T-cell receptor or HLA gene editing and forms the basis of a diverse portfolio of investigational therapies that target EBV, the root cause of certain diseases. Atara is headquartered in Southern California. For more information, visit atarabio.com and follow @Atarabio on X and LinkedIn. Forward-Looking Statements This press release contains or may imply "forward-looking statements" within the meaning of Section 27A of the Securities Act of 1933 and Section 21E of the Securities Exchange Act of 1934. For example, forward-looking statements include statements regarding: (1) the development, timing and progress of tab-cel, including the timing and results of the Type A meeting and the potential path forward for the timely accelerated approval of EBVALLO™, the potential characteristics and benefits of tab-cel, and the results of, and prospects for bringing tab-cel to U.S. patients with EBV+ PTLD, the global partnership with Pierre Fabre Medicament involving tab-cel, and the potential financial benefits to Atara as a result of the global partnership with Pierre Fabre Medicament, including the receipt, timing and amount of any payments to be received by Atara thereunder; (2) the timing of the $9.0 million cash payment to HCRx; (3) Atara’s cash runway, receipt of potential milestone payments, and estimated reduction in operating expenses, including Atara’s ability to fund its planned operations to year-end 2026; and (4) Atara’s evaluation of strategic alternatives and ability to consummate one or more strategic transactions. Because such statements deal with future events and are based on Atara’s current expectations, they are subject to various risks and uncertainties and actual results, performance or achievements of Atara could differ materially from those described in or implied by the statements in this press release. These forward-looking statements are subject to risks and uncertainties, including, without limitation, risks and uncertainties associated with the costly and time-consuming pharmaceutical product development process and the uncertainty of clinical success; risks related to FDA’s review of the resubmitted BLA for tab-cel; our ability to access capital, and the sufficiency of Atara’s cash resources and access to additional capital on favorable terms or at all; the timing of the strategic review process; whether Atara will pursue any strategic alternatives; in the event Atara pursues a strategic alternative, that the strategic alternative may not be attractive or ultimately consummated; whether any strategic alternative will result in additional value for Atara and its stockholders; whether the process will have an adverse impact on Atara and other risks and uncertainties affecting Atara, including those discussed in Atara’s filings with the Securities and Exchange Commission, including in the "Risk Factors" and "Management’s Discussion and Analysis of Financial Condition and Results of Operations" sections of the Company’s most recently filed periodic reports on Form 10-K and Form 10-Q and subsequent filings and in the documents incorporated by reference therein. Except as otherwise required by law, Atara disclaims any intention or obligation to update or revise any forward-looking statements, which speak only as of the date hereof, whether as a result of new information, future events or circumstances or otherwise. Financials View source version on businesswire.com: https://www.businesswire.com/news/home/20260316154875/en/ Contacts Investor and Media Relations Amber Daugherty Sr. Director, Strategy and Operations [email protected]

Tab-cel Prescription Drug User Fee Act (PDUFA) Target Action Date of January 10, 2026 Atara has completed the transfer of substantially all tab-cel activities, including BLA sponsorship, and associated costs to Pierre Fabre Laboratories Approval of BLA would unlock a $40 Million milestone payment from Pierre Fabre Laboratories THOUSAND OAKS, Calif., November 12, 2025--(BUSINESS WIRE)--Atara Biotherapeutics, Inc. (Nasdaq: ATRA), 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 diseases, today reported financial results for the third quarter 2025 and business updates. Tabelecleucel (tab-cel® or Ebvallo™) for Post-Transplant Lymphoproliferative Disease (PTLD) The U.S. Food and Drug Administration (FDA) has accepted the filing of Atara’s Biologics License Application (BLA) for tabelecleucel (tab-cel®) indicated as monotherapy for treatment of adult and pediatric patients two years of age and older with Epstein-Barr virus positive post-transplant lymphoproliferative disease (EBV+ PTLD) who have received at least one prior therapy. There are no FDA approved therapies in this treatment setting. The BLA has been granted Priority Review with a Class 2 Resubmission Prescription Drug User Fee Act (PDUFA) target action date of January 10, 2026. Atara expects to receive an additional $40 million milestone payment from Pierre Fabre Laboratories contingent upon FDA approval of the tab-cel BLA. In October, Atara completed the transfer of regulatory activities, including BLA sponsorship, to Pierre Fabre Laboratories. Atara will continue to support Pierre Fabre Laboratories, at Pierre Fabre Laboratories expense, with certain regulatory activities related to the BLA. Substantially all operational activities and associated costs related to tab-cel have been transitioned to Pierre Fabre Laboratories. Corporate Updates Strategic Alternatives Evaluation: As previously communicated, Atara continues to actively explore and assess potential strategic alternatives with the goal of maximizing shareholder value. Organizational Restructuring: In October 2025, Atara announced a reduction in its workforce that impacted approximately 29% of its current employees, retaining approximately 15 employees essential to executing on the Company’s strategic priorities. Financial Update: Third Quarter 2025 Financial Results: Cash, cash equivalents and short-term investments as of September 30, 2025, totaled $13.7 million, as compared to $22.3 million as of June 30, 2025. Net cash used in operating activities was $9.8 million for the third quarter 2025, as compared to $4.0 million in the same period in 2024. Net cash used in operating activities increased by $5.8 million year-over-year, primarily driven by a decrease in cash receipts from Pierre Fabre in the third quarter 2025 after the BLA acceptance milestone and a sale of tab-cel intermediates inventory were completed in the same period in 2024, this was partially offset by a decrease in operating expenses in the third quarter 2025. Atara reported net loss of $4.3 million, or $0.32 per share for the third quarter 2025 as compared to $21.9 million or $2.93 per share for the same period in 2024. Total revenues were $3.5 million for the third quarter 2025, as compared to $40.2 million for the same period in 2024. Total revenues decreased by $36.7 million year-over-year, primarily due to the accelerated recognition of deferred revenue and additional upfront and milestone payments received in the same period 2024 as a result of the A&R Commercialization Agreement, effective December 2023. In addition, the decrease is due to the accelerated recognition of deferred revenue in the first and second quarters 2025 following the transition of manufacturing, development and safety responsibilities to Pierre Fabre Laboratories. Total costs and operating expenses include non-cash stock-based compensation, depreciation and amortization expenses of $1.3 million for the third quarter 2025, as compared to $7.6 million for the same period in 2024. Research and development expenses were $2.9 million for the third quarter 2025, as compared to $43.9 million for the same period in 2024. Research and development expenses include $0.3 million of non-cash stock-based compensation expenses for the third quarter 2025, as compared to $2.9 million for the same period in 2024. General and administrative expenses were $4.0 million for the third quarter 2025, as compared to $10.4 million for the same period in 2024. General and administrative expenses include $0.9 million of non-cash stock-based compensation expenses for the third quarter 2025, as compared to $3.5 million for the same period in 2024. 2025 Outlook and Cash Runway: Under its commercialization agreement with Pierre Fabre Medicament, Atara is eligible to receive a $40 million milestone payment upon FDA approval of the tab-cel BLA. In addition, Atara will be eligible to receive double-digit tiered royalties as a percentage of net sales and milestones related to commercial sales of EBVALLO. We anticipate the full-year 2025 operating expenses will decrease by at least 60% compared to 2024, driven by the transition of substantially all tab-cel activities and associated costs to Pierre Fabre Laboratories as well as the implementation of operational efficiencies in the first half of the year. Atara projects that cash, cash equivalents and short-term investments as of September 30, 2025, combined with the net proceeds of the milestone payment upon tab-cel BLA approval under its commercialization agreement with Pierre Fabre Medicament, will provide significant cash runway and flexibility for the company to execute on its strategic priorities. About Atara Biotherapeutics, Inc. Atara is harnessing the natural power of the immune system to develop off-the-shelf cell therapies for difficult-to-treat cancers and autoimmune conditions that can be rapidly delivered to patients from inventory. With cutting-edge science and differentiated approach, Atara is the first company in the world to receive regulatory approval of an allogeneic T-cell immunotherapy. Our advanced and versatile T-cell platform does not require T-cell receptor or HLA gene editing and forms the basis of a diverse portfolio of investigational therapies that target EBV, the root cause of certain diseases. Atara is headquartered in Southern California. For more information, visit atarabio.com and follow @Atarabio on X and LinkedIn. Forward-Looking Statements This press release contains or may imply "forward-looking statements" within the meaning of Section 27A of the Securities Act of 1933 and Section 21E of the Securities Exchange Act of 1934. For example, forward-looking statements include statements regarding: (1) the development, timing and progress of tab-cel, including the timing for FDA review of the resubmission of the BLA, the potential characteristics and benefits of tab-cel, and the results of, and prospects for, the global partnership with Pierre Fabre Medicament involving tab-cel, and the potential financial benefits to Atara as a result of the global partnership with Pierre Fabre Medicament, including the receipt, timing and amount of any payments to be received by Atara thereunder; (2) Atara’s cash runway, receipt of potential milestone payments, and estimated reduction in operating expenses; and (3) Atara’s evaluation of strategic alternatives and ability to consummate one or more strategic transactions. Because such statements deal with future events and are based on Atara’s current expectations, they are subject to various risks and uncertainties and actual results, performance or achievements of Atara could differ materially from those described in or implied by the statements in this press release. These forward-looking statements are subject to risks and uncertainties, including, without limitation, risks and uncertainties associated with the costly and time-consuming pharmaceutical product development process and the uncertainty of clinical success; risks related to FDA’s review of the resubmitted BLA for tab-cel; our ability to access capital, and the sufficiency of Atara’s cash resources and access to additional capital on favorable terms or at all; the timing of the strategic review process; whether Atara will pursue any strategic alternatives; in the event Atara pursues a strategic alternative, that the strategic alternative may not be attractive or ultimately consummated; whether any strategic alternative will result in additional value for Atara and its stockholders; whether the process will have an adverse impact on Atara and other risks and uncertainties affecting Atara, including those discussed in Atara’s filings with the Securities and Exchange Commission, including in the "Risk Factors" and "Management’s Discussion and Analysis of Financial Condition and Results of Operations" sections of the Company’s most recently filed periodic reports on Form 10-K and Form 10-Q and subsequent filings and in the documents incorporated by reference therein. Except as otherwise required by law, Atara disclaims any intention or obligation to update or revise any forward-looking statements, which speak only as of the date hereof, whether as a result of new information, future events or circumstances or otherwise. Financials View source version on businesswire.com: https://www.businesswire.com/news/home/20251112949094/en/ Contacts Investor and Media Relations Amber Daugherty Sr. Director, Strategy and Operations [email protected]

Tab-cel Prescription Drug User Fee Act (PDUFA) Target Action Date of January 10, 2026 Atara has transferred substantially all operational activities and associated costs related to tab-cel to Pierre Fabre Laboratories Atara has resumed its evaluation of strategic options Approval of BLA would unlock a $40 Million milestone payment from Pierre Fabre Laboratories, materially extending cash runway THOUSAND OAKS, Calif., August 11, 2025--(BUSINESS WIRE)--Atara Biotherapeutics, Inc. (Nasdaq: ATRA), 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 diseases, today reported financial results for the second quarter 2025 and business updates. Tabelecleucel (tab-cel® or Ebvallo™) for Post-Transplant Lymphoproliferative Disease (PTLD) The U.S. Food and Drug Administration (FDA) has accepted the filing of Atara’s Biologics License Application (BLA) for tabelecleucel (tab-cel®) indicated as monotherapy for treatment of adult and pediatric patients two years of age and older with Epstein-Barr virus positive post-transplant lymphoproliferative disease (EBV+ PTLD) who have received at least one prior therapy. There are no FDA approved therapies in this treatment setting. The BLA has been granted Priority Review with a Class 2 Resubmission Prescription Drug User Fee Act (PDUFA) target action date of January 10, 2026. In July, the Company completed transferring substantially all operational activities and associated costs related to tab-cel to Pierre Fabre Laboratories. The sponsorship of the BLA continues to be maintained by the Company. Corporate Updates Strategic Options Evaluation: In April 2025, the Company temporarily paused its review of strategic alternatives pending resubmission of the tab-cel BLA. The Company has resumed its evaluation of strategic options following the resubmission of the tab-cel BLA. These options may include, but are not limited to, an acquisition, merger, reverse merger, other business combinations, licensing, sale of assets, or other strategic transactions. It is possible that Atara may not pursue a strategic alternative or transaction or that any strategic alternative or transaction, if pursued, will not be completed on attractive terms, or that a strategic alternative or transaction may not ultimately be consummated. Financial Update: Second Quarter 2025 Financial Results: Cash, cash equivalents and short-term investments as of June 30, 2025, totaled $22.3 million, as compared to $13.8 million as of March 31, 2025 Net cash used in operating activities was $7.4 million for the second quarter 2025, as compared to $10.6 million in the same period in 2024 Total revenues were $17.6 million for the second quarter 2025, as compared to $28.6 million for the same period in 2024. Total revenues decreased by $11.0 million year-over-year, primarily due to the accelerated recognition of deferred revenue in the first quarter 2025 following the transition of manufacturing responsibilities to Pierre Fabre Laboratories. As a result, less deferred revenue remained available for recognition in the comparative period. Total costs and operating expenses include non-cash stock-based compensation, depreciation and amortization expenses of $3.0 million for the second quarter 2025, as compared to $7.7 million for the same period in 2024 Research and development expenses were $7.3 million for the second quarter 2025, as compared to $33.3 million for the same period in 2024 Research and development expenses include $0.7 million of non-cash stock-based compensation expenses for the second quarter 2025, as compared to $3.3 million for the same period in 2024 General and administrative expenses were $6.5 million for the second quarter 2025, as compared to $8.9 million for the same period in 2024 General and administrative expenses include $2.1 million of non-cash stock-based compensation expenses for the second quarter 2025, as compared to $3.0 million for the same period in 2024 Atara reported net income of $2.4 million, or $0.20 basic earnings per share and $0.19 diluted earnings per share for the second quarter 2025. The net income position is due to the acceleration of revenue recognized following the transition of tab-cel development and safety responsibilities to Pierre Fabre Laboratories in July 2025 2025 Outlook and Cash Runway: Under its commercialization agreement with Pierre Fabre Medicament, Atara is eligible to receive a $40 million milestone payment upon FDA approval of the tab-cel BLA. In addition, Atara will be eligible to receive double-digit tiered royalties as a percentage of net sales and milestones related to commercial sales of EBVALLO. We anticipate the full-year 2025 operating expenses will decrease by at least 60% compared to 2024, driven by the transition of substantially all tab-cel activities and associated costs to Pierre Fabre Laboratories as well as the implementation of operational efficiencies in the first half of the year. Atara projects that cash, cash equivalents and short-term investments as of June 30, 2025, combined with the proceeds of the milestone payment upon tab-cel BLA approval under its commercialization agreement with Pierre Fabre Medicament, will provide significant cash runway and flexibility for the company to execute on its strategic priorities. About Atara Biotherapeutics, Inc. Atara is harnessing the natural power of the immune system to develop off-the-shelf cell therapies for difficult-to-treat cancers and autoimmune conditions that can be rapidly delivered to patients from inventory. With cutting-edge science and differentiated approach, Atara is the first company in the world to receive regulatory approval of an allogeneic T-cell immunotherapy. Our advanced and versatile T-cell platform does not require T-cell receptor or HLA gene editing and forms the basis of a diverse portfolio of investigational therapies that target EBV, the root cause of certain diseases. Atara is headquartered in Southern California. For more information, visit atarabio.com and follow @Atarabio on X and LinkedIn. Forward-Looking Statements This press release contains or may imply "forward-looking statements" within the meaning of Section 27A of the Securities Act of 1933 and Section 21E of the Securities Exchange Act of 1934. For example, forward-looking statements include statements regarding: (1) the development, timing and progress of tab-cel, including the timing for FDA review of the resubmission of the BLA, the potential characteristics and benefits of tab-cel, and the results of, and prospects for, the global partnership with Pierre Fabre Medicament involving tab-cel, and the potential financial benefits to Atara as a result of the global partnership with Pierre Fabre Medicament, including the receipt, timing and amount of any payments to be received by Atara thereunder; (2) Atara’s cash runway, receipt of potential milestone payments, and estimated reduction in operating expenses; and (3) Atara’s evaluation of strategic alternatives and ability to consummate one or more strategic transactions. Because such statements deal with future events and are based on Atara’s current expectations, they are subject to various risks and uncertainties and actual results, performance or achievements of Atara could differ materially from those described in or implied by the statements in this press release. These forward-looking statements are subject to risks and uncertainties, including, without limitation, risks and uncertainties associated with the costly and time-consuming pharmaceutical product development process and the uncertainty of clinical success; risks related to FDA’s review of the resubmitted BLA for tab-cel; our ability to access capital, and the sufficiency of Atara’s cash resources and access to additional capital on favorable terms or at all; the timing of the strategic review process; whether Atara will pursue any strategic alternatives; in the event Atara pursues a strategic alternative, that the strategic alternative may not be attractive or ultimately consummated; whether any strategic alternative will result in additional value for Atara and its stockholders; whether the process will have an adverse impact on Atara and other risks and uncertainties affecting Atara, including those discussed in Atara’s filings with the Securities and Exchange Commission, including in the "Risk Factors" and "Management’s Discussion and Analysis of Financial Condition and Results of Operations" sections of the Company’s most recently filed periodic reports on Form 10-K and Form 10-Q and subsequent filings and in the documents incorporated by reference therein. Except as otherwise required by law, Atara disclaims any intention or obligation to update or revise any forward-looking statements, which speak only as of the date hereof, whether as a result of new information, future events or circumstances or otherwise. Financials View source version on businesswire.com: https://www.businesswire.com/news/home/20250811258417/en/ Contacts Investor and Media Relations Amber Daugherty Sr. Director, Strategy and Operations [email protected]