Real-World Results Demonstrate Objective Response Rate (ORR) of 67% in 24 EBV+ PTLD Patients

91% Overall Survival (OS) at One Year for Patients Responding to Tab-cel Compared to 34% for Non-Responders

Tab-cel Safety Profile Consistent with Phase 3 ALLELE Study Findings

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 announced updated effectiveness and safety data for tabelecleucel (tab-cel^® or EBVALLO™) from the multicenter Expanded Access Program (EAP) study in Europe. The results will be featured in a poster presentation at the 2023 American Society of Clinical Oncology (ASCO) Annual Meeting taking place June 2-6 in Chicago.

Atara supported 27 EAP requests in Europe for patients with relapsed or refractory (r/r) Epstein-Barr virus-positive post-transplant lymphoproliferative disease (EBV+ PTLD) following solid organ transplant (SOT) or hematopoietic cell transplant (HCT). 24 EBV+ PTLD patients, 16 SOT recipients and eight HCT recipients, consented to use of data and received at least one dose of tab-cel, including four patients with EBV+ primary central nervous system (PCNS) PTLD.

An objective response rate (ORR) of 66.7% (16/24) was observed for both SOT and HCT groups (95% CI: 44.7, 84.4), 56.3% (9/16) for patients following SOT (95% CI: 29.9, 80.2) and 87.5% (7/8) for HCT patients (95% CI: 47.3, 99.7) with a best overall response of Complete Response (CR; 33.3%; n=4, SOT, n=4, HCT) or Partial Response (PR; 33.3%; n=5, SOT, n=3, HCT).

"These real-world results affirm the favorable risk-benefit profile seen in the pivotal Phase 3 ALLELE study which supported tab-cel as the first-ever allogeneic T-cell immunotherapy approved," said AJ Joshi, MD, Chief Medical Officer at Atara. "Tab-cel was well tolerated and delivered a one-year survival rate of nearly 91% in responders, reinforcing its potential to address an urgent unmet medical need for EBV+ PTLD patients.”

The median time to response (TTR) in all patients was 1.0 month (range: 0.8–2.2). Of the subgroup of patients with EBV+ PCNS PTLD, three out of four (75%; 95% CI: 19.4, 99.4) treated patients achieved a response with one CR and two PRs.

One-year survival rates were 73.7% (95% CI: 47.3, 88.3) across both groups, 66.5% for SOT patients (95% CI: 32.7, 86.2) and 87.5% for HCT patients (95% CI: 38.7, 98.1). EBV+ PTLD patients responding to tab-cel had longer one-year survival compared to the non-responders, with a one-year survival rate of 90.9% (95% CI: 50.8, 98.7) versus 34.3% (95% CI: 4.8, 68.5) for non-responders.

“These data provide important insights on the effectiveness of EBVALLO™ in the real-world treatment setting,” said Dr. Sylvain Choquet, Head of the Clinical Hematology Department at Pitié-Salpêtrière, Paris, France. “Findings further reinforce the clinical profile already established for EBVALLO™, underscoring its potential as new treatment option for an ultra-rare and highly aggressive form of lymphoma that occurs in some transplant patients.”

Safety findings in this real-world program were consistent with previously published data from clinical studies. All treatment-emergent adverse events (TEAEs) were assessed as unrelated to tab-cel by the treating physician and were consistent with patients’ underlying diseases. Detailed results on baseline demographics and disease characteristics, and additional safety data including tab-cel exposure details, will be shared at the conference.

Pierre Fabre leads all commercialization, distribution, medical and regulatory activities for Ebvallo^TM in Europe, Middle East, Africa and other selected markets.

Poster Presentation Details:

Title: Effectiveness and safety outcomes in patients with EBV+ PTLD treated with allogeneic EBV-specific T-cell immunotherapy (tabelecleucel) under an expanded access program (EAP) in Europe

Presenting Author: Ralf Trappe, M.D., DIAKO Evangelisches Diakonie-Krankenhaus Bremen, Bremen, Germany

Date & Time: June 5, 2023, at 8-11 a.m. CDT / 6-9 a.m. PDT

Abstract Number: 7521

Poster Number: 72

Session: Hematologic Malignancies—Lymphoma and Chronic Lymphocytic Leukemia

Location: McCormick Place Convention Center Chicago, Hall A

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, including multiple sclerosis, that can be rapidly delivered to patients within days. 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 Epstein-Barr virus (EBV) 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, in addition to next-generation CAR-Ts designed for best-in-class opportunities across a broad range of non-EBV-associated liquid and solid tumors. Atara is headquartered in Southern California. For more information, visit atarabio.com and follow @Atarabio on Twitter 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 tab-cel: the development, timing and progress of tab-cel, including data from tab-cel EAP and clinical trials, the potential characteristics and benefits of tab-cel, Atara’s ability to successfully advance the development of tab-cel and its programs, and Pierre Fabre’s activities relating to the commercialization of EBVALLO™ in Europe and the timing thereof. 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; the COVID-19 pandemic and the war in Ukraine, which may significantly impact (i) our business, research, clinical development plans and operations, including our operations in Southern California and Denver and at our clinical trial sites, as well as the business or operations of our third-party manufacturer, contract research organizations or other third parties with whom we conduct business, (ii) our ability to access capital, and (iii) the value of our common stock; the sufficiency of Atara’s cash resources and need for additional capital; and other risks and uncertainties affecting Atara’s and its development programs, 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.

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