Combined Analysis That Includes First Reported Data from Multicohort Phase 2 EBVision Trial Consistent with Previous Single-Center Experience

Pooled Analysis Shows 77.8% Objective Response Rate (ORR) in 18 EBV+ CNS PTLD Patients, Including First Line PTLD Setting and Promising Long-Term Survival

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 positive new data for tabelecleucel (tab-cel^® or EBVALLO™) in patients with relapsed or refractory (r/r) or treatment-naïve Epstein-Barr virus-positive post-transplant lymphoproliferative disease involving the central nervous system (CNS) (EBV+ CNS PTLD) following solid organ transplant (SOT) or hematopoietic cell transplant (HCT). These results will be presented as an oral session at the European Society for Medical Oncology Immuno-Oncology (ESMO I‑O) Annual Congress taking place December 6-8, 2023, in Geneva, Switzerland.

The clinical experience from this combined analysis of four single-arm, open-label studies, including the multicohort Phase 2 EBVision trial (NCT04554914, n=4) expands on previous data from two single-center, Phase 2 studies (NCT00002663, n=10; NCT01498484, n=2), and multicenter, expanded-access protocol (NCT02822495, n=2).

“EBV+ CNS PTLD is a rare but extremely serious disease, and patients often face a poor prognosis that underscores the urgent medical need,” said AJ Joshi, M.D., Executive Vice President, Chief Medical Officer at Atara. “We’re pleased to share new multicenter data, including the first results from our ongoing multicohort EBVision trial and first clinical trial report of treatment with tab-cel in the first line setting. Tab-cel shows a strong objective response rate in these high-risk patients with a favorable safety profile for patients with EBV-driven diseases.”

In this pooled analysis, a total of 18 patients, including one previously untreated patient, with EBV+ CNS PTLD received cycles of three weekly infusions of tab-cel at ~2x10⁶ cells/kg. Key endpoints were objective response rate (ORR), overall survival (OS), and safety parameters. Patients received a median (range) of 1 (0 to 5) lines of prior therapy.

An ORR of 77.8% (14/18) was observed in all patients (95% CI: 52.4, 93.6), with a best overall response of Complete Response (CR; 38.9%; n=7) or Partial Response (PR; 38.9%; n=7). The median time to response (TTR) in all patients was 1.8 months (range: 0.7–6.4).

The estimated one-year overall survival (OS) rate was 70.6% (95% CI: 43.0, 86.6) for all patients. The one-year OS rate for responders was 85.7% versus 0% for non-responders.

Tab-cel was well-tolerated. No reports of serious treatment-emergent adverse events, including neurotoxicity, organ rejection, graft versus host disease, or tumor flare reaction of any grade, were identified related to tab-cel.

Detailed results on baseline demographics, disease characteristics, best overall response, OS, and additional safety data including tab-cel exposure details, will be presented on December 7 in the Proffered Paper Session 2.

Oral Presentation Details:

Title: Clinical Experience of Tabelecleucel in Epstein-Barr Virus-Positive Post-transplant Lymphoproliferative Disease (EBV+ PTLD) Involving the Central Nervous System

Presenting Author: John Patton, M.D., Ph.D., James Comprehensive Cancer Center, The Ohio State University, Columbus, OH

Date & Time: December 7, 2023, at 2:15 - 3:45 p.m. CET / 5:15 - 6:45 a.m. PST

Presentation Number: 49O

Session: Proffered Paper Session 2

Location: Palexpo Congress Centre, Room B

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 AlloCAR-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 X (formerly known as 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 the development, timing and progress of tabelecleucel (tab-cel^® or EBVALLO™), the potential characteristics and benefits of tabelecleucel (tab-cel^® or EBVALLO™), including data and analyses from the EBVision study and the timing of when such data will be received and communicated. 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 wars in Ukraine and the Middle East, 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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