Atara Biotherapeutics Presents Positive Tab-cel® Long-Term Overall Survival Data for Epstein-Barr Virus-Driven Post-Transplant Lymphoproliferative Disease After Solid Organ Transplant at ATC 2021 Virtual Connect

All patients with a complete response (CR) or a partial response (PR) to tab-cel^® alive at one year

Overall tab-cel^® survival benefit demonstrated across previous treatment subgroups

Phase 2 results validate potential life-saving benefit of treatment with tab-cel^® in seriously ill patient population with no approved therapeutic options

Atara Biotherapeutics, Inc. (Nasdaq: ATRA), a pioneer in T-cell immunotherapy, leveraging its novel allogeneic EBV T-cell platform to develop transformative therapies for patients with cancer and autoimmune diseases, today announced a combined long-term overall survival (OS) analysis from three clinical studies of tabelecleucel (tab-cel^®) in patients with Epstein-Barr virus-driven post-transplant lymphoproliferative disease (EBV⁺ PTLD) after solid organ transplantation (SOT). The results are featured in an oral plenary presentation at the American Transplant Congress (ATC 2021 Virtual Connect), taking place June 4-9, 2021.

Combined objective response rate (ORR) and OS data across two SOT subgroups – patients relapsed or refractory (R/R) to rituximab monotherapy and patients R/R to rituximab + chemotherapy (CT) – showed one- and two-year OS for patients achieving either complete response (CR) or those achieving partial response (PR). Data presented at ATC 2021 confirm benefit of tab-cel in SOT PTLD and show similar one- and two-year probability of OS irrespective of patients achieving CR or PR (according to Lugano criteria). Treatment response and OS data were assessed from two completed single-arm, Phase 2 studies (95-024, NCT00002663 and 11-130, NCT01498484) and the multi-center expanded access (EAP-201) study (NCT02822495).

“Patients who have received a solid organ transplant such as a new kidney, lung, heart or liver and go on to develop EBV⁺ PTLD that is relapsed or refractory to rituximab monotherapy or R-chemotherapy face a poor prognosis, with median survival of only about three months,” said Jakob Dupont, M.D., Head of Global Research & Development at Atara. “There is a significant unmet need in these patients for whom there are no approved therapies, let alone therapies specifically designed to treat EBV⁺ PTLD. Combined data from across three clinical studies in SOT recipients with relapsed or refractory disease demonstrated similar long-term survival benefit in those who had either partial or complete response to treatment. These data indicate that tab-cel may help address an urgent unmet need in these patients with high rates of mortality.”

All SOT recipients with EBV⁺ PTLD R/R to rituximab as monotherapy or combined with chemotherapy were treated with tabelecleucel, receiving a median (range) of 2.0 (1-9) cycles

Atara has previously shown benefit in patients with EBV⁺ PTLD after SOT who responded to tab-cel, including up to 100 percent two-year survival rates^1,2. Data presented at EBMT 2021 demonstrated similar results in terms of overall survival in EBV⁺ PTLD patients who received tab-cel following hematopoietic cell transplantation (HCT).

Safety

Tab-cel was well-tolerated in this immunocompromised population with high disease burden and multiple comorbidities. Notably, there was no emerging safety concern and no instances of tumor flare reaction, infusion-related reactions, graft versus host disease (GvHD), cytokine release syndrome (CRS), neurotoxicity or organ rejection reported in these patients.

“We are excited to see the data presented at ATC 2021 reinforce the clinical benefit in patients who responded to tab-cel, including up to 100 percent two-year survival rates,” said Pascal Touchon, President and Chief Executive Officer at Atara. “Atara understands the imperative to provide treatment options for these very sick, treatment-refractory and immunocompromised patients.”

Atara Presentation at ATC 2021:

Title: Overall Survival by Best Overall Response with Tabelecleucel in Patients with Epstein-Barr Virus-Driven Post-Transplant Lymphoproliferative Disease after Solid Organ Transplant

Date & Time: Monday, June 7, 2021 at 10:30 a.m. ET

Oral Session & Number: Plenary Oral Abstract Session 3

About Atara Biotherapeutics, Inc.

Atara Biotherapeutics, Inc. (@Atarabio) is a pioneer in T-cell immunotherapy leveraging its novel allogeneic EBV T-cell platform to develop transformative therapies for patients with serious diseases including solid tumors, hematologic cancers and autoimmune disease. With our lead program in Phase 3 clinical development, Atara is the most advanced allogeneic T-cell immunotherapy company and intends to rapidly deliver off-the-shelf treatments to patients with high unmet medical need. Our platform leverages the unique biology of EBV T cells and has the capability to treat a wide range of EBV-associated diseases, or other serious diseases through incorporation of engineered CARs (chimeric antigen receptors) or TCRs (T-cell receptors). Atara is applying this one platform to create a robust pipeline including: tab-cel in Phase 3 development for Epstein-Barr virus-driven post-transplant lymphoproliferative disease (EBV⁺ PTLD) and other EBV-driven diseases; ATA188, a T-cell immunotherapy targeting EBV antigens as a potential treatment for multiple sclerosis; and multiple next-generation chimeric antigen receptor T-cell (CAR-T) immunotherapies for both solid tumors and hematologic malignancies. Improving patients’ lives is our mission and we will never stop working to bring transformative therapies to those in need. Atara is headquartered in South San Francisco and our leading-edge research, development and manufacturing facility is based in Thousand Oaks, California. For additional information about the company, please visit atarabio.com and follow us 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: the potential benefits, safety and efficacy of tab-cel; the timing and progress of tab-cel, including data and results from tab-cel clinical trials, the timing of the initiation or submission of the BLA and MAA for tab-cel, Atara’s ability to successfully advance the development of tab-cel; and Atara’s ability to advance development of its programs. Because such statements deal with future events and are based on Atara Biotherapeutics' current expectations, they are subject to various risks and uncertainties and actual results, performance or achievements of Atara Biotherapeutics 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 ongoing COVID-19 pandemic, which may significantly impact (i) our business, research, clinical development plans and operations, including our operations in South San Francisco and Southern California 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 Biotherapeutics' filings with the Securities and Exchange Commission (SEC), 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 Biotherapeutics 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.

1. Prockop S et al. ASH 2019
2. Prockop S et al. JCI 2020

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