Atara Biotherapeutics, Inc. (Nasdaq: ATRA), a leader in T-cell immunotherapy, developing transformative therapies for patients with cancer and autoimmune diseases, today reported Memorial Sloan Kettering Cancer Center’s (MSK) notification to the U.S. Food and Drug Administration (FDA) of a fatal serious adverse event (SAE) associated with a patient treated in the ongoing Phase 1, MSK-conducted dose-escalation clinical study of autologous mesothelin CAR T, ATA2271. MSK has voluntarily paused enrollment of new patients in the study on a temporary basis while additional information regarding the case is gathered and reviewed. The FDA has notified MSK of its agreement with this approach.

ATA2271 is a next-generation, autologous chimeric antigen receptor (CAR) T-cell therapy targeting mesothelin currently under clinical investigation in patients with malignant pleural mesothelioma. The single case involved a patient with a history of multiple malignancies and other comorbidities undergoing treatment for advanced recurrent mesothelioma. MSK is in the process of further evaluating the occurrence, including the extent of the relationship of the event to ATA2271.

“The safety of every patient participating in studies we are funding or conducting is of the utmost priority for Atara,” said Jakob Dupont, MD, Head of Global Research & Development at Atara. “Clinical evaluation of the case remains ongoing, and we are working closely with investigators at MSK, who are conducting the ATA2271 study under their IND, to establish the underlying causes of the event. We anticipate providing a further update in the coming weeks following further discussion and consultation with MSK.”

The median survival of treated patients with malignant pleural mesothelioma is 9-17 months even with successful completion of a combination of chemotherapy, aggressive surgical resection, and radiation therapy. The first six patients enrolled in the two lowest dose cohorts received either 1x10⁶ cells/kg (patients 1-3) or 3x10⁶ cells/kg (patient 4-6) intrapleural ATA2271. Within these two cohorts, no dose limiting toxicities have been reported to date. The patient event being reported relates to the first patient in a third, higher-dose cohort (6x10⁶ cells/kg).

The temporary pause in ATA2271 study enrollment does not impact the IND-enabling work currently underway to advance ATA3271, a separate, off-the-shelf, allogeneic CAR-T therapy targeting mesothelin using next-generation PD1DNR and 1XX CAR technologies for patients with advanced mesothelioma. ATA3271, ATA3219, tab-cel, and ATA188 all utilize Atara’s allogeneic EBV T-cell platform, the safety and tolerability of which has been validated by clinical studies and experience in approximately 400 patients in various disease areas with no observed cytokine release syndrome (CRS) to date.

MSK Disclosure: MSK has intellectual property rights and associated interests by virtue of licensing agreements between MSK and Atara.

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 and currently under review to support registration in Europe, 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, which does not require TCR or HLA gene editing, 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 timing and progress of (i) the ATA2271 program; (ii) the ATA2271 clinical trial, and preliminary clinical data; (iii) ATA2271 preclinical development and preclinical data; (iv) the safety and efficacy of Atara’s product candidates, including ATA2271; (v) MSK’s ability to successfully advance the development of ATA2271; and (vi) Atara’s ability to successfully advance the development of its CAR T programs. 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 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’s 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 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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