Significant Progress Achieved Against Strategic Priorities for ATA188, Tab-cel^® and CAR T Programs in 2021

ATA188 Granted FDA Fast Track Designation for Both Non-Active PPMS and Non-Active SPMS in Recognition of Potential to Address Significant Unmet Medical Need

Tab-cel^® on Track to be First Ever Allogeneic Off-The-Shelf T-cell Immunotherapy Approved in EU in 2022

Presentation on Wednesday, January 12 at 5:15 p.m. EST / 2:15 p.m. PST

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 Pascal Touchon, President and Chief Executive Officer of Atara, will present the Company’s 2021 accomplishments across strategic priorities and key upcoming catalysts at the 40^th Annual J.P. Morgan Healthcare Conference on Wednesday, January 12 at 2:15 p.m. PST / 5:15 p.m. EST.

“Atara made significant progress in 2021, including presentation of positive data from our pivotal Phase 3 ALLELE study and EU regulatory submission for tab-cel; new data confirming our conviction for ATA188 as the first investigational therapy to potentially reverse disability in progressive multiple sclerosis, now further validated by FDA Fast Track designation; and promising early safety and persistence data for our potentially best-in-class allogeneic CAR T portfolio that does not require TCR or HLA gene editing,” said Pascal Touchon, President and Chief Executive Officer of Atara. “With the interim analysis from our EMBOLD study of ATA188, a planned BLA submission and the potential groundbreaking EU approval for tab-cel, the first ever allogeneic, off-the-shelf T-cell therapy to reach this stage, 2022 will be an exciting year for Atara and patients in significant need.”

Tabelecleucel (tab-cel^®) for Post-Transplant Lymphoproliferative Disease (PTLD)

• Continued progress with the U.S. Food and Drug Administration (FDA), including productive engagement with CBER and a Type B CMC meeting scheduled for Q1 2022
• Atara plans to complete the Biologics License Application (BLA) submission for patients with EBV+ PTLD in Q2 2022
  • U.S. approval of BLA for patients with EBV+ PTLD anticipated in H1 2023
• Following successful interactions with EMA, Atara submitted a Marketing Authorization Application (MAA) for tab-cel in patients with EBV+ PTLD, the first ever for an allogeneic, off-the-shelf T-cell therapy, in November 2021. With the granting of Accelerated Assessment, the Company anticipates a decision regarding EU approval in Q4 2022
• First presentation of positive data from the pivotal Phase 3 ALLELE study, reinforcing the transformative potential of tab-cel, as an oral session at the 63^rd American Society of Hematology (ASH) Annual Meeting in December 2021
  • Data demonstrated a 50% objective response rate (ORR) and durability of response with 89% of patients responding to treatment surviving after one year, compared with 32% in non-responders
• In a second oral presentation at ASH, longer term data from Phase 2 and Expanded Access Protocol (EAP) studies showed two-year survival benefit of over 86% in responders whether they achieved a complete response (CR) or partial response (PR) and median OS of 54.6 months
• Continued favorable tab-cel safety profile and no new safety signals with more than 180 PTLD patients treated to date
• EBV+ PTLD is a rare and potentially life-threatening cancer that may occur following a solid organ transplant (SOT) or allogeneic hematopoietic cell transplant (HCT). For patients with EBV+ PTLD, the median survival is only 0.7 to 4.1 months after failure of initial therapy. There are currently no EMA- or FDA-approved treatments indicated for these patients

Tab-cel for Potential Additional Indications

• Enrollment is continuing at sites in the potential label expansion multi-cohort Phase 2 study evaluating six patient populations within EBV+ immunodeficiency-associated lymphoproliferative diseases (IA-LPDs) and other EBV-driven diseases
• First data from the multi-cohort study planned to be presented in 2023

ATA188 for Progressive Multiple Sclerosis (MS)

• FDA has granted Fast Track designation for ATA188 in non-active primary progressive multiple sclerosis (PPMS) and non-active secondary progressive multiple sclerosis (SPMS), two populations with high unmet medical need and limited treatment options
  • A Fast Track designation expedites the review of drugs filling an unmet medical need to treat serious conditions to get important therapies to patients faster; once received, this designation allows early and frequent communication with FDA throughout the development and review process
• Atara is continuing to make good progress enrolling the Phase 2 randomized, double-blind, placebo-controlled dose-expansion EMBOLD study evaluating the efficacy and safety of ATA188 in patients with progressive MS
• A formal interim analysis is planned for Q2 2022, including efficacy and safety, to optimize the likelihood of success in Phase 2 and confirm current development strategy
• Following the interim analysis, the Company will communicate next steps for the program, including rationale, while still maintaining the integrity of the study
• Atara plans to conduct pivotal Phase 3 studies at the conclusion of the Phase 2 study and is actively exploring partnership opportunities
  • One Phase 3 study will focus on non-active SPMS, for which no approved therapies currently exist in U.S. or EU
  • A separate study will focus on non-active PPMS, which has very few treatment options in most countries and approved therapies are of limited efficacy
  • The vast majority of people with PPMS and SPMS have non-active disease
• Overall, increasing research activity and support within the academic community for the hypothesis of EBV as a driver of MS pathogenesis

CAR T Programs

• Atara continues to advance our CAR T programs in liquid and solid tumors, which include a differentiated approach to allogeneic cell therapy, with no gene editing of the T-cell receptor (TCR) and next generation CAR technologies to enhance expansion and persistence of functional T cells

ATA2271/ATA3271 (Solid Tumors Over-Expressing Mesothelin)

• Global strategic collaboration for ATA2271 and ATA3271 with Bayer continues to progress well with advancement of the mesothelin-partnered CAR T immunotherapy programs
• Data presented at ESMO-IO in December 2021 showed promising early safety and persistence of armored CAR T, ATA2271, in patients with advanced mesothelioma; infusions for the first two patient cohorts have now been completed
• Atara is continuing to make progress on IND-enabling studies for ATA3271, an off-the-shelf, allogeneic CAR-T therapy targeting mesothelin using next-generation PD-1 dominant negative receptor (DNR) and 1XX CAR co-stimulatory signaling domain technologies for patients with advanced mesothelioma, and expects a filing in Q4 2022

ATA3219 (B-cell Malignancies)

• Atara continues to advance development of ATA3219, a potential best-in-class allogeneic CD19 CAR T therapy that does not require TCR or human leukocyte antigen (HLA) gene editing, leveraging our next-generation 1XX CAR co-stimulatory signaling domain and allogeneic EBV T-cell platform
• New pre-clinical data (on file) demonstrated optimized version of ATA3219 with an enhanced memory phenotype, leads to both strong proliferative potential and potent antitumor activity supporting a best-in-class profile
• Atara expects to submit an IND for B-cell malignancies in Q4 2022

A live audio webcast of the presentation will be available by visiting the Investors & Media – News & Events section of atarabio.com on Wednesday, January 12, at 5:15 p.m. EST / 2:15 p.m. PST. An archived replay of the webcast will be available on the Company's website for 30 days following the live presentation. A new corporate presentation will be available on Monday, January 10 at 8:30 a.m. EST / 5:30 a.m. PST.

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: (1) the potential benefits, safety and efficacy of tab-cel^®; the timing and progress of tab-cel^®, including (i) data and analyses from the ALLELE study, (ii) tab-cel^® clinical trials, and the timing and outcome of Atara’s discussions with the FDA regarding a BLA submission for tab-cel^®, (iii) the timing and decision of the EMA regarding the MAA for tab-cel^®, (iv) the timing of the initiation or submission of the BLA, (v) Atara’s ability to successfully advance the development of tab-cel^®, including for potential additional indications, (vi) Atara’s activities in anticipation of potential tab-cel^® approval and commercial launch in the U.S., including the timing thereof, (vii) Atara’s collaboration with Pierre Fabre for commercializing tab-cel^® in Europe, Middle East, Africa and other emerging markets, including the timing thereof, and (viii) the potential competition for tab-cel^®; (2) the potential benefits, safety and efficacy of ATA188; the timing and progress of ATA188, including (i) data and analyses from the ATA188 OLE study, (ii) data and analyses from the EMBOLD study, including from the planned interim analysis, including the timing thereof, (iii) the timing, design and outcome of potential additional ATA188 clinical trials, (iv) Atara’s ability to successfully advance the development of ATA188; and (v) partnering options for ATA188; (3) the timing and progress of its CAR T programs, including (i) ATA2271 clinical trial; (ii) ATA3271 and ATA3219 preclinical development, including the timing of regulatory submissions for such product candidates, (iii) progress of the strategic collaboration with Bayer for ATA2271 and ATA3271, and (iv) Atara’s ability to successfully advance the development of its CAR T programs; and (4) Atara’s research and development activities and manufacturing activities, including the development and progress thereof; (5) Atara’s ability to advance development of its 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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