Atara Biotherapeutics Announces Completion of Enrollment in PINTA 745 Phase 2 Clinical Trial in End-Stage Renal Disease Patients With Protein Energy Wasting

Preliminary Top-Line Data Expected by the End of the Fourth Quarter of 2015

SOUTH SAN FRANCISCO, Calif., Aug. 31, 2015 (GLOBE NEWSWIRE) -- Atara Biotherapeutics, Inc. (Nasdaq:ATRA), a biopharmaceutical company with a focus on developing innovative therapies for patients with debilitating diseases, today announced that it completed enrollment in its blinded, randomized, PINTA 745 Phase 2 clinical trial in End-Stage Renal Disease (ESRD) patients with Protein Energy Wasting (PEW). The company expects to report preliminary top-line data by the end of the fourth quarter of 2015.

PINTA 745 is a peptibody that binds myostatin and inhibits its corresponding signal transduction, thereby blocking the negative regulation of skeletal muscle growth. Atara Bio is conducting a Phase 2 trial in patients with ESRD who are also suffering from PEW at six US-based sites. PEW refers to a state of muscle wasting, inflammation and malnutrition that increases patients' risk for infections, cardiovascular disease and other complications. The company believes that patients with PEW may benefit from the muscle-building demonstrated in earlier clinical trials and anti-inflammatory properties of PINTA 745 demonstrated in preclinical studies. The clinical trial was designed to provide proof of concept data for ESRD patients.

"Atara Bio is pleased to report the completion of enrollment to the PINTA 745 trial and looks forward to reviewing the data towards the end of this year," said Christopher Haqq, MD, Chief Medical Officer of Atara Bio.

About Atara Biotherapeutics, Inc.

Atara Biotherapeutics, Inc. is a biopharmaceutical company focused on developing innovative therapies for patients with debilitating diseases. Atara Bio's programs include molecularly targeted product candidates and T-cell product candidates. Molecularly targeted product candidates include PINTA 745, STM 434 and ATA 842, members of the TGF-beta family of proteins that target myostatin and activin, and have demonstrated the potential to have therapeutic benefit in a number of clinical indications. T-cell product candidates include EBV-CTL, CMV-CTL and WT1-CTL.

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. Because such statements deal with future events and are based on Atara Bio's current expectations, they are subject to various risks and uncertainties and actual results, performance or achievements of Atara Bio could differ materially from those described in or implied by the statements in this press release. For example, forward-looking statements include statements regarding reporting of preliminary top-line data by the end of the fourth quarter of 2015 and the evaluation of the data to guide future development of PINTA 745.These forward-looking statements are subject to other risks and uncertainties, including those discussed under the heading "Risk Factors" in Atara Bio's quarterly report on Form 10-Q filed with the Securities and Exchange Commission (SEC) on August 6, 2015, including the documents incorporated by reference therein and subsequent filings with the SEC. Except as otherwise required by law, Atara Bio 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.

CONTACT: INVESTOR & MEDIA CONTACT:
         Tina Gullotta
         Atara Biotherapeutics, Inc.
         650-741-1613
         tgullotta@atarabio.com

Released August 31, 2015