Atara Bio's T-Cell Product Candidate Activated Against Wilms' Tumor 1 Protein Demonstrates Encouraging Results in Patients With Plasma Cell Leukemia

Data Presented at the 15th International Myeloma Workshop

SOUTH SAN FRANCISCO, Calif., Sept. 24, 2015 (GLOBE NEWSWIRE) -- Atara Biotherapeutics, Inc. (Nasdaq:ATRA), today announced that its collaborating investigators at Memorial Sloan Kettering Cancer Center (MSK) presented clinical data on cytotoxic T lymphocytes (CTL) activated against Wilms' Tumor 1 (WT1-CTL) at the 15^th International Myeloma Workshop in Rome, Italy. The WT1-CTL product candidate targets cancers expressing the Wilms Tumor 1, or WT1, antigen. The data is derived from the treatment of patients with relapsed-refractory Multiple Myeloma (MM), including Plasma Cell Leukemia (PCL), with WT1-CTL after allogeneic hematopoietic cell transplantation (alloHCT). Dr. Guenther Koehne, MD, and colleagues, presented the following top-line clinical data from an ongoing phase 1 study:

• WT1, the tumor associated antigen, was detected on malignant plasma cells in those patients tested.
• The subjects were treated with alloHCT followed by administration of three infusions of WT1-CTLs.
• By one year, of seven subjects with relapsed-refractory MM or PCL receiving an alloHCT and treated with WT1-CTLs, three achieved a complete remission (CR), one achieved a partial response (PR), two had stable disease (SD) and one had progressive disease.
• Adverse events reported were consistent with those typically observed in this transplant population.

The details of the poster presentation are below:

In June 2015, Atara Bio licensed from MSK exclusive, world-wide rights to three clinical stage, allogeneic T-cell therapies for the treatment of cancers and persistent viral infections, including WT1-CTL. The WT1-CTL product candidate is being developed as a potential third party, donor-derived, "off-the-shelf" T-cell product candidate designed to target and destroy cancer cells that overexpress WT1 protein.

About Multiple Myeloma and PCL

Multiple Myeloma, a malignancy of the plasma cell, is the second most common cancer of the blood-forming system with approximately 26,850 new cases and 11,240 deaths estimated in the US for 2015. Of those new cases, approximately two to four percent are PCL, with an aggressive clinical course. Median overall survival for PCL is 4.5-12.6 months.

About WT1-CTL

The WT1-CTL product candidate targets cancers expressing the antigen Wilms Tumor 1, or WT1. WT1 is an intracellular protein that is overexpressed in a number of cancers, including acute myeloid leukemia, or AML, multiple myeloma, or MM, and non-small cell lung, breast, pancreatic, ovarian, and colorectal cancers. The WT1-CTL product candidate is currently being studied in two ongoing Phase 1 clinical studies to test safety and initial anti-tumor efficacy of donor derived WT1-CTL in patients with AML and multiple myeloma. (NCT00620633 and NCT01758328).

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 the clinical development of product candidates and Atara Bio's collaboration with MSK. 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 September 24, 2015