Atara Biotherapeutics Presents New Preclinical Data on ATA3271, a Next-Generation Allogeneic Mesothelin-Targeted CAR T to Treat Solid Tumors, at the 35th Society for Immunotherapy of Cancer Annual Meeting (SITC 2020)

Atara’s allogeneic CAR T therapy leverages the combination of cell intrinsic PD1DNR checkpoint inhibition and 1XX CAR signaling technologies built on the Company’s novel EBV T-cell platform

Preclinical findings demonstrate potent antitumor activity, persistence and low toxicity profile of ATA3271, supporting further clinical investigation

SOUTH SAN FRANCISCO, CA, USA I November 12, 2020 IAtara 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 serious diseases including solid tumors, hematologic cancers and autoimmune disease, today announced the presentation of the first preclinical evaluation of ATA3271, a next-generation, off-the-shelf, allogeneic EBV CAR T-cell therapy targeting mesothelin designed for the treatment of solid tumors. These data are being featured in a poster presentation at the 35th Society for Immunotherapy of Cancer Annual Meeting (SITC 2020), November 11-14, 2020.

“We have made meaningful progress advancing IND-enabling studies for ATA3271, an allogeneic mesothelin CAR T, which leverages our differentiated EBV T-cell platform and utilizes the PD1DNR and 1XX technologies to improve efficacy, persistence, and durability of response. Such innovative CAR T design addresses key hurdles for realizing the potential for CAR T therapies in solid tumor settings,” said Jakob Dupont, Global Head of Research and Development at Atara. “Mesothelin, an antigen associated with aggressive solid tumors, is a promising target for tumor-specific therapy and combined with our EBV T-cell platform and the PD1DNR and 1XX technologies has led to the potent preclinical antitumor activity of ATA3271 that functionally persists after multiple tumor cell challenges.”

Results presented at SITC detail findings from in vitro and in vivo evaluation of ATA3271. Specifically, in vitro functional studies show potent antitumor activity of ATA3271 against mesothelin-expressing cell lines, with potency maintained in the presence of high tumor PD-L1 expression. These data support the design of ATA3271, which expresses a dominant negative version of PD-1 receptor, to maintain function in the presence of suppressive checkpoint ligands commonly associated with solid tumor microenvironments. In addition, results further support the combined functional design of ATA3271’s 1XX costimulatory domain technology in maintaining memory phenotype while limiting cell exhaustion in the context of repeated tumor cell challenges.

Furthermore, ATA3271 retains reduced allocytotoxic function against HLA mismatched targets, a characteristic that is associated with Atara’s allogeneic EBV T-cell platform that leverages enrichment of endogenous EBV-TCR function to decrease clinical risks for GvHD. We also believe that our allogeneic EBV CAR T-cell platform may prevent cellular exhaustion and augment in vivo expansion.

In vivo, ATA3271 exhibited potent antitumor activity and significant survival benefit in mice implanted with MGM-PDL1 cells that highly express both mesothelin as well as PD-L1. This in vivo potency was demonstrated without evident toxicities. All mice treated with ATA3271 (n=10) survived through the study duration, while control mice (n=10) all died within a median duration of 25 days (15- to 35-day survival range), post tumor implantation. Evidence in six of ten mice also showed that ATA3271 persisted in vivo by day 51. Ex vivo analysis of a subset of these persistent cell populations (n=4) demonstrated maintenance of phenotypic memory markers over the duration of the in vivo activity.

Mesothelin is a tumor-specific antigen that is commonly expressed at high levels on the cell surface in many aggressive solid tumors including mesothelioma, triple-negative breast cancer, esophageal cancer, ovarian cancer, pancreatic cancer and non-small cell lung cancer and is an attractive target for immune-based therapies. Both in vitro and in vivo results for ATA3271 suggest that allogeneic mesothelin-CAR-engineered EBV T cells are a promising approach for the treatment of mesothelin-positive cancers.

“The results presented today further support the continued development of our allogeneic mesothelin-targeted next-generation CAR T program,” said AJ Joshi, M.D., Senior Vice President and Chief Medical Officer at Atara. “We look forward to building upon these foundational preclinical studies to advance ATA3271 in the clinic with the goal of bringing a potentially transformative therapeutic option to treat aggressive solid tumors including mesothelioma.”

Atara’s next generation CAR T immunotherapy franchise for mesothelin also includes autologous ATA2271. The U.S. Food and Drug Administration (FDA) recently accepted an Investigational New Drug (IND) application to initiate a Phase 1 clinical study of ATA2271 for the treatment of advanced mesothelioma.

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® (tabelecleucel) in Phase 3 development for Epstein-Barr virus-driven post-transplant lymphoproliferative disease (EBV+ PTLD); 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.

SOURCE: Atara Biothereapeutics

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