On March 31, 2019 Atara Biotherapeutics, Inc. (Nasdaq: ATRA), a leading off-the-shelf, allogeneic T-cell immunotherapy company developing novel treatments for patients with cancer, autoimmune and viral diseases, reported that the Company’s collaborators at Memorial Sloan Kettering Cancer Center (MSK), Prasad S. Adusumilli, M.D., and Michel Sadelain, M.D., Ph.D., presented encouraging results from an ongoing MSK investigator-sponsored Phase 1 clinical study (NCT02414269) of a mesothelin-targeted CAR T immunotherapy for patients with mesothelin-associated malignant pleural solid tumors, primarily mesothelioma, who progressed following prior standard platinum-containing chemotherapy (Press release, Atara Biotherapeutics, MAR 31, 2019, View Source [SID1234534786]). Mesothelin-targeted, autologous CAR T cells delivered regionally were well-tolerated and showed encouraging anti-tumor activity in combination with pembrolizumab, a PD-1 checkpoint inhibitor. The findings will be presented today in the Advances in Novel Immunotherapeutics oral session at the American Association of Cancer Research (AACR) (Free AACR Whitepaper) Annual Meeting 2019 in Atlanta, Georgia.

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"Clinical results presented by our MSK collaborators reaffirm mesothelin as a promising target for patients with advanced mesothelioma and establish an important proof-of-concept advance for CAR T immunotherapy in solid tumors," said Dietmar Berger, M.D., Ph.D., Global Head of Research and Development of Atara Biotherapeutics. "These encouraging safety results and anti-tumor responses observed by lead investigator Dr. Adusumilli in combination with a PD-1 checkpoint inhibitor, support our plans to progress development of a next-generation, mesothelin-targeted CAR T immunotherapy using MSK’s novel 1XX CAR signaling domain and PD-1 dominant negative receptor (DNR) checkpoint inhibition technologies for patients with mesothelin-associated solid tumors."

The Phase 1 clinical study recruited 21 patients, 19 with malignant pleural mesothelioma (MPM), one with metastatic lung cancer and one with metastatic breast cancer, who received a median of 3 prior treatment regimens, to evaluate the safety and potential anti-tumor activity of a CD28-costimulated, mesothelin-targeted autologous CAR T immunotherapy. The study included six dose cohorts with administration directly to the tumor site using regional delivery techniques, initially at a low CAR T dose without lymphodepleting chemotherapy, followed by increasing CAR T dose cohorts with lymphodepletion. A subset of these patients was subsequently treated with pembrolizumab, a PD-1 checkpoint inhibitor.

Mesothelin-targeted, autologous CAR T administration was found to be generally well-tolerated with no CAR T-related toxicities higher than grade 2 observed based on monitoring multiple clinical, radiological, and laboratory parameters. CAR T cells were found to be persistent in the peripheral blood for 13 of the 21 patients during the 38-week evaluation, and their presence was associated with evidence of tumor regression on imaging studies.

Best overall response rate (ORR) for a subset of 11 MPM patients with minimum follow-up time of 3 months who also received pembrolizumab and lymphodepleting chemotherapy was 72% including 2 durable complete metabolic responses (CMR) on PET imaging and 6 partial responses (PR). Six of the 11 patients in this subset were programmed cell death ligand 1 (PD-L1) negative, defined as undetectable expression of PD-L1 in tumor cells by immunohistochemistry, with 4 of the 8 total responses observed in PD-L1 negative patients (1 CMR and 3 PR).

Following progression on standard platinum-containing chemotherapy, the expected ORR for patients with MPM treated with a checkpoint inhibitor is estimated between 5%-29% with one patient achieving a CR across multiple studies.1-5

MSK is also investigating mesothelin-targeted CAR T cells for patients with mesothelin-associated advanced breast cancer (NCT02792114). Additional results from these ongoing studies are expected to be presented at upcoming scientific congresses.

Presentation CT036: A Phase I clinical trial of malignant pleural disease treated with regionally delivered autologous mesothelin-targeted CAR T cells: Safety and efficacy
Session CTMS01: Advances in Novel Immunotherapeutics
Presentation Date and Time:Sunday, March 31, 2019 from 3:20 pm – 3:35 pm EDT
Location:Room A411 – Georgia World Congress Center
Authors:Prasad S. Adusumilli, Marjorie Zauderer, Valerie Rusch, Roisin O’Cearbhaill, Amy Zhu, Daniel Ngai, Erin McGee, Navin Chintala, John Messinger, Alain Vincent, Elizabeth Halton, Claudia Diamonte, John Pineda, Shanu Modi, Steve Solomon, David R Jones, Renier Brentjens, Isabelle Riviere, Michel Sadelain
Affiliations:Memorial Sloan Kettering Cancer Center