Abstract CT036: A phase I clinical trial of malignant pleural disease treated with regionally delivered autologous mesothelin-targeted CAR T cells: Safety and efficacy

Background: Malignant pleural disease (MPD) from primary malignant pleural mesothelioma (MPM) or secondary metastatic disease (lung and breast cancers) affects more than 150,000 patients a year in the US alone. We developed chimeric antigen receptors (CARs) to target mesothelin (MSLN), a cell-surface antigen that we have shown is highly expressed in MPD, is associated with aggressiveness and poor survival, and has low expression in normal tissues. Methods: Using a second-generation CD28-costimulated MSLN CAR with the Icaspase-9 safety gene (IcasM28z), we initiated a phase I clinical trial (NCT02414269) to determine the safety and maximum tolerated dose of intrapleurally administered CAR T cells. Patients with biopsy-proven MPD expressing MSLN were eligible for the study. A single dose of IcasM28z CAR T cells was administered intrapleurally (with or without cyclophosphamide preconditioning) by either pleural catheter or an interventional radiology procedure. On-target, off-tumor toxicity, serial serum soluble MSLN-related peptide (SMRP) levels and C-reactive protein levels were assessed, and CT and PET scans were performed, in addition to routine clinical and laboratory tests. Results: Twenty-one patients with MPD (19 MPM, 1 lung cancer, 1 breast cancer) were treated (40% received ≥3 lines of prior therapy). Eighteen of the 21 patients received cyclophosphamide preconditioning (3E5 - 1E7 CAR T cells/kg); the first cohort did not receive cyclophosphamide. Twelve patients were administered CAR T cells using an interventional radiology procedure. One patient had febrile neutropenia (grade 3) related to cyclophosphamide. No CAR T-cell-related toxicities higher than grade 2 were observed. The last cohorts of patients were admitted 2 weeks after infusion with a temperature of 101°F and fatigue. Intense monitoring for on-target, off-tumor toxicity by clinical (chest or abdominal pain), radiological (CT/PET or echocardiogram for pericardial effusion, ascites), laboratory (troponin elevation), and other (electrocardiogram) evaluation found no evidence of toxicity. One patient successfully underwent curative-intent surgical resection 6 weeks after CAR T-cell infusion. CAR T cells were detected in the peripheral blood of 13 patients (day 1 to 38 weeks), as evidenced by vector copy number. T-cell persistence was associated with decreased serum SMRP levels (>50% compared to pretreatment) and evidence of tumor regression on imaging studies. Once lack of toxicity had been established (6-17 weeks after CAR T-cell infusion), 14 patients received anti-PD1 checkpoint blockade agents (1-21 cycles), off protocol, with no toxicity. The best response among the 19 MPM patients (13 patients received anti-PD1 agent; PD-L1 Conclusion: In this phase I clinical trial, intrapleurally administered MSLN-targeted CAR T cells had no evidence of on-target, off-tumor or therapy related toxicity, and there was evidence of CAR T-cell antitumor activity. MSLN-targeted CAR T-cell therapy combined with anti-PD1 agents shows encouraging clinical outcomes, thus a combination therapy trial is planned to recruit patients in the second quarter of 2019. Citation Format: Prasad S. Adusumilli, Marjorie G. Zauderer, Valerie W. Rusch, Roisin E. O9Cearbhaill, Amy Zhu, Daniel A. Ngai, Erin McGee, Navin K. Chintala, John C. Messinger, Alain Vincent, Elizabeth F. Halton, Claudia Diamonte, John Pineda, Shanu Modi, Stephen B. Solomon, David R. Jones, Renier J. Brentjens, Isabelle Riviere, Michel Sadelain. A phase I clinical trial of malignant pleural disease treated with regionally delivered autologous mesothelin-targeted CAR T cells: Safety and efficacy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr CT036.