Regional delivery of mesothelin-targeted CAR T cells for pleural cancers: Safety and preliminary efficacy in combination with anti-PD-1 agent.

Abstract

2511 Background: We conducted a phase I dose escalation trial of first-in-human autologous chimeric antigen receptor (CAR) T-cell immunotherapy targeting mesothelin (MSLN), a cell-surface antigen that is highly expressed in pleural cancers- malignant pleural mesothelioma (MPM) and metastatic lung and breast cancers. Methods: A single dose of CD28-costimulated MSLN CAR T cells with the I-caspase-9 safety gene was administered intrapleurally in patients with MSLN-expressing pleural tumors. Following a 3+3 design, patients were treated in dose escalating cohorts (dose range 3E5 to 1E7 CAR T cells/kg) following IV cyclophosphamide lymphodepletion (first 3 patients did not receive cyclophosphamide). A subset of MPM patients received subsequent anti-PD-1 therapy, off-protocol, which we have shown to prolong CAR T-cell functional persistence in preclinical models. Results: Twenty patients (18 MPM, 1 lung cancer, 1 breast cancer) were treated (prior lines of therapy 1–8, 35% received ≥3 lines of therapy). No CAR T-cell–related toxicities higher than grade 1 were observed. 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 EKG evaluation found no evidence of toxicity. Fourteen MPM patients received subsequent anti-PD1 therapy (1–21 cycles, pretreatment tumor PD-L1 < 10% in all patients except one), with 1 patient developing grade 3 pneumonitis that responded to steroid treatment. CAR T cells were detected in the peripheral blood of 13 of 14 patients (1-39 weeks). At data cut-off date (Jan 31, 2019), among 14 MPM patients that received combination therapy (follow-up 13-77 weeks, median 31 weeks), best responses included 2 patients with complete metabolic response on PET (62 and 39 weeks ongoing); 5 partial responses and 4 stable disease by investigator assessment. Conclusions: Intrapleurally administered MSLN-targeted CAR T cells were safe. Encouraging antitumor activity of MSLN-targeted CAR T-cell therapy was observed when combined with anti-PD1 therapy and shows promise for future development of this approach. Clinical trial information: NCT02414269.