Safety and efficacy of chimeric antigen receptor T cells modified to target mesothelin and express PD-1 antibodies in patients with relapsed/refractory solid cancers in a phase I trial.

3039 Background: The limitations of chimeric antigen receptor T cells (CAR-T) in solid tumors are immunosuppressive tumor microenvironment and difficult infiltration to tumor. In order to reduce on-target off-tumor toxicities and circumvent the immune-suppressive tumor microenvironment(TME), we modified autologous CAR-T to be specific for mesothelin (MSLN) on cancer cells and secrete PD-1 antibodies (aPD1-MSLN-CAR T cells). Here, we report the safety and efficacy of aPD1-MSLN-CAR T cells in 10 patients with relapsed/refractory solid cancers in this single-arm, open-label, first-in-human phase I pilot study (ClinicalTrial.gov: NCT03615313). Methods: aPD1-MSLN-CAR T cells were prepared from peripheral blood mononuclear cells and engineered using PiggyBac Transposon System to target MSLN and secrete PD-1 antibodies. 10 patients with mesothelin positive relapsed/refractory solid cancers after failure to standard therapies were treated with aPD1-MSLN-CAR T cells for two or more cycles until disease progression or intolerable toxicity. The dose escalation of CAR T cells was designed to be 5×10 6 /kg, 5×10 7 /kg, and 1×10 8 /kg, respectively. Adverse events were evaluated according to CTCAE-V4.03 and clinical response was assessed by RECIST 1.1. CAR expression was analyzed using quantitative real-time polymerase chain reaction. PD-1 antibodies were detected by ELISA. Serum IL-2, IL-4, IL-6, IL-10, IFN-γ and TNF-α were measured using flow cytometry. Results: The most common adverse events were mild fatigue and fever. Abdominal pain was also observed in 1 patient. Grade 1 and 2 cytokine release syndromes were observed without neurologic symptoms in 10 patients. After aPD1-MSLN-mRNA-CAR T cells treatment, 2 patients (20%) achieved partial response (PR), 4 (40%) remained stable (SD), and the rest 4 (40%) patients developed disease progression (PD). The median PFS was 97 days [95% CI (13, 180)] estimated by Kaplan-Meier method. Conclusions: These findings lend support that the combination of modified CAR T cells targeting MSLN with PD1 inhibition for solid tumors is safe. Modified CAR-T cells expressing PD-1 antibodies maybe an option to improve CAR-T efficacy as a result of refined TME. Clinical trial information: NCT03615313 . [Table: see text]