PROJECT ABSTRACT The success of chimeric antigen receptor (CAR) T-cell therapy in solid tumors requires antigen targets with no on-target, off-tumor toxicity, effective tumor infiltration, cytotoxicity and proliferation in an immunosuppressive environment, and revival of antigen stress-induced exhausted CAR T cells. We translated CD28-costimulated CARs (M28z) that target mesothelin (MSLN), a cancer-associated antigen that we have documented expression in majority of solid tumors; 64 patients have been treated to date, with no on-target, off-tumor toxicity. Having demonstrated that regionally administered CAR T cells avoid pulmonary sequestration and benefit from early antigen-activated CD4 helper CAR T-cell function, we delivered CAR T cells intrapleurally in patients with malignant pleural mesothelioma (MPM), promoting tumor infiltration. To address T-cell exhaustion, we either treated patients with anti-PD1 agent after CAR T cells or employed tumor-specific checkpoint blockade by CAR T-cell intrinsic PD1 dominant negative receptor (PD1DNR); 34 patients have been treated to date, with no CAR- or PD1DNR-related toxicities and with responses by imaging, and increased survival. To promote IFNγ-mediated cytotoxicity shown to be essential for solid tumor killing, we exploited a c-KIT mutation, D816V (KITv), as a costimulatory domain. KITv CAR T cells show antigen- activation induced IFNγ signaling, enhanced cytotoxicity, and when added as signal 3 to CD28 (signal 2), provide a synergistic function, resist TGFβ-mediated suppression, and prolong functional persistence. Clinically available kinase inhibitors provide an on/off, tunable safety switch for KITv CAR T cells. To effectively deliver these next-generation CAR T cells to solid tumors, we developed a translational strategy of non- ablative, tumor-targeted radiation therapy (RT) to generate a chemokine gradient that facilitates systemically administered CAR T-cell chemotaxis, tumor infiltration, proliferation, and pe