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New therapeutic options for patients with ovarian cancer are urgently needed. Therefore, we evaluated the efficacy of two second-generation mesothelin (MSLN)-directed CAR T cells in orthotopic mouse models of ovarian cancer. Treatment with CAR T cells expressing an MSLN CAR construct including the CD28 domain (M28z) significantly prolonged survival, but no persistent tumor control was observed. Despite lower response rates, MSLN-4-1BB (MBBz) CAR T cells induced long-term remission in some SKOV3-bearing mice. Tumor-infiltrating M28z and MBBz CAR T cells upregulated PD-1 and LAG3 in an antigendependent manner while MSLN þ tumor cells expressed the corresponding ligands (PD-L1 and HLA-DR), demonstrating that coin-hibitory pathways impede CAR T-cell persistence in the ovarian tumor microenvironment. Furthermore, profiling plasma soluble factors identified a cluster of M28z-and MBBz-treated mice characterized by elevated T-cell secreted factors that had increased survival, higher CD8 þ T-cell tumor infiltration, less exhausted CAR T-cell phenotypes, and increased HLA-DR expression by tumor cells. Altogether, our study demonstrates the therapeutic potential of MSLN-CAR T cells to treat ovarian cancer.Significance: These findings demonstrate that MSLN-directed CAR T cells can provide antitumor immunity against ovarian cancer.

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