Improved survival of chimeric antigen receptor-engineered T (CAR-T) and tumor-specific T cells caused by anti-programmed cell death protein 1 single-chain variable fragment-producing CAR-T cells

Chimeric antigen receptor-engineered T (CAR-T)-cell therapy holds significant promise for the treatment of hematological malignancies, especially for B-cell leukemia and lymphoma. However, its efficacy against non-hematological malignancies has been limited as a result of several biological problems characteristic of the tumor microenvironment of solid tumors. One of the main hurdles is the heterogeneous nature of tumor-associated antigens (TAA) expressed in solid tumors. Another hurdle is the inefficient activation and limited persistence of CAR-T cells, mainly as a result of T-cell exhaustion caused by immunosuppressive factors in the tumor microenvironment. In the present study, to address these problems, we engineered CAR-T cells to produce antagonistic anti-programmed cell death protein 1 (PD-1) single-chain variable fragment (scFv), by which PD-1-dependent inhibitory signals in CAR-T cells and adjacent tumor-specific non-CAR-T cells are attenuated. In mouse solid tumor models, PD-1 scFv-producing CAR-T cells induced potent therapeutic effects superior to those of conventional CAR-T cells, along with a significant reduction of apoptotic cell death not only in CAR-T cells themselves but also in TAA-specific T cells in the tumor tissue. In addition, the treatment with anti-PD-1 scFv-producing CAR-T cells resulted in an increased concentration of PD-1 scFv in tumor tissue but not in sera, suggesting an induction of less severe systemic immune-related adverse events. Hence, the present study developed anti-PD-1 scFv-producing CAR-T cell technology and explored its cellular mechanisms underlying potent antitumor efficacy.