Antitumor activities of chimeric antigen receptor t cells targeting mucin-1 with self-secreting anti PD-1 IgG antibody

Abstract

Chimeric antigen receptor (CAR) T cells have achieved notable success in treating hematological malignancies and are now being extensively studied as a strategy to overcome tumor immunosuppressive microenvironment in solid tumors. Mucin-1 (MUC1) is overexpressed in various solid tumors. CAR T cells targeting MUC1 have demonstrated promising therapeutic potential for solid tumors. However, CAR T cell therapy for solid tumors is challenged by the immunosuppressive tumor microenvironment, particularly the overexpression of programmed death-ligand 1 (PD-L1), which contributes to T cell exhaustion and dysfunction. The combination of anti PD-1 therapy with CAR T cells may enhance therapeutic outcomes in solid tumors. We engineered MUC1-targeting CAR T cells that secrete an anti PD-1 IgG derived from nivolumab (MUC1.PD1). We assessed anti-tumor activity, T cell proliferation, and the expression of exhaustion markers following a repeated antigen stimulation assay. Additionally, the anti-tumor efficacy of these CAR T cells was evaluated in a cholangiocarcinoma xenograft mouse model. CAR expression in MUC1.PD1 CAR T cells was 63.7% ± 3.96%, which was lower than that of conventional MUC1 CAR T cells (82.8% ± 3.68%). Cell subset analysis revealed a higher proportion of CD8+ T cells compared to CD4+ T cells. Cytolytic activity was assessed using 293T cells and MUC1+/PD-L1+ cholangiocarcinoma cell lines (HuCCT-1 and KKU-213). Both CAR T cell types exhibited dose-dependent cytotoxic activity against HuCCT-1 and KKU-213 but not against 293T cells, demonstrating antigen specificity. Their cytolytic activities were comparable. In a repeated antigen stimulation assay, MUC1.PD1 CAR T cells displayed greater proliferation and lower PD-1 expression. Furthermore, MUC1.PD1 CAR T cells significantly reduced tumor growth in the HuCCT-1 xenograft model. The engineering of CAR T cells to secrete an anti PD-1 antibody enhances therapeutic efficacy compared to second-generation CAR T cells. This improvement is partly attributed to enhanced T cell proliferation and reduced PD-1 expression following repeated antigen stimulation. These findings suggest that this approach may offer a promising strategy to improve CAR T cell therapy for solid tumors.