Abstract
Immune checkpoint inhibitors have emerged as a frontline treatment of a variety of malignancies. However, only a subset of patients respond to these therapies, and many initial responders eventually develop resistance, leading to tumor relapse. Programmed death protein 1 is one of the checkpoint inhibitors that is expressed on activated T cells and suppresses the antitumor immune response when binding to its ligand, programmed death ligand 1, on tumor cells. Previous studies indicated that loss-of-function mutations in the IFN-γ pathway could result in acquired resistance to immune checkpoint inhibitors in human patients with cancer. Here, we investigated the effects of the IFN-γ receptor downexpression on the response to an anti-PD-1 antibody (αPD1) in a murine colorectal cancer model and the underlying mechanisms of resistance. IFN-γ receptor (IFNGR) 1 was knocked down in MC38 cells, a murine colon adenocarcinoma cell line using IFNGR1 short hairpin RNA (shRNA) lentiviral particles. Then, MC38 IFNGR1 knockdown (KD) cells and negative control (SC) cells were used in this study. In the C57BL/6 xenograft model, the KD tumor demonstrated resistance to αPD1 in comparison with SC cells. The observed treatment resistance might be associated with reduced tumor-infiltrating immune cells (TILs). When mixed, the resistant (KD) and control cells (SC) grew in spatially separated tumor areas, and αPD1 did not impact this pattern of spatial distribution. Our findings have proved that downregulation of the IFNGR1 endowed resistance to αPD1 and provided the potential mechanisms involving the TILs. SIGNIFICANCE STATEMENT: Immunological checkpoint blockades have achieved substantial efficacy in a variety of tumors. However, only a subset of patients respond to these therapies, and innate and acquired resistance is widely present. Our study found that the downregulation of the IFN-γ receptor caused resistance to an anti-PD-1 antibody in a murine colorectal cancer model associated with the reduced tumor-infiltrating lymphocytes. Our findings have substantial implications for improving the efficacy of checkpoint blockades.