Because tumor-specific features of MCPyV+ MCC may differ from this model and given historical limitations in mouse-human translation of immunotherapies, we focused further validation efforts on demonstrating proof-of-principle efficacy in MCC patient samples, including antigen-specific expansion, activation, and proliferation; IFN-γ secretion; and HLA-matched tumor cell killing. This evidence concerns the gene IFNG and Merkel cell skin cancer.