An improved cytotoxic effect of tumor-specific T cells following PD-1 knockout was also reported in preclinical studies of other cancer models, such as in a cultured gastric cancer cell line,56 and in mice subcutaneously injected with either a fibrosarcoma cell line,58 a multiple myeloma (MM) cell line,59 or a liver cancer cell line.60 Here, PDCD1 is linked to neoplasm.