While treatment of anti-PD-1 antibody markedly retarded tumor progression (Fig. 5B, D) and significantly improved overall survival (Fig. 5E) in mice bearing B16F10/pLKO tumors, it did not affect both tumor progression (Fig. 5C, D) and overall survival (Fig. 5F) in mice bearing B16F10/shDRG2 tumors. Here, PDCD1 is linked to neoplasm.