In the present study, we explored the feasibility of a novel cancer immunotherapy with a WT1 oral cancer vaccine as a combination therapy with following anti-PD-1 antibody and as a monotherapy for anti-PD-1 antibody-poorly responsive tumor and elucidated the immunological mechanism of action of this oral cancer vaccine using a mouse bladder cancer syngeneic tumor model. The gene discussed is PDCD1; the disease is cancer.