Antitumor effect of oral cancer vaccine with Bifidobacterium delivering WT1 protein to gut immune system is superior to WT1 peptide vaccine

Despite the revolutionary progress of immune checkpoint inhibitors (CPIs) for cancer immunotherapy, CPIs are effective only in a subset of patients. Combining CPIs and cancer vaccines to achieve better clinical outcomes is a reasonable approach since CPI enhances cancer vaccine-induced tumor-associated antigen (TAA) specific CTL. Among the various TAAs so far identified, WT1 protein is one of the most promising TAAs as a cancer vaccine target. Until now clinical trials of WT1 vaccine have demonstrated only modest clinical efficacy. These WT1 vaccines were based on peptides or dendritic cells (DCs), and there was no oral cancer vaccine. Recently, we developed a WT1 oral cancer vaccine using a recombinant Bifidobacterium displaying WT1 protein, which can efficiently deliver WT1 protein to the gut immune system, and we demonstrated that this oral cancer vaccine had a significant anti-tumor effect in a C1498-WT1 murine leukemia syngeneic tumor model. The WT1 protein displayed in this vaccine consists of about 70% of the WT1 amino acid sequence including multiple known CD4 and CD8 T-cell epitopes of WT1. In this commentary, we introduce our recent data indicating the superior anti-tumor effect of a WT1 oral cancer vaccine delivering WT1 protein to the gut immune system compared to a peptide vaccine.