Soluble PD-1-based vaccine targeting MUC1 VNTR and survivin improves anti-tumor effect

Soluble PD-1 (sPD1) can bind with ligands PD-L1/PD-L2 on the surface of dendritic cells (DCs). Therefore, a sPD1 vaccine fused with an immunogen can increase T cell activation against cancer. Here, we constructed a MUC1 and survivin (MS) combination gene tumor vaccine expressing MS fused with soluble PD-1 (sPD1/MS). To investigate whether the sPD1/MS fusion vaccine could enhance tumor-specific immune responses, its immunogenicity and anti-tumor activity were examined after intramuscular immunization in mice. Compared with the MS DNA vaccine, the specific cytolysis rate of the sPD1/MS fusion DNA vaccine was increased from 21.64% to 34.77%. Moreover, the sPD1/MS vaccine increased the tumor suppression rate from 17.18% to 30.96% and prolonged survival from 6.96% to 19.44% in a murine colorectal cancer model. Combining the sPD1/MS vaccine with oxaliplatin improved the tumor suppression rate to 74.71% in the murine colorectal cancer model. The sPD1/MS vaccine could also exert a good anti-tumor effect, increasing the tumor infiltrated CD8⁺ T cells by 6.5-fold (from 0.10% to 0.65%) in the murine lung cancer model. In conclusion, the sPD1/MS vaccine showed good immunogenicity and anti-tumor effect by activating lymphocytes effectively.