Intratumor injection of BCG Ag85A high-affinity peptides enhanced anti-tumor efficacy in PPD-positive melanoma.

As one of the scheduled immunization vaccines worldwide, virtually all individuals have been vaccinated with BCG vaccine. In order to verify the hypothesis that delivering BCG high-affinity peptides to tumor areas could activate the existing BCG memory T cells to attack tumor, we firstly predicted the HLA-A*0201 high-affinity peptides of BCG Ag85A protein (KLIANNTRV, GLPVEYLQV), and then, A375 melanoma cells and HLA-A*0201 PBMCs (from PPD-positive adults) were added to co-incubated with the predicted peptides in vitro. We found that the predicted BCG high-affinity peptides could be directly loaded onto the surface of tumor cells, enhancing the tumor-killing efficacy of PBMCs from PPD-positive volunteer. Then, we constructed PPD-positive mice model bearing B16F10 subcutaneous tumors and found that intratumor injection of BCG Ag85A high-affinity peptides (SGGANSPAL, YHPQQFVYAGAMSGLLD) enhanced the anti-tumor efficacy in PPD-positive melanoma mice. Along with the better anti-tumor efficacy, the expression of PDL1 on tumor cell surface was also increased, and stronger antitumor effects occurred when further combined with anti-PD1 antibody. For microenvironment analysis, the proportion of effector memory T cells was increased and the better treatment efficacy may be attributed to the elevated effector memory CD4 + T cells within the tumor. In conclusion, using the existing immune response of BCG vaccine by delivering high-affinity peptides of BCG to tumor area is a safe and promising therapy for cancer.