Immunization with placenta-specific 1 (plac1) induces potent anti-tumor responses and prolongs survival in a mouse model of melanoma.

PURPOSE: Melanoma is a malignant and metastatic form of skin cancer, which is not diagnosed in early stages of the disease. Nowadays, immunotherapy is changing the treatment landscape for metastatic melanoma. Placenta-specific1 (PLAC1) is a cancer-testis-placenta (CTP) antigen with differential expression in melanoma tissues. Here, we evaluated the potential of plac1 to induce anti-cancer immune responses as well as to prevent cancer development in a mouse model of melanoma.

METHODS

Two proteins containing full extracellular domain (ED) of mouse plac1+KDEL3 and full ED of mouse plac1+ tetanus toxin P2 and P30+ pan DR epitope (PADRE) ​+ ​KDEL3 were produced and injected in mice to evaluate their capacity to induce anti-cancer immune responses as well as their potential to prevent melanoma development. Induction of plac1-specific humoral and cellular responses as well as tumor-associated parameters were tested in a series of 36 mice.

RESULTS

Sera of mice immunized with ED ​+ ​P2P30+PADRE ​+ ​KDEL3 contained antibodies able to react with surface plac1 in B16F10 ​cells. Both proteins induced proliferative cellular immune responses against B16F10 ​cells and plac1-specific cytotoxic T cells (CTL) and CD107a ​+ ​CTL responses, which was higher in mice immunized with ED ​+ ​P2P30+PADRE ​+ ​KDEL3. Splenocytes of mice vaccinated with ED ​+ ​P2P30+PADRE ​+ ​KDEL3 exerted a significant cytotoxicity against B16F10 ​cells. Vaccination with ED ​+ ​P2P30+PADRE ​+ ​KDEL3 significantly delayed B16F10-induced tumor onset, reduced tumor growth, and increased survival. Tumors induced by B16F10 expressed plac1 in vivo.

CONCLUSION

Our results pave the way for development of effective melanoma preventive vaccine in humans, although further studies are needed.