Tumor cell membrane-bound heat shock protein 70 elicits antitumor immunity

A novel membrane-bound heat shock protein 70 (mbHSP70) was expressed on the surface of the mouse mastocytoma cell line P815 to enhance immunogenicity of tumor cells. The in vivo effect of mbHSP70 was evaluated by comparing the growth of mbHSP70 cells to that of mock-transfected cells in DBA/2 mice. Fifty percent mice rejected mbHSP70 cells while 100% mice developed tumors in the counterparts. We then tested whether vaccination with these cells would elicit a protective antitumor response by injecting mice with either inactivated mbHSP70 cells or mock-transfected cells and challenging them with wild-type P815 cells. MbHSP70 cells-treated mice grew small tumors that soon disappeared in all animals. In contrast, 60% of animals receiving the mock-transfected cells vaccine grew large tumors and died. Lymphocytes from mbHSP70-vaccinated mice were able to kill wild-type P815 cells, suggesting that the antitumor response involved CTL. However, the activity of NK from mbHSP70 and mock-transfected cells vaccinated mice also increased. It implied that the non-specific immunity was also involved in tumor rejection. These findings indicate that the tumor cell membrane-bound HSP70 can be used as cancer vaccine to elicit protective antitumor immunity.