Abstract
Tumor microenvironments include a number of fibrin clots due to the microbleeding caused by cancer cell invasion into blood vessels, which suggests the potential utility of a platelet vector for systemic cancer treatment. We previously reported that inactivated Sendai virus (hemagglutinating virus of Japan; HVJ) envelope (HVJ-E) activates anti-tumor immunity and induces cancer cell-selective apoptosis. The hemagglutination activity that blocks the systemic administration of HVJ-E was dramatically attenuated by incorporation into platelets. Platelets incorporating HVJ-E (PH complex) were then injected into the tail veins of B16F10 melanoma-bearing mice. The PH complex primarily accumulated in tumor tissues and caused the significant accumulation of various immune cells in the tumor bed. Injections of the PH complex to the melanoma-bearing mouse significantly reduced the tumor size, and the tumor growth was ultimately arrested. Secretion of the chemokine regulated upon activation normal T-expressed and presumably secreted (RANTES) was upregulated following PH stimulation. The RANTES-depletion in melanoma-bearing mice significantly attenuated the cytotoxic T lymphocyte activity and led to a dramatic abrogation of the mouse melanoma suppression induced by the PH complex. Thus, a platelet vector incorporating viral particles, a Trojan horse for cancer treatment, will provide a new approach for cancer therapy using oncolytic viruses.