A novel immunotherapeutic approach to melanoma-bearing hosts with protein-transduction domain-containing immunogenic foreign antigens.

Background: Active immunotherapy is accomplished by two critical factors; (1) induction of strong antigen-specific immune responses, and (2) abundant expression of antigen-epitopes on target cells. Previously, we have shown that the nona-arginine protein-transduction domain (R9-PTD) induced efficient protein-antigen transduction to a variety of cell types in vitro and in vivo. We have also demonstrated that intradermal (i.d.) injections of R9-PTD-containing immunogenic foreign antigens (rR9-OVA) induced dual immunological effects: the induction of OVA-specific Tc1- and Th1-dominant immune responses, and the induction of CTL-mediated immune responses at the injection area by expressing OVA-epitopes.

Objective And Methods: We investigated and compared the antitumor effects by intratumoral (i.t.) injections of rR9-containing natural tumor-associated autoantigen (TAA) and other rR9-containing proteins, including rR9-OVA, into B16 melanoma.

Results: Our results clearly demonstrate that multiple i.t. injections of rR9-OVA, but not rR9-containing TAA, elicited strong antitumor effects in B16-bearing mice, and resulted in complete tumor regression in some (50%) animals. These antitumor effects were abrogated by depletion of CD8(+) T cells, and SIINFEKL-specific CTL lysed rR9-OVA-treated B16 cells in vitro. I.t. injections with rR9-OVA altered the proportion of CD4(+) T cell subsets in B16-bearing mice. Interestingly, B16-tumor growth at the untreated site was also reduced following multiple injections of rR9-OVA at the other B16 tumor site. Finally, we confirmed that mice that had rejected B16 tumors by i.t. injections of rR9-OVA subsequently acquired CTL activities to Trp2-epitope/B16 cells.

Conclusion: Multiple i.t. injections of rR9-PTD-containing immunogenic foreign Ags elicit strong antitumor effects, and thereby may provide important clinical benefits to melanoma patients.