Intracutaneous genetic immunization with autologous melanoma-associated antigen Pmel17/gp100 induces T cell-mediated tumor protection in vivo

Using the differentiation antigen Pmel17/gp100 to genetically immunize C57B L/6 mice (H-2(b)), we and others noticed that only mice that had received t he human homolog but not animals injected with the murine counterpart were protected against the growth of syngeneic B16 melanoma cells. The goal of t his study was to determine whether the state of nonresponsiveness to the au toantigen Pmel17/gp100 can be broken by immunization with a plasmid DNA con struct encoding the autologous form of the molecule. A construct containing the murine form of Pmel17 was administered intradermally to DBA/2 mice (H- 2(d)), which were then investigated for the presence of Pmel17/gp100-specif ic immunity. We show that administration of plasmid DNA coding for the auto logous melanoma-associated antigen Pmel17/ gp100 protects DBA/2 mice agains t the growth of Pmel17-positive M3 melanoma cells but not against Pmel17-ne gative M3 melanoma cells or unrelated P815 mastocytoma cells. Cell depletio n experiments demonstrated that this protective effect is mediated by T lym phocytes. The notion that Pmel17/gp100 represents the biologically relevant target in this system was supported by the obsewations (i) that recipients of Pmel17/gp100 DNA mount an antigen-specific cytotoxic T lymphocyte respo nse and (ii) that M3 tumors growing in mice immunized with autologous Pmel1 7/gp100 had lost expression of this melanoma-associated antigen whereas M3 melanomas appearing in control-vector-treated animals were still Pmel17/gp1 00-positive. These results indicate that intracutaneous genetic immunizatio n with autologous melanoma-associated antigen Pmel17/gp100 encoding plasmid DNA can lead to protection against melanoma cells as a result of the induc tion of a melanoma-associated antigen-specific and protective T-cell-mediat ed immune response.