Density of GM3 with Normal Primary Structure Determines Mouse Melanoma Antigenicity; a New Concept of Tumor Antigen

We attempted to induce anti‐melanoma cytotoxic T cells (CTL) and suppressor T cells (Ts) inhibiting CTL generation by using liposomes carrying various densities of GM3 as tumor antigens. We found that liposomes carrying 6–16 mol% of GM3 with normal primary structure successfully generated anti‐melanoma CTL and suppressor T cells, while liposomes with GM3 outside this range had little or no such activity. Anti‐melanoma CTL induced by GM3(NeuGc)‐liposomes belonged to CD4 ‐ /CD8 ‐ double‐negative CD3 + CTL while GM3(NeuAc)‐liposomes induced two types of T cells, CD4 + T cells and double‐negative I‐J positive T cells which mediated inhibition of the induction of anti‐melanoma CTL responses. These cell types were tbe same as those induced by mitomycin C‐treated melanoma cells for CTL induction and soluble melanoma antigen for Ts generation. The results clearly demonstrate that even GM3 with normal primary structure can, at a certain density, generate melanoma antlgenicity.