title: Immunogenic variants of a murine fibrosarcoma induced by mutagenesis: requirement of viable cells for antigen-specific cross-protection.
abstract: The purpose of the study was to investigate the immunological and biological consequences of neoantigen expression by immunogenic tumor variants (Imm+) following in vitro treatment with the mutagen 1-methyl-3-nitro-1-nitrosoguanidine. The weakly immunogenic murine fibrosarcoma MCA-F was used because we have previously characterized the tumor-specific transplantation antigen expressed by this tumor. Immunogenic variant clones were obtained at high frequency following four treatments with 1-methyl-3-nitro-1-nitrosoguanidine. The immunogenicity of the Imm+ clones was confirmed by their progressive growth in immunosuppressed C3H/HeN mice and their lack of growth in normal syngeneic (C3H/HeN mice. The immune response engendered in immunocompetent mice after a single immunization with viable Imm+ cells was tumor specific, completely protecting hosts against challenge with 10,000-fold the minimum tumorigenic dose of parental MCA-F cells, but not against 10 minimum tumorigenic doses of the non-cross-reactive tumor MCA-D. The strong cross-protection elicited by Imm+ neoantigens against the parental tumor-specific transplantation antigen was not observed when soluble extracts or isolated plasma membranes of Imm+ cells were used for immunization. Immunogenic variant cells inactivated using either mitomycin C or gamma-irradiation also demonstrated a significantly diminished immunoprotective activity against challenge with the parent tumor. However, inactivated Imm+ cells and their isolated plasma membranes still expressed sufficient neoantigen to completely protect mice against homotypic Imm+, but not parental challenge. These results suggest that (a) the MCA-F Imm+ variants express neoantigens capable of engendering a strong specific as well as cross-protective immunity against challenge with either the parent or the variant and (b) the associative recognition of neoantigen and TSTA that results in strong cross-protection against challenge with the parent tumor requires immunization with viable Imm+ cells for full expression of the immunogenic phenotype.
mesh_terms: D000818:Animals; D000951:Antigens, Neoplasm / Q000276:immunology*; D002470:Cell Survival; D005260:Female; D005354:Fibrosarcoma / Q000276:immunology*; D006649:Histocompatibility Antigens / Q000276:immunology*; D007114:Immunization; D008769:Methylnitronitrosoguanidine; D051379:Mice; D008809:Mice, Inbred C3H; D008937:Mitomycins / Q000494:pharmacology; D009154:Mutation; D014612:Vaccines / Q000276:immunology
chemical_list: D000951:Antigens, Neoplasm; D006649:Histocompatibility Antigens; D008937:Mitomycins; D014612:Vaccines; C029237:tumor-associated transplantation antigen; D008769:Methylnitronitrosoguanidine