Expression of H-2 antigens and inducibility of antitumor immune responses in various tumor cell clones established from methylcholanthrene-induced fibrosarcomas.

A large number of fibrosarcoma cell lines was established in vitro from a tumor mass induced freshly by inoculating 3-methylcholanthrene (MCA) subcutaneously (sc) into C3H/HeN mice, and more than five clones were isolated from each cell line by the limiting dilution technique. The present study investigated a) qualitative and quantitative comparison of the immunogenicity [tumor-associated transplantation antigen (TATA) activity] of different tumor clones and b) the relationship between such immunogenicity and the expression of H-2 class I antigens. When TATA were compared between different clones from the same tumor, these TATA were revealed to be cross-reactive to each other. On the other hand, the comparison of TATA between clones from different tumors demonstrated the existence of individually unique TATA in these clones. In addition to qualitative heterogeneity of TATA from different tumors, the magnitude of immunogenicity was also heterogeneous in the individual clones established. Whether or not such quantitative heterogeneity of immunogenic strength was related to the expression of H-2 (class I) antigens was examined by flow microfluorometry studies using anti-H-2k antibodies. The results demonstrated that there was no correlation between TATA activity capable of inducing in vivo tumor resistance and the expression of H-2 antigens. This contrasted with parallelism between the expression of H-2 antigens and inducibility of cytotoxic T lymphocytes (CTL) or lysability of tumor cell clones by CTL. These results are discussed in the context of the cellular mechanism of tumor cell eradication in vivo and the regulation of cell surface H-2 expression in vitro and in vivo.