Immunogenicity and cross-protection among B16 melanoma variants with differing proclivities to metastasize

We report here the lack of any relationship between immunogenicity and the potential to metastasize among four B16 melanoma variants. Groups of C57BL/6J mice were immunized with one of four B16 variant lines (maintained by serial IM passage) that were shown in separate experiments to produce the following incidences of pulmonary metastases four to six weeks after isograft excision: M1, 10%-15%; M2 10%-20%; M3, 75%-80%; and M4, 75%-90%. After immunization, mice were challenged with one of the four variant lines in a crisscross fashion. Two challenge doses for each line were chosen on the basis of earlier experiments showing 100% and 50% challenge tumor take in nonimmunized animals. Despite earlier work published from this laboratory showing that splenocytes harvested from immunized mice could distinguish antigenic differences among the B16 variants, we could find no significant difference in immunogenicity or cross-protection among the lines regardless of their metastatic potential. We conclude that no correlation exists between the antigenic differences shown by in vitro splenocyte-mediated cytotoxicity assays among the B16 variants and in vivo immunogenicity or cross-protection experiments. Futhermore, the relationship (if any) between immunogenicity and the ability to metastasize among these B16 variants is not straightforward.