H-2K double transfectants of tumor cells as antimetastatic cellular vaccines in heterozygous recipients. Implications for the T cell repertoire.

In this study we demonstrate that antitumor CTL repertoire restricted to a single MHC class I allele is higher in homozygous than in heterozygous mice. Consequently, transfection of two parental H-2K genes, but not of a single H-2K gene into a highly metastatic H-2K-negative tumor clone, resulted in abrogation of metastatic properties in F1 recipients. Clones of the 3LL carcinoma, which are low H-2Kb expressors, are nonimmunogenic and highly metastatic. Transfection of H-2K genes converted cells of such clones to nonmetastatic in syngeneic homozygous mice. However, in semi-syngeneic heterozygous mice, single H-2K transfectants retained their metastatic phenotype. In such heterozygous mice, i.e., in (H-2d x H-2b)F1, or in (H-2k x H-2b)F1, transfection of the two parental H-2K genes was required for complete abolishment of the metastatic phenotypes. In fact, in these heterozygous animals, even the local growth (i.e., tumorigenicity) of the double H-2K transfectants was significantly suppressed. These observations are attributed to the difference between homozygous and heterozygous mice with regard to the T cell repertoire restricted to a single H-2K-tumor-associated antigen complex. The reduced tumorigenicity and the complete abrogation of the metastatic phenotype was a function of a high immunogenic competence of the double transfectants in F1 heterozygous mice, which was significantly higher than that of single transfectants, as measured by the induction of CTL and of their precursors. Immunization of F1 mice by inactivated double transfectants conferred protection against metastasis formation by a subsequent graft of the parental D122 cells. Single transfectants were only marginally effective in conferring such protection. Applying an immunotherapy protocol, we observed that a series of vaccinations with double transfectants of animals already carrying a parental tumor reduced significantly the generation of metastasis by the otherwise highly metastatic D122 cells.