Relationship between tumor formation and cell-mediated immunity in hamsters with transplanted HVJ (Sendai virus)-carrying tumor cells.

Using macrophage migration inhibition (MMI) and the cell-mediated cytotoxicity (CMC) test, the cell-mediated immune response in hamsters with transplanted HVJ-carrying tumor cells (THEL-HVJ or THEL-HVJpits) was examined in relation to the lowered transplantability of the cells. The cells cultured at a temperature (34 degrees) permissive for HVJpits (temperature-sensitive HVJ) showed significantly lowered transplantability in hamsters. After shifting the cell culture temperature up to 39 degrees (non-permissive for HVJpits) for 5 days, THEL-HVJpits cells which had lost their cellular HVJ antigens regained the same high transplantability observed in parent THEl cells. However, culture of the cells at 37 degrees (partially permissive) for 24 hr did not significantly affect their tumor-forming ability with lowered transplantability, in spite of a considerable reduction in cellular HVJ antigens. The MMI test on hamsters with transplanted THEL-HVJ or THEL-HVJpits cells cultured at 34 degrees (MMI/THEL-HVJ 24 or MMI/THEL-HVJpits 34) was more markedly positive, and for a longer period (1 to 4 weeks), than the same test on hamsters inoculated with THEL cells. However, the MMI/THEL-HVJpits 39 cells acquired lowered reactivity like those from THEL-tumor bearing animals, while MMI/THEL-HVJpits 37 cells were still positive, just as in MMI/THEL-HVJpits 34. In the CMC test, much more cytotoxic activity was observed in spleen cells from hamsters with transplanted THEL-HVJpits cells than in those from THEL-transplaned animals; there was a general correspondence with the results obtained in the above MMI test. These findings strongly indicate that the lowered transplantability of HVJ-carrying tumor cells may be due to a significant induction of cell-mediated immune responses. It is suggested that cell membrane antigens modified (xenogenized) by the complete or partial expression of HVJ genomes carried may play an important part in this induction in vivo.