[Induction of activated natural killer cells by the streptococcal preparation OK432 (I). Induction from spleen cells of normal or tumor-bearing mouse primed in vivo and subsequently challenged in vitro with OK432].

The present study shows that natural killer cell-mediated cytotoxicity of BALB/c mouse spleen cells to syngeneic tumor cells was augmented by in vivo priming or in vitro stimulation with the streptococcal preparation OK432. The augmentation of spleen cell cytotoxicity to syngeneic tumor cells by in vivo priming alone with OK432 was lower than that obtained by in vitro stimulation alone with OK432. When the murine spleen cells primed in vivo with OK432 were rechallenged in vitro with OK432 at various intervals, the natural cytotoxicity was more strongly enhanced than that seen with in vitro stimulation alone. The cell surface phenotype of killer cells activated with OK432 was Thy1+ and asialo GM1+, suggesting the activated natural killer cell. Mice were transplanted with syngeneic colon adenocarcinoma cells, and primed in vivo with OK432, and then their spleen cells were subsequently challenged in vitro with OK432. These cells displayed a strong cytotoxic activity not only to the transplanted adenocarcinoma cells but also to other syngeneic tumor cells.