Enhancement of tumor cell susceptibility to lymphokine-activated killer cells by treatment with the streptococcal preparation OK432

We investigated whether tumor cell lysis by LAK cells was augmented by treatment with OK432in vitro. NK and LAK activity against K562 cells was not enhanced by their treatment with OK432. In contrast, the susceptibility of OK432-treated Daudi and KATO-III cells to lysis by LAK cells was enhanced. Succinate dehydrogenase activity and RNA synthesis were impaired in Daudi and KATO-III cells by treatment with OK432, and moreover the expression of HLA Class I antigen and ₂-microglobulin was inhibited in OK432-treated KATO-III cells. Thus, it is suggested that the enhancement of the susceptibility of OK432-treated tumor cells with regard to succinate dehydrogenase activity, RNA synthesis, and HLA Class I antigen expression.