[Induction of LAK cells in peritoneal cavity of mice after ip injection of OK-432 and antitumor effect of these LAK cells].

More than 50% of BALB/c mice bearing BAMC-1 ascites tumor were completely cured after five consecutive (once every two days) ip injections of a 0.1 mg dose of OK-432, starting on day 2 of tumor implant. The antitumor effect of OK-432 was not abolished by prior anti-asialo GM1 serum treatment, which apparently caused the disappearance of NK cells. However in athymic nude mice or in antithymocyte globulin treated euthymic BALB/c mice, the same treatment increased the mice's length of survival, but they didn't recover from the tumor-death. Peritoneal exudate cells (PEC) obtained on day 12 from OK-432 treated BAMC-1 bearing mice were tested for cytotoxicity in vitro against fresh BAMC-1 tumor cells, NK-resistant allogeneic tumor cells (EL4, P815 and B16) and NK-sensitive allogenic YAC-1 cells. These PEC were found to be capable of lysing syngeneic BAMC-1 tumor cells together with the other tumor cells, and the effect was abolished when PEC received anti-Thy 1 treatment. These results indicate that T-cells play a determinative role in the immunotherapeutic effect of OK-432. The cells responsible for killing BAMC-1 and other tumor cells appeared between day 8-12 in the peritoneal exudate and were characterized as a kind of lymphokine activated killer (LAK) cell.