Augmentation of natural killer (NK) cell activity by a streptococcal preparation, OK-432, in patients with malignant tumors.

Recently, a streptococcal preparation, OK-432 has been used successfully as an immunopotentiator for immunotherapy in patients with malignant tumors in Japan. In this paper, we report that the administration of OK-432 augments the cytotoxic activity of peripheral blood lymphoid cells against a natural killer (NK) cell-sensitive erythroleukemic cell line, K562, in tumor patients. In patients before or after surgery, sufficient amounts of OK-432 strongly augmented the cytotoxic activity within 3 days after the initial administration of OK-432. Thereafter the levels of cytotoxicity declined rapidly. The administration of a lower dose of OK-432 gave a lower increase in cytotoxicity. Enhanced cytotoxicity occurred with the reintroduction of OK-432 but remained at lower levels of activity. Characterization and fractionation of OK-432-induced effector cells revealed that the augmented cytotoxicity seemed to be carried mainly by NK cells. A low titer of interferon was detected in 3 of 10 patients within 72 hr after the first inoculation of the agent. Furthermore, we discuss the potency of OK-432 for the induction of interferon in detail.