Natural killer (NK) activity in children with acute lymphoblastic leukemia.

The natural killer (NK) activity against K 562 target cells was explored in 20 children with acute lymphoblastic leukemia (ALL). Three of 5 patients examined at the time of diagnosis had normal NK activity. Two patients, who had more than 80% circulating blasts had significantly low NK activity. The level of NK activity of these 5 patients was inversely proportional to the percentage of blast cells contaminating the effector cell populations. After initiating induction chemotherapy, the NK activity decreased in spite of disappearance of circulating blasts. After complete remission, their NK activity returned to normal levels, and was rather higher than that of onset of the disease. NK activity of 15 children with ALL remaining in continuous complete remission was as high as that of healthy children and healthy adults in spite of intensive maintenance chemotherapy for 1/2 to 4 years. This was thought to be due to intermittent dose-schedule of the maintenance chemotherapy. 127