Natural killer activity of pediatric patients with acute lymphoblastic leukemia in remission.

We examined the natural killer (NK) activity of pediatric patients with acute lymphoblastic leukemia (ALL) in remission by using several methods, including a newly established single cell assay. HNK-1 antigen-positive cells, which are now considered to assume NK activity, were not decreased in the patients, although the NK activity of the patients was found to be depressed. Neither monocyte depletion nor the addition of interferon-alpha improved the decreased NK activity of the patients. According to the results of the single cell assay, conjugate-forming cells (effector cells that form conjugates with target cells), lytic conjugate-forming cells (fractions of conjugate-forming cells that actually go on to kill target cells) and the recycling activity of NK cells were all decreased in the patients. Thus, it is apparent that there were defects in several steps of NK activity in the patients. The NK activity of 19 patients was further studied successively to investigate the correlation between NK activity and clinical course. The longest observation period was 38 months. Six bone marrow relapses of leukemia occurred, but the NK activity of these patients at the time of relapse or at the previous test was not necessarily depressed as compared to that of the other patients.