Natural killer cell activity in patients with multiple myeloma

The level of natural killer (NK) cell activity was studied in peripheral blood samples from 22 patients with multiple myeloma (13 males, nine females) and a group of age- and sex-matched controls. In a cytostatic assay against K-562 cells the patients showed significantly lower activity than controls (P less than 0.001 for an effector:target ratio = 30:1) and 11 of 22 patients did not reach 50% at this E:T compared with 1 of 18 controls. The percentage of lymphocytes binding to or killing K-562 cells, as judged by a single-cell assay, was not decreased in the patient group, which implies that the decreased cytostatic activity was caused by a functional defect rather than a decline in numbers. In vitro exposure to interferon produced significant (P less than 0.025) stimulation of cytostatic activity in samples from both groups of subjects, but on an individual basis 10 of 22 patients and 4 of 18 controls showed no significant response (P greater than 0.05). This study supports the findings of others of impaired NK cell function in hemopoietic malignancies, which may have implications for the pathophysiology of these disorders.