Lack of natural killer cell activity in hairy cell leukemia patients and partial restoration with interleukin-2

Natural Killer (NK) cell activity was studied in ten hairy cell leukemia (HCL) patients by means of a 4-hour cytotoxicity assay using mononuclear cells isolated from either the spleen or peripheral blood. Identical assays were performed on individuals who were either normal or had nonmalignant hematologic disorders. HCL patients had a significant decrease in NK cell activity at all effector-to-target ratios compared with the control group. Effects of interleukin-2 (IL-2) on NK activity were studied in four patients. After a 3-day in vitro incubation with IL-2, there was a marked increase in NK activity of mononuclear cells obtained from each of these patients. On the basis of the results it can be hypothesized that susceptibility to infections, which are commonly encountered in HCL patients, may be due in part to a low level of NK activity. Based on the apparent augmentation of NK activity in vitro, it might be of interest to initiate a clinical trial with IL-2 in patients with HCL.