Modulation of Natural Killer Cell-mediated Cytotoxicity by Partially Purified and Cloned Interferon-α¹ Free

We have studied peripheral blood of 35 normal individuals, 28 solid-cancer patients, and 14 leukemic patients for natural killer (NK) cell cytotoxicity to K-562 and CEM tumor cells in a ⁵¹Cr release cytotoxicity assay. We have found that both normal individuals and solid-cancer patients could be grouped into high (NK-HR), medium (NK-MR), and low (NK-LR) NK cell responder categories with regard to their degree of NK cell activities. However, in general, NK-HRs were found to be prevalent in normal donor population and NK-LRs in cancer patients. Leukemic patients always exhibited the NK-LR status. The difference between NK-HRs and NK-MRs appeared to be due to the relative decrease in number of active NK cells. In contrast, the NK-LR status could not be contributed to decrease of NK cells because of the dichotomy in NK cell doseresponse patterns of NK-LRs versus those of NK-HRs and NK-MRs. Eighteen cancer patients undergoing interferon-α (IFN-α) therapy (3 × 10⁶ units, i.m., daily) were also tested for NK cell activities after single or multiple IFN-α injections. There was a highly significant and consistent increase in NK cell cytotoxicity of patients with the NK-LR and NK-MR phenotypes following one injection of IFN-α. In contrast to the NK-LR and NK-MR group of patients, most patients displaying the NK-HR phenotype failed to show any NK cell augmentation following any number of IFN-α injections (up to 119).

We have also tested NK cell activities of cancer patients undergoing treatment with low (3 × 10⁶ units) and high (36 × 10⁶ and 50 × 10⁶ units) doses of clone A of recombinant IFN-α (IFN-αrA). In these studies, all patients receiving the lower dose of IFN-αrA and three of five patients receiving the higher doses of IFN-αrA displayed augmented NK cell activity 24 hr after a single i.m. injection. Analysis of patients receiving the low dose of IFN-αrA in a single-cell assay suggested that this agent did not modulate tumor-NK cell-binding properties but augmented significantly NK cell cytotoxicity and killing of already-bound tumor targets.