Depression of natural killer cytotoxicity after in vivo administration of recombinant leukocyte interferon.

One hundred thirty-four patients with a variety of malignancies were treated in two phase I clinical trials of recombinant leukocyte A interferon (IFL-rA) produced by recombinant DNA methodology. IFL-rA was given by intra-muscular injection either twice daily or three times weekly for 28 days. Extensive monitoring of natural killer (NK) cell cytotoxicity was done on these patients with rigorously standardized assays and determination of the inherent variability of NK function for each individual. Interferon, as used in these two treatment regimens, failed to produce an appreciable increase in NK activity; in the majority of patients, there was no significant change in NK activity from the pretreatment baseline levels. An unexpected finding was the depression of NK activity in 30% of the patients. The data have been analyzed in terms of their possible relationship to dose and schedules of IFL-rA administration and to antitumor response.