Monitoring of interferon therapy by assay of (2'--5') oligo-isoadenylate synthetase in human peripheral white blood cells.

With the increasing number of patients undergoing experimental interferon therapy, there is a need for a method for monitoring how the patients respond to the drug. Interferon induces in cells exposed to it the accumulation of several enzymes, among them the (2'-5') oligo-A synthetase. A simple method previously developed was used to measure this enzyme in extracts of a small number of peripheral white blood cells. In 60 healthy volunteers, the enzyme level in the mononuclear cell fraction was found to be relatively high and constant. Daily intramuscular injections of 1--2 x 10(6) units leukocyte type interferon (IFN-alpha) increased the enzyme level 7--8 fold in mononuclear cells and in granulocytes. The enzyme stayed high until IFN injections were stopped. Patients with defective response to IFN were identified. We propose that this method be used for continuous monitoring of the patient's response whenever interferon therapy is undertaken.