Administration of recombinant interferon γ to cancer patients enhances monocyte secretion of hydrogen peroxide

Recombinant interferon γ (rIFN-γ) activates macrophage antimicrobial and antitumor functions and related metabolic processes, including secretion of reactive oxygen intermediates in mice and in cultured mouse and human macrophages. To look for similar actions in man, we monitored the H₂O₂ secretory capacity of monocytes from cancer patients receiving intravenous rIFN-γ at 0.1, 0.5, or 1.0 mg/m² of body area over 6 hr daily or over 1 hr on alternate days. Monocytes taken just before the first infusion served as controls and were comparable to normal donor monocytes in secretion of H₂O₂. Monocytes from 11 of the 13 subjects (85%) studied through 20 treatment cycles responded to rIFN-γ with elevation in H₂O₂ secretion ≥67% of the tests conducted >1-hr after the start of treatment. Five of the five subjects tested had monocytes with diminished H₂O₂ secretory capacity when tested immediately after a 1-hr infusion of rIRN-γ, at which time the amount of adherent mononuclear cell protein recovered from the blood averaged only 24% of the control. At all other times tested (from 6 hr to 5 days after infusion) combined results for all subjects showed enhancement of H₂O₂ releasing capacity. Statistically significant mean increases ranged from 1.4- to 2.8-fold above the control and included the sets in which monocytes collected 24 hr following a single infusion were assayed the same day or the next. By the criterion of enhanced H₂O₂ secretory capacity, the ability of rIFN-γ to activate mononuclear phagocytes is manifest upon its administration to patients with advanced malignancy.