Prevention of vaccinia lesions in Rhesus monkeys by human leucocyte and fibroblast interferon.

The prophylactic antiviral activity of systemically administered human interferon preparations was tested in 36 rhesus monkeys against vaccinia virus injected into the skin. All nine control monkeys developed typical vaccinia skin lesions. Eight of nine monkeys treated with daily intramuscular injections of leucocyte interferon (5 x 10(5) units/kg) from day -1 to day +7 after vaccination were completely protected. No lesions developed after discontinuation of therapy. Administration of the same amounts of leucocytic interferon intravenously (i.v.) was equally effective. Daily intramuscular (i.m.) injections of lower doses of leucocyte interferon (1.25 c 10(5) units/kg; 0.5 x 10(5) units/kg) decreased the severity of the skin lesions. Lesion scores correlated inversely with the dose of interferon. Four of six animals receiving daily i.m. injections of fibroblast interferon (5 x 10(5) units/kg) and one of three animals treated i.v. with the same dose were protected against vaccinia virus, and the lesions in the other monkeys were smaller. Intramuscular injections of 5 x 10(5) units/kg of fibroblast interferon or 1.25 x 10(5) units/kg of leucocyte interferon resulted in comparable serum levels and had comparable efficacy in reducing lesion scores.