Efficacy of Interferon in the Treatment of Mice with Established Friend Virus Leukemia

DBA/2 mice are 100% susceptible to Friend leukemia virus and begin to die 26 days after virus inoculation. Sendai virus (parainfluenza 1) inoculated intraperitoneally into leukemic mice 30 days after Friend virus prolonged survival by 12 days. Evidence that Sendai virus prolongs the life of leukemic mice through the action of interferon derives from the following observations: (a) Sendai virus induced large amounts of interferon; (b) Statolon (an extract from the mold Penicillium stoloniferum), when injected 28 days after Friend virus, also induced large amounts of interferon and prolonged survival by 11 days; and (c) interferon itself injected intraperitoneally daily for 10 days commencing 31 days after Friend virus prolonged survival by an average of 9 days. However, when interferon injections were continued daily until death of the mice, survival was no longer than in mice which received only 10 daily injections. This study represents a successful application of interferon as a therapeutic agent in an established virus-induced neoplastic disease. However, the development in mice of a state refractory to the leukemia-inhibiting effects of interferon after 10 days' administration indicates that interferon may not be effective in the long-term treatment of virus-induced leukemia.