The stimulating effect of complete Freund's adjuvant on tumour induction by polyoma virus in mice and By Rous sarcoma virus in rats

Complete Freund's adjuvant was shown to greatly stimulate viral oncogenesis both in the case of polyoma virus in mice and in the case of Rous sarcoma virus in rats. Tumours appeared in 74% of CC57BR/Mv mice infected when newborn with polyoma virus — adjuvant emulsion, whereas control mice injected with virus alone failed to develop tumours. Rous virus (Carr‐Zilber strain) and adjuvant when administered together as emulsions to Wistar rats (newborn or sucklings as well as 2.5‐month‐old animals) resulted in a 100% tumour incidence. In control animals treated with the virus alone when 0–4 days old, tumour incidence was no more than 30–40%; no tumours appeared in control animals which received virus alone when they were more than 2 weeks old. A significant stimulating effect of Freund's adjuvant was also revealed when the virus was inoculated into 4‐ to 15‐day‐old rats which received adjuvants as neonates. Thirty per cent of rats given virus — adjuvant emulsion produced measurable quantities of complement‐fixing antibodies to soluble antigens of Rous sarcoma, while in animals given virus alone such antibodies were not demonstrable. It is suggested that the stimulating action of complete Freund's adjuvant on polyoma and Rous oncogenesis is based upon a mechanism similar to the classical “enhancement phenomenon”.