Effect of a Rauscher leukemia virus vaccine upon chemical oncogenesis in the mouse.

The concept that type-C RNA viruses serve as determinants of chemically induced cancer would be supported if immunization against such viruses reduced the incidence of methylcholanthrene-induced sarcomas. A formalin vaccine was employed which was able to protect mice against the development of virus-induced Rauscher leukemia: 8/12 vaccinated mice survived versus 1/12 controls. When mice so immunized were challenged with near-threshold doses of chemical carcinogen, sarcoma incidence and death latency did not differ between vaccinated and control groups: within 10 months, a 320 mug dose of methylcholanthrene induced 100% sarcomas in both groups, while a 64 mug dose induced 62% and 65% tumors in vaccinated and control mice respectively. Thus, a relevant postulate of the oncogene hypothesis could not be supported by these studies. Formalin treatment neutralizes the oncogenic effect of mouse leukemia viruses yiwlding preparations that are immunogenic and can be successfully used as vaccines to protect against virus-induced leukemia (5). The finding of murine leukemia viruses in chemically induced tumors (1, 2) poses the question of whether these viruses are present in the tumors as passengers, or whether they are etiologically involved in the process of tumor induction. An approach to answering this question would be to challenge with chemical carcinogens mice which have been vaccinated with leukemia virus. If the virus were somehow involved in tumor induction, antiviral immunization might conceivably interfere with chemical carcinogenesis. Whitmire and Huebner (9) have reported that mice immunized with formalin-treated leukemia viruses, become resistant to sarcomagenesis by methylcholanthrene. Repetition of this experiment by Gericke and Chandra (6) gave non-significant differences between experimental and control groups. The present paper deals with the effect of immunization against Rauscher leukemia virus upon tumor induction by near-threshold doses of methylcholanthrene.