Specific simian virus 40 (SV40)-induced immunity against transplantable SV40 tumor in Syrian hamsters: abrogation by BCG vaccination.

Syrian hamsters were immunized with simian virus 40 (SV40) and/or BCG (in different time and sequence combinations) and were subsequently challenged with SV40-induced transplantable tumor cells. Immunization of hamsters with some but not all BCG preparations alone induced high levels of resistance to SV40 transplantable tumor cells. The immunization with SV40 of hamsters preliminarily inoculated with BCG induced antitumor immunity, the level of which was equal to resistance induced by immunization of normal animals with SV40. No cumulative effects of BCG and SV40 immunizations were noticed in any of our experiments even when BCG prepartions alone induced considerable increase of antitumor resistance. Inoculation of animals with the mixture of SV40 and BCG was generally less effective than that with SV40 alone. Inoculation of BCG preparations into hamsters preimmunized with SV40 resulted in the complete or partial abrogation of the resistance induced by SV40. All preparations of BCG, independent from their antitumor activity per se, decreased the resistance induced by SV40. The effect of this BCG-induced abrogation of resistance was observed in animals immunized with SV40 7-427 days before inoculation of BCG. The effect was not short-term, as it was still observed 3 months after BCG inoculation.