Stimulatory effect of immunization on tumor induction by Moloney murine sarcoma virus

Adult mice were immunized with varying doses of inactivated Moloney murine leukemia virus (M-MuLV). Eight weeks after immunization, mice were challenged with a dose of Moloney murine sarcoma virus (M-MuSV) that could induce tumors in approximately 50% of normal animals. Mice immunized with high doses of M-MuLV (10(10) particles) had significantly decreased tumor incidences, whereas mice immunized with low doses of M-MuLV (10(2) particles) had significnatly increased tumor incidences compared to those in nonimmunized controls. The stimulatory effect could be abrogated by the irradiation of mice with 450 rads 24 hours prior to M-MuSV challenge, whereas the inhibitory effect was resistant to this irradiation procedure. The results suggested that immunization with virus can either stimulate or inhibit virus-induced tumorigenesis, depending on the dose of virus used for immunization.