In Vitro Detection of Immune Responses to MTV-Induced Mammary Tumors: Activity of Spleen Cell Preparations from Both MTV-Free and MTV-Infected Mice

BALB/cfC3H mice, neonatally infected with mammary tumor virus (MTV), can respond immunologically to MTV-associated antigens on tumor cells: spleen cells from both normal adult females and females which have developed MTV-induced mammary tumors significantly inhibit growth and survival of target tumor cells in culture. Essentially the same level of reactivity is observed in normal BALB/cfC3H females between the ages of 8 and 32 weeks. Tumor-donor spleen cells are considerably more active. An unexpected finding was the observation that supposedly MTV-free BALB/c adult females also possess spleen cells specifically reactive against MTV-induced mammary tumor cells. The only mice tested whose spleen cells were not reactive were BALB/c females younger than 14 weeks of age. BALB/c serum blocked activity of BALB/c but not BALB/cfC3H spleen cells, and BALB/cfC3H serum blocked activity of BALB/cfC3H but not BALB/c spleen cells; thus, the two groups of mice are responding to different MTV-associated antigens on the target cells. Tumor-donors respond to both types of antigens, and also to tumor-specific antigens.