Syngeneic antitumor and antiembryo immunization affecting pregnancy in mice

Groups of virgin BALB/c female were immunized against methylcholanthrene, SV40-induced or spontaneous syngeneic sarcoma cells or against syngeneic mitomycin-C blocked embryonic cells. Females were then mated to syngeneic males and observed for pregnancy rate and size of litters. To mimic the antiembryo immunization occurring during normal pregnancy, other experimental groups were added in which midgestational embryo fragments were kept in cell-impermeable diffusion chambers placed in the peritoneal cavity of virgin femals for 20 days, and removed before mating these females with syngeneic males. In all cases, antitumor and antiembryo immunization significantly reduced the number of successful pregnancies after the 1st mating while the second pregnancy appeared to be unaffected by the treatment. A significant reduction in the mean litter size was found, in mice immunized with embryonic tissues or with the SV40-induced sarcoma but not in those immunized with methylcholanthrene-induced or spontaneous tumors.