The possibility that fetal
antigens take part in
tumor immunity has been investigated to a limited extent, but the results of these studies have been controversial. It is not clear that
tumor inhibition shown in some systems is due to an immune reaction. In the present study, performed in a weakly immunogenic
tumor system (Lewis T241
fibrosarcoma in inbred C57BL/6J mice), immunization of mice with syngeneic fetal cells resulted in striking inhibition of growth and
metastases of
tumors. Mice that had gone through single pregnancies also showed a decreased rate of
tumor growth and
tumor metastases. Further studies have shown that the
tumor inhibitory response evoked by fetal cell immunization is due to fetal
antigens, and the male specific
HY antigen is not responsible for antitumor response. Injection of
tumor cells mixed with spleen cells from mice immunized with syngeneic fetal cells into normal mice resulted in significant inhibition of
tumor growth and
metastases in the Winn neutralization assay. Syngeneic fetal cells, normal adult spleen cells, or spleen cells from C57BL/6 mice immunized with allogeneic fetal cells did not inhibit
tumor growth or
metastases. These results show that
tumor inhibition following fetal cell immunization is due to an immune reaction and is not due to a nonimmune physiologic process. Further analysis of effector cells showed them to be of the T-cell type.