Cross-reacting antigens in chemically induced sarcomas are fetal determinants.

Serologic cross-reactivity has been demonstrated among three MCA-induced sarcomas in C57BL/6N female mice (MCA-2, MCA-3, and MCA-12) with a microcytotoxicity assay. Serum from mice bearing MCA-3 tumor was cytotoxic to both MCA-2 and MCA-3 tumor cells at a titer of 1:8. Sequential absorptions of this serum with syngeneic embryo cells completely eliminate cytotoxicity against MCA-2 cells without affecting the cytotoxic titer against MCA-3 cells. Serum hyperimmune to the MCA-3 tumor reacted with MCA-3, MCA-2, and MCA-12 tumors. Absorption of this serum with embryo cells eliminated cytotoxicity against MCA-2 and MCA-12 cells, but was incapable of lowering the titer against MCA-3 cells below 1:40. Similarly, serum hyperimmune to MCA-2 tumor was lytic to MCA-2, MCA-3, and MCA-12 before absorption, but was lytic only to MCA-2 cells after absorption with sygeneic embryo cells. Thus, the in vitro cross-reactivity between MCA-induced sarcomas is due to a common fetal antigen(s), which is distinct from the individual tumor-specific antigens of each tumor. Since these tumors do not exhibit cross-reactivity in in vivo challenge experiments, it appears that this fetal antigen is not responsible for in vivo immune protection.