Cross reacting antigens in chemically induced sarcomas are fetal determinants

Serologic cross reactivity has been demonstrated among 3 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 eliminated 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 syngeneic 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.