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Proceedings: Escape from immune destruction by the host through shedding of surface antigens: is this a characteristic shared by malignant and embryonic cells?

Summary The hypothesis is advanced that macromolecules normally found only in embryonic and fetal cells are also found in tumors because malignant cells, like the fetus, must develop mechanisms to avoid immunological destruction by the host. While anatomical factors play an important role in the “escape” of the fetus as well as the tumor, they are not by themselves adequate. In tumors, the shedding of antigens in a soluble form provides powerful protection because such antigens compete with the tumor for the effector processes of the immune response. Soluble antigens form adducts with antibodies as well as cytotoxic cells, which are then no longer capable of killing the tumor cells. Evidence is presented that the rate of spontaneous shedding of antigen may determine in part the growth pattern of the tumor in vivo. Sarcoma cells, which shed antigen rapidly, metastasize more readily than those with a slow spontaneous release of antigen. It is proposed that rapid shedding of transplantation antigens is a characteristic of embryonic cells and tumors.