Fetal antigens in nonneoplastic conditions.

During studies that showed the presence of fetal antigens on the surface of human malignant melanoma tumor cells, polyvalent antisera specific for human fetal tissues of varying ages were developed. These reagents demonstrated varying patterns of expression of fetal antigens at different ages in various tissues of the human fetus. The possibility that nonneoplastic adult cells showing either maturation arrest or excessive proliferation also might express fetal antigens led to studies of human bone marrow. Although normal bone marrow cells expressed low levels of fetal antigens, large amounts were seen on bone marrow cells of patients with anemias due to iron, B12, or folic acid deficiencies, as well as on those with leukemia. Moreover, normal adult tissues adapted to long-term culture also expressed fetal antigens. After 3 weeks in organ culture adult human skin showed morphological changes similar to those seen in fetal periderm and strongly expressed fetal antigens. In addition, lymphoblasts in long-term cultured human lymphoid cell lines established from normal donors also carried surface fetal antigens. These latter antigens were shared with neoplastic B-cells (chronic lymphocytic leukemia) but not with T-cells. Their expression varied with the cell cycle. The reexpression of fetal antigens on malignant cells is thought to signal a basic derangement in the control of differentiation which is considered to be peculiar to neoplasia. However, these studies indicate that normal adult cells also may reexpress fetal antigens under circumstances unrelated to neoplasia but associated with either maturation arrest or rapid and excessive proliferation.