Embryonic antigens in malignancy and pregnancy: common denominators in immune regulation.

There is mounting that the majority of malignant tumours of humans and rodents carry embryonic determinants (EA) associated with the cell membrane. The evolutionary and developmental purpose of these determinants seems to be related to their biochemical and structural role in the cell membrane. True EAs are uniquely expressed on germinal, embryonic and some fetal cell membranes and are not expressed in adult tissues nor in regenerating tissues. The immunological role of EA in fetal development in utero is still obscure. It is known that maternal IgG and cytotoxic T lymphocytes are produced in response to EA expressed in utero. Immunoregulatory interactions between suppressor, helper and cytotoxic T lymphocytes sensitized to EA during pregnancy have been detected in mice and hamsters bearing a variety of tumours. The same immunological events may occur in humans. The biological product of the retrogenic process that leads to the expression of EA in the emerging malignant cell clone seems to be intimately associated with the promotion of tumour-protective immune responses in the host which mimic the immune responses in pregnancy aimed at protecting the EA+ fetus from maternal immune attack. The description of the immunoregulatory perturbations generated by EA during the induction of cancer may eventually provide effective and predictable attack points for immunological intervention in the control of malignancy. This paper describes methods for detecting EA and considers some immunoregulatory traits found in response to EA expression.