The functional significance of tumour-associated cell surface alterations of embryonic and unknown origin

Can fetal antigens be used for prophylactic immunization?

Even if the inoculation of fetal tissue cells were a dependable and uniformly successful method of protecting experimental animals against chemically or virally induced tumours, it would for obvious reasons still not be feasible to use fetal tissues for such a purpose in human beings. Among possible substitutes syngeneic spermatozoa were tested on the grounds that they are the only adult cells that express T-alleles, but neither they nor teratocarcinoma cells protected mice against tumours raised by 3-methylcholanthrene. Testicular and thymic cells and tissue fragments have given effective protection in a number of experiments and it is noteworthy that fetal tissues, testicular cells and thymus cells are cross-reactive in respect of anti-embryo antibodies. Testicular cells probably act like fetal cells and, like fetal cells, are very prone to give rise to 'enhancement'. Thymic cells do not 'enhance' and may act quite differently. The variability of results--a source of grave concern--is attributed to the insensitivity of the test system which is ill-adapted to show up low degrees of protection.

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.