Search

The purpose of this study was to ascertain whether the protection afforded to adult mice against the induction and growth of 3-methylcholanthrene-induced tumours by prior exposure to syngeneic fetal cells has an immunological basis. Adult CBA mice were inoculated with fetal cells according to a variety of protocols and the sera were tested for their ability to bind to fetal and adult tissue cells, using a staphylococcal protein A binding assay. All 10 sera tested showed some degree of binding though this varied from strong to weak, and there was some cross-reactivity with adult thymic cells but relatively little with adult spleen cells. Absorption studies were carried out with one of these sera and with two others raised against testicular and thymic cells, respectively. The absorption patterns obtained so far suggest that fetal cells possess at least three, and possibly up to five, distinct antigens. Although none of the anti-fetal sera were produced with a sensitizing protocol identical with that used in in vivo protection, some of them were so close as to suggest that protection is associated with, and perhaps causally related to, these IgG antibodies. The in vitro evidence presented here, together with the in vivo data of P. B. Medawar & R. Hunt, shows that antigens are shared between fetal cells and adult thymic and testicular cells. It therefore lends support to the notion that the production of a vaccine against anaplastic neoplasms, using immunogens derived from adult tissues, is within the realms of possibility.

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.