The Use of Enhancement in Studying Tumor Antigens1

I have been asked to discuss the use of immunologie en hancement in studying tumor antigens. Strictly speaking, there is little to say on this topic, for although enhancement has attracted much experimental attention, most investigations have been designed to find out more about the phenomenon itself. It has not been widely used as a technic for studying tumor antigens. In some early work on what we now know to have been an example of enhancement, Casey (7) attempted to extract a growth-promoting factor from the Brown Pearce tumor of rabbits, and he used the capacity of the extracts to induce enhanced growth of the tumor as an assay. However, he was unable to identify the growth-promoting factor(s) precisely. Later when the immunologie basis of enhancement had been established, Kandutsch and Stimpfling (24) used it for assaying H-2 antigen-containing material prepared from the A strain sarcoma, Sa l. But assay methods based on en hancement lack precision and convenience. More recent work on the characterization of H-2 and human histocompatibility antigens has usually involved testing for the activity of an extract by its capacity to inhibit specifically a cytotoxic isoantibody reaction in vitro. Such tests do not permit one to conclude that an active extract is immunogenic, and in prov ing this point an assay method based on enhancement may be useful. Nevertheless, the relevance of immunologie enhancement to the study of tumors is considerable, and I will discuss the subject from this wider point of view. It should be mentioned here that there are a number of detailed reviews on enhance ment (2, 22, 28). In this article I will discuss some of the newer experimental work and attempt to emphasize some aspects of enhancement which have not been stressed in the past.