Specificity of cell membrane antigens in prostatic cancer

Mice bearing a 3 methylcholanthrene induced fibrosarcoma (MCAM 7) transplant in the right leg underwent surgical excision of the tumor and showed specific resistance to subsequent challenges with that identical tumor line. An in vivo response to tumor specific antigens (MCAM 7 antigen) solubilized by hypertonic potassium chloride was measured by 24 hr footpad swelling response in mice immunized to the tumor from which the antigens were extracted. These observations suggested that the transplantable MCAM 7 fibrosarcoma could produce immunity toward the solubilized MCAM 7 tumor antigens and that this tumor immunity could be measured by footpad swelling response to injection of the solubilized antigens, an indication of cell mediated immunity. The footpad swelling response was also monitored in relation to the extent of tumor growth. Mice received MCAM 7 tumor transplants by injection of 5 x 10⁶ tumor cells and were tested for footpad swelling response at intervals following tumor transfer. A significant footpad response to injected MCAM 7 antigens was present 10 days following tumor transfer; at this time signs of tumor growth were only minimally detectable. The footpad swelling response to injected antigens disappeared by 28 days following initial tumor transfer; at this time the tumor diameters were in excess of 1.0 cm. Surgical removal of tumor at this point promptly restored footpad responses within 24 hr. Similar techniques have been applied to patients bearing adenocarcinoma of the prostate, where skin testing was substituted for the measurement of footpad swelling in animals. Seven patients with known prostatic carcinoma were given intradermal injections of soluble tumor antigens extracted from their own tumors. Three of the seven patients exhibited a cutaneous delayed type hypersensitivity response to the injected autologous tumor extracts. No positive reactions were observed in response to solubilized components of control tissues, including benign prostatic hyperplasia. The significance of the demonstrated concomitant immunity in these patients has not been resolved. However, these observations suggest that some patients bearing adenocarcinoma of the prostate can exhibit an immunologic response to specific antigens present in their own neoplasms.