Modulation of human tumor antigen expression.

With membrane-enriched fractions prepared from human metastatic breast tissue used as immunogen, a group of monoclonal antibodies (MAbs) were generated that recognized several distinct antigens on breast and other carcinomas. The antibodies were found to react with established human tumor cells in culture as well as in immunohistochemical protocols using sections of primary and metastatic lesions. One MAb, B72.3, demonstrated a high degree of selective reactivity for human carcinomas in that no reactivity was found with a large number of different normal tissues. These MAbs were used to demonstrate the heterogeneity of expression of the tumor antigens as well as the intrinsic cellular factors (i.e., cell-cycle kinetics and clonal variability) that modulate their expression. Additional studies showed that recombinant human leukocyte interferon can act as a potent regulator of surface antigen expression on human carcinoma cells. Analysis of these cells by radioimmunoassay or flow cytometry revealed that interferon treatment resulted in a higher percentage of the cell population that bind the MAb to the surface antigen. Furthermore, interferon treatment also increases the level of expression for particular tumor antigen throughout the tumor cell population. Experimental models were also developed to investigate the active localization of a radiolabeled MAb by a human tumor xenograft in athymic mice. The results demonstrate active uptake of an 125I-B6.2 by a transplantable human breast tumor that expressed significant quantities of the B6.2-reactive 90 kD tumor antigen. In contrast, a human melanoma cell line grown as a solid, subcutaneous tumor in athymic mice did not localize the labeled B6.2 and does not express the associated 90 kD antigen. We report the generation and characterization of anti-breast carcinoma MAbs. These immunologic probes were used to study relevant breast tumor antigens, the factors that influence their level of expression, and the ability of human tumors grown in athymic mice to localize radiolabeled antibodies.