Monoclonal antibodies against human breast tumor-associated antigens: characterization of B21 antigen.

Abstract

Monoclonal antibodies (MAbs) show promise in the early detection and monitoring of cancer and may have therapeutic applications as well. The purpose of this study was to characterize MAb B21, a novel murine-derived antibody that has strong reactivity with MCF-7 and T47D cell lines from human breast cancer. A number of MAbs that react with breast cancer cell lines were obtained from cultured mouse spleen cells, and one, MAb B21, was selected for detailed analysis. MAb B21 was characterized by immunocytochemical, immunofluorescence, immunoprecipitation, and Western blotting procedures. We found a strong reactivity of MAb B21 with cultured breast cancer cells and cells from human breast tumors, although some reactivity was seen sporadically in non-breast or normal tissue. Negligible reactivity was detected in a series of non-breast cell lines and with normal breast epithelial cell line MCF-10A. However, when MCF-10A cells were permeabilized, allowing the antibody to penetrate within the cells, reaction became apparent. MCF-10A cells, when transfected with the oncogene c-Ha-ras (MCF-10T), gave a positive immunostaining similar to that observed with MCF-7 and T47D cells. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis of L-[35S]methionine-labeled MCF-7 and T47D cell extracts showed distinct immunoprecipitated components, with molecular weight values ranging from 150,000 to 20,000 with the addition of MAb B21. Western blot assays using MAb B21 of SDS-PAGE fractionated/electroblotted proteins from breast cancer cell lines and MCF-10A cells showed specific reaction with a 95,000 component. Our results indicate that B21 antigen is expressed in neoplastic cells of epithelial origin, mainly breast cancer, and to a minor extent in other cell lines. In addition, MAb B21 recognizes an antigen that is differentially localized during cell transformation. Our future studies will address the full characterization of MAb B21 and explore its capacity as a tool for therapeutic manipulation.