Monoclonal antibodies directed to different tumor-associated antigens on a murine mammary tumor cell line, MM46.

Seven monoclonal antibodies to a murine mammary carcinoma MM46 were produced by fusing a mouse hybridoma cell line Sp2/O-Ag14 or a myeloma cell line P3-X63-Ag8-U1 with spleen cells from C3H/He mice immunized with MM46. Their specificities were investigated by the complement-dependent cytotoxicity test and binding inhibition assay using 125I-labeled monoclonal antibodies. The complement-dependent cytotoxicity test showed that all of them reacted with MM antigen-positive tumor cells such as MM46 and FM3A/R. Three of them reacted with both C57BL/6 lymph node cells and EL4 tumor cells, suggesting that these 3 antibodies recognize Ly-6.2 antigen. One reacted with all tumor cells so far tested (MM46, FM3A/R, MM48, MH134, and Meth A) except EL4. One antibody that cross-reacted with MH134 was also obtained. Binding inhibition assay confirmed hat the 7 monoclonal antibodies detected at least 4 different epitopes on MM46. These results suggest that there are at least 4 different molecules on the cell surface of MM46: namely, molecules that are 1) restricted to MM antigen-positive tumor cells, 2) present on several tumor cells, 3) broadly distributed on tumor cells, and 4) cross-reactive with Ly antigen.