Production of monoclonal antibodies against MM antigen: The serologic identification of MM antigen with Ly-6.2 alloantigen

Monoclonal antibodies against MM46, an ascitic mouse mammary tumor of C3H/He, were produced by fusing mouse myeloma cell line NS-1 with spleen cells from (BALB/c x C3H/HeN)F₁ mice hyperimmunized with MM46, an MM antigen-positive tumor. Eight antibodies showed cytotoxicity against MM46, but not against MM48, an MM antigen-negative ascitic mammary tumor, and one hybridoma produced an agglutinating antibody. One of the cytotoxic monoclonal antibodies, 3-3-C, was selected, and the strain distribution and the tissue distribution of MM antigen were studied. The results demonstrated that MM antigen had a strain distribution identical to Ly-6.2 antigen, and a similar tissue distribution. Therefore, the characterization of MM antigen and Ly-6.2 antigen was investigated. Ly-6.2 antibody was shown to be cytotoxic for MM46, but not for MM48, in accordance with 3-3-C. Genetic segregation analysis of MM and Ly-6.2 antigens in 33 backcross mice demonstrated complete accordance between these two antigens. In addition, MM antigen phenotype of an Ly-6.2 congenic strain C3H.B6-Ly-6^b, was studied, and it was found to be positive in contrast to C3H/HeN. Furthermore, cross-absorption studies revealed that both MM46 cells and C3H.B6-Ly-6^b lymph node cells could absorb cytotoxic activities of 3-3-C and monoclonal anti-Ly-6.2 antibody. The results so far obtained suggested strongly that these two loci controlling expression of MM and Ly-6.2 antigens were identical or very closely linked.