Characterization of higher avidity monoclonal antibodies produced by murine B-cell hybridoma variants selected for increased antigen binding of membrane Ig.

Somatic mutation in the Ig genes plays a major role in the increase of antibody affinity observed in secondary immunologic responses. It has been shown that the mechanism responsible for the high rate of somatic mutation in the Ig genes was active not only in normal B lymphocytes but also in B-cell hybridomas secreting mAb. Also, it has been reported that B-cell hybridomas were positive for membrane Ig of the same specificity as the secreted mAb. The presence of membrane Ig suggested that somatic variants secreting mAb of higher affinity could be selected by the increased capacity of these hybridoma cells to bind immobilized Ag. This hypothesis was tested with hybridoma cells secreting an IgM mAb reacting with the A Ag of the ABO blood group system. In two selection experiments, we have isolated several variant cell lines secreting mAb of increased avidity for the A Ag under similar IgM concentrations. Biochemical characterization of one of the variant mAb indicated that the mutation responsible for the increased avidity has occurred in the heavy chain gene. The method developed may have profound implications for the diagnostic and therapeutic use of mAb and will permit the study, in an in vitro system, of the role of somatic mutations in antibody diversity.