Clonal analysis of a human antibody response: Quantitation of precursors of antibody-producing cells and generation and characterization of monoclonal IgM, IgG, and IgA to rabies virus

We quantitated and characterized the changes in the human B cell repertoire, at the clonal level, before and after immunization with rabies virus. Moreover, we generated 10 monoclonal cell lines producing IgM, IgG, and IgA antibodies to the virus. We found that in healthy subjects, not previously exposed to the virus, nearly 2% of the circulating B lymphocytes were committed to the production of antibodies that bound the virus. These B cells expressed the surface CD5 molecule. The antibodies they produced were polyreactive IgM that displayed a relatively low affinity for the virus components (K(d), 1.0-2.4 x 10^-6 g/μl). After immunization, different anti-virus (IgG and IgA) antibody-producing cells consistently appeared in the circulation and increased from <0.005% to >10% of the total B cells committed to the production of IgG and IgA, respectively. Most of such B cells do not express CD5 and produce monoreactive antibodies of high affinity for rabies virus (K(d), 6.5 x 10^-9 to 1.2 x 10^-10 g/μl). One of these IgG mAbs efficiently neutralized rabies virus in vitro and in vivo, as detailed elsewhere (Dietzschold, B., P. Casali, Y. Ueki, M. Gore, C.E. Rupprecht, A.L. Notkins, and H. Koprowski, manuscript submitted for publication). Hybridization experiments using probes specific for the different human V gene segment families revealed that cell precursors producing low affinity IgM binding to rabies virus utilized a restricted number of V(H) gene segments (i.e., only members of the V(H)IIIb subfamily), whereas cell precursors producing high affinity IgG and IgA to rabies virus utilized an assortment of different V(H) gene segments (i.e., members of the V(H)I, V(H)III, V(H)IV, and V(H)VI families and V(H)IIIb subfamily). In conclusion, our studies show that EBV transformation in conjunction with limiting dilution technology and somatic cell hybridization techniques are useful methods for quantitating, at the B cell clonal level, the human antibody response to foreign Ags and for generating human mAbs of predetermined specificity and high affinity.