Monoclonal antibodies isolated without screening by analyzing the variable-gene repertoire of plasma cells

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Abstract
Isolation of antigen-specific monoclonal antibodies (mAbs) and antibody fragments relies on high-throughput screening of immortalized B cells or recombinant antibody libraries. We bypassed the screening step by using high-throughput DNA sequencing and bioinformatic analysis to mine antibody variable region (V)-gene repertoires from bone marrow plasma cells (BMPC) of immunized mice. BMPCs, which cannot be immortalized, produce the vast majority of circulating antibodies. We found that the V-gene repertoire of BMPCs becomes highly polarized after immunization, with the most abundant sequences represented at frequencies between approximately 1% and >10% of the total repertoire. We paired the most abundant variable heavy (V(H)) and variable light (V(L)) genes based on their relative frequencies, reconstructed them using automated gene synthesis, and expressed recombinant antibodies in bacteria or mammalian cells. Antibodies generated in this manner from six mice, each immunized with one of three antigens were overwhelmingly antigen specific (21/27 or 78%). Those generated from a mouse with high serum titers had nanomolar binding affinities.