Deep mining of the antigen-specific plasma/plasmablast cell antibody repertoire using droplet microfluidics

Characterization of IgGs, the most prevalent class of circulating antibody following vaccination or infection, remains limited by the lack of high-throughput techniques to characterize both the activity and the sequence of antibodies secreted by plasma cells­. Here we describe CelliGO, a droplet-based microfluidics system combining high-throughput single-cell screening of millions of IgG-secreting cells, based on the activity of the secreted IgG, with single-cell sequencing of paired antibody V genes. We analyzed IgG repertoire diversity, clonal expansion and somatic hypermutation in mice immunized with a vaccine target, a multifunctional enzyme or a membrane-bound cancer target. Immunization and screening using soluble protein antigens or cells expressing the membrane protein antigen yielded 100-1,000 IgG sequences per mouse. Of the 77 recombinant antibodies tested, 93% bound the soluble antigen and 14% the membrane antigen, with predominantly sub-nanomolar and sub-micromolar affinities, respectively. CelliGO promises to be a powerful tool to investigate immune responses and for therapeutic antibody discovery.