Rapid immunization and antibody redesign platform discovers broadly neutralizing antibodies against non-immunized SARS-CoV-2 variant.

From COVID-19, we learned valuable lessons related to the development of broadly neutralizing antibodies (bnAbs). Here, we present a discovery platform termed Express Hu-mAb System that integrates a fully human Ab-producing transchromosomic (TC-mAb) mouse, a rapid immunization procedure, and a CHO cell-based mammalian display system (MDS) to generate bnAbs against the non-immunized SARS-CoV-2 variant in 60-90 days. Rapid 30-day immunization of a TC-mAb mouse resulted in increased titers, elevated antibody concentration, and production of anti-serum that neutralized the non-immunized BA.1. Single B cell analysis without using fluorescent antigen probe identified clonotypes that recapitulated immune responses associated with the COVID-19. Importantly, we generated 25 bnAb candidates based on the abundance of sequence reads, determined 14 binders (56%), and identified clonotype 11 as a bnAb that neutralizes the non-immunized BA.5 in 60 days. Next, exploiting a TC-mAb mouse whose anti-serum neutralized only the Wuhan strain, we constructed a chain-shuffled immunoglobulin cDNA library with sufficient diversity of 4.3-6.2 × 104 CHO cells. We then applied the MDS to redesign bnAb candidates, and identified M5419S09Ab01 that neutralizes the BA.5 in 90 days. Taken together, this work demonstrates speed, efficiency, and simplicity of our platform to discover bnAbs against the phylogenetically distinct viral variant with optimal developability and manufacturability.