Antibody from Single Human VH-rearranging Mouse Potently Neutralizes All SARS-CoV-2 Variants Through BA.5 by Inhibiting Membrane Fusion

Here, we describe a mouse model in which the primary B cell receptor (BCR) repertoire is generated solely through V(D)J recombination of a human VH1-2 heavy chain (HC) and, substantially, a human Vk1-33 light chain (LC). Thus, primary humanized BCR repertoire diversity in these mice derives from immensely diverse HC and LC antigen-contact complementarity-region-3 (CDR3) sequences generated de novo by non-templated junctional modifications during V(D)J recombination. We assayed the V usage and CDR3 diversity in this mouse model by HTGTS-repertoire sequencing. Immunizing this human VH1-2/Vk1-33-rearranging model with prototype SARS-CoV-2 spike protein immunogens elicited several VH1-2/Vk1-33-based nAbs. Of these, SP1-77 potently and broadly neutralized all SARS-CoV-2 variants through BA.5. Cryo-EM studies revealed that SP1-77 binds RBD away from the ACE2 receptor-binding-motif via a striking CDR3-dominated mode of recognition. Lattice-light-sheet-microscopy-based studies confirmed that SP1-77 did not block ACE2-mediated viral attachment or subsequent endocytosis, but rather blocked membrane fusion. The SP1-77 binding epitope and neutralization mechanism may offer additional strategies for designing vaccines that robustly neutralize emerging SARS-CoV-2 variants. Overall design: High-thoughput sequencing of splenic B cell receptor repertoire