Single-Chain B cell receptor mice as a novel tool for antibody generation and exploring B cell signaling

Abstract Conventional antibodies consist of a pair of heavy and light dimers, while heavy-chain only antibodies (HCAbs), like those found in camelid and shark species, lack a domain critical for light chain binding and develop without a light chain. HCAbs have unique physiochemical properties that confer advantages: they are smaller, have greater accessibility to their target antigens, higher hydrophilicity, higher tissue penetrance, and greater conformational stability under environmental stresses compared to conventional Abs. They are also highly amendable to biochemical engineering. We have generated a mouse model, that can produce HCAbs from the endogenous murine heavy chain locus. We have shown that these mice undergo efficient B cell development in the bone marrow and generate a diverse repertoire of B cells that populate all peripheral immune compartments. Single-cell sequencing of B cells revealed some biases in VH and JH usage, but highlighted the tremendous diversity of rearrangements that give rise to B cells bearing HCAbs. With these mice, we have been able to generate antigen specific HCAbs to the SARS-CoV2 spike protein that have a K Din the nM range, measured via bio-layer interferometry. Further, the IgG3dCH1 mice provide us with a novel model to understand how single domain B cell receptors (BCRs) function in comparison to conventional heavy/light chain BCRs. We have observed single-chain BCRs have distinct transcriptional profiles by single-cell sequencing and support higher plasma cell differentiation in vitro and in vivo. These data highlight the utility of our small animal platform for the generation of clinically relevant HCAbs, and as a model to study the biology of HCAb encoding B cells which remain poorly understood. Bernard Levine Postdoctoral Fellowship, R43AI136141