Facundo D. Batista

To explore the use of human B cell receptor (BCR) knock-in mice for broadening antibody responses, we diversified CR3022, a monoclonal antibody (mAb) originally identified in a 2003 severe acute respiratory syndrome coronavirus (SARS-CoV) convalescent patient. This mAb targets a conserved epitope on the coronavirus receptor-binding domain (RBD). We took advantage of high- and low-affinity CR3022 BCR knock-in mice and immunized them with SARS-CoV-2 Wuhan RBD trimers to expand the breadth of these antibodies toward this virus. The resulting antibodies retained the ability to neutralize SARS-CoV and exhibited enhanced affinity and neutralization against the SARS-CoV-2 WA1/2020 strain, as well as the Delta (B.1.617.2) and Omicron KP.3 variants. They also showed broadened reactivity to two bat coronaviruses: WIV1 and, to a lesser potency, BtKY72. Structural analysis revealed key mutations that enhanced binding and neutralization, highlighting the importance of epitope accessibility and variant-specific conformations in antibody diversification. These findings demonstrate that human BCR-expressing mouse models can generate effective antibodies with broad neutralizing activity against viral epitopes.

Vaccines remain the most effective tool to prevent infectious diseases. Here, we introduce an in vitro booster vaccination approach that relies on antigen-dependent activation of human memory B cells in culture. This stimulation induces antigen-specific B cell proliferation, differentiation of B cells into plasma cells, and robust antibody secretion after a few days of culture. We validated this strategy using cells from healthy donors to retrieve human antibodies against tetanus toxoid and influenza hemagglutinin (HA) from H1N1 and newly emergent subtypes such as H5N1 and H7N9. Anti-HA antibodies were cross-reactive against multiple subtypes, and some showed neutralizing activity. Although these antibodies may have arisen as a result of previous influenza infection, we also obtained gp120-reactive antibodies from non–HIV-infected donors, indicating that we can generate antibodies without prior antigenic exposure. Overall, our novel approach can be used to rapidly produce therapeutic antibodies and has the potential to assess the immunogenicity of candidate antigens, which could be exploited in future vaccine development.