Tu212 - Drivers of differential antibody breadth in SARS-CoV-2 mRNA vaccination and infection

Abstract Text: The cellular, immunogenetic and antigenic factors that affect the breadth of viral antigen variants recognized by human antibody responses are poorly defined. mRNA vaccination for SARS-CoV-2 (CoV-2) results in initial polyclonal antibody mixtures of greater breadth compared to those stimulated by viral infection. Publicly available CoV-2 binding antibodies characterized during the pandemic are relatively few in number, biased toward neutralizing antibodies, and characterized for binding to few variants, primarily due to the expense and labor required for monoclonal antibody production/characterization. To markedly scale up human antibody analysis to address difficult questions such as the molecular determinants of serological breadth, we have developed highly multiplexed panels of DNA-tagged CoV-2 antigens from up to 20 viral variants to label, sort and enable B cell receptor and transcriptome sequencing of 6,262 antigen-binding B cells from peripheral blood of mRNA vaccinees, infected patients and lymphoid tissues of deceased organ donors. Antigen-specific B cells were enriched in a circulating class-switched memory subset with evidence of recent germinal center exposure and progressive somatic hypermutation over time, and atypical B cells that had minimal mutation accumulation. Surprisingly, mRNA vaccination preferentially stimulates B cells expressing B cell receptors with inherently high antigen binding breadth, compared to infection-stimulated B cell clones. The results from this scaled-up analysis enable systematic modeling of the B cell subset, antigen exposure and BCR composition determinants of antigen binding breadth, a topic of increasing importance as mRNA vaccination is evaluated for other viruses with high mutation rates contributing to evasion of human antibody responses.