Enhancing antibody responses by multivalent antigen display on thymus-independent DNA origami scaffolds

Multivalent antigen display is a well-established design principle to enhance humoral immunity elicited by subunit vaccines. Protein-based virus-like particles (VLPs) are an important vaccine platform that implements this principle but also contain thymus-dependent off-target epitopes, thereby generating neutralizing and defocused antibody responses against the scaffold itself. Here, we present DNA origami as an alternative platform to display the receptor binding domain (RBD) of SARS-CoV-2. DNA-based scaffolds provide nanoscale control over antigen organization and, as thymus-independent antigens, are expected to induce only extrafollicular B-cell responses. Our icosahedral DNA-based VLPs elicited valency-dependent BCR signaling in two reporter B-cell lines, with corresponding increases in RBD-specific antibody responses following sequential immunization in mice. Mouse sera also neutralized the Wuhan strain of SARS-CoV-2--but did not contain boosted, DNA-specific antibodies. Thus, multivalent display using DNA origami can enhance immunogenicity of protein antigens without generating scaffold-directed immunological memory and may prove useful for rational vaccine design.

Naive human B cells can neutralize SARS-CoV-2 through recognition of its receptor binding domain

Exposure to a pathogen elicits an adaptive immune response aimed to control and eradicate. Interrogating the abundance and specificity of the naive B cell repertoire contributes to understanding how to potentially elicit protective responses. Here, we isolated naive B cells from 8 seronegative human donors targeting the SARS-CoV-2 receptor-binding domain (RBD). Single B cell analysis showed diverse gene usage with no restricted complementarity determining region lengths. We show that recombinant antibodies engage SARS-CoV-2 RBD, circulating variants, and pre-emergent coronaviruses. Representative antibodies signal in a B cell activation assay and can be affinity matured through directed evolution. Structural analysis of a naive antibody in complex with spike shows a conserved mode of recognition shared with infection-induced antibodies. Lastly, both naive and affinity-matured antibodies can neutralize SARS-CoV-2. Understanding the naive repertoire may inform potential responses recognizing variants or emerging coronaviruses enabling the development of pan-coronavirus vaccines aimed at engaging germline responses. One Sentence SummaryIsolation of antibody germline precursors targeting the receptor binding domain of coronaviruses.