Rationally Designed Immunogens Enable Immune Focusing Following SARS-CoV-2 Spike Imprinting

Abstract

Eliciting antibodies to surface-exposed viral glycoproteins can generate protective responses that control and prevent future infections. Targeting conserved sites may reduce the likelihood of viral escape and limit spread of related viruses with pandemic potential. Here, we leveraged rational immunogen design to focus humoral responses on conserved epitopes. Using glycan engineering and epitope scaffolding, we directed murine serum antibody responses to conserved receptor binding motif (RBM) and domain (RBD) epitopes in the context of SARS-CoV-2 spike imprinting. Whereas all engineered immunogens elicited a robust SARS-CoV-2-neutralizing serum response, the RBM-focusing immunogens exhibited increased potency against related sarbecoviruses, SARS-CoV, WIV1-CoV, RaTG13-CoV, and SHC014-CoV; structural characterization of representative antibodies defined a conserved epitope. Furthermore, the RBM-focused sera conferred protection against SARS-CoV-2 challenge. Thus, RBM focusing is a promising strategy to elicit breadth across emerging sarbecoviruses without compromising SARS-CoV-2 protection. Broadly, these engineering strategies are adaptable to other viral glycoproteins for targeting conserved epitopes.

Funding: We acknowledge funding from NIH R01s AI146779 (AGS), AI124378, AI137057 and AI153098 (DL), R01 AI157155 (MSD) and a Massachusetts Consortium on Pathogenesis Readiness (MassCPR) grant (AGS); training grants: NIGMS T32 GM007753 (BMH, TMC); T32 AI007245 (JF); F31 Al138368 (MS); F30 AI160908 (BMH). ABB is supported by the National Institutes for Drug Abuse (NIDA) Avenir New Innovator Award DP2DA040254, the MGH Transformative Scholars Program as well as funding from the Charles H. Hood Foundation (ABB). This independent research was supported by the Gilead Sciences Research Scholars Program in HIV (ABB). JBC is supported by a Helen Hay Whitney Foundation postdoctoral fellowship.

Declaration of Interests: BMH, TMC, and AGS have filed a provisional patent for the described immunogens. MSD is a consultant for Inbios, Vir Biotechnology, and Carnival Corporation, and on the Scientific Advisory Boards of Moderna and Immunome. The Diamond laboratory has received unrelated funding support in sponsored research agreements from Vir Biotechnology, Moderna, and Emergent BioSolutions.

Ethics Approval Statement: All experiments were conducted with institutional IACUC approval (MGH protocol 2014N000252). Animal studies were carried out in accordance with the recommendations in the Guide for the Care and Use of Laboratory Animals of the National Institutes of Health. The protocols were approved by the Institutional Animal Care and Use Committee at the Washington University School of Medicine (assurance number A3381–01).

Keywords: immunogen design, glycan, immune focusing, SARS-CoV-2, Coronavirus