Engineering a SARS-CoV-2 vaccine targeting the RBD cryptic-face via immunofocusing

The receptor-binding domain (RBD) of the SARS-CoV-2 spike protein is the main target of neutralizing antibodies. Although they are infrequently elicited during infection or vaccination, antibodies that bind to the conformation-specific cryptic face of the RBD display remarkable breadth of binding and neutralization across Sarbecoviruses. Here, we employed the immunofocusing technique PMD (protect, modify, deprotect) to create RBD immunogens (PMD-RBD) specifically designed to focus the antibody response towards the cryptic-face epitope recognized by the broadly neutralizing antibody S2X259. Immunization with PMD-RBD antigens induced robust binding titers and broad neutralizing activity against homologous and heterologous Sarbecovirus strains. A serum-depletion assay provided direct evidence that PMD successfully skewed the polyclonal antibody response towards the cryptic face of the RBD. Our work demonstrates the ability of PMD to overcome immunodominance and refocus humoral immunity, with implications for the development of broader and more resilient vaccines against current and emerging viruses with pandemic potential. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=97 SRC="FIGDIR/small/597541v1_ufig1.gif" ALT="Figure 1"> View larger version (28K): org.highwire.dtl.DTLVardef@12f1b1eorg.highwire.dtl.DTLVardef@19d6adforg.highwire.dtl.DTLVardef@1d392ccorg.highwire.dtl.DTLVardef@14aa8a2_HPS_FORMAT_FIGEXP M_FIG C_FIG SYNOPSISUsing the immunofocusing technique protect, modify, deprotect (PMD) we engineer SARS-CoV-2 receptor-binding domain (RBD) immunogens that generate broadly neutralizing antibodies against the conserved cryptic face. The ability to refocus humoral immunity to broadly conserved epitopes has important implications for the design of universal vaccines.