One dose of COVID-19 nanoparticle vaccine REVC-128 provides protection against SARS-CoV-2 challenge at two weeks post immunization

A COVID-19 vaccine with capability to induce early protection is needed to efficiently eliminate viral spread. Here, we demonstrate the development of a nanoparticle vaccine candidate, REVC-128, in which multiple trimeric spike ectodomain subunits with glycine (G) at position 614 were multimerized onto a nanoparticle. In-vitro characterization of this vaccine confirms its structural and antigenic integrity. In-vivo immunogenicity evaluation in mice indicates that a single dose of this vaccine induces potent serum neutralizing antibody titer at two weeks post immunization, which is significantly higher than titer induced by trimeric spike protein without nanoparticle presentation. The comparison of serum binding to spike subunits between animals immunized by spike with and without nanoparticle presentation indicates that nanoparticle prefers the display of spike RBD (Receptor-Binding Domain) over S2 subunit, likely resulting in a more neutralizing but less cross-reactive antibody response. Moreover, a Syrian golden hamster in-vivo model for SARS-CoV-2 virus challenge was implemented at two weeks post a single dose of REVC-128 immunization. The results show that vaccination protects hamsters against SARS-CoV-2 virus challenge with evidence of steady body weight, suppressed viral loads and alleviation of tissue damage (lung and nares) for protected animals, compared with ~10% weight loss, higher viral loads and tissue damage in unprotected animals. Furthermore, the data show that vaccine REVC-128 is thermostable at up to 37{degrees}C for at least 4 weeks. These findings, along with a long history of safety for protein vaccines, suggest that the REVC-128 is a safe, stable and efficacious single-shot vaccine candidate to induce the earliest protection against SARS-CoV-2 infection.

Structural and functional ramifications of antigenic drift in recent SARS-CoV-2 variants

The protective efficacy of neutralizing antibodies (nAbs) elicited during natural infection with SARS-CoV-2 and by vaccination based on its spike protein has been compromised with emergence of the recent SARS-CoV-2 variants. Residues E484 and K417 in the receptor-binding site (RBS) are both mutated in lineages first described in South Africa (B.1.351) and Brazil (B.1.1.28.1). The nAbs isolated from SARS-CoV-2 patients are preferentially encoded by certain heavy-chain germline genes and the two most frequently elicited antibody families (IGHV3-53/3-66 and IGHV1-2) can each bind the RBS in two different binding modes. However, their binding and neutralization are abrogated by either the E484K or K417N mutation, whereas nAbs to the cross-reactive CR3022 and S309 sites are largely unaffected. This structural and functional analysis illustrates why mutations at E484 and K417 adversely affect major classes of nAbs to SARS-CoV-2 with consequences for next-generation COVID-19 vaccines.