Design of the SARS-CoV-2 RBD vaccine antigen improves neutralizing antibody response

Abstract

The receptor binding domain (RBD) of the SARS-CoV-2 spike protein is the primary target of neutralizing antibodies and is a component of almost all vaccine candidates. Here, RBD immunogens were created with stabilizing amino acid changes that improve the neutralizing antibody response, as well as characteristics for production, storage, and distribution. A computational design and in vitro screening platform identified three improved immunogens, each with approximately nine amino acid changes relative to the native RBD sequence and four key changes conserved between immunogens. The changes are adaptable to all vaccine platforms, are compatible with established changes in SARS-CoV-2 vaccines, and are compatible with mutations in emerging variants of concern. The immunogens elicit higher levels of neutralizing antibodies than native RBD, focus the immune response to structured neutralizing epitopes, and have increased production yields and thermostability. Incorporating these variant-independent amino acid changes in next-generation vaccines may enhance the neutralizing antibody response and lead to pan-SARS-CoV-2 protection.

ALiCE®: A versatile, high yielding and scalable eukaryotic cell-free protein synthesis (CFPS) system

“…This protein is considered an important target for developing a SARS subunit vaccine. Indeed, the majority of the potent neutralising antibodies against SARS-CoV-2 target the RBD 30 , but reports differ on whether RBD alone or full S1 subunits of the spike are more potent vaccines in terms of IgG and IgA induction 31,32 .To explore this concept, we expressed both RBD and this S1 subunit from the pALiCE02 vector and with different HaloTag and Strep-II tag conformations. Antigen reactivity to two commercial antibodies was initially assessed, selected based on the recognition of either linear or conformational RBD epitopes.…”

Structural and Computational Design of a SARS-2 Spike Antigen with Increased Receptor Binding Domain Exposure and Improved Immunogenicity

“…This highlights an urgent need for improved vaccines capable of broad protection again VoCs. Some strategies taken to improve protective efficacy have included focusing the immune response towards the RBD through multivalent display of the RBD on nanoparticles, or through the modification of the RBD sequence [27, 28]. In the case of nanoparticles, mosaic display of RBDs from diverse sarbecoviruses was capable of neutralizing SARS-CoV-2 variants, including Omicron, and was protective against challenge with SARS-2 Delta variant and SARS-1 in NHPs [27].…”

Protein-protein conjugation enhances the immunogenicity of SARS-CoV-2 receptor-binding domain (RBD) vaccines

“…The RBD/Ace2 blocking assay was performed, as described previously (Dickey et al, 2021). Nunc MaxiSorp plates (ThermoFisher Scientific) were coated with 100 mL 0.32 mg/mL purified RBD diluted in 50 mM Na-carbonate pH 9.5.…”

“…IC 50 values for each animal were log-transformed and plotted, along with the geometric mean value for each group. Serum mediated neutralization of viral entry into Ace2 expressing cells were assayed using a pseudovirus consisting of spike protein (WA-1) and expressing luciferase reporter gene as described previously (Dickey et al, 2021). Mouse serum was diluted in a triplicate 5-fold series from 1:10 to 1:781,250.…”

“…Efforts to develop RBD-based vaccines have resulted in two successful vaccines, a Tetanus Toxoid conjugate of RBD with Alum adjuvant (Soberana 02) and RBD adjuvanted with Alum and CpG 1018 (Corbevaxä), currently approved for human use in Cuba and India, respectively (Toledo-Romani et al, 2021;Nanishi et al, 2021;Valdes-Balbin et al, 2021). Strategies to enhance the immunogenicity of RBD involve the structural optimization of the antigen and/or presentation of the antigen in particulate, multimeric formats such as nanoparticles or virus-like particles (VLPs) (Dickey et al, 2021;Hsieh et al, 2020;Nguyen and Tolia, 2021;Walls et al, 2020;Saunders et al, 2021;Gaspar et al, 2021;Tan et al, 2021;Geng et al, 2021;Volpatti et al, 2021;Wong et al, 2022).…”