Yeast-expressed SARS-CoV recombinant receptor-binding domain (RBD219-N1) formulated with aluminum hydroxide induces protective immunity and reduces immune enhancement

Abstract

Highlights A SARS-CoV recombinant protein-based receptor binding domain (RBD) vaccine on alum provides high neutralizing antibody titers eliciting 100% protection (survival) against homologous SARS CoV virus challenge. A SARS-CoV RBD vaccine on alum prevents pulmonary cellular infiltrates upon virus challenge. A SARS-CoV RBD vaccine on alum greatly reduces lung eosinophils compared to a vaccine comprised of the SARS-CoV S protein. The SARS-CoV RBD vaccine on alum is being developed as a human vaccine.

Design of a highly thermotolerant, immunogenic SARS-CoV-2 spike fragment

“…Recently, various RBD-derived subunit vaccine candidates have been tested for immunogenicity employing varying fragment lengths, fusion adaptors (Fc, dimers), and adjuvants. No antibody-dependent enhancement of infection, immunopathologies, or Th2 bias has been observed with the SARS-CoV-2 RBD subunit derivatives examined so far ( 42 , 43 , 44 , 45 ). Three independent studies used RBD-Fc fusions with one study using RBD residues 331 to 527, another used RBD-Fc from Sino Biologicals (residues not mentioned), and a third used a full-length S1-Fc fusion (residues 14–685) reporting viral neutralizing antibody titers of ∼100 to 400, 1280, and NT 50 derived from pseudoviral neutralizations of 378 respectively ( 43 , 44 , 46 ).…”

“…The RBD fragment could also be expressed at high yield in the microbial host P. pastoris and was properly folded, stable, and immunogenic. Interestingly, an alhydrogel adjuvanted formulation of a related SARS-CoV-1 RBD construct was recently shown to be immunogenic and protect mice from SARS-CoV-1 challenge ( 42 ). Unfortunately, in the present study when pRBD was used as an immunogen, the elicited antibodies were poorly reactive with either the mammalian cell–expressed RBD or the corresponding spike ectodomain.…”

Process Development and Scale-up Optimization of the SARS-CoV-2 Receptor Binding Domain-Based Vaccine Candidate, RBD219-N1C1

“…Building on our experience with the RBD of the SARS-CoV spike protein [5,7,4], the SARS-CoV-2 RBD was cloned and expressed in the yeast Pichia pastoris [8]. Yeast has a track 69 record of serving as a host organism for the production of multiple regulatory-approved and 70 prequalified recombinant subunit vaccines, including vaccines for Hepatitis B, Influenza B, 71 human papillomavirus, as well as for Diphtheria and Tetanus [1,19].…”

Recombinant protein vaccines, a proven approach against coronavirus pandemics

“…Formulated with CpG as an adjuvant, it entered a Phase I/II clinical trial in India in November 2020 [ 80 ]. This follows the prior production of a recombinant SARS-CoV RBD antigen in the same system; formulated with alum, this antigen-induced high neutralizing antibody titers and 100% protection in mice after viral challenge [ 81 , 82 ].…”

“…Aluminum-based formulations generally induce a strong humoral immune response in combination with the secretion of Th2-biased cytokines (e.g., IL-4, IL-6, IL-10). While some studies found that candidate SARS-CoV vaccines formulated with aluminum induced specific Th2-biased responses and possibly induced lung eosinophilic immunopathology in mice [ 101 ], other studies found no direct evidence linking aluminum to enhanced eosinophilia [ 82 ]. The true cause of the undesired immune response remains under discussion [ 62 , 102 ].…”