Abstract
There is an urgent need for an accessible and low-cost COVID-19 vaccine suitable for low- and middle-income countries. Here, we report on the development of a SARS-CoV-2 receptor-binding domain (RBD) protein, expressed at high levels in yeast ( Pichia pastoris ), as a suitable vaccine candidate against COVID-19. After introducing two modifications into the wild-type RBD gene to reduce yeast-derived hyperglycosylation and improve stability during protein expression, we show that the recombinant protein, RBD219-N1C1, is equivalent to the wild-type RBD recombinant protein (RBD219-WT) in an in vitro ACE-2 binding assay. Immunogenicity studies of RBD219-N1C1 and RBD219-WT proteins formulated with Alhydrogel® were conducted in mice, and, after two doses, both the RBD219-WT and RBD219-N1C1 vaccines induced high levels of binding IgG antibodies. Using a SARS-CoV-2 pseudovirus, we further showed that sera obtained after a two-dose immunization schedule of the vaccines were sufficient to elicit strong neutralizing antibody titers in the 1:1,000 to 1:10,000 range, for both antigens tested. The vaccines induced IFN-γ IL-6, and IL-10 secretion, among other cytokines. Overall, these data suggest that the RBD219-N1C1 recombinant protein, produced in yeast, is suitable for further evaluation as a human COVID-19 vaccine, in particular, in an Alhydrogel® containing formulation and possibly in combination with other immunostimulants.
Keywords: ACE-2; COVID-19; RBD; alum; coronavirus; pseudovirus.
【저자키워드】 COVID-19, coronavirus, ACE-2, pseudovirus, RBD, alum, 【초록키워드】 SARS-CoV-2, Vaccine, COVID-19 vaccine, immunogenicity, Cytokines, IL-6, in vitro, immunization, Antigen, Protein, stability, IgG antibodies, pseudovirus, mice, sera, vaccine candidate, SARS-CoV-2 pseudovirus, IL-10, yeast, IFN-γ, Neutralizing antibody titer, binding, Pichia pastoris, Combination, These data, secretion, domain, protein expression, wild-type, doses, Modification, RBD gene, IMPROVE, produced, tested, conducted, expressed, elicit, reduce, the vaccine, 【제목키워드】 SARS-CoV-2, mice, T-cell immunity, domain, candidate vaccine, stimulate, virus neutralizing antibody,