Non-glycosylated SARS-CoV-2 RBD elicited a robust neutralizing antibody response in mice.

The glycosylated receptor-binding domain (glycoRBD) of SARS-CoV-2 can induce protective neutralizing antibodies to function as a vaccine. However, it is unclear whether vaccines using non-glycosylated RBD (non-glycoRBD) can induce protective immunity. Here, we report the efficacy of a SARS-CoV-2 non-glycoRBD vaccine produced by prokaryotic system in mice. The recombinant non-glycoRBD protein was overexpressed in Escherichia coli in the form of inclusion bodies, and was obtained after renaturation and three-step purification. From HPLC analysis, the purity of the RBD was 99%. Additionally, angiotensin converting enzyme 2 (ACE2)-binding assays revealed that E.coli-derived non-glycoRBD had binding activity consistent with glycoRBD. The RBD was formulated with CpG ODN and Al(OH)3 adjuvants and the obtained RBD candidate vaccine elicited potent antibody responses and neutralized SARS-CoV-2 wild-type, Delta, and Omicron pseudoviruses. In summary, our data showed that a non-glycoRBD candidate vaccine produced by E.coli provided a robust immune response and had pseudovirus neutralizing activity, making it a solid candidate vaccine for protection against SARS-CoV-2.

Kappa-RBD produced by glycoengineered Pichia pastoris elicited high neutralizing antibody titers against pseudoviruses of SARS-CoV-2 variants.

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) kappa (B.1.617.1) variant represented the main variant of concern (VOC) for the epidemic in India in May 2021. We have previously established a technology platform for rapidly preparing SARS-CoV-2 receptor-binding domain (RBD) candidate vaccines based on glycoengineered Pichia pastoris. Our previous study revealed that the wild-type RBD (WT-RBD) formulated with aluminum hydroxide and CpG 2006 adjuvant effectively induces neutralizing antibodies in BALB/c mice. In the present study, a glycoengineered P. pastoris expression system was used to prepare recombinant kappa-RBD candidate vaccine. Kappa-RBD formulated with CpG and alum induced BALB/c mice to produce a potent antigen-specific antibody response and neutralizing antibody titers against pseudoviruses of SARS-CoV-2 kappa, delta, lambda, beta, and omicron variants and WT. Therefore, the recombinant kappa-RBD vaccine has sufficient potency to be a promising COVID-19 vaccine candidate.

A Vaccine Based on the Receptor-Binding Domain of the Spike Protein Expressed in Glycoengineered Pichia pastoris Targeting SARS-CoV-2 Stimulates Neutralizing and Protective Antibody Responses.

In 2020 and 2021, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a novel coronavirus, caused a global pandemic. Vaccines are expected to reduce the pressure of prevention and control, and have become the most effective strategy to solve the pandemic crisis. SARS-CoV-2 infects the host by binding to the cellular receptor angiotensin converting enzyme 2 (ACE2) via the receptor-binding domain (RBD) of the surface spike (S) glycoprotein. In this study, a candidate vaccine based on a RBD recombinant subunit was prepared by means of a novel glycoengineered yeast Pichia pastoris expression system with characteristics of glycosylation modification similar to those of mammalian cells. The candidate vaccine effectively stimulated mice to produce high-titer anti-RBD specific antibody. Furthermore, the specific antibody titer and virus-neutralizing antibody (NAb) titer induced by the vaccine were increased significantly by the combination of the double adjuvants Al(OH)3 and CpG. Our results showed that the virus-NAb lasted for more than six months in mice. To summarize, we have obtained a SARS-CoV-2 vaccine based on the RBD of the S glycoprotein expressed in glycoengineered Pichia pastoris, which stimulates neutralizing and protective antibody responses. A technical route for fucose-free complex-type N-glycosylation modified recombinant subunit vaccine preparation has been established.