Abstract
Massive production of efficacious SARS-CoV-2 vaccines is essential for controlling the ongoing COVID-19 pandemic. We report here the preclinical development of yeast-produced receptor-binding domain (RBD)-based recombinant protein SARS-CoV-2 vaccines. We found that monomeric RBD of SARS-CoV-2 could be efficiently produced as a secreted protein from transformed Pichia pastoris (P. pastoris) yeast. Yeast-derived RBD-monomer possessed functional conformation and was able to elicit protective level of neutralizing antibodies in mice. We further designed and expressed a genetically linked dimeric RBD protein in yeast. The engineered dimeric RBD was more potent than the monomeric RBD in inducing long-lasting neutralizing antibodies. Mice immunized with either monomeric RBD or dimeric RBD were effectively protected from live SARS-CoV-2 virus challenge even at 18 weeks after the last vaccine dose. Importantly, we found that the antisera raised against the RBD of a single SARS-CoV-2 prototype strain could effectively neutralize the two predominant circulating variants B.1.1.7 and B.1.351, implying broad-spectrum protective potential of the RBD-based vaccines. Our data demonstrate that yeast-derived RBD-based recombinant SARS-CoV-2 vaccines are feasible and efficacious, opening up a new avenue for rapid and cost-effective production of SARS-CoV-2 vaccines to achieve global immunization.
Highlights
The pandemic of coronavirus disease 2019 (COVID-19), caused by the newly emerged severe acute respiratoryS2, which are responsible for receptor binding and membrane fusion, respectively
Purified receptor-binding domain (RBD) was subjected to treatment with endoglycosidases endo-N-acetylglucosaminidase H (endo H) or PNGase F, which cleave within the chitobiose core of high mannose and some hybrid oligosaccharides from N-linked glycoproteins or remove all N-linked oligosaccharides from glycoproteins, respectively[25]
These results indicated that yeast-produced monomeric RBD is glycosylated with N-glycans
Summary
The pandemic of coronavirus disease 2019 (COVID-19), caused by the newly emerged severe acute respiratoryS2, which are responsible for receptor binding and membrane fusion, respectively. Most vaccines use or express SARS-CoV-2 S or its RBD as the vaccine antigen, because they are the main inducer of neutralizing antibodies[15,16,17]. Insect cell- or mammalian cell-produced recombinant SARS-CoV-2 S or RBD protein vaccines have been shown to potently induce neutralizing antibodies in preclinical and clinical trials[12,13,18,19,20]. One of these recombinant protein-based candidate vaccines, the CHO cell-produced dimeric tandem-repeat RBD vaccine, has recently been authorized for emergency use in humans[12]. Despite the successful demonstration of the CHO cell-derived recombinant RBD vaccine, such a technology and its associated production facility are not available in most developing countries, calling for a more cost-effective and widely used recombinant expression system that may allow rapid adaptation by vaccine manufacturers in developing countries for local production of recombinant RBD protein vaccines
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