Comparative Immunogenicity of the Recombinant Receptor-Binding Domain of Protein S SARS-CoV-2 Obtained in Prokaryotic and Mammalian Expression Systems.

Iuliia A Merkuleva,Andrey P Rudometov,Larisa I Karpenko,Ekaterina A Volosnikova,Valentina S Nesmeyanova,Dmitry N Shcherbakov,Anastasiya A Isaeva,Svetlana V Belenkaya,Alexander A Ilyichev,Anton N Chikaev,Oleg V Pyankov,Arseniya A Shelemba,Elena I Kazachinskaia,Sophia S Borisevich,Daniil V Shanshin,Anna V Zaykovskaya,Mariya B Borgoyakova,Tatiana I Esina

doi:10.3390/vaccines10010096

Abstract

The receptor-binding domain (RBD) of the protein S SARS-CoV-2 is considered to be one of the appealing targets for developing a vaccine against COVID-19. The choice of an expression system is essential when developing subunit vaccines, as it ensures the effective synthesis of the correctly folded target protein, and maintains its antigenic and immunogenic properties. Here, we describe the production of a recombinant RBD protein using prokaryotic (pRBD) and mammalian (mRBD) expression systems, and compare the immunogenicity of prokaryotic and mammalian-expressed RBD using a BALB/c mice model. An analysis of the sera from mice immunized with both variants of the protein revealed that the mRBD expressed in CHO cells provides a significantly stronger humoral immune response compared with the RBD expressed in E.coli cells. A specific antibody titer of sera from mice immunized with mRBD was ten-fold higher than the sera from the mice that received pRBD in ELISA, and about 100-fold higher in a neutralization test. The data obtained suggests that mRBD is capable of inducing neutralizing antibodies against SARS-CoV-2.

Highlights

The COVID-19 pandemic caused by the SARS-CoV-2 virus has made vaccine development a top biomedical priority of modern healthcare
SARS-CoV-2 S glycoprotein mediates the binding of the virus to target cells through the ACE2 receptor, leading to its penetration into cells [15,16] and the development of infection
It has been shown that receptor-binding domain (RBD) is highly immunogenic, and RBD-specific antibodies possess the neutralizing activity that prevents humans and animals from being infected [16,20,21]

Summary

Introduction

The COVID-19 pandemic caused by the SARS-CoV-2 virus has made vaccine development a top biomedical priority of modern healthcare. According to the WHO, at the beginning of 2021, more than 250 candidate vaccines against SARS-CoV-2 were at the clinical and preclinical study stages (https://www.who.int/publications/m/item/draft-landscapeof-covid-19-candidate-vaccines (accessed on 11 December 2021)). Viral-vectored vaccines can elicit a specific immune response with neutralizing activity and protection, but they could induce anti-vector immunity or present pre-existing immunity, causing some harmful immune responses. DNA and nanoparticle vaccines maintain a strong safety profile; they have lower immunogenicity. Subunit vaccines are generally safe without causing potential harmful immune responses, making them promising vaccine candidates. Subunit vaccines may target specific, well-defined neutralizing epitopes, with improved immunogenicity and/or efficacy [2,3,4]. Subunit vaccines are easy to scale up to large-scale production; they have relative thermal stability and are suitable for shipment in a lyophilized form [5]

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