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

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.

Are Hamsters a Suitable Model for Evaluating the Immunogenicity of RBD-Based Anti-COVID-19 Subunit Vaccines?

Currently, SARS-CoV-2 spike receptor-binding-domain (RBD)-based vaccines are considered one of the most effective weapons against COVID-19. During the first step of assessing vaccine immunogenicity, a mouse model is often used. In this paper, we tested the use of five experimental animals (mice, hamsters, rabbits, ferrets, and chickens) for RBD immunogenicity assessments. The humoral immune response was evaluated by ELISA and virus-neutralization assays. The data obtained show hamsters to be the least suitable candidates for RBD immunogenicity testing and, hence, assessing the protective efficacy of RBD-based vaccines.

Neutralizing monoclonal antibodies against Russian strain of the West Nile virus.

We have developed a panel of 16 hybridomas secreting neutralizing monoclonal antibodies (Nt- MAbs) to Russian isolate (LEIV-Vlg99-27889-human) of the West Nile virus (WNV). Most of the Nt-Mabs were either IgG1 or IgG3 subtypes. Nine of the 16 neutralizing MAbs detected WNV protein E in Western blot. According to their Nt-activities, Western blot results and cross-reactivity, the MAbs were divided into four groups. Monoclonal antibodies from group I were able to neutralize WNV strains Vlg99-27889, Vlg00-27924, Hp-94, A-1640, A-72, Tur-2914, and Eg101. The Nt-activity of MAbs from groups II-IV towards these WNV strains was variable. Recombinant fragments E(1-180), E(1-321), and E(260-466) of protein E were used for preliminary mapping of domains recognized by Nt-MAbs. Only five Nt-MAbs were able to react with the recombinant polypeptides. The MAbs 9E2, 7G9, 11G3, and 7E6 from group Ia recognized Nt-epitope(s) between amino acids 321 and 466 of protein E and Nt-MAb 4F11 (group III) reacted with residues 1-180. This demonstrates that two discrete regions of protein E are involved in neutralization of WNV. Our data on immunochemical, biological activities of Nt-MAbs and mapping of Nt-epitopes using recombinant polypeptides suggest at least 13 different Nt-epitopes for WNV.