A Novel Bacterium-Like Particle Vaccine Displaying the MERS-CoV Receptor-Binding Domain Induces Specific Mucosal and Systemic Immune Responses in Mice.

Cuiling Wang ,Yuwei Gao,Tiecheng Wang,Wenzhao Sun ,Guohua Li,Xianzhu Xia,Hualei Wang,Yang Bi ,Entao Li,Chuanyu Liu,Ying Zhang,Hang Chi,Pei Huang,Jianzhong Wang,Shengnan Zhang,Ran Mo ,Na Feng,Feihu Yan,Zhenshan Wang,Hongli Jin,Yongkun Zhao

doi:10.3390/v11090799

Abstract

Middle East respiratory syndrome coronavirus (MERS-CoV), a new coronavirus that has been causing severe and fatal acute respiratory illnesses in humans since its outbreak in 2012, has raised public fear worldwide. The development of prophylactics and therapeutics is urgently needed to prevent and control MERS-CoV infections. In this study, a bacterium (Lactococcus lactis)-like particle (BLP) vaccine displaying the MERS-CoV receptor-binding domain (RBD) was developed, and gram-positive enhancer matrix (GEM) particles were used as substrates to externally bind to the MERS-CoV RBD through a protein anchor (PA). The designs included different numbers of lysin motif (LysM) repeats in the PAs linked by linkers (RBD-linker-PA2 (RLP2), RBD-linker-PA3 (RLP3) and RBD-PA3 (RP3)), and three LysM repeats and a linker in the fusion proteins increased the binding activity to the RBD. The specific immune responses were tested by intranasally immunizing mice with RLP3-GEM with or without the adjuvant GEL01. The results showed that GEL01-adjuvanted RLP3-GEM increased the systemic humoral, cellular and local mucosal immune responses in the mouse model, especially in the intestinal tract. The above results indicate that the MERS-CoV BLP product has the potential to be developed into a promising mucosal candidate vaccine to protect against MERS-CoV infections.

Highlights

Middle East respiratory syndrome coronavirus (MERS-CoV), a beta coronavirus, causes severe and lethal acute respiratory disease in humans and is remarkably different from other human coronaviruses, Viruses 2019, 11, 799; doi:10.3390/v11090799 www.mdpi.com/journal/virusesViruses 2019, 11, 799 including HCoV-229E, HCoVNL63, HCoV-HKU1, and HCoV-OC43, which are known to cause mild respiratory infections [1,2]
The Immunofluorescence Assay (IFA) results showed that compared to the control cells, the Sf9 cells expressing RLP2, RLP3, and RP3 proteins emitted strong green fluorescence signals with an anti-MERS-S polyclonal antibody for receptor-binding domain (RBD), suggesting that the expressed fusion proteins have good antigenicity (Figure 1c–g)
RLP3 -gram-positive enhancer matrix (GEM) plus GEL01 group (Figure 4f). These results showed that mucosal immune responses were induced by the RLP3 -GEM candidate vaccine, and the effect was significantly increased by the adjuvant GEL01

Summary

Introduction

Middle East respiratory syndrome coronavirus (MERS-CoV), a beta coronavirus, causes severe and lethal acute respiratory disease in humans and is remarkably different from other human coronaviruses, Viruses 2019, 11, 799; doi:10.3390/v11090799 www.mdpi.com/journal/virusesViruses 2019, 11, 799 including HCoV-229E, HCoVNL63, HCoV-HKU1, and HCoV-OC43, which are known to cause mild respiratory infections [1,2]. In May. 2015 the MERS outbreak in South Korea, which was the largest outbreak outside the Middle East and caused 36 deaths in 186 cases from a single infected person [4,5]; this outbreak raised the concerns of a potential global MERS-CoV pandemic. Since MERS-CoV is a respiratory pathogen, any MERS-CoV vaccination that induces antigen-specific secretory IgA (sIgA) antibodies at the mucosal surfaces probably has the effects of preventing MERS-CoV replication at the site of virus infection [7]. The mode of MERS-CoV transmission is not clearly understood, but one study has proven that the human intestinal tract may be a new transmission route for MERS-CoV [8], indicating that antigen-specific sIgA antibodies in the gastrointestinal mucosa are a considerable indicator. There is an urgent need to develop an effective mucosal immune vaccine against MERS-CoV, especially those inducing gastrointestinal mucosal immunity

Methods

Results

Conclusion