Recombinant Adenoviral Vaccine Carrying the S1 Subunit of the Middle East Respiratory Syndrome Coronavirus (MER‐CoV) Spike Gene Can Elicit Cellular Immune Response in Mice

Abstract

Middle East respiratory syndrome (MERS‐CoV) coronavirus has distributed in a vast area of Middle East countries since 2012. Then the virustransmitted to other continents with high morbidity and mortality rates. Neither drug nor vaccine is currently available against MERS. Spike protein is the main immunogenic part of the MERS‐CoV. Its role in viral entry and replication has been established. As well, it contains the S1 subunit which has the receptor binding domain (RBD). The latest has a prominent role in binding with the host DPP4 and elicit protective immunity. In this study, a recombinant adenoviral‐based vaccine carrying the S1 subunit of MERS‐CoV genome was constructed. Experimental mice were immunized intramuscularly with the vaccine and boosted intranasally three weeks later. Experimental animals were distributed randomly into three groups; group 1 received the recombinant vector vaccine; group 2 received only adenovirus vector and the last group served as control group that were injected with phosphate buffer saline (PBS). The expression of the S1 protein in kidneys and lungs was detected using conventional PCR method targeting 1142 bp region within the S1 subunit at week 3 and 5 post vaccination as well as by Immunohistochemistry technique at week 6. Immune response was evaluated in cell culture obtained from different experimental groups after in vitro stimulation with a specific 9‐mer epitope within the S1 protein (CYSSLILDY). Cytokines such as IFN‐γ, IL‐12 and IL‐4 were analyzed in cell culture supernatant by enzyme linked immunosorbant assay (ELISA) and by qRT‐PCR for only IFN‐γ and IL‐4 in culture cell pellet. In addition, specific antibody response in serum of the experimental animals was also investigated at week 4 and 6 after vaccination. It was revealed that the S1 protein was present in lung and kidney of the vaccinated animals. In Immunohistochemistry technique the S1 protein was clearly expressed in the proximal tubules of mouse kidney of vaccinated animals. This vaccine elicited specific S1‐IgG antibody response which was detected in the sera of the vaccinated mice at week 4 and 6. The results also revealed a significant increase in the amount of Th1‐related cytokines (IFN‐γ and IL‐12), and significant decrease in the Th2‐related cytokine (IL‐4) in the splenocytes cell culture of the vaccinated group was noticed in comparing with those in control groups (vector and PBS). Similar results were shown in the qRT‐PCR analysis to the IFN‐γ and IL‐4 genes expression. These findings reveal that the recombinant adenovirus vaccine carrying the MERS‐S1 subunit can elicit Th1‐immune response (cellular immunity) in mice, and give a promise to develop an effective vaccine that can control and might prevent MERS‐CoV human infection in the futureSupport or Funding InformationJUST deanship grant No. 20140275