Middle East Respiratory Syndrome Coronavirus (MERS-CoV) spike protein as a DNA candidate vaccine

Background Middle East respiratory syndrome coronavirus (MERS-CoV) has become a global public health threat as it is capable of causing life-threatening disease with lower respiratory tract involvement, with a case fatality rate of ∼37.5%. So, ongoing efforts to develop MERS-CoV vaccines are mandatory, and their immunity profiles against different antigens and correlation with protection should be assessed. Aim The present study aimed to assess the neutralizing capacity of MERS-CoV spike (S) structural protein as a DNA-based candidate vaccine in mice models. Materials and methods The spike structural protein gene of MERS-CoV was amplified and cloned using pcDNA3.1 (negative) mammalian expression vector and competent Escherichia coli, for immunization of BALB/c mice as a DNA candidate vaccine, followed by a booster dose after 2 weeks. Sera of mice were collected within 8 weeks after prime vaccination for evaluation of the neutralizing capacity of DNA vaccine using plaque reduction neutralization test (PRNT) assay compared with the neutralizing capacity of inactivated whole virus vaccine, and also a group of mice was injected with empty vector in phosphate-buffered saline (PBS); PBS-pcDNA3.1 (negative) was used as a negative control. Results PRNT50 showed complete neutralization in mice vaccinated with inactivated MERS-CoV vaccine (PRNT50 titer, ∼1 : 160) 6 and 8 weeks of first immunization (P<0.01). The negative control group of mice injected with PBS-pcDNA3.1 (negative) did not show any neutralizing antibodies against MERS-CoV at 2, 4, 6, and 8 weeks after prime vaccination. The mice vaccinated with S gene-based DNA vaccine (pcDNA3.1-S) showed a significant increase of neutralizing antibodies against MERS-CoV strain NC163/2014 at week 8 after prime vaccination with PRNT50 titer, ∼1 : 80. Conclusion These results reported that the spike gene-expressed protein is a major immunogenic protein in MERS-CoV, so it would be recommended in future vaccine development.