Immunogenicity and protective efficacy of an EV71 virus-like particle vaccine against lethal challenge in newborn mice

Abstract

Enterovirus 71(EV71) has caused severe epidemics of hand, foot and mouth disease (HFMD) in the Asia Pacific in recent years, particularly in infants and pre-school children. It has become a serious public health threat, as currently there are no approved vaccines or antiviral drugs for EV71 infection. Many EV71 vaccines have been under development worldwide, however the main focus is inactivated EV71 vaccines. For example, the inactivated EV71 vaccine has recently finished phase III clinical trial in Mainland China. There have been very few studies on EV71 virus like particles (VLPs). In this study, the immunogenicity and protective potency of the EV71 VLPs produced in insect cells were evaluated in mice with different dosages. Our results showed that EV71 VLPs could elicit high titers of neutralizing antibodies (NTAbs) in a dose-dependent manner and NTAbs were sustained after the second injection with an average GMT (geometric mean titer) level from 19 to 2960 in immunized mice. Survival rates were 100%, 100%, 85%, and 40% after challenge with 15 LD₅₀ (median lethal dose) of EV71 in these newborn mice, respectively. ED₅₀ (50% effective dose) of VLPs was 0.20 μg/dose in newborn mice, while NTAb titer under this dosage was about 50. Passive protection was determined with 2 methods and demonstrated that the survival rates were positively correlated with NTAb titers, which at 24 and 54 induced 50% survival rates in experimental animals. The ED₅₀ of VLP vaccines and the passive NTAb titers were also analyzed. The maternal NTAb titer was similar as the passive NTAb titer in the mouse model challenged with our lethal mouse EV71 strain. Hence, our work has provided preliminary data on the protection potency of VLPs as a vaccine candidate and would facilitate future VLP vaccine development.

Keywords:

• ED₅₀ (50% effective dose)
• enterovirus 71
• hand foot and mouth disease
• HFMD
• VLP vaccine
• immunogenicity

Disclosure of Potential Conflicts of Interest

No potential conflicts of interest were disclosed.

Funding

This work was supported by the National 12 th Five Major Special Projects Funding Program (No. 2012ZX10004701) and National High Technology Research and Development Program (“863” program, No. 2012AA02A402) from the Ministry of Science and Technology of the People's Republic of China.