Long-term immunogenicity studies of formalin-inactivated enterovirus 71 whole-virion vaccine in macaques.

Chia-Chyi Liu,Yen-Hung Chow,Jen-Ren Wang,Chyi-Sing Hwang,Pele Chong,Suh-Chin Wu,Ai-Hsiang Chou,Jen-Ron Chiang,Wun-Syue Yang,Sze-Hsien Wu,Chin-Cheng Huang,Chien-Hsiung Pan,Dan-Chin Tsai,Shan Lu

doi:10.1371/journal.pone.0106756

Abstract

Enterovirus 71 (EV71) has caused epidemics of hand, foot and mouth diseases in Asia during the past decades and no vaccine is available. A formalin-inactivated EV71 candidate vaccine (EV71vac) based on B4 subgenotype has previously been developed and found to elicit strong neutralizing antibody responses in mice and humans. In this study, we evaluated the long-term immunogenicity and safety of this EV71vac in a non-human primate model. Juvenile macaques were immunized at 0, 3 and 6 weeks either with 10 or 5 µg doses of EV71vac formulated with AlPO4 adjuvant, or PBS as control. During the 56 weeks of studies, no fever nor local redness and swelling at sites of injections was observed in the immunized macaques. After single immunization, 100% seroconversion based on 4-fold increased in neutralization titer (Nt) was detected in EV71vac immunized monkeys but not PBS controls. A dose-dependent IgG antibody response was observed in monkeys receiving EV71vac immunization. The Nt of EV71vac immunized macaques had reached the peak after 3 vaccinations, then decreased gradually; however, the GMT of neutralizing antibody in the EV71vac immunized macaques were still above 100 at the end of the study. Correspondingly, both dose- and time-dependent interferon-γ and CD4+ T cell responses were detected in monkeys receiving EV71vac. Interestingly, similar to human responses, the dominant T cell epitopes of macaques were identified mainly in VP2 and VP3 regions. In addition, strong cross-neutralizing antibodies against most EV71 subgenotypes except some C2 and C4b strains, and Coxsackievirus A16 were observed. In summary, our results indicate that EV71vac elicits dose-dependent T-cell and antibody responses in macaques that could be a good animal model for evaluating the long-term immune responses elicited by EV71 vaccines.

Highlights

Enterovirus 71 (EV71), a non-enveloped RNA virus of the family Picornaviridae, genus Enterovirus was first identified in California 45 years ago and subsequently reported in many parts of world [1,2]
EV71 and Coxsackievirus A16 (CVA16) are two major enteroviruses that cause epidemics of hand-foot-and-mouth disease (HFMD), but EV71 infection is associated with severe neurological diseases in young children [2]
Given that EV71 epidemics happen frequently in Asia-Pacific countries [2,9], it is important for an EV71 vaccine to offer safe and long-term protection

Summary

Introduction

Enterovirus 71 (EV71), a non-enveloped RNA virus of the family Picornaviridae, genus Enterovirus was first identified in California 45 years ago and subsequently reported in many parts of world [1,2]. EV71 and Coxsackievirus A16 (CVA16) are two major enteroviruses that cause epidemics of hand-foot-and-mouth disease (HFMD), but EV71 infection is associated with severe neurological diseases in young children [2]. Genetic mutation and recombination between the RNA genome are known to contribute to the evolution of enterovirus [3,4]. Evidences of the intratypic and intertypic recombination in enterovirus have been reported during the recent epidemic in Asia. The intertypic recombination of genes derived from EV71 and other enteroviruses such as CVA16, 14 and 4 had been happened to the emergence of subgenotype C4a and C4b [6]. The same phenomenon was reported in subgenotype B and C2 [7,8]. The recombination process could allow EV71 to escape the host immunity and cause epidemic. Neither a prophylactic vaccine nor antiviral therapy against HFMD is available

Methods

Results

Conclusion