Development of an Enterovirus 71 Vaccine Efficacy Test Using Human Scavenger Receptor B2 Transgenic Mice

Abstract

Enterovirus 71 (EV71) is a causative agent of hand-foot-mouth disease, and it sometimes causes severe neurological disease. Development of effective vaccines and animal models to evaluate vaccine candidates are needed. However, the animal models currently used for vaccine efficacy testing, monkeys and neonatal mice, have economic, ethical, and practical drawbacks. In addition, EV71 strains prepared for lethal challenge often develop decreased virulence during propagation in cell culture. To overcome these problems, we used a mouse model expressing human scavenger receptor B2 (hSCARB2) that showed lifelong susceptibility to EV71. We selected virulent EV71 strains belonging to the subgenogroups B4, B5, C1, C2, and C4 and propagated them using a culture method for EV71 without an apparent reduction in virulence. Here, we describe a novel EV71 vaccine efficacy test based on these hSCARB2 transgenic (Tg) mice and these virulent viruses. Adult Tg mice were immunized subcutaneously with formalin-inactivated EV71. The vaccine elicited sufficient levels of neutralizing antibodies in the immunized mice. The mice were subjected to lethal challenge with virulent viruses via intravenous injection. Survival, clinical signs, and body weight changes were observed for 2 weeks. Most immunized mice survived without clinical signs or histopathological lesions. The viral replication in immunized mice was much lower than that in nonimmunized mice. Mice immunized with the EV71 vaccine were only partially protected against lethal challenge with coxsackievirus A16. These results indicate that this new model is useful for in vivo EV71 vaccine efficacy testing. IMPORTANCE The development of new vaccines for EV71 relies on the availability of small animal models suitable for in vivo efficacy testing. Monkeys and neonatal mice have been used, but the use of these animals has several drawbacks, including high costs, limited susceptibility, and poor experimental reproducibility. In addition, the related ethical issues are considerable. The new efficacy test based on hSCARB2 Tg mice and virulent EV71 strains propagated in genetically modified cell lines presented here can overcome these disadvantages and is expected to accelerate the development of new EV71 vaccines.

A practical method for evaluating thein vivoefficacy of EVA-71 vaccine using a hSCARB2 knock-in mouse model

“…The body weight, clinical symptoms, viral load, pathological changes, and upregulation of cytokines can be used as evaluation indicators, alone or in combination, according to different requirements. Ayumi et al described a similar method of evaluating the efficacy of EV-A71 in vivo [ 21 ] using a transgenic mouse expressing hSCARB2, but a traditional vaccination procedure was used, and the test depends on a high-dose challenge with a virulent strain.…”

“…The in vivo protection efficacy of vaccines is of great concern to manufacturers, regulators and consumers. Animal models that are susceptible to the virus are essential for assessing the protective effect of a vaccine [20][21] . Both non-human primate and mouse models of EV-A71 infection have been developed 2,[22][23][24] .…”

Development of animal models for emerging infectious diseases by breaking the barrier of species susceptibility to human pathogens

“…Animal models of EV71 infection have generally been developed using neonatal mice, which exhibit obvious limitations in vaccine protection evaluation due to the short susceptibility period in neonatal mice. hSCARB2 (an EV71 receptor) transgenic mice show lifelong susceptibility to EV71 and were used to develop an adult model for lethal EV71 challenge, which resolved the bottleneck of evaluating the efficiency of EV71 vaccine candidates [ 34 ].…”

Inhibitory of EV-A71 virus-induced apoptosis by ZVAD through ROS mediated signaling pathways

“…Since then, outbreaks of HFMD have been documented in countries of the Asia (Xiao et al, 2018;Xing et al, 2014;Xu et al, 2019), including Singapore, Malaysia, China and so on, which takes huge losses to social economy. Although the vaccine of EV-A71 has been approved for the prevention of hand, foot and mouth disease, it is still facing various problems: time-consuming, laborious and low antibody titer (Chong et al, 2015;Imura et al, 2020a;Imura et al, 2020b). Currently, the pathogenicity of EV-A71 is not entirely understood and there are no effective antiviral treatments to treat EV-A71induced HFMD.…”