EV71: an emerging infectious disease vaccine target in the Far East?

Intranasal immunization with curdlan induce Th17 responses and enhance protection against enterovirus 71

Mucosal surfaces are in contact with the external environment and protect the body from infection by various microbes. To prevent infectious diseases at the first line of defense, the establishment of pathogen-specific mucosal immunity by mucosal vaccine delivery is needed. Curdlan, a 1,3-β-glucan has a strong immunostimulatory effect when delivered as a vaccine adjuvant. Here, we investigated whether intranasal administration of curdlan and antigen (Ag) could induce sufficient mucosal immune responses and protect against viral infections. Intranasal co-administration of curdlan and OVA increased OVA-specific IgG and IgA Abs in both serum and mucosal secretions. In addition, intranasal co-administration of curdlan and OVA induced the differentiation of OVA-specific Th1/Th17 cells in the draining lymph nodes. To investigate the protective immunity of curdlan against viral infection, intranasal co-administration of curdlan with recombinant VP1 of EV71 C4a was administered and showed enhanced protection against enterovirus 71 in a passive serum transfer model using neonatal hSCARB2 mice, although intranasal administration of VP1 plus curdlan increased VP1-specific helper T cells responses but not mucosal IgA. Next, Mongolian gerbils were intranasally immunized with curdlan plus VP1, and they had effective protection against EV71 C4a infection, while decreasing viral infection and tissue damage by inducing Th17 responses. These results indicated that intranasal curdlan with Ag improved Ag-specific protective immunity by enhancing mucosal IgA and Th17 against viral infection. Our results suggest that curdlan is an advantageous candidate as a mucosal adjuvant and delivery vehicle for the development of mucosal vaccines.

Epidemiological Investigation of Feline Upper Respiratory Tract Infection Encourages a Geographically Specific FCV Vaccine

A total of 1158 cats with feline upper respiratory tract infection were incorporated from twenty animal hospitals in Wuhan, China, from April 2019 to April 2022 to investigate the epidemiology of feline calicivirus (FCV), herpesvirus-1 (FHV-1), Mycoplasma felis (M. felis) and Chlamydia felis (C. felis) for the development of a geographically-specific FCV vaccine with reference to prevalence and risk factors for infection. The 871 samples (75.2%) of kittens were younger than 12 months, of which 693 were males, and 456 were females. Among the samples, 443 were British shorthair cats, accounting for 38.3%, and 252 were Chinese rural cats, accounting for 21.8%. PCR/RT-PCR detection of the above four viruses (FCV, FHV-1, M. felis, and C. felis) in the upper respiratory tract of cats showed that the total positive samples were 744 (64.3%), including 465 positive samples of feline calicivirus, accounting for 40.2% of the total 1158 samples. There were 311 positive samples of M. felis, accounting for 26.9% of the total samples, ranked second in clinical practice. The 180 positive samples of feline herpesvirus accounted for 15.5%, and 85 positive samples of Chlamydia felis accounted for 7.3%. Among them, the number of positive samples of single pathogenic infections was 493, accounting for 66.3% of the total 744 positive samples. Double, triple, and quadruple infections accounted for 28.2%, 5.0%, and 0.5%, respectively, with the highest proportion of single infections. The molecular biological characteristics of the 17 isolated FCVd strains in Wuhan were further analyzed. It was found that the F9 vaccine strain and the antigenic epitopes in the 5'HVR of the E region were collated with the F9 vaccine strain. Moreover, phylogenetic tree analysis showed that the strains related to the F9 and 255 vaccines were distantly related, leading to the failure of the vaccine. In addition, the strains associated with the F9 and 255 vaccines were distant, which might lead to vaccine failure in anticipation of the development of a more phylogenetically close FCV vaccine in China and may require the development of a vaccine for a locally related FCV strain.

Effect of difference between EV-A71 virus epidemic strain and "vaccine strain" on neutralizing antibody titer

Hand, foot and mouth disease was mainly caused by EV-A71 virus. The main antigen structure of VP1 region of EV-A71 was easily varied. Here, we investigated the seroprevalence of EV-A71 based on a large group of healthy individuals in Beijing, China, in order to study the effectiveness of EV-A71 vaccine in a real-world setting. BrCr and the clinical strain isolated from the Chinese mainland in 2008 ("vaccine strain:"CMU4232/BJ/CHN/2008), EV-A71 C4 epidemic strains isolated in 2010, 2013, and 2016, were tested for neutralizing antibodies (NtAb) in every year. Phylogenetic tree analysis of the EV-A71 strains above, as well as amino acid composition homologous sequence analysis were applied. The "vaccine strain" has 83.0% homology with FY23, H07 and FY7VP5. It belongs to the same branch of C4a as 10 C4, 13 C4 and 16 C4, and differs from the amino acid sites 283 and 293 of 16 C4. Compared with "vaccine strains," there was a significant difference between the 50-59 years old age group when the NtAb titer of 16 C4 strain was 1:512-1:1024. Our results suggest that changes in the functional epitopes of NtAb caused by amino acid 283 and 293 loci in EV-A71 strains may affect the production of neutralizing antibodies.

Optimizing laboratory-based surveillance networks for monitoring multi-genotype or multi-serotype infections

With the aid of laboratory typing techniques, infectious disease surveillance networks have the opportunity to obtain powerful information on the emergence, circulation, and evolution of multiple genotypes, serotypes or other subtypes of pathogens, informing understanding of transmission dynamics and strategies for prevention and control. The volume of typing performed on clinical isolates is typically limited by its ability to inform clinical care, cost and logistical constraints, especially in comparison with the capacity to monitor clinical reports of disease occurrence, which remains the most widespread form of public health surveillance. Viewing clinical disease reports as arising from a latent mixture of pathogen subtypes, laboratory typing of a subset of clinical cases can provide inference on the proportion of clinical cases attributable to each subtype (i.e., the mixture components). Optimizing protocols for the selection of isolates for typing by weighting specific subpopulations, locations, time periods, or case characteristics (e.g., disease severity), may improve inference of the frequency and distribution of pathogen subtypes within and between populations. Here, we apply the Disease Surveillance Informatics Optimization and Simulation (DIOS) framework to simulate and optimize hand foot and mouth disease (HFMD) surveillance in a high-burden region of western China. We identify laboratory surveillance designs that significantly outperform the existing network: the optimal network reduced mean absolute error in estimated serotype-specific incidence rates by 14.1%; similarly, the optimal network for monitoring severe cases reduced mean absolute error in serotype-specific incidence rates by 13.3%. In both cases, the optimal network designs achieved improved inference without increasing subtyping effort. We demonstrate how the DIOS framework can be used to optimize surveillance networks by augmenting clinical diagnostic data with limited laboratory typing resources, while adapting to specific, local surveillance objectives and constraints.

A novel polypeptide vaccine and Adjuvant Formulation of EV71

Hand foot and mouth disease (HFMD) is an infectious disease mainly caused by enterovirus 71 (EV 71). However, the effective treatment is limited currently. The aim of this study was to investigate the activity of the vaccine including the EV71 polypeptides mixed with a novel adjuvant containing CpG oligodeoxynucleotides (CpG ODNs). After collecting mouse sera, we determined the antibody concentration in serum by enzyme-linked immunosorbent assays (ELISA). Then CD19+ CD27+ B cells in the spleen were analyzed by flow cytometry. The assay revealed that a substantial increase in antibody titers was achieved. This indicates a high level of immunogenicity for peptide vaccine and the good stability of adjuvant, also suggests that the combination of vaccine and adjuvant can stimulate the production of high-level antibodies and CD19+ CD27+ B lymphocytes in mice. Furthermore, the antibody could effectively identify EV71 inactivated virus. The results demonstrated that the autonomous construction of EV71 polypeptide vaccine had a good immunogenicity. Moreover, the peptide vaccine injection with a novel adjuvant, which is easy to prepare, could cause a high antibody level of EV71, and shown a good application prospect.

A practical method for evaluating the in vivo efficacy of EVA-71 vaccine using a hSCARB2 knock-in mouse model

Hand-foot-and-mouth disease is a contagious disease common among children under 5 years old worldwide. It is caused by strains of enterovirus, especially EV-A71, which can lead to severe disease. Vaccines are the only way to fight this disease. Accordingly, it is necessary to establish an efficient and accurate methodology to evaluate vaccine efficacy in vivo. Here, we established a practical method using a hSCARB2 knock-in mouse model, which was susceptible to EV-A71 infection at 5-6 weeks of age, to directly determine the efficacy of vaccines. Unlike traditional approaches, one-week-old hSCARB2 mice were immunized twice with a licensed vaccine, with an interval of a week. The titre of antibodies was measured after 1 week. Mice at 4 weeks of age were challenged with EV-A71 intraperitoneally and intracranially, respectively. The unimmunized hSCARB2 mice displayed systemic clinical symptoms and succumbed to the disease at a rate of approximately 50%. High viral loads were detected in the lungs, brain, and muscles, accompanied by clear pathological changes. The expression of IL-1β, IL-13, IL-17, and TNF-α was significantly upregulated. By contrast, the immunized group was practically normal and indistinguishable from the control mice. These results indicate that the hSCARB2 knock-in mouse is susceptible to infection in adulthood, and the in vivo efficacy of EV-A71 vaccine could be directly evaluated in this mouse model. The method developed here may be used in the development of new vaccines against HFMD or quality control of licensed vaccines.

A single mutation in the cis-acting replication element identified within the EV-A71 2C-coding region causes defects in virus production in cell culture

ABSTRACTEnterovirus A71 (EV-A71) can cause hand, foot and mouth disease with neurological and systemic complications, most frequently affecting children and infants. We describe a cis-acting replication element (cre) with a conserved stem-loop structure within the EV-A71 2C-coding region. By site-directed mutagenesis and reverse genetics using the EV-A71 full-length genome and the EV-A71 replicon containing the firefly luciferase reporter gene in place of the P1 region, the stem-loop structure and the AAACA in the loop of the cre were confirmed to be required for the EV-A71 replication phenotype. EV-A71 genomes containing a mutation at the first or third A residue of AAACA could not be recovered. Insertion of a wild-type cre from EV-A71 or poliovirus in the 5'UTR led to successful recovery of the replication of nonviable mutants. Furthermore, the cre mutants showed lower binding capacity with the host cellular factor IGF2BP2, knockdown of which resulted in a significant decrease in EV-A71 production. All the available evidence shows the location independence but functional importance of the interaction of the cre with the cellular host for efficient production of EV-A71, contributing to the growing body of knowledge regarding picornavirus cres.

Viral determinants that drive Enterovirus-A71 fitness and virulence

Hand, Foot and Mouth Disease (HFMD) is usually a self-limiting, mild childhood disease that is caused mainly by Coxsackie virus A16 (CVA16) and Enterovirus A71 (EV-A71), both members of the Picornaviridae family. However, recurring HFMD outbreaks and epidemics due to EV-A71 infection in the Western Pacific region, and the propensity of EV-A71 strains to cause severe neurological complications have made this neurotropic virus a serious public health concern in afflicted countries. High mutation rate leading to viral quasispecies combined with frequent intra- and inter-typic recombination events amongst co-circulating EV-A71 strains have contributed to the great diversity and fast evolution of EV-A71 genomes, making impossible any accurate prediction of the next epidemic strain. Comparative genome sequence analyses and mutagenesis approaches have led to the identification of a number of viral determinants involved in EV-A71 fitness and virulence. These viral determinants include amino acid residues located in the structural proteins of the virus, affecting attachment to the host cell surface, receptor binding, and uncoating events. Critical residues in non-structural proteins have also been identified, including 2C, 3A, 3C proteases and the RNA-dependent RNA polymerase. Finally, mutations altering key secondary structures in the 5’ untranslated region were also found to influence EV-A71 fitness and virulence. While our current understanding of EV-A71 pathogenesis remains fragmented, these studies may help in the rational design of effective treatments and broadly protective vaccine candidates.

Honeysuckle Aqueous Extracts Induced let-7a Suppress EV71 Replication and Pathogenesis In Vitro and In Vivo and Is Predicted to Inhibit SARS-CoV-2

Honeysuckle (Lonicera japonica Thunb) is a traditional Chinese medicine (TCM) with an antipathogenic activity. MicroRNAs (miRNAs) are small non-coding RNA molecules that are ubiquitously expressed in cells. Endogenous miRNA may function as an innate response to block pathogen invasion. The miRNA expression profiles of both mice and humans after the ingestion of honeysuckle were obtained. Fifteen overexpressed miRNAs overlapped and were predicted to be capable of targeting three viruses: dengue virus (DENV), enterovirus 71 (EV71) and SARS-CoV-2. Among them, let-7a was examined to be capable of targeting the EV71 RNA genome by reporter assay and Western blotting. Moreover, honeysuckle-induced let-7a suppression of EV71 RNA and protein expression as well as viral replication were investigated both in vitro and in vivo. We demonstrated that let-7a targeted EV71 at the predicted sequences using luciferase reporter plasmids as well as two infectious replicons (pMP4-y-5 and pTOPO-4643). The suppression of EV71 replication and viral load was demonstrated in two cell lines by luciferase activity, RT-PCR, real-time PCR, Western blotting and plaque assay. Furthermore, EV71-infected suckling mice fed honeysuckle extract or inoculated with let-7a showed decreased clinical scores and a prolonged survival time accompanied with decreased viral RNA, protein expression and virus titer. The ingestion of honeysuckle attenuates EV71 replication and related pathogenesis partially through the upregulation of let-7a expression both in vitro and in vivo. Our previous report and the current findings imply that both honeysuckle and upregulated let-7a can execute a suppressive function against the replication of DENV and EV71. Taken together, this evidence indicates that honeysuckle can induce the expression of let-7a and that this miRNA as well as 11 other miRNAs have great potential to prevent and suppress EV71 replication.

GATA1/SP1 and miR-874 mediate enterovirus-71-induced apoptosis in a granzyme-B-dependent manner in Jurkat cells

Enterovirus 71 (EV71)-induced T lymphocyte apoptosis plays an important role in hand, foot, and mouth disease (HFMD), and granzyme B (GZMB) has been shown to be critical for this process. However, the mechanisms underlying GZMB-mediated apoptosis of T lymphocytes remain unknown. In this study, we investigated whether transcription factors and microRNAs (miRNAs) are involved in GZMB-mediated apoptosis of T lymphocytes in response to EV71 infection. Our findings indicated that EV71 infection significantly induced apoptosis in Jurkat cells, a human T lymphocytes cell line, as revealed in flow cytometric analysis. Furthermore, EV71 increased the expression of pro-apoptosis Bcl-2-associated X (Bax) and cleaved caspase 3 but decreased the expression of anti-apoptosis B-cell lymphoma protein 2 (Bcl2). GZMB knockdown decreased cell apoptosis and prevented EV71-induced changes in the expression of Bax, cleaved caspase 3, and Bcl2 in Jurkat cells, highlighting the role of GZMB as a key factor in EV71-induced apoptosis. Our study also indicated that overexpression of the transcription factors GATA binding factor 1 (GATA1) and specificity protein 1 (SP1) significantly increased luciferase activity when this gene was inserted in the GZMB 3' untranslated region (3'UTR). GATA1/SP1 overexpression induced cell apoptosis, increased the expression of Bax and cleaved caspase 3, and decreased the expression of Bcl2. Finally, our results suggested that miR-874 plays an essential role in GZMB-mediated cell apoptosis, since an miR-874 mimic decreases the expression of GZMB by targeting its 3'UTR. Collectively, these data indicated that GATA1/SP1 and miR-874 mediate EV71-induced apoptosis in a granzyme B-dependent manner. This signaling pathway may provide a new pharmacological target for the prevention and treatment of HFMD.

Vaccine development and therapeutic design for 2019-nCoV/SARS-CoV-2: Challenges and chances

The ongoing outbreak of the recently emerged 2019 novel coronavirus (nCoV), which has seriously threatened global health security, is caused by severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) with high morbidity and mortality. Despite the burden of the disease worldwide, still, no licensed vaccine or any specific drug against 2019‐nCoV is available. Data from several countries show that few repurposed drugs using existing antiviral drugs have not (so far) been satisfactory and more recently were proven to be even highly toxic. These findings underline an urgent need for preventative and therapeutic interventions designed to target specific aspects of 2019‐nCoV. Again the major factor in this urgency is that the process of data acquisition by physical experiment is time‐consuming and expensive to obtain. Scientific simulations and more in‐depth data analysis permit to validate or refute drug repurposing opportunities predicted via target similarity profiling to speed up the development of a new more effective anti‐2019‐nCoV therapy especially where in vitro and/or in vivo data are not yet available. In addition, several research programs are being developed, aiming at the exploration of vaccines to prevent and treat the 2019‐nCoV. Computational‐based technology has given us the tools to explore and identify potentially effective drug and/or vaccine candidates which can effectively shorten the time and reduce the operating cost. The aim of the present review is to address the available information on molecular determinants in disease pathobiology modules and define the computational approaches employed in systematic drug repositioning and vaccine development settings for SARS‐CoV‐2.

Enterovirus A71 capsid protein VP1 increases blood-brain barrier permeability and virus receptor vimentin on the brain endothelial cells

Enterovirus A71 (EV-A71) is the major cause of severe hand-foot-and-mouth diseases (HFMD), especially encephalitis and other nervous system diseases. EV-A71 capsid protein VP1 mediates virus attachment and is the important virulence factor in the EV-A71pathogenesis. In this study, we explored the roles of VP1 in the permeability of blood-brain barrier (BBB). Sera albumin, Evans blue, and dextran leaked into brain parenchyma of the 1-week-old C57BL/6J mice intracranially injected with VP1 recombinant protein. VP1 also increased the permeability of the brain endothelial cells monolayer, an in vitro BBB model. Tight junction protein claudin-5 was reduced in the brain tissues or brain endothelial cells treated with VP1. In contrast, VP1 increased the expression of virus receptor vimentin, which could be blocked with VP1 neutralization antibody. Vimentin expression in the VP1-treated brain endothelial cells was regulated by TGF-β/Smad-3 and NF-κB signal pathways. Moreover, vimentin over-expression was accompanied with compromised BBB. From these studies, we conclude that EV-A71 virus capsid protein VP1 disrupted BBB and increased virus receptor vimentin, which both may contribute to the virus entrance into brain and EV-A71 CNS infection.

Pathogenesis of hand-foot-mouth disease caused by enterovirus 71

Hand-foot-mouth disease (HFMD) is a global infectious disease. The infected population is mainly infants and young children. Enterovirus 71 (EV71) is the main pathogen. In addition to HFMD, EV71 infection can also affect the nervous system and other organs, resulting in aseptic meningitis, brainstem encephalitis, and poliomyelitis-like paralysis, causing serious harm to children's health. At present, the pathogenesis of HFMD caused by EV71 is still unclear, and there is no effective treatment. In this paper, we discuss the factors influencing EV71 infection from the aspects of virus gene recombination and spontaneous mutation, host genes, and receptor sites, review the pathogenesis of HFMD caused by EV71 based on the study findings from animal infection models, and explore the main problems in the study of pathogenesis of this condition, in order to provide reference for the prevention and treatment of HFMD and for the development of new drugs or effective vaccines for EV71 infection.

Exploiting the Lymph-Node-Amplifying Effect for Potent Systemic and Gastrointestinal Immune Responses via Polymer/Lipid Nanoparticles

Parenteral vaccinations are not able to elicit effective systemic and gastrointestinal immune protection simultaneously because the lymphocytes are typically restricted to primed tissues. Although all-trans retinoic acid (atRA) was reported to trigger the gut-homing of immunocytes, the bioavailability and systemic immune responses remain limited for use in robust enteric vaccinations. Here, we show that co-delivery of atRA, CpG oligodeoxynucleotides (CpG), and antigens via engineered polymer/lipid nanoparticles (PLNPs) could exploit the amplifying function of draining lymph nodes (DLNs) for potent gut tropism and immune activations. After intramuscular injection, forming an immune-potentiated environment at the injection site, the PLNPs induced the designated transfer of primed dendritic cells (DCs) to the DLNs instead of the gastrointestinal tissues. Within the DLNs, the immune-potentiated environment markedly amplified the antigen presentation and homing receptor switch among immunocytes, which simultaneously stimulated the preferential dissipation of activated lymphocytes in the peripheral and gastrointestinal tissues, that is, exerted a DLN-amplifying effect. Compared with current atRA-containing formulations, the PLNPs not only boosted potent IgG secretions and T cell activations in the peripheral tissue but also provoked robust T cell homing and antigen-specific IgA levels in the gastrointestinal tracts in both ovalbumin and EV71 vaccinations. These data indicate that exploiting DLN amplification can stimulate potent systemic and gastrointestinal responses for more efficient enteric vaccinations.

Transmission and serotype features of hand foot mouth disease in household contacts in Dong Thap, Vietnam

Background

Hand, foot and mouth disease (HFMD) has emerged as a major public health issue in Vietnam since 2003. We aimed to investigate the household transmission of HFMD and its causative viruses from 150 households in a high incidence province in Vietnam.

Methods

A longitudinal study was conducted in patients presenting to the provincial hospital with a HFMD-like syndrome, along with their household members between April and August 2014 in Dong Thap Province. Each participant was followed up for 2 weeks. We enrolled 150 patients aged under 15 who were clinically diagnosed with HFMD in Dong Thap Hospital, 600 household members, and 581/600 household members completed the study. All participants were interviewed using a standard questionnaire. Throat swabs and blood samples were taken for molecular detection of viruses and assessment of neutralizing antibodies, respectively. Index cases were defined using a clinical case definition, household contact cases were defined using a similar definition applied to the 2 weeks before admission and 2 weeks after discharge of the index case. Characteristics of index cases, household contacts, the attack rate, serotype features and related factors of HFMD were reported.

Result

Among 150 index cases, 113 were laboratory confirmed: 90/150 were RT-PCR-positive, 101/142 had a ≥ 4-fold increase of neutralizing antibody against Enterovirus A71 (EV-A71), Coxsackievirus (CV) A6 or CV-A16 across the two samples collected. 80/150 (53%) were males, and 45/150 (30%) were under the age of 1. The predominant serotype was CV-A6, identified in 57/87 (65.5%) of the specimens. No deaths were reported. Among 581 household contacts, 148 were laboratory confirmed: 12/581 were RT-PCR-positive, 142/545 had a ≥ 4-fold increase of neutralizing antibodies against EV-A71, CV-A6 or CV-A16; 4 cases experienced HFMD in the past 4 weeks. Attack rate among household contacts was 148/581 (25.5%). In 7/12 (58%) instances, the index and secondary cases were infected with the same serotype. Having a relationship to index case was significantly associated with EV infection.

Conclusion

The attack rate among household contacts was relatively high (25.5%) in this study and it seems justified to also consider the household setting as an additional target for intervention programs.

Ferritin nanocage-based antigen delivery nanoplatforms: epitope engineering for peptide vaccine design

Biomedical applications and nanotechnological advances, including constrained synthesis, multimodal imaging, drug delivery, and bioassay, have strongly benefited from employing ferritin nanocages due to their remarkable properties of easy engineering, great biocompatible features, large capacity and so on. In this study, ferritin nanocages were used to display epitopes (model antigens derived from Enterovirus 71 (EV71) with different length) on C- and N-terminals and the loop zone to search for the optimal position for the fusion of the epitopes to the vaccine platform. The longest epitope displayed on the N-terminal and loop zone as well as the second longest peptide displayed on the loop zone of ferritin resulted in 100% passive protection of newborn BALB/c mice from the lethal EV71. This suggests that peptides fused onto the loop zone of ferritin could induce strong immune response. Our results increase the versatility of the vaccine platform and provide more options for the production of stable constructs, suggesting the potential future clinical applicability of ferritin-based antigen delivery nanoplatforms.

Advances in Vaccines

Vaccines represent one of the most important advances in science and medicine, helping people around the world in preventing the spread of infectious diseases. However, there are still gaps in vaccination programs in many countries. Out of 11.2 million children born in EU region, more than 500,000 infants did not receive the complete three-dose series of diphtheria, pertussis, and tetanus vaccine before the first birthday. Data shows that there were more than 30,000 measles cases in the European region in recent years, and measles cases are rising in the USA. There are about 20 million children in the world still not getting adequate coverage of basic vaccines. Emerging infectious diseases such as malaria, Ebola virus disease, and Zika virus disease also threaten public health around the world. This chapter provides an overview of recent advances in vaccine development and technologies, manufacturing, characterization of various vaccines, challenges, and strategies in vaccine clinical development. It also provides an overview of recently approved major vaccines for human use.

Enterovirus A71 Infection and Neurologic Disease, Madrid, Spain, 2016

For children with brainstem encephalitis or encephalomyelitis, clinicians should look for enterovirus and not limit testing to cerebrospinal fluid.

We conducted an observational study from January 2016 through January 2017 of patients admitted to a reference pediatric hospital in Madrid, Spain, for neurologic symptoms and enterovirus infection. Among the 30 patients, the most common signs and symptoms were fever, lethargy, myoclonic jerks, and ataxia. Real-time PCR detected enterovirus in the cerebrospinal fluid of 8 patients, nasopharyngeal aspirate in 17, and anal swab samples of 5. The enterovirus was genotyped for 25 of 30 patients; enterovirus A71 was the most common serotype (21/25) and the only serotype detected in patients with brainstem encephalitis or encephalomyelitis. Treatment was intravenous immunoglobulins for 21 patients and corticosteroids for 17. Admission to the pediatric intensive care unit was required for 14 patients. All patients survived. At admission, among patients with the most severe disease, leukocytes were elevated. For children with brainstem encephalitis or encephalomyelitis, clinicians should look for enterovirus and not limit testing to cerebrospinal fluid.

Neutrophil extracellular traps induced by VP1 contribute to pulmonary edema during EV71 infection

Pulmonary edema is a fatal complication of EV71-associated hand, foot, and mouth disease (HFMD). The pathogenesis of EV71-induced pulmonary edema remains largely unclear. In this study, we aimed to explore the roles of the capsid protein VP1 in the occurrence of EV71-induced pulmonary edema. The intranasal inoculation of recombinant VP1 protein caused lung inflammation with an elevation of inflammatory cytokines and neutrophils infiltration. Moreover, neutrophil extracellular traps (NETs) were observed in the lung parenchyma of the mice treated with VP1. VP1 directly induced the formation of NETs, which depended on PAD4. VP1 also damaged the lung barrier via the reduction of the tight junction protein occludin. Moreover, the EV71 attachment receptor vimentin was increased upon VP1 administration. In contrast, NETs decreased vimentin levels, suggesting a novel role for NETs in viral immune defense. These results evidenced a direct role of VP1 in EV71-induced pulmonary edema and demonstrated that NETs may be both harmful and beneficial in EV71 infection.

A neonatal mouse model of central nervous system infections caused by Coxsackievirus B5

As one of the key members of the coxsackievirus B group, coxsackievirus B5 (CV-B5) can cause many central nervous system diseases, such as viral encephalitis, aseptic meningitis, and acute flaccid paralysis. Notably, epidemiological data indicate that outbreaks of CV-B5-associated central nervous system (CNS) diseases have been reported worldwide throughout history. In this study, which was conducted to promote CV-B5 vaccine and anti-virus drug research, a 3-day-old BALB/c mouse model was established using a CV-B5 clinical isolate (CV-B5/JS417) as the challenge strain. Mice challenged with CV-B5/JS417 exhibited a series of neural clinical symptoms and death with necrosis of neuronal cells in the cerebral cortex and the entire spinal cord, hindlimb muscles, and cardiomyocytes. The viral load of each tissue at various post-challenge time points suggested that CV-B5 replicated in the small intestine and was subsequently transmitted to various organs via viremia; the virus potentially entered the brain through the spinal axons, causing neuronal cell necrosis. In addition, this mouse model was used to evaluate the protective effect of a CV-B5 vaccine. The results indicated that both the inactivated CV-B5 vaccine and anti-CVB5 serum significantly protected mice from a lethal infection of CV-B5/JS417 by producing neutralizing antibodies. In summary, the first CV-B5 neonatal mouse model has been established and can sustain CNS infections in a manner similar to that observed in humans. This model will be a useful tool for studies on pathogenesis, vaccines, and anti-viral drug evaluations.

Five-year immunity persistence following immunization with inactivated enterovirus 71 type (EV71) vaccine in healthy children: A further observation

The longevity of antibodies induced by inactivated enterovirus 71 type (EV71) vaccine is not well studied. To estimate the immunity persistence following two-dose vaccination of EV71 vaccine, a five-year follow-up study was conducted as an extension of a Phase III clinical trial. In this study, a sub-cohort of volunteers who was eligible for enrollment and randomly administrated either 2 dose EV71 vaccine or placebo in the phase III clinical trial was selected, and then further observed 64 months post the 1st vaccination. 211 Subjects (106 vaccine subjects and 105 placebo subjects) who provided a full series of blood samples (at all the sampling points) were included in the final analyzed population. Seropositive rate (SR) and geometric mean titer (GMT) of the neutralizing antibodies (NAb) was calculated to detect the dynamic profiles of EV71 vaccine-induced immunogenicity. SR at the 5th year remained 94.34% in the vaccine subjects, with a GMT of 141.42. The SR was 71.43% in the placebo subjects, with a GMT of 71.83. Despite natural infection consistently promoted the NAb increase in the placebo subjects, the SR and GMT in vaccine subjects remained significantly higher than that in the placebo subjects at all the sampling points. The inactivated EV71 vaccine-induced immunity had a good persistence, within 5 years following the primary vaccination.

Human Enterovirus 71 Protein Displayed on the Surface of Saccharomyces cerevisiae as an Oral Vaccine

Human enterovirus 71 (EV-A71), a major agent of hand, foot, and mouth disease, has become an important public health issue in recent years. No effective antiviral or vaccines against EV-A71 infection are currently available. EV-A71 infection intrudes bodies through the gastric mucosal surface and it is necessary to enhance mucosal immune response to protect children from these pathogens. Recently, the majority of EV-A71 vaccine candidates have been developed for parenteral immunization. However, parenteral vaccine candidates often induce poor mucosal responses. On the other hand, oral vaccines could induce effective mucosal and systemic immunity, and could be easily and safely administered. Thus, proper oral vaccines have attached more interest compared with parenteral vaccine. In this study, the major immunogenic capsid protein of EV-A71 was displayed on the surface of Saccharomyces cerevisiae. Oral immunization of mice with surface-displayed VP1 S. cerevisiae induced systemic humoral and mucosal immune responses, including virus-neutralizing titers, VP1-specific antibody, and the induction of Th1 immune responses in the spleen. Furthermore, oral immunization of mother mice with surface-displayed VP1 S. cerevisiae conferred protection to neonatal mice against the lethal EV-A71 infection. Furthermore, we observed that multiple boost immunization as well as higher immunization dosage could induce higher EV-A71-specific immune response. Our results demonstrated that surface-displayed VP1 S. cerevisiae could be used as potential oral vaccine against EV-A71 infection.

Alanine scanning mutagenesis of SP70 epitope in characterizing species‑specific antibodies induced by enterovirus 71‑based antigens

The enterovirus 71 (EV71) SP70 epitope, derived from amino acids 208‑222 of VP1, is a neutralizing epitope. The present study aimed to assess the inter‑species differences of the antibodies induced by EV71‑based antigens in responses to SP70 mutant peptides. BALB/c mice and Lou/C rats were immunized with EV71 SP70. Monoclonal antibodies (Mabs) were produced by hybridoma clones. Serum polyclonal antibodies (Pabs) were produced from BALB/c mice and New Zealand white rabbits immunized with recombinant EV71 VP1 (rEV71‑VP1) protein or inactivated EV71. Micro‑neutralization and immunofluorescence assays were used to evaluate the capacity of the antibodies to bind to EV71. Reactivity of Mabs and Pabs to mutated SP70 were determined by alanine scanning mutagenesis. Furthermore, serums from EV71‑infected patients were collected to examine the affinity of SP70 antibody in the serum to mutated SP70, using competitive ELISA. The binding affinity of mouse Mabs to the SP70 epitope was increased by alanine substitution at sites of 210, 212, 213, 214, and 221. The binding affinity of rat Mabs to the SP70 epitope was increased by alanine substitution at sites 210, 217, 219, and 221. Mouse serum Pabs elicited by inactivated EV71 bound wild‑type SP70, but lost affinity for mutated peptides. Conversely, rabbit serum Pabs elicited by inactivated EV71 robustly recognized SP70 mutants. Mouse serum Pabs elicited by rEV71‑VP1 presented the same trend as mouse Mabs. Mutations at sites 214, 215, and 217 led to loss of recognition by rabbit Pabs elicited by rEV71‑VP1, while most mutations did not influence antibody binding. Compared with the wild‑type, mutations at the sites 209, 219 and 221 of SP70 lead to increased affinity with the serum antibodies produced by the EV71‑infected patients. Antibody responses triggered by inactivated EV71, rEV71‑VP1 and EV71 SP70 differed among species in neutralizing capacity and affinity for SP70 mutant peptides.

The Process of Wrapping Virus Revealed by a Force Tracing Technique and Simulations

Viral entry into the host cell is the first step of virus infection; however, its dynamic process via endocytosis remains largely elusive. Here, the force tracing technique and single particle simulation are combined to investigate the invagination of single human enterovirus 71 (HEV71, a positive single-stranded RNA virus that is associated with hand, foot, and mouth disease) via cell membranes during its host cell entry. The experimental results reveal that the HEV71 invaginates in membrane vesicles at a force of 58 ± 16 pN, a duration time of 278 ± 68 ms. The simulation further shows that the virus can reach a partially wrapped state very fast, then the upper surface of the virus is covered by the membrane traveling over a long period of time. Combining the experiment with the simulation, the mechanism of membrane wrapping of virus is uncovered, which provides new insights into how the cell is operated to initiate the endocytosis of virus.

An inactivated hand-foot-and-mouth disease vaccine using the enterovirus 71 (C4a) strain isolated from a Korean patient induces a strong immunogenic response in mice

Enterovirus 71 (EV71) is a major causative agent of hand-foot-and-mouth disease (HFMD) frequently occurring in children. HFMD induced by EV71 can cause serious health problems and has been reported worldwide, particularly in the Asia-Pacific region. In this study, we assessed the immunogenicity of a formalin-inactivated HFMD vaccine using an EV71 strain (FI-EV71 C4a) isolated from a Korean patient. The vaccine candidate was evaluated in mice to determine the vaccination doses and vaccine schedules. BALB/c mice were intramuscularly administered 5, 10, or 20 μg FI-EV71 vaccine, followed by a booster 2 weeks later. EV71-specific antibodies and neutralizing antibodies were induced and maintained until the end of the experimental period in all vaccinated groups. To determine the effectiveness of adjuvant for the EV71 vaccine, three adjuvants, i.e., aluminium hydroxide gel, monophosphoryl lipid A, and polyinosinic-polycytidylic acid, were administered separately with the FI-EV71 vaccine to mice via the intramuscular route. Mice administered the FI-EV71 vaccine formulated with all three adjuvants induced a significantly increased antibody response compared with that of the single adjuvant groups. The vaccinated group with triple adjuvants exhibited more rapid induction of EV71-specific and neutralizing antibodies than the other groups. These results suggested that the role of adjuvant in inactivated vaccine was important for eliciting effective immune responses against EV71. In conclusion, our results showed that FI-EV71 was a potential candidate vaccine for prevention of EV71 infection.

Enhancing enterovirus A71 vaccine production yield by microcarrier profusion bioreactor culture

Hand, foot and mouth diseases (HFMD) are mainly caused by Enterovirus A71 (EV-A71) infections. Clinical trials in Asia conducted with formalin-inactivated EV-A71 vaccine candidates produced from serum-free Vero cell culture using either roller bottle or cell factory technology, are found to be safe and highly efficacious. To increase vaccine yields and reduce the production costs, the bioprocess improvement for EV-A71 vaccine manufacturing is currently being investigated. The parameters that could affect and enhance the production yields of EV-A71 virus growth in the microcarrier bioreactor were investigated. The medium replacement culture strategy included a multi-harvested semi-batch process and perfusion technology and was found to increase the production yields more than 7-14 folds. Based on the western blot and cryo-EM analyses of the EV-A71 virus particles produced from either the multi-harvested semi-batch (MHSBC) or perfusion cultures were found to be similar to those virus particles obtained from the single batch culture. Mouse immunogenicity studies indicate that the EV-A71 vaccine candidates produced from the perfusion culture have similar potency to those obtained from single batch bioprocess. The physical structures of the EV-A71 particles revealed by the cryo-EM analysis were found to be spherical capsid particles. These results provide feasible technical bioprocesses for increasing virus yields and the scale up of EV-A71 vaccine manufacturing using the bioreactor cell culture methods.

Amphotericin B Inhibits Enterovirus 71 Replication by Impeding Viral Entry

Enterovirus 71 (EV71) infection causes hand-foot-and-mouth disease that leads to cardiopulmonary complications and death in young children. There is thus an urgent need to find new treatments to control EV71 infection. In this study, we report potent inhibition of EV71 by a polyene antibiotic Amphotericin B. Amphotericin B profoundly diminished the expression of EV71 RNA and viral proteins in the RD cells and the HEK293 cells. As a result, EV71 production was inhibited by Amphotericin B with an EC50 (50% effective concentration) of 1.75 μM in RD cells and 0.32 μM in 293 cells. In addition to EV71, EV68 was also strongly inhibited by Amphotericin B. Results of mechanistic studies revealed that Amphotericin B targeted the early stage of EV71 infection through impairing the attachment and internalization of EV71 by host cells. As an effective anti-fungi drug, Amphotericin B thus holds the promise of formulating a novel therapeutic to treat EV71 infection.

The Current Status of the Disease Caused by Enterovirus 71 Infections: Epidemiology, Pathogenesis, Molecular Epidemiology, and Vaccine Development

Enterovirus 71 (EV71) infections have a major public health impact in the Asia-Pacific region. We reviewed the epidemiology, pathogenesis, and molecular epidemiology of EV71 infection as well as EV71 vaccine development. Previous studies were found using the search terms "enterovirus 71" and "epidemiology" or "pathogenesis" or "molecular epidemiology" or "vaccine" in Medline and PubMed. Articles that were not published in the English language, manuscripts without an abstract, and opinion articles were excluded from the review. The reported epidemiology of cases caused by EV71 infection varied from country to country; seasonal variations in incidence were observed. Most cases of EV71 infection that resulted in hospitalization for complications occurred in children less than five years old. The brainstem was the most likely major target of EV71 infection. The emergence of the EV71 epidemic in the Asia-Pacific region has been associated with the circulation of different genetic lineages (genotypes B3, B4, C1, C2, and C4) that appear to be undergoing rapid evolutionary changes. The relationship between the gene structure of the EV71 virus and the factors that ensure its survival, circulation, and evasion of immunity is still unknown. EV71 infection has emerged as an important global public health problem. Vaccine development, including the development of inactivated whole-virus live attenuated, subviral particles, and DNA vaccines, has been progressing.

Human IgG Fc promotes expression, secretion and immunogenicity of enterovirus 71 VP1 protein

Enterovirus (EV71) can cause severe neurological diseases, but the underlying pathogenesis remains unclear. The capsid protein, viral protein 1 (VP1), plays a critical role in the pathogenicity of EV71. High level expression and secretion of VP1 protein are necessary for structure, function and immunogenicity in its natural conformation. In our previous studies, 5 codon-optimized VP1 DNA vaccines, including wt-VP1, tPA-VP1, VP1-d, VP1-hFc and VP1-mFc, were constructed and analyzed. They expressed VP1 protein, but the levels of secretion and immunogenicity of these VP1 constructs were significantly different (P<0.05). In this study, we further investigated the protein levels of these constructs and determined that all of these constructs expressed VP1 protein. The secretion level was increased by including a tPA leader sequence, which was further increased by fusing human IgG Fc (hFc) to VP1. VP1-hFc demonstrated the most potent immunogenicity in mice. Furthermore, hFc domain could be used to purify VP1-hFc protein for additional studies.

Protein microarray-mediated detection of antienterovirus antibodies in serum

Objective

To utilize prokaryotic gene expression and protein microarray to develop and evaluate a sensitive, accurate protein microarray assay for detecting antienterovirus antibodies in serum samples from patients with hand, foot and mouth disease (HFMD). Enterovirus 71 (EV71) and coxsackievirus A16 (CA16), two common causative agents for HFMD, were used for assay development.

Methods

Serum was collected from patients with HFMD and healthy controls. EV71 and CA16 VP1 and VP3 genes were expressed in transfected Escherichia coli; the resultant VP1 and 3 proteins were used in a microarray assay for human serum EV71 and CA16 immunoglobulin (Ig) M and IgG. To validate the microarray assay, serum samples were tested for EV71 IgM using enzyme-linked immunosorbent assay (ELISA).

Results

Out of 50 patients with HFMD, EV71 IgM and CA16 IgM was detected in 80% and 44% of serum samples, respectively, using protein microarray, and EV71 IgM was detected in 78% of samples using ELISA. Protein microarray and ELISA showed 100% specificity for EV71-IgM detection.

Conclusion

The protein microarray assay developed in the present study shows potential as a sensitive technique for detecting EV71 IgM in serum samples from patients with HFMD.

Simultaneous Point-of-Care Detection of Enterovirus 71 and Coxsackievirus B3

Human enterovirus 71 (EV71) is one of the pathogens that causes hand, foot, and mouth disease (HFMD), which generally leads to neurological diseases and fatal complications among children. Since the early clinical symptoms from EV71 infection are very similar to those from Coxsackievirus B3 (CVB3) infection, a robust and sensitive detection method that can be used to distinguish EV71 and CVB3 is urgently needed for prompting medical treatment of related diseases. Herein, based on immunomagnetic nanobeads and fluorescent semiconductor CdSe quantum dots (QDs), a method for simultaneous point-of-care detection of EV71 and CVB3 is proposed. The synchronous detection of EV71 and CVB3 virions was achieved within 45 min with high specificity and repeatability. The limits of detection are 858 copies/500 μL for EV71 and 809 copies/500 μL for CVB3.This proposed method was further validated with 20 human throat swab samples obtained from EV71 or CVB3 positive cases, with results 93.3% consistent with those by the real-time PCR method, demonstrating the potential of this method for clinical quantification of EV71 and CVB3. The method may also facilitate the prevention and treatment of the diseases.

Global quantitative proteomic analysis of human glioma cells profiled host protein expression in response to enterovirus type 71 infection

Enterovirus 71 (EV71) is one of the leading causes of hand, foot and mouth disease with neurological complications in some cases. To study the pathogenesis of EV71 infection, large-scale analyses of EV71 infected cells have been performed. However, most of these studies employed rhabdomyosarcoma (RD) cells or used transcriptomic strategy. Here, we performed SILAC-based quantitative proteomic analysis of EV71-infected U251 cells, a human glioma cell line. A total of 3125 host proteins were quantified, in which 451 were differentially regulated as a result of EV71 infection at 8 or 20 hpi or both. Gene Ontology analysis indicates the regulated proteins were enriched in "metabolic process", "biological regulation" and "cellular process", implying that these biological processes were affected by EV71 infection. Furthermore, functional study indicated that TRAF2 and TRAF6 among the up-regulated proteins could inhibit the replication of EV71 at the early phase post infection, and the anti-EV71 function of both proteins was independent of interferon β. Our study not only provided an overview of cellular response to EV71 infection in a human glioma cell line, but also found that TRAF2 and TRAF6 might be potential targets to inhibit the replication of EV71. All MS data have been deposited in the ProteomeXchange with identifier PXD002454 (http://proteomecentral.proteomexchange.org/dataset/PXD002454).

Inactivated Enterovirus 71 Vaccine Produced by 200-L Scale Serum-Free Microcarrier Bioreactor System Provides Cross-Protective Efficacy in Human SCARB2 Transgenic Mouse

Epidemics and outbreaks caused by infections of several subgenotypes of EV71 and other serotypes of coxsackie A viruses have raised serious public health concerns in the Asia-Pacific region. These concerns highlight the urgent need to develop a scalable manufacturing platform for producing an effective and sufficient quantity of vaccines against deadly enteroviruses. In this report, we present a platform for the large-scale production of a vaccine based on the inactivated EV71(E59-B4) virus. The viruses were produced in Vero cells in a 200 L bioreactor with serum-free medium, and the viral titer reached 10(7) TCID50/mL 10 days after infection when using an MOI of 10(-4). The EV71 virus particles were harvested and purified by sucrose density gradient centrifugation. Fractions containing viral particles were pooled based on ELISA and SDS-PAGE. TEM was used to characterize the morphologies of the viral particles. To evaluate the cross-protective efficacy of the EV71 vaccine, the pooled antigens were combined with squalene-based adjuvant (AddaVAX) or aluminum phosphate (AlPO4) and tested in human SCARB2 transgenic (Tg) mice. The Tg mice immunized with either the AddaVAX- or AlPO4-adjuvanted EV71 vaccine were fully protected from challenges by the subgenotype C2 and C4 viruses, and surviving animals did not show any degree of neurological paralysis symptoms or muscle damage. Vaccine treatments significantly reduced virus antigen presented in the central nervous system of Tg mice and alleviated the virus-associated inflammatory response. These results strongly suggest that this preparation results in an efficacious vaccine and that the microcarrier/bioreactor platform offers a superior alternative to the previously described roller-bottle system.

Acute gastroenteritis outbreak caused by a GII.6 norovirus

AIM: To report an acute gastroenteritis outbreak caused by a genogroup 2 genotype 6 (GII.6) strain norovirus in Shanghai, China.

METHODS: Noroviruses are responsible for approximately half of all reported gastroenteritis outbreaks in many countries. Genogroup 2 genotype 4 strains are the most prevalent. Rare outbreaks caused by GII.6 strains have been reported. An acute gastroenteritis outbreak occurred in an elementary school in Shanghai in December of 2013. Field and molecular epidemiologic investigations were conducted.

RESULTS: The outbreak was limited to one class in an elementary school located in southwest Shanghai. The age of the students ranged from 9 to 10 years. The first case emerged on December 10, 2013, and the last case emerged on December 14, 2013. The cases peaked on December 11, 2013, with 21 new cases. Of 45 students in the class, 32 were affected. The main symptom was gastroenteritis, and 15.6% (5/32) of the cases exhibited a fever. A field epidemiologic investigation showed the pathogen may have been transmitted to the elementary school from employees in a delicatessen via the first case student, who had eaten food from the delicatessen one day before the gastroenteritis episodes began. A molecular epidemiologic investigation identified the cause of the gastroenteritis as norovirus strain GII.6; the viral sequence of the student cases showed 100% homology with that of the shop employees. Genetic relatedness analyses showed that the new viral strain is closely related to previously reported GII.6 sequences, especially to a strain reported in Japan.

CONCLUSION: This is the first report to show that norovirus strain GII.6 can cause a gastroenteritis outbreak. Thus, the prevalence of GII.6 noroviruses requires attention.

High-yield production of recombinant virus-like particles of enterovirus 71 in Pichia pastoris and their protective efficacy against oral viral challenge in mice

Enterovirus 71 (EV71) is one of the major causative pathogens of hand, foot and mouth disease (HFMD), which is highly prevalent in the Asia-Pacific regions. Severe HFMD cases with neurological complications and even death are often associated with EV71 infections. However, no licensed EV71 vaccine is currently available. Recombinant virus-like particles (VLPs) of EV71 have been produced and shown to be a promising vaccine candidate in preclinical studies. However, the performance of current recombinant expression systems for EV71 VLP production remains unsatisfactory with regard to VLP yield and manufacturing procedure, and thus hinders further product development. In this study, we evaluated the expression of EV71 VLPs in Pichia pastoris and determined their protective efficacy in mouse models of EV71 infections. We showed that EV71 VLPs could be produced at high levels up to 4.9% of total soluble protein in transgenic P. pastoris yeast co-expressing P1 and 3CD proteins of EV71. The resulting yeast-produced VLPs potently induced neutralizing antibodies against homologous and heterologous EV71 strains in mice. More importantly, maternal immunization with VLPs protected neonatal mice in both intraperitoneal and oral challenge experiments. Collectively, these results demonstrated the success of simple, high-yield production of EV71 VLPs in transgenic P. pastoris, thus lifting the major roadblock in commercial development of VLP-based EV71 vaccines.

Novel recombinant chimeric virus-like particle is immunogenic and protective against both enterovirus 71 and coxsackievirus A16 in mice

Hand-foot-and-mouth disease (HFMD) has been recognized as an important global public health issue, which is predominantly caused by enterovirus 71 (EV-A71) and coxsackievirus A16 (CVA16). There is no available vaccine against HFMD. An ideal HFMD vaccine should be bivalent against both EV-A71 and CVA16. Here, a novel strategy to produce bivalent HFMD vaccine based on chimeric EV-A71 virus-like particles (ChiEV-A71 VLPs) was proposed and illustrated. The neutralizing epitope SP70 within the capsid protein VP1 of EV-A71 was replaced with that of CVA16 in ChiEV-A71 VLPs. Structural modeling revealed that the replaced CVA16-SP70 epitope is well exposed on the surface of ChiEV-A71 VLPs. These VLPs produced in Saccharomyces cerevisiae exhibited similarity in both protein composition and morphology as naive EV-A71 VLPs. Immunization with ChiEV-A71 VLPs in mice elicited robust Th1/Th2 dependent immune responses against EV-A71 and CVA16. Furthermore, passive immunization with anti-ChiEV-A71 VLPs sera conferred full protection against lethal challenge of both EV-A71 and CVA16 infection in neonatal mice. These results suggested that this chimeric vaccine, ChiEV-A71 might have the potential to be further developed as a bivalent HFMD vaccine in the near future. Such chimeric enterovirus VLPs provide an alternative platform for bivalent HFMD vaccine development.

Towards broadly protective polyvalent vaccines against hand, foot and mouth disease

Hand, foot, and mouth disease (HFMD) caused by multiple enterovirus infections is a serious health threat to children in the Asia-Pacific region. This article reviews progresses in the development of vaccines for HFMD and discusses the need for polyvalent HFMD vaccines for conferring broad-spectrum protection.

EV71 vaccine, an invaluable gift for children

Enterovirus 71 (EV71) is a major pathogen for severe hand, foot and mouth disease (HFMD). Development of vaccines against EV71 would be the most effective approach to prevent the EV71 outbreak. Research and development (R&D) of EV71 vaccine was carried out in several Asian countries. Currently three companies in mainland China have completed Phase III clinical trials of inactivated EV71 whole-virus vaccines, whereas the other two companies have completed Phase I clinical trials separately in Taiwan and in Singapore. Results from those clinical trials have indicated high safety and immunogenicity of EV71 vaccine. Protective efficacies were over 90% on EV71-associated HFMD and over 80% on other EV71-associated diseases. In this paper, we summarize the results from three EV71 vaccine Phase III clinical trials and discuss the challenges of incorporating EV71 vaccine into Expanded Program on Immunization (EPI) in countries with EV71 epidemics.

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

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.

Delivery of human EV71 receptors by adeno-associated virus increases EV71 infection-induced local inflammation in adult mice

Enterovirus71 (EV71) is now recognized as an emerging neurotropic virus in Asia and one major causative agent of hand-foot-mouth diseases (HFMD). However potential animal models for vaccine development are limited to young mice. In this study, we used an adeno-associated virus (AAV) vector to introduce the human EV71 receptors P-selectin glycoprotein ligand-1 (hPSGL1) or a scavenger receptor class-B member-2 (hSCARB2) into adult ICR mice to change their susceptibility to EV71 infection. Mice were administered AAV-hSCARB2 or AAV-hPSGL1 through intravenous and oral routes. After three weeks, expression of human SCARB2 and PSGL1 was detected in various organs. After infection with EV71, we found that the EV71 viral load in AAV-hSCARB2- or AAV-hPSGL1-transduced mice was higher than that of the control mice in both the brain and intestines. The presence of EV71 viral particles in tissues was confirmed using immunohistochemistry analysis. Moreover, inflammatory cytokines were induced in the brain and intestines of AAV-hSCARB2- or AAV-hPSGL1-transduced mice after EV71 infection but not in wild-type mice. However, neurological disease was not observed in these animals. Taken together, we successfully infected adult mice with live EV71 and induced local inflammation using an AAV delivery system.