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

Epidemiological characteristics and trends of hand-foot-mouth disease in Shanghai, China from 2011 to 2021

Hand, foot and mouth disease (HFMD) is a kind of infectious disease caused by enterovirus infection. In this study we analysed the epidemiological characteristics and time trends of HFMD, vaccination status and vaccine protection effect assessment of EV71 vaccine from 2011 to 2021 in Huangpu District, Shanghai, China. HFMD cases showed a decreasing trend year by year from 2011 to 2021, from 122 cases reported in 2012 to 7 cases in 2020, and 12 cases in 2021. Etiological diagnosis was CV-A6 in 185 cases (29.8%), CV-A16 in 209 cases (33.7%), EV-A71 in 118 cases (19.0%) and other enteroviruses in 109 cases (17.6%). After the launch of EV71 vaccine, a total of 32,221 doses of EV71 vaccine were administered between 2016 and 2021. The case-control results showed that there was no evidence to support the effectiveness of EV71 vaccine, OR (95% CI) =0.52 (0.12 ~ 2.3), p = 0.37. The epidemic strains have changed. Surveillance and management of HFMD remain very important in the future and EV71 vaccine is considered to be included in National Immunization Program.

Combating coxsackievirus B infections

Coxsackieviruses B (CVB) are small, non-enveloped, single-stranded RNA viruses belonging to the Enterovirus genus of the Picornaviridae family. They are common worldwide and cause a wide variety of human diseases ranging from those having relatively mild symptoms to severe acute and chronic pathologies such as cardiomyopathy and type 1 diabetes. The development of safe and effective strategies to combat these viruses remains a challenge. The present review outlines current approaches to control CVB infections and associated diseases. Various drugs targeting viral or host proteins involved in viral replication as well as vaccines have been developed and shown potential to prevent or combat CVB infections in vitro and in vivo in animal models. Repurposed drugs and alternative strategies targeting miRNAs or based on plant extracts and probiotics and their derivatives have also shown antiviral effects against CVB. In addition, clinical trials with vaccines and drugs are underway and offer hope for the prevention or treatment of CVB-induced diseases.

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.

Persistent coxsackievirus B infection and pathogenesis of type 1 diabetes mellitus

Enteroviruses are believed to trigger or accelerate islet autoimmunity in genetically susceptible individuals, thereby resulting in loss of functional insulin-producing β-cells and type 1 diabetes mellitus (T1DM). Although enteroviruses are primarily involved in acute and lytic infections in vitro and in vivo, they can also establish a persistent infection. Prospective epidemiological studies have strongly associated the persistence of enteroviruses, especially coxsackievirus B (CVB), with the appearance of islet autoantibodies and an increased risk of T1DM. CVB can persist in pancreatic ductal and β-cells, which leads to structural or functional alterations of these cells, and to a chronic inflammatory response that promotes recruitment and activation of pre-existing autoreactive T cells and β-cell autoimmune destruction. CVB persistence in other sites, such as the intestine, blood cells and thymus, has been described; these sites could serve as a reservoir for infection or reinfection of the pancreas, and this persistence could have a role in the disturbance of tolerance to β-cells. This Review addresses the involvement of persistent enterovirus infection in triggering islet autoimmunity and T1DM, as well as current strategies to control enterovirus infections for preventing or reducing the risk of T1DM onset.

Immunogenicity and Safety of an Inactivated Enterovirus 71 Vaccine Administered Simultaneously with Hepatitis B Virus Vaccine, Group A Meningococcal Polysaccharide Vaccine, Measles-Rubella Combined Vaccine and Japanese Encephalitis Vaccine: A Multi-Center, Randomized, Controlled Clinical Trial in China

Background: The aim of this study was to investigate the immunogenicity and safety of the enterovirus 71 vaccine (EV71 vaccine) administered alone or simultaneously. Methods: A multi-center, open-label, randomized controlled trial was performed involving 1080 healthy infants aged 6 months or 8 months from Shandong, Shanxi, Shaanxi, and Hunan provinces. These infants were divided into four simultaneous administration groups and EV71 vaccine separate administration group. Blood samples were collected from the infants before the first vaccination and after the completion of the vaccination. This trial was registered in the Clinical Trials Registry (NCT03519568). Results: A total of 895 were included in the per-protocol analysis. The seroconversion rates of antibodies against EV71 in four simultaneous administration groups (98.44% (189/192), 94.57% (122/129), 99.47% (187/188) and 98.45% (190/193)) were non-inferior to EV71 vaccine separate administration group (97.93% [189/193]) respectively. Fever was the most common adverse event, the pairwise comparison tests showed no difference in the incidence rate of solicited, systemic or local adverse events. Three serious adverse events related to the vaccination were reported. Conclusions: The evidence of immunogenicity and safety supports that the EV71 vaccine administered simultaneously with vaccines need to be administered during the same period of time recommended in China.

Fighting Enteroviral Infections to Prevent Type 1 Diabetes

Enteroviruses (EVs), especially coxsackieviruses B (CVB), are believed to trigger or accelerate islet autoimmunity in genetically susceptible individuals that results in type 1 diabetes (T1D). Therefore, strategies are needed to fight against EV infections. There are no approved antiviral drugs currently available, but various antiviral drugs targeting viral or host cell proteins and vaccines have recently shown potential to combat CVB infections and may be used as new therapeutic strategies to prevent or reduce the risk of T1D and/or preserve β-cell function among patients with islet autoantibodies or T1D.

Fucosylated oligosaccharide Lacto-N-fucopentaose I ameliorates enterovirus 71 infection by inhibiting apoptosis

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LNFPI reduced capsid protein VP1 to block virus adsorption.

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LNFPI promoted CDK2 and reduced cyclin E to recover S phase block.

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LNFPI inhibited cell apoptosis via reduction of Sphingomonas and Stenotrophomonas.

Enterovirus 71 (EV71) is the main cause of hand, foot and mouth disease that results in high rates of severe diseases in small children. Lacto-N-fucopentaose I (LNFPI) can inhibit pathogen invasion and regulate intestinal flora. However, whether LNFPI inhibits EV71 infection remains unknown. In this study, we examined the effect and mechanism of LNFPI against EV71. LNFPI reduced capsid protein VP1 to block virus adsorption, inhibited cyclin E transcription and promoted CDK2 expression in EV71-induced human rhabdomyosarcoma cells, thereby causing virus-induced S phase arrest and inhibiting death receptor and mitochondria-induced apoptosis. The effects of LNFPI on apoptosis were further confirmed in Caenorhabditis elegans. The correlation analysis revealed that LNFPI inhibited cell apoptosis by reducing the abundance of Sphingomonas, Stenotrophomonas and Achromatic, which are associated with pro-apoptotic genes in C. elegans, and by increasing the abundance of Micromonospora, which is related to apoptotic inhibition. These findings lead to further recommendations for LNFPI supplementation in infant formula, as it could offer antiviral benefits to formula-fed infants.

Regulation of host factor γ-H2AX level and location by enterovirus A71 for viral replication

Numerous viruses manipulate host factors for viral production. We demonstrated that human enterovirus A71 (EVA71), a primary causative agent for hand, foot, and mouth disease (HFMD), increased the level of the DNA damage response (DDR) marker γ-H2AX. DDR is primarily mediated by the ataxia telangiectasia mutated (ATM), ATM and Rad3-related (ATR), or DNA-dependent protein kinase (DNA-PK) pathways. Upregulation of γ-H2AX by EVA71 was dependent on the ATR but not the ATM or DNA-PK pathway. As a nuclear factor, there is no previous evidence of cytoplasmic distribution of γ-H2AX. However, the present findings demonstrated that EVA71 encouraged the localization of γ-H2AX to the cytoplasm. Of note, γ-H2AX formed a complex with structural protein VP3, non-structural protein 3D, and the viral genome. Treatment with an inhibitor or CRISPR/Cas9 technology to decrease or silence the expression of γ-H2AX decreased viral genome replication in host cells; this effect was accompanied by decreased viral protein expression and virions. In animal experiments, caffeine was used to inhibit DDR; the results revealed that caffeine protected neonatal mice from death after infection with EVA71, laying the foundation for new therapeutic applications of caffeine. More importantly, in children with HFMD, γ-H2AX was upregulated in peripheral blood lymphocytes. The consistent in vitro and in vivo data on γ-H2AX from this study suggested that caffeine or other inhibitors of DDR might be novel therapeutic agents for HFMD.

Preclinical evaluation of recombinant HFMD vaccine based on enterovirus 71 (EV71) virus-like particles (VLP): Immunogenicity, efficacy and toxicology

Enterovirus 71 (EV71) is one of the major causative agents for hand, foot and mouth disease (HFMD) in children. Currently, three inactivated EV71 vaccines have been approved by Chinese government. We previously demonstrated that recombinant EV71 virus-like particles (VLP) produced in Pichia pastoris can be produced at a high yield with a simple manufacturing process, and the candidate vaccine elicited protective humoral immune responses in mice. In present study, the nonclinical immunogenicity, efficacy and toxicity of the EV71 vaccine was comprehensively evaluated in rodents and non-human primates. The immunogenicity assessment showed that EV71 VLPs vaccine elicited high and persistent neutralizing antibody responses, which could be comparable with a licensed inactivated vaccine in animals. The immune sera of vaccinated mice also exhibited cross-neutralization activities to the heterologous subtypes of EV71. Both passive and maternal antigen specific antibodies protected the neonatal mice against the lethal EV71 challenge. Furthermore, nonclinical safety assessment of EV71 VLP vaccine showed no signs of systemic toxicity in animals. Therefore, the excellent immunogenicity, efficacy and toxicology data supported further evaluation of the VLP-based EV71 vaccine in humans.

Enterovirus A71 Vaccines

Enterovirus A71 (EV-A71) is a major causative agent of hand, foot, and mouth disease (HFMD) and herpangina. Moreover, EV-A71 infection can lead to neurological complications and death. Vaccination is the most efficient way to control virus infection. There are currently three inactivated, whole EV-A71 vaccines licensed by the China NMPA (National Medical Products Administration). Several other types of vaccines, such as virus-like particles and recombinant VP1 (capsid protein), are also under development. In this review, we discuss recent advances in the development of EV-A71 vaccines.

The transfer and decay of maternal antibodies against enterovirus A71, and dynamics of antibodies due to later natural infections in Chinese infants: a longitudinal, paired mother-neonate cohort study

BACKGROUND

Since 1997, epidemics of hand, foot, and mouth disease associated with enterovirus A71 (EV-A71) have affected children younger than 5 years in the Asia-Pacific region, including mainland China. EV-A71 vaccines have been licensed for use in children aged 6-71 months in China, but not for infants younger than 6 months. We aimed to assess the dynamics of maternal EV-A71 antibodies to inform choice of potential vaccination strategies to protect infants younger than 6 months, because they have a substantial burden of disease.

METHODS

We did a longitudinal cohort study with mother-neonate pairs in local hospitals in southern China during 2013-18. We collected cord blood from neonates and venous blood from mothers at delivery. We followed up and collected blood samples from the children at ages 2, 4, 6, 12, 24, and 36 months and tested for the presence of neutralising antibodies against EV-A71 with virus neutralisation assays. Seropositivity, or protective titre, was defined as a neutralisation antibody titre of 16 or higher. We estimated the seroprevalence, geometric mean titre (GMT), and transfer ratio of maternal antibodies. We used a binomial distribution to derive the 95% CIs of seroprevalence. Seropositivity between mothers and neonates was compared by use of an agreement (κ), while GMTs were compared by use of paired Student's t tests.

FINDINGS

Between Sept 20, 2013, and Oct 14, 2015, 1054 mothers with 1066 neonates were enrolled. The EV-A71 GMT was similar among pairs of neonates (22·7, 95% CI 20·8-24·9) and mothers (22·1, 95% CI 20·2-24·1; p=0·20). The mean transfer ratio of maternal antibodies was 1·03 (95% CI 0·98-1·08). Although 705 (66%) of 1066 neonates acquired protective concentrations of EV-A71 antibodies from mothers, these declined rapidly, with a half-life of 42 days (95% CI 40-44). The time to loss of protective immunity was extended to 5 months in neonates with mothers who had titres of 128 or higher. By age 30 months, 28% of children had become seropositive because of natural infection.

INTERPRETATION

EV-A71 maternal antibodies were efficiently transferred to neonates, but declined quickly to below the protective threshold, particularly among those whose mothers had low antibody titres. Our findings suggest that maternal vaccination could be explored to provide neonatal protection against EV-A71 through maternal antibodies. Catch-up vaccination between ages 6 months to 5 years could provide protection to the approximately 30-90% of children that have not had natural EV-A71 infection by that age.

FUNDING

National Science Fund for Distinguished Young Scholars, National Natural Science Foundation of China.

Beclin1 Binds to Enterovirus 71 3D Protein to Promote the Virus Replication

Enterovirus 71 (EV71) is the main pathogen causing hand-foot-mouth disease (HFMD) in infants and children, which can also lead to severe neurological diseases and even death. Therefore, understanding the replication mechanism of EV71 is of great significance for the prevention and control of EV71-induced diseases. Beclin1 (BECN1, a mammalian homologue of ATG6 in yeast) is an important core protein for the initiation and the normal process of autophagy in cells. In addition to its involvement in autophagy, Beclin1 has also been reported to play an important role in cancer and innate immune signaling pathways. However, the role of Beclin1 in EV71 replication remains elusive. Here, we primarily found that Beclin1 facilitates EV71 replication in human rhabdomyosarcoma (RD) cells and the autophagy was actually induced, but Beclin1 was not significantly affected at either mRNA level or protein level during early EV71 infection. Further studies discovered that Beclin1 could interacts with EV71 non-structural protein 3D mainly through its evolutionary conserved domain (ECD) and coiled-coiled domain (CCD), thus promoting the replication of EV71 in human rhabdomyosarcoma (RD) cells and human astroglioma (U251) cells. Collectively, we reveal a novel regulatory mechanism associated with Beclin1 to promote EV71 replication, thus providing a potential therapeutic target for the prevention and control of EV71-associated diseases.

Genetic recombination in fast-spreading coxsackievirus A6 variants: a potential role in evolution and pathogenicity

Hand, foot, and mouth disease (HFMD) is a common global epidemic. From 2008 onwards, many HFMD outbreaks caused by coxsackievirus A6 (CV-A6) have been reported worldwide. Since 2013, with a dramatically increasing number of CV-A6-related HFMD cases, CV-A6 has become the predominant HFMD pathogen in mainland China. Phylogenetic analysis based on the VP1 capsid gene revealed that subtype D3 dominated the CV-A6 outbreaks. Here, we performed a large-scale (near) full-length genetic analysis of global and Chinese CV-A6 variants, including 158 newly sequenced samples collected extensively in mainland China between 2010 and 2018. During the global transmission of subtype D3 of CV-A6, the noncapsid gene continued recombining, giving rise to a series of viable recombinant hybrids designated evolutionary lineages, and each lineage displayed internal consistency in both genetic and epidemiological features. The emergence of lineage –A since 2005 has triggered CV-A6 outbreaks worldwide, with a rate of evolution estimated at 4.17 × 10⁻³ substitutions site^-1 year⁻¹ based on a large number of monophyletic open reading frame sequences, and created a series of lineages chronologically through varied noncapsid recombination events. In mainland China, lineage –A has generated another two novel widespread lineages (–J and –L) through recombination within the enterovirus A gene pool, with robust estimates of occurrence time. Lineage –A, –J, and –L infections presented dissimilar clinical manifestations, indicating that the conservation of the CV-A6 capsid gene resulted in high transmissibility, but the lineage-specific noncapsid gene might influence pathogenicity. Potentially important amino acid substitutions were further predicted among CV-A6 variants. The evolutionary phenomenon of noncapsid polymorphism within the same subtype observed in CV-A6 was uncommon in other leading HFMD pathogens; such frequent recombination happened in fast-spreading CV-A6, indicating that the recovery of deleterious genomes may still be ongoing within CV-A6 quasispecies. CV-A6-related HFMD outbreaks have caused a significant public health burden and pose a great threat to children’s health; therefore, further surveillance is greatly needed to understand the full genetic diversity of CV-A6 in mainland China.

Immunization with a fusion protein vaccine candidate generated from truncated peptides of human enterovirus 71 protects mice from lethal enterovirus 71 infections

Background

Prophylactic vaccines are critical in preventing hand, foot, and mouth disease (HFMD) primarily caused by human enterovirus 71 (EV71) infection. Children aged less than 5 years are especially susceptible to EV71 infections. In addition to the development of vaccines containing the inactivated virus, those containing virus-like particles (VLPs) with repeated antigens also constitute an effective preventive strategy for EV71 infections, with safety and productivity advantages. We previously developed a fusion protein composed with truncated peptides of the EV71 capsid protein, which assembled into spherical particles. This study aimed to assess the immunoprotective effects of this fusion protein as a vaccine candidate in a mouse model of EV71 infection.

Methods

To evaluate the protective effect of fusion protein vaccine candidate, neonatal mice born by immunized female mice, as well as normal neonatal mice immunized twice were infected with EV71 virus. Whereafter, the survival rates, clinical scores and viral loads were measured.

Results

The high dosage and booster immunization helped induce specific serum antibodies with high neutralization titers, which were transferred to neonatal mice, thereby facilitating effective resistance towards EV71 infection. An active immune response was also observed in neonatal mice which generated following immunization.

Conclusions

The present results suggest that this fusion protein is a suitable vaccine candidate in treating EV71 infections.

Willingness of parents to vaccinate their 6-60-month-old children with EV71 vaccines: a cross-sectional study in rural areas of northern Jiangsu Province

Enterovirus 71 (EV71) is the dominant pathogen in severe and fatal hand-foot-mouth disease (HFMD) cases. Since 2015, three inactivated EV71 vaccines have been approved in China. The vaccination coverage of the EV71 vaccine has been relatively low, especially in rural areas. A cross-sectional survey from July 19 to August 22, 2018, was conducted in three rural counties of northern Jiangsu Province among parents of children aged 6-60 months. We adopted a pretested validated questionnaire to assess knowledge, awareness, and attitude of HFMD and EV71 vaccines among respondents and used univariate and multivariate binary logistic analyses to explore potential factors associated with the acceptance of EV71 vaccines. Of the 1,112 parents who participated, 87.8% were willing to vaccinate their children with EV71 vaccines. Parents over 40 y old were less likely to have their children vaccinated [adjusted odds ratio (aOR) = 2.12, 95% confidence interval (CI): 1.13-3.97]. Parents who lived in Ganyu (aOR = 0.50, 95% CI: 0.31-0.79) or Xinyi county (aOR = 0.33, 95% CI: 0.20-0.53), had a university or higher degree (aOR = 0.26, 95% CI: 0.11-0.64), had good knowledge of EV71 vaccines (aOR = 0.81, 95% CI: 0.67-0.98), perceived their children's disease susceptibility, and worried about the severity of HFMD had a higher willingness to vaccinate their children. Most parents were willing to vaccinate their children against EV71-related HFMD. Parental age, location, education level, knowledge of EV71 vaccines, concern about susceptibility, and severity of HFMD were all factors that influenced willingness to vaccinate.

A neonatal murine model of coxsackievirus A4 infection for evaluation of vaccines and antiviral drugs

Coxsackievirus A4 (CVA4) infection can cause hand, foot and mouth disease (HFMD), an epidemic illness affecting neonatal and paediatric cohorts, which can develop to severe neurological disease with high mortality. In this study, we established the first ICR mouse model of CVA4 infection for the evaluation of inactivated vaccines and antiviral drug screening. The CVA4 YT226R strain was selected to infect the neonatal mice and three infectious factors were optimized to establish the infection model. The 3-day-old neonatal mice exhibited clinical symptoms such as hind limb paralysis and death. The severe inflammatory reactions were closely related to the abnormal expression of the acute phase response proinflammatory cytokine IL-6 and an imbalance in the IFN-γ/IL-4 ratio. Importantly, the inactivated CVA4 whole-virus vaccine induced humoral immune responses in adult females and the maternal antibodies afforded mice complete protection against lethal dose challenges of homologous or heterologous CVA4 strains. Both IFN-α2a and antiserum inhibited the replication of CVA4 and increased the survival rates of neonatal mice during the early stages of infection. This neonatal murine model of CVA4 infection will be useful for the development of prophylactic and therapeutic vaccines and for screening of antiviral drugs targeting CVA4 to decrease morbidity and mortality.

Short-term dynamic changes in neutralizing antibodies against enterovirus 71 after vaccination

BACKGROUND

Short-term dynamic changes in neutralizing antibodies against EV71 and EV71-IgM after inactivated EV71 vaccine injection are unknown.

METHODS

This study was designed as a randomized, open-label study and was registered at ClinicalTrials.gov (NCT03278132). In total, 120 healthy infants aged 6-35 months were randomized 1:1:1 to provide a second blood sample on day 10, day 20, or day 30 after the first vaccine dose, respectively.

RESULTS

According to the per-protocol set, a rapid immune response against EV71 was observed 10 days after the first EV71 vaccine dose, with antibody titers ≥1:8 in 89.19% of participants (95% CI: 74.58-96.97%) on day 10, in 80.65% (95% CI: 62.53-92.55%) on day 20, in 66.67% (95% CI: 49.03-81.44%) on day 30, and in 100% (95% CI: 96.52%-.) on day 60. Based on an ELISA, the percentages of participants positive for EV71-IgM on day 0 and day 60 were 1.71% (2 out of 117) and 82.86% (87 out of 105), respectively.

CONCLUSIONS

The EV71 vaccine could be used for contingency vaccination to further control EV71-associated disease outbreaks. Caution should be taken in using the EV71-IgM test for rapid EV71 infection diagnosis after EV71 vaccine administration.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov NCT03278132.

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.

Antivirals and vaccines for Enterovirus A71

Enterovirus A71 (EV-A71) is an important emerging virus posing a threat to children under five years old. EV-A71 infection in infants or young children can cause hand-foot-and-mouth disease, herpangina, or severe neurological complications. However, there are still no effective antivirals for treatment of these infections. In this review, we summarize the antiviral compounds developed to date based on various targets of the EV-A71 life cycle. Moreover, development of a vaccine would be the most effective approach to prevent EV-A71 infection. Therefore, we also summarize the development and clinical progress of various candidate EV-A71 vaccines, including inactivated whole virus, recombinant VP1 protein, synthetic peptides, viral-like particles, and live attenuated vaccines.

Development and characterization of an enterovirus 71 (EV71) virus-like particles (VLPs) vaccine produced in Pichia pastoris

Enterovirus 71 (EV71) is one of the major causative agents for hand, foot and mouth disease (HFMD) in children. Although there are three inactivated virus-based HFMD vaccines licensed in China, alternative approaches have been taken to produce an effective and safer vaccine that is easier to manufacture in large scale. Among these, a virus-like particles (VLPs) based EV71 vaccine is under active development. For this purpose, an efficient methodology for the production of EV71-VLPs by recombinant technology is needed. We here report the construction and expression of the P1 and 3C genes of EV71 in Pichia pastoris for producing VLP-based EV71 vaccine antigen with a high yield and simple manufacturing process. Based on codon-optimized P1 and 3C genes, EV71-VLPs were efficiently expressed in Pichia pastoris system, and the expression level reached 270 mg/L. Biochemical and biophysical analyses showed that the produced EV71-VLPs consisted of processed VP0, VP1, and VP3 present as ~35nm spherical particles. The immune response as a function of EV71-VLPs and adjuvant dose ratio was investigated for vaccine development. Immunization with EV71-VLPs of 1-5 µg/dose and adjuvant of 225 µg/dose induced robust neutralizing antibody responses in mice and provided effective protection against lethal challenge in both maternally transferred antibody and passive transfer protection mouse models. Therefore, the yeast produced EV71-VLPs antigen is a promising candidate for the development of a vaccine against HFMD.

An inactivated enterovirus 71 vaccine is safe and immunogenic in healthy adults: A phase I, double blind, randomized, placebo-controlled, study of two dosages

BACKGROUND

Hand, foot and mouth disease (HFMD), especially that caused by enterovirus 71 (EV71) infection, is a public health concern in the Asia-Pacific region. We report a phase I clinical trial of an EV71 candidate vaccine (INV21) based on a binary ethylenimine inactivated B2 sub-genotype formulated with aluminum hydroxide.

METHODS

In this double-blind, placebo-controlled, randomized, dose escalation study adult volunteers received two vaccinations 28 days apart of low or high dose formulations of the candidate vaccine and were then monitored for safety and reactogenicity for four weeks after each dose, and for their immune responses up to 28 weeks.

RESULTS

Of 36 adults enrolled, 35 completed the study as planned. Either no or mild adverse events were observed, mainly injection site pain and tiredness. Seroconversion was 100% after two vaccinations. High geometric mean neutralizing antibody titers (GMT) were observed 14 days post first dose, peaking 14 days post second dose (at Day 42) in both high and low dose groups; GMTs on days 14, 28, 42, and 56 were 128, 81, 323, 203 and 144, 100, 451, 351 in low- and high-dose groups, respectively. Titers for both doses declined gradually to Day 196 but remained higher than baseline and the placebo groups, which had low GMTs throughout the duration of the study. Cross-neutralizing antibody activity against heterologous sub-genotypes was demonstrated.

CONCLUSION

These data show that the EV71 candidate vaccine is safe and immunogenic in adults and supports further clinical development as a potential pediatric vaccine by initiating a dose-escalation study for determining the dose-dependent safety and immunogenicity of the vaccine in young naïve children.

Recent development of enterovirus A vaccine candidates for the prevention of hand, foot, and mouth disease

INTRODUCTION

Hand, foot, and mouth disease (HFMD) is a childhood illness commonly caused by enterovirus A. Enterovirus A71 (EV-A71) and coxsackievirus A16 (CV-A16) are the most commonly identified viruses associated with HFMD. Recently, outbreaks caused by different enterovirus A including CV-A6 and CV-A10 are increasing. Being available now to protect against EV-A71 infection, inactivated EV-A71 vaccines cannot prevent coxsackievirus infections, thus limiting their general application in controlling HFMD. Multivalent HFMD vaccines are suggested to have broad cross-neutralizing responses against these emerging enteroviruses.

AREAS COVERED

We discuss the recent development of enterovirus A vaccines including the inactivated whole-virion vaccine and virus-like particle vaccine candidates and review the information of neutralization epitopes of these viruses.

EXPERT COMMENTARY

Evaluation of the efficacy and safety of the coxsackievirus vaccine and the multivalent HFMD vaccine candidates in clinical trials is urgently required. Epitopic analysis showed that common immunodominant sites exist across these enteroviruses. However, variations of amino acid residues in these regions limit the induction of cross-neutralization antibodies, and therefore, a multivalent HFMD vaccine is required for broad protection against HFMD. With the inclusion of major circulating viruses in the development of multivalent HFMD vaccines, an increase in the success in HFMD control is anticipated.