Implications of Age-Dependent Immune Responses to Enterovirus 71 Infection for Disease Pathogenesis and Vaccine Design

Suppression of innate and acquired immunity in severe hand foot and mouth disease caused by EV71 infections in children

Hand, foot, and mouth disease (HFMD) is a common children infectious disease caused by human enteroviruses. Most of the cases have minimal symptoms, however, some patients may develop serious neurological, cardiac complications, or even death. The pathological mechanism leading to severe HFMD is not clearly understood, and the immunological status of the individual patient may play an important role. Transcriptomes of peripheral blood mononuclear cells from EV71-infected patients (n = 45) and healthy controls (n = 36) were examined. Immune pathways were up-regulated in patients with mild disease symptoms (n = 11, M) compared to the healthy controls (n = 36, H), demonstrating an effective anti-viral response upon EV71 infection. However, in patients with severe symptoms (n = 23, S) as well as severe patients following treatment (n = 11, A), their innate and acquired immune pathways were down-regulated, indicating a global immunity suppression. Such immune suppression characteristics could thus provide an opportunity for early EV-71 infection prognosis prediction. Based on our cohort, an SVM model using RNA-seq expression levels of five genes (MCL1, ZBTB37, PLEKHM1P, IFNAR2 and YEATS2) was developed and achieved a high ROC-AUC (91·3%) in predicting severe HFMD. Meanwhile, qPCR fold-changes method was performed based three genes (MCL1, IFNAR2 and YEATS2) on additional cohort. This qPCR method achieved a ROC-AUC of 78.6% in predicting severe HFMD, which the patients could be distinguished in 2-3 h. Therefore, our models demonstrate the possibility of HFMD severity prediction based on the selected biomarkers that predict severe HFMD effectively.

Insight into the Enterovirus A71: A review

Enterovirus A71 is a major causative pathogen of hand, foot and mouth disease. It has become a global public health threat, and is especially important for infants and young children in the Asian-Pacific countries. The enterovirus A71 is a non-enveloped virus of the Picornaviridae family having a single-stranded positive-sense RNA genome of about 7.4 kb which encodes the structural and nonstructural proteins. Currently there are no US FDA-approved vaccines or antiviral therapy available against enterovirus A71 infection. Although enterovirus A71 vaccines have been licenced in China, clinically approved vaccines for widespread vaccination programs are lacking. Substantial progress has recently been achieved on understanding the structure and function of enterovirus A71 proteins together with information on the viral genetic diversity and geographic distribution. The present review is intended to provide an overview on our current understanding of the molecular biology and epidemiology of enterovirus A71 which will aid the development of vaccines, therapeutics and other control strategies so as to bolster the preparedness for future enterovirus A71 outbreaks.

Efficacy, safety, and immunogenicity of an inactivated, adjuvanted enterovirus 71 vaccine in infants and children: a multiregion, double-blind, randomised, placebo-controlled, phase 3 trial

BACKGROUND

Children are susceptible to severe or fatal enterovirus 71 (EV71) infections. We aimed to evaluate the efficacy, safety, and immunogenicity of EV71vac, an aluminium phosphate-adjuvanted inactivated EV71 vaccine in children aged 2-71 months.

METHODS

We did a randomised, double-blinded, placebo-controlled, phase 3 trial at five hospitals in Taiwan and two in Vietnam. Children aged 2-71 months were stratified by country and age, and randomly assigned (1:1) to receive two doses of EV71vac or placebo via intramuscular injection 56 days apart. Children aged 2-23 months received a third booster dose on day 366. The primary endpoint was the clinical efficacy of the total vaccinated cohort against EV71-associated diseases during the follow-up period, from 14 days after the second dose to when 15 cases of EV71 infections were confirmed in the per-protocol population. Our safety analysis included all participants who received at least one dose of EV71vac. This trial is registered with ClinicalTrials.gov, NCT03865238, and is complete.

FINDINGS

Between April 23 and Dec 25, 2019, of 3663 children assessed, 3061 were randomly assigned, of whom 3049 were vaccinated: 1521 children in the EV71vac group and 1528 in the placebo group. By May 20, 2021, our primary efficacy analysis included 2959 children, with 1476 children in the EV71vac group and 1483 children in the placebo group. The vaccine efficacy of EV71vac was 96·8% (95% CI 85·5-100) against EV71 associated diseases (p<0·0001). The percentage of participants who reported solicited adverse events were similar in both groups: 865 (56·9%) in the EV71vac group and 852 (55·8%) in the placebo group. Almost all reported solicited adverse events were mild and self-limited.

INTERPRETATION

EV71vac is safe, well-tolerated, and highly effective in preventing EV71 associated diseases in children aged 2-71 months.

FUNDING

Medigen Vaccine Biologics and A+ Industrial Innovative R&D Program of the Ministry of Economic Affairs, Taiwan.

Interplays between Enterovirus A71 and the innate immune system

Enterovirus A71 (EV-A71) is a growing threat to public health, particularly in the Asia-Pacific region. EV-A71 infection is most prevalent in infants and children and causes a wide spectrum of clinical complications, including hand-foot-and-mouth disease (HFMD), pulmonary and neurological disorders. The pathogenesis of EV-A71 infection is poorly understood at present. It is likely that viral factors and host immunity, and their interplay, affect the pathogenesis and outcome of EV-A71 infection. The mammalian innate immune system forms the first layer of defense against viral infections and triggers activation of adaptive immunity leading to full protection. In this review, we discuss recent advances in our understanding of the interaction between EV-A71 and the innate immune system. We discuss the role of pattern-recognition receptors (PRRs), including Toll-like receptors (TLRs), RIG-I-like receptors (RLRs), and inflammasomes, in the detection of EV-A71 infection and induction of antiviral immunity. As a counteraction, EV-A71 viral proteins target multiple innate immune pathways to facilitate viral replication in host cells. These novel insights at the virus-host interphase may support the future development of vaccines and therapeutics against EV-A71 infection.

Immunogenicity, safety, cross-reaction, and immune persistence of an inactivated enterovirus A71 vaccine in children aged from two months to 11 years in Taiwan

BACKGROUND

To fight against enterovirus A71 (EV-A71)-associated diseases, vaccine development was initiated in Taiwan focusing on two-month-old infants.

METHODS

We conducted a phase II, double-blind, randomised, placebo-controlled study on infants and children aged two months to 11 years. This study was conducted in 4 parts (2a, 2b, 2c, and 2d) with age de-escalation sequentially. Two doses were administered with a 28-day or 56-day interval. Participants aged two months to <two years received a booster dose at one year after the first dose. During the surveillance period, solicited adverse events (AEs) and unsolicited AEs were recorded for safety evaluation. Blood samples were collected for neutralising antibody assay at various times. Immune persistence and booster effects were also assessed.

RESULTS

A total of 363 children completed the study. Most AEs were mild and unrelated to treatment. No vaccine-related serious adverse events (SAEs) were reported. Geometric mean titres (GMTs) of serum neutralising antibody titres increased profoundly. Most participants in the vaccine groups achieved defined seroprotection (neutralization titre ≥ 1:32) after the second vaccination and persisted for two years. Furthermore, the EV-A71 vaccine could provide a cross-reaction against other EV-A71 strain genotypes: B5, C4a, C4b, and C5.

CONCLUSIONS

The mid dose of the EV-A71 vaccine elicited high immune response and were tolerable in participants aged between two months and 11 years in all dosing groups.

Effect of enterovirus infections on asthma in young children: A national cohort study

BACKGROUND

We conducted a cohort study to determine the relationship between enterovirus (EV) infection and asthma.

MATERIALS AND METHODS

From the National Health Insurance Research Database of Taiwan, we identified patients who received a new diagnosis of asthma and concurrent treatment between January 2000 and December 2011 (EV cohort: n = 208 213; non-EV cohort: n = 208 213). Cox proportional hazards regression analysis was performed to determine and compare the adjusted hazard ratios (aHRs) of asthma between these 2 cohorts. Kaplan-Meier analysis was conducted to assess the differences in the cumulative incidence curves of asthma between the 2 cohorts.

RESULTS

The overall aHR of asthma was 1.48-fold higher in the EV cohort than in the non-EV cohort (95% confidence interval = 1.45-1.50). The aHR of asthma was higher in the EV cohort than in the non-EV cohort, comprising children aged ≤5 years, regardless of sex, sociodemographic factors (urbanization level and parental occupation) or comorbidities. The risk of asthma was higher in 1-3, 4-6, 7-9 and 10-12 months (all P < .001), particularly in those with a higher frequency of admission (>5 per year).

CONCLUSION

The incidence of asthma was higher in the EV cohort than in the non-EV cohort, comprising children aged ≤5 years, regardless of sex, urbanization level, parental occupation or season. In particular, the risk of asthma was higher in children with a higher frequency of admission, even in the absence of atopy or other respiratory infections.

Immunopathogenesis and Virus-Host Interactions of Enterovirus 71 in Patients with Hand, Foot and Mouth Disease

Enterovirus 71 (EV71) is a global infectious disease that affects millions of people. The virus is the main etiological agent for hand, foot, and mouth disease with outbreaks and epidemics being reported globally. Infection can cause severe neurological, cardiac, and respiratory problems in children under the age of 5. Despite on-going efforts, little is known about the pathogenesis of EV71, how the host immune system responds to the virus and the molecular mechanisms behind these responses. Moreover, current animal models remain limited, because they do not recapitulate similar disease patterns and symptoms observed in humans. In this review the role of the host-viral interactions of EV71 are discussed together with the various models available to examine: how EV71 utilizes its proteins to cleave host factors and proteins, aiding virus replication; how EV71 uses its own viral proteins to disrupt host immune responses and aid in its immune evasion. These discoveries along with others, such as the EV71 crystal structure, have provided possible targets for treatment and drug interventions.

A Selective Bottleneck Shapes the Evolutionary Mutant Spectra of Enterovirus A71 during Viral Dissemination in Humans

RNA viruses accumulate mutations to rapidly adapt to environmental changes. Enterovirus A71 (EV-A71) causes various clinical manifestations with occasional severe neurological complications. However, the mechanism by which EV-A71 evolves within the human body is unclear. Utilizing deep sequencing and haplotype analyses of viruses from various tissues of an autopsy patient, we sought to define the evolutionary pathway by which enterovirus A71 evolves fitness for invading the central nervous system in humans. Broad mutant spectra with divergent mutations were observed at the initial infection sites in the respiratory and digestive systems. After viral invasion, we identified a haplotype switch and dominant haplotype, with glycine at VP1 residue 31 (VP1-31G) in viral particles disseminated into the integumentary and central nervous systems. In vitro viral growth and fitness analyses indicated that VP1-31G conferred growth and a fitness advantage in human neuronal cells, whereas VP1-31D conferred enhanced replication in human colorectal cells. A higher proportion of VP1-31G was also found among fatal cases, suggesting that it may facilitate central nervous system infection in humans. Our data provide the first glimpse of EV-A71 quasispecies from oral tissues to the central nervous system within humans, showing broad implications for the surveillance and pathogenesis of this reemerging viral pathogen.IMPORTANCE EV-A71 continues to be a worldwide burden to public health. Although EV-A71 is the major etiological agent of hand, foot, and mouth disease, it can also cause neurological pulmonary edema, encephalitis, and even death, especially in children. Understanding selection processes enabling dissemination and accurately estimating EV-A71 diversity during invasion in humans are critical for applications in viral pathogenesis and vaccine studies. Here, we define a selection bottleneck appearing in respiratory and digestive tissues. Glycine substitution at VP1 residue 31 helps viruses break through the bottleneck and invade the central nervous system. This substitution is also advantageous for replication in neuronal cells in vitro Considering that fatal cases contain enhanced glycine substitution at VP1-31, we suggest that the increased prevalence of VP1-31G may alter viral tropism and aid central nervous system invasion. Our findings provide new insights into a dynamic mutant spectral switch active during acute viral infection with emerging viral pathogens.

[Association of TLR3-1377C/T gene polymorphisms and expression with susceptibility to enterovirus 71 encephalitis in children]

OBJECTIVE

To investigate the association of gene polymorphisms of Toll-like receptor 3 (TLR3)-1377C/T and expression of TLR3 with the susceptibility to enterovirus 71 (EV71) encephalitis in children.

METHODS

A total of 187 children with EV71 infection (59 children in the encephalitis group and 128 in the non-encephalitis group) and 232 children who underwent physical examination were enrolled in the case-control study. Polymerase chain reaction-restriction fragment length polymorphism was used to detect the TLR3-1377C/T gene polymorphisms. ELISA was used to measure the serum level of TLR3.

RESULTS

There were no significant differences in the genotype and allele frequencies of TLR3-1377C/T between the non-encephalitis group and the encephalitis group. Compared with the control group, the encephalitis group and the non-encephalitis group had significant increases in the serum level of TLR3 (P<0.05), and the non-encephalitis group had the highest level (P<0.05). The encephalitis group had a significantly higher EV71 viral load than the non-encephalitis group (P<0.01). The children aged <1 year or ≥1 year in the encephalitis group and the non-encephalitis group had significant increases in the serum level of TLR3 compared with their counterparts in the control group (P<0.05), and the children aged <1 year or ≥1 year in the non-encephalitis group had a significantly higher serum level of TLR3 than those in the encephalitis group (P<0.05). In the encephalitis group, the children aged ≥1 year had a significantly higher TLR3 concentration than those aged <1 year (P<0.05), and there were no significant differences in the TLR3 concentration between the children aged ≥1 year and <1 year in the non-encephalitis group and the control group. In the encephalitis group, the proportion of children aged <1 year was significantly higher than those aged ≥1 year (P<0.05).

CONCLUSIONS

The TLR3-1377C/T gene polymorphisms are not significantly associated with the development of EV71 encephalitis. Low expression of TLR3 might weaken the inhibitory effect on virus replication and promote the development of EV71 encephalitis. The deficiency in the expression of TLR3 in serum after EV71 infection might be an important factor for the development of encephalitis in infants.

Efficacy and safety of interferon-α2b spray in the treatment of hand, foot, and mouth disease: a multicenter, randomized, double-blind trial

Hand, foot, and mouth disease (HFMD) is a common infectious enterovirus disease, occurring mostly in infants and children younger than 7 years with potentially fatal complications. Therefore, we evaluated the clinical efficacy and safety of recombinant human interferon (IFN)-α2b spray for treating mild HFMD in 400 patients in a randomized, open, controlled clinical trial. The patients were randomized to the IFN-α2b spray and placebo groups, and their temperature, skin rash, oral lesions, and appetite were monitored, while pathogen levels and safety were evaluated with a 7-day follow-up. The mean age of the patients was 20.1 ± 10.2 months. The median duration of fever, oral ulcers or vesicles (or both), and skin rash in addition to median time to regain appetite in the IFN-α2b spray group were shorter than they were in the placebo group. The number of virus-positive cases differed statistically between the two groups for the three follow-up detections. Additionally, the incidences of adverse events (AEs) and severe AEs (SAEs) were not significantly different between the two groups, and the SAEs were evidently unrelated to the IFN-α2b spray or placebo. Therefore, the IFN-α2b spray is suitable for topical treatment of HFMD, and it rapidly relieved fever, promoted oral lesions and subsidence of rash, enhanced appetite, promoted disease recovery, and was safe for application.

Update of enterovirus 71 infection: epidemiology, pathogenesis and vaccine

Enterovirus 71 (EV71) is a neurotropic human pathogen that is the causative agent of hand foot and mouth disease (HFMD), herpangina and brain stem encephalitis. Recurrent EV71 epidemics of various scales have occurred in the Asia-Pacific region. Several specific cell surface molecules serve as the receptors for EV71. Identification of the receptors is an important step to understand EV71 disease. Cytokines, lymphocytes and monocytes contribute significantly to EV71 pathogenesis. The interaction of EV71 and receptors may be associated with the cytokines immunopathogenesis. Some animal models have been established and aim to explore the pathogenesis of EV71 infections. EV71 antibodies can neutralize or enhance infection at subneutralizing levels. These results are important for EV71 vaccine and therapeutics design. Several clinical trials of human inactivated EV71 vaccine have recently been completed. The purpose of this review is to summarize recent discoveries about the epidemiology and pathogenesis of EV71 and provide insights into human vaccine development.

Is Infant Immunity Actively Suppressed or Immature?

Almost 7 million children under the age 5 die each year, and most of these deaths are attributable to vaccine-preventable infections. Young infants respond poorly to infections and vaccines. In particular, dendritic cells secrete less IL-12 and IL-18, CD8^pos T cells and NK cells have defective cytolysis and cytokine production, and CD4^pos T cell responses tend to bias towards a Th2 phenotype and promotion of regulatory T cells (T_regs). The basis for these differences is not well understood and may be in part explained by epigenetic differences, as well as immaturity of the infant's immune system. Here we present a third possibility, which involves active suppression by immune regulatory cells and place in context the immune suppressive pathways of mesenchymal stromal cells (MSC), myeloid-derived suppressor cells (MDSC), CD5^pos B cells, and T_regs. The immune pathways that these immune regulatory cells inhibit are similar to those that are defective in the infant. Therefore, the immune deficiencies seen in infants could be explained, in part, by active suppressive cells, indicating potential new avenues for intervention.