Enterovirus virus-like-particle and inactivated poliovirus vaccines do not elicit substantive cross-reactive antibody responses

Human enteroviruses are the most common human pathogen with over 300 distinct genotypes. Previous work with poliovirus has suggested that it is possible to generate antibody responses in humans and animals that can recognize members of multiple enterovirus species. However, cross protective immunity across multiple enteroviruses is not observed epidemiologically in humans. Here we investigated whether immunization of mice or baboons with inactivated poliovirus or enterovirus virus-like-particles (VLPs) vaccines generates antibody responses that can recognize enterovirus D68 or A71. We found that mice only generated antibodies specific for the antigen they were immunized with, and repeated immunization failed to generate cross-reactive antibody responses as measured by both ELISA and neutralization assay. Immunization of baboons with IPV failed to generate neutralizing antibody responses against enterovirus D68 or A71. These results suggest that a multivalent approach to enterovirus vaccination is necessary to protect against enterovirus disease in vulnerable populations.

Global prevalence and case fatality rate of Enterovirus D68 infections, a systematic review and meta-analysis

A substantial amount of epidemiological data has been reported on Enterovirus D68 (EV-D68) infections after the 2014 outbreak. Our goal was to map the case fatality rate (CFR) and prevalence of current and past EV-D68 infections. We conducted a systematic review (PROSPERO, CRD42021229255) with published articles on EV-68 infections in PubMed, Embase, Web of Science and Global Index Medicus up to January 2021. We determined prevalences using a model random effect. Of the 4,329 articles retrieved from the databases, 89 studies that met the inclusion criteria were from 39 different countries with apparently healthy individuals and patients with acute respiratory infections, acute flaccid myelitis and asthma-related diseases. The CFR estimate revealed occasional deaths (7/1353) related to EV-D68 infections in patients with severe acute respiratory infections. Analyses showed that the combined prevalence of current and past EV-D68 infections was 4% (95% CI = 3.1–5.0) and 66.3% (95% CI = 40.0–88.2), respectively. The highest prevalences were in hospital outbreaks, developed countries, children under 5, after 2014, and in patients with acute flaccid myelitis and asthma-related diseases. The present study shows sporadic deaths linked to severe respiratory EV-D68 infections. The study also highlights a low prevalence of current EV-D68 infections as opposed to the existence of EV-D68 antibodies in almost all participants of the included studies. These findings therefore highlight the need to implement and/or strengthen continuous surveillance of EV-D68 infections in hospitals and in the community for the anticipation of the response to future epidemics.

Enterovirus D68 (EV-D68) infections represent a global public health concern. EV-D68 are detected in apparently healthy subjects and patients with acute respiratory illnesses, acute flaccid myelitis, and asthma-related illnesses. Enterovirus D68 was first described in 1962 and exhibited sporadic circulation until August 2014 when outbreaks of EV-D68 infections were reported in the USA and Canada mainly in children with acute flaccid myelitis and severe acute respiratory disease. We systematically reviewed the literature on EV-D68 infections globally in the present study to determine the case fatality rate and prevalence of current and past infections. Our results show sporadic deaths in patients with severe acute respiratory EV-D68 infections. Our data also show a low prevalence of EV-D68 in current infections unlike the presence of EV-D68 antibodies (past infections) in almost all individuals of all ages. EV-D68 infections were more prevalent in hospital outbreaks, industrialized countries, children < 5 years, and patients with acute flaccid myelitis and asthma-related diseases. These data highlight the need to strengthen the surveillance of EV-D68 infections.

Seroepidemiology of enterovirus D68 in a healthy population in Beijing, China, between 2012 and 2017: A retrospective study

To investigate the seroepidemiological features of enterovirus D68 (EV-D68) in the healthy population from 2012 to 2017 in Beijing, China. A retrospective cross-sectional investigation was conducted using serum specimens collected from healthy individuals in Beijing from 2012 to 2017. These samples were tested for neutralization antibodies (NtAbs) against EV-D68. The sera from six EV-D68 infected patients in the acute or convalescent phase were used to determine the protection level of NtAbs against EV-D68. The geometric means of the titers (GMT) of EV-D68 NtAbs in 2012 and 2017 were 92.82 and 242.91, respectively; the seroprevalences of EV-D68 were 89.43% and 98.43%, respectively. The GMT reached its peak in the 11 to 15 age group in 2012, while in 16 to 20 age group in 2017. We also observed that EV-D68 NtAbs titers of six sera from the acute phase were all less than equal to  1:64 and that of three sera from the convalescent phase were all more than 1:64. Anti-EV-D68 NtAbs in the population remained low from 2012 to 2016 but increased significantly in 2017. Although most of the EV-D68 infections remain undetected in Beijing, the risk of a large outbreak of EV-D68 exists and should be taken seriously.

Functional and structural characterization of a two-MAb cocktail for delayed treatment of enterovirus D68 infections

Enterovirus D68 (EV-D68) is an emerging pathogen associated with respiratory diseases and/or acute flaccid myelitis. Here, two MAbs, 2H12 and 8F12, raised against EV-D68 virus-like particle (VLP), show distinct preference in binding VLP and virion and in neutralizing different EV-D68 strains. A combination of 2H12 and 8F12 exhibits balanced and potent neutralization effects and confers broader protection in mice than single MAbs when given at onset of symptoms. Cryo-EM structures of EV-D68 virion complexed with 2H12 or 8F12 show that both antibodies bind to the canyon region of the virion, creating steric hindrance for sialic acid receptor binding. Additionally, 2H12 binding can impair virion integrity and trigger premature viral uncoating. We also capture an uncoating intermediate induced by 2H12 binding, not previously described for picornaviruses. Our study elucidates the structural basis and neutralizing mechanisms of the 2H12 and 8F12 MAbs and supports further development of the 2H12/8F12 cocktail as a broad-spectrum therapeutic agent against EV-D68 infections in humans.

Antibodies to Enteroviruses in Cerebrospinal Fluid of Patients with Acute Flaccid Myelitis

Acute flaccid myelitis (AFM) has caused motor paralysis in >560 children in the United States since 2014. The temporal association of enterovirus (EV) outbreaks with increases in AFM cases and reports of fever, respiratory, or gastrointestinal illness prior to AFM in >90% of cases suggest a role for infectious agents. Cerebrospinal fluid (CSF) from 14 AFM and 5 non-AFM patients with central nervous system (CNS) diseases in 2018 were investigated by viral-capture high-throughput sequencing (VirCapSeq-VERT system). These CSF and serum samples, as well as multiple controls, were tested for antibodies to human EVs using peptide microarrays. EV RNA was confirmed in CSF from only 1 adult AFM case and 1 non-AFM case. In contrast, antibodies to EV peptides were present in CSF of 11 of 14 AFM patients (79%), significantly higher than controls, including non-AFM patients (1/5 [20%]), children with Kawasaki disease (0/10), and adults with non-AFM CNS diseases (2/11 [18%]) (P = 0.023, 0.0001, and 0.0028, respectively). Six of 14 CSF samples (43%) and 8 of 11 sera (73%) from AFM patients were immunoreactive to an EV-D68-specific peptide, whereas the three control groups were not immunoreactive in either CSF (0/5, 0/10, and 0/11; P = 0.008, 0.0003, and 0.035, respectively) or sera (0/2, 0/8, and 0/5; P = 0.139, 0.002, and 0.009, respectively).IMPORTANCE The presence in cerebrospinal fluid of antibodies to EV peptides at higher levels than non-AFM controls supports the plausibility of a link between EV infection and AFM that warrants further investigation and has the potential to lead to strategies for diagnosis and prevention of disease.

Neutralizing Antibody against Enterovirus D68 in Children and Adults before 2014 Outbreak, Kansas City, Missouri, USA1

We evaluated enterovirus D68 seroprevalence in Kansas City, Missouri, USA, from samples obtained during 2012-2013. Neutralizing antibodies against Fermon and the dominant 2014 Missouri isolate were universally detected. Titers increased with age. Widespread circulation of enterovirus D68 occurred before the 2014 outbreak. Research is needed to determine a surrogate of protection.

Enterovirus D68 infection induces IL-17-dependent neutrophilic airway inflammation and hyperresponsiveness

Enterovirus D68 (EV-D68) shares biologic features with rhinovirus (RV). In 2014, a nationwide outbreak of EV-D68 was associated with severe asthma-like symptoms. We sought to develop a mouse model of EV-D68 infection and determine the mechanisms underlying airway disease. BALB/c mice were inoculated intranasally with EV-D68 (2014 isolate), RV-A1B, or sham, alone or in combination with anti-IL-17A or house dust mite (HDM) treatment. Like RV-A1B, lung EV-D68 viral RNA peaked 12 hours after infection. EV-D68 induced airway inflammation, expression of cytokines (TNF-α, IL-6, IL-12b, IL-17A, CXCL1, CXCL2, CXCL10, and CCL2), and airway hyperresponsiveness, which were suppressed by anti-IL-17A antibody. Neutrophilic inflammation and airway responsiveness were significantly higher after EV-D68 compared with RV-A1B infection. Flow cytometry showed increased lineage-, NKp46-, RORγt+ IL-17+ILC3s and γδ T cells in the lungs of EV-D68-treated mice compared with those in RV-treated mice. EV-D68 infection of HDM-exposed mice induced additive or synergistic increases in BAL neutrophils and eosinophils and expression of IL-17, CCL11, IL-5, and Muc5AC. Finally, patients from the 2014 epidemic period with EV-D68 showed significantly higher nasopharyngeal IL-17 mRNA levels compared with patients with RV-A infection. EV-D68 infection induces IL-17-dependent airway inflammation and hyperresponsiveness, which is greater than that generated by RV-A1B, consistent with the clinical picture of severe asthma-like symptoms.

A cross-sectional seroepidemiology study of EV-D68 in China

Enterovirus 68 (EV-D68) is associated with respiratory diseases, such as acute upper respiratory tract infections (URTIs), lower respiratory tract infections (LRTIs), pneumonia, neurological diseases, and acute flaccid myelitis (AFM). In recent years, there have been global outbreaks of EV-D68 epidemics. However, there is no effective vaccine against EV-D68, and the understanding of the seroprevalence characteristics of EV-D68 is limited. To evaluate the epidemiological features of this emerging infection in mainland China, serum samples from 20 pairs of pregnant women and their neonates, 405 infants and children (ages 1 month-15 years), and 50 adults were collected to measure EV-D68 neutralizing antibodies (NtAbs). The results showed that the geometric mean titers (GMTs) of pregnant women and their neonates were 168 (95%CI: 93.6-301.7) and 162.3 (95%CI: 89.9-293.1), respectively. The seroprevalence rate of EV-D68 antibodies was negatively correlated with age in 1-month-old to 12-month-old infants (84% for 1-month-old infants vs 10% for 1-year-old infants), whereas it was positively correlated with age for 1-year-old to 15-year-old children (10% for 1-year-old children vs 92% for 15-year-old children). This study evaluated maternal antibodies against EV-D68 in neonates. Our results showed that if mothers had high levels of anti-EV-D68 NtAbs, the NtAbs titers in their neonates were also high. The GMTs and seroprevalence rates of each age group indicated that EV-D68 infection was very common in China. Periodical EV-D68 seroprevalence surveys and vaccination campaigns should be the top priority for preventing EV-D68 infection.

A Mouse Model of Enterovirus D68 Infection for Assessment of the Efficacy of Inactivated Vaccine

In recent years, enterovirus D68 (EVD68) has been reported increasingly to be associated with severe respiratory tract infections and acute flaccid myelitis (AFM) in children all over the world. Yet, no effective vaccines or antiviral drugs are currently available for EVD68. Although several experimental animal models have been developed, immunogenicity and protective efficacy of inactivated EVD68 vaccines has not been fully evaluated. To promote the development of vaccines, we established an Institute of Cancer Research (ICR) suckling mouse model of EVD68 infection in this study. The results showed that ICR neonatal mice up to about nine days of age were susceptible to infection with EVD68 clinical strain US/MO/14-18947 by intraperitoneal injection. The infected mice exhibited progressive limb paralysis prior to death and the mortality of mice was age- and virus dose-dependent. Tissue viral load analysis showed that limb muscle and spinal cord were the major sites of viral replication. Moreover, histopathologic examination revealed the severe necrosis of the limb and juxtaspinal muscles, suggesting that US/MO/14-18947 has a strong tropism toward muscle tissues. Additionally, β-propiolactone-inactivated EVD68 vaccine showed high purity and quality and induced robust EVD68-specific neutralizing antibody responses in adult mice. Importantly, results from both antisera transfer and maternal immunization experiments clearly showed that inactivated EVD68 vaccine was able to protect against lethal viral infection in the mouse model. In short, these results demonstrate the successful establishment of the mouse model of EVD68 infection for evaluating candidate vaccines against EVD68 and also provide important information for the development of inactivated virus-based EVD68 vaccines.

Non-polio Enterovirus detection with acute flaccid paralysis: A systematic review

Acute flaccid paralysis (AFP), as defined by the World Health Organization (WHO), is characterized by an acute onset of limb weakness. In the post-polio era, other enterovirus (EV) serotypes associated with AFP may become more prominent. This study aims to collate the data on the non-polio enteroviruses (NPEV) associated with AFP. A systematic review of published case reports, case series, and surveillance studies of AFP from 1960 through 2017 was undertaken. Data were collected including the country of the study, number of specimens positive for NPEV and available clinical data. The majority of studies originated from Asia. In surveillance studies, EV 71 (a serotype of Enterovirus A) was the most commonly detected serotype with AFP, followed by Enterovirus B serotype echovirus 11 and then Enterovirus B serotype echovirus 11. In case studies and case reports, EV 71 and EV 68 (a serotype of Enterovirus D), were the most commonly detected NPEV. As poliovirus eradication continues, there is a need to ensure that AFP surveillance will also detect other potentially vaccine preventable viruses.

3C Protease of Enterovirus D68 Inhibits Cellular Defense Mediated by Interferon Regulatory Factor 7

Human enterovirus 68 (EV-D68) is a member of the EV-D species, which belongs to the EV genus of the Picornaviridae family. Over the past several years, clusters of EV-D68 infections have occurred worldwide. A recent outbreak in the United States is the largest one associated with severe respiratory illness and neurological complication. Although clinical symptoms are recognized, the virus remains poorly understood. Here we report that EV-D68 inhibits innate antiviral immunity by downregulation of interferon regulatory factor 7 (IRF7), an immune factor with a pivotal role in viral pathogenesis. This process depends on 3C(pro), an EV-D68-encoded protease, to mediate IRF7 cleavage. When expressed in host cells, 3C(pro) targets Q167 and Q189 within the constitutive activation domain, resulting in cleavage of IRF7. Accordingly, wild-type IRF7 is fully active. However, IRF7 cleavage abrogated its capacity to activate type I interferon expression and limit replication of EV-D68. Notably, IRF7 cleavage strictly requires the protease activity of 3C(pro). Together, these results suggest that a dynamic interplay between 3C(pro) and IRF7 may determine the outcome of EV-D68 infection.

IMPORTANCE

EV-D68 is a globally emerging pathogen, but the molecular basis of EV-D68 pathogenesis is unclear. Here we report that EV-D68 inhibits innate immune responses by targeting an immune factor, IRF7. This involves the 3C protease encoded by EV-D68, which mediates the cleavage of IRF7. These observations suggest that the 3C(pro)-IRF7 interaction may represent an interface that dictates EV-D68 infection.

Immunogenicity of enterovirus 70 capsid protein VP1 and its non-overlapping N- and C-terminal fragments

Currently no practical treatment method or effective virus vaccine is available for acute hemorrhagic conjunctivitis (AHC) caused by enterovirus 70 (EV70). Antibodies to UV-inactivated EV70 (J670/71 epidemic isolate) and to the inclusion bodies of recombinant proteins of full-length EV70 VP1 (GST-VP1m), its non-overlapping terminal fragments N138 (1-138 aa) and C170 (141-310 aa) (or GST-N138m and GST-C170) were developed in rabbits. The anti-EV70 neutralizing activities of the rabbit sera were determined by standard neutralization assays. The antibodies to UV-inactivated EV70, were immuno-reactive with EV70 capsid proteins VP1 and VP3 of four EV70 epidemic isolates (KW/97, T260/74, J670/71 and AE/72) in Western-blot analysis, and immunoprecipitated the capsid proteins VP1 and VP3 from the cell lysates of virus-infected human Chang's conjunctival (HCC) cells. The antibodies to GST-VP1m, GST-N138m and GST-C170, immunoprecipitated only the VP1 proteins of the four EV70 isolates. Anti-EV70 J670/71 antibodies and the antibodies to the three recombinant VP1 proteins were all capable of immunoprecipitating EV70 whole-virus of the four EV70 epidemic isolates grown in HCC cells. The anti-EV70 virion antibodies neutralized EV70 isolates with titers of 6000-10,000 units/ml while the antibodies to GST-VP1m, GST-N138m or GST-C170 neutralized EV70 isolates with titers of 20-320units/ml. The results suggest that (a) immunization with bacterially produced recombinant EV70 VP1 and its non-overlapping N- and C-terminal fragments, was capable of eliciting EV70-neutralizing antibodies; (b) the neutralization titers of antibodies to the recombinant VP1 proteins were lower than that of antibodies to the UV-inactivated EV70 virions; and (c) the non-overlapping N138 and C170 fragments of EV70 VP1 both harbor independent anti-EV70 neutralization antigenic sites.

Systemic and ocular antibody responses to inactivated acute hemorrhagic conjunctivitis (AHC) virus; enterovirus 70 (EV70)

PURPOSE

Evaluate the immune response in rabbits injected with EV70, the agent of acute hemorrhagic conjunctivitis (AHC) and AHC associated neuropathy.

METHODS

Rabbits were injected intramuscularly with uv-light inactivated EV70 isolate J670/71. Neutralizing activity against EV70 was quantified in serum and tear samples and the immunoglobulin (Ig) classes of the neutralizing activity in serum identified by sucrose gradient ultra-centrifugation. Adjuvant muramyl dipeptide (MDP) was applied topically to assess the role of ocular inflammation on levels of neutralizing antibody, proteins and Ig in tears. The protective effects of human and rabbit sera and interferon-alpha (IFN-alpha) against EV70 were compared in human conjunctival and lens cells.

RESULTS

Sera collected at 6 and 13 d contained 19S IgM anti-EV70 neutralizing antibody, while serum collected 21 d post injection contained 19S IgM and 7S IgG anti-EV70 neutralizing antibody. Low titers of anti-EV70 activity (< or =30 U/ml) were detected in tears of seropositive rabbits. MDP induction of conjunctivitis in seropositive rabbits increased tear IgG concentration (3-fold) and anti-EV70 neutralizing antibody titers (> or =10-fold). The protective effect of the rabbit and human sera against EV70 infection in conjunctival, but not lens epithelial cells, was enhanced by the addition of IFN-alpha.

CONCLUSIONS

Immunization with uv-light inactivated EV70 elicits a classical humoral immune response in rabbits. The protective activity of serum in EV70-infected human conjunctival cells, but not lens cells, was increased by IFN-alpha. Adjuvant MDP-induced conjunctivitis, increased blood-conjunctival barrier (BCB) permeability and anti-EV70 neutralizing activity in tear of seropositive rabbits. The results suggest immunization with inactivated EV70 could provide systemic as well as ocular protection during natural EV70 infection.