A Novel Neutralizing Antibody Specific to the DE Loop of VP1 Can Inhibit EV-D68 Infection in Mice

In vitro and in vivo models for the study of EV-D68 infection

Enterovirus D68 (EV-D68) is one of hundreds of non-polio enteroviruses that typically cause cold-like respiratory illness. The first EV-D68 outbreak in the United States in 2014 aroused widespread concern among the public and health authorities. The infection was found to be associated with increased surveillance of acute flaccid myelitis, a neurological condition that causes limb paralysis in conjunction with spinal cord inflammation. In vitro studies utilising two-dimensional (2D) and three-dimensional (3D) culture systems have been employed to elucidate the pathogenic mechanism of EV-D68. Various animal models have also been developed to investigate viral tropism and distribution, pathogenesis, and immune responses during EV-D68 infection. EV-D68 infections have primarily been investigated in respiratory, intestinal and neural cell lines/tissues, as well as in small-size immunocompetent rodent models that were limited to a young age. Some studies have implemented strategies to overcome the barriers by using immunodeficient mice or virus adaptation. Although the existing models may not fully recapitulate both respiratory and neurological disease observed in human EV-D68 infection, they have been valuable for studying pathogenesis and evaluating potential vaccine or therapeutic candidates. In this review, we summarise the methodologies and findings from each experimental model and discuss their applications and limitations.

Different T-cell and B-cell repertoire elicited by the SARS-CoV-2 inactivated vaccine and S1 subunit vaccine in rhesus macaques

Multiple types of SARS-CoV-2 vaccines have been used worldwide, but summarizing their immunologic efficacy post-vaccination remains challenging. The BCR and TCR sequencing based on single-cell sorting makes it possible to evaluate the vaccine-induced immune responses of B or T cells. In this study, we compared the repertoire diversities of B cells and T cells between a whole-virus inactivated vaccine and an S1 protein subunit vaccine in rhesus macaques. We found that the inactivated vaccine could induce a large antigen-specific-BCR repertoire with longer VH CDR3 (21 aa), while the CD3+ TCR α chains of the two vaccine groups showed a similar TCRV/J usage frequency. Detailed analysis of the TCR and BCR repertoires might be of interest for further understanding of the mechanisms of vaccine-induced immune responses.

Respiratory illness virus infections with special emphasis on COVID-19

Viruses that emerge pose challenges for treatment options as their uniqueness would not know completely. Hence, many viruses are causing high morbidity and mortality for a long time. Despite large diversity, viruses share common characteristics for infection. At least 12 different respiratory-borne viruses are reported belonging to various virus taxonomic families. Many of these viruses multiply and cause damage to the upper and lower respiratory tracts. The description of these viruses in comparison with each other concerning their epidemiology, molecular characteristics, disease manifestations, diagnosis and treatment is lacking. Such information helps diagnose, differentiate, and formulate the control measures faster. The leading cause of acute illness worldwide is acute respiratory infections (ARIs) and are responsible for nearly 4 million deaths every year, mostly in young children and infants. Lower respiratory tract infections are the fourth most common cause of death globally, after non-infectious chronic conditions. This review aims to present the characteristics of different viruses causing respiratory infections, highlighting the uniqueness of SARS-CoV-2. We expect this review to help understand the similarities and differences among the closely related viruses causing respiratory infections and formulate specific preventive or control measures.

Structure of Human Enterovirus 70 and Its Inhibition by Capsid-Binding Compounds

Enterovirus 70 (EV70) is a human pathogen belonging to the family Picornaviridae. EV70 is transmitted by eye secretions and causes acute hemorrhagic conjunctivitis, a serious eye disease. Despite the severity of the disease caused by EV70, its structure is unknown. Here, we present the structures of the EV70 virion, altered particle, and empty capsid determined by cryo-electron microscopy. The capsid of EV70 is composed of the subunits VP1, VP2, VP3, and VP4. The partially collapsed hydrophobic pocket located in VP1 of the EV70 virion is not occupied by a pocket factor, which is commonly present in other enteroviruses. Nevertheless, we show that the pocket can be targeted by the antiviral compounds WIN51711 and pleconaril, which block virus infection. The inhibitors prevent genome release by stabilizing EV70 particles. Knowledge of the structures of complexes of EV70 with inhibitors will enable the development of capsid-binding therapeutics against this virus.

IMPORTANCE Globally distributed enterovirus 70 (EV70) causes local outbreaks of acute hemorrhagic conjunctivitis. The discharge from infected eyes enables the high-efficiency transmission of EV70 in overcrowded areas with low hygienic standards. Currently, only symptomatic treatments are available. We determined the structures of EV70 in its native form, the genome release intermediate, and the empty capsid resulting from genome release. Furthermore, we elucidated the structures of EV70 in complex with two inhibitors that block virus infection, and we describe the mechanism of their binding to the virus capsid. These results enable the development of therapeutics against EV70.

Animal Models of Enterovirus D68 Infection and Disease

Human enterovirus D68 (EV-D68) is a globally reemerging respiratory pathogen that is associated with the development of acute flaccid myelitis (AFM) in children. Currently, there are no approved vaccines or treatments for EV-D68 infection, and there is a paucity of data related to the virus and host-specific factors that predict disease severity and progression to the neurologic syndrome. EV-D68 infection of various animal models has served as an important platform for characterization and comparison of disease pathogenesis between historic and contemporary isolates. Still, there are significant gaps in our knowledge of EV-D68 pathogenesis that constrain the development and evaluation of targeted vaccines and antiviral therapies. Continued refinement and characterization of animal models that faithfully reproduce key elements of EV-D68 infection and disease is essential for ensuring public health preparedness for future EV-D68 outbreaks.

The pathogenesis and virulence of enterovirus-D68 infection

In 2014, enterovirus D68 (EV-D68) emerged causing outbreaks of severe respiratory disease in children worldwide. In a subset of patients, EV-D68 infection was associated with the development of central nervous system (CNS) complications, including acute flaccid myelitis (AFM). Since then, the number of reported outbreaks has risen biennially, which emphasizes the need to unravel the systemic pathogenesis in humans. We present here a comprehensive review on the different stages of the pathogenesis of EV-D68 infection – infection in the respiratory tract, systemic dissemination and infection of the CNS – based on observations in humans as well as experimental in vitro and in vivo studies. This review highlights the knowledge gaps on the mechanisms of systemic dissemination, routes of entry into the CNS and mechanisms to induce AFM or other CNS complications, as well as the role of virus and host factors in the pathogenesis of EV-D68.

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.

Enterovirus D68 molecular and cellular biology and pathogenesis

In recent years, enterovirus D68 (EV-D68) has advanced from a rarely detected respiratory virus to a widespread pathogen responsible for increasing rates of severe respiratory illness and acute flaccid myelitis (AFM) in children worldwide. In this review, we discuss the accumulating data on the molecular features of EV-D68 and place these into the context of enterovirus biology in general. We highlight similarities and differences with other enteroviruses and genetic divergence from own historical prototype strains of EV-D68. These include changes in capsid antigens, host cell receptor usage, and viral RNA metabolism collectively leading to increased virulence. Furthermore, we discuss the impact of EV-D68 infection on the biology of its host cells, and how these changes are hypothesized to contribute to motor neuron toxicity in AFM. We highlight areas in need of further research, including the identification of its primary receptor and an understanding of the pathogenic cascade leading to motor neuron injury in AFM. Finally, we discuss the epidemiology of the EV-D68 and potential therapeutic approaches.

A cross-reactive mouse monoclonal antibody against rhinovirus mediates phagocytosis in vitro

Rhinoviruses (RVs) are the main cause of the common cold worldwide. To date, more than 160 types of the virus have been recognized, categorized into three major species - A, B, and C. There are currently no approved vaccines available to prevent infection with RVs. To elicit antibodies against conserved regions located on capsid proteins of RV A viruses, mice were sequentially vaccinated with DNA plasmids encoding capsid proteins of different RV A types. After a final boost with whole virus, antibody-expressing hybridomas were generated. After isotyping, 11 monoclonal antibodies (mAbs) expressing an IgG subtype Fc-domain were selected for further expansion and purification. Three mAbs showed cross-reactivity against multiple strains of RV A viruses by ELISA, including strains A1A, A1B, A15, A16 and A49. Other mAbs had strain-specific binding patterns, with the majority of mAbs showing reactivity to RV-A15, the strain used for the final vaccination. We found that the RV-A15-specific mAbs, but not the cross-reactive mAbs, had neutralizing activity against RV-A15. An antibody dependent cellular phagocytosis (ADCP) assay revealed substantial ADCP activity for one of the cross-reactive mAbs. Epitope mapping of the neutralizing mAbs via escape mutant virus generation revealed a shared binding epitope on VP1 of RV-A15 for several neutralizing mAbs. The epitope of the ADCP-active, non-neutralizing mAb was determined by microarray analysis of peptides generated from the VP1 capsid protein. VP1-specific, cross-reactive antibodies, especially those with ADCP activity, could contribute to protection against RV infections.

Single B cells reveal the antibody responses of rhesus macaques immunized with an inactivated enterovirus D68 vaccine

Enterovirus D68 (EV-D68) infection may cause severe respiratory system manifestations in pediatric populations. Because of the lack of an effective preventive vaccine or specific therapeutic drug for this infection, the development of EV-D68-specific vaccines and antibodies has become increasingly important. In this study, we prepared an experimental EV-D68 vaccine inactivated by formaldehyde and found that the serum of rhesus macaques immunized with the inactivated EV-D68 vaccine exhibited potent neutralizing activity against EV-D68 virus in vitro. Subsequently, the antibody-mediated immune response of B cells elicited by the inactivated vaccine was evaluated in a rhesus monkey model. The binding activity, in vitro neutralization activity, and sequence properties of 28 paired antibodies from the rhesus macaques’ EV-D68-specific single memory B cells were analyzed, and the EV-D68 VP1-specific antibody group was found to be the main constituent in vivo. Intriguingly, we also found a synergistic effect among the E15, E18 and E20 monoclonal antibodies from the rhesus macaques. Furthermore, we demonstrated the protective efficacy of maternal antibodies in suckling C57BL/6 mice. This study provides valuable information for the future development of EV-D68 vaccines.

Current Understanding of Human Enterovirus D68

Human enterovirus D68 (EV-D68), a member of the species Enterovirus D of the Picornaviridae family, was first isolated in 1962 in the United States. EV-D68 infection was only infrequently reported until an outbreak occurred in 2014 in the US; since then, it has continued to increase worldwide. EV-D68 infection leads to severe respiratory illness and has recently been reported to be linked to the development of the neurogenic disease known as acute flaccid myelitis (AFM), mostly in children, seriously endangering public health. Hitherto, treatment options for EV-D68 infections were limited to supportive care, and as yet there are no approved, specific antiviral drugs or vaccines. Research on EV-D68 has mainly focused on its epidemiology, and its virologic characteristics and pathogenesis still need to be further explored. Here, we provide an overview of current research on EV-D68, including the genotypes and genetic characteristics of recent epidemics, the mechanism of infection and virus-host interactions, and its relationship to acute flaccid myelitis (AFM), in order to broaden our understanding of the biological features of EV-D68 and provide a basis for the development of effective antiviral agents.

Discovery of Quinoline Analogues as Potent Antivirals against Enterovirus D68 (EV-D68)

Enterovirus D68 (EV-D68) is an atypical nonpolio enterovirus that mainly infects the respiratory system of humans, leading to moderate-to-severe respiratory diseases. In rare cases, EV-D68 can spread to the central nervous system and cause paralysis in infected patients, especially young children and immunocompromised individuals. There is currently no approved vaccine or antiviral available for the prevention and treatment of EV-D68. In this study, we aimed to improve the antiviral potency and selectivity of a previously reported EV-D68 inhibitor, dibucaine, through structure-activity relationship studies. In total, 60 compounds were synthesized and tested against EV-D68 using the viral cytopathic effect assay. Three compounds 10a, 12a, and 12c were identified to have significantly improved potency (EC₅₀ < 1 μM) and a high selectivity index (>180) compared with dibucaine against five different strains of EV-D68 viruses. These compounds also showed potent antiviral activity in neuronal cells, such as A172 and SH-SY5Y cells, suggesting they might be further developed for the treatment of both respiratory infection as well as neuronal infection.