Enterovirus 71 (EV71) is a major causative agent of hand, food, and mouth disease, which frequently occurs in young children. Since there are 11 subgenotypes (A, B1 to B5, and C1 to C5) within EV71, an EV71 vaccine capable of protecting against all of these subgenotypes is desirable. We report here the vaccine potential and protective mechanism of two chimeric virus-like particles (VLPs) presenting conserved neutralizing epitopes of EV71. We show that fusions of hepatitis B core antigen (HBc) with the SP55 or SP70 epitope of EV71, designated HBcSP55 and HBcSP70, respectively, can be rapidly generated and self-assembled into VLPs with the epitopes displayed on the surface. Immunization with the chimeric VLPs induced carrier-and epitope-specific antibody responses in mice. Anti-HBcSP55 and anti-HBcSP70 sera, but not anti-HBc sera, were able to neutralize in vitro multiple genotypes and strains of EV71. Importantly, passive immunization with anti-HBcSP55 or anti-HBcSP70 sera protected neonatal mice against lethal EV71 infections. Interestingly, anti-HBcSP70 sera could inhibit EV71 attachment to susceptible cells, whereas anti-HBcSP55 sera could not. However, both antisera were able to neutralize EV71 infection in vitro at the postattachment stage. The divergent mechanism of neutralization and protection conferred by anti-SP70 and anti-SP55 sera is in part attributed to their respective ability to bind authentic viral particles. Collectively, our study not only demonstrates that chimeric VLPs displaying the SP55 and SP70 epitopes are promising candidates for a broad-spectrum EV71 vaccine but also reveals distinct mechanisms of neutralization by the SP55-and SP70-targeted antibodies. E nterovirus 71 (EV71) is the major causative agent of hand, foot, and mouth disease, which is prevalent in the Asia-Pacific region. EV71 infection may result in severe neurological complications and even death (1-3). However, there is currently no available EV71 vaccine (4, 5).EV71 is a member of the enterovirus genus of the Picornaviridae family. It possesses a single-stranded, positive-sense RNA genome, which is encapsidated within an icosahedral capsid consisting of 60 copies of each of VP1, VP2, VP3, and VP4 subunit proteins. Based on the VP1 sequence, EV71 is categorized into three genotypes (A, B, and C), which can be further divided into eleven subgenotypes (A, B1 to B5, and C1 to C5) (reviewed in references 1 and 2). Thus, an EV71 vaccine capable of protecting against all of these subgenotypes is desirable.Increasing evidence has established that neutralizing antibodies play a key role in in vivo protection against lethal EV71 infection (reviewed in references 4 and 5). For example, Foo et al. showed that passive transfer of neutralizing antisera protects recipient mice against lethal EV71 challenge (6). Inactivated wholevirus and recombinant EV71 virus-like particles (VLPs) containing all capsid subunit proteins could elicit potent neutralizing antibodies (reviewed in references 4 and 5). Besides intact capsids, VP1 has been sh...

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Enterovirus 71 (EV71) is the main pathogen responsible for hand, foot and mouth disease with severe neurological complications and even death in young children. We have recently identified a highly potent anti-EV71 neutralizing monoclonal antibody, termed D5. Here we investigated the structural basis for recognition of EV71 by the antibody D5. Four three-dimensional structures of EV71 particles in complex with IgG or Fab of D5 were reconstructed by cryo-electron microscopy (cryo-EM) single particle analysis all at subnanometer resolutions. The most critical EV71 mature virion-Fab structure was resolved to a resolution of 4.8 Å, which is rare in cryo-EM studies of virus-antibody complex so far. The structures reveal a bivalent binding pattern of D5 antibody across the icosahedral 2-fold axis on mature virion, suggesting that D5 binding may rigidify virions to prevent their conformational changes required for subsequent RNA release. Moreover, we also identified that the complementary determining region 3 (CDR3) of D5 heavy chain directly interacts with the extremely conserved VP1 GH-loop of EV71, which was validated by biochemical and virological assays. We further showed that D5 is indeed able to neutralize a variety of EV71 genotypes and strains. Moreover, D5 could potently confer protection in a mouse model of EV71 infection. Since the conserved VP1 GH-loop is involved in EV71 binding with its uncoating receptor, the scavenger receptor class B, member 2 (SCARB2), the broadly neutralizing ability of D5 might attribute to its inhibition of EV71 from binding SCARB2. Altogether, our results elucidate the structural basis for the binding and neutralization of EV71 by the broadly neutralizing antibody D5, thereby enhancing our understanding of antibody-based protection against EV71 infection.

Antibodies play a critical role in immunity against enterovirus 71 (EV71). However, how EV71-specific antibodies neutralize infections remains poorly understood. Here we report the working mechanism for a group of three monoclonal antibodies (MAbs) that potently neutralize EV71. We found that these three MAbs (termed D5, H7, and C4, respectively) recognize the same conserved neutralizing epitope within the VP1 GH loop of EV71. Single MAbs in this group, exemplified by D5, could inhibit EV71 infection in cell cultures at both the pre-and postattachment stages in a cell type-independent manner. Specifically, MAb treatment resulted in the blockade of multiple steps of EV71 entry, including virus attachment, internalization, and subsequent uncoating and RNA release. Furthermore, we show that the D5 and C4 antibodies can interfere with EV71 binding to its key receptors, including heparan sulfate, SCARB2, and PSGL-1, thus providing a possible explanation for the observed multi-inhibitory function of the MAbs. Collectively, our study unravels the mechanism of neutralization by a unique group of anti-EV71 MAbs targeting the conserved VP1 GH loop. The findings should enhance our understanding of MAb-mediated immunity against enterovirus infections and accelerate the development of MAb-based anti-EV71 therapeutic drugs. IMPORTANCEEnterovirus 71 (EV71) is a major causative agent of hand, foot, and mouth disease (HFMD), which has caused significant morbidities and mortalities in young children. Neither a vaccine nor an antiviral drug is available. Neutralizing antibodies are major protective components in EV71 immunity. Here, we unraveled an unusual mechanism of EV71 neutralization by a group of three neutralizing monoclonal antibodies (MAbs). All of these MAbs bound the same conserved epitope located at the VP1 GH loop of EV71. Interestingly, mechanistic studies showed that single antibodies in this MAb group could block EV71 attachment and internalization during the viral entry process and interfere with EV71 binding to heparan sulfate, SCARB2, and PSGL-1 molecules, which are key receptors involved in different steps of EV71 entry. Our findings greatly enhance the understanding of the interplays among EV71, neutralizing antibodies, and host receptors, which in turn should facilitate the development of an MAbbased anti-EV71 therapy. E nterovirus 71 (EV71) is one of the major causative agents of hand, foot, and mouth disease (HFMD), which has been prevalent in Southeast Asia (1). Patients with severe HFMD cases manifest neurological complications, such as brainstem encephalitis and pulmonary edema, resulting in death, and such cases are often associated with EV71 infection (2). No prophylactic vaccine against EV71 infection or therapeutic drug for EV71 infection is available. Even though inactivated whole-virus-based EV71 vaccines have progressed into clinical trials (3, 4), their licensure faces serious challenges (5). Thus, the development of efficacious antiviral drugs for the treatment of EV71-infected patients ...

MoS2-based PTT with high therapeutic efficacy and minimal side-effects could show potential for improving cancer and infectious disease treatments.

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