Identification of conserved neutralizing linear epitopes within the VP1 protein of coxsackievirus A16

Human enterovirus 71 (EV71) and coxsackievirus A16 (CVA16) are the two major causative agents for hand-foot-and-mouth disease (HFMD). Previously, we demonstrated that a virus-like particle (VLP) for EV71 produced from Saccharomyces cerevisiae is a potential vaccine candidate against EV71 infection, and an EV71/CVA16 chimeric VLP can elicit protective immune responses against both virus infections. Here, we presented the crystal structures of both VLPs, showing that both the linear and conformational neutralization epitopes identified in EV71 are mostly preserved on both VLPs. The replacement of only 4 residues in the VP1 GH loop converted strongly negatively charged surface patches formed by portions of the SP70 epitope in EV71 VLP into a relatively neutral surface in the chimeric VLP, which likely accounted for the additional neutralization capability of the chimeric VLP against CVA16 infection. Such local variations in the amino acid sequences and the surface charge potential are also present in different types of polioviruses. In comparison to EV71 VLP, the chimeric VLP exhibits structural changes at the local site of amino acid replacement and the surface loops of all capsid proteins. This is consistent with the observation that the VP1 GH loop located near the pseudo-3-fold junction is involved in extensive interactions with other capsid regions. Furthermore, portions of VP0 and VP1 in EV71 VLP are at least transiently exposed, revealing the structural flexibility of the VLP. Together, our structural analysis provided insights into the structural basis of enterovirus neutralization and novel vaccine design against HFMD and other enterovirus-associated diseases. IMPORTANCEOur previous studies demonstrated that the enterovirus 71 (EV71) virus-like particle (VLP) produced from yeast is a vaccine candidate against EV71 infection and that a chimeric EV71/coxsackievirus A16 (CVA16) VLP with the replacement of 4 amino acids in the VP1 GH loop can confer protection against both EV71 and CVA16 infections. This study reported the crystal structures of both the EV71 VLP and the chimeric EV71/CVA16 VLP and revealed that the major neutralization epitopes of EV71 are mostly preserved in both VLPs. In addition, the mutated VP1 GH loop in the chimeric VLP is well exposed on the particle surface and exhibits a surface charge potential different from that contributed by the original VP1 GH loop in EV71 VLP. Together, this study provided insights into the structural basis of enterovirus neutralization and evidence that the yeast-produced VLPs can be developed into novel vaccines against hand-foot-and-mouth disease (HFMD) and other enterovirus-associated diseases. Hand-foot-and-mouth disease (HFMD) is a worldwide infectious disease in infants and young children that may lead to death. In recent years, numerous outbreaks of HFMD have occurred in the Asia-Pacific regions, causing significant morbidity and mortality (1). The number of reported fatal cases of HFMD in mainland China has reached over 3,000 since 2008 (www .c...

mentioning

confidence: 63%

Crystal Structures of Yeast-Produced Enterovirus 71 and Enterovirus 71/Coxsackievirus A16 Chimeric Virus-Like Particles Provide the Structural Basis for Novel Vaccine Design against Hand-Foot-and-Mouth Disease

Lyu

et al. 2015

“…3B). Using a peptide screening method similar to Foo's, Shi et al identified 6 linear neutralizing epitopes of CA16 VP1 protein (38).…”

Section: Resultsmentioning

confidence: 99%

“…Various candidates against EV71 or CA16 virus, including inactivated vaccines (3,(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22), live attenuated vaccines (23,24), subunit vaccines based on the VP1 protein (25), virus-like particle (VLP) vaccines (26)(27)(28)(29)(30)(31)(32)(33)(34), and epitopebased vaccines (35)(36)(37)(38)(39), were shown to possess various levels of efficacy in animal studies or human clinical trials. In particular, inactivated EV71 vaccines showed promising results against EV71-associated diseases in recent phase 3 clinical studies conducted in mainland China (20)(21)(22).…”

mentioning

confidence: 99%

Cryo-Electron Microscopy Study of Insect Cell-Expressed Enterovirus 71 and Coxsackievirus A16 Virus-Like Particles Provides a Structural Basis for Vaccine Development

Gong

Zhu

Zhou

et al. 2014

Enterovirus 71 (EV71) and coxsackievirus A16 (CA16) are the two most common etiological agents responsible for the epidemics of hand, foot, and mouth disease (HFMD), a childhood illness with occasional severe neurological complications. A number of vaccine candidates against EV71 or CA16 have been reported; however, no vaccine is currently available for clinical use. Here, we generated a secreted version of EV71 and CA16 virus-like particles (VLPs) using a baculovirus-insect cell expression system and reconstructed the three-dimensional (3D) structures of both VLPs by cryo-electron microscopy (cryo-EM) single-particle analysis at 5.2-Å and 5.5-Å resolutions, respectively. The reconstruction results showed that the cryo-EM structures of EV71 and CA16 VLPs highly resemble the recently published crystal structures for EV71 natural empty particles and CA16 135S-like expanded particles, respectively. Our cryo-EM analysis also revealed that the majority of previously identified linear neutralizing epitopes are well preserved on the surface of EV71 and CA16 VLPs. In addition, both VLPs were able to induce efficiently neutralizing antibodies against various strains of EV71 and CA16 viruses in mouse immunization. These studies provide a structural basis for the development of insect cell-expressed VLP vaccines and for a potential bivalent VLP vaccine against both EV71-and CA16-associated HFMD. IMPORTANCEThe recent outbreaks of hand, foot, and mouth disease (HFMD) in the Asia Pacific region spurred the search for effective vaccines against EV71 and CA16 viruses, the two most common etiological agents responsible for HFMD. In this paper, we show that secreted versions of EV71 and CA16 VLPs generated in the baculovirus-insect cell expression system highly resemble the crystal structures of their viral conterparts and that the majority of previously identified linear neutralizing epitopes are well preserved on the VLP surfaces. In addition, the generated VLPs can efficiently induce neutralizing antibodies against various strains of EV71 and CA16 viruses in mouse immunization. These studies provide a structural basis for the development of insect cell-expressed VLP vaccines and for a potential bivalent VLP vaccine against both EV71-and CA16-associated HFMD. Hand, foot, and mouth disease (HFMD) most frequently occurs in infants or children under 5 years old. Although most cases are mild and self-limited, HFMD can in some cases cause severe symptoms, such as myocarditis, pulmonary edema, and central nervous system complications ranging from flaccid paralysis to fatal encephalitis (1, 2). The recent epidemics of HFMD led to serious public health threats in the Asia Pacific region. In China, 1.16 million and 1.77 million cases of HFMD, including 353 and 905 deaths, were reported for 2009 and 2010, respectively (3). Etiologic studies revealed that enteroviruses, especially enterovirus 71 (EV71) and coxsackievirus A16 (CA16), are the most common causative agents responsible for HFMD epidemics (4-6). A clinical survey of the...

“…The specific IgG responses in serum samples were determined by ELISA as described previously (22,25) with some modifications. Briefly, 96-well plate was coated with of 50 ng of HBc (PuZhen Biotech, Shanghai, China)/well or 200 ng of peptide diluted in PBS/well, followed by incubation at 4°C for 12 h. Then and after each of the following steps, the plate was washed three times with PBST buffer (PBS with 0.05% Tween 20).…”

Section: Cells and Virusesmentioning

confidence: 99%

Chimeric Virus-Like Particle Vaccines Displaying Conserved Enterovirus 71 Epitopes Elicit Protective Neutralizing Antibodies in Mice through Divergent Mechanisms

et al. 2014

Self Cite

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...