Combined peptides of human enterovirus 71 protect against virus infection in mice

Protection against enterovirus 71 with neutralizing epitope incorporation within adenovirus type 3 hexon

Enterovirus 71 (EV71) is responsible for hand, foot and mouth disease with high mortality among children. Various neutralizing B cell epitopes of EV71 have been identified as potential vaccine candidates. Capsid-incorporation of antigens into adenovirus (Ad) has been developed for a novel vaccine approach. We constructed Ad3-based EV71 vaccine vectors by incorporating a neutralizing epitope SP70 containing 15 amino acids derived from capsid protein VP1 of EV71 within the different surface-exposed domains of the capsid protein hexon of Ad3EGFP, a recombinant adenovirus type 3 (Ad3) expressing enhanced green fluorescence protein. Thermostability and growth kinetic assays suggested that the SP70 epitope incorporation into hypervariable region (HVR1, HVR2, or HVR7) of the hexon did not affect Ad fitness. The SP70 epitopes were thought to be exposed on all hexon-modified intact virion surfaces. Repeated administration of BALB/c mice with the modified Ads resulted in boosting of the anti-SP70 humoral immune response. Importantly, the modified Ads immunization of mother mice conferred protection in vivo to neonatal mice against the lethal EV71 challenge, and the modified Ads-immunized mice serum also conferred passive protection against the lethal challenge in newborn mice. Compared with the recombinant GST-fused SP70 protein immunization, immunization with the Ads containing SP70 in HVR1 or HVR2 elicited higher SP70-specific IgG titers, higher neutralization titers, and conferred more effective protection to neonatal mice. Thus, this study provides valuable information for hexon-modified Ad3 vector development as a promising EV71 vaccine candidate and as an epitope-delivering vehicle for other pathogens.

Mouse adaptation of a sub-genogroup B5 strain of human enterovirus 71 is associated with a novel lysine to glutamic acid substitution at position 244 in protein VP1

Most human enterovirus 71 (HEV71) strains infect only primates and are unable to cause clinically apparent infection in mice. Here we describe a mouse-adapted HEV71 strain that belongs to sub-genogroup B5 with increased virulence in newborn BALB/c mice. The mouse-virulent strain was initially selected by serial passage of a HEV71 clinical isolate (HEV71-B5) in Chinese hamster ovary (CHO) cells (CHO-B5), followed by serial passage in newborn mice. Virus from the fifth mouse passage was cultured twice on Vero cells and designated as MP-B5. MP-B5 induces severe disease of high mortality in newborn mice in a dose-dependent manner. Skeletal muscle is the primary site of virus replication and results in severe myositis. CHO-B5 harbours a single amino acid substitution (K(149) → I) in the VP2 capsid protein. Five additional nucleotide sequence changes were identified in MP-B5, two of which are located in the 5' UTR and the three within the open reading frame (ORF). Two of the ORF mutations resulted in deduced amino acid changes in the capsid protein VP1: S(241) → L and K(244) → E; the third ORF mutation was a synonymous C → T change at nucleotide position 6072 within the 3D polymerase gene. Infectious cDNA clone-derived mutant virus populations of HEV71 belonging to sub-genogroup B3 (CHO-26 M) that contain the VP1 mutations identified in MP-B5 were generated in order to determine the mutation(s) responsible for mouse virulence. Only viruses expressing the VP1 (K(244) → E) mutation were virulent in 5-day-old BALB/c mice, indicating that the VP1 (K(244) → E) change is the critical genetic determinant of mouse adaptation and virulence in this model.

Recent advances in the molecular epidemiology and control of human enterovirus 71 infection

Human enterovirus 71 (HEV71) has emerged as an important cause of viral encephalitis in the Southeast Asia over the past 15 years. A pattern of increased epidemic activity and endemic circulation of HEV71 has been observed since 1997 and is associated with the regular emergence of new genetic lineages. Although the reason for this increase in HEV71 circulation remains unknown, evidence is accumulating that recombination events may drive the evolution of new genetic lineages. Prevention of HEV71 epidemics is likely to require the development of an effective vaccine. Fortunately, several candidate EV71 vaccines have recently been reported, several of which have been shown to be effective in animal models and commenced clinical trial in 2010. Furthermore, ongoing investigations into the molecular basis of HEV71 infection and virulence have pointed the way towards novel approaches to live attenuated vaccine development.

Lycorine reduces mortality of human enterovirus 71-infected mice by inhibiting virus replication

Human enterovirus 71 (EV71) infection causes hand, foot and mouth disease in children under 6 years old and this infection occasionally induces severe neurological complications. No vaccines or drugs are clinical available to control EV71 epidemics. In present study, we show that treatment with lycorine reduced the viral cytopathic effect (CPE) on rhabdomyosarcoma (RD) cells by inhibiting virus replication. Analysis of this inhibitory effect of lycorine on viral proteins synthesis suggests that lycorine blocks the elongation of the viral polyprotein during translation. Lycorine treatment of mice challenged with a lethal dose of EV71 resulted in reduction of mortality, clinical scores and pathological changes in the muscles of mice, which were achieved through inhibition of viral replication. When mice were infected with a moderate dose of EV71, lycorine treatment was able to protect them from paralysis. Lycorine may be a potential drug candidate for the clinical treatment of EV71-infected patients.

Display of VP1 on the surface of baculovirus and its immunogenicity against heterologous human enterovirus 71 strains in mice

BACKGROUND

Human Enterovirus 71 (EV71) is a common cause of hand, foot and mouth disease (HFMD) in young children. It is often associated with severe neurological diseases and has caused high mortalities in recent outbreaks across the Asia Pacific region. Currently, there is no effective vaccine and antiviral agents available against EV71 infections. VP1 is one of the major immunogenic capsid protein of EV71 and plays a crucial role in viral infection. Antibodies against VP1 are important for virus neutralization.

METHODOLOGY/PRINCIPAL FINDING

In the present study, infectious EV71 viruses were generated from their synthetic complementary DNA using the human RNA polymerase I reverse genetics system. Secondly, the major immunogenic capsid protein (VP1) of EV71-Fuyang (subgenogroup C4) was displayed on the surface of recombinant baculovirus Bac-Pie1-gp64-VP1 as gp64 fusion protein under a novel White Spot Syndrome Virus (WSSV) immediate early ie1 promoter. Baculovirus expressed VP1 was able to maintain its structural and antigenic conformity as indicated by immunofluorescence assay and western blot analysis. Interestingly, our results with confocal microscopy revealed that VP1 was able to localize on the plasma membrane of insect cells infected with recombinant baculovirus. In addition, we demonstrated with transmission electron microscopy that baculovirus successfully acquired VP1 from the insect cell membrane via the budding process. After two immunizations in mice, Bac-Pie1-gp64-VP1 elicited neutralization antibody titer of 1∶64 against EV71 (subgenogroup C4) in an in vitro neutralization assay. Furthermore, the antisera showed high cross-neutralization activities against all 11 subgenogroup EV71 strains.

CONCLUSION

Our results illustrated that Bac-Pie1-gp64-VP1 retained native epitopes of VP1 and acted as an effective EV71 vaccine candidate which would enable rapid production without any biosafety concerns.

Formalin-inactivated vaccine provokes cross-protective immunity in a mouse model of human enterovirus 71 infection

Human enterovirus 71 (HEV71) has emerged as a major cause of epidemics of hand, foot and mouth disease associated with severe neurological sequelae in the Asia-Pacific region. In this study, a passive protection mouse model was used to evaluate the protective efficacy of formalin-inactivated HEV71 vaccines derived from a Chinese C4 genotype strain. Pregnant mice were immunised using a prime/boost strategy and ≥50U of vaccine protected five-day-old pups from lethal challenge with a mouse-adapted (B3 genotype) strain of HEV71. Immunised mice developed a neutralising antibody response to both the immunising C4 strain and to the mouse-adapted strain. Mice born to immunised dams showed significantly less myositis and reduced viral loads in tissues.