Development of live attenuated Enterovirus 71 vaccine strains that confer protection against lethal challenge in mice

Abstract

Besides causing mild hand, foot and mouth infections, Enterovirus A71 (EV-A71) is associated with neurological complications and fatality. With concerns about rising EV-A71 virulence, there is an urgency for more effective vaccines. The live attenuated vaccine (LAV) is a more valuable vaccine as it can elicit both humoral and cellular immune responses. A miRNA-based vaccine strain (pIY) carrying let-7a and miR-124a target genes in the EV-A71 genome which has a partial deletion in the 5′NTR (∆11 bp) and G64R mutation (3Dp°l) was designed. The viral RNA copy number and viral titers of the pIY strain were significantly lower in SHSY-5Y cells that expressed both let-7a and miR-124a. Inhibition of the cognate miRNAs expressed in RD and SHSY-5Y cells demonstrated de-repression of viral mRNA translation. A previously constructed multiply mutated strain, MMS and the pIY vaccine strain were assessed in their ability to protect 4-week old mice from hind limb paralysis. The MMS showed higher amounts of IFN-γ ex vivo than the pIY vaccine strain. There was absence of EV-A71 antigen in the skeletal muscles and spinal cord micrographs of mice vaccinated with the MMS and pIY strains. The MMS and pIY strains are promising LAV candidates developed against severe EV-A71 infections.

Harnessing host–virus evolution in antiviral therapy and immunotherapy

“…Notably, similar effects were obtained in mice rendered genetically unresponsive to IFN, which nevertheless generated protective antibodies against reinfection by between 10 and 10 000 times the LD 50 of wild‐type PV . This approach was recently used by Yee et al . towards developing a live attenuated vaccine for enterovirus 71.…”

Antivirals and vaccines for Enterovirus A71

“…Another study also indicated that EV-A71 with the RdRp-G64R and RdRp-L123F mutations attenuated the virulence of the virus in an AG129 mouse model [108]. Yee et al [109] constructed an miRNA-based EV-A71 vaccine strain, pIY, which carried let-7a and miR-124a target genes. They found that the viral yield of the pIY strain was much lower than that of the EV-A71 wild-type B4 strain 41 in SHY-5Y cells.…”

Insights into innate and adaptive immune responses in vaccine development against EV-A71

“…34,35 High levels of neutralizing antibody (NtAb) titres, together with IFN-γ secretion following vaccination, were able to confer 100% protection against hind limb paralysis from EV-A71 challenge, suggesting that humoral immune response might be able to protect mice from being killed by high viral load. 36…”

“…44 In fact, there are a few successful LAVs that are used today, such as the attenuated yellow fever vaccine, influenza vaccine, chickenpox vaccine and the measles, mumps, and rubella vaccines. Recently, two LAVs against EV-A71 were constructed by Yee and colleagues; 36 one is a multiply mutated strain (MMS) and the other, the pIY strain, carried two additional micro-RNAs (Let 7a and MicroRNA 124) in the EV-A71 genome, which carried a deletion in the 5′NTR and a G64R mutation. This study demonstrated that both MMS and pIY strains were genetically stable after 20 serial passes in vitro .…”

“…This study demonstrated that both MMS and pIY strains were genetically stable after 20 serial passes in vitro . Both MMS and pIY vaccine strains showed high immunogenicity with broad protective neutralizing antibodies against several EV-A71 subgenotypes (B3, B4, C1 and C4) and both vaccine strains could confer protection against challenge with a mouse-adapted EV-A71 (MAV) strain, 36 thus suggesting that both MMS and pIY are promising LAV candidates against EV-A71 infection. Besides eliciting neutralizing titres ranging from 1:16 to 1:32 against several subgenotypes of EV-A71, significant IFN-γ levels indicating good cellular responses were observed.…”