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

Pinn Tsin Isabel Yee,Chit Laa Poh,Kien Chai Ong,Soon Hao Tan,Kum Thong Wong,Sharifah Syed Hassan,Kuan Onn Tan

doi:10.1038/s41598-019-41285-z

Pinn Tsin Isabel Yee, Chit Laa Poh + Show 5 more

Open Access

https://doi.org/10.1038/s41598-019-41285-z

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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.

Highlights

The hand, foot, and mouth disease (HFMD) is generally manifested as a mild illness but neurological complications such as encephalomyelitis, acute flaccid paralysis and aseptic meningitis have occurred in infants and young children below 6 years of age[1]
Mice that were inoculated with PBS reached an average health score of 4 at day 8 post-infection. This was based on the health score of clinical disease which was evaluated as follows: 0, healthy; 1, ruffled hair, hunchbacked; 2, reduced mobility; 3, limb weakness; and 4, hind limb paralysis. These results showed that when the pIY miRNA vaccine strain and the MMS were administered by the i.p. route, they were able to confer 100% protection against hind limb paralysis following Enterovirus A71 (EV-A71) (MAV) challenge (Fig. 5b)
The results demonstrated the significance of the MMS, pIY vaccine strains and the inactivated vaccine (IV) in their capability to prevent systemic spread and EV-A71 replication in vivo

Summary

Introduction

The hand, foot, and mouth disease (HFMD) is generally manifested as a mild illness but neurological complications such as encephalomyelitis, acute flaccid paralysis and aseptic meningitis have occurred in infants and young children below 6 years of age[1]. As cellular miRNAs have such diverse tissue-specific distributions, the attenuation effects of the pIY vaccine strain carrying both miRNAs let-7a and miR-124a were assessed to demonstrate that the vaccine strain could decrease viral pathogenesis in different cell types. This attenuation could be due to the binding between the endogenous cellular miRNA and the viral miRNA target sequences, inducing miRNA cleavage and causing significant reduction of viral replications. We evaluated the ability of the MMS and the miRNA strain (pIY) to act as vaccines in protecting mice against a mouse adapted virus strain (MAV) in challenge studies[17]

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