Molecular Basis of Live-Attenuated Influenza Virus

Wen He,Huamin Han,Bin Gao,Ge Zhang,Lei Wang,Wei Wang,Paulo Lee Ho

doi:10.1371/journal.pone.0060413

Abstract

Human influenza is a seasonal disease associated with significant morbidity and mortality. The most effective means for controlling infection and thereby reducing morbidity and mortality is vaccination with a three inactivated influenza virus strains mixture, or by intranasal administration of a group of three different live attenuated influenza vaccine strains. Comparing to the inactivated vaccine, the attenuated live viruses allow better elicitation of a long-lasting and broader immune (humoral and cellular) response that represents a naturally occurring transient infection. The cold-adapted (ca) influenza A/AA/6/60 (H2N2) (AA ca) virus is the backbone for the live attenuated trivalent seasonal influenza vaccine licensed in the United States. Similarly, the influenza A components of live-attenuated vaccines used in Russia have been prepared as reassortants of the cold-adapted (ca) H2N2 viruses, A/Leningrad/134/17/57-ca (Len/17) and A/Leningrad/134/47/57-ca (Len/47) along with virulent epidemic strains. However, the mechanism of temperature-sensitive attenuation is largely elusive. To understand how modification at genetic level of influenza virus would result in attenuation of human influenza virus A/PR/8/34 (H1N1,A/PR8), we investigated the involvement of key mutations in the PB1 and/or PB2 genes in attenuation of influenza virus in vitro and in vivo. We have demonstrated that a few of residues in PB1 and PB2 are critical for the phenotypes of live attenuated, temperature sensitive influenza viruses by minigenome assay and real-time PCR. The information of these mutation loci could be used for elucidation of mechanism of temperature-sensitive attenuation and as a new strategy for influenza vaccine development.

Highlights

Influenza A viruses belong to Orthomyxoviridae family viruses and are highly contagious pathogens for both human and animals
As a major cause for winter respiratory infection, seasonal influenza contributes the biggest number of morbidity and mortality each year
Our studies suggested that these mutation loci for the preparation of Live attenuated influenza vaccines (LAIVs) could be useful for vaccine design against seasonal influenza

Summary

Introduction

Influenza A viruses belong to Orthomyxoviridae family viruses and are highly contagious pathogens for both human and animals. Two different types of vaccines, inactivated and live attenuated viruses are currently licensed for the prevention of seasonal influenza [2,3,4,5]. Reassortants of cold-adapted (ca) influenza donor strains have been used as live -attenuated vaccines for direct administration to the respiratory tract. Live attenuated influenza vaccines (LAIVs) are 6:2 genetic reassortants that are currently produced using reverse genetics, in which the six internal protein gene segments (PB2, PB1, PA, NP, M and NS) are derived from the vaccine donor strains (A/Ann Arbor/6/60 H2N2 or B/Ann Arbor/1/66), reassorted with the hemagglutinin (HA) and the neuraminidase (NA) gene segments from the appropriate contemporary wild-type (wt) viruses [12]. Our studies suggested that these mutation loci for the preparation of LAIV could be useful for vaccine design against seasonal influenza

Results

Discussion

Findings

Materials and Methods