The impact of codon optimization in H5N1 vaccine
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Influenza H5N1 poses a significant threat to global health in both agricultural world and general populations due to the highly virulent nature of this virus. The potential of mutations or recombination’s of this virus with other Influenza strains could lead to the generation of pandemic strain of the virus capable of bridging the infectivity divide between avian species to human. Currently, for all Influenza infections, vaccination remains the primary strategy for prevention and control. Many vaccine strategies have been developed in an attempt to combat the threat from avian flu. Codon optimization has been used to improve vaccine efficacy for many vaccines, which rely on in vivo expression of a protein antigen. In this study, two types of vaccine platforms were used to evaluate the differential effect of codon optimization of the hemagglutinin (HA) gene of the highly pathogenic avian influenza H5N1 virus, A/Indonesia/5/05 (Ind05) on the level of protection and immune response provided against lethal challenge. Taking advantage of the degenerate nature of codon usage, a codon optimized gene was synthesized to enhance the use of codons represented by the most abundant tRNAs. The codon optimized HA gene produces a protein, which remains identical to the wild type protein regardless of codon changes but is theoretically expressed at higher level based on codon usage. The synthesized genes were cloned into a DNA plasmid based expression vector as well as a replication competent VSV viral vector. In vitro expression studies, using both a HA-expression plasmid and a recombinant VSV HA-virus, compared expression between optimized- and wild type-HA constructs. Vaccination with both optimized HA and wild type HA DNA vaccine platforms and recombinant VSV HA viruses, followed by lethal challenge with Ind05, was then used to determine the relative efficacy of each vaccine and subsequent immune response in a mouse model.