In vitro evolution of H5N1 avian influenza virus toward human-type receptor specificity

Acquisition of alpha 2-6 sialoside receptor specificity by alpha 2-3 specific highly-pathogenic avian influenza viruses (H5N1) is thought to be a prerequisite for efficient transmission in humans. By in vitro selection for binding alpha 2-6 sialosides, we identified four variant viruses with amino acid substitutions in the hemagglutinin (S227N, D187G. E190G, and Q196R) that revealed modestly increased alpha 2-6 and minimally decreased alpha 2-3 binding by glycan array analysis. However, a mutant virus combining Q196R with mutations from previous pandemic viruses (Q226L and G228S) revealed predominantly alpha 2-6 binding. Unlike the wild type H5N1, this mutant virus was transmitted by direct contact in the ferret model although not by airborne respiratory droplets. However, a reassortant virus with the mutant hemagglutinin, a human N2 neuraminidase and internal genes from an H5N1 virus was partially transmitted via respiratory droplets. The complex changes required for airborne transmissibility in ferrets suggest that extensive evolution is needed for H5N1 transmissibility in humans. Published by Elsevier Inc.