The role of gene segment interactions in driving the emergence of dominant gene constellations during influenza virus reassortment

A segmented genome enables influenza virus to undergo reassortment when two viruses infect the same cell. Resulting reassorted progeny have a spectrum of gene constellations and potentially different phenotypes. Although reassortment is involved in the creation of pandemic influenza strains and is routinely used to produce influenza vaccines, our understanding of the factors that drive the emergence of dominant gene constellations during this process is incomplete. Using an influenza vaccine seed production model, reassortant genotypes were tracked through the reassortment process under antibody selective pressure. We discovered that certain gene constellations conferring low replicative fitness were selected at the expense of more fit progeny. Nevertheless, relatively unfit reassortants likely provide high hemagglutinin antigen yields through co-production of non-infectious particles and/or by more hemagglutinin molecules per virion. Our data illustrate the dynamics and complexity of reassortment and highlight how gene segment interactions formed during packaging, in addition to antibody pressure, restrict the final viruses that dominate.