Poster Sessions

V -5

Suman Das

S. Das, S. Hensley, G. Russ, W. Gerhard, J. Bennink, J. Yewdell

Hemagglutinin antigenic evolution: the past dictates the future

Abstract: The influenza A virus hemagglutinin (HA) glycoprotein mediates virion binding to sialic acid residues on the host cell surface and the subsequent fusion of viral and cellular membranes. Antibodies to HA neutralize viral infectivity in vitro and can provide functional sterilizing immunity in vivo. Antigenic drift in HA results from the accumulation of point mutations in neutralizing antibody epitopes, and is a barrier to developing vaccines that provide long lasting immunity. It is not clear why influenza viruses demonstrate frequent antigen variation in humans while other RNA viruses with similar intrinsic mutation rates exhibit much less variability. One possibility is that HA possesses unique structural plasticity that enables it to evolve antigenically ad infinitum. To better understand antigenic drift, A/Puerto Rico/8/34 virus escape mutants were selected sequentially using a panel of 12 mouse anti-HA mAbs. Sequential 12 (S12) no longer reacts with any of a very large panel of mouse anti-HA mAbs, and demonstrates no cross-reactivity with mouse or ferret anti-PR8 antisera. Sequencing of viral RNA revealed that each selection step results in the accumulation of one (or occasionally two) non-synonymous mutations in the globular domain of the HA. Remarkably, most of the mutations that occur in the sequential series are unique compared to a panel of mutants selected from wt virus via single mAb selection. Similarly, when we used one mAb to select a large panel of escape mutants from wt virus or sequential variants in the series. Sequencing revealed that variants of PR8 or S7/S8 selected with the same antibody demonstrate distinct repertoire mutants. These findings strongly suggest that substitutions in one epitope influence future substitutions selected by other antibodies. If this is true, then predicting antigenic drift will simply not be possible, since drift can follow a very large number of paths with the actual path determined by stochastic events that cannot be anticipated.