Biophysical characterization of influenza A virions.

Antigenic drift of the influenza A virus requires that vaccine production is targeted to the strains circulating each year. Live-attenuated influenza A vaccine manufacturing is used to produce intact virions with the surface antigens of the circulating strains. Influenza A typically contains a large percentage (>90%) of non-infective virions. The ribonucleoprotein (RNP) content, virion structure, and aggregation are factors that are thought to have an impact on infectivity. However, these factors are difficult to study because of the intrinsic variability in virion size, shape and overall structural integrity. Negative stain TEM for total particle counts and cryoTEM for detailed size/structural analysis are established benchmark techniques for virus characterization. Other methods may be valuable for certain sample types or circumstances. The aim of this work is to establish a benchmark comparison between orthogonal biophysical techniques for particle counts, population size distribution, structural integrity, and aggregate levels. NTA and FFF-MALS rapidly provided total counts, size distribution, and aggregate/elongated virion content. CryoTEM with size analysis and fraction counting yielded detailed information about the pleomorphism of the sample. The structural integrity of virions was inferred from multi-signal AUC-SV and CryoTEM. The current work provides a comparative assessment and a baseline for the selection of biophysical tools for the determination of particle counts, aggregation and pleomorphic characteristics of influenza A virus.