Low voltage electron microscopy: An emerging tool for AAV characterization

Transmission electron microscopy has become a standard characterization tool for adeno-associated virus-based gene therapy products. However, cost and expertise requirements place in-house traditional transmission electron microscope systems out of reach for many companies in the field. Recently developed low voltage electron microscopes can fulfill many of the needs for adeno-associated virus characterization at a fraction of the cost. Example applications are discussed, including empty/full analysis, broken/incomplete capsid identification, and aggregate/high-molecular-weight species characterization. Our low voltage electron microscopy empty/full analysis agrees with orthogonal methods widely used in industry. Furthermore, analysis of broken/incomplete capsid morphologies using traditional transmission electron microscopy and low voltage electron microscopy shed light on a plausible mechanism for incomplete capsid aggregation that involves mutual passivation of open edges. A comprehensive analysis of AAV preparations using low voltage electron microscopy has been established.