Cesium chloride- and iodixanol-based density gradients represent the core step in most protocols for serotype-independent adeno-associated virus (AAV) purification. However, despite controversial reports about purity and bioactivity of AAV vectors derived from each of these protocols, systematic comparisons of variants of these methods are sparse. Strobel and colleagues from Boehringer Ingelheim Pharma recently carried out a study, published in Human Gene Therapy Methods, illustrating that iodixanol-purified AAV preparations show higher vector purity but harbor more (~20%) empty particles as compared to CsCl-purified vectors (<1%). Using mass spectrometry, the team analyzed prominent protein impurities in the AAV vector product, thereby identifying known and new possibly AAV-interacting proteins as major contaminants.
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