Anion-exchange HPLC assay for separation and quantification of empty and full capsids in multiple adeno-associated virus serotypes

Gene therapy has entered a new era where numerous therapies for severe and rare diseases are generating robust and compelling clinical results. The rapid improvements in gene therapies over the past few years can be attributed to better scientific understanding of the critical quality attributes that contribute to a safe and efficacious product, as well as a better understanding of the manufacturing processes that are required to yield consistent products, which routinely meet the quality standards required for clinical studies. Of particular concern is the need for an effective, quality control (QC)-compatible, and versatile test method for the quantification of empty and full capsids in recombinant adeno-associated virus (rAAV) samples from multiple serotypes. In that regard, we describe the development of a QC-compatible anion-exchange chromatography method consisting of a modular discontinuous gradient to achieve full baseline peak separation and quantification of empty and full AAV capsids. Using an rAAV6 vector, our assay was shown to be precise, linear, robust, and accurate—correlating well with orthogonal methods such as analytical ultracentrifugation (AUC) and cryogenic transmission electron microscopy (Cryo-TEM). Additionally, we demonstrate the versatility of our approach by adapting the method to separate and quantify empty/full capsids in samples from several rAAV serotypes.