Comparison of analytical techniques to quantitate the capsid content of adeno-associated viral vectors

Adeno-associated virus (AAV) vectors, which contain a DNA transgene packaged into a protein capsid, have shown tremendous therapeutic potential in recent years. An inherent characteristic of the manufacturing process is production of empty capsids that lack the transgene and are therefore unable to provide the intended therapeutic benefit. The effect of empty capsids on clinical outcomes is not well understood, but there are immunogenicity and efficacy concerns, and these empty capsids are considered a product-related impurity. Therefore, empty capsids should be controlled during the manufacturing process and monitored through analytical testing, but there are limited techniques available that are capable of quantifying capsid content and even fewer that are amenable to validation and implementation as registered release tests in a regulated environment. In addition, there is currently not a widely accepted gold standard technique for quantifying capsid content, and the understanding of how the results compare between different orthogonal technologies is limited. The current study utilizes a comprehensive assessment to evaluate diverse analytical techniques for their ability to quantitate capsid content.