A Highly Precise Method for the Quantitation of rAAV Cellular Uptake by ddPCR

Recombinant adeno-associated virus (rAAV) has emerged as a leading vehicle for human gene therapy. An accurate and precise infectious titer assay is critical for assessing rAAV quality, potency, and product stability. The current gold standard for measuring rAAV infectivity is the median tissue culture infectivity dose (TCID50) method, which is laborious and highly variable. In the past several years, the droplet digital PCR (ddPCR) technology has made profound impacts on gene therapy analytics as it provides absolute DNA copy quantitation and is more accurate and precise than qPCR. In this article, we leveraged the ddPCR technology and developed a method to quantify rAAV cellular uptake in vitro. The results demonstrated that our method is consistent with TCID50 but is significantly more precise. Utilizing a stable AAV receptor (AAVR) cell line, this method can be implemented as a platform approach for various AAV serotypes and target genes. Moreover, the method is stability indicating, as desired for a potency assay. In conclusion, a novel rAAV uptake assay has been developed which reflects the mechanism of action of rAAV, and is accurate, precise and sensitive to product quality; thus overcoming many of the challenges of the traditional TCID50 method. It is particularly useful for initial rAAV product quality assessment and can contribute to a robust assay matrix with other product-specific potency assays for late-stage programs.