Challenges in Development and Qualification of PCR/dPCR Assays for Gene Therapy Biodistribution and Viral Shedding Assessment

Gene therapies are part of a larger class of advanced therapies that aim to treat disease via delivery of recombinant genetic material. A gene therapy product has two components, the delivery system (viral vector or non-viral) and the transgene (DNA or RNA). These therapies act via replacement of a non-functional gene, silencing of a disease-causing gene, or introduction of a new or modified gene with the goal of generating a therapeutic response in patients. Gene therapy biodistribution and viral vector shedding must be evaluated during non-clinical testing. Polymerase chain reaction (PCR) has emerged as the technique of choice to quantify the gene therapy product and the transferred genetic material in study samples. With increasing numbers of gene therapies in pre-clinical development, there has been a concomitant increase in the use of PCR in bioanalytical laboratories. A major challenge in this space is the lack of formal guidance for the development, characterization, and validation of PCR assays. This article will focus on the opportunities and challenges in developing and characterizing non-GLP, digital PCR assays for AAV gene therapy products. AAV vectors are currently the most common viral delivery system, however many of the insights presented will be applicable to other delivery systems.