A quantitative PCR screening method for adeno-associated viral vector 2-mediated gene doping

Gene therapy is currently prohibited in human and equine athletes and novel analytical methods are needed for its detection. Most in vivo products use non-integrating, recombinant viral vectors derived from adeno-associated virus (AAV) to deliver transgenes into cells, where they are transcribed and translated into functional proteins. Although the majority of wild-type AAV (WTAAV) DNA is removed from recombinant AAV (rAAV) vectors, some sequences are conserved. The goal of this study was to develop a quantitative polymerase chain reaction (QPCR) screening test targeting conserved AAV sequences to enable theoretical detection of all rAAV gene therapy products, regardless of encoded transgenes while excluding the presence of WTAAV DNA in horses. Primer sets were developed and validated to target an AAV2 sequence highly conserved across rAAV viral vectors and a sequence only found in wild type AAV2 (WTAAV2). Six horses were administered an intra-articular injection of rAAV. Plasma and synovial fluid were collected on days 0, 1, 2, 4, 7, 14, 28, 56, and 84. Using QPCR, rAAV was detected in plasma for up to 2–4 days in all horses. rAAV DNA was detected for 28 days in synovial fluid from two horses for which synovial fluid samples were available. No WTAAV2 DNA was detected in any sample. This is the first study to develop a QPCR test capable of screening for rAAV vectors that may be used for gene doping in horses.