Delivery and evaluation of recombinant adeno-associated viral vectors in the equine distal extremity for the treatment of laminitis

Administration and detection of gene therapy in horses: A systematic review

Gene therapy uses genetic modification of cells to produce a therapeutic effect. Defective or missing genes can be repaired or replaced, or gene expression can be modified using a variety of technologies. Repair of defective genes can be achieved using specialized gene editing tools. Gene addition promotes gene expression by introducing synthetic copies of genes of interest (transgenes) into cells where they are transcribed and translated into therapeutic proteins. Protein production can also be modified using therapies that regulate gene expression. Gene therapy is currently prohibited in both human and equine athletes because of the potential to induce production of performance-enhancing proteins in the athlete's body, also referred to as "gene doping." Detection of gene doping is challenging and necessitates development of creative, novel analytical methods for doping control. Methods for detection of gene doping must be specific to and will vary depending on the type of gene therapy. The purpose of this paper is to present the results of a systematic review of gene editing, gene therapy, and detection of gene doping in horses. Based on the published literature, gene therapy has been administered to horses in a large number of experimental studies and a smaller number of clinical cases. Detection of gene therapy is possible using a combination of PCR and sequencing technologies. This summary can provide a basis for discussion of appropriate and inappropriate uses for gene therapy in horses by the veterinary community and guide expansion of methods to detect inappropriate uses by the regulatory community.

Optimization and implementation of four duplex qPCR assays for gene doping control in horseracing

The concern about gene doping has remained high in horseracing and other equestrian competitions. Our laboratory has previously developed a duplex quantitative polymerase chain reaction (qPCR) assay capable of detecting in equine blood the human erythropoietin (hEPO) transgene and equine tubulin α 4a (TUBA4A) gene as an internal control, the latter providing quality control over DNA extraction and qPCR. This study aimed to optimize the method for routine testing of regulatory samples. The use of an automated DNA extraction system has increased the sample throughput, consistency of DNA extraction and recovery of reference materials. The use of reduced concentration of primers and hydrolysis probe for internal control minimized their competition with transgene amplification and improved the assay sensitivity. Spike-in of an exogenous internal control at low concentration for plasma analysis has also been validated. Using the new workflow, four duplex qPCR assays have been developed for the detection of transgenes, namely hEPO, human growth hormone (hGH), insulin-like growth factor 1 (hIGF-1), and equine EPO (eEPO). The estimated limits of detection (LODs) of each transgene were 2,000 copies/mL of blood and 200 copies/mL of plasma. This method could detect the presence of transgene in blood and plasma collected from a horse administered intramuscularly (IM) with recombinant adeno-associated virus (rAAV) carrying the hEPO transgene. A longer detection time was observed in blood than in plasma. The methods have been applied to the screening of over a thousand official racehorse samples since June 2020 for the presence of these transgenes.

The Big Picture in Better Understanding the Equine Foot

The multiple topics summarized in this article and discussed in detail in this issue of VCNA are comprehensive and in-depth, exploring concepts and clinical experiences for state-of-the-art care of the equine foot. The research on the equine foot will translate to the clinical setting and with this the compassionate care of the horse.

A duplex qPCR assay for human erythropoietin (EPO) transgene to control gene doping in horses

The misuse of genetic manipulation technology to enhance athletic performance is termed gene doping which is prohibited in human sports, horseracing, and equestrian sports. Although many qPCR assays have been developed, most assays employ genomic DNA (gDNA) from humans, non-human primates, and mice as a background and they may not be applicable for testing horse samples. This study aimed to develop a qPCR assay for the detection of human erythropoietin (hEPO) transgene in horse blood cells where the viral vectors used in gene therapy can reside for months. For the detection of hEPO transgene, the performance of three sets of primers and a hydrolysis probe for hEPO were compared. One set showed adequate specificity, sensitivity, amplification efficiency, and a dynamic range of detection in the presence of horse gDNA. The assay was duplexed with the detection of horse tubulin α 4A (TUBA4A) gene as an endogenous internal control in order to prevent false-negative results due to poor recovery and storage of extracted DNA and/or qPCR experimental variation. For the extraction of hEPO-plasmid, the QIAGEN Gentra Puregene blood kit was shown to recover the majority (62%) of hEPO-plasmid from spiked horse blood cells. The specificity and limit of detection (LOD) of the duplex qPCR assay were determined in accordance with MIQE guidelines. These findings supported the application of this duplex qPCR assay to the detection of hEPO transgene in horse blood cells.

Quantitative and Digital Droplet-Based AAV Genome Titration

The adeno-associated viral vector (AAV) platform has developed into a primary modality for efficient in vivo, and in more limited settings, in vitro or ex vivo gene transfer. Its applications range from a tool for experimental purposes to preclinical and clinical gene therapy. The ability to accurately and reproducibly quantify vector concentration is critical for any of these applications. While several quantification assays are available, here we outline a detailed protocol for the quantification of DNase-I protected vector genomes reliant on the polymerase chain reaction (PCR) as a measure of the active component of the vector, namely its transgene cargo. With the emergence of droplet digital PCR (ddPCR), we provide side-by-side protocols for traditional TaqMan™ real-time, quantitative PCR (qPCR) and ddPCR, as well as comparative data generated with both methods. Lastly, we discuss the importance of the use of surfactant (here, Pluronic^® F-68) in the execution of the assay to limit DNA and AAV adherence to various carriers during the titration, particularly at low concentrations. We believe these protocols can lead to reduced variability and increased comparability between AAV studies.