Use of equine embryo-derived mesenchymal stromal cells and their extracellular vesicles as a treatment for persistent breeding-induced endometritis in susceptible mares

Abstract

Persistent breeding induced endometritis (PBIE) is a significant cause of infertility in mares. The development of a safe, universal, readily available therapeutic to manage PBIE and facilitate an optimal uterine environment for embryo development and implantation would potentially improve pregnancy rates in susceptible mares. Mesenchymal stromal cells (MSCs) are being used increasingly as a therapeutic mediator for inflammatory conditions such as endometritis. Early gestation tissue provides a unique source of multipotent stem cells that exhibit immunomodulatory, proliferation, and differentiation properties. Extracellular vesicles (EVs) are nanometre sized, membrane enclosed structures released by cells that play a crucial role in mediating cellular communication through the shuttling of their cargo of bioactive molecules. This study involved two clinical trials aimed to utilise D32 embryo-derived mesenchymal stromal cells (EDMSCs) and their EVs as a potential therapeutic modality for PBIE in mares. The aim of Experiment 1 was to determine the efficacy of an intrauterine deposition of EDMSCs and their EVs 24 h prior to being challenged by intrauterine insemination with a dose of pooled dead sperm PBIE-susceptible (Troedsson and Woodward. Reproductive Biology. 2016;16:8-12) mares (n=5) in a controlled cross-over designedexperiment. In Experiment 2 a cohort of client-owned thoroughbred mares (n=37; 40 estrous cycles) from farms that were previously involved in a large-scale epidemiological study in which the average first cycle pregnancy rate in mares was 53.6% (Firth, et al. New Zealand Veterinary Journal. 2012;60:329-334) were utilized. The mares were identified as being susceptible to PBIE with a history of failing to become pregnant on >2 consecutive estrous cycles despite intense breeding management and use of a fertile stallion/s received intrauterine EDMSCs or their EVs 24 h prior to natural mating. A significant reduction in uterine fluid volume was observed at both 12 and 24 h after insemination in Experiment 1 when mares were pre-treated with either EDMSCs or their EVs compared to placebo (control) treatment (p>0.05). In Experiment 2, 9 of 19 (47%) mares treated with EDMSC and 13 of 20 (65%) mares treated with EVs prior to natural mating were pregnant after the first cycle, and 12 of 18 (67%) mares treated with EDMSCs and 15 of 19 (79%) mares treated with EVs had conceived by the end of the breeding season. These preliminary clinical studies are the first report of the use of EDMSCs or their EVs as a potential therapy for the management of PBIE in susceptible mares.