Amniotic mesenchymal stromal/stem cell–derived extracellular vesicles for equine chronic degenerative endometritis treatment

Background: Equine chronic degenerative endometritis (CDE) is a progressive process characterized by endometrial fibrosis that could be responsible for alterations of uterine environment and foetal-maternal communication. Objectives: The aim of this study was to try to restore this communication by intrauterine administrations of amniotic cell-derived extracellular vesicles (AMC-EVs) in a case series. Study design: Twelve mares were selected on the basis of their reproductive history of early embryonic loss or abortion and clinical suspicion of CDE subsequently verified with histopathological examination of endometrial biopsies. Methods: Gynaecological and ultrasound examinations and histopathological examination of endometrial biopsies were performed. Mares were divided into two groups: Seven mares in Group 1 received a single treatment cycle (corresponding to two intrauterine AMC-EV administrations), whereas five mares of Group 2 received two treatment cycles (corresponding to four intrauterine AMC-EV administrations). Each administration was of 20 billion AMC-EVs diluted in 50 mL of sterile saline solution. Results: Eleven mares were able to establish pregnancy after the treatment with AMC-EVs without significant difference in pregnancy outcomes between one or two treatment cycles (six out of seven mares of Group 1 and all mares of Group 2 were pregnant), suggesting that one cycle may be sufficient. The histological condition of their endometrium did not show any improvement in Kenney-Doig classification, meaning AMC-EVs did not exert regenerative activity but probably contributed to re-establishing a functional paracrine interaction between embryo and maternal tissues. Main limitations: This study has the limitation of the small number of animals enrolled and the lack of a control group. However, considering the large number of past artificial insemination attempts for each animal enrolled in this study, each mare could be considered self-control. Conclusions: It would seem possible that AMC-EVs supported and enhanced foetal-maternal communication that was compromised by CDE.