PIWIL1 and Azoospermia: Similar to our results, several studies affirmed that UCMSCs transplanted into mice with azoospermia induced by busulfan resumed the expression of Miwi, Vasa, and Scp3 [10], and exosomes of urine-derived stem cells transplanted into nonobstructive azoospermia mice facilitated spermatogenesis by enhancing the expression of Pou5f1, Prm1, Sycp3, and Dazl [14].