Orbital fat-derived stem cells prevented the damaged testis from apoptosis. (A) Testis in the sham operation group (Ctrl) was negative for DNA fragmentation. (B) Torsion–detorsion (T/D) induced massive apoptotic bodies which were positive for terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) stain in the cell nucleus located at the seminiferous tubule. (C) Only few apoptotic bodies could be seen in damaged testis with orbital fat-derived stem cell (OFSC) injection. (D) OFSCs abrogated the testicular torsion-induced caspase 3 expression. (E) The protein levels of bax were undetectable in the sham operation group (Ctrl) and T/D with OFSCs.