Effect of cold storage and cryopreservation of immature non-human primate testicular tissue on spermatogonial stem cell potential in xenografts. 
Successful cryopreservation of gonadal tissue is an important factor in guaranteeing the fertility preservation via germ cell or testicular tissue transplantation.  The aim of this study was to evaluate the effects of cooling and cryopreservation on spermatogonial stem cell survival and function of immature non-human primate testicular tissue xenografted to nude mice.  Group 1 (control group) received subcutaneous grafts of fresh immature rhesus monkey testes.  The treatment groups received grafts after 24 h cooling in ice-cold medium (Group 2), after 24 h of cryopreservation without cryoprotectant (Group 3), with ethylene glycol (Group 4: 1.4 M) or with dimethylsulphoxide (DMSO) (group 5: 1.4 M; group 6: 0.7 M), using cooling rates of 0.5 degrees C/min.  The graft number, weight and histology were examined 3-5 months later.  After xenografting, grafts from fresh and cooled tissue showed good survival and spermatogenic induction to spermatocytes.  Cryopreservation in 1.4 M DMSO also allowed grafts to initiate spermatogenesis.  In contrast, 0.7 M DMSO and ethylene glycol showed inferior protection.  Our observations suggest that cryopreservation of immature primate testis is a feasible approach to maintain spermatogonial stem cells and may serve as a promising tool for fertility preservation of prepubertal boys.  The possibility to delay the transplantation of cooled samples suggests an option for clinical centralization of testicular tissue cryopreservation.