Is in？vitro organotypic culture the key to spermatogenesis of human immature testicular tissue? - Fertility and Sterility

Pediatric cancers, though uncommon, are on the rise. As of 2014, there were almost 210,000 male survivors of childhood cancers that were diagnosed from ages 0 to 19 years in the United States. With improved therapies and discovered cures, this number will continue to rise as these patients continue to survive into adulthood (1x1in: N. Howlader, A.M. Noone, M. Krapcho, D. Miller, K. Bishop, C.L. Kosary, (Eds.) SEER cancer statistics review (CSR), 1975–2014. National Cancer Institute, Bethesda, MD; 2018 (Available at:)https://seer.cancer.gov/csr/1975_2014/. Google ScholarSee all References)(1). Unfortunately, many of these therapies have gonadotoxic effects and challenge these men's ability to father children. Therefore, it is imperative to address fertility preservation in this patient population before inducing these deleterious effects. If the boys are able to produce ejaculate with sperm or have sperm already formed in their testes, these sperm can be cryopreserved, a method used successfully since the 1950s. Unfortunately, if these boys are prepubertal, they have only spermatogonial stem cells (SSCs); for these patients, a sample of their immature testicular tissue (ITT) or germ cell suspensions can be taken and cryopreserved by only experimental means at present because there are no clear methods to later induce spermatogenesis with production of sperm. Thus, fertility preservation in this patient population remains a challenge. Although xenografting or autologous transplantation of ITT may prove to be a viable option for retrieving human sperm, as has been shown in nonhuman animal models, these are invasive methods and have the potential for introducing malignant cells into the host. In contrast, in vitro maturation methods of producing sperm bypasses these potential drawbacks. In addition, preservation of SSCs instead of sperm offers the unique advantage for potentially unlimited replication of genetic information. By 1937, spermatogenesis was initiated in neonatal mouse testicular tissue on a clot up to the pachytene stage of meiosis. However, it was not until 2011 when Soto et al. revolutionized the process by documenting not only in vitro complete spermatogenesis of fresh neonatal mouse tissue, but also frozen-thawed neonatal mouse tissue, into viable sperm. To prove viability of these sperm, they then microinseminated eggs, leading to healthy fertile offspring (2x2Sato, T., Katagiri, K., Gohbara, A., Inoue, K., Ogonuki, N., Ogura, A. et al. In vitro production of functional sperm in cultured neonatal mouse testes. Nature. 2011; 471: 504–508