Thy‐1 + cells isolated from adult human testicular tissues express human embryonic stem cell genes OCT3/4 and NANOG and may include spermatogonial stem cells

Purpose Spermatogonial stem cells (SSCs) are self‐renewing cells whose progeny are committed to differentiate into spermatozoa; this is a life‐long process in male mammals. There are several methods for obtaining enriched populations of mouse SSCs, and immunological separation using surface antigens is a commonly used technique. The study of human SSCs is much less advanced. Methods We used biopsied human testicular tissues [obstructive azoospermia patients ( n = 5) and patients who underwent a testis biopsy as part of an evaluation for infertility ( n = 7)] to obtain Thy‐1 + cells. Thy‐1—a glycosyl phosphatidylinositol‐anchored surface antigen—is a marker uniquely expressed on SSCs that is used to isolate SSC‐enriched cell populations in mice. The Thy‐1 + cells from human testicular tissues were cultured in a basic system consisting of serum‐free medium and mitotically inactivated STO (SIM mouse embryo‐derived thioguanine‐ and ouabain‐resistant) cell feeders with added growth factors: glial cell line‐derived neurotrophic factor (GDNF), basic fibroblast growth factor (bFGF), and GDNF‐family receptor α1 (GFRα‐1). Results The Thy‐1 + cells were maintained in vitro using this system for 1 week. The Thy‐1 + cells expressed OCT3/4 and alkaline phosphatase, like mouse SSCs. They also expressed NANOG. Thy‐1 + cells injected into nude mice did not cause tumor formation over a period of at least 6 months. Conclusions These results support the possibility that the Thy‐1 + cell population included human SSCs, and that Thy‐1 may be a marker for human SSCs.