Objective
To identify and characterize myometrial/fibroid stem cells by specific stem cell markers in human myometrium, and to better understand the stem cell contribution in the development of uterine fibroids. Design: Prospective, experimental human and animal study. Setting: University research laboratory. Patient(s)/animal(s): Women undergoing hysterectomy for treatment of symptomatic uterine fibroids and female NOD/SCID/IL-2Rγ(null) mice. Intervention(s): Identification and isolation of stem cells from human fibroids and adjacent myometrium tissues using Stro-1/CD44-specific surface markers. Main outcome measure(s): Flow cytometry, semiquantitative polymerase chain reaction, clonogenicity assays, cell culture, molecular analysis, immunocyto-histochemistry, in vitro differentiation, and xenotransplantation assays. Result(s): Using Stro-1/CD44 surface markers, we were able to isolate stem cells from adjacent myometrium and human fibroid tissues. The undifferentiated status of isolated cells was confirmed by the expression of ABCG2 transporter, as well as additional stem cell markers OCT4, NANOG, and GDB3, and the low expression of steroid receptors ERα and PR-A/PR-B. Mesodermal cell origin was established by the presence of typical mesenchymal markers (CD90, CD105, and CD73) and absence of hematopoietic stem cell markers (CD34, CD45), and confirmed by the ability of these cells to differentiate in vitro into adipocytes, osteocytes, and chondrocytes. Finally, their functional capability to form fibroid-like lesions was established in a xenotransplantation mouse model. The injected cells labeled with superparamagnetic iron oxide were tracked by both magnetic resonance imaging and fluorescence imaging, thus demonstrating the regenerative potential of putative fibroid stem cells in vivo.