Identification and characterization of the human leiomyoma side population as putative tumor-initiating cells.

OBJECTIVE: To isolate and characterize human leiomyoma stem cells by the side population (SP) method.
DESIGN: Prospective experimental human and animal study.
SETTING: University research laboratory-affiliated infertility clinic. PATIENT(S): Women undergoing laparoscopic myomectomy. ANIMAL(S): Female non-obese diabetic severe combined immune deficiency (NOD-SCID) mutation mice. INTERVENTION(S): Obtainment of human leiomyoma SP cells as candidate tumor-initiating cells and establishment of two leiomyoma SP lines. MAIN OUTCOME MEASURE(S): Flow cytometry, semiquantitative polymerase chain reaction, clonogenicity assays, cDNA microarrays hybridization, cell culture, karyotype, molecular analysis, immunocytochemistry, in vitro differentiation, xenotransplantation assays, immunohistochemistry. RESULT(S): SP cells from human leiomyomas were isolated, identified, and characterized. Two leiomyoma's SP cell lines with a normal karyotype were thus established. Undifferentiated status was confirmed by the expression of OCT-4, NANOG, DNMT3B, GDF3. Presence of typical mesenchymal markers (CD90, CD105, CD73) and absence of hematopoietic stem cell markers (CD34, CD45) supported their mesodermal origin. Mesenchymal lineage commitment was also demonstrated by their ability to differentiate in vitro into adipogenic and osteogenic lineages. Finally, their functional capability was established in an animal model by leiomyoma tissue reconstruction. CONCLUSION(S): SP cells from human leiomyoma exhibit key features of tumor-initiating cells, opening up new possibilities of understanding the origin and developing new nonsurgical approaches for leiomyomas.