Human Uterine Leiomyoma Stem/Progenitor Cells Expressing CD34 and CD49b Initiate Tumors In Vivo

Context: Uterine leiomyoma is the most common benign tumor in reproductive-age women. Using a dye-exclusion technique, we previously identified a side population of leiomyoma cells exhibiting stem cell characteristics. However, unless mixed with mature myometrial cells, these leiomyoma side population cells did not survive or grow well in vitro or in vivo. Objective: The objective of this study was to identify cell surface markers to isolate leiomyoma stem/progenitor cells. Design: Real-time PCR screening was used to identify cell surface markers preferentially expressed in leiomyoma side population cells. In vitro colony-formation assay and in vivo tumor-regeneration assay were used to demonstrate functions of leiomyoma stem/progenitor cells. Results: We found significantly elevated CD49b and CD34 gene expression in side population cells compared with main population cells. Leiomyoma cells were sorted into three populations based on the expression of CD34 and CD49b: CD34(+)/CD49b(+), CD34(+)/CD49b(-), and CD34(-)/CD49b(-) cells, with the majority of the side population cells residing in the CD34(+)/CD49b(-) fraction. Of these populations, CD34(+)/CD49b(+) cells expressed the lowest levels of estrogen receptor-alpha, progesterone receptor, and alpha-smooth muscle actin, but the highest levels of KLF4, NANOG, SOX2, and OCT4, confirming their more undifferentiated status. The stemness of CD34(+)/CD49b(+) cells was also demonstrated by their strongest in vitro colony-formation capacity and in vivo tumor-regeneration ability. Conclusions: CD34 and CD49b are cell surface markers that can be used to enrich a subpopulation of leiomyoma cells possessing stem/progenitor cell properties; this technique will accelerate efforts to develop new therapies for uterine leiomyoma.