Clonogenically Culturing and Expanding CD34+ Liver Cancer Stem Cells in Vitro

Abstract

A large number of cancer stem cells (CSCs) have been isolated and identified; however, none has been cultured in an unlimited manner in vitro without losing tumorigenicity and multipotency. In this study, we successfully clonogenically cultured a newly identified CD34+ liver CSC (LCSC) on feeder cells up to 22 passages (to date) without losing CSC property. Cloned CD34+ LCSC formed a round packed morphology and it could also be cryopreserved and recultured. Stem cell markers, CD34, CD117, and SOX2; normal liver stem cell markers, alpha fetoprotein, CK19, CK18, and OV6; putative CSC markers, CD44, CD133, EpCAM, and CD90; as well as CD31 were expressed in cloned CD34+ LCSC. SOX2 was the major factor in maintaining this LCSC before colonization, and interestingly, OCT4, SOX2, NAONG, Klf4, c-Myc, and Lin28 were upregulated in association with symmetric self-renewal for colony growth of CD34+ LCSC on feeder cells. Gene expression patterns of in vitro differentiation were consistent with our in vivo finding; furthermore, the tumorigenicity of cloned CD34+ LCSC was not different from uncloned CD34+ LCSC sorted from parental PLC. These results show that our cloned CD34+ LCSC maintained CSC property, including self-renewal, bipotency, and tumorigenicity after long-term culture, demonstrating that this LCSC can be cultured in an unlimited manner in vitro. Thus, establishing pure population of CSCs isolated from the patients will provide an opportunity to explore the mechanisms of tumorigenesis and cancer development, and to identify unique biomarkers presenting potential indicators of drug efficacy against CSCs for establishment of a novel strategy for cancer therapy.