Identification and characterization of tumorigenic liver cancer stem/progenitor cells. Ma Stephanie,Chan Kwok-Wah,Hu Liang,Lee Terence Kin-Wah,Wo Jana Yim-Hung,Ng Irene Oi-Lin,Zheng Bo-Jian,Guan Xin-Yuan Gastroenterology BACKGROUND & AIMS:Recent efforts in stem cell biology suggest that tumors are organized in a hierarchy of heterogeneous cell populations and that the capability to maintain tumor formation/growth specifically resides in a small population of cells called cancer stem cells (CSCs). The aim of this study is to identify, isolate, and characterize the CSC population that drives and maintains hepatocellular carcinoma (HCC) growth and metastasis. METHODS:Normal stem cells involved in liver regeneration were identified using a severe partial hepatectomy model. Purified HCC cells, with or without expression of the identified normal stem cell phenotype, were evaluated, based on their tumorigenic potential and exhibition of defined stem/progenitor cell-like properties, to determine whether liver CSCs can be or partly be identified by this surface marker. RESULTS:We report the identification and isolation of a population of CSCs expressing a CD133 surface phenotype from human liver cell lines. CD133(+) cells possess a greater colony-forming efficiency, higher proliferative output, and greater ability to form tumor in vivo. These cells are endowed with characteristics similar to those of progenitor cells including the expression of "stemness" genes, the ability to self-renew, and the ability to differentiate into nonhepatocyte-like lineages. Furthermore, CD133 is found to represent only a minority of the tumor cell population in human HCC specimens. CONCLUSIONS:We report the identification of a CSC population in HCC characterized by their CD133 phenotype. The identification of tumorigenic liver CSCs could provide new insight into the HCC tumorigenic process and possibly bear great therapeutic implications. 10.1053/j.gastro.2007.04.025

Identification of human brain tumour initiating cells. Singh Sheila K,Hawkins Cynthia,Clarke Ian D,Squire Jeremy A,Bayani Jane,Hide Takuichiro,Henkelman R Mark,Cusimano Michael D,Dirks Peter B Nature The cancer stem cell (CSC) hypothesis suggests that neoplastic clones are maintained exclusively by a rare fraction of cells with stem cell properties. Although the existence of CSCs in human leukaemia is established, little evidence exists for CSCs in solid tumours, except for breast cancer. Recently, we prospectively isolated a CD133+ cell subpopulation from human brain tumours that exhibited stem cell properties in vitro. However, the true measures of CSCs are their capacity for self renewal and exact recapitulation of the original tumour. Here we report the development of a xenograft assay that identified human brain tumour initiating cells that initiate tumours in vivo. Only the CD133+ brain tumour fraction contains cells that are capable of tumour initiation in NOD-SCID (non-obese diabetic, severe combined immunodeficient) mouse brains. Injection of as few as 100 CD133+ cells produced a tumour that could be serially transplanted and was a phenocopy of the patient's original tumour, whereas injection of 10(5) CD133- cells engrafted but did not cause a tumour. Thus, the identification of brain tumour initiating cells provides insights into human brain tumour pathogenesis, giving strong support for the CSC hypothesis as the basis for many solid tumours, and establishes a previously unidentified cellular target for more effective cancer therapies. 10.1038/nature03128

Prospective identification of tumorigenic breast cancer cells. Proceedings of the National Academy of Sciences of the United States of America Breast cancer is the most common malignancy in United States women, accounting for >40,000 deaths each year. These breast tumors are comprised of phenotypically diverse populations of breast cancer cells. Using a model in which human breast cancer cells were grown in immunocompromised mice, we found that only a minority of breast cancer cells had the ability to form new tumors. We were able to distinguish the tumorigenic (tumor initiating) from the nontumorigenic cancer cells based on cell surface marker expression. We prospectively identified and isolated the tumorigenic cells as CD44(+)CD24(-/low)Lineage(-) in eight of nine patients. As few as 100 cells with this phenotype were able to form tumors in mice, whereas tens of thousands of cells with alternate phenotypes failed to form tumors. The tumorigenic subpopulation could be serially passaged: each time cells within this population generated new tumors containing additional CD44(+)CD24(-/low)Lineage(-) tumorigenic cells as well as the phenotypically diverse mixed populations of nontumorigenic cells present in the initial tumor. The ability to prospectively identify tumorigenic cancer cells will facilitate the elucidation of pathways that regulate their growth and survival. Furthermore, because these cells drive tumor development, strategies designed to target this population may lead to more effective therapies. 10.1073/pnas.0530291100