Biomedical Engineering Reference
In-Depth Information
on expression of CD24 and CD44 also yielded two populations of cells:
CD24+CD44
and CD24
CD44+ (Ma J, Guest I, Ilic Z, Grant D,
Zang M, Glinsky G, Sell S, Fractionation of mouse mammary cancer stem
cells, in preparation; see also Cho et al., 1998, for a similar model). The
CD24+CD44
population is epithelial, whereas the CD24
CD44+ popula-
tion is mesenchymal, suggesting that, in the mouse cancers, this type of
fractionation actually separates epithelial cancer cells from fibroblastic stromal
cells.
2.2.2 Liver Cancer
Specific markers that appear to identify stem-like cells in human HCCs include
CD133 (Yin et al., 2007; Ma et al., 2007, 2008), CD90 (Fang et al., 2008; Yan
et al., 2008), ABCG2 (Zen et al., 2007), EpCAM (epithelial cell adhesion
molecule; Yamashita et al., 2008), and Met (Kaposi-Novak et al., 2006).
CD133 and CD90 expression is associated with fetal liver cell marker expres-
sion, tumor initiation, culture in vitro, and chemoresistance (Yin et al., 2007;
Ma et al., 2007, 2008), all properties attributed to cancer stem cells.
2.2.3 Cancer Stem Cell Isolation and Transplantability
Although it is implied by the authors that fractionation of the human breast
cancer cells, liver cancer cells, and other cancers results in purification of cancer
stem cells, this may not actually be the case. Thus, so far, the population of the
breast cancer cells with tumor-initiating ability has been found to consist of a
much larger population of the cells than is the case for other cancer stem cell
models. Additional work is required to determine whether there really is a stem
cell in breast or liver cancer that is different from most of the other cells in that
cancer. Also, the question of the efficiency of transplantability of human cancer
cells to immunodeficient mice, as compared to the efficiency of transplantation
of mouse cancer cells to syngeneic mice (Kelly et al., 2007), must be addressed.
A marked discrepancy, if demonstrated, could explain why one population of
cells from the human mammary cancers is unable to initiate tumors on trans-
plantation to SCIDmice. The application of mammary gland stem cell markers,
such as endoglin and prion protein, could perhaps better characterize the
putative breast cancer stem cell (Liao et al., 2007).
2.3 Cancer Stem Cells or Resting Cancer Cells
Although the concept that cancers contain stem cells has recently been revisited
(Reya et al., 2001; Wicha et al., 2006; Tan et al., 2006), it is a topic has been
debated for some time. For example, in 1994, contrasting views were published
by Trott (1994) and by Denekamp (1994). Trott (1994) reviewed the data that a
