One of the features of stem/progenitor cells is the expression of stem cell markers. Therefore we performed qRT-PCR for several common stem cell markers including CD44, CD133, Sca-1 and SOX2 in the sorted cells. Interestingly, CD44 was expressed in both CCSP + and CCSP 2 populations at similar levels. In contrast, CD133, Sca-1 and Sox2 demonstrated much lower but detectable levels in CCSP + cells than the levels in CCSP 2 cells. These data indicate that CCSP + cells express stem cell markers, although at low levels ( Figure 4 ).