Mesenchymal stem cells as all-round supporters in a normal and neoplastic microenvironment

Mesenchymal stem cells (MSC) can be identified in and isolated from nearly all kinds of human tissues. MSC are often synonymously termed stromal cells while other reports distinguish MSC as a precursor of stromal cells. As firstly described, bone marrow-derived human MSC (BM-hMSC) still represent the most frequently investigated hMSC population to compare their properties to those of other tissue-originating hMSC populations [1]. Among these are hMSC from adipose tissue [2], peripheral blood [3], heart [4], and lung [5] but more recently, special attention was also given to hMSC obtained from a variety of different neonatal tissues. These post-natal tissues represent a useful ethically non-controversial alternative providing certain advantages as a consistent and enriched MSC source which is easily accessible. These tissues include MSC from the amniotic fluid [6], amniotic membrane [7-9], chorionic membrane [10], chorionic villi [11], decidua [10], whole placenta [12,13], cord blood [14], Wharton's jelly [15] and whole umbilical cord (UC-MSC) [16].The hMSC originating from different human tissues or organs are designated as stem/stromal or stem-like cells since they share functional properties such as continuous cell cycle progression and plasticity by the capability to differentiate at least along the mesodermal lineage. However, several tissue-originating MSC display significant differences in their proliferative capacities. According to the tissue-specific microenvironment of the diverse MSC populations, UC-MSC exhibit a higher proliferation potential than BM-MSC [17-19]. Thus, the mean doubling time of the UC-MSC revealed about 24？h and remained almost constant for up to 10 cell passages. In contrast, the population doubling time of BM-MSC reached approximately 40？h and considerably increased already after 6 cell passages [20]. Likewise, adipose tissue-derived MSC also demonstrated an elevated growth rate as compared to BM-MSC [21]. Morphological evaluations rev