Searching for alternative sources of postnatal human mesenchymal stem cells: candidate MSC-like cells from umbilical cord.

Mesenchymal stem cells (MSCs) have the capability for renewal and differentiation into various lineages of mesenchymal tissues. These features of MSCs attract a lot of attention from investigators in the context of cell-based therapies of several human diseases. Despite the fact that bone marrow represents the main available source of MSCs, the use of bone marrow-derived cells is not always acceptable due to the high degree of viral infection and the significant drop in cell number and proliferative/differentiation capacity with age. Thus, the search for possible alternative MSC sources remains to be validated. Umbilical cord blood is a rich source of hematopoietic stem/progenitor cells and does not contain mesenchymal progenitors. However, MSCs circulate in the blood of preterm fetuses and may be successfully isolated and expanded. Where these cells home at the end of gestation is not clear. In this investigation, we have made an attempt to isolate MSCs from the subendothelial layer of umbilical cord vein using two standard methodological approaches: the routine isolation of human umbilical vein endothelial cell protocol and culture of isolated cells under conditions appropriate for bone-marrow-derived MSCs. Our results suggest that cord vasculature contains a high number of MSC-like elements forming colonies of fibroblastoid cells that may be successfully expanded in culture. These MSC-like cells contain no endothelium- or leukocyte-specific antigens but express alpha-smooth muscle actin and several mesenchymal cell markers. Therefore, umbilical cord/placenta stroma could be regarded as an alternative source of MSCs for experimental and clinical needs.