The aim of this study was to demonstrate the existence of circulating mesenchymal stem cells (MSC) in the human umbilical cord blood (hUCB) and to evaluate the chondrogenic differentiation potential of hUCB-derived MSC in vitro.

Fifty hUCB harvests were cultured in media supplemented with 10% fetal bovine serum. The adherent fibroblast-like cells were characterized by immunophenotyping and induced to differentiate into chondrocytes in the pellet culture with and without BMP-6. This study performed RTPCR of the chondrogenic markers, Safranin-O stain and type II collagen immunohistochemical stain.

The mononuclear cells isolated from hUCB formed adherent colonies with an attached wellspread fibroblast-like morphology. The cells positively expressed the MSC-related antigens, but did not express the hematopoietic, HLA-DR, endothelial, or osteoclast antigens and could be induced to differentiate into chondrocytes under proper stimulation. BMP-6 increased the size of the pellet and the mRNA levels for aggrecan, type II collagen and type IX collagen and enhanced the levels of proteoglycan synthesis during chondrogenic differentiation.

The homogenous fibroblast-like cells developed in cultures from hUCB with chondrogenic differentiation potential were considered to be MSC. Furthermore, it was found that BMP-6 enhanced chondrogenic differentiation of the hUCB-derived MSC in the pellet culture.