Multiparameter flow cytometry for the characterisation of extracellular markers on human mesenchymal stem cells.

Extracellular surface proteins are used to identify fully-functional human mesenchymal stem cells (hMSCs) in a mixed population. Here, a multiparameter flow cytometry assay was developed to examine the expression of several bone marrow-derived hMSC markers simultaneously at the single cell level. The multiparameter approach demonstrates a depth of analysis that goes far beyond the conventional single or dual staining methods. CD73, CD90 and CD105 were chosen as positive markers as they are expressed on multipotent hMSCs, whilst CD34 and HLA-DR were chosen as negative indicators. Single colour analysis suggested a population purity of 100 %; in contrast, when analysed via the multiparameter method, the CD73(+ve)/CD105(+ve)/CD90(+ve)/HLA-DR(-ve)/CD34(-ve) phenotypes represented 94.5 ± 1.3 % of the total cell population. Also, although CD271 has been posited as a definite early stage hMSC marker, here we show it is not present on pre-passage cells, highlighting the need for careful marker selection.