Human mesenchymal stem cells (hMSCs) have attracted much attention for tissue 
repair and wound healing because of their self-renewal capacity and 
multipotentiality. In order to mediate an effective therapy, substantial numbers 
of cells are required, which necessitates extensive sub-culturing and expansion 
of hMSCs. Throughout ex vivo expansion, the cells undergo telomere shortening, 
and critically short telomeres can trigger loss of cell viability. Telomeres are 
nucleoprotein structures that cap the ends of chromosomes, and serve to protect 
the DNA from the degradation which occurs due to the end-replication problem in 
all eukaryotes. As hMSCs have only a finite ability for self-renewal like most 
somatic cells, assaying for telomere length in hMSCs provides critical 
information on the replicative capacity of the cells, an important criterion in 
the selection of hMSCs for therapy. Telomere length is generally quantified by 
Southern blotting and fluorescence in situ hybridization, and more recently by 
PCR-based methods. Here we describe the quantification of hMSC telomere length 
by real-time PCR; our results demonstrate the effect of telomere shortening on 
the proliferation and clonogenicity of hMSCs. Thus, this assay constitutes a 
useful tool for the determination of relative telomere length in hMSCs.