Human embryonic stem cell telomere length impacts directly on clonal progenitor isolation frequency

The pluripotentiality of human embryonic stem cells is expected to yield an abundance of clinically useful cell types. Using physiologic oxygen culture systems, we show that it is possible to isolate highly proliferative clonal progenitor cells from partially differentiated human embryonic stem cells. These progenitors have similar, though not identical, immunophenotypes with a resemblance to bone marrow-derived adherent stem cells. Through telomere length analysis of multiple early senescing clones, we were able to show that the starting telomere length of a human embryonic stem cell line impacts on the proliferative potential of clonally isolated partially differentiated mortal progeny. Proliferative clones undergo growth arrest with telomere lengths consistent with telomere-driven replicative senescence. To bypass this phenomenon, we transduced progenitor cells with ectopic hTERT (the limiting catalytic component of telomerase). This enabled telomerase immortalization without affecting differentiation potential or immunophenotype. In summary we describe the derivation of clonal progenitor cells from human embryonic stem cells and the relevance of parental cell telomere length to the frequency of highly proliferative clone isolation.