Abstract
Although telomerase is expressed in hematopoietic stem cells, blood behaves as any other somatic tissue with inexorable telomere decline in blood leucocytes during normal aging. The telomere length of leucocytes is shorter in malignant cells, as well as in subjects with aplastic anemia or following bone marrow transplantation. Telomere shortening has been used to examine precursor-product relationships: Telomere changes in committed leucocytes have been used to make inferences about replicative events in rare stem cell populations. These inferences rest on certain assumptions and the validity of these assumptions is not proven, especially where hematopoiesis is abnormal, such as following bone marrow transplantation or during disease processes. It is not necessarily valid therefore to infer replicative stress at the level of the haemopoietic stem cell from the finding of telomere shortening in blood leucocytes in these conditions.
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