Accelerated telomere shortening in hematological lineages is limited to the first year following stem cell transplantation

Using quantitative fluorescence in situ hybridization and flow cytometry, t he telomere length of telomere repeat sequences after stem cell transplanta tion (SCT) were measured. The study included the telomeres of peripheral bl ood monocytes that should reflect the length of telomeres in stem cells and the telomeres of T lymphocytes that could shorten as a result of periphera l expansion. The loss of telomeres in monocytes and in memory T cells, alth ough accelerated initially, became comparable to the loss of telomeres in h ealthy controls from the second year after transplantation. In addition, th e telomere length in the naive T cells that were produced by the thymus was comparable to the telomere length in the naive T cells of the donor. Compa red to the total length of telomeres available, the loss of telomere repeat s in leukocytes after SCT resembles the accelerated shortening seen in earl y childhood and remains, therefore, relatively insignificant. (C) 2001 by T he American Society of Hematology.