Telomeres and telomerase in hematologic neoplasia.

Normal hematopoietic cells express telomerase activity, however the presence of telomerase does not necessarily imply stable and thus unchanging telomere length. Gradual telomere loss with aging and rapid cycling of hematopoietic stem cells might contribute to immunosenescence, exhausted hematopoiesis, and increased likelihood of malignant transformation. In leukemias and lymphomas, telomere length may reflect the cellular proliferative history, prior to immortalization. The level of telomerase activity is generally influenced by the fraction of cells in the proliferative pool. Shortened telomeres and high telomerase activity almost always correlates with disease severity in hematologic neoplasias such as relapsed leukemia and high-grade lymphomas, indicating that measurement of telomere length and telomerase activity might be useful to monitor disease condition. Since the mode of action of telomerase inhibitors may require telomeric shortening before induction of apoptosis, anti-telomerase therapy might be helpful for adjuvant therapy following conventional chemotherapy, in vitro purging of neoplastic cells in stem cell transplantation, and treating minimal residual disease. Some promising areas of tissue engineering include rejuvenation of hematopoietic stem cells for improving stem cell transplants or enhancing general immunity for older patients.