Telomere Biology in T Cells: An Important Brake on the Road of Their Life Span?

Telomeres and telomerase play an essential role in the regulation of the life span of human cells. Telomeres shorten progressively with each cell division, as well as in response to other causes, eventually leading to cell senescence and apoptosis. In contrast to most human somatic cells, T cells and certain B cells express the telomerase complex upon activation or stimulation, which compensates for telomere attrition to some degree. Telomerase reactivation has most likely evolved to extend the life span of certain T cells and B cells in order to adequately fulfill immune responses despite massive cellular expansion. Pathologic or abnormal reactivation of telomerase, however, is one of the hallmarks of cancer cells, and seems to be one of the key elements for developing T- and B-cell neoplasias. Manipulation of the telomere/telomerase complex in both normal and malignant T and B cells is highly attractive for therapeutic strategies.