Telomerase activity might persist in the human thymus throughout life

Thymocytes maintain immune activity through telomere elongation in rats under hypoxic conditions

The main purpose of the present study was to investigate the change in thymocyte telomere length of rats exposed to different hypoxic conditions for different periods of time, as well as its effect on the immune system. A total of 110 male Wistar rats were randomly assigned to one of the three following groups: i) Sea level (SL) group, in which 10 rats were maintained at an altitude of 10 m; ii) moderate altitude (MA) group, in which 50 rats were maintained at an altitude of 2,260 m and then randomly sacrificed on days 1, 3, 7, 15 and 30 (n=10 each); and iii) simulated high altitude (SHA) group, in which 50 rats were maintained at a simulated altitude of 5,000 m, and then randomly sacrificed on days 1, 3, 7, 15 and 30 (n=10 each). The morphological changes of the thymus were observed, while the telomere length, the mRNA and protein expression levels of telomerase reverse transcriptase (TERT), and the peripheral blood lymphocyte count were measured. The results indicated that hypoxia induced morphological changes and apoptosis in thymocytes, as well as atrophy of the thymus tissue, and resulted in a significant increase in telomere length and TERT mRNA and protein expression levels. This effect appeared to be more pronounced in the SHA group compared with that in the MA group; however, no statistically significant changes were observed in the peripheral blood lymphocyte count. Based on these findings, the hypoxia-associated loss of thymic function appears to be only quantitative and not qualitative, and the thymus may be able to maintain its immune function even under hypoxic conditions.

Telomerase reverse transcriptase as target for anti-tumor T cell responses in humans

Human telomerase reverse transcriptase, a ribonucleoprotein intimately connected with the process of cell immortalization, is overexpressed in the vast majority of cancer cells, irrespective of their histological origin. Telomerase is currently viewed as the first antigen with the characteristics of common tumor antigen in humans, and it constitutes a potentially valuable target for attempts to control tumors through CD8 T cell immunity. Telomerase is a self antigen, making it possible that self tolerance imposes severe restrictions on our ability to generate effective anti-tumor immune responses in humans. In this article we review current studies on the antigenic and immunogenic properties of the human telomerase reverse transcriptase, placing them in the context of self tolerance and the size of the available CD8 T cell repertoire restricted by the HLA A2 molecule.