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.