In order to understand the reasons for unsatisfactory results of T cell-centred immunotherapies and to set more effective anti-cancer protocols, studies were performed aimed at characterizing anti-telomerase immune responses as well as regulatory/suppressor immune pathways in human cancer.Telomerase is considered an universal tumor associated antigen due to its high rate of expression by cancers (90%).The analysis of frequency and cytolytic function of circulating CD8+ T lymphocytes specific for the p540 telomerase peptide in a series of 27 HLA-A2+ cancer patients showed that the majority of cancer patients have circulating telomerase-specific CD8+ T lymphocytes.CTL lines able to kill telomerase-positive tumor cells, including autologous cancer cells, could be ex vivo expanded from some, but not all, cancer patients.The results of the study support the development of clinical protocols using telomerase peptides as immunizing agent but also underline the necessity to immunologically study single patients before undergoing tumor antigen-specific vaccination.