Targeting telomerase in b-cell chronic lymphocytic leukemia

Telomerase reverse transcriptase (TERT) is considered a key universal tumor associated antigen, since it is overexpressed in more than 85% of tumor cells. When TERT is reactivated in tumor cells, the enzyme is processed and its antigenic peptides are presented in association with the class I molecules of the major histocompatibility complex, promoting tumor recognition by specific cytotoxic T-lymphocytes. Recently, our group demonstrated that the adoptive cell transfer of mouse TERT198-205-specific cytotoxic T-lymphocytes were able to control the progression of several transplantable tumor models but, at the same time, the repeated administration induced a temporary autoimmune depletion of B cells. We had therefore hypotized that these results could represent a promising background for the treatment of haematologic B cell malignancies, such as B-cell chronic lymphocytic leukemia. Telomerase expression and activity is generally low or absent in normal cells, except for male germline, embryonic and hematopoietic stem cells, while it is usually elevated in malignant B cells. Moreover TERT expression and functional activity is reported to directly correlate with a worst prognosis of leukemic patients. We developed a passive immunotherapeutic approach based on the adoptive transfer of specific TERT cytotoxic T-lymphocytes both in murine B cell leukemia cancer models but also in a humanized context in which immunodeficient mice were engrafted with human leukemic cells and treated with specific engineered anti h-TERT T lymphocytes. In murine setting, we took advantage of a highly aggressive B-cell malignancy derived by IgH.TE transgenic mice, which displayed common characteristics with human B-cell chronic lymphocytic leukemia. patients such as the expansion of a CD19+/CD5+ clonal cell population expressing high levels of active telomerase. mTERT198-205-specific cytotoxic T-lymphocytes could recognize these malignant B cells both in vitro and in vivo: ~70% of treated IgH.TE-derived B cell tumor-bearing mice with the adoptive transfer of mTERT specific cytotoxic T-lymphocytes achieved complete remission. Confident about these data, we translated our work hypothesis into human setting. We cloned the hTERT865-873-specific full-length rearranged TCR / genes from our previously isolated cytotoxic T-lymphocyte clone and inserted into a novel retroviral expression vector to infect naive peripheral blood mononucleated cells, creating selective hTERT865-873-specific CTLs. These cytotoxic T cells were able to recognize both immortalized B-cell malignancies and peripheral blood mononucleated cells from leukemic patients expressing hTERT865-873 in an HLA-A2-restricted manner, both in vitro and in vivo. In fact, TERT specific adoptive transfer in leukemic immune-deficient NOG mice led to a significant reduction in the spreading of neoplastic cells in secondary organs. Moreover, hTERT865-873 specific T cells controlled the engraftment of human primary B-cell chronic lymphocytic leukemia cells in humanized NOG mice, thus confirming not only the efficacy, but also the specificity and safety of our immunotherapeutic approach. These findings suggest that naturally processed hTERT865-873/HLA-A2+ complexes presented on the surface of B-malignancies are sufficiently immunogenic to be recognized by hTERT865-873-specific cytotoxic T cells. Gene-modified T cells successfully killed malignant B cell, but not normal cells and hematopoietic progenitors, in an HLA-restricted manner both in vitro and in vivo. Our experimental observations therefore support the development of a novel hTERT865-873-targeting redirected T cell-based immunotherapy for B-cell chronic lymphocytic leukemia patients, that can also be potentially translated in clinic to treat tumors with different histology.