Differential lysis of tumors by polyclonal T cell lines and T cell clones specific for hTERT

The human telomerase reverse transcriptase hTERT is overexpressed in most human tumors and contributes importantly to oncogenesis by maintaining the integrity of telomeric DNA. Despite being a self-antigen, the hTERT enzyme is immunogenic. Peptides derived from hTERT have been shown both in vitro and in vivo to drive the activation and proliferation of peptide-specific T lymphocytes. An HLA-A2-binding peptide from hTERT (I540, ILAKFLHWL) has been used to generate peptide-specific T cells in vitro and in vivo in patients that lyse telomerase-positive tumors in an MHC-restricted fashion. Although these and other data suggest that I540 is naturally processed and presented on the surface of certain tumor cells, there are reports that I540-specific T cells, and in particular, T cell clones, do not lyse tumors in vitro. Here, we compared cytotoxic function of I540-specfic T cell clones vs. polyclonal T cell lines, including clones and lines generated from the same donor. We found that I540-specific polyclonal T cell lines lyse telomerase-positive tumors whereas non-specific polyclonal T cell lines and I540-specific T cell clones do not. Estimated TCR avidity for I540, as well as cell surface expression of CD45RO, CD45RA, CD28, CD27, CD57 and CD62L were similar between lines and clones. V beta usage, however, differed such that the majority of the I540-specific TCR repertoire found in polyclonal T cell lines was not represented in clones generated from the same source material. Thus, I540-specific T cells can vary in cytotoxic potential depending on the method of generation, isolation and expansion.