Peptide-major histocompatibility complex class I complex: from the structural and molecular basis to pharmacological principles and therapeutic applications

Lack of tumor recognition by hTERT peptide 540-548-specific CD8(+) T cells from melanoma patients reveals inefficient antigen processing

Telomerase is a ribonucleoprotein complex responsible for the maintenance of the length of the telomeres during cell division, which is active in germ-line cells as well as in the vast majority of tumors but not in most normal tissues. The wide expression of the human telomerase catalytic subunit (hTERT) in tumors makes it an interesting candidate vaccine for cancer. hTERT-derived peptide 540-548 (hTERT(540)) has been recently shown to be recognized in an HLA-A*0201-restricted fashion by T cell lines derived from peptide-stimulated peripheral blood mononuclear cells (PBMC) from healthy donors. As a first step to the inclusion of this peptide in immunotherapy clinical trials, it is crucial to assess hTERT(540)-specific T cell reactivity in cancer patients as well as the ability of hTERT-specific CD8(+) T lymphocytes to recognize and lyse hTERT-expressing target cells. Here, we have analyzed the CD8(+) T cell response to peptide hTERT(540) in HLA-A*0201 melanoma patients by using fluorescent HLA-A*0201/hTERT(540) peptide tetramers. HLA-A*0201/hTERT(540) tetramer(+) CD8(+) T cells were readily detected in peptide-stimulated PBMC from a significant proportion of patients and could be isolated by tetramer-guided cell sorting. hTERT(540)-specific CD8(+) T cells were able to specifically recognize HLA-A*0201 cells either pulsed with peptide or transiently transfected with a minigene encoding the minimal epitope. In contrast, they failed to recognize hTERT-expressing HLA-A*0201(+) target cells. Furthermore, in vitro proteasome digestion studies revealed inadequate hTERT processing. Altogether, these results raise questions on the use of hTERT(540) peptide for cancer immunotherapy.

Molecular and functional dissection of the H-2Db-restricted subdominant cytotoxic T-cell response to lymphocytic choriomeningitis virus

Infection of H-2b mice with lymphocytic choriomeningitis virus (LCMV) generates an H-2Db-restricted cytotoxic T-lymphocyte (CTL) response whose subdominant component is directed against the GP92-101 (CSANNSHHYI) epitope. The aim of this study was to identify the functional parameters accounting for this subdominance. We found that the two naturally occurring (genetically encoded and posttranslationally modified) forms of LCMV GP92-101 were immunogenic, did not act as T-cell antagonists, and bound efficiently to but were unable to form stable complexes with H-2Db, a crucial factor for immunodominance. Thus, the H-2Db-restricted subdominant CTL response to LCMV resulted not from altered T-cell activation but from impaired major histocompatibility complex presentation properties.