A TGF beta RII frameshift-mutation-derived CTL epitope recognised by HLA-A2-restricted CD8(+) T cells

Microsatellite instability (MSI) is recognised as genome-wide alterations i n repetitive DNA sequences caused by defects in the DNA mismatch repair mac hinery. Such mutation patterns have been found in almost all analysed malig nancies from patients with hereditary non-polyposis colorectal cancer, and in approximately 15% of sporadic colorectal cancers. In cancers with the MS I phenotype, micro satellite-like sequences in coding regions of various ca ncer-related genes, including transforming growth factor beta receptor type II (TGF beta RII), are targets for mutations. The TGF beta RII gene harbou rs a 10-bp polyadenine tract, and mutations within this region are found in 90% of colorectal cancers with MSI. The frameshift mutations result in new amino acid sequences in the C-terminal part of the proteins, prematurely t erminating where a novel stop codon appears. In this study we have defined a new cytotoxic T lymphocyte (CTL) epitope (RLSSCVPVA), carrying a good HLA -A*0201 binding motif. and resulting from the most common frameshift mutati on in TGF beta RII. A CTL line and several CTL clones were generated from a n HLA-A2(+) normal donor by repeated stimulation of T cells with dendritic cells pulsed with the peptide. One of the CTL clones was able to kill an HL A-A2(+) colon cancer cell line harbouring mutant TGF beta RII. This epitope may be a valuable component in cancer vaccines directed at MSI-positive ca rcinomas.