Specific T-cell immunity against Ki-ras peptides in patients with pancreatic and colorectal cancers.

Mutations of codon 12 in the Ki-ras gene are frequently found in pancreatic and colorectal cancers. It has been demonstrated that human T-cells have the potential to recognise tumours expressing mutated ras-derived peptides. However, it remains unclear whether T-cells from a given individual can recognise the mutant peptides, which are expressed in that individual's tumour tissues. Mutations of the Ki-ras oncogene were analysed by the mutant-allele-specific amplification (MASA) method in pancreatic and colorectal tumour tissues, and T-cell responses against mutated Ki-ras-derived peptides were measured by [(3)H]thymidine incorporation and IFN-gamma production assays. Specific T-cell responses against Ki-ras-products were found in cancer patients, whereas no immune response was observed in normal individuals (P<0.01). Six of the eight pancreatic cancer patients (75%) and nine of 26 colorectal cancer patients (35%) had T-cell responses to mutated Ki-ras-derived-peptides. T-cell response in a given individual cannot recognise the same mutated ras peptide, which is expressed in that individual's tumour tissues. However, pancreatic and colorectal cancer patients have T-cell immunity against Ki-ras-peptides, and this provides potential target for cancer immunotherapy.