[CD4+ T-cell immunity and Ab responses to mutant ras protein in pancreas and colon cancer patients].

Mutated p21 ras protein contains single substituted amino acid residue. It can be considered as cancer-specific protein. The current study examined whether T-cell and Ab responses to mutant p21 ras protein and/or peptide can be detected in patients with pancreatic or colon cancer. Studies focused on the aspartic acid substitution in amino acid position 12(ras D12) as the commonest mutation in gastrointestinal malignancy. IgA antibodies directed against mutated ras D12 protein were detected in 51 of 160 (31.8%) colon cancer patients, but only in 1 of 40 (2.5%) normals. The greater incidence of antibody in cancer patients provides evidence that immunization to the ras proteins occurred as a result of the malignancy. Seven of sixteen (43.7%) pancreas cancer patients responded to ras D12 peptide. T cell responses to ras D12 peptides were detected in only 2 of 25 (8.0%) colon cancer patients. None of the 11 normal individuals tested had positive responses to normal or mutant ras p21 proteins and/or peptides. Thus, Ab and CD4+ T cell immunity to the mutated segment of ras protein is present in some patients with gastrointestinal cancer.