Expression of a suppressive p15E-related epitope in colorectal and gastric cancer.

mRNA for the suppressive epitope of p15E was found to be present in 24 of 30 samples of human colorectal cancer and in all four specimens of gastric cancer. mRNA for p15E was seldom seen in nonmalignant colonic or gastric mucosa but, when present, was associated with inflammatory or pre-malignant conditions of the digestive tract. Synthetic peptides derived from the conserved p15E sequence were found to suppress some aspects of the immune response implicated in anti-tumour activity. These data suggest that a p15E-related material with immunomodulatory properties is elaborated within human tumours, either by the tumour itself or as a normal component of the endogenous anti-tumour reaction.