EXPRESSION OF COSTIMULATORY MOLECULES, B7-1 AND B7-2 ON HUMAN GASTRIC-CARCINOMA

Costimulation of T cells via B7-1 and B7-2 molecules on a tumor has be en shown to be important for eliciting cell-mediated antitumor immunit y. We studied the surface expression of B7-1 and B7-2 in 24 cases of g astric carcinoma from the primary locus, 20 cases of metastatic carcin oma from malignant ascites, 20 cases of benign gastric mucosa and 7 ga stric carcinoma cell lines by two-color flow cytometry with mAb CD80 a nd CD86. The B7-1 and B7-2 molecules were expressed by 6 cell lines, a nd I cell line showed the predominant expression of B7-2 but not B7-1. Almost all patients with primary gastric carcinoma and benign gastric mucosa showed high levels of expression of the B7-1 and B7-2, reveali ng approximately 40%-60% positive cells. However, the percentage of B7 -1-positive cells of poorly differentiated primary carcinomas was sign ificantly lower than that of well-differentiated carcinoma and normal mucosa (P<0.01). Furthermore, all of the metastatic carcinoma cells re vealed consistently very low or undetectable levels of expression of t he B7-1 molecule, only 8 % (mean) of cells being positive, despite sho wing higher levels of B7-2 expression. Thus, it seems likely that decr eased or deleted expression of B7-1 correlates with the grade of tumor differentiation, tumor progression and metastasis. These results sugg est that the B7-1 molecule on the gastric carcinoma bearing CD80(+)CD8 6(+) is abrogated during tumor invasion and/or metastasis, and the tur ner finally acquires the CD80(-)CD86(+) phenotype. Consequently, inade quate B7-1 costimulation may contribute to the escape of tumors from d estruction by the host's immune system.