HLA-A2 Presents Shared Tumor-associated Antigens Derived from Endogenous Proteins in Ovarian Cancer

Tumor-associated lymphocytes (TAL) from the malignant ascites and tumor-infiltrating lymphocytes (TIL) from the solid tumor were isolated from six consecutive untreated ovarian cancer patients. Tumor-specific CTL were generated from both TAL and TIL using solid phase anti-CD3, low dose IL-2 (50 IU/ml), and repeated tumor stimulation. The specificity of TAL and TIL was tested in standard cytotoxicity assays using autologous tumor, several allogeneic ovarian tumors, and the NK-sensitive cell line, K562. Anti-HLA-A-B-C mAb, W6/32, was used to demonstrate that these tumor-specific TAL and TIL were HLA class I-restricted. The ability of the ascitic and solid tumor to present Ag by HLA class I was assessed using Brefeldin A, a fungal metabolite that blocks the endogenous Ag-processing pathway in the viral model. Brefeldin A significantly inhibited tumor-specific cytotoxicity as well as HLA class I expression on the cell surface, suggesting an endogenous source of tumor-associated Ag. Despite previous reports of antigenic heterogeneity in ovarian cancer, shared tumor-associated Ag were shown to exist in this disease as demonstrated by significant allogeneic recognition of HLA-A2-matched patients as opposed to unmatched controls. Specifically, CTL from HLA-A2+ patients lysed HLA-A2+ allogeneic targets significantly better than HLA-A2- allogeneic or HLA-A2+ melanoma targets. There was no such difference with HLA-A2- effectors. Furthermore, HLA-A2 was confirmed to be a major restriction element in ovarian cancer by the blocking of HLA-A2+ effectors against both autologous and allogeneic HLA-A2+ targets with the anti-HLA-A2 mAb, BB7.2. These findings verify a similar lymphocyte/tumor interaction as has been documented in melanoma, suggesting a common mechanism of recognition of these human tumors by lymphocytes.