This study was carried out to determine whether HLA class I or class II expression on ovarian tumor cells and lymphocytic infiltration of the epithelial ovarian carcinoma (EOC) tissues were responsible for the ability to expand tumor-infiltrating lymphocytes (TIL) in vitro in low concentrations of recombinant interleukin-2 (rIL-2). Immunohistochemical analysis was performed using monoclonal antibodies that recognize framework determinants of either HLA class I or HLA class II or leukocyte differentiation antigens (LCA, CD3, CD4, and CD8). Cryostat sections of EOC had HLA class I and HLA class II expression on at least 5% of tumor cells in 18 of 20 specimens (90%). From another portion of the same tumor specimens T-cell lines were developed from TIL in low concentrations of rIL-2 (200-600 IU/ml) in 7 of 17 patients. Tumors from which TIL were expanded in vitro with rIL-2 had significantly higher proportions of HLA class I-positive tumor cells (73 +/- 10%) compared to tumors from which TIL failed to grow (40 +/- 10%) (P = 0.036). However, there was no difference in the proportions of HLA class II-positive tumor cells between the two groups. Tumor specimens of patients whose TIL were expanded in rIL-2 had significantly higher numbers per field (423 +/- 114 vs 154 +/- 20; P = 0.005) and proportions (90 +/- 3% vs 77 +/- 4%; P = 0.023) of infiltrating CD3+ cells, significantly higher numbers per field (115 +/- 44 vs 19 +/- 5; P = 0.003) and proportions (25 +/- 5% vs 11 +/- 2%; P = 0.017) of CD8+ cells and significantly higher numbers per field of CD4+ cells (318 +/- 101 vs 113 +/- 18; P = 0.025), in comparison to tumor specimens from patients whose TIL did not grow in vitro. Significant correlations were observed between the proportions of HLA class I-positive EOC tumor cells and the numbers of infiltrating LCA-positive cells (r = 0.67; P = 0.005) CD3+ cells (r = 0.70; P = 0.002), CD4+ cells (r = 0.69; P = 0.003), and CD8+ cells (r = 0.82; P = 0.001). The proportions of HLA class II-positive tumor cells correlated positively (r = 0.45; P = 0.049) only with the numbers of CD8+-infiltrating cells. In conclusion, we report here that HLA class I expression on EOC cells correlates with T-cell infiltration in vivo and T-cell expansion in vitro, in low concentrations of rIL-2.