Tumor-infiltrating lymphocytes cultured in recombinant interleukin-2: enhancement of growth, cytotoxicity, and phenotypic expression of cytotoxic T-cell antigens by cyclophosphamide given intravenously prior to tumor harvest.

Tumor-infiltrating lymphocytes (TILs) have potent antitumor effects in murine models of advanced disease. Although these cells are 50-100 times more potent than lymphokine-activated killer cells against micrometastases, their antitumor benefits are virtually nonexistent against large tumor burdens unless cyclophosphamide is added to the immunotherapy regimen. In an effort to determine the effects of cyclophosphamide on TILs obtained from tumor-bearing animals, we harvested tumors from animals having received either 0, 50, or 100 mg/kg cyclophosphamide intravenously and investigated the expansion, cytotoxicity, and phenotypic expression of these TILs co-cultured in vitro with recombinant interleukin-2. TILs obtained from animals given cyclophosphamide, demonstrated a greater fold expansion than TILs obtained from normal animals (mean fold expansion on day 59 of culture: 85, 400, and 150 for TILs obtained from animals given 0, 50, and 100 mg/kg cyclophosphamide, n = 3 consecutive experiments). In addition, these TILs demonstrated enhanced cytotoxicity compared to controls [effector to target ratio 4:1, day 16 TILs, % lysis: 24, 35, and 45%, cyclophosphamide 0, 50, and 100 mg/kg, respectively, against the MCA-102 sarcoma, natural killer (NK) insensitive tumor; 29, 38, and 56% against the YAC-1 lymphoma, NK sensitive tumor]. Similar results were seen with day 34 and day 59 TILs. When phenotypic analysis was performed, TILs obtained from animals given cyclophosphamide consistently demonstrated a greater percent expression of the Thy1.2 and Lyt-2 antigens up to day 59 of culture when the experiments were terminated. The NK cell marker 49H.8 was expressed on the majority of TILs and its expression did not change with respect to the cyclophosphamide concentration. The increase in TIL number and cytotoxicity seen with cyclophosphamide given intravenously before tumor harvest could have important ramifications for human immunotherapy with TILs.