ABSTRACT
Cytotoxic T-lymphocyte (CTL) and lymphokine activated killer (LAK) cell (fraction II) precursors with a density of 1.077-1.067 g/ml and suppressor cells (fraction I) with a density of 1.067-1.056 g/ml were isolated by the separation of cancer patient peripheral blood mononuclear cells (MNC) on a Percoll gradient. Cells from fraction I inhibited the generation of CTL in mixed lymphocyte-tumor culture (MLTC) and LAK cells when added to fraction II lymphocytes at a ratio of 1:1 at the beginning of the culture. The effect was dependent on the dose of added suppressor cells and resistant to mitomycin-C treatment. Treatment of cell fractions prior to culture with monoclonal antibodies and complement showed that CTL precursors and suppressor cells were OKT3+/OKT8+. Cells from fraction I possessed suppressor activity in all patients examined but only in 4 of 10 healthy donors. Studies of monocytes and T-lymphocytes isolated from fraction I demonstrated that in cancer patients both monocytes and T-lymphocytes functioned as suppressors whereas in healthy donors, the monocytes mediated suppression. The data obtained provide evidence for an increased suppressor cell activity in cancer patients which can inhibit the generation of cytotoxic antitumor response with interleukin-2 (IL-2) in vitro.
