The influence of lnterleukin-2 and lymphokine-activated killer cells on normal hemopoietic stem cells

Background: Adoptive immunoiherapy by using interlcukin 2 (1L-2) and lympho-kine-activatcd killer cells (LAK cells) is known to induce life threatening side effects on normal tissue, also on hemopoiesis. Material and methods: With regard to using the LAK cell concept for the elimination of residual tumor cells we investigated its influence on normal hemopoietic progenitors and stem cells from normal bone marrow in the CFU-GM-assay and in long-term bone marrow cultures. It could be shown that IL-2 and LAK-cells do not affect clonogenic cells dramatically when the cells are immobilized in agar and cell-to-cell contacts are avoided. When bone marrow cells were preincubated with IL-2 they were stimulated at low concentrations (100 U/ml) and low incubation limes (10 h). High concentrations (300 U/ml) applicated for 24 h caused a significant inhibition of colony formation. LAK cells led also to a significant inhibition of GM-CFC when the cells were preincubated with LAK cells for 18 hours in a liquid medium before plating in agar. Long-term bone marrow cultures (LTBMC) grown in presence of 200 U/ml IL-2 had a reduced output of GM-CFC and a reduced adherent layer. This effect was more pronounced in two-stage LTBMCs where the adherent layer detached in 3 of 5 experiments. In two stage LTBMC initiated with T-cell depleted bone marrow the GM-CFC production was also reduced but the adherent layer was morphologically unimpaired. Supcrnalants of LTBMC contained increased levels of tumor necrosis factor (TNF) but did not inhibit GM-CFCs in the agar assay. Our results indicate that IL-2- and LAK-cell-mediated inhibition of hemopoiesis is rather due to cellular mechanisms requiring intimate cell contacts than to released humoral factors.