SmmuaryIn order to assess the potential of interleukin 7 (IL-7) as an immunotherapeutic agent in human melanoma, we have evaluated the in vitro activity of IL-7-induced lymphokine-activated killer (LAK) cells from patients with advanced melanoma against allogeneic and autologous melanoma cells. Peripheral blood lymphocytes (PBLs) from 14 patients with stage III melanoma were isolated and incubated in the presence of 1,000 U ml-' IL-7 and 1 U ml-' IL-2 for comparison. LAK-ell activity was determined by a 24 h cytotoxicity assay using MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide]. The activity of IL-7-induced LAK cells against two allogeneic melanoma cell lines was 32.7% (± 17.9) against SK-Mel-37 and 38.1% (± 12.5) against SK-Mel-23 at an effector-to-target (En ratio of 20:1. The activity of IL-2-induced LAK cells was significantly higher against SK-Mel-37 (78 ± 24.6%) and against SK-Mel-23 (73.5 ± 19.7%). IL-7 and suboptimal doses of IL-2 (10 U ml-I) were found to have a co-stimulatory on lymphocyte proliferation as well as on LAK activity. Against autologous melanoma cells, the activity of IL-7-and IL-2-induced LAK cells did not differ significantly (55.8 ± 25.6% versus 68.7 ± 21.7% respectively). In two patients, IL-7-induced LAK-cell activity against autologous melanoma cells exceeded even that of IL-2 significantly (67% vs 35% and 95% vs 82%). Levels of tumour necrosis factor a (TNF-x) in the supernatants of LAK-cell cultures generated by IL-7 were lower than those of IL-2-generated LAK-cell cultures. These results suggest that IL-7 is a potential alternative to immunotherapy with IL-2 in terms of efficacy and possible side-effects and encourages pilot studies with IL-7 in melanoma patients.