EFFECTS OF LYMPHOKINE-ACTIVATED KILLER-CELLS ON MELANOMA NODULES MAINTAINED IN 3-DIMENSIONAL CULTURE

Lymphokine activated killer (LAK) cells were cocultivated from 2 to 6 days with WM266 metastatic melanoma cells maintained as nodules in org anotypic culture. The LAK cells in suspension were allowed to deposit freely on the nodule surface from where they could infiltrate spontane ously into the nodules. Immunohistochemical studies were done to local ize the LAK cells as well as electron microscopical observations for e ffector/target membrane contacts. Proliferation of the nodules was tes ted and also that of the LAK cells after coculturing using tritiated t hymidine incorporation into DNA. Cell death was determined by arrest o f thymidine incorporation and total nodule disintegration. Infiltratio n rate of LAK cells into the nodules was low: after coculturing 5% of the nodule cells were LAK cells. Although close membrane contacts and cytoplasmic fusions between effector and target cells leading to tumor cell apoptosis were observed, this direct cytolytic process seemed to be too infrequent for the induction of total nodule disintegration at day 6. Therefore, the indirect pathway to cytolysis might be predomin ant implying, among other cytokines, soluble TNF. On the other hand, L AK cell proliferation diminished strongly after coculturing (down to 1 1%) but the cytotoxicity was significantly enhanced (18% higher) sugge sting an enhancement of differentiation. This might account for the pe culiar efficacy of LAK cells on melanomas in vivo and it would be of i nterest to study this phenomenon further.