Variables and specificity of in vitro lymphocyte-mediated cytotoxicity in human melanoma

In vitro cell-mediated cytotoxicity (CMC) assays have been carried out in human melanoma system with blood effector lymphocytes on [3H]proline-labeled target cells in a 48-hr microcytotoxicity technique. Three lymphocyte purification procedures (Ficoll:Hypaque gradient, plasma gel sedimentation followed by nylon column incubation, and plasma gel sedimentation followed by separation with nylon powder and glass beads) are compared in parallel experiments for characteristic effector cell composition and cytotoxic potential against target cells of dissimilar histology. The cytotoxicity is defined by the loss of target cell 3H cpm as measured by residual target cell 3H cpm in individual microwell following incubation with lymphocytes. Target cell 3H cpm loss by test lymphocytes is compared with target cell 3H cpm loss by several age and sex matched control lymphocytes (from normal donors and unrelated cancer patients); further comparison between the various control lymphocytes is also made in each assay. As control for target cells, autologous fibroblasts and homologous tumor cells of dissimilar histology are always included in each assay. Specific cytotoxicity is defined as statistically significant and selective destruction of only melanoma cells by the test lymphocytes as compared to the control lymphocytes. Significant but nonselective destruction of 2 or more target cells of unrelated histology is regarded as nonspecific cytotoxicity, while no destruction of any target cells signifies no cytotoxicity. The Ficoll:Hypaque preparations consistently exhibit the highest nonlymphocytic cell contamination (8 to 16%); the nonlymphocytic cells are, almost exclusively, monocytes. They also produce relatively high percentage of thymus independent (B) cells (8 to 15%). The ultimate cell composition of the 2 plasma gel-nylon preparations is essentially identical. In either plasma gel-nylon preparations, the nonlymphocytic contamination is minimal (0 to 4%) and thymus-dependent (T) cell percentage is considerably higher (92 to 99%) with none or few B cells.