Spontaneous and antibody-dependent cellular cytotoxicity in melanoma patients and healthy control presons

Spontaneous cell-mediated cytotoxicity (SCMC) and antibody-dependent cellular cytotoxicity (ADCC) against 51Cr labeled allogeneic target cells of a human melanoma cell line (IGR3) were determined with purified effector lymphocytes and defibrinated whole blood from 14 melanoma patients and 13 healthy control persons. Peripheral blood lymphocytes were isolated by Ficoll gradient centrifugation (fraction F); subsequently the phagocytic and adherent cells were removed and the supernating cell population (fraction fff) was passaged through IgG anti-IgG columns to obtain a B cell free lymphocyte suspension (fraction fff-c). cells from the 3 lymphocyte fractions and from defibrinated whole blood were simultaneously tested for cytotoxic activity against unsensitized IGR3 target cells (SCMC assay) and IGR3 cells perviously sensitized with a rabbit anti-melanoma IgG (ADCC assay). Dose-response curves were established with all lymphocyte fractions and with whole blood. The following results were obtained. 1. With all lymphocyte fractions tested, ADCC was approximately 15 time higher than SCMC, whereas with whole blood, the difference tended to be less pronounced. 2. Elimination of phagoctic and adherent cells had no significant effect on SCMC and ADCC. 3. Passage over IgG anti-IgG columns drastically reduced cytotoxicity in both assays without, however, completely abolishing it. 4. The only difference seen between lymphocyte cytotoxicity of melanoma patients and control persons was a slight, but non-significant depression of SCMC and ADCC in melanoma patients. The results confirm and extend our previous report that SCMC against an allogeneic tumor cell-line is due to not-specific "Null" or "K" cell-activity rather than to specific T cell cytotoxicity. In one experiment freshly explanted melanoma cells were labeled with 51Cr and reacted wiht autologous blood and purified lymphocyte fractions. It was found that cellular cytotoxicity depending on serum factors (ADCC) was an effective lytic mechanism, whereas T cell-mediated cytotoxicity could not be demonstrated.