Abstract
Unconjugated monoclonal antibodies (mAb) kill tumor cells in vivo by activating immune functions. One of these is ADCC (antibody-dependent cellular cytotoxicity). The efficacy of mAbs might be augmented if the cytotoxic capacity of the effector cells could be increased. In this study the augmenting effect of granulocyte-colony-stimulating factor (G-CSF), granulocyte/macrophage(GM)-CSF and macrophage(M)-CSF was analyzed. Effector cells [peripheral blood mononuclear cells (PBMC) or granulocytes] were activated for 4-6 h by the respective CSF and assayed in an 18-h Cr51-release assay. Human colorectal, lymphoma, glioma and melanoma cell lines were target cells. Mouse mAbs of different isotypes, as well as chimeric and humanized mAbs, were used. mAbs having the human Fc part of the IgG molecule were the most effective. The killing capacity of PBMC as well as of granulocytes was statistically significantly enhanced when mAbs were added. M-CSF and GM-CSF were the best CSF for augmenting the lytic capacity of PBMC in ADCC. G-CSF had no significant effect on PBMC. Spontaneous cytolysis of PBMC was significantly augmented only by M-CSF. Granulocytes were, in general, significantly less effective than PBMC but may be equally effective killer cells together with mouse or human mAbs of the IgG1 isotype, particularly against melanoma cells. Granulocytes may also be significantly stimulated to increased lytic capacity when activated with G-CSF or GM-CSF. On the basis of the present evaluation, clinical trials in tumor patients are warranted, combining mAbs with GM-CSF or M-CSF. Preference might be given to GM-CSF as this cytokine activates both PBMC and granulocytes.