Polymorphonuclear leukocytes (PMNs) mediate antibody-dependent cellular cytotoxicity (ADCC), which is increased by the addition of granulocyte-macrophage colony-stimulating factor (GM-CSF). We sought to determine whether PMN ADCC also would be increased by the addition of an antibody/GM-CSF fusion protein and whether this would be associated with the up-regulation and activation of Mac-1 (CD11b/CD18) and with azurophil granule exocytosis. ADCC against LA-N-1 human neuroblastoma cells was evaluated with 4-hour calcein acetoxymethyl ester (calcein-AM) microcytotoxicity assay, electron microscopy, and multiparameter flow cytometry. With the calcein-AM assay, LA-N-1 cell survival was 10%, 55%, and 75% when PMN ADCC was mediated by the antidisialoganglioside (anti-GD2) immunocytokine hu14.
IntroductionAntibody-cytokine fusion proteins combine the targeting ability of antibodies with the immune stimulation of cytokines for cancer immunotherapy. 1 Studies in mice of antidisialoganglioside (anti-GD2)/interleukin-2 and anti-GD2/lymphotoxin-␣ fusion proteins (immunocytokines) demonstrated the eradication of hepatic metastases of neuroblastoma 2,3 and the induction of protective immunity against melanoma. 4 These and other immunocytokine strategies have been based on the stimulation of NK-cell-or T-cell-mediated responses. Polymorphonuclear leukocytes (PMNs) constitute the largest population of white blood cells, and they can mediate antibody-dependent cellular cytotoxicity (ADCC) against tumor cells. [5][6][7][8][9] In vitro studies demonstrated the strong facilitation of PMN ADCC against neuroblastoma cells by mixing granulocytemacrophage colony-stimulating factor (GM-CSF) with an anti-GD2 antibody and by a human-mouse chimeric anti-GD2/GM-CSF immunocytokine. 5,10 Fc receptors (FcR) involved in PMN ADCC may include Fc␥RII (CD32) and Fc␥RIII (CD16), which are constitutively expressed, and Fc␥RI (CD64), which is induced by interferon-␥ and G-CSF. 11,12 In addition, Fc␣RI of PMNs may be activated by constructing bispecific monoclonal antibodies (mAbs) that recognize a target cell molecule and Fc␣RI. 13 Binding of an antibody-cytokine fusion protein to FcR may be affected by the physical presence of the cytokine or by the cytokinemodulating FcR expression. 14,15 FcRs used by PMNs in ADCC with anti-GD2/GM-CSF immunocytokines have not yet been determined. 2 -Integrin receptors, particularly Mac-1 (␣ m  2 , CD11b/CD18, and complement receptor type 3), have been reported to have an essential role in PMN ADCC against neuroblastoma, lymphoma, and breast cancer cell lines. 5,13,16 Mac-1 is a major PMN  2 -integrin receptor that, on activation, acquires the ability to bind multiple ligands and to mediate several adhesion-dependent processes, including phagocytosis, superoxide production, and degranulation. 17 It recently has been demonstrated that Mac-1 function is necessary for PMN spreading on antibody-coated targets and for tumor cytolysis. 13 FcR and GM-CSF receptors activate Mac-1 For personal use only. on May 12, 2018. by ...