Production of human macrophages with potent antitumor properties (MAK) by culture of monocytes in the presence of GM-CSF and 1,25-dihydroxy vitamin D3.

Antitumoral macrophages (MAK) were obtained by the culture of human mononuclear cells in hydrophobic bags. From one cytapheresis, up to 10(9) mature macrophages could be purified by elutriation after one week of culture in IMDM medium in the presence of 2% human AB serum. These MAK cells were used for adoptive treatment in metastatic cancer patient with no dose-limiting toxicity. The present study aimed to improve the average MAK yield by addition of GM-CSF and of dihydroxy-cholecalciferol. The differentiated macrophages obtained presented higher antitumoral functionality in response to rh-IFN gamma than in their absence. These MAK presented all the differentiation antigens of cytotoxic macrophages compared to MAK cells differentiated in standard medium. They killed human tumor targets effectively in vitro at a low (1/1) effector/tumor ratio; furthermore, the antitumoral activity reached by MAK cells after IFN gamma activation appeared to be stabilized for several days.

Adoptive immunotherapy with bispecific antibodies: targeting through macrophages.

We report on two applications of bispecific antibodies to enhance the antitumoral function of human macrophages: (1) use of rhuIFN gamma (recombinant human IFN gamma) encapsulated in human red blood cells coated with anti-Fc gamma RI/anti-RhD+ bispecific antibodies to target and to activate human macrophages; encapsulated rhuIFN gamma was more potent than free IFN gamma in activating mature macrophages in vitro, demonstrating the efficacy of this delivery system to initiate in situ activation of macrophages and also to maintain a high antitumoral efficacy of macrophages with less side effects than after systemic injection of IFN gamma; (2) targeting of activated macrophages to tumours by bispecific antibodies directed against macrophage Fc gamma RI and against human adenocarcinoma antigen; differentiated human macrophages became cytotoxic for human adenocarcinoma in vitro and in vivo (tumours implanted in nude mice) when activated by rhuIFN gamma; this effect was increased in the presence of bispecific antibodies. These two approaches were aimed at increasing the efficacy of cellular immunotherapies using activated macrophages as effector cells (macrophage-activated killer, or MAK), an adoptive therapy which we have developed. Bispecific antibodies could increase specific homing and activation of cytotoxic MAK effectors at tumour sites.