Monoclonal antibody Daratumumab promotes macrophage-mediated anti-myeloma phagocytic activity via engaging FC gamma receptor and activation of macrophages.

Daratumumab (DAR) is novel human anti-CD38 IgG1, high-affinity human monoclonal antibody having broad-spectrum killing activity. The antibody is recommended to treat multiple myeloma. Recently Antibody-dependent cellular phagocytosis (ADCP) have been identified as the potential mechanism of DAR in addition to complement-dependent cytotoxicity (CDC) and antibody-dependent cell-mediated cytotoxicity (ADCC). In the present study we evaluated the effect of Daratumumab on other effector cells of multiple myeloma. Luciferase+ MM.1R GFP cells were selected for the study. For immune-compromised multiple myeloma tumour xenograft mouse model we used severe combined immunodeficient beige (SCID-beige), NOD SCID gamma (NSG) and C57Bl/6j mice. Bioluminescence imaging was carried by injecting luciferin, and in vivo confocal microscopy was done for tracing bone marrow niches. Spleen and tumours were submitted to immunophenotypic analysis. MTT assay was done for cell proliferation studies. We established tumour xenograft mouse model. It was found that DAR showed significant anti-tumour effect in tumour xenograft multiple myeloma mice. We found that DAR showed anti-tumour activity via Fc-FcγR interaction with macrophages. DAR induced phenotypic activation of macrophages in mice and resulted in ADCP of cancerous cells via interacting Fc-FcγR in vitro. The study suggested that DAR exerted anti-tumour activity in multiple myeloma by interacting with Fc-FcγR.