Monocyte‐ and Macrophage‐Mediated Antibody Sequestration Attenuates Anti‐Epidermal Growth Factor Receptor Antibody Efficacy in the Tumor Microenvironment

Tumor‐associated monocytes and macrophages are abundant in the tumor microenvironment (TME) and can influence the therapeutic accessibility of antibody drugs. However, the impact of macrophage‐mediated antibody sequestration on the therapeutic efficacy of anti‐epidermal growth factor receptor (EGFR) therapy remains unclear. This study aimed to assess whether monocytes and macrophages attenuate anti‐EGFR therapeutic efficacy by sequestering antibodies. We established a transwell‐based co‐culture platform using human THP‐1 monocytes or macrophages and EGFR‐positive DiFi colorectal cancer cells to evaluate macrophage‐associated antibody sequestration. In vivo xenograft assays, flow cytometric uptake analyses and inhibitor‐based functional studies were performed using the anti‐EGFR monoclonal antibodies cetuximab and panitumumab. Xenograft models co‐implanted with THP‐1 cells demonstrated attenuated responses to anti‐EGFR antibodies compared to tumor‐only models. Monocytes and macrophages significantly reduced the growth‐inhibitory effects of cetuximab and panitumumab in co‐culture. Antibody uptake was increased in THP‐1 cells and THP‐1‐derived macrophages. Fc receptor blockade and uptake‐associated inhibitors partially suppressed antibody uptake and restored antibody‐mediated anti‐tumor activity, suggesting the involvement of FcγR‐dependent and FcγR‐independent pathways. Monocyte‐ and macrophage‐mediated antibody sequestration attenuates anti‐EGFR therapeutic efficacy by reducing antibody accessibility to tumor cells. The established co‐culture platform provides a useful bioanalytical assay system to screen and evaluate antibody accessibility and macrophage‐associated sequestration during the preclinical development of antibody therapeutics.