CD47-SIRPα Blockade Sensitizes Head and Neck Squamous Cell Carcinoma to Cetuximab by Enhancing Macrophage Adhesion to Cancer Cells

Developing effective treatments for patients with head and neck squamous cell carcinoma (HNSCC) is a significant challenge. Cetuximab, a first-line targeted therapy for HNSCC, exhibits limited efficacy. Here, we used pooled CRISPR screening to find targets that can synergize with cetuximab and identified CD47 as the leading candidate. Rather than inhibiting cancer cell proliferation, CD47 inhibition promoted cetuximab-triggered antibody-dependent cellular phagocytosis (ADCP), thereby enhancing macrophage-mediated cancer cell removal. The combination of CD47-signal-regulatory protein α (SIRPα) blockade and cetuximab demonstrated strong anticancer activity in vivo. In addition to blocking the phagocytosis checkpoint, CD47-SIRPα inhibition upregulated CD11b/CD18 on the surface of macrophages, which accelerated intercellular adhesion between macrophages and cancer cells to enhance subsequent phagocytosis. Inhibition of the interaction between macrophage CD11b/CD18 and cancer cell intercellular adhesion molecule-1 (ICAM1) eliminated the intercellular adhesion and phagocytosis induced by CD47-SIRPα blockade. Thus, CD47-SIRPα blockade enhances ADCP through CD11b/CD18-ICAM1-mediated intercellular adhesion and sensitizes HNSCC to cetuximab. Significance: CD47-SIRPα blockade increases surface CD11b/CD18 on macrophages to enhance adhesion to cancer cells, resulting in robust synergistic phagocytosis in combination with cetuximab treatment in head and neck squamous cell carcinoma.