Mavrilimumab (CAM 3001) is a monoclonal antibody with antiviral activity that targets the α subunit of the granulocytic-macrophage colony-stimulating factor (GM-CSF) receptor, inhibiting downstream intracellular GM-CSF signaling. GM-CSF may contribute to an overactive inflammatory response linked to respiratory failure and death and could be used to study rheumatoid arthritis.