Long-term (up to 3.3 years) treatment with mavrilimumab, an antibody that targets granulocyte–macrophage colony-stimulating factor receptor-α, was safe and effective in patients with rheumatoid arthritis in two phase IIb studies and a phase II open-label extension study. In total, 442 patients received mavrilimumab in combination with methotrexate. In the extension study, 65.0% and 40.6% of patients achieved DAS28-CRP <3.2 and <2.6, respectively, at week 122. Most treatment-related adverse events were mild or moderate in severity.