A subsequent phase IIb trial (EARTH EXPLORER 1), demonstrated that mavrilimumab represented a rapid, effective and well‐tolerated potential treatment for RA patients who had previously failed treatment with conventional disease‐modifying anti‐rheumatic drugs (DMARDs), and even biologicals (anti‐cytokine therapies) targeting other inflammatory pathways 107, and this emphasized an important pathogenic role for the GM‐CSF axis in difficult‐to‐treat RA. Here, CSF2 is linked to rheumatoid arthritis.