GM-CSF may be a very effective target in SpA based on the pre-clinical data from our group and others which show an expansion of GM-CSF-producing CD4 and CD8 cells in the blood and synovial fluid of patients with axial SpA [59••] compared to healthy donors and RA inflammatory control patients suggesting this pathway may be more relevant in SpA than RA. This evidence concerns the gene CD4 and rheumatoid arthritis.