In the gut of patients with Crohn's disease (CD), one of the major forms of inflammatory bowel diseases in humans, distinct subsets of T helper (Th) cells produce large amounts of cytokines, which are supposed to orchestrate the immuno-inflammatory process leading to the tissue damage. Indeed, cytokine blockers, including the three licensed anti-TNF-alpha and the neutralizing IL-12/p40 antibodies, have already been tested with success in CD. More than one third of patients do not respond to these treatments and response can wane with time. Moreover, blockade of such cytokines has been reported to associate with development of severe side effects and/or new immune-mediated pathologies. These findings and our better understanding of cytokine-associated effector pathways of tissue destruction suggest the necessity of novel cytokine-based therapies in CD.