Competing interests: Dr NH reports personal fees from Celgene, Inc, personal fees from Abbvie, Inc, outside the submitted work; Dr BS reports personal fees from AbbVie, personal fees from Amgen, personal fees from Bristol-Myers Squibb, grants, personal fees and non-financial support from Celgene, personal fees and non-financial support from Janssen, personal fees and non-financial support from MedImmune, grants, personal fees and non-financial support from Takeda, personal fees from Akros Pharma, personal fees from Arena Pharmaceuticals, personal fees from Boehringer-Ingelheim, personal fees from Forward Pharma, personal fees from Immune Pharmaceuticals, personal fees and non-financial support from Lilly, personal fees from Shire, personal fees from Synergy Pharmaceuticals, personal fees from Theravance Biopharma R&D, personal fees from TiGenix, personal fees from TopiVert Pharma, personal fees from Receptos, personal fees from Allergan, personal fees from EnGene, personal fees from Target PharmaSolutions, personal fees from Lycera, personal fees from Lyndra, personal fees from Ironwood Pharmaceuticals, personal fees from Salix, personal fees from Vivelix Pharmaceuticals, personal fees from UCB, personal fees from Oppilan Pharmaceuticals, personal fees from Gilead, personal fees from Rheos Medicines, personal fees from Seres Therapeutics, personal fees from 4D Pharma, personal fees from Capella Bioscience, personal fees from Otsuka, personal fees from Ferring, personal fees from Protagonist Therapeutics, personal fees from Palatin Technologies, grants, personal fees and non-financial support from Pfizer, outside the submitted work. Dr JC reports grants and other from AbbVie, other from Amgen, other from Boehringer-Ingelheim, other from Arena Pharmaceuticals, other from Celgene Corporation, other from Celltrion, other from Enterome, other from Eli Lilly, other from Ferring Pharmaceuticals, other from Genentech, grants and other from Janssen and Janssen, other from Medimmune, other from Merck & Co, other from Nextbiotix, other from Novartis Pharmaceuticals Corporation, other from Otsuka Pharmaceutical Development & Commercialization, Inc, other from Pfizer, other from Protagonist, other from Second Genome, other from Gilead, other from Seres Therapeutics, other from Shire, grants and other from Takeda, other from Theradiag, other from Intestinal Biotech Development, other from Genfit, other from Zealand Pharma, outside the submitted work.