Aminosalicylates, thiopurines, and steroids were routinely used as treatments for inflammatory bowel disease before the introduction of biological agents in the late 1990s. The first biologics consisted of antibodies targeting tumour necrosis factor-α (TNF-α), such as infliximab, adalimumab, golimumab, and certolizumab pegol. In the following years, Vedolizumab (antibody against α4β7 integrin) and ustekinumab (anti-IL12/23 IgG1 kappa human monoclonal antibody) were put into routine use whereas natalizumab (antibody against the α4β1 and α4β7 integrins) was abandoned due to its fatal side effect, multifocal leukoencephalopathy (PML). Tofacitinib (an orally administered small molecule that mainly inhibits JAK1 and JAK 3) is a small molecule and was approved for the treatment of moderate to severe UC patients by the U.S. FDA in June 2018.

Currently, there are also novel drugs on their way to the market that are under late-phase trials. Anti-integrin molecule etrolizumab (anti-integrin, β7subunit) has additional inhibitory effects on the αEβ7-mediated retention of lymphocytes in the gut epithelium. SHP-647 is an anti-MAdCAM IgG2 antibody directed against the gut-specific endothelial adhesion molecule. Risankizumab, brazikumab, mirikizumab, and guselkumab are anti-cytokine molecules binding to IL-23. Briakinumab is a human monoclonal antibody against IL-12 and IL-23. There are also small molecules as novel drugs with similar pathways as the ones on the market such as Filgotinib, upadacitinib (JAK1 inhibitor). Mongersen (SMAD7 antisense oligonucleotide) is a novel oral drug containing the specific SMAD7 antisense oligonucleotide. Apremilast (PDE4 inhibitor) inhibits the breakdown cyclic adenosine monophosphate (cAMP). Anti-trafficking molecules are ozanimod and etrasimod which are Sphingosine 1P receptor modulators. Combination treatments with various agents using different pathways, faecal transplantation and stem cell transplantation are other treatment options in IBD. In spite of many therapeutic alternatives, the nature of the disease can be changed just in a subgroup of patients and several problems are still unsolved and new therapies are urgently needed. Understanding of the involved cytokines, the pathways, genetics, microbiota factors, and the microbiome pave the way to a better treatment with lesser side effects and mucosal and even histological healing.

In this Special Issue, new treatment options and novel molecules will be discussed in the target of tailored treatment of IBD and prevention of progression and even onset of the disease. Original research and review articles are welcome.

Potential topics include but are not limited to the following:

• Faecal transplantation in inflammatory bowel disease
• Janus Kinase inhibitors in inflammatory bowel disease
• Anti-trafficking treatments in inflammatory bowel disease
• Combination treatment for reduced immunogenicity in inflammatory bowel disease
• Combination treatment for synergic interactions in inflammatory bowel disease
• Early surgery treatment for inflammatory bowel disease
• Stem cell treatment for inflammatory bowel disease
• Treatment alternatives against cytokines in inflammatory bowel disease
• Current and potential applications of anti-TNF agents for inflammatory bowel disease treatment
• Novel small molecules used in inflammatory bowel disease treatments
• Diet treatment for inflammatory bowel disease in adults