TNF and Crohn disease: Ustekinumab is a biologic that has been approved for the treatment of Crohn’s disease since 2016, which targets interleukin-23 and interleukin-12, which are both involved in the T-helper pathways thought to have a role in the pathogenesis of Crohn’s disease; however, similar to TNF-inhibitors, there has been a demonstrated loss of response to ustekinumab in about one-third of patients [29].