Histopathological predictor of response to mirikizumab in active ulcerative colitis.

This case series reports three patients with active ulcerative colitis (UC) successfully treated with mirikizumab, a selective IL-23p19 monoclonal antibody. Mirikizumab was initiated based on both clinical presentation and a histopathological marker-high neutrophilic infiltration of the colonic epithelium classified as Geboes Grade 3.2-which reflects an IL-23/Th17-driven inflammatory phenotype. The cases included: an elderly man with acute severe pancolitis and primary nonresponse to infliximab; a middle-aged woman with steroid-dependent left-sided UC and inadequate response to adalimumab and ustekinumab; and a young biologic-naïve woman with steroid-refractory UC and bowel urgency. All three patients demonstrated high epithelial neutrophilic infiltration (Geboes Grade 3.2). These cases demonstrate the potential utility of histology-guided biologic selection and support Geboes Grade 3.2 as a candidate predictive biomarker for IL-23 inhibitor response in UC.