• Britt Roosenboom, Carmen S Horjus Talabur Horje, Carolijn Smids, Jan Willem Leeuwis, Elly van Koolwijk, Marcel J M Groenen, Peter J Wahab, and Ellen G van Lochem.
• Department of Gastroenterology and Hepatology, Rijnstate Crohn & Colitis Center, Rijnstate Hospital, Arnhem, The Netherlands.
• Scand. J. Gastroenterol. 2021 Jun 1; 56 (6): 671-679.

BackgroundImmunotherapy, targeting programmed death-1 (PD-1) enhances antitumor T-cell activity in patients with malignancies. Blocking PD-1 or its ligand may lead to fulminant colitis as serious adverse event in these patients. Since little is known of the presence and role of PD-1+T cells in colitis of different etiologies, we determined PD-1+T cells in mucosal specimens of patients with inflammatory bowel disease, infectious colitis (InfC), immunotherapy-related colitis (ImC) and healthy controls (HC).MethodsNewly diagnosed patients with ulcerative colitis (UC, n = 73), Crohn's disease (CD, n = 50), InfC (n = 5), ImC (n = 8) and HC (n = 8) were included. Baseline inflamed colonic biopsies were studied with immunohistochemistry and flowcytometry.ResultsUsing immunohistochemistry, PD-1 was not present on lymphocytes in the epithelium of all patients, nor in HC. The percentage PD-1+ of all lymphocytes in the lamina propria was 40% in UC, 5% in InfC, 3% in ImC and 0% in HC. Flowcytometry showed significant higher percentages of PD-1+T cells in inflamed biopsy specimens of UC patients (22%) compared to all other groups: CD patients (13%), InfC (12%), ImC (5%) and HC (6%).ConclusionThere are relevant differences in distribution and frequencies of mucosal PD-1+ T-cell subsets in patients with UC, CD, InfC and ImC, supporting the hypothesis that these types of colitis are driven by different immunological pathways. The increased numbers of PD-1+ and PD-L1+ lymphocytes in the colonic mucosa of UC patients suggest that the PD-1/PD-L1 pathway might be more activated in UC than in CD.

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