P095 PD-1 expressing T cells in patients with different types of colitis
Abstract Background Immunotherapy-related colitis is a frequent adverse event in patients with malignancies, treated with inhibitors targeting programmed death-1 (PD-1). This treatment leads to enhancement of lymphocyte activity, thereby generating antitumor T-cell activity. The role of PD-1+ T cells in the pathophysiology of different types of colitis is unclear. Therefore, we aimed to study the presence of PD-1+ T cells in inflammatory bowel disease (IBD), infectious colitis and healthy controls compared with anti-PD-1-related colitis. Methods We performed a prospective cohort study. Newly diagnosed patients with ulcerative colitis (UC, n = 51), Crohn’s disease (CD, n = 29), infectious colitis (n = 4), anti-PD-1-related colitis (n = 5) and healthy controls (n = 6) were included. Baseline colonic biopsy specimens were collected for immunohistochemistry identifying PD-1+ and PD-L1+ lymphocytes in the epithelium and lamina propria separately and for immunophenotyping by flow cytometry identifying PD-1+ T-cell subsets. Results Using immunohistochemistry, PD-1 was not present on lymphocytes in the epithelium of patients with any type of colitis, nor in healthy controls. Of all lymphocytes in the lamina propria, % PD-1 expression was 40% in UC, 5% in infectious colitis, 3% in anti-PD-1-related colitis and 0% in healthy controls. PD-L1 was expressed on lymphocytes in the epithelium and lamina propria of UC patients (12.5% and 40%) and in infectious colitis (1% and 30%), whereas in anti-PD-1-related colitis (0% and 15%) and healthy controls (0% and 15%) no PD-L1+ lymphocytes were demonstrated in the epithelium. Flowcytometry showed higher percentages of PD-1+ T cells in biopsy specimens of UC patients (25.2% (IQR 17.9–35.6)) compared with all other groups; CD patients (13.5% (5.0–25.3), p = 0.001), infectious colitis (9.8% (4.7–17.4), p = 0.005), anti-PD-1-related colitis (1.5% (1.1–2.1), p = 0.001) and healthy controls (14.3% (4.9–28.2), p = 0.08). In IBD and infectious colitis, the majority of PD-1+ T cells were CD4+ (84.8% (76.5–90.5), while in anti-PD-1-related colitis the majority of PD-1+ T cells were CD8+ (76.2% (68.5–82.1)). PD-1+ T cells in all patient groups were mainly effector T cells (CD45Ro+). Conclusion In patients with different types of colitis and in healthy controls, PD-1 was only expressed on T cells in the lamina propria and not in the epithelium. The percentage of PD-1+ T cells was significantly higher in patients with UC compared with patients with CD or infectious colitis and healthy controls. As expected PD-1+ T cells were nearly absent in patients with anti-PD-1-related colitis.