P0506 AZD7798, a monoclonal antibody depleting CCR9+ T cells, with the potential to target hard-to-treat small bowel Crohn’s disease

Abstract Background Crohn’s disease (CD) can affect any part of the gastrointestinal tract, but about 30% of patients have inflammation restricted to the ileum. In clinical trials, patients are typically enrolled irrespective of the disease localisation, with clinical outcomes focusing on a broad patient population. Anecdotally, small bowel healing in CD is often reported as challenging. Our aims were to investigate the unmet need in treating ileal CD and explore potential drug targets for this patient subpopulation. Methods A systematic review and meta-analysis was conducted of efficacy by disease location (Montreal classification L1 + L2) in placebo-controlled clinical trials in CD. As this revealed markedly different outcomes in ileal compared to colonic CD, transcriptomic data from 1185 small and large intestine biopsies of 594 CD patients were explored to identify potential small bowel specific drug targets, from which the chemokine receptor CCR9 emerged as high interest. AZD7798, a monoclonal antibody designed to deplete CCR9+ T cells, was evaluated in a randomized, placebo-controlled, double-blind first-in-human healthy volunteer study (NCT05452304), and in small bowel Crohn’s patients in a PET imaging study (NCT06053424). Results In the meta-analysis, marked differences were observed in efficacy of existing CD treatments in small compared to large bowel disease (Fig.1). Outcomes across mechanisms of action were not significantly different from placebo in small bowel CD (OR 1. 07, 95% CI 0.64-1.78, p=0.79) yet were superior in colonic CD (OR 3.86, 95% CI 2.75-5.42, p<0.001). Next, transcriptomic analyses identified CCR9 and its ligand CCL25 as highly and selectively expressed in terminal ileum compared to large bowel. Subsequently AZD7798, a CCR9+ T cell depleting antibody, was evaluated in 106 healthy participants in a first-in-human study, and in 6 CD patients in a Phase 1b study. There were no SAEs or treatment discontinuations, and rapid and sustained depletion of CCR9+ T cells in blood was observed in both studies. Moreover, AZD7798 reduced target cells in small bowel in CD patients as detected using a novel CCR9 tracer (Fig.2). Conclusion Ileal CD represents a high unmet need patient subpopulation, where existing treatments appear less effective than for colonic disease. CCR9 is identified as an attractive target for small bowel-dominant inflammation. AZD7798, a first-in-class CCR9+ T cell depleting antibody, demonstrated acceptable safety and tolerability alongside sustained CCR9+ T cell reductions in blood and small intestine.