DOP02 αEβ7 positive γδ T cells are associated with mucosal healing in Ulcerative Colitis and have a homeostatic immunophenotype
Dart, R.(1,2);Zlatareva, I.(1,2);Irving, P.(1,3);Hayday, A.(1,2)
(1)King's College London, Peter Gorer Department of Immunobiology, London, United Kingdom;(2)Francis Crick Institute, Immunosurveillance Lab, London, United Kingdom;(3)Guy's and St Thomas Hospital, Department of Gastroenterology, London, United Kingdom
Background
α4β7 blockade is a well-established therapy in ulcerative colitis (UC), acting in part by preventing lymphocyte ingress into the mucosa. The β7 unit of the α4β7 heterodimer is shared by αΕβ7, which is expressed on both tissue resident memory cells and γδ intra-epithelial lymphocytes (IEL). It was hypothesised that targeting both α4- and αΕβ7 might be more efficacious; however mixed results from phase III studies of β7 blockade asks questions of the biological relevance of different αEβ7 expressing cells.
Methods
Colonic biopsies were obtained during endoscopy from >40 subjects. Lymphocytes were isolated using short term culture or digested from whole tissue. RNA sequencing was performed on αΕβ7pos and αΕβ7neg colonic γδ T cells from 4 donors and findings were validated by flow cytometry.
Results
αΕβ7 is widely expressed on TCRαβ CD8 cells and γδ IEL in both non-IBD controls and the uninflamed mucosa in UC, but its expression is significantly reduced on analogous subsets harvested from inflamed UC. On further study, the capacity of TCRαβ CD8 T cells to make TNFα and IFNγ on stimulation is similar between αΕβ7pos and αΕβ7neg cells, whereas in the γδ T cell compartment αΕβ7neg cells produce significantly more pro-inflammatory cytokine than their homeostatic αΕβ7pos counterparts. To examine the cells’ biology further, γδ T cells were isolated according to their αΕβ7 status and RNAseq undertaken. This revealed a distinct signature with αΕβ7neg cells demonstrating an activated phenotype high in markers such as CD18, CD5 and lymphoid homing receptor CCR7 whereas αΕβ7pos cells demonstrate a homeostatic tissue-resident phenotype, expressing immune checkpoints TIGIT and CD101 and gut-homing marker CCR9. On culturing tissue from non-IBD controls in pro-inflammatory cytokines, IL-12 and IL-18, the γδ T cell compartment down-regulated αΕβ7 and TIGIT and upregulated CD18, in part recapitulating a disease phenotype. On examining previously affected mucosa of patients who have achieved mucosal healing, αEβ7 expression of the γδ T cells returned to a profile resembling non-IBD controls whereas the expression levels in the inflamed mucosa remained predictably low.
Conclusion
This study demonstrates that αΕβ7 expression is low in active UC but restored in mucosal healing. αΕβ7neg cells are proinflammatory with a distinct phenotype which may in part be recapitulated by inflammatory cytokines in vitro; whereas αΕβ7pos cells demonstrate a homeostatic phenotype, which may both reflect and maintain steady state barrier integrity. Hence in terms of γδ T cells, pharmacological β7 blockade has potential to interfere with the homeostatic roles of αΕβ7 expressing cells while having little effect on a potentially pathogenic subset of tissue αΕβ7neg γδ cells.