P009 Integrin-b7+ cytotoxic MAIT cells are expanded in the colon of Ulcerative Colitis patients, correlate with disease severity and are targeted by vedolizumab therapy

Abstract

Abstract Background Mucosal-associated invariant T (MAIT) cells are major histocompatibility complex (MHC) class Ib-restricted innate-like lymphocytes with anti-bacterial functions that are enriched at mucosal sites. Their role in ulcerative colitis (UC) is unknown. Methods Colonic biopsies and peripheral blood were collected from patients with active UC (n=34) and healthy control subjects (n=14). Peripheral blood mononuclear cells (PBMC) and Lamina propria mononuclear cells (LPMC) were isolated and activated in vitro with PMA/ionomycin followed by surface and intracellular staining and multiparametric flow cytometry analysis. T cell populations, including gamma delta T cells (TCR gamma delta+), iNKT cells (TCR Vα24-Jα18+), MAIT cells (TCR Vα7.2+ CD161+), CD4, CD8 T cells and their intracellular expression of IL17A, TNF, IFN-g, IL22, IL13 and granzyme B (GZMB) were determined. MAIT cells were further characterised as CD8+, CD4+, CD8 CD4 double positive (DP), CD8 CD4 double negative (DN) cells and expression of the gut homing integrin-b7. Results DN cells were the most common MAIT subset in the colon and were significantly increased in both UC patients and HC subjects compared to peripheral blood. In UC, DN MAIT cells exhibited a cytotoxic phenotype, with significantly higher production of Granzyme B (median 45.0% of cells) compared to DN MAIT cells in HC (median 17%, P<0.005). DN MAIT cells in UC gut also co-produced significantly higher proportion of IL17A (median 22% in UC vs 7% in HC, P<0.006) and TNF (median 61% in UC vs 10% in HC, P<0.02) compared to DN MAIT cells from HC. In UC patients, the proportional abundance of cytotoxic DN MAIT cells accumulating in the colon significantly correlated with disease activity (UCEIS) score (r2=0.34, P<0.0007). The number of DN MAIT cells expressing integrin-b7 was also significantly higher in UC patients compared to HC (median 66% in UC vs 32% in HC, p<0.001). In UC patients initiated on vedolizumab therapy, the proportional abundance of cytotoxic, DN MAIT cells accumulating in the colon significantly fell at week 14 in comparison with their pre-treatment abundance (median 25% vs 51%, P<0.001). Following vedolizumab induction, the reduction in the abundance of colonic cytotoxic DN MAIT cells correlated with endoscopic improvement (r2=0.45, p=0.0085). Conclusion DN MAIT cells with cytolytic activity and augmented expression of multiple cytokines are enriched in the colon of UC patients in numbers that correlate with the magnitude of mucosal injury. Vedolizumab treatment reduces DN MAIT cell accumulation in the colon and the magnitude of reduction correlates with treatment response.