Peripheral blood, liver and intestine-specific lymphocytes in primary sclerosing cholangitis and inflammatory bowel disease
Keywords: inflammatory bowel disease
primary sclerosing cholangitis
ulcerative colitis
CCR9
vedolizumab
fine needle aspiration
Crohn's disease
integrin alpha4beta7

Primary sclerosing cholangitis (PSC) is an immune-mediated fibroinflammatory condition of the biliary system which often carries a poor prognosis. Despite significant research efforts, there is no known medical therapy which can slow the progression of disease. It is linked with inflammatory bowel disease (IBD) and there are some limited data which suggest a role for gut-homing lymphocytes in the pathophysiology of the disease.
I revealed via flow cytometry that patients with PSC had a reduced proportion of CCR9+ T-cells and mucosa associated innate-like T-cells (MAITs) within the peripheral blood as compared with controls. Furthermore, I was able to demonstrate an immunological difference within the ileum of patients with PSC/IBD as compared with IBD alone; namely that there is a reduced proportion of CCR9+ T-cells in the PSC ileum, lending evidence to the notion that the IBD in PSC is its own immunologically distinct disease.
Utilising the technique of fine needle aspiration (FNA) of the liver, I found there was no difference in the proportion of gut-homing T-cells (i.e. CCR9+ or β7+) within the livers of patients with PSC compared with liver controls (LC). However, a subset of patients in both PSC and LC cohorts had a relative abundance of hepatic CCR9+ T-cells, though no correlation could be found with fibrosis or inflammatory measures. Patients with PSC, however, had higher hepatic proportions of MAITs and CD69+ CD8+ memory T-cells compared with LC, indicating a potential role in the pathophysiology of the disease. I was able to demonstrate that FNA liver could successfully be used for single cell RNAseq.
Vedolizumab (VDZ) is a monoclonal antibody which targets α4β7 on T-cells, thereby theoretically preventing migration of lymphocytes to the gut. It is a licensed therapy in IBD but its use in PSC has not been established. I was able to demonstrate for the first time in humans that VDZ does indeed reduce the proportion of 􏰀7+ T-cells within the colon, establishing proof of concept. Furthermore, CCR9+/􏰀7+ CD4+ T-cells rise within the peripheral blood with VDZ indicating their being prevented from leaving the circulation.
There was a heterogenous clinical hepatic response to VDZ among 102 patients with PSC/IBD, as evaluated by change in alkaline phosphatase (ALP). Around 20% of patients with PSC/IBD has a clinically significant drop in ALP of >20% from baseline. However, overall, the ALP rose with VDZ by a small amount. The IBD in PSC responded to a similar beneficial degree as in IBD alone, supporting its use for active IBD in PSC.
A subset of patients with PSC had a significant rise in their ALP with VDZ and were investigated with liver biopsy, which revealed an increased proportion of T-cells which were CCR9+ compared with patients not on VDZ. These data suggest that in some patients with PSC, VDZ may cause a redistribution of gut-homing T-cells from the gut and peripheral blood to the liver, which has not been apparent among patients with IBD alone, though further investigation is warranted.
Overall, this thesis provides a comprehensive analysis of peripheral blood, intestinal and hepatic lymphocytes in PSC compared with controls, as well as evaluating the effects of VDZ in these settings at a clinical and cellular level.