CyTOF and microbiota analysis on Crohn*s disease-associated and idiopathic perianal fistulas

Perianal fistulas are a common clinical problem in patients with Crohn*s
disease. The cumulative incidence of perianal fistulas is estimated at 23-26%
after 20 years of CD 1, 2. Even with the best available medical treatment for
this condition, the chance of complete healing for an extended period of time
is less than 50% and the enduring remission rates of complex perianal fistulas
remains low at 37.0%. Also patients without Crohn*s disease can develop
fistulas without any known underlying cause. These patient groups are treated
differently. Patients with Crohn*s disease will receive preferably anti-TNF
therapy together with local surgery, while patients without Crohn*s disease
will only receive local surgical treatment.
The current understanding of the pathophysiology of CD-associated perianal
fistulas, though not complete, seems to involve at least two mechanisms. First
the immune cells with the epithelial-to-mesenchymal transition (EMT) and matrix
remodelling enzymes.In addition the matrix metalloproteinases (MMPs), which are
enzymes that can degrade all components of the extracellular matrix (ECM).
Furthermore, our unpublished data on cytokine profiles in perianal fistulas
showed high amounts of several inflammatory cytokines inside the fistulas.The
second aspect of the pathophysiology involves the microbiota. The innate immune
system recognizes general microbe-associated molecular patterns. The adaptive
immune system is also programmed by commensal microbiota and microbes have been
shown to impact the differentiation of T cell populations. Commensal bacteria
are also capable of modulating the host innate immune system to promote their
own fitness in the intestinal niche. So it is not surprising that our immune
system, and especially the mucosal immune system, has developed an intricate
connection with our associated microbiota.
Fibroblasts, which are abdundantly present in fistulas, were recently reported
to regulate Th1 cell activity in inflammatory bowel diseases (IBD) and specific
fibroblasts subsets were identified and associated with IBD. However, studies
about their role in the pathogenesis of CD-associated fistulas are lacking. In
this study we would like to compare the immune subsets, microbiota and
fibroblasts in perianal fistulas of patients with Crohn*s disease and without
Crohn*s disease. CyTOF analysis will be used to compare the subsets of immune
cells in great detail.

To determine the differences in immune cell populations, microbiota and
fibroblasts between fistulas from patients with and without Crohn*s disease.

Prospective cohort study. At day of surgery extra blood will be drawn and a
feces sample will be collected from the patients. During surgery 4 biopsies
from the rectum will be taken. The fistula scraping (waste material) and a swab
of the fistula tract will also be collected.

Burden: in addition to regular care (which includes the fistula surgery);
- A feces sample will be collected before surgery.
- Venepuncture; if feasible blood will be drawn from the entrance that is
already there.
- A swab of the fistula tract will be collected.Will be taken during surgery
(under anesthesia) and will cause no extra burden.
- 4 biopsies of the rectum during surgery. Will be taken during surgery (under
anesthesia) and will cause no extra burden. However there is a small risk on
bleeding after biopsy (<0.1%).

Benefit: there will be no direct benefit for the individual patient. However
patients with perianal fistulas suffer from a disease that is very hard to
treat. This study will provide new information about the pathogenesis of
perianal fistulas and can thereby help to develop new therapies.