TL1A signalling linked to perianal fistulas in Crohn's disease, even on anti-TNF therapy

Design

Single-cell RNA sequencing and functional laboratory study

Population

Rectal biopsies from 31 patients with Crohn's disease, with or without perianal fistulas

Primary outcome

Cellular and transcriptomic signature of perianal fistulising disease

Effect

Fistula-specific signature via TL1A-lymphotoxin/IL-22 axis, independent of TNF

Perianal fistulas affect about one in five people with Crohn's disease. This laboratory study used single-cell RNA sequencing of rectal biopsies from 31 patients with and without perianal fistulising disease, and functional experiments in cells and tissue.

The rectal mucosa of patients with fistulas carried a distinct signature independent of luminal inflammation, with more fibroblasts and matrix-degrading enzymes. The authors trace it to TL1A activation in CD4 T cells, acting through lymphotoxin and interleukin-22, a pathway that stays active under anti-TNF therapy.

This is mechanistic work. It may help explain why some fistulas persist despite anti-TNF treatment, and it supports trials of TL1A inhibitors, which are in development, for this complication.

• Recognise that perianal disease can progress even when luminal inflammation is controlled.
• Manage fistulas jointly with a colorectal surgeon, with MRI to define anatomy.
• Consider clinical trial referral for fistulas refractory to anti-TNF therapy.
• Treat this as research-stage; it does not change current treatment.

Why it matters

It offers a biological reason why some fistulas do not heal on anti-TNF drugs, and a target to test.

Don't overread it

Laboratory findings in 31 patients; no treatment effect has been tested.

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