Background

CEA-specific T cell responses identify colorectal cancer (CRC) patients exhibiting poor survival post-surgery (1). This is surprising, since CEA-specific T cells are capable of targeting and killing cancer cells. It has been suggested invasion of a leaky epithelium by microbial products triggers epithelial proliferation and drives tumour growth (2). We hypothesized that CEA-responsive patients exhibit damaged intestinal epithelia, thus facilitating tumour growth via the generation of a permissive inflammatory environment.

Methods

An Ussing chamber was used to objectively measure gut permeability of murine models of intestinal inflammation and CRC (DSS treated, FoxP3 DTR and APC KO), and human colonic specimens obtained from patients undergoing endoscopy. Permeability is assessed by electrophysiological measurements using a four Ag/AgCl electrode current clamp method and by diffusion of fluorescently labelled molecules.

Results

Colonic samples show segmental variation in permeability, with higher transepithelial resistance (TER) in the proximal and ascending sections of the murine and human colon respectively, compared to mid and sigmoidal areas. Treatment of mice with 3% DSS showed increased 4-kDa FITC-dextran flux and reduction of TER values (P= 0.0001). Autoimmune induced intestinal inflammation through depletion of FoxP3⁺ regulatory T cells also induced intestinal barrier dysfunction with a 9-fold increase in 4-kDa FITC-dextran passage at the mid-section of the colon, accompanied by a reduction in TER. Furthermore, in a mouse model of CRC, increased flux of 4-kDa FITC-dextran was detected within seven days after depletion of the tumour suppressor gene APC.

Conclusion

The Ussing chamber system is a valuable tool for assessing intestinal permeability, providing a reliable output. We show for the first time that depletion of regulatory T cells causes barrier dysfunction and that permeability changes can be detected at very early stages in a mouse model of CRC. On-going human work will investigate intestinal permeability within CEA-responsive and non-responsive CRC patients.