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OP32 A novel mechanism of colonic epithelial-T-cell cross-talk is dysregulated in IBD

R. J. Dart*1,2,3, P. Vantourout1,2, P. M. Irving3, A. Hayday1,2

1King’s College London, Peter Gorer Department of Immunobiology, London, UK, 2Francis Crick Institute, Immunosurveillance Lab, London, UK, 3Guy’s and St Thomas Hospital, Department of Gastroenterology, London, UK

Background

Epithelial dysfunction is an early initiating factor of inflammatory bowel disease (IBD), yet the immunological consequences of this remain enigmatic. Juxtaposed to epithelial cells are specialised intraepithelial γδ T cells, implicated in maintaining tissue integrity. We have shown that specific members of the Butyrophilin-like (BTNL) protein family are restricted to intestine epithelial cells and are profound γδ T-cell regulators. Thus, Btnl1−/− mice show selective depletion of a signature intestinal γδ subset.1 This axis is conserved in humans, where signature colon-resident, Vγ4+ γδ T cells are selectively regulated by direct interactions between their TCRs and a BTNL3/8 heteromer.2 Here we investigated whether such selective regulation of human colonic γδ cells by BTNL3 + 8 is perturbed in IBD and have examined factors which may modulate this.

Methods

We used a short-term whole gut explant culture to isolate γδ T cells from colonic biopsies obtained at endoscopy from healthy donors, facilitating flow-cytometric phenotyping and functional studies.

Results

In most non-IBD controls, co-culture of colonic lymphocytes with HEK293T cells co-transduced with BTNL3 + 8 resulted in profound TCR down-regulation in T cells reactive to an antibody specific for Vγ2/3/4 chains. In non-IBD controls, expression of αΕβ7, a marker of epithelial residence, by Vγ2/3/4+ cells, was associated with TCR down-regulation responses to BTNL3 + 8, whereas Vγ2/3/4+αΕβ7 cells, which were generally the minority, had markedly attenuated or absent assay responses. In many patients with IBD, we found significantly reduced αΕβ7 expression by Vγ2/3/4+ cells, and a severe attenuation or loss of BTNL-dependent Vγ2/3/4 TCR down-regulation. Phenocopying the situation in disease; addition to the organ culture of pro-inflammatory cytokines IL-12 and IL-18 (but not IL-1β and IL-23) lead to down regulation of αΕβ7 on γδ T cells and a consequent attenuation of response to BTNLs. This clearly implicates specific cytokines in the disruption of the functional γδ-BTNL axis evident in disease. Further characterisation of αΕβ7 γδ T cells demonstrated an activated pro-inflammatory phenotype in comparison to quiescent αΕβ7+ γδ T cells.

Conclusion

We describe a novel and important axis by which epithelial cells maintain homeostasis of the γδ T cell compartment, and which is frequently dysregulated in IBD. Our data may support the use of IL-12 blockade in restoring this axis whilst IL-23 may be redundant in this setting, with implications for future therapeutic strategies. Furthermore, therapeutic blockade of αΕβ7 has the potential to disrupt an important axis in the human colon, which may exacerbate disease given the precociously active, pro-inflammatory nature of αΕβ7 γδ T cells.

References

1. Di Marco Barros R, Roberts NA, Dart RJ, et al. Epithelia use butyrophilin-like molecules to shape organ-specific gammadelta T cell compartments. Cell 2016;167:203–18.

2. Melandri D, Zlatareva I, Chaleil RAG, et al. The γδTCR combines innate immunity with adaptive immunity by utilizing spatially distinct regions for agonist selection and antigen responsiveness. Nat Immunol 2018;19:1352–65.