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Background & Aims: γδ T cells comprise a substantial proportion of tissue-associated lymphocytes. However, our current understanding of human γδ T cells is primarily based on peripheral blood subsets, while the immunobiology of tissue-associated subsets remains largely unclear. Therefore, we aimed to elucidate the T cell receptor (TCR) diversity, immunophenotype and function of γδ T cells in the human liver., Methods: We characterised the TCR repertoire, immunophenotype and function of human liver infiltrating γδ T cells, by TCR sequencing analysis, flow cytometry, in situ hybridisation and immunohistochemistry. We focussed on the predominant tissue-associated Vδ2 - γδ subset, which is implicated in liver immunopathology., Results: Intrahepatic Vδ2 - γδ T cells were highly clonally focussed, with single expanded clonotypes featuring complex, private TCR rearrangements frequently dominating the compartment. Such T cells were predominantly CD27 lo/- effector lymphocytes, whereas naïve CD27 hi , TCR-diverse populations present in matched blood were generally absent in the liver. Furthermore, while a CD45RA hi Vδ2 - γδ effector subset present in both liver and peripheral blood contained overlapping TCR clonotypes, the liver Vδ2 - γδ T cell pool also included a phenotypically distinct CD45RA lo effector compartment that was enriched for expression of the tissue tropism marker CD69, the hepatic homing chemokine receptors CXCR3 and CXCR6, and liver-restricted TCR clonotypes, suggestive of intrahepatic tissue residency. Liver infiltrating Vδ2 - γδ cells were capable of polyfunctional cytokine secretion, and unlike peripheral blood subsets, were responsive to both TCR and innate stimuli., Conclusion: These findings suggest that the ability of Vδ2 - γδ T cells to undergo clonotypic expansion and differentiation is crucial in permitting access to solid tissues, such as the liver, which results in functionally distinct peripheral and liver-resident memory γδ T cell subsets. They also highlight the inherent functional plasticity within the Vδ2 - γδ T cell compartment and provide information that could be used for the design of cellular therapies that suppress liver inflammation or combat liver cancer., Lay Summary: γδ T cells are frequently enriched in many solid tissues, however the immunobiology of such tissue-associated subsets in humans has remained unclear. We show that intrahepatic γδ T cells are enriched for clonally expanded effector T cells, whereas naïve γδ T cells are largely excluded. Moreover, whereas a distinct proportion of circulating T cell clonotypes was present in both the liver tissue and peripheral blood, a functionally and clonotypically distinct population of liver-resident γδ T cells was also evident. Our findings suggest that factors triggering γδ T cell clonal selection and differentiation, such as infection, can drive enrichment of γδ T cells into liver tissue, allowing the development of functionally distinct tissue-restricted memory populations specialised in local hepatic immunosurveillance., (Copyright © 2018 European Association for the Study of the Liver. Published by Elsevier B.V. All rights reserved.)

Vδ2 + T cells form the predominant human γδ T-cell population in peripheral blood and mediate T-cell receptor (TCR)-dependent anti-microbial and anti-tumour immunity. Here we show that the Vδ2 + compartment comprises both innate-like and adaptive subsets. Vγ9 + Vδ2 + T cells display semi-invariant TCR repertoires, featuring public Vγ9 TCR sequences equivalent in cord and adult blood. By contrast, we also identify a separate, Vγ9 - Vδ2 + T-cell subset that typically has a CD27 hi CCR7 + CD28 + IL-7Rα + naive-like phenotype and a diverse TCR repertoire, however in response to viral infection, undergoes clonal expansion and differentiation to a CD27 lo CD45RA + CX 3 CR1 + granzymeA/B + effector phenotype. Consistent with a function in solid tissue immunosurveillance, we detect human intrahepatic Vγ9 - Vδ2 + T cells featuring dominant clonal expansions and an effector phenotype. These findings redefine human γδ T-cell subsets by delineating the Vδ2 + T-cell compartment into innate-like (Vγ9 + ) and adaptive (Vγ9 - ) subsets, which have distinct functions in microbial immunosurveillance.

Background & Aims: Mucosal-Associated Invariant T (MAIT) cells are innate-like T cells characterised by the invariant TCR-chain, Vα7.2-Jα33, and are restricted by MR1, which presents bacterial vitamin B metabolites. They are important for antibacterial immunity at mucosal sites; however, detailed characteristics of liver-infiltrating MAIT (LI-MAIT) and their role in biliary immune surveillance remain unexplored., Methods: The phenotype and intrahepatic localisation of human LI-MAIT cells was examined in diseased and normal livers. MAIT cell activation in response to E. coli-exposed macrophages, biliary epithelial cells (BEC) and liver B cells was assessed with/without anti-MR1., Results: Intrahepatic MAIT cells predominantly localised to bile ducts in the portal tracts. Consistent with this distribution, they expressed biliary tropic chemokine receptors CCR6, CXCR6, and integrin αEβ7. LI-MAIT cells were also present in the hepatic sinusoids and possessed tissue-homing chemokine receptor CXCR3 and integrins LFA-1 and VLA-4, suggesting their recruitment via hepatic sinusoids. LI-MAIT cells were enriched in the parenchyma of acute liver failure livers compared to chronic diseased livers. LI-MAIT cells had an activated, effector memory phenotype, expressed α4β7 and receptors for IL-12, IL-18, and IL-23. Importantly, in response to E. coli-exposed macrophages, liver B cells and BEC, MAIT cells upregulated IFN-γ and CD40 Ligand and degranulated in an MR1-dependent, cytokine-independent manner. In addition, diseased liver MAIT cells expressed T-bet and RORγt and the cytokines IFN-γ, TNF-α, and IL-17., Conclusions: Our findings provide the first evidence of an immune surveillance effector response for MAIT cells towards BEC in human liver; thus they could be manipulated for treatment of biliary disease in the future., (Copyright © 2016 European Association for the Study of the Liver. Published by Elsevier B.V. All rights reserved.)