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The presence of CD8 + T cells in the cytoplasm of biliary epithelial cells (BEC) has been correlated with biliary damage associated with primary biliary cholangitis (PBC). Here, we characterise the mechanism of CD8 + T cell invasion into BEC. CD8 + T cells observed within BEC were large, eccentric, and expressed E-cadherin, CD103 and CD69. They were also not contained within secondary vesicles. Internalisation required cytoskeletal rearrangements which facilitated contact with BEC. Internalised CD8 + T cells were observed in both non-cirrhotic and cirrhotic diseased liver tissues but enriched in PBC patients, both during active disease and at the time of transplantation. E-cadherin expression by CD8 + T cells correlated with frequency of internalisation of these cells into BEC. E-cadherin + CD8 + T cells formed β-catenin-associated interactions with BEC, were larger than E-cadherin - CD8 + T cells and invaded into BEC more frequently. Overall, we unveil a distinct cell-in-cell structure process in the liver detailing the invasion of E-cadherin + CD103 + CD69 + CD8 + T cells into BEC., (© 2024. The Author(s).)

Objective: Tissue-resident memory T cells (T RM ) are vital immune sentinels that provide protective immunity. While hepatic CD8 + T RM have been well described, little is known about the location, phenotype and function of CD4 + T RM ., Design: We used multiparametric flow cytometry, histological assessment and novel human tissue coculture systems to interrogate the ex vivo phenotype, function and generation of the intrahepatic CD4 + T-cell compartment. We also used leukocytes isolated from human leukocyte antigen (HLA)-disparate liver allografts to assess long-term retention., Results: Hepatic CD4 + T cells were delineated into three distinct populations based on CD69 expression: CD69 - , CD69 INT and CD69 HI . CD69 HI CD4 + cells were identified as tissue-resident CD4 + T cells on the basis of their exclusion from the circulation, phenotypical profile (CXCR6 + CD49a + S1PR1 - PD-1 + ) and long-term persistence within the pool of donor-derived leukcoocytes in HLA-disparate liver allografts. CD69 HI CD4 + T cells produced robust type 1 polyfunctional cytokine responses on stimulation. Conversely, CD69 INT CD4 + T cells represented a more heterogenous population containing cells with a more activated phenotype, a distinct chemokine receptor profile (CX 3 CR1 + CXCR3 + CXCR1 + ) and a bias towards interleukin-4 production. While CD69 INT CD4 + T cells could be found in the circulation and lymph nodes, these cells also formed part of the long-term resident pool, persisting in HLA-mismatched allografts. Notably, frequencies of CD69 INT CD4 + T cells correlated with necroinflammatory scores in chronic hepatitis B infection. Finally, we demonstrated that interaction with hepatic epithelia was sufficient to generate CD69 INT CD4 + T cells, while additional signals from the liver microenvironment were required to generate liver-resident CD69 HI CD4 + T cells., Conclusions: High and intermediate CD69 expressions mark human hepatic CD4 + T RM and a novel functionally distinct recirculating population, respectively, both shaped by the liver microenvironment to achieve diverse immunosurveillance., Competing Interests: Competing interests: BW collaborated with and received funding from Bioniz. LJP sat on advisory boards/provided consultancy for Gilead Sciences and SQZ Biotech. KA was funded by a studentship with Dr Falk. MKM received research funding from Gilead Sciences, Hoffmann La Roche and Immunocore. MKM sat on advisory boards/provided consultancy for Gilead, Hoffmann La Roche, Immunocore, VIR, Galapagos NV, GSK, Abbvie and Freeline. ZS collaborated with Bioniz and AstraZeneca and consulted for Boehringer Ingelheim. All other authors declare no conflict of interest., (© Author(s) (or their employer(s)) 2022. Re-use permitted under CC BY. Published by BMJ.)