The Human Liver Microenvironment Shapes the Homing and Function of CD4 T-cell Populations

Objective: Tissue-resident memory T cells (T) are vital immune sentinels that provide protective immunity. While hepatic CD8 T have been well described, little is known about the location, phenotype and function of CD4 T.

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 and CD69. CD69CD4 cells were identified as tissue-resident CD4 T cells on the basis of their exclusion from the circulation, phenotypical profile (CXCR6CD49aS1PR1PD-1) and long-term persistence within the pool of donor-derived leukcoocytes in HLA-disparate liver allografts. CD69CD4 T cells produced robust type 1 polyfunctional cytokine responses on stimulation. Conversely, CD69CD4 T cells represented a more heterogenous population containing cells with a more activated phenotype, a distinct chemokine receptor profile (CXCR1CXCR3CXCR1) and a bias towards interleukin-4 production. While CD69CD4 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 CD69CD4 T cells correlated with necroinflammatory scores in chronic hepatitis B infection. Finally, we demonstrated that interaction with hepatic epithelia was sufficient to generate CD69CD4 T cells, while additional signals from the liver microenvironment were required to generate liver-resident CD69CD4 T cells.

Conclusions: High and intermediate CD69 expressions mark human hepatic CD4 T and a novel functionally distinct recirculating population, respectively, both shaped by the liver microenvironment to achieve diverse immunosurveillance.