The human liver microenvironment shapes the homing and function of CD4+T-cell populations
Authors: Wiggins Benjamin G. , Pallett Laura J. , Li Xiaoyan , Davies Scott P. , Amin Oliver E. , Gill Upkar S. , Patel Arzoo M. , Aliazis Konstantinos , Liu Yuxin S. , Reynolds Gary M. , Hirschfield Gideon , Kennedy Patrick T.F. , Huang Yuehua , Maini Mala K. , Stamataki Zania 
Published: August 2020

ABSTRACTBackground & AimsTissue-resident memory T cells (TRM) are important immune sentinels that provide efficientin situimmunity. Liver-resident CD8+TRMhave been previously described, and contribute to viral control in persistent hepatotropic infections. However, little is known regarding liver CD4+TRMcells. Here we profiled resident and non-resident intrahepatic CD4+T cell subsets, assessing their phenotype, function, differential generation requirements and roles in hepatotropic infection.MethodsLiver tissue was obtained from 173 subjects with (n=109) or without (n=64) hepatic pathology. Multiparametric flow cytometry and immunofluorescence imaging examined T cell phenotype, functionality and location. Liver T cell function was determined after stimulation with anti-CD3/CD28 and PMA/Ionomycin. Co-cultures of blood-derived lymphocytes with hepatocyte cell lines, primary biliary epithelial cells, and precision-cut autologous liver slices were used to investigate the acquisition of liver-resident phenotypes.ResultsCD69 expression delineated two distinct subsets in the human liver. CD69HIcells were identified as CD4+TRMdue to exclusion from the circulation, a residency-associated phenotype (CXCR6+CD49a+S1PR1-PD-1+), restriction to specific liver niches, and ability to produce robust type-1 multifunctional cytokine responses. Conversely, CD69INTwere an activated T cell population also found in the peripheral circulation, with a distinct homing profile (CX3CR1+CXCR3+CXCR1+), and a bias towards IL-4 production. Frequencies of CD69INTcells correlated with the degree of fibrosis in chronic hepatitis B virus infection. Interaction with hepatic epithelia was sufficient to generate CD69INTcells, while additional signals from the liver microenvironment were required to generate liver-resident CD69HIcells.ConclusionsIntermediate and high CD69 expression demarcates two discrete intrahepatic CD4+T cell subsets with distinct developmental and functional profiles.Graphical AbstractHighlightsCD69HI(CXCR6+CD49a+S1PR1-PD-1+) are the CD4+TRMof the human liverHepatic CD69INTCD4+T-cells are distinct, activated, and recirculation-competentStimulation evokes respective IFN-γ and IL-4 responses in CD69HIand CD69INTcellsCD69INTcell frequencies correlate with worsening fibrosis in chronic HBV patientsLiver slice cultures allow differentiation of CD69INTand CD69HIcells from bloodLay summaryTissue-resident memory T cells (TRM) orchestrate regional immune responses, but much of the biology of liver-resident CD4+TRMremains unknown. We found high expression of cell-surface protein CD69 defined hepatic CD4+TRM, while simultaneously uncovering a distinct novel recirculatory CD69INTCD4+T cell subset. Both subsets displayed unique immune receptor profiles, were functionally skewed towards type-1 and type-2 responses respectively, and had distinct generation requirements, highlighting the potential for differential roles in the immunopathology of chronic liver diseases.