Localization of memory CD8+ T cells to lymphoid or peripheral tissues is believed to correlate with proliferative capacity or effector function. Here we demonstrate that the fractalkine-receptor/CX3CR1 distinguishes memory CD8+ T cells with cytotoxic effector function from those with proliferative capacity, independent of tissue-homing properties. CX3CR1-based transcriptome and proteome-profiling defines a core signature of memory CD8+ T cells with effector function. We find CD62LhiCX3CR1+ memory T cells that reside within lymph nodes. This population shows distinct migration patterns and positioning in proximity to pathogen entry sites. Virus-specific CX3CR1+ memory CD8+ T cells are scarce during chronic infection in humans and mice but increase when infection is controlled spontaneously or by therapeutic intervention. This CX3CR1-based functional classification will help to resolve the principles of protective CD8+ T-cell memory.

Chronic carriers of hepatitis B virus (HBV) usually show hepatitis B surface antigen (HBsAg) in their sera, which is considered the best marker for acute and chronic HBV infection. In some individuals, however, this antigen cannot be detected by routine serological assays despite the presence of virus in liver and peripheral blood. One reason for this lack of HBsAg might be mutations in the part of the molecule recognized by specific antibodies. To test this hypothesis, the HBV S gene sequences were determined of isolates from 33 virus carriers who were negative for HBsAg but showed antibodies against the virus core (anti-HBc) as the only serological marker of hepatitis B. Isolates from 36 HBsAg-positive patients served as controls. In both groups, a considerable number of novel mutations were found. In isolates from individuals with anti-HBc reactivity only, the variability of the major hydrophilic loop of HBsAg, the main target for neutralizing and diagnostic antibodies, was raised significantly when compared with the residual protein (22. 6 vs 9.4 mutations per 1000 amino acids; P<0.001) and with the corresponding region in the controls (22.6 vs 7.5 exchanges per 1000 residues; P<0.001). A similar hypervariable spot was identified in the reverse transcriptase domain of the viral polymerase, encoded by the same nucleotide sequence in an overlapping reading frame. These findings suggest that at least some of the chronic low-level carriers of HBV, where surface antigen is not detected, could be infected by diagnostic escape mutants and/or by variants with impaired replication.

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Regulatory myeloid immune cells, such as myeloid-derived suppressor cells (MDSCs), populate inflamed or cancer tissue and block immune cell effector functions. Lack of mechanistic insight 54 into MDSC suppressive activity and a marker for their identification hampered attempts to 55 overcome T cell-inhibition and unleash anti-cancer immunity. Here we report that human MDSCs 56 were characterized by strongly reduced metabolism and conferred this compromised metabolic 57 state to CD8 + T cells thereby paralyzing their effector functions. We identified accumulation of the dicarbonyl-radical methylglyoxal, generated by semicarbazide-sensitive amine oxidase (SSAO), to cause the metabolic phenotype of MDSCs and MDSC-mediated paralysis of CD8 + T cells. In a murine cancer model, neutralization of dicarbonyl-activity overcame MDSC-mediated T cell-suppression and together with checkpoint inhibition improved efficacy of cancer immune therapy. Our results identify the dicarbonyl methylglyoxal as marker metabolite for MDSCs that mediates T cell paralysis and can serve as target to improve cancer immune therapy. Results 92 Dormant metabolic phenotype in MDSCs 93Suppressive myeloid cells arise during chronic inflammation in tissues 17 , and tissue stromal cells 94 induce transition of monocytes into monocytic MDSCs 16 . We exploited this capacity of stromal cells to convert human peripheral blood monocytes into MDSCs, which are phenotypically similar 96 to CD14 + HLA-DR -/low suppressive myeloid cells directly isolated from cancer patients 16 , to characterize the mechanism of MDSC-mediated T cell suppression. Transcriptome analysis showed less than 200 differentially expressed genes between MDSCs and monocytes, which did not include surface molecules suitable for phenotypic discrimination or known immune suppressive mediators to explain their suppressive activity (supplementary table I-IV, Extended Data Fig. 1). Consistently, blockade of known immune suppressive mediators did not prevent MDSC-mediated T cell suppression (Extended Data Fig. 2). Surprisingly, we found downregulation of genes encoding glycolysis-related enzymes in MDSCs (Fig. 1a, and Extended Data Table V).Indeed, MDSCs showed reduced glucose uptake and Glut1 surface expression (Fig. 1b), the main transporter mediating glucose uptake in immune cells. As predicted from gene expression analysis, hexokinase activity was lower in MDSCs (Fig. 1c). To validate these results, we isolated CD14 + HLA-DR -/lo cells from tumor tissue of patients with hepatocellular carcinoma by enzymatic digestion followed by density centrifugation and flow cytometric cell sorting. We confirmed reduced glucose uptake and hexokinase activity in CD14 + HLA-DR -/low cells isolated from tumor tissue of cancer patients (Fig. 1d,e, and Extended Data Table VI), which are considered to represent MDSCs. Strikingly, MDSCs failed to utilize glucose for glycolysis and also showed reduced cellular bioenergetics, i.e. lower mitochondrial membrane potential quantified by the potentiometric mitochondrial ...

Pathogen-induced immune responses prevent the establishment of transplantation tolerance in experimental animal models. Whether this occurs in humans as well remains unclear. The development of operational tolerance in liver transplant recipients with chronic hepatitis C virus (HCV) infection allows us to address this question. We conducted a clinical trial of immunosuppression withdrawal in HCV-infected adult liver recipients to elucidate (i) the mechanisms through which allograft tolerance can be established in the presence of an ongoing inflammatory response and (ii) whether anti-HCV heterologous immune responses influence this phenomenon. Of 34 enrolled liver recipients, drug withdrawal was successful in 17 patients (50%). Tolerance was associated with intrahepatic overexpression of type I interferon and immunoregulatory genes and with an expansion of exhausted PD1/CTLA4/2B4-positive HCV-specific circulating CD8(+) T cells. These findings were already present before immunosuppression was discontinued and were specific for HCV infection. In contrast, the magnitude of HCV-induced proinflammatory gene expression and the breadth of anti-HCV effector T cell responses did not influence drug withdrawal outcome. Our data suggest that in humans, persistent viral infections exert immunoregulatory effects that could contribute to the restraining of alloimmune responses, and do not necessarily preclude the development of allograft tolerance.