The interaction defect of accessory molecules is responsible for the poor ex vivo response to human antigens of mouse T helper cells

Mouse T cells fail to respond to xenogeneic pig and human antigens using the direct antigen‐presenting pathway. The poor response by mouse CD8 cells is because of multiple defects in the molecular interactions between mouse CD8 cells and xenogeneic antigen‐presenting cells (APCs). Using human CD4/DR3⁺, mouse CD4^?/major histocompatibility complex (MHC) class II ^? mice, we investigated the defects in molecular interaction responsible for the poor response to xenogeneic antigens by naïve mouse CD4⁺ cells. Mouse CD4 cells failed to respond to human leucocyte antigen (HLA)‐DR3 expressed on mouse APCs but developed a strong response to alloantigens, indicating a defect in the interaction between mouse CD4 and HLA‐DR3 molecules. Human CD4⁺/mouse CD4^– mouse T cells respond poorly to human and pig APCs but not allogeneic APCs, indicating that accessory molecular interactions are deficient across highly separated species. Adding mouse interleukin‐2 (IL‐2) to the mixed lymphocyte reaction system did not improve the poor response to human or pig antigens by mouse or human CD4⁺/mouse CD4^– mouse T cells. Therefore, multiple molecular interactions deficient between mouse CD4 cells and human or pig APCs may lead to the poor response to xenogeneic antigens by naïve mouse CD4 cells.     

Mouse pancreatic beta cells express MHC class II and stimulate CD4+ T cells to proliferate

Type 1 diabetes results from destruction of pancreatic beta cells by autoreactive T cells. Both CD4⁺ and CD8⁺ T cells have been shown to mediate beta‐cell killing. While CD8⁺ T cells can directly recognize MHC class I on beta cells, the interaction between CD4⁺ T cells and beta cells remains unclear. Genetic association studies have strongly implicated HLA‐DQ alleles in human type 1 diabetes. Here we studied MHC class II expression on beta cells in nonobese diabetic mice that were induced to develop diabetes by diabetogenic CD4⁺ T cells with T‐cell receptors that recognize beta‐cell antigens. Acute infiltration of CD4⁺ T cells in islets occurred with rapid onset of diabetes. Beta cells from islets with immune infiltration expressed MHC class II mRNA and protein. Exposure of beta cells to IFN‐γ increased MHC class II gene expression, and blocking IFN‐γ signaling in beta cells inhibited MHC class II upregulation. IFN‐γ also increased HLA‐DR expression in human islets. MHC class II⁺ beta cells stimulated the proliferation of beta‐cell‐specific CD4⁺ T cells. Our study indicates that MHC class II molecules may play an important role in beta‐cell interaction with CD4⁺ T cells in the development of type 1 diabetes.     

The CD8+HLA‐DR+ T cells expanded in HIV‐1 infection are qualitatively identical to those from healthy controls

HIV‐induced immune activation leads to expansion of a subset of human CD8⁺ T cells expressing HLA‐DR antigens. Expansion of CD8⁺HLA‐DR⁺ T cells can be also observed in non‐HIV settings including several autoimmune diseases and aging. Although these cells are felt to represent “immune exhaustion” and/or to be anergic, their precise role in host defense has remained unclear. Here, we report that this subset of cells exhibits a restricted repertoire, shows evidence of multiple rounds of division, but lacks markers of recent TCR engagement. Detailed cell cycle analysis revealed that compared with their CD8⁺HLA‐DR^? counterpart, the CD8⁺HLA‐DR⁺ T‐cell pool contained an increased fraction of cells in S‐phase with elevated levels of the G2/M regulators: cyclin A2, CDC25C, Cdc2 (CDK1), indicating that these cells are not truly anergic but rather experiencing proliferation in vivo. Together, these data support a hypothesis that antigen stimulation leads to the initial expansion of a CD8⁺ pool of cells in vivo that undergo further expansion independent of ongoing TCR engagement. No qualitative differences were noted between CD8⁺HLA‐DR⁺ cells from HIV⁺ and HIV^? donors, indicating that the generation of CD8⁺HLA‐DR⁺ T cells is a part of normal immune regulation that is exaggerated in the setting of HIV‐1 infection.     

Presence of HLA‐DR Molecules and HLA‐DRB1 mRNA in Circulating CD4+ T Cells

The human major histocompatibility complex class II isotype HLA‐DR is currently used as an activation marker for T cells. However, whether an endogenous protein expression or a molecular acquisition accounts for the presence of HLA‐DR on T cells remains undetermined and still controversial. To further characterize this phenomenon, we compared several aspects of the presence of the HLA‐DR protein to the presence of associated mRNA (HLA‐DRB1), focusing on human T cells from peripheral blood of healthy individuals. Using a flow cytometric approach, we determined that the HLA‐DR observed on CD4⁺ T cells was almost exclusively cell surface‐associated, while for autologous CD19⁺ B cells, the protein could be located in the plasma membrane as well as in the cytoplasm. Moreover, negligible expression levels of HLA‐DRB1 were found in CD4⁺ T cells, using an HLA‐DRB1 allele‐specific qPCR assay. Finally, the presence of HLA‐DR was not confined to activated CD4⁺ and CD8⁺ T cells, as evaluated by the co‐expression of CD25. The functional role of the HLA‐DR molecule on T cells remains enigmatic; however, this study presents evidence of fundamental differences for the presence of HLA‐DR on T cells from HLA‐DR in the context of antigen‐presenting cells, which is a well‐known phenomenon. Although an inducible endogenous protein expression cannot be excluded for the T cells, our findings suggest that a re‐evaluation of the HLA‐DR as a T cells activation marker is warranted.     

Effective antigen presentation to helper T cells by human eosinophils

Although eosinophils are inflammatory cells, there is increasing attention on their immunomodulatory roles. For example, murine eosinophils can present antigen to CD4⁺ T helper (Th) cells, but it remains unclear whether human eosinophils also have this ability. This study determined whether human eosinophils present a range of antigens, including allergens, to activate Th cells, and characterized their expression of MHC class II and co‐stimulatory molecules required for effective presentation. Human peripheral blood eosinophils purified from non‐allergic donors were pulsed with the antigens house dust mite extract (HDM), Timothy Grass extract (TG) or Mycobacterium tuberculosis purified protein derivative (PPD), before co‐culture with autologous CD4⁺ Th cells. Proliferative and cytokine responses were measured, with eosinophil expression of HLA‐DR/DP/DQ and the co‐stimulatory molecules CD40, CD80 and CD86 determined by flow cytometry. Eosinophils pulsed with HDM, TG or PPD drove Th cell proliferation, with the response strength dependent on antigen concentration. The cytokine responses varied with donor and antigen, and were not biased towards any particular Th subset, often including combinations of pro‐ and anti‐inflammatory cytokines. Eosinophils up‐regulated surface expression of HLA‐DR/DP/DQ, CD80, CD86 and CD40 in culture, increases that were sustained over 5 days when incubated with antigens, including HDM, or the major allergens it contains, Der p I or Der p II. Human eosinophils can, therefore, act as effective antigen‐presenting cells to stimulate varied Th cell responses against a panel of antigens including HDM, TG or PPD, an ability that may help to determine the development of allergic disease.     

Distinct effects of CD86-mediated costimulation on resting versus activated human CD4+ T cells

CD80 and CD86 are important in the initiation of T cell immunity. Although their costimulatory function has long been appreciated, it remains unclear whether the biological significance of the two B7 isoforms resides in their different patterns and kinetics of expression or whether differences exist in their function. We have addressed this issue using HLA‐DR1 transfectants co‐expressing CD80, CD86, or both molecules as stimulators for naïve, memory, and activated human CD4⁺ T cells. Both CD80 and CD86 efficiently costimulated alloresponses by unseparated peripheral blood CD4⁺ T cells; however, CD86 was substantially inferior in costimulating alloresponses by separated memory T cells, and completely incompetent in costimulating three human T cell clones. Furthermore, CD80/CD86 double transfectants stimulated lower responses by the clones than cells expressing CD80 alone. That CD86 was actively inhibitory rather than merely neutral was evidenced by the increase in response to the double CD80/CD86 APC when anti‐CD86 antibody was added. Furthermore, addition of anti‐CTLA‐4 Fab to cultures of HLA‐DR1 transfectants co‐expressing CD86, fully restored the proliferative response. These results indicate that CD80 and CD86 mediate distinct signals in previously activated T cells, and demonstrate that CTLA‐4 ligation may dominate the outcome of CD86‐mediated costimulation of activated CD4⁺ T cells.     

Accelerated thymopoiesis and improved T‐cell responses in HLA‐A2/‐DR2 transgenic BRGS‐based human immune system mice

Human immune system (HIS) mouse models provide a robust in vivo platform to study human immunity. Nevertheless, the signals that guide human lymphocyte differentiation in HIS mice remain poorly understood. Here, we have developed a novel Balb/c Rag2^?/? Il2rg^?/? Sirpa^NOD (BRGS) HIS mouse model expressing human HLA‐A2 and ‐DR2 transgenes (BRGSA2DR2). When comparing BRGS and BRGSA2DR2 HIS mice engrafted with human CD34⁺ stem cells, a more rapid emergence of T cells in the circulation of hosts bearing human HLA was shown, which may reflect a more efficient human T‐cell development in the mouse thymus. Development of CD4⁺ and CD8⁺ T cells was accelerated in BRGSA2DR2 HIS mice and generated more balanced B and T‐cell compartments in peripheral lymphoid organs. Both B‐ and T‐cell function appeared enhanced in the presence of human HLA transgenes with higher levels of class switched Ig, increased percentages of polyfunctional T cells and clear evidence for antigen‐specific T‐cell responses following immunization. Taken together, the presence of human HLA class I and II molecules can improve multiple aspects of human B‐ and T‐cell homeostasis and function in the BRGS‐based HIS mouse model.     

Effects of type II collagen epitope carbamylation and citrullination in human leucocyte antigen (HLA)‐DR4+ monozygotic twins discordant for rheumatoid arthritis

The aim of this study is to investigate the effect of the native, citrullinated or carbamylated type II human collagen T cell‐ and B cell‐epitopes on the adaptive immune response in rheumatoid arthritis (RA). Peripheral blood T and B cells obtained from a human leucocyte D4‐related (antigen DR4^? HLA‐DR4)⁺ woman with early RA, her healthy monozygotic twin and an unrelated HLA‐DR3⁺ woman with early RA were analysed for activation (CD154/CD69), apoptosis (annexin/7‐aminoactinomycin), cytokine production [interferon (IFN)γ/interleukin (IL)?17/IL‐4/IL‐10/IL‐6] and functional phenotype (CD45Ra/CCR7) after stimulation with the collagen native T cell epitope (T261‐273), the K264 carbamylated T cell epitope (carT261–273), the native B cell epitope (B359–369) or the R360 citrullinated B cell epitope (citB359–369), and the combinations of these. The T cell memory compartment was activated by T cell epitopes in both discordant DR4⁺ twins, but not in the DR3⁺ RA. The collagen‐specific activation of CD4⁺ T cells was induced with both the native and carbamylated T cell epitopes only in the RA twin. Both T cell epitopes also induced IL‐17 production in the RA twin, but a greater IL‐4 and IL‐10 response in the healthy twin. The citrullinated B cell epitope, particularly when combined with the carbamylated T cell epitope, induced B cell activation and an increased IL‐6/IL‐10 ratio in the RA twin compared to a greater IL‐10 production in the healthy twin. Our data suggest that circulating collagen‐specific T and B cells are found in HLA‐DR4⁺ subjects, but only RA activated cells express co‐stimulatory molecules and produce proinflammatory cytokines. Carbamylation and citrullination further modulate the activation and cytokine polarization of T and B cells.     

The CD4+ T‐cell epitope‐binding register is a critical parameter when generating functional HLA‐DR tetramers with promiscuous peptides

Detection of CD4⁺ T cells specific for tumor‐associated antigens is critical to investigate the spontaneous tumor immunosurveillance and to monitor immunotherapy protocols in patients. We investigated the ability of HLA‐DR^*1101 multimers to detect CD4⁺ T cells specific for three highly promiscuous MAGE‐A3 derived peptides: MAGE‐A3_191–205 (p39), MAGE‐A3_281–295 (p57) and MAGE‐A3_286–300 (p58). Tetramers stained specific CD4⁺ T cells only when loaded with p39, although all peptides activated the specific T cells when presented by plastic‐bound HLA‐DR^*1101 monomers. This suggested that tetramer staining ability was determined by the mode rather than the affinity of peptide binding to HLA‐DR^*1101. We hypothesized that peptides should bear a single P1 anchor residue to bind all arms of the multimer in a homogeneous register to generate peptide‐HLA‐DR conformers with maximal avidity. Bioinformatics analysis indicated that p39 contained one putative P1 anchor residue, whereas the other two peptides contained multiple ones. Designing p57 and p58 analogues containing a single anchor residue generated HLA‐DR^*1101 tetramers that stained specific CD4⁺ T cells. Producing HLA‐DR^*1101 monomers linked with the optimized MAGE‐A3 analogues, but not with the original epitopes, further improved tetramer efficiency. Optimization of CD4⁺ T‐cell epitope‐binding registers is thus critical to generate functional HLA‐DR tetramers.     

Circulating CD4+ and CD8+ T cells are activated in inflammatory bowel disease and are associated with plasma markers of inflammation

Inflammatory bowel disease (IBD) is characterized by damage to the gut mucosa and systemic inflammation. We sought to evaluate the role of chronic inflammation on circulating T‐cell activation in human subjects with Crohn's disease and ulcerative colitis. We studied 54 patients with IBD and 28 healthy controls. T‐cell activation and cycling were assessed in whole blood samples by flow cytometry. Levels of lipopolysaccharide (LPS) were measured in serum by Limulus amoebocyte lysate assay, and plasma levels of inflammatory markers and LPS‐binding proteins were measured by ELISA. The proportions of circulating CD4⁺ and CD8⁺ T lymphocytes in cycle (Ki67⁺) are increased in patients with IBD compared with these proportions in controls. CD8⁺ T cells from patients with IBD are also enriched for cells that expressed CD38 and HLA‐DR, and proportions of these cells are related to plasma levels of interleukin‐6 and C‐reactive protein in these patients. Intracellular interleukin‐2 and interferon‐γ levels were elevated in resting and polyclonally activated CD4⁺ and CD8⁺ T cells in patients with IBD when compared with levels from healthy controls. Surprisingly, we did not find increased levels of LPS in the serum of patients with IBD. We did, however, find a signature of recent microbial translocation, as levels of LPS‐binding protein are increased in the plasma of patients with IBD compared with plasma levels in healthy controls; LPS‐binding protein levels are also directly related to proportions of CD38 HLA‐DR‐expressing CD4⁺ and CD8⁺ T cells. Local damage to the gastrointestinal tract in IBD may result in systemic inflammation and T‐cell activation.     

Genetically modified human CD4+ T cells can be evaluated in vivo without lethal graft‐versus‐host disease

Adoptive cell immunotherapy for human diseases, including the use of T cells modified to express an anti‐tumour T‐cell receptor (TCR) or chimeric antigen receptor, is showing promise as an effective treatment modality. Further advances would be accelerated by the availability of a mouse model that would permit human T‐cell engineering protocols and proposed genetic modifications to be evaluated in vivo. NOD‐scid IL2rγ^null (NSG) mice accept the engraftment of mature human T cells; however, long‐term evaluation of transferred cells has been hampered by the xenogeneic graft‐versus‐host disease (GVHD) that occurs soon after cell transfer. We modified human primary CD4⁺ T cells by lentiviral transduction to express a human TCR that recognizes a pancreatic beta cell‐derived peptide in the context of HLA‐DR4. The TCR‐transduced cells were transferred to NSG mice engineered to express HLA‐DR4 and to be deficient for murine class II MHC molecules. CD4⁺ T‐cell‐depleted peripheral blood mononuclear cells were also transferred to facilitate engraftment. The transduced cells exhibited long‐term survival (up to 3 months post‐transfer) and lethal GVHD was not observed. This favourable outcome was dependent upon the pre‐transfer T‐cell transduction and culture conditions, which influenced both the kinetics of engraftment and the development of GVHD. This approach should now permit human T‐cell transduction protocols and genetic modifications to be evaluated in vivo, and it should also facilitate the development of human disease models that incorporate human T cells.     

Diminished expression of CD59 on activated CD8+ T cells undergoing apoptosis in systemic lupus erythematosus and Sjögren's syndrome

The present study was undertaken to examine the phenotype of T cells undergoing in vitro apoptosis in patients with autoimmune diseases such as systemic lupus erythematosus (SLE) and primary Sjögren's syndrome (SS). Compared with normal controls, we found diminished expression of CD59 antigen (one of the cell‐surface complement‐regulatory proteins) on CD8⁺ T cells, but not on CD4⁺ T cells, from patients with SLE and SS. Three‐colour immunofluorescence analysis revealed that these CD59^dim CD8⁺ T cells were activated T cells, expressing both human leucocyte antigen (HLA)‐DR and CD45RO antigens. In addition, these CD59^dim CD8⁺ T cells were more susceptible to in vitro apoptosis than CD59^bright CD8⁺ T cells. In two patients with active lupus, the percentage of CD59^dim CD8⁺ T cells was significantly decreased after steroid therapy. These findings suggest that decreased expression of CD59 antigen on in vivo‐activated CD8⁺ T cells may be correlated with disease activity and may be involved in activation‐induced apoptosis in patients with SLE and SS.     

Functional islet‐specific Treg can be generated from CD4+CD25− T cells of healthy and type 1 diabetic subjects

CD4⁺CD25⁺FOXP3⁺ Treg cells require TCR engagement for suppressive function, thus ensuring that suppression occurs only in the presence of specific antigens; however, to date no studies have addressed the function of self‐antigen‐specific Treg in humans. These studies were designed to determine whether peripheral generation and function of islet antigen‐specific adaptive Treg are defective in human subjects with type 1 diabetes (T1D). Islet antigen‐specific adaptive Treg were induced in vitro by activation of CD4⁺FOXP3^? T cells with glutamic acid decarboxylase and islet‐specific glucose‐6‐phosphate catalytic subunit‐related protein peptides in the context of T1D‐associated HLA‐DRβ alleles. Antigen‐specific Treg were characterized using flow cytometry for FOXP3 and class II tetramer and assessed for the ability to inhibit proliferation. These adaptive Treg were then compared with influenza‐specific Treg from the same study population. The function of tetramer⁺ cells that expressed FOXP3 was similar for both influenza and islet antigens generated from control and T1D subjects. In fact, the potency of suppression correlated with FOXP3 expression, not antigen specificity. Thus, these data suggest that development of functional adaptive Treg can occur in response to islet antigens and activation of islet‐specific Treg may potentially be used as a targeted immunotherapy in T1D.     

The impact of HLA class I and EBV latency‐II antigen‐specific CD8+ T cells on the pathogenesis of EBV+ Hodgkin lymphoma

In 40% of cases of classical Hodgkin lymphoma (cHL), Epstein–Barr virus (EBV) latency‐II antigens [EBV nuclear antigen 1 (EBNA1)/latent membrane protein (LMP)1/LMP2A] are present (EBV⁺cHL) in the malignant cells and antigen presentation is intact. Previous studies have shown consistently that HLA‐A*02 is protective in EBV⁺cHL, yet its role in disease pathogenesis is unknown. To explore the basis for this observation, gene expression was assessed in 33 cHL nodes. Interestingly, CD8 and LMP2A expression were correlated strongly and, for a given LMP2A level, CD8 was elevated markedly in HLA‐A*02^– versus HLA‐A*02⁺ EBV⁺cHL patients, suggesting that LMP2A‐specific CD8⁺ T cell anti‐tumoral immunity may be relatively ineffective in HLA‐A*02^– EBV⁺cHL. To ascertain the impact of HLA class I on EBV latency antigen‐specific immunodominance, we used a stepwise functional T cell approach. In newly diagnosed EBV⁺cHL, the magnitude of ex‐vivo LMP1/2A‐specific CD8⁺ T cell responses was elevated in HLA‐A*02⁺ patients. Furthermore, in a controlled in‐vitro assay, LMP2A‐specific CD8⁺ T cells from healthy HLA‐A*02 heterozygotes expanded to a greater extent with HLA‐A*02‐restricted compared to non‐HLA‐A*02‐restricted cell lines. In an extensive analysis of HLA class I‐restricted immunity, immunodominant EBNA3A/3B/3C‐specific CD8⁺ T cell responses were stimulated by numerous HLA class I molecules, whereas the subdominant LMP1/2A‐specific responses were confined largely to HLA‐A*02. Our results demonstrate that HLA‐A*02 mediates a modest, but none the less stronger, EBV‐specific CD8⁺ T cell response than non‐HLA‐A*02 alleles, an effect confined to EBV latency‐II antigens. Thus, the protective effect of HLA‐A*02 against EBV⁺cHL is not a surrogate association, but reflects the impact of HLA class I on EBV latency‐II antigen‐specific CD8⁺ T cell hierarchies.     

Characterization of the human CD4+ T‐cell repertoire specific for major histocompatibility class I‐restricted antigens

While CD4⁺ T lymphocytes usually recognize antigens in the context of major histocompatibility (MHC) class II alleles, occurrence of MHC class‐I restricted CD4⁺ T cells has been reported sporadically. Taking advantage of a highly sensitive MHC tetramer‐based enrichment approach allowing detection and isolation of scarce Ag‐specific T cells, we performed a systematic comparative analysis of HLA‐A*0201‐restricted CD4⁺ and CD8⁺ T‐cell lines directed against several immunodominant viral or tumoral antigens. CD4⁺ T cells directed against every peptide‐MHC class I complexes tested were detected in all donors. These cells yielded strong cytotoxic and T helper 1 cytokine responses when incubated with HLA‐A2⁺ target cells carrying the relevant epitopes. HLA‐A2‐restricted CD4⁺ T cells were seldom expanded in immune HLA‐A2⁺ donors, suggesting that they are not usually engaged in in vivo immune responses against the corresponding peptide‐MHC class I complexes. However, these T cells expressed TCR of very high affinity and were expanded following ex vivo stimulation by relevant tumor cells. Therefore, we describe a versatile and efficient strategy for generation of MHC class‐I restricted T helper cells and high affinity TCR that could be used for adoptive T‐cell transfer‐ or TCR gene transfer‐based immunotherapies.     

Regulation of HLA-DR and co-stimulatory molecule expression on natural killer T cells by granulocyte-macrophage colony-stimulating factor

A subset of mononuclear cells present in most tissues coexpresses receptors of both natural killer (NK) and T cells. Although linked to antiviral immunity, the function of these putative NKT cells is uncertain. We present evidence that human CD56⁺ DR^? NKT cells exhibit hybrid adaptive and innate immune functions. These cells spontaneously lysed tumour cell targets and upon engagement of T‐cell antigen receptors secreted the cytokines interferon‐γ and granulocyte–macrophage colony‐stimulating factor (GM‐CSF). Conversely, GM‐CSF treatment transformed the NKT cells into dendritic cells, inducing rapid expression of HLA‐DR and the co‐stimulatory molecules CD80 and CD86. The ability to stimulate tetanus toxoid‐specific responses from naïve T cells was acquired within 3 days of activating CD56⁺ NKT cells with GM‐CSF. These results suggest a potential role for NKT cells in the initiation and control of primary immunity during the acute phase of infection.     

The induction of autoimmune hepatitis in the human leucocyte antigen‐DR4 non‐obese diabetic mice autoimmune hepatitis mouse model

Autoimmune hepatitis (AIH) is a chronic liver disease characterized by progressive inflammation, female preponderance and seropositivity for autoantibodies such as anti‐smooth muscle actin and/or anti‐nuclear, anti‐liver kidney microsomal type 1 (anti‐LKM1) and anti‐liver cytosol type 1 (anti‐LC1) in more than 80% of cases. AIH is linked strongly to several major histocompatibility complex (MHC) alleles, including human leucocyte antigen (HLA)‐DR3, ‐DR7 and ‐DR13. HLA‐DR4 has the second strongest association with adult AIH, after HLA‐DR3. We investigated the role of HLA‐DR4 in the development of AIH by immunization of HLA‐DR4 (DR4) transgenic non‐obese diabetic (NOD) mice with DNA coding for human CYP2D6/FTCD fusion autoantigen. Immunization of DR4 mice leads to sustained mild liver injury, as assessed biochemically by elevated alanine aminotransferase, histologically by interface hepatitis, plasma cell infiltration and mild fibrosis and immunologically by the development of anti‐LKM1/anti‐LC1 antibodies. In addition, livers from DR4 mice had fewer regulatory T cells (T_regs), which had decreased programmed death (PD)‐1 expression. Splenic T_regs from these mice also showed impaired inhibitory capacity. Furthermore, DR4 expression enhanced the activation status of CD8⁺ T cells, macrophages and dendritic cells in naive DR4 mice compared to naive wild‐type (WT) NOD mice. Our results demonstrate that HLA‐DR4 is a susceptibility factor for the development of AIH. Impaired suppressive function of T_regs and reduced PD‐1 expression may result in spontaneous activation of key immune cell subsets, such as antigen‐presenting cells and CD8⁺ T effectors, facilitating the induction of AIH and persistent liver damage.     

Specific CD8+ T cells recognize human herpesvirus 6B

The importance of human herpesvirus 6 (HHV‐6) species as human pathogens is increasingly appreciated. However, we do not understand how infection is controlled in healthy virus carriers, and why control fails in patients with disease. Other persistent viruses are under continuous surveillance by antigen‐specific T cells, and specific T‐cell repertoires have been well characterized for some of them. In contrast, knowledge on HHV‐6‐specific T‐cell responses is limited, and missing for CD8⁺ T cells. Here we identify CD8⁺ T‐cell responses to HHV‐6B, the most widespread HHV‐6 species, in healthy virus carriers. HHV‐6B‐specific CD8⁺ T‐cell lines and clones recognized HLA‐A2‐restricted peptides from the viral structural proteins U54 and U11, and displayed various antigen‐specific antiviral effector functions. These CD8⁺ T cells specifically recognized HHV‐6B‐infected primary CD4⁺ T cells in an HLA‐restricted manner, produced antiviral cytokines, and killed infected cells, whereas HHV‐6A‐infected cells were not recognized. Thus, HHV‐6B‐specific CD8⁺ T cells are likely to contribute to control of infection, overcoming the immunomodulatory effects exerted by the virus. Potentially, HHV‐6‐associated disease could be addressed by active or passive immunotherapy that reconstitutes virus‐specific CD8⁺ T‐cell responses.     

Tolerogenic dendritic cells impede priming of naïve CD8+ T cells and deplete memory CD8+ T cells

Type 1 diabetes is a T‐cell‐mediated autoimmune disease in which autoreactive CD8⁺ T cells destroy the insulin‐producing pancreatic beta cells. Vitamin D3 and dexamethasone‐modulated dendritic cells (Combi‐DCs) loaded with islet antigens inducing islet‐specific regulatory CD4⁺ T cells may offer a tissue‐specific intervention therapy. The effect of Combi‐DCs on CD8⁺ T cells, however, remains unknown. To investigate the interaction of CD8⁺ T cells with Combi‐DCs presenting epitopes on HLA class I, naive, and memory CD8⁺ T cells were co‐cultured with DCs and proliferation and function of peptide‐specific T cells were analyzed. Antigen‐loaded Combi‐DCs were unable to prime naïve CD8⁺ T cells to proliferate, although a proportion of T cells converted to a memory phenotype. Moreover, expansion of CD8⁺ T cells that had been primed by mature monocyte‐derived DCs (moDCs) was curtailed by Combi‐DCs in co‐cultures. Combi‐DCs expanded memory T cells once, but CD8⁺ T‐cell numbers collapsed by subsequent re‐stimulation with Combi‐DCs. Our data point that (re)activation of CD8⁺ T cells by antigen‐pulsed Combi‐DCs does not promote, but rather deteriorates, CD8⁺ T‐cell immunity. Yet, Combi‐DCs pulsed with CD8⁺ T‐cell epitopes also act as targets of cytotoxicity, which is undesirable for survival of Combi‐DCs infused into patients in therapeutic immune intervention strategies.     

Primary and secondary hemophagocytic lymphohistiocytosis have different patterns of T‐cell activation,differentiation and repertoire

Hemophagocytic lymphohistiocytosis (HLH) is a life‐threatening inflammatory syndrome characterized by hyperactivation of lymphocytes and histiocytes. T cells play a key role in HLH pathogenesis, but their differentiation pattern is not well characterized in patients with active HLH. We compared T‐cell activation patterns between patients with familial HLH (1°HLH), 2°HLH without apparent infectious trigger (2°HLH) and 2°HLH induced by a viral infection (2°V‐HLH). Polyclonal CD8⁺ T cells are highly activated in 1°HLH and 2°V‐HLH, but less in 2°HLH as assessed by HLA‐DR expression and marker combination with CD45RA, CCR7, CD127, PD‐1 and CD57. Absence of increased HLA‐DR expression on T cells excluded active 1° HLH with high sensitivity and specificity. A high proportion of polyclonal CD127^?CD4⁺ T cells expressing HLA‐DR, CD57, and perforin is a signature of infants with 1°HLH, much less prominent in virus‐associated 2°HLH. The similar pattern and extent of CD8⁺ T‐cell activation compared to 2° V‐HLH is compatible with a viral trigger of 1°HLH. However, in most 1°HLH patients no triggering infection was documented and the unique activation of cytotoxic CD4⁺ T cells indicates that the overall T‐cell response in 1°HLH is different. This may reflect different pathways of pathogenesis of these two HLH variants.