CD4+CD7− T Cells: A Separate Subpopulation of Memory T Cells?

The CD7 molecule is apparently involved in T cell activation but is absent in a substantial subpopulation of human T cells under physiological and certain pathological conditions. The majority of CD7^– T cells expresses TCR / and is of CD4⁺ helper and CD45R0⁺CD45RA^– memory phenotype. After birth, percentages and absolute numbers of circulating CD7^– T cells increase significantly during aging. A number of molecules thought to be involved in organ-specific T cell homing are preferentially expressed within the subset of CD4⁺CD7^– T cells. Specific absence of CD7 antigen expression on T cells is observed in a variety of pathologic conditions such as cutaneous T cell lymphoma, HIV infection, rheumatoid arthritis, and kidney transplantation. Current in vitro results suggest that specific downregulation of CD7 antigen expression in T cells reflects a separate and stable differentiation state occurring late in the immune response. Expansion of CD7^– T cells in vivo has been found in certain diseases associated with chronically repeated T cell stimulation. The potential pathophysiological significance of this T cell subset in certain human diseases is discussed.     

Antigen-Driven Clonal Accumulation of Peritoneal γδ T Cells in vivo

How the clonality of γδ T cells changes in response to exogenous antigens is uncertain. Here we analyzed kinetics of Vγ1.1 and Vγ2 T cell clonality after intraperitoneal injection of purified protein derivatives (PPD) by the heterogeneity of the third complementarity determining region (CDR3) length in Vγ1.1-Jγ4-Cγ4 and Vγ2-Jγ1-Cγ1 junctions. The V-J junctions were analyzed in intrahepatic lymphocytes (IHL), spleen cells, and peritoneal exudate cells (PEC) by polyacrylamide gel electrophoresis. γδ T cells expressing Vγ1.1 and Vγ2 genes were heterogeneous in normal mice. Accumulation of specific Vγ1.1 T cell clones was transiently detected 7 days after the injection in PEC, but no accumulation was observed in IHL and spleen cells. The accumulated clones disappeared by 4 weeks. Transient accumulation of Vγ2 T cell clones was also observed in PEC at the early phase after the injection. These results suggest that γδ T cells with specific TCR respond to PPD and temporary accumulate in the peritoneal cavity, but not in liver and spleen.     

Generation and Regulation of CD8＋ Regulatory T Cells

Research into the suppressive activity of CD4＋FoxP3＋ T regulatory cells （Treg） has defined a sublineage of CD4＋ cells that contribute to self-tolerance and resistance to autoimmune disease. Much less attention has been given to the potential contribution of regulatory sublineages of CD8＋ cells. Analysis of a small fraction of CD8＋ cells that target autoreactive CD4＋ cells through recognition of the MHC class Ib molecule Qa-1 in mouse and HLA-E in human has revitalized interest in CD8＋ Treg. Here we summarize recent progress and future directions of research into the role of this CD8＋ sublineage in resistance to autoimmune disease. Cellular ＆ Molecular Immunology. 2008; 5（6）：401-406.     

Function of Helper T Cells in the Memory CTL-mediated Anti-tumor Immunity

CD4 Tcellsarerequiredforthegenerationandmainte nanceofcytolyticCD8 Tcellsandareessentialforthe generationofbothcellularandhumoralimmuneresponses. However,thecontributionofCD4 Tcellstothemainte nanceofanti tumorimmunityisstillthesubjectofintense investig…     

Distinct Pattern of Human Vδ1 γδ T Cells Recognizing MICA

γδT cells represent one unique recognition pattern,the limited recognition,which distinguishes from the specificrecognition for αβT cells and pattern recognition for macrophages.Vδ1 γδT cell is the major subset of human γδT cells,which predominates in mucosal tissue including the intestinal epithelia.Presently,a few antigens thathuman Vδ1TCR can recognize have been identified.Among them,MHC class I chain-related molecules A (MICA)have been studied most intensively.Besides Vδ1TCR,MICA is also the ligand of NKG2D,a C-type lectin-likeactivating immunoreceptor.In human,only Vδ1 cells can simultaneously express both types of receptors of MICAwhile NK cells,αβT cells and other subsets of γδT cells likewise express NKG2D.Although the precisemechanisms are still enigmatic,this distinct pattern of Vδ1 cells recognizing MICA predicts unique biologicalsignificance of Vδ1 cells in immune defense.Recent years,some progresses have been made in this issue.In thisreview we summarize the related reports and put forward some novel views based on our group's studies.Cellular& Molecular Immunology.2005;2(4):253-258.     

Accumulation of Activated Invariant Natural Killer T Cells in the Tumor Microenvironment after α-Galactosylceramide-Pulsed Antigen Presenting Cells

Purpose

The intravenous administration of α-Galactosylceramide (α-GalCer)-pulsed antigen presenting cells (APCs) is well tolerated and the increased IFN-γ producing cells in the peripheral blood after the treatment appeared to be associated with prolonged survival. An exploratory study protocol was designed with the preoperative administration of α-GalCer-pulsed APCs to clarify the mechanisms of these findings, while especially focusing on the precise tumor site.

Methods

Patients with operable advanced lung cancer received an intravenous injection of α-GalCer-pulsed APCs before surgery. The resected lung and tumor infiltrating lymphocytes (TILs) as well as peripheral blood mononuclear cells were collected and the invariant NKT (iNKT) cell-specific immune responses were analyzed.

Results

Four patients completed the study protocol. We observed a significant increase in iNKT cell numbers in the TILs and augmented IFN-γ production by the α-GalCer-stimulated TILs.

Conclusion

The administration of α-GalCer-pulsed APCs successfully induced the dramatic infiltration and activation of iNKT cells in the tumor microenvironment.     

Engineering Human Peripheral Blood Stem Cell Grafts that Are Depleted of Naïve T Cells and Retain Functional Pathogen-Specific Memory T Cells

Graft-versus-host disease (GVHD) is a frequent major complication of allogeneic hematopoietic cell transplantation (HCT). Approaches that selectively deplete T cells that cause GVHD from allogeneic stem cell grafts and preserve T cells specific for pathogens may improve HCT outcomes. It has been hypothesized that the majority of T cells that can cause GVHD reside within the naïve T cell (T_N) subset, and previous studies performed in mouse models and with human cells in vitro support this hypothesis. As a prelude to translating these findings to the clinic, we developed and evaluated a novel 2-step clinically compliant procedure for manipulating peripheral blood stem cells (PBSC) to remove T_N, preserve CD34⁺ hematopoietic stem cells, and provide for a fixed dose of memory T cells (T_M) that includes T cells with specificity for common opportunistic pathogens encountered after HCT. Our studies demonstrate effective and reproducible performance of the immunomagnetic cell selection procedure for depleting T_N. Moreover, after cell processing, the CD45RA-depleted PBSC products are enriched for CD4⁺ and CD8⁺ T_M with a central memory phenotype and contain T_M cells that are capable of proliferating and producing effector cytokines in response to opportunistic pathogens.     

Pleural Mesothelial Cells Promote Expansion of IL-17–Producing CD8+ T Cells in Tuberculous Pleural Effusion

IL-17–producing CD8⁺ T lymphocytes (Tc17 cells) have recently been detected in many cancers and autoimmune diseases. However, the possible implication of Tc17 cells in tuberculous pleural effusion remains unclarified. In this study, distribution and phenotypic features of Tc17 cells in both tuberculous pleural effusion (TPE) and peripheral blood from patients with tuberculosis were determined. The effects of proinflammatory cytokines and local accessory cells (pleural mesothelial cells) on Tc17 cell expansion were also explored. We found that TPE contained more Tc17 cells than the blood. Compared with IFN-γ–producing CD8⁺ T cells, Tc17 cells displayed higher expression of chemokine receptors (CCRs) and lower expression of cytotoxic molecules. In particularly, Tc17 cells in TPE exhibited high expression levels of CCR6, which could migrate in response to CCL20. Furthermore, IL-1β, IL-6, IL-23, or their various combinations could promote Tc17 cell expansion from CD8⁺ T cells, whereas the proliferative response of Tc17 cells to above cytokines was lower than that of Th17 cells. Pleural mesothelial cells (PMCs) were able to stimulate Tc17 cell expansion via cell contact in an IL-1β/IL-6/IL-23 independent fashion. Thus this study demonstrates that Tc17 cells marks a subset of non-cytotoxic, CCR6⁺ CD8⁺ T lymphocytes with low proliferative capacity. The overrepresentation of Tc17 cells in TPE may be due to Tc17 cell expansion stimulated by pleural proinflammatory cytokines and to recruitment of Tc17 cells from peripheral blood. Additionally, PMCs may promote the production of IL-17 by CD8⁺ T cells at sites of TPE via cell–cell interactions.     

How do Regulatory T Cells Work?

CD4⁺ T cells are commonly divided into regulatory T (Treg) cells and conventional T helper (Th) cells. Th cells control adaptive immunity against pathogens and cancer by activating other effector immune cells. Treg cells are defined as CD4⁺ T cells in charge of suppressing potentially deleterious activities of Th cells. This review briefly summarizes the current knowledge in the Treg field and defines some key questions that remain to be answered. Suggested functions for Treg cells include: prevention of autoimmune diseases by maintaining self-tolerance; suppression of allergy, asthma and pathogen-induced immunopathology; feto-maternal tolerance; and oral tolerance. Identification of Treg cells remains problematic, because accumulating evidence suggests that all the presently-used Treg markers (CD25, CTLA-4, GITR, LAG-3, CD127 and Foxp3) represent general T-cell activation markers, rather than being truly Treg-specific. Treg-cell activation is antigen-specific, which implies that suppressive activities of Treg cells are antigen-dependent. It has been proposed that Treg cells would be self-reactive, but extensive TCR repertoire analysis suggests that self-reactivity may be the exception rather than the rule. The classification of Treg cells as a separate lineage remains controversial because the ability to suppress is not an exclusive Treg property. Suppressive activities attributed to Treg cells may in reality, at least in some experimental settings, be exerted by conventional Th cell subsets, such as Th1, Th2, Th17 and T follicular (Tfh) cells. Recent reports have also demonstrated that Foxp3⁺ Treg cells may differentiate in vivo into conventional effector Th cells, with or without concomitant downregulation of Foxp3.     

Reduced Immune Response to Borrelia burgdorferi in the Absence of �æ� T Cells

Little is known regarding the function of γδ T cells, although they accumulate at sites of inflammation in infections and autoimmune disorders. We previously observed that γδ T cells in vitro are activated by Borrelia burgdorferi in a TLR2-dependent manner. We now observe that the activated γδ T cells can in turn stimulate dendritic cells in vitro to produce cytokines and chemokines that are important for the adaptive immune response. This suggested that in vivo γδ T cells may assist in activating the adaptive immune response. We examined this possibility in vivo and observed that γδ T cells are activated and expand in number during Borrelia infection, and this was reduced in the absence of TLR2. Furthermore, in the absence of γδ T cells, there was a significantly blunted response of adaptive immunity, as reflected in reduced expansion of T and B cells and reduced serum levels of anti-Borrelia antibodies, cytokines, and chemokines. This paralleled a greater Borrelia burden in γδ-deficient mice as well as more cardiac inflammation. These findings are consistent with a model of γδ T cells functioning to promote the adaptive immune response during infection.     

Neuropilin-1: The Glue between Regulatory T Cells and Dendritic Cells?

The interaction between dendritic cells and regulatory T cells is critical for the maintenance of self-tolerance. In this issue of Immunity, Sarris et al. (2008) find that Neuropilin-1 contributes to the prolonged interaction of regulatory T cells with dendritic cells.     

Early Reconstitution of NK and γδ T Cells and Its Implication for the Design of Post-Transplant Immunotherapy

Relapse is the most frequent cause of treatment failure after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Natural killer (NK) cells and γδ T cells reconstitute early after allo-HSCT, contribute to tumor immunosurveillance via major histocompatibility complex–independent mechanisms and do not induce graft-versus-host disease. Here we performed a quantitative and qualitative analysis of the NK and γδ T cell repertoire in healthy individuals, recipients of HLA-matched sibling or unrelated donor allo-HSCT (MSD/MUD-HSCT) and umbilical cord blood-HSCT (UCB-HSCT). NK cells are present at high frequencies in all allo-HSCT recipients. Immune reconstitution (IR) of vδ2⁺?cells depended on stem cell source. In MSD/MUD-HSCT recipients, vδ2⁺?comprise up to 8% of the total lymphocyte pool, whereas vδ2⁺?T cells are barely detectable in UCB-HSCT recipients. Vδ1⁺?IR was driven by CMV reactivation and was comparable between MSD/MUD-HSCT and UCB-HSCT. Strategies to augment NK cell mediated tumor responses, similar to IL-15 and antibodies, also induced vδ2⁺?T cell responses against a variety of different tumor targets. Vδ1⁺?γδ T cells were induced less by these same stimuli. We also identified elevated expression of the checkpoint inhibitory molecule TIGIT (T cell Ig and ITIM domain), which is also observed on tumor-infiltrating lymphocytes and epidermal γδ T cells. Collectively, these data show multiple strategies that can result in a synergized NK and γδ T cell antitumor response. In the light of recent developments of low-toxicity allo-HSCT platforms, these interventions may contribute to the prevention of early relapse.     

Do Regulatory T Cells Play a Role in the Control of Homeostatic Proliferation?

The control of peripheral lymphocyte numbers is a fundamental aspect of the immune system. Regulatory T cells are involved in the suppression of autoimmune, antitumor, allergic, and other inflammatory responses, as well as in facilitating graft acceptance. In this paper, we discuss whether the control of homeostatic proliferation is another facet of the immune system that is controlled by regulatory T cells. A review of the published data connecting regulatory T cells with the control of homeostatic proliferation indicates that several key questions remain open. One of these relates to the stage at which regulatory T cells could play a role (i.e., T-cell proliferation vs. survival).     

Epigenomic-Guided Mass Cytometry Profiling Reveals Disease-Specific Features of Exhausted CD8 T Cells

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The ex vivo Microenviroments in MLTC of Poorly Immunogenic Tumor Cells Facilitate Polarization of CD4^＋ CD25^＋ Regulatory T Cells

CD4^＋CD25^＋ regulatory T （TR） cells play an important role in maintaining a balanced peripheral immune system. Recent studies have shown that TR cells may also play a key role in suppressing anti-tumor immune response. In order to investigate the tumor immune microenvironment and its influence on TR polarization, poorly immunogenic tumor cell line Ds （C57BL/6, H-2^b）, immunogenic tumor cell lines FBL3 （C57BL/6, H-2^b） and H22 BALB/c, H-2^d） were used to establish the syngeneic/allogeneic, poorly immunogenic/immunogenic mixed lymphocytes-tumor cell culture （MLTC）. Our results revealed that the proportion of CD4^＋CD25^＋ T cells in MLTC of syngeneic primed splenocytes stimulated with D5 tumor cells was higher than that with H22 cells （0.43% vs 0.044%, and the similar results appeared in allogeneic splenocytes stimulated with D5 tumor cells （0.39% vs 0.04%）. The splenocytes stimulated with supernatant from syngeneic MLTC of D5 tumor cells demonstrated higher proportion of CD4^＋CD25^＋ cells than that from allogeneic MLTC of D5 tumor cells, and the splenocytes stimulated with supernatant from syngeneic or allogeneic MLTC of H22 tumor cells generated lower proportion of CD4^＋CD25^＋ T cells than that of D5 tumor cells. The TGF-β1 and Th2-oriented cytokines （IL-4 and IL-10） were dominated in supernatants of syngeneic MLTC of poorly immunogenic tumor cells. Our results provided useful information for studying the mechanisms underlying tumor immune surveillance as well as for the tumor immunotherapy.     

Reconstitution of Interleukin-17–Producing T Helper Cells after Allogeneic Hematopoietic Cell Transplantation

Interleukin 17A (IL-17)-producing CD4⁺ T helper type 17 (Th17) cells have recently drawn attention as possible effector cells of acute graft-versus-host disease (GVHD) after allogeneic hematopoietic cell transplantation (HCT) in murine models. Their role after allogeneic HCT in humans is unknown. In this prospective study, Th17, Th1/17, and Th1 cells were quantified in the peripheral blood of 80 patients within the first 3 months after allogeneic HCT using intracellular cytokine staining and flow cytometry. Within the observation period, Th1, Th1/17, and Th17 cells did not reconstitute to levels of healthy control subjects. In contrast to Th1 cells, no further expansion of Th1/17 and Th17 cells was observed during the first month after HCT. Antithymocyte globulin during conditioning significantly reduced the frequency of Th1/17 and Th17 cells but not of Th1 cells. Acute GVHD was not associated with significant changes in the size of the Th1, Th1/17, or Th17 cell subsets. Cytomegalovirus reactivation triggered the expansion of all T helper subsets, and Th1 cells showed the strongest increase. In contrast, no significant changes were found in the T helper cell compartment of patients with bacterial infections compared with time-matched control subjects. In conclusion, quantitative reconstitution of Th1, Th1/17, and Th17 cells is impaired within the first 3 months after HCT, especially when antithymocyte globulin is administered during conditioning. Cytomegalovirus reactivation, but not acute GVHD or bacterial infection, triggered the absolute expansion of these T cell subsets.     

Self-Reactive CD4+ T Cells and B Cells in the Blood in Health and Autoimmune Disease: Increased Frequency of Thyroglobulin-Reactive Cells in Graves’ Disease

The mechanisms underlying activation of potentially self-reactive circulating B cells and T cells remain unclear. We measured the uptake of a self-antigen, thyroglobulin, by antigen presenting cells, and the subsequent proliferation of CD4⁺ T cells and B cells from healthy controls and patients with autoimmune thyroiditis. In Hashimoto's thyroiditis, B cells bound increased amounts of thyroglobulin in a complement- and autoantibody-dependent manner, and the thyroglobulin-elicited proliferation of CD4⁺ T cells and B cells was complement dependent. Increased proportions of Tg-responsive CD4⁺ T cells and B cells were found in patients with Graves’ disease. Notably, both patient groups and healthy controls exhibited higher proliferative responses to thyroglobulin than to a foreign recall antigen, tetanus toxoid. Our results suggest that self-tolerance can be broken by exposure of circulating lymphocytes to high local concentrations of self-antigen, and that complement plays a role in the maintenance of autoimmune processes, at least in Hashimoto's thyroiditis.     

Intratumoral Expression of MIP-1β Induces Antitumor Responses in a Pre-Established Tumor Model through Chemoattracting T Cells and NK Cells

Direct intratumoral introduction of therapeutic or regulatory genes is a developing technology with potential application for cancer gene therapy. Macrophage inflammatory protein-1 beta (MIP-1β) is a chemokine which can chemoattract immune cells such as T cells. In the present study, murine colorectal adenocarcinoma CT26 cells were transfected with a recombinant adenovirus (AdhMIP-1β) carrying the human MIP-1β gene. 24h post-transfection, hMIP-1β levels reached approximately 980 pg/ml in supernatants of 10^6 hMIP-1β-transfected CT26 cells. Moreover, the supernatants exhibited chemotactic activity for CD8^ T cells, CD4^ T cells, NK cells and immature DCs. Intratumoral injection of AdhMIP-1β significantly inhibited tumor growth and prolonged the survival time of tumor-bearing mice. Intratumoral hMIP-1β gene transfer also induced powerful tumor-specific CTL responses in vivo. The therapeutic effects of hMIP-1β gene therapy were greatly reduced following in vivo depletion of both CD4^ and CD8~ T cells, but were unaffected by depletion of single T cell subsets. Immune cell depletion experiments also revealed that NK cells played an important role in hMIP-1β-induced antitumor responses. These results suggest that intratumoral expression of hMIP-1β has the potential effect to induce host antitumor immunity and may prove to be a useful form of cancer gene therapy.