Uterine Natural Killer Cells： Their Choices, Their Missions

Uterine natural killer(uNK)cells,sharing many characters with peripheral blood natural killer(pNK)cells,are amajor uterine lymphocyte population at early gestational stages during normal pregnancy in placental mammals.The functions of uNK cells include cytokine production and cytotoxcity that are regulated by signals throughactivating and inhibitory receptors.UNK cells differ from pNK cells however and contribute to the structuralchanges that accompany the differentiation of the maternal-fetal interface.Immunological mechanisms mustprovide a balanced environment for uNK cell proliferation,differentiation and activation through intricatesignaling pathways.An improved knowledge of mechanisms regulating uNK cells development and the cytokinenetwork at the maternal-fetal interface of mice and humans might be useful to harness the power of these cells formaintenance of pregnancy.Cellular & Molecular Immunology.2005;2(2):123-129.     

Natural Killer Cells： Biology and Clinical Use in Cancer Therapy

Natural killer (NK) cells have the ability to mediate both bone marrow rejection and promote engraftment,aswell as the ability to elicit potent anti-tumor effects.However the clinical results for these processes are stillelusive.Greater understanding of NK cell biology,from activating and inhibitory receptor functions to the roleof NK cells in allogeneic transplantation,needs to be appreciated in order to draw out the clinical potential ofNK cells.Mechanisms of bone marrow cell (BMC) rejection are known to be dependant on inhibitory receptorsspecific for major histocompatibility complex (MHC) molecules and on activating receptors that have manypotential ligands.The modulation of activating and inhibitory receptors may hold the key to clinical successinvolving NK cells.Pre-clinical studies in mice have shown that different combinations of activating andinhibitory receptors on NK cells can reduce graft-versus-host disease (GVHD),promote engraftment,andprovide superior graft-versus-tumor (GVT) responses.Recent clinical data have shown that the use ofKIR-ligand incompatibility produces tremendous graft-versus-leukemia effect in patients with acute myeloidleukemia at high risk of relapse.This review will attempt to be a synthesis of current knowledge concerning NKcells,their involvement in BMT,and their use as an immunotherapy for cancer and other hematologicmalignancies.Cellular & Molecular Immunology.2004;1(1):12-21.     

The Plasticity of γδ T Cells： Innate Immunity,Antigen Presentation and New Immunotherapy

Several signals influence dendritic cell （DC） functions and consequent the immune responses to infectious pathogens. Our recent findings provide a new model of intervention on DCs implicating human γδ T cell stimuli. Vγ/9Vδ2 T cells represent the major subset of circulating human γδ T cells and can be activated by non-peptidic molecules derived from different microorganisms or abnormal metabolic routes. With activated-Vγ/9Vδ2 T cell co-culture, immature DCs acquire features of mature DCs, such as increasing the migratory activity, up-regulating the chemokine receptors, and triggering the Thl immune response. Similar to the NK-derived signals, DC activation is mediated by soluble factors as well as cell-to-cell contact. Many non-peptidic molecules including nitrogen- containing bisphosphonates and pyrophosphomonoester drugs, can stimulate the activity of Vγ/9Vδ2 T cells in vitro and in vivo. The relatively low in vivo toxicity of many of these drugs makes possible novel vaccine and immune-based strategies against infectious diseases.     

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.     

Naturally Occurring Self-Reactive CD4^＋CD25^＋ Regulatory T Cells： Universal Immune Code

Naturally occurring thymus-arisen CD4^＋CD25^＋ regulatory T （Treg） cells are considered to play a central role in self-tolerance. Precise signals that promote the development of Treg cells remain elusive, but considerable evidence suggests that costimulatory molecules, cytokines, the nature of the TCR and the niche or the context in which the T cell encounters antigen in the thymus play important roles. Analysis of TCR from Treg cells has demonstrated that a large proportion of this population has a higher avidity to self-antigen in comparison with TCR from CD4^＋CD25^＋ cells and that peripheral antigen is required for their development, maintenance, or expansion. Treg cells have been shown to undergo expansion in the periphery, likely regulated by the presence of self-antigen. Many studies have shown that the involvement of Treg cells in the tolerance induction is antigen-specific, even with MHC-mismatched, in transplantation/graft versus host disease （GVHD）, autoimmunity, cancer, and pregnancy. Theses studies concluded a vital role for self-reactive Treg cells in maintenance of the body integrity. Based on those studies, we hypothesize that self-reactive Treg cells are shared among all healthy individuals and recognize same self-antigens and their TCR encodes for few dominant antigens of each organ which defines the healthy self. These dominant self antigens can be regarded as ＂universal immune code＂. Cellular ＆ Molecular Immunology.     

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.     

Understanding the Regulatory Roles of Natural Killer T Cells in Rheumatoid Arthritis: T Helper Cell Differentiation Dependent or Independent?

Rheumatoid arthritis (RA) is the most common chronic systemic autoimmune disease. This disease is thought to be caused by pathogenic T cells. Th1, Th2, Th17 and Treg cells have been implicated in the pathogenesis of RA. These Th cells differentiate from CD4+ T cells primarily due to the effects of cytokines. Natural killer T (NKT) cells are a distinct subset of lymphocytes that can rapidly secrete massive amount of cytokines, including IL‐2, IL‐4, IL‐12 and IFN‐γ. Numerous studies showed that NKT cells can influence the differentiation of CD4+ T cells via cytokines in vitro. These findings suggest that NKT cells play an important role in RA by polarizing Th1, Th2, Th17 and Treg cells. In view of the complexity of RA, we discussed whether NKT cells really influence the development of RA through regulating the differentiation of Th cells.     

The Qa-1 Dependent CD8^＋ T Cell Mediated Regulatory Pathway

The immune system has evolved a variety of regulatory mechanisms to ensure the peripheral self-tolerance as well as the optimal capacity to elicit effective anti-infection immunity. At present, there is no satisfactory conceptual framework to explain how the peripheral immunity is regulated at a biological system level, which enables the immune system to perform its essential functions to mount effective immunity to virtually any foreign antigens but avoid harmful immune responses to self. In this regard, during the past few years, an “affinity/avidity model of peripheral T cell regulation” has been proposed and tested, which opens up a new paradigm to understand how the peripheral immunity, to both self and foreign antigens, is regulated. The paradigm is based on the discovery of a subset CD8^＋ T cells with TCRs which specifically recognize a unique set of self-peptides presented by the MHC class Ib molecule Qa-I differentially expressed on T cells as a function of the affinity/avidity of T cell activation. These Qa-1 restricted CD8^＋ T cells represent an example of how the immune system utilizes a unified mechanism to regulate adaptive immunity to both self and foreign antigens. Thus, by selectively down-regulating T cells of intermediate affinity/avidity, to any antigens, the immune system controls the adaptive immunity without the necessity to distinguish self from non-self in the periphery at the level of T cell regulation. Cellular ＆ Molecular Immunology. 2005;2（3）：161-167.     

Deficiency of Mouse CD4^＋CD25^＋Foxp3^＋ Regulatory T Cells in Xenogeneic Pig Thymus-Grafted Nude Mice Suffering from Autoimmune Diseases

Xenogeneic thymus transplantation can efficiently induce specific immune tolerance to donor antigens in athymic recipients. However, many nude mice suffer from autoimmune diseases （AID） for over 10 weeks after xenogeneic thymus transplantation. CD4^＋CD25^＋Foxp3^＋ regulatory T （Treg） cells were recently determined to play a pivotal role in keeping immune tolerance in humans and mice. Thus, we investigated this subpopulation of Treg cells in the periphery of pig thymus-grafted nude mice suffering from AID. Our results showed that the expression of Foxp3, CTLA-4 and GITR on mouse CD4^＋CD25^＋ T cells and the ratio of CD4^＋CD25^＋Foxp3^＋ Treg cells to CD4^＋ T cells were significantly decreased in the periphery of pig thymus-grafted nude mice suffering from AID, compared with healthy pig or mouse thymus-grafted nude mice. Furthermore, mouse CD4^＋CD25^＋ T cells in pig thymus-grafted nude mice suffering from AID showed more severe deficiency in immunosuppressive function compared with the counterpart in xenogeneic pig or syngeneic thymus-grafted nude mice without AID. Thus, the decreased frequency, altered phenotype and functional deficiency of mouse CD4^＋CD25^＋ Treg cells in pig thymus-grafted nude mice may contribute to the development of AID in this model.     

The Role of Innate Immune Cells in the Response of Heat-Treated Mycobacterium tuberculosis （M.tb） Antigens Stimulating PBMCs

The proliferation response of γδT cells to the antigen from heat-treated Mycobacterium tuberculosis H37Ra(M.tb Ag)was used as a good model in γδT cell research.From preliminary research it is found that activatedNK cells positively elevated γδT cells proliferation after simulating PBMCs with M.tb Ag.To investigatedifferent behaviors of NK cells,γδNKT cells,γδT cells and relationships between these cell subsets,activationand proliferation of different cell subsets of PBMCs in response to M.tb Ag were analyzed.We demonstratedthat NK cells,γδNKT cells and γδT cells could be activated after stimulation with M.tb Ag.γδNKT cells and γδTcells proliferated while the number of NK cells decreased after 11 day-simulation with M.tb Ag.Meanwhile,atthe early time of stimulation the cytotoxicity of PBMCs was enhanced.Cellular & Molecular Immunology.2004;1(6):467-470.     

The fate of regulatory T cells： survival or apoptosis

Foxp3＋ regulatory T cells （Tregs） are unique in their immunosuppressive abilities and contribution to immune regulation. However, the homeostatic processes and survival programs that maintain the Treg population remain unclear. Here, we highlight the recent study by Pierson et al.,1 which dissected the regulatory mechanisms of Treg home- ostasis and survival.     

Early Cytomegalovirus Reactivation and Expansion of CD56brightCD16dim/−DNAM1+ Natural Killer Cells Are Associated with Antileukemia Effect after Haploidentical Stem Cell Transplantation in Acute Leukemia

Cytomegalovirus (CMV) infection is a major complication after allogeneic hematopoietic stem cell transplantation but is suggested to exert a strong antileukemia effect in part due to alterations in the composition of natural killer (NK) cells. We evaluated the impact of early CMV reactivation and changes in NK cell subset recovery on relapse rate and survival after haploidentical stem cell transplantation (haploSCT) for acute leukemia. Fifty patients with acute leukemia who received haploSCT were analyzed. Expression of T cells and specific receptors (NKG2A, NKG2D, DNAM1, and CD57) on circulating NK cells (CD56^brightCD16^dim/– or CD56^dimCD16⁺ cells) was serially measured using multiparametric flow cytometry. CMV reactivation during the first 100 days was observed in 41 patients (82%) at a median of 23 days after haploSCT. The incidence of acute graft-versus-host disease (GVHD) and chronic GVHD tended to be higher in patients with CMV reactivation, although this difference was not statistically significant. Multivariate analysis showed that CMV reactivation (P = .011) and a dose of infused T cells > 3.2 × 10⁸/kg (P = .027) were independent predictors of a reduced relapse risk and only CMV reactivation (P = .029) was an independent predictor of improved leukemia-free survival. CD56^brightCD16^dim/?DNAM1⁺NK cell counts increased from day 30 to 90 in patients with CMV reactivation but decreased after day 30 in patients without CMV reactivation. An increase in CD56^brightCD16^dim/?DNAM1⁺ NK cells was not associated with the occurrence of chronic GVHD but was associated with a reduced cumulative relapse rate (16.4% versus 58.0%, P = .019). Multivariate analysis indicates that an increase in the CD56^brightCD16^dim/?DNAM1⁺NK cell count was an independent predictor of reduced relapse risk. Our study demonstrates a significant correlation between low relapse rates and CMV reactivation as well as the recovery of CD56^brightCD16^dim/?DNAM1⁺ NK cells, providing valuable information for understanding the plausible immunologic mechanism of the graft-versus-leukemia effect.     

CD52 as both a marker and an effector molecule of T cells with regulatory action： Identification of novel regulatory T cells

Regulation of immune responses is central to an effective clearance of pathogens. An effective immune response is also necessary for preventing the development of cancer and auto- immune diseases and for maintaining homeostasis. Although the thymus is the central lymphoid organ that regulates immune responses for self-tol- erance during the maturation of T cells, regulatory immune cells are still required for the proper functioning of mature immune cells in the periphery. Regulatory cells are a subpopulation of immune cells that suppress proliferation and cytokine production by other immune cells in res- ponse to antigenic stimulation.