Interactions between NKT cells and Tregs are required for tolerance to combined bone marrow and organ transplants. Blood. 2012;119:1581-1589. [PMID: 22174155 DOI: 10.1182/blood-2011-08-371948]

Clonal Deletion Established via Invariant NKT Cell Activation and Costimulatory Blockade Requires In Vivo Expansion of Regulatory T Cells

Recently, the immune-regulating potential of invariant natural killer T (iNKT) cells has attracted considerable attention. We previously reported that a combination treatment with a liposomal ligand for iNKT cells and an anti-CD154 antibody in a sublethally irradiated murine bone marrow transplant (BMT) model resulted in the establishment of mixed hematopoietic chimerism through in vivo expansion of regulatory T cells (Tregs). Herein, we show the lack of alloreactivity of CD8(+) T cells in chimeras and an early expansion of donor-derived dendritic cells (DCs) in the recipient thymi accompanied by a sequential reduction in the donor-reactive Vβ-T cell receptor repertoire, suggesting a contribution of clonal deletion in this model. Since thymic expansion of donor DCs and the reduction in the donor-reactive T cell repertoire were precluded with Treg depletion, we presumed that Tregs should preform before the establishment of clonal deletion. In contrast, the mice thymectomized before BMT failed to increase the number of Tregs and to establish CD8(+) T cell tolerance, suggesting the presence of mutual dependence between the thymic donor-DCs and Tregs. These results provide new insights into the regulatory mechanisms that actively promote clonal deletion.

Use of hematopoietic cell transplants to achieve tolerance in patients with solid organ transplants

The goals of tolerance in patients with solid organ transplants are to eliminate the lifelong need for immunosuppressive (IS) drugs and to prevent graft loss due to rejection or drug toxicity. Tolerance with complete withdrawal of IS drugs has been achieved in recipients of HLA-matched and mismatched living donor kidney transplants in 3 medical centers using hematopoietic cell transplants to establish mixed or complete chimerism.

NK Cell and CD4+FoxP3+ Regulatory T Cell Based Therapies for Hematopoietic Stem Cell Engraftment

Allogeneic hematopoietic cell transplantation (HCT) is a powerful therapy to treat multiple hematological diseases. The intensive conditioning regimens used to allow for donor hematopoietic stem cell (HSC) engraftment are often associated with severe toxicity, delayed immune reconstitution, life-threatening infections, and thus higher relapse rates. Additionally, due to the high incidence of graft versus host disease (GvHD), HCT protocols have evolved to prevent such disease that has a detrimental impact on antitumor and antiviral responses. Here, we analyzed the role of host T and natural killer (NK) cells in the rejection of donor HSC engraftment as well as the impact of donor regulatory T cells (Treg) and NK cells on HSC engraftment. We review some of the current strategies that utilize NK or Treg to improve allogeneic HCT therapy in order to accomplish better HSC engraftment and immune reconstitution and achieve a lower incidence of cancer relapse, opportunistic infections, and GvHD.

Engraftment of embryonic stem cells and differentiated progeny by host conditioning with total lymphoid irradiation and regulatory T cells

Embryonic stem cells (ESCs) hold promise for the treatment of many medical conditions; however, their utility is limited by immune rejection. The objective of our study is to establish tolerance or promote engraftment of transplanted ESCs as well as mature cell populations derived from ESCs. Luciferase (luc(+))-expressing ESCs were utilized to monitor the survival of the ESCs and differentiated progeny in living recipients. Allogeneic recipients conditioned with fractioned total lymphoid irradiation (TLI) and anti-thymocyte serum (ATS) or TLI plus regulatory T cells (T(reg)) promoted engraftment of ESC allografts after transplantation. Following these treatments, the engraftment of transplanted terminally differentiated endothelial cells derived from ESCs was also significantly enhanced. Our findings provide clinically translatable strategies of inducing tolerance to adoptively transferred ESCs for cell replacement therapy of medical disorders.

Regulatory T Cell Immunotherapy in Immune-Mediated Diseases

Broad clinical interest rapidly followed the recent discovery of different subpopulations of T cells that have immune regulatory properties and a number of studies have been conducted aiming to dissect the translational potential of these promising cells. In this review we will focus on forkhead box P3 (FoxP3) positive regulatory T cells, T regulatory type 1 cells and invariant natural killer T cells (iNKT). We will analyze their ability to correct immune dysregulation in animal models of immune mediated diseases and we will examine the first clinical approaches where these cells have been directly or indirectly employed. We will discuss successes, challenges and limitations that rose in the road to the clinical use of regulatory T cells.

Cellular mechanisms of CCL22-mediated attenuation of autoimmune diabetes

Autoimmune destruction of insulin-producing β cells in type 1 diabetes and islet transplantation involves a variety of immune pathways but is primarily mediated by self-reactive T cells. Chemokines can modulate local immune responses in inflammation and tumors by recruiting immune cells. We have reported that expression of the chemokine CCL22 in pancreatic β cells in the NOD mouse prevents autoimmune attack by recruiting T regulatory cells (Tregs), protecting mice from diabetes. In this study we show that invariant NKT cells are also recruited to CCL22-expressing islet transplants and are required for CCL22-mediated protection from autoimmunity. Moreover, CCL22 induces an influx of plasmacytoid dendritic cells, which correlates with higher levels of IDO in CCL22-expressing islet grafts. In addition to its chemotactic properties, we found that CCL22 activates Tregs and promotes their ability to induce expression of IDO by dendritic cells. Islet CCL22 expression thus produces a tolerogenic milieu through the interplay of Tregs, invariant NKT cells, and plasmacytoid dendritic cells, which results in suppression of effector T cell responses and protection of β cells. The immunomodulatory properties of CCL22 could be harnessed for prevention of graft rejection and type 1 diabetes as well as other autoimmune disorders.

Transplantation tolerance and its outcome during infections and inflammation

Much progress has been made toward understanding the mechanistic basis of transplantation tolerance in experimental models, which implicates clonal deletion of alloreactive T and B cells, induction of cell-intrinsic hyporesponsiveness, and dominant regulatory cells mediating infectious tolerance and linked suppression. Despite encouraging success in the laboratory, achieving tolerance in the clinic remains challenging, although the basis for these challenges is beginning to be understood. Heterologous memory alloreactive T cells generated by infections prior to transplantation have been shown to be a critical barrier to tolerance induction. Furthermore, infections at the time of transplantation and tolerance induction provide a pro-inflammatory milieu that alters the stability and function of regulatory T cells as well as the activation requirements and differentiation of effector T cells. Thus, infections can result in enhanced alloreactivity, resistance to tolerance induction, and destabilization of the established tolerance state. We speculate that these experimental findings have relevance to the clinic, where infections have been associated with allograft rejection and may be a causal event precipitating the loss of grafts after long periods of stable operational tolerance. Understanding the mechanisms by which infections prevent and destabilize tolerance can lead to therapies that promote stable life-long tolerance in transplant recipients.

Path to clinical transplantation tolerance and prevention of graft-versus-host disease

Although organ and bone marrow transplantations are life-saving procedures for patients with terminal diseases, the requirement for the lifelong use of immunosuppressive drugs to prevent organ graft rejection and the development of graft versus host disease (GVHD) remain important problems. Experimental approaches to solve these problems, first in preclinical models and then in clinical studies, developed at Stanford during the past 40 years are summarized in this article. The approaches use fractionated radiation of the lymphoid tissues, a procedure initially developed to treat Hodgkin's disease, to alter the immune system such that tolerance to organ transplants can be achieved and GVHD can be prevented after the establishment of chimerism. In both instances, the desired goal was achieved when the balance of immune cells was changed to favor regulatory innate and adaptive immune cells that suppress the conventional immune cells that ordinarily promote inflammation and tissue injury.

Requirement for interactions of natural killer T cells and myeloid-derived suppressor cells for transplantation tolerance

The goal of the study was to elucidate the cellular and molecular mechanisms by which a clinically applicable immune tolerance regimen of combined bone marrow and heart transplants in mice results in mixed chimerism and graft acceptance. The conditioning regimen of lymphoid irradiation and anti-T cell antibodies changed the balance of cells in the lymphoid tissues to create a tolerogenic microenvironment favoring the increase of natural killer T (NKT) cells, CD4+ CD25+ regulatory T cells and Gr-1+ CD11b+ myeloid-derived suppressor cells (MDSCs), over conventional T cells (Tcons). The depletion of MDSCs abrogated chimerism and tolerance, and add back of these purified cells was restorative. The conditioning regimen activated the MDSCs as judged by the increased expression of arginase-1, IL-4Rα and programmed death ligand 1, and the activated cells gained the capacity to suppress the proliferation of Tcons to alloantigens in the mixed leukocyte reaction. MDSC activation was dependent on the presence of host invariant NKT cells. The conditioning regimen polarized the host invariant NKT cells toward IL-4 secretion, and MDSC activation was dependent on IL-4. In conclusion, there was a requirement for MDSCs for chimerism and tolerance, and their suppressive function was dependent on their interactions with NKT cells and IL-4.

Regulatory T-cell therapy in the induction of transplant tolerance: the issue of subpopulations

Clinical tolerance induction to permit minimization or cessation of immunosuppressive drugs is one of the key research goals in solid organ transplantation. The use of ex vivo expanded or manipulated immunologic cells, including CD4CD25FOXP3 regulatory T cells (Tregs), to achieve this aim is already a reality, with several trials currently recruiting patients. Tregs are a highly suppressive, nonredundant, population of regulatory cells that prevent the development of autoimmune diseases in mammals. Data from transplanted humans and animal models support the notion that Tregs can mediate both induction and adoptive transfer of transplantation tolerance. However, human Tregs are highly heterogeneous and include subpopulations with the potential to produce the proinflammatory cytokine interleukin-17, which has been linked to transplant rejection. Tregs are also small in number in the peripheral circulation, thus they require ex vivo expansion before infusion into man. Selection of the most appropriate Treg population for cell therapy is, therefore, a critical step in ensuring successful clinical outcomes. In this review, we discuss Treg subpopulations, their subdivision based on nonmutually exclusive criteria of origin, expression of immunologic markers and function, availability in the peripheral blood of patients awaiting transplantation, and their suitability for programs of cell-based therapy.

MHC-mismatched mice liver transplantation promotes tumor growth in liver graft

Liver transplantation is a final therapeutic option for treatment of hepatic malignancies, but local recurrence remains high after surgery. However, the underlying mechanisms of local tumor recurrence are still unknown. We speculated that immunological status of transplanted liver may contribute to the progress of tumor development. CT-26 tumor cells are injected into graft after allogeneic or syngeneic liver transplantation. The growth pattern of tumor and the co-relationship of regulatory T cell and effector T cells in liver graft were observed and investigated at 3d, 6d, 9d and 15d post-transplantation. The Hepatic Replacement Area of tumor in allogeneic grafts was significantly larger than that in syngeneic grafts. The activation of tumor growth in allografts was due to the dysfunction of effector T cells mediated by regulatory T cells in liver graft. Using nude mice model, we further confirmed that regulatory T cells from allograft significantly weaken the function of effector T cells in vivo. Our data has showed that MHC-mismatched mice liver transplantation can promote tumor growth in liver graft. For the first time, we demonstrated that susceptibility to tumor development in liver graft is due to the down-regulation of effector T cells' function mediated by the regulatory T cells.

A novel approach inducing transplant tolerance by activated invariant natural killer T cells with costimulatory blockade

Invariant natural killer T (iNKT) cells are one of the innate lymphocytes that regulate immunity, although it is still elusive how iNKT cells should be manipulated for transplant tolerance. Here, we describe the potential of a novel approach using a ligand for iNKT cells and suboptimal dosage of antibody for CD40-CD40 ligand (L) blockade as a powerful method for mixed chimerism establishment after allogenic bone marrow transplantation in sublethally irradiated fully allo recipients. Mixed-chimera mice accepted subsequent cardiac allografts in a donor-specific manner. High amounts of type 2 helper T cytokines were detected right after iNKT cell activation, while subsequent interferon-gamma production by NK cells was effectively inhibited by CD40/CD40L blockade. Tolerogenic components, such as CD11c(low) mPDCA1(+) plasmacytoid dendritic cells and activated regulatory T cells (Tregs) expressing CD103, KLRG-1 and PD-1, were subsequently augmented. Those activating Tregs seem to be required for the establishment of chimerism because depletion of the Tregs 1 day before allogenic cell transfer resulted in a chimerism brake. These results collectively suggest that our new protocol makes it possible to induce donor-specific tolerance by enhancement of the innate ability for immune tolerance in place of the conventional immunosuppression.

Ly108 expression distinguishes subsets of invariant NKT cells that help autoantibody production and secrete IL-21 from those that secrete IL-17 in lupus prone NZB/W mice

Lupus is a systemic autoimmune disease characterized by anti-nuclear antibodies in humans and genetically susceptible NZB/W mice that can cause immune complex glomerulonephritis. T cells contribute to lupus pathogenesis by secreting pro-inflammatory cytokines such as IL-17, and by interacting with B cells and secreting helper factors such as IL-21 that promote production of IgG autoantibodies. In the current study, we determined whether purified NKT cells or far more numerous conventional non-NKT cells in the spleen of NZB/W female mice secrete IL-17 and/or IL-21 after TCR activation in vitro, and provide help for spontaneous IgG autoantibody production by purified splenic CD19(+) B cells. Whereas invariant NKT cells secreted large amounts of IL-17 and IL-21, and helped B cells, non-NKT cells did not. The subset of IL-17 secreting NZB/W NKT cells expressed the Ly108(lo)CD4(-)NK1.1(-) phenotype, whereas the IL-21 secreting subset expressed the Ly108(hi)CD4(+)NK1.1(-) phenotype and helped B cells secrete a variety of IgG anti-nuclear antibodies. α-galactocylceramide enhanced the helper activity of NZB/W and B6.Sle1b NKT cells for IgG autoantibody secretion by syngeneic B cells. In conclusion, different subsets of iNKT cells from mice with genetic susceptibility to lupus can contribute to pathogenesis by secreting pro-inflammatory cytokines and helping autoantibody production.

The immunoregulatory role of type I and type II NKT cells in cancer and other diseases

NKT cells are CD1d-restricted T cells that recognize lipid antigens. They also have been shown to play critical roles in the regulation of immune responses. In the immune responses against tumors, two subsets of NKT cells, type I and type II, play opposing roles and cross-regulate each other. As members of both the innate and adaptive immune systems, which form a network of multiple components, they also interact with other immune components. Here, we discuss the function of NKT cells in tumor immunity and their interaction with other regulatory cells, especially CD4(+)CD25(+)Foxp3(+) regulatory T cells.

Role of type 1 natural killer T cells in pulmonary immunity

Mucosal sites are populated by a multitude of innate lymphoid cells and "innate-like" T lymphocytes expressing semiconserved T-cell receptors. Among the latter group, interest in type I natural killer T (NKT) cells has gained considerable momentum over the last decade. Exposure to NKT cell antigens is likely to occur continuously at mucosal sites. For this reason, and as they rapidly respond to stress-induced environmental cytokines, NKT cells are important contributors to immune and inflammatory responses. Here, we review the dual role of mucosal NKT cells during immune responses and pathologies with a particular focus on the lungs. Their role during pulmonary acute and chronic inflammation and respiratory infections is outlined. Whether NKT cells might provide a future attractive therapeutic target for treating human respiratory diseases is discussed.

Bacterial CD1d-restricted glycolipids induce IL-10 production by human regulatory T cells upon cross-talk with invariant NKT cells

Invariant NKT (iNKT) cells and CD4(+)CD25(+)FOXP3(+) regulatory T cells (Tregs) are important immune regulatory T cells with Ag reactivity to glycolipids and peptides, respectively. However, the functional interplay between these cells in humans is poorly understood. We show that Tregs suppress iNKT cell proliferation induced by CD1d-restricted glycolipids, including bacterial-derived diacylglycerols, as well as by innate-like activation. Inhibition was related to the potency of iNKT agonists, making diacylglycerol iNKT responses very prone to suppression. Cytokine production by iNKT cells was differentially modulated by Tregs because IL-4 production was reduced more profoundly compared with IFN-γ. A compelling observation was the significant production of IL-10 by Tregs after cell contact with iNKT cells, in particular in the presence of bacterial diacylglycerols. These iNKT-primed Tregs showed increased FOXP3 expression and superior suppressive function. Suppression of iNKT cell responses, but not conventional T cell responses, was IL-10 dependent, suggesting that there is a clear difference in mechanism between the Treg-mediated inhibition of these cell types. Our data highlight a physiologically relevant interaction between human iNKT and Tregs upon pathogen-derived glycolipid recognition that has a significant impact on the design of iNKT cell-based therapeutics.

Lymphodepletional strategies in transplantation

Because lymphocytes were shown to mediate transplant rejection, their depletion has been studied as a mechanism of preventing rejection and perhaps inducing immunologic tolerance. Agents that profoundly deplete lymphocytes have included monoclonal antibodies, cytotoxic drugs, and radiation. We have studied several such agents but focused on antibodies that deplete not only peripheral blood lymphocytes, but also lymph node lymphocytes. Depletion of lymph node T lymphocytes appears to permit peripheral tolerance at least for T cells in animal models. Nevertheless, B-cell responses may be resistant to such approaches, and T memory cells are likewise relatively resistant to depleting antibodies. We review the experimental and clinical approaches to depletion strategies and outline some of the pitfalls of depletion, such as limitations of currently available agents, duration of tolerance, infection, and malignancy. It is notable that most tolerogenic strategies that have been attempted experimentally and clinically include depleting agents even when they are not named as the underlying strategy. Thus, there is an implicitly acknowledged role for reducing the precursor frequency of donor antigen-specific lymphocytes when approaching the daunting goal of transplant tolerance.

Natural Killer Dendritic Cells Enhance Immune Responses Elicited by α -Galactosylceramide-Stimulated Natural Killer T Cells

Natural killer dendritic cells (NKDCs) possess potent anti-tumor activity, but the cellular effect of NKDC interactions with other innate immune cells is unclear. In this study, we demonstrate that the interaction of NKDCs and natural killer T (NKT) cells is required for the anti-tumor immune responses that are elicited by α-galactosylceramide (α-GC) in mice. The rapid and strong expression of interferon-γ by NKDCs after α-GC stimulation was dependent on NKT cells. Various NK and DC molecular markers and cytotoxic molecules were up-regulated following α-GC administration. This up-regulation could improve NKDC presentation of tumor antigens and increase cytotoxicity against tumor cells. NKDCs were required for the stimulation of DCs, NK cells, and NKT cells. The strong anti-tumor immune responses elicited by α-GC may be due to the down-regulation of regulatory T cells. Furthermore, the depletion of NKDCs dampened the tumor clearance mediated by α-GC-stimulated NKT cells in vivo. Taken together, these results indicate that complex interactions of innate immune cells might be required to achieve optimal anti-tumor immune responses during the early stages of tumorigenesis.

Mechanism of immune tolerance induced by donor derived immature dendritic cells in rat high-risk corneal transplantation

AIM

To study the role of immature dendritic cells (imDCs) on immune tolerance in rat penetrating keratoplasty (PKP) in high-risk eyes and to investigate the mechanism of immune hyporesponsiveness induced by donor-derived imDCs.

METHODS

Seventy-five SD rats (recipient) and 39 Wistar rats (donor) were randomly divided into 3 groups: control, imDC and mature dendritic cell (mDC) group respectively. Using a model of orthotopic corneal transplantation in which allografts were placed in neovascularized high-risk eyes of recipient rat. Corneal neovascularization was induced by alkaline burn in the central cornea of recipient rat. Recipients in imDC group or mDC group were injected donor bone marrow-derived imDCs or mDCs of 1×10(6) respectively 1 week before corneal transplantation via tail vein. Control rat received the same volume of PBS. In each group, 16 recipients were kept for determination of survival time and other 9 recipients were executed on day 3, 7 and 14 after transplantation. Cornea was harvested for hematoxylin-eosin staining and acute rejection evaluation, Western blot was used to detect the expression level of Foxp3.

RESULTS

The mean survival time of imDC group was significantly longer than that of control and mDC groups (all P<0.05). The expression level of Foxp3 on CD4(+)CD25(+)T cells of imDC group (2.24±0.18) was significantly higher than that in the control (1.68±0.09) and mDC groups (1.46±0.13) (all P<0.05).

CONCLUSION

Donor-derived imDC is an effective treatment in inducing immune hyporesponsiveness in rat PKP. The mechanism of immune tolerance induced by imDC might be inhibit T lymphocytes responsiveness by regulatory T cells.

Immune tolerance and transplantation

Successful allogeneic hematopoietic stem cell transplantation (HSCT) and solid organ transplantation require development of a degree of immune tolerance against allogeneic antigens. T lymphocytes play a critical role in allograft rejection, graft failure, and graft-versus-host disease (GVHD). T-cell tolerance occurs by two different mechanisms: (1) depletion of self-reactive T cells during their maturation in the thymus (central tolerance), and (2) suppression/elimination of self-reactive mature T cells in the periphery (peripheral tolerance). Induction of transplant tolerance improves transplantation outcomes. Adoptive immunotherapy with immune suppressor cells including regulatory T cells, natural killer (NK)-T cells, veto cells, and facilitating cells are promising therapies for modulation of immune tolerance. Achieving mixed chimerism with the combination of thymic irradiation and T-cell-depleting antibodies, costimulatory molecule blockade with/without inhibitory signal activation, and elimination of alloreactive T cells with varying methods including pre- or post-transplant cyclophosphamide administration appear to be effective in inducing transplant tolerance.

Loss of effector and anti-inflammatory natural killer T lymphocyte function in pathogenic simian immunodeficiency virus infection

Chronic immune activation is a key determinant of AIDS progression in HIV-infected humans and simian immunodeficiency virus (SIV)-infected macaques but is singularly absent in SIV-infected natural hosts. To investigate whether natural killer T (NKT) lymphocytes contribute to the differential modulation of immune activation in AIDS-susceptible and AIDS-resistant hosts, we compared NKT function in macaques and sooty mangabeys in the absence and presence of SIV infection. Cynomolgus macaques had significantly higher frequencies of circulating invariant NKT lymphocytes compared to both rhesus macaques and AIDS-resistant sooty mangabeys. Despite this difference, mangabey NKT lymphocytes were functionally distinct from both macaque species in their ability to secrete significantly more IFN-γ, IL-13, and IL-17 in response to CD1d/α-galactosylceramide stimulation. While NKT number and function remained intact in SIV-infected mangabeys, there was a profound reduction in NKT activation-induced, but not mitogen-induced, secretion of IFN-γ, IL-2, IL-10, and TGF-β in SIV-infected macaques. SIV-infected macaques also showed a selective decline in CD4⁺ NKT lymphocytes which correlated significantly with an increase in circulating activated memory CD4⁺ T lymphocytes. Macaques with lower pre-infection NKT frequencies showed a significantly greater CD4⁺ T lymphocyte decline post SIV infection. The disparate effect of SIV infection on NKT function in mangabeys and macaques could be a manifestation of their differential susceptibility to AIDS. Alternately, these data also raise the possibility that loss of anti-inflammatory NKT function promotes chronic immune activation in pathogenic SIV infection, while intact NKT function helps to protect natural hosts from developing immunodeficiency and aberrant immune activation.

Several African nonhuman primate species such as sooty mangabeys are naturally infected with SIV and maintain high levels of viral replication without developing AIDS. SIV-infected natural hosts do not show evidence of increased chronic immune activation, a feature that distinguishes them from AIDS-susceptible SIV-infected Asian macaques. In this study we compared natural killer T (NKT) lymphocytes, a unique subset of innate T lymphocytes with anti-inflammatory properties, in AIDS-resistant and AIDS-susceptible hosts. Sooty mangabey NKT cells retained normal functionality following SIV infection and were more potent than macaque NKT cells in their ability to produce interferon-γ and secrete anti-inflammatory cytokines. In contrast, NKT cells of SIV-infected macaques were markedly hypo-functional with regards to secretion of anti-inflammatory and effector cytokines and showed an association between loss of CD4⁺ NKT cells and increased immune activation. These findings suggest that dysfunctional NKT cells may promote increased immune activation in AIDS-susceptible hosts while intact effector and anti-inflammatory NKT cells could help to prevent immunodeficiency and increased immune activation in natural hosts.

Emerging concepts in haematopoietic cell transplantation

Haematopoietic cell transplantation (HCT) is the most widely used form of cellular therapy. It is the only known cure for some haematological malignancies and has recently been used in additional clinical settings, such as allograft tolerance induction and treatment of autoimmune diseases. Recent advances have enabled HCT in a wider range of patients with improved outcomes. This Review summarizes the latest developments in this therapy, focusing on issues that will affect future advancement.

S. Tolerance and withdrawal of immunosuppressive drugs in patients given kidney and hematopoietic cell transplants

Sixteen patients conditioned with total lymphoid irradiation (TLI) and antithymocyte globulin (ATG) were given kidney transplants and an injection of CD34+ hematopoietic progenitor cells and T cells from HLA-matched donors in a tolerance induction protocol. Blood cell monitoring included changes in chimerism, balance of T-cell subsets and responses to donor alloantigens. Fifteen patients developed multilineage chimerism without graft-versus-host disease (GVHD), and eight with chimerism for at least 6 months were withdrawn from antirejection medications for 1-3 years (mean, 28 months) without subsequent rejection episodes. Four chimeric patients have just completed or are in the midst of drug withdrawal, and four patients were not withdrawn due to return of underlying disease or rejection episodes. Blood cells from all patients showed early high ratios of CD4+CD25+ regulatory T cells and NKT cells versus conventional naive CD4+ T cells, and those off drugs showed specific unresponsiveness to donor alloantigens. In conclusion, TLI and ATG promoted the development of persistent chimerism and tolerance in a cohort of patients given kidney transplants and hematopoietic donor cell infusions. All 16 patients had excellent graft function at the last observation point with or without maintenance drugs.

Natural killer T cell based Immunotherapy

Natural killer T (NKT) cells play an important immunoregulatory role and are thought to bridge the innate and adaptive immune responses. Following activation through cognate interactions with lipid antigen presented in the context of CD1d molecules, NKT cells rapidly produce a plethora of cytokines and can also mediate cytotoxicity. Due to their potent effector functions, extensive research has been performed to increase our understanding on how to effectively modulate these cells. In fact, NKT cell agonists have been used as vaccine adjuvants to enhance antigen specific T and B cell responses to infections and malignancy. In this review, we will focus on recent advances in NKT cell-based vaccination strategies. Given the role that NKT cells play in autoimmune disease, infectious diseases, cancer, transplant immunology and dermatology, it is important to understand how to effectively guide their effector functions in order to develop novel immunotherapeutic strategies.