Host-Residual Invariant NK T Cells Attenuate Graft-versus-Host Immunity

Single-cell transcriptomic profiling reveals diversity in human iNKT cells across hematologic tissues

Invariant natural killer T (iNKT) cells are evolutionarily conserved innate lymphocytes important for protection against pathogens, malignancies, and graft-versus-host disease, with potential for universal donor cellular therapies. While mouse studies reveal transcriptionally and functionally distinct subsets, a comprehensive understanding of human iNKT cell heterogeneity is limited. Herein, we delineate the transcriptomic diversity of human iNKT cells from multiple immunologically relevant hematologic tissues. Human iNKT cells express naive/precursor, transitional, and T helper (Th)1/17/NK-like transcriptional profiles, partially contrasting with findings in mice. Additionally, these data uncover transcription factor dynamics not previously described in mice and reveal a T effector memory RA+-like population. Further, two distinct expression patterns of human CD8+ iNKT cells are described-one resembling naive/precursor cells and another resembling Th1/17/NK-like cells, with predominant expression of CD8αα protein. These critical insights into the transcriptional heterogeneity of human iNKT cells will facilitate future functional studies and inform iNKT-based cellular therapy development.

The contribution of the intestinal microbiome to immune recovery after HCT

Allogenic hematopoietic stem-cell transplantation (allo-HCT) is a curative-intent immunotherapy for high-risk hematological malignancies and immune deficiencies. Allo-HCT carries a high risk of treatment-related mortality (TRM), largely due to infection or graft-versus-host disease (GVHD). Robust immune recovery is essential for optimal patient outcomes, given the immunologic graft-versus-leukemia effect prevents relapse, and functional innate and adaptive immunity are both needed for the prevention and control of infection. Most simply, we measure immune recovery by enumerating donor lymphocyte subsets in circulation. In functional terms, ideal immune recovery is more difficult to define, and current lab techniques are limited to the measurement of specific vaccine-responses or mitogens ex vivo. Clinically, poor immune function manifests as problematic infection with viral, bacterial and fungal organisms. Furthermore, the ideal recovering immune system is capable of exerting graft-versus-tumor effects to prevent relapse, and does not induce graft-versus-host disease. Large clinical observational studies have linked loss of diversity within the gut microbiome with adverse transplant outcomes including decreased overall survival and increased acute and chronic GVHD. Furthermore, the correlation between intestinal microbial communities and numeric lymphocyte recovery has now been reported using a number of approaches. Large sets of clinically available white blood cell count data, clinical flow cytometry of lymphocyte subsets and bespoke flow cytometry analyses designed to capture microbiota-specific T cells (e.g. Mucosal-associated invariant T cells, subsets of the gd T cells) have all been leveraged in an attempt to understand links between the microbiota and the recovering immune system in HCT patients. Additionally, preclinical studies suggest an immunomodulatory role for bacterial metabolites (including butyrate, secondary bile acids, and indole derivatives from tryptophan metabolism) in transplant outcomes, though further studies are needed to unravel mechanisms relevant to the post-HCT setting. An understanding of mechanistic relationships between the intestinal microbiome and post-transplant outcomes is necessary for reduction of risk associated with transplant, to inform prophylactic procedures, and ensure optimal immune reconstitution without alloreactivity. Here, we summarize the current understanding of the complex relationship between bacterial communities, their individual members, and the metabolites they produce with immune function in both the allo-HCT and steady-state setting.

Sphingolipid metabolism in T cell responses after allogeneic hematopoietic cell transplantation

Allogeneic hematopoietic cell transplantation (allo-HCT) is an effective immunotherapy against hematopoietic malignancies. The infused donor lymphocytes attack malignant cells and normal tissues, termed a graft-verse-leukemia (GVL) effect and graft-verse-host (GVH) response or disease (GVHD), respectively. Although engineering techniques toward donor graft selection have made HCT more specific and effective, primary tumor relapse and GVHD are still major concerns post allo-HCT. High-dose systemic steroids remain to be the first line of GVHD treatment, which may lead to steroid-refractory GVHD with a dismal outcome. Therefore, identifying novel therapeutic strategies that prevent GVHD while preserving GVL activity is highly warranted. Sphingolipid metabolism and metabolites play pivotal roles in regulating T-cell homeostasis and biological functions. In this review, we summarized the recent research progress in this evolving field of sphingolipids with a focus on alloreactive T-cell responses in the context of allo-HCT. We discussed how sphingolipid metabolism regulates T-cell mediated GVH and GVL responses in allo-HCT and presented the rationale and means to target sphingolipid metabolism for the control of GVHD and leukemia relapse.

Activation of natural killer T cells enhances the function of regulatory T-cell therapy in suppressing murine GVHD

Cellular therapy with regulatory T cells (Tregs) has shown promising results for suppressing graft-versus-host disease (GVHD) while preserving graft vs tumor effects in animal models and phase 1/2 clinical trials. However, a paucity of Tregs in the peripheral blood makes it difficult to acquire sufficient numbers of cells and hampers further clinical application. Invariant natural killer T (iNKT) cells constitute another compartment of regulatory cells that ameliorate GVHD through activation of Tregs after their own activation with α-galactosylceramide (α-GalCer) or adoptive transfer. We demonstrate here that a single administration of α-GalCer liposome (α-GalCer-lipo) enhanced the in vivo expansion of Tregs after adoptive transfer in a murine GVHD model and improved therapeutic efficacy of Treg therapy even after injection of otherwise suboptimal cell numbers. Host iNKT cells rather than donor iNKT cells were required for GVHD suppression because the survival benefit of α-GalCer-lipo administration was not shown in the transplantation of cells from wild-type (WT) C57BL/6 mice into Jα18-/- iNKT cell-deficient BALB/c mice, whereas it was observed from Jα18-/- C57BL/6 donor mice into WT BALB/c recipient mice. The combination of iNKT cell activation and Treg adoptive therapy may make Treg therapy more feasible and safer by enhancing the efficacy and reducing the number of Tregs required.

Donor Treg expansion by liposomal α-galactosylceramide modulates Tfh cells and prevents sclerodermatous chronic graft-versus-host disease

Background and Aim

Chronic graft‐versus‐host disease (cGVHD) is a major cause of nonrelapse morbidity and mortality following hematopoietic stem cell transplantation (HSCT). α‐Galactosylceramide (α‐GC) is a synthetic glycolipid that is recognized by the invariant T‐cell receptor of invariant natural killer T (iNKT) cells in a CD1d‐restricted manner. Stimulation of iNKT cells by α‐GC leads to the production of not only immune‐stimulatory cytokines but also immune‐regulatory cytokines followed by regulatory T‐cell (Treg) expansion in vivo.

Methods

We investigated the effect of iNKT stimulation by liposomal α‐GC just after transplant on the subsequent immune reconstitution and the development of sclerodermatous cGVHD.

Results

Our study showed that multiple administrations of liposomal α‐GC modulated both host‐ and donor‐derived iNKT cell homeostasis and induced an early expansion of donor Tregs. We also demonstrated that the immune modulation of the acute phase was followed by the decreased levels of CXCL13 in plasma and follicular helper T cells in lymph nodes, which inhibited germinal center formation, resulting in the efficient prevention of sclerodermatous cGVHD.

Conclusions

These data demonstrated an important coordination of T‐ and B‐cell immunity in the pathogenesis of cGVHD and may provide a novel clinical strategy for the induction of immune tolerance after allogeneic HSCT.

An Unconventional View of T Cell Reconstitution After Allogeneic Hematopoietic Cell Transplantation

Allogeneic hematopoietic cell transplantation (allo-HCT) is performed as curative-intent therapy for hematologic malignancies and non-malignant hematologic, immunological and metabolic disorders, however, its broader implementation is limited by high rates of transplantation-related complications and a 2-year mortality that approaches 50%. Robust reconstitution of a functioning innate and adaptive immune system is a critical contributor to good long-term patient outcomes, primarily to prevent and overcome post-transplantation infectious complications and ensure adequate graft-versus-leukemia effects. There is increasing evidence that unconventional T cells may have an important immunomodulatory role after allo-HCT, which may be at least partially dependent on the post-transplantation intestinal microbiome. Here we discuss the role of immune reconstitution in allo-HCT outcome, focusing on unconventional T cells, specifically mucosal-associated invariant T (MAIT) cells, γδ (gd) T cells, and invariant NK T (iNKT) cells. We provide an overview of the mechanistic preclinical and associative clinical studies that have been performed. We also discuss the emerging role of the intestinal microbiome with regard to hematopoietic function and overall immune reconstitution.

Innate Immune Determinants of Graft-Versus-Host Disease and Bidirectional Immune Tolerance in Allogeneic Transplantation

The success of tissue transplantation from a healthy donor to a diseased individual (allo-transplantation) is regulated by the immune systems of both donor and recipient. Developing a state of specific non-reactivity between donor and recipient, while maintaining the salutary effects of immune function in the recipient, is called “immune (transplantation) tolerance”. In the classic early post-transplant period, minimizing bidirectional donor ←→ recipient reactivity requires the administration of immunosuppressive drugs, which have deleterious side effects (severe immunodeficiency, opportunistic infections, and neoplasia, in addition to drug-specific reactions and organ toxicities). Inducing immune tolerance directly through donor and recipient immune cells, particularly via subsets of immune regulatory cells, has helped to significantly reduce side effects associated with multiple immunosuppressive drugs after allo-transplantation. The innate and adaptive arms of the immune system are both implicated in inducing immune tolerance. In the present article, we will review innate immune subset manipulations and their potential applications in hematopoietic stem cell transplantation (HSCT) to cure malignant and non-malignant hematological disorders by inducing long-lasting donor ←→ recipient (bidirectional) immune tolerance and reduced graft-versus-host disease (GVHD). These innate immunotherapeutic strategies to promote long-term immune allo-transplant tolerance include myeloid-derived suppressor cells (MDSCs), regulatory macrophages, tolerogenic dendritic cells (tDCs), Natural Killer (NK) cells, invariant Natural Killer T (iNKT) cells, gamma delta T (γδ-T) cells and mesenchymal stromal cells (MSCs).

Long-term treatment with the P2X7 receptor antagonist Brilliant Blue G reduces liver inflammation in a humanized mouse model of graft-versus-host disease

Allogeneic haematopoietic stem cell transplantation (HSCT) is a frequent curative therapy for numerous haematological malignancies. However, HSCT is limited by the occurrence of graft-versus-host disease (GVHD), with current therapies restricted to general immunosuppression. Activation of the P2X7 receptor by extracellular adenosine triphosphate (ATP) causes inflammation and tissue damage in GVHD. Short-term pharmacological blockade of P2X7 has been shown to reduce clinical disease and/or reduce inflammatory markers in allogeneic and humanized mouse models of GVHD. The current study demonstrates that long-term P2X7 blockade by intra-peritoneal injection of Brilliant Blue G (BBG) thrice weekly for up to 10 weeks did not impact human (h) peripheral blood mononuclear cell (PBMC) engraftment, predominantly T cells, in blood at 3 weeks post-hPBMC injection or in spleens at end-point in humanized mice. Histological analysis demonstrated long-term BBG treatment reduced leukocyte infiltration in the livers of humanized mice. Immunohistochemical analysis demonstrated that BBG treatment reduced liver apoptosis. Long-term BBG treatment did not alter clinical disease, mRNA expression of pro-inflammatory markers in tissues or serum human interferon (IFN)-γ concentrations. Therefore, this study demonstrates that P2X7 activation plays a role in GVHD pathogenesis in the livers of humanized mice, supporting a role for this receptor in GVHD development in HSCT recipients.

The impact of donor characteristics on the invariant natural killer T cells of granulocyte-colony-stimulating factor-mobilized marrow grafts and peripheral blood grafts

INTRODUCTION

Invariant natural killer T cells (iNKTs) are a rare but vital subset of immunomodulatory T cells and play an important role in allogeneic hematopoietic stem cell trans-plantation (HSCT). The association of donor characteristics with the number and frequency of the iNKTs subsets in allografts remains poorly understood. In this paper, we prospectively investigate the association of donor characteristics with iNKTs dose and frequency in granulocyte-colony-stimulating factor (G-CSF) mobilized marrow and peripheral blood harvests.

MATERIALS AND METHODS

100 bone marrow (BM) units and 100 peripheral blood (PB) units from 100 healthy donors were examined. Parameters including donor age, sex, weight, height, BMI and blood count [including white blood cells (WBCs), lymphocytes and monocytes] at three time points [donor's steady state before G-CSF administration, the day of G-BM harvesting and the day of G-PB apheresis] were analyzed to explore the impact of donor characteristics on iNKTs composition in BM and PB grafts.

RESULTS

Multivariate analysis showed monocyte counts before G-BM harvest could predict higher frequency of iNKTs in WBC (OR = 2.593, 95%CI: 1.128-5.961, p = 0.025), higher total CD4+ iNKTs dose (OR = 2.250, 95%CI: 1.011-5.008, p = 0.047) and higher total iNKTs dose (OR = 2.662, 95%CI: 1.187-5.970, p = 0.017) in mixture allografts.

DISCUSSION

The results suggested that monocyte counts pre G-BM harvest could predict the yield of total CD4+ iNKTs and total iNKTs in mixture allografts. The male and older donors were associated with a higher dose of total CD4- iNKTs in mixture allografts.

Invariant Natural Killer T Cells As Suppressors of Graft-versus-Host Disease in Allogeneic Hematopoietic Stem Cell Transplantation

Invariant natural killer T (iNKT) cells serve as a bridge between innate and adaptive immunity and have been shown to play an important role in immune regulation, defense against pathogens, and cancer immunity. Recent data also suggest that this compartment of the immune system plays a significant role in reducing graft-versus-host disease (GVHD) in the setting of allogeneic hematopoietic stem cell transplantation. Murine studies have shown that boosting iNKT numbers through certain conditioning regimens or adoptive transfer leads to suppression of acute or chronic GVHD. Preclinical work reveals that iNKT cells exert their suppressive function by expanding regulatory T cells in vivo, though the exact mechanism by which this occurs has yet to be fully elucidated. Human studies have demonstrated that a higher number of iNKT cells in the graft or in the peripheral blood of the recipient post-transplantation are associated with a reduction in GVHD risk, importantly without a loss of graft-versus-tumor effect. In two separate analyses of many immune cell subsets in allogeneic grafts, iNKT cell dose was the only parameter associated with a significant improvement in GVHD or in GVHD-free progression-free survival. Failure to reconstitute iNKT cells following allogeneic transplantation has also been associated with an increased risk of relapse. These data demonstrate that iNKT cells hold promise for future clinical application in the prevention of GVHD in allogeneic stem cell transplantation and warrant further study of the immunoregulatory functions of iNKT cells in this setting.

NKT cell subsets as key participants in liver physiology and pathology

Natural killer T (NKT) cells are innate-like lymphocytes that generally recognize lipid antigens and are enriched in microvascular compartments of the liver. NKT cells can be activated by self- or microbial-lipid antigens and by signaling through toll-like receptors. Following activation, NKT cells rapidly secrete pro-inflammatory or anti-inflammatory cytokines and chemokines, and thereby determine the milieu for subsequent immunity or tolerance. It is becoming clear that two different subsets of NKT cells-type I and type II-have different modes of antigen recognition and have opposing roles in inflammatory liver diseases. Here we focus mainly on the roles of both NKT cell subsets in the maintenance of immune tolerance and inflammatory diseases in liver. Furthermore, how the differential activation of type I and type II NKT cells influences other innate cells and adaptive immune cells to result in important consequences for tissue integrity is discussed. It is crucial that better reagents, including CD1d tetramers, be used in clinical studies to define the roles of NKT cells in liver diseases in patients.

The Extended Family of CD1d-Restricted NKT Cells: Sifting through a Mixed Bag of TCRs, Antigens, and Functions

Natural killer T (NKT) cells comprise a family of specialized T cells that recognize lipid antigens presented by CD1d. Based on their T cell receptor (TCR) usage and antigen specificities, CD1d-restricted NKT cells have been divided into two main subsets: type I NKT cells that use a canonical invariant TCR α-chain and recognize α-galactosylceramide (α-GalCer), and type II NKT cells that use a more diverse αβ TCR repertoire and do not recognize α-GalCer. In addition, α-GalCer-reactive NKT cells that use non-canonical αβ TCRs and CD1d-restricted T cells that use γδ or δ/αβ TCRs have recently been identified, revealing further diversity among CD1d-restricted T cells. Importantly, in addition to their distinct antigen specificities, functional differences are beginning to emerge between the different members of the CD1d-restricted T cell family. In this review, while using type I NKT cells as comparison, we will focus on type II NKT cells and the other non-invariant CD1d-restricted T cell subsets, and discuss our current understanding of the antigens they recognize, the formation of stimulatory CD1d/antigen complexes, the modes of TCR-mediated antigen recognition, and the mechanisms and consequences of their activation that underlie their function in antimicrobial responses, anti-tumor immunity, and autoimmunity.

A radio-resistant perforin-expressing lymphoid population controls allogeneic T cell engraftment, activation, and onset of graft-versus-host disease in mice

Immunosuppressive pretransplantation conditioning is essential for donor cell engraftment in allogeneic bone marrow transplantation (BMT). The role of residual postconditioning recipient immunity in determining engraftment is poorly understood. We examined the role of recipient perforin in the kinetics of donor cell engraftment. MHC-mismatched BMT mouse models demonstrated that both the rate and proportion of donor lymphoid cell engraftment and expansion of effector memory donor T cells in both spleen and BM were significantly increased within 5 to 7 days post-BMT in perforin-deficient (pfn(-/-)) recipients, compared with wild-type. In wild-type recipients, depletion of natural killer (NK) cells before BMT enhanced donor lymphoid cell engraftment to that seen in pfn(-/-) recipients. This demonstrated that a perforin-dependent, NK-mediated, host-versus-graft (HVG) effect limits the rate of donor engraftment and T cell activation. Radiation-resistant natural killer T (NKT) cells survived in the BM of lethally irradiated mice and may drive NK cell activation, resulting in the HVG effect. Furthermore, reduced pretransplant irradiation doses in pfn(-/-) recipients permitted long-term donor lymphoid cell engraftment. These findings suggest that suppression of perforin activity or selective depletion of recipient NK cells before BMT could be used to improve donor stem cell engraftment, in turn allowing for the reduction of pretransplant conditioning.

CD4+ invariant natural killer T cells protect from murine GVHD lethality through expansion of donor CD4+CD25+FoxP3+ regulatory T cells

Dysregulated donor T cells lead to destruction of host tissues resulting in graft-versus-host disease (GVHD) after allogeneic hematopoietic cell transplantation (HCT). We investigated the impact of highly purified (>95%) donor CD4(+) invariant natural killer T (iNKT) cells on GVHD in a murine model of allogeneic HCT. We found that low doses of adoptively transferred donor CD4(+) iNKT cells protect from GVHD morbidity and mortality through an expansion of donor CD4(+)CD25(+)FoxP3(+) regulatory T cells (Tregs). These Tregs express high levels of the Ikaros transcription factor Helios and expand from the Treg pool of the donor graft. Furthermore, CD4(+) iNKT cells preserve T-cell-mediated graft-versus-tumor effects. Our studies reveal new aspects of the cellular interplay between iNKT cells and Tregs in the context of tolerance induction after allogeneic HCT and set the stage for clinical translation.

Regulatory T cells and natural killer T cells for modulation of GVHD following allogeneic hematopoietic cell transplantation

Alloreactivity of donor lymphocytes leads to graft-versus-host disease (GVHD) contributing to significant morbidity and mortality following allogeneic hematopoietic cell transplantation (HCT). Within the past decade, significant progress has been made in elucidating the mechanisms underlying the immunologic dysregulation characteristic of GVHD. The recent discoveries of different cell subpopulations with immune regulatory function has led to a number of studies aimed at understanding their role in allogeneic HCT and possible application for the prevention and treatment of GVHD and a host of other immune-mediated diseases. Preclinical animal modeling has helped define the potential roles of distinct populations of regulatory cells that have progressed to clinical translation with promising early results.

Flagellin, a TLR5 agonist, reduces graft-versus-host disease in allogeneic hematopoietic stem cell transplantation recipients while enhancing antiviral immunity

Graft-versus-host disease (GVHD) is a major cause of morbidity and mortality in patients treated with allogeneic hematopoietic stem cell transplantation (HSCT). Posttransplant immunosuppressive drugs incompletely control GVHD and increase susceptibility to opportunistic infections. In this study, we used flagellin, a TLR5 agonist protein (∼50 kDa) extracted from bacterial flagella, as a novel experimental treatment strategy to reduce both acute and chronic GVHD in allogeneic HSCT recipients. On the basis of the radioprotective effects of flagellin, we hypothesized that flagellin could ameliorate GVHD in lethally irradiated murine models of allogeneic HSCT. Two doses of highly purified flagellin (administered 3 h before irradiation and 24 h after HSCT) reduced GVHD and led to better survival in both H-2(b) → CB6F1 and H-2(K) → B6 allogeneic HSCT models while preserving >99% donor T cell chimerism. Flagellin treatment preserved long-term posttransplant immune reconstitution characterized by more donor thymic-derived CD4(+)CD25(+)Foxp3(+) regulatory T cells and significantly enhanced antiviral immunity after murine CMV infection. The proliferation index and activation status of donor spleen-derived T cells and serum concentration of proinflammatory cytokines in flagellin-treated recipients were reduced significantly within 4 d posttransplant compared with those of the PBS-treated control recipients. Allogeneic transplantation of radiation chimeras previously engrafted with TLR5 knockout hematopoietic cells showed that interactions between flagellin and TLR5 expressed on both donor hematopoietic and host nonhematopoietic cells were required to reduce GVHD. Thus, the peritransplant administration of flagellin is a novel therapeutic approach to control GVHD while preserving posttransplant donor immunity.

Novel treatment concepts for graft-versus-host disease

Acute and chronic graft-versus-host disease (GVHD) are potentially lethal complications after stem cell transplantation (SCT). Steroids are the appropriate first-line treatment for both. However, if patients do not adequately benefit from steroid therapy, mortality is high and standardized treatment algorithms are lacking. This is mainly because of limited data from prospective, randomized clinical trials. In addition, most of the available treatment options only induce clinical benefits in a limited proportion of patients. Thus, there is an urgent clinical need to develop more potent immunosuppressive treatment strategies for patients suffering from acute or chronic steroid-refractory GVHD while maintaining the graft versus tumor effect to avoid a potential rise in relapse-related mortality. The increasing knowledge about host- as well as donor-derived variables favoring GVHD development and the increasing armamentarium of immune-modulatory agents entering preclinical and clinical research will probably allow more effective treatment of GVHD in the future. This review describes novel developments in the treatment of steroid-refractory GVHD, with a special focus on the rationale behind promising pharmacologic compounds or up-coming cellular therapies.

α-GalCer administration after allogeneic bone marrow transplantation improves immune reconstitution in mice

OBJECTIVE

To explore the effect of α- galactosyleramide( α-GalCer ) on immune reconstitution under acute graft-versus-host disease (aGVHD).

METHODS

BALB/c mice were transplanted wit hallogeneic C57BL/6 bone marrow cells and splenocytes (both 1×10(7))after receiving lethal total-body irradiation. α-GalCer (100 ug/kg) or vehicle (dimethylsulfoxide) was administered intraperitoneally immediately after transplantation. The effects of α-GalCer on immune reconstitution,proliferation of T cells and B cells, hematopoiesis,and thymic microenvironment were assessed.

RESULTS

The α-GalCer group exhibited higher percentages of CD3(+),CD4(+), CD8(+), B220(+), CD40(+), and CD86(+)cells compared with the vehicle group . The number of colony forming unit per 1000 CD34(+) cells in the α-GalCer group was higher than in the vehicle group ( P=0.0012).In vitro proliferation assays showed that the α-GalCer group had higher percentages of CD3(+), CD4(+), CD8(+),and B220(+) cells compared with the vehicle group. As for the results of in vivo proliferation assays, the numbers of CD3(+), CD4(+), CD8(+), and B220(+)cells were higher in the α-GalCer group than in the normal group ,especially the number of B220(+) cells ( P=0.007).Significant difference was not found in thymocyte count between the α-GalCer group and the vehicle group, nor in the percentages of CD3(+), CD4(+), and CD8(+) cells.

CONCLUSION

Administration of α-GalCer after allogeneic bone marrow transplantation may promote immune reconstitution in the presence of aGVHD.

Early and late extensive chronic graft-versus-host disease in children is characterized by different Th1/Th2 cytokine profiles: findings of the Children's Oncology Group Study ASCT0031

Numerous mechanisms underlie chronic graft-versus-host disease (cGVHD), including skewing of Th1/Th2 cytokine expression. There are biological differences between early-onset and late-onset cGVHD. To test whether different Th1/Th2 cytokines are associated with early- or late-onset cGVHD, peripheral blood was collected from 63 children enrolled on the Children's Oncology Group Phase III trial ASCT0031 evaluating hydroxychloroquine therapy for newly diagnosed extensive cGVHD. mRNA expression of interferon (IFN)-γ and interleukin (IL)-2, -4, and -10 from stimulated peripheral blood mononuclear cells was evaluated by quantitative polymerase chain reaction. Early-onset cGVHD (n = 33) was characterized by decreased expression of IFN-γ and IL-2 mRNA after nonspecific phorbol 12-myristate 13-acetate-ionomycin stimulation. In contrast, late-onset cGVHD (n = 11) was characterized by decreased expression of IL-4 and IL-2 mRNA after anti-CD3 stimulation of T cells. Receiver-operating characteristic curve analysis revealed that IFN-γ expression was correlated with the absence of early cGVHD (area under the curve [AUC] = 0.77) and that IL-4 (AUC = 0.89) and IL-2 (AUC = 0.84) expression was correlated with the absence of late cGVHD. There was no correlation between cytokine expression and a specific immune cell subset. Increased expression of Foxp3 mRNA was seen in early-onset cGVHD and late controls. The different time-dependent cytokine profiles in patients with newly diagnosed cGVHD suggests that the mechanisms underlying cGVHD are temporally regulated. Although larger validation studies are needed, our data suggest that cytokine profiles have a potential use as biomarkers for the diagnosis of cGVHD.

Invariant NK T cells: potential for immunotherapeutic targeting with glycolipid antigens

Invariant NK T (iNKT) cells are a subset of T lymphocytes that recognize glycolipid antigens bound with the antigen-presenting molecule CD1d. iNKT cells have potent immunoregulatory activities that can promote or suppress immune responses during different pathological conditions. These immunoregulatory properties can be harnessed for therapeutic purposes with cognate glycolipid antigens, such as the marine sponge-derived glycosphingolipid α-galactosylceramide. Preclinical studies have shown substantial promise for iNKT cell-based treatments of infections, cancer and autoimmune and inflammatory diseases. Translation of these preclinical studies to the clinic, while faced with some obstacles, has already had some initial success. In this article, we review the immunodulatory activities of iNKT cells and the potential for developing iNKT cell-based prophylactic and curative therapies of human disease.

The role of natural killer T cells in costimulation blockade-based mixed chimerism

Distinct lymphocyte populations have been identified that either promote or impede the establishment of chimerism and tolerance through allogeneic bone marrow transplantation (BMT). Natural killer T (NKT) cells have pleiotropic regulatory properties capable of either augmenting or downmodulating various immune responses. We investigated in this study whether NKT cells affect outcome in mixed chimerism models employing fully mismatched nonmyeloablative BMT with costimulation blockade (CB). The absence of NKT cells had no detectable effect on chimerism or skin graft tolerance after conditioning with 3Gy total body irradiation (TBI), and a limited positive effect with 1Gy TBI. Stimulation of NKT cells with alpha-galactosylceramide (alpha-gal) at the time of BMT prevented chimerism and tolerance. Activation of recipient (as opposed to donor) NKT cells was necessary and sufficient for the alpha-gal effect. The detrimental effect of NKT activation was also observed in the absence of T cells after conditioning with in vivo T-cell depletion (TCD). NKT cells triggered rejection of BM via NK cells as chimerism and tolerance were not abrogated when NKT cells were stimulated in the absence of both NK cells and T cells. Thus, activation of NKT cells at the time of BMT overcomes the effects of CB, inhibiting the establishment of chimerism and tolerance.

Low doses of natural killer T cells provide protection from acute graft-versus-host disease via an IL-4-dependent mechanism

CD4(+) natural killer T (NKT) cells, along with CD4(+)CD25(+) regulatory T cells (Tregs), are capable of controlling aberrant immune reactions. We explored the adoptive transfer of highly purified (> 95%) CD4(+)NKT cells in a murine model of allogeneic hematopoietic cell transplantation (HCT). NKT cells follow a migration and proliferation pattern similar to that of conventional T cells (Tcons), migrating initially to secondary lymphoid organs followed by infiltration of graft-versus-host disease (GVHD) target tissues. NKT cells persist for more than 100 days and do not cause significant morbidity or mortality. Doses of NKT cells as low as 1.0 × 10(4) cells suppress GVHD caused by 5.0 × 10(5) Tcons in an interleukin-4 (IL-4)-dependent mechanism. Protective doses of NKT cells minimally affect Tcon proliferation, but cause significant reductions in interferon-γ (IFN-γ) and tumor necrosis factor-α (TNF-α) production by donor Tcons and in skin, spleen, and gastrointestinal pathology. In addition, NKT cells do not impact the graft-versus-tumor (GVT) effect of Tcons against B-cell lymphoma-1 (BCL-1) tumors. These studies elucidate the biologic function of donor-type CD4(+)NKT cells in suppressing GVHD in an allogeneic transplantation setting, demonstrating clinical potential in reducing GVHD in HCT.

Natural killer T cells in health and disease

Natural killer T (NKT) cells are a subset of T lymphocytes that share surface markers and functional characteristics with both conventional T lymphocytes and natural killer cells. Most NKT cells express a semi-invariant T cell receptor that reacts with glycolipid antigens presented by the major histocompatibility complex class I-related protein CD1d on the surface of antigen-presenting cells. NKT cells become activated during a variety of infections and inflammatory conditions, rapidly producing large amounts of immunomodulatory cytokines. NKT cells can influence the activation state and functional properties of multiple other cell types in the immune system and, thus, modulate immune responses against infectious agents, autoantigens, tumors, tissue grafts and allergens. One attractive aspect of NKT cells is that their immunomodulatory activities can be readily harnessed with cognate glycolipid antigens, such as the marine sponge-derived glycosphingolipid alpha-galactosylceramide. These properties of NKT cells are being exploited for therapeutic intervention to prevent or treat cancer, infections, and autoimmune and inflammatory diseases.

Invariant natural killer T cells: bridging innate and adaptive immunity

Cells of the innate immune system interact with pathogens via conserved pattern-recognition receptors, whereas cells of the adaptive immune system recognize pathogens through diverse, antigen-specific receptors that are generated by somatic DNA rearrangement. Invariant natural killer T (iNKT) cells are a subset of lymphocytes that bridge the innate and adaptive immune systems. Although iNKT cells express T cell receptors that are generated by somatic DNA rearrangement, these receptors are semi-invariant and interact with a limited set of lipid and glycolipid antigens, thus resembling the pattern-recognition receptors of the innate immune system. Functionally, iNKT cells most closely resemble cells of the innate immune system, as they rapidly elicit their effector functions following activation, and fail to develop immunological memory. iNKT cells can become activated in response to a variety of stimuli and participate in the regulation of various immune responses. Activated iNKT cells produce several cytokines with the capacity to jump-start and modulate an adaptive immune response. A variety of glycolipid antigens that can differentially elicit distinct effector functions in iNKT cells have been identified. These reagents have been employed to test the hypothesis that iNKT cells can be harnessed for therapeutic purposes in human diseases. Here, we review the innate-like properties and functions of iNKT cells and discuss their interactions with other cell types of the immune system.

Adoptive therapy by transfusing expanded donor murine natural killer T cells can suppress acute graft-versus-host disease in allogeneic bone marrow transplantation

BACKGROUND

Invariant natural killer T cells (iNKT cells) may suppress graft-versus-host disease (GVHD) after allogeneic transplantation. The purpose of this study was to investigate the therapeutic potential of iNKT cells from major histocompatibility complex (MHC)-mismatched donors for preventing GVHD after allogeneic bone marrow transplantation (BMT).

STUDY DESIGN AND METHODS

In vitro, mouse iNKT cells were expanded with alpha-galactosylceramide and interleukin (IL)-2 treatment. In the NKT-treated group, lethally irradiated DBA/2(H-2K(d)) mice were adoptively transferred with expanded iNKT, bone marrow (BM), and spleen cells (SCs) from C57BL/6 (H-2K(b)) mice. Recipients in the control group were transferred only BM and SCs. The two groups were compared in survival, weight, histopathologic specimens, and serum cytokine analysis.

RESULTS

In the iNKT-treated group, 80% of mice survived past Day 60 after BMT, but all died within 38 days in the control group. The mice treated with iNKT did not exhibit signs of GVHD after Day 42 except for a change in fur color. There were higher IL-4 levels by Day 7 in serum of mice that received iNKT compared to those without iNKT treatment, while the interferon-gamma levels showed no significant difference between two groups. Levels of IL-2 and IL-5 increased by Day 21 only in iNKT-treated mice.

CONCLUSION

The results suggest that donor iNKT cells could alleviate GVHD symptoms and prolong survival after MHC-mismatched allogeneic BMT, which may be associated with the maintenance in IL-4 levels. These findings indicate that the therapy based on iNKT cells from MHC-mismatched donors has great potential in protection against GVHD after allogeneic hematopoietic stem cell transplantation.

[Immunological evaluation for CML and its possibility for an immunotherapy]

Chronic myelogenous leukemia (CML) is associated with the Ph1 chromosome translocation, which produces a chimeric tyrosine-specific kinase gene, the product of the fusion of the BCR gene and the ABL gene. The immune system has long been implicated in the control of CML. We found oligoclonal T cell responses in treated patients with IFN-alpha or leukemic dendritic cells. Also other groups treated chronic phase CML (CP-CML) patients with various leukemic antigen peptides, resulted in apparent immune response and clinical response. Imatinib mesylate is currently used as the first line therapy for CP-CML patients. Although it selectively targets the ABL portion of BCR-ABL protein as a reversible tyrosine kinase inhibitor, it cannot kill the leukemic stem cells of CML. To find a possibility to enhance the immunity in imatinib-treated CML patients by combining it with immunotherapy, we summarized the immune response of innate and adaptive immunity in CML. Development of such immunotherapeutic strategies would be a promising approach to treat the imatinib-treated CML-CP patients.

Human invariant natural killer T cells: implications for immunotherapy

Human invariant natural killer T cells are a unique lymphocyte population that have an invariant T-cell receptor and recognize glycolipids instead of peptides in the restriction of CD1d molecules. These natural killer T cells play important roles in anti-tumor immunity, transplantation immunity, allergy, autoimmunity and microbial immunity. Since human natural killer T cells show high-level biological activity such as cytokine production, an anti-tumor effect and regulatory T-cell control, they may be a useful tool in immune-cell therapy. In this review, we summarize the immune responses mediated by human natural killer T cells, especially in tumor and transplantation immunity, and discuss their potential in clinical applications.

Invariant natural killer T cell-natural killer cell interactions dictate transplantation outcome after alpha-galactosylceramide administration

Invariant natural killer T cells (iNKT cells) have pivotal roles in graft-versus-host disease (GVHD) and graft-versus-leukemia (GVL) effects. iNKT cells are activated through their T-cell receptors by glycolipid moieties (typically the alpha-galactosylceramide [alpha-GalCer] derivative KRN7000) presented within CD1d. We investigated the ability of modified alpha-GalCer molecules to differentially modulate alloreactivity and GVL. KRN7000 and the N-acyl variant, C20:2, were administered in multiple well-established murine models of allogeneic stem cell transplantation. The highly potent and specific activation of all type I NKT cells with C20:2 failed to exacerbate and in most settings inhibited GVHD late after transplantation, whereas effects on GVL were variable. In contrast, the administration of KRN7000 induced hyperacute GVHD and early mortality in all models tested. Administration of KRN7000, but not C20:2, was found to result in downstream interleukin (IL)-12 and dendritic cell (DC)-dependent natural killer (NK)- and conventional T-cell activation. Specific depletion of host DCs, IL-12, or donor NK cells prevented this pathogenic response and the induction of hyperacute GVHD. These data demonstrate the ability of profound iNKT activation to modulate both the innate and adaptive immune response via the DC-NK-cell interaction and raise concern for the use of alpha-GalCer therapeutically to modulate GVHD and GVL effects.

Differences in Bcl-2 expression by T-cell subsets alter their balance after in vivo irradiation to favor CD4+Bcl-2hi NKT cells

Although it is well known that in vivo radiation depletes immune cells via the Bcl-2 apoptotic pathway, a more nuanced analysis of the changes in the balance of immune-cell subsets is needed to understand the impact of radiation on immune function. We show the balance of T-cell subsets changes after increasing single doses of total body irradiation (TBI) or after fractionated irradiation of the lymphoid tissues (TLI) of mice due to differences in radioresistance and Bcl-2 expression of the NKT-cell and non-NKT subsets to favor CD4(+)Bcl-2(hi) NKT cells. Reduction of the Bcl-2(lo) mature T-cell subsets was at least 100-fold greater than that of the Bcl-2(hi) subsets. CD4(+) NKT cells upregulated Bcl-2 after TBI and TLI and developed a Th2 bias after TLI, whereas non-NKT cells failed to do so. Our previous studies showed TLI protects against graft versus host disease in wild-type, but not in NKT-cell-deficient mice. The present study shows that NKT cells have a protective function even after TBI, and these cells are tenfold more abundant after an equal dose of TLI. In conclusion, differential expression of Bcl-2 contributes to the changes in T-cell subsets and immune function after irradiation.

Harnessing human CD1d restricted T cells for tumor immunity: progress and challenges

Glycolipid reactive CD1d restricted natural killer T (NKT) cells represent a distinct population of T cells implicated in the regulation of immune responses in a broad range of diseases including cancer. Several studies have demonstrated the capacity of NKT cells bearing an invariant T cell receptor (iNKT cells) to recruit both innate and adaptive anti-tumor immunity and mediate tumor rejection in mice. Early phase clinical studies in humans have demonstrated the capacity of dendritic cells (DCs) to mediate expansion of NKT cells in vivo. However several challenges need to be overcome in order to effectively harness the properties of these cells in the clinic.

Immunomodulation and pharmacological strategies in the treatment of graft-versus-host disease

BACKGROUND

Allogeneic hematopoietic stem cell transplantation offers great promise for the treatment of a variety of diseases including malignancies and other diseases of hematopoietic origin. However, morbidity and mortality due to graft-versus-host disease (GVHD) remain a major barrier to its application.

OBJECTIVE

This review will provide an overview of the pathophysiology of GVHD and discuss the recent advances in GVHD management in both preclinical and clinical studies.

METHODS

An extensive literature search on PubMed from 1995 to 2008 was performed.

RESULTS/CONCLUSION

There has been much progress in our understanding of GVHD and finding new means to control acute GVHD. While these approaches hold promise, as yet none has been able to replace the standard methods we may use routinely to decrease the incidence of the condition.

Peripheral blood progenitor cell product contains Th1-biased noninvariant CD1d-reactive natural killer T cells: implications for posttransplant survival

OBJECTIVE

Bone marrow (BM) Th1 populations can contribute to graft-vs-leukemia responses. Granulocyte/granulocyte macrophage colony-stimulating factor (CSF)-mobilized peripheral blood progenitor cells (PBPC) have become widely accepted alternatives to BM transplantation. T cells coexpressing natural killer cell proteins (NKT) include a CD1d-reactive subset that influences immunity by rapidly producing large amounts of Th1 and/or Th2 cytokines dependent upon microenvironment and disease. There are two types of CD1d-reactive NKT. iNKT express a semi-invariant T-cell receptor-alpha. Other noninvariant CD1d-reactive NKT from BM and liver produce large amounts of interleukin-4 or interferon-gamma, respectively, and within the intestine can be biased in either direction. Recent data suggests that NKT might contribute to clinical benefits of PBPC.

MATERIALS AND METHODS

To address these issues, we phenotypically and functionally studied PBPC NKT.

RESULTS

Similarly to BM, NKT-like cells were common in allogeneic and autologous PBPC, there were relatively few classical iNKT, but high CD1d-reactivity concentrated in NKT fractions. Significantly, PBPC CD1d-reactive cells were relatively Th1-biased and their presence was associated with better prognosis. Granulocyte CSF treatment of BM to yield PBPC in vivo as well as in vitro Th2-polarizes conventional T cells and iNKT. However, granulocyte CSF treatment of BM in vitro produced Th1-biased NKT, providing a mechanism for opposite polarization of NKT from BM vs PBPC.

CONCLUSIONS

These results suggest distinct Th1 CD1d-reactive NKT cells could stimulate anti-tumor responses from those previously described, which can suppress graft-vs-host disease.

The role of NKT cells in tumor immunity

NKT cells are a relatively newly recognized member of the immune community, with profound effects on the rest of the immune system despite their small numbers. They are true T cells with a T cell receptor (TCR), but unlike conventional T cells that detect peptide antigens presented by conventional major histocompatibility (MHC) molecules, NKT cells recognize lipid antigens presented by CD1d, a nonclassical MHC molecule. As members of both the innate and adaptive immune systems, they bridge the gap between these, and respond rapidly to set the tone for subsequent immune responses. They fill a unique niche in providing the immune system a cellular arm to recognize lipid antigens. They play both effector and regulatory roles in infectious and autoimmune diseases. Furthermore, subsets of NKT cells can play distinct and sometimes opposing roles. In cancer, type I NKT cells, defined by their invariant TCR using Valpha14Jalpha18 in mice and Valpha24Jalpha18 in humans, are mostly protective, by producing interferon-gamma to activate NK and CD8(+) T cells and by activating dendritic cells to make IL-12. In contrast, type II NKT cells, characterized by more diverse TCRs recognizing lipids presented by CD1d, primarily inhibit tumor immunity. Moreover, type I and type II NKT cells counter-regulate each other, forming a new immunoregulatory axis. Because NKT cells respond rapidly, the balance along this axis can greatly influence other immune responses that follow. Therefore, learning to manipulate the balance along the NKT regulatory axis may be critical to devising successful immunotherapies for cancer.

Donor bone marrow type II (non-Valpha14Jalpha18 CD1d-restricted) NKT cells suppress graft-versus-host disease by producing IFN-gamma and IL-4

NKT cells in donor bone marrow (BM) have been demonstrated to protect against graft-vs-host disease (GVHD) following BM transplantation. Murine NKT cells are divided into two distinct subsets based on the invariant Valpha14Jalpha18 TCR expression. However, details of the subset and mechanisms of the BM NKT cells involved in suppressing GVHD have not been clarified. Irradiated BALB/c or C3H/HeN mice administered B6 or Jalpha18(-/-) BM cells show attenuation of GVHD, whereas recipients given CD1d(-/-) BM cells did not show attenuation. Moreover, coinjection of BM non-Valpha14Jalpha18 CD1d-restricted (type II) NKT cells and CD1d(-/-) BM cells suppressed GVHD, whereas coinjection of BM Valpha14Jalpha18 TCR (type I) NKT cells did not. These protective effects on GVHD depended upon IFN-gamma-producing type II NKT cells, which induced the apoptosis of donor T cells. The splenocytes of mice administered BM cells from B6.IL-4(-/-) or Jalpha18(-/-)IL-4(-/-) mice produced lower levels of IL-4 and IL-10 than the splenocytes of mice transplanted with BM cells from B6, B6.IFN-gamma(-/-), Jalpha18(-/-), or Jalpha18(-/-)IFN-gamma(-/-) mice. Taken together, our results show that IFN-gamma-producing BM type II NKT cells suppress GVHD by inducing the apoptosis of donor T cells, while IL-4-producing BM type II NKT cells protect against GVHD by deviating the immune system toward a Th2-type response.

Spontaneous tolerance involving natural killer T cells after hepatic grafting in mice

The liver contains significant numbers of invariant natural killer T (iNKT) cells, which have an invariant T cell receptor-alpha chain and are activated in a CD1d-restricted manner. We examined the role of iNKT cells in the spontaneous tolerance of the major histocompatibility antigen complex-mismatched liver allograft model using Jalpha18 knockout mice that lack iNKT cells. Liver allografts lacking iNKT cells manifested not only infiltration but also hemorrhage and necrosis with significant reduction of graft survival and much less induction of tolerance compared with wild type (WT) liver allograft. In addition, allografts lacking iNKT cells grafted into iNKT-deficient recipients result in more severe inflammation than when grafted into WT recipients, while there was no significant difference with respect to induction of tolerance and graft survival. These results demonstrated that iNKT cells, especially donor-residual iNKT cells, constitute immune regulatory cells that play an important role in induction of allograft tolerance.

Immunobiology of allogeneic hematopoietic stem cell transplantation

Allogeneic hematopoietic stem cell transplantation (HSCT) has evolved into an effective adoptive cellular immunotherapy for the treatment of a number of cancers. The immunobiology of allogeneic HSCT is unique in transplantation in that it involves potential immune recognition and attack between both donor and host. Much of the immunobiology of allogeneic HSCT has been gleaned from preclinical models and correlation with clinical observations. We review our current understanding of some of the issues that affect the success of this therapy, including host-versus-graft (HVG) reactions, graft-versus-host disease (GVHD), graft-versus-tumor (GVT) activity, and restoration of functional immunity to prevent transplant-related opportunistic infections. We also review new strategies to optimize the GVT and improve overall immune function while reducing GVHD and graft rejection.

High-content flow cytometry and temporal data analysis for defining a cellular signature of graft-versus-host disease

Acute graft-versus-host disease (GVHD) is diagnosed by clinical and histologic criteria that are often nonspecific and typically apparent only after the disease is well established. Because GvHD is mediated by donor T cells and other immune effector cells, we sought to determine whether changes within a wide array of peripheral blood lymphocyte populations could predict the development of GvHD. Peripheral blood samples from 31 patients undergoing allogeneic blood and marrow transplant were analyzed for the proportion of 121 different subpopulations defined by 4-color combinations of lymphocyte phenotypic and activation markers at progressive time points posttransplant. Samples were processed using a newly developed high content flow cytometry technique and subjected to a spline- and functional linear discriminant analysis (FLDA)-based temporal analysis technique. This strategy identified a consistent posttransplant increase in the proportion and extent of fluctuation of CD3+CD4+CD8beta+ cells in patients who developed GVHD compared to those that did not. Although larger prospective clinical studies will be necessary to validate these results, this study demonstrates that high-content flow cytometry coupled with temporal analysis is a powerful approach for developing new diagnostic tools, and may be useful for developing a sensitive and specific predictive test for GVHD.

An essential role for IFN-gamma in regulation of alloreactive CD8 T cells following allogeneic hematopoietic cell transplantation

We previously found that CD8 T cells from IFN-gamma gene knockout (GKO) donors induce more severe lethal GVHD compared with CD8 T cells from wild-type (WT) donors in fully MHC-mismatched strain combinations. In this study, we investigated the mechanisms by which IFN-gamma inhibits GVHD in a parent --> F1 (B6 --> B6D2F1) allogeneic HCT (allo-HCT) model. IFN-gamma was strongly protective against GVHD in this parent --> F1 haplotype-mismatched allo-HCT model. Irradiated B6D2F1 mice that received GKO B6 CD4-depleted splenocytes developed lethal GVHD with severe lung and liver injury, whereas those receiving a similar cell population from WT B6 donors survived long term. Donor CD8 cells showed rapid activation, accelerated cell division, and reduced/delayed activation-induced cell death in allogeneic recipients in which donor cells were incapable of producing IFN-gamma. In consequence, the numbers of activated/effector (ie, CD25+, CD62L-, and CD44(high)) donor CD8 T cells in the recipients of GKO allo-HCT significantly exceeded those in mice receiving WT allo-HCT. These data show that IFN-gamma negatively regulates the CD8 T cell response by inhibiting cell division and promoting cell death and suggest that blockade of IFN-gamma could augment the severity of GVHD in patients undergoing allo-HCT.

Efficacy and Limitations of Natural Killer Cell Depletion in Cyclophosphamide-Induced Tolerance

PURPOSE

We previously developed a cyclophosphamide (CP)-induced tolerance protocol, consisting of an intravenous injection of 1 x 10(8) donor spleen cells (SC) given on day 0 and an intraperitoneal injection of 200 mg/kg CP given on day 2. In the present study, we modified this protocol with natural killer cell (NK) depletion in recipient mice, and evaluated the efficacy of tolerance induction.

METHODS

We used B10.D2 (H-2d; IE+) and B10 (H-2b; IE-) mice as both donors and recipients. The recipient mice were treated with donor SC, CP, and donor bone marrow cells (BMCs) with or without NK depletion.

RESULTS

A higher level of mixed chimerism was achieved in the NK-depleted recipients. Survival of both the skin and heart donor grafts was significantly prolonged in the NK-depleted recipients. Donor reactive Vbeta11+ T cells were found at the same level as in untreated control mice. Pretreatment with recipient NK cell depletion was effective in inducing higher levels of donor mixed chimerism; however, permanent engraftment of donor bone marrow was not achieved.

CONCLUSION

Survival of donor grafts was remarkably prolonged in the NK cell-depleted group, but transplantation tolerance could not be induced. Our results suggest that NK cell depletion in CP-induced tolerance conditioning has some effect on the induction of donor-specific tolerance.

Regulatory T Cells and Transplantation Tolerance

In the past decade, several types of regulatory T cells (Tregs) have been identified to play a pivotal role in the control of autoimmunity and transplantation tolerance in rodents and in human beings, including innate regulatory NKT cells and gammadelta T cells, naturally occurring FoxP3 expressing CD4(+)CD25(+) T cells, and in-vitro induced Tregs including interleuking-10 (IL-10)-secreting Tr1 CD4(+) T cells, TGF-beta-producing Th3 CD4(+) T cells, anergic CD4(+) T cells, CD8(+)CD28(-) and CD3(+)CD4(-)CD8(-) T cells. Recent studies have shown that innate and adaptive Tregs may be linked and act in concert to mediate immunosuppression. As our understanding of regulatory T cell populations has substantially advanced, compelling evidence support the prospect that in-vitro expanded, patient-tailored Tregs with indirect anti-donor allospecificity could be potential reagents as adoptive cell therapy for individualized medicine to promote clinical transplantation tolerance.

CCR5 in T Cell-Mediated Liver Diseases: What’s Going On?

The chemokine receptor CCR5 came into worldwide prominence a decade ago when it was identified as one of the major coreceptors for HIV infectivity. However, subsequent studies suggested an important modulatory role for CCR5 in the inflammatory response. Specifically, CCR5 has been reported to directly regulate T cell function in autoimmune diseases, including multiple sclerosis, rheumatoid arthritis, and type 1 diabetes. Moreover, T cell-mediated immune responses are proposed to be critical in the pathogenesis of autoimmune and viral liver diseases, and recent clinical and experimental studies have also implicated CCR5 in the pathogenesis of autoimmune and viral liver diseases. Therefore, in this brief review, we highlight the evidence that supports an important role of CCR5 in the pathophysiology of T cell-mediated liver diseases with specific emphasis on autoimmune and viral liver diseases.

Natural killer T cells and haemopoiesis

Invariant natural killer T (iNKT) cells are a small but powerful subset of regulatory T cells involved in the modulation of a variety of normal and pathological immune responses. In contrast to conventional or other types of regulatory T cells, they are activated by glycolipid and phospholipid ligands that are presented to them by the non-polymorphic, major histocompatibility complex class I-like molecule CD1d. The in-depth understanding of their function has resulted in successful, iNKT cell-centred experimental therapeutic interventions including prevention of graft-versus-host disease and anti-leukaemia effects. Extending these successes into the clinical arena will require better understanding of their contribution to the pathogenesis of human, including haematological, diseases.

Graft-versus-host disease in recipients of grafts from natural killer T cell-deficient (Jalpha281(-/-)) donors

Valpha14i natural killer T cells (NKT cells) are a CD1-restricted subset of NKT cells that express an invariable Valpha14+ Jalpha281+ alphabeta T-cell receptor. To determine whether the absence of Valpha14i NKT cells from the graft affects the development of acute GVHD, we induced GVH reactions using Jalpha281(-/-) mice as donors in the C57BL/6-->(C57BL/6 x DBA/2)F1-hybrid strain combination. Recipients of grafts from Jalpha281(-/-) donors were not protected from either the morbidity or the severe wasting syndrome associated with the development of acute GVHD, but the concentrations of some T helper 1 (Th1) and Th2 cytokines were different from those seen in recipients of grafts from wild-type donors. Interferon-gamma was seen earlier (day 4) in recipients of grafts from Jalpha281(-/-) donors but did not reach the concentrations seen in recipients of grafts from wild-type donors on day 8 (P < 0.02). On day 8, the amount of tumour necrosis factor-alpha released into the serum following the injection of a small amount of lipopolysaccharide was lower in recipients of grafts from Jalpha281(-/-) donors (P < 0.02). The amount of interleukin (IL)-5 was also lower in recipients of grafts from Jalpha281(-/-) donors, when compared to the concentration seen in recipients of grafts from wild-type donors (P < 0.002). IL-13 was seen in recipients of grafts from Jalpha281(-/-) donors but not in recipients of grafts from wild-type donors. Our findings show that the absence of donor Valpha14i NKT cells is associated with lower concentrations of some Th1 cytokines. We also observed higher IL-13 concentrations and lower IL-5 concentrations in recipients of grafts from Jalpha281(-/-) donors indicating a variable effect on Th2 cytokine production.

Modulation of acute graft-versus-host disease and chimerism after adoptive transfer of in vitro-expanded invariant Valpha14 natural killer T cells

Mouse natural killer T cells with an invariant Valpha14-Jalpha18 TCR rearrangement (Valpha14i NKT cells) are able to regulate immune responses through rapid and large amounts of Th1 and Th2 cytokine production. It has been reported that in vivo administration of the Valpha14i NKT cell ligand, alpha-galactosylceramide (alpha-GalCer) significantly reduced morbidity and mortality of acute graft-versus-host disease (GVHD) in mice. In this study, we examined whether adoptive transfer of in vitro-expanded Valpha14i NKT cells using alpha-GalCer and IL-2 could modulate acute GVHD in the transplantation of spleen cells of C57BL/6 mice into (B6xDBA/2) F(1) mice. We found that the adoptive transfer of cultured spleen cells with a combination of alpha-GalCer and IL-2, which contained many Valpha14i NKT cells, modulated acute GVHD by exhibiting long-term mixed chimerism and reducing liver damage. Subsequently, the transfer of Valpha14i NKT cells purified from spleen cells cultured with alpha-GalCer and IL-2 also inhibited acute GVHD. This inhibition of acute GVHD by Valpha14i NKT cells was blocked by anti-IL-4 but not by anti-IFN-gamma monoclonal antibody. Therefore, the inhibition was dependent on IL-4 production by Valpha14i NKT cells. Our findings highlight the therapeutic potential of in vitro-expanded Valpha14i NKT cells for the prevention of acute GVHD after allogeneic hematopoietic stem cell transplantation.

Stem cell mobilization with G-CSF analogs: a rational approach to separate GVHD and GVL?

The separation of graft-versus-host disease (GVHD) and graft-versus-leukemia (GVL) remains the "holy grail" of allogeneic stem cell transplantation, and improvements are urgently needed to allow more effective therapy of malignant disease. The use of G-CSF-mobilized peripheral blood as a clinical stem cell source is associated with enhanced GVL effects without amplification of significant acute GVHD. Preclinical studies have demonstrated that G-CSF modulates donor T cell function before transplantation, promoting T(H)2 differentiation and regulatory T cell function. In addition, the expansion of immature antigen-presenting cells (APCs) and plasmacytoid dendritic cells (DCs) favors the maintenance of this pattern of T cell differentiation after transplantation. Although these patterns of T cell differentiation attenuate acute GVHD, they do not have an impact on the cytolytic pathways of the CD8(+) T cells that are critical for effective GVL. Recently, it has been demonstrated that modification of G-CSF, either by pegylation of the native cytokine or conjugation to Flt-3L, results in the expansion and activation of donor iNKT cells, which significantly augment CD8(+) T cell-mediated cytotoxicity and GVL effects after transplantation. Given that these cytokines also enhance the expansion of regulatory T cells and APCs, they further separate GVHD and GVL, offering potential clinical advantages for the transplant recipient.

Human Invariant NKT Cells Are Required for Effective In Vitro Alloresponses

NKT cells are a small subset of regulatory T cells conserved in humans and mice. In humans they express the Valpha24Jalpha18 invariant chain (hence invariant NKT (iNKT) cells) and are restricted by the glycolipid-presenting molecule CD1d. In mice, iNKT cells may enhance or inhibit anti-infectious and antitumor T cell responses but suppress autoimmune and alloreactive responses. We postulated that iNKT cells might also modulate human alloreactive responses. Using MLR assays we demonstrate that in the presence of the CD1d-presented glycolipid alpha-galactosylceramide (alphaGC) alloreactivity is enhanced (37 +/- 12%; p < 0.001) in an iNKT cell-dependent manner. iNKT cells are activated early during the course of the MLR, presumably by natural ligands. In MLR performed without exogenous ligands, depletion of iNKT cells significantly diminished the alloresponse in terms of proliferation (58.8 +/- 24%; p < 0.001) and IFN-gamma secretion (43.2 +/- 15.2%; p < 0.001). Importantly, adding back fresh iNKT cells restored the reactivity of iNKT cell-depleted MLR to near baseline levels. CD1d-blocking mAbs equally reduced the reactivity of the iNKT cell-replete and -depleted MLR compared with IgG control, indicating that the effect of iNKT cells in the in vitro alloresponse is CD1d-dependent. These findings suggest that human iNKT cells, although not essential for its development, can enhance the alloreactive response.