IL-18 prevents the development of chronic graft-versus-host disease in mice

Kynurenine pathway activation and deviation to anthranilic and kynurenic acid in fibrosing chronic graft-versus-host disease

Fibrosing chronic graft-versus-host disease (cGVHD) is a debilitating complication of allogeneic stem cell transplantation (alloSCT). A driver of fibrosis is the kynurenine (Kyn) pathway, and Kyn metabolism patterns and cytokines may influence cGVHD severity and manifestation (fibrosing versus gastrointestinal [GI] cGVHD). Using a liquid chromatography-tandem mass spectrometry approach on sera obtained from 425 patients with allografts, we identified high CXCL9, high indoleamine-2,3-dioxygenase (IDO) activity, and an activated Kyn pathway as common characteristics in all cGVHD subtypes. Specific Kyn metabolism patterns could be identified for non-severe cGVHD, severe GI cGVHD, and fibrosing cGVHD, respectively. Specifically, fibrosing cGVHD was associated with a distinct pathway shift toward anthranilic and kynurenic acid, correlating with reduced activity of the vitamin-B2-dependent kynurenine monooxygenase, low vitamin B6, and increased interleukin-18. The Kyn metabolite signature is a candidate biomarker for severe fibrosing cGVHD and provides a rationale for translational trials on prophylactic vitamin B2/B6 supplementation for cGVHD prevention.

High IDO activity and an activated Kyn pathway are common in all cGVHD subtypes

Specific Kyn metabolism patterns were identified for gastrointestinal and fibrosing cGVHD

A pathway shift toward anthranilic and kynurenic acid was found in fibrosing cGVHD

A rationale for vitamin B2/B6 adjustment for cGVHD prevention is presented

Myeloid differentiation factor 88 signaling in donor T cells accelerates graft-versus-host disease

Myeloid differentiation factor 88 (MyD88) signaling has a crucial role in activation of both innate and adoptive immunity. MyD88 transduces signals via Toll-like receptor and interleukin-1 receptor superfamily to the NFκB pathway and inflammasome by forming a molecular complex with interleukin-1 receptor-associated kinase 4. The MyD88/interleukin-1 receptor-associated kinase 4 pathway plays an important role, not only in innate immunity, but also T-cell immunity; however, its role in donor T cells on the pathophysiology of graft-versus-host disease (GvHD) remains to be elucidated. We addressed this issue by using MyD88-deficient T cells in a mouse model of allogeneic hematopoietic stem cell transplantation (allo-SCT). While MyD88-deficient and wild-type T cells proliferated equivalently after transplantation, MyD88-deficient T cells demonstrated impaired survival and differentiation toward Th1, Tc1, and Th17, and induced less severe GvHD compared to wild-type T cells. Administration of interleukin-1 receptor-associated kinase 4 inhibitor PF-06650833 significantly ameliorated GvHD after allo-SCT. These results thus demonstrate that donor T-cell MyD88/interleukin-1 receptor-associated kinase 4 pathway is a novel therapeutic target against GvHD after allo-SCT.

Osteopontin attenuates acute gastrointestinal graft-versus-host disease by preventing apoptosis of intestinal epithelial cells

BACKGROUND AND AIMS

Acute graft-versus-host disease (GVHD) is a major complication after allogeneic hematopoietic stem cell transplantation, which often targets gastrointestinal (GI) tract. Osteopontin (OPN) plays an important physiological role in the efficient development of Th1 immune responses and cell survival by inhibiting apoptosis. The role of OPN in acute GI-GVHD is poorly understood. In the present study, we investigated the role of OPN in donor T cells in the pathogenicity of acute GI-GVHD.

METHODS

OPN knockout (KO) mice and C57BL/6 (B6) mice were used as donors, and (C57BL/6 × DBA/2) F1 (BDF1) mice were used as allograft recipients. Mice with acute GI-GVHD were divided into three groups: the control group (BDF1→BDF1), B6 group (B6→BDF1), and OPN-KO group (OPN-KO→BDF1). Bone marrow cells and spleen cells from donors were transplanted to lethally irradiated recipients. Clinical GVHD scores were assessed daily. Recipients were euthanized on day 7 after transplantation, and colons and small intestines were collected for various analyses.

RESULTS

The clinical GVHD score in the OPN-KO group was significantly increased compared with the B6 and control groups. We observed a difference in the severity of colonic GVHD between the OPN-KO group and B6 group, but not small intestinal-GVHD between these groups. Interferon-γ, Tumor necrosis factor-α, Interleukin-17A, and Interleukin-18 gene expression in the OPN-KO group was differed between the colon and small intestine. Flow cytometric analysis revealed that the fluorescence intensity of splenic and colonic CD8 T cells expressing Fas Ligand was increased in the OPN-KO group compared with the B6 group.

CONCLUSION

We demonstrated that the importance of OPN in T cells in the onset of acute GI-GVHD involves regulating apoptosis of the intestinal cell via the Fas-Fas Ligand pathway.

The chemokine system: a possible therapeutic target in acute graft versus host disease

Allogeneic hematopoetic stem cell transplantation often presents the only chance for cure in a number of malignant and nonmalignant hematologic diseases. However, its beneficial effects are counterweighed by the development of potentially lethal complications, most importantly the development of acute and chronic graft-vs.-host disease (GVHD). Alloantigen-reactive immune responses mediate injury and destruction of GVHD target organs, including the gastrointestinal tract, the liver, the skin, and the lung. Donor leukocyte infiltration into the respective tissues is orchestrated by interactions between chemokines and chemokine receptors, which will be reviewed using a basic science - clinical comparative approach.

Acute graft-versus-host disease: from the bench to the bedside

During the past decade, progress in basic immunology has been impressive. In parallel, whereas our understanding of the pathophysiology of acute graft-versus-host disease (GVHD) has greatly improved, so has our knowledge of the complexities of the immune system. Much of the immunobiology of acute GVHD has been gleaned from preclinical models and far less from correlations with clinical observations or therapeutic interventions. In this review, we summarize some of the major advances in GVHD pathophysiology, including the translation of these from the bench to the bedside, and discuss preclinical approaches that warrant further exploration in the clinic.

The IL-12 Role in Donor Cell Engraftment in a Murine Model of Semiallogenic GVH Disease with Signs of Autoimmune Disease

We analyzed the IL-12 effect in an autoimmune disease induced in a semiallogenic murine model of graft-vs-host disease (GVHD) Balb/c semiallogenic lymphoid cells i.v. infected in hybrid mice (Balb/c x A/J) F1 (CAF). IL-12 was administered 1 h before cell transplantation following two different protocols: (a) injecting 2 microg of mrIL-12 (murine recombinant IL-12) per mouse before the first semiallogenic cell injection; or (b) injecting the 2 microg of mrIL-12 fractionated in 5 days. ATh1 response was produced but an acute GVHD did not appear although differences in class I and II major histocompatibility complex (MHC) antigens were present. Four days after the semiallogenic cell transfer, IL-12 treated mice showed a marked reduction in the percent of spleen B cells compared with CAF1 control and CAF1 + Balb/c GVHD mice. After 5-6 months of follow-up, the donor cell chimerism increased significantly in spleen (70 +/- 31 vs. 43 +/- 31%) and in thymus. Flow cytometry of spleen lymphocytes demonstrated that donor chimerism was made up of TCD4, TCD8 and B lymphocytes and was higher in animals injected with IL-12. Moreover, CD8 T lymphocytes were 100% donor origin in the IL-12-injected group of GVHD animals and 50% origin in the IL-12-non-injected CAF1 + Balb/c group of animals. This paper shows that: (1) IL- 12 may play a role in the mechanisms of donor cell engraftment, probably produced by a CTL donor anti-host mechanism; (2) no acute GVHD was induced in spite of class I and II MHC differences; (3) IL-12 did not show any effect on the AR-like clinical signs of disease developed in this model of GVHD although histological subclinical signs were less frequent, and no glomerulonephritis was detected in the IL-12-treated GVHD mice.

Immunologic states of autoimmune diseases

The etiology and immunologic states of autoimmune diseases have mainly been discussed without consideration of extrathymic T cells, which exist in the liver, intestine, and excretion glands. Because extrathymic T cells are autoreactive and are often simultaneously activated along with autoantibody-producing B-1 cells, these extrathymic T cells and B-1 cells should be introduced when considering the immunologic states of autoimmune diseases. The immunologic states of autoimmune diseases resemble those of aging, chronic GVH disease, and malarial infection. Namely, under all these conditions, conventional T and B cells are rather suppressed concomitant with thymic atrophy or involution. In contrast, extrathymic T cells and B-1 cells are inversely activated at this time. These facts suggest that the immunologic states of autoimmune diseases should be reevaluated by introducing the concept of extrathymic T cells and autoantibody-producing B-1 cells, which might be primordial lymphocytes in phylogeny.

Hepatocyte growth factor prevents lupus nephritis in a murine lupus model of chronic graft-versus-host disease

Chronic graft-versus-host disease (GVHD) induced in (C57BL/6 x DBA/2) F1 (BDF1) mice by the injection of DBA/2 mouse spleen cells represents histopathological changes associated with systemic lupus erythematosus (SLE), primary biliary cirrhosis (PBC) and Sjogren's syndrome (SS), as indicated by glomerulonephritis, lymphocyte infiltration into the periportal area of the liver and salivary glands. We determined the therapeutic effect of hepatocyte growth factor (HGF) gene transfection on lupus using this chronic GVHD model. Chronic GVHD mice were injected in the gluteal muscle with either HVJ liposomes containing 8 microg of the human HGF expression vector (HGF-HVJ liposomes) or mock vector (untreated control). Gene transfer was repeated at 2-week intervals during 12 weeks. HGF gene transfection effectively prevented the proteinuria and histopathological changes associated with glomerulonephritis. While liver and salivary gland sections from untreated GVHD mice showed prominent PBC- and SS-like changes, HGF gene transfection reduced these histopathological changes. HGF gene transfection greatly reduced the number of splenic B cells, host B cell major histocompatibility complex class II expression, and serum levels of IgG and anti-DNA antibodies. IL-4 mRNA expression in the spleen, liver, and kidneys was significantly decreased by HGF gene transfection. CD28 expression on DBA/2 CD4+ T cells was decreased by the addition of recombinant HGF in vitro. Furthermore, IL-4 production by DBA/2 CD4+ T cells stimulated by irradiated BDF1 dendritic cells was significantly inhibited by the addition of recombinant HGF in vitro. These results suggest that HGF gene transfection inhibited T helper 2 immune responses and reduced lupus nephritis, autoimmune sialoadenitis, and cholangitis in chronic GVHD mice. HGF may represent a novel strategy for the treatment of SLE, SS and PBC.

Induction of allergic inflammation by interleukin-18 in experimental animal models

Interleukin-18 (IL-18) has been regarded as a proinflammatory cytokine because of its potent interferon-gamma-inducing activity. However, mutant mice that release excess amounts of IL-18 spontaneously develop pruritic chronic dermatitis-like atopic dermatitis (AD), suggesting the importance of IL-18 for the development of AD. Intriguingly, depletion of il-18 but not stat6, an essential transcriptional factor for IL-4 signaling, rescues the mice from AD, indicating IL-18-dependent, T-helper 2 (Th2) cell-independent AD. This type of AD is classified as innate-type allergy in contrast to Th2 cell-dependent ordinary allergy. Consistent with the previous studies, mice transferred with antigen-specific Th1 cells exhibit no airway hyperresponsiveness and respiratory eosinophilic inflammation after challenge with antigen alone. However, they suffer from asthma upon challenge with antigen plus IL-18, with comparable levels of both the alterations as in those transferred with Th2 cells following challenge with antigen. The former type of asthma is categorized as Th1-associated allergy. Therefore, it is definitely necessary to evaluate whether individual allergic disorders involve either of these IL-18-mediated pathways or a Th2-mediated one.

Chronic graft-versus-host disease after granulocyte colony-stimulating factor-mobilized allogeneic stem cell transplantation: the role of donor T-cell dose and differentiation

The use of granulocyte colony-stimulating factor (G-CSF)-mobilized peripheral blood as a source of stem cells has resulted in a high incidence of severe chronic graft-versus-host disease (cGVHD), which compromises the outcome of clinical allogeneic stem cell transplantation. We have studied the effect of G-CSF on both immune complex and fibrotic cGVHD directed to major (DBA/2 --> B6D2F1) or minor (B10.D2 --> BALB/c) histocompatibility antigens. In both models, donor pretreatment with G-CSF reduced cGVHD mortality in association with type 2 differentiation. However, after escalation of the donor T-cell dose, scleroderma occurred in 90% of the recipients of grafts from G-CSF-treated donors. In contrast, only 11% of the recipients of control grafts developed scleroderma, and the severity of hepatic cGVHD was also reduced. Mixing studies confirmed that in the presence of high donor T-cell doses, the severity of scleroderma was determined by the non-T-cell fraction of grafts from G-CSF-treated donors. These data confirm that the induction of cGVHD after donor treatment with G-CSF is dependent on the transfer of large numbers of donor T cells in conjunction with a putatively expanded myeloid lineage, providing a further rationale for the limitation of cell dose in allogeneic stem cell transplantation.

Involvement of Interleukin-18 in Acute Graft-Versus-Host Disease in Mice

BACKGROUND

Interleukin (IL)-18 stimulates T helper 1 (Th1)-mediated immune responses and the development of cytotoxic T lymphocytes (CTLs). Antihost CTLs are major effectors in acute graft-versus-host disease (aGvHD), a potentially fatal complication after allogeneic stem-cell transplantation. We investigated the relevant role of IL-18 in the development of aGvHD in mice.

METHODS

Irradiated (C57BL/6x DBA/2) F1 (BDF1) mice transplanted with wild-type (WT) C57BL/6 (B6) splenocytes were compared with those transplanted with IL-18Ralpha-deficient B6 splenocytes with respect to Th1 development, CTL activity, severity of aGvHD, and survival.

RESULTS

Transplantation of WT B6 spleen cells into BDF1 mice induced aGvHD that was accompanied by elevation of both serum IL-18 levels and IL-18 receptor alpha chain (IL-18Ralpha) expression on engrafted T cells. The transplantation of WT B6 cells also induced high antihost CTL activity in host spleen, whereas transplantation of IL-18Ralpha-deficient B6 cells exhibited significantly reduced antihost-specific CTL activity, indicating that IL-18Ralpha-deficient CTLs were less cytotoxic than IL-18Ralpha-expressing CTLs. Moreover, the hosts receiving transplants with the IL-18Ralpha-deficient B6 cells had fewer fatal tissue injuries and increased their survival rates as compared with those receiving transplants with WT cells. Nevertheless, Th1 development in the hosts was the same, regardless of the type of donor cells.

CONCLUSIONS

These results suggest that Th1 induction and baseline CTL activity in aGvHD occur in the absence of IL-18, but endogenous IL-18 further accelerates aGvHD reaction to its full-blown manifestation. Thus, IL-18 may be involved in the development aGvHD by enhancing CTL activity.

Interleukin-18: recent advances

PURPOSE OF REVIEW

Interleukin-18 (IL-18) has potent immunomodulatory effects. It is the only cytokine with a unique capacity to induce T helper 1 or T helper 2 polarization, depending on the immunologic context. Serum levels of IL-18 are increased in many human diseases and it has been implicated in the pathogenesis of several immune-mediated processes. Some of the recent key advances in the immunobiology of IL-18 are discussed in this review.

RECENT FINDINGS

Recent data from several laboratories have shed light on the structure of IL-18; the signaling cascades that are initiated; and its role on modulating T cells, dendritic cells, and natural killer cell function. Several new reports have expanded and delineated the role of IL-18 in a multitude of diseases, but only recent advances in the role of IL-18 in three disease processes (acute graft-versus-host disease, insulin-dependent diabetes, and sepsis), where it appears to play paradoxic roles are discussed.

SUMMARY

Although emerging data shed more light on the complex role of IL-18 in immune reactions, they also pose more questions. Given the pleiotropic, complex, and at times paradoxic effects of IL-18 in various disease processes, better understanding of its immunobiology might lead to the development of IL-18 and/or its antagonists as therapeutic agents against immune-mediated diseases.

Recent advances in the treatment of graft-versus-host disease

Graft-versus-host disease (GVHD) is a lethal complication of allogeneic hematopoietic stem cell transplantation (HSCT) where immunocompetent donor T cells attack the genetically disparate host cells. The predominant symptoms of acute GVHD occur in the skin, liver, and intestine. Induction of acute GVHD can be divided into three phases: recipient conditioning, donor T cell activation, and effector cell-mediated GVHD. Chronic GVHD usually appears up to 100 days after HSCT and is characterized by symptoms similar to those observed for autoimmune disease. It is possible that chronic GVHD is the result of autoreactive T cells that escaped negative selection due to damage to the thymus from conditioning regimens, acute GVHD, and/or age related atrophy. Recent advances in the understanding of the basic mechanisms involved in GVHD pathophysiology have led to new strategies designed to block GVHD. This review focuses on recent developments in the treatment of GVHD, including insights gained from our own experimental studies.

Chronic graft versus host disease

The ability to cure increasing numbers of individuals for malignant and non-malignant diseases with the use of stem cell transplantation has resulted in a growing number of long-term survivors with unique medical issues. Chronic graft versus host disease (GvHD) continues to be a significant problem in the allogeneic stem cell transplant setting and, as we continue to use alternative stem cell sources and attempt to modulate the immune system to increase an anti-tumour effect, we will probably see rising numbers of patients with this complication. The capacity to treat this problem and improve both the immediate quality of life as well as long-term effects is imperative and requires the ability of haematologists/oncologists to identify chronic GvHD and its multi-organ system presentations. We describe the risk factors for developing chronic GvHD, its presentation and the current treatment options for both initial therapy and secondary treatment.

Patient interleukin-18 GCG haplotype associates with improved survival and decreased transplant-related mortality after unrelated-donor bone marrow transplantation

Interleukin-18 (IL-18), a proinflammatory cytokine, is elevated in patients with acute graft-versus-host disease (aGVHD). IL-18 induces Th1 differentiation and cytotoxic T-lymphocyte function, both of which have been implicated in the pathogenesis of aGVHD. However, recent studies have shown that neutralization of IL-18 by antibodies leads to an increased risk of aGVHD-related mortality while administration of IL-18 significantly improved survival. We have genotyped a cohort of 157 patient/donor pairs undergoing unrelated donor bone marrow transplantation (BMT) for three polymorphisms recently identified in the promoter of the IL-18 gene: G-137C, C-607A and G-656T. Using phase software, three main haplotypes were reconstructed: GCG, CAT and GAT. We found no association between the occurrence of aGVHD and patient/donor haplotypes. The presence of the GCG haplotype in patients was associated with significantly decreased risk of transplant-related mortality at 100 d (23% in patients with GCG vs. 48% in patients without GCG, P < 0.01) and at 1 year (36% vs. 65%, P < 0.01). The presence of the GCG haplotype in patients was also associated with improved survival (57% vs. 32%, P < 0.01). Cox regression analysis showed that the presence of the GCG haplotype was associated with a twofold increased probability of survival. These data suggest that the IL-18 promoter GCG haplotype may influence survival after unrelated donor BMT without altering the risk of aGVHD.

Increased expression of IL-18 in cutaneous graft-versus-host disease

Interleukin-18 (IL-18) is an 18-kDa cytokine produced by lipopolysaccharide (LPS)-activated macrophages or Kupffer cells. In addition, IL-18 is also produced by many different types of cells and tissues, including epidermal keratinocytes, the adrenal cortex, and the brain. IL-18 acts on the immune system to increase IFN-gamma production from T and NK cells to enhance NK cell cytotoxicity and to activate Th1 cell proliferation. It is considered that the tissue expression of cytokines and cell adhesion molecules such as ICAM-1 are common in graft-versus-host disease (GVHD). Recent evidence suggests that IL-18 is a cytokine relevant in the pathogenesis of GVHD. Despite the potential importance of IL-18 in GVHD, the distribution of IL-18 production in cutaneous GVHD has not been fully investigated. In this study, the expression of IL-18 in the cutaneous GVHD was investigated. Formalin-fixed, paraffin-embedded tissue sections were obtained, and immunohistochemical analysis was performed to detect IL-18 and ICAM-1 expression according to the acute and chronic GVHD. Immunohistochemical analysis confirmed the enhanced IL-18 expression levels in the early stage (grade 1) of acute GVHD and the late stage (sclerodermoid) of chronic GVHD compared to the other stages. In contrast, the ICAM-1 expression level was constant at all stages. Our findings indicate that IL-18 is a significant pathogenic indicator in cutaneous GVHD, and the tissue expression of IL-18 seems to be associated with the pathogenesis of acute and chronic GVHD.

Paradoxical effects of interleukin-18 on the severity of acute graft-versus-host disease mediated by CD4+ and CD8+ T-cell subsets after experimental allogeneic bone marrow transplantation

Administration of exogenous interleukin-18 (IL-18) regulates experimental acute graft-versus-host disease (GVHD) in a Fas-dependent manner when donor CD4(+) T cells are required for mortality after experimental allogeneic bone marrow transplantation (BMT). However, CD4(+) and CD8(+) T cells can induce acute GVHD after clinical allogeneic BMT, and the role of IL-18 in CD8(+)-mediated acute GVHD is unknown. We, therefore, determined the role of IL-18 in GVHD mediated by CD4(+) or CD8(+) T cells across major histocompatibility complex (MHC) class II- and class I-disparate allogeneic BMT, respectively. Administering IL-18 significantly increased survival in CD4(+)-mediated GVHD but reduced survival in CD8(+)-mediated GVHD. This increase in deaths was associated with significantly greater clinical, biochemical, and histopathologic parameters of GVHD damage and was independent of Fas expression on donor T cells. Administering IL-18 significantly enhanced allospecific cytotoxic function and expansion of CD8(+) cells. Endogenous IL-18 was critical to GVHD mediated by CD8(+) donor T cells because IL-18 receptor-deficient donors caused significantly less GVHD but exacerbated CD4(+)-mediated, GVHD-related death. Furthermore, administering anti-IL-18 monoclonal antibody significantly reduced CD8(+)-mediated, GVHD-related death. Together these findings demonstrate that IL-18 has paradoxical effects on CD4(+) and CD8(+) cell-mediated GVHD.

The Pathophysiology of Chronic Graft-versus-Host Disease

Chronic graft-versus-host disease (GVHD) still remains the most significant complication after allogeneic hematopoietic stem cell transplantation. The disease usually appears after day 100 and is characterized by signs and symptoms similar to autoimmune diseases. The pathophysiology of chronic GVHD is poorly understood because of the lack of highly satisfactory animal models and basic studies in patients. It has not been clearly determined whether the disease is a distinct entity or a continuation of acute GVHD. In experimental and clinical studies of chronic GVHD, thymic atrophy, lymphocyte depletion, and autoantibody formation have been described. Conditioning regimens and acute GVHD may disrupt thymic function and dysregulate the negative selection process of potentially autoreactive T-lymphocytes. Disruption of thymic apoptosis and failure to eliminate the majority of self-reactive lymphocytes may lead to impairment of lymphocyte homeostasis and self tolerance. Expansion and effector functions of autoreactive T-cells will then promote autoreactive B-cell activation and production of autoantibodies with target-organ damage. Chronic GVHD requires continuous CD4+ T-cell help for B-cells and is known as T-helper 2 (Th2) disease. Murine models have demonstrated the roles of interleukin (IL)-12 and IL-18 in chronic GVHD. IL-12 may cause an increase in donor CD8+ cytotoxic T-cells leading to conversion of chronic GVHD to an acute form. In contrast, IL-18 prevents chronic GVHD by decreasing numbers of CD4+ (Th2) cells and host-reactive B-cell activation and reducing alloantigen-specific immune response. Mouse and human cellular genomics coupled with advances in cell biology in donor-recipient tolerance will improve our understanding of transplantation immunology and may offer new approaches to the challenge of ameliorating chronic GVHD.

Determinants of Antileukemia Effects of Allogeneic NK Cells

In HLA-nonidentical bone marrow transplantation, we studied the characteristics of donor NK cells, recipient leukemia cells, and the cytokine environment that predict the antileukemia effects of allogeneic NK cells. We found that the risk of relapse in pediatric patients with hematologic malignancies was best predicted by a model taking into consideration the presence of inhibitory killer cell Ig-like receptors (KIRs) on the donor's NK cells and the absence of corresponding KIR ligand in the recipient's HLA repertoire (a receptor-ligand model). The risk of relapse was prognosticated less precisely by the Perugia donor-recipient KIR ligand-ligand mismatch model or by a natural cytotoxicity model. In contrast to the ligand-ligand model, we found that the new receptor-ligand model was accurate when analysis was applied to patients with lymphoid malignancy. These findings corroborate our observations that the recipient's KIR repertoire, which was derived from highly purified, HLA-disparate CD34+ cells, resumed a donor-specific pattern within 3 mo of transplantation, but did not correlate evidently with the donor or recipient ligand repertoire. In an in vitro assay and an in vivo mouse model, human NK cell cytotoxicity toward human leukemia cells with 11q23 chromosomal rearrangement increased with the number of receptor-ligand mismatch pairs or prestimulation with IL-12 and IL-18. These findings provide new insights into the determinants of antileukemia effects of allogeneic NK cells and therapeutic strategies.

Pathogenesis and treatment of graft-versus-host disease after bone marrow transplant

Stem cell transplantation is being used to treat a number of hematologic malignancies as well as hematologic and immune deficiency states. The ages of patients being offered this therapy and the donor marrow sources have been expanded. One persistent problem has been graft-versus-host disease (GVHD). This article reviews the basic biology of GVHD, clinical manifestations of acute and chronic GVHD, prophylaxis and treatment of acute GVHD, and treatment of chronic GVHD.

Role of interleukin-18 in acute graft-vs-host disease

Allogeneic hematopoietic cell transplantation (HCT) has emerged as an important therapeutic option for several malignant and nonmalignant diseases. In addition to delivering systemic chemoradiotherapy, the therapeutic potential of allogeneic HCT relies on the graft-vs-leukemia (GVL) effect, which eradicates residual malignant cells by way of immunologic mechanisms. Unfortunately, GVL effects are closely associated with graft-vs-host disease (GVHD), the major complication of allogeneic HCT. Separation of the toxicity of acute GVHD from the beneficial GVL effects remains a major challenge to expanding the utility of this effective treatment modality. The pathophysiology of acute GVHD involves dysregulation of inflammatory cytokine cascades and donor T-cell responses to host alloantigens. Interleukin 18 (IL-18) is a recently discovered cytokine with potent immunomodulatory effects. This unique cytokine has the capacity to induce Th1 or Th2 polarization, depending on the immunologic context. The level of IL-18 is increased in acute GVHD, but this cytokine's role in the pathophysiology of acute GVHD is complex. It reduces the severity of acute GVHD as a T helper 1 (Th1)-inducing cytokine when administered early after bone-marrow transplant to the lethally irradiated recipients. When administered to the donor, it can also reduce the severity of acute GVHD, as a T helper 2 (Th2)-inducing cytokine. Despite reducing the severity of acute GVHD, IL-18 preserves the GVL effect after bone-marrow transplant. Thus IL-18 has the remarkable capacity to modulate acute GVHD when administered either to the donor or the recipient through distinct mechanisms.

Pretreatment of donors with interleukin-18 attenuates acute graft-versus-host disease via STAT6 and preserves graft-versus-leukemia effects

Interleukin-18 (IL-18) is a unique cytokine that modulates both T(H)1/T(H)2 responses, but its ability to modulate diseases through induction of T(H)2 cytokines is unclear. It has been shown to play an important role in allogeneic bone marrow transplantation (BMT). Because immune responses of allogeneic BM donors may affect acute graft-versus-host disease (GVHD), we investigated the effect of pretreating BM transplant donors with IL-18 on the severity of acute GVHD using a well-characterized experimental BMT model (BALB/c-->B6). Pretreatment of allogeneic BM transplant donors with IL-18 significantly improved survival (80% vs 0%; P <.001), and reduced clinical, biochemical, and pathologic indices of acute GVHD in BM transplant recipients. IL-18 pretreatment was associated with reduced interferon gamma (IFN-gamma) and greater IL-4 secretion by donor T cells after BMT. Acute GVHD mortality was reduced when IL-18 was administered to donors deficient in IFN-gamma and signal transducer and activator of transcription 4 (STAT4) but not STAT6 signaling molecules, suggesting a critical role for STAT6 signaling in IL-18's protective effect. IL-18 treatment did not alter donor CD8(+) cytotoxic T-lymphocyte (CTL) activity and preserved graft-versus-leukemia (GVL) effects after allogeneic BMT (70% vs 10%; P <.01). Together these data illustrate that pretreatment of donors with IL-18 prior to allogeneic BMT attenuates acute GVHD in a STAT6-dependent mechanism while preserving GVL effects.

Chronic graft-versus-host disease

Chronic graft-versus-host disease (GVHD) remains a vexing and dangerous complication of allogeneic stem cell transplantation. Mild forms of chronic GVHD are often manageable with local or low-dose systemic immunosuppression and do not affect long-term survival. In contrast, more severe forms of chronic GVHD require intensive medical management and adversely affect survival. This report reviews current concepts of the pathogenesis, clinical risk factors, classification systems, organ manifestations, and available treatments for chronic GVHD. It also provides a comprehensive listing of the published clinical trials aimed at prevention and primary treatment of chronic GVHD.

The flavonoid Kaempferol suppresses the graft-versus-host reaction by inhibiting type 1 cytokine production and CD8+ T cell engraftment

We have here examined the immunoregulatory effects of a natural flavonoid, Kaempferol, on T cells. Kaempferol suppressed IFN-gamma and IL-2 production but not that of IL-4 by T cells and shifted the Th1/Th2 balance into the Th2 phenotype. In C57BL/6 anti-BDF1 MLC, Kaempferol inhibited the development and expansion of type 1 effector CD8+ T cells and diminished allospecific CTL activity. Based on these in vitro results, we evaluated the effects of Kaempferol treatment on the development of C57BL/6-into-BDF1 acute graft-versus-host disease (GVHD). Brief administration of Kaempferol led to early recovery from body weight loss, increased survival, and reduced tissue injury in the liver and large intestine. Kaempferol treatment activated Th2 cells and the engraftment of donor cells and also diminished GVHD-associated antihost CTL activity. Thus, our study indicates that Kaempferol has the capacity to modulate the Th1/Th2 balance and could be useful for the treatment of cell-mediated immune diseases, such as acute GVHD.

IL-18-independent cytotoxic T lymphocyte activation and IFN-gamma production during experimental acute graft-versus-host disease

Acute graft-versus-host disease (GvHD) is a serious complication after allogeneic bone marrow transplantation. Donor-derived T cells infiltrate recipient target organs and cause severe tissue damage, often leading to death of the affected patient. Tissue destruction is a direct result of donor CD8+ T cell activation and cell-mediated cytotoxicity. IL-18 is a novel pro-inflammatory cytokine with potent T(h)1 immune response-promoting and cytotoxic T lymphocyte (CTL)-inducing activity. IL-18 is strongly induced in experimental mouse models and human patients with acute GvHD. However, the precise role of IL-18 in the development of acute GvHD is still unknown. In this study, we have used IL-18-binding protein, a soluble IL-18 decoy receptor, to specifically neutralize IL-18 in vivo and in vitro. Our results demonstrate that IL-18 is induced during GvHD. However, its effect in the induction of GvHD appears to be redundant, since neutralization of IL-18 does not alter any disease parameter analyzed. Our study further shows that IFN-gamma production and CTL induction upon activation by T cell mitogens or by alloantigen does not involve IL-18-mediated amplification, in contrast to lipopolysaccharide-induced IFN-gamma production. We conclude that IL-18 expression correlates with the course of GvHD; however, its effect is dispensable for IFN-gamma and CTL induction for the initiation phase of this disease, most likely due to direct, IL-18-independent, CTL activation.

The combination of soluble IL-18Ralpha and IL-18Rbeta chains inhibits IL-18-induced IFN-gamma

Although the beta chain of interleukin-18 receptor (IL-18Rbeta) is required for signaling, the soluble (extracellular) form does not bind IL-18, and its role in inhibiting IL-18 is unclear. In the present study, both the soluble human IL-18 ligand binding alpha chain (sIL-18Ralpha) and the sIL-18Rbeta chain were investigated for inhibition of IL-18-induced interferon-gamma (IFN-gamma) production in human peripheral blood mononuclear cells (PBMC), whole blood, and KG-1 macrophage and natural killer (NK) cell lines. Neutralization of IL-18 by soluble receptors was compared with that of the IL-18 binding protein (IL-18BP). An equimolar concentration IL-18BP inhibited 90% of IL-18 activity, whereas a 4-fold molar excess of sIL-18Ralpha had no effect. A dimeric construct of sIL-18Ralpha linked to the Fc domain of IgG1 (sIL-18Ralpha:Fc) increased IL-18 activity 2.5-fold. In PBMC stimulated with lypopolysaccharide (LPS) or in whole blood stimulated with Staphylococcus epidermidis, 3 nM IL-18BP reduced IFN-gamma by 80%, whereas IL-18Ralpha:Fc had no effect. A construct of the sIL-18Rbeta linked to Fc (sIL-18Rbeta:Fc) did not affect IL-18-induced IFN-gamma even at 80-fold molar excess of IL-18. However, the combination of both soluble receptors reduced IFN-gamma by 80%. In KG-1 cells, a 50% reduction in IL-18 activity was observed using an 80-fold molar excess of sIL-18Ralpha:Fc but only in the presence of sIL-18Rbeta:Fc. Similarly, a 50% reduction was observed using sIL-18Rbeta:Fc in the presence of a molar excess of sIL-18Ralpha:Fc. Similar inhibition was observed in NK cells. These studies reveal that the combination of the ligand-binding and the nonligand-binding extracellular domains of IL-18R is needed to inhibit IL-18, whereas IL-18BP neutralizes at equimolar concentration.

High-dose recombinant interleukin-18 induces an effective Th1 immune response to murine MOPC-315 plasmacytoma

Interleukin (IL)-18 has profound antitumor activity when administered at high doses as a single agent for prolonged periods in BALB/c mice bearing late, well-established MOPC-315 tumors. Management with a qD x 27 schedule resulted in regression of tumors in all animals receiving 5 mg/kg/d. A protracted daily management regimen appears to be necessary to induce regression in this advanced tumor model. Biologic markers were assessed and appear to be potentially useful in evaluating the immunologic and antitumor activity of IL-18. The biomarkers of IL-18's immunologic activity include, but are not limited to, IL-1alpha, IL-2, IL-8, IL-10, IL-12, IL-13, interferon-gamma, tumor necrosis factor-alpha, and granulocyte-macrophage colony-stimulating factor. The profile of these circulating cytokines and their expression levels at baseline, and after IL-18 delivery, can be measured in the serum, as well as from splenocytes of mice or human peripheral blood mononuclear cells derived from either normal subjects or patients with cancer. We compared IL-18 and IL-12 alone or in combination for their ability to induce cytokine production and natural killer cytolytic activity. Our data support the notion that IL-18 induces a predominantly Th1 response, and that the mechanism of IL-18 activity differs from that of IL-12. The biologic activity of IL-18 management revealed by increases in serum levels of cytokines and enhancement of natural killer cytolytic activity will be useful as clinical trials initiate in 2002. Expression of interferon-gamma and granulocyte-macrophage colony-stimulating factor serum levels correlates directly over a broad dose escalation with the level of IL-18. Therefore, this provides a convenient pharmacodynamic reference to the biologic response to IL-18 that may serve to guide the conduct of clinical trials.

Stem cell transplantation: supportive care and long-term complications

With increasing hematopoietic stem cell transplant (HSCT) activity and improvement in outcomes, there are many thousands of HSCT survivors currently being followed by non-transplant clinicians for their healthcare. Several types of late sequelae from HSCT have been noted, and awareness of these complications is important in minimizing late morbidity and mortality. Late effects can include toxicities from the treatment regimen, infections from immunodeficiency, endocrine disturbances, growth impairment, psychosocial adjustment disorders, second malignancies, and chronic graft-versus-host disease (GVHD). A variety of risk factors for these complications have been noted. The clinician should be alert to the potential for these health issues. Preventive and treatment strategies can minimize morbidity from these problems and optimize outcomes.

Understanding the alloresponse: new approaches to graft-versus-host disease prevention

Graft-versus-host disease (GVHD) has been the primary limitation to the wider application of allogeneic bone marrow transplantation (BMT). GVHD occurs when donor T cells react to host antigens on antigen-presenting cells (APCs) and attack host tissues, with sequential activation of donor T cells and monocytes/macrophages. The net effects of dysregulated cytokine production in this complex system are the severe inflammatory manifestations that we recognize as clinical acute GVHD. Long-term outcomes are also adversely affected by chronic GVHD, which has distinctive clinical and pathologic manifestations that mimic autoimmune disease, although its exact pathogenesis remains ambiguous. The ultimate goal for preventing GVHD is the induction of specific tolerance to host antigens, thereby maintaining favorable aspects of donor immunity. Tolerance may be achieved by costimulatory blockade, deletion of activated cells, suppression by regulatory T cells, and immune deviation. This report will focus on these mechanisms as they relate to the pathophysiology of acute GVHD.

Interleukin-18 regulates acute graft-versus-host disease by enhancing Fas-mediated donor T cell apoptosis

Interleukin (IL)-18 is a recently discovered cytokine that modulates both T helper type 1 (Th1) and Th2 responses. IL-18 is elevated during acute graft-versus-host disease (GVHD). We investigated the role of IL-18 in this disorder using a well characterized murine bone marrow transplantation (BMT) model (B6 --> B6D2F1). Surprisingly, blockade of IL-18 accelerated acute GVHD-related mortality. In contrast, administration of IL-18 reduced serum tumor necrosis factor (TNF)-alpha and lipopolysaccharide (LPS) levels, decreased intestinal histopathology, and resulted in significantly improved survival (75 vs. 15%, P < 0.001). Administration of IL-18 attenuated early donor T cell expansion and was associated with increased Fas expression and greater apoptosis of donor T cells. The administration of IL-18 no longer protected BMT recipients from GVHD when Fas deficient (lpr) mice were used as donors. IL-18 also lost its ability to protect against acute GVHD when interferon (IFN)-gamma knockout mice were used as donors. Together, these results demonstrate that IL-18 regulates acute GVHD by inducing enhanced Fas-mediated apoptosis of donor T cells early after BMT, and donor IFN-gamma is critical for this protective effect.

Resistance to xenobiotic-induced autoimmunity maps to chromosome 1

Although evidence indicates that environmental factors play a major role in precipitating systemic autoimmunity in genetically susceptible individuals, little is known about the mechanisms involved. Certain heavy metals, such as mercury, are potent environmental immunostimulants that produce a number of immunopathologic sequelae, including lymphoproliferation, hypergammaglobulinemia, and overt systemic autoimmunity. Predisposition to such metal-induced immunopathology has been shown to be influenced by both MHC and non-MHC genes, as well as susceptibility to spontaneous lupus, in mice and other experimental animals. Among the various mouse strains examined to date, the DBA/2 appears to uniquely lack susceptibility to mercury-induced autoimmunity (HgIA), despite expressing a susceptible H-2 haplotype (H-2d). To define the genetic basis for this trait, two genome-wide scans were conducted using F2 intercrosses of the DBA/2 strain with either the SJL or NZB strains, both of which are highly susceptible to HgIA. A single major quantitative trait locus on chromosome 1, designated Hmr1, was shown to be common to both crosses and encompassed a region containing several lupus susceptibility loci. Hmr1 was linked to glomerular immune complex deposits and not autoantibody production, suggesting that DBA/2 resistance to HgIA may primarily involve the later stages of disease pathogenesis. Identification and characterization of susceptibility/resistance genes and mechanisms relevant to the immunopathogenesis of mercury-induced autoimmunity should provide important insights into the pathogenesis of autoimmunity and may reveal novel targets for intervention.

Interleukin-18 regulates both Th1 and Th2 responses

Although interleukin-18 is structurally homologous to IL-1 and its receptor belongs to the IL-1R/Toll-like receptor (TLR) superfamily, its function is quite different from that of IL-1. IL-18 is produced not only by types of immune cells but also by non-immune cells. In collaboration with IL-12, IL-18 stimulates Th1-mediated immune responses, which play a critical role in the host defense against infection with intracellular microbes through the induction of IFN-gamma. However, the overproduction of IL-12 and IL-18 induces severe inflammatory disorders, suggesting that IL-18 is a potent proinflammatory cytokine that has pathophysiological roles in several inflammatory conditions. IL-18 mRNA is expressed in a wide range of cells including Kupffer cells, macrophages, T cells, B cells, dendritic cells, osteoblasts, keratinocytes, astrocytes, and microglia. Thus, the pathophysiological role of IL-18 has been extensively tested in the organs that contain these cells. Somewhat surprisingly, IL-18 alone can stimulate Th2 cytokine production as well as allergic inflammation. Therefore, the functions of IL-18 in vivo are very heterogeneous and complicated. In principle, IL-18 enhances the IL-12-driven Th1 immune responses, but it can also stimulate Th2 immune responses in the absence of IL-12.