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

The complex web of FasL: cell type-specific roles in affecting and controlling acute graft-vs-host disease

FasL has divergent roles in both causing graft-vs-host disease and preventing this condition, which depends on the immune cell type that expresses it.

The delicate balance of graft versus leukemia and graft versus host disease after allogeneic hematopoietic stem cell transplantation

INTRODUCTION

The curative basis of allogeneic hematopoietic stem cell transplantation (HSCT) relies in part upon the graft versus leukemia (GvL) effect, whereby donor immune cells recognize and eliminate recipient malignant cells. However, alloreactivity of donor cells against recipient tissues may also be deleterious. Chronic graft versus host disease (cGvHD) is an immunologic phenomenon wherein alloreactive donor T cells aberrantly react against host tissues, leading to damaging inflammatory symptoms.

AREAS COVERED

Here, we discuss biological insights into GvL and cGvHD and strategies to balance the prevention of GvHD with maintenance of GvL in modern HSCT.

EXPERT OPINION/COMMENTARY

Relapse remains the leading cause of mortality after HSCT with rates as high as 40% for some diseases. GvHD is a major cause of morbidity after HSCT, occurring in up to half of patients and responsible for 15-20% of deaths after HSCT. Intriguingly, the development of chronic GvHD may be linked to lower relapse rates after HSCT, suggesting that GvL and GvHD may be complementary sides of the immunologic foundation of HSCT. The ability to fine tune the balance of GvL and GvHD will lead to improvements in survival, relapse rates, and quality of life for patients undergoing HSCT.

Dissecting the regulatory network of transcription factors in T cell phenotype/functioning during GVHD and GVT

Transcription factors play a major role in regulation and orchestration of immune responses. The immunological context of the response can alter the regulatory networks required for proper functioning. While these networks have been well-studied in canonical immune contexts like infection, the transcription factor landscape during alloactivation remains unclear. This review addresses how transcription factors contribute to the functioning of mature alloactivated T cells. This review will also examine how these factors form a regulatory network to control alloresponses, with a focus specifically on those factors expressed by and controlling activity of T cells of the various subsets involved in graft-versus-host disease (GVHD) and graft-versus-tumor (GVT) responses.

Danger-associated extracellular ATP counters MDSC therapeutic efficacy in acute GVHD

Myeloid-derived suppressor cells (MDSCs) can subdue inflammation. In mice with acute graft-versus-host disease (GVHD), donor MDSC infusion enhances survival that is only partial and transient because of MDSC inflammasome activation early posttransfer, resulting in differentiation and loss of suppressor function. Here we demonstrate that conditioning regimen-induced adenosine triphosphate (ATP) release is a primary driver of MDSC dysfunction through ATP receptor (P2x7R) engagement and NLR pyrin family domain 3 (NLRP3) inflammasome activation. P2x7R or NLRP3 knockout (KO) donor MDSCs provided significantly higher survival than wild-type (WT) MDSCs. Although in vivo pharmacologic targeting of NLRP3 or P2x7R promoted recipient survival, indicating in vivo biologic effects, no synergistic survival advantage was seen when combined with MDSCs. Because activated inflammasomes release mature interleukin-1β (IL-1β), we expected that IL-1β KO donor MDSCs would be superior in subverting GVHD, but such MDSCs proved inferior relative to WT. IL-1β release and IL-1 receptor expression was required for optimal MDSC function, and exogenous IL-1β added to suppression assays that included MDSCs increased suppressor potency. These data indicate that prolonged systemic NLRP3 inflammasome inhibition and decreased IL-1β could diminish survival in GVHD. However, loss of inflammasome activation and IL-1β release restricted to MDSCs rather than systemic inhibition allowed non-MDSC IL-1β signaling, improving survival. Extracellular ATP catalysis with peritransplant apyrase administered into the peritoneum, the ATP release site, synergized with WT MDSCs, as did regulatory T-cell infusion, which we showed reduced but did not eliminate MDSC inflammasome activation, as assessed with a novel inflammasome reporter strain. These findings will inform future clinical using MDSCs to decrease alloresponses in inflammatory environments.

iNKT cells and hematopoietic stem cell transplantation: Two-phase activation of iNKT cells may improve outcome

Invariant natural killer T cells (iNKT) produce large amounts of different cytokines which can influence differentiation, polarization and activation of immune cells, particularly NK and T cells. iNKT have been shown to suppress GvHD and promote anti-tumor and anti-pathogen immunity. There are highly specific and safe synthetic ligands such as alpha-galactosylceramide (α-GalCer) and C20:2 which activate iNKT cells toward relatively Th1 and Th2 pathways, respectively. Bone marrow transplantation (BMT) or 'hematopoietic stem cell transplantation' (HSCT) is effective for leukemia and lymphoma through 'graft-versus-leukemia' (GVL) immunity. However, frequent serious complications include graft-versus-host-disease (GVHD), opportunistic infections and relapse. Both GVHD and GVL are mediated by T cells. Manipulating iNKT by different lipid analogues in early and late phases after transplantation may suppress GVHD and graft rejection and enhance GVL effect, as well as resistance to opportunistic infections and so, could be a novel and effective strategy for improving HSCT outcome.

Strategies for Enhancing and Preserving Anti-leukemia Effects Without Aggravating Graft-Versus-Host Disease

Allogeneic stem cell transplantation (allo-SCT) is a curable method for the treatment of hematological malignancies. In the past two decades, the establishment of haploidentical transplant modalities make “everyone has a donor” become a reality. However, graft-versus-host disease (GVHD) and relapse remain the major two causes of death either in the human leukocyte antigen (HLA)-matched transplant or haploidentical transplant settings, both of which restrict the improvement of transplant outcomes. Preclinical mice model showed that both donor-derived T cells and natural killer (NK) cells play important role in the pathogenesis of GVHD and the effects of graft-versus-leukemia (GVL). Hence, understanding the immune mechanisms of GVHD and GVL would provide potential strategies for the control of leukemia relapse without aggravating GVHD. The purpose of the current review is to summarize the biology of GVHD and GVL responses in preclinical models and to discuss potential novel therapeutic strategies to reduce the relapse rate after allo-SCT. We will also review the approaches, including optimal donor selection and, conditioning regimens, donor lymphocyte infusion, BCR/ABL-specific CTL, and chimeric antigen receptor-modified T cells, which have been successfully used in the clinic to enhance and preserve anti-leukemia activity, especially GVL effects, without aggravating GVHD or alleviate GVHD.

Helminth-Induced Production of TGF-β and Suppression of Graft-versus-Host Disease Is Dependent on IL-4 Production by Host Cells

Helminths stimulate the secretion of Th2 cytokines, like IL-4, and suppress lethal graft-versus-host disease (GVHD) after bone marrow transplantation. This suppression depends on the production of immune-modulatory TGF-β and is associated with TGF-β-dependent in vivo expansion of Foxp3⁺ regulatory T cells (Treg). In vivo expansion of Tregs is under investigation for its potential as a therapy for GVHD. Nonetheless, the mechanism of induced and TGF-β-dependent in vivo expansion of Tregs, in a Th2 polarized environment after helminth infection, is unknown. In this study, we show that helminth-induced IL-4 production by host cells is critical to the induction and maintenance of TGF-β secretion, TGF-β-dependent expansion of Foxp3⁺ Tregs, and the suppression of GVHD. In mice with GVHD, the expanding donor Tregs express the Th2-driving transcription factor, GATA3, which is required for helminth-induced production of IL-4 and TGF-β. In contrast, TGF-β is not necessary for GATA3 expression by Foxp3⁺ Tregs or by Foxp3^- CD4 T cells. Various cell types of innate or adaptive immune compartments produce high quantities of IL-4 after helminth infection. As a result, IL-4-mediated suppression of GVHD does not require invariant NKT cells of the host, a cell type known to produce IL-4 and suppress GVHD in other models. Thus, TGF-β generation, in a manner dependent on IL-4 secretion by host cells and GATA3 expression, constitutes a critical effector arm of helminthic immune modulation that promotes the in vivo expansion of Tregs and suppresses GVHD.

Targeting JAK2 reduces GVHD and xenograft rejection through regulation of T cell differentiation

Janus kinase 2 (JAK2) signal transduction is a critical mediator of the immune response. JAK2 is implicated in the onset of graft-versus-host disease (GVHD), which is a significant cause of transplant-related mortality after allogeneic hematopoietic cell transplantation (allo-HCT). Transfer of JAK2^-/- donor T cells to allogeneic recipients leads to attenuated GVHD yet maintains graft-versus-leukemia. Th1 differentiation among JAK2^-/- T cells is significantly decreased compared with wild-type controls. Conversely, iTreg and Th2 polarization is significantly increased among JAK2^-/- T cells. Pacritinib is a multikinase inhibitor with potent activity against JAK2. Pacritinib significantly reduces GVHD and xenogeneic skin graft rejection in distinct rodent models and maintains donor antitumor immunity. Moreover, pacritinib spares iTregs and polarizes Th2 responses as observed among JAK2^-/- T cells. Collectively, these data clearly identify JAK2 as a therapeutic target to control donor alloreactivity and promote iTreg responses after allo-HCT or solid organ transplantation. As such, a phase I/II acute GVHD prevention trial combining pacritinib with standard immune suppression after allo-HCT is actively being investigated (https://clinicaltrials.gov/ct2/show/NCT02891603).

TNFR2: The new Treg switch?

Three recent publications identified the TNF/TNR2 pathway as a new target to reduce graft-versus-host-disease through regulatory T cells activation or to potentially switch on a strong anti-leukemic effect through regulatory T cells blockade in allogeneic hematopoietic stem cell transplantation. This identified the TNF/TNR2 pathway as a swith and as a new target for immune checkpoint therapy to modulate the immune regulation in this clinical setting.

Therapeutics for Graft-versus-Host Disease: From Conventional Therapies to Novel Virotherapeutic Strategies

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) has a curative potential for many hematologic malignancies and blood diseases. However, the success of allo-HSCT is limited by graft-versus-host disease (GVHD), an immunological syndrome that involves inflammation and tissue damage mediated by donor lymphocytes. Despite immune suppression, GVHD is highly incident even after allo-HSCT using human leukocyte antigen (HLA)-matched donors. Therefore, alternative and more effective therapies are needed to prevent or control GVHD while preserving the beneficial graft-versus-cancer (GVC) effects against residual disease. Among novel therapeutics for GVHD, oncolytic viruses such as myxoma virus (MYXV) are receiving increased attention due to their dual role in controlling GVHD while preserving or augmenting GVC. This review focuses on the molecular basis of GVHD, as well as state-of-the-art advances in developing novel therapies to prevent or control GVHD while minimizing impact on GVC. Recent literature regarding conventional and the emerging therapies are summarized, with special emphasis on virotherapy to prevent GVHD. Recent advances using preclinical models with oncolytic viruses such as MYXV to ameliorate the deleterious consequences of GVHD, while maintaining or improving the anti-cancer benefits of GVC will be reviewed.

GVHD-associated, inflammasome-mediated loss of function in adoptively transferred myeloid-derived suppressor cells

Myeloid-derived suppressor cells (MDSCs) are a naturally occurring immune regulatory population associated with inhibition of ongoing inflammatory responses. In vitro generation of MDSCs from bone marrow has been shown to enhance survival in an acute model of lethal graft-versus-host disease (GVHD). However, donor MDSC infusion only partially ameliorates GVHD lethality. In order to improve the potential therapeutic benefit and ultimately survival outcomes, we set out to investigate the fate of MDSCs after transfer in the setting of acute GVHD (aGVHD). MDSCs transferred to lethally irradiated recipients of allogeneic donor hematopoietic grafts are exposed to an intense inflammatory environment associated with aGVHD, which we now show directly undermines their suppressive capacity. Under a conditioning regimen and GVHD inflammatory settings, MDSCs rapidly lose suppressor function and their potential to inhibit GVHD lethality, which is associated with their induced conversion toward a mature inflammasome-activated state. We find even brief in vitro exposure to inflammasome-activating mediators negates the suppressive potential of cultured murine and human-derived MDSCs. Consistent with a role for the inflammasome, donor MDSCs deficient in the adaptor ASC (apoptosis-associated speck-like protein containing a CARD), which assembles inflammasome complexes, conferred improved survival of mice developing GVHD compared with wild-type donor MDSCs. These data suggest the use of MDSCs as a therapeutic approach for preventing GVHD and other systemic inflammatory conditions will be more effective when combined with approaches limiting in vivo MDSC inflammasome activation, empowering MDSCs to maintain their suppressive potential.

The IL-33/ST2 axis augments effector T-cell responses during acute GVHD

Interleukin (IL)-33 binding to the receptor suppression of tumorigenicity 2 (ST2) produces pro-inflammatory and anti-inflammatory effects. Increased levels of soluble ST2 (sST2) are a biomarker for steroid-refractory graft-versus-host disease (GVHD) and mortality. However, whether sST2 has a role as an immune modulator or only as a biomarker during GVHD was unclear. We show increased IL-33 production by nonhematopoietic cells in the gastrointestinal (GI) tract in mice post-conditioning and patients during GVHD. Exogenous IL-33 administration during the peak inflammatory response worsened GVHD. Conversely, GVHD lethality and tumor necrosis factor-α production was significantly reduced in il33(-/-) recipients. ST2 was upregulated on murine and human alloreactive T cells and sST2 increased as experimental GVHD progressed. Concordantly, st2(-/-) vs wild-type (WT) donor T cells had a marked reduction in GVHD lethality and GI histopathology. Alloantigen-induced IL-18 receptor upregulation was lower in st2(-/-) T cells, and linked to reduced interferon-γ production by st2(-/-) vs WT T cells during GVHD. Blockade of IL-33/ST2 interactions during allogeneic-hematopoietic cell transplantation by exogenous ST2-Fc infusions had a marked reduction in GVHD lethality, indicating a role of ST2 as a decoy receptor modulating GVHD. Together, these studies point to the IL-33/ST2 axis as a novel and potent target for GVHD therapy.

CCR7 guides migration of mesenchymal stem cell to secondary lymphoid organs: a novel approach to separate GvHD from GvL effect

Inefficient homing of systemically infused mesenchymal stem cells (MSCs) limits the efficacy of existing MSC-based clinical graft-versus-host disease (GvHD) therapies. Secondary lymphoid organs (SLOs) are the major niches for generating immune responses or tolerance. MSCs home to a wide range of organs, but rarely to SLOs after intravenous infusion. Thus, we hypothesized that targeted migration of MSCs into SLOs may significantly improve their immunomodulatory effect. Here, chemokine receptor 7 (CCR7) gene, encoding a receptor that specifically guides migration of immune cells into SLOs, was engineered into a murine MSC line C3H10T1/2 by retrovirus transfection system (MSCs/CCR7). We found that infusion of MSCs/CCR7 potently prolonged the survival of GvHD mouse model. The infused MSCs/CCR7 migrate to SLOs, relocate in proximity with T lymphocytes, therefore, potently inhibited their proliferation, activation, and cytotoxicity. Natural killer (NK) cells contribute to the early control of leukemia relapse. Although MSCs/CCR7 inhibited NK cell activity in vitro coculture, they did not impact on the proportion and cytotoxic capacities of NK cells in the peripheral blood of GvHD mice. In an EL4 leukemia cell loaded GvHD model, MSCs/CCR7 infusion preserved the graft-versus-leukemia (GvL) effect. In conclusion, this study demonstrates that CCR7 guides migration of MSCs to SLOs and thus highly intensify their in vivo immunomodulatory effect while preserving the GvL activity. This exciting therapeutic strategy may improve the clinical efficacy of MSC based therapy for immune diseases.

Current and future approaches for control of graft-versus-host disease

Graft-versus-host disease (GVHD), both acute and chronic, remains one of the major barriers to improving outcomes after allogeneic stem cell transplantation. The pathophysiology of GVHD is complex and incompletely understood. GVHD is believed to arise from the interaction of: tissue damage and proinflammatory cytokines causing activation of antigen-presenting cells (APCs, donor T-cell activation by APCs and cytokines and host tissue injury by effector T lymphocytes and proinflammatory cytokines. There is also a role for additional lymphocyte subtypes (naive and memory T cells, regulatory T cells, natural killer T cells and B cells) in GVHD pathogenesis. Strategies to improve donor-recipient HLA match, and to minimize conditioning toxicity, cytokine release and APC and effector T-lymphocyte activation, will likely improve prophylaxis of acute (and possibly chronic) GVHD. Therapy of established acute and chronic GVHD is still heavily dependent on corticosteroids, despite their limited efficacy and considerable toxicity. Novel agents (and/or combinations of agents) comprising pharmacologic, biologic and cellular therapies targeting specific steps or subsets involved in immune activation will likely comprise future advances in GVHD control. This article reviews the current state of knowledge regarding the prevention and treatment of acute and chronic GVHD. Novel approaches currently undergoing evaluation are also highlighted.

Immunoregulation of GVHD by triggering the innate immune system with CpG

Stimulation of Toll-like receptors by oligodeoxynucleotide sequences containing a CpG motif provides signals capable of triggering the innate and adaptive immune systems, thereby leading either to stimulation or suppression of immunoreactivities. Similar immunoregulatory capabilities are necessary for achieving the fine balance between engraftment and graft-versus-host disease required in the setup of allogeneic cell therapy. Ligation of CpG to its Toll-like receptors can be accomplished by treatment of the host or pretransplant treatment of the donor in vivo. These different strategies are presented in this review, which summarizes the attempts to maximize beneficial alloreactivity against malignant or other undesirable host cells, while controlling graft-versus-host disease.

HDAC inhibition and graft versus host disease

Histone deacetylase (HDAC) inhibitors are currently used clinically as anticancer drugs. Recent data have demonstrated that some of these drugs have potent antiinflammatory or immunomodulatory effects at noncytotoxic doses. The immunomodulatory effects have shown potential for therapeutic benefit after allogeneic bone marrow transplantation in several experimental models of graft versus host disease (GVHD). These effects, at least in part, result from the ability of HDAC inhibitors (HDACi) to suppress the function of host antigen presenting cells such as dendritic cells (DC). HDACi reduce the dendritic cell (DC) responses, in part, by enhancing the expression of indoleamine 2,3-dioxygenase (IDO) in a signal transducer and activator of transcription-3 (STAT-3) dependent manner. They also alter the function of other immune cells such as T regulatory cells and natural killer (NK) cells, which also play important roles in the biology of GVHD. Based on these observations, a clinical trial has been launched to evaluate the impact of HDAC inhibitors on clinical GVHD. The experimental, mechanistic studies along with the brief preliminary observations from the ongoing clinical trial are discussed in this review.

Proteasome inhibition and allogeneic hematopoietic stem cell transplantation: a review

The proteasome and its associated ubiquitin protein modification system have proved to be an important therapeutic target in the treatment of multiple myeloma and other cancers. In addition to direct antitumor effects, proteasome inhibition also exerts strong effects on nonneoplastic immune cells. This indicates that proteasome inhibition, through the use of agents like bortezomib, could be used therapeutically to modulate immune responses. In this review we explore the emerging data, both preclinical and clinical, highlighting the importance of proteasome targeting of immunologic responses, primarily in the context of allogeneic hematopoietic stem cell transplantation (HSCT), both for the control of transplant-related toxicities like acute and chronic graft-versus-host disease (aGVHD, cGHVHD), and for improved malignant disease control after allogeneic HSCT.

New perspectives on the biology of acute GVHD

The use of allogeneic hematopoietic cell transplantation (HCT) has increased as new techniques have been developed for transplantation in patients who previously would not have been considered HCT candidates. However, its efficacy continued to be limited by the development of frequent and severe acute GVHD. The complex and intricate pathophysiology of acute GVHD is a consequence of interactions between the donor and host innate and adaptive immune responses. Multiple inflammatory molecules and cell types are implicated in the development of GVHD that can be categorized as: (1) triggers that initiate GVHD by therapy-induced tissue damage and the antigen disparities between host and graft tissue; (2) sensors that detect the triggers, that is, process and present alloantigens; (3) mediators such as T-cell subsets (naive, memory, regulatory, Th17 and natural killer T cells) and (4) the effectors and amplifiers that cause damage of the target organs. These multiple inflammatory molecules and cell types that are implicated in the development of GVHD have been described with models that use stepwise cascades. Herein, we provide a novel perspective on the immunobiology of acute GVHD and briefly discuss some of the outstanding questions and limitations of the model systems.

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.

Selective effects of cyclosporine a on Th2-skewed dendritic cells matured with viral-like stimulus by means of toll-like receptors

Successful prevention of allograft rejection and graft-versus-host disease with immunosuppression depends on controlled balance of Th1 and Th2 immune responses to establish tolerance and fight infection. Here, we have analyzed the effects of cyclosporine A (CsA) on the differentiation and functions of dendritic cells (DC2) that induce Th2 T cells. DC2 were differentiated from monocytes in the presence of CsA and were matured with viral or bacterial agonists (poly[I:C] or lipopolysaccharide). DC2 differentiation was not affected by CsA. In contrast, cytokine responses were altered with inhibition of interleukin-10 production in poly(I:C)-matured DC2. Surprisingly, interleukin-10 secretion by immature DC2 was increased after CsA treatment. Internalization was impaired in treated DC2, and CsA decreased the T-cell proliferative capacity of DC2 matured with poly(I:C), but not with lipopolysaccharide. In conclusion, CsA altered T-cell activating functions of DC2 with, notably, a regulatory phenotype for immature DC2 and opposite effects on poly(I:C)-matured cells.

Polymorphisms of cytokine and innate immunity genes and GVHD

In the last 10 years, non-HLA genotypes have been investigated for their potential roles in the occurrence and severity of graft-versus-host disease (GVHD) as well as for their contribution to overall transplant-related mortality, infectious episodes, and overall survival. This chapter will review the latest results of cytokine gene polymorphisms between patient and donor which may cause the production of high or low levels of cytokines during the three-stage process of the GVHD 'cytokine storm'. More recent investigations into innate immunity and the interaction with subsequent downstream cytokine production and ultimate tissue damage are discussed. The potential of these non-HLA genetics to aid in predicting GVHD and post-transplant survival and the relevance of this information to the clinic are reviewed.

Manipulating the immune system for anti-tumor responses and transplant tolerance via mixed hematopoietic chimerism

SUMMARY

Stem cells (SCs) with varying potentiality have the capacity to repair injured tissues. While promising animal data have been obtained, allogeneic SCs and their progeny are subject to immune-mediated rejection. Here, we review the potential of hematopoietic stem cells (HSCs) to promote immune tolerance to allogeneic and xenogeneic organs and tissues, to reverse autoimmunity, and to be used optimally to cure hematologic malignancies. We also review the mechanisms by which hematopoietic cell transplantation (HCT) can promote anti-tumor responses and establish donor-specific transplantation tolerance. We discuss the barriers to clinical translation of animal studies and describe some recent studies indicating how they can be overcome. The recent achievements of durable mixed chimerism across human leukocyte antigen barriers without graft-versus-host disease and of organ allograft tolerance through combined kidney and bone marrow transplantation suggest that the potential of this approach for use in the treatment of many human diseases may ultimately be realized.

Combined Th2 cytokine deficiency in donor T cells aggravates experimental acute graft-vs-host disease

The role of T helper (Th) 1 and Th2 polarization in acute graft-vs-host-disease (GVHD) is unclear. We investigated the role of Th2 cytokine secretion by utilizing donor T cells that cannot make interleukin (IL)-4, IL-5, IL-9, and IL-13 from quadruple cytokine-deficient (Quad-KO) animals in a well-characterized BALB/c-->C57BL/6 model of allogeneic bone marrow transplantation. B6 recipients of BALB/c Quad-KO T cells demonstrated greater clinical severity, target organ damage, and mortality from GVHD than recipients of BALB/c wild-type (WT) T cells. When compared with donor T cells that are deficient in signal transducers and activators of transcription 6 signaling or the signature Th2 cytokine, IL-4, Quad-KO T cells demonstrated greater GVHD mortality. Mechanistic studies demonstrated that Quad-KO T cells demonstrated enhanced T-cell proliferation than WT T cells when stimulated with either allogeneic antigen-presenting cells or with nonspecific stimuli, such as anti-CD3 monoclonal antibody. Quad-KO T cells also secreted greater amounts of Th1 cytokines and IL-17 compared to WT T cells. Deficiency of Th2 cytokines, however, did not alter the allospecific cytotoxic responses, the numbers of immunoregulatory CD4(+)CD25(+) Foxp3(+) T cells or their suppressive functions. Our data thus unequivocally demonstrate that deficiency of the four classical Th2 cytokine enhances T-cell proliferative responses and aggravates GVHD.

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.

Pretransplant treatment of donors with immunomodulators to control graft-versus-host disease (GVHD) in transplant recipients

OBJECTIVE

Prevention of graft-versus-host disease (GVHD) by pretransplant donor treatment with known immunomodulators like complete Freund's adjuvant (CFA) and synthetic oligo-deoxynucleotides expressing CpG motifs (CpG).

METHODS

Induction of GVHD by inoculation of C57BL/6 (C57) splenocytes into sublethally irradiated (BALB/c x C57BL/6) F1 (F1) mice. Splenocytes were derived from either naive C57 mice or from C57 mice that were treated previously with the immunomodulators.

RESULTS

Inoculation of CFA or CpG into C57 mice led to an increase in the total number of spleen cells and resulted in activation of immunoregulatory cells that significantly suppressed mixed allogeneic lymphocyte reaction in vitro. CFA-treated C57 splenocytes led to GVHD-related death in only 14 out of 61 F1 recipients while the remaining 47 mice survived without disease for more than 200 days. Pretransplant treatment of donor C57 mice with GpG emulsified in incomplete Freund's adjuvant resulted in 19/20 GVHD-free survivors of sublethally irradiated F1 mice for more than 200 days. In contrast, naive C57 splenocytes injected into sublethally irradiated F1 recipients induced severe GVHD, which resulted in the death of 77/78 recipient mice (median of survival was 16 days).

CONCLUSION

Our results suggest that adjuvant-induced immunoregulation of donor cells prior to allogeneic cell therapy may augur a new strategy that will bring the benefits of safe cellular immunotherapy aiming to eradicate malignant and nonmalignant pathological cells while avoiding or minimizing the risk of GVHD.

Haematopoietic stem cell transplantation: can our genes predict clinical outcome?

Haematopoietic stem cell transplantation (HSCT) is currently the only curative treatment for many patients with malignant and non-malignant haematological diseases. The success of HSCT is greatly reduced by the development of complications, which include graft-versus-host disease (GVHD), relapse and infection. Human leukocyte antigen (HLA) matching of patients and donors is essential, but does not completely prevent these complications; non-HLA genes may also have an impact upon transplant outcome. Polymorphisms within genes that are associated with an individual's capability to mount an immune response to alloantigen and infectious pathogens and/or response to drugs (pharmacogenomics) are all currently being studied for their association with HSCT outcome. This review summarises the potential role of non-HLA polymorphisms in predicting HSCT outcome, from studies on retrospective transplant cohorts of HLA-identical siblings and matched unrelated donors. The clinical relevance and interpretation of non-HLA genetics, and how these could be used alongside clinical risk factors in HSCT, are also discussed.

Host-derived interleukin-18 differentially impacts regulatory and conventional T cell expansion during acute graft-versus-host disease

Interleukin (IL)-18 stimulates T helper 1 (Th1) and Th2-mediated immune responses, and has been shown to modulate acute graft-versus-host disease (aGVHD). It is still unknown whether increased IL-18 levels during aGVHD are of host or donor origin, and how the absence of IL-18 has an impact on migration and expansion of conventional CD4(+)CD25(-)(Tconv) and CD4(+)CD25(+) regulatory (Treg) T cells in vivo. By utilizing IL-18 gene-deficient donor versus recipient animals we found that the major cytokine production during the early phase of aGVHD induction was recipient derived, whereas donor hematopoietic cells contributed significantly less. By generating IL-18(-/-) luciferase transgenic mice we were able to investigate the impact of IL-18 on Tconv and Treg expansion and trafficking with in vivo bioluminescence imaging. Although migration to secondary lymphoid organs did not have a significantly impact from the absence of host IL-18, Tconv but not Treg expansion increased significantly. Absence of host IL-18 production translated into lower IFN-gamma levels in the early phase after transplantation. We conclude that host-derived IL-18 is a major factor for IFN-gamma production that may have a protective effect on CD4(+)-mediated aGVHD, but is nonessential for Treg expansion in an allogeneic environment.

Pathophysiology of acute graft-versus-host disease: recent advances

Allogeneic hematopoietic stem cell transplantation (HSCT) is a potentially curative therapy for many malignant and nonmalignant hematologic diseases. Donor T cells from the allografts are critical for the success of this effective therapy. Unfortunately these T cells not only recognize and attack the disease cells/tissues but also the other normal tissues of the recipient as "foreign" or "nonself" and cause severe, immune-mediated toxicity, graft-versus-host disease (GVHD). Several insights into the complex pathophysiology of GVHD have been gained from recent experimental observations, which show that acute GVHD is a consequence of interactions between both the donor and the host innate and adaptive immune systems. These insights have identified a role for a variety of cytokines, chemokines, novel T-cell subsets (naĩve, memory, regulatory, and NKT cells) and for non-T cells of both the donor and the host (antigen presenting cells, delta T cells, B cells, and NK cells) in modulating the induction, severity, and maintenance of acute GVHD. This review will focus on the immunobiology of experimental acute GVHD with an emphasis on the recent observations.

Interleukin-18 genetics and inflammatory disease susceptibility

IL18 was mapped to 11q22.2-22.3 in 1998. Owing to interleukin (IL)-18's important and novel role in immunomodulation, the gene itself has been subject to scrutiny, with the aim of discovering variants that may impact on disease susceptibility and/or progression. Despite being sequenced numerous times in different populations, no non-synonymous variants have been found. However, a number of polymorphisms within the proximal promoter have been verified that may interfere with transcription-factor-binding sites. Much of the subsequent association analyses have centred on these variants, but have yielded no consistent results, despite numerous different study populations being genotyped. IL18 has recently been resequenced in its entirety, enabling the tagging-single-nucleotide polymorphism (tSNP) methodology to be adopted. This approach has yielded interesting results, with genetic variation being shown to affect protein levels, and risk. This review aims to compile and reflect on the association data of interest published to date, with a focus on the diseases related to aberrant inflammatory control.

Biological response modifiers as adjuncts to stem cell transplantation

Cytokines produced by immune and non-immune cells serve as potent mediators with the properties of signal cells that coordinate the immune response. They are delivered by cells either to the systemic circulation or to the local environment. They are being used at present in the field of stem cell transplantation (SCT) in order to improve transplant outcome. This paper reviews the existing data on pre-, peri- and post-SCT treatment with cytokines.

Shared biology of GVHD and GVT effects: Potential methods of separation

The difficult separation of clinical graft-versus-tumor (GVT) effects from graft-versus-host disease (GVHD) reflects their shared biology. Experimental approaches to mediate GVT effects while limiting GVHD include: (1) allograft T cell depletion followed by immune enhancement; (2) modulation of T cell dose or T cell subset composition; (3) donor lymphocyte infusion; (4) reduced-intensity host preparation; (5) modulation of Th1/Th2 and Tc1/Tc2 cell balance; (6) cytokine therapy or neutralization; (7) T regulatory cell therapy; (8) co-stimulatory pathway modulation; (9) chemokine pathway modulation; (10) induction of antigen-specific T cells; (11) alloreactive NK cell therapy; and (12) targeted pharmaceutical inhibition of proteosome, mammalian target of rapamycin, and histone deacetylase pathways. Clearly, a multitude of approaches exist that hold promise for separating GVT effects from GVHD. Future success in this endeavor will require a strong commitment towards translational research and continued advances in cell, vaccine, cytokine, monoclonal antibody, and targeted molecular therapy.

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.

Effect of IL-18 and sIL2R on aGVHD occurrence after hematopoietic stem cell transplantation in some Iranian patients

BACKGROUND

Graft-versus-host disease is one of the major complications after allogeneic bone marrow transplantation, but it is not easy to anticipate the onset. Cytokines released by type 1 T helper cells are thought to play a pivotal role in acute graft-versus-host disease aGVHD. The ability to predict the likely occurrence of graft-versus-host-disease (GVHD) after Hematopoietic Stem cell Transplantation (HSCT) would be extremely valuable. By serially measuring serum levels of soluble IL-2 receptor (sIL-2R), IL-18 and following allogeneic HSCT we tried to define their effect on aGVHD as a complication of transplantation and determine useful markers for aGVHD predictors.

SAMPLES AND METHODS

Serum sIL-2R, IL-18, levels were measured by sandwich ELISA in 219 sera samples from 39 patients (with hematological disorders before and after allogeneic HSCT) and 28 controls. All patients received transplants from HLA-identical siblings.

RESULTS

23 (58.9%) patients developed aGVHD (I-IV) and serum levels of sIL-2R and IL-18, in sera drawn before transplantation, in patients with acute graft-versus-host disease (aGVHD(+)), were increased in comparison to patients without acute graft-versus-host disease (aGVHD(-)) and to a control group and there were no significant differences in serum levels of sIL-2R and IL-18 in aGVHD(-) patients and controls. Serum level of IL-18, in aGVHD(+) patients, was increased during days 3-24 after HSCT, and there was a significant difference according to GVHD severity. In majority of patients with acute GVHD (60%), the peak levels of IL-18 and sIL-2R were achieved on day 10 after HSCT and the rise in sIL-2R and IL-18 preceded the clinical signs of GVHD (mean day 15 after BMT). The level of IL-18 in patients with aGVHD strongly correlated with the severity of aGVHD on Day 10 after HSCT. IL-18 level (before HSCT), in patients who received Busulfan and Fludarabin which were used to treat aGVHD, was lower than in patients who received Busulfan and Cyclophosphamide.

CONCLUSION

Our data concluded that IL-18 plays an important role in the development of aGVHD and the IL-18 level might be an indicator of aGVHD, reflecting the severity of the disease. These findings suggest that IL-18 may play an important role in the pathogenesis of aGVHD and that measurement of serum IL-18 levels can be a useful indicator of aGVHD.

NKT cell-dependent leukemia eradication following stem cell mobilization with potent G-CSF analogs

NKT cells have pivotal roles in immune regulation and tumor immunosurveillance. We report that the G-CSF and FMS-like tyrosine kinase 3 ligand (Flt-3L) chimeric cytokine, progenipoietin-1, markedly expands the splenic and hepatic NKT cell population and enhances functional responses to alpha-galactosylceramide. In a murine model of allogeneic stem cell transplantation, donor NKT cells promoted host DC activation and enhanced perforin-restricted CD8+ T cell cytotoxicity against host-type antigens. Following leukemic challenge, donor treatment with progenipoietin-1 significantly improved overall survival when compared with G-CSF or control, attributable to reduced graft-versus-host disease mortality and paradoxical augmentation of graft-versus-leukemia (GVL) effects. Enhanced cellular cytotoxicity was dependent on donor NKT cells, and leukemia clearance was profoundly impaired in recipients of NKT cell-deficient grafts. Enhanced cytotoxicity and GVL effects were not associated with Flt-3L signaling or effects on DCs but were reproduced by prolonged G-CSF receptor engagement with pegylated G-CSF. Thus, modified G-CSF signaling during stem cell mobilization augments NKT cell-dependent CD8+ cytotoxicity, effectively separating graft-versus-host disease and GVL and greatly expanding the potential applicability of allogeneic stem cell transplantation for the therapy of malignant disease.

Bone marrow transplantation and approaches to avoid graft-versus-host disease (GVHD)

Haematopoietic stem cell transplantation (HSCT) offers promise for the treatment of haematological and immune disorders, solid tumours, and as a tolerance inducing regimen for organ transplantation. Allogeneic HSCTs engraftment requires immunosuppression and the anti-tumour effects are dependent upon the immune effector cells that are contained within or generated from the donor graft. However, significant toxicities currently limit its efficacy. These problems include: (i) graft-versus-host disease (GVHD) in which donor T cells attack the recipient resulting in multi-organ attack and morbidity, (ii) a profound period of immune deficiency following HSCT, and (iii) donor graft rejection. Currently available methods to prevent or treat GVHD with systemic immunosuppression can lead to impaired immune recovery, increased opportunistic infections, and higher relapse rates. This review will provide an overview of GVHD pathophysiology and discuss the roles of various cells, pathways, and factors in the GVHD generation process and in the preservation of graft-versus-tumour effects. Variables that need to be taken into consideration in attempting to extrapolate preclinical results to the clinical paradigm will be highlighted.

Immaturity of IL-18 gene expression and protein production in cord blood (CB) versus peripheral blood (PB) mononuclear cells and differential effects in natural killer (NK) cell development and function

We have previously demonstrated dysregulation of IL-12 and IL-15 gene and protein expression between activated cord blood (CB) versus peripheral blood (PB) mononuclear cells (MNCs). In the present study, we compared IL-18 gene expression and protein production and IL-18 mRNA half-life in basal versus activated CB versus PB MNCs, the effects of IL-18 +/- IL-12 on MNCs IFN-gamma protein production and ex vivo expansion and activation of CB with IL-12 + IL-2 + anti-CD3 +/- IL-18. Basal and activated levels of IL-18 were significantly higher in PB versus CB MNCs (P < 0.05). IL-18 mRNA was coincidental with protein levels and significantly lower in CB (P < 0.05) and its half-life significantly shorter in CB versus PB MNCs (P < 0.05). IL-18 synergistically with IL-12 induced IFN-gamma production from PB greater than CB MNCs (P < 0.05). NK cells expansion (P < 0.001) and cytotoxicity (P < 0.01) was significantly increased with IL-12 + IL-2 + anti-CD3 and IL-18. In summary IL-18 gene expression and protein production are significantly decreased in activated CB versus PB MNCs, in part secondary to increased degradation of CB IL-18 mRNA. These results may have implications for the mechanism(s) in part responsible for the immaturity of CB T-cell immunity.

Stimulation of Host NKT Cells by Synthetic Glycolipid Regulates Acute Graft-versus-Host Disease by Inducing Th2 Polarization of Donor T Cells

NKT cells are a unique immunoregulatory T cell population that produces large amounts of cytokines. We have investigated whether stimulation of host NKT cells could modulate acute graft-vs-host disease (GVHD) in mice. Injection of the synthetic NKT cell ligand alpha-galactosylceramide (alpha-GalCer) to recipient mice on day 0 following allogeneic bone marrow transplantation promoted Th2 polarization of donor T cells and a dramatic reduction of serum TNF-alpha, a critical mediator of GVHD. A single injection of alpha-GalCer to recipient mice significantly reduced morbidity and mortality of GVHD. However, the same treatment was unable to confer protection against GVHD in NKT cell-deficient CD1d knockout (CD1d(-/-)) or IL-4(-/-) recipient mice or when STAT6(-/-) mice were used as donors, indicating the critical role of host NKT cells, host production of IL-4, and Th2 cytokine responses mediated by donor T cells on the protective effects of alpha-GalCer against GVHD. Thus, stimulation of host NKT cells through administration of NKT ligand can regulate acute GVHD by inducing Th2 polarization of donor T cells via STAT6-dependent mechanisms and might represent a novel strategy for prevention of acute GVHD.

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.

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.

The Mortimer M. Bortin lecture

The graft-versus-leukemia effect of allogeneic blood or marrow transplantation is a dramatic example of the power of the immune system to eradicate malignant disease. In this personal essay, adapted from the inaugural Mortimer M. Bortin Lecture presented at the 2004 Tandem BMT Meetings, the author recounts early efforts by Bortin and others to manipulate the graft-versus-leukemia effect and separate it from the potentially fatal complications of graft-versus-host disease.

Immunobiology of acute graft-versus-host disease

Graft-versus-host disease (GVHD) has been the primary limitation to the wider application of allogeneic bone marrow transplantation (BMT). The immunobiology of acute GVHD is complex and can be conceptualized to be a three-step process. In step 1, the conditioning regimen (irradiation and/or chemotherapy) leads to the damage and activation of host tissues and induces the secretion of inflammatory cytokines TNF-alpha and IL-1. As a consequence expression of MHC antigens and adhesion molecules is increased, thus enhancing the recognition of host alloantigens by donor T cells. Donor T-cell activation in step 2 is characterized by donor T-cell interaction with host APCs and subsequent proliferation, differentiation, and secretion of cytokines. Cytokines such as IL-2 and IFN-gamma enhance T-cell expansion, induce cytotoxic T cells (CTL) and natural killer (NK) cell responses, and prime additional mononuclear phagocytes to produce TNF-alpha and IL-1. These inflammatory cytokines in turn stimulate production of inflammatory chemokines, thus recruiting effector cells into target organs. In step 3, effector functions of mononuclear phagocytes are triggered via a secondary signal provided by lipopolysaccharide (LPS) that leaks through the intestinal mucosa damaged during step 1. This mechanism may result in the amplification of local tissue injury and further promotion of an inflammatory response, which, together with the CTL and NK components, leads to target tissue destruction in the transplant host.

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.

Histone deacetylase inhibitor suberoylanilide hydroxamic acid reduces acute graft-versus-host disease and preserves graft-versus-leukemia effect

Acute graft-versus-host disease (GVHD) and leukemic relapse are the two major obstacles to successful outcomes after allogeneic bone marrow transplantation (BMT), an effective therapy for hematological malignancies. Several studies have demonstrated that the dysregulation of proinflammatory cytokines and the loss of gastrointestinal tract integrity contribute to GVHD, whereas the donor cytotoxic responses are critical for graft-versus-leukemia (GVL) preservation. Suberoylanilide hydroxamic acid (SAHA) is currently in clinical trials as an antitumor agent; it inhibits the activity of histone deacetylases and at low doses exhibits antiinflammatory effects by reducing the production of proinflammatory cytokines. Using two well characterized mouse models of BMT, we have studied the effects of SAHA on GVHD severity and GVL activity. Administration of SAHA from day +3 to day +7 after BMT reduced serum levels of the proinflammatory cytokines and decreased intestinal histopathology, clinical severity, and mortality from acute GVHD compared with vehicle-treated animals. However, SAHA had no effect on donor T cell proliferative and cytotoxic responses to host antigens in vivo or in vitro. When mice received lethal doses of tumor cells at the time of BMT, administration of SAHA did not impair GVL activity and resulted in significantly improved leukemia-free survival by using two different tumor and donor/recipient combinations. These findings reveal a critical role for histone deacetylase inhibition in the proinflammatory events contributing to GVHD and suggest that this class of pharmacologic agents may provide a strategy to reduce GVHD while preserving cytotoxic T cell responses to host antigens and maintaining beneficial GVL effects.

Gene transfer of pro-IL-18 and IL-1β converting enzyme cDNA induces potent antitumor effects in L1210 cells

We report in a murine model of acute lymphoid leukemia L1210 the potent antitumor efficiency of a combinatorial delivery of pro-IL-18 gene modified L1210 (Lp18) and IL-1beta converting enzyme (ICE) gene modified L1210 (LpICE). Live leukemia cells Lp18 or Lp18 plus LpICE showed apparently reduced leukemogenicity with a survival rate of 40 or 50% at 50 days after intraperitoneal (i.p.) inoculation of a lethal dose of cells, respectively. Combination of Lp18 and LpICE was capable of inhibiting accumulation of bloody ascites, synergistically superior to Lp18 or LpICE alone. All surviving mice were rechallenged with parental L1210 cells at day 50, and all survived up to day 80, suggesting that gene-modified cells induced immune protection. Moreover, NK cytotoxicity and CTL activity were both enhanced in mice injected with Lp18, especially Lp18 plus LpICE. Levels of IFN-gamma were not altered significantly by inoculation of Lp18 or Lp18 plus LpICE. Our results demonstrate that IL-18 is a useful candidate gene in gene therapy of lymphoma or lymphoid leukemia, and ex vivo combinatorial delivery of Lp18 plus LpICE either as a single approach or as an adjunct to concomitant radiotherapy or chemotherapy, may be more efficient in a situation of minimal residual disease.

Repifermin (keratinocyte growth factor-2) reduces the severity of graft-versus-host disease while preserving a graft-versus-leukemia effect

Graft-versus-host disease (GVHD) is the principal complication after allogeneic bone marrow transplantation (BMT). Reductions in systemic GVHD are frequently associated with a corresponding diminishment of the graft-versus-leukemia (GVL) response. In this study, we tested the effects of a novel recombinant human keratinocyte growth factor, repifermin (keratinocyte growth factor-2), on the induction of GVHD in a well-defined murine BMT model (B6 --> B6D2F1). Administration of repifermin (5 mg/kg/d) to allogeneic BMT recipients resulted in a significant decrease in both systemic GVHD and target organ histopathology. Repifermin treatment also reduced serum levels of tumor necrosis factor alpha and lipopolysaccharide compared with control mice. In contrast, repifermin did not affect T-cell proliferation, cytokine production, or cytotoxic responses to host antigens. When 2000 host-derived P815 (H-2(d)) leukemia cells were added to the bone marrow inoculum, repifermin preserved GVL effects and resulted in significantly delayed mortality compared with control-treated allogeneic BMT recipients. Collectively, these data suggest that repifermin administration may represent a novel strategy to separate the toxicity of GVHD from the beneficial GVL effects after allogeneic BMT.

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.