Fas ligand-induced caspase-1-dependent accumulation of interleukin-18 in mice with acute graft-versus-host disease

Ambivalent role of FasL in murine acute graft-versus-host-disease

Fas ligand is increased in several immune-mediated diseases, including acute graft-versus-host disease, a donor cell-mediated disorder post-hematopoietic stem cell transplantation. In this disease, Fas ligand is involved in T-cell-mediated damage to host tissues. However, the role of its expression on donor non-T cells has, so far, never been addressed. Using a well-established CD4- and CD8-mediated graft-versus-host disease murine model, we found that precocious gut damage and mice mortality are increased with a graft of donor T- and B-depleted bone marrow cells devoid of Fas ligand as compared with their wild-type counterparts. Interestingly, serum levels of both soluble Fas ligand and IL-18 are drastically reduced in the recipients of Fas ligand-deficient grafts, indicating that soluble Fas ligand stems from donor bone marrow-derived cells. In addition, the correlation between the concentrations of these 2 cytokines suggests that IL-18 production arises through a soluble Fas ligand-driven mechanism. These data highlight the importance of Fas ligand-dependent production in IL-18 production and in mitigating acute graft-versus-host disease. Overall, our data reveal the functional duality of Fas ligand according to its source.

Various forms of tissue damage and danger signals following hematopoietic stem-cell transplantation

Hematopoietic stem-cell transplantation (HSCT) is the most potent curative therapy for many malignant and non-malignant disorders. Unfortunately, a major complication of HSCT is graft-versus-host disease (GVHD), which is mediated by tissue damage resulting from the conditioning regimens before the transplantation and the alloreaction of dual immune components (activated donor T-cells and recipient’s antigen-presenting cells). This tissue damage leads to the release of alarmins and the triggering of pathogen-recognition receptors that activate the innate immune system and subsequently the adaptive immune system. Alarmins, which are of endogenous origin, together with the exogenous pathogen-associated molecular patterns (PAMPs) elicit similar responses of danger signals and represent the group of damage-associated molecular patterns (DAMPs). Effector cells of innate and adaptive immunity that are activated by PAMPs or alarmins can secrete other alarmins and amplify the immune responses. These complex interactions and loops between alarmins and PAMPs are particularly potent at inducing and then aggravating the GVHD reaction. In this review, we highlight the role of these tissue damaging molecules and their signaling pathways. Interestingly, some DAMPs and PAMPs are organ specific and GVHD-induced and have been shown to be interesting biomarkers. Some of these molecules may represent potential targets for novel therapeutic approaches.

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.

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.

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.

Involvement of neutrophil recruitment and protease-activated receptor 2 activation in the induction of IL-18 in mice

Activated neutrophils produce serine proteases, which activate cells through protease-activated receptor 2 (PAR2). As proteinase 3 (PR3) induces the secretion of interleukin (IL)-18 from epithelial cells in combination with lipopolysaccharide (LPS) in vitro, we examined whether neutrophils, serine proteases, and PAR2 are involved in the induction of serum IL-18 and IL-18-dependent liver injury in mice treated with heat-killed Propionibacterium acnes and LPS. LPS-induced serum IL-18 levels in P. acnes-primed mice were reduced significantly by anti-Gr-1 injection (depletion of neutrophils and macrophages) but not by a macrophage "suicide" technique, using liposomes encapsulating clodronate. The IL-18 induction was decreased significantly by coadministration of a serine protease inhibitor [Nafamostat mesilate (FUT-175)] with LPS. Serum levels of tumor necrosis factor alpha and liver enzymes induced by P. acnes and LPS were abolished by anti-Gr-1 treatment, and concomitantly, liver injury (necrotic change and granuloma formation) and Gr-1(+) cell infiltration into the liver were prevented by the treatment. A deficiency of PAR2 in mice significantly impaired IL-18 induction by treatment with P. acnes and LPS, and only slight pathological changes in hepatic tissues occurred in the PAR2-deficient mice treated with P. acnes and LPS. Furthermore, coadministration of exogenous murine PR3 or a synthetic PAR2 agonist (ASKH95) with LPS in the anti-Gr-1-treated mice restored the serum IL-18 levels to those in control mice treated with P. acnes and LPS. These results indicate that neutrophil recruitment and PAR2 activation by neutrophil serine proteases are critically involved in the induction of IL-18 and IL-18-dependent liver injury in vivo.

Pathophysiological roles for IL-18 in inflammatory arthritis

IL-18 is a unique cytokine with prominently wide spectrum biological actions. Among these, its IFN-gamma/TNF-alpha-inducing activity primarily contributes to the development of various inflammatory diseases including inflammatory arthritis. IL-18 levels correlate with the disease activity of rheumatoid arthritis (RA) and osteoarthritis (OA). IL-18 is spontaneously released from RA synovial cells and OA chondrocytes and seems to participate in the development of the inflammatory and destructive alterations of joints via induction of TNF-alpha, a potent effector molecule. TNF-alpha, in turn, increases IL-18 expression in RA synovial cells. Recent clinical trials have revealed the efficacy of TNF-alpha in RA with a reduction in circulatory IL-18 levels. These may implicate the positive circuit between IL-18 and TNF-alpha for development of RA. As IL-18-deficient mice evade collagen-induced arthritis in a mouse RA model, therapeutics targeting IL-18 may be beneficial against RA/OA. Here, the authors review the possible roles of IL-18 in inflammatory arthritis.

Cytokine expression during acute graft-versus-host disease after allogeneic peripheral stem cell transplantation

Acute graft-versus-host disease (aGVHD) is one of the major problems following allogeneic peripheral blood stem cell transplantation (allo-PBSCT). In order to investigate the pathogenesis of human aGVHD, we analyzed cytokine gene expression and cytokine secretion by peripheral blood mononuclear cells (PBMC) in 30 patients who underwent allo-PBSCT. In this study, reverse transcription-polymerase chain reaction (RT-PCR) was used to explore the mRNA expression of interleukin (IL)-2, interferon (IFN)-gamma, IL-4, IL-10 and IL-12 in the PBMC of allo-PBSCT patients with aGVHD and in controls. The concentrations of these cytokines and of IL-18 were also measured by means of ELISA in medium obtained from cultured leukocytes after stimulation with PHA or LPS. Compared with the normal allo-PBSCT group (n=14), IL-2 and IFN-gamma were detected more frequently in aGVHD group (n=16). IL-12 and IL-18 were elevated, while IL-10 level decreased in the same group. There is no difference in IL-4 gene expression between patients with or without aGVHD, but the concentration of IL-4 for patients with grade II-IV aGVHD decreased. These data suggest that IL-2, IFN-gamma, IL-12 and IL-18 play important roles in the development of aGVHD in humans.

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.

Endotoxemic acute renal failure is attenuated in caspase-1-deficient mice

Caspase-1-deficient (-/-) mice are protected against sepsis-induced hypotension and mortality. We investigated the role of caspase-1 and its associated cytokines in a nonhypotensive model of endotoxemic acute renal failure (ARF). Mice were injected intraperitoneally with 2.5 mg of LPS that induces endotoxemic ARF. On immunoblot analysis of whole kidney, there was an increase in caspase-1 protein in LPS-treated mice compared with vehicle-treated controls. In LPS-treated mice, the glomerular filtration rate (GFR) was significantly higher in caspase-1 -/- vs. wild-type mice at 16 and 36 h after LPS. To determine the mechanism of this protection, the caspase-1-activated cytokines IL-1beta and IL-18 were investigated. IL-1beta and IL-18 protein were significantly increased in the kidneys of LPS- vs. vehicle-treated mice. To determine the role of these cytokines, mice were treated with recombinant IL-1 receptor antagonist (IL-1Ra) or IL-18-neutralizing antiserum. In LPS-treated mice, GFR was not different in IL-1Ra-treated or IL-18-neutralizing antiserum-treated or combination therapy (IL-1Ra plus IL-18-neutralizing antiserum-treated) compared with control mice. In addition, tubular cell apoptosis, neutrophil infiltration, myeloperoxidase activity, caspase-3 activity, and calpain activity were not different between wild-type and caspase-1 -/- mice with endotoxemic ARF. In LPS- vs. vehicle-treated wild-type mice, renal IL-1alpha was significantly increased. In both LPS- and vehicle-treated caspase-1 -/- mice, renal IL-1alpha was very low. In summary, caspase-1 -/- mice are functionally protected against endotoxemic ARF. Neutralization of IL-1beta and IL-18 is not functionally protective. The role of the intracellular proinflammatory cytokine IL-1alpha in endotoxemic ARF merits further study.

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.

Increase of interleukin-18 serum levels after engraftment correlates with acute graft-versus-host disease in allogeneic peripheral blood stem cell transplantation

PURPOSE

Acute graft-versus-host disease (GvHD) is a constant and severe complication after allogeneic stem cell transplantation regularly involving skin, liver, gut, and lungs. The cytokine interleukin-18 (IL-18) has been shown to increase in patients who develop acute GvHD after bone marrow tranplantation (BMT).

MATERIALS AND METHODS

Here, we measured IL-18 serum levels after peripheral blood stem cell transplantation (PBSCT) at several characteristic time points in 24 patients (median age 46 years). Patients received a median of 7.3 x 10(6)/kg bodyweight CD34-positive blood stem cells from HLA-matched family donors (n = 5), matched unrelated donors (n = 18), and one mismatched unrelated donor. GvHD prophylaxis consisted of cyclosporin A alone or combined with methotrexate and/or mycophenolate mofetil.

RESULTS

In 14 patients we observed no GvHD or only GvHD grade I whereas ten patients developed GvHD grade II-IV post transplant. Low, intermediate, and high levels of serum IL-18 were found in patients after allogeneic PBSCT independently of GvHD after transplantation. In contrast to GvHD arising after BMT, there was no clear correlation between absolute IL-18 serum levels and GvHD grade after PBSCT. However, the individual time course of IL-18 serum level after engraftment correlates with acute GvHD after PBSCT. In detail, an increase of serum IL-18 of at least 1.6-fold after engraftment is associated with acute GvHD II or higher with a sensitivity of three out of four. Using the 1.6 "cut-off" for IL-18 increase after engraftment, a specificity of up to 100% can be achieved.

CONCLUSION

The time course of IL-18 serum levels might be used for GvHD prediction after PBSCT comparable to absolute serum levels after BMT.

The molecular basis of salivary gland involvement in graft--vs.--host disease

During the past two decades, the involvement of salivary glands in graft vs. host disease (GVHD) had been intensively researched and published. GVHD occurs in 40-70% of patients treated with bone marrow and peripheral blood stem cell transplantation (PBSCT), and improved survival rates have led to a continuously increasing number of GVHD patients suffering from induced salivary insult. Limited studies suggest that a large percentage of GVHD patients is affected and that the induced salivary dysfunction occurs rapidly following the transplantation. It affects both major and minor salivary glands and reflects the severity of the disease. Moreover, profound sialochemical alterations may be diagnostic of GVHD. An additional reason for this vast research is that GVHD, as an autoimmune-like disease, seemed to be an appropriate model for studying a much more prevalent and well-known and well-studied autoimmune disease involving salivary glands: Sjögren's syndrome. The purpose of the current review-which is, to the best of our knowledge, the first of its kind-is to describe the GVHD-related sialometric and sialochemical data published in the past two decades for both major and minor salivary glands and to discuss the pathogenesis and molecular basis of the disease.

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.

Differential Upregulation of Interleukin-18 Receptor α Chain Between CD4+ and CD8+ T Cells During Acute Graft-Versus-Host Disease in Mice

Interleukin-18 (IL-18), a unique cytokine that stimulates both T helper 1 (Th1) and Th2 responses, is associated with acute graft-versus-host disease (aGVHD), the major limiting toxicity following allogeneic stem cell transplantation. Here, we investigated the mechanism underlying the upregulation of IL-18 receptor (IL-18R) expression on T cells in murine aGVHD models. The induction of aGVHD elevated host serum IL-12 levels and increased expression of IL-18Ralpha chain (IL-18Ralpha) on engrafted T cells, in particular on CD8+ T cells. However, IL-18Ralpha expression did not increase on the CD4+ T cells of an IL-12-deficient host, indicating the IL-12-dependent upregulation of IL-18Ralpha expression on CD4+ T cells during aGVHD. Purified donor CD8+ T cells transferred in the host increased IL-18Ralpha expression. In vitro experiments showed that IL-18Ralpha expression upregulated on CD8+ T cells but not on CD4+ T cells on stimulation through the T cell receptor (TCR). These results suggest that IL-18Ralpha expression is differentially upregulated between CD4+ and CD8+ T cells during aGVHD, depending on endogenous IL-12 and TCR engagement, respectively.

Interleukin-18 enhances the production of interferon-gamma (IFN-γ) by allergen-specific and unspecific stimulated cord blood mononuclear cells

BACKGROUND

IL-18 is a pleiotropic cytokine involved in the polarisation of T-cell response. This study was performed to determine whether or not IL-18 is detectable in phytohemagglutinin (PHA) or betalactoglobulin (BLG) stimulated supernatants of cord blood mononuclear cells (CBMC) and to study the in vitro effect of IL-18 on the interferon (IFN)-gaamma and IL-13 release of CBMC of healthy neonates.

METHODS

CBMC of neonates were isolated by Ficoll density centrifugation. The cytokines IFN-gamma, IL-13 and IL-18 in the cell culture supernatants were measured using the ELISA technique following stimulation with a unspecific (PHA 20 microg/ml) and an allergen-specific stimulus (BLG 25 microg/ml). In order to study the in vitro effect of IL-18, CBMC were stimulated either with medium alone or with IL-18, IL-18 + PHA and IL-18 + BLG.

RESULTS

IL-18 levels in supernatants of CBMC were low and did not vary significantly between unstimulated and PHA or BLG stimulated cell cultures (median 21.4; 23.5 and 15.5 pg/ml, respectively). IFN-gamma and IL-13 levels were significantly higher in response to PHA and BLG (PHA: IFN-gamma, 6154; IL-13, 4357; BLG: IFN-gamma, 801; IL-13, 249 pg/ml) compared to unstimulated cell cultures. The addition of IL-18 to PHA or BLG stimulated CBMC significantly enhanced the IFN-gamma release (PHA: 6154; PHA + IL-18: 13474, p = 0.0001; BLG: 801; BLG + IL-18: 1077, p = 0.008). In comparison to incubation without IL-18, the release of IL-13 was invariable or even reduced, when CBMC were stimulated with PHA + IL-18 (4026, p = 0.16) or BLG + IL-18 (124, p = 0.0001) compared to stimulation of CBMC with PHA (4357 pg/ml) or BLG (249 pg/ml) alone.

CONCLUSIONS

IL-18 is detectable in supernatants of CBMC. We observed a significant effect of IL-18 + PHA as well as IL-18 + BLG on IFN-gamma release in vitro. Based on our findings we conclude that IL-18 could act as a strong TH1-inducing factor on stimulated CBMC also in vivo.

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.

Antitumor effects of bisphosphonates

BACKGROUND

Bisphosphonates are widely used to treat skeletal complications of malignancy. These drugs accumulate in bone where they inhibit osteoclastic bone resorption and reduce the local release of factors that stimulate tumor growth. The mechanism of action of bisphosphonates is dependent on chemical structure: Nonnitrogen-containing compounds (e.g., etidronate, clodronate) are metabolized into cytotoxic analogues of ATP, whereas the more potent nitrogen-containing compounds (N-BPs; e.g., pamidronate, ibandronate, zoledronic acid) inhibit protein prenylation, thus affecting cell function and survival. Because protein prenylation is required by all cells, not just osteoclasts, the possibility arises that N-BPs could also affect the viability of tumor cells.

METHODS

Several groups have investigated the in vitro effects of bisphosphonates, either alone or in combination with other antineoplastic agents, on the viability and metastatic properties of many tumor cell types. Similarly, the effect of bisphosphonate treatment on osteolysis and tumor burden has been studied in a variety of animal tumor models.

RESULTS

In vitro, submicromolar concentrations of N-BPs inhibited tumor cell adhesion and reduced invasion through extracellular matrix. At higher concentrations, antiproliferative and proapoptotic effects have been reported. In animal models of bone metastases, bisphosphonate treatment markedly reduced osteolytic lesions. There is also evidence of a reduction in tumor burden in bone and occasionally in other organs. Survival may be prolonged, but bisphosphonates do not appear to inhibit the growth of primary soft tissue tumors or orthotopic xenografts.

CONCLUSIONS

The cell culture data clearly demonstrated that N-BPs exert antitumor properties and interact synergistically with other antineoplastic agents. As bisphosphonates accumulate in bone, they can also exert cytostatic effects on tumor cells in bone metastases, either directly or indirectly via osteoclast inhibition and alterations in the bone microenvironment. Further in vivo research is now required to optimize the dosing regimen of N-BPs to exploit fully their antitumor potential.

Mechanisms of bisphosphonate effects on osteoclasts, tumor cell growth, and metastasis

Bisphosphonates are potent inhibitors of osteoclast-mediated bone resorption that also exhibit antitumor activity. There is now extensive in vitro evidence that bisphosphonates inhibit proliferation and induce apoptosis of tumor cell lines. In addition, they appear to inhibit tumor cell adhesion and invasion of the extracellular matrix. These data are supported by a growing body of evidence from animal models demonstrating that bisphosphonates can reduce skeletal tumor burden. This may reflect direct antitumor effects or indirect effects via osteoclast inhibition and alteration of the bone microenvironment. Research has begun to shed light on the complex mechanisms by which bisphosphonates inhibit bone resorption and interfere with the formation and growth of bone lesions. Nitrogen-containing bisphosphonates inhibit protein prenylation and thereby short-circuit intracellular signaling via small guanine triphosphatases, such as Ras, which require membrane localization. As a result of these biochemical effects on the mevalonate pathway, bisphosphonates appear to modulate the expression of bcl-2 leading to caspase-dependent apoptosis, inhibit matrix metalloproteinases, downregulate alphavbeta3 and alphavbeta5 integrins, and increase expression of osteoprotegerin, thereby antagonizing osteoclastogenesis. Further preclinical studies are ongoing to fully elucidate these biochemical mechanisms, and well-designed clinical trials are necessary to investigate whether the antitumor potential of bisphosphonates can be realized in the clinical setting.

Cytokines, viruses, and graft-versus-host disease

Proinflammatory cytokines released by host tissues during conditioning treatment and interferon gamma released from donor T cells play a major role in acute graft-versus-host disease (GVHD). In the past year the interaction of cytokines has been elucidated further. Host antigen-presenting cells play a key role in the induction of allogeneic recognition. Their activity is modulated by cytokines such as flt3-ligand, viruses, and donor T cells. Expansion of donor T cells is crucial for the pathogenesis of acute GVHD. Cytokines of the T helper 1 response-IFN-gamma, IL-12, and IL-18-regulate the expansion of donor and host cells via the induction of Fas and FasL and subsequent apoptosis. However TNF-alpha, FasL, and IL-1 also cause damage to target cells. Cytokine and receptor gene polymorphism has an impact on the activity of both host and donor cell activation. Genetic factors, conditioning treatment, lipopolysaccharides (LPS) from gram-negative microorganisms, viral infections, and donor T cells determine the activity level of host antigen-presenting cells and macrophages, which have an impact on acute GVHD and other complications of allogeneic stem cell transplantation.

Bisphosphonates in cancer therapy

Bisphosphonates inhibit osteoclast-mediated bone resorption in metastatic bone disease. A wealth of preclinical data have begun to shed light on the complex mechanisms by which bisphosphonates inhibit bone resorption and interfere with the formation and growth of bone metastases. Nitrogen-containing bisphosphonates inhibit the mevalonate pathway, which results in the inhibition of osteoclast function and the induction of apoptosis in osteoclasts and tumor cells alike. There is now extensive evidence that bisphosphonates have cytostatic activity against tumor cell lines and inhibit tumor cell adhesion and invasion of the extracellular matrix. These data are supported by a growing body of evidence from animal models demonstrating that bisphosphonates can reduce skeletal tumor burden. However, it remains unclear whether this reduction reflects a direct antitumor effect or an indirect effect via osteoclast inhibition and alteration of the bone microenvironment. Further preclinical studies are needed to elucidate these biochemical mechanisms fully; ultimately, well-controlled clinical trials will be required to investigate whether the antitumor potential of bisphosphonates translates into a significant clinical benefit for patients with cancer.

Increased expression of interleukin-18 receptor on T lymphocytes in patients with acute graft-versus-host disease after allogeneic bone marrow transplantation

Acute graft-versus-host disease (aGVHD), a potentially fatal side effect of allogeneic bone marrow transplantation (BMT), is initiated by the action of donor-derived T lymphocytes. We have shown previously that aGVHD is associated with elevated serum levels of interleukin-18 (IL-18). In this study, we analyzed the expression of the IL-18 receptor (IL-18R) on T lymphocytes of BMT patients with aGVHD. Flow cytometric analysis showed that in healthy subjects, a small population of CD4+ T cells expressed IL-18Ralpha, whereas a relatively large population of CD8+ T cells expressed IL-18Ralpha. In aGVHD patients, there were marked increases in the proportion of CD4+ or CD8+ T cells that express IL-18Ralpha. RT-PCR assays showed elevation of IL-18Ralpha and IL-18Rbeta mRNA levels in CD8+ T cells in aGVHD patients. These findings suggest that the expression of IL-18R is upregulated in T cells in patients with aGVHD and that the IL-18/IL-18R system is active during aGVHD.

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.

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.

Cancer vaccines for hematologic malignancies

BACKGROUND

Improvements in the identification of tumor-associated antigens and in our understanding of the mechanisms regulating antitumor immune responses have revived interest in the use of therapeutic cancer vaccination. Due to their unique characteristics, hematologic malignancies represent an ideal target for vaccine-based therapeutic interventions.

METHODS

A review of published vaccine studies in experimental models as well as the results of clinical trials using vaccines for patients with hematologic tumors is presented.

RESULTS

Tumor vaccine strategies can be divided into two categories: antigen-specific strategies, in which the tumor antigens have been identified and can be isolated to develop a molecularly defined vaccine, and cellular or non-antigen-specific, in which the tumor-specific antigens are unknown but presumed to exist within the material used to generate the vaccine. Early clinical trials have shown not only the feasibility and safety of either approach but also the obstacles in therapeutic cancer vaccination as an effective treatment modality for hematologic malignancies.

CONCLUSIONS

Active immunization using current cancer vaccine approaches is feasible and safe. Although no major successes have been reported, the positive clinical results observed in some patients support the potential for therapeutic cancer vaccination in the management of hematologic malignancies. Results of studies that are testing vaccine formulations, targets, and settings (eg, bone marrow transplantation) may support the use of cancer vaccination as an efficient therapeutic strategy against tumors of hematologic origin.

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.