Differential roles of IL-1 and TNF-alpha on graft-versus-host disease and graft versus leukemia

Enforced gut homing of murine regulatory T cells reduces early graft-versus-host disease severity

Damage to the gastrointestinal tract following allogeneic hematopoietic stem cell transplantation is a significant contributor to the severity and perpetuation of graft-versus-host disease. In preclinical models and clinical trials, we showed that infusing high numbers of regulatory T cells reduces graft-versus-host disease incidence. Despite no change in in vitro suppressive function, transfer of ex vivo expanded regulatory T cells transduced to overexpress G protein-coupled receptor 15 or C-C motif chemokine receptor 9, specific homing receptors for colon or small intestine, respectively, lessened graft-versus-host disease severity in mice. Increased regulatory T cell frequency and retention within the gastrointestinal tissues of mice that received gut homing T cells correlated with lower inflammation and gut damage early post-transplant, decreased graft-versus-host disease severity, and prolonged survival compared with those receiving control transduced regulatory T cells. These data provide evidence that enforced targeting of ex vivo expanded regulatory T cells to the gastrointestinal tract diminishes gut injury and is associated with decreased graft-versus-host disease severity.

Milestones in acute GVHD pathophysiology

In the past 65 years, over 25 000 referenced articles have been published on graft-versus-host disease (GVHD). Although this included clinically orientated papers or publications on chronic GVHD, the conservative estimate of scientific publications still contains several thousands of documents on the pathophysiology of acute GVHD. Thus, summarizing what we believe are prominent publications that can be considered milestones in our knowledge of this disease is a challenging and inherently biased task. Here we review from a historical perspective what can be regarded as publications that have made the field move forward. We also included several references of reviews on aspects we could not cover in detail.

Donor T cell DNMT3a regulates alloreactivity in mouse models of hematopoietic stem cell transplantation

DNA methyltransferase 3a (DNMT3a) is an important part of the epigenetic machinery that stabilizes patterns of activated T cell responses. We hypothesized that donor T cell DNMT3a regulates alloreactivity after allogeneic blood and marrow transplantation (allo-BMT). T cell conditional Dnmt3a KO mice were used as donors in allo-BMT models. Mice receiving allo-BMT from KO donors developed severe acute graft-versus-host disease (aGVHD), with increases in inflammatory cytokine levels and organ histopathology scores. KO T cells migrated and proliferated in secondary lymphoid organs earlier and demonstrated an advantage in trafficking to the small intestine. Donor T cell subsets were purified after BMT for whole-genome bisulfite sequencing (WGBS) and RNA-Seq. KO T cells had global methylation similar to that of WT cells, with distinct, localized areas of hypomethylation. Using a highly sensitive computational method, we produced a comprehensive profile of the altered epigenome landscape. Hypomethylation corresponded with changes in gene expression in several pathways of T cell signaling and differentiation. Additionally, Dnmt3a-KO T cells resulted in superior graft-versus-tumor activity. Our findings demonstrate a critical role for DNMT3a in regulating T cell alloreactivity and reveal pathways that control T cell tolerance. These results also provide a platform for deciphering clinical data that associate donor DNMT3a mutations with increased GVHD, decreased relapse, and improved survival.

Retention of Donor T Cells in Lymphohematopoietic Tissue and Augmentation of Tissue PD-L1 Protection for Prevention of GVHD While Preserving GVL Activity

Allogeneic hematopoietic cell transplantation (Allo-HCT) is a curative therapy for hematological malignancies (i.e., leukemia and lymphoma) due to the graft-versus-leukemia (GVL) activity mediated by alloreactive T cells that can eliminate residual malignant cells and prevent relapse. However, the same alloreactive T cells can cause a serious side effect, known as graft-versus-host disease (GVHD). GVHD and GVL occur in distinct organ and tissues, with GVHD occurring in target organs (e.g., the gut, liver, lung, skin, etc.) and GVL in lympho-hematopoietic tissues where hematological cancer cells primarily reside. Currently used immunosuppressive drugs for the treatment of GVHD inhibit donor T cell activation and expansion, resulting in a decrease in both GVHD and GVL activity that is associated with cancer relapse. To prevent GVHD, it is important to allow full activation and expansion of alloreactive T cells in the lympho-hematopoietic tissues, as well as prevent donor T cells from migrating into the GVHD target tissues, and tolerize infiltrating T cells via protective mechanisms, such as PD-L1 interacting with PD-1, in the target tissues. In this review, we will summarize major approaches that prevent donor T cell migration into GVHD target tissues and approaches that augment tolerization of the infiltrating T cells in the GVHD target tissues while preserving strong GVL activity in the lympho-hematopoietic tissues.

Increased efficacy of dual proinflammatory cytokine blockade on acute GVHD while maintaining GVT effects

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) remains a potential curative option for treating a variety of hematologic diseases, but acute and chronic graft-versus-host disease (GVHD) remain major barriers limiting efficacy. Acute gut GVHD occurs with marked increases in proinflammatory cytokines (including TNF and IL-6), which we recently demonstrated was exacerbated in obesity resulting in severe gastrointestinal pathology. Given the pleiotropic and overlapping effects of these 2 cytokines, we assessed the impact of dual TNF and IL-6R blockade on GVHD as well as graft-versus tumor (GVT) effects in different mouse GVHD models. Early administration of combined blockade resulted in greater protection and survival from acute gut GVHD compared with single blockade regimens and even development of later chronic skin GVHD. Importantly, double cytokine blockade preserved GVT effects reinforcing that GVT and GVHD can be delineated and may result in greater efficacy in allo-HSCT.

Demethylating therapy increases anti-CD123 CAR T cell cytotoxicity against acute myeloid leukemia

Successful treatment of acute myeloid leukemia (AML) with chimeric antigen receptor (CAR) T cells is hampered by toxicity on normal hematopoietic progenitor cells and low CAR T cell persistence. Here, we develop third-generation anti-CD123 CAR T cells with a humanized CSL362-based ScFv and a CD28-OX40-CD3ζ intracellular signaling domain. This CAR demonstrates anti-AML activity without affecting the healthy hematopoietic system, or causing epithelial tissue damage in a xenograft model. CD123 expression on leukemia cells increases upon 5'-Azacitidine (AZA) treatment. AZA treatment of leukemia-bearing mice causes an increase in CTLA-4negative anti-CD123 CAR T cell numbers following infusion. Functionally, the CTLA-4negative anti-CD123 CAR T cells exhibit superior cytotoxicity against AML cells, accompanied by higher TNFα production and enhanced downstream phosphorylation of key T cell activation molecules. Our findings indicate that AZA increases the immunogenicity of AML cells, enhancing recognition and elimination of malignant cells by highly efficient CTLA-4negative anti-CD123 CAR T cells.

The Pathophysiology and Treatment of Graft-Versus-Host Disease: Lessons Learnt From Animal Models

Allogeneic hematopoietic cell transplantation (HCT) is a curative treatment for hematologic malignancies, bone marrow failure syndromes, and inherited immunodeficiencies and metabolic diseases. Graft-versus-host disease (GVHD) is the major life-threatening complication after allogeneic HCT. New insights into the pathophysiology of GVHD garnered from our understanding of the immunological pathways within animal models have been pivotal in driving new therapeutic paradigms in the clinic. Successful clinical translations include histocompatibility matching, GVHD prophylaxis using cyclosporine and methotrexate, posttransplant cyclophosphamide, and the use of broad kinase inhibitors that inhibit cytokine signaling (e.g. ruxolitinib). New approaches focus on naïve T cell depletion, targeted cytokine modulation and the inhibition of co-stimulation. This review highlights the use of animal transplantation models to guide new therapeutic principles.

Deletion of AMPK minimizes graft-versus-host disease through an early impact on effector donor T cells

Allogeneic hematopoietic stem cell transplantation is a viable treatment for multiple hematologic diseases, but its application is often limited by graft-versus-host disease (GVHD), where donor T cells attack host tissues in the skin, liver, and gastrointestinal tract. Here, we examined the role of the cellular energy sensor AMP kinase (AMPK) in alloreactive T cells during GVHD development. Early posttransplant, AMPK activity increased more than 15-fold in allogeneic T cells, and transplantation of T cells deficient in both AMPKα1 and AMPKα2 decreased GVHD severity in multiple disease models. Importantly, a lack of AMPK lessened GVHD without compromising antileukemia responses or impairing lymphopenia-driven immune reconstitution. Mechanistically, absence of AMPK decreased both CD4⁺ and CD8⁺ effector T cell numbers as early as day 3 posttransplant, while simultaneously increasing regulatory T cell (Treg) percentages. Improvements in GVHD resulted from cell-intrinsic perturbations in conventional effector T cells as depletion of donor Tregs had minimal impact on AMPK-related improvements. Together, these results highlight a specific role for AMPK in allogeneic effector T cells early posttransplant and suggest that AMPK inhibition may be an innovative approach to mitigate GVHD while preserving graft-versus-leukemia responses and maintaining robust immune reconstitution.

Human multipotent adult progenitor cells effectively reduce graft-vs-host disease while preserving graft-vs-leukemia activity

Graft‐vs‐host disease (GvHD) limits successful outcomes following allogeneic blood and marrow transplantation (allo‐BMT). We examined whether the administration of human, bone marrow‐derived, multipotent adult progenitor cells (MAPCs™) could regulate experimental GvHD. The immunoregulatory capacity of MAPC cells was evaluated in vivo using established murine GvHD models. Injection of MAPC cells on day +1 (D1) and +4 (D4) significantly reduced T‐cell expansion and the numbers of donor‐derived, Tumor Necrosis Factor Alpha (TNFα) and Interferon Gamma (IFNγ)‐producing, CD4+ and CD8+ cells by D10 compared with untreated controls. These findings were associated with reductions in serum levels of TNFα and IFNγ, intestinal and hepatic inflammation and systemic GvHD as measured by survival and clinical score. Biodistribution studies showed that MAPC cells tracked from the lung and to the liver, spleen, and mesenteric nodes within 24 hours after injection. MAPC cells inhibited mouse T‐cell proliferation in vitro and this effect was associated with reduced T‐cell activation and inflammatory cytokine secretion and robust increases in the concentrations of Prostaglandin E2 (PGE2) and Transforming Growth Factor Beta (TGFβ). Indomethacin and E‐prostanoid 2 (EP2) receptor antagonism both reversed while EP2 agonism restored MAPC cell‐mediated in vitro T‐cell suppression, confirming the role for PGE2. Furthermore, cyclo‐oxygenase inhibition following allo‐BMT abrogated the protective effects of MAPC cells. Importantly, MAPC cells had no effect on the generation cytotoxic T lymphocyte activity in vitro, and the administration of MAPC cells in the setting of leukemic challenge resulted in superior leukemia‐free survival. Collectively, these data provide valuable information regarding the biodistribution and regulatory capacity of MAPC cells, which may inform future clinical trial design.

Caspase-1 inhibition ameliorates murine acute graft versus host disease by modulating the Th1/Th17/Treg balance

Our previous studies have implicated Caspase-1 signaling in driving the proinflammatory state of acute graft versus host disease (aGVHD). Therefore, we aimed to elucidate the mechanism of Caspase-1 in in murine models of aGVHD through specific inhibition of its activity with the decoy peptide Ac-YVAD-CMK. We transplanted bone marrow from donor C57BL/6 (H-2b) mice into recipient BALB/c (H-2Kd) mice and randomized the recipients into the following treatment cohorts: (1) allogeneic hematopoietic stem cell transplantation and splenic cell infusion control (PBS group); (2) low dose Ac-YVAD-CMK (AC low group); (3) and high dose Ac-YVAD-CMK (AC high group). Indeed, we observed that Caspase-1 inhibition by Ac-YVAD-CMK ameliorated pathological damage and inflammation in the liver, lungs, and colon elicited by aGVHD. This was associated with reduced mortality secondary to aGVHD. Mechanistically, we found that Caspase-1 inhibition modulated donor T cell expansion, restored the balance of Th1/Th17/Treg subsets, and markedly decreased serum levels and aGVHD target organ mRNA expression of IL-1β, IL-18, and HMGB1. Thus, we demonstrate that inhibition of Caspase-1 by Ac-YVAD-CMK mitigates murine aGVHD by regulating Th1/Th17/Treg balance and attenuating its characteristic proinflammatory state.

Immunomodulatory Effects of Bendamustine in Hematopoietic Cell Transplantation

Bendamustine (BEN) is a unique alkylating agent with efficacy against a broad range of hematological malignancies, although investigations have only recently started to delve into its immunomodulatory effects. These immunomodulatory properties of BEN in the context of hematopoietic cell transplantation (HCT) are reviewed here. Pre- and post-transplant use of BEN in multiple murine models have consistently resulted in reduced GvHD and enhanced GvL, with significant changes to key immunological cell populations, including T-cells, myeloid derived suppressor cells (MDSCs), and dendritic cells (DCs). Further, in vitro studies find that BEN enhances the suppressive function of MDSCs, skews DCs toward cDC1s, enhances Flt3 expression on DCs, increases B-cell production of IL-10, inhibits STAT3 activation, and suppresses proliferation of T- and B-cells. Overall, BEN has a broad range of immunomodulatory effects that, as they are further elucidated, may be exploited to improve clinical outcomes. As such, clinical trials are currently underway investigating new potential applications of BEN in the setting of allogeneic HCT.

Cytokines and costimulation in acute graft-versus-host disease

Allogeneic hematopoietic stem cell transplantation (alloSCT) is an important curative therapy for high-risk hematological malignancies, but the development of severe and/or steroid-refractory acute graft-versus-host disease (aGVHD) remains a significant limitation to optimal outcomes. New approaches to prevent and treat aGVHD remain an unmet need that can be best addressed by understanding the complex disease pathophysiology. It is now clear that chemoradiotherapy used prior to alloSCT induces the release of endogenous alarmins (eg, HMGB-1, ATP, IL-1α, IL-33) from recipient tissue. Exogenous pathogen-derived molecules (eg, lipopolysaccharide, nucleic acids) also translocate from the gastrointestinal tract lumen. Together, these danger signals activate antigen-presenting cells (APCs) to efficiently present alloantigen to donor T cells while releasing cytokines (eg, interleukin-12 [IL-12], IL-23, IL-6, IL-27, IL-10, transforming growth factor-β) that expand and differentiate both pathogenic and regulatory donor T cells. Concurrent costimulatory signals at the APC-T-cell interface (eg, CD80/CD86-CD28, CD40-CD40L, OX40L-OX40, CD155/CD112-DNAM-1) and subsequent coinhibitory signals (eg, CD80/CD86-CTLA4, PDL1/2-PD1, CD155/CD112-TIGIT) are critical to the acquisition of effector T-cell function and ensuing secretion of pathogenic cytokines (eg, IL-17, interferon-γ, tissue necrosis factor, granulocyte-macrophage colony-stimulating factor) and cytolytic degranulation pathway effectors (eg, perforin/granzyme). This review focuses on the combination of cytokine and costimulatory networks at the T-cell surface that culminates in effector function and subsequent aGVHD in target tissue. Together, these pathways now represent robust and clinically tractable targets for preventing the initiation of deleterious immunity after alloSCT.

Graft-versus-host disease of the CNS is mediated by TNF upregulation in microglia

Acute graft-versus-host disease (GVHD) can affect the central nervous system (CNS). The role of microglia in CNS-GVHD remains undefined. In agreement with microglia activation, we found that profound morphological changes and MHC-II and CD80 upregulation occurred upon GVHD induction. RNA sequencing-based analysis of purified microglia obtained from mice with CNS-GVHD revealed TNF upregulation. Selective TNF gene deletion in microglia of Cx3cr1creER Tnffl/- mice reduced MHC-II expression and decreased CNS T cell infiltrates and VCAM-1+ endothelial cells. GVHD increased microglia TGF-β-activated kinase-1 (TAK1) activation and NF-κB/p38 MAPK signaling. Selective Tak1 deletion in microglia using Cx3cr1creER Tak1fl/fl mice resulted in reduced TNF production and microglial MHC-II and improved neurocognitive activity. Pharmacological TAK1 inhibition reduced TNF production and MHC-II expression by microglia, Th1 and Th17 T cell infiltrates, and VCAM-1+ endothelial cells and improved neurocognitive activity, without blocking graft-versus-leukemia effects. Consistent with these findings in mice, we observed increased activation and TNF production of microglia in the CNS of GVHD patients. In summary, we prove a role for microglia in CNS-GVHD, identify the TAK1/TNF/MHC-II axis as a mediator of CNS-GVHD, and provide a TAK1 inhibitor-based approach against GVHD-induced neurotoxicity.

ASC Modulates CTL Cytotoxicity and Transplant Outcome Independent of the Inflammasome

The adaptor protein ASC (apoptosis-associated speck-like protein containing a CARD) is known to facilitate caspase-1 activation, which is essential for innate host immunity via the formation of the inflammasome complex, a multiprotein structure responsible for processing IL1β and IL18 into their active moieties. Here, we demonstrated that ASC-deficient CD8⁺ T cells failed to induce severe graft-versus-host disease (GVHD) and had impaired capacity for graft rejection and graft-versus-leukemia (GVL) activity. These effects were inflammasome independent because GVHD lethality was not altered in recipients of caspase-1/11-deficient T cells. We also demonstrated that ASC deficiency resulted in a decrease in cytolytic function, with a reduction in granzyme B secretion and CD107a expression by CD8⁺ T cells. Altogether, our findings highlight that ASC represents an attractive therapeutic target for improving outcomes of clinical transplantation.

The primacy of gastrointestinal tract antigen-presenting cells in lethal graft-versus-host disease

Allogeneic stem cell transplantation is a cornerstone of curative therapy for high-risk and/or advanced hematological malignancies but remains limited by graft-versus-host disease (GVHD). GVHD is initiated by the interaction between recipient antigen-presenting cells (APCs) and donor T cells, culminating in T-cell differentiation along pathogenic type-1 and type-17 paradigms at the expense of tolerogenic regulatory T-cell patterns. Type-1 and type-17 T cells secrete cytokines (eg, granulocyte-macrophage colony-stimulating factor and interferon-γ) critical to the cytokine storm that amplifies expansion of donor APCs and their alloantigen presentation. It has become increasingly clear that pathogenic donor T-cell differentiation is initiated by both professional recipient APCs (eg, dendritic cells [DCs]) and nonprofessional APCs (eg, epithelial and mesenchymal cells), particularly within the gastrointestinal (GI) tract. In the immediate peritransplantation period, these APCs are profoundly modified by pathogen-associated molecular pattern (PAMP)/damage-associated molecular pattern (DAMP) signals derived from conditioning and intestinal microbiota. Subsequently, donor DCs in the GI tract are activated by DAMP/PAMP signals in the colon that gain access to the lamina propria once the mucosal barrier mucosa is compromised by GVHD. This results in donor DC expansion and alloantigen presentation in the colon and subsequent migration into the mesenteric lymph nodes. Here, new donor T cells are primed, expanded, differentiated, and imprinted with gut-homing integrins permissive of migration into the damaged GI tract, resulting in the lethal feed-forward cascade of GVHD. These new insights into our understanding of the cellular and molecular factors initiating GVHD, both spatially and temporally, give rise to a number of logical therapeutic targets, focusing on the inhibition of APC function in the GI tract.

Inhibition of inositol kinase B controls acute and chronic graft-versus-host disease

T-cell activation releases inositol 1,4,5-trisphosphate (IP3), inducing cytoplasmic calcium (Ca2+) influx. In turn, inositol 1,4,5-trisphosphate 3-kinase B (Itpkb) phosphorylates IP3 to negatively regulate and thereby tightly control Ca2+ fluxes that are essential for mature T-cell activation and differentiation and protection from cell death. Itpkb pathway inhibition increases intracellular Ca2+, induces apoptosis of activated T cells, and can control T-cell-mediated autoimmunity. In this study, we employed genetic and pharmacological approaches to inhibit Itpkb signaling as a means of controlling graft-versus-host disease (GVHD). Murine-induced, Itpkb-deleted (Itpkb-/-) T cells attenuated acute GVHD in 2 models without eliminating A20-luciferase B-cell lymphoma graft-versus-leukemia (GVL). A highly potent, selective inhibitor, GNF362, ameliorated acute GVHD without impairing GVL against 2 acute myeloid leukemia lines (MLL-AF9-eGFP and C1498-luciferase). Compared with FK506, GNF362 more selectively deleted donor alloreactive vs nominal antigen-responsive T cells. Consistent with these data and as compared with FK506, GNF362 had favorable acute GVHD and GVL properties against MLL-AF9-eGFP cells. In chronic GVHD preclinical models that have a pathophysiology distinct from acute GVHD, Itpkb-/- donor T cells reduced active chronic GVHD in a multiorgan system model of bronchiolitis obliterans (BO), driven by germinal center reactions and resulting in target organ fibrosis. GNF362 treatment reduced active chronic GVHD in both BO and scleroderma models. Thus, intact Itpkb signaling is essential to drive acute GVHD pathogenesis and sustain active chronic GVHD, pointing toward a novel clinical application to prevent acute or treat chronic GVHD.

Advances in understanding the pathogenesis of graft-versus-host disease

Acute graft-versus-host disease (GVHD) remains a major complication after allogeneic haematopoietic stem cell transplantation (allo-HSCT). The emergence of different immuno-prophylaxis strategies, such as post-transplant cyclophosphamide or anti-thymocyteglobulin has reduced the incidence of acute GVHD in recent years. The biology of the acute GVHD we observe in the clinic may change due to the use of novel immuno-stimulatory agents, including immune checkpoint inhibitors or anti-neoplastic immune-modifiers, like lenalidomide, given before or after allo-HSCT. Here we discuss the recent advances in our understanding of acute GVHD with a focus on early events of the disease, including tissue damaging factors, innate immune cells, costimulatory pathways, immune cell signalling, immuno-regulatory cell types, biomarkers of GVHD and regenerative approaches. New insight in the pathogenesis of acute GVHD has revealed the role of pro-inflammatory intracellular signalling, defects in intestinal tissue regeneration and anti-bacterial defence, as well as a reduced diversity of the microbiome, which will be the basis for the development of novel therapies.

Targeting Regulatory T Cells by Addressing Tumor Necrosis Factor and Its Receptors in Allogeneic Hematopoietic Cell Transplantation and Cancer

An intricate network of molecular and cellular actors orchestrates the delicate balance between effector immune responses and immune tolerance. The pleiotropic cytokine tumor necrosis factor-alpha (TNF) proves as a pivotal protagonist promoting but also suppressing immune responses. These opposite actions are accomplished through specialist cell types responding to TNF via TNF receptors TNFR1 and TNFR2. Recent findings highlight the importance of TNFR2 as a key regulator of activated natural FoxP3⁺ regulatory T cells (Tregs) in inflammatory conditions, such as acute graft-vs.-host disease (GvHD) and the tumor microenvironment. Here we review recent advances in our understanding of TNFR2 signaling in T cells and discuss how these can reconcile seemingly conflicting observations when manipulating TNF and TNFRs. As TNFR2 emerges as a new and attractive target we furthermore pinpoint strategies and potential pitfalls for therapeutic targeting of TNFR2 for cancer treatment and immune tolerance after allogeneic hematopoietic cell transplantation.

TNFR2 signaling modulates immunity after allogeneic hematopoietic cell transplantation

Tumor necrosis factor-α (TNF-α) signaling through TNF receptor 2 (TNFR2) plays a complex immune regulatory role in allogeneic hematopoietic cell transplantation (HCT). TNF-α is rapidly released in the circulation after the conditioning regimen with chemotherapy and/or radiotherapy. It activates the function of donor alloreactive T cells and donor Natural Killer cells and promotes graft versus tumor effects. However, donor alloreactive T cells also attack host tissues and cause graft versus host disease (GVHD), a life-threatening complication of HCT. Indeed, anti-TNF-α therapy has been used to treat steroid-refractory GVHD. Recent studies have highlighted another role for TNFR2 signaling, as it enhances the function of immune cells with suppressive properties, in particular CD4⁺Foxp3⁺ regulatory T cells (Tregs). Various clinical trials are employing Treg-based treatments to prevent or treat GVHD. The present review will discuss the effects of TNFR2 signaling in the setting of allogeneic HCT, the implications for the use of anti-TNF-α therapy to treat GVHD and the clinical perspectives of strategies that specifically target this pathway.

MicroRNAs as important regulators of the NLRP3 inflammasome

Inflammasomes are a group of cytosolic multi-protein signaling complexes that regulate maturation of the interleukin (IL)-1 family cytokines IL-1β and IL-18 through activation of inflammatory caspase-1. The NOD-like receptor family, pyrin domain containing 3 (NLRP3) inflammasome is the best characterized and consists of several key components that are assembled and activated in response to different endogenous and exogenous signals. The NLRP3 inflammasome is common to a number of human inflammatory diseases and its targeting may lead to novel anti-inflammatory therapy. NLRP3 inflammasome activation is tightly regulated by different mechanisms especially post-transcriptional modulation via microRNAs (miRNA). MicroRNAs are small endogenous noncoding RNAs that are 21-23 nucleotides in length and control the expression of various genes through binding to the 3'-untranslated regions of the respective mRNA and subsequent post-transcriptional regulation. MicroRNAs have recently been recognized as crucial regulators of the NLRP3 inflammasome. In this review, we summarize the current understanding of the role of miRNAs in the regulation of NLRP3 inflammasome complexes and their impact on the pathogenesis of inflammatory disease processes.

The A2A receptor agonist CGS 21680 has beneficial and adverse effects on disease development in a humanised mouse model of graft-versus-host disease

Allogeneic hematopoietic stem cell transplantation (HSCT) is a curative method for blood cancers and other blood disorders, but is limited by the development of graft-versus-host disease (GVHD). GVHD results in inflammatory damage to the host liver, gastrointestinal tract and skin, resulting in high rates of morbidity and mortality in HSCT recipients. Activation of the A_2A receptor has been previously demonstrated to reduce disease in allogeneic mouse models of GVHD. This study aimed to investigate the effect of A_2A activation on disease development in a humanised mouse model of GVHD. Immunodeficient non-obese diabetic-severe combined immunodeficiency-interleukin (IL)-2 receptor γ^null (NSG) mice injected with human (h) peripheral blood mononuclear cells (hPBMCs), were treated with either the A_2A agonist CGS 21680 or control vehicle. Contrary to the beneficial effect of A_2A activation in allogeneic mouse models, CGS 21680 increased weight loss, and failed to reduce the clinical score or increase survival in this humanised mouse model of GVHD. Moreover, CGS 21680 reduced T regulatory cells and increased serum human IL-6 concentrations. Conversely, CGS 21680 reduced serum human tumour necrosis factor (TNF)-α concentrations and leukocyte infiltration into the liver, indicating that A_2A activation can, in part, reduce molecular and histological GVHD in this model. Notably, CGS 21680 also prevented healthy weight gain in NSG mice not engrafted with hPBMCs suggesting that this compound may be suppressing appetite or metabolism. Therefore, the potential benefits of A_2A activation in reducing GVHD in HSCT recipients may be limited and confounded by adverse impacts on weight, decreased T regulatory cell frequency and increased IL-6 production.

Animal Models for Preclinical Development of Allogeneic Hematopoietic Cell Transplantation

Since its inception in the 1950s, hematopoietic cell transplantation (HCT) has become a highly effective clinical treatment for malignant and nonmalignant hematological disorders. This milestone in cancer therapy was only possible through decades of intensive research using murine and canine animal models that overcame what appeared in the early days to be insurmountable obstacles. Conditioning protocols for tumor ablation and immunosuppression of the recipient using irradiation and chemotherapeutic drugs were developed in mouse and dog models as well as postgrafting immunosuppression methods essential for dependable donor cell engraftment. The random-bred canine was particularly important in defining the role of histocompatibility barriers and the development of the nonmyeloablative transplantation procedure, making HCT available to elderly patients with comorbidities. Two complications limit the success of HCT: disease relapse and graft versus host disease. Studies in both mice and dogs have made significant progress toward reducing and to some degree eliminating patient morbidity and mortality associated with both disease relapse and graft versus host disease. However, more investigation is needed to make HCT more effective, safer, and available as a treatment modality for other non-life-threatening diseases such as autoimmune disorders. Here, we focus our review on the contributions made by both the murine and canine models for the successful past and future development of HCT.

Associations between febrile neutropenia-related parameters and the risk of acute GVHD or non-relapse mortality after allogeneic hematopoietic stem cell transplantation

Infection and inflammation can induce acute graft-vs.-host disease (aGVHD). We hypothesized that febrile neutropenia early after allogeneic hematopoietic cell transplantation (HCT) would increase the risk of aGVHD and non-relapse mortality (NRM). We retrospectively evaluated the impact of fever, C-reactive protein (CRP) concentration and blood stream infection (BSI) early after HCT on the incidence of grade II-IV aGVHD and NRM in 227 patients. Within 7 days after HCT, 91 (40.1%) patients experienced fever for at least 2 days (early-FN group). BSI occurred in 27 (11.9%) patients and the maximum CRP concentration was 2.57 mg/dl in the median. In a multivariate analysis, early-FN (hazard ratio (HR) 1.81, P = 0.007) and older recipient age (HR 1.68, P = 0.019) were significantly associated with the incidence of grade II-IV aGVHD. High-CRP and BSI were not significant risk factors for grade II-IV aGVHD. On the other hand, high-CRP was significantly associated with the incidence of NRM (HR 2.67, P = 0.004) in a multivariate analysis. In conclusion, although fever, CRP elevation and BSI are considered to be closely related events, they had different effects on the incidence of aGVHD and NRM. The development of early-FN after HCT may predict the risk of aGVHD.

Proinflammatory Cytokine and Adipokine Levels in Adult Unrelated Marrow Donors Are Not Associated with Hematopoietic Cell Transplantation Outcomes

Graft-versus-host disease (GVHD) is a frequent cause of morbidity and mortality after allogeneic hematopoietic cell transplantation (allo-HCT). GVHD occurs when donor lymphocytes are activated by inflammatory cytokines and alloantigens. The role of donor biologic characteristics, such as basal inflammation, has not been investigated as a risk factor for GVHD but is theoretically transferrable to the recipient. We evaluated donor serum and plasma concentrations of cytokines and adipokines (IL-1β, IL-6, tumor necrosis factor [TNF]-α, leptin, suppression of tumorigenicity-2, and adiponectin) from test (n = 210) and replication (n = 250) cohorts of matched, unrelated transplant peripheral blood stem cell recipients identified through the Center for International Blood and Marrow Transplantation Research between 2000 and 2011 for hematologic malignancies. Hazard ratios were estimated for acute (grades II to IV and III to IV) and chronic GVHD, overall survival, disease-free survival, transplant-related mortality, and relapse for each cytokine or adipokine, adjusting for significant covariates. The lowest cytokine quartile was considered as the reference group for each model. To account for multiple testing P < .01 was considered the threshold for significance. In the test cohort a borderline significant association was identified between donor serum IL-1β concentrations and grades III to IV acute GVHD in the recipient (P = .01), and a significant inverse association was identified between donor TNF-α concentrations and chronic GVHD (P = .006). These findings were not validated in the replication cohort. Although the initial associations between cytokine levels and allo-HCT outcomes were not validated, the idea that donor characteristics may be transferable to the recipient remains an exciting area for future research.

Memory T cells: A helpful guard for allogeneic hematopoietic stem cell transplantation without causing graft-versus-host disease

Graft-versus-host disease (GVHD) is a major complication of allogeneic hematopoietic stem cell transplantation (AHSCT) and the major cause of nonrelapse morbidity and mortality of AHSCT. In AHSCT, donor T cells facilitate hematopoietic stem cell (HSC) engraftment, contribute to anti-infection immunity, and mediate graft-versus-leukemia (GVL) responses. However, activated alloreactive T cells also attack recipient cells in vital organs, leading to GVHD. Different T-cell subsets, including naïve T (T_N) cells, memory T (T_M) cells, and regulatory T (T_reg) cells mediate different forms of GVHD and GVL; T_N cells mediate severe GVHD, whereas T_M cells do not cause GVHD, but preserve T-cell function including GVL. In addition, metabolic reprogramming controls T-cell differentiation and activation in these disease states. This minireview focuses on the role and the related mechanisms of T_M cells in AHSCT, and the potential manipulation of T cells in AHSCT.

Targeting the interleukin-1 pathway in patients with hematological disorders

Interleukin-1α (IL-1α) and IL-1β are potent inflammatory cytokines that activate local and systemic inflammatory processes and are involved in protective immune responses against infections. However, their dysregulated production and signaling can aggravate tissue damage during infection, inflammatory diseases, and chemotherapy-induced intestinal mucositis. Additionally, cytokines of the IL-1 family play an important role in homeostatic as well as "emergency" hematopoiesis and are involved in the pathogenesis of several myeloid and lymphoid hematological malignancies. In the pathogenesis of intestinal mucositis and graft-versus-host disease (GVHD), these cytokines are considered pivotal during the initiation as well as propagation phase, and insights from animal studies suggest that targeting the IL-1 pathway can significantly ameliorate mucositis and GVHD. Moreover, IL-1α and IL-1β might prove to be valuable targets for both prevention and treatment of cancer and cancer therapy-related complications, and the first clinical studies have already been performed in the setting of hematological malignancies. In this review, we will discuss the role of cytokines of the IL-1 family in hematological malignancies, chemotherapy-induced intestinal mucositis, and GVHD, and speculate on possibilities of therapeutically targeting the IL-1 pathway in hematological patients.

Citrulline and Monocyte-Derived Macrophage Reactivity before Conditioning Predict Acute Graft-versus-Host Disease

During conditioning, intestinal damage induces microbial translocation which primes macrophage reactivity and leads to donor-derived T cell stimulation. Little is known about the role of intestinal health and macrophage reactivity before conditioning in the development of acute graft-versus-host disease (aGVHD) in patients undergoing allogeneic hematopoietic cell transplantation (allo-HCT). We assessed (1) citrulline, a surrogate marker of functional enterocyte mass and (2) circulating monocyte-derived macrophage reactivity, before allo-HCT. Forty-seven consecutive patients were prospectively included. Citrulline levels from blood samples withdrawn 30 days before transplantation were assessed using liquid chromatography combined with mass spectrometry. Monocyte-derived macrophages were isolated and incubated with 5 pathogen-associated molecular patterns: lipopolysaccharide, PamCSK4, flagellin, muramyl dipeptide, and curdlan. Multiplex fluorescent immunoassay on culture supernatant assessed levels of TNF-α, IL-1β, IL-6, and IL-10 in each condition. Citrulline and cytokine levels were analyzed relatively to aGVHD onset within 100 days after transplantation. Citrulline levels were lower in the aGVHD group (n = 20) than in the no-aGVHD group (n = 27) (P = .005). Conversely, IL-6 and IL-10 were greater in aGVHD group, especially after curdlan stimulation (P = .005 and P = .012). Citrulline levels ≤20 µmol/L, IL-6 ≥ 332 pg/mL, and IL-10 ≥ 90 pg/mL were associated with aGVHD development (log-rank test, P = .002, P = .041, and P < .0001, respectively). In multivariate analysis, IL-10 ≥ 90 pg/mL, myeloablative conditioning, and citrulline ≤20 µmol/L remained independent factors of aGVHD development (hazard ratio [HR],  8.18, P = .0003; HR, 4.28, P = .006; and HR, 4.43, P = .01, respectively). Preconditioning citrulline and monocyte-derived macrophage reactivity are objective surrogate markers suitable to identify patients at risk of developing aGVHD. This work highlights the influence of preconditioning status in aGVHD development.

The Biology of Chronic Graft-versus-Host Disease: A Task Force Report from the National Institutes of Health Consensus Development Project on Criteria for Clinical Trials in Chronic Graft-versus-Host Disease

Chronic graft-versus-host disease (GVHD) is the leading cause of late, nonrelapse mortality and disability in allogeneic hematopoietic cell transplantation recipients and a major obstacle to improving outcomes. The biology of chronic GVHD remains enigmatic, but understanding the underpinnings of the immunologic mechanisms responsible for the initiation and progression of disease is fundamental to developing effective prevention and treatment strategies. The goals of this task force review are as follows: This document is intended as a review of our understanding of chronic GVHD biology and therapies resulting from preclinical studies, and as a platform for developing innovative clinical strategies to prevent and treat chronic GVHD.

Danger Signals and Graft-versus-host Disease: Current Understanding and Future Perspectives

Graft-versus-host response after allogeneic hematopoietic stem cell transplantation (allo-HCT) represents one of the most intense inflammatory responses observed in humans. Host conditioning facilitates engraftment of donor cells, but the tissue injury caused from it primes the critical first steps in the development of acute graft-versus-host disease (GVHD). Tissue injuries release pro-inflammatory cytokines (such as TNF-α, IL-1β, and IL-6) through widespread stimulation of pattern recognition receptors (PRRs) by the release of danger stimuli, such as damage-associated molecular patterns (DAMPs) and pathogen-associated molecular patterns (PAMPs). DAMPs and PAMPs function as potent stimulators for host and donor-derived antigen presenting cells (APCs) that in turn activate and amplify the responses of alloreactive donor T cells. Emerging data also point towards a role for suppression of DAMP induced inflammation by the APCs and donor T cells in mitigating GVHD severity. In this review, we summarize the current understanding on the role of danger stimuli, such as the DAMPs and PAMPs, in GVHD.

Hydrogen, a potential safeguard for graft-versus-host disease and graft ischemia-reperfusion injury?

Post-transplant complications such as graft-versus-host disease and graft ischemia-reperfusion injury are crucial challenges in transplantation. Hydrogen can act as a potential antioxidant, playing a preventive role against post-transplant complications in animal models of multiple organ transplantation. Herein, the authors review the current literature regarding the effects of hydrogen on graft ischemia-reperfusion injury and graft-versus-host disease. Existing data on the effects of hydrogen on ischemia-reperfusion injury related to organ transplantation are specifically reviewed and coupled with further suggestions for future work. The reviewed studies showed that hydrogen (inhaled or dissolved in saline) improved the outcomes of organ transplantation by decreasing oxidative stress and inflammation at both the transplanted organ and the systemic levels. In conclusion, a substantial body of experimental evidence suggests that hydrogen can significantly alleviate transplantation-related ischemia-reperfusion injury and have a therapeutic effect on graft-versus-host disease, mainly via inhibition of inflammatory cytokine secretion and reduction of oxidative stress through several underlying mechanisms. Further animal experiments and preliminary human clinical trials will lay the foundation for hydrogen use as a drug in the clinic.

Preclinical models of acute and chronic graft-versus-host disease: how predictive are they for a successful clinical translation?

Despite major advances in recent years, graft-versus-host disease (GVHD) remains a major life-threatening complication of allogeneic hematopoietic cell transplantation (allo-HCT). To improve our therapeutic armory against GVHD, preclinical evidence is most frequently generated in mouse and large animal models of GVHD. However, because every model has shortcomings, it is important to understand how predictive the different models are and why certain findings in these models could not be translated into the clinic. Weaknesses of the animal GVHD models include the irradiation only-based conditioning regimen, the homogenous donor/recipient genetics in mice, canine or non-human primates (NHP), anatomic site of T cells used for transfer in mice, the homogenous microbial environment in mice housed under specific pathogen-free conditions, and the lack of pharmacologic GVHD prevention in control groups. Despite these major differences toward clinical allo-HCT, findings generated in animal models of GVHD have led to the current gold standards for GVHD prophylaxis and therapy. The homogenous nature of the preclinical models allows for reproducibility, which is key for the characterization of the role of a new cytokine, chemokine, transcription factor, microRNA, kinase, or immune cell population in the context of GVHD. Therefore, when carefully balancing reasons to apply small and large animal models, it becomes evident that they are valuable tools to generate preclinical hypotheses, which then have to be rigorously evaluated in the clinical setting. In this study, we discuss several clinical approaches that were motivated by preclinical evidence, novel NHP models and their advantages, and highlight the recent advances in understanding the pathophysiology of GVHD.

Preclinical modeling of hematopoietic stem cell transplantation - advantages and limitations

Hematopoietic stem cell transplantation, which was first successfully performed in the 1950s, remains a critical therapeutic modality for treatment of a diverse array of diseases, including a multitude of hematological malignancies, autoimmune disorders, amyloidosis and inherited genetic hematological disorders. Although great advances have been made in understanding and application of this therapy, significant complications still exist, warranting further investigation. Of critical importance, graft-versus-host disease (GVHD), in both acute and chronic forms, remains a major complication of hematopoietic stem cell transplantation, responsible for both the development of chronic illness and morbidity, as well as mortality. Use of an appropriate preclinical model may provide significant insight into the mechanistic pathways leading to the development and progression of graft-versus-host disease, as well as cancer in general. However, existing preclinical modeling systems exhibit significant limitations, and development of models that recapitulate the complex and comprehensive clinical scenario and provide a tool by which therapeutic intervention may be developed and assessed is of utmost importance. Here, we review the present status of the field of graft-versus-host disease research. We discuss and summarize the preclinical models currently in use, as well as their advantages and limitations.

A preclinical acute GVHD mouse model based on chemotherapy conditioning and MHC-matched transplantation

Animal disease models have been criticized for lack of resemblance to human illnesses, hampering transfer of knowledge from preclinical research to clinical medicine. In the field of allogeneic hematopoietic stem cell transplantation (allo-HSCT), it is standard practice to study GVHD in lethal TBI-based murine models. Frequently, MHC-mismatched donors are used in GVHD models. In contrast, in clinical allo-HSCT conditioning with chemotherapy (+/-TBI) is common and donors are often MHC-matched. Aiming at a more clinically oriented situation, we established and characterized a murine MHC-matched, minor histocompatibility antigen mismatched GVHD model (LP/J [H2k(b)]-->C57BL/6 [H2k(b)]) using busulfan and cyclophosphamide conditioning. We found typical clinical and histological features of acute GVHD. T-cell infiltration, GVHD-specific damage and systemic inflammation were similar to observations made in patients after allo-HSCT. In survivors of acute GVHD, we found expansion of CD4+ T cells and the development of scleroderma-like chronic GVHD. The use of chemotherapy-based, minor histocompatibility antigen (miHA)-mismatched GVHD animal models may be a good option when studying clinically relevant questions in the field of allo-HSCT.

Human mesenchymal stromal cells attenuate graft-versus-host disease and maintain graft-versus-leukemia activity following experimental allogeneic bone marrow transplantation

We sought to define the effects and underlying mechanisms of human, marrow-derived mesenchymal stromal cells (hMSCs) on graft-versus-host disease (GvHD) and graft-versus-leukemia (GvL) activity. Irradiated B6D2F1 mice given C57BL/6 BM and splenic T cells and treated with hMSCs had reduced systemic GvHD, donor T-cell expansion, and serum TNFα and IFNγ levels. Bioluminescence imaging demonstrated that hMSCs redistributed from lungs to abdominal organs within 72 hours, and target tissues harvested from hMSC-treated allogeneic BMT (alloBMT) mice had less GvHD than untreated controls. Cryoimaging more precisely revealed that hMSCs preferentially distributed to splenic marginal zones and regulated T-cell expansion in the white pulp. Importantly, hMSCs had no effect on in vitro cytotoxic T-cell activity and preserved potent GvL effects in vivo. Mixed leukocyte cultures containing hMSCs exhibited decreased T-cell proliferation, reduced TNFα, IFNγ, and IL-10 but increased PGE2 levels. Indomethacin and E-prostanoid 2 (EP2) receptor antagonisms both reversed while EP2 agonism restored hMSC-mediated in vitro T-cell suppression, confirming the role for PGE2 . Furthermore, cyclo-oxygenase inhibition following alloBMT abrogated the protective effects of hMSCs. Together, our data show that hMSCs preserve GvL activity and attenuate GvHD and reveal that hMSC biodistribute to secondary lymphoid organs wherein they attenuate alloreactive T-cell proliferation likely through PGE2 induction.

Cytokines in Graft-versus-Host Disease

Graft-versus-host disease (GVHD) is a complication of allogeneic bone marrow transplantation whereby transplanted naive and marrow-derived T cells damage recipient tissue through similar mechanisms to those that allow destruction of malignant cells, the therapeutic intent of bone marrow transplantation. The manifestations and severity of GVHD are highly variable and are influenced by the proportions of naive cells maturing along regulatory T cell, Th1, Th2, or Th17 phenotypes. This maturation is largely influenced by local cytokines, which, in turn, activate transcription factors and drive development toward a dominant phenotype. In addition, proinflammatory cytokines exert direct effects on GVHD target tissues. Our knowledge of the role that cytokines play in orchestrating GVHD is expanding rapidly and parallels other infective and inflammatory conditions in which a predominant T cell signature is causative of pathology. Because a broad spectrum of cytokine therapies is now routinely used in clinical practice, they are increasingly relevant to transplant medicine.

Intestinal barrier loss as a critical pathogenic link between inflammatory bowel disease and graft-versus-host disease

Compromised intestinal barrier function is a prominent feature of inflammatory bowel disease (IBD). However, links between intestinal barrier loss and disease extend much further, including documented associations with celiac disease, type I diabetes, rheumatoid arthritis, and multiple sclerosis. Intestinal barrier loss has also been proposed to have a critical role in the pathogenesis of graft-versus-host disease (GVHD), a serious, potentially fatal consequence of hematopoietic stem cell transplantation. Experimental evidence has begun to support this view, as barrier loss and its role in initiating and establishing a pathogenic inflammatory cycle in GVHD is emerging. Here we discuss similarities between IBD and GVHD, mechanisms of intestinal barrier loss in these diseases, and the crosstalk between barrier loss and the immune system, with a special focus on natural killer (NK) cells. Unanswered questions and future research directions on the topic are discussed along with implications for treatment.

Mature T cell responses are controlled by microRNA-142

T cell proliferation is critical for immune responses; however, the molecular mechanisms that mediate the proliferative response are poorly understood. MicroRNAs (miRs) regulate various molecular processes, including development and function of the immune system. Here, utilizing multiple complementary genetic and molecular approaches, we investigated the contribution of a hematopoietic-specific miR, miR-142, in regulating T cell responses. T cell development was not affected in animals with a targeted deletion of Mir142; however, T cell proliferation was markedly reduced following stimulation both in vitro and in multiple murine models of graft-versus-host disease (GVHD). miR-142-deficient T cells demonstrated substantial cell-cycling defects, and microarray and bioinformatics analyses revealed upregulation of genes involved in cell cycling. Moreover, 2 predicted miR-142 target genes, the atypical E2F transcription factors E2f7 and E2f8, were most highly upregulated in miR-142-deficient cells. Clustered regularly interspaced short palindromic repeat interference-mediated (CRISPRi-mediated) silencing of E2F7 and E2F8 in miR-142-deficient T cells ameliorated cell-cycling defects and reduced GVHD, and overexpression of these factors in WT T cells inhibited the proliferative response. Together, these results identify a link between hematopoietic-specific miR-142 and atypical E2F transcription factors in the regulation of mature T cell cycling and suggest that targeting this interaction may be relevant for mitigating GVHD.

MicroRNA-155-deficient dendritic cells cause less severe GVHD through reduced migration and defective inflammasome activation

The successful treatment of acute leukemias with allogeneic hematopoietic cell transplantation (allo-HCT) is limited by acute graft-versus-host disease (GVHD). Because microRNA-155 (miR-155) regulates activation of the innate immune system, we aimed to determine its function in dendritic cells (DCs) during GVHD in an experimental model. We observed that miR-155 deficiency of the recipient led to improved survival, reduced serum levels of proinflammatory cytokines, and lower GVHD histopathology scores. In addition, miR-155(-/-) bone marrow chimeric mice receiving allo-HCT and miR-155(-/-) DCs showed that miR-155 deficiency in the DC compartment was responsible for protection from GVHD. Activated miR-155(-/-) DCs displayed lower expression of various purinergic receptors and impaired migration toward adenosine triphosphate (ATP). Microarray analysis of lipopolysaccharide/ATP-stimulated miR-155(-/-) DCs revealed mitogen-activated protein kinase pathway dysregulation and reduced inflammasome-associated gene expression. Consistent with this gene expression data, we observed reduced ERK activation, caspase-1 cleavage, and IL-1β production in miR-155(-/-) DCs. The connection between miR-155 and inflammasome activation was supported by the fact that Nlrp3/miR-155 double-knockout allo-HCT recipient mice had no increased protection from GVHD compared with Nlrp3(-/-) recipients. This study indicates that during GVHD, miR-155 promotes DC migration toward sites of ATP release accompanied by inflammasome activation. Inhibiting proinflammatory miR-155 by antagomir treatment could help reduce this complication of allo-HCT.

Administration of hydrogen-rich saline in mice with allogeneic hematopoietic stem-cell transplantation

Background

Hydrogen, as a novel antioxidant, has been shown to selectively reduce the level of hydroxyl radicals and alleviate acute oxidative stress in many animal experiments. Hydrogen-rich saline provides a high concentration of hydrogen that can be easily and safely applied. Allogeneic hematopoietic stem-cell transplantation (HSCT) has been the most curative therapy for hematological malignancies. However, acute graft-versus-host disease (aGVHD) is the main cause of death in post-transplantation patients. In this study, we examined whether hydrogen-rich saline would show favorable effects on acute GVHD in mice.

Material/Methods

After lethal irradiation, BALB/c mice received bone marrow transplantation from C57BL/6 mice. Hydrogen-rich saline (5 ml/kg) was given to recipient mice in the hydrogen group once a day by intraperitoneal injection, and saline (5 ml/kg) was given to recipient mice in the saline group. Survival rates were monitored, clinical and pathological scores of aGVHD were determined after bone marrow transplantation (BMT), and the serum cytokine levels were examined on the 7^th day after BMT.

Result

This study proves that hydrogen-rich saline increased the survival rate, reduced clinical and histopathological scores of aGVHD, promoted the recovery of white blood cells, reduced the serum cytokine levels, and reversed tissue damage after transplantation in mice.

Conclusions

Hydrogen has potential as an effective and safe therapeutic agent in aGVHD.

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.

MiR-146a regulates the TRAF6/TNF-axis in donor T cells during GVHD

This study deciphers the regulatory role of miR-146a during GVHD in mice. In humans, the minor genotype of the SNP rs2910164, which reduces expression of miR-146a, was associated with higher GVHD severity.

Human leukocyte antigen DR surface expression on CD14+ monocytes during adverse events after hematopoietic stem cell transplantation

The human leukocyte antigen DR surface expression on CD14+ monocytes reflects the degree to which these cells have been activated. Given the central role monocytes and macrophages play in the immune system, a decreased human leukocyte antigen DR expression on CD14+ monocytes results in a hallmark of altered immune status during systemic inflammatory response syndrome. We hypothesize that human leukocyte antigen DR expression might be similarly altered after hematopoietic stem cell transplantation and during post-transplant complications. Using flow cytometry, this study investigates the human leukocyte antigen DR surface expression of CD14+ monocytes in 30 pediatric and young adult patients up to 1 year after hematopoietic stem cell transplantation. Normal values were derived from a control group of healthy children, adolescents, and young adults. Human leukocyte antigen DR expression decreased significantly prior and during bacterial infection or sepsis. By contrast, human leukocyte antigen DR expression levels were elevated before and at the time of viremia. Human leukocyte antigen DR expression was also elevated during acute graft-versus-host disease. In contrast, the expression was reduced when patients had hepatic veno-occlusive disease. A significant decrease of human leukocyte antigen DR expression was associated with a relapse of the underlying disease and before death. Human leukocyte antigen DR expression on CD14+ monocytes appears to be a promising parameter that might allow identification of patients at risk after hematopoietic stem cell transplantation.

Mesenchymal stromal cells infusions improve refractory chronic graft versus host disease through an increase of CD5+ regulatory B cells producing interleukin 10

Refractory chronic graft-versus-host disease (cGVHD) is a significant complication resulting from allogeneic hematopoietic stem cell transplantation (HSCT). Mesenchymal stromal cells (MSCs) have shown promise for treating refractory cGVHD, but the favorable effects of MSCs therapy in cGVHD are complex and not fully understood. In this prospective clinical study, 20 of 23 cGVHD patients had a complete response or partial response in a 12-month follow-up study. The most marked improvements in cGVHD symptoms were observed in the skin, oral mucosa and liver. Clinical improvement was accompanied by a significantly increased number of interleukin (IL)-10-producing CD5+ B cells. Importantly, CD5+ B cells from cGVHD patients showed increased IL-10 expression after MSCs treatment, which was associated with reduced inflammatory cytokine production by T cells. Mechanistically, MSCs could promote the survival and proliferation of CD5+ regulatory B cells (Bregs), and indoleamine 2, 3-dioxygenase partially participates in the MSC-mediated effects on Breg cells. Thus, CD5+ Breg cells may have an important role in the process of MSC-induced amelioration of refractory cGVHD and may provide new clues to reveal novel mechanisms of action for MSCs.

The role of pattern-recognition receptors in graft-versus-host disease and graft-versus-leukemia after allogeneic stem cell transplantation

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is the only treatment with curative potential for certain aggressive hematopoietic malignancies. Its success is limited by acute graft-versus-host disease (GVHD), a life-threatening complication that occurs when allo-reactive donor T cells attack recipient organs. There is growing evidence that microbes and innate pattern-recognition receptors (PRRs) such as toll-like receptors (TLR) and nod-like receptors (NLR) are critically involved in the pathogenesis of acute GVHD. Currently, a widely accepted model postulates that intensive chemotherapy and/or total-body irradiation during pre-transplant conditioning results in tissue damage and a loss of epithelial barrier function. Subsequent translocation of bacterial components as well as release of endogenous danger molecules stimulate PRRs of host antigen-presenting cells to trigger the production of pro-inflammatory cytokines (cytokine storm) that modulate T cell allo-reactivity against host tissues, but eventually also the beneficial graft-versus-leukemia (GVL) effect. Given the limitations of existing immunosuppressive therapies, a better understanding of the molecular mechanisms that govern GVHD versus GVL is urgently needed. This may ultimately allow to design modulators, which protect from GvHD but preserve donor T-cell attack on hematologic malignancies. Here, we will briefly summarize current knowledge about the role of innate immunity in the pathogenesis of GVHD and GVL following allo-HSCT.

The biology of graft-versus-host disease: experimental systems instructing clinical practice

The last 6 decades have seen major advances in the understanding of immunologic diseases, driven by preclinical animal models. Indeed, bone marrow transplantation (BMT) has its genesis in rodent models dating back to the 1950s. Allogeneic BMT and its major complication, graft-versus-host disease (GVHD), represent a paradigm for the translation of preclinical concepts into clinical practice. The appreciation that GVHD can be thought of as a stepwise escalation in immune activation characterized by eventual massive target tissue apoptosis has allowed the design of rational approaches to better manage patients. Here, we describe the pathophysiology of GVHD as defined in preclinical models, focusing on the successes and failures of this research to instruct and translate clinical practice. We also provide a commentary on the limitations of these models so that they may be better appreciated and addressed in future studies. Notable preclinical successes include the definition of modern immune suppression, reductions in conditioning intensity, posttransplant cyclophosphamide, and the promotion of regulatory T-cell reconstitution. New strategies including naïve T-cell depletion, focused cytokine and chemokine inhibition, and the blockade of costimulation now also appear highly promising and very likely to translate into patients in the near future.