Addition of interleukin-6 inhibition with tocilizumab to standard graft-versus-host disease prophylaxis after allogeneic stem-cell transplantation: a phase 1/2 trial

Novel approaches for preventing acute graft-versus-host disease after allogeneic hematopoietic stem cell transplantation

INTRODUCTION

Allogeneic hematopoietic stem cell transplantation (alloHSCT) offers potential curative treatment for a wide range of malignant and nonmalignant hematological disorders. However, its success may be limited by post-transplant acute graft-versus-host disease (aGVHD), a systemic syndrome in which donor's immune cells attack healthy tissues in the immunocompromised host. aGVHD is one of the main causes of morbidity and mortality after alloHSCT. Despite standard GVHD prophylaxis regimens, aGVHD still develops in approximately 40-60% of alloHSCT recipients.

AREAS COVERED

In this review, after a brief summary of current knowledge on the pathogenesis of aGVHD, the authors review the current combination of a calcineurin inhibitor with an antimetabolite with or without added anti-thymocyte globulin (ATG) and emerging strategies for GVHD prevention.

EXPERT OPINION

A new understanding of the involvement of cytokines, intracellular signaling pathways, epigenetics and immunoregulatory cells in GVHD pathogenesis will lead to new standards for aGVHD prophylaxis allowing better prevention of severe aGVHD without affecting graft-versus-tumor effects.

Emerging drugs for graft-versus-host disease

INTRODUCTION

Graft-versus-host disease (GVHD) leads to significant morbidity and mortality after allogeneic stem cell transplantation. While corticosteroids alone are adequate in some cases, they are often insufficient, leading to poor quality of life associated with the symptoms of disease, or mortality from infection and GVHD. Moreover, corticosteroids have significant side effects and often do not lead to durable responses. New therapies are needed to improve the development and progression of acute and chronic GVHD.

AREAS COVERED

We discuss the spectrum of emerging drugs for GVHD prevention and therapy. Cellular therapies will be briefly discussed. The available pre-clinical and clinical data regarding monoclonal antibodies, interleukin-2, alpha-1 antitrypsin, histone deacetylase inhibitors, tyrosine kinase inhibitors, and proteasome inhibitors will be reviewed.

EXPERT OPINION

Although therapies emerging for GVHD remain promising, most of these drugs are still in early phase clinical trials and require randomized comparisons before formal conclusions can be drawn. It is likely that in the near future some of these agents will show improvements in response when compared with corticosteroids alone. Although it is difficult to predict which of these agents will be most promising, alpha-1 antitrypsin, ruxolitinib and interleukin-2 have demonstrated encouraging results.

Alvocidib (flavopiridol) for the treatment of chronic lymphocytic leukemia

INTRODUCTION

Alvocidib, which has orphan drug designation in chronic lymphocytic leukemia (CLL) from the FDA and the EMA, is a plant-derived semisynthetic flavone that acts as a cyclin-dependent kinase inhibitor. It induces apoptosis in CLL cells in vitro and was introduced into clinical trials in CLL as an intravenous infusion in 1997, which proved disappointing. Since the drug avidly binds to plasma proteins, higher serum concentrations were required for clinical antileukemia activity than those suggested by in vitro studies. Subsequent studies utilizing bolus plus infusional doses revealed significant activity against CLL, even in patients with unfavorable characteristics. However, significant toxicity including high rates of major tumor lysis syndrome, cytokine release syndrome and secretory diarrhea were also observed.

AREAS COVERED

The chemistry, pharmacodynamics, pharmacokinetics and metabolism of alvocidib are briefly discussed and phase I-II studies in CLL are discussed in detail. To date, no phase III studies in CLL have been reported.

EXPERT OPINION

A number of much less toxic drugs with similar efficacy against CLL both with and without unfavorable cytogenetics have come to market. Furthermore, enthusiasm for the development of alvocidib as a single agent for the treatment of CLL has waned, primarily due to its toxicity.

Therapeutic targets and emerging treatment options in gastrointestinal acute graft-versus-host disease

Introduction

Graft-versus-host disease (GVHD) continues to be the major lethal complication of allogeneic hematopoietic stem cell transplantation (HCT) but the standard of care, high dose steroids, has not changed in 40 years. Approximately 50% of GVHD patients will develop steroid refractory disease, typically involving the gastrointestinal (GI) tract, which has a very poor prognosis. Newly developed GVHD biomarker-based risk scores provide the first opportunity to treat patients at the onset of symptoms according to risk of steroid failure. Furthermore, improvements in our understanding of the pathobiology of GVHD, its different signaling pathways, involved cytokines, and the role of post-translational and epigenetic modifications, has identified new therapeutic targets for clinical trials.

Areas covered

This manuscript summarizes the pathophysiology, diagnosis, staging, current and new targeted therapies for GVHD, with an emphasis on GI GVHD. A literature search on PubMed was undertaken and the most relevant references included.

Expert Opinion

The standard treatment for GVHD, high dose steroids, offers less than optimal outcomes as well as significant toxicities. Better treatments, especially for GI GVHD, are needed to reduce non-relapse mortality after allogeneic HCT. The identification of high risk patients through a biomarker-defined scoring system offers a personalized approach to a disease that still requires significant research attention.

Alloantigen presentation and graft-versus-host disease: fuel for the fire

Allogeneic stem cell transplantation (SCT) is a unique procedure, primarily in patients with hematopoietic malignancies, involving chemoradiotherapy followed by the introduction of donor hematopoietic and immune cells into an inflamed and lymphopenic environment. Interruption of the process by which recipient alloantigen is presented to donor T cells to generate graft-versus-host disease (GVHD) represents an attractive therapeutic strategy to prevent morbidity and mortality after SCT and has been increasingly studied in the last 15 years. However, the immune activation resulting in GVHD has no physiological equivalent in nature; alloantigen is ubiquitous, persists indefinitely, and can be presented by multiple cell types at numerous sites, often on incompatible major histocompatibility complex, and occurs in the context of intense inflammation early after SCT. The recognition that alloantigen presentation is also critical to the development of immunological tolerance via both deletional and regulatory mechanisms further adds to this complexity. Finally, GVHD itself appears capable of inhibiting the presentation of microbiological antigens by donor dendritic cells late after SCT that is mandatory for the establishment of effective pathogen-specific immunity. Here, we review our current understanding of alloantigen, its presentation by various antigen-presenting cells, subsequent recognition by donor T cells, and the potential of therapeutic strategies interrupting this disease-initiating process to modify transplant outcome.

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

Allogeneic haematopoietic stem cell transplantation (HCT) is a potent immunotherapy with curative potential for several haematological disorders. Overcoming the immunological barrier of acute graft-versus-host disease (GVHD) remains a fundamental impediment to expanding the efficacy of HCT. GVHD reflects a complex pathological interaction between the innate and adaptive immune systems of the host and donor. Over the past decade there has been a tremendous advancement in our understanding of the cellular and molecular underpinnings of this devastating disease. In this review, we cover several recently appreciated facets of GVHD pathogenesis including novel extracellular mediators of inflammation, immune subsets, intracellular signal transduction, post-translation modifications and epigenetic regulation. We begin to develop general themes regarding the immunological pathways in GVHD pathogenesis, discuss critical outstanding questions, and explore new avenues for GVHD treatment and prevention.

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.

Translational opportunities for targeting the Th17 axis in acute graft-vs.-host disease

Allogeneic stem cell transplantation (allo-SCT) is a curative therapy for different life-threatening malignant and non-malignant hematologic disorders. Acute graft-vs.-host disease (aGVHD) and particularly gastrointestinal aGVHD remains a major source of morbidity and mortality following allo-SCT, which limits the use of this treatment in a broader spectrum of patients. Better understanding of aGVHD pathophysiology is indispensable to identify new therapeutic targets for aGVHD prevention and therapy. Growing amount of data suggest a role for T helper (Th)17 cells in aGVHD pathophysiology. In this review, we will discuss the current knowledge in this area in animal models and in humans. We will then describe new potential treatments for aGVHD along the Th17 axis.

All pain, no gain: Tc17 phantoms in GVHD

Elusive CD8+ T cells that transiently secrete interleukin (IL)-17 cause graft-versus-host disease (GVHD) but do not contribute to beneficial graft-versus-leukemia (GVL) responses, as reported by Gartlan et al in this issue of Blood. GVHD remains a lethal and morbid complication of allogeneic bone marrow transplantation, but GVHD is tightly linked to beneficial GVL effects, and removal of donor T cells that cause GVHD also diminish GVL, leading to greater relapse after bone marrow transplantation (BMT). This elegant paper from the laboratory of Geoffrey Hill has identified a rare “night fury” T-cell subset that causes much pain with no gain, a finding that may take us one large step closer to the long sought after goal of separating GVL and GVHD.

Murine allogeneic CD19 CAR T cells harbor potent antileukemic activity but have the potential to mediate lethal GVHD

Acute lymphoblastic leukemia (ALL) persisting or relapsing following bone marrow transplantation (BMT) has a dismal prognosis. Success with chimeric antigen receptor (CAR) T cells offers an opportunity to treat these patients with leukemia-redirected donor-derived T cells, which may be more functional than T cells derived from patients with leukemia but have the potential to mediate graft-versus-host disease (GVHD). We, together with others, have previously demonstrated tumor-specific T-cell dysfunction in the allogeneic environment. Here, we studied CAR T-cell function following BMT using an immunocompetent murine model of minor mismatched allogeneic transplantation followed by donor-derived CD19-CAR T cells. Allogeneic donor-derived CD19-CAR T cells eliminated residual ALL with equal potency to those administered after syngeneic BMT. Surprisingly, allogeneic CAR T cells mediated lethal acute GVHD with early mortality, which is atypical for this minor mismatch model. We demonstrated that both allogeneic and syngeneic CAR T cells show initial expansion as effector T cells, with a higher peak but rapid deletion of allogeneic CAR T cells. Interestingly, CAR-mediated acute GVHD was only seen in the presence of leukemia, suggesting CAR-target interactions induced GVHD. Indeed, serum interleukin (IL)-6 was elevated only in the presence of both leukemia and CAR T cells, and IL-6 neutralization ameliorated the severity of GVHD in a delayed donor lymphocyte infusion model. Finally, allogeneic CD4(+) CAR T cells were responsible for GVHD, which correlated with their ability to produce IL-6 upon CAR stimulation. Altogether, we demonstrate that donor-derived allogeneic CAR T cells are active but have the capacity to drive GVHD.

MicroRNA-181a, a potential diagnosis marker, alleviates acute graft versus host disease by regulating IFN-γ production

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a valuable therapeutic strategy for a wide variety of diseases. Acute graft-versus-host disease (aGVHD) is a major complication in up to 75% of allo-HSCT. The absence of a reliable predicative marker for aGVHD onset prevents preemptive treatment and impedes widespread and successful application of this therapy. In this study we found that after allo-HSCT, the levels of miR-181a were reduced significantly prior to the onset of aGVHD. More importantly, the degree of its reduction correlated with the severity of aGVHD. Mechanistically, miR-181a affects the function of T lymphocytes by down-regulating IFN-γ in a dose-dependent manner. Meanwhile, we confirmed that miR-181a can effectively preserve the anti-leukemic effect in vitro. Using a murine allo-HSCT model, we demonstrated that murine miR-181b, the human miR-181a homolog, served as an effective predictor of aGVHD. Moreover, expression of this microRNA ameliorated the severity of aGVHD. Collectively, these results show that the level of miR-181a may serve as a reliable marker for the diagnosis and prognosis the onset of aGVHD. Am. J. Hematol. 90:998-1007, 2015. © 2015 Wiley Periodicals, Inc.

Fulminant skin GvHD with a cytokine pattern resemblant of cytokine release syndrome successfully treated with multimodal immunosuppression including tocilizumab

Acute Graft-versus-Host-Disease (GvHD) is a potentially life-threatening complication after allogeneic stem cell transplantation. If not treated early and adequately, the complex immunological mechanisms may lead to a self-perpetuating cycle of alloreactivity, which is then associated with a high mortality. Here we assessed the cytokine profile on a daily basis in a patient with grade 4 skin GvHD, demonstrating a signature resembling cytokine-release-syndrome. After multimodal immunosuppressive intervention, including treatment with the IL6 receptor-blocking antibody tocilizumab, the severe clinical symptoms unexpectedly resolved within 48 hr.

Acute Graft-versus-Host Disease: Novel Biological Insights

Graft-versus-host disease (GVHD) continues to be a leading cause of morbidity and mortality after allogeneic hematopoietic stem cell transplantation. Recent insights into intestinal homeostasis and uncovering of new pathways and targets have greatly reconciled our understanding of GVHD pathophysiology and will reshape contemporary GVHD prophylaxis and treatment. Gastrointestinal (GI) GVHD is the major cause of mortality. Emerging data indicate that intestinal stem cells (ISCs) and their niche Paneth cells are targeted, resulting in dysregulation of the intestinal homeostasis and microbial ecology. The microbiota and their metabolites shape the immune system and intestinal homeostasis, and they may alter host susceptibility to GVHD. Protection of the ISC niche system and modification of the intestinal microbiota and metabolome to restore intestinal homeostasis may, thus, represent a novel approach to modulate GVHD and infection. Damage to the intestine plays a central role in amplifying systemic GVHD by propagating a proinflammatory cytokine milieu. Molecular targeting to inhibit kinase signaling may be a promising approach to treat GVHD, ideally via targeting the redundant effect of multiple cytokines on immune cells and enterocytes. In this review, we discuss insights on the biology of GI GVHD, interaction of microflora and metabolome with the hosts, identification of potential new target organs, and identification and targeting of novel T cell-signaling pathways. Better understanding of GVHD biology will, thus, pave a way to develop novel treatment strategies with great clinical benefits.

Pathogenesis of Myeloproliferative Neoplasms: Role and Mechanisms of Chronic Inflammation

Myeloproliferative neoplasms (MPNs) are a heterogeneous group of clonal diseases characterized by the excessive and chronic production of mature cells from one or several of the myeloid lineages. Recent advances in the biology of MPNs have greatly facilitated their molecular diagnosis since most patients present with mutation(s) in the JAK2, MPL, or CALR genes. Yet the roles played by these mutations in the pathogenesis and main complications of the different subtypes of MPNs are not fully elucidated. Importantly, chronic inflammation has long been associated with MPN disease and some of the symptoms and complications can be linked to inflammation. Moreover, the JAK inhibitor clinical trials showed that the reduction of symptoms linked to inflammation was beneficial to patients even in the absence of significant decrease in the JAK2-V617F mutant load. These observations suggested that part of the inflammation observed in patients with JAK2-mutated MPNs may not be the consequence of JAK2 mutation. The aim of this paper is to review the different aspects of inflammation in MPNs, the molecular mechanisms involved, the role of specific genetic defects, and the evidence that increased production of certain cytokines depends or not on MPN-associated mutations, and to discuss possible nongenetic causes of inflammation.

A Critical Care and Transplantation-Based Approach to Acute Respiratory Failure after Hematopoietic Stem Cell Transplantation in Children

Acute respiratory failure contributes significantly to nonrelapse mortality after allogeneic hematopoietic stem cell transplantation. Although there is a trend of improved survival over time, mortality remains unacceptably high. An understanding of the pathophysiology of early respiratory failure, opportunities for targeted therapy, assessment of the patient at risk, optimal use of noninvasive positive pressure ventilation, strategies to improve alveolar recruitment, appropriate fluid management, care of the patient with chronic lung disease, and importantly, a team approach between critical care and transplantation services may improve outcomes.

•

Outcomes from acute respiratory failure after hematopoietic stem cell transplantation remain unacceptably high.

•

The review focuses on strategies to improve these outcomes.

Tc17 cells are a proinflammatory, plastic lineage of pathogenic CD8+ T cells that induce GVHD without antileukemic effects

Donor-derived Tc17 cells differentiate early after allogeneic transplant in response to IL-6 and alloantigen presentation by host DCs. Tc17 are highly proinflammatory and pathogenic posttransplant, but exert limited or no GVL activity.

Approaches for the prevention of graft-versus-host disease following hematopoietic cell transplantation

Allogeneic hematopoietic cell transplantation (HCT) is an important therapeutic option for malignant and non-malignant diseases, but the more widespread application of the therapy remains limited by the occurrence of graft versus host disease (GVHD). GVHD results from immune-mediated injury by donor immune cells against tissues in the HCT recipient, and can be characterized as acute or chronic depending on the time of onset and site of organ involvement. The majority of efforts have focused on GVHD prevention. Calcineurin inhibitors are the most widely used agents and are included in almost all regimens. Despite current prophylaxis strategies, 40-70% of patients remain at risk for developing GVHD. Herein, we review standard and emerging therapies used in GVHD management.

Donor colonic CD103+ dendritic cells determine the severity of acute graft-versus-host disease

The primacy of the gastrointestinal (GI) tract in dictating the outcome of graft-versus-host disease (GVHD) is broadly accepted; however, the mechanisms controlling this effect are poorly understood. Here, we demonstrate that GVHD markedly enhances alloantigen presentation within the mesenteric lymph nodes (mLNs), mediated by donor CD103(+)CD11b(-) dendritic cells (DCs) that migrate from the colon under the influence of CCR7. Expansion and differentiation of donor T cells specifically within the mLNs is driven by profound levels of alloantigen, IL-12, and IL-6 promoted by Toll-like receptor (TLR) and receptor for advanced glycation end products (RAGE) signals. Critically, alloantigen presentation in the mLNs imprints gut-homing integrin signatures on donor T cells, leading to their emigration into the GI tract where they mediate fulminant disease. These data identify a critical, anatomically distinct, donor DC subset that amplifies GVHD. We thus highlight multiple therapeutic targets and the ability of GVHD, once initiated by recipient antigen-presenting cells, to generate a profound, localized, and lethal feed-forward cascade of donor DC-mediated indirect alloantigen presentation and cytokine secretion within the GI tract.

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.

Donor colonic CD103+ dendritic cells determine the severity of acute graft-versus-host disease

Koyama et al. show that GVHD markedly enhances alloantigen presentation within the mesenteric lymph nodes, mediated by donor CD103⁺CD11b⁻ DCs that migrate from the colon under the influence of CCR7. This antigen presentation imprints gut-homing integrin signatures on donor T cells, leading to their migration to the GI tract where they mediate fulminant disease.

The primacy of the gastrointestinal (GI) tract in dictating the outcome of graft-versus-host disease (GVHD) is broadly accepted; however, the mechanisms controlling this effect are poorly understood. Here, we demonstrate that GVHD markedly enhances alloantigen presentation within the mesenteric lymph nodes (mLNs), mediated by donor CD103⁺CD11b⁻ dendritic cells (DCs) that migrate from the colon under the influence of CCR7. Expansion and differentiation of donor T cells specifically within the mLNs is driven by profound levels of alloantigen, IL-12, and IL-6 promoted by Toll-like receptor (TLR) and receptor for advanced glycation end products (RAGE) signals. Critically, alloantigen presentation in the mLNs imprints gut-homing integrin signatures on donor T cells, leading to their emigration into the GI tract where they mediate fulminant disease. These data identify a critical, anatomically distinct, donor DC subset that amplifies GVHD. We thus highlight multiple therapeutic targets and the ability of GVHD, once initiated by recipient antigen-presenting cells, to generate a profound, localized, and lethal feed-forward cascade of donor DC–mediated indirect alloantigen presentation and cytokine secretion within the GI tract.

The primacy of IL-6 in IPS?

In this issue of Blood, Varelias and colleagues demonstrate a central role of interleukin (IL)-6 in idiopathic pneumonia syndrome (IPS) after allogeneic stem cell transplantation (SCT) in both mice and humans.

Outcomes of acute leukemia patients transplanted with naive T cell-depleted stem cell grafts

BACKGROUND

Graft-versus-host disease (GVHD) is a major cause of morbidity and mortality following allogeneic hematopoietic stem cell transplantation (HCT). In mice, naive T cells (TN) cause more severe GVHD than memory T cells (TM). We hypothesized that selective depletion of TN from human allogeneic peripheral blood stem cell (PBSC) grafts would reduce GVHD and provide sufficient numbers of hematopoietic stem cells and TM to permit hematopoietic engraftment and the transfer of pathogen-specific T cells from donor to recipient, respectively.

METHODS

In a single-arm clinical trial, we transplanted 35 patients with high-risk leukemia with TN-depleted PBSC grafts following conditioning with total body irradiation, thiotepa, and fludarabine. GVHD prophylactic management was with tacrolimus immunosuppression alone. Subjects received CD34-selected PBSCs and a defined dose of TM purged of CD45RA+ TN. Primary and secondary objectives included engraftment, acute and chronic GVHD, and immune reconstitution.

RESULTS

All recipients of TN-depleted PBSCs engrafted. The incidence of acute GVHD was not reduced; however, GVHD in these patients was universally corticosteroid responsive. Chronic GVHD was remarkably infrequent (9%; median follow-up 932 days) compared with historical rates of approximately 50% with T cell-replete grafts. TM in the graft resulted in rapid T cell recovery and transfer of protective virus-specific immunity. Excessive rates of infection or relapse did not occur and overall survival was 78% at 2 years.

CONCLUSION

Depletion of TN from stem cell allografts reduces the incidence of chronic GVHD, while preserving the transfer of functional T cell memory.

TRIAL REGISTRATION

ClinicalTrials.gov (NCT 00914940).

A concise review on extracorporeal photochemotherapy: Where we began and where we are now and where are we going!

Currently, more than 1080 peer-reviewed papers are displayed on PubMed when initiating a search for therapeutic indications and mechanisms of action of extracorporeal photochemotherapy (ECP). This concise review focuses mainly on some prevalent and traditional treatment-resistant disorders with an emphasis on immunologic complications emerging from stem cell and solid organ transplantation.

Immune biomarkers: the promises and pitfalls of personalized medicine

Substantial progress in molecular immunology, coupled with an increasing focus on translational research and an enthusiasm for personalized medicine, has resulted in a rapid expansion in the field of immune biomarkers in recent years. In this Science and Society article, we provide a conceptual overview of the field and discuss the progress that has been made so far, as well as the future potential in the context of the scientific, logistical, financial, legal and ethical framework within which this research is being carried out and translated into clinical use.

Advances and challenges in immunotherapy for solid organ and hematopoietic stem cell transplantation

Although major advances have been made in solid organ and hematopoietic stem cell transplantation in the last 50 years, big challenges remain. This review outlines the current immunological limitations for hematopoietic stem cell and solid organ transplantation and discusses new immune-modulating therapies in preclinical development and in clinical trials that may allow these obstacles to be overcome.

Lung parenchyma-derived IL-6 promotes IL-17A-dependent acute lung injury after allogeneic stem cell transplantation

Idiopathic pneumonia syndrome (IPS) is a relatively common, frequently fatal clinical entity, characterized by noninfectious acute lung inflammation following allogeneic stem cell transplantation (SCT), the mechanisms of which are unclear. In this study, we demonstrate that immune suppression with cyclosporin after SCT limits T-helper cell (Th) 1 differentiation and interferon-γ secretion by donor T cells, which is critical for inhibiting interleukin (IL)-6 generation from lung parenchyma during an alloimmune response. Thereafter, local IL-6 secretion induces donor alloantigen-specific Th17 cells to preferentially expand within the lung, and blockade of IL-17A or transplantation of grafts lacking the IL-17 receptor prevents disease. Studies using IL-6(-/-) recipients or IL-6 blockade demonstrate that IL-6 is the critical driver of donor Th17 differentiation within the lung. Importantly, IL-6 is also dysregulated in patients undergoing clinical SCT and is present at very high levels in the plasma of patients with IPS compared with SCT recipients without complications. Furthermore, at the time of diagnosis, plasma IL-6 levels were higher in a subset of IPS patients who were nonresponsive to steroids and anti-tumor necrosis factor therapy. In sum, pulmonary-derived IL-6 promotes IPS via the induction of Th17 differentiation, and strategies that target these cytokines represent logical therapeutic approaches for IPS.

Graft-versus-host disease versus graft-versus-leukemia

Graft-versus-host disease (GVHD) is a significant clinical problem after allogenic hematopoietic cell transplantation (HCT) associated with substantial morbidity and mortality that limits the potential utility of transplantation. Associated with GVHD is the well-recognized phenomenon of the graft-versus-leukemia (GVL) effect that results in reduced risk of disease relapse. GVL effects have been observed after treatment for a broad range of hematological malignancies. Both GVHD and GVL are the results of T cell-effector functions that frames a major question in the field of how linked are these two phenomena. A major goal of basic science and translational research has been to develop strategies to reduce the risk of GVHD while maintaining or enhancing GVL. In this review, a number of different strategies developed from preclinical animal models will be explored with a focus on those approaches that have been extended to the clinic in an attempt to achieve this goal. Needless to say, there is no proven strategy; however, with the use of modern technology and clinical translation, there has been substantial progress toward this goal of reducing the risks of GVHD while promoting and enhancing GVL responses.