Cytolytic pathways in haematopoietic stem-cell transplantation

Inhibition of histone methylation arrests ongoing graft-versus-host disease in mice by selectively inducing apoptosis of alloreactive effector T cells

Histone methylation is thought to be important for regulating Ag-driven T-cell responses. However, little is known about the effect of modulating histone methylation on inflammatory T-cell responses. We demonstrate that in vivo administration of the histone methylation inhibitor 3-deazaneplanocin A (DZNep) arrests ongoing GVHD in mice after allogeneic BM transplantation. DZNep caused selective apoptosis in alloantigen-activated T cells mediating host tissue injury. This effect was associated with the ability of DZNep to selectively reduce trimethylation of histone H3 lysine 27, deplete the histone methyltransferase Ezh2 specific to trimethylation of histone H3 lysine 27, and activate proapoptotic gene Bim repressed by Ezh2 in antigenic-activated T cells. In contrast, DZNep did not affect the survival of alloantigen-unresponsive T cells in vivo and naive T cells stimulated by IL-2 or IL-7 in vitro. Importantly, inhibition of histone methylation by DZNep treatment in vivo preserved the antileukemia activity of donor T cells and did not impair the recovery of hematopoiesis and lymphocytes, leading to significantly improved survival of recipients after allogeneic BM transplantation. Our findings indicate that modulation of histone methylation may have significant implications in the development of novel approaches to treat ongoing GVHD and other T cell-mediated inflammatory disorders in a broad context.

Immunoregulatory effects of human dental pulp-derived stem cells on T cells: comparison of transwell co-culture and mixed lymphocyte reaction systems

BACKGROUND AIMS. Studies performed using human and animal models have indicated the immunoregulatory capability of mesenchymal stromal cells in several lineages. We investigated whether human dental pulp-derived stem cells (hDP-SC) have regulatory effects on phytohemagglutinin (PHA)-activated CD3(+) T cells. We aimed to define the regulatory mechanisms associated with hDP-SC that occur in mixed lymphocyte reaction (MLR) and transwell systems with PHA-CD3(+) T cells and hDP-SC at a ratio of 1:1. METHODS. Proliferation, apoptosis and pro- and anti-inflammatory cytokines of PHA-CD3(+)T cells, the expression of Regulatory T cells (Treg) markers and some regulatory factors related to hDP-SC, were studied in Both transwell and MLR are co-cultures systems. RESULTS. Anti-proliferative and apoptotic effects of hDP-SC were determined in co-culture systems. Elevated expression levels of human leukocyte antigen (HLA)-G, hepatocyte growth factor (HGF)-β1, intracellular adhesion molecule (ICAM-1)-1, interleukin (IL)-6, IL-10, transforming growth factor (TGF)-β1, vascular adhesion molecule (VCAM)-1 and vascular endothelial growth factor (VEGF) by hDP-SC were detected in the co-culture systems. We observed decreased expression levels of pro-inflammatory cytokines [interferon (IFN)-γ, IL-2, IL-6 receptor (R), IL-12, Interleukin-17A (IL-17A), tumor necrosis factor (TNF)-α] and increased expression levels of anti-inflammatory cytokine [inducible protein (IP)-10] from PHA-CD3(+) T cells in the transwell system. Expression of Treg (CD4(+) CD25(+) Foxp3(+)) markers was significantly induced by hDP-SC in both co-culture systems. We observed apoptosis of PHA-CD3(+) T cells with 24 h using time-lapse camera photographs and active caspase labeling; it is likely that paracrine soluble factors and molecular signals secreted by hDP-SC led this apoptosis. CONCLUSIONS. We suggest that hDP-SC have potent immunoregulatory functions because of their soluble factors and cytokines via paracrine mechanisms associated with PHA-CD3(+) T cells, which could contribute to clinical therapies.

Graft-versus-leukemia (GVL) against mouse blast-crisis chronic myelogenous leukemia (BC-CML) and chronic-phase chronic myelogenous leukemia (CP-CML): shared mechanisms of T cell killing, but programmed death ligands render CP-CML and not BC-CML GVL resistant

Graft-versus-leukemia (GVL) against chronic-phase chronic myelogenous leukemia (CP-CML) is potent, but it is less efficacious against acute leukemias and blast-crisis chronic myelogenous leukemia (BC-CML). The mechanisms underlying GVL resistance are unknown. Previously, we found that alloreactive T cell targeting of GVL-sensitive bcr-abl-induced mouse CP-CML (mCP-CML) required TCR-MHC interactions and that multiple and redundant killing mechanisms were in play. To better understand why BC-CML is resistant to GVL, we performed a comprehensive analysis of GVL against mouse BC-CML (mBC-CML) induced by the retroviral transfer of the bcr-abl and NUP98/HOXA9 fusion cDNAs. Like human BC-CML, mBC-CML was GVL resistant, and this was not due to accelerated kinetics or a greater leukemia burden. To study T cell recognition and killing mechanisms, we generated a panel of gene-deficient leukemias by transducing bone marrow from gene-deficient mice. T cell target recognition absolutely required that mBC-CML cells express MHC molecules. GVL against both mCP-CML and mBC-CML required leukemia expression of ICAM-1. We hypothesized that mBC-CML would be resistant to some of the killing mechanisms sufficient to eliminate mCP-CML, but we found instead that the same mechanisms were effective against both types of leukemia, because GVL was similar against wild-type or mBC-CML genetically lacking Fas, TRAIL-R, Fas/TRAIL-R, or TNFR1/R2 or when donor T cells were perforin(-/-). However, mCP-CML, but not mBC-CML, relied on expression of programmed death-1 ligands 1 and 2 (PD-L1/L2) to resist T cell killing, because only GVL against mCP-CML was augmented when leukemias lacked PD-L1/L2. Thus, mBC-CML cells have cell-intrinsic mechanisms, distinct from mCP-CML cells, which protect them from T cell killing.

Abrogation of donor T-cell IL-21 signaling leads to tissue-specific modulation of immunity and separation of GVHD from GVL

IL-21 is a proinflammatory cytokine produced by Th17 cells. Abrogation of IL-21 signaling has recently been shown to reduce GVHD while retaining graft-versus-leukemia/lymphoma (GVL) responses. However, the mechanisms by which IL-21 may lead to a separation of GVHD and GVL remain incompletely understood. In a murine MHC-mismatched BM transplantation model, we observed that IL-21 receptor knockout (IL-21R KO) donor T cells mediate decreased systemic and gastrointestinal GVHD in recipients of a transplant. This reduction in GVHD was associated with expansion of transplanted donor regulatory T cells and with tissue-specific modulation of Th-cell function. IL-21R KO and wild-type donor T cells showed equivalent alloactivation, but IL-21R KO T cells showed decreased infiltration and inflammatory cytokine production within the mesenteric lymph nodes. However, Th-cell cytokine production was maintained peripherally, and IL-21R KO T cells mediated equivalent immunity against A20 and P815 hematopoietic tumors. In summary, abrogation of IL-21 signaling in donor T cells leads to tissue-specific modulation of immunity, such that gastrointestinal GVHD is reduced, but peripheral T-cell function and GVL capacity are retained. IL-21 is thus an exciting target for therapeutic intervention and improvement of clinical transplantation outcomes.

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

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

HDAC inhibition and graft versus host disease

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

Kinetics of CD4+ and CD8alpha+ T-cell subsets in graft-versus-host reaction (GVHR) in ginbuna crucian carp Carassius auratus langsdorfii

We have previously demonstrated the presence of graft-versus-host reaction (GVHR) in fish employing a model system of clonal triploid ginbuna and tetraploid ginbuna-goldfish hybrids. To elucidate the role of CD8alpha+ T cells in the induction of GVHR, we investigate the kinetics of CD4+ and CD8+ T-cell subsets in GVHR along with the pathological changes associated with GVH disease (GVHD) in ginbuna. GVHR was not induced with a leukocyte fraction lacking CD8alpha+ T cells separated by magnetic cell sorting. Ploidy and immunofluorescence analysis revealed that CD4+ and CD8alpha+ T cells from sensitized donors greatly increased in the host trunk kidney, constituting more than 80% of total cells 1-2 weeks after donor cell injection, while those from non-sensitized donors constituted less than 50% of cells present. The increase of CD4+ T cells was greater and more rapid than that of CD8alpha+ T cells. The number of donor CD4+ and CD8alpha+ T cells was highest in trunk kidney followed by spleen. Increases in donor CD4+ and CD8alpha+ T cells were also found in liver and PBL, although the percentages were not as high. Pathologic changes similar to those in human and murine acute GVHD were observed in the lymphoid organs as well as target organs such as skin, liver and intestine, including the destruction of cells and tissues and massive leukocyte infiltration. The pathologic changes became more severe with the increase of CD8alpha+ T cells. These results suggest that donor-derived CD8alpha+ T cells play essential roles for the induction of acute GVHR/D in teleosts as in mammals.

Notch signaling is a critical regulator of allogeneic CD4+ T-cell responses mediating graft-versus-host disease

Graft-versus-host disease (GVHD) remains the major barrier to the success of allogeneic hematopoietic stem cell transplantation (HSCT). GVHD is caused by donor T cells that mediate host tissue injury through multiple inflammatory mechanisms. Blockade of individual effector molecules has limited efficacy in controlling GVHD. Here, we report that Notch signaling is a potent regulator of T-cell activation, differentiation, and function during acute GVHD. Inhibition of canonical Notch signaling in donor T cells markedly reduced GVHD severity and mortality in mouse models of allogeneic HSCT. Although Notch-deprived T cells proliferated and expanded in response to alloantigens in vivo, their ability to produce interleukin-2 and inflammatory cytokines was defective, and both CD4(+) and CD8(+) T cells failed to up-regulate selected effector molecules. Notch inhibition decreased the accumulation of alloreactive T cells in the intestine, a key GVHD target organ. However, Notch-deprived alloreactive CD4(+) T cells retained significant cytotoxic potential and antileukemic activity, leading to improved overall survival of the recipients. These results identify Notch as a novel essential regulator of pathogenic CD4(+) T-cell responses during acute GVHD and suggest that Notch signaling in T cells should be investigated as a therapeutic target after allogeneic HSCT.

Pathogenesis and management of graft-versus-host disease

Allogeneic hematopoietic cell transplantation (HCT) is an important therapeutic option for various malignant and nonmalignant conditions. As allogeneic HCT continues to increase, greater attention is given to improvements in supportive care, infectious prophylaxis, immunosuppressive medications, and DNA-based tissue typing. However, graft versus host disease (GVHD) remains the most frequent and serious complication following allogeneic HCT and limits the broader application of this important therapy. Recent advances in the understanding of the pathogenesis of GVHD have led to new approaches to its management, including using it to preserve the graft versus leukemia effect following allogeneic transplant. This article reviews the important elements in the complex immunologic interactions involving cytokine networks, chemokine gradients, and the direct mediators of cellular cytotoxicity that cause clinical GVHD, and discusses the risk factors and strategies for management of GVHD.

Recurrent spontaneous gastrointestinal graft-versus-host disease in autologous hematopoietic stem cell transplantation

Acute graft-versus-host disease (GVHD) is a major complication after allogeneic stem cell transplantation (SCT). A similar manifestation involving skin, gastrointestinal (GI) mucosa, and liver can occur after autologous hematopoietic SCT (autoHSCT), either spontaneously or after treatment with cyclosporine or interferon. Severity of spontaneous GI GVHD among patients treated with autoHSCT is variable. Recurrent spontaneous GI GVHD induced by succeeding cycles of chemotherapy has rarely been reported and is poorly understood. Enteric-coated budesonide has been studied extensively in Crohn's disease, and beclomethasone has been studied in GI GVHD. There are no comparative studies between these drugs for GI GVHD. Furthermore, GI GVHD has to be considered when microbiologic workup remains negative during the workup of persistent diarrhea in autoHSCT. Endoscopic appearances can be normal, and pathologic diagnosis is essential. Further research into risk factors involving type of chemotherapy, interval between chemotherapies, and gene polymorphisms have to be considered for better understanding of autologous GVHD. We report for the first time a patient with spontaneous recurrent GI GVHD after autoHSCT for multiple myeloma with predominant lower GI symptoms and excellent response to enteric-coated budesonide therapy.

Allogeneic haematopoietic stem cell transplantation: individualized stem cell and immune therapy of cancer

The year 2009 marked the fiftieth anniversary of the first successful allogeneic haematopoietic stem cell transplant (HSCT). The field of HSCT has pioneered some of the most exciting areas of research today. HSCT was the original stem cell therapy, the first cancer immune therapy and the earliest example of individualized cancer therapy. In this Timeline article we review the history of the development of HSCT and major advances made in the past 50 years. We highlight accomplishments made by researchers who continue to strive to improve outcomes for patients and increase the availability of this potentially life-saving therapy for patients with otherwise incurable malignancies.

NCI First International Workshop on The Biology, Prevention, and Treatment of Relapse After Allogeneic Hematopoietic Stem Cell Transplantation: Report from the Committee on the Biology Underlying Recurrence of Malignant Disease following Allogeneic HSCT: Graft-versus-Tumor/Leukemia Reaction

The success of allogeneic hematopoietic stem cell transplantation (HSCT) depends on the infusion of benign stem cells as well as lymphocytes capable of participating in a graft-versus-tumor/leukemia (GVL) reaction. Clinical proof of concept is derived from studies showing increased relapse after the infusion of lymphocyte depleted hematopoietic grafts as well as the therapeutic efficacy of donor lymphocyte infusions without chemotherapy to treat relapse in some diseases. Despite this knowledge, relapse after allogeneic HSCT is common with rates approaching 40% in those with high-risk disease. In this review, we cover the basic biology and potential application to exploit adaptive T cell responses, minor histocompatibility antigens, contraction and suppression mechanisms that hinder immune responses, adaptive B cell responses and innate NK cell responses, all orchestrated in a GVL reaction. Optimal strategies to precisely balance immune responses to favor GVL without harmful graft-versus-host disease (GVHD) are needed to protect against relapse, treat persistent disease and improve disease-free survival after HSCT.

The cytolytic molecules Fas ligand and TRAIL are required for murine thymic graft-versus-host disease

Thymic graft-versus-host disease (tGVHD) can contribute to profound T cell deficiency and repertoire restriction after allogeneic BM transplantation (allo-BMT). However, the cellular mechanisms of tGVHD and interactions between donor alloreactive T cells and thymic tissues remain poorly defined. Using clinically relevant murine allo-BMT models, we show here that even minimal numbers of donor alloreactive T cells, which caused mild nonlethal systemic graft-versus-host disease, were sufficient to damage the thymus, delay T lineage reconstitution, and compromise donor peripheral T cell function. Furthermore, to mediate tGVHD, donor alloreactive T cells required trafficking molecules, including CCR9, L selectin, P selectin glycoprotein ligand-1, the integrin subunits alphaE and beta7, CCR2, and CXCR3, and costimulatory/inhibitory molecules, including Ox40 and carcinoembryonic antigen-associated cell adhesion molecule 1. We found that radiation in BMT conditioning regimens upregulated expression of the death receptors Fas and death receptor 5 (DR5) on thymic stromal cells (especially epithelium), while decreasing expression of the antiapoptotic regulator cellular caspase-8-like inhibitory protein. Donor alloreactive T cells used the cognate proteins FasL and TNF-related apoptosis-inducing ligand (TRAIL) (but not TNF or perforin) to mediate tGVHD, thereby damaging thymic stromal cells, cytoarchitecture, and function. Strategies that interfere with Fas/FasL and TRAIL/DR5 interactions may therefore represent a means to attenuate tGVHD and improve T cell reconstitution in allo-BMT recipients.

New perspectives on the biology of acute GVHD

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

Relapse after allogeneic hematopoietic cell therapy

Disease relapse remains a major cause of mortality following allogeneic hematopoietic cell transplantation (HCT). Over the past decade, our understanding of the biology underlying the graft-versus-tumor/leukemia (GVT) effect has increased greatly; however, several other factors affect the occurrence and outcome of relapse, including conditioning regimen, type of allograft, and the histology, status, and sensitivity to chemotherapy of the disease being treated. The mainstay of relapse treatment is donor lymphocyte infusion (DLI), but the efficacy of DLI is quite variable depending on disease histology and state. As such, there is a significant need for novel therapies and strategies for relapse following allogeneic HCT, particularly in patients for whom DLI is not an option. The National Cancer Institute is sponsoring an international workshop to address issues and research questions relative to the biology, natural history, prevention, and treatment of relapse following allogeneic HCT.

Superagonistic CD28 stimulation of allogeneic T cells protects from acute graft-versus-host disease

Acute graft-versus-host disease (aGVHD) often precludes successful immunotherapy of hematologic malignancies with allogeneic T cells. Therefore, we investigated the effect of immunomodulatory superagonistic anti-CD28 monoclonal antibodies (CD28-SA) on the capacity of allogeneic T cells to mediate both aGVHD and the protective graft-versus-tumor (GVT) response. In vivo pretreatment of donor C57BL/6 mice or short-term in vitro culture of donor lymph node cells with a CD28-SA efficiently protected BALB/c recipient mice from aGVHD. This protection strongly relied on the presence of CD28-SA-activated CD4+ CD25+ Foxp3+ regulatory T cells in the donor T-cell inoculum. With respect to the GVT response, CD28-SA-prestimulated T cells were still as potent in clearing lymphoma cells as were T cells without CD28-SA preactivation. Taken together, our data suggest that CD28-SA stimulation of bulk leukocyte cultures in vitro markedly increases the therapeutic window for adoptive immunotherapy with allogeneic T cells in vivo.

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

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

Emerging drugs for acute graft-versus-host disease

The number of allogeneic hematopoietic cell transplantations (HCT) continues to increase. More than 15,000 allogeneic transplantations are performed annually. The graft-versus-leukemia/tumor effect during allogeneic HCT effectively eradicates many hematological malignancies. The development of novel strategies that use donor leukocyte infusions, nonmyeloablative conditioning and umbilical cord blood transplantation have helped expand the indications for allogeneic HCT over the past several years, especially among older patients. Yet the major complication of allogeneic HCT, graft-versus-host disease, remains lethal and limits wider application of allogeneic HCT. In this article, we review current practice and recent advances made in prevention and treatment of graft-versus-host disease.

Immunomodulatory effects of mesenchymal stem cells involved in favoring type 2 T cell subsets

Graft-vs.-host disease (GVHD) caused by immunologic activated cells remains a real problem in human allogeneic hematopoetic stem cell transplantation. Mesenchymal stem cells (MSCs) play some important roles on immunomodulatory. We developed a parent-into-F1 model of acute GVHD to evaluate the mechanisms involved in immunological mediated damage and the immunomodulatory effect of the MSCs on GVHD. The recipients, BABL/cxC57BL/6 (H-2(bxd)) F1 mice, received 8.5Gy total-body gamma irradiation ((6)(0)C(O)), then rescued with C57BL/6 (H-2(b)) mice (donors) bone marrow cells and induced acute GVHD by adding donor splenocytes. The MSCs culture-expanded from C57BL/6 (H-2(b)) mice were infused to recipients simultaneity in the experimental group. The severity of GVHD was evaluated by histopathologic examination of target organs including liver, intestine, and claw skin and a clinical manifestation scoring system. We analyzed the distribution of peripheral blood T cell subsets of recipients by flow cytometry and measured the expression of CXCR3 on activated T cells in target organs by immunohistochemistry staining. Our results suggested the tissue damage initiated by GVHD was significantly alleviated in the MSCs treated mice, and the proportion of type 2 T cells in peripheral blood was higher in the MSCs treated mice than in the control group. Although the overall survival rate did not significantly improved in the mice with MSCs infusion, the immunomodulatory effect of MSCs was possibly related to favor type 2 T cell subsets and decrease chemokine receptor CXCR3 expression on activated T cells.

Cytolytic T cells induce ceramide-rich platforms in target cell membranes to initiate graft-versus-host disease

Alloreactive donor cytolytic T lymphocytes play a critical role in pathophysiology of acute graft-versus-host disease (GVHD). As GVHD progression involves tumor necrosis factor superfamily receptor activation, and as apoptotic signaling for some tumor necrosis factor superfamily receptors might involve acid sphingomyelinase (ASMase)-mediated ceramide generation, we hypothesized that ASMase deletion would ameliorate GVHD. Using clinically relevant mouse models of acute GVHD in which allogeneic bone marrow and T cells were transplanted into asmase+/+ and asmase(-/-) hosts, we identify host ASMase as critical for full-blown GVHD. Lack of host ASMase reduced the acute inflammatory phase of GVHD, attenuating cytokine storm, CD8+ T-cell proliferation/activation, and apoptosis of relevant graft-versus-host target cells (hepatocytes, intestinal, and skin cells). Organ injury was diminished in asmase(-/-) hosts, and morbidity and mortality improved at 90 days after transplantation. Resistance to cytolytic T lymphocyte-induced apoptosis was found at the target cell membrane if hepatocytes lack ASMase, as hepatocyte apoptosis required target cell ceramide generation for formation of ceramide-rich macrodomains, sites concentrating proapoptotic Fas. These studies indicate a requirement for target cell ASMase in evolution of GVHD in liver, small intestines, and skin and provide potential new targets for disease management.

Mouse models of bone marrow transplantation

Over the last 50 years, mouse models of bone marrow transplantation have provided the critical links between graft-versus-host disease (GVHD) and graft-versus-leukemia (GVL) pathophysiology and clinical practice. The initial insight from mouse models that GVHD and GVL were T cell dependent has long been confirmed clinically. More recent translations from mouse models have included the important role of inflammatory cytokines in GVHD. Newly developed concepts relating to the ability of antigen presenting cell (APC) and T cell subsets to mediate GVHD now promise significant clinical advances. The ability to use knockout and transgenic approaches to dissect mechanisms of GVHD and GVL mean that mouse systems will continue as the predominant preclinical platform. The basic transplant approach in these models, coupled with modern "real-time" immunologic imaging of GVHD and GVL is discussed.

Central memory CD8+ T cells induce graft-versus-host disease and mediate graft-versus-leukemia

In allogeneic hemopoietic stem cell transplantation, mature donor alphabeta T cells in the allograft promote T cell reconstitution in the recipient and mediate the graft-vs-leukemia (GVL) effect. Unfortunately, donor T cells can attack nonmalignant host tissues and cause graft-vs-host disease (GVHD). It has previously been shown that effector memory T cells not primed to alloantigen do not cause GVHD yet transfer functional T cell memory and mediate GVL. Recently, central memory T cells (T(CM)) have also been reported to not cause GVHD. In contrast, in this study, we demonstrate that purified CD8(+) T(CM) not specifically primed to alloantigens mediate GVHD in the MHC-mismatched C57BL/6 (B6)-->BALB/c and the MHC-matched, multiple minor histocompatibility Ag-mismatched C3H.SW-->B6 strain pairings. CD8(+) T(CM) and naive T cells (T(N)) caused similar histological disease in liver, skin, and bowel. B6 CD8(+) T(CM) and T(N) similarly expanded in BALB/c recipients, and the majority of their progeny produced IFN-gamma upon restimulation. However, in both models, CD8(+) T(CM) induced milder clinical GVHD than did CD8(+) T(N). Nonetheless, CD8(+) T(CM) and T(N) were similarly potent mediators of GVL against a mouse model of chronic-phase chronic myelogenous leukemia. Thus, in contrast to what was previously thought, CD8(+) T(CM) are capable of inducing GVHD and are substantially different from T(EM) but only subtly so from T(N).

STIM1-independent T cell development and effector function in vivo

Store-operated Ca(2+) entry (SOCE) is believed to be of pivotal importance in T cell physiology. To test this hypothesis, we generated mice constitutively lacking the SOCE-regulating Ca(2+) sensor stromal interaction molecule 1 (STIM1). In vitro analyses showed that SOCE and Ag receptor complex-triggered Ca(2+) flux into STIM1-deficient T cells is virtually abolished. In vivo, STIM1-deficient mice developed a lymphoproliferative disease despite normal thymic T cell maturation and normal frequencies of CD4(+)Foxp3(+) regulatory T cells. Unexpectedly, STIM1-deficient bone marrow chimeric mice mounted humoral immune responses after vaccination and STIM1-deficient T cells were capable of inducing acute graft-versus-host disease following adoptive transfer into allogeneic hosts. These results demonstrate that STIM1-dependent SOCE is crucial for homeostatic T cell proliferation, but of much lesser importance for thymic T cell differentiation or T cell effector functions.

Graft-versus-host disease

Haemopoietic-cell transplantation (HCT) is an intensive therapy used to treat high-risk haematological malignant disorders and other life-threatening haematological and genetic diseases. The main complication of HCT is graft-versus-host disease (GVHD), an immunological disorder that affects many organ systems, including the gastrointestinal tract, liver, skin, and lungs. The number of patients with this complication continues to grow, and many return home from transplant centres after HCT requiring continued treatment with immunosuppressive drugs that increases their risks for serious infections and other complications. In this Seminar, we review our understanding of the risk factors and causes of GHVD, the cellular and cytokine networks implicated in its pathophysiology, and current strategies to prevent and treat the disease. We also summarise supportive-care measures that are essential for management of this medically fragile population.

A preliminary gene expression profile of acute graft-versus-host disease

Allogeneic hematopoietic stem cell transplantation (HSCT) is the treatment of choice for high-risk hematological malignancies, yet a major complication associated with this therapy is acute graft-versus-host disease (GVHD). Despite a well-defined pathophysiological mechanism, there are no definitive markers for predicting acute GVHD development or progression to advanced stages. In the current study, we enrolled four acute GVHD and four acute GVHD-free recipients of allogeneic HSCT and collected peripheral blood just prior to onset of clinical acute GVHD for analysis on Affymetrix GeneChip Human Genome U133 Plus 2.0 microarrays. We noted significant differences in expression of 1,658 genes between control and acute GVHD patients, based on an analysis of covariance (ANCOVA) by type of transplant, a pooled error estimate, and a false discovery rate (FDR) of 10%. In conclusion, we offer the first report of a preliminary molecular signature of acute GVHD in allogeneic HSCT patients.

IL-17 contributes to CD4-mediated graft-versus-host disease

CD4(+) interleukin-17 (IL-17)(+) T cells (Th17 cells) have been implicated in allograft rejection of solid organs and several autoimmune diseases. However, the functional role of Th17 cells in the development of acute graft-versus-host disease (GVHD) has not been well-characterized. We detected significant numbers of alloreactive CD4(+) donor T cells expressing IL-17, IL-17F, or IL-22 in the lymphoid organs of recipients of an allogeneic bone marrow transplant. We found no differences in GVHD mortality or graft-versus-tumor (GVT) activity between wild type (WT) and IL-17(-/-) T-cell recipients. However, upon transfer of murine IL-17(-/-) CD4(+) T cells in an allogeneic BMT model, GVHD development was significantly delayed behind recipients of WT CD4(+) T cells, yet overall GVHD mortality was unaffected. Moreover, recipients of IL-17(-/-) CD4(+) T cells had significantly fewer Th1 cells during the early stages of GVHD. Furthermore, we observed a decrease in the number of IFN-gamma-secreting macrophages and granulocytes and decreased production of proinflammatory cytokines (interferon [IFN]-gamma, IL-4, and IL-6) in recipients of IL-17(-/-) CD4(+) T cells. We conclude that IL-17 is dispensable for GVHD and GVT activity by whole T cells, but contributes to the early development of CD4-mediated GVHD by promoting production of proinflammatory cytokines.

Breaking of CD8+ T cell tolerance through in vivo ligation of CD40 results in inhibition of chronic graft-versus-host disease and complete donor cell engraftment

In the DBA/2 --> unirradiated (C57BL/6 x DBA/2)F(1) model of chronic graft-vs-host disease (cGVHD), donor CD4(+) T cells play a critical role in breaking host B cell tolerance, while donor CD8(+) T cells are rapidly removed and the remaining cells fall into anergy. Previously we have demonstrated that in vivo ligation of GITR (glucocorticoid-induced TNF receptor-related gene) can activate donor CD8(+) T cells, subsequently converting the disease pattern from cGVHD to an acute form. In this study, we investigated the effect of an agonistic mAb against CD40 on cGVHD. Treatment of anti-CD40 mAb inhibited the production of anti-DNA IgG1 autoantibody and the development of glomerulonephritis. The inhibition of cGVHD occurred because anti-CD40 mAb prevented donor CD8(+) T cell anergy such that subsequently activated donor CD8(+) T cells deleted host CD4(+) T cells and host B cells involved in autoantibody production. Additionally, functionally activated donor CD8(+) T cells induced full engraftment of donor hematopoietic cells and exhibited an increased graft-vs-leukemia effect. However, induction of acute GVHD by donor CD8(+) T cells seemed to be not so apparent. Further CTL analysis indicated that there were lower levels of donor CTL activity against host cells in mice that received anti-CD40 mAb, compared with mice that received anti-GITR mAb. Taken together, our results suggest that a different intensity of donor CTL activity is required for removal of host hematopoietic cells, including leukemia vs induction of acute GVHD.

Interleukin-23 secretion by donor antigen-presenting cells is critical for organ-specific pathology in graft-versus-host disease

Damage to the gastrointestinal tract during graft-versus-host disease (GVHD) from the conditioning regimen in conjunction with alloreactive donor T cells plays a pivotal role in the pathogenesis of this disease. In this study, we have identified secretion of interleukin-23 (IL-23) by donor antigen-presenting cells (APCs) as a critical event in the induction of GVHD of the colon linking conditioning regimen-induced mucosal injury and lipopolysaccharide (LPS) translocation to subsequent proinflammatory cytokine production and GVHD-associated pathologic damage. In the absence of donor APC-derived IL-23 secretion, there is a selective and profound reduction in pathologic damage as well as a marked reduction in LPS and proinflammatory cytokine production in the colon microenvironment. The downstream proinflammatory effects of IL-23 are dependent upon donor-derived secretion of interferon-gamma (IFN-gamma), but are independent of donor IL-17 production. These findings define a novel organ-specific role for IL-23 in the pathophysiology of GVHD and demonstrate that IL-23 can direct tissue-specific pathology within the context of a systemic inflammatory disorder. Furthermore, these studies also identify IL-23 as a potential therapeutic target for the prevention of this life-threatening disorder.

Vascular endothelium and graft-versus-host disease

Vascular endothelial cells are an exposed target tissue for immune-mediated injury during graft-versus-host disease (GVHD). However, widespread endothelial death resulting in multi-organ failure similar to that in hyperacute solid-organ transplant rejection is not observed during GVHD. The rather mild endothelial injury seen in histological samples from affected skin biopsies contrasts with severe epithelial injury observed sometimes simultaneously. The elucidation of the mechanisms that influence endothelial susceptibility to immune-mediated injury would explain this paradox and may help to separate GVHD from the beneficial graft-versus-leukaemia effect. Transplant-associated microangiopathy, veno-occlusive disease and accelerated arteriosclerosis are vascular injury syndromes that occur after allogeneic stem-cell transplantation. Biomarkers are needed to identify individuals at risk of developing these complications. Treatments that have been found to be particularly effective for these specific endothelial injury syndromes need to be tested in larger clinical trials.

Differential effects of donor T-cell cytokines on outcome with continuous bortezomib administration after allogeneic bone marrow transplantation

Dissociating graft-versus-tumor (GVT) effect from acute graft-versus-host disease (GVHD) still remains a great challenge in allogeneic bone marrow transplantation (allo-BMT). Bortezomib, a proteasome inhibitor, has shown impressive efficacy as a single agent in patients with hematologic malignancies but can result in toxicity when administered late after allogeneic transplantation in murine models of GVHD. In the current study, the effects of T-cell subsets and their associated cytokines on the efficacy of bortezomib in murine allogeneic BMT were investigated. Increased levels of serum tumor necrosis factor-alpha (TNFalpha) and interferon-gamma (IFNgamma) were observed after allo-BMT and continuous bortezomib administration. Bortezomib-induced GVHD-dependent mortality was preventable by depletion of CD4(+) but not CD8(+) T cells from the donor graft. The improved survival correlated with markedly reduced serum TNFalpha but not IFNgamma levels. Transfer of Tnf(-/-) T cells also protected recipients from bortezomib-induced GVHD-dependent toxicity. Importantly, prolonged administration of bortezomib after transplantation of purified CD8(+) T cells resulted in enhanced GVT response, which was dependent on donor CD8(+) T cell-derived IFNgamma. These results indicate that decreased toxicity and increased efficacy of bortezomib in murine allo-BMT can be achieved by removal of CD4(+) T cells from the graft or by inhibiting TNFalpha.

CD8+ but not CD4+ T cells require cognate interactions with target tissues to mediate GVHD across only minor H antigens, whereas both CD4+ and CD8+ T cells require direct leukemic contact to mediate GVL

Whether T-cell antigen receptors (TCR) on donor T cells require direct interactions with major histocompatibility complex class I or class II (MHCI/MHCII) molecules on target cells to mediate graft-versus-host disease (GVHD) and graft-versus-leukemia (GVL) is a fundamental question in allogeneic stem-cell transplantation (alloSCT). In MHC-mismatched mouse models, these contacts were not required for GVHD. However, this conclusion may not apply to MHC-matched, multiple minor histocompatibility antigen-mismatched alloSCT, the most common type performed clinically. To address this, we used wild-type (wt)-->MHCI-/- or wt-->MHCII-/- bone marrow chimeras as recipients in GVHD experiments. For GVL experiments, we used MHCI-/- or MHCII-/- chronic-phase CML cells created by expressing the BCR-ABL cDNA in bone marrow from MHCI-/- or MHCII-/- mice. TCR/MHCI contact was obligatory for both CD8-mediated GVHD and GVL. In contrast, CD4 cells induced GVHD in wt-->MHCII-/- chimeras, whereas MHCII-/- mCP-CML was GVL-resistant. Donor CD4 cells infiltrated affected skin and bowel in wt-->MHCII-/- recipients, indicating that they mediated GVHD by acting locally. Thus, CD4 cells use distinct effector mechanisms in GVHD and GVL: direct cytolytic action is required for GVL but not for GVHD. If these noncytolytic pathways can be inhibited, then GVHD might be ameliorated while preserving GVL.

Dissociated production of perforin, granzyme B, and IFN-gamma by HIV-specific CD8(+) cells in HIV infection

CD8(+) T cells play a crucial role in the control of viral infections such as HIV. The functional characterization of HIV-specific CD8(+) T cells has so far been largely restricted to studies of IFN-gamma. The TCR-triggered release of the effector molecules perforin (PFN) and granzyme B (GzB), however, is thought to be a central pathway for the destruction of virus-infected target cells by CD8(+) effector T cells. Here we would like to address two major findings. On the one hand we propose that ex vivo measurements of PFN and GzB secretion via ELISPOT may permit the distinction between in vivo resting versus activated CD8(+) memory T cells in healthy and HIV-infected individuals. Therefore, extending the present standard of IFN-gamma measurements to the analysis of PFN and GzB release in functional T cell assays will provide new insights into CD8(+) effector T cell functions. It should enable the evaluation of therapeutic vaccination efficacy by its ability to reactivate and convert IFN-gamma-positive, but GzB- and PFN-negative memory CD8(+) T cells into PFN/GzB-secreting effector cells. On the other hand, we report on a frequent ex vivo dissociation of the HIV peptide-induced secretion of PFN and GzB in chronic HIV infection underlining CD8(+) effector T cell diversity in this disease--an aspect that also has to be accounted for in immune monitoring approaches.

Effector memory CD4+ T cells mediate graft-versus-leukemia without inducing graft-versus-host disease

Much of the efficacy of allogeneic hematopoietic stem cell transplantation (alloSCT) in curing hematologic malignancies is due to a graft-versus-leukemia (GVL) effect mediated by donor T cells that recognize recipient alloantigens on leukemic cells. Donor T cells are also important for reconstituting immunity in the recipient. Unfortunately, donor T cells can attack nonmalignant host tissues and cause graft-versus-host disease (GVHD). We previously reported that donor CD4(+) effector memory T cells (T(EMs)) do not cause GVHD but transfer functional T-cell memory. In the present work, we demonstrate in an MHC-mismatched model that CD4(+) T(EMs) (unprimed to recipient antigens) mediate GVL against clinically relevant mouse models of chronic phase and blast crisis chronic myelogenous leukemia, without causing GVHD. By creating gene-deficient leukemias and using perforin-deficient T cells, we demonstrate that direct cytolytic function is essential for T(EM)-mediated GVL, but that GVL is retained when killing via FasL, TNF-alpha, TRAIL, and perforin is individually impaired. However, T(EM)-mediated GVL was diminished when both FasL and perforin pathways were blocked. Taken together, our studies identify T(EMs) as a clinically applicable cell therapy for promoting GVL and immune reconstitution, particularly in MHC-mismatched haploidentical alloSCTs in which T cell-depleted allografts are commonly used to minimize GVHD.

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

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

IFN-gamma and Fas ligand are required for graft-versus-tumor activity against renal cell carcinoma in the absence of lethal graft-versus-host disease

To determine the mechanisms of graft-versus-tumor (GVT) activity in the absence of graft-versus-host disease (GVHD) against a solid tumor, we established two allogeneic bone marrow transplantation models with a murine renal cell carcinoma (RENCA). The addition of 0.3 x 10(6) donor CD8(+) T cells to the allograft increased the survival of tumor-bearing mice without causing GVHD. The analysis of CD8(+) T cells deficient in cytotoxic molecules demonstrated that anti-RENCA activity is dependent on IFN-gamma and Fas ligand (FasL), but does not require soluble or membrane-bound TNF-alpha, perforin, or TRAIL. Recipients of IFN-gamma(-/-) CD8(+) T cells are unable to reject RENCA compared with recipients of wild-type CD8(+) T cells and, importantly, neither group develops severe GVHD. IFN-gamma(-/-) CD8(+) T cells derived from transplanted mice are less able to kill RENCA cells in vitro, while pretreatment of RENCA cells with IFN-gamma enhances class I and FasL expression and rescues the lytic capacity of IFN-gamma(-/-) CD8(+) T cells. These results demonstrate that the addition of low numbers of selected donor CD8(+) T cells to the allograft can mediate GVT activity without lethal GVHD against murine renal cell carcinoma, and this GVT activity is dependent on IFN-gamma and FasL.

Long-term follow-up of patients treated with daclizumab for steroid-refractory acute graft-vs-host disease

Daclizumab has been shown to have activity in acute GVHD, but appears to be associated with an increased risk of infection. To investigate further the long-term effects of daclizumab, we performed a retrospective review of 57 patients who underwent an allogeneic hematopoietic stem cell transplant from January 1993 through June 2000 and were treated with daclizumab for steroid-refractory acute GVHD. The median number of daclizumab doses given was 5 (range 1-22). GVHD was assessed at baseline, days 15, 29 and 43. By day 43, 54% patients had an improvement in their overall GVHD score, including 76% patients aged < or =18. Opportunistic infections developed in 95% patients. Forty-three patients (75%) died following treatment with daclizumab. The causes of death included active GVHD and infection (79%), active GVHD (5%), chronic GVHD (2%) and relapse (14%). Patients with grade 3-4 GVHD had a significantly shorter median survival than patients with grade 1-2 GVHD (2.0 vs 5.1 months, P=0.001). Daclizumab has no infusion-related toxicity, is active in steroid-refractory GVHD, especially among pediatric patients, but is associated with significant morbidity and mortality due to infectious complications. Careful patient selection and aggressive prophylaxis against viral and fungal infections are recommended.

CD95 ligand-dependant endothelial cell death initiates oral mucosa damage in a murine model of acute graft versus host disease

Oral mucosa lesions are one of the common pathological consequences of acute graft versus host disease (aGVHD), the major complication of allogeneic bone marrow transplantation caused by mature T lymphocytes of donor origin. Oral mucosa damage in aGVHD is characterized by apoptosis induction in the basal keratinocytes, associated with immune effector T-cell infiltration, but its pathogenesis remains unclear because these lesions might result from the patient conditioning therapy that includes radiation and/or chemotherapy. Here, using a murine model of aGVHD that does not involve any conditioning treatment, we show that the earliest detectable oral mucosa lesion is apoptosis of the endothelial cells from chorion capillaries, which precedes basal keratinocyte apoptosis induction. Neither vascular damage nor epithelial-cell death occurred in recipients of allogeneic lymphocytes from CD95 ligand (CD95L)-defective mice. Our findings indicate that oral mucosa lesions in aGVHD are initiated by endothelial-cell death and require CD95L expression by the allogeneic lymphocytes. This early vascular damage may contribute to the induction of further tissue damage in the oral mucosa, through the induction of hypoxia and vascular leakage of immune cells or soluble proapoptotic mediators.

Homeostatic expansion and repertoire regeneration of donor T cells during graft versus host disease is constrained by the host environment

Graft versus host disease (GVHD) typically results in impaired T-cell reconstitution characterized by lymphopenia and repertoire skewing. One of the major causes of inadequate T-cell reconstitution is that T-cell survival and expansion in the periphery are impaired. In this report, we have performed adoptive transfer studies to determine whether the quantitative reduction in T-cell numbers is due to an intrinsic T-cell defect or whether the environmental milieu deleteriously affects T-cell expansion. These studies demonstrate that T cells obtained from animals with graft-versus-host disease (GVHD) are capable of significant expansion and renormalization of an inverted CD4/CD8 ratio when they are removed from this environment. Moreover, these cells can generate complex T-cell repertoires early after transplantation and are functionally competent to respond to third-party alloantigens. Our data indicate that T cells from mice undergoing GVHD can respond to homeostatic signals in the periphery and are not intrinsically compromised once they are removed from the GVHD environment. We thereby conclude that the host environment and not an intrinsic T-cell defect is primarily responsible for the lack of effective T-cell expansion and diversification of complex T-cell repertoires that occurs during GVHD.

Remodeling specific immunity by use of MHC tetramers: demonstration in a graft-versus-host disease model

Major histocompatibility complex (MHC) molecules carrying selected peptides will bind specifically to their cognate T-cell receptor on individual clones of reactive T cells. Fluorescently labeled, tetrameric MHC-peptide complexes have been widely used to detect and quantitate antigen-specific T-cell populations via flow cytometry. We hypothesized that such MHC-peptide tetramers could also be used to selectively deplete unique reactive T-cell populations, while leaving the remaining T-cell repertoire and immune response intact. In this report, we successfully demonstrate that a tetramer-based depletion of T cells can be achieved in a murine model of allogeneic bone marrow transplantation. Depletion of a specific alloreactive population of donor splenocytes (< 0.5% of CD8+ T cells) prior to transplantation significantly decreased morbidity and mortality from graft-versus-host disease. There was no early regrowth of the antigen-specific T cells in the recipient and in vivo T-cell proliferation was greatly reduced as well. Survival was increased more than 3-fold over controls, yet the inherent antitumor activity of the transplant was retained. This method also provides the proof-of-concept for similar strategies to selectively remove other unwanted T-cell clones, which could result in novel therapies for certain autoimmune disorders, T-cell malignancies, and solid organ graft rejection.

Approaches to graft-vs-host disease

Graft-vs-host disease (GVHD) is one of the most difficult problems in stem cell transplantation. It is best considered in the context of the normal immune response. The role of the immune system is to identify and eliminate foreign antigens. In the case of GVHD, the antigens are minor histocompatibility antigens (mHA) recognized in an inflammatory milieu. The immune system cannot reasonably be expected to selectively recognize microbial antigens and ignore mHA. This approach would require the generation of selective tolerance--something that clearly occurs but which we have frustratingly little control over. While we can often treat and remit even life-threatening GVHD, the consequence has been the development of fatal opportunistic infections. The challenge is to change our style of thinking about GVHD to allow a transition from a 'nuclear winter' approach that controls GVHD at the price of infection, to a more selective patient approach that recognizes the limitations of immunosuppressive therapy.

NF-kappaB as a target for the prevention of graft-versus-host disease: comparative efficacy of bortezomib and PS-1145

NF-kappaB is a transcription factor that controls the expression of a number of genes important for mediating immune and inflammatory responses. In this study, we examined whether bortezomib and PS-1145, each of which inhibits NF-kappaB, could protect mice from lethal graft-versus-host disease (GVHD), which is characterized by immune activation and proinflammatory cytokine production. When administered within the first 2 days after transplantation, bortezomib and PS-1145 both protected mice from fatal GVHD, did not compromise donor engraftment, and effected marked reduction in the levels of serum cytokines that are normally increased during GVHD. Extending the course of bortezomib administration or delaying the initiation of this agent for as few as 3 days after bone marrow transplantation (BMT), however, significantly exacerbated GVHD-dependent mortality because of severe pathological damage in the colon. In contrast, prolonged administration of PS-1145, which, unlike bortezomib, is a selective inhibitor of NF-kappaB, caused no early toxicity and resulted in more complete protection than that observed with an abbreviated PS-1145 treatment schedule. These results confirm a critical role for NF-kappaB in the pathophysiology of GVHD and indicate that targeted inhibition of NF-kappaB may have a superior therapeutic index and may constitute a viable therapeutic approach to reduce GVHD severity.

CCR2 is required for CD8-induced graft-versus-host disease

Graft-versus-host disease (GVHD) is a major complication of allogeneic hematopoietic stem cell transplantation (HSCT). Migration of donor-derived T cells into GVHD target organs plays a critical role in the development of GVHD and chemokines and their receptors are important molecules involved in this process. Here, we demonstrate in murine bone marrow transplantation models that the expression of the inflammatory CC chemokine receptor 2 (CCR2) on donor-derived CD8+ T cells is relevant for the control of CD8+ T-cell migration and development of GVHD. Recipients of CCR2-deficient (CCR2-/-) CD8+ T cells developed less damage of gut and liver than recipients of wild-type CD8+ T cells, which correlated with a reduction in overall GVHD morbidity and mortality. Assessment of donor CD8+ T-cell target organ infiltration revealed that CCR2-/- CD8+ T cells have an intrinsic migratory defect to the gut and liver. Other causes for the reduction in GVHD could be excluded, as alloreactive proliferation, activation, IFN-gamma production and cytotoxicity of CCR2-/- CD8+ T cells were intact. Interestingly, the graft-versus-tumor effect mediated by CCR2-/- CD8+ T cells was preserved, which suggests that interference with T-cell migration by blockade of CCR2 signaling can separate GVHD from GVT activity.

Graft-versus-lymphoma effects: clinical review, policy proposals, and immunobiology

The indubitable existence of a graft-versus-lymphoma (GVL) effect is difficult to prove directly. This article reviews the difficulties in interpreting the current literature in this field and, with a number of caveats, argues for the existence of a clinically meaningful GVL effect in follicular, mantle cell, small lymphocytic, and Hodgkin lymphomas. The evidence, however, for a potent GVL effect in diffuse large-cell lymphoma and Burkitt lymphoma is not convincing. Policies for allografting in lymphoma are proposed on the basis of this evidence. The immunobiology of GVL effects is discussed--in particular, the expression of HLA class I and II and co-stimulatory molecules on lymphomas that influence the generation of alloreactive T cells--together with future directions in immunotherapy that may help to eradicate chemoresistant disease.

Vascular Endothelial Cells Have Impaired Capacity to Present Immunodominant, Antigenic Peptides: A Mechanism of Cell Type-Specific Immune Escape

Vascular endothelial cells (EC) are an exposed target tissue in the course of CTL-mediated alloimmune diseases such as graft-vs-host disease (GVHD) or solid organ transplant rejection. The outcome of an interaction between CTL and target cells is determined by the amount of Ag presented and the costimulatory signals delivered by the target cells. We compared human EC with leukocytes and epithelial cells as targets for peptide-specific, MHC class I-restricted CTL clones. EC were poor targets for immunodominant CTL. Both endogenously processed antigenic proteins and exogenously added antigenic peptides are presented at 50- to 5000-fold lower levels on EC compared with any other target cell analyzed. This quantitative difference fully explained the poor CTL-mediated killing of EC. There was no evidence that lack of costimulation would contribute significantly to this cell type-specific difference in CTL activation. An HLA-A2-specific CTL clone that killed a broad selection of HLA A2-positive target cells equally well, killed EC less efficiently. Our data suggest that EC present a different Ag repertoire compared with other cell types. By this mechanism, these cells may escape an attack by effector CTL, which have been educated by professional APCs and are specific for immunodominant antigenic peptides.