Donor treatment with pegylated G-CSF augments the generation of IL-10-producing regulatory T cells and promotes transplantation tolerance

Treatment of Crohn's disease with colony-stimulating factors: An overview

Current treatments for Crohn's disease are aimed at suppressing excessive immune activation in the bowel walls. However, alternative strategies can be drawn. These involve the augmentation of the innate immune response, in the hypothesis that patients affected with Crohn's disease are characterized by a relative immunodeficiency, with failure of the defensive barrier to luminal microbes and microbial products, resulting in a chronic inflammatory process sustained by T-cells. Alternatively, therapy could act by enhancing the number or the activity of subpopulations of T regulatory cells, able to reduce T-cell activation. Colony-stimulating factors are substances that could be efficacious in these settings. In fact, besides in vitro and animal studies, some human studies have been conducted in recent years with both granulocyte-macrophage colony-stimulating factor and granulocyte colony-stimulating factor, the results of which are reported here.

The multifaceted effects of granulocyte colony-stimulating factor in immunomodulation and potential roles in intestinal immune homeostasis

The three colony-stimulating factors, granulocyte/macrophage colony-stimulating factor (GM-CSF), macrophage colony-stimulating factor (M-CSF), and granulocyte colony-stimulating factor (G-CSF), have been regarded as immunostimulators because of their role in granulocyte and myeloid hematopoiesis and immune function. However, unlike GM-CSF and M-CSF, G-CSF possesses immunosuppressive effects on other immune cells including monocytes/macrophages, dendritic cells, and T lymphocytes when exogenously administered. Given the immunomodulatory effects of exogenous G-CSF, endogenous G-CSF may also play an important role in maintaining local immune homeostasis in tissue in which it is highly and constitutively produced. This review highlights the potential role of G-CSF in immunomodulation and intestinal immune homeostasis.

Effects of pegylated G-CSF on immune cell number and function in patients with gynecological malignancies

Background

Pegylated granulocyte colony-stimulating factor (G-CSF; pegfilgrastim) is a longer-acting form of G-CSF, whose effects on dendritic cell (DC) and regulatory T cell (Treg) mobilization, and on the in vivo and ex vivo release of immune modulating cytokines remain unexplored.

Methods

Twelve patients with gynecological cancers received carboplatin/paclitaxel chemotherapy and single-dose pegfilgrastim as prophylaxis of febrile neutropenia. Peripheral blood was collected prior to pegfilgrastim administration (day 0) and on days +7, +11 and +21, to quantify immunoregulatory cytokines and to assess type 1 DC (DC1), type 2 DC (DC2) and Treg cell mobilization. In vitro-differentiated, monocyte-derived DC were used to investigate endocytic activity, expression of DC maturation antigens and ability to activate allogeneic T-cell proliferation.

Results

Pegfilgrastim increased the frequency of circulating DC1 and DC2 precursors. In contrast, CD4⁺FoxP3⁺ bona fide Treg cells were unchanged compared with baseline. Serum levels of hepatocyte growth factor and interleukin (IL)-12p40, but not transforming growth factor-β1 or immune suppressive kynurenines, significantly increased after pegfilgrastim administration. Interestingly, pegfilgrastim fostered in vitro monocytic secretion of IL-12p40 and IL-12p70 when compared with unconjugated G-CSF. Finally, DC populations differentiated in vitro after clinical provision of pegfilgrastim were phenotypically mature, possessed low endocytic activity, and incited a robust T-cell proliferative response.

Conclusions

Pegfilgrastim induced significant changes in immune cell number and function. The enhancement of monocytic IL-12 secretion portends favorable implications for pegfilgrastim administration to patients with cancer, a clinical context where the induction of immune deviation would be highly undesirable.

Granulocyte-colony stimulating factor drives the in vitro differentiation of human dendritic cells that induce anergy in naïve T cells

G-CSF is a modulator of T-cell and DC functions. Previous reports show that monocytes from G-CSF-treated (post-G) healthy donors differentiate into tolerogenic DC in vitro in the presence of autologous serum, containing high levels of IL-10 and IFN-α, and in turn induce type 1 Treg (Tr1) cells. However, the direct effect of G-CSF on DC differentiation was not investigated. Here, we show that monocytes differentiated in the presence of exogenous G-CSF (G-DC) remain CD14(+) CD1a(-) , but acquire a DC-like morphology, express CD83 and CD86 and low levels of the tolerogenic markers Ig-like transcript (ILT)4 and HLA-G. G-DC spontaneously produce IL-10 and, upon stimulation, low levels of IL-12. G-DC display low stimulatory capacity and induce anergy in naïve T cells, but do not confer suppressive function. Therefore, in vitro differentiation of monocyte-derived DC in the presence of G-CSF can replicate some but not all features of post-G DC. These findings indicate that the tolerogenic properties of G-CSF do not exclusively reside in its direct effect on DC, which in turn induce T-cell anergy, but also in its ability to generate a tolerogenic milieu in vivo, which is necessary for Tr1 cell induction and cannot be replicated in vitro.

SOCS3 regulates graft-versus-host disease

Suppressor of cytokine signaling-3 (SOCS3) is the main intracellular regulator of signaling by granulocyte colony-stimulating factor, an immune-modulatory cytokine used to mobilize stem cells for transplantation. We have therefore studied the contribution of SOCS3 to the spectrum of graft-versus-host disease (GVHD) after allogeneic stem cell transplantation (SCT). Grafts from SOCS3(-/Deltavav) donor mice in which SOCS3 deficiency is restricted to the hematopoietic compartment had an augmented capacity to induce acute GVHD. With the use of SOCS3(-/DeltaLysM) and SOCS3(-/Deltalck) donors in which SOCS3 deficiency was restricted to the myeloid or T-cell lineage, respectively, we confirmed SOCS3 deficiency promoted acute GVHD mortality and histopathology within the gastrointestinal tract by effects solely within the donor T cell. SOCS3(-/Deltalck) donor T cells underwent enhanced alloantigen-dependent proliferation and generation of interleukin-10 (IL-10), IL-17, and interferon-gamma (IFNgamma) after SCT. The enhanced capacity of the SOCS3(-/Deltalck) donor T cell to induce acute GVHD was dependent on IFNgamma but independent of IL-10 or IL-17. Surprisingly, SOCS3(-/Deltalck) donor T cells also induced severe, transforming growth factor beta- and IFNgamma-dependent, sclerodermatous GVHD. Thus, the delivery of small molecule SOCS3 mimetics may prove to be useful for the inhibition of both acute and chronic GVHD.

Stem cell mobilization with G-CSF induces type 17 differentiation and promotes scleroderma

The recent shift to the use of stem cells mobilized by granulocyte colony-stimulating factor (G-CSF) for hematopoietic transplantation has increased chronic graftversus-host disease (GVHD), although the mechanisms of this are unclear. We have found that G-CSF invokes potent type 17 rather than type 1 or type 2 differentiation. The amplification of interleukin-17 (IL-17) production by G-CSF occurs in both CD4 and CD8 conventional T cells and is dependent on, and downstream of, G-CSF-induced IL-21 signaling. Importantly, donor IL-17A controls the infiltration of macrophages into skin and cutaneous fibrosis, manifesting late after transplantation as scleroderma. Interestingly, donor CD8 T cells were the predominant source of IL-17A after transplantation and could mediate scleroderma independently of CD4 T cells. This study provides a logical explanation for the propensity of allogeneic stem cell transplantation to invoke sclerodermatous GVHD and suggests a therapeutic strategy for intervention.

Comparison of unmobilized and mobilized graft characteristics and the implications of cell subsets on autologous and allogeneic transplantation outcomes

Autologous and allogeneic hematopoietic stem cell transplantation (HSCT) are considered the standard of care for many malignancies, including lymphoma, myeloma, and some leukemias. In many cases, mobilized peripheral blood has become the preferred source of hematopoietic stem cells. The efficacy of different mobilization regimens and transplantation outcomes based on cell doses has been well studied; however, the characteristics of the stem cell graft may be of equal importance with respect to patient outcomes following autologous or allogeneic HSCT. This review summarizes available preclinical and clinical data for bone marrow and mobilized peripheral blood HSCT characteristics, defined as the cell types found in the graft as well as their gene expression profiles. It also explores how graft characteristics can affect bone marrow homing, engraftment, immune reconstitution, and other posttransplantation outcomes in both the allogeneic and autologous HSCT settings.

Function and dysfunction of dendritic cells in autoimmune rheumatic diseases

Dendritic cells (DC) have been implicated both in initiation of immunity and in immune tolerance. The mechanisms whereby tolerogenic DC may induce and maintain peripheral tolerance include the generation or expansion of regulatory T cells (Treg) and the promotion of T-cell anergy or deletion. A wide spectrum of hematopoietic growth factors and cytokines are endowed with the ability to differentiate tolerogenic DC both in vitro and in vivo. Based on this knowledge, therapeutic vaccination with cytokine-modulated tolerogenic DC has been applied to animal models of autoimmune disorders. This article will review the current experimental evidence underpinning DC dysfunction in rheumatic autoimmune diseases and will discuss how the manipulation of DC and Treg number and function may control undesired T-cell responses.

Invariant natural killer T cell-natural killer cell interactions dictate transplantation outcome after alpha-galactosylceramide administration

Invariant natural killer T cells (iNKT cells) have pivotal roles in graft-versus-host disease (GVHD) and graft-versus-leukemia (GVL) effects. iNKT cells are activated through their T-cell receptors by glycolipid moieties (typically the alpha-galactosylceramide [alpha-GalCer] derivative KRN7000) presented within CD1d. We investigated the ability of modified alpha-GalCer molecules to differentially modulate alloreactivity and GVL. KRN7000 and the N-acyl variant, C20:2, were administered in multiple well-established murine models of allogeneic stem cell transplantation. The highly potent and specific activation of all type I NKT cells with C20:2 failed to exacerbate and in most settings inhibited GVHD late after transplantation, whereas effects on GVL were variable. In contrast, the administration of KRN7000 induced hyperacute GVHD and early mortality in all models tested. Administration of KRN7000, but not C20:2, was found to result in downstream interleukin (IL)-12 and dendritic cell (DC)-dependent natural killer (NK)- and conventional T-cell activation. Specific depletion of host DCs, IL-12, or donor NK cells prevented this pathogenic response and the induction of hyperacute GVHD. These data demonstrate the ability of profound iNKT activation to modulate both the innate and adaptive immune response via the DC-NK-cell interaction and raise concern for the use of alpha-GalCer therapeutically to modulate GVHD and GVL effects.

Induction of natural killer T cell-dependent alloreactivity by administration of granulocyte colony-stimulating factor after bone marrow transplantation

Granulocyte colony-stimulating factor (G-CSF) is often used to hasten neutrophil recovery after allogeneic bone marrow transplantation (BMT), but the clinical and immunological consequences evoked remain unclear. We examined the effect of G-CSF administration after transplantation in mouse models and found that exposure to either standard G-CSF or pegylated-G-CSF soon after BMT substantially increased graft-versus-host disease (GVHD). This effect was dependent on total body irradiation (TBI) rendering host dendritic cells (DCs) responsive to G-CSF by upregulating their expression of the G-CSF receptor. Stimulation of host DCs by G-CSF subsequently unleashed a cascade of events characterized by donor natural killer T cell (NKT cell) activation, interferon-gamma secretion and CD40-dependent amplification of donor cytotoxic T lymphocyte function during the effector phase of GVHD. Crucially, the detrimental effects of G-CSF were only present when it was administered after TBI conditioning and at a time when residual host antigen presenting cells were still present, perhaps explaining the conflicting and somewhat controversial clinical studies from the large European and North American BMT registries. These data have major implications for the use of G-CSF in disease states where NKT cell activation may have effects on outcome.

Graft-versus-host disease prevents the maturation of plasmacytoid dendritic cells

The role of Ag presenting cell subsets in graft-versus-host disease (GVHD) remains unclear. We have thus examined the ability of plasmacytoid dendritic cells (pDC) to modulate transplant outcome. Surprisingly, host pDC were exquisitely sensitive to total body irradiation and were depleted before transplantation, thus allowing us to focus on donor pDC [corrected]. The depletion of all pDC from bone marrow grafts resulted in an acceleration of GVHD mortality while the depletion of mature pDC from G-CSF mobilized splenic grafts had no effect. Thus, donor bone marrow pDC, but not mature pDC contained within stem cell grafts attenuate acute GVHD. In the presence of GVHD, donor pDC completely failed to reconstitute although a CD11clow120G8+ precursor DC reconstituted in an exaggerated and transient manner. These cells expressed Flt-3, the macrophage colony stimulating factor receptor and, consistent with a common dendritic cell (DC) precursor, were capable of differentiation into pDC and conventional DC in vivo in the absence of GVHD. These precursors were MHC class II+ and CD80/86+ but lacked CD40, were actively presenting host Ag and inhibited GVHD and T cell proliferation in a contact-dependent fashion. These data demonstrate that GVHD prevents the maturation of pDC and instead promotes the generation of a suppressive precursor DC, further contributing to the state of immune paralysis after transplantation.

SHIP limits immunoregulatory capacity in the T-cell compartment

Regulatory T cells (T(regs)) play a pivotal role in preventing autoimmunity, graft-versus-host disease (GVHD), and organ graft rejection. We previously showed that either germline or induced SH2 domain-containing inositol 5-phosphatase (SHIP) deficiency in the host abrogates GVHD. Here we show that SHIP deficiency promotes an increase of CD4(+)CD25(+)FoxP3(+) T(regs) and CD4(+)CD25(-)FoxP3(+)"naive" T cells in the periphery that display increased CD103, glucocorticoid-induced tumor necrosis factor receptor-related protein (GITR), OX40, and FcgammaRII/III expression. SHIP deficiency does not compromise T(reg) function because SHIP-deficient CD3(+)CD4(+)CD25(+) T(regs) are as suppressive as wild-type (WT) CD3(+)CD4(+)CD25(+) T(reg). Interestingly, like conventional T(regs), SHIP(-/-) CD4(+)CD25(-) T cells are unresponsive to major histocompatibility complex (MHC)-mismatched stimulators and suppress allogeneic responses by T cells in vitro. In addition, SHIP(-/-) CD4(+)CD25(-) T cells mediate reduced lethal GVHD on adoptive transfer to MHC-mismatched hosts. Furthermore, hosts with induced SHIP deficiency exhibit delayed rejection of MHC-mismatched cardiac grafts. Thus, SHIP is required for robust graft-versus-host and host-versus-graft responses by CD4(+) T cell and limits their immunoregulatory capacity. These findings further define the immunosuppressive mechanisms that result from SHIP deficiency and provide additional justification for targeting SHIP in clinical transplantation.

Effects and safety of granulocyte colony-stimulating factor in healthy volunteers

PURPOSE OF REVIEW

Recombinant human granulocyte colony-stimulating factor (rhG-CSF) is now widely used in normal donors for collection of peripheral blood progenitor cells for allogeneic transplantation and granulocytes for transfusion. Currently available data on biologic and molecular effects, and safety of rhG-CSF in normal healthy volunteers are reviewed.

RECENT FINDINGS

In addition to its known activating role on neutrophil kinetics and functional status, rhG-CSF administration can affect monocytes, lymphocytes and the hemostatic system. Granulocyte colony-stimulating factor receptors were identified in a variety of nonmyeloid tissues, although their role and functional activity have not always been well defined. Moreover, rhG-CSF is capable of modulating complex cytokine networks and can impact the inflammatory response. In addition to its known mobilizing role for peripheral blood progenitor cells, rhG-CSF can mobilize dendritic and endothelial progenitor cells as well. On a clinical level, serious rhG-CSF-related adverse events are well described (e.g. splenic rupture) but remain rare.

SUMMARY

rhG-CSF effects in healthy volunteers, although normally transient and self-limiting, are now believed to be more complex and heterogeneous than previously thought. Although rhG-CSF administration to healthy volunteers continues to have a favorable risk-benefit profile, these new findings have implications for safeguarding the safety of normal individuals.

Successful granulocyte-colony stimulating factor treatment of Crohn's disease is associated with the appearance of circulating interleukin-10-producing T cells and increased lamina propria plasmacytoid dendritic cells

Granulocyte-colony stimulating factor (G-CSF) has proved to be a successful therapy for some patients with Crohn's disease. Given the known ability of G-CSF to exert anti-T helper 1 effects and to induce interleukin (IL)-10-secreting regulatory T cells, we studied whether clinical benefit from G-CSF therapy in active Crohn's disease was associated with decreased inflammatory cytokine production and/or increased regulatory responses. Crohn's patients were treated with G-CSF (5 microg/kg/day subcutaneously) for 4 weeks and changes in cell phenotype, cytokine production and dendritic cell subsets were measured in the peripheral blood and colonic mucosal biopsies using flow cytometry, enzyme-linked immunosorbent assay and immunocytochemistry. Crohn's patients who achieved a clinical response or remission based on the decrease in the Crohn's disease activity index differed from non-responding patients in several important ways: at the end of treatment, responding patients had significantly more CD4(+) memory T cells producing IL-10 in the peripheral blood; they also had a greatly enhanced CD123(+) plasmacytoid dendritic cell infiltration of the lamina propria. Interferon-gamma production capacity was not changed significantly except in non-responders, where it increased. These data show that clinical benefit from G-CSF treatment in Crohn's disease is accompanied by significant induction of IL-10 secreting T cells as well as increases in plasmacytoid dendritic cells in the lamina propria of the inflamed gut mucosa.

Th2 cell therapy of established acute graft-versus-host disease requires IL-4 and IL-10 and is abrogated by IL-2 or host-type antigen-presenting cells

Delayed donor Th2 cell infusion permits a graft-versus-tumor (GVT) effect to occur with subsequent amelioration of established graft-versus-host disease (GVHD). Relative to GVHD controls (B6-into-BALB/c model), recipients of delayed Th2 cells (day 14 post-BMT) had increased survival (3/3 experiments [exp]; each exp P < .0001) and reduced GVHD by histology analysis 5 days post-Th2 infusion without increased tumor burden (3 of 3 exp; each exp P < or = .02). Th2 cell-mediated amelioration of GVHD was associated with greatly reduced allospecific IFN-gamma secretion, in vivo augmentation of allospecific IL-4 and IL-10 secretion, and reduction in donor CD8(+) T cell number post-BMT (3 of 3 exp; each comparison, P < or = .003). To better understand the molecular mechanism of this GVHD therapy, Th2 cells were generated from wild-type (WT), IL-4 deficient (KO), or IL-10 KO donors: remarkably, recipients of IL-4 or IL-10 KO Th2 cells had no survival advantage, no improvement in GVHD by histology, no reduction in CD8(+) T cell expansion post-BMT, and no in vivo shift toward type II cytokines. We reasoned that IL-2 and alloantigen availability may be limiting factors for Th2 cell therapy, and as such, evaluated whether coadministration of IL-2 or coinfusion of host-type antigen-presenting cells (APC) might intensify the anti-GVHD effect. However, contrary to these hypotheses, concomitant IL-2 therapy or APC administration fully abrogated the Th2 cell-mediated survival advantage and histology-defined GVHD reduction, reduced Th2 cell expansion in vivo while promoting CD8(+) T cell expansion from cells originating from the initial allograft, and impaired type II polarization in vivo. In conclusion, Th2 cell therapy can rapidly ameliorate severe GVHD via IL-4 and IL-10 mediated mechanisms, and potentially, via IL-2 consumption and APC modulation mechanisms.

Cell biology and clinical promise of G-CSF: immunomodulation and neuroprotection

In the light of the enthusiasm to use of recombinant human granulocyte colony-stimulating factor (G-CSF) for immunomodulation and neuroprotection, it should be remembered that the current knowledge is based on a century of laborious research. G-CSF is a pleiotropic cytokine playing a major role as regulator of haematopoiesis. Although the precise mechanisms of G-CSF are not known, there is growing evidence supporting the notion that G-CSF also exerts profound immunoregulatory effect in adaptive immunity and has a neuroprotective role in both cerebral ischemia and neurodegeneration. Here, we describe the immunomodulation and the neuroprotection that can be achieved with G-CSF, and summarize possible mechanisms of G-CSF as a potential therapeutic agent in autoimmune diseases and neurological disorders. Our understanding of these novel sites of action of G-CSF has opened therapeutic avenues for the treatment of autoimmune diseases and neurological disorders, and has translated the beneficial effects of G-CSF from basic experiments to clinical patients.

Granulocyte colony-stimulating factor: molecular mechanisms of action during steady state and 'emergency' hematopoiesis

Neutrophils are phagocytes whose principal function is to maintain anti-bacterial immunity. Neutrophils ingest and kill invading bacteria, releasing cytotoxic, chemotactic and inflammatory mediators at sites of infection. This serves to control the immediate host immune response and attract other cells, such as macrophages and dendritic cells, which are important for establishing long-term adaptive immunity. Neutrophils thus contribute to both the initiation and the maintenance of inflammation at sites of infection. Aberrant neutrophil activity is deleterious; suppressed responses can cause extreme susceptibility to infection while overactivation can lead to excessive inflammation and tissue damage. This review will focus on neutrophil regulation by granulocyte colony-stimulating factor (G-CSF), the principal cytokine controlling neutrophil development and function. The review will emphasize the molecular aspects of G-CSF-driven granulopoiesis in steady state (healthy) conditions and during demand-driven or 'emergency' conditions elicited by infection or clinical administration of G-CSF. Understanding the molecular control of granulopoiesis will aid in the development of new approaches designed to treat disorders of neutrophil production and function.

Inflammatory cell infiltration of tumors: Jekyll or Hyde

Inflammatory cell infiltration of tumors contributes either positively or negatively to tumor invasion, growth, metastasis, and patient outcomes, creating a Dr. Jekyll or Mr. Hyde conundrum when examining mechanisms of action. This is due to tumor heterogeneity and the diversity of the inflammatory cell phenotypes that infiltrate primary and metastatic lesions. Tumor infiltration by macrophages is generally associated with neoangiogenesis and negative outcomes, whereas dendritic cell (DC) infiltration is typically associated with a positive clinical outcome in association with their ability to present tumor antigens (Ags) and induce Ag-specific T cell responses. Myeloid-derived suppressor cells (MDSCs) also infiltrate tumors, inhibiting immune responses and facilitating tumor growth and metastasis. In contrast, T cell infiltration of tumors provides a positive prognostic surrogate, although subset analyses suggest that not all infiltrating T cells predict a positive outcome. In general, infiltration by CD8(+) T cells predicts a positive outcome, while CD4(+) cells predict a negative outcome. Therefore, the analysis of cellular phenotypes and potentially spatial distribution of infiltrating cells are critical for an accurate assessment of outcome. Similarly, cellular infiltration of metastatic foci is also a critical parameter for inducing therapeutic responses, as well as establishing tumor dormancy. Current strategies for cellular, gene, and molecular therapies are focused on the manipulation of infiltrating cellular populations. Within this review, we discuss the role of tumor infiltrating, myeloid-monocytic cells, and T lymphocytes, as well as their potential for tumor control, immunosuppression, and facilitation of metastasis.

Biologic and molecular effects of granulocyte colony-stimulating factor in healthy individuals: recent findings and current challenges

Recombinant human granulocyte colony-stimulating factor (rhG-CSF) is widely used in healthy donors for collection of peripheral blood progenitor cells (PBPCs) for allogeneic transplantation and granulocytes for transfusion. The spectrum of its biologic and molecular activities in healthy individuals is coming into sharper focus, creating a unique set of challenges and clarifying the need to monitor and safeguard donor safety. Accumulating evidence indicates that rhG-CSF effects are not limited to the myeloid cell lineage. This may reflect the presence of functional G-CSF receptors on other cell types and tissues, as well as rhG-CSF-induced modulation of cytokine networks. While most rhG-CSF-induced effects are transient and self-limiting, preliminary, provocative data have suggested the possibility of a more durable effect on the chromosomal integrity of lymphocytes. While these reports have not been validated and have been subject to criticism, they are prompting prospective studies and monitoring efforts to determine whether there is a significant risk of long-term adverse events (eg, hematologic malignancies) in healthy PBPC and granulocyte donors. Based on the totality of information that is currently available, the administration of rhG-CSF to healthy donors for the purpose of PBPC donation continues to have a favorable risk-benefit profile.

Granulocyte colony-stimulating factor for the induction of T-cell tolerance

In recent years, investigators have unraveled a previously unrecognized role for granulocyte colony-stimulating factor (G-CSF) in the regulation of T-cell and dendritic cell functions. The experimental evidence in favor of G-CSF-mediated immune regulation includes the ability to skew T-cell cytokine secretion to T-helper type 2 responses, and to promote regulatory T-cell and tolerogenic dendritic cell differentiation. Accordingly, beneficial effects of G-CSF have been detected in animal models of immune-mediated diseases, including posttransplantation graft-versus-host disease, experimental autoimmune encephalomyelitis, lupus nephritis, inflammatory bowel disease, and diabetes. The growing body of evidence supporting a novel role for G-CSF in the induction of T-cell tolerance is reviewed herein.

Hepatitis C is associated with perturbation of intrahepatic myeloid and plasmacytoid dendritic cell function

BACKGROUND/AIMS

In most cases infection with hepatitis C results in chronic infection as a consequence of viral subversion and failed anti-viral immune responses. The suggestion that dendritic cells are defective in chronic HCV infection led us to investigate the phenotype and function of liver-derived myeloid (mDC) and plasmacytoid (pDC) dendritic cells in patients with chronic HCV infection.

METHODS

Liver DCs were isolated without expansion in cytokines from human liver allowing us to study unmanipulated tissue-resident DCs ex vivo.

RESULTS

Compared with mDCs isolated from non-infected inflamed liver mDCs from HCV-infected liver (a) demonstrated higher expression of MHC class II, CD86 and CD123, (b) were more efficient stimulators of allogeneic T-cells and (c) secreted less IL-10. Reduced IL-10 secretion may be a factor in the enhanced functional properties of mDCs from HCV infected liver because antibody depletion of IL-10 enhanced the ability of mDCs from non-infected liver to stimulate T-cells. In contrast, pDCs were present at lower frequencies in HCV-infected liver and expressed higher levels of the regulatory receptor BDCA-2.

CONCLUSIONS

In HCV-infected liver the combination of enhanced mDC function and a reduced number of pDCs may contribute to viral persistence in the face of persistent inflammation.

Hematopoietic Growth Factors Including Keratinocyte Growth Factor in Allogeneic and Autologous Stem Cell Transplantation

The aim of hematopoietic stem cell transplantation (HSCT) is to cure patients of malignancies, autoimmune diseases, and immunodeficiency disorders by redirecting the immune system: the often described graft-versus-leukemia (GVL) or graft-versus-tumor (GVT) effects. Unfortunately, fulfillment of this goal is often hampered by relapse of the underlying disease, graft-versus-host disease (GVHD), or severe opportunistic infections, which account for the majority of post-transplantation deaths. Moreover, studies of long-term survivors of transplantation indicate an accelerated immune aging due to the transplantation procedure itself, preceding chemo- or radiotherapy, and acute and chronic GVHD. Significant advances have been made towards overcoming these obstacles by enhancing immune reconstitution with hematopoietic growth factors (HGFs) such as granulocyte colony-stimulating factor (G-CSF) or erythropoietin (EPO) or through the application of cytokines. In addition, there are approaches to promote the thymic-dependent development of naive T cells, which are prepared for the interaction with a multitude of pathogens. Examples are the application of keratinocyte growth factor (KGF), neuroendocrine hormones such as growth hormone or prolactin, sex hormone ablation, or the invention of a three-dimensional artificial thymus based on a cytomatrix. Might these measures result in a higher rate of healthy and fully recovered patients? Here we review progress in each of these areas.

Dendritic cell-regulatory T-cell interactions control self-directed immunity

In addition to their immunostimulatory capacity, dendritic cells (DCs) play a crucial role in central and peripheral tolerance mechanisms. In the absence of an infection, immature DCs constantly take up, process and present self-antigens to specific T cells, which leads to the induction of T-cell anergy or deletion. In recent years, several additional mechanisms have been identified by which DCs constantly downregulate immune responses to maintain immunological tolerance. Among these are the complex interactions between several DC subtypes and different types of regulatory T cells. In this review, we summarize recent key findings and concepts in this field.

Comparison of outcomes after transplantation of peripheral blood stem cells versus bone marrow following an identical nonmyeloablative conditioning regimen

This is the first study to examine the outcomes in 54 patients with hematologic malignancies who received an HLA-matched related donor bone marrow (BM, n = 42) or GCSF-mobilized peripheral blood stem cells (PBSC, n = 12) following identical nonmyeloablative conditioning with the intention of induction of mixed chimerism (MC) followed by prophylactic donor leukocyte infusion (pDLI) to convert MC to full donor chimerism (FDC) and capture a graft-versus-tumor effect without clinical graft-versus-host disease (GVHD). Neutrophil and platelet recovery were faster and transfusion requirement was less in PBSC recipients (P < 0.05). A total of 48% of BMT recipients achieved FDC with a median conversion time of 84 days, including 13 following pDLI. In contrast, 83% (P = 0.04) in the PBSC group had spontaneous FDC at a median of 14 days, precluding the administration of pDLI. There was no significant difference in the incidences of acute or chronic GVHD, though the rates of chronic GVHD were considerably higher in PBSC group than in the BM group (6/7, 86% vs 10/24, 42%). CD4 and CD8 T-cell recovery was faster in PBSC recipients. In PBSC recipients, a higher number of CD34+ cells was associated with increased rates of severe, grade III-IV acute GVHD.

IFNgamma differentially controls the development of idiopathic pneumonia syndrome and GVHD of the gastrointestinal tract

Although proinflammatory cytokines are key mediators of tissue damage during graft-versus-host disease (GVHD), IFNgamma has previously been attributed with both protective and pathogenic effects. We have resolved this paradox by using wild-type (wt), IFNgamma(-/-), and IFNgammaR(-/-) mice as donors or recipients in well-described models of allogeneic stem cell transplantation (SCT). We show that donor-derived IFNgamma augments acute GVHD via direct effects on (1) the donor T cell to promote T helper 1 (Th1) differentiation and (2) the gastrointestinal (GI) tract to augment inflammatory cytokine generation. However, these detrimental effects are overwhelmed by a protective role of IFNgamma in preventing the development of idiopathic pneumonia syndrome (IPS). This is the result of direct effects on pulmonary parenchyma to prevent donor cell migration and expansion within the lung. Thus, IFNgamma is the key cytokine differentially controlling the development of IPS and gastrointestinal GVHD after allogeneic SCT.

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

Allogeneic stem cell transplantation (SCT) remains the definitive immunotherapy for malignancy. However, morbidity and mortality due to graft-vs.-host disease (GVHD) remains the major barrier to its advancement. Emerging experimental data highlights the immuno-modulatory roles of diverse cell populations in GVHD, including regulatory T cells, natural killer (NK) cells, NK T cells, gammadelta T cells, and antigen presenting cells (APC). Knowledge of the pathophysiology of GVHD has driven the investigation of new rational strategies to both prevent severe GVHD and treat steroid-refractory GVHD. Novel cytokine inhibitors, immune-suppressant agents known to preserve or even promote regulatory T-cell function and the depletion of specific alloreactive T-cell sub-populations all promise significant advances in the near future. As our knowledge and therapeutic options expand, the ability to limit GVHD whilst preserving anti-microbial and tumour responses becomes a realistic prospect.

Effector and regulatory T-cell function is differentially regulated by RelB within antigen-presenting cells during GVHD

Antigen-presenting cells (APCs) are critical for the initiation of graft-versus-host disease (GVHD), although the responsible APC subset and molecular mechanisms remain unclear. Because dendritic cells (DCs) are the most potent APCs and the NF-kB/Rel family member RelB is associated with DC maturation and potent APC function, we examined their role in GVHD. Within 4 hours of total body irradiation, RelB nuclear translocation was increased and restricted to CD11c(hi) DCs within the host APC compartment. Furthermore, the transient depletion of CD11c(hi) donor DCs that reconstitute in the second week after transplantation resulted in a transient decrease in GVHD severity. By using RelB(-/-) bone marrow chimeras as transplant recipients or RelB(-/-) donor bone marrow, we demonstrate that the induction and maintenance of GVHD is critically dependent on this transcription factor within both host and donor APCs. Critically, RelB within APCs was required for the expansion of donor helper T cell type 1 (Th1) effectors and subsequent alloreactivity, but not the peripheral expansion or function of donor FoxP3(+) regulatory T cells. These data suggest that the targeted inhibition of nuclear RelB translocation within APCs represents an attractive therapeutic strategy to dissociate effector and regulatory T-cell function in settings of Th1-mediated tissue injury.

Mobilization of bone marrow-derived progenitors

Bone marrow (BM) is a source of various stem and progenitor cells in the adult, and it is able to regenerate a variety of tissues following transplantation. In the 1970s the first BM stem cells identified were hematopoietic stem cells (HSCs). HSCs have the potential to differentiate into all myeloid (including erythroid) and lymphoid cell lineages in vitro and reconstitute the entire hematopoietic and immune systems following transplantation in vivo. More recently, nonhematopoietic stem and progenitor cells have been identified that can differentiate into other cell types such as endothelial progenitor cells (EPCs), contributing to the neovascularization of tumors as well as ischemic tissues, and mesenchymal stem cells (MSCs), which are able to differentiate into many cells of ectodermal, endodermal, and mesodermal origins in vitro as well as in vivo. Following adequate stimulation, stem and progenitor cells can be forced out of the BM to circulate into the peripheral blood, a phenomenon called "mobilization." This chapter reviews the molecular mechanisms behind mobilization and how these have led to the various strategies employed to mobilize BM-derived stem and progenitor cells in experimental and clinical settings. Mobilization of HSCs will be reviewed first, as it has been best-explored--being used extensively in clinics to transplant large numbers of HSCs to rescue cancer patients requiring hematopoietic reconstitution--and provides a paradigm that can be generalized to the mobilization of other types of BM-derived stem and progenitor cells in order to repair other tissues.

Mechanisms of hematopoietic stem cell mobilization: When innate immunity assails the cells that make blood and bone

Mobilization is now used worldwide to collect large numbers of hematopoietic stem and progenitor cells (HSPCs) for transplantation. Although the first mobilizing agents were discovered largely by accident, discovery of more efficient mobilizing agents will require a better understanding of the molecular mechanisms responsible. During the past 5 years, a number of mechanisms have been identified, shedding new light on the dynamics of the hematopoietic system in vivo and on the intricate relationship between hematopoiesis, innate immunity, and bone. After briefly reviewing the mechanisms by which circulating HSPCs home into the bone marrow and what keeps them there, the current knowledge of mechanisms responsible for HSPC mobilization in response to hematopoietic growth factors such as granulocyte colony-stimulating factor, chemotherapy, chemokines, and polyanions will be discussed together with current strategies developed to further increase HSPC mobilization.

Host B cells produce IL-10 following TBI and attenuate acute GVHD after allogeneic bone marrow transplantation

Host antigen-presenting cells (APCs) are known to be critical for the induction of graft-versus-host disease (GVHD) after allogeneic bone marrow transplantation (BMT), but the relative contribution of specific APC subsets remains unclear. We have studied the role of host B cells in GVHD by using B-cell-deficient microMT mice as BMT recipients in a model of CD4-dependent GVHD to major histocompatibility complex antigens. We demonstrate that acute GVHD is initially augmented in microMT recipients relative to wild-type recipients (mortality: 85% vs 44%, P < .01), and this is the result of an increase in donor T-cell proliferation, expansion, and inflammatory cytokine production early after BMT. Recipient B cells were depleted 28-fold at the time of BMT by total body irradiation (TBI) administered 24 hours earlier, and we demonstrate that TBI rapidly induces sustained interleukin-10 (IL-10) generation from B cells but not dendritic cells (DCs) or other cellular populations within the spleen. Finally, recipient mice in which B cells are unable to produce IL-10 due to homologous gene deletion develop more severe acute GVHD than recipient mice in which B cells are wild type. Thus, the induction of IL-10 in host B cells during conditioning attenuates experimental acute GVHD.

Allogeneic Stem Cell Transplantation with Peripheral Blood Stem Cells Mobilized by Pegylated G-CSF

Mobilization of stem cells with pegylated granulocyte colony-stimulating factor (peg-G-CSF) modulates donor T- and natural killer T-cell (NKT-cell) functions, thus separating graft-versus-host from graft-versus-leukemia disease in animal models. We report a phase I/II study that analyzed the feasibility of mobilizing stem cells from normal donors with peg-G-CSF and the ability of these cells to restore hematopoiesis in allogeneic transplant recipients after myeloablative conditioning. Administration of 6 mg of peg-G-CSF resulted in suboptimal stem cell mobilization, with a peak peripheral blood CD34+ count of 29+/-5/microL. Apheresis 4 days after peg-G-CSF yielded 2.7+/-.4x10(6) CD34+ cells/kg recipient weight, and all donors required a second collection on day 5 to yield a total of 4.2+/-.5x10(6) CD34+ cells/kg recipient weight. After escalation of the dose to 12 mg, the peak CD34+ count was 99+/-11/microL and 12 of 13 donors collected sufficient stem cells for transplantation in a single apheresis (8.9+/-1.4x10(6) CD34+ cells/kg recipient weight). Late transient increases in serum hepatic transaminases were noted, but other side effects (predominantly bone pain) were otherwise similar to those seen in donors mobilized with standard G-CSF. Median neutrophil and platelet engraftments occurred on days 18 and 14, respectively, after transplantation and were identical to those seen with in recipients of grafts mobilized with standard G-CSF. With a median follow-up of 357 days, the incidence of grade II-IV acute graft-versus-host disease was 50% and there have been no relapses to date. Mobilization of stem cells with peg-G-CSF in normal donors is feasible and 12 mg results in mobilization characteristics similar to those of standard G-CSF.

Tolerogenic dendritic cells: cytokine modulation comes of age

Dendritic cells (DCs) include a heterogeneous family of professional APCs involved in initiation of immunity and in immunologic tolerance. Specifically, peripheral tolerance can be achieved and maintained by promoting regulatory T-cell (Treg) responses and/or T-cell anergy or deletion. Until recently, immature developmental stages of DC differentiation were believed to induce T-cell anergy or Treg cells, whereas DCs transformed into mature DCs by activation stimuli were thought to represent immunogenic DCs capable of inciting primary T-cell responses. This paradigm has been challenged by the demonstration of Treg-cell expansion by antigen-bearing, fully mature DCs. Similarly, semimature DCs with a distinctive interleukin 10 (IL-10)+ IL-12- cytokine production profile might be endowed with tolerogenic functions, supporting the concept that DC maturation per se should no longer be considered as a distinguishing feature of immunogenic as opposed to tolerogenic DCs (TDCs). Cytokine-modulated TDCs reflect an incomplete or altered status of monocyte differentiation and promote in vitro induction of Treg cells and/or in vivo protection from autoimmune diseases. Several growth factors, including IL-10, transforming growth factor beta (TGF-beta), granulocyte colony-stimulating factor (G-CSF), hepatocyte growth factor (HGF), and vasoactive intestinal peptide (VIP), modulate DC maturation and favor the differentiation of TDCs. From a therapeutic standpoint, cytokine-modulated TDCs might be beneficial for prevention and/or treatment of posttransplantation graft-versus-host disease (GVHD) and autoimmunity.

Granulocyte colony-stimulating factor: a novel mediator of T cell tolerance

In recent years, several investigators have unraveled a previously unrecognized role for G-CSF in the regulation of T cell and dendritic cell functions. The experimental evidence in favor of G-CSF-mediated immune regulation includes the ability to switch T cell cytokine secretion profile to Th2 responses and the promotion of regulatory T cell and tolerogenic dendritic cell differentiation. Interestingly, G-CSF is beneficial in animals for the prevention and/or treatment of immune-mediated diseases, e.g., graft-vs-host disease, multiple sclerosis, systemic lupus erythematosus, inflammatory bowel disease, and diabetes, suggesting a potential role in human autoimmune diseases. This review summarizes the growing body of evidence that supports a critical role for G-CSF as a novel mediator of T cell tolerance.

Stem cell mobilization with G-CSF analogs: a rational approach to separate GVHD and GVL?

The separation of graft-versus-host disease (GVHD) and graft-versus-leukemia (GVL) remains the "holy grail" of allogeneic stem cell transplantation, and improvements are urgently needed to allow more effective therapy of malignant disease. The use of G-CSF-mobilized peripheral blood as a clinical stem cell source is associated with enhanced GVL effects without amplification of significant acute GVHD. Preclinical studies have demonstrated that G-CSF modulates donor T cell function before transplantation, promoting T(H)2 differentiation and regulatory T cell function. In addition, the expansion of immature antigen-presenting cells (APCs) and plasmacytoid dendritic cells (DCs) favors the maintenance of this pattern of T cell differentiation after transplantation. Although these patterns of T cell differentiation attenuate acute GVHD, they do not have an impact on the cytolytic pathways of the CD8(+) T cells that are critical for effective GVL. Recently, it has been demonstrated that modification of G-CSF, either by pegylation of the native cytokine or conjugation to Flt-3L, results in the expansion and activation of donor iNKT cells, which significantly augment CD8(+) T cell-mediated cytotoxicity and GVL effects after transplantation. Given that these cytokines also enhance the expansion of regulatory T cells and APCs, they further separate GVHD and GVL, offering potential clinical advantages for the transplant recipient.

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

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

TGF-beta in allogeneic stem cell transplantation: friend or foe?

Donor treatment with granulocyte-colony-stimulating factor (G-CSF) attenuates the ability of donor T cells to induce acute graft-versus-host disease (aGVHD) but increases the severity of chronic GVHD (cGVHD). We investigated the role of the regulatory cytokine transforming growth factor beta (TGF-beta) in this paradox in well-established murine models of aGVHD and cGVHD wherein recipients undergo transplantation with splenocytes from donors treated with G-CSF. Neutralization of TGF-beta after stem-cell transplantation (SCT) significantly increased the severity of aGVHD, and the concurrent prevention of interleukin-10 (IL-10) production further exaggerated this effect. Early after SCT, donor T cells were the predominant source of TGF-beta and were able to attenuate aGVHD in a TGF-beta-dependent fashion. Although the neutralization of TGF-beta augmented the proliferation and expansion of donor T cells after SCT, it paradoxically impaired cellular cytotoxicity to host antigens and associated graft-versus-leukemia (GVL) effects. In cGVHD, neutralization of TGF-beta from day 14 after SCT attenuated histologic abnormalities, and CD11b+ mononuclear cells infiltrating sclerodermatous skin produced 50-fold more TGF-beta than corresponding T cells. Thus, though the production of TGF-beta by donor T cells early after transplantation attenuates aGVHD and is required for optimal GVL, the production of TGF-beta late after SCT is preferentially from mononuclear cells and mediates cGVHD. These data have important implications for the timing of therapeutic TGF-beta neutralization to prevent cGVHD after allogeneic SCT.

New strategies for mobilization of hematopoietic stem cells

A significant number of tumor patients fail peripheral blood progenitor cell (PBPC) mobilization and thus cannot receive potentially curative high-dose chemotherapy with subsequently required PBPC transplantation. New insights into the physiology of mobilization have revealed the pivotal role of the CXCR4/stromal derived factor-1α receptor–ligand interaction for stem cell retention in the bone marrow. New CXCR4 antagonists such as AMD3100 are currently in clinical studies. They act synergistically with the established mobilizing agent granulocyte colony-stimulating factor (G-CSF); thus, patients can collect more PBPCs in fewer apheresis sessions, and others that previously failed can now successfully collect sufficient PBPCs for transplantation. Experimental and clinical data suggest that the quality of AMD3100-mobilized PBPC may even be superior to PBPCs mobilized following standard therapy. CXCR4 antagonists are the most exciting development in the field of PBPC mobilization for over a decade. Additionally, new analogs of G-CSF are being introduced with favorable pharmacologic features.

Granulocyte and granulocyte-macrophage colony-stimulating factors in allografts: Uses, misuses, misconceptions, and future applications

Despite more than 10 years experience using growth factors after allogeneic stem cell transplantation (ASCT), their state in this has not been elucidated. Most studies show that they accelerate myeloid recovery, regardless of whether they are instituted on day 0 or day 10 after transplant. However, this does not correlate with an improvement in the outcome. One disadvantage is that granulocyte colony-stimulating factor (G-CSF) prophylaxis is associated with slower platelet engraftment due to an increase in platelet aggregation. There is also no agreement as regards the value of G-CSF given as prophylaxis after ASCT, the effects on graft-vs-host disease (GVHD), and the survival rate. A large retrospective study from Europe showed that patients with acute leukemia who received bone marrow from HLA-identical siblings and were treated with G-CSF ran a higher risk of acute and chronic GVHD and transplant-related mortality, while the survival and the leukemia-free survival rates were reduced. In contrast, a meta-analysis of 18 small studies showed no evidence of an increase in acute and chronic GVHD, using G-CSF as prophylaxis after ASCT. Two studies from the Center for International Blood and Marrow Transplant Research showed contradictory data. When G-CSF is given to the recipient as prophylaxis, the levels of soluble interleukin-2 receptor-alpha increase, which aggravates GVHD. When it is given to the donor, G-CSF polarizes T cells to produce T-helper cell-2 cytokines, which reduce GVHD after transplantation. G-CSF has no effect on relapse. Available findings suggest that there is no indication to use G-CSF as prophylaxis after ASCT.

Cytokine expanded myeloid precursors function as regulatory antigen-presenting cells and promote tolerance through IL-10-producing regulatory T cells

The initiation of graft-vs-host disease (GVHD) after stem cell transplantation is dependent on direct Ag presentation by host APCs, whereas the effect of donor APC populations is unclear. We studied the role of indirect Ag presentation in allogenic T cell responses by adding populations of cytokine-expanded donor APC to hemopoietic grafts that would otherwise induce lethal GVHD. Progenipoietin-1 (a synthetic G-CSF/Flt-3 ligand molecule) and G-CSF expanded myeloid dendritic cells (DC), plasmacytoid DC, and a novel granulocyte-monocyte precursor population (GM) that differentiate into class II+,CD80/CD86+,CD40- APC during GVHD. Whereas addition of plasmacytoid and myeloid donor DC augmented GVHD, GM cells promoted transplant tolerance by MHC class II-restricted generation of IL-10-secreting, Ag-specific regulatory T cells. Importantly, although GM cells abrogated GVHD, graft-vs-leukemia effects were preserved. Thus, a population of cytokine-expanded GM precursors function as regulatory APCs, suggesting that G-CSF derivatives may have application in disorders characterized by a loss of self-tolerance.

The immunomodulatory effects of regulatory T cells: implications for immune regulation in the skin

Regulatory T cells are thought to have a critical role in the suppression of immune responses. In addition to the prevention of the development of autoimmunity, they are also thought to have a role in the prevention of allergic responses to environmental allergens, immune responses to tumours and the development of memory responses to chronic infections. They have been isolated within the skin and have been shown to express surface markers that enable skin-specific migration, suggesting that regulatory T cells have a functional role in the skin. There is accumulating evidence to suggest that regulatory T cells may be involved in numerous skin disorders and may also be modified by various therapeutic agents used to treat these disorders. We review the evidence for the presence of this T-cell subset in humans, the suppressive effects of regulatory T cells, and their role in the skin.

Regulatory T cells and tolerogenic dendritic cells: from basic biology to clinical applications

The induction of antigen (Ag)-specific tolerance is critical for the prevention of autoimmunity and maintenance of immune homeostasis. Recently, attention has been focused on induction of active suppression by regulatory T cells (Treg cells). Also, a role for dendritic cells (DCs) in the promotion of peripheral tolerance has been demonstrated by several studies and is the subject of intensive investigation. It is currently believed that the maturation/activation state of DCs might be a control point for the induction of peripheral tolerance through modifications of the activation state of T cells. Several lines of experimental evidence suggest that unique DC subsets or discrete functional states of the DCs might be devoted to the promotion of Treg cell differentiation. The present review summarizes the emerging literature on the developmental origin and function of human Treg cells and tolerogenic/regulatory DCs. Furthermore, clinical implications of these studies for cellular therapy of immune-mediated pathologies are discussed.