Granulocyte-colony stimulating factor increases CD123hi blood dendritic cells with altered CD62L and CCR7 expression

Immunological effects of vaccines combined with granulocyte colony-stimulating factor on a murine WEHI-3 leukemia model

Granulocyte colony-stimulating factor (G-CSF) mobilizes regulatory T cells (Tregs) from bone marrow into the peripheral blood, by reducing the expression of stromal cell-derived factor-1α (SDF-1α). However, G-CSF has rarely been studied in acute myeloid leukemia (AML) immunotherapy. The present study performed a Transwell migration assay in vitro to determine the contribution of SDF-1α to the migration of leukemia cells, and the effects of G-CSF were evaluated. The effects of G-CSF on SDF-1α and Tregs in the AML microenvironment were examined, by employing a WEHI-3-grafted BALB/c mouse AML model (AML-M4). It is evident that G-CSF reversed immunosuppression of the AML microenvironment by reducing SDF-1α in bone marrow and elevating Tregs in the peripheral blood in in vivo studies. Furthermore, AML mice treated with vaccines combined with G-CSF achieved a longer survival time than those treated with vaccines without G-CSF, showing the efficiency of the regimen. The present study demonstrates the effects of G-CSF on the mobilization of leukemia cells and Tregs into the peripheral blood. In addition, immunotherapy with G-CSF priming represents a promising therapeutic strategy of targeting the immunosuppression.

Granulocyte colony-stimulating factor impairs CD8(+) T cell functionality by interfering with central activation elements

Besides mobilizing stem cells into the periphery, granulocyte colony-stimulating factor (G-CSF) has been shown to influence various types of innate and adaptive immune cells. For example, it impairs the effector function of cytotoxic T lymphocytes (CTLs). It is assumed that this effect is mediated indirectly by monocytes, regulatory T cells and immunomodulatory cytokines influenced by G-CSF. In this study, isolated G-CSF-treated CD8(+) T cells were stimulated antigen-dependently with peptide-major histocompatibility complex (pMHC)-coupled artificial antigen-presenting cells (aAPCs) or stimulated antigen-independently with anti-CD3/CD28 stimulator beads. By measuring the changes in interferon (IFN)-γ and granzyme B expression at the mRNA and protein level, we showed for the first time that G-CSF has a direct effect on CD8(+) CTLs, which was confirmed based on the reduced production of IFN-γ and granzyme B by the cytotoxic T cell line TALL-104 after G-CSF treatment. By investigating further elements affected by G-CSF in CTLs from stem cell donors and untreated controls, we found a decreased phosphorylation of extracellular-regulated kinase (ERK)1/2, lymphocyte-specific protein tyrosine kinase (Lck) and CD3ζ after G-CSF treatment. Additionally, miRNA-155 and activation marker expression levels were reduced. In summary, our results show that G-CSF directly influences the effector function of cytotoxic CD8(+) T cells and affects various elements of T cell activation.

Mechanisms for T cell tolerance induced with granulocyte colony-stimulating factor

Granulocyte colony-stimulating factor (G-CSF) has been widely accepted as a mediator of T cell tolerance. The immune modulatory effect of G-CSF on T cells is believed to be mediated exclusively through other effector cells, such as monocytes, tolerogenic dendritic cells (DC), and myeloid-derived suppressor cells. Recent advances confirmed the direct effects of G-CSF in inducing immune tolerance of T cells through the G-CSF-G-CSF receptor pathway and related molecular mechanisms. This review aims to summarize the findings associated with the direct and indirect mechanisms for T cell tolerance induced with G-CSF. The role of G-CSF in preventing graft-versus-host disease (GVHD) and in treating autoimmune diseases (ADs) is also discussed. It is conceivable that G-CSF and immune cell compositions, such as tolerogenic DC and CD4(+)CD25(+)Foxp3(+) T cells, modulated by G-CSF could become an integral part of the immunomodulatory therapies against GVHD and ADs in the future.

Nanoparticles modify dendritic cell homeostasis and induce non-specific effects on immunity to malaria

BACKGROUND

Many current vaccines to a specific pathogen influence responses to other pathogens in a process called heterologous immunity. We propose that their particulate nature contributes to non-specific effects. Herein, we demonstrate polystyrene nanoparticles modulate dendritic cell (DC) homeostasis, thereby promoting a persistent enhanced state of immune readiness to a subsequent infectious challenge.

METHODS

Particles (approximately 40 nm and 500 nm carboxylated polystyrene nanoparticles; PSNPs) alone or conjugated to a model antigen were injected in mice, and DCs in draining lymph nodes (dLNs) and bone-marrow (BM) quantified by flow cytometry. BM cells were tested for capacity to generate DCs upon culture with granulocyte and macrophage colony stimulating factor. Mice were challenged with Plasmodium yoelli. Blood parasitaemias were monitored by GIEMSA. Sera was analyzed for antibodies by ELISA.

RESULTS

Intradermal administration of 40 nm PSNPs induced anti-inflammatory cytokines, chemokines and growth factors, increased numbers and proportions of DCs in the dLN, and increased the capacity of BM to generate DCs. Consistent with these unexpected changes, 40 nm PSNPs pre-injected mice had enhanced ability to generate immunity to a subsequent malarial infection.

CONCLUSIONS

Intradermal administration of 40 nm PSNPs modifies DC homeostasis, which may at least in part explain the observed beneficial heterologous effects of current particulate vaccines. Further nanotechnological developments may exploit such strategies to promote beneficial non-specific effects.

Allometric dose retranslation unveiled substantial immunological side effects of granulocyte colony-stimulating factor after stroke

BACKGROUND AND PURPOSE

Granulocyte colony-stimulating factor (GCSF) showed robust neuroprotective and neuroregenerative properties after stroke in rodents but failed to meet study end points in patients. Because immunologic side effects of GCSF may have escaped preclinical testing because of nonallometric dose translation, we hypothesized those as possible reasons.

METHODS

Stroke was induced in C57BL/6 mice by 45-minute filament middle cerebral artery occlusion. GCSF was administered at 50 and 832.5 μg/kg body weight. Treatment was controlled by vehicle injection, sham surgery, and naive animals. Immune cell counts were assessed in blood, spleen, and brain by multidimensional flow cytometry 1 day after stroke.

RESULTS

High-dose GCSF significantly altered myeloid and T-cell subpopulations in blood and spleen and caused a tremendous increase of monocytes/macrophages infiltrating the ischemic brain.

CONCLUSIONS

Dose-dependent immunomodulation superimposes central nervous system-specific effects of GCSF after stroke. Adaption of dose or treatment time may overcome this drawback.

Cellular mechanism for granulocyte-colony stimulating factor in the prevention of graft-versus-host disease in combined bone marrow and peripheral blood transplantation for hematological malignancies: the composition in collection

Despite improvements in transplant immunology and clinical and supportive care, acute graft-versus-host disease (aGVHD) remains a clinical challenge and a major cause of morbidity and mortality for patients after allogeneic hematopoietic stem cell transplantation (HSCT). Many ways have been used to prevent and treat aGVHD, however, long-term survival remains poor. The key to improve aGVHD outcomes may, in fact, rest upon successful initial therapy. The HLA-matched HSCT was limited by the shortage of suitable donors. Unmanipulated haploidentical/mismatched related transplantation with combined granulocyte-colony stimulating factor (G-CSF)-mobilized peripheral blood stem cells and G-CSF-mobilized bone marrow as a stronger aGVHD inhibition and graft-versus-leukemia effect, has been developed as an alternative transplantation strategy for patients with hematologic malignancies for the advantage of immediate donor availability, ability to select the best of many relatives, controlled graft composition and immediate access to donor-derived cellular therapies if required after transplantation. G-CSF is a potent hematopoietic cytokine, which is produced by fibroblasts, monocytes, and endothelial cells. G-CSF regulates production of neutrophils within the bone marrow and affects neutrophil progenitor proliferation, maturation and is also involved in mobilization of granulocytes, stem and progenitor cells, which has an important role in this transplantation. In this article, we review the possible mechanism for this combined G-CSF-mobilized HSCT in the prevention of aGVHD. Monocytes, T cells, Tregs cells, DC, adhesive molecule, NK cell/KIR ligand mismatching and mesenchymal stem cells may be involved in this transplantation.

Kinetics of rebounding of lymphoid and myeloid cells in mouse peripheral blood, spleen and bone marrow after treatment with cyclophosphamide

Recently, we showed that post cyclophosphamide (CTX) microenvironment benefits the function of transferred T cells. Analysis of the kinetics of cellular recovery after CTX treatment showed that a single 4 mg/mouse CTX treatment decreased the absolute number of leukocytes in the peripheral blood (PBL) at days 3-15, and in the spleen and bone marrow (BM) at days 3-6. The absolute numbers of CD11c(+)CD11b(-) and CD11c(+)CD11b(+) dendritic cells (DCs), CD11b(+) and Ly6G(+) myeloid cells, T and B cells, CD4(+)CD25(+) T regulatory (T(reg)) cells, and NK1.1(+) cells also decreased. The cell numbers returned to control levels during the recovery phase. The absolute numbers of B cells remained low for 3 weeks. The numbers of DCs increased in PBL and spleen at day 9 but returned to control levels at day 15. These data indicate that CTX alters the cellular microenvironment in kinetics that might be precisely targeted to benefit the host.

The chemokine system in allogeneic stem-cell transplantation: a possible therapeutic target?

Further improvements in allogeneic stem-cell transplantation will probably depend on a better balance between immunosuppression to control graft-versus-host disease and immunological reconstitution sufficient to ensure engraftment, reduction of infection-related mortality and maintenance of post-transplant antileukemic immune reactivity. The chemokine network is an important part of the immune system, and, in addition, CXCL12/CXCR4 seem to be essential for granulocyte colony-stimulating factor-induced stem-cell mobilization. Partial ex vivo graft T-cell depletion based on the expression of specific chemokine receptors involved in T-cell recruitment to graft-versus-host disease target organs may also become a future therapeutic strategy; an alternative approach could be pharmacological inhibition (single-receptor inhibitors or dual-receptor inhibitors) in vivo of specific chemokine receptors involved in this T-cell recruitment. Future clinical studies should therefore be based on a better characterization of various immunocompetent cells, including their chemokine receptor profile, both in the allografts and during post-transplant reconstitution.

Mobilisation strategies for normal and malignant cells

This review evaluates the latest information on the mobilisation of haemopoietic stem cells for transplantation, with the focus on what is the current best practice and how new understanding of the bone marrow stem cell niche provides new insights into optimising mobilisation regimens. The review then looks at the mobilisation of mesenchymal stromal cells, immune cells as well as malignant cells and what clinical implications there are.

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.

Dendritic cell recovery post-lymphodepletion: a potential mechanism for anti-cancer adoptive T cell therapy and vaccination

Adoptive transfer of autologous tumor-reactive T cells holds promise as a cancer immunotherapy. In this approach, T cells are harvested from a tumor-bearing host, expanded in vitro and infused back to the same host. Conditioning of the recipient host with a lymphodepletion regimen of chemotherapy or radiotherapy before adoptive T cell transfer has been shown to substantially improve survival and anti-tumor responses of the transferred cells. These effects are further enhanced when the adoptive T cell transfer is followed by vaccination with tumor antigens in combination with a potent immune adjuvant. Although significant progress has been made toward an understanding of the reasons underlying the beneficial effects of lymphodepletion to T cell adoptive therapy, the precise mechanisms remain poorly understood. Recent studies, including ours, would indicate a more central role for antigen presenting cells, in particular dendritic cells. Unraveling the exact role of these important cells in mediation of the beneficial effects of lymphodepletion could provide novel pathways toward the rational design of more effective anti-cancer immunotherapy. This article focuses on how the frequency, phenotype, and functions of dendritic cells are altered during the lymphopenic and recovery phases post-induction of lymphodepletion, and how they affect the anti-tumor responses of adoptively transferred T cells.

Cyclophosphamide induces dynamic alterations in the host microenvironments resulting in a Flt3 ligand-dependent expansion of dendritic cells

Preconditioning a recipient host with lymphodepletion can markedly augment adoptive T cell therapy. However, the precise mechanisms involved are poorly understood. In a recent study, we observed a significant increase in the circulating levels of dendritic cells (DCs; CD11c(+)CD11b(+)) during the recovery from cyclophosphamide (CTX)-induced lymphodepletion. Herein, we demonstrate that the CTX-induced DC expansion was not altered by adjuvant chemotherapy or tumor burden but was augmented by coadministration of granulocyte-colony stimulating factor. Although the increase in the number of DCs was preceded by a systemic expansion of a population expressing the phenotype of myeloid-derived suppressor cells (Gr-1(+)CD11b(+)), depletion of these Gr-1(+) cells had no effect on the noted expansion. Moreover, when Gr-1(high)CD11b(high) cells were sorted from CTX-treated mice and adoptively transferred into control or CTX-treated recipients, they did not differentiate into DCs. Post-CTX expansion of DCs was associated with proliferation of DCs in bone marrow (BM) during the lymphopenic phase and in the blood and spleen during the recovery phase. Furthermore, adoptive transfer of BM cells from CTX-treated mice produced equal numbers of DCs in the blood of either CTX-treated or untreated recipients. CTX induced a dynamic surge in the expression of growth factors and chemokines in BM, where CCR2 and Flt3 signaling pathways were critical for DC expansion. In sum, our data suggest that CTX induces proliferation of DCs in BM prior to their expansion in the periphery. Targeting DCs at these phases would significantly improve their contribution to the clinical application of lymphodepletion to adoptive immunotherapy.

Cyclophosphamide induces bone marrow to yield higher numbers of precursor dendritic cells in vitro capable of functional antigen presentation to T cells in vivo

We have shown recently that cyclophosphamide (CTX) treatment induced a marked increase in the numbers of immature dendritic cells (DCs) in blood, coinciding with enhanced antigen-specific responses of the adoptively transferred CD8(+) T cells. Because this DC expansion was preceded by DC proliferation in bone marrow (BM), we tested whether BM post CTX treatment can generate higher numbers of functional DCs. BM was harvested three days after treatment of C57BL/6 mice with PBS or CTX and cultured with GM-CSF/IL-4 in vitro. Compared with control, BM from CTX-treated mice showed faster generation and yielded higher numbers of DCs with superior activation in response to toll-like receptor (TLR) agonists. Vaccination with peptide-pulsed DCs generated from BM from CTX-treated mice induced comparable adjuvant effects to those induced by control DCs. Taken together, post CTX BM harbors higher numbers of DC precursors capable of differentiating into functional DCs, which be targeted to create host microenvironment riches in activated DCs upon treatment with TLR agonists.

[Dendritic cells in hypertrophied adenoid at children with otitis media with effusion]

INTRODUCTION

The adenoids are organized as lymphoepithelial structures that play an important role in protecting both the upper respiratory and alimentary tract regions. This functions requires dendritic cells (DC) which are one of the major populations of immune cells. Due to the presence of specific receptors (DC) are able to respond to both intra- and extracellular antigens. Dendritic cells activating immunological response in tonsil contribute formation immunologic competent cells on necessity of rolling inflammatory process in middle ear.

AIM OF STUDY

An investigation was executed in hypertrophied adenoids with or without otitis media with effusion.

METHODS

By flow cytometry percentage of CD11c+ myeloid DC and 123+ plasmacytoid DC in hypertrophied adenoid and hypertrophied adenoid and otitis media with effusion was analyzed.

RESULTS

The percentage of CD11c+ myeloid DC and 123+ plasmacytoid DC was similar in hypertrophied adenoid and otitis media with effusion compored to the control group.

CONCLUSIONS

Our data show that part of dendritic cells has not on course of inflammatory process influence rolling in middle ear.

Recovery from cyclophosphamide-induced lymphopenia results in expansion of immature dendritic cells which can mediate enhanced prime-boost vaccination antitumor responses in vivo when stimulated with the TLR3 agonist poly(I:C)

Recent preclinical studies suggest that vaccination following adoptive transfer of CD8(+) T cells into a lymphopenic host can augment the therapeutic antitumor responses of the transferred cells. However, the mechanism by which the lymphopenic microenvironment benefits Ag-specific CD8(+) T cell responses remains elusive. We show herein that induction of lymphodepletion by a single 4 mg cyclophosphamide (CTX) treatment induces a marked expansion of immature dendritic cells (DCs) in the peripheral blood on days 8-16 post-CTX (termed restoration phase). In vitro, these DCs were functional, because they showed normal phagocytosis and effective Ag presentation capability upon activation. In vivo, administration of the TLR3 agonist poly(I:C) at the peak of DC expansion (day 12 postlymphopenia) induced inflammatory cytokine production and increases in the number of activated DCs in lymph nodes. Importantly, boosting with gp100(25-33) melanoma peptide combined with poly(I:C) 12 days after an initial priming with the same regimen significantly increased the expansion and the antitumor efficacy of adoptively transferred pmel-1 CD8(+) T cells. These responses were abrogated after depletion of activated DCs during Ag boosting. In conclusion, our data show that CTX treatment induces, during the restoration phase, expansion of immature DCs, which are functional and can be exploited in vivo to foster more effective antitumor adoptive immunotherapy strategies.

Human dendritic cells and transplant outcome

Early interest in dendritic cells (DC) in transplantation centered on the role of graft interstitial DC in the instigation of rejection. Much information has subsequently accumulated concerning the phenotypic and functional diversity of these rare, migratory, bone marrow-derived antigen-presenting cells, and their role in the induction and regulation of immunity. Detailed insights have emerged from studies of freshly isolated or in vitro-propagated DC, and from analyses of their function in experimental animal models. The functional plasticity of these uniquely well-equipped antigen-presenting cells is reflected in their ability not only to induce alloimmune responses, but also to serve as potential targets and therapeutic agents for the long-term improvement of transplant outcome. Notably, however, a great deal remains to be understood about the immunobiology of DC populations in relation to human transplant outcome. Herein, we briefly review aspects of human DC biology in organ and bone marrow transplantation, the potential of these cells for monitoring outcome, and the role of DC in development of vaccines to protect against infectious disease or to promote allograft tolerance.

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.

Activated circulating dendritic cells after hematopoietic stem cell transplantation predict acute graft-versus-host disease

BACKGROUND

Dendritic cells (DC) are central to the development of acute graft-versus-host disease (GVHD) following allogeneic hematopoietic stem cell transplantation (alloHSCT). We hypothesized that DC activation status determines the severity of GVHD and that activated DC may be detected in the circulation prior to clinical presentation of GVHD.

METHODS

Following transplant, blood samples were obtained twice weekly from alloHSCT patients. Myeloid (CD11c+) and plasmacytoid (CD123hi) DC were enumerated by flow cytometry, and activated myeloid DC were identified using the CMRF-44 monoclonal antibody.

RESULTS

Of 40 alloHSCT patients, 26 developed acute GVHD. Severity of GVHD was associated with low total blood DC counts (P=0.007) and with low myeloid and plasmacytoid DC numbers (P=0.015 and 0.003). The CMRF-44 antigen was expressed on blood CD11c+ DC in all cases prior to GVHD onset, whereas of the 14 patients without GVHD, seven had no CMRF-44+ CD11c DC. Patients with CMRF-44+ CD11c+ DC in more than 20% of samples were more likely to subsequently develop acute GVHD (P=0.001, odds ratio=37.1), while patients who developed grade 2-4 GVHD had prior higher percentages of CMRF-44+ CD11c+ DC compared to grade 0-1 GVHD patients (P=0.001). CMRF-44 expression on >7.9% CD11c+ DC predicted for subsequent development of GVHD with a sensitivity of 87.5% and specificity of 79.2%.

CONCLUSIONS

Activation status, as assessed by CMRF-44 antigen expression, of blood CD11c+ DC is highly associated with acute GVHD and these cells may be targets for therapeutic intervention.

Human peripheral blood dendritic cells and monocyte subsets display similar chemokine receptor expression profiles with differential migratory responses

Human antigen presenting cells (APC) found in peripheral blood are considered to be precursors that have been released from the bone marrow and are in transit to the peripheral tissues. These APC populations include myeloid dendritic cells (mDC), plasmacytoid DC (pDC) and monocytes (Mo). To assign specialized functional roles and stages of development for APCs, CD33 expressing APC subsets were examined for their capacity to respond to chemokines. Three major CD33(+) subsets including CD33(bright)CD14(bright) Mo, CD33(bright)CD14(-) CD11c(+) mDC and CD33(dim)CD14(-) pDC were present. Dendritic cells subsets and Mo expressed low levels of CC and CXC receptors, but distinctive chemokine receptor expression profiles were not observed. The percentage of cells expressing a particular chemokine receptor varied from donor to donor and over time in the same donor. Myeloid DC and Mo but not pDC migrated toward CXCL12 in a concentration dependent manner. Monocytes and pDC, but not myeloid DC, were attracted by high concentrations of CXCL10. All CD33(+) subsets migrated in a concentration dependent manner toward CCL19, but responded less robustly to CCL21. CCL20 was not chemoattractant for any population. Despite the finding that APC did not exhibit unique surface chemokine receptor expression patterns, they exhibited differential migration to CXCL12, CXCL10 and CCL21 but not to CCL20 or CCL19.

Dendritic cell-based immunotherapy

Dendritic cells (DCs) play a crucial role in the induction of antigen-specific T-cell responses, and therefore their use for the active immunotherapy of malignancies has been studied with considerable interest. More than a decade has passed since the publication of the first clinical data of DC-based vaccines, and through this and subsequent studies, a number of important developmental insights have been gleaned. These include the ideal source and type of DCs, the discovery of novel antigens and methods of loading DCs, the role of DC maturation, and the most efficient route of immunization. The generation of immune responses against tumor antigens after DC immunization has been demonstrated, and favorable clinical responses have been reported in some patients; however, it is difficult to pool the results as a whole, and thus the body of data remains inconclusive, in part because of varying DC preparation and vaccination protocols, the use of different forms of antigens, and, most importantly, a lack of rigorous criteria for defining clinical responses. As such, the standardization of clinical and immunologic criteria utilized, as well as DC preparations employed, will allow for the comparison of results across multiple clinical studies and is required in order for future trials to measure the true value and role of this treatment modality. In addition, issues regarding the optimal dose and clinical setting for the application of DC vaccines remain to be resolved, and recent clinical studies have been designed to begin to address these questions.

Plasmacytoid dendritic cells: in vivo regulators of alloimmune reactivity?

Dendritic cells (DC) exhibit remarkable plasticity in terms of their ability to induce and regulate innate and adaptive immune responses. Human and mouse interferon alpha-producing plasmacytoid (p) DC have been found to regulate allogeneic T cell responses in vitro. Evidence is emerging that pDC may also regulate immune reactivity in vivo, including the responses that underlie graft-versus-host disease and organ transplant rejection. These cells may also offer potential for therapy of adverse immune responses and the promotion of tolerance induction.

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.

Vaccine strategies to treat lymphoproliferative disorders

Lymphoproliferative disorders, including follicular lymphoma (FL), multiple myeloma (MM) and chronic lymphatic leukaemia (CLL), are slowly progressive malignancies which remain incurable despite advances in therapy. Harnessing the immune system to recognise and destroy tumours is a promising new approach to treating these diseases. Dendritic cells (DC) are unique antigen-presenting cells that play a central role in the initiation and direction of immune responses. DC loaded ex vivo with tumour-associated antigens and administered as a vaccine have already shown promise in early clinical trials for a number of lymphoproliferative disorders, but the need for improvement is widely agreed. Recent advances in the understanding of basic DC biology and lessons from early clinical trials have provided exciting new insights into the generation of anti-tumour immune responses and the design of vaccine strategies. In this review we provide an overview of our current understanding of DC biology and their function in patients with lymphoproliferative disorders. We discuss the current status of clinical trials and new approaches to exploit the antigen presenting capacity of DC to design vaccines of the future.

The sphingosine-1-phosphate receptor agonist FTY720 modulates dendritic cell trafficking in vivo

The pro-drug FTY720 is undergoing phase III clinical trials for prevention of allograft rejection. After phosphorylation, FTY720 targets the G protein-coupled-sphingosine-1-phosphate receptor 1 (S1PR1) on lymphocytes, thereby inhibiting their egress from lymphoid organs and their recirculation to inflammatory sites. Potential effects on dendritic cell (DC) trafficking have not been evaluated. Here, we demonstrate the expression of all five S1PR subtypes (S1PR1-5) by murine DCs. Administration of FTY720 to C57BL/10 mice markedly reduced circulating T and B lymphocytes within 24 h, but not blood-borne DCs, which were enhanced significantly for up to 96 h, while DCs in lymph nodes and spleen were reduced. Numbers of adoptively transferred, fluorochrome-labeled syngeneic or allogeneic DCs in blood were increased significantly in FTY720-treated animals, while donor-derived DCs and allostimulatory activity for host naïve T cells within the spleen were reduced. Administration of the selective S1PR1 agonist SEW2871 significantly enhanced circulating DC numbers. Flow analysis revealed that CD11b, CD31/PECAM-1, CD54/ICAM-1 and CCR7 expression on blood-borne DCs was downregulated following FTY720 administration. Transendothelial migration of FTY720-P-treated immature DCs to the CCR7 ligand CCL19 was reduced. These novel data suggest that modulation of DC trafficking by FTY720 may contribute to its immunosuppressive effects.

Immunoselection of functional CMRF-56+ blood dendritic cells from multiple myeloma patients for immunotherapy

Dendritic cells (DCs) loaded with tumor-associated antigens are a promising treatment to prevent disease relapse in patients with multiple myeloma (MM). Early-phase clinical trials have shown safety, efficacy, and immunologic responses in MM, but a key issue now is the isolation of a functional, clinically relevant DC preparation. The authors have described a unique blood DC (BDC) isolation platform based on positive immunoselection with the CMRF-56 antibody. To validate this as a feasible source of BDCs for immunotherapy, the authors undertook a quantitative and functional analysis of BDCs in MM patients and healthy donors. These data show that MM patients have similar numbers of CD11c+CD16+ and CD11c+CD16- BDCs but about half the number of CD11c-CD123+ BDCs in whole blood compared with healthy donors. BDCs could be isolated by CMRF-56+ immunoselection from all MM patients tested, with similar yields and purity to healthy donors. These BDCs could be activated ex vivo with poly I:C or LPS. Furthermore, CMRF-56+ preparations could induce potent CD4+ and CD8+ T-lymphocyte responses in both MM patients and healthy donors. These data suggest that BDCs with in vitro functional integrity can be isolated from MM patients in sufficient numbers to justify a clinical trial.

Disparate ability of murine CD8alpha- and CD8alpha+ dendritic cell subsets to traverse endothelium is not determined by differential CD11b expression

Upon Ag uptake and response to maturation stimuli, dendritic cells (DC) are directed through lymphatic or blood vessel endothelium to T cell areas of secondary lymphoid tissues by the constitutively expressed CC chemokines CCL19 and CCL21. We have shown that mature (m) murine CD8alpha+ DC exhibit poorer migratory ability to these chemokines than classic CD8alpha- DC by quantifying their in vitro chemotaxis through unmodified Transwell filters. We hypothesized that lower surface expression (compared to CD8alpha- mDC) of the adhesion molecule CD11b on CD8alpha+ DC might limit their ability to adhere to filter pores in vitro and/or endothelium in vitro/in vivo. To test the role of this and/or other adhesion molecules (CD11a, CD31, CD54 and CD62L) in regulating murine DC subset migration, we used specific mAbs to block their function and quantified their migration through resting or tumour necrosis factor (TNF)-alpha-activated endothelial cell (EC) layered-Transwell filters. Both CD8alpha+ and CD8alpha- subsets migrated through resting EC (albeit less than in the absence of EC) in response to CCL19 and CCL21, and migration through TNF-alpha-activated EC was enhanced. In contrast to reports concerning human DC, transendothelial migration of the murine DC subsets was not dependent on CD11b, CD31, or CD62L expression by these cells. CD54 and CD11a, however, were at least partly involved in DC/EC interactions. This is the first report to examine adhesion molecules involved in transendothelial migration of murine DC subsets.

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.

Either interleukin-12 or interferon-γ can correct the dendritic cell defect induced by transforming growth factor β 1 in patients with myeloma

The poor response to immunotherapy in patients with multiple myeloma (MM) indicates that a better understanding of any defects in the immune response in these patients is required before effective therapeutic strategies can be developed. Recently we reported that high potency (CMRF44(+)) dendritic cells (DC) in the peripheral blood of patients with MM failed to significantly up-regulate the expression of the B7 co-stimulatory molecules, CD80 and CD86, in response to an appropriate signal from soluble trimeric human CD40 ligand. This defect was caused by transforming growth factor beta(1) (TGFbeta(1)) and interleukin (IL)-10, produced by malignant plasma cells, and the defect was neutralized in vitro with anti-TGFbeta(1). As this defect could impact on immunotherapeutic strategies and may be a major cause of the failure of recent trials, it was important to identify a more clinically useful agent that could correct the defect in vivo. In this study of 59 MM patients, the relative and absolute numbers of blood DC were only significantly decreased in patients with stage III disease and CD80 up-regulation was reduced in both stage I and stage III. It was demonstrated that both IL-12 and interferon-gamma neutralized the failure to stimulate CD80 up-regulation by huCD40LT in vitro. IL-12 did not cause a change in the distribution of DC subsets that were predominantly myeloid (CD11c+ and CDw123-) suggesting that there would be a predominantly T-helper cell type response. The addition of IL-12 or interferon-gamma to future immunotherapy trials involving these patients should be considered.

DC in multiple myeloma immunotherapy

Therapy for patients with multiple myeloma (MM) is currently unsatisfactory and most patients eventually succumb to relapsed disease. DCs are a subset of leukocytes with the capacity to initiate and control the adaptive immune response against many cancers, including MM. In MM patients, in vivo DC function is often abnormal, however, it appears that it can be restored by in vitro manipulation. This has led to the development of DC immunotherapy for MM patients. We review the background research leading to the recognition of an anti-MM immune response, and discuss abnormalities in DC function, potential tumor-associated Ags, and the results of clinical trials of DC immunotherapy in MM patients.

Reconstitution dynamics of plasmacytoid and myeloid dendritic cell precursors after allogeneic myeloablative hematopoietic stem cell transplantation

Dendritic cells (DCs) are fundamental for immunity. We investigated reconstitution of plasmacytoid DC (PDC) and myeloid DC (My-DC) precursors in the first 2 months after allogeneic hematopoietic stem cell transplantation (Allo-HSCT). Circulating DCs were monitored from the earliest phase of hematopoietic reconstitution in 43 children given standard therapy to prevent graft-versus-host disease (GVHD) and either treated or untreated with granulocyte colony-stimulating factor (G-CSF) after HSCT. In patients without GVHD, both My-DCs and PDCs reached consistently high absolute values during the initial phase. Time of engraftment did not differ between My-DCs and PDCs, regardless of administration of G-CSF. Treatment with G-CSF (1) accelerated early recovery of My-DC absolute numbers; (2) was associated with lower numbers of both My-DCs and PDCs in the later phase; and (3) significantly reduced the proportion of interleukin-12 (IL-12)-secreting cells. In some patients who developed acute GVHD, we found high numbers of circulating DC precursors during the early phase of this complication. However, treatment with steroids invariably induced rapid decrease of PDCs. Altogether, these data provide an evaluation of DC release after Allo-HSCT, indicate that postgrafting administration of G-CSF impairs the appearance of IL-12-producing DCs, and suggest that DC homeostasis may be disrupted at onset of GVHD.

Chemotherapy plus G-CSF mobilized peripheral blood stem cell harvests from acute myeloid leukaemia patients contain large amounts of polyclonal myeloid linneg CD11cpos dendritic precursor cells

Dendritic cells (DC) are potent antigen-presenting cells that can induce effective tumour-specific T-cell responses. This study investigated leucapheresis products as source of DC precursors in 48 patients undergoing autologous peripheral blood stem cell (PBSC) transplantation for haematological malignancies. Strikingly, high-dose cytarabine and etoposide plus granulocyte colony stimulating factor (G-CSF) mobilized PBSC harvests from acute myeloid leukaemia (AML) patients containing the highest number of myeloid lin(neg)CD11c(pos) DC (mean: 7.04 x 106/kg, range: 1.46-19.67) which was 18.1-fold higher than in non-AML patients mobilized using chemotherapy (CT) regimens plus G-CSF. Clonality of purified lin(neg)CD11c(pos) DC from CT plus G-CSF mobilized AML patients (n = 8 ) was assessed using the human androgen-receptor locus methylation, disclosing a polyclonal pattern in five female patients. These cells displayed morphological and phenotypic features of myeloid DC precursors with expression of HLA-DR, HLA-ABC, CD86, CCR5 and CD54 molecules but lacking CD80, CD83, CD1a and CD40 antigens. Short-term culture with autologous leukaemic cell lysates plus tumour necrosis factor-alpha yielded maturated myeloid DC capable of triggering interleukin-2 and interferon-gamma production by autologous T-lymphocytes. These findings suggest that the use of post-remission CT and G-CSF as mobilizing regimen in AML patients generates PBSC containing high doses of polyclonal myeloid lin(neg)CD11c(pos) DC precursors, which could be used to design feasible immunotherapy protocols.

Monitoring dendritic cells in clinical practice using a new whole blood single-platform TruCOUNT assay

Dendritic cells (DC) from distinct DC subsets are essential contributors to normal human immune responses. Despite this, reliable assays that enable DC to be counted precisely have been slow to evolve. We have now developed a new single-platform flow cytometric assay based on TruCOUNT beads and the whole blood "Lyse/No-Wash" protocol that allows precise counting of the CD14(-) blood DC subsets: CD11c(+)CD16(-) DC, CD11c(+)CD16(+) DC, CD123(hi) DC, CD1c(+) DC and BDCA-3(+) DC. This assay requires 50 microl of whole blood; does not rely on a hematology blood analyser for the absolute DC counts; allows DC counting in EDTA samples 24 h after collection; and is suitable for cord blood and peripheral blood. The data is highly reproducible with intra-assay and inter-assay coefficients of variation less than 3% and 11%, respectively. This assay does not produce the DC-T lymphocyte conjugates that result in DC counting abnormalities in conventional gradient-density separation procedures. Using the TruCOUNT assay, we established that absolute blood DC counts reduce with age in healthy individuals. In preliminary studies, we found a significantly lower absolute blood CD11c(+)CD16(+) DC count in stage III/IV versus stage I/II breast carcinoma patients and a lower absolute blood CD123(hi) DC count in multiple myeloma patients, compared to age-matched controls. These data indicate that scientific progress in DC counting technology will lead to the global standardization of DC counting and allow clinically meaningful data to be obtained.