Granulocyte colony-stimulating factor-induced immature myeloid cells inhibit acute graft-versus-host disease lethality through an indoleamine dioxygenase-independent mechanism

Immune Modulation by Myeloid-Derived Suppressor Cells in Diabetic Kidney Disease

Diabetic kidney disease (DKD) frequently leads to end-stage renal disease and other life-threatening illnesses. The dysregulation of glomerular cell types, including mesangial cells, endothelial cells, and podocytes, appears to play a vital role in the development of DKD. Myeloid-derived suppressor cells (MDSCs) exhibit immunoregulatory and anti-inflammatory properties through the depletion of L-arginine that is required by T cells, through generation of oxidative stress, interference with T-cell recruitment and viability, proliferation of regulatory T cells, and through the promotion of pro-tumorigenic functions. Under hyperglycemic conditions, mouse mesangial cells reportedly produce higher levels of fibronectin and pro-inflammatory cytokines. Moreover, the number of MDSCs is noticeably decreased, weakening inhibitory immune activities, and creating an inflammatory environment. In diabetic mice, immunotherapy with MDSCs that were induced by a combination of granulocyte-macrophage colony-stimulating factor, interleukin (IL)-1β, and IL-6, reduced kidney to body weight ratio, fibronectin expression, and fibronectin accumulation in renal glomeruli, thus ameliorating DKD. In conclusion, MDSCs exhibit anti-inflammatory activities that help improve renal fibrosis in diabetic mice. The therapeutic targeting of the proliferative or immunomodulatory pathways of MDSCs may represent an alternative immunotherapeutic strategy for DKD.

Steroid-Refractory Gut Graft-Versus-Host Disease: What We Have Learned From Basic Immunology and Experimental Mouse Model

Intestinal graft-versus-host disease (Gut-GVHD) is one of the major causes of mortality after allogeneic hematopoietic stem cell transplantation (allo-HSCT). While systemic glucocorticoids (GCs) comprise the first-line treatment option, the response rate for GCs varies from 30% to 50%. The prognosis for patients with steroid-refractory acute Gut-GVHD (SR-Gut-aGVHD) remains dismal. The mechanisms underlying steroid resistance are unclear, and apart from ruxolitinib, there are no approved treatments for SR-Gut-aGVHD. In this review, we provide an overview of the current biological understanding of experimental SR-Gut-aGVHD pathogenesis, the advanced technology that can be applied to the human SR-Gut-aGVHD studies, and the potential novel therapeutic options for patients with SR-Gut-aGVHD.

Graft-Versus-Host Disease Prevention by In Vitro-Generated Myeloid-Derived Suppressor Cells Is Exclusively Mediated by the CD11b+CD11c+ MDSC Subpopulation

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of myeloid progenitor cells that dampen overwhelming adaptive immune responses through multiple mechanisms and are recognized as an attractive novel immune intervention therapy for counteracting the destructive effects of graft- versus -host disease (GVHD) developing after allogeneic bone marrow transplantation (BMT). MDSCs can be produced in great numbers for cellular therapy, but they present a mixture of subsets whose functions in GVHD prevention are undefined. Here, we generated MDSCs in vitro from murine BM cells in the presence of GM-CSF and defined the integrin CD11c as a marker to subdivide MDSCs into two functional subgroups: CD11b+CD11c+ and CD11b+CD11c− MDSCs. Isolated CD11b+CD11c+ and CD11b+CD11c− MDSCs both inhibited alloantigen-stimulated T-cell proliferation in vitro, although CD11b+CD11c+ MDSCs were more efficient and expressed higher levels of different immunosuppressive molecules. Likewise, expression of surface markers such as MHC class II, CD80, CD86, or PD-L1 further delineated both subsets. Most importantly, only the adoptive transfer of CD11b+CD11c+ MDSCs into a single MHC class I-disparate allogeneic BMT model prevented GVHD development and strongly decreased disease-induced mortality, while CD11b+CD11c− MDSCs were totally ineffective. Surprisingly, allogeneic T-cell homing and expansion in lymphatic and GVHD target organs were not affected by cotransplanted CD11b+CD11c+ MDSCs indicating a clear contradiction between in vitro and in vivo functions of MDSCs. However, CD11b+CD11c+ MDSCs shifted immune responses towards type 2 immunity reflected by increased Th2-specific cytokine expression of allogeneic T cells. Induction of type 2 immunity was mandatory for GVHD prevention, since CD11b+CD11c+ MDSCs were ineffective if recipients were reconstituted with STAT6-deficient T cells unable to differentiate into Th2 cells. Most importantly, the beneficial graft- versus -tumor (GVT) effect was maintained in the presence of CD11b+CD11c+ MDSCs since syngeneic tumor cells were efficiently eradicated. Strong differences in the transcriptomic landscape of both subpopulations underlined their functional differences. Defining CD11b+CD11c+ MDSCs as the subset of in vitro-generated MDSCs able to inhibit GVHD development might help to increase efficiency of MDSC therapy and to further delineate relevant target molecules and signaling pathways responsible for GVHD prevention.

Metabolic reprogramming of myeloid-derived suppressor cells: An innovative approach confronting challenges

Immune cells such as T cells, macrophages, dendritic cells, and other immunoregulatory cells undergo metabolic reprogramming in cancer and inflammation-derived microenvironment to meet specific physiologic and functional demands. Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of immature myeloid cells that are characterized by immunosuppressive activity, which plays a key role in host immune homeostasis. In this review, we have discussed the core metabolic pathways, including glycolysis, lipid and fatty acid biosynthesis, and amino acid metabolism in the MDSCs under various pathologic situations. Metabolic reprogramming is a determinant of the phenotype and functions of MDSCs, and is therefore a novel therapeutic possibility in various diseases.

The Role of Myeloid-Derived Suppressor Cells (MDSCs) in Graft-versus-Host Disease (GVHD)

Background: Myeloid-derived suppressor cells (MDSCs) are implicated in the complex interplay involving graft-versus-leukemia (GVL) effects and graft-versus-host disease (GVHD) after allogeneic hematopoietic stem cell transplantation (allo-HCT) in hematologic malignancies. Methods: A review of literature through PubMed was undertaken to summarize the published evidence on the pathophysiology and clinical implications of MDSCs in allo-HCT. Literature sources published in English since 1978 were searched, using the terms Natural Suppressor (NS) cells, MDSCs, GVHD, and allo-HCT. Results: In vivo studies demonstrated that MDSCs derived from mobilization protocols could strongly suppress allo-responses mediated by T cells and enhance T-Reg activity, thus inhibiting GVHD toxicity. However, the influence of MDSCs on the GVL effect is not fully defined. Conclusions: The induction or maintenance of MDSC suppressive function would be advantageous in suppressing inflammation associated with GVHD. Pathways involved in MDSC metabolism and the inflammasome signaling are a promising field of study to elucidate the function of MDSCs in the pathogenesis of GVHD and translate these findings to a clinical setting.

Immunomodulatory Effects of Bendamustine in Hematopoietic Cell Transplantation

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

Myeloid-derived suppressor cells as cellular immunotherapy in transplantation and autoimmune diseases

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of immature myeloid cells, which have been characterized for their immunosuppressive capacity through multiple mechanisms. These cells have been extensively studied in the field of tumor immunity. Emerging evidence has highlighted its essential role in maintaining immune tolerance in transplantation and autoimmunity. Because of their robust immune inhibitory activities, there has been growing interest in MDSC-based cellular therapy. Various pre-clinical studies have demonstrated that the adoptive transfer of MDCS represented a promising therapeutic strategy for immune-related disorders. In this review, we summarize relevant studies of MDSC-based cell therapy in transplantation and autoimmune diseases and discuss the challenges and future directions for clinical application of MDSC-based cell therapy.

Myeloid-Derived Suppressor Cells in the Context of Allogeneic Hematopoietic Stem Cell Transplantation

Myeloid-derived suppressor cells (MDSCs) are innate immune cells that acquire the capacity to suppress adaptive immune responses. In the context of allogeneic hematopoietic stem cell transplantation (allo-HSCT), MDSCs (in the donor graft and in the recipient, after allo-HSCT) might mediate immune suppression through multiple mechanisms. However, it remains unclear how MDSCs can be distinguished from their normal myeloid counterparts in the hematopoietic stem cell donor graft and during immune reconstitution after allo-HSCT in the recipient. Our ability to understand their exact role in allo-HSCT is limited by the absence of a specific gene signature or surface markers for identifying MDSCs among myeloid cells and by their plasticity in different microenvironments. According to various studies, MDSCs might induce transplant tolerance and control graft vs. host disease (GVHD), but their impact on the graft vs. tumor effect (GVT) is not fully understood. In fact, we know that MDSCs commonly expand in patients with cancer, and they are thought to promote hematological malignancy progression. However, little is known about whether depleting them might be an effective strategy for enhancing GVT effects. Here, we review data published over the past 40 years on allo-HSCT to delineate the different MDSC subsets, and their abilities to induce transplant tolerance and preserve the GVT effect. This review will provide a basis for determining whether one MDSC subset might be proposed as the most appropriate candidate for cellular therapies, due to its ability to modulate GVHD.

Pegbovigrastim Treatment around Parturition Enhances Postpartum Immune Response Gene Network Expression of whole Blood Leukocytes in Holstein and Simmental Cows

Simple Summary

The innate and adaptive immune system of dairy cows is impaired during the transition period, leading to an increase in susceptibility to infectious disease. Pegbovigrastim is a recombinant form of a granulocyte colony-stimulating factor that stimulates differentiation of hemopoietic stem cells to granulocytes and shortens maturation time within the bone marrow and release in circulation. The objective of the present study was to explore the effect of pegbovigrastim on whole blood leukocytes by analyzing the expression of 34 genes involved in immune and inflammatory responses immediately after calving in Simmental, a dual-purpose cow breed selected for both meat and milk production, and Holstein, a cow breed highly specialized for milk production. This study provides insight into immune cell functions impacted by pegbovigrastim treatment. Treatment of cows with pegbovigrastim increased the mRNA abundance level of most genes investigated, suggesting a thorough activation of the immune machinery during the critical post-partum period.

Abstract

Pegbovigrastim is a commercial long-acting analog of bovine granulocyte colony-stimulating factor (rbG-CSF) that promotes the increased count and functionality of polymorphonuclear cells in dairy cows around the time of parturition. We hypothesized that pegbovigrastim administered to periparturient cows at approximately seven days before parturition and within 24 hours after calving could affect the profiles of gene networks involved in leukocyte function. Blood was collected on Day 3 after calving from treated groups (pegbovigrastim (PEG); 13 Simmental (seven multiparous and six primiparous) and 13 Holstein (seven multiparous and six primiparous) cows) that received pegbovigrastim (Imrestor; Elanco Animal Health) and controls (CTR; 13 Simmental (seven multiparous and six primiparous) and 13 Holstein (six multiparous and seven primiparous) cows) that received saline solution. Blood from all cows was sampled from the jugular vein in a PAXgene Blood RNA System tube (Preanalytix, Hombrechtikon, Switzerland) for RNA extraction. The RT-qPCR analysis was performed to investigate a panel of 34 genes of interest, representing recognition, immune mediation, migration, cell adhesion, antimicrobial strategies, inflammatory cascade, oxidative pattern, and leukotrienes in whole blood leukocytes. Normalized data were subjected to the MIXED model of SAS (ver. 9.4) with treatment, breed, parity, and their interaction as fixed effects. Compared with CTR, whole blood leukocytes of PEG cows had higher expression of genes involved in recognition and immune modulation (CD14, CD16, MYD88, TLR2, and TLR4), cell adhesion (ITGB2, ITGAL, TLN1, SELL, SELPLG, and CD44), antimicrobial activity (MMP9, LTF, and LCN2), and inflammatory cascade (CASP1, TNFRSF1A, IL1B, IL1R, IL18, IRAK1, NLRP3, and S100A8). This suggested an improvement of migration, adhesion, and antimicrobial ability and an enhanced inflammatory response, which in turn could trigger immune cell activation and enhance function. Expression of SOD2 and ALOX5 was also greater in the PEG group. In contrast, compared with CTR cows, PEG led to lower expression of RPL13A, ALOX15, IL8, and TNF. Overall, leukocytes from Simmental compared with Holstein cows had greater expression of IDO1, RPL13A, ALOX5, CD44, CX3CR1, ITGB2, and TNFA, whereas expression of CD16 and TLR2 was lower. Overall, compared with multiparous cows, primiparous cows had higher expression of IL1B, IL18, MYD88, SELL, and TLR2 and lower expression of MMP9. Simmental cows seemed more sensitive to induction of the immune system after calving, as revealed by the greater abundance of genes involved in immune system adaptation, regardless of pegbovigrastim treatment. Primiparous cows undergoing a new stress condition with respect to older cows were characterized by leukocytes with a higher inflammatory response. In conclusion, pegbovigrastim led to higher expression levels of most genes involved in the processes investigated, suggesting a thorough activation of the immune machinery during the critical post-partum period.

G-CSF-induced macrophage polarization and mobilization may prevent acute graft-versus-host disease after allogeneic hematopoietic stem cell transplantation

Macrophages (MΦs) are an important immune cell population that are essential for tissue homeostasis and disease pathogenesis. MΦs are now classified as either M1, which produce pro-inflammatory cytokines, or M2, which produce antiinflammatory cytokines. The impact of granulocyte colony-stimulating factor (G-CSF) on MΦs in humans is unclear. Moreover, little is known about the association between MΦ subsets in allografts and the occurrence of acute graft-versus-host disease (aGVHD) in patients who undergo allogeneic hematopoietic stem cell transplantation (allo-HSCT). In the current study, we found that the M1/M2 ratio was markedly decreased in both G-CSF-treated bone marrow (post-BM) and G-CSF-treated peripheral blood from healthy donors. Post-BM MΦs exhibited reduced migration and increased phagocytosis. Moreover, post-BM MΦs reduced the percentage of Th1 and Tc1 lineages and increased the percentage of Th2, Tc2, and Treg lineages. Patients who received BM grafts with a higher M1/M2 ratio exhibited a higher incidence of grade 2-4 aGVHD. In summary, our data indicate that G-CSF decreases the M1/M2 ratio in BM grafts from healthy donors, which may contribute to preventing the occurrence of grade 2-4 aGVHD in patients after allo-HSCT.

Bendamustine with Total Body Irradiation Limits Murine Graft-versus-Host Disease in Part Through Effects on Myeloid-Derived Suppressor Cells

Graft-versus-host disease (GVHD) remains a significant challenge in allogeneic hematopoietic cell transplantation (HCT). An underinvestigated strategy to reduce GVHD is the modification of the preparative conditioning regimen. In the present study, we aimed to evaluate GVHD associated with bendamustine (BEN) conditioning in conjunction with total body irradiation (TBI) as an alternative to the standard myeloablative regimen of cyclophosphamide (CY) and TBI. We demonstrate that BEN-TBI conditioning, although facilitating complete donor chimerism, results in significantly less GVHD compared with CY-TBI. In BEN-TBI-conditioned mice, suppressive CD11b⁺Gr-1^high myeloid cells are increased in the blood, bone marrow, spleen, and intestines. When Gr-1^high cells are depleted before transplantation, the beneficial effects of BEN-TBI are partially lost. Alternatively, administration of granulocyte colony-stimulating factor, which promotes CD11b⁺Gr-1⁺ myeloid cell expansion, is associated with a trend toward increased survival in BEN-TBI-conditioned mice. These findings indicate a potential role of myeloid-derived suppressor cells in the mechanism by which BEN allows engraftment with reduced GVHD. BEN-TBI conditioning may present a safer alternative to CY-TBI conditioning for allogeneic HCT.

The Effect of Immunosuppressive Drugs on MDSCs in Transplantation

Myeloid-derived suppressor cells (MDSCs) are a group of innate immune cells that regulates both innate and adaptive immune responses. In recent years, MDSCs were shown to play an important negative regulatory role in transplant immunology even upstream of regulatory T cells. In certain cases, MDSCs are closely involved in transplantation immune tolerance induction and maintenance. It is known that some immunosuppressant drugs negatively regulate MDSCs but others have positive effects on MDSCs in different transplant cases. We herein summarized our recent insights into the regulatory roles of MDSCs in transplantation specially focusing on the effects of immunosuppressive drugs on MDSCs and their mechanisms of action. Studies on the effects of immunosuppressive drugs on MDSCs will significantly expand our understanding of immunosuppressive drugs on immune regulatory cells in transplantation and offer new insights into transplant tolerance. We hope to emphasize our concern for the negative effects of immunosuppressive agents on MDSCs, which may potentially attenuate the immune tolerance induction in transplanted recipients.

Innate Immunity in the Persistent Inflammation, Immunosuppression, and Catabolism Syndrome and Its Implications for Therapy

Clinical and technological advances promoting early hemorrhage control and physiologic resuscitation as well as early diagnosis and optimal treatment of sepsis have significantly decreased in-hospital mortality for many critically ill patient populations. However, a substantial proportion of severe trauma and sepsis survivors will develop protracted organ dysfunction termed chronic critical illness (CCI), defined as ≥14 days requiring intensive care unit (ICU) resources with ongoing organ dysfunction. A subset of CCI patients will develop the persistent inflammation, immunosuppression, and catabolism syndrome (PICS), and these individuals are predisposed to a poor quality of life and indolent death. We propose that CCI and PICS after trauma or sepsis are the result of an inappropriate bone marrow response characterized by the generation of dysfunctional myeloid populations at the expense of lympho- and erythropoiesis. This review describes similarities among CCI/PICS phenotypes in sepsis, cancer, and aging and reviews the role of aberrant myelopoiesis in the pathophysiology of CCI and PICS. In addition, we characterize pathogen recognition, the interface between innate and adaptive immune systems, and therapeutic approaches including immune modulators, gut microbiota support, and nutritional and exercise therapy. Finally, we discuss the future of diagnostic and prognostic approaches guided by machine and deep-learning models trained and validated on big data to identify patients for whom these approaches will yield the greatest benefits. A deeper understanding of the pathophysiology of CCI and PICS and continued investigation into novel therapies harbor the potential to improve the current dismal long-term outcomes for critically ill post-injury and post-infection patients.

Role of myeloid-derived suppressor cells in allogeneic hematopoietic cell transplantation

Graft-versus-host disease (GVHD) can be a devastating complication for as many as a third of patients undergoing allogeneic hematopoietic stem cell transplantation (allo-HCT). A role for myeloid cells in the amplification of GVHD has been demonstrated; however, less is understood about a potential regulatory role that myeloid cells play or whether such cells may be manipulated and applied therapeutically. Myeloid-derived suppressor cells (MDSCs) are a naturally occurring immune regulatory population that are engaged and expand shortly after many forms of immune distress, including cancer, trauma, and infection. As MDSCs are often associated with chronic disease, inflammation, and even the promotion of tumor growth (regarding angiogenesis/metastasis), they can appear to be predictors of poor outcomes and therefore, vilified; yet, this association doesn't match with their perceived function of suppressing inflammation. Here, we explore the role of MDSC in GVHD in an attempt to investigate potential synergies that may be promoted, leading to better patient outcomes after allo-HCT.

High-dosage granulocyte colony stimulating factor treatment alters monocyte trafficking to the brain after experimental stroke

Ischemic stroke elicits a prompt inflammatory response that is characterized by a well-timed recruitment of peripheral immune cells to the brain. Among these, monocytes play a particularly important, but multifaceted role and have been increasingly recognized to affect stroke outcome. Granulocyte colony stimulating factor (GCSF) is known for its immunosuppressive actions on mononuclear cells, but previous studies in the stroke field were mainly confined to its neuroprotective actions. Herein, we investigated whether GCSF affects post-stroke inflammation in a mouse model of focal brain ischemia by modulating monocyte responses. Treatment with GCSF was controlled by vehicle injection, sham surgery and naive animals. Despite a significant monocytosis, high-dosage GCSF reduced the number of brain-infiltrating monocytes/macrophages four days after stroke. Lower numbers of mononuclear phagocytes in the brain were associated with smaller cerebral edema and improved motor outcome after stroke. GCSF treatment over 72h, but not 24h diminished integrin expression on circulating Ly6C+ inflammatory monocytes. In vitro experiments further revealed that GCSF strongly promotes interleukin (IL)-10 secretion by activated mononuclear cells. Blockade of the IL-10 receptor partly reversed GCSF-induced downregulation of integrin surface expression. Overall, our results suggest that high-dosage GCSF mitigates monocyte infiltration after stroke, likely by attenuating integrin-mediated adhesion to the brain endothelium in an IL-10-dependent manner. Lower amounts of mononuclear cells in the brain translate to less severe brain edema and functional impairment and thus support a harmful role of Ly6C+ inflammatory monocytes in the acute stage of stroke.

Increased expression of TLR9 associated with pro-inflammatory S100A8 and IL-8 in diabetic wounds could lead to unresolved inflammation in type 2 diabetes mellitus (T2DM) cases with impaired wound healing

BACKGROUND

Type 2 diabetes mellitus (T2DM) is characterized by persistent hyperglycemia which causes a chain of abrupt biochemical and physiological changes. Immune dys-regulation is the hallmark of T2DM that could contribute to prolonged inflammation causing transformation of wounds into non-healing chronic ulcers. Toll like receptor -9 (TLR9) is a major receptor involved in innate immune regulation. TLR9 activation induces release of pro-inflammatory molecules like S100A8 and interleukin-8 (IL-8) by myeloid cells causing migration of myeloid cells to the site of inflammation. We hypothesized that pro-inflammatory S100A8 and IL-8 proteins could cause persistent inflammation in chronic wounds like diabetic foot ulcer (DFU) and may contribute to impaired wound healing in T2DM patients.

MATERIALS AND METHODS

Expression of TLR9 and its downstream effector molecules S100A8, and IL-8 were analyzed in chronic diabetic wound and non-diabetic control wound tissue samples by semiquantitative reverse transcriptase - polymerase chain reaction (RT-PCR), quantitative RT-PCR, western blot and immunofluorescence. CD11b(+)CD33(+) myeloid cells were analyzed by flow cytometry.

RESULTS

TLR9 message and protein were higher in diabetic wounds compared to control wounds (p=0.03, t=2.21 for TLR9 mRNA; p=<0.001, t=4.21 for TLR9 protein). TLR9 down-stream effector molecules S100A8 and IL-8 were also increased in diabetic wounds (p=0.003, t=3.1 for S100A8 mRNA; p=0.04, t=2.04 for IL-8). CD11b(+) CD33(+) myeloid cells were decreased in T2DM as compared to non-diabetic controls (p=0.001, t=3.6). DFU subjects had higher levels of CD11b(+) CD33(+) myeloid cells as compared to non-DFU T2DM control (p=0.003, t=2.8). Infection in the wound microenvironment could be the cause of increase in CD11b(+)CD33(+) myeloid cells in DFU (p=0.03, t=2.5).

CONCLUSION

The up-regulation of myeloid cell-derived pro-inflammatory molecules S100A8 and IL-8 in combination with lower levels of CD11b(+) CD33(+) myeloid cells may cause the impairment of wound healing in T2DM subjects leading to chronic ulcers.

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.

Effect of upregulated TLR2 expression from G-CSF-mobilized donor grafts on acute graft-versus-host disease

Our previous study demonstrated that G-CSF treatment increased the expression of TLR2 in donor grafts; this contributed to rapid engraftment after allogeneic hematopoietic stem cell transplantation (HSCT) in mice. In the current study, we investigated the effects of upregulated TLR2 expression in G-CSF-mobilized donor grafts on acute graft-versus-host disease (GVHD). We found that TLR2 was highly expressed on myeloid cell populations but not T and B cells from the spleens of G-CSF-treated donor mice. After transplantation, the mortality and disease severity in recipients were not significantly different between G-CSF-treated TLR2-/- and wt donor grafts. Although endogenous TLR2 ligand was detected in the serum of both recipients, T cells from TLR2-/- and wt donors have the same ability regarding alloreactivity. Moreover, the blockade of TLR2 signaling in recipients by administering anti-TLR2 blocking antibody after BMT did not lead to a significant difference in acute GVHD compared with control IgG treatment. However, the hematopoietic ability of G-CSF-mobilized lin−c-kit+ HSCs from TLR2-/- donor grafts was lower than that from wt donor grafts. Our results demonstrate that upregulated TLR2 expression in G-CSF-mobilized donor grafts has no effect on acute GVHD, suggesting that TLR2 is a valuable target for increasing HSCT efficiency in order to enhance engraftment without exacerbating acute GVHD.

The Role and Potential Therapeutic Application of Myeloid-Derived Suppressor Cells in Allo- and Autoimmunity

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of cells that consists of myeloid progenitor cells and immature myeloid cells. They have been identified as a cell population that may affect the activation of CD4(+) and CD8(+) T-cells to regulate the immune response negatively, which makes them attractive targets for the treatment of transplantation and autoimmune diseases. Several studies have suggested the potential suppressive effect of MDSCs on allo- and autoimmune responses. Conversely, MDSCs have also been found at various stages of differentiation, accumulating during pathological situations, not only during tumor development but also in a variety of inflammatory immune responses, bone marrow transplantation, and some autoimmune diseases. These findings appear to be contradictory. In this review, we summarize the roles of MDSCs in different transplantation and autoimmune diseases models as well as the potential to target these cells for therapeutic benefit.

G-CSF mobilizes CD34 + regulatory monocytes that inhibit graft-versus-host disease

G-SCF–mobilized CD34 + monocytes inhibit graft-versus-host disease by the production of nitric oxide and the induction of regulatory T cells.

Reciprocal relationship between myeloid-derived suppressor cells and T cells

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous group of myeloid cells that play a major role in the regulation of immune responses in many pathological conditions. These cells have a common myeloid origin, relatively immature state, common genetic and biochemical profiles, and, most importantly, the ability to inhibit immune responses. Although initial studies of MDSCs were almost exclusively performed in tumor-bearing mice or cancer patients, in recent years, it became clear that MDSCs play a critical role in the regulation of different types of inflammation that are not directly associated with cancer. In this review we discuss the nature of the complex relationship between MDSCs and the different populations of CD4(+) T cells.

Dynamic change and impact of myeloid-derived suppressor cells in allogeneic bone marrow transplantation in mice

Myeloid-derived suppressor cells (MDSCs) are a group of myeloid cells composed of hematopoietic progenitor cells, immature macrophages, dendritic cells, and granulocytes, which accumulate in inflammatory diseases and various cancers. Here, we investigated the dynamic changes and effects of MDSCs in graft-versus-host disease (GVHD) development and/or tumor relapse after syngeneic and allogeneic bone marrow transplantation (BMT). We found that adding functional MDSCs in donor graft alleviated GVHD, whereas removal of MDSCs in vivo exacerbated GVHD. After T cell-deplete BMT, MDSCs transiently accumulated in the blood and spleen of recipients without GVHD. In contrast, after T cell-replete BMT, the levels of blood MDSCs were constantly elevated in recipients with GVHD. MDSC accumulation positively correlated with the severity of GVHD. Additionally, MDSC accumulation was further increased upon tumor relapse. Although MDSCs isolated from both syngeneic and allogeneic BMT recipients inhibited T cell proliferation in response to alloantigen stimulation ex vivo, MDSCs from the recipients with GVHD showed much higher suppressive potency compared with those from recipients without GVHD. These results indicate that MDSCs can regulate the immune response in acute GVHD, and possibly tumor relapse, subsequent to allogeneic BMT.

G-CSF-induced myeloid cells stimulated by TLR2 enhance engraftment after allogeneic hematopoietic stem cell transplantation

A high frequency of G-CSF-mobilized myeloid cells (gMCs) in a donor graft accelerates hematopoietic recovery after peripheral blood stem cell transplantation (PBSCT). However, because of the limited functional efficacy of gMCs, repeated transfusions of gMCs are frequently required. In this study, we investigated a strategy to improve the functional capacity of gMCs during hematopoietic engraftment after allogeneic transplantation. We found that toll-like receptor 2 (TLR2) is constitutively expressed on gMCs. Treating gMCs with the synthetic TLR2 ligand Pam(3)CSK(4) (PAM) dramatically enhanced IL-10 and TNF-α production. However, PAM treatment does not induce substantial cellular maturation. Moreover, PAM treatment significantly improved gMC survival. PAM treated gMCs significantly promoted myeloid differentiation of donor hematopoietic stem cells (HSCs), resulting in accelerated engraftment after allogeneic transplantation. Our data suggest that TLR2-stimulated gMCs may be a novel cellular therapeutic for increasing the efficiency of allogeneic hematopoietic stem cell transplantation (HSCT) by reducing infectious complications associated with delayed engraftment.

G-CSF stem cell mobilization in human donors induces polymorphonuclear and mononuclear myeloid-derived suppressor cells

The role of myeloid-derived suppressor cells (MDSC) is emerging in transplantation. An expansion of myeloid progenitor cells with suppressive capacity has been reported to occur as a bystander phenomenon in the course of allogeneic hematopoietic stem cell transplantation (allo-HSCT) protocols, particularly, in mice during bone marrow chimerism induction and in human stem cell donors during G-CSF-mobilization protocols. Hypothesizing that such 'regulatory myeloid cells' play a role in regulating post-transplant T-cell alloreactivity, we performed a phenotypical and functional characterization of these cells in peripheral blood stem cell grafts of G-CSF-treated donors. We demonstrate that expanding myeloid cells in the peripheral blood of G-CSF-mobilized donors comprise the typical phenotype of the mononuclear and polymorphonuclear MDSC-subtypes that were recently described in cancer patients, and that both MDSC-subsets have the capacity to regulate alloreactive T-cell responses in-vitro. This study provides the basis for investigating the clinical relevance of MDSC and MDSC-subtypes in human allo-HSCT.

Activation of MDL-1 (CLEC5A) on immature myeloid cells triggers lethal shock in mice

Systemic inflammatory response syndrome (SIRS) is a potentially lethal condition, as it can progress to shock, multi-organ failure, and death. It can be triggered by infection, tissue damage, or hemorrhage. The role of tissue injury in the progression from SIRS to shock is incompletely understood. Here, we show that treatment of mice with concanavalin A (ConA) to induce liver injury triggered a G-CSF-dependent hepatic infiltration of CD11b+Gr-1+Ly6G+Ly6C+ immature myeloid cells that expressed the orphan receptor myeloid DAP12-associated lectin-1 (MDL-1; also known as CLEC5A). Activation of MDL-1 using dengue virus or an agonist MDL-1-specific antibody in the ConA-treated mice resulted in shock. The MDL-1+ cells were pathogenic, and in vivo depletion of MDL-1+ cells provided protection. Triggering MDL-1 on these cells induced production of NO and TNF-α, which were found to be elevated in the serum of treated mice and required for MDL-1-induced shock. Surprisingly, MDL-1-induced NO and TNF-α production required eNOS but not iNOS. Activation of DAP12, DAP10, Syk, PI3K, and Akt was critical for MDL-1-induced shock. In addition, Akt physically interacted with and activated eNOS. Therefore, triggering of MDL-1 on immature myeloid cells and production of NO and TNF-α may play a critical role in the pathogenesis of shock. Targeting the MDL-1/Syk/PI3K/Akt/eNOS pathway represents a potential new therapeutic strategy to prevent the progression of SIRS to shock.

IDO in human gut graft-versus-host disease

Although rodent graft-versus-host disease (GVHD) models have suggested that indoleamine 2,3-dioxygenase (IDO) is a critical regulator of gastrointestinal GVHD, parallel human studies on IDO expression have not been reported. IDO expression was assessed in 20 patients who underwent duodenal biopsy. IDO was upregulated in epithelial cells. In situ analyses reveal that macrophages and dendritic cells stain positive for IDO, but that most of the IDO(+) cells were a novel population of CD3(+)CD4(+)IDO(+) cells. The proportion of CD4(+)IDO(+) T cells was significantly higher in patients with moderate GVHD. In situ regulatory T cell and Th17 numbers correlated with overall severity. Although needing confirmatory results from larger sample sets, these data are consistent with the hypothesis that IDO is involved in regulating gastrointestinal GVHD.

Ultraviolet irradiation of mice reduces the competency of bone marrow-derived CD11c+ cells via an indomethacin-inhibitable pathway

Direct UV irradiation of dendritic cells and Langerhans cells reduces their Ag presenting ability. However, the effects of UV on CD11c(+) cells located distally to the point of irradiation are poorly understood. Three days after UV irradiation (8 kJ/m(2)) of BALB/c mice, bone marrow cells were isolated and cultured for 7 d with IL-4 and GM-CSF for the propagation of CD11c(+) cells. Bone marrow-derived CD11c(+) cells from UV-irradiated or nonirradiated mice were loaded with dinitrobenzene sulfonic acid and injected into the ear pinnas of naive BALB/c mice. After 7 d, the ears were painted with 2,4-dinitro-1-fluorobenzene and the ear swelling determined 24 h later. A reduced contact hypersensitivity response was found in mice injected with CD11c(+) cells from the UV-irradiated animals compared with those injected with cells from the nonirradiated animals. Further, a long-lasting suppression of the memory response to 2,4-dinitro-1-fluorobenzene was created. This suppressed response corresponded to increased IL-10 and PGE(2) secretion by freshly isolated bone marrow cells from UV-irradiated mice, and to increased myelopoiesis. The reduction in competence of bone marrow-derived CD11c(+) cells from UV-irradiated mice was not due to delayed maturation, as it was maintained upon LPS exposure prior to CD11c(+) cell purification. The UV-induced effect was reversed by the administration of indomethacin to mice prior to UV irradiation and could be reproduced by s.c. PGE(2). These results show that UV irradiation of mice can affect the function of bone marrow-derived CD11c(+) cells via a mechanism inhibitable by indomethacin; this pathway is likely to contribute to systemic UV-induced immunosuppression.

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.