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

Natural killer cells 56bright16- have higher counts in the umbilical cord blood than in the adult peripheral blood

INTRODUCTION AND HYPOTHESIS

Umbilical cord blood (UCB) is an alternative source of hematopoietic stem cells for allogeneic hematopoietic stem cell transplantation in the absence of a compatible donor. The UCB transplantation has a lower incidence of chronic graft versus host disease (GvHD), but is associated with slower engraftment and slower immune reconstitution, compared to other sources. Dendritic cells (DCs) and Natural Killer cells (NKs) play a central role in the development of GvHD and the graft versus leukemia (GvL) effect, as well as in the control of infectious complications.

METHOD

We quantified by multiparametric flow cytometry monocytes, lymphocytes, NK cells, and DCs, including their subsets, in UCB samples from 54 healthy newborns and peripheral blood (PB) from 25 healthy adult volunteers.

RESULTS

In the UCB samples, there were higher counts of NK cells 56bright16- (median 0.024 × 109/L), compared to the PB samples (0.012 × 109/L, p < 0.0001), NK 56dim16bright (median 0.446 × 109/L vs. 0.259 × 109/L for PB samples, p = 0.001) and plasmacytoid dendritic cells (pDCs, median 0.008 × 109/L for UCB samples vs. 0.006 × 109/L for PB samples, p = 0.03). Moreover, non-classic monocyte counts were lower in UCB than in PB (median 0.024 × 109/L vs. 0.051 × 109/L, respectively, p < 0.0001).

CONCLUSION

In conclusion, there were higher counts of NK cells and pDCs and lower counts of non-classic monocytes in UCB than in PB from healthy individuals. These findings might explain the lower incidence and severity of chronic GvHD, although maintaining the GvL effect, in UCB transplant recipients, compared to other stem cell sources.

CD11c participates in triggering acute graft-versus-host disease during bone marrow transplantation

CD11c is a canonical dendritic cell (DC) marker with poorly defined functions in the immune system. Here, we found that blocking CD11c on human peripheral blood mononuclear cell‐derived DCs (MoDCs) inhibited the proliferation of CD4⁺ T cells and the differentiation into IFN‐γ‐producing T helper 1 (Th1) cells, which were critical in acute graft‐versus‐host disease (aGVHD) pathogenesis. Using allogeneic bone marrow transplantation (allo‐BMT) murine models, we consistently found that CD11c‐deficient recipient mice had alleviated aGVHD symptoms for the decreased IFN‐γ‐expressing CD4⁺ Th1 cells and CD8⁺ T cells. Transcriptional analysis showed that CD11c participated in several immune regulation functions including maintaining antigen presentation of APCs. CD11c‐deficient bone marrow‐derived DCs (BMDCs) impaired the antigen presentation function in coculture assay. Mechanistically, CD11c interacted with MHCII and Hsp90 and participated in the phosphorylation of Akt and Erk1/2 in DCs after multiple inflammatory stimulations. Therefore, CD11c played crucial roles in triggering aGVHD and might serve as a potential target for the prevention and treatment of aGVHD.

Human invariant natural killer T cells promote tolerance by preferential apoptosis induction of conventional dendritic cells

Graft-versus-host disease (GvHD) is a major cause of morbidity and mortality after allogeneic hematopoietic cell transplantation. We recently showed in murine studies and in vitro human models that adoptively transferred invariant natural killer T (iNKT) cells protect from GvHD and promote graft-versus-leukemia effects. The cellular mechanisms underlying GvHD prevention by iNKT cells in humans, however, remain unknown. In order to study relevant cellular interactions, dendritic cells (DC) were either generated from monocytes or isolated directly from blood of healthy donors or GvHD patients and co-cultured in a mixed lymphocyte reaction (MLR) with T cells obtained from healthy donors or transplantation bags. Addition of culture-expanded iNKT cells to the MLR-induced DC apoptosis in a cell contact-dependent manner, thereby preventing T-cell activation and proliferation. Annexin V/propidium iodide staining and image stream assays showed that CD4⁺CD8^–, CD4^–CD8⁺ and double negative iNKT cells are similarly able to induce DC apoptosis. Further MLR assays revealed that conventional DC (cDC) but not plasmacytoid DC (pDC) could induce alloreactive T-cell activation and proliferation. Interestingly, cDC were also more susceptible to apoptosis induced by iNKT cells, which correlates with their higher CD1d expression, leading to a bias in favor of pDC. Remarkably, these results could also be observed in GvHD patients. We propose a new mechanism how ex vivo expanded human iNKT cells prevent alloreactivity of T cells. iNKT cells modulate T-cell responses by selective apoptosis of DC subsets, resulting in suppression of T-cell activation and proliferation while enabling beneficial immune responses through pDC.

Effects of decitabine on allogeneic immune reactions of donor lymphocyte infusion via activation of dendritic cells

Background

Successful prevention of post-transplantation relapse after donor lymphocyte infusion (DLI) depends on its capability to mediate an effective graft-versus-leukemia (GVL) response while minimizing DLI-related toxicity, including graft-versus-host disease (GVHD).

Methods

We assessed the effects of decitabine (DEC), a hypomethylating agent, upon allogeneic immune reaction in a murine model of DLI.

Results

Significantly greater tumor growth retardation and survival prolongation occurred in mice administered with 1.0 mg/kg DEC for 5 days (DEC-1.0) than in control or DEC-0.1 mice. Upon prompt DEC and DLI co-administration, dendritic cells (DCs) were activated; DEC-1.0/DLI induced severe GVHD, and survival was significantly lower than with DLI alone or DEC-0.1/DLI treatments. IFN-γ and CD28 levels were higher in splenic DCs of DEC-1.0 mice than in those of control mice. Assessment of delayed DLI co-administration with DEC, when IFN-γ levels were normalized to control levels, revealed that DEC-1.0/DLI successfully facilitated tumor management without causing severe GVHD.

Conclusions

Our results suggest that DEC primes allogeneic immune reactions of DLI via DC activation, and GVHD and GVL effects are separable through optimal DLI timing based on DEC-induced increase in IFN-γ expression levels.

Distinguishing human peripheral blood CD16+ myeloid cells based on phenotypic characteristics

Myeloid lineage cells present in human peripheral blood include dendritic cells (DC) and monocytes. The DC are identified phenotypically as HLA-DR⁺ cells that lack major cell surface lineage markers for T cells (CD3), B cells (CD19, CD20), NK cells (CD56), red blood cells (CD235a), hematopoietic stem cells (CD34), and Mo that express CD14. Both DC and Mo can be phenotypically divided into subsets. DC are divided into plasmacytoid DC, which are CD11c^- , CD304⁺ , CD85g⁺ , and myeloid DC that are CD11c⁺ . The CD11c⁺ DC are readily classified as CD1c⁺ DC and CD141⁺ DC. Monocytes are broadly divided into the CD14⁺ CD16^- (classical) and CD14^dim CD16⁺ subsets (nonclassical). A population of myeloid-derived cells that have DC characteristics, that is, HLA-DR⁺ and lacking lineage markers including CD14, but express CD16 are generally clustered with CD14^dim CD16⁺ monocytes. We used high-dimensional clustering analyses of fluorescence and mass cytometry data, to delineate CD14⁺ monocytes, CD14^dim CD16⁺ monocytes (CD16⁺ Mo), and CD14^- CD16⁺ DC (CD16⁺ DC). We sought to identify the functional and kinetic relationship of CD16⁺ DC to CD16⁺ Mo. We demonstrate that differentiation of CD16⁺ DC and CD16⁺ Mo during activation with IFNγ in vitro and as a result of an allo-hematopoietic cell transplant (HCT) in vivo resulted in distinct populations. Recovery of blood CD16⁺ DC in both auto- and allo-(HCT) patients after myeloablative conditioning showed similar reconstitution and activation kinetics to CD16⁺ Mo. Finally, we show that expression of the cell surface markers CD300c, CCR5, and CLEC5a can distinguish the cell populations phenotypically paving the way for functional differentiation as new reagents become available.

Differences of Immune Reconstitution of Dendritic Cells in Pediatric GvHD Patients After Allogenic Stem Cell Transplantation

BACKGROUND

Hematopoietic stem cell transplantation (HSCT) is a life-saving procedure for children with a variety of (non) malignant conditions. GvHD is a severe complication with high morbidity and mortality. The pathogenesis remains unclear. We studied dendritic cell (DC) reconstitution to detect potential differences, which may improve our knowledge in the development of chronic GvHD (cGvHD).

PROCEDURE

We examined immune reconstitution (T, B, and NK cells and dendritic cells) at defined time points in a pediatric cohort who underwent 61 allogeneic HSCTs.

RESULTS

Regarding DC reconstitution we found a fast reconstitution of the DC compartment negatively correlated with age. After HSCT, both myeloid DC (mDC) and plasmacytoid DC (pDC) counts recover to pre-HSCT levels within 2 months. Higher CCR7 positive cell counts were found in patients receiving TBI during engraftment and during the whole posttransplant period we found a correlation with an improved outcome. In cGVHD patients decreased total DC counts and increased pDCs were found after day+100. No relevant correlation was achieved regarding to HLA-matching, stem cell manipulation of the graft as well as HSCT-indication compared with different DC counts.

DISCUSSION

Pathogenesis of cGvHD remains complex. Our data suggest an influence of dendritic cells, which may contribute to the clinical picture and should be further investigated in future studies.

Dendritic Cell Regulation of Graft-Vs.-Host Disease: Immunostimulation and Tolerance

Graft-vs.-host disease (GVHD) remains a significant cause of morbidity and mortality after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Significant progresses have been made in defining the dichotomous role of dendritic cells (DCs) in the development of GVHD. Host-derived DCs are important to elicit allogeneic T cell responses, whereas certain donor-types of DCs derived from newly engrafted hematopoietic stem/progenitor cells (HSPCs) can amply this graft-vs.-host reaction. In contrast, some DCs also play non-redundant roles in mediating immune tolerance. They induce apoptotic deletion of host-reactive donor T cells while promoting expansion and function of regulatory T cells (Treg). Unfortunately, this tolerogenic effect of DCs is impaired during GVHD. Severe GVHD in patients subject to allo-HSCT is associated with significantly decreased number of circulating peripheral blood DCs during engraftment. Existing studies reveal that GVHD causes delayed reconstitution of donor DCs from engrafted HSPCs, impairs the antigen presentation function of newly generated DCs and reduces the capacity of DCs to regulate Treg. The present review will discuss the importance of DCs in alloimmunity and the mechanism underlying DC reconstitution after allo-HSCT.

The cell surface phenotype of human dendritic cells

Dendritic cells (DC) are bone marrow derived leucocytes that are part of the mononuclear phagocytic system. These are surveillance cells found in all tissues and, as specialised antigen presenting cells, direct immune responses. Membrane molecules on the DC surface form a landscape that defines them as leucocytes and part of the mononuclear phagocytic system, interacts with their environment and directs interactions with other cells. This review describes the DC surface landscape, reflects on the different molecules confirmed to be on their surface and how they provide the basis for manipulation and translation of the potent functions of these cells into new diagnostics and immune therapies for the clinic.

Dendritic Cell Recovery Impacts Outcomes after Umbilical Cord Blood and Sibling Donor Transplantation for Hematologic Malignancies

Dendritic cells (DCs) orchestrate immune responses after allogeneic hematopoietic cell transplantation (HCT). We studied the association of donor myeloid DCs (mDCs) and plasmacytoid DCs (pDCs) recovery in the landmark analysis of umbilical cord blood (UCB) and matched related donor (RD) HCT. Eighty patients (42 UCB and 38 RD recipients) with a day 100 blood sample were included in the analysis. Median age was 51 years (range, 20 to 71). Most patients had acute leukemia (50%) or lymphoma (23%) and received reduced-intensity conditioning (75%). After transplantation, UCB recipients had higher DC counts than RD recipients reaching normal levels at day 100 after transplantation (UCB median 4.7 cells/µL versus RD median 1.7 cells/µL). UCB recipients with high day 100 pDCs levels (≥ median) had 2-fold lower risk of relapse compared with those with pDC^low (14% versus 28%, P = .29) and a trend to improved 1-year survival in multivariate analysis with hazard ratio of .22 (95% confidence interval, .04 to 1.05; P = .057). Cytomegalovirus (CMV) reactivation had adverse impact on DC reconstitution at day 100 in both UCB and RD groups and almost exclusively affected the mDC subset (CMV reactivation: mDC 3.2 cells/µL versus no CMV reactivation: 7.8 cells/µL; P = .004). Collectively, these data suggest that high levels of circulating pDCs at day 100 after UCB transplantation confer a survival advantage at 1 year.

Mouse nidovirus LDV infection alleviates graft versus host disease and induces type I IFN-dependent inhibition of dendritic cells and allo-responsive T cells

Introduction

Viruses have developed multiple mechanisms to alter immune reactions. In 1969, it was reported that lactate dehydrogenase‐elevating virus (LDV), a single stranded positive sense mouse nidovirus, delays skin allograft rejection and inhibits spleen alterations in graft versus host disease (GVHD). As the underlying mechanisms have remained unresolved and given the need for new therapies of this disease, we reassessed the effects of the virus on GVHD and tried to uncover its mode of action.

Methods

GVHD was induced by transfer of parent (B6) spleen cells to non‐infected or LDV‐infected B6D2F1 recipients. In vitro mixed‐lymhocyte culture (MLC) reactions were used to test the effects of the virus on antigen‐presenting cells (APC) and responder T cells.

Results

LDV infection resulted in a threefold increase in survival rate with reduced weight loss and liver inflammation but with the establishment of permanent chimerism that correlated with decreased interleukine (IL)‐27 and interferon (IFN)γ plasma levels. Infected mice showed a transient elimination of splenic CD11b+ and CD8α+ conventional dendritic cells (cDCs) required for allogeneic CD4 and CD8 T cell responses in vitro. This drop of APC numbers was not observed with APCs derived from toll‐like receptor (TLR)7‐deficient mice. A second effect of the virus was a decreased T cell proliferation and IFNγ production during MLC without detectable changes in Foxp3+ regulatory T cell (Tregs) numbers. Both cDC and responder T cell inhibition were type I IFN dependent. Although the suppressive effects were very transient, the GVHD inhibition was long‐lasting.

Conclusion

A type I IFN‐dependent suppression of DC and T cells just after donor spleen cell transplantation induces permanent chimerism and donor cell implantation in a parent to F1 spleen cell transplantation model. If this procedure can be extended to full allogeneic bone marrow transplantation, it could open new therapeutic perspectives for hematopoietic stem cell transplantation (HSCT).

Azithromycin modulates immune response of human monocyte-derived dendritic cells and CD4+ T cells

Azithromycin (AZM) is a macrolide antibiotic that exhibits anti-inflammatory activity aside from its antimicrobial effect, a feature that may ameliorate certain inflammatory disorders and prevent graft-versus-host disease in patients receiving stem cell transplantation. In the present study, we investigated the ability of AZM to influence the function of human monocyte-derived dendritic cells (DCs) and CD4⁺ T cells. We found that AZM down-regulated CD80, CD86, and HLA-DR expression in lipopolysaccharide (LPS)-stimulated DCs and suppressed interleukin (IL)-6, IL-10, IL-12, and tumor necrosis factor-alpha production in these cells. In addition, AZM increased endocytosis and/or expression of Toll-like receptor (TLR)2, TLR4, and TLR9 in DCs and suppressed anti-CD3/CD28-induced CD4⁺ T cell proliferation and interferon-gamma production, an effect that was synergistic with dexamethasone. Finally, AZM suppressed DC-induced allogeneic T cell proliferation and cytokine production. Our study demonstrates that AZM modulates DC and CD4⁺ T cell function and may be of therapeutic benefit in various inflammatory disorders.

The Role of Biomarkers in the Diagnosis and Risk Stratification of Acute Graft-versus-Host Disease: A Systematic Review

Allogeneic hematopoietic cell transplantation (HCT) is an increasingly used curative modality for hematologic malignancies and other benign conditions. Attempts to reduce morbidity and mortality and improve survival in patients undergoing HCT are crucial. The ability to diagnose acute graft-versus-host disease (aGVHD) in a timely manner, or to even predict aGVHD before clinical manifestations, along with the accurate stratification of these patients, are critical steps to improve the treatment and outcomes of these patients. Many novel biomarkers that may help achieve these goals have been studied recently. This overview is intended to assist clinicians and investigators by providing a comprehensive review and analytical interpretation of the current knowledge concerning aGVHD and biomarkers likely to prove useful in diagnosis and risk stratification of this condition, along with the difficulties that hamper this approach.

Immunosuppressive human anti-CD83 monoclonal antibody depletion of activated dendritic cells in transplantation

Current immunosuppressive/anti-inflammatory agents target the responding effector arm of the immune response and their nonspecific action increases the risk of infection and malignancy. These effects impact on their use in allogeneic haematopoietic cell transplantation and other forms of transplantation. Interventions that target activated dendritic cells (DCs) have the potential to suppress the induction of undesired immune responses (for example, graft versus host disease (GVHD) or transplant rejection) and to leave protective T-cell immune responses intact (for example, cytomegalovirus (CMV) immunity). We developed a human IgG1 monoclonal antibody (mAb), 3C12, specific for CD83, which is expressed on activated but not resting DC. The 3C12 mAb and an affinity improved version, 3C12C, depleted CD83(+) cells by CD16(+) NK cell-mediated antibody-dependent cellular cytotoxicity, and inhibited allogeneic T-cell proliferation in vitro. A single dose of 3C12C prevented human peripheral blood mononuclear cell-induced acute GVHD in SCID mouse recipients. The mAb 3C12C depleted CMRF-44(+)CD83(bright) activated DC but spared CD83(dim/-) DC in vivo. It reduced human T-cell activation in vivo and maintained the proportion of CD4(+) FoxP3(+) CD25(+) Treg cells and also viral-specific CD8(+) T cells. The anti-CD83 mAb, 3C12C, merits further evaluation as a new immunosuppressive agent in transplantation.

Low Counts of Plasmacytoid Dendritic Cells after Engraftment Are Associated with High Early Mortality after Allogeneic Stem Cell Transplantation

Dendritic cells (DCs) are antigen-presenting cells that drive immune responses and tolerance and are divided in different subsets: myeloid DCs (mDCs: lineage-; HLA-DR+, 11c+), plasmacytoid dendritic cells (pDCs: HLA-DR+, CD123+), and monocyte-derived DCs (moDC: lineage-, 11c+, 16+). After hematopoietic stem cell transplantation (HSCT), low DC counts in the recipients' peripheral blood (PB) have been associated with worse outcomes, but the relevance of DC graft content remains unclear, and there are few data in the setting of unrelated donor HSCT. We evaluated the DC graft content and monitored DC recovery in PB from 111 HSCT recipients (median age, 17 years; range 1 to 74), who received bone marrow (46%), umbilical cord blood (32%), or PB (22%) from unrelated (81%) or related donors (19%). In 86 patients with sustained allogeneic recovery, patients with higher counts of all DC subsets (pDC, mDC, and moDC) 3 weeks after engraftment had lower incidence of nonrelapse mortality (NMR) and acute graft-versus-host disease (aGVHD) and better survival. pDC counts were associated with more striking results: patients with higher pDC counts had much lower incidences of NRM (3% versus 47%, P < .0001), lower incidence of aGVHD (24% versus 67%, P < .0001), and better overall survival (92% versus 45%, P < .0001). In contrast, higher pDC counts in the graft was associated with an increased risk of aGVHD (55% versus 26%, P = .02). Our results indicate that DC counts are closely correlated with HSCT outcomes and warrant further prospective evaluation and possible early therapeutic interventions to ameliorate severe aGVHD and decrease mortality.

Opportunities and challenges of proteomics in pediatric patients: circulating biomarkers after hematopoietic stem cell transplantation as a successful example

Biomarkers have the potential to improve diagnosis and prognosis, facilitate-targeted treatment, and reduce health care costs. Thus, there is great hope that biomarkers will be integrated in all clinical decisions in the near future. A decade ago, the biomarker field was launched with great enthusiasm because MS revealed that blood contains a rich library of candidate biomarkers. However, biomarker research has not yet delivered on its promise due to several limitations: (i) improper sample handling and tracking as well as limited sample availability in the pediatric population, (ii) omission of appropriate controls in original study designs, (iii) lability and low abundance of interesting biomarkers in blood, and (iv) the inability to mechanistically tie biomarker presence to disease biology. These limitations as well as successful strategies to overcome them are discussed in this review. Several advances in biomarker discovery and validation have been made in hematopoietic stem cell transplantation, the current most effective tumor immunotherapy, and these could serve as examples for other conditions. This review provides fresh optimism that biomarkers clinically relevant in pediatrics are closer to being realized based on: (i) a uniform protocol for low-volume blood collection and preservation, (ii) inclusion of well-controlled independent cohorts, (iii) novel technologies and instrumentation with low analytical sensitivity, and (iv) integrated animal models for exploring potential biomarkers and targeted therapies.

Graft-versus-host disease biomarkers: omics and personalized medicine

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is the most effective form of tumor immunotherapy available to date and the frequency of transplants continues to increase worldwide. However, while allo-HSCT usually induces a beneficial graft-versus leukemia effect, a major source of morbidity and mortality following allo-HSCT is graft-versus-host disease (GVHD). Currently available diagnostic and staging tools frequently fail to identify those at higher risk for GVHD morbidity, treatment unresponsiveness, and death. Furthermore, there are shortcomings in the risk stratification of patients before GVHD clinical signs develop. In parallel, recent years have been characterized by an explosive evolution of omics technologies, largely due to technological advancements in chemistry, engineering, and bioinformatics. Building on these opportunities, plasma biomarkers have been identified and validated as promising diagnostic and prognostic tools for acute GVHD. This review summarizes current information on the types of GVHD biomarkers, the omics tools used to identify them, the biomarkers currently validated as acute GVHD markers, and future recommendations for incorporating biomarkers into new grading algorithms for risk-stratifying patients and creating more personalized treatment courses. Future directions will include randomized evaluations of these biomarkers in multicenter prospective studies while extending on the need for biomarkers of chronic GVHD.

Methods of detection of immune reconstitution and T regulatory cells by flow cytometry

Allogeneic hematopoietic stem cell therapy (HSCT) remains one of the few curative treatments for high-risk hematological malignancies (high-risk leukemia, myelodysplastic syndromes, advanced myeloproliferative disorders, high-risk lymphomas, and multiple myeloma) and is currently applied in more than 15,000 patients per year in Europe. Following HSCT, patients experience a period of reconstitution of the immune system, which seems to be highly dependent on conditioning, immunosuppression regimes, and the level of adverse events the patients experience. During this reconstitution period, the patient is immune compromised and susceptible to opportunistic infections and disease relapse. Consequently, a large number of clinical studies have been devoted to monitoring the recovery of the immune system following HSCT in the hopes of determining which cellular subsets are indicative of a favorable outcome. In this chapter we review the methods that have been employed to monitor the immune reconstitution and what clinical observations have been made. Of particular interest is the regulatory T cell (Treg) subset, which has been associated with tolerance and has been the subject of recent clinical trials as a possible cellular therapy for rejection reactions. Finally we will detail a proposed methodology for the flow cytometric assessment of cellular reconstitution post-HSCT.

Alterations in chemokine receptor CCR5 expression on blood dendritic cells correlate with acute graft-versus-host disease

BACKGROUND

Dendritic cells (DC) are important in the development of acute graft-versus-host disease (GVHD) after allogeneic hemopoietic cell transplantation (alloHCT). The trafficking of immature DC from blood to GVHD target organs is likely to be regulated by chemokine receptors.

METHODS

We performed flow cytometry to document the expression of chemokine receptors on circulating DC and correlated the findings after alloHCT with occurrence of acute GVHD.

RESULTS

In normal individuals, plasmacytoid DC (pDC) expressed high levels of CCR5, whereas the major CD16 myeloid DC subpopulation lacked CCR5. However, its expression on CD16 cells was induced by culture in allogeneic mixed lymphocyte reaction supernatant, an effect largely mediated by interferon-γ. CCR5 was expressed on a significant proportion of CD16 DC in 42 alloHCT patients, whereas it was down-regulated on pDC. The maximum percentage of CCR5CD16 DC, at any time after transplantation, correlated with acute GVHD, whereas the minimum CCR5 on pDC showed a similar correlation. Before developing signs of GVHD, the maximum percentage CCR5CD16 DC was higher in patients with GVHD grades II to IV than in GVHD grades 0 and I, whereas the minimum percentage CCR5 on pDC was lower in GVHD grades II to IV than in GVHD grades 0 and I. CCR5 levels more than 20.5% on CD16 myeloid DC and less than 22.6% on CD123 pDC correlated with subsequent GVHD grades II to IV with high sensitivities and specificities.

CONCLUSIONS

These observations may reflect DC activation and altered homing during the alloimmune response and could allow early diagnosis and therapeutic intervention before the clinical diagnosis of GVHD.

Reconstitution of 6-sulfo LacNAc dendritic cells after allogeneic stem-cell transplantation

BACKGROUND

Infections and acute graft-versus-host disease (GvHD) represent major complications of allogeneic stem-cell transplantation (SCT). Dendritic cells (DCs) display an extraordinary capacity to induce innate and adaptive immune responses. Therefore, they play a crucial role in the elimination of pathogens and in the pathogenesis of acute GvHD. 6-Sulfo LacNAc DCs (slanDCs) are a major subpopulation of human blood DCs with a high proinflammatory capacity. We investigated for the first time the reconstitution of slanDCs in the blood of patients after SCT and the modulation of their frequency by bacterial infection, cytomegalovirus (CMV) reactivation, and acute GvHD.

METHODS

The frequency of slanDCs, CD1c myeloid DCs (mDCs), and plasmacytoid DCs (pDCs) in the peripheral blood was quantified by flow cytometry in 80 patients after SCT. To assess individual DC subsets, we used pregating of the HLADRLin subset and antibodies against slanDCs, blood DC antigen 1 (CD1c mDCs), and blood DC antigen 2 (pDCs).

RESULTS

SlanDCs showed the slowest reconstitution in the first month after SCT compared with CD1c mDCs and pDCs. Interestingly, in the second and third months after SCT, their percentage steadily increased, and slanDCs were the most abundant DC subset. In addition, we observed a markedly reduced frequency of slanDCs in the blood of patients with bacterial infection, CMV reactivation, or severe acute GvHD. Furthermore, slanDCs showed the most prominent reduction after steroid treatment of acute GvHD.

CONCLUSIONS

These results indicate that SCT-associated complications such as bacterial infection, CMV reactivation, and acute GvHD can significantly modulate the frequency of slanDCs.

Discovery and validation of graft-versus-host disease biomarkers

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is the most effective tumor immunotherapy available. Although allo-HSCT provides beneficial graft-versus-tumor effects, acute GVHD (aGVHD) is the primary source of morbidity and mortality after HSCT. Diagnosis of aGVHD is typically based on clinical symptoms in one or more of the main target organs (skin, liver, gastrointestinal tract) and confirmed by biopsy. However, currently available diagnostic and staging tools often fail to identify patients at higher risk of GVHD progression, unresponsiveness to therapy, or death. In addition, there are shortcomings in the prediction of GVHD before clinical signs develop, indicating the urgent need for noninvasive and reliable laboratory tests. Through the continuing evolution of proteomics technologies seen in recent years, plasma biomarkers have been identified and validated as promising diagnostic tools for GVHD and prognostic tools for nonrelapse mortality. These biomarkers may facilitate timely and selective therapeutic intervention but should be more widely validated and incorporated into a new grading system for risk stratification of patients and better-customized treatment. This review identifies biomarkers for detecting GVHD, summarizes current information on aGVHD biomarkers, proposes future prospects for the blinded evaluation of these biomarkers, and discusses the need for biomarkers of chronic GVHD.

New ways to separate graft-versus-host disease and graft-versus-tumour effects after allogeneic haematopoietic stem cell transplantation

A major challenge to transplant immunologists and physicians remains the separation of harmful graft-versus-host disease (GvHD) and beneficial graft-versus-tumour (GvT) effects after allogeneic haematopoietic stem cell transplantation. Recent advances in our understanding of the allogeneic immune response provide potential new opportunities to achieve this goal. Three potential new approaches that capitalize on this new knowledge are considered in depth; the manipulation of organ-specific cytokines and other pro-inflammatory signals, the selective manipulation of donor effector T cell migration, and the development of cell-mediated immunosuppressive strategies using donor-derived regulatory T cells. These new approaches could provide strategies for local control of allogeneic immune responses, a new paradigm to separate GvHD and GvT effects. Although these strategies are currently in their infancy and have challenges to successful translation to clinical practice, all have exciting potential for the future.

Dendritic cells and regulation of graft-versus-host disease and graft-versus-leukemia activity

Hematopoietic stem cell transplantation is the only curative treatment for many malignant hematologic diseases, with an often critical graft-versus-leukemia effect. Despite peritransplant prophylaxis, GVHD remains a significant cause of posthematopoietic stem cell transplantation morbidity and mortality. Traditional therapies have targeted T cells, yet immunostimulatory dendritic cells (DCs) are critical in the pathogenesis of GVHD. Furthermore, DCs also have tolerogenic properties. Monitoring of DC characteristics may be predictive of outcome, and therapies that target DCs are innovative and promising. DCs may be targeted in vivo or tolerogenic (tol) DCs may be generated in vitro and given in the peritransplant period. Other cellular therapies, notably regulatory T cells (T(reg)) and mesenchymal stem cells, mediate important effects through DCs and show promise for the prevention and treatment of GVHD in early human studies. Therapies are likely to be more effective if they have synergistic effects or target both DCs and T cells in vivo, such as tolDCs or T(reg). Given the effectiveness of tolDCs in experimental models of GVHD and their safety in early human studies for type 1 diabetes, it is crucial that tolDCs be investigated in the prevention and treatment of human GVHD while ensuring conservation of graft-versus-leukemia effects.

The potential of patients' peripheral blood mononuclear cells to differentiate into dendritic cells after hematopoietic stem cell transplantation

AIMS

Although hematopoietic stem cell transplantation (HSCT) is a curative treatment for many hematological disorders, there is persistent immunosuppression in both allogeneic and autologous HSCT. Dendritic cells (DCs) play key roles in the immune system. This study investigated whether the DC progenitor cells within patients' peripheral blood after HSCT have the potential to differentiate into DCs.

MAIN METHODS

Twenty-eight patients were included in this study, and peripheral blood samples were basically taken before starting the conditioning regimen, on the day of transplantation (day 0), and on days +14, +28, +42, +70 and +170 after transplantation. Immature DCs (iDCs) were induced from adherent mononuclear cells by using recombinant human granulocyte-macrophage colony-stimulating factor plus interleukin-4.

KEY FINDINGS

The iDCs expressed cell surface antigens such as CD40 and HLA-DR, and they had phagocytotic activity, thus showing the characteristics of iDCs. The induction of iDCs was possible from day +14 after HSCT. However, there were differences between allogeneic and autologous HSCT in the expression of CCR5 in iDCs at day +14 after transplantation. Furthermore, the up-regulation of maturation-related antigens by maturation stimuli was higher after HSCT compared with before HSCT.

SIGNIFICANCE

We demonstrated that patients' peripheral blood mononuclear cells have the potential to differentiate into DCs beginning on day +14 after HSCT, although some differences exist between allogeneic and autologous HSCT and between before and after HSCT.

HLA-G level on monocytoid dendritic cells correlates with regulatory T-cell Foxp3 expression in liver transplant tolerance. Transplantation. 2011;91:1132-1140. [PMID: 21423069 DOI: 10.1097/tp.0b013e31821414c9]

BACKGROUND

Human leukocyte antigen (HLA)-G is a nonclassical HLA class I molecule expressed as membrane-bound and soluble isoforms. Interaction of HLA-G with its receptor, immunoglobulin-like transcript 4 on dendritic cells (DCs) down-regulates their T-cell stimulatory ability.

METHODS

We examined expression of HLA-G, immunoglobulin-like transcript 4, other immune regulatory molecules (inducible costimulator ligand and glucocorticoid-induced tumor necrosis factor-related receptor ligand), and the activation marker CMRF44 on circulating monocytoid dendritic cell (mDC) and plasmacytoid dendritic cell by monoclonal antibody staining and flow cytometry. Three groups of stable liver transplant recipients: operationally tolerant (TOL), prospective immunosuppressive drug weaning, and maintenance immunosuppression (MI) were studied, together with healthy controls (HC). Serum HLA-G levels were measured by enzyme-linked immunosorbent assay.

RESULTS

In TOL patients, monocytoid dendritic cell (mDC) but not plasmacytoid dendritic cell expressed higher HLA-G than in MI patients or HC. In TOL patients, the incidence of CD4(+)CD25(hi)CD127(-) regulatory T cells (Treg) and the intensity of Treg forkhead box p3 (Foxp3) expression were significantly higher than in the MI group. HLA-G expression on circulating mDC correlated significantly with that of Foxp3 in the TOL group. There was no correlation between immunosuppressive drug (tacrolimus) dose or trough level and HLA-G expression or Treg frequency or Foxp3 expression. The incidence of patients with circulating HLA-G levels more than 100 ng/mL was highest in the TOL group, although statistical significance was not achieved.

CONCLUSIONS

Higher HLA-G expression on circulating mDC in TOL recipients compared with MI or HC, suggests a possible role of HLA-G in immune regulation possibly mediated by enhanced host Treg Foxp3 expression.

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.

Review of human DC subtypes

Dendritic cells (DC) are critical to the induction and regulation of the innate and adaptive immune responses. They have been implicated in the pathogenesis of many autoimmune and chronic inflammatory diseases as well as contributing to the development of tumours by their lack of appropriate function. As such, understanding human DC biology provides the insight needed to develop applications for their use in the treatment of diseases. Currently, studies on mouse DC outnumber those on human cells; however, the comparison between mouse and human models has been somewhat misleading due to the basic biological and practical differences between the two models. In this review, we summarise the current understanding of human DC subtypes by describing the phenotype of the populations and how this relates to function. We also hope to clarify the differences in nomenclature between the human and mouse models that have arisen by way of the different experimental models.

Dendritic cells and acute graft-versus-host disease after allogeneic stem cell transplantation

The wider use of allogeneic stem cell transplantation (allo-SCT) is still limited by the immunologic recognition and destruction of host tissues, termed graft-versus-host disease (GVHD). The role of inflammatory cytokines and their impact on immune effectors (mainly CD4+ and CD8+ T) cells has been extensively studied in the context of GVHD occurring after standard myeloablative allo-SCT. However, recent data suggested that GVHD pathophysiology is likely to involve more complex interactions where antigen-presenting cells, especially dendritic cells (DCs), may play a major role at time of initiation of acute GVHD. In addition, the wider use of reduced intensity and less toxic conditioning (RIC) regimens prior to allo-SCT would allow better visualization of the fine functions of immune effectors, thereby offering a window of opportunities to better decipher the intimate pathophysiological mechanisms underlying GVHD. The aim of this concise review is to synthesize the available research evidence on the role of DCs as in vivo regulators of GVHD, and their interactions with other immune effectors.

Kinetics of dendritic cells reconstitution and costimulatory molecules expression after myeloablative allogeneic haematopoetic stem cell transplantation: implications for the development of acute graft-versus host disease

Allogeneic hematopoetic stem cell transplantation (HSCT) represents a unique opportunity to monitor the kinetics of reconstitution of dendritic cells (DCs) and their dynamics in distinct pathologies. We analyzed DCs reconstitution after myeloablative HSCT. We separately analyzed patients with acute GVHD. DCs were monitored from the earliest phase of hematopoetic reconstitution until day +365. Both myeloid DCs and plasmacytoid DCs appeared at earliest stages after engraftment and relative numbers within white blood cells compartment peaked between days 19-25 after HSCT. Their proportion then gradually declined and absolute numbers of both DC subsets remained lower than in controls during the whole follow-up. Patients with acute GVHD had significantly lower numbers of circulating DCs. Decrease in DC counts preceded onset of clinical symptoms by at least 24 h and was independent of corticosteroids administration. This study reveals quantification of plasmacytoid and myeloid DCs as a potential biomarker for the prediction of acute GVHD development.

Antibody to the dendritic cell surface activation antigen CD83 prevents acute graft-versus-host disease

Allogeneic (allo) hematopoietic stem cell transplantation is an effective therapy for hematological malignancies but it is limited by acute graft-versus-host disease (GVHD). Dendritic cells (DC) play a major role in the allo T cell stimulation causing GVHD. Current immunosuppressive measures to control GVHD target T cells but compromise posttransplant immunity in the patient, particularly to cytomegalovirus (CMV) and residual malignant cells. We showed that treatment of allo mixed lymphocyte cultures with activated human DC-depleting CD83 antibody suppressed alloproliferation but preserved T cell numbers, including those specific for CMV. We also tested CD83 antibody in the human T cell-dependent peripheral blood mononuclear cell transplanted SCID (hu-SCID) mouse model of GVHD. We showed that this model requires human DC and that CD83 antibody treatment prevented GVHD but, unlike conventional immunosuppressants, did not prevent engraftment of human T cells, including cytotoxic T lymphocytes (CTL) responsive to viruses and malignant cells. Immunization of CD83 antibody-treated hu-SCID mice with irradiated human leukemic cell lines induced allo antileukemic CTL effectors in vivo that lysed (51)Cr-labeled leukemic target cells in vitro without further stimulation. Antibodies that target activated DC are a promising new therapeutic approach to the control of GVHD.

Reduced intensity conditioning for allogeneic hematopoietic stem-cell transplant determines the kinetics of acute graft-versus-host disease

BACKGROUND

Preparative myeloablative conditioning regimens for allogeneic hematopoietic stem-cell transplantation (HSCT) may control malignancy and facilitate engraftment but also contribute to transplant related mortality, cytokine release, and acute graft-versus-host disease (GVHD). Reduced intensity conditioning (RIC) regimens have decreased transplant related mortality but the incidence of acute GVHD, while delayed, remains unchanged. There are currently no in vivo allogeneic models of RIC HSCT, limiting studies into the mechanism behind RIC-associated GVHD.

METHODS

We developed two RIC HSCT models that result in delayed onset GVHD (major histocompatibility complex mismatched (UBI-GFP/BL6 [H-2]-->BALB/c [H-2]) and major histocompatibility complex matched, minor histocompatibility mismatched (UBI-GFP/BL6 [H-2]-->BALB.B [H-2])) enabling the effect of RIC on chimerism, dendritic cell (DC) chimerism, and GVHD to be investigated.

RESULTS

In contrast with myeloablative conditioning, we observed that RIC-associated delayed-onset GVHD is characterized by low production of tumor necrosis factor-alpha, maintenance of host DC, phenotypic DC activation, increased T-regulatory cell numbers, and a delayed emergence of activated donor DC. Furthermore, changes to the peritransplant milieu in the recipient after RIC lead to the altered activation of DC and the induction of T-regulatory responses. Reduced intensity conditioning recipients suffer less early damage to GVHD target organs. However, as donor cells engraft, activated donor DC and rising levels of tumor necrosis factor-alpha are associated with a later onset of severe GVHD.

CONCLUSIONS

Delineating the mechanisms underlying delayed onset GVHD in RIC HSCT recipients is vital to improve the prediction of disease onset and allow more targeted interventions for acute GVHD.

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.

Plasmacytoid dendritic cell count on day 28 in HLA-matched related allogeneic peripheral blood stem cell transplant predicts the incidence of acute and chronic GVHD

Dendritic cells (DC) are antigen-presenting cells involved in induction and regulation of immune responses. We investigated the impact of the number of infused and day 28 dendritic cells on the development of acute and chronic GVHD (aGVHD, cGVHD). Monocytoid (MC) and plasmacytoid (PC) dendritic cells were characterized as lin(-)HLA-DR(+)CD11c(+) and lin(-)HLA-DR(+)CD123(+), respectively. Sixty-eight consecutive patients who underwent HLA matched related granuloyte-colony stimulating factor (G-CSF) mobilized allogeneic PBSCT, from February 2005 to May 2006, were included in the analysis. Twenty-three patients developed aGVHD (grade II-IV) and 21 patients had cGVHD. On a univariate analysis the day 28 total DC and the day 28 MC and PC dendritic cells as continuous variables were significantly associated with development of aGVHD and cGVHD. Using an ROC plot analysis a cutoff value for total DC = 10.7/microL, MC = 9.7/microL, and PC = 4.5/microL on day 28 gave the highest likelihood ratios for aGVHD (2.7, 2.14, and 3.29, respectively). On a multivariate analysis, a low day 28 PC (<or=4.5/microL) together with patient age retained their risk for aGVHD (hazard ratio [HR] = 65.1 and 1.0, P-values .000 and .036, respectively), whereas for cGVHD only a low day 28 PC remained significant (HR = 11.8, P = .008). These results suggest that the PC dendritic cell count in the peripheral blood on day 28 is a strong predictor for development of GVHD in recipients of an allogeneic matched related PBSCT.

Cord blood CD34+ cells cultured with FLT3L, stem cell factor, interleukin-6, and IL-3 produce CD11c+CD1a-/c- myeloid dendritic cells

Methods that allow expansion of myeloid dendritic cells (MDCs) from CD34(+) cells are potentially important for boosting anti-leukemic responses after cord blood (CB) hematopoietic stem cell transplantation (HSCT). We showed that the combination of early-acting cytokines FLT3-ligand (FL), stem cell factor (SCF), interleukin (IL)-3, and IL-6 supported the generation of CD11c(+)CD16() CD1a()/c() MDCs from CB CD34(+) cells or CB myeloid precursors. Early-acting cytokine-derived MDCs were maintained within the myeloid CD33(+)CD14()CD15() precursors with a mean of 4 x 10(6) cells generated from 1-4 x 10(4) CB CD34(+) cells or myeloid precursors after 2 weeks. After 8-12 days of culture the MDCs expressed higher levels of HLA-DR antigen but lower levels of CD40 and CD86 antigen, compared to adult blood MDCs. At this stage of differentiation, the early-acting cytokine-derived MDCs had acquired the ability to induce greater allogeneic T cell proliferation than monocytes or granulocytes derived from same culture. Early-acting cytokine-derived MDCs exposed to the cytokine cocktail (CC) comprising IL-1beta, IL-6, tumor necrosis factor (TNF)-alpha, and prostaglandin E (PGE)-2, upregulated the surface co-stimulatory molecules CD40 and CD86 and enhanced allogeneic T cell proliferation, as is characteristic of MDCs maturation. The reliable production of MDCs from CB CD34(+) cells provides a novel way to study their lineage commitment pathway(s) and also a potential means of enriching CB with MDCs to improve prospects for DC immunotherapy following CB HSCT.

Progress in acute graft versus host disease

PURPOSE OF REVIEW

The aim of this article is to highlight both experimental and clinical studies contributing to our present understanding of acute graft versus host disease.

RECENT FINDINGS

New cellular players and new molecules in induction, modulation and treatment of graft versus host disease are reported. The contribution of antigen presenting cells to induction of graft versus host disease and graft versus leukemia effects is well understood in animal models and now needs confirmation in human analyses. Both, regulatory T cells and mesenchymal stem cells are a new hope for prophylaxis and treatment. Receptors of innate immunity, homing molecules and chemokines regulate activation and trafficking of these cellular players and may be used for selective blockade, activation or cell selection.

SUMMARY

Better understanding of the early events involved in graft versus host disease should allow risk adapted and more precise early or even preemptive treatment of graft versus host disease.