Achievement of Tolerance Induction to Prevent Acute Graft-vs.-Host Disease

High sensitivity of host Helios+/Neuropilin-1+ Treg to pretransplant conditioning hampers development of OX40bright/integrin-β7+ regulatory cells in acute gastrointestinal GvHD

This study sought to compare the behavior of Treg subsets displaying different coexpression patterns of Neuropilin-1 (Nrp1) and Helios, under the influence of gut stress unrelated to hematopoietic stem cell transplantation, pretransplantation conditioning, and posttransplant gastrointestinal acute graft versus host disease (GI-aGvHD). Host CD4+/CD25hi/Foxp3+ Treg cells, identified by flow cytometry, were isolated from various tissues of mice affected by these stressors. Expression of CD25, CTLA-4, CD39, OX40, integrin-β7, LAG3, TGFβ/LAP, granzyme-A, -B, and interleukin-10 was compared in four Treg subsets displaying Helios or Nrp1 only, both or none. Fluorescence-activated cell sorter-sorted Treg subsets, displaying markers affected in a conditioning- and GI-aGVHD-restricted manner, were further investigated by transcriptome profiling and T-cell suppression assays. We found that conditioning by irradiation greatly diminished the relative frequency of Helios+/Nrp1+ Treg, shifting the balance toward Helios-/Nrp1- Treg in the host. Upregulation of integrin-β7 and OX40 occurred in GI-aGvHD-dependent manner in Helios+/Nrp1+ cells but not in Helios-/Nrp1- Treg. Sorted Treg subsets, confirmed to overexpress Nrp1, Helios, OX40, or integrin-β7, displayed superior immunosuppressive activity and enrichment in activation-related messenger RNA transcripts. Our data suggest that conditioning-induced shrinkage of the Nrp1+/Helios+ Treg subset may contribute to the development of GI-GvHD by impairing gut homing and decreasing the efficiency of Treg-mediated immunosuppression.

The graft versus leukemia effect: donor lymphocyte infusions and cellular therapy

Allogeneic hematopoietic stem cell transplantation (HSCT) is a potentially curative therapy for many hematologic malignancies as well as non-malignant conditions. Part of the curative basis underlying HSCT for hematologic malignancies relies upon induction of the graft versus leukemia (GVL) effect in which donor immune cells recognize and eliminate residual malignant cells within the recipient, thereby maintaining remission. GVL is a clinically evident phenomenon; however, specific cell types responsible for inducing this effect and molecular mechanisms involved remain largely undefined. One of the best examples of GVL is observed after donor lymphocyte infusions (DLI), an established therapy for relapsed disease or incipient/anticipated relapse. DLI involves infusion of peripheral blood lymphocytes from the original HSCT donor into the recipient. Sustained remission can be observed in 20-80% of patients treated with DLI depending upon the underlying disease and the intrinsic burden of targeted cells. In this review, we will discuss current knowledge about mechanisms of GVL after DLI, experimental strategies for augmenting GVL by manipulation of DLI (e.g. neoantigen vaccination, specific cell type selection/depletion) and research outlook for improving DLI and cellular immunotherapies for hematologic malignancies through better molecular definition of the GVL effect.

Exopolysaccharide-Treated Dendritic Cells Effectively Ameliorate Acute Graft-versus-Host Disease

Graft-versus-host disease (GVHD) is a primary and often lethal complication of allogenic hematopoietic stem cell transplantation (HSCT). Prophylactic regimens for GVHD are given as standard pretransplantation therapy; however, up to 50% of these patients develop acute GVHD (aGVHD) and require additional immunosuppressive intervention. Using a mouse GVHD model, we previously showed that injecting mice with exopolysaccharide (EPS) from Bacillus subtilis prior to GVHD induction significantly increased 80-day survival after transplantation of complete allogeneic major histocompatibility complex-mismatched cells. To ask whether EPS might also inhibit GVHD in humans, we used humanized NSG-HLA-A2 mice and induced GVHD by i.v. injection of A2neg human peripheral blood mononuclear cells (PBMCs). Because we could not inject human donors with EPS, we transferred EPS-pretreated dendritic cells (DCs) to inhibit aGVHD. We derived these DCs from CD34+ human cord blood cells, treated them with EPS, and then injected them together with PBMCs into the NSG-HLA-A2 mice. We found that all mice that received untreated DCs were dead by day 35, whereas 25% of mice receiving EPS-treated DCs (EPS-DCs) survived. This DC cell therapy could be readily translatable to humans, because we can generate large numbers of human EPS-DCs and use them as an "off the shelf" treatment for patients undergoing HSCT.

Donor T cell STAT3 deficiency enables tissue PD-L1-dependent prevention of graft-versus-host disease while preserving graft-versus-leukemia activity

STAT3 deficiency (STAT3-/-) in donor T cells prevents graft-versus-host disease (GVHD), but the impact on graft-versus-leukemia (GVL) activity and mechanisms of GVHD prevention remains unclear. Here, using murine models of GVHD, we show that STAT3-/- donor T cells induced only mild reversible acute GVHD while preserving GVL effects against nonsusceptible acute lymphoblastic leukemia (ALL) cells in a donor T cell dose-dependent manner. GVHD prevention depended on programmed death ligand 1/programmed cell death protein 1 (PD-L1/PD-1) signaling. In GVHD target tissues, STAT3 deficiency amplified PD-L1/PD-1 inhibition of glutathione (GSH)/Myc pathways that regulate metabolic reprogramming in activated T cells, with decreased glycolytic and mitochondrial ATP production and increased mitochondrial ROS production and dysfunction, leading to tissue-specific deletion of host-reactive T cells and prevention of GVHD. Mitochondrial STAT3 deficiency alone did not reduce GSH expression or prevent GVHD. In lymphoid tissues, the lack of host-tissue PD-L1 interaction with PD-1 reduced the inhibition of the GSH/Myc pathway despite reduced GSH production caused by STAT3 deficiency and allowed donor T cell functions that mediate GVL activity. Therefore, STAT3 deficiency in donor T cells augments PD-1 signaling-mediated inhibition of GSH/Myc pathways and augments dysfunction of T cells in GVHD target tissues while sparing T cells in lymphoid tissues, leading to prevention of GVHD while preserving GVL effects.

After Bone Marrow Transplantation, the Cell-Intrinsic Th2 Pathway Promotes Recipient T Lymphocyte Survival and Regulates Graft-versus-Host Disease

Recipient T cells can aggravate or regulate lethal and devastating graft-versus-host disease (GVHD) after bone marrow transplantation (BMT). In this context, we have shown before that intestinal immune conditioning with helminths is associated with survival of recipient T cells and Th2 pathway-dependent regulation of GVHD. We investigated the mechanism of survival of recipient T cells and their contribution to GVHD pathogenesis in this helminth infection and BMT model after myeloablative preparation with total body irradiation in mice. Our results indicate that the helminth-induced Th2 pathway directly promotes the survival of recipient T cells after total body irradiation. Th2 cells also directly stimulate recipient T cells to produce TGF-β, which is required to regulate donor T cell-mediated immune attack of GVHD and can thereby contribute to recipient T cell survival after BMT. Moreover, we show that recipient T cells, conditioned to produce Th2 cytokines and TGF-β after helminth infection, are fundamentally necessary for GVHD regulation. Taken together, reprogrammed or immune-conditioned recipient T cells after helminth infection are crucial elements of Th2- and TGF-β-dependent regulation of GVHD after BMT, and their survival is dependent on cell-intrinsic Th2 signaling.

Long noncoding RNA LINC01882 ameliorates aGVHD via skewing CD4+ T cell differentiation toward Treg cells

Acute graft-versus-host disease (aGVHD) is a severe T cell-mediated immune response after allogeneic hematopoietic stem cell transplantation (allo-HSCT), the molecular mechanisms remain to be elucidated and novel treatments are necessary to be developed. In the present study, we found that the expression of long noncoding RNA (lncRNA) LINC01882 decreased significantly in the peripheral blood CD4⁺ T lymphocytes of patients with aGVHD than non-aGVHD patients. In addition, lncRNA LINC01882 overexpression promoted Treg differentiation but exhibited no effects on Th17 percentages, while its knockdown resulted in opposite effects. Mechanistically, lncRNA LINC01882 could competitively bind with let-7b-5p to prevent the degradation of its target gene smad2, which acts as a promoter in Treg differentiation. Furthermore, the mice cotransplanted with LINC01882-overexpressed CD4⁺ T cells with PBMCs had a lower histological GVHD score and higher survival rate compared with control mice. In conclusion, our study discloses a novel LINC01882/let-7b-5p/smad2 pathway in the modulation of aGVHD and indicates that lncRNA LINC01882 could be a promising biomarker and therapeutic target for patients with aGVHD.

Allogeneic stem cell transplantation in the treatment of acute myeloid leukemia: An overview of obstacles and opportunities

As an important treatment for acute myeloid leukemia, allogeneic hematopoietic stem cell transplantation (allo-HSCT) plays an important role in reducing relapse and improving long-term survival. With rapid advancements in basic research in molecular biology and immunology and with deepening understanding of the biological characteristics of hematopoietic stem cells, allo-HSCT has been widely applied in clinical practice. During allo-HSCT, preconditioning, the donor, and the source of stem cells can be tailored to the patient’s conditions, greatly broadening the indications for HSCT, with clear survival benefits. However, the risks associated with allo-HSCT remain high, i.e. hematopoietic reconstitution failure, delayed immune reconstitution, graft-versus-host disease, and post-transplant relapse, which are bottlenecks for further improvements in allo-HSCT efficacy and have become hot topics in the field of HSCT. Other bottlenecks recognized in the current treatment of individuals diagnosed with acute myeloid leukemia and subjected to allo-HSCT include the selection of the most appropriate conditioning regimen and post-transplantation management. In this paper, we reviewed the progress of relevant research regarding these aspects.

Analysis of factors associated with hematopoietic stem-cell retransplantation: a case-control study

OBJECTIVE

to analyze the factors associated with the failure of Hematopoietic Stem Cell Transplantation (HSCT) in patients undergoing Hematopoietic Stem Cell Retransplantation (HSCR).

METHOD

this study implemented a quantitative approach and was a case-control type which addressed patients undergoing HSCR. To do so, a paired sample of two controls was used for each case (2:1). The case group consisted of the medical records of all patients who underwent HSCR (28) and the control group (56) of those who underwent only one transplant. Three variables guided the pairing: gender, diagnosis and type of transplant.

RESULTS

a total of 24 (85.71%) patients in the case group were re-transplanted due to disease relapse and four (14.29%) due to graft failure. There was a statistical difference in the analysis between patients who did not use ursodeoxycholic acid, opioid analgesics and immunosuppressants. The need for HSCR among those who used these medications inappropriately was 16.12, 12.79 and 4.5 times more likely, respectively, than those who used them correctly.

CONCLUSION

there was a difference regarding the reasons which led to the retransplantation and the analyzed subjects, and this study concluded that the predictive reason for retransplantation in the studied sample was disease relapse.

Analysis of factors associated with hematopoietic stem-cell retransplantation: a case-control study

Objective:

to analyze the factors associated with the failure of Hematopoietic Stem Cell Transplantation (HSCT) in patients undergoing Hematopoietic Stem Cell Retransplantation (HSCR).

Method:

this study implemented a quantitative approach and was a case-control type which addressed patients undergoing HSCR. To do so, a paired sample of two controls was used for each case (2:1). The case group consisted of the medical records of all patients who underwent HSCR (28) and the control group (56) of those who underwent only one transplant. Three variables guided the pairing: gender, diagnosis and type of transplant.

Results:

a total of 24 (85.71%) patients in the case group were re-transplanted due to disease relapse and four (14.29%) due to graft failure. There was a statistical difference in the analysis between patients who did not use ursodeoxycholic acid, opioid analgesics and immunosuppressants. The need for HSCR among those who used these medications inappropriately was 16.12, 12.79 and 4.5 times more likely, respectively, than those who used them correctly.

Conclusion:

there was a difference regarding the reasons which led to the retransplantation and the analyzed subjects, and this study concluded that the predictive reason for retransplantation in the studied sample was disease relapse.

Análisis de factores asociados al Retrasplante de Células Madre Hematopoyéticas: un estudio de caso-control

Resumen Objetivo: analizar los factores asociados con el fracaso del Trasplante de Células Madre Hematopoyéticas (TCMH) en pacientes sometidos al Retrasplante de Células Madre Hematopoyéticas (RCMH). Método: estudio cuantitativo de tipo caso-control que abordó pacientes sometidos al RCMH. Para esto, se utilizó una muestra pareada de dos controles para cada caso (2:1). El grupo caso estuvo formado por los registros médicos de todos los pacientes que fueron sometidos al RCMH (28) y el grupo control (56) por los que fueron sometidos a un solo trasplante. Tres variables guiaron el emparejamiento: género, diagnóstico y tipo de trasplante. Resultados: un total de 24 (85.71%) pacientes en el grupo caso fueron retransplantados debido a la recaída de la enfermedad y 4 (14.29%) por el fracaso del injerto. Hubo una diferencia estadística en el análisis entre los pacientes que no usaron ácido ursodesoxicólico, analgésicos opioides e inmunosupresores. La necesidad de RCMH entre los que usaron estos medicamentos de manera inapropiada se encontraba 16,12 - 12,79 y 4,5 veces más probable, respectivamente, que aquellos que los usaron correctamente. Conclusión: hubo diferencia en cuanto a las razones que llevaron al retrasplante de los sujetos analizados. Este estudio concluyó que la razón predictiva del retrasplante, en la muestra estudiada, fue la recidiva de la enfermedad.

Graft-versus-host disease depletes plasmacytoid dendritic cell progenitors to impair tolerance induction

Graft-versus-host disease (GVHD) causes failed reconstitution of donor plasmacytoid dendritic cells (pDCs) that are critical for immune protection and tolerance. We used both murine and human systems to uncover the mechanisms whereby GVHD induces donor pDC defects. GVHD depleted Flt3-expressing donor multipotent progenitors (MPPs) that sustained pDCs, leading to impaired generation of pDCs. MPP loss was associated with decreased amounts of MPP-producing hematopoietic stem cells (HSCs) and oxidative stress-induced death of proliferating MPPs. Additionally, alloreactive T cells produced GM-CSF to inhibit MPP expression of Tcf4, the transcription factor essential for pDC development, subverting MPP production of pDCs. GM-CSF did not affect the maturation of pDC precursors. Notably, enhanced recovery of donor pDCs upon adoptive transfer early after allogeneic HSC transplantation repressed GVHD and restored the de novo generation of donor pDCs in recipient mice. pDCs suppressed the proliferation and expansion of activated autologous T cells via a type I IFN signaling-dependent mechanism. They also produced PD-L1 and LILRB4 to inhibit T cell production of IFN-γ. We thus demonstrate that GVHD impairs the reconstitution of tolerogenic donor pDCs by depleting DC progenitors rather than by preventing pDC maturation. MPPs are an important target to effectively bolster pDC reconstitution for controlling GVHD.

Regulatory T Cell Therapy of Graft-versus-Host Disease: Advances and Challenges

Graft-versus-host disease (GVHD) is the leading cause of morbidity and mortality after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Immunomodulation using regulatory T cells (Tregs) offers an exciting option to prevent and/or treat GVHD as these cells naturally function to maintain immune homeostasis, can induce tolerance following HSCT, and have a tissue reparative function. Studies to date have established a clinical safety profile for polyclonal Tregs. Functional enhancement through genetic engineering offers the possibility of improved potency, specificity, and persistence. In this review, we provide the most up to date preclinical and clinical data on Treg cell therapy with a particular focus on GVHD. We discuss the different Treg subtypes and highlight the pharmacological and genetic approaches under investigation to enhance the application of Tregs in allo-HSCT. Lastly, we discuss the remaining challenges for optimal clinical translation and provide insights as to future directions of the field.

Human Amniotic Mesenchymal Stem Cells Inhibit aGVHD by Regulating Balance of Treg and T Effector Cells

Background

Acute graft versus host disease (aGVHD) remains a leading cause of transplant-related mortality following allogeneic haematopoietic cell transplantation (allo-HCT). Human amniotic mesenchymal stem cells (hAMSCs) are a novel mesenchymal stem cells (MSCs), which have stronger proliferation and immunomodulatory ability compared with bone marrow mesenchymal stem cells (BM-MSCs). Besides, as the amniotic membrane is often treated as medical waste after delivery, hAMSCs can be obtained conveniently and noninvasively. The aim of this study was to explore the therapeutic efficacy and underlying mechanisms of hAMSCs transplantation for the humanized aGVHD mouse model.

Methods

We established a humanized aGVHD mouse model by transplanting human peripheral blood mononuclear cells (PBMCs) into NOD-Prkdc^scidIL2rγ^null (NPG) mice, human amniotic membrane collected from discarded placenta of healthy pregnant women after delivery and hAMSCs were extracted from amniotic membrane and expanded in vitro. Mice were divided into untreated group (Control), aGVHD group (aGVHD), and hAMSCs treatment group (aGVHD+hAMSCs), the hAMSCs labeled with GFP were administered to aGVHD mice to explore the homing ability of hAMSCs. T effector and regulatory T cells (Tregs) levels and cytokines of each group in target organs were detected by flow cytometry and cytometric bead array (CBA), respectively.

Results

We successfully established a humanized aGVHD mouse model using NPG mice. The hAMSCs have the ability to inhibit aGVHD in this mouse model through reduced villous blunting and lymphocyte infiltration of the gut while reducing inflammatory edema, tissue destruction and lymphocyte infiltration into the parenchyma of the liver and lung. hAMSCs suppressed CD3+CD4+ T and CD3+CD8+ T cell expression and increased the proportion of Tregs, and besides, hAMSCs can reduce the levels of IL-17A, INF-γ, and TNF in aGVHD target organs.

Conclusion

The NPG murine environment was capable of activating human T cells to produce aGVHD pathology to mimic aGVHD as in humans. The hAMSCs controlled aGVHD by decreasing inflammatory cytokine secretion within target organs by modulating the balance of Tregs and T effector cells in humanized mice.

GVHD Pathogenesis, Prevention and Treatment: Lessons From Humanized Mouse Transplant Models

Graft-vs-host disease (GVHD) is the most common cause of non-relapse mortality following allogeneic hematopoietic stem cell transplantation (HSCT) despite advances in conditioning regimens, HLA genotyping and immune suppression. While murine studies have yielded important insights into the cellular responses of GVHD, differences between murine and human biology has hindered the translation of novel therapies into the clinic. Recently, the field has expanded the ability to investigate primary human T cell responses through the transplantation of human T cells into immunodeficient mice. These xenogeneic HSCT models benefit from the human T cell receptors, CD4 and CD8 proteins having cross-reactivity to murine MHC in addition to several cytokines and co-stimulatory proteins. This has allowed for the direct assessment of key factors in GVHD pathogenesis to be investigated prior to entering clinical trials. In this review, we will summarize the current state of clinical GVHD research and discuss how xenogeneic HSCT models will aid in advancing the current pipeline of novel GVHD prophylaxis therapies into the clinic.

Activation of natural killer T cells enhances the function of regulatory T-cell therapy in suppressing murine GVHD

Cellular therapy with regulatory T cells (Tregs) has shown promising results for suppressing graft-versus-host disease (GVHD) while preserving graft vs tumor effects in animal models and phase 1/2 clinical trials. However, a paucity of Tregs in the peripheral blood makes it difficult to acquire sufficient numbers of cells and hampers further clinical application. Invariant natural killer T (iNKT) cells constitute another compartment of regulatory cells that ameliorate GVHD through activation of Tregs after their own activation with α-galactosylceramide (α-GalCer) or adoptive transfer. We demonstrate here that a single administration of α-GalCer liposome (α-GalCer-lipo) enhanced the in vivo expansion of Tregs after adoptive transfer in a murine GVHD model and improved therapeutic efficacy of Treg therapy even after injection of otherwise suboptimal cell numbers. Host iNKT cells rather than donor iNKT cells were required for GVHD suppression because the survival benefit of α-GalCer-lipo administration was not shown in the transplantation of cells from wild-type (WT) C57BL/6 mice into Jα18-/- iNKT cell-deficient BALB/c mice, whereas it was observed from Jα18-/- C57BL/6 donor mice into WT BALB/c recipient mice. The combination of iNKT cell activation and Treg adoptive therapy may make Treg therapy more feasible and safer by enhancing the efficacy and reducing the number of Tregs required.

Cellular and molecular profiling of T-cell subsets at the onset of human acute GVHD

The cellular and molecular processes involved in acute graft-versus-host disease (aGVHD) development early after allogeneic hematopoietic cell transplantation (HCT) in humans remain largely unknown. We have performed multiparameter immunophenotyping and molecular profiling of CD4+ and CD8+ T cells in 2 independent cohorts of patients undergoing HCT, as well as in their HLA-identical sibling donors. Cellular profiling using spectral flow cytometry showed an incomplete reconstitution of the T-cell compartment in recipients without aGVHD early after transplantation, as well as a shift toward an effector memory phenotype, paralleled by depletion of the naive T-cell pool. Molecular profiling of T-cell populations in donors vs recipients without aGVHD revealed increased pathway activity of >40 gene modules in recipients. These pathways were associated in particular with T-cell activation, adhesion, migration, and effector functions. Cellular profiles from recipients developing aGVHD displayed an enrichment of cells with a T memory stem cell-like phenotype compared with recipients without aGVHD. Comparison of gene profiles from these recipients revealed that transforming growth factor-β (TGF-β) signaling was most significantly downregulated, whereas the pathway activity of NF-κB-associated transcription factors and signaling pathways were increased, at aGVHD onset. This study suggests that the integration of cellular and molecular profiles provides new insights into the development of aGVHD in humans.

Current Concepts and Advances in Graft-Versus-Host Disease Immunology

Worldwide, each year over 30,000 patients undergo an allogeneic hema-topoietic stem cell transplantation with the intent to cure high-risk hematologic malignancy, immunodeficiency, metabolic disease, or a life-threatening bone marrow failure syndrome. Despite substantial advances in donor selection and conditioning regimens and greater availability of allograft sources, transplant recipients still endure the morbidity and mortality of graft-versus-host disease (GVHD). Herein, we identify key aspects of acute and chronic GVHD pathophysiology, including host/donor cell effectors, gut dysbiosis, immune system and cytokine imbalance, and the interface between inflammation and tissue fibrosis. In particular, we also summarize the translational application of this heightened understanding of immune dysregulation in the design of novel therapies to prevent and treat GVHD.

Bone marrow Tregs mediate stromal cell function and support hematopoiesis via IL-10

The nonimmune roles of Tregs have been described in various tissues, including the BM. In this study, we comprehensively phenotyped marrow Tregs, elucidating their key features and tissue-specific functions. We show that marrow Tregs are migratory and home back to the marrow. For trafficking, marrow Tregs use S1P gradients, and disruption of this axis allows for specific targeting of the marrow Treg pool. Following Treg depletion, the function and phenotype of both mesenchymal stromal cells (MSCs) and hematopoietic stem cells (HSCs) was impaired. Transplantation also revealed that a Treg-depleted niche has a reduced capacity to support hematopoiesis. Finally, we found that marrow Tregs are high producers of IL-10 and that Treg-secreted IL-10 has direct effects on MSC function. This is the first report to our knowledge revealing that Treg-secreted IL-10 is necessary for stromal cell maintenance, and our work outlines an alternative mechanism by which this cytokine regulates hematopoiesis.

Low rates of anti-recipient isohemagglutinins in ABO incompatible hematopoietic stem cell transplants

INTRODUCTION

Isohemagglutinins occur naturally and form in an 'opposite' (antigen-negative) pattern to a patient's ABO blood type. Patients undergoing minor and bidirectional ABO incompatible hematopoietic stem cell transplantation (HSCT) may demonstrate detectable antibodies against their native blood type. In this study, we sought to characterize the rates of such antibody formation and evaluate the clinical significance of our findings.

MATERIALS AND METHODS

An internal database of HSCT patients at an academic medical center was queried for ABO incompatible transplant patients from 2009-2019. Serum typing results, clinical histories, and laboratory data were compiled and reviewed.

RESULTS

A total of 182 minor and bidirectional ABO incompatible HSCT patients were identified. Anti-recipient isohemagglutinins were found in 9% (16/182) of the HSCT patients. The rate was higher in patients with minor incompatibility (12%: 15/127) versus bidirectional ABO incompatibility (2%: 1/55) (p = 0.04). No anti-recipient isohemagglutinins were identified in umbilical cord HSCT patients (0%: 0/7). Serologic agglutination reactions of recipient isohemagglutinins were overall mostly weak (13/16 weak + to 1+). There was a trend towards a higher rate of acute graft-versus-host-disease in patients with anti-recipient isohemagglutinins compared to those without (75% vs. 53%; p = 0.12), though not statistically significant. Rates of alloimmunization to minor red cell antigens were similar between the two groups. Few patients showed laboratory evidence of hemolysis at 12 months follow up.

DISCUSSION AND CONCLUSIONS

Anti-recipient isohemagglutinins occur at low rates in ABO incompatible HSCT and are significantly more common in minor ABO incompatible transplant compared to bidirectional transplants. Larger cohort studies are needed to better understand the relationship between anti-recipient isohemagglutinins and HSCT outcomes.

Comparison of Tacrolimus and Cyclosporine Combined With Methotrexate for Graft Versus Host Disease Prophylaxis After Allogeneic Hematopoietic Cell Transplantation

BACKGROUND

After patients receive hematopoietic stem cell transplantation (HSCT), both cyclosporine (CsA) and tacrolimus (TAC) in combination with methotrexate (MTX) are recommended as the standard prophylaxis strategy for graft versus host disease (GVHD) by the European Group of Blood and Marrow Transplantation. However, the advantage of TAC combined with MTX lacks conclusive evidence.

METHODS

We searched online databases for studies comparing CsA + MTX and TAC + MTX in patients who received HSCT. The odds ratio (OR) and 95% confidence interval (CI) were applied to compare the pooled data.

RESULTS

We found a significant reduction in the grade II to IV acute GVHD (aGVHD) rate (OR, 0.42; CI, 0.28-0.61; P < 0.00001), grade III to IV aGVHD rate (OR, 0.59; CI, 0.38-0.92; P = 0.02), chronic GVHD rate (OR, 0.79; CI, 0.62-1.00; P = 0.05), and nonrelapse mortality rate (OR, 0.62; CI, 0.40-0.95; P = 0.03) and an increase in the overall survival (OS) rate (only in those received from unrelated donor) (OR, 1.30; CI, 1.15-1.48; P < 0.0001) in the TAC + MTX group. Similar outcomes occurred for the relapse rate and disease-free survival rate in both groups.

CONCLUSIONS

TAC + MTX has a superior effect in the prevention of aGVHD in patients who received HSCT and further prolongs the OS in patients who received from unrelated donor transplants. CsA + MTX prolongs the OS in patients who received HSCT from HLA-identical sibling donors. The leukemic relapse and disease-free survival rate were not different between the 2 regimens. Thus, we conclude that TAC + MTX was superior to CsA + MTX, especially for HSCT patients with nonmalignant disorders. Further studies are still required to evaluate the effect of TAC or CsA combined with other suppressors in the treatment regimen following HSCT.

Wharton's Jelly Mesenchymal Stromal Cells from Human Umbilical Cord: a Close-up on Immunomodulatory Molecules Featured In Situ and In Vitro

Therapeutic options for end-stage organ failure are often limited to whole organ transplantation. The tolerance or rejection of the transplanted organ is driven by both early non-specific innate and specific adaptive responses. The use of mesenchymal stromal cells (MSCs) is considered a promising tool in regenerative medicine. Human umbilical cord (HUC) is an easily available source of MSCs, without relevant ethical issues. Moreover, Wharton's jelly-derived MSCs (WJ-MSCs), showed consistent immunomodulatory features that may be useful to promote immune tolerance in the host after transplantation. Few data are available on the phenotype of WJ-MSCs in situ. We investigated the expression of immune-related molecules, such as HLAs, IDO, CD276/B7-H3, and others, both in situ (HUC) and in in vitro-cultured WJ-MSCs. Morphological and biochemical techniques were used to define the expression of such molecules. In addition, we focused on the possible role of CD276/B7-H3 on T cells proliferation inhibition. We assessed CD276/B7-H3 expression by WJ-MSCs both in situ and alongside cell culture. WJ-MSCs were able to suppress T cell proliferation in mixed lymphocyte reaction (MLR). Moreover, we describe for the first time a specific role for CD276/B7-H3, since the immunomodulatory ability of WJ-MSCs was abolished upon anti-CD276/B7-H3 antibody addition to the MLR. These results further detail the immune regulation properties and tolerance induction exerted by human WJ-MSCs, in particular pointing to CD276/B7-H3 as one of the main involved factors. These data further suggest WJ-MSCs as potent tools to modulate local immune response in "support-type" regenerative medicine approaches.

Targeting Histone Deacetylases to Modulate Graft-Versus-Host Disease and Graft-Versus-Leukemia

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is the main therapeutic strategy for patients with both malignant and nonmalignant disorders. The therapeutic benefits of allo-HSCT in malignant disorders are primarily derived from the graft-versus-leukemia (GvL) effect, in which T cells in the donor graft recognize and eradicate residual malignant cells. However, the same donor T cells can also recognize normal host tissues as foreign, leading to the development of graft-versus-host disease (GvHD), which is difficult to separate from GvL and is the most frequent and serious complication following allo-HSCT. Inhibition of donor T cell toxicity helps in reducing GvHD but also restricts GvL activity. Therefore, developing a novel therapeutic strategy that selectively suppresses GvHD without affecting GvL is essential. Recent studies have shown that inhibition of histone deacetylases (HDACs) not only inhibits the growth of tumor cells but also regulates the cytotoxic activity of T cells. Here, we compile the known therapeutic potential of HDAC inhibitors in preventing several stages of GvHD pathogenesis. Furthermore, we will also review the current clinical features of HDAC inhibitors in preventing and treating GvHD as well as maintaining GvL.

Defibrotide inhibits donor leucocyte-endothelial interactions and protects against acute graft-versus-host disease

Allogeneic hematopoietic stem cell transplantation (allo‐HCT) is an effective therapy for the treatment of high‐risk haematological malignant disorders and other life‐threatening haematological and genetic diseases. Acute graft‐versus‐host disease (aGvHD) remains the most frequent cause of non‐relapse mortality following allo‐HCT and limits its extensive clinical application. Current pharmacologic agents used for prophylaxis and treatment of aGvHD are not uniformly successful and have serious secondary side effects. Therefore, more effective and safe prophylaxis and therapy for aGvHD are an unmet clinical need. Defibrotide is a multi‐target drug successfully employed for prophylaxis and treatment of veno‐occlusive disease/sinusoidal obstruction syndrome. Recent preliminary clinical data have suggested some efficacy of defibrotide in the prevention of aGvHD after allo‐HCT. Using a fully MHC‐mismatched murine model of allo‐HCT, we report here that defibrotide, either in prophylaxis or treatment, is effective in preventing T cell and neutrophil infiltration and aGvHD‐associated tissue injury, thus reducing aGvHD incidence and severity, with significantly improved survival after allo‐HCT. Moreover, we performed in vitro mechanistic studies using human cells revealing that defibrotide inhibits leucocyte‐endothelial interactions by down‐regulating expression of key endothelial adhesion molecules involved in leucocyte trafficking. Together, these findings provide evidence that defibrotide may represent an effective and safe clinical alternative for both prophylaxis and treatment of aGvHD after allo‐HCT, paving the way for new therapeutic approaches.

Bendamustine with total body irradiation conditioning yields tolerant T-cells while preserving T-cell-dependent graft-versus-leukemia

Graft-versus-host disease (GvHD) remains a significant impediment to allogeneic hematopoietic cell transplantation (HCT) success, necessitating studies focused on alleviating GvHD, while preserving the graft-versus-leukemia (GvL) effect. Based on our previous studies showing bendamustine with total body irradiation (BEN-TBI) conditioning reduces GvHD compared to the current clinical standard of care cyclophosphamide (CY)-TBI in a murine MHC-mismatched bone marrow transplantation (BMT) model, this study aimed to evaluate the role and fate of donor T-cells following BEN-TBI conditioning. We demonstrate that BEN-TBI reduces GvHD compared to CY-TBI independently of T regulatory cells (Tregs). BEN-TBI conditioned mice have a smaller proportion and less activated donor T-cells, with lower CD47 expression, early post-transplant, but no sustained phenotypic differences in T-cells. In BEN-TBI conditioned mice, donor T-cells gain tolerance specific to host MHC antigens. Though these T-cells are tolerant to host antigens, we demonstrate that BEN-TBI preserves a T-cell-dependent GvL effect. These findings indicate that BEN-TBI conditioning reduces GvHD without compromising GvL, warranting its further investigation as a potentially safer and more efficacious clinical alternative to CY-TBI.

Therapeutic options for steroid-refractory acute and chronic GVHD: an evolving landscape

Introduction: The traditional therapeutic modalities to manage SR-acute GVHD have focused on the inhibition of the alloreactive T-cell response, while in the setting of SR-chronic GVHD the focus has been on a combination of T-cell and B-cell targeting strategies. However, new therapeutic modalities have shown promise. The purpose of this review is to summarize the current treatment landscape of SR-acute and chronic GVHD.Areas covered: A systematic search of MEDLINE, EMBASE, and clinicaltrials.gov databases for published articles, abstracts, and clinical trials pertaining to available therapeutic modalities for SR-acute and SR-chronic GVHD was conducted. Also highlighted is a number of ongoing clinical trials in both SR-acute and SR-chronic GVHD with strategies targeting the JAK-1/2 pathway, the Treg:Tcon ratio, the immunomodulation mediated by mesenchymal stem cells, and the gut microbiome, among others. Expert opinion: Ruxolitinib has emerged as the preferred therapeutic modality for SR-acute GVHD, with alpha-1-antitrypsin and extracorporeal photophoresis (ECP) being reasonable alternatives. Ruxolitinib and Ibrutinib are among the preferred options for SR-chronic GVHD, with ECP being a viable alternative particularly if the skin is involved. A number of novel therapeutic modalities, including those enhancing the activity of regulatory T-cells have shown great promise in early phase trials of SR-chronic GVHD.