Irradiation Is an Early Determinant of Endothelial Injury During Hematopoietic Stem Cell Transplantation

EPC infusion ameliorates acute graft-versus-host disease-related endothelial injury after allogeneic bone marrow transplantation

Introduction

Graft-versus-host disease (GVHD) damages vascular endothelium. Endothelial progenitor cell (EPC) can differentiate to endothelial cell and promote angiogenesis, but its role in endothelial damage in GVHD is unclear.

Methods

In this study, we intend to assess whether EPC infusion promotes the repair of endothelial injury in GVHD mouse model. Male BALB/c mice were randomly divided into 5 groups: control group, total body irradiation group (TBI group), allogeneic bone marrow transplantation group (Allo-BMT group), acute graft versus host disease group (GVHD group), EPC infusion group (GVHD+EPC group) followed by analysis of mice survival, acute GVHD (aGVHD) score, T cell infiltration by immunofluorescence, as well as continuity of vascular endothelium in liver.

Results

Compared with Allo-BMT group, the clinical and pathological score of aGVHD mice were higher. On day 21 after transplantation, a large number of mononuclear cell infiltrations were seen in the target tissues of aGVHD mice and mice died within 30 days. In addition, aGVHD group also presented increased subendothelial infiltration of CD3+ T cells in the liver, decreased VE-cadherin expression and elevated major histocompatibility complex (MHC) II molecule expression in the endothelium. Moreover, expression of MHC-II molecule increased in endothelial cell after irradiation injury and LPS stimulation, indicating abnormally activated endothelial cell with antigen-presenting function. Interestingly, infusion of EPC reduced the clinical and pathological score of aGVHD, decreased infiltration of mononuclear cells, improved survival as well as upregulated VE-cadherin and downregulated MHC-II molecule.

Discussion

EPC infusion can mobilize to affected endothelium to decrease the infiltration of T cells and pathological endothelial activation contributing to ameliorating the damage of endothelium. EPC infusion combined with bone marrow transplantation might be a perspective strategy for the prevention and treatment of aGVHD.

Putting function back in dysfunction: Endothelial diseases and current therapies in hematopoietic stem cell transplantation and cellular therapies

Endothelial dysfunction is characterized by altered vascular permeability and prothrombotic, pro-inflammatory phenotypes. Endothelial dysfunction results in end-organ damage and has been associated with diverse disease pathologies. Complications observed after hematopoietic stem cell transplantation (HCT) and chimeric antigen receptor-T cell (CAR-T) therapy for hematologic and neoplastic disorders share overlapping clinical manifestations and there is increasing evidence linking these complications to endothelial dysfunction. Despite advances in supportive care and treatments, end-organ toxicity remains the leading cause of mortality. A new strategy to mitigate endothelial dysfunction could lead to improvement of clinical outcomes for patients. Statins have demonstrated pleiotropic effects of immunomodulatory and endothelial protection by various molecular mechanisms. Recent applications in immune-mediated diseases such as autoimmune disorders, chronic inflammatory conditions, and graft-versus-host disease (GVHD) have shown promising results. In this review, we cover the mechanisms underlying endothelial dysfunction in GVHD and CAR-T cell-related toxicities. We summarize the current knowledge about statins and other agents used as endothelial protectants. We propose further studies using statins for prophylaxis and prevention of end-organ damage related to extensive endothelial dysfunction in HCT and CAR-T.

PEDF promotes the repair of bone marrow endothelial cell injury and accelerates hematopoietic reconstruction after bone marrow transplantation

Background

Preconditioning before bone marrow transplantation such as irradiation causes vascular endothelial cells damage and promoting the repair of damaged endothelial cells is beneficial for hematopoietic reconstitution. Pigment epithelium-derived factor (PEDF) regulates vascular permeability. However, PEDF’s role in the repair of damaged endothelial cells during preconditioning remains unclear. The purpose of our study is to investigate PEDF’s effect on preconditioning-induced damage of endothelial cells and hematopoietic reconstitution.

Methods

Damaged endothelial cells induced by irradiation was co-cultured with hematopoietic stem cells (HSC) in the absence or presence of PEDF followed by analysis of HSC number, cell cycle, colony formation and differentiation. In addition, PEDF was injected into mice model of bone marrow transplantation followed by analysis of bone marrow injury, HSC number and peripheral hematopoietic reconstitution as well as the secretion of cytokines (SCF, TGF-β, IL-6 and TNF-α). Comparisons between two groups were performed by student t-test and multiple groups by one-way or two-way ANOVA.

Results

Damaged endothelial cells reduced HSC expansion and colony formation, induced HSC cell cycle arrest and apoptosis and promoted HSC differentiation as well as decreased PEDF expression. Addition of PEDF increased CD144 expression in damaged endothelial cells and inhibited the increase of endothelial permeability, which were abolished after addition of PEDF receptor inhibitor Atglistatin. Additionally, PEDF ameliorated the inhibitory effect of damaged endothelial cells on HSC expansion in vitro. Finally, PEDF accelerated hematopoietic reconstitution after bone marrow transplantation in mice and promoted the secretion of SCF, TGF-β and IL-6.

Conclusions

PEDF inhibits the increased endothelial permeability induced by irradiation and reverse the inhibitory effect of injured endothelial cells on hematopoietic stem cells and promote hematopoietic reconstruction.

Circulating endothelial cell count: a reliable marker of endothelial damage in patients undergoing hematopoietic stem cell transplantation

The physio-pathologic interrelationships between endothelium and GvHD have been better elucidated and have led to definition of the entity 'endothelial GvHD' as an essential early phase prior to the clinical presentation of acute GvHD. Using the CellSearch system, we analyzed circulating endothelial cells (CEC) in 90 allogeneic hematopoietic stem cell transplantation (allo-HSCT) patients at the following time-points: T1 (pre-conditioning), T2 (pre-transplant), T3 (engraftment), T4 (onset of GvHD) and T5 (1 week after steroid treatment). Although CEC changes in allo-HSCT represent a dynamic phenomenon influenced by many variables (that is, conditioning, immunosuppressive treatments, engraftment syndrome and infections), we showed that CEC peaks were constantly seen at onset of acute GvHD and invariably returned to pre-transplant values after treatment response. Since we showed that CEC changes during allo-HSCT has rapid kinetics that may be easily missed if blood samples are drawn at pre-fixed time-points, we rather suggest an 'on demand' evaluation of CEC counts right at onset of GvHD clinical symptoms to possibly help differentiate GvHD from other non-endothelial complications. We confirm that CEC changes are a suitable biomarker to monitor endothelial damage in patients undergoing allo-transplantation and hold the potential to become a useful tool to support GvHD diagnosis (ClinicalTrials.gov NCT02064972).

[Effects of allogeneic hematopoietic stem cell transplantation in combination with infusion of endothelial progenitor cells on bone marrow inflammatory injury]

Objective: To explore effects of allogeneic hematopoietic stem cell transplantation (HSCT) in combination with infusion of endothelial progenitor cells (EPC) on bone marrow inflammatory injury. Methods: 6-8 weeks BALB/c (H-2K(d)) mice after lethal dose of irradiation (TBI) were subjected to allogeneic bone marrow transplantation (BMT group) or co-transplantation of EPC (EPC group) . Samples of bone marrow cells of mice in each group on days 7,14,21,28 after transplantation were obtained to detect EPC cultural and cell chimeric rates by flow cytometer. Mice were sacrificed on days 7, 14, 21 and 28 post HSCT to analyze bone marrow pathology by H&E staining, the infiltration of macrophages and neutrophils by Western blot, validation expression levels of inflammatory complexes nlrp1、nlrp6 and its downstream molecules casepase-1 by Q-PCR and Western blot. Results: Cell chimeric rate on day 7 after transplantation in EPC group[ (91.65±2.77) %] was significantly higher than in BMT group[ (83.69±1.26) %]. Alleviated osteomyelitis injury and inflammatory cell infiltration in EPC group were observed when compared with BMT mice. Also significant reductions of the levels of nlrp1、nlrp6、casepase-1 transcription complexes in EPC mice were noted when compared with BMT ones. Conclusion: Co-transplantation of HSC and EPC could alleviate inflammatory cell infiltration and activation of the complex to promote the repair of bone marrow.

Raiders of the lost mark - endothelial cells and their role in transplantation for hematologic malignancies

Endothelial cells (EC) are crucial for normal angiogenesis and important for patients with leukemia, myeloma, and lymphoma during and after hematopoietic stem cell transplantation (HSCT). Knowledge of endothelial dysfunction in hematologic malignancies is provided by translational studies analyzing soluble endothelial markers, morphologic and functional changes of EC cultured in patients' sera or enumeration of circulating EC or endothelial progenitor cells (EPC). EC are important for stem cell homing and maintenance. Endothelial activation or damage is a central component in the pathogenesis of several complications after HSCT, like acute and chronic graft-versus-host disease, sinusoidal obstruction syndrome, capillary leak syndrome, engraftment syndrome, diffuse alveolar syndrome, idiopathic pneumonia syndrome, and transplant-associated microangiopathy. Finally, EC or EPC may facilitate tumor cell survival thus representing potential factors for both disease progression and relapse in hematologic malignancies.

A murine model of hepatic veno-occlusive disease induced by allogeneic hematopoietic stem cell transplantation

Hepatic veno-occlusive disease (HVOD) is a life-threatening complication of bone marrow stem cell transplantation. The understanding of this clinical condition is hampered by the lack of suitable animal models. Here, we present a murine (BALB/c-based) model of HVOD induced by allogeneic hematopoietic stem cell transplantation (allo-HSCT). The chimerism rate of bone marrow was measured on days 5 and 10, while the chimerism rate of peripheral blood was measured on day 15 after allo-HSCT. Percentages of peripheral reticulocytes and serum levels of bilirubin and alanine aminotransferase (as liver function tests) were measured on days 5, 10, 15, 20, and 30. Livers were obtained on days 5, 10, 15, 20, and 30, and fixed in formaldehyde or glutaric dialdehyde. Liver slices were processed using the hematoxylin-eosin, Masson's trichrome, or immunohistochemistry staining, and examined by light or transmission electron microscopy. Sinusoidal damages were the earliest pathological changes occurring in the allo-HSCT-induced HVOD, followed by coagulative necrosis of liver cells. The liver cell necrosis was later attenuated and sinusoidal endothelial cell morphology improved. However, on day 30, the edema and necrosis of liver cells became aggravated again. Furthermore, sinusoidal lining cell regeneration and partly attenuated liver cell necrosis were followed by the moderate to severe central vein fibrosis. In conclusion, we have successfully established a murine model of HSCT-HVOD. This model develops moderate to severe HVOD which cannot heal without intervention.

Differential regulation of ferritin subunits and iron transport proteins: an effect of targeted hepatic X-irradiation

The current study aimed to investigate radiation-induced regulation of iron proteins including ferritin subunits in rats. Rat livers were selectively irradiated in vivo at 25 Gy. This dose can be used to model radiation effects to the liver without inducing overt radiation-induced liver disease. Sham-irradiated rats served as controls. Isolated hepatocytes were irradiated at 8 Gy. Ferritin light polypeptide (FTL) was detectable in the serum of sham-irradiated rats with an increase after irradiation. Liver irradiation increased hepatic protein expression of both ferritin subunits. A rather early increase (3 h) was observed for hepatic TfR1 and Fpn-1 followed by a decrease at 12 h. The increase in TfR2 persisted over the observed time. Parallel to the elevation of AST levels, a significant increase (24 h) in hepatic iron content was measured. Complete blood count analysis showed a significant decrease in leukocyte number with an early increase in neutrophil granulocytes and a decrease in lymphocytes. In vitro, a significant increase in ferritin subunits at mRNA level was detected after irradiation which was further induced with a combination treatment of irradiation and acute phase cytokine. Irradiation can directly alter the expression of ferritin subunits and this response can be strongly influenced by radiation-induced proinflammatory cytokines. FTL can be used as a serum marker for early phase radiation-induced liver damage.

Infusion of endothelial progenitor cells accelerates hematopoietic and immune reconstitution, and ameliorates the graft-versus-host disease after hematopoietic stem cell transplantation

Hematopoietic stem cells transplantation (HSCT) causes endothelial cell damage, disrupting hematopoietic microenviroment and leading to various complications. We hypothesized that infusion of endothelial progenitor cells (EPCs) may improve endothelium repair, facilitate hematopoietic reconstitution, and alleviate complications associated with HSCT. C57Bl6, and BALB/c mice received total body irradiation followed by infusion of C57Bl6-derived bone marrow (BM) cells, with or without concomitant infusion of C57Bl6-derived EPCs. The time course of hematopoietic and immune reconstitution and the severity of the graft-versus-host disease (GVHD) were monitored. Further, to confirm that EPCs promote endothelial cell recovery, HSCT mice were treated with anti-VE-cadherin antibody targeting the endothelium. The EPCs-treated mice exhibited accelerated recovery of BM vasculature, cellularity, hematopoietic stem and progenitor cell recovery, improved counts of lymphocyte subsets in peripheral blood, and facilitated spleen structure reconstruction. EPCs infusion also ameliorated the GVHD in the C57Bl6 → BALB/c allo-HSCT model. Systemic administration of anti-VE-cadherin antibody significantly delayed hematological and immune reconstitution in the EPCs-infused mice. In conclusion, our data demonstrate that infusion of EPCs augments the hematopoietic and immune reconstitution, and alleviates the GVHD. These findings further highlight the relationship between the microvascular recovery, hematopoietic and immune reconstitution, and the GVHD.

Endothelial and epithelial barriers in graft-versus-host disease

Endothelial and epithelial cells form selectively permeable barriers that separate tissue compartments. These cells coordinate movement between the lumen and tissue via the transcellular and paracellular pathways. The primary determinant of paracellular permeability is the tight junction, which forms an apical belt-like structure around endothelial and epithelial cells. This chapter discusses endothelial and epithelial barriers in graft-versus-host disease after allogeneic bone marrow transplantation, with a focus on the tight junction and its role in regulating paracellular permeability. Recent studies suggest that in graft-versus-host disease, pathological increases in paracellular permeability, or barrier dysfunction, are initiated by pretransplant conditioning and sustained by alloreactive cells and the proinflammatory milieu. The intestinal epithelium is a significant focus, as it is a target organ of graft-versus-host disease, and the mechanisms of barrier regulation in intestinal epithelium have been well characterized. Finally, we propose a model that incorporates endothelial and epithelial barrier dysfunction in graft-versus-host disease and discuss modulating barrier properties as a therapeutic approach.

Increased numbers of circulating ECs are associated with systemic GVHD

INTRODUCTION

Circulating endothelial cells (ECs) are known to reflect endothelial injury, and endothelial injury is associated with graft-versus-host disease (GVHD). We hypothesised that circulating ECs might be associated with systemic acute graft-versus-host disease (aGVHD).

METHODS

BALB/c (H-2k(d) ) mice were treated with total body irradiation and then infused with C57B/6-derived T-cell-depleted bone marrow (TCD-BM) cells or TCD-BM cells and splenocytes. Cyclosporine was used to prevent aGVHD. Circulating ECs and allogeneic lymphocytes were analysed by flow cytometry at multiple time points. The morphology and ultrastructure of the endothelium were examined by light microscopy or transmission electron microscopy.

RESULTS

The results indicated that the number of circulating ECs peaked at day 5 after lethal irradiation in all mice; allogenic transplanted mice (TCD-BM cells and splenocytes) developed typical aGVHD beginning at day 7, exhibiting both histological and clinical symptoms of disease. Circulating ECs peaked a second time at day 9 with aGVHD progression. However, following the administration of CSA, an absence of or a reduction in the amount of subsequent endothelial injury was observed.

CONCLUSION

Circulating ECs might be associated with systemic aGVHD.

Adult endothelial progenitor cells retain hematopoiesis potential

Hematopoietic stem cells (HSCs) are derived from endothelium in the aortic-gonado-mesonephric (AGM) region during embryogenesis. But little is known about whether endothelial progenitor cells (EPCs) retain hematopoiesis potential after birth. In this study, we isolated adult EPCs from the bone marrow of C57BL/6 mice and identified them with an endothelial functional assay and by the CD31(+) CD133(+) CD45(-/dim) VEGFR2(+) phenotype. EPCs isolated from green fluorescence protein (GFP) transgenic C57BL/6 mice were cotransfused with bone marrow cells from wild-type C57BL/6 mice into lethally irradiated BABL/c mice. One month after transplantation, granulocytes (25.73 ± 5.43%) and lymphocytes (12.68 ± 3.26%) in peripheral blood showed GFP(+), referred to as donor EPC-derived blood cells. After an additional month, the percentage of GFP(+) granulocytes decreased to (3.69 ± 1.43%), whereas the percentage of GFP(+) lymphocytes showed no significant difference. Most of the GFP(+) elements showed a diffuse distribution in the spleen; but some were present as aggregates forming lymphoid nodules. GFP(+) endothelial cells were observed in the liver sinusoids, intestinal villi, and lung of recipient mice. These results indicated that adult EPCs not only took part in vasculogenesis, but also retained hematopoietic ability.

Vascular endothelium changes after conditioning in hematopoietic stem cell transplantation: role of cyclophosphamide and busulfan

Vascular endothelial injury, a feature of some complications of hematopoietic stem cell transplantation (HSCT), is characterized by increased endothelial cells. We investigated that classical pretreatment drugs in HSCT could result in vascular endothelial injury in mice. Six-to eight-week-old female BALB/c mice were divided into a control group, a cyclophosphamide group (60 mg/kg per day for 2 days) and a busulfan group (4 mg/kg per day for 4 days). We observed the general state of health and regularly counted the number of white blood cells. Circulating endothelial cells and their progenitors were estimated by flow cytometry. Morphologic endothelial changes were analyzed with optical and transmission electron microscopy. After conditioning with cyclophosphamide or busulfan, white blood cells fell to a low number with injuries noted on hematoxylin and eosin-stained pathology sections. Circulating endothelial cells and their progenitors peaked significantly higher than in the control group. Vascular endothelial injuries were observed in the 2 experimental groups by transmission electron microscopy. These data support the hypothesis the vascular endothelial injury occurs during conditioning with cyclophosphamide or busulfan for HSCT, with simultaneous mobilization of endothelial progenitor cells.