Acute Graft-vs.-Host Disease-Associated Endothelial Activation in vitro Is Prevented by Defibrotide

Late transplant-associated thrombotic microangiopathy verified in bone marrow biopsy specimens is associated with chronic GVHD and viral infections

OBJECTIVES

To describe late transplant-associated thrombotic microangiopathy (TA-TMA) as chronic endothelial complication in bone marrow (BM) after allogeneic hematopoietic stem cell transplantation (HSCT).

METHODS

BM specimens along with conventional diagnostic parameters were assessed in 14 single-institutional patients with late TA-TMA (more than 100 days after HCST), including 11 late with history of early TA-TMA, 10 with early TA-TMA (within 100 days), and 12 non TA-TMA patients. Three non-HSCT patients served as control. The time points of BM biopsy were +1086, +798, +396, and +363 days after HSCT, respectively.

RESULTS

Late TA-TMA patients showed an increase of CD34+ and von Willebrand Factor (VWF)+ microvascular endothelial cells with atypical VWF+ conglomerates forming thickened VWF+ plaque sinus in the BM compared to patients without late TA-TMA and non-HSCT. Severe chronic (p = .002), steroid-refractory GVHD (p = .007) and reactivation of HHV6 (p = .002), EBV (p = .003), and adenovirus (p = .005) were pronounced in late TA-TMA. Overall and relapse-free survival were shorter in late TA-TMA than in patients without late TA-TMA (5-year OS and RFS: 78.6% vs. 90.2%, 71.4% vs. 86.4%, respectively).

CONCLUSION

Chronic allo-immune microangiopathy in BM associated with chronic, steroid-refractory GVHD and/or viral infections are key findings of late, high-risk TA-TMA, which deserves clinical attention.

The critical role of endothelial cell in the toxicity associated with chimeric antigen receptor T cell therapy and intervention strategies

Chimeric antigen receptor (CAR)-T cell therapy has shown promising results in patients with hematological malignancies. However, many patients still have poor prognoses or even fatal outcomes due to the life-threatening toxicities associated with the therapy. Moreover, even after improving the known influencing factors (such as number or type of CAR-T infusion) related to CAR-T cell infusion, the results remain unsatisfactory. In recent years, it has been found that endothelial cells (ECs), which are key components of the organization, play a crucial role in various aspects of immune system activation and inflammatory response. The levels of typical markers of endothelial activation positively correlated with the severity of cytokine release syndrome (CRS) and immune effector cell-associated neurotoxic syndrome (ICANS), suggesting that ECs are important targets for intervention and toxicity prevention. This review focuses on the critical role of ECs in CRS and ICANS and the intervention strategies adopted.

Endothelial activation and damage as a common pathological substrate in different pathologies and cell therapy complications

The endothelium is a biologically active interface with multiple functions, some of them common throughout the vascular tree, and others that depend on its anatomical location. Endothelial cells are continually exposed to cellular and humoral factors, and to all those elements (biological, chemical, or hemodynamic) that circulate in blood at a certain time. It can adapt to different stimuli but this capability may be lost if the stimuli are strong enough and/or persistent in time. If the endothelium loses its adaptability it may become dysfunctional, becoming a potential real danger to the host. Endothelial dysfunction is present in multiple clinical conditions, such as chronic kidney disease, obesity, major depression, pregnancy-related complications, septic syndromes, COVID-19, and thrombotic microangiopathies, among other pathologies, but also in association with cell therapies, such as hematopoietic stem cell transplantation and treatment with chimeric antigen receptor T cells. In these diverse conditions, evidence suggests that the presence and severity of endothelial dysfunction correlate with the severity of the associated disease. More importantly, endothelial dysfunction has a strong diagnostic and prognostic value for the development of critical complications that, although may differ according to the underlying disease, have a vascular background in common. Our multidisciplinary team of women has devoted many years to exploring the role of the endothelium in association with the mentioned diseases and conditions. Our research group has characterized some of the mechanisms and also proposed biomarkers of endothelial damage. A better knowledge would provide therapeutic strategies either to prevent or to treat endothelial dysfunction.

Endothelial cell activation mediated by cold ischemia-released mitochondria is partially inhibited by defibrotide and impacts on early allograft function following liver transplantation

DAMPs (danger-associated molecular patterns) are self-molecules of the organism that appear after damage. The endothelium plays several roles in organ rejection, such as presenting alloantigens to T cells and contributing to the development of inflammation and thrombosis. This study aimed to assess whether DAMPs present in the organ preservation solution (OPS) after cold ischemic storage (CIS) contribute to exacerbating the endothelial response to an inflammatory challenge and whether defibrotide treatment could counteract this effect. The activation of cultured human umbilical vein endothelial cells (HUVECs) was analyzed after challenging with end-ischemic OPS (eiOPS) obtained after CIS. Additionally, transwell assays were performed to study the ability of eiOPS to attract lymphocytes across the endothelium. The study revealed that eiOPS upregulated the expression of MCP-1 and IL-6 in HUVECs. Moreover, eiOPS increased the membrane expression of ICAM-1and HLA-DR, which facilitated leukocyte migration toward a chemokine gradient. Furthermore, eiOPS demonstrated its chemoattractant ability. This activation was mediated by free mitochondria. Defibrotide was found to partially inhibit the eiOPS-mediated activation. Moreover, the eiOPS-mediated activation of endothelial cells (ECs) correlated with early allograft dysfunction in liver transplant patients. Our finding provide support for the hypothesis that mitochondria released during cold ischemia could trigger EC activation, leading to complications in graft outcomes. Therefore, the analysis and quantification of free mitochondria in the eiOPS samples obtained after CIS could provide a predictive value for monitoring the progression of transplantation. Moreover, defibrotide emerges as a promising therapeutic agent to mitigate the damage induced by ischemia in donated organs.

Defibrotide modulates pulmonary endothelial cell activation and protects against lung inflammation in pre-clinical models of LPS-induced lung injury and idiopathic pneumonia syndrome

Introduction

A multiple organ dysfunction syndrome (MODS) workshop convened by the National Institute of Child Health and Human Development in 2015 identified acute respiratory distress syndrome (ARDS) and complications of allogeneic blood and marrow transplantation (allo-BMT) as contributors to MODS in pediatric patients. Pulmonary dysfunction also remains a significant complication of allo-BMT. Idiopathic pneumonia syndrome (IPS) defines non-infectious, acute, lung injury that occurs post-transplant. Injury and activation to endothelial cells (ECs) contribute to each form of lung inflammation.

Methods

Two murine models were employed. In an ARDS model, naïve B6 mice receive an intravenous (i.v.) injection of lipopolysaccharide (LPS). In the established model of IPS, naïve B6D2F1 mice receive lethal total body irradiation followed by BMT from either allogeneic (B6) or syngeneic (B6D2F1) donors. Lung inflammation was subsequently assessed in each scenario.

Results

Intravenous injection of LPS to B6 mice resulted in enhanced mRNA expression of TNFα, IL-6, Ang-2, E-, and P-selectin in whole lung homogenates. The expression of Ang-2 in this context is regulated in part by TNFα. Additionally, EC activation was associated with increased total protein and cellularity in broncho-alveolar lavage fluid (BALF). Similar findings were noted during the development of experimental IPS. We hypothesized that interventions maintaining EC integrity would reduce the severity of ARDS and IPS. Defibrotide (DF) is FDA approved for the treatment of BMT patients with sinusoidal obstruction syndrome and renal or pulmonary dysfunction. DF stabilizes activated ECs and protect them from further injury. Intravenous administration of DF before and after LPS injection significantly reduced mRNA expression of TNFα, IL6, Ang-2, E-, and P-selectin compared to controls. BALF showed decreased cellularity, reflecting less EC damage and leak. Allogeneic BMT mice were treated from day -1 through day 14 with DF intraperitoneally, and lungs were harvested at 3 weeks. Compared to controls, DF treatment reduced mRNA expression of TNFα, IL6, Ang-2, E-, and P- selectin, BALF cellularity, and lung histopathology.

Conclusion

The administration of DF modulates EC injury in models of ARDS and IPS. Cytokine inhibition in combination with agents that stabilize EC integrity may be an attractive strategy for patients in each setting.

Characterization of the endotheliopathy, innate-immune activation and hemostatic imbalance underlying CAR-T cell toxicities: laboratory tools for an early and differential diagnosis

BACKGROUND

Chimeric antigen receptor (CAR)-T cell-based immunotherapy constitutes a revolutionary advance for treatment of relapsed/refractory hematological malignancies. Nevertheless, cytokine release and immune effector cell-associated neurotoxicity syndromes are life-threatening toxicities in which the endothelium could be a pathophysiological substrate. Furthermore, differential diagnosis from sepsis, highly incident in these patients, is challenging. Suitable laboratory tools could be determinant for their appropriate management.

METHODS

Sixty-two patients treated with CAR-T cell immunotherapy for hematological malignancies (n=46 with CD19-positive diseases, n=16 with multiple myeloma) were included. Plasma samples were obtained: before CAR-T cell infusion (baseline); after 24-48 hours; at suspicion of any toxicity onset and 24-48 hours after immunomodulatory treatment. Biomarkers of endothelial dysfunction (soluble vascular cell adhesion molecule 1 (sVCAM-1), soluble TNF receptor 1 (sTNFRI), thrombomodulin (TM), soluble suppression of tumorigenesis-2 factor (ST2), angiopoietin-2 (Ang-2)), innate immunity activation (neutrophil extracellular traps (NETs), soluble C5b-9 (sC5b-9)) and hemostasis/fibrinolysis (von Willebrand Factor antigen (VWF:Ag), ADAMTS-13 (A13), α2-antiplasmin (α2-AP), plasminogen activator inhibitor-1 antigen (PAI-1 Ag)) were measured and compared with those in cohorts of patients with sepsis and healthy donors.

RESULTS

Patients who developed CAR-T cell toxicities presented increased levels of sVCAM-1, sTNFRI and ST2 at the clinical onset versus postinfusion values. Twenty-four hours after infusion, ST2 levels were good predictors of any CAR-T cell toxicity, and combination of ST2, Ang-2 and NETs differentiated patients requiring intensive care unit admission from those with milder clinical presentations. Association of Ang-2, NETs, sC5b-9, VWF:Ag and PAI-1 Ag showed excellent discrimination between severe CAR-T cell toxicities and sepsis.

CONCLUSIONS

This study provides relevant contributions to the current knowledge of the CAR-T cell toxicities pathophysiology. Markers of endotheliopathy, innate immunity activation and hemostatic imbalance appear as potential laboratory tools for their prediction, severity and differential diagnosis.

Harmonizing Definitions for Diagnostic Criteria and Prognostic Assessment of Transplantation-Associated Thrombotic Microangiopathy: A Report on Behalf of the European Society for Blood and Marrow Transplantation, American Society for Transplantation and Cellular Therapy, Asia-Pacific Blood and Marrow Transplantation Group, and Center for International Blood and Marrow Transplant Research

Transplantation-associated thrombotic microangiopathy (TA-TMA) is an increasingly recognized complication of hematopoietic cell transplantation (HCT) associated with significant morbidity and mortality. However, TA-TMA is a clinical diagnosis, and multiple criteria have been proposed without universal application. Although some patients have a self-resolving disease, others progress to multiorgan failure and/or death. Poor prognostic features also are not uniformly accepted. The lack of harmonization of diagnostic and prognostic markers has precluded multi-institutional studies to better understand incidence and outcomes. Even current interventional trials use different criteria, making it challenging to interpret the data. To address this urgent need, the American Society for Transplantation and Cellular Therapy, Center for International Bone Marrow Transplant Research, Asia-Pacific Blood and Marrow Transplantation, and European Society for Blood and Marrow Transplantation nominated representatives for an expert panel tasked with reaching consensus on diagnostic and prognostic criteria. The panel reviewed literature, generated consensus statements regarding diagnostic and prognostic features of TA-TMA using the Delphi method, and identified future directions of investigation. Consensus was reached on 4 key concepts: (1) TA-TMA can be diagnosed using clinical and laboratory criteria or tissue biopsy of kidney or gastrointestinal tissue; however, biopsy is not required; (2) consensus diagnostic criteria are proposed using the modified Jodele criteria with additional definitions of anemia and thrombocytopenia. TA-TMA is diagnosed when ≥4 of the following 7 features occur twice within 14 days: anemia, defined as failure to achieve transfusion independence despite neutrophil engraftment; hemoglobin decline by ≥1 g/dL or new-onset transfusion dependence; thrombocytopenia, defined as failure to achieve platelet engraftment, higher-than-expected transfusion needs, refractory to platelet transfusions, or ≥50% reduction in baseline platelet count after full platelet engraftment; lactate dehydrogenase (LDH) exceeding the upper limit of normal (ULN); schistocytes; hypertension; soluble C5b-9 (sC5b-9) exceeding the ULN; and proteinuria (≥1 mg/mg random urine protein-to-creatinine ratio [rUPCR]); (3) patients with any of the following features are at increased risk of nonrelapse mortality and should be stratified as high-risk TA-TMA: elevated sC5b-9, LDH ≥2 times the ULN, rUPCR ≥1 mg/mg, multiorgan dysfunction, concurrent grade II-IV acute graft-versus-host disease (GVHD), or infection (bacterial or viral); and (4) all allogeneic and pediatric autologous HCT recipients with neuroblastoma should be screened weekly for TA-TMA during the first 100 days post-HCT. Patients diagnosed with TA-TMA should be risk-stratified, and those with high-risk disease should be offered participation in a clinical trial for TA-TMA-directed therapy if available. We propose that these criteria and risk stratification features be used in data registries, prospective studies, and clinical practice across international settings. This harmonization will facilitate the investigation of TA-TMA across populations diverse in race, ethnicity, age, disease indications, and transplantation characteristics. As these criteria are widely used, we expect continued refinement as necessary. Efforts to identify more specific diagnostic and prognostic biomarkers are a top priority of the field. Finally, an investigation of the impact of TA-TMA-directed treatment, particularly in the setting of concurrent highly morbid complications, such as steroid-refractory GVHD and infection, is critically needed.

Statin-based endothelial prophylaxis and outcome after allogeneic stem cell transplantation

BACKGROUND

Allogeneic haematopoietic stem cell transplantation (alloSCT) often remains the only curative therapy for hematologic malignancies. Although the management of transplant-associated adverse events considerably improved over the last decades, nonrelapse mortality (NRM) remains a challenge, and endothelial dysfunction was identified as a major contributor to NRM.

METHODS

Statin-based endothelial prophylaxis (SEP) has been implemented in the standard of care in our transplant centre to reduce NRM caused by endothelial injury. Here, we retrospectively analysed the impact of SEP on clinical outcome in a cohort of 347 alloSCT patients.

RESULTS

SEP (n = 209) was associated with significantly reduced NRM (hazard ratio 0.61, 95% CI 0.38-0.96) and better overall survival (OS) after acute graft-versus-host disease (HR 0.59, 95% CI 0.37-0.93). Subgroup analyses showed that the NRM benefit was mainly found in patients with an intermediate endothelial activation and stress index (EASIX), while relapse risk was not affected. On day 100 post-alloSCT, patients receiving SEP had significantly higher levels of the rate-limiting enzyme of tryptophan metabolism, indoleamine 2,3-dioxygenase (IDO), higher kynurenine to tryptophan ratios as a proxy of IDO activity and tended to have lower levels of the endothelial injury marker ST2 (p = .055). No significant differences in interferon-gamma or IL18 levels were observed. These biomarker signatures suggest that the beneficial effects of SEP might be mediated by both endothelial protection and immunomodulation.

CONCLUSIONS

Together, these data suggest that SEP improves NRM and OS post-alloSCT in particular in patients with intermediate endothelial risk and provide first mechanistic clues about its potential mode of action.

Mafosfamide, a cyclophosphamide analog, causes a proinflammatory response and increased permeability on endothelial cells in vitro

Post-transplantation cyclophosphamide (PTCy) has decreased GVHD incidence. Endothelial damage in allo-HCT is caused by multiple factors, including conditioning treatments and some immunosupressants, and underlies HCT-complications as GVHD. Nevertheless, the specific impact of PTCy on the endothelium remains unclear. We evaluated the effect of mafosfamide (MAF), an active Cy analog, on endothelial cells (ECs) vs. cyclosporine A (CSA), with known damaging endothelial effect. ECs were exposed to MAF and CSA to explore changes in endothelial damage markers: (i) surface VCAM-1, (ii) leukocyte adhesion on ECs, (iii) VE-cadherin expression, (iv) production of VWF, and (v) activation of intracellular signaling proteins (p38MAPK, Akt). Results obtained (expressed in folds vs. controls) indicate that both compounds increased VCAM-1 expression (3.1 ± 0.3 and 2.8 ± 0.6, respectively, p < 0.01), with higher leukocyte adhesion (5.5 ± 0.6, p < 0.05, and 2.8 ± 0.4, respectively). VE-cadherin decreased with MAF (0.8 ± 0.1, p < 0.01), whereas no effect was observed with CSA. Production of VWF augmented with CSA (1.4 ± 0.1, p < 0.01), but diminished with MAF (0.9 ± 0.1, p < 0.05). p38MAPK activation occurred with both compounds, being more intense and faster with CSA. Both drugs activated Akt, with superior MAF effect at longer exposure. Therefore, the cyclophosphamide analog MAF is not exempt from a proinflammatory effect on the endothelium, though without modifying the subendothelial characteristics.

Role of endothelial cells in graft-versus-host disease

To date, the only curative treatment for high-risk or refractory hematologic malignancies non-responsive to standard chemotherapy is allogeneic hematopoietic transplantation (allo-HCT). Acute graft-versus-host disease (GVHD) is a donor T cell-mediated immunological disorder that is frequently fatal and the leading cause of non-relapse mortality (NRM) in patients post allo-HCT. The pathogenesis of acute GVHD involves recognition of minor and/or major HLA mismatched host antigens by donor T cells followed by expansion, migration and finally end-organ damage due to combination of inflammatory cytokine secretion and direct cytotoxic effects. The endothelium is a thin layer of endothelial cells (EC) that line the innermost portion of the blood vessels and a key regulator in vascular homeostasis and inflammatory responses. Endothelial cells are activated by a wide range of inflammatory mediators including bacterial products, contents released from dying/apoptotic cells and cytokines and respond by secreting cytokines/chemokines that facilitate the recruitment of innate and adaptive immune cells to the site of inflammation. Endothelial cells can also be damaged prior to transplant as well as by alloreactive donor T cells. Prolonged EC activation results in dysfunction that plays a role in multiple post-transplant complications including but not limited to veno-occlusive disease (VOD), transplant associated thrombotic microangiopathy (TA-TMA), and idiopathic pneumonia syndrome. In this mini review, we summarize the biology of endothelial cells, factors regulating EC activation and the role of ECs in inflammation and GVHD pathogenesis.

Vascular endotheliitis associated with infections: Its pathogenetic role and therapeutic implication

Vascular endothelial cells are major participants in and regulators of immune responses and inflammation. Vascular endotheliitis is regarded as a host immune-inflammatory response of the endothelium forming the inner surface of blood vessels in association with a direct consequence of infectious pathogen invasion. Vascular endotheliitis and consequent endothelial dysfunction can be a principle determinant of microvascular failure, which would favor impaired perfusion, tissue hypoxia, and subsequent organ failure. Emerging evidence suggests the role of vascular endotheliitis in the pathogenesis of coronavirus disease 2019 (COVID-19) and its related complications. Thus, once initiated, vascular endotheliitis and resultant cytokine storm cause systemic hyperinflammation and a thrombotic phenomenon in COVID-19, leading to acute respiratory distress syndrome and widespread organ damage. Vascular endotheliitis also appears to be a contributory factor to vasculopathy and coagulopathy in sepsis that is defined as life-threatening organ dysfunction due to a dysregulated response of the host to infection. Therefore, protecting endothelial cells and reversing vascular endotheliitis may be a leading therapeutic goal for these diseases associated with vascular endotheliitis. In this review, we outline the etiological and pathogenic importance of vascular endotheliitis in infection-related inflammatory diseases, including COVID-19, and possible mechanisms leading to vascular endotheliitis. We also discuss pharmacological agents which may be now considered as potential endotheliitis-based treatment modalities for those diseases.

Impact of Defibrotide in the Prevention of Acute Graft-Versus-Host Disease Following Allogeneic Hematopoietic Cell Transplantation

BACKGROUND

Defibrotide is indicated for patients who develop severe sinusoidal obstructive syndrome following allogeneic hematopoietic cell transplantation (allo-HCT). Preclinical data suggested that defibrotide carries a prophylactic effect against acute graft-versus-host disease (aGVHD).

OBJECTIVE

The purpose of this study was to investigate the effect of defibrotide on the incidence and severity of aGVHD.

METHODS

This single-center retrospective study included all consecutive transplanted patients between January 2014 and December 2018. A propensity score based on 10 predefined confounders was used to estimate the effect of defibrotide on aGVHD via inverse probability of treatment weighting (IPTW).

RESULTS

Of the 482 included patients, 64 received defibrotide (defibrotide group) and 418 did not (control group). Regarding main patient characteristics and transplantation modalities, the two groups were comparable, except for a predominance of men in the defibrotide group. The median age was 55 years (interquartile range [IQR]: 40-62). Patients received allo-HCT from HLA-matched related donor (28.6%), HLA-matched unrelated donor (50.8%), haplo-identical donor (13.4%), or mismatched unrelated donor (7.0%). Stem cell source was either bone marrow (49.6%) or peripheral blood (50.4%). After using IPTW, exposure to defibrotide was not significantly associated with occurrence of aGVHD (HR = 0.97; 95% CI 0.62-1.52; P = .9) or occurrence of severe aGVHD (HR = 1.89, 95% CI: 0.98-3.66; P = .058).

CONCLUSION AND RELEVANCE

Defibrotide does not seem to have a protective effect on aGVHD in patients undergoing allo-HCT. Based on what has been reported to date and on these results, defibrotide should not be considered for the prevention of aGVHD outside clinical trials.

A systematic review of diagnostic, prognostic, and risk blood and urine biomarkers of transplant-associated thrombotic microangiopathy

Transplant-associated thrombotic microangiopathy (TA-TMA) is an increasingly recognized complication of allogeneic and autologous hematopoietic cellular therapy (HCT), associated with significant morbidity and mortality. Although the central drivers of the disease are thought to be endothelial damage and complement activation, no specific diagnostic biomarkers have been identified. TA-TMA is typically diagnosed using criteria comprised of non-specific clinical and laboratory features. Some patients will have a self-remitting course, but more than half develop multi-organ dysfunction or die, making prognostic biomarkers critical. Prevention of TA-TMA, an approach central to other HCT complications such as graft-versus-host disease, is largely untested in part due to a lack of identified early high-risk biomarkers. We conducted a systematic review to summarize the diagnostic, early risk, and prognostic biomarkers of TA-TMA. We screened the titles and abstracts of 1524 citations. After screening out duplications, we read the abstracts of 979 papers and fully reviewed 132 full-text publications. Thirty-one publications fulfilled the inclusion criteria of more than five patients with TA-TMA and a reported measure of association with diagnosis, prognosis, or risk of later development of the disease. Fourteen studies (45%) were with adults, 12 (39%) were with children <18 years old, three included both children and adults, and two did not report age. There were 53 biomarker or biomarker signature entries, and a total of 27 unique biomarkers. Only four biomarkers reported sensitivity and specificity. The single biomarker with the most robust data was sC5b-9, which conferred diagnostic, prognostic, and risk implications. Studies of combinations of biomarkers were rare. No meta-analyses were performed because of significant heterogeneity between studies. The limitations of studies included small sample size, study designs with a high risk of bias (i.e., case-control), the timing of sample collection, and the selection of controls. Furthermore, only two (6%) studies included a training and validation cohort. Cut-off points are needed to stratify groups, as most biomarkers do not have normal values, or normal values cannot be assumed in the HCT setting. In the future, multi-institutional, collaborative efforts are needed to perform rigorously designed, prospective studies with serially enrolled patients, with samples collected at the time of TA-TMA diagnosis, careful selection of controls, and validation of selected biomarkers and cut-off points in a separate cohort.

Is the Endothelium the Missing Link in the Pathophysiology and Treatment of COVID-19 Complications?

Patients with COVID-19 present a wide spectrum of disease severity, from asymptomatic cases in the majority to serious disease leading to critical care and even death. Clinically, four different scenarios occur within the typical disease timeline: first, an incubation and asymptomatic period; second, a stage with mild symptoms due mainly to the virus itself; third, in up to 20% of the patients, a stage with severe symptoms where a hyperinflammatory response with a cytokine storm driven by host immunity induces acute respiratory distress syndrome; and finally, a post-acute sequelae (PASC) phase, which present symptoms that can range from mild or annoying to actually quite incapacitating. Although the most common manifestation is acute respiratory failure of the lungs, other organs are also frequently involved. The clinical manifestations of the COVID-19 infection support a key role for endothelial dysfunction in the pathobiology of this condition. The virus enters into the organism via its interaction with angiotensin-converting enzyme 2-receptor that is present prominently in the alveoli, but also in endothelial cells, which can be directly infected by the virus. Cytokine release syndrome can also drive endothelial damage independently. Consequently, a distinctive feature of SARS-CoV-2 infection is vascular harm, with severe endothelial injury, widespread thrombosis, microangiopathy, and neo-angiogenesis in response to endothelial damage. Therefore, endothelial dysfunction seems to be the pathophysiological substrate for severe COVID-19 complications. Biomarkers of endothelial injury could constitute strong indicators of disease progression and severity. In addition, the endothelium could represent a very attractive target to both prevent and treat these complications. To establish an adequate therapy, the underlying pathophysiology and corresponding clinical stage should be clearly identified. In this review, the clinical features of COVID-19, the central role of the endothelium in COVID-19 and in other pathologies, and the potential of specific therapies aimed at protecting the endothelium in COVID-19 patients are addressed.

Distinctive Biomarker Features in the Endotheliopathy of COVID-19 and Septic Syndromes

BACKGROUND

Endotheliopathy is a key element in COVID-19 pathophysiology, contributing to both morbidity and mortality. Biomarkers distinguishing different COVID-19 phenotypes from sepsis syndrome remain poorly understood.

OBJECTIVE

To characterize circulating biomarkers of endothelial damage in different COVID-19 clinical disease stages compared with sepsis syndrome and normal volunteers.

METHODS

Patients with COVID-19 pneumonia (n = 49) were classified into moderate, severe, or critical (life-threatening) disease. Plasma samples were collected within 48 to 72 h of hospitalization to analyze endothelial activation markers, including soluble Vascular Cell Adhesion Molecule-1 (sVCAM-1), von Willebrand Factor (VWF), A disintegrin-like and metalloprotease with thrombospondin type 1 motif no. 13 (ADAMTS-13) activity, thrombomodulin (TM), and soluble TNF receptor I (sTNFRI); heparan sulfate (HS) for endothelial glycocalyx degradation; C5b9 deposits on endothelial cells in culture and soluble C5b9 for complement activation; circulating dsDNA for neutrophil extracellular traps (NETs) presence, and α2-antiplasmin and PAI-1 as parameters of fibrinolysis. We compared the level of each biomarker in all three COVID-19 groups and healthy donors as controls (n = 45). Results in critically ill COVID-19 patients were compared with other intensive care unit (ICU) patients with septic shock (SS, n = 14), sepsis (S, n = 7), and noninfectious systemic inflammatory response syndrome (NI-SIRS, n = 7).

RESULTS

All analyzed biomarkers were increased in COVID-19 patients versus controls (P < 0.001), except for ADAMTS-13 activity that was normal in both groups. The increased expression of sVCAM-1, VWF, sTNFRI, and HS was related to COVID-19 disease severity (P < 0.05). Several differences in these parameters were found between ICU groups: SS patients showed significantly higher levels of VWF, TM, sTNFRI, and NETS compared with critical COVID-19 patients and ADAMTS-13 activity was significantly lover in SS, S, and NI-SIRS versus critical COVID-19 (P < 0.001). Furthermore, α2-antiplasmin activity was higher in critical COVID-19 versus NI-SIRS (P < 0.01) and SS (P < 0.001), whereas PAI-1 levels were significantly lower in COVID-19 patients compared with NI-SIRS, S, and SS patients (P < 0.01).

CONCLUSIONS

COVID-19 patients present with increased circulating endothelial stress products, complement activation, and fibrinolytic dysregulation, associated with disease severity. COVID-19 endotheliopathy differs from SS, in which endothelial damage is also a critical feature of pathobiology. These biomarkers could help to stratify the severity of COVID-19 disease and may also provide information to guide specific therapeutic strategies to mitigate endotheliopathy progression.

The importance of endothelial protection: the emerging role of defibrotide in reversing endothelial injury and its sequelae

Hepatic veno-occlusive disease/sinusoidal obstruction syndrome (VOD/SOS), a potentially life-threatening complication of hematopoietic cell transplantation (HCT), results from prolonged sinusoidal endothelial cell activation and profound endothelial cell damage, with sequelae. Defibrotide, the only drug approved in the United States and Europe for treating VOD/SOS post-HCT, has European Commission orphan drug designation for preventing graft-versus-host disease (GvHD), associated with endothelial dysfunction. This endothelial cell protector and stabilizing agent restores thrombo-fibrinolytic balance and preserves endothelial homeostasis through antithrombotic, fibrinolytic, anti-inflammatory, anti-oxidative, and anti-adhesive activity. Defibrotide also preserves endothelial cell structure by inhibiting heparanase activity. Evidence suggests that downregulating p38 mitogen-activated protein kinase (MAPK) and histone deacetylases (HDACs) is key to defibrotide’s endothelial protective effects; phosphatidylinositol 3-kinase/Akt (PI3K/AKT) potentially links defibrotide interaction with the endothelial cell membrane and downstream effects. Despite defibrotide’s being most extensively studied in VOD/SOS, emerging preclinical and clinical data support defibrotide for treating or preventing other conditions driven by endothelial cell activation, dysfunction, and/or damage, such as GvHD, transplant-associated thrombotic microangiopathy, or chimeric antigen receptor T-cell (CAR-T) therapy-associated neurotoxicity, underpinned by cytokine release syndrome and endotheliitis. Further preclinical and clinical studies will explore defibrotide’s potential utility in a broader range of disorders resulting from endothelial cell activation and dysfunction.

Early Endothelial Activation in a Mouse Model of Graft vs Host Disease Following Chemotherapy

Allogenic hematopoietic stem cell transplant (allo-HSCT) can lead to sinusoidal obstruction syndrome (SOS) and graft-versus-host disease (GvHD) in some individuals. GvHD is characterised by an immune triggered response that arises due to donor T cells recognizing the recipient tissue as “foreign”. SOS results in impaired liver function due to microvascular thrombosis and consequent obstruction of liver sinusoids. Endothelial damage occurs following chemotherapy and allo-HSCT and is strongly associated with GvHD onset as well as hepatic SOS. Animal models of GvHD are rarely clinically relevant, and endothelial dysfunction remains uncharacterised. Here we established and characterised a clinically relevant model of GvHD wherein Balb/C mice were subjected to myeloablative chemotherapy followed by transplantation of bone marrow (BM) cells± splenic T-cells from C57Bl6 mice, resulting in a mismatch of major histocompatibility complexes (MHC). Onset of disease indicated by weight loss and apoptosis in the liver and intestine was discovered at day 6 post-transplant in mice receiving BM+T-cells, with established GvHD detectable by histology of the liver within 3 weeks. Together with significant increases in pro-inflammatory cytokine gene expression in the liver and intestine, histopathological signs of GvHD and a significant increase in CD4+ and CD8+ effector and memory T-cells were seen. Endothelial activation including upregulation of vascular cell adhesion molecule (VCAM)- 1 and downregulation of endothelial nitric oxide synthase (eNOS) as well as thrombosis in the liver indicated concomitant hepatic SOS. Our findings confirm that endothelial activation is an early sign of acute GvHD and SOS in a clinically relevant mouse model of GvHD based on myeloablative chemotherapy. Preventing endothelial activation may be a viable therapeutic strategy to prevent GvHD.

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.

Defibrotide: potential for treating endothelial dysfunction related to viral and post-infectious syndromes

INTRODUCTION

Defibrotide (DF) is a polyribonucleotide with antithrombotic, pro-fibrinolytic, and anti-inflammatory effects on endothelium. These effects and the established safety of DF present DF as a strong candidate to treat viral and post-infectious syndromes involving endothelial dysfunction.

AREAS COVERED

We discuss DF and other therapeutic agents that have the potential to target endothelial components of pathogenesis in viral and post-infectious syndromes. We introduce defibrotide (DF), describe its mechanisms of action, and explore its established pleiotropic effects on the endothelium. We describe the established pathophysiology of Coronavirus Disease 2019 (COVID-19) and highlight the processes specific to COVID-19 potentially modulated by DF. We also present influenza A and viral hemorrhagic fevers, especially those caused by hantavirus, Ebola virus, and dengue virus, as viral syndromes in which DF might serve therapeutic benefit. Finally, we offer our opinion on novel treatment strategies targeting endothelial dysfunction in viral infections and their severe manifestations.

EXPERT OPINION

Given the critical role of endothelial dysfunction in numerous infectious syndromes, in particular COVID-19, therapeutic pharmacology for these conditions should increasingly prioritize endothelial stabilization. Several agents with endothelial protective properties should be further studied as treatments for severe viral infections and vasculitides, especially where other therapeutic modalities have failed.

Von Willebrand Factor, Factor VIII, and Other Acute Phase Reactants as Biomarkers of Inflammation and Endothelial Dysfunction in Chronic Graft-Versus-Host Disease

Chronic graft-versus-host disease (cGvHD) is an immune mediated late complication of allogeneic hematopoietic stem cell transplantation (alloHSCT). Discovery of adequate biomarkers could identify high-risk patients and provide an effective pre-emptive intervention or early modification of therapeutic strategy, thus reducing prevalence and severity of the disease among long-term survivors of alloHSCT. Inflammation, endothelial injury, and endothelial dysfunction are involved in cGvHD development. Altered levels of acute phase reactants have shown a strong correlation with the activity of several immune mediated disorders and are routinely used in clinical practice. Since elevated von Willebrand factor (VWF) and factor VIII (FVIII) levels have been described as acute phase reactants that may indicate endothelial dysfunction and inflammation in different settings, including chronic autoimmune diseases, they could serve as potential candidate biomarkers of cGvHD. In this review we focused on reported data regarding VWF and FVIII as well as other markers of inflammation and endothelial dysfunction, evaluating their potential role in cGvHD.

Acute Graft-versus-Host-Disease Other Than Typical Targets: Between Myths and Facts

Donor alloreactivity after allogeneic hematopoietic stem cell transplantation results in graft-versus-host reaction (GVHR) that may affect different organs. While skin, liver, and gastrointestinal tract are well-recognized targets of such alloreactivity early after transplant, commonly identified as acute graft-versus-host-disease (aGVHD), there is accumulating evidence from the literature that early GVHR may be directed also against other tissues. In particular, organs such as kidney, bone marrow, central nervous system, and lungs may be involved in patients experiencing aGVHD, but whether these sites represent targets or collateral damages of donor alloreactivity is matter of debate. This review summarizes the current knowledge, the potential applications, and the clinical relevance of GFHR in nontypical target organs during aGVHD. The objective of this article is to lay the basis for future efforts aiming at including these organs in grading and management of aGVHD.

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.

The induction strategies administered in the treatment of multiple myeloma exhibit a deleterious effect on the endothelium

Multiple myeloma induction treatment includes proteasome inhibitors (PI) and immunomodulatory agents at present. The incidence of engraftment syndrome, a transplant complication potentially related to endothelium, has increased in the last years. Our aim was to investigate whether bortezomib (Velcade, V), thalidomide (T), and dexamethasone (D) affect the endothelium, and explore defibrotide (DF) as protective agent. Endothelial cells (ECs) in culture were exposed to the compounds separately or in combination, without (VTD) and with DF (VTD + DF). Changes in markers of: (i) inflammation (ICAM-1 expression and leukocyte adhesion), (ii) VWF production, (iii) cell permeability (VE-cadherin expression and cell monolayer integrity), and (iv) oxidative stress (ROS production and eNOS expression) were measured. ICAM-1 and VWF expression increased significantly in VTD but were similar to controls in VTD + DF. Separately, bortezomib was the main deleterious agent whereas dexamethasone showed no harmful effect. Leukocyte adhesion showed similar trends. VE-cadherin expression was lower in VTD and normalized in VTD + DF. EC permeability increased only with bortezomib. No changes were observed in oxidative stress markers. Our results demonstrate that bortezomib damages the endothelium, and DF prevents this effect. A better knowledge of the induction drugs impact will allow the design of measures to protect the endothelium.