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

Neurological involvement in hematopoietic stem cell transplantation-associated thrombotic microangiopathy

Transplantation-associated thrombotic microangiopathy (TA-TMA) is a well-recognized serious complication of hematopoietic stem cell transplantation (HSCT). The understanding of TA-TMA pathophysiology has expanded in recent years. Dysregulation of the complement system is thought to cause endothelial injury and, consequently, microvascular thrombosis and tissue damage. TA-TMA can affect multiple organs, and each organ exhibits specific features of injury. Central nervous system (CNS) manifestations of TA-TMA include posterior reversible encephalopathy syndrome, seizures, and encephalopathy. The development of neurological dysfunction is associated with a significantly lower overall survival in patients with TA-TMA. However, there are currently no established histopathological or radiological criteria for the diagnosis of CNS TMA. Patients who receive total body irradiation (TBI), calcineurin inhibitors (CNI), and severe acute and chronic graft-versus-host disease (GVHD) are at a high risk of experiencing neurological complications related to TA-TMA and should be considered for directed TA-TMA therapy. However, the incidence and clinical manifestations of TA-TMA neurotoxicity remain unclear. Studies specifically examining the involvement of CNS in TMA syndromes are limited. In this review, we discuss clinical manifestations and imaging abnormalities in patients with nervous system involvement in TA-TMA. We summarize the mechanisms underlying TA-TMA and its neurological complications, including endothelial injury, evidence of complement activation, and treatment options for TA-TMA.

Evaluation of Circulating Endothelial Cells as Direct Marker of Endothelial Damage in Allo-Transplant Recipients at High Risk of Hepatic Veno-Occlusive Disease/Sinusoidal Obstruction Syndrome

Sinusoidal obstruction syndrome (SOS), also known as veno-occlusive disease (VOD), is a rare but potentially fatal complication following allogenic hematopoietic cell transplantation (allo-HCT). Timely identification of SOS/VOD to allow for prompt treatment is critical, but identifying a VOD-predictive biomarker remains challenging. Given the pivotal role of endothelial dysfunction in SOS/VOD pathophysiology, the CECinVOD study prospectively evaluated levels of circulating endothelial cells (CECs) in patients undergoing allo-HCT with a myeloablative conditioning (MAC) regimen to investigate the potential of CEC level in predicting and diagnosing SOS/VOD. A total of 150 patients from 11 Italian bone marrow transplantation units were enrolled. All participants were age >18 years and received a MAC regimen, putting them at elevated risk of developing SOS/VOD. Overall, 6 cases of SOS/VOD (4%) were recorded. CECs were detected using the Food and Drug Administration-approved CellSearch system, an immunomagnetic selection-based platform incorporating ferrofluid nanoparticles and fluorescent-labeled antibodies, and were defined as CD146+, CD105+, DAPI+, or CD45-. Blood samples were collected at the following time points: before (T0) and at the end of conditioning treatment (T1), at neutrophil engraftment (T2), and at 7 to 10 days postengraftment (T3). For patients who developed VOD, additional samples were collected at any suspected or proven VOD onset (T4) and weekly during defibrotide treatment (T5 to T8). A baseline CEC count >17/mL was associated with an elevated risk of SOS/VOD (P = .04), along with bilirubin level >1.5 mg/mL and a haploidentical donor hematopoietic stem cell source. Postconditioning regimen (T1) CEC levels were elevated (P = .02), and levels were further increased at engraftment (P < .0001). Additionally, patients developing SOS/VOD after engraftment, especially those with late-onset SOS/VOD, showed a markedly higher relative increase (>150%) in CEC count. Multivariate analysis supported these findings, along with a high Endothelial Activation and Stress Index (EASIX) score at engraftment (T2). Finally, CEC kinetics corresponded with defibrotide treatment. After the start of therapy (T4), CEC levels showed an initial increase in the first week (T5), followed by a progressive decrease during VOD treatment (T6 and T7) and a return to pre-SOS/VOD onset levels at resolution of the complication. This prospective multicenter study reveals a low incidence of SOS/VOD in high-risk patients compared to historical data, in line with recent reports. The results from the CECinVOD study collectively confirm the endothelial injury in allo-HCT and its role in in the development of SOS/VOD, suggesting that CEC level can be a valuable biomarker for diagnosing SOS/VOD and identifying patients at greater risk of this complication, especially late-onset SOS/VOD. Furthermore, CEC kinetics may support treatment strategies by providing insight into the optimal timing for discontinuing defibrotide treatment.

Origins and functional differences of blood endothelial cells

The interests in blood endothelial cells arise from their therapeutic potential in vascular repair and regeneration. Our understanding of blood endothelial cells that exist in the circulation has been evolving significantly from the original concept of endothelial progenitor cells. Many studies have uncovered heterogeneities of blood endothelial subtypes where some cells express both endothelial and hematopoietic antigens, and others possess either mature or immature endothelial markers. Due to the lack of definitive cell marker identities, there have been momentums in the field to adopt a technical-oriented labeling system based on the cells' involvement in postnatal neovascularization and cell culture derivatives. Our review streamlines nomenclatures for blood endothelial subtypes and standardizes understanding of their functional differences. Broadly, we will discuss about myeloid angiogenic cells (MACs), endothelial colony-forming cells (ECFCs), blood outgrowth endothelial cells (BOECs) and circulating endothelial cells (CECs). The strategic location of blood endothelial cells confers them essential roles in supporting physiological processes. MACs exert angiogenic effects through paracrine mechanisms, while ECFCs are recruited to sites of vascular injury to participate directly in new vessel formation. BOECs are an in vitro derivative of ECFCs. CECs are shed into the bloodstream from damaged vessels, hence reflective of endothelial dysfunction. With clarity on the functional attributes of blood endothelial subtypes, we present recent advances in their applications in disease modelling, along with serving as biomarkers of vascular tissue homeostasis.

Isolation of circulating endothelial cells provides tool to determine endothelial cell senescence in blood samples

Circulating endothelial cells (CEC) are arising as biomarkers for vascular diseases. However, whether they can be utilized as markers of endothelial cell (EC) senescence in vivo remains unknown. Here, we present a protocol to isolate circulating endothelial cells for a characterization of their senescent signature. Further, we characterize different models of EC senescence induction in vitro and show similar patterns of senescence being upregulated in CECs of aged patients as compared to young volunteers. Replication-(ageing), etoposide-(DNA damage) and angiotensin II-(ROS) induced senescence models showed the expected cell morphology and proliferation-reduction effects. Expression of senescence-associated secretory phenotype markers was specifically upregulated in replication-induced EC senescence. All models showed reduced telomere lengths and induction of the INK4a/ARF locus. Additional p14ARF-p21 pathway activation was observed in replication- and etoposide-induced EC senescence. Next, we established a combined magnetic activated- and fluorescence activated cell sorting (MACS-FACS) based protocol for CEC isolation. Interestingly, CECs isolated from aged volunteers showed similar senescence marker patterns as replication- and etoposide-induced senescence models. Here, we provide first proof of senescence in human blood derived circulating endothelial cells. These results hint towards an exciting future of using CECs as mirror cells for in vivo endothelial cell senescence, of particular interest in the context of endothelial dysfunction and cardiovascular diseases.

Metformin pretreatment ameliorates busulfan-induced liver endothelial toxicity during haematopoietic stem cell transplantation

The success of Haematopoietic cell transplantation (HCT) is often limited by regimen-related toxicity (RRT) caused by conditioning regimen drugs. Among different conditioning drugs, busulfan (Bu) and treosulfan (Treo), although widely used in HCT, exhibit different toxicity profiles, the mechanism of which is still unclear. Here we investigated the effects of Bu and Treo in endothelial cells. While both Bu and Treo induced DNA damage in endothelial cells, we observed Bu alone to induce oxidative stress and sustained activation of phospho-ERK1/2, leading to apoptosis. However, Treo-treated cells exhibited no oxidative stress/apoptosis of endothelial cells. Screening of pharmacological inhibitors of both ROS and p-ERK revealed that metformin effectively ameliorates Bu-mediated toxicity in endothelial cells. In Balb/c mice, we observed a significant reduction in bone marrow endothelial cells in Bu-treated mice compared to Treo-treated mice. Further, liver sinusoidal endothelial cells (LSEC) was damaged by Bu, which is implicated in liver vasculature and their functional capacity to uptake FITC-albumin. However, Treo-treated mice liver vasculature was morphologically and functionally normal. When mice were pretreated with metformin followed by Bu, LSECs damage was ameliorated morphologically and functionally. Bone marrow transplants done on these mice did not affect the engraftment of donor cells.

Preconditioning Modified-Easix as a Predictor of Prognosis in Allogeneic Hematopoietic Stem Cell Transplant Recipients

Allogeneic hematopoietic stem cell transplantation (alloHCT) is associated with severe complications, most of which share a common physiopathological background characterized by endothelial dysfunction. A novel risk assessment model, endothelial activation and stress index (EASIX), has been introduced as a predictor of endothelial activation. This retrospective study was performed to evaluate the predictive impact of EASIX/modified-EASIX (mEASIX) on transplant outcome. Medical records of 398 alloHCT recipients [median age: 43(17-71) years; M/F: 243/155] were examined. EASIX/mEASIX were calculated at specific time points before and after transplantation. EASIX/mEASIX were significantly associated with transplant complications including engraftment syndrome, sinusoidal obstruction syndrome, febrile neutropenia and transplant associated thrombotic microangiopathy. The probability of overall survival was significantly higher in low-preconditioning mEASIX (day -7) group (37% vs 25.2%; p = 0.008; HR: 2.057; 95% CI: 1.208-3.504). The probabilities of day30 mortality (2.9% vs 19.4%; p = 0.017; HR: 7.028; 95% CI: 1.418-34.836), day100 mortality (9% vs 33%; p = 0.004; HR: 4.469; 95% CI: 1.619-12.336) and non relapse mortality (44.8% vs 61.4%; p = 0.005; HR: 2.551; 95% CI: 1.318-4.941) were lower in low-preconditioning mEASIX (day -7) group. This retrospective cohort analysis demonstrates the significant impact of EASIX/mEASIX on transplant complications and survival. Prospective analyses are mandatory to assess the predictive role of EASIX/mEASIX in clinical practice.

Circulating Endothelial Cell Kinetic in Patients with Multiple Myeloma Who Receive Autologous Hematopoietic Stem Cell Transplantation

INTRODUCTION

Neoangiogenesis has a crucial role in multiple myeloma (MM), and circulating endothelial cells (CECs) contribute to neovascularization by inducing tumor progression and metastasis and by repairing damage to bone marrow vasculature after stem cell transplantation (HSC). We recently proved in a national multicenter study the possibility to reach a high-level standardization in CEC count and analysis based on a polychromatic flow cytometry Lyotube (BD). Our study aimed at assessing the kinetics of CECs in patients with MM undergoing autologous hematopoietic stem cell transplantation (Au-HSCT).

METHODS

Blood samples for analysis were collected at different time points before (T0, T1) and after (T2, T3, T4) Au-HSCT. For each sample, 20 × 106 leukocytes were processed as already described (Lanuti 2016 e 2018) through a multistep procedure. CECs were eventually identified as 7-ADDneg/Syto16pos/CD45neg/CD34pos/CD146pos.

RESULTS

Twenty-six MM patients were enrolled in the study. Overall, we observed a constant increase of CECs values from T0 to T3 (day of neutrophil engraftment) followed by decrease at T4 (100 days after transplantation). Using the median value of CECs at T3, we could define a cut-off concentration of 618/mL, with patients with more infective complications having CECs above that value (9/13 vs. 2/13; p = 0.005).

CONCLUSION

CECs value may be a function of endothelial damage caused by conditioning regimen, as suggested by the increase of their level during the engraftment period. A more severe endothelial damage is reflected by the increase of infective complications in patients with higher CECs value at T3.

Endothelial Dysfunction Syndromes after Allogeneic Stem Cell Transplantation

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) remains the only therapy with a curative potential for a variety of malignant and non-malignant diseases. The major limitation of the procedure is the significant morbidity and mortality mainly associated with the development of graft versus host disease (GVHD) as well as with a series of complications related to endothelial injury, such as sinusoidal obstruction syndrome/veno-occlusive disease (SOS/VOD), transplant-associated thrombotic microangiopathy (TA-TMA), etc. Endothelial cells (ECs) are key players in the maintenance of vascular homeostasis and during allo-HSCT are confronted by multiple challenges, such as the toxicity from conditioning, the administration of calcineurin inhibitors, the immunosuppression associated infections, and the donor alloreactivity against host tissues. The early diagnosis of endothelial dysfunction syndromes is of paramount importance for the development of effective prophylactic and therapeutic strategies. There is an urgent need for the better understanding of the pathogenetic mechanisms as well as for the identification of novel biomarkers for the early diagnosis of endothelial damage. This review summarizes the current knowledge on the biology of the endothelial dysfunction syndromes after allo-HSCT, along with the respective therapeutic approaches, and discusses the strengths and weaknesses of possible biomarkers of endothelial damage and dysfunction.

Circulating Endothelial Cells: A New Possible Marker of Endothelial Damage in Kawasaki Disease, Multisystem Inflammatory Syndrome in Children and Acute SARS-CoV-2 Infection

BACKGROUND

Kawasaki Disease (KD) and Multisystem Inflammatory Syndrome in Children (MIS-C) are pediatric diseases characterized by systemic inflammation and vascular injury, potentially leading to coronary artery lesions (CALs). Data on vascular injury occurring during acute COVID-19 (AC19) in children are still lacking. The aim of our study was to investigate endothelial injury in KD-, MIS-C- and AC19-dosing circulating endothelial cells (CECs).

METHODS

We conducted a multicenter prospective study. CECs were enumerated by CellSearch technology through the immunomagnetic capture of CD146-positive cells from whole blood.

RESULTS

We enrolled 9 KD, 20 MIS-C and 10 AC19. During the acute stage, the AC19 and KD patients had higher CECs levels than the MIS-C patients. From the acute to subacute phase, a significant CEC increase was observed in the KD patients, while a mild decrease was detected in the MIS-C patients. Cellular clusters/syncytia were more common in the KD patients. No correlation between CECs and CALs were found in the MIS-C patients. The incidence of CALs in the KD group was too low to investigate this correlation.

CONCLUSIONS

Our study suggests a possible role of CECs as biomarkers of systemic inflammation and endothelial dysfunction in KD and MIS-C and different mechanisms of vascular injury in these diseases. Further larger studies are needed.

Circulating endothelial cells and endothelial progenitor cells as potential predictors of acute GVHD after allogeneic hematopoietic stem cell transplantation

OBJECTIVE

Acute graft-versus-host disease (aGVHD) is a major cause of treatment-related mortality after allogeneic hematopoietic stem cell transplantation. Endothelial cell damage may trigger the initiation of aGVHD.

METHODS

Endothelial damage and repair were evaluated by counting circulating endothelial cells (CECs) and endothelial progenitor cells (EPCs) in 17 allogeneic hematopoietic stem cell transplantation patients at pre-conditioning, day 0, day 7, day 14, day 30, and day 60 by multicolor flow cytometry. Von Willebrand factor activity was simultaneously measured.

RESULTS

Eight patients developed aGVHD and were compared to non-aGVHD patients. Patients' characteristics were not different, except for previous treatment courses. There was no difference in von Willebrand factor activity between the two groups. Both CEC and EPC counts were decreased on day 7 and day 14 and then increased thereafter. The CEC count on day 7 was significantly lower in the aGVHD group than in the non-aGVHD group (p = .0401). Restoration of the EPC count on day 60 was significantly suppressed in the aGVHD group (p = .0464). The CEC count on day 7 could predict aGVHD development (AUC 0.8214, p = .0372).

CONCLUSION

The present results showed that CEC count on day 7 could be a predictor of aGVHD.

Early vascular endothelial complications after hematopoietic cell transplantation: Role of the endotheliopathy in biomarkers and target therapies development

This work aims to review the role of endothelial dysfunction underlying the main complications appearing early after autologous and allogeneic hematopoietic cell transplantation (HCT). The endothelial damage as the pathophysiological substrate of sinusoidal obstruction syndrome (SOS) is well established. However, there is growing evidence of the involvement of endothelial dysfunction in other complications, such as acute graft-versus-host disease (aGVHD) and transplant-associated thrombotic microangiopathy (TA-TMAs). Moreover, HCT-related endotheliopathy is not only limited to the HCT setting, as there is increasing evidence of its implication in complications derived from other cellular therapies. We also review the incidence and the risk factors of the main HCT complications and the biological evidence of the endothelial involvement and other linked pathways in their development. In addition, we cover the state of the art regarding the potential use of the biomarkers of endotheliopathy in the prediction, the early diagnosis, and the follow-up of the HCT complications and summarize current knowledge points to the endothelium and the other linked pathways described as potential targets for the prevention and treatment of HCT-complications. Lastly, the endothelium-focused therapeutic strategies that are emerging and might have a potential impact on the survival and quality of life of post-HCT-patients are additionally reviewed.

Comparative Mutational Profiling of Hematopoietic Progenitor Cells and Circulating Endothelial Cells (CECs) in Patients with Primary Myelofibrosis

A role of endothelial cells (ECs) in Primary Myelofibrosis (PMF) was supposed since JAK2 mutation was found in endothelial precursor cells (EPCs) and in ECs captured by laser microdissection. By Cell Search method, the circulating endothelial cells (CECs) from 14 PMF patients and 5 healthy controls have been isolated and compared by NGS with CD34+Hematopoietic stem and progenitors cells (HSPCs) for panel of 54 myeloid-associated mutations. PMF patients had higher levels of CECs. No mutation was found in HSPCs and CECs from controls, while CECs from PMF patients presented several somatic mutations. 72% of evaluable patients shared at least one mutation between HSPCs and CECs. 2 patients shared the JAK2 mutation, together with ABL1, IDH1, TET2 and ASXL1, KMT2A, respectively. 6 out of 8 shared only NON MPN-driver mutations: TET2 and NOTCH1 in one case; individual paired mutations in TP53, KIT, SRSF2, NOTCH1 and WT1, in the other cases. In conclusion, 70% of PMF patients shared at least one mutation between HSPCs and CECs. These latter harbored several myeloid-associated mutations, besides JAK2V617F mutation. Our results support a primary involvement of EC in PMF and provide a new methodological approach for further studies exploring the role of the “neoplastic” vascular niche.

Endothelial cell dysfunction: a key determinant for the outcome of allogeneic stem cell transplantation

Allogeneic hematopoietic stem cell transplantation (alloSCT) carries the promise of cure for many malignant and non-malignant diseases of the lympho-hematopoietic system. Although outcome has improved considerably since the pioneering Seattle achievements more than 5 decades ago, non-relapse mortality (NRM) remains a major burden of alloSCT. There is increasing evidence that endothelial dysfunction is involved in many of the life-threatening complications of alloSCT, such as sinusoidal obstruction syndrome/venoocclusive disease, transplant-associated thrombotic microangiopathy, and refractory acute graft-versus host disease. This review delineates the role of the endothelium in severe complications after alloSCT and describes the current status of search for biomarkers predicting endothelial complications, including markers of endothelial vulnerability and markers of endothelial injury. Finally, implications of our current understanding of transplant-associated endothelial pathology for prevention and management of complications after alloSCT are discussed.

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.

Transplant-associated thrombotic microangiopathy: elucidating prevention strategies and identifying high-risk patients

INTRODUCTION

Hematopoietic stem cell transplantation-associated thrombotic microangiopathy (TA-TMA) is a severe complication of transplant. TA-TMA is a multifactorial disease where generalized endothelial dysfunction leads to microangiopathic hemolytic anemia, intravascular platelet activation, and formation of microthrombi leading to end-organ injury. It is essential to identify patients at risk for this complication and to implement early interventions to improve TA-TMA associated transplant outcomes.

AREAS COVERED

Recognition of TA-TMA and associated multi-organ injury, risk predictors, contributing factors, differential diagnosis and targeting complement pathway in TA-TMA by summarizing peer reviewed manuscripts.

EXPERT OPINION

TA-TMA is an important transplant complication. Diagnostic and risk criteria are established in children and young adults and risk-based targeted therapies have been proposed using complement blockers. The immediate goal is to extend this work into adult stem cell transplant recipients by implementing universal TA-TMA screening practices. This will facilitate early TA-TMA diagnosis and targeted interventions, which will further improve survival. While complement blocking therapy is effective, about one third of patients are refractory to treatment and those patients commonly die. The next hurdle for the field is identifying reasons for failure, optimizing strategies for complement modifying therapy and searching for additional targetable pathways of endothelial injury.

Endothelial damage and dysfunction in acute graft-versus-host disease

Clinical studies suggested that endothelial dysfunction and damage could be involved in the development and severity of acute graft-versus-host disease (aGVHD). Accordingly, we found increased percentage of apoptotic Casp3+ blood vessels in duodenal and colonic mucosa biopsies of patients with severe aGVHD. In murine experimental aGVHD, we detected severe microstructural endothelial damage and reduced endothelial pericyte coverage accompanied by reduced expression of endothelial tight junction proteins leading to increased endothelial leakage in aGVHD target organs. During intestinal aGVHD, colonic vasculature structurally changed, reflected by increased vessel branching and vessel diameter. Because recent data demonstrated an association of endothelium-related factors and steroid refractory aGVHD (SR-aGVHD), we analyzed human biopsies and murine tissues from SR-aGVHD. We found extensive tissue damage but low levels of alloreactive T cell infiltration in target organs, providing the rationale for T-cell independent SR-aGVHD treatment strategies. Consequently, we tested the endothelium-protective PDE5 inhibitor sildenafil, which reduced apoptosis and improved metabolic activity of endothelial cells in vitro. Accordingly, sildenafil treatment improved survival and reduced target organ damage during experimental SR-aGVHD. Our results demonstrate extensive damage, structural changes, and dysfunction of the vasculature during aGVHD. Therapeutic intervention by endothelium-protecting agents is an attractive approach for SR-aGVHD complementing current anti-inflammatory treatment options.

Endothelial impairment evaluation by peripheral arterial tonometry in pediatric endocrinopathies: A narrative review

Endothelial dysfunction (ED) is characterized by an imbalance between vasodilator and vasoconstriction agents. Several pathological conditions clinically diagnosed in childhood and adolescence are characterized by ED and increased risk for early development of microangiopathic and macroangiopathic impairment, in particular type 1 diabetes mellitus (T1DM), T2DM, obesity, metabolic syndromeand pituitary dysfunction associated to various endocrinopathies. More recently insulin resistance following chemotherapy or radiotherapy for tumors, bone marrow transplantation for hematological malignancies (i.e., cancer survivors), or immunosuppressive treatment for solid organ transplantation has been observed. Assessment of ED by means of non-invasive techniques is the gold standard for early ED detection before clinical manifestation. It is aimed to recognize patients at risk and to avoid the development and progression of more serious illnesses. Reactive hyperemia-peripheral artery tonometry is a noninvasive technique to assess peripheral endothelial function by measuring modifications in digital pulse volume during reactive hyperemia, and represents a non-invasive, reproducible and operator-independent tool able to detect precocious ED. This narrative review aimed to provide an overview of the most important papers regarding ED detection by EndoPat 2000 in children and adolescents with different endocrine diseases. A comprehensive search of English language articles was performed in the MEDLINE database without using other search filters except the publication interval between 2005 and 2020.

Biomarkers for Early Complications of Endothelial Origin After Allogeneic Hematopoietic Stem Cell Transplantation: Do They Have a Potential Clinical Role?

Endothelial cell (EC) dysfunction causes a number of early and life-threatening post hematopoietic stem cell transplant (HCT) complications that result in a rapid clinical decline. The main early complications are graft-vs.-host disease (GVHD), transplant associated thrombotic microangiopathy (TA-TMA), and sinusoidal obstruction syndrome (SOS). Post-HCT endothelial dysfunction occurs as a result of chemotherapy, infections, and allogeneic reactivity. Despite major advances in transplant immunology and improvements in supportive care medicine, these complications represent a major obstacle for successful HCT. In recent years, different biomarkers have been investigated for early detection of post-transplant endothelial cell dysfunction, but few have been validated. In this review we will define GVHD, TA-TMA and SOS, summarize the current data available in HCT biomarker research and identify promising biomarkers for detection and diagnosis of early HCT complications.

Hematopoietic Stem Cell Niche During Homeostasis, Malignancy, and Bone Marrow Transplantation

Self-renewal and multidirectional differentiation of hematopoietic stem cells (HSCs) are strictly regulated by numerous cellular components and cytokines in the bone marrow (BM) microenvironment. Several cell types that regulate HSC niche have been identified, including both non-hematopoietic cells and HSC-derived cells. Specific changes in the niche composition can result in hematological malignancies. Furthermore, processes such as homing, proliferation, and differentiation of HSCs are strongly controlled by the BM niche and have been reported to be related to the success of hematopoietic stem cell transplantation (HSCT). Single-cell sequencing and in vivo imaging are powerful techniques to study BM microenvironment in hematological malignancies and after HSCT. In this review, we discuss how different components of the BM niche, particularly non-hematopoietic and hematopoietic cells, regulate normal hematopoiesis, and changes in the BM niche in leukemia and after HSCT. We believe that this comprehensive review will provide clues for further research on improving HSCT efficiency and exploring potential therapeutic targets for leukemia.

Biomarkers for acute and chronic graft versus host disease: state of the art

INTRODUCTION

Despite significant advances in treatment and prevention, graft-versus-host disease (GVHD) still represents the main cause of morbidity and mortality after allogeneic hematopoietic stem cell transplantation. Thus, considerable research efforts have been made to find and validate reliable biomarkers for diagnosis, prognosis, and risk stratification of GVHD.

AREAS COVERED

In this review the most recent evidences on different types of biomarkers studied for GVHD, such as genetic, plasmatic, cellular markers, and those associated with microbiome, were summarized. A comprehensive search of peer-review literature was performed in PubMed including meta-analysis, preclinical and clinical trials, using the terms: cellular and plasma biomarkers, graft-versus-host disease, cytokines, and allogeneic hematopoietic stem cell transplantation.

EXPERT OPINION

In the near future, several validated biomarkers will be available to help clinicians in the diagnosis of GVHD, the identification of patients at high risk of GVHD development and in patients' stratification according to its severity. Then, immunosuppressive treatment could be tailored to each patient's real needs. However, more efforts are needed to achieve this goal. Although most of the proposed biomarkers currently lack validation with large-scale clinical data, their study led to improved knowledge of the biological basis of GVHD, and ultimately to implementation of GHVD treatment.

Potential Novel Biomarkers in Chronic Graft-Versus-Host Disease

Prognostic, diagnostic or predictive biomarkers are urgently needed for assessment of chronic graft-versus-host disease (cGvHD), a major risk for patients undergoing allogeneic hematopoietic stem cell transplantation. The main goal of this review generated within the COST Action EUROGRAFT "Integrated European Network on Chronic Graft Versus Host Disease" was to identify potential novel biomarkers for cGvHD besides the widely accepted molecular and cellular biomarkers. Thus, the focus was on cellular biomarkers, alloantibodies, glycomics, endothelial derived particles, extracellular vesicles, microbiome, epigenetic and neurologic changes in cGvHD patients. Both host-reactive antibodies in general, and particularly alloantibodies have been associated with cGvHD and require further consideration. Glycans attached to IgG modulate its activity and represent a promising predictive and/or stratification biomarker for cGVHD. Furthermore, epigenetic changes such as microRNAs and DNA methylation represent potential biomarkers for monitoring cGvHD patients and novel targets for developing new treatment approaches. Finally, the microbiome likely affects the pathophysiology of cGvHD; bacterial strains as well as microbial metabolites could display potential biomarkers for dysbiosis and risk for the development of cGvHD. In summary, although there are no validated biomarkers currently available for clinical use to better inform on the diagnosis, prognosis or prediction of outcome for cGvHD, many novel sources of potential markers have shown promise and warrant further investigation using well characterized, multi-center patient cohorts.

Endothelial injury and thrombotic microangiopathy in COVID-19: Treatment with the lectin-pathway inhibitor narsoplimab

In COVID-19, acute respiratory distress syndrome (ARDS) and thrombotic events are frequent, life-threatening complications. Autopsies commonly show arterial thrombosis and severe endothelial damage. Endothelial damage, which can play an early and central pathogenic role in ARDS and thrombosis, activates the lectin pathway of complement. Mannan-binding lectin-associated serine protease-2 (MASP-2), the lectin pathway's effector enzyme, binds the nucleocapsid protein of severe acute respiratory syndrome-associated coronavirus-2 (SARS-CoV-2), resulting in complement activation and lung injury. Narsoplimab, a fully human immunoglobulin gamma 4 (IgG4) monoclonal antibody against MASP-2, inhibits lectin pathway activation and has anticoagulant effects. In this study, the first time a lectin-pathway inhibitor was used to treat COVID-19, six COVID-19 patients with ARDS requiring continuous positive airway pressure (CPAP) or intubation received narsoplimab under compassionate use. At baseline and during treatment, circulating endothelial cell (CEC) counts and serum levels of interleukin-6 (IL-6), interleukin-8 (IL-8), C-reactive protein (CRP) and lactate dehydrogenase (LDH) were assessed. Narsoplimab treatment was associated with rapid and sustained reduction of CEC and concurrent reduction of serum IL-6, IL-8, CRP and LDH. Narsoplimab was well tolerated; no adverse drug reactions were reported. Two control groups were used for retrospective comparison, both showing significantly higher mortality than the narsoplimab-treated group. All narsoplimab-treated patients recovered and survived. Narsoplimab may be an effective treatment for COVID-19 by reducing COVID-19-related endothelial cell damage and the resultant inflammation and thrombotic risk.

Critical Care of Hematopoietic Stem Cell Transplant Patients

Life-threatening complications are frequent after hematopoietic stem cell transplant (HSCT), and optimum critical care is essential to ensuring good outcomes. The immunologic consequences of HSCT result in a markedly different host response to critical illness. Infection is the most common cause of critical illness but noninfectious complications are frequent. Respiratory failure or sepsis are the typical presentations but the sequelae of HSCT can affect nearly any organ system. Pattern recognition can facilitate anticipation and early intervention in post-HSCT critical illness. HSCT critical care is a multidisciplinary endeavor. Continued investigation and focus on process improvement will continue to improve outcomes.

Allogeneic reactivity-mediated endothelial cell complications after HSCT: a plea for consensual definitions

Endothelial cell (EC) activation has been suspected of triggering a group of rare and dismal complications that can occur after allogeneic hematopoietic stem cell transplantation (HSCT). Capillary leak syndrome, engraftment syndrome, transplant-associated microangiopathy, diffuse alveolar hemorrhage, and idiopathic pneumonia syndrome are the main nosological entities. Post-HSCT endotheliitis can be triggered by chemotherapy, infections, and calcineurin inhibitors, but allogeneic reactivity is claimed to be the common denominator. Endothelial damages are thought to activate several deleterious pathways (proapoptotic, procoagulant, proinflammatory) and can lead to multiorgan failure; however, clinical manifestations of each syndrome overlap, and their relationship with graft-versus-host disease could be minimal. The lack of well-defined diagnostic criteria does not allow for a clear-cut comparison in the current literature. Therapeutic efforts have been made to intercept the pathogenic mechanisms leading to EC dysfunction, but remission rates and survival remain mostly unsatisfactory. In this article, we have reviewed the incidence, clinical features, and treatment approaches of EC activation syndromes, and we plead for the development of internationally accepted standard definitions.

Prognostic plasma biomarkers of early complications and graft-versus-host disease in patients undergoing allogeneic hematopoietic stem cell transplantation

Early complications post hematopoietic stem cell transplantation (HSCT) such as sinusoidal obstruction syndrome (SOS) and graft versus host disease (GVHD) can be life threatening. Although several biomarkers have been identified to correlate with these complications and their response to treatment, these are yet to be used in clinical practice. Here, we evaluated circulating endothelial cells (CECs) (n = 26) and plasma biomarkers (ST2, REG3α, VCAM1, ICAM1, TIM3) (N = 210) at early time points, to determine their association with early complications post-HSCT. Elevated CEC counts at the end of conditioning was associated with GVHD, indicating endothelial damage during HSCT. Plasma levels of REG3α, VCAM1, ICAM1, and TIM3 on day 14 (D14) and D14 ICAM1 and D28 ST2 were significantly higher in patients with SOS and aGVHD, respectively. Upon sub-group analysis, D28 ST2, D14/D28 REG3α, and D14ICAM1 levels were significantly higher in patients with gastrointestinal GVHD, while D28ST2 was higher in those with skin/liver GVHD. High ST2 levels on D28 was significantly associated with non-relapse mortality (NRM) and overall survival. Our results suggest that elevated ST2 levels on D28 could predict the likelihood of developing aGVHD and could influence NRM and OS.

Endothelial cell function and endothelial-related disorders following haematopoietic cell transplantation

Use of haematopoietic cell transplantation (HCT) in the treatment of haematologic and neoplastic diseases may lead to life-threatening complications that cause substantial morbidity and mortality if untreated. In addition to patient- and disease-related factors, toxicity associated with HCT puts patients at risk for complications that share a similar pathophysiology involving endothelial cells (ECs). Normally, the endothelium plays a role in maintaining homeostasis, including regulation of coagulation, vascular tone, permeability and inflammatory processes. When activated, ECs acquire cellular features that may lead to phenotypic changes that induce procoagulant, pro-inflammatory and pro-apoptotic mediators leading to EC dysfunction and damage. Elevated levels of coagulation factors, cytokines and adhesion molecules are indicative of endothelial dysfunction, and endothelial damage may lead to clinical signs and symptoms of pathological post-HCT conditions, including veno-occlusive disease/sinusoidal obstruction syndrome, graft-versus-host disease, transplant-associated thrombotic microangiopathy and idiopathic pneumonia syndrome/diffuse alveolar haemorrhage. The endothelium represents a rational target for preventing and treating HCT complications arising from EC dysfunction and damage. Additionally, markers of endothelial damage may be useful in improving diagnosis of HCT-related complications and monitoring treatment effect. Continued research to effectively manage EC activation, injury and dysfunction may be important in improving patient outcomes after HCT.

Extracorporeal Photopheresis (ECP) and the Potential of Novel Biomarkers in Optimizing Management of Acute and Chronic Graft vs. Host Disease (GvHD)

As the use of hematopoietic stem cell transplantation (HSCT) has become a more widespread and effective treatment for hematological malignant and non-malignant conditions, the need to minimize the harmful effects of graft- vs.-host disease (GvHD) has become more important in achieving good outcomes. With diagnosis of GvHD reliant on its clinical manifestations, research into biomarkers for the diagnosis, progression, and even for the prediction of disease, is imperative to combating the high levels of morbidity and mortality post-HSCT. Despite the development of novel treatment approaches to GvHD, corticosteroids remain the standard first-line treatment, with immunosuppressant therapies as second-line options. These strategies however have significant limitations and associated complications. Extracorporeal Photopheresis (ECP) has shown to be effective and safe in treating patients with symptomatic GvHD. ECP has been shown to have varied effects on multiple parts of the immune system and does not appear to increase the risk of relapse or infection in the post HSCT setting. Even so, ECP can be logistically more complex to organize and requires patients to be sufficiently stable. This review aims to summarize the potential role of biomarkers to help guide individualized treatment decisions in patients with acute and chronic GvHD. In relation to ECP, robust biomarkers of GvHD will be highly useful in informing patient selection, intensity and duration of the ECP schedule, monitoring of response and other treatment decisions alongside the concurrent administration of other GvHD therapies. Further research is warranted to establish how GvHD biomarkers are best incorporated into ECP treatment pathways with the goal of tailoring ECP to the needs of individual patients and maximizing benefit.

Early Prediction of Cardiovascular Risk after Hematopoietic Cell Transplantation: Are We There Yet?

Cardiovascular (CV) events have emerged as a major cause of morbidity and mortality among hematopoietic cell transplantation (HCT) survivors. Accumulating evidence supports the presence of increased CV risk in HCT recipients. Most studies have focused mainly on traditional CV risk factors, such as the metabolic syndrome and hypertension. However, detection of these factors suggests the development of irreversible overt clinical atherosclerosis. Therefore, earlier prediction of CV risk is needed to prevent CV morbidity and mortality in these patients. In the field of CV research, endothelial dysfunction is considered an early event in the pathophysiology of CV risk factors, and a number of markers have been proposed for its assessment. In addition, markers of subclinical target organ damage have been introduced to implement CV risk prediction and early preventive or intensive therapeutic interventions. Furthermore, a number of CV models have been suggested aiming for optimal stratification of patients. Preliminary studies have indicated excess CV risk using these early markers in HCT recipients. However, their role in the pathophysiology and clinical practice in HCT survivors remains largely understudied. Taking into account the need for increased awareness from treating physicians in this evolving setting, we conducted a state-of-the-art review aiming to summarize current knowledge on endothelial dysfunction, subclinical target organ damage, and CV risk prediction in HCT survivors.

Endothelial Dysfunction in Hematopoietic Cell Transplantation

The goal of this review is to look at the role of endothelial damage and dysfunction in the initiation and development of early complications that appear after hematopoietic cell transplantation (HCT). These early complications share overlapping clinical manifestations and the suspicion of underlying endothelial damage. Several studies using different approaches, such as animal and in vitro models, the analysis of soluble biomarkers and clinical findings have provided evidence of this endothelial dysfunction. Historically, the first complication in which the role of endothelial damage was elucidated was the veno-oclusive disease/sinusoidal obstructive syndrome. In the last two decades, increasing evidence of the implication of the endothelium in the pathophysiology of other syndromes such as capillary leak syndrome, transplant-associated microangiopathy, or even graft versus host disease has accumulated. This knowledge opens up potential pharmacologic interventions to prevent/and/or treat endothelial damage and, therefore, to improve the outcome of patients receiving HCT.

Counting circulating endothelial cells in allo-HSCT: an ad hoc designed polychromatic flowcytometry-based panel versus the CellSearch System

Physio-pathologic interrelationships between endothelial layer and graft-versus-host disease (GVHD) have been described leading to assess the entity “endothelial GVHD” as the early step for clinical manifestations of acute GVHD. The availability of the CellSearch system has allowed us to monitor Circulating Endothelial Cells (CEC) changes in allogeneic hematopoietic stem cell transplantation (allo-HSCT) as useful tool to help clinicians in GVHD diagnostic definition. We have compared CEC counts generated by an ad hoc designed polychromatic-flowcytometry (PFC) Lyotube with those of the CellSearch system. CEC were counted in parallel at 5 timepoints in 50 patients with malignant hematologic disorders undergoing allo-HSCT (ClinicalTrials.gov, NCT02064972). Spearman rank correlation showed significant association between CEC values at all time points (p = 0.0001). The limits of agreement was demonstrated by Bland Altman plot analysis, showing bias not significant at T1, T3, T4, while at T2 and T5 resulted not estimable. Moreover, Passing Bablok regression analysis showed not significant differences between BD Lyotube and CellSearch system. We show that CEC counts, generated with either the CellSearch system or the PFC-based panel, have a superimposable kinetic in allo-HSCT patients and that both counting procedures hold the potential to enter clinical routine as a suitable tool to assist clinicians in GVHD diagnosis.