Genetic Susceptibility in Endothelial Injury Syndromes after Hematopoietic Cell Transplantation and Other Cellular Therapies: Climbing a Steep Hill

Hematopoietic stem cell transplantation (HSCT) remains a cornerstone in the management of patients with hematological malignancies. Endothelial injury syndromes, such as HSCT-associated thrombotic microangiopathy (HSCT-TMA), veno-occlusive disease/sinusoidal obstruction syndrome (SOS/VOD), and capillary leak syndrome (CLS), constitute complications after HSCT. Moreover, endothelial damage is prevalent after immunotherapy with chimeric antigen receptor-T (CAR-T) and can be manifested with cytokine release syndrome (CRS) or immune effector cell-associated neurotoxicity syndrome (ICANS). Our literature review aims to investigate the genetic susceptibility in endothelial injury syndromes after HSCT and CAR-T cell therapy. Variations in complement pathway- and endothelial function-related genes have been associated with the development of HSCT-TMA. In these genes, CFHR5, CFHR1, CFHR3, CFI, ADAMTS13, CFB, C3, C4, C5, and MASP1 are included. Thus, patients with these variations might have a predisposition to complement activation, which is also exaggerated by other factors (such as acute graft-versus-host disease, infections, and calcineurin inhibitors). Few studies have examined the genetic susceptibility to SOS/VOD syndrome, and the implicated genes include CFH, methylenetetrahydrofolate reductase, and heparinase. Finally, specific mutations have been associated with the onset of CRS (PFKFB4, CX3CR1) and ICANS (PPM1D, DNMT3A, TE2, ASXL1). More research is essential in this field to achieve better outcomes for our patients.

Endothelial Activation and Stress Index (EASIX) to predict mortality after allogeneic stem cell transplantation: a prospective study

BACKGROUND

We previously reported that the "Endothelial Activation and Stress Index" (EASIX; ((creatinine×lactate dehydrogenase)÷thrombocytes)) measured before start of conditioning predicts mortality after allogeneic hematopoietic stem cell transplantation (alloSCT) when used as continuous score. For broad clinical implementation, a prospectively validated EASIX-pre cut-off is needed that defines a high-risk cohort and is easy to use.

METHOD

In the current study, we first performed a retrospective cohort analysis in n=2022 alloSCT recipients and identified an optimal cut-off for predicting non-relapse mortality (NRM) as EASIX-pre=3. For cut-off validation, we conducted a multicenter prospective study with inclusion of n=317 first alloSCTs from peripheral blood stem cell in adult patients with acute leukemia, lymphoma or myelodysplastic syndrome/myeloproliferative neoplasms in the European Society for Blood and Marrow Transplantation network.

RESULTS

Twenty-three % (n=74) of alloSCT recipients had EASIX-pre ≥3 taken before conditioning. NRM at 2 years was 31.1% in the high EASIX group versus 11.5% in the low EASIX group (p<0.001). Patients with high EASIX-pre also had worse 2 years overall survival (51.6% vs 70.9%; p=0.002). We were able to validate the cut-off and found that EASIX ≥3 was associated with more than twofold increased risk for NRM in multivariate analysis (HR=2.18, 95% CI 1.2 to 3.94; p=0.01). No statistically significant difference could be observed for the incidence of relapse.

CONCLUSIONS

The results of this study provide a prospectively validated standard laboratory biomarker index to estimate the transplant-related mortality risk after alloSCT. EASIX ≥3 taken before conditioning identifies a population of alloSCT recipients who have a more than twofold increased risk of treatment-related mortality.

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.

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.

Thrombotic Microangiopathy: Multi-Institutional Review of Pediatric Patients Who Underwent HSCT

Thrombotic microangiopathy (TMA) is a rare but serious complication of hematopoietic stem cell transplantation (HSCT). The purpose of our study is to estimate the incidence, prevalence, and analyze the risk factors and outcome of TMA in children receiving HSCT. Patients under the age of 21 who underwent HSCT at one of the 42 Pediatric Health Information System (PHIS) hospitals from 2000–2012 were analyzed, including demographics, hospitalizations, TMA, and other HSCT-related complications. From 2000 to 2012, a total of 12,369 unique pediatric patients who received HSCT were identified. Among these, 93 (0.8%) children were identified to have the diagnosis of TMA. TMA was significantly associated with allogeneic HSCT, peripheral blood stem cell trasnplants (PBSCT), cytomegalovirus (CMV), human herpes virus 6 (HHV6), fungal infection, graft-versus-host disease (GVHD), and veno-occlusive disease (VOD) (p = 0.01). Multivariate logistic regression analysis of mortality showed only HHV6 was an independent risk factor associated with increased mortality in patients with TMA (hazard ratio: 2.86 [1.01, 8.39], p = 0.05). The prevalence of TMA in our study is 0.8% with a mortality in our pediatric TMA cohort of 30%, which is in contrast to the higher mortality reported in previously published, small-case series. HHV6 emerged as not only a risk factor for TMA but also as associated with increased mortality in these patients.

Endothelial injury, F-actin and vitamin-D binding protein after hematopoietic stem cell transplant and association with clinical outcomes

Endothelial injury after hematopoietic stem cell transplant is an important initiating factor for early transplant toxicities of thrombotic microangiopathy and acute graft versus host disease. We hypothesized that release of the angiopathic molecule filamentous actin (F-actin) from hematopoietic cells lysed during conditioning prior to stem cell transplant would be associated with clinical outcomes. We detected F-actin in the blood of 52% of stem cell transplant recipients in the first 14 days after transplant, and children with detectable F-actin had a significantly elevated risk of thrombotic microangiopathy (P=0.03) and non-relapse mortality (P=0.04). F-actin is cleared from the circulation by vitamin D binding protein (VDBP) so we expected that higher levels of VDBP would improve outcomes. In a cohort of 190 children receiving an allogeneic transplant, risk of thrombotic microangiopathy was reduced in those with serum concentrations of VDBP above the median at day 30 (10% vs. 31%, P=0.01), and graft versus host disease and non-relapse mortality were reduced in those with levels above the median at day 100 (3% vs. 18%, P=0.04 and 0% vs. 15%, P=0.002). Western blot analyses demonstrated actin-VDBP complexes in the blood, which cleared by day 21-28. Our data support modulation of cytokine secretion and macrophage phenotype by VDBP later after transplant. Taken together, our data identify an association between Factin, a mediator of endothelial damage, and VDBP, an actin scavenger, as modifiers of risk of clinical consequences of endothelial injury.

Genetic justification of severe COVID-19 using a rigorous algorithm

Recent studies suggest excessive complement activation in severe coronavirus disease-19 (COVID-19). The latter shares common characteristics with complement-mediated thrombotic microangiopathy (TMA). We hypothesized that genetic susceptibility would be evident in patients with severe COVID-19 (similar to TMA) and associated with disease severity. We analyzed genetic and clinical data from 97 patients hospitalized for COVID-19. Through targeted next-generation-sequencing we found an ADAMTS13 variant in 49 patients, along with two risk factor variants (C3, 21 patients; CFH,34 patients). 31 (32%) patients had a combination of these, which was independently associated with ICU hospitalization (p = 0.022). Analysis of almost infinite variant combinations showed that patients with rs1042580 in thrombomodulin and without rs800292 in complement factor H did not require ICU hospitalization. We also observed gender differences in ADAMTS13 and complement-related variants. In light of encouraging results by complement inhibitors, our study highlights a patient population that might benefit from early initiation of specific treatment.

Polymorphisms in CXCR3 ligands predict early CXCL9 recovery and severe chronic GVHD

Chronic graft-versus-host disease (cGVHD) is a major cause of mortality and morbidity after allogeneic stem cell transplantation (alloSCT). The individual risk of severe cGVHD remains difficult to predict and may involve CXCR3 ligands. This study investigated the role of single-nucleotide polymorphisms (SNPs) of CXCL4, CXCL9, CXCL10, and CXCL11, and their day +28 serum levels, in cGVHD pathogenesis. Eighteen CXCR3 and CXCL4, CXCL9-11 SNPs as well as peri-transplant CXCL9-11 serum levels were analyzed in 688 patients without (training cohort; n = 287) or with statin-based endothelial protection cohort (n = 401). Clinical outcomes were correlated to serum levels and SNP status. Significant polymorphisms were further analyzed by luciferase reporter assays. Findings were validated in an independent cohort (n = 202). A combined genetic risk comprising four CXCR3 ligand SNPs was significantly associated with increased risk of severe cGVHD in both training cohort (hazard ratio (HR) 2.48, 95% confidence interval (CI) 1.33-4.64, P = 0.004) and validation cohort (HR 2.95, 95% CI 1.56-5.58, P = 0.001). In reporter assays, significantly reduced suppressive effects of calcineurin inhibitors in constructs with variant alleles of rs884304 (P < 0.001) and rs884004 (P < 0.001) were observed. CXCL9 serum levels at day +28 after alloSCT correlated with both genetic risk and risk of severe cGVHD (HR 1.38, 95% CI 1.10-1.73, P = 0.006). This study identifies patients with high genetic risk to develop severe cGVHD.

IL-1 and CD40/CD40L platelet complex: elements of induction of Crohn's disease and new therapeutic targets

Ulcerative colitis (UC) and Crohn's disease (CD) are chronic and multifactorial diseases that affect the intestinal tract, both characterized by recurrent inflammation of the intestinal mucosa, resulting in abdominal pain, diarrhea, vomiting and, rectal bleeding. Inflammatory bowel diseases (IBD) regroup these two disorders. The exact pathological mechanism of IBD remains ambiguous and poorly known. In genetically predisposed patients, defects in intestinal mucosal barrier are due to an uncontrolled inflammatory response to normal flora. In addition to the genetic predisposition, these defects could be triggered by environmental factors or by a specific lifestyle which is widely accepted as etiological hypothesis. The involvement of the CD40/CD40L platelet complex in the development of IBD has been overwhelmingly demonstrated. CD40L is climacteric in cell signalling in innate and adaptive immunity, the CD40L expression on the platelet cell surface gives them an immunological competence. The IL-1, a major inflammation mediator could be involved in different ways in the development of IBD. Here, we provide a comprehensive review regarding the role of platelet CD40/CD40L in the pathophysiological effect of IL-1 in the development of Crohn's disease (CD). This review could potentially help future approaches aiming to target these two pathways for therapeutic purposes and elucidate the immunological mechanisms driving gut inflammation.

Risk Factors for Transplant-Associated Thrombotic Microangiopathy after Autologous Hematopoietic Cell Transplant in High-Risk Neuroblastoma

High-risk neuroblastoma has a poor prognosis, and research studies have shown that increasing the intensity of therapy improves outcomes. Autologous hematopoietic cell transplant (aHCT) as consolidation therapy confers a significant survival advantage but is accompanied by significant morbidity. Transplant-associated thrombotic microangiopathy (TA-TMA) is a life-threatening complication caused by endothelial injury that often leads to hemolytic anemia, microthrombotic platelet consumption, and renal injury. Here we investigated the incidence, potential risk factors, and sequelae of TA-TMA in patients with high-risk neuroblastoma. We conducted a retrospective chart review of all patients (n = 141) with neuroblastoma in our institutions who underwent aHCT from 2000 to 2017. Ten patients (7%) developed TA-TMA. The patients in the TA-TMA group were similar to the rest of the subjects in demographics, disease burden, prior therapies, renal function, and timing of transplant. The type of conditioning regimen was the only statistically significant pretransplant variable (P < .001). Six of 15 patients (40%) intended to receive tandem transplants (cyclophosphamide/thiotepa and then carboplatin/etoposide/melphalan (CEM)), 4 of 68 patients (6%) who received conditioning with single CEM, and none of the 56 patients who received busulfan/melphalan were diagnosed with TA-TMA. Patients with TA-TMA were more likely to require intensive care unit transfer, have a longer length of stay in the hospital, and experience a delay or change in their subsequent therapy. In our cohort overall, patients with a delay in therapy after transplant appeared to have a worse overall survival, although the difference was not statistically significant. Because of this high incidence and significant morbidity, we have implemented standardized screening for TA-TMA during and after transplant. We anticipate that screening will lead to earlier intervention and decreased severity of disease.

EASIX and mortality after allogeneic stem cell transplantation

Allogeneic stem cell transplantation (alloSCT) is an effective immunotherapy in patients with hematological malignancies. Endothelial dysfunction was linked to major complications after alloSCT. We asked the question if the "Endothelial Activation and Stress Index" (EASIX; [(creatinine × LDH) ÷ thrombocytes]) can predict mortality after alloSCT. We performed a retrospective cohort analysis in five alloSCT centers in the USA and Germany. EASIX was assessed prior to conditioning (EASIX-pre) and correlated with mortality in 755 patients of a training cohort in multivariable models. The predictive model established in the training cohort was validated in 1267 adult allo-recipients. Increasing EASIX-pre predicted lower overall survival (OS) after alloSCT, and successful model validation was achieved for the validation cohort. We found that EASIX-pre predicts OS irrespective of established scores. Moreover, EASIX-pre was also a significant prognostic factor for transplant-associated microangiopathy. Finally, EASIX-pre correlated with biomarkers of endothelial homeostasis such as CXCL8, interleukin-18, and insulin-like-growth-factor-1 serum levels. This study establishes EASIX-pre based on a standard laboratory biomarker panel as a predictor of individual risk of mortality after alloSCT independently from established clinical criteria.

Transplant-Associated Thrombotic Microangiopathy in Pediatric Hematopoietic Cell Transplant Recipients: A Practical Approach to Diagnosis and Management

Transplant-associated thrombotic microangiopathy (TA-TMA) is an endothelial damage syndrome that is increasingly identified as a complication of both autologous and allogeneic hematopoietic cell transplantation (HCT) in children. If not promptly diagnosed and treated, TA-TMA can lead to significant morbidity (e.g., permanent renal injury) or mortality. However, as the recognition of the early stages of TA-TMA may be difficult, we propose a TA-TMA "triad" of hypertension, thrombocytopenia (or platelet transfusion refractoriness), and elevated lactate dehydrogenase (LDH). While not diagnostic, this triad should prompt further evaluation for TA-TMA. There is increased understanding of the risk factors for the development of TA-TMA, including those which are inherent (e.g., race, genetics), transplant approach-related (e.g., second HCT, use of HLA-mismatched donors), and related to post-transplant events (e.g., receipt of calcineurin inhibitors, development of graft-vs. -host-disease, or certain infections). This understanding should lead to enhanced screening for TA-TMA signs and symptoms in high-risk patients. The pathophysiology of TA-TMA is complex, resulting from a cycle of activation of endothelial cells to produce a pro-coagulant state, along with activation of antigen-presenting cells and lymphocytes, as well as activation of the complement cascade and microthrombi formation. This has led to the formulation of a "Three-Hit Hypothesis" in which patients with either an underlying predisposition to complement activation or pre-existing endothelial injury (Hit 1) undergo a toxic conditioning regimen causing endothelial injury (Hit 2), and then additional insults are triggered by medications, alloreactivity, infections, and/or antibodies (Hit 3). Understanding this cycle of injury permits the development of a specific TA-TMA treatment algorithm designed to treat both the triggers and the drivers of the endothelial injury. Finally, several intriguing approaches to TA-TMA prophylaxis have been identified. Future work on the development of a single diagnostic test with high specificity and sensitivity, and the development of a robust risk-scoring system, will further improve the management of this serious post-transplant complication.