Synergistic interactions between interferon-gamma and TRAIL modulate c-FLIP in endothelial cells, mediating their lineage-specific sensitivity to thrombotic thrombocytopenic purpura plasma-associated apoptosis

MASP2 inhibition by narsoplimab suppresses endotheliopathies characteristic of transplant-associated thrombotic microangiopathy: in vitro and ex vivo evidence

Transplant-associated thrombotic microangiopathy (TA-TMA) is an endotheliopathy complicating up to 30% of allogeneic hematopoietic stem cell transplants (alloHSCT). Positive feedback loops among complement, pro-inflammatory, pro-apoptotic, and coagulation cascade likely assume dominant roles at different disease stages. We hypothesized that mannose-binding lectin-associated serine protease 2 (MASP2), principal activator of the lectin complement system, is involved in the microvascular endothelial cell (MVEC) injury characteristic of TA-TMA through pathways that are susceptible to suppression by anti-MASP2 monoclonal antibody narsoplimab. Pre-treatment plasmas from 8 of 9 TA-TMA patients achieving a complete TMA response in a narsoplimab clinical trial activated caspase 8, the initial step in apoptotic injury, in human MVEC. This was reduced to control levels following narsoplimab treatment in 7 of the 8 subjects. Plasmas from 8 individuals in an observational TA-TMA study, but not 8 alloHSCT subjects without TMA, similarly activated caspase 8, which was blocked in vitro by narsoplimab. mRNA sequencing of MVEC exposed to TA-TMA or control plasmas with and without narsoplimab suggested potential mechanisms of action. The top 40 narsoplimab-affected transcripts included upregulation of SerpinB2, which blocks apoptosis by inactivating procaspase 3; CHAC1, which inhibits apoptosis in association with mitigation of oxidative stress responses; and pro-angiogenesis proteins TM4SF18, ASPM, and ESM1. Narsoplimab also suppressed transcripts encoding pro-apoptotic and pro-inflammatory proteins ZNF521, IL1R1, Fibulin-5, aggrecan, SLC14A1, and LOX1, and TMEM204, which disrupts vascular integrity. Our data suggest benefits to narsoplimab use in high-risk TA-TMA and provide a potential mechanistic basis for the clinical efficacy of narsoplimab in this disorder.

Defibrotide mitigates endothelial cell injury induced by plasmas from patients with COVID-19 and related vasculopathies

Background and objectives

COVID-19 progression is characterized by systemic small vessel arterial and venous thrombosis. Microvascular endothelial cell (MVEC) activation and injury, platelet activation, and histopathologic features characteristic of acute COVID-19 also describe certain thrombotic microangiopathies, including atypical hemolytic-uremic syndrome (aHUS), thrombotic thrombocytopenic purpura (TTP), and hematopoietic stem cell transplant (HSCT)-associated veno-occlusive disease (VOD). We explored the effect of clinically relevant doses of defibrotide, approved for HSCT-associated VOD, on MVEC activation/injury.

Methods

Human dermal MVEC were exposed to plasmas from patients with acute TMAs or acute COVID-19 in the presence and absence of defibrotide (5 μg/ml) and caspase 8, a marker of EC activation and apoptosis, was assessed. RNAseq was used to explore potential mechanisms of defibrotide activity.

Results

Defibrotide suppressed TMA plasma-induced caspase 8 activation in MVEC (mean 60.2 % inhibition for COVID-19; p = 0.0008). RNAseq identified six major cellular pathways associated with defibrotide's alteration of COVID-19-associated MVEC changes: TNF-α signaling; IL-17 signaling; extracellular matrix (ECM)-EC receptor and platelet receptor interactions; ECM formation; endothelin activity; and fibrosis. Communications across these pathways were revealed by STRING analyses. Forty transcripts showing the greatest changes induced by defibrotide in COVID-19 plasma/MVEC cultures included: claudin 14 and F11R (JAM), important in maintaining EC tight junctions; SOCS3 and TNFRSF18, involved in suppression of inflammation; RAMP3 and transgelin, which promote angiogenesis; and RGS5, which regulates caspase activation and apoptosis.

Conclusion

Our data, in the context of a recent clinical trial in severe COVID-19, suggest benefits to further exploration of defibrotide and these pathways in COVID-19 and related endotheliopathies.

Complement Mediated Endothelial Damage in Thrombotic Microangiopathies

Thrombotic microangiopathies (TMA) constitute a group of different disorders that have a common underlying mechanism: the endothelial damage. These disorders may exhibit different mechanisms of endothelial injury depending on the pathological trigger. However, over the last decades, the potential role of the complement system (CS) has gained prominence in their pathogenesis. This is partly due to the great efficacy of complement-inhibitors in atypical hemolytic syndrome (aHUS), a TMA form where the primary defect is an alternative complement pathway dysregulation over endothelial cells (genetic and/or adquired). Complement involvement has also been demonstrated in other forms of TMA, such as thrombotic thrombocytopenic purpura (TTP) and in Shiga toxin-producing Escherichia coli hemolytic uremic syndrome (STEC-HUS), as well as in secondary TMAs, in which complement activation occurs in the context of other diseases. However, at present, there is scarce evidence about the efficacy of complement-targeted therapies in these entities. The relationship between complement dysregulation and endothelial damage as the main causes of TMA will be reviewed here. Moreover, the different clinical trials evaluating the use of complement-inhibitors for the treatment of patients suffering from different TMA-associated disorders are summarized, as a clear example of the entry into a new era of personalized medicine in its management.

MASP2 levels are elevated in thrombotic microangiopathies: association with microvascular endothelial cell injury and suppression by anti-MASP2 antibody narsoplimab

Involvement of the alternative complement pathway (AP) in microvascular endothelial cell (MVEC) injury characteristic of a thrombotic microangiopathy (TMA) is well documented. However, the role of the lectin pathway (LP) of complement has not been explored. We examined mannose-binding lectin associated serine protease (MASP2), the effector enzyme of the LP, in thrombotic thrombocytopenic purpura, atypical hemolytic uremic syndrome and post-allogeneic hematopoietic stem cell transplantation (alloHSCT) TMAs. Plasma MASP2 and terminal complement component sC5b-9 levels were assessed by enzyme-linked immunosorbent assay (ELISA). Human MVEC were exposed to patient plasmas, and the effect of the anti-MASP2 human monoclonal antibody narsoplimab on plasma-induced MVEC activation was assessed by caspase 8 activity. MASP2 levels were highly elevated in all TMA patients versus controls. The relatively lower MASP2 levels in alloHSCT patients with TMAs compared to levels in alloHSCT patients who did not develop a TMA, and a significant decrease in variance of MASP2 levels in the former, may reflect MASP2 consumption at sites of disease activity. Plasmas from 14 of the 22 TMA patients tested (64%) induced significant MVEC caspase 8 activation. This was suppressed by clinically relevant levels of narsoplimab (1·2 μg/ml) for all 14 patients, with a mean 65·7% inhibition (36.8-99.4%; P < 0·0001). In conclusion, the LP of complement is activated in TMAs of diverse etiology. Inhibition of MASP2 reduces TMA plasma-mediated MVEC injury in vitro. LP inhibition therefore may be of therapeutic benefit in these disorders.

Conservation of structure and function in vertebrate c-FLIP proteins despite rapid evolutionary change

Cellular FLICE-like inhibitory protein (c-FLIP, gene symbol CFLAR) was first identified as a negative regulator of death receptor-mediated apoptosis in mammals. To understand the ubiquity and diversity of the c-FLIP protein subfamily during evolution, c-FLIP orthologs were identified from a comprehensive range of vertebrates, including birds, amphibians, and fish, and were characterized by combining experimental and computational analysis. Predictions of three-dimensional protein structures and molecular phylogenetic analysis indicated that the conserved structural features of c-FLIP proteins are all derived from an ancestral caspase-8, although they rapidly diverged from the subfamily consisting of caspases-8, -10, and -18. The functional role of the c-FLIP subfamily members is nearly ubiquitous throughout vertebrates. Exogenous expression of non-mammalian c-FLIP proteins in cultured mammalian cells suppressed death receptor-mediated apoptosis, implying that all of these proteins possess anti-apoptotic activity. Furthermore, non-mammalian c-FLIP proteins induced NF-κB activation much like their mammalian counterparts. The CFLAR mRNAs were synthesized during frog and fish embryogenesis. Overexpression of a truncated mutant of c-FLIP in the Xenopus laevis embryos by mRNA microinjection caused thorax edema and abnormal constriction of the abdomen. Depletion of cflar transcripts in zebrafish resulted in developmental abnormalities accompanied by edema and irregular red blood cell flow. Thus, our results demonstrate that c-FLIP/CFLAR is conserved in both protein structure and function in several vertebrate species, and suggest a significant role of c-FLIP in embryonic development.

Immune-mediated vascular injury and dysfunction in transplant arteriosclerosis

Solid organ transplantation is the only treatment for end-stage organ failure but this life-saving procedure is limited by immune-mediated rejection of most grafts. Blood vessels within transplanted organs are targeted by the immune system and the resultant vascular damage is a main contributor to acute and chronic graft failure. The vasculature is a unique tissue with specific immunological properties. This review discusses the interactions of the immune system with blood vessels in transplanted organs and how these interactions lead to the development of transplant arteriosclerosis, a leading cause of heart transplant failure.

c-FLIP maintains tissue homeostasis by preventing apoptosis and programmed necrosis

As a catalytically inactive homolog of caspase-8, a proapoptotic initiator caspase, c-FLIP blocks apoptosis by binding to and inhibiting caspase-8. The transcription factor nuclear factor κB (NF-κB) plays a pivotal role in maintaining the homeostasis of the intestine and the liver by preventing death receptor-induced apoptosis, and c-FLIP plays a role in the NF-κB-dependent protection of cells from death receptor signaling. Because c-Flip-deficient mice die in utero, we generated conditional c-Flip-deficient mice to investigate the contribution of c-FLIP to homeostasis of the intestine and the liver at developmental and postnatal stages. Intestinal epithelial cell (IEC)- or hepatocyte-specific deletion of c-Flip resulted in perinatal lethality as a result of the enhanced apoptosis and programmed necrosis of the IECs and the hepatocytes. Deficiency in the gene encoding tumor necrosis factor-α (TNF-α) receptor 1 (Tnfr1) partially rescued perinatal lethality and the development of colitis in IEC-specific c-Flip-deficient mice but did not rescue perinatal lethality in hepatocyte-specific c-Flip-deficient mice. Moreover, adult mice with interferon (IFN)-inducible deficiency in c-Flip died from hepatitis soon after depletion of c-FLIP. Pretreatment of IFN-inducible c-Flip-deficient mice with a mixture of neutralizing antibodies against TNF-α, Fas ligand (FasL), and TNF-related apoptosis-inducing ligand (TRAIL) prevented hepatitis. Together, these results suggest that c-FLIP controls the homeostasis of IECs and hepatocytes by preventing cell death induced by TNF-α, FasL, and TRAIL.

TRAIL signaling and synergy mechanisms used in TRAIL-based combination therapies

TRAIL and agonistic antibodies raised against TRAIL death receptors are highly promising new anticancer agents. In this brief review, we describe the recent advances in the molecular understanding of TRAIL signaling and the progress made in using TRAIL or agonistic antibodies clinically in mono- and combination therapies. Synergies have been reported in various scenarios of TRAIL-based multidrug treatments, and these can be used to potentiate the efficacy of therapies targeting TRAIL death receptors. We pay particular attention to structure the current knowledge on the diverse molecular mechanisms that are thought to give rise to these synergies and describe how different signaling features evoking synergies can be associated with distinct classes of drugs used in TRAIL-based combination treatments.

Pharmacological modulation of cell death in atherosclerosis: a promising approach towards plaque stabilization?

Despite tremendous advances over the last 15 years in identifying vulnerable atherosclerotic plaques, the incidence of death and disability caused by such lesions still remains the number one health threat in developed countries. Therefore, new systemic or focal therapies aimed at decreasing the overall burden of disease, and a change to a more benign phenotype, are needed. Because cell death is a prominent feature of advanced atherosclerotic plaques with a major impact on plaque destabilization, an increasing number of compounds targeting the apoptotic or autophagic machinery in atherosclerosis are being explored, predominantly at the preclinical level. This review will provide an overview of these compounds, with a focus on both inhibition and stimulation of cell death, to prevent acute coronary syndromes and sudden cardiac death.

Rituximab treatment for thrombotic thrombocytopenic purpura associated with human immunodeficiency virus failing extensive treatment with plasma exchange: a report of two cases

In an urban area with a 3% prevalence of HIV infection, two women presented in a 1-year period with AIDS and thrombotic thrombocytopenic purpura (TTP). TTP was diagnosed in each patient based on the presence of thrombocytopenia, schistocytes, and markedly elevated lactate dehydrogenase (LDH) activity. Initial treatment with plasma exchange resulted in resolution of these abnormalities. However, the discontinuation of plasma exchange resulted in the prompt recurrence of laboratory abnormalities diagnostic for TTP. Treatment failure was established after observing 6 and 4 such responses requiring 41 and 40 episodes of plasma exchange for each patient, respectively. Patients were subsequently treated with 2-4 doses of weekly rituximab resulting in durable remission. These patients are now 21 and 9 months beyond rituximab treatment. Rituximab appears to be safe and effective in this setting.

Long-term results of the children's cancer group studies for childhood acute lymphoblastic leukemia 1983-2002: a Children's Oncology Group Report

The Children's Cancer Group enrolled 13 298 young people age <21 years on 1 of 16 protocols between 1983 and 2002. Outcomes were examined in three time periods, 1983-1988, 1989-1995, 1996-2002. Over the three intervals, 10-year event-free survival (EFS) for Rome/National Cancer Institute standard risk (SR) and higher risk (HR) B-precursor patients was 68 and 58%, 77 and 63%, and 78 and 67%, respectively, whereas for SR and HR T-cell patients, EFS was 65 and 56%, 78 and 68%, and 70 and 72%, respectively. Five-year EFS for infants was 36, 38, and 43%, respectively. Seminal randomized studies led to a number of important findings. Stronger post-induction intensification improved outcome for both SR and HR patients. With improved systemic therapy, additional intrathecal (IT) methotrexate effectively replaced cranial radiation. For SR patients receiving three-drug induction, iso-toxic substitution of dexamethasone for prednisone improved EFS. Pegylated asparaginase safely and effectively replaced native asparaginase. Thus, rational therapy modifications yielded better outcomes for both SR and HR patients. These trials provide the platforms for current Children's Oncology Group trials.