The Pathophysiology of Acquired Aplastic Anemia: Current Concepts Revisited.

Idiopathic acquired aplastic anemia is a rare, life-threatening bone marrow failure syndrome characterized by cytopenias and hypocellular bone marrow. The pathophysiology is unknown; the most favored model is of a dysregulated immune system leading to autoreactive T-cell destruction of hematopoietic stem and progenitor cells in a genetically susceptible host. The authors review the literature and propose that the major driver of acquired aplastic anemia is a combination of hematopoietic stem and progenitor cells intrinsic defects and an inappropriately activated immune response in the setting of a viral infection. Alterations in bone marrow microenvironment may also contribute to the disease process.

Randomized phase 2 trial of regadenoson for treatment of acute vaso-occlusive crises in sickle cell disease.

Adenosine A2A receptor (A2AR) agonists have been shown to decrease tissue inflammation induced by hypoxia/reoxygenation in mice with sickle cell disease (SCD). The key mediator of the A2AR agonist's anti-inflammatory effects is a minor lymphocyte subset, invariant natural killer T (iNKT) cells. We tested the hypothesis that administration of an A2AR agonist in patients with SCD would decrease iNKT cell activation and dampen the severity of vaso-occlusive (VO) crises. In a phase 2, randomized, placebo-controlled trial, we administered a 48-hour infusion of the A2AR agonist regadenoson (1.44 µg/kg per hour) to patients with SCD during VO crises to produce a plasma concentration of ∼5 nM, a concentration known from prior studies to suppress iNKT cell activation in SCD. The primary outcome measure was a >30% reduction in the percentage of activated iNKT cells. Ninety-two patients with SCD were randomized to receive a 48-hour infusion of regadenoson or placebo, in addition to standard-of-care treatment, during hospital admission for a VO crisis and had analyzable iNKT cell samples. The proportion of subjects who demonstrated a reduction of >30% in activated iNKT cells was not significantly different between the regadenoson and placebo arms (43% vs 23%; P = .07). There were also no differences between regadenoson and placebo groups in length of hospital stay, mean total opioid use, or pain scores. These data demonstrate that a low-dose infusion of regadenoson intended to reduce the activity of iNKT cells is not sufficient to produce a statistically significant reduction in such activation or in measures of clinical efficacy. This trial was registered at www.clinicaltrials.gov as #NCT01788631.

Thalassemia: a look to the future.

To assess the future of a clinical science one must first assess the rate of accrual of understanding in the past century. From the time of Cooley's description (1925) to 1964, the year of the first Symposium, progress was glacial because the molecular biology revolution in medicine was in its infancy and therapy other than transfusion was impossible. But between 1964 and 2015, progress has been huge on every front. Our patients ushered in the molecular biology revolution in medicine. They have benefited from far better understanding of molecular pathophysiology, substantial improvements in transfusion and chelation, more effective stem cell transplantation, the beginnings of gene therapy, and now major advances in our capacity to reinduce fetal hemoglobin. We have only lagged in the application of prevention technology in the less developed world that suffers the most from thalassemia and sickle cell disease. We must redouble our efforts to spare patients from these cruel diseases.

Advances in sickle cell therapies in the hydroxyurea era.

In the hydroxyurea era, insights into mechanisms downstream of erythrocyte sickling have led to new therapeutic approaches for patients with sickle cell disease (SCD). Therapies have been developed that target vascular adhesion, inflammation and hemolysis, including innovative biologics directed against P-selectin and invariant natural killer T cells. Advances in hematopoietic stem cell transplant and gene therapy may also provide more opportunities for cures in the near future. Several clinical studies are underway to determine the safety and efficacy of these new treatments. Novel approaches to treat SCD are desperately needed, since current therapies are limited and rates of morbidity and mortality remain high.

The role of adenosine signaling in sickle cell therapeutics.

Data suggest a role for adenosine signaling in the pathogenesis of sickle cell disease (SCD). Signaling through the adenosine A2A receptor (A2AR) has demonstrated beneficial effects. Activation of A2ARs decreases inflammation with SCD by blocking activation of invariant natural killer T cells. Decreased inflammation may reduce the severity of vasoocclusive crises. Adenosine signaling through the adenosine A2B receptor (A2BR) may be detrimental in SCD. Whether adenosine signaling predominantly occurs through A2ARs or A2BRs may depend on differing levels of adenosine and disease state (steady state versus crisis). There may be opportunities to develop novel therapeutic approaches targeting A2ARs and/or A2BRs for patients with SCD.

NF-κB is activated in CD4+ iNKT cells by sickle cell disease and mediates rapid induction of adenosine A2A receptors.

Reperfusion injury following tissue ischemia occurs as a consequence of vaso-occlusion that is initiated by activation of invariant natural killer T (iNKT) cells. Sickle cell disease (SDC) results in widely disseminated microvascular ischemia and reperfusion injury as a result of vaso-occlusion by rigid and adhesive sickle red blood cells. In mice, iNKT cell activation requires NF-κB signaling and can be inhibited by the activation of anti-inflammatory adenosine A2A receptors (A2ARs). Human iNKT cells are divided into subsets of CD4+ and CD4- cells. In this study we found that human CD4+ iNKT cells, but not CD4- cells undergo rapid NF-κB activation (phosphorylation of NF-κB on p65) and induction of A2ARs (detected with a monoclonal antibody 7F6-G5-A2) during SCD painful vaso-occlusive crises. These findings indicate that SCD primarily activates the CD4+ subset of iNKT cells. Activation of NF-κB and induction of A2ARs is concordant, i.e. only CD4+ iNKT cells with activated NF-κB expressed high levels of A2ARs. iNKT cells that are not activated during pVOC express low levels of A2AR immunoreactivity. These finding suggest that A2AR transcription may be induced in CD4+ iNKT cells as a result of NF-κB activation in SCD. In order to test this hypothesis further we examined cultured human iNKT cells. In cultured cells, blockade of NF-κB with Bay 11-7082 or IKK inhibitor VII prevented rapid induction of A2AR mRNA and protein upon iNKT activation. In conclusion, NF-κB-mediated induction of A2ARs in iNKT cells may serve as a counter-regulatory mechanism to limit the extent and duration of inflammatory immune responses. As activated iNKT cells express high levels of A2ARs following their activation, they may become highly sensitive to inhibition by A2AR agonists.

Hemoglobin disorders: a look to the future.

In this issue of Blood, Locatelli et al compare the results of histocompatible family donor bone marrow and cord blood transplants (BMT and CBT) for severe ß thalassemia (SBT) and sickle cell disease (SCD) as experienced by the Eurocord and European Blood and Marrow Transplantation group and collaborating centers in the United States, Hong Kong, and Israel between 1994 and 2005. Obviously, many changes in medical care and particularly MHC typing occurred over that decade, so this retrospective represents a moving target, but some firm points can be made for which we are indebted to this excellent group.

Sickle cell vaso-occlusion causes activation of iNKT cells that is decreased by the adenosine A2A receptor agonist regadenoson.

Adenosine A2A receptor (A2AR) agonists reduce invariant natural killer T (iNKT) cell activation and decrease inflammation in sickle cell disease (SCD) mice. We conducted a phase 1 trial of the A2AR agonist regadenoson in adults with SCD. The target dose was 1.44 µg/kg/h. iNKT cell activation was evaluated using antibodies targeting the p65 subunit of nuclear factor-κB (phospho-NF-κB p65), interferon-γ (IFN-γ), and A2AR. Regadenoson was administered to 27 adults with SCD. We examined 21 patients at steady state and 6 during painful vaso-occlusive crises (pVOC). iNKT cell activation was also measured in 14 African-American controls. During pVOC, the fraction of iNKT cells demonstrating increased phospho-NF-κB p65 and A2AR expression was significantly higher compared with controls (P < .01) and steady-state patients (P < .05). IFN-γ expression was also significantly higher compared with controls (P = .02). After a 24-hour infusion of regadenoson during pVOC, phospho-NF-κB p65 activation in iNKT cells decreased compared to baseline by a median of 48% (P = .03) to levels similar to controls and steady-state SCD. No toxicities were identified. Infusional regadenoson administered to adults with SCD at 1.44 µg/kg/h during pVOC decreases activation of iNKT cells without toxicity.

Exome sequencing identifies GATA1 mutations resulting in Diamond-Blackfan anemia.

Diamond-Blackfan anemia (DBA) is a hypoplastic anemia characterized by impaired production of red blood cells, with approximately half of all cases attributed to ribosomal protein gene mutations. We performed exome sequencing on two siblings who had no known pathogenic mutations for DBA and identified a mutation in the gene encoding the hematopoietic transcription factor GATA1. This mutation, which occurred at a splice site of the GATA1 gene, impaired production of the full-length form of the protein. We further identified an additional patient carrying a distinct mutation at the same splice site of the GATA1 gene. These findings provide insight into the pathogenesis of DBA, showing that the reduction in erythropoiesis associated with the disease can arise from causes other than defects in ribosomal protein genes. These results also illustrate the multifactorial role of GATA1 in human hematopoiesis.

Sickle cell disease (SCD), iNKT cells, and regadenoson infusion.

A humanized murine sickle cell-disease (SCD) model (NY1DD) has been used to study ischemia/reperfusion injury (IRI) in sickle cell anemia, and iNKT cells (a very small subset of murine and human T cells) have been found to instigate such injury in this model. Furthermore, levels of activated iNKT cells are generally elevated in the circulation of patients with SCD. Because activated iNKT cells are rich in adenosine A2A receptors which, when agonized, down-regulate the inflammatory cytokine expression that characterizes the cells, we have conducted a phase 1 trial of a constant infusion of low-dose regadenoson (an adenosine analogue with high A2A receptor specificity) to determine its safety and the capacity of a safe dose to down-regulate circulating iNKT cells in patients with SCD. We have found two dose rates that are both safe and effective and now plan a controlled Phase 2B clinical trial to determine whether our highest dose, administered as a 48-hour constant infusion, will induce faster remission in both painful vaso-occlusive crisis (pVOC) and acute chest syndrome (ACS).

Targeting iNKT cells for the treatment of sickle cell disease.

Sickle cell disease (SCD) causes widely disseminated vaso-occlusive episodes. Building on evidence implicating invariant NKT (iNKT) cells in the pathogenesis of ischemia/reperfusion injury, recent studies demonstrate that blockade of iNKT cell activation in mice with SCD reduces pulmonary inflammation and injury. In patients with SCD, iNKT cells in blood are increased in absolute number and activated in comparison to healthy controls. iNKT cell activation is reduced by agonists of adenosine 2A receptors (A(2A)Rs) such as the clinically approved coronary vasodilator, regadenoson. An ongoing multi-center, dose-finding and safety trial of infused regadenoson, has been initiated and is providing preliminary data about its safety and efficacy to treat SCD. Very high accumulation of adenosine may have deleterious effects in SCD through activation of adenosine 2B receptors that are insensitive to regadenoson. Future possible therapeutic approaches for treating SCD include selective A(2B)R antagonists and antibodies that deplete iNKT cells.

Diamond Blackfan anemia treatment: past, present, and future.

Despite significant improvements in our understanding of the pathophysiology of Diamond Blackfan anemia (DBA), there have been few advances in therapy. The cornerstones of treatment remain corticosteroids, chronic red blood cell transfusions, and hematopoietic stem cell transplantation, each of which is fraught with complications. In this article, we will review the history of therapies that have been offered to patients with DBA, summarize the current standard of care, including management of side effects, and discuss novel therapeutics that are being developed in the context of the research into the roles of ribosomal haplo-insufficiency and p53 activation in Diamond Blackfan anemia.

Thalassemia: an overview of 50 years of clinical research.

The thalassemias are attributable to the defective production of the α- and ß-globin polypeptides of hemoglobin. Significant discoveries have illuminated the pathophysiology and enhanced the prevention and treatment of the thalassemias, and this article reviews many of the advances that have occurred in the past 50 years. However, the application of new approaches to the treatment of these disorders has been slow, particularly in the developing world where the diseases are common, but there is definite progress. This article emphasizes how the increasing knowledge of cellular and molecular biology are facilitating the development of more effective therapies for these patients.

Sickle cell disease and stroke.

Twenty-four percent of sickle cell disease (SCD) patients have a stroke by the age of 45 years. Blood transfusions decrease stroke risk in patients deemed high risk by transcranial Doppler. However, transcranial Doppler has poor specificity, and transfusions are limited by alloimmunization and iron overload. Transfusion withdrawal may be associated with an increased rebound stroke risk. Extended blood typing decreases alloimmunization in SCD but is not universally adopted. Transfusions for thalassemia begun in early childhood are associated with lower rates of alloimmunization than are seen in SCD, suggesting immune tolerance. Optimal oxygen transport efficiency occurs at a relatively low hematocrit for SCD patients because of hyperviscosity. Consequently, exchange rather than simple transfusions are more effective in improving oxygen transport efficiency, but the former are technically more demanding and require more blood units. Although viscosity is of importance in the noncerebral manifestations of SCD, inflammation may play a larger role than viscosity in the development of large-vessel stroke. The future of SCD stroke management lies in the avoidance of transfusion. Hydroxyurea and anti-inflammatory measures may reduce the need for transfusion. Recent genome-wide association studies may provide methods for modulating fetal hemoglobin production enough to attenuate stroke risk and other complications of SCD.

Musings on genome medicine: cholesterol and coronary artery disease.

Cholesterol levels and not inflammatory markers are the major variables that pose a risk of coronary artery disease. Diabetes greatly increases the risk at any cholesterol level. Coronary artery disease and cancer are linked by a common protein - an apoptotic protein that also functions as a regulator of insulin secretion.

Musings on genome medicine: cancer genetics and the promise of effective treatment.

Cancer is the most common acquired genetic disease. Great progress has been made in documenting the genetic abnormalities that cause the disease, and in the future each tumor will be subjected to genetic analysis and the appropriate combination of drugs selected. Although there are serious technological and cost hurdles to surmount and resistance and continued mutation will be a constant problem, the way is clear to rational therapy.