Joshua J. Field

NKT cells mediate pulmonary inflammation and dysfunction in murine sickle cell disease through production of IFN-γ and CXCR3 chemokines

Ischemia-reperfusion injury (IRI) triggers an inflammatory cascade that is initiated by the activation of CD1d-restricted iNKT cells. In sickle cell disease (SCD), misshapen erythrocytes evoke repeated transient bouts of microvascular IRI. Compared with C57BL/6 controls, NY1DD mice have more numerous and activated (CD69(+), interferon-gamma(+) [IFN-gamma(+)]) lung, liver, and spleen iNKT cells that are hyperresponsive to hypoxia/reoxygenation. NY1DD mice have increased pulmonary levels of IFN-gamma, IFN-gamma-inducible chemokines (CXCL9, CXCL10), and elevated numbers of lymphocytes expressing the chemokine receptor CXCR3. Treating NY1DD mice with anti-CD1d antibody to inhibit iNKT cell activation reverses baseline pulmonary dysfunction manifested as elevated vascular permeability, decreased arterial oxygen saturation, and increased numbers of activated leukocytes. Anti-CD1d antibodies decrease pulmonary levels of IFN-gamma and CXCR3 chemokines. Neutralization of CXCR3 receptors ameliorates pulmonary dysfunction. Crossing NY1DD to lymphocyte-deficient Rag1(-/-) mice decreases pulmonary dysfunction. This is counteracted by the adoptive transfer of 1 million NKT cells. Like mice, people with SCD have increased numbers of activated circulating iNKT cells expressing CXCR3. Together, these data indicate that iNKT cells play a pivotal role in sustaining inflammation in SCD mice by a pathway involving IFN-gamma and production of chemotactic CXCR3 chemokines and that this mechanism may translate to human disease.

P-Selectin–Mediated Platelet-Neutrophil Aggregate Formation Activates Neutrophils in Mouse and Human Sickle Cell Disease*

Objective—To determine the role of platelets in stimulating mouse and human neutrophil activation and pulmonary injury in sickle cell disease (SCD). Methods and Results—Both platelet and neutrophil activation occur in SCD, but the interdependence of these events is unknown. Platelet activation and binding to leukocytes were measured in mice and patients with SCD and in controls. Relative to controls, blood obtained from mice or patients with SCD contained significantly elevated platelet-neutrophil aggregates (PNAs). Both platelets and neutrophils found in sickle PNAs were activated. Multispectral imaging (ImageStream) and conventional flow cytometry revealed a subpopulation of activated neutrophils with multiple adhered platelets that expressed significantly more CD11b and exhibited greater oxidative activity than single neutrophils. On average, wild-type and sickle PNAs contained 1.1 and 2.6 platelets per neutrophil, respectively. Hypoxia/reoxygenation induced a further increase in PNAs in mice with SCD and additional activation of both platelets and neutrophils. The pretreatment of mice with SCD with clopidogrel or P-selectin antibody reduced the formation of PNAs and neutrophil activation and decreased lung vascular permeability. Conclusion—Our findings suggest that platelet binding activates neutrophils and contributes to a chronic inflammatory state and pulmonary dysfunction in SCD. The inhibition of platelet activation may be useful to decrease tissue injury in SCD, particularly during the early stages of vaso-occlusive crises.

Risk factors for hospital readmission within 30 days: A new quality measure for children with sickle cell disease†

The National Association of Childrens Hospitals and Related Institutions (NACHRI) established hospital readmission within 30 days as a benchmark for quality care in children with Sickle Cell Disease (SCD). Among children with SCD, limited data exists to identify risk factors for readmission and whether they are modifiable.

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.

Sustained response with rituximab in patients with thrombotic thrombocytopenic purpura: A report of 13 cases and review of the literature

Idiopathic thrombotic thrombocytopenic purpura (TTP) is a life‐threatening disease mediated by autoantibodies directed against ADAMTS‐13. A number of small series and case reports have shown promising results with rituximab in refractory or relapsed TTP. In this report, we present 13 patients with TTP treated with rituximab. Twelve of the 13 patients (92%) achieved complete response; no subsequent relapses occurred with median follow‐up of 24 months (range, 13–84 months). The addition of rituximab to standard therapy appears to be effective in sustaining long‐term remission in TTP. However, the optimal dosing and timing of rituximab warrant further investigation. Am. J. Hematol., 2009.

Airway Hyperresponsiveness in Children With Sickle Cell Anemia

BACKGROUND The high prevalence of airway hyperresponsiveness (AHR) among children with sickle cell anemia (SCA) remains unexplained. METHODS To determine the relationship between AHR, features of asthma, and clinical characteristics of SCA, we conducted a multicenter, prospective cohort study of children with SCA. Dose response slope (DRS) was calculated to describe methacholine responsiveness, because 30% of participants did not achieve a 20% decrease in FEV1 after inhalation of the highest methacholine concentration, 25 mg/mL. Multiple linear regression analysis was done to identify independent predictors of DRS. RESULTS Methacholine challenge was performed in 99 children with SCA aged 5.6 to 19.9 years (median, 12.8 years). Fifty-four (55%) children had a provocative concentration of methacholine producing a 20% decrease in FEV1<4 mg/mL. In a multivariate analysis, independent associations were found between increased methacholine responsiveness and age (P<.001), IgE (P=.009), and lactate dehydrogenase (LDH) levels (P=.005). There was no association between methacholine responsiveness and a parent report of a doctor diagnosis of asthma (P=.986). Other characteristics of asthma were not associated with methacholine responsiveness, including positive skin tests to aeroallergens, exhaled nitric oxide, peripheral blood eosinophil count, and pulmonary function measures indicating airflow obstruction. CONCLUSIONS In children with SCA, AHR to methacholine is prevalent. Younger age, serum IgE concentration, and LDH level, a marker of hemolysis, are associated with AHR. With the exception of serum IgE, no signs or symptoms of an allergic diathesis are associated with AHR. Although the relationship between methacholine responsiveness and LDH suggests that factors related to SCA may contribute to AHR, these results will need to be validated in future studies.

Rituximab for the treatment of patients with very high-titre acquired factor VIII inhibitors refractory to conventional chemotherapy

Summary.  Acquired factor VIII (FVIII) inhibitors are a rare cause of coagulopathy which are associated with a high mortality rate. Treatment of bleeding episodes is often difficult and may vary with the degree of titre elevation. Individuals with very high‐titre antibodies [>100 Bethesda units mL−1 (BU)] may have difficulty achieving a complete sustained remission and, consequently, various treatments including immunosuppression, cytotoxic chemotherapy and plasmapheresis have been reported. Rituximab is an anti‐CD20 monoclonal antibody which has demonstrated efficacy in the treatment of individuals with acquired FVIII inhibitors, however there is limited data in the subgroup of patients with inhibitor titres >100 BU. In this study, we present four patients with acquired FVIII inhibitor titres >100 BU who were resistant to initial therapy with cyclophosphamide, vincristine and prednisone. The patients’ inhibitor titres ranged from 249 BU mL−1 to 725 BU mL−1 and all received 4 weekly infusions of rituximab at 375 mg m−2. Each patient partially responded to rituximab therapy with an improvement in inhibitor titres and FVIII activity, however, three of the four patients relapsed thereafter. The individual who did not relapse achieved a partial response for 13 months and then died of causes unrelated to her coagulopathy. We conclude that in patients with acquired FVIII inhibitors and titres >100 BU, treatment with rituximab alone is effective but not sufficient to achieve a sustained response. Rituximab in combination with other therapies may provide a better result in this high‐risk population.

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.

Acute pain in children and adults with sickle cell disease: management in the absence of evidence-based guidelines

Purpose of reviewAcute, vaso-occlusive pain is the most characteristic complication of sickle cell disease (SCD). Although there has been rigorous work examining the pathogenesis of vaso-occlusion, fewer studies have focused on approaches to the clinical management of acute pain. In this review, we will examine the epidemiology and management strategies of acute pain events and we will identify limitations in the best available studies. Recent findingsMost acute pain events in adults with SCD are managed at home without physician contact. Prior descriptions of the natural history of pain episodes from the Cooperative Study of Sickle Cell Disease relied on physician contact, limiting the generalizability of these findings to current practice. Patient-controlled analgesia has replaced on-demand therapy to become the standard for management of severe pain events in children and adults with SCD requiring hospital admission. SummaryUnfortunately, most clinical practice guidelines for the management of acute pain are not based on randomized clinical trials. As a result, our practice of pain management is primarily limited to expert opinion and inferences from observational studies. Additional clinical trials in management of acute pain in children and adults with SCD are critical for the development of evidence-based guidelines.

Recurrent, severe wheezing is associated with morbidity and mortality in adults with sickle cell disease.

Prior studies of asthma in children with sickle cell disease (SCD) were based on reports of a doctor‐diagnosis of asthma with limited description of asthma features. Doctor‐diagnoses of asthma may represent asthma or wheezing unrelated to asthma. Objectives of this study were to determine if asthma characteristics are present in adults with a doctor‐diagnosis of asthma and/or wheezing, and to examine the relationship between doctor‐diagnosis of asthma, wheezing and SCD morbidity. This was an observational cohort study of 114 adults with SCD who completed respiratory symptom questionnaires and had serum IgE measurements. A subset of 79 participants completed pulmonary function testing. Survival analysis was based on a mean prospective follow‐up of 28 months and data were censored at the time of death or loss to follow‐up. Adults reporting a doctor‐diagnosis of asthma (N = 34) were more likely to have features of asthma including wheeze, eczema, family history of asthma, and an elevated IgE level (all P < 0.05). However, there was no difference in pain or ACS rate, lung function, or risk of death between adults with and without a doctor‐diagnosis of asthma. In contrast, adults who reported recurrent, severe episodes of wheezing (N = 34), regardless of asthma, had twice the rates of pain and ACS, decreased lung function and increased risk of death compared with adults without recurrent, severe wheezing. Asthma features were not associated with recurrent, severe wheezing. Our data suggest that wheezing in SCD may occur independently of asthma and is a marker of disease severity. Am. J. Hematol. 2011.