Owen P. Smith

Mutations of JAK2 in acute lymphoblastic leukaemias associated with Down's syndrome

BACKGROUND Children with Downs syndrome have a greatly increased risk of acute megakaryoblastic and acute lymphoblastic leukaemias. Acute megakaryoblastic leukaemia in Downs syndrome is characterised by a somatic mutation in GATA1. Constitutive activation of the JAK/STAT (Janus kinase and signal transducer and activator of transcription) pathway occurs in several haematopoietic malignant diseases. We tested the hypothesis that mutations in JAK2 might be a common molecular event in acute lymphoblastic leukaemia associated with Downs syndrome. METHODS JAK2 DNA mutational analysis was done on diagnostic bone marrow samples obtained from 88 patients with Downs syndrome-associated acute lymphoblastic leukaemia; and 216 patients with sporadic acute lymphoblastic leukaemia, Downs syndrome-associated acute megakaryoblastic leukaemia, and essential thrombocythaemia. Functional consequences of identified mutations were studied in mouse haematopoietic progenitor cells. FINDINGS Somatically acquired JAK2 mutations were identified in 16 (18%) patients with Downs syndrome-associated acute lymphoblastic leukaemia. The only patient with non-Downs syndrome-associated leukaemia but with a JAK2 mutation had an isochromosome 21q. Children with a JAK2 mutation were younger (mean [SE] age 4.5 years [0.86] vs 8.6 years [0.59], p<0.0001) at diagnosis. Five mutant alleles were identified, each affecting a highly conserved arginine residue (R683). These mutations immortalised primary mouse haematopoietic progenitor cells in vitro, and caused constitutive Jak/Stat activation and cytokine-independent growth of BaF3 cells, which was sensitive to pharmacological inhibition with JAK inhibitor I. In modelling studies of the JAK2 pseudokinase domain, R683 was situated in an exposed conserved region separated from the one implicated in myeloproliferative disorders. INTERPRETATION A specific genotype-phenotype association exists between the type of somatic mutation within the JAK2 pseudokinase domain and the development of B-lymphoid or myeloid neoplasms. Somatically acquired R683 JAK2 mutations define a distinct acute lymphoblastic leukaemia subgroup that is uniquely associated with trisomy 21. JAK2 inhibitors could be useful for treatment of this leukaemia. FUNDING Israel Trade Ministry, Israel Science Ministry, Jewish National Fund UK, Sam Waxman Cancer Research Foundation, Israel Science Foundation, Israel Cancer Association, Curtis Katz, Constantiner Institute for Molecular Genetics, German-Israel Foundation, and European Commission FP6 Integrated Project EUROHEAR.

Activated protein C inhibits lipopolysaccharide-induced nuclear translocation of nuclear factor kappaB (NF-kappaB) and tumour necrosis factor alpha (TNF-alpha) production in the THP-1 monocytic cell line

Activated protein C (APC) protects against sepsis in animal models and inhibits the lipopolysacharide (LPS)‐induced elaboration of proinflammatory cytokines from monocytes. The molecular mechanism responsible for this property is unknown. We assessed the effect of APC on LPS‐induced tumour necrosis factor α (TNF‐α) production and on the activation of the central proinflammatory transcription factor nuclear factor‐κB (NF‐κB) in a THP‐1 cell line. Cells were preincubated with varying concentrations of APC (200 µg/ml, 100 µg/ml and 20 µg/ml) before addition of LPS (100 ng/ml and 10 µg/ml). APC inhibited LPS‐induced production of TNF‐α both in the presence and absence of fetal calf serum (FCS), although the effect was less marked with 10% FCS. APC also inhibited LPS‐induced activation of NF‐κB, with APC (200 µg/ml) abolishing the effect of LPS (100 ng/ml). The ability of APC to inhibit LPS‐induced translocation of NF‐κB is likely to be a significant event given the critical role of the latter in the host inflammatory response.

Use of protein-C concentrate, heparin, and haemodiafiltration in meningococcus-induced purpura fulminans

BACKGROUND Inflammatory and coagulation processes are both affected in meningococcaemia. Severe acquired protein-C deficiency in meningococcaemia is usually associated with substantial mortality: in survivors, skin grafts, amputation, and end-organ failure are not uncommon. Protein C is a natural anticoagulant and also has important anti-inflammatory activity. We assessed the effects of early replacement therapy with protein-C concentrate together with continuous veno-venous haemodiafiltration and conventional treatment in meningococcaemia. METHODS 12 patients aged between 3 months and 27 years with meningococcaemia and severe acquired protein-C deficiency (mean 0.20 IU/mL) were studied. All patients had septic shock, widespread purpura, skin necrosis, and disseminated intravascular coagulopathy. After a test dose of protein-C concentrate, patients received a continuous infusion with the dose adjusted daily to keep the plasma concentration between 0.8 and 1.2 IU/mL. 11 patients were given unfractionated intravenous heparin (10-15 IU kg-1 h-1). Nine patients had haemodiafiltration and one had peritoneal dialysis. The Glasgow meningococcal septicaemia prognostic score and the paediatric risk of mortality score predicted a minimum mortality of 80% and 57%, respectively. FINDINGS No patient died. No adverse reactions to the treatment were seen. Two patients had lower-limb amputations, one of whom had a thrombotic cerebrovascular accident; both patients had received the protein-C concentrate and heparin later than the rest of the group (60 h [16.97] vs 12 h [3.13]). One patient developed chronic renal failure despite receiving protein-C infusion 15 h after admission. INTERPRETATION The acquired severe deficiency of protein C in meningococcaemia contributes to the pathogenesis of the thrombotic necrotic lesions in the skin and other organs and probably has an important role in the inflammatory response. Protein-C therapy is merely one approach to improve the host response in this syndrome. We suggest that a double-blind, randomised, controlled multicentre trial is needed to confirm our results.

X-linked lymphoproliferative disease due to SAP/SH2D1A deficiency: a multicenter study on the manifestations, management and outcome of the disease

X-linked lymphoproliferative disease (XLP1) is a rare immunodeficiency characterized by severe immune dysregulation and caused by mutations in the SH2D1A/SAP gene. Clinical manifestations are varied and include hemophagocytic lymphohistiocytosis (HLH), lymphoma and dysgammaglobulinemia, often triggered by Epstein-Barr virus infection. Historical data published before improved treatment regimens shows very poor outcome. We describe a large cohort of 91 genetically defined XLP1 patients collected from centers worldwide and report characteristics and outcome data for 43 patients receiving hematopoietic stem cell transplant (HSCT) and 48 untransplanted patients. The advent of better treatment strategies for HLH and malignancy has greatly reduced mortality for these patients, but HLH still remains the most severe feature of XLP1. Survival after allogeneic HSCT is 81.4% with good immune reconstitution in the large majority of patients and little evidence of posttransplant lymphoproliferative disease. However, survival falls to 50% in patients with HLH as a feature of disease. Untransplanted patients have an overall survival of 62.5% with the majority on immunoglobulin replacement therapy, but the outcome for those untransplanted after HLH is extremely poor (18.8%). HSCT should be undertaken in all patients with HLH, because outcome without transplant is extremely poor. The outcome of HSCT for other manifestations of XLP1 is very good, and if HSCT is not undertaken immediately, patients must be monitored closely for evidence of disease progression.

Recombinant FVIIa in the management of uncontrolled hemorrhage

BACKGROUND: Recombinant FVIIa (rFVIIa/NovoSeven) is a novel hemostatic agent originally developed to treat patients with hemophilia who had developed inhibitors. Several case reports have suggested that rFVIIa may be effective in treating patients without a pre‐existing bleeding disorder who have uncontrolled bleeding.

Elevated factor VIII levels and risk of venous thrombosis.

Modern thrombophilia testing fails to identify any underlying prothrombotic tendency in a significant number of patients presenting with objectively confirmed venous thromboemboembolism (VTE). This observation has led to a search for other novel inherited or acquired human thrombophilias. Although a number of putative mechanisms have been described, the evidence behind many of these candidates remains weak. In contrast, an increasing body of work supports the hypothesis that increased plasma factor VIII (FVIII) levels may be important in this context. An association between elevated plasma FVIII levels and VTE was first described in the Leiden Thrombophilia Study (LETS). Subsequently, these conclusions have been supported by an increasing number of independent case–control studies. Cumulatively, these studies have clearly demonstrated that high FVIII levels constitute a prevalent, dose‐dependent risk factor for VTE. Furthermore, more recent studies have shown that the risk of recurrent venous thrombosis is also significantly increased in patients with high FVIII levels. In this review, we present the evidence supporting the hypothesis that elevated FVIII levels constitute a clinically important thrombophilia. In addition, we examine the biological mechanisms that may underlie persistently elevated FVIII levels, and the pathways through which high FVIII may serve to increase thrombotic risk.

Infectious purpura fulminans: diagnosis and treatment.

Purpura fulminans is a term used to describe an acute, often lethal, syndrome of disseminated intravascular coagulation (DIC) and purpuric skin. The skin lesion is rapidly progressive, characterized by microvascular thrombosis in the dermis which ultimately results in perivascular haemorrhage and necrosis with minimal inflammation. Clinically the lesion can be distinguished from simple haemorrhage into the skin, in that the lesions of purpura fulminans are usually raised, indurated, and have a circumferential area of redness, and over time the lesions coalesce, blister and break down reflecting tissue necrosis. Although these lesions are frequently attributed to haemorrhage, skin biopsies clearly reveal that the pathophysiological lesions are in fact dermal vessel thromboses. The microvasculature of other body organs is also affected which ultimately results in necrosis and dysfunction. Inherited and acquired abnormalities of the protein C (PC) anticoagulant pathway are now believed to be responsible for the majority of patients with this clinical syndrome. The three commonest clinical situations where purpura fulminans is seen are severe bacterial infections, especially meningococcal disease, homozygous PC or protein S (PS) deficiency and autoimmune PS or PC deficiency. Rarer clinical conditions associated with purpura fulminans include warfarin-induced skin necrosis, cholestasis and antiphospholipid syndrome (Adcock & Hicks, 1990).

Low-molecular weight and unfractionated heparins induce a downregulation of inflammation: decreased levels of proinflammatory cytokines and nuclear factor-κB in LPS-stimulated human monocytes

Unfractionated heparin (UFH) and low‐molecular weight heparin (LMWH) are well defined anticoagulant agents. Recent data suggest that both LMWH and UFH may also have potent anti‐inflammatory properties; however, their mechanism of action responsible for the anti‐inflammatory effect is not yet fully elucidated. This study was designed to assess the effect of LMWH and UFH on human monocytes production of inflammatory markers and nuclear translocation of nuclear factor (NF)‐κB. Cultured monocytes were pretreated for 15 min with LMWH or UFH (10 μg and 1 μg/million cells) before stimulation with lipopolysaccharide (LPS) at a dose of 1 ng/million cells. Proinflammatory cytokines tumour necrosis factor (TNF)‐α, interleukin (IL)‐8, IL‐6 and IL‐1β release were subsequently measured by enzyme‐linked immunosorbent assay at 6 h, and nuclear translocation of the proinflammatory NF‐κB was assessed at 2 h. Treatment with pharmacological doses of LMWH and UFH significantly attenuated LPS‐induced production of TNF‐α, IL‐8, IL‐6 and IL‐1β as well as NF‐κB translocation. These results indicate equivalent and significant heparin anti‐inflammatory properties at low doses on monocyte‐mediated immune response. The inhibition of NF‐κB activation certainly represents one of the mechanisms by which heparin exerts its anti‐inflammatory effect. LMWH and UFH therefore appear as potential therapeutic inhibitors of inflammation.

Prevalence, clinical characteristics, and prognosis of GATA2-related myelodysplastic syndromes in children and adolescents

Germline GATA2 mutations cause cellular deficiencies with high propensity for myeloid disease. We investigated 426 children and adolescents with primary myelodysplastic syndrome (MDS) and 82 cases with secondary MDS enrolled in 2 consecutive prospective studies of the European Working Group of MDS in Childhood (EWOG-MDS) conducted in Germany over a period of 15 years. Germline GATA2 mutations accounted for 15% of advanced and 7% of all primary MDS cases, but were absent in children with MDS secondary to therapy or acquired aplastic anemia. Mutation carriers were older at diagnosis and more likely to present with monosomy 7 and advanced disease compared with wild-type cases. For stratified analysis according to karyotype, 108 additional primary MDS patients registered with EWOG-MDS were studied. Overall, we identified 57 MDS patients with germline GATA2 mutations. GATA2 mutations were highly prevalent among patients with monosomy 7 (37%, all ages) reaching its peak in adolescence (72% of adolescents with monosomy 7). Unexpectedly, monocytosis was more frequent in GATA2-mutated patients. However, when adjusted for the selection bias from monosomy 7, mutational status had no effect on the hematologic phenotype. Finally, overall survival and outcome of hematopoietic stem cell transplantation (HSCT) were not influenced by mutational status. This study identifies GATA2 mutations as the most common germline defect predisposing to pediatric MDS with a very high prevalence in adolescents with monosomy 7. GATA2 mutations do not confer poor prognosis in childhood MDS. However, the high risk for progression to advanced disease must guide decision-making toward timely HSCT.

A Novel Primary Immunodeficiency with Specific Natural-Killer Cell Deficiency Maps to the Centromeric Region of Chromosome 8

We describe four children with a novel primary immunodeficiency consisting of specific natural-killer (NK) cell deficiency and susceptibility to viral diseases. One child developed an Epstein-Barr virus-driven lymphoproliferative disorder; two others developed severe respiratory illnesses of probable viral etiology. The four patients are related and belong to a large inbred kindred of Irish nomadic descent, which suggests autosomal recessive inheritance of this defect. A genomewide scan identified a single 12-Mb region on chromosome 8p11.23-q11.21 that was linked to this immunodeficiency (maximum LOD score 4.51). The mapping of the disease-causing genomic region paves the way for the identification of a novel pathway governing NK cell differentiation in humans.