Induction of megakaryocytes to synthesize and store a releasable pool of human factor VIII

von Willebrand factor (VWF) is a complex plasma glycoprotein that modulates platelet adhesion at the site of a vascular injury, and it also serves as a carrier protein for factor (F)VIII. As megakaryocytes are the only hematopoietic lineage to naturally synthesize and store VWF within alpha-granules, this study was performed to determine if expression of a FVIII transgene in megakaryocytes could lead to trafficking and storage of FVIII with VWF in platelet alpha-granules. Isolex selected CD34+ cells from human G-CSF mobilized peripheral blood cells (PBC) and murine bone marrow were transduced with a retrovirus encoding the B-domain deleted form of human FVIII (BDD-FVIII). Cells were then induced with cytokines to form a population of multiple lineages including megakaryocytes. Chromogenic analysis of culture supernatant from FVIII-transduced human cells demonstrated synthesis of functional FVIII. Treatment of cells with agonists of platelet activation (ADP, epinephrine, and thrombin receptor-activating peptide) resulted in the release of VWF antigen and active FVIII into the supernatant from transduced cells. Immunofluorescence analysis of cultured human and murine megakaryocytes revealed a punctate pattern of staining for FVIII that was consistent with staining for VWF. Electron microscopy of transduced megakaryocytes using immunogold-conjugated antibodies colocalized FVIII and VWF within the alpha-granules. FVIII retained its association with VWF in human platelets isolated from the peripheral blood of NOD/SCID mice at 2-6 weeks post-transplant of transduced human PBC. These results suggest feasibility for the development of a locally inducible secretory pool of FVIII in platelets of patients with hemophilia A.

Joint range-of-motion limitations among young males with hemophilia: prevalence and risk factors

Chronic joint disease from repeated bleeding into joints is a serious complication of hemophilia. To measure the extent of and to identify risk factors for deviations from normal in joint range of motion (ROM), we used cross-sectional data collected from 4343 males with hemophilia aged 2 to 19 years who received care at 136 US hemophilia treatment centers (HTCs). Factors examined included age, race/ethnicity, family history, insurance status, age at diagnosis and first HTC visit, frequency of HTC visits, hemophilia type, bleeding frequency, prophylaxis use, inhibitor status, body mass index (BMI), and recent orthopedic procedures. Trained personnel using a standard protocol obtained ROM measurements on 10 joints (hips, knees, shoulders, elbows, and ankles). Analyses used multiple linear regression to model overall ROM limitation separately by disease severity. For persons in all severity groups, joint ROM limitation was positively associated with older age, nonwhite race, and increased BMI. For those with severe disease, ROM limitation was also positively associated with number of bleeds and was greater for those with inhibitors or recent orthopedic procedures. We conclude that ROM limitations begin at an early age, especially for those with severe and moderate disease, and that BMI is an important, potentially modifiable risk factor.

Gene therapy for platelet disorders: studies with Glanzmann's thrombasthenia

Current research aimed at correcting platelet defects are designed to further our knowledge in the use of hematopoietic stem cells for gene therapies of hemorrhagic disorders. Information gained from these studies may be directly applicable to treatment of disorders affecting platelets (e.g. Glanzmann's thrombasthenia, Bernard Soulier syndrome, gray platelet syndrome, and von Willebrand disease) as well as other disorders affecting distinct hematopoietic cell lineages. This work specifically addresses three questions: (i) can bone marrow stem cells be given sufficient genetic information to induce abnormal megakaryocytes to synthesize transgene products that help newly formed platelets to participate in normal hemostasis? (ii) can the newly synthesized receptor be maintained as a platelet-specific protein at therapeutic levels for a reasonable period of time? and (iii) will newly expressed proteins be tolerated by the immune system or become a target for B- and T-cell mediated immunity resulting in the premature destruction and clearing of the genetically altered megakaryocytes and platelets? Answers to these questions should indicate the feasibility of targeting platelets with genetic therapies that will in turn enable better management of patients with inherited bleeding disorders. The long-range benefit of this research will be an improved understanding of the regulation of protein expression during normal megakaryocytopoiesis, and the accumulation of additional scientific knowledge about normal platelet function and the way in which platelets and other cells recognize and interact with each other.

Phase 1 trial of FVIII gene transfer for severe hemophilia A using a retroviral construct administered by peripheral intravenous infusion

In a phase 1 dose escalation study, 13 subjects with hemophilia A received by peripheral intravenous infusion a retroviral vector carrying a B-domain-deleted human factor VIII (hFVIII) gene. Infusions were well tolerated. Tests for replication competent retrovirus have been negative. Polymerase chain reaction (PCR) analyses demonstrate the persistence of vector gene sequences in peripheral blood mononuclear cells in 3 of 3 subjects tested. Factor VIII was measured in serial samples using both a one-stage clotting assay and a chromogenic assay. While no subject had sustained FVIII increases, 9 subjects had FVIII higher than 1% on at least 2 occasions 5 or more days after infusion of exogenous FVIII, with isolated levels that ranged from 2.3% to 19%. Pharmacokinetic parameters of exogenous FVIII infused into subjects 13 weeks after vector infusion showed an increased half-life (T1/2; P <.02) and area under the curve (AUC, P <.04) compared with prestudy values. Bleeding frequency decreased in 5 subjects compared with historical rates. These results demonstrate that this retroviral vector (hFVIII(V)) is safe and, in some subjects, persists more than a year in peripheral blood mononuclear cells, with measurable factor VIII levels and with increased available FVIII activity (increased T1/2 and AUC) after infusion of exogenous FVIII concentrate.

The ras-binding domain of ral GDS-like protein-2 as a ras inhibitor in smooth muscle cells

This study was undertaken to determine whether the response of smooth muscle cells to mitogens can be inhibited by inactivating ras with the ral GDS like protein-2 ras-binding domain (RGL2-RBD). RGL2 is a member of the ral GDS family of proteins that contains a carboxy terminal ras-binding domain which binds the GTP ligated form of ras and rap and a CDC25 homology domain with the structural features of a guanine nucleotide exchange factor. The effect of ras signaling on the smooth muscle cell growth factor response was studied using rat aortic A10 smooth muscle cells transfected with a plasmid that encoded the RGL2-RBD. RGL2-RBD transfection resulted in a 12-fold reduction in the number of clonal colonies that were obtained after selection, and dramatically slowed cell cycle progression. RGBL2-RBD reduced DNA synthesis and inhibited platelet derived growth factor (PDGF)-mediated activation of the MAPK pathway. These findings indicated that interfering with ras signaling inhibits smooth muscle cell proliferation and raise the possibility that ras signaling inhibition might be used therapeutically to control smooth muscle proliferation after vascular injury.

Bleeding due to disruption of a cargo-specific ER-to-Golgi transport complex

Mutations in LMAN1 (also called ERGIC-53) result in combined deficiency of factor V and factor VIII (F5F8D), an autosomal recessive bleeding disorder characterized by coordinate reduction of both clotting proteins. LMAN1 is a mannose-binding type 1 transmembrane protein localized to the endoplasmic reticulum-Golgi intermediate compartment (ERGIC; refs. 2,3), suggesting that F5F8D could result from a defect in secretion of factor V and factor VIII (ref. 4). Correctly folded proteins destined for secretion are packaged in the ER into COPII-coated vesicles, which subsequently fuse to form the ERGIC. Secretion of certain abundant proteins suggests a default pathway requiring no export signals (bulk flow; refs. 6,7). An alternative mechanism involves selective packaging of secreted proteins with the help of specific cargo receptors. The latter model would be consistent with mutations in LMAN1 causing a selective block to export of factor V and factor VIII. But approximately 30% of individuals with F5F8D have normal levels of LMAN1, suggesting that mutations in another gene may also be associated with F5F8D. Here we show that inactivating mutations in MCFD2 cause F5F8D with a phenotype indistinguishable from that caused by mutations in LMAN1. MCFD2 is localized to the ERGIC through a direct, calcium-dependent interaction with LMAN1. These findings suggest that the MCFD2-LMAN1 complex forms a specific cargo receptor for the ER-to-Golgi transport of selected proteins.

Identification of T-cell epitopes in clotting factor IX and lack of tolerance in inbred mice

Immune responses to the factor IX protein pose problems for hemophilia B patients who develop antibodies against factor IX and for potential future treatment with gene therapy. To better define the response to human factor IX, we analyzed T-cell responses to human factor IX in factor IX knockout mice on BALB/c and C57BL/6 (B6) backgrounds, both strains having CD4+ T cells that proliferate in response to human factor IX. Surprisingly, wild-type mice have similar factor IX-recognizing CD4+ T cells. We defined a dominant CD4+ epitope for each strain (CVETGVKITVVAGEH for BALB/c and LLELDEPLVLNSYVTPIC for B6) that was recognized by both factor IX knockout and wild-type mice. While human factor IX did not cross-react with the mouse homologs of these epitopes, immunization with peptides from murine factor IX stimulated proliferation in factor IX knockout mice and wild-type mice, demonstrating a failure to delete murine factor IX-specific T cells in normal mice.

Hepatitis C in adults and adolescents with hemophilia: a randomized, controlled trial of interferon alfa-2b and ribavirin

Adolescents and adults with inherited disorders of coagulation have one of the highest prevalence rates of hepatitis C among known risk groups. Few data are available on the use of combination therapy with interferon and ribavirin in this population. Patients 13 years of age and older who were positive for hepatitis C virus (HCV) RNA by polymerase chain reaction and negative for human immunodeficiency virus were randomized to receive interferon alfa-2b (3 million units 3 times a week) plus ribavirin (1,000 mg/day) or interferon alfa-2b alone for 48 weeks with 24 weeks of posttreatment follow-up. Patients started on interferon alone who remained positive for HCV RNA at week 12 crossed over to treatment with interferon plus ribavirin. A total of 113 patients were treated. Thirty-seven patients were younger than 18 years. At the end of treatment, 18 of 56 (32%) treated with interferon plus ribavirin and 6 of 57 (11%) treated with interferon alone were negative for HCV RNA (P =.005). Sustained virologic response in the combination arm was 29% (16 of 56) compared with 7% (4 of 57) for those started on interferon alone (P =.027). Among adolescents younger than 18 years who were treated with combination therapy, 10 of 17 (59%) had sustained response compared with 6 of 39 (15%) of adult patients on the same regimen (P =.001). In conclusion, in this U.S. multicenter, randomized trial of therapy for HCV in patients with inherited bleeding disorders, sustained virologic response rate was significantly improved for patients treated with interferon and ribavirin compared with those started on interferon alone. Adolescents treated with combination therapy had a significantly higher sustained response than adults did on the same regimen.

Clinical use of a rapid collagen binding assay for von Willebrand factor cleaving protease in patients with thrombotic thrombocytopenic purpura

A simple collagen binding assay (CBA) for measuring activity of the von Willebrand factor cleaving protease in clinical samples is described, and results of fifty masked plasmapheresis samples rom patients with TTP/HUS and other diseases are presented. There was 97.5% concordance between the CBA and a multimer gel assay. The CBA identified low protease activity in 78% of patients who had a clinical syndrome consistent with TTP/HUS and in 2 of 10 sick controls, giving it a positive predictive value of 0.94. The heterogeneity regarding the presence or absence of vWF protease activity in patients with TTP/HUS was confirmed by finding a low negative predictive value of 0.50 with the CBA. The CBA detected inhibitors of the protease in 26 of 29 patients (90%) with TTP/HUS and low protease activity levels. The CBA is a useful clinical assay for examining von Willebrand factor protease activity and detecting inhibitors against the protease.

End-stage liver disease in persons with hemophilia and transfusion-associated infections

Many persons with hemophilia were infected with hepatitis C and B viruses (HCV, HBV) and HIV, but the consequences of these transfusion-acquired infections are poorly defined. We estimated the risk of HCV-related end-stage liver disease (ESLD) and the associations of age, HBV, and HIV with that risk. All 1816 HCV-seropositive hemophilic patients at 16 centers were followed for up to 16 years. Of these, 624 were HIV(-) and 1192 were HIV-coinfected; 135 had persistent HBV surface antigenemia, 1374 had resolved HBV infection, and 287 were HBV-uninfected. ESLD was defined as bleeding esophageal varices, hepatic encephalopathy, persistent ascites, or death excluding nonhepatic causes of these conditions. Competing risk models were used to estimate the annual hazard rate and cumulative incidence of ESLD. Proportional hazards models were used to estimate relative hazards of ESLD with covariates. ESLD developed in 127 of the HCV/HIV-coinfected participants, with an estimated 16-year cumulative incidence of 14.0% (95% confidence interval [CI], 11.6%-16.4%). Without HIV, 10 HCV-infected participants developed ESLD, for a significantly lower cumulative incidence of 2.6% (95% CI, 1.0%-4.3%, P <.0001). ESLD risk increased steeply with age in both groups. With HIV, ESLD risk was increased 8.1-fold (95% CI, 1.9-35.2) with HBV surface antigenemia, 2.1-fold (95% CI, 1.3-3.3) with fewer than 0.2 x 10(9)/L (200/microL) CD4(+) lymphocytes, and 1.04-fold (95% CI, 1.03-1.06) per year of age. Thus, HIV is associated with a markedly increased risk of HCV-related ESLD for persons with hemophilia, particularly with HBV infection, low CD4(+) lymphocytes, or older age.

Hemophilia gene therapy: update

Gene transfer is an exciting and potentially important treatment approach for hemophilia A and B. Four phase I clinical trials of the safety of gene transfer in hemophilia A or B have been completed and two more trials are currently underway. The results of these trials indicate that gene transfer in hemophilia with the vectors and doses used is safe and well tolerated. Efforts continue to understand the basic biology and improve the efficiency of gene transfer.

Relationships between Rap1b, affinity modulation of integrin alpha IIbbeta 3, and the actin cytoskeleton

The affinity of integrin alpha(IIb)beta(3) for fibrinogen is controlled by inside-out signals that are triggered by agonists like thrombin. Agonist treatment of platelets also activates Rap1b, a small GTPase known to promote integrin-dependent adhesion of other cells. Therefore, we investigated the role of Rap1b in alpha(IIb)beta(3) function by viral transduction of GFP-Rap1 chimeras into murine megakaryocytes, which exhibit inside-out signaling similar to platelets. Expression of constitutively active GFP-Rap1b (V12) had no effect on unstimulated megakaryocytes, but it greatly augmented fibrinogen binding to alpha(IIb)beta(3) induced by a PAR4 thrombin receptor agonist (p < 0.01). The Rap1b effect was cell-autonomous and was prevented by pre-treating cells with cytochalasin D or latrunculin A to inhibit actin polymerization. Rap1b-dependent fibrinogen binding to megakaryocytes was blocked by POW-2, a novel monovalent antibody Fab fragment specific for high affinity murine alpha(IIb)beta(3). In contrast to GFP-Rap1b (V12), expression of GFP-Rap1GAP, which deactivates endogenous Rap1, inhibited agonist-induced fibrinogen binding (p < 0.01), as did dominant-negative GFP-Rap1b (N17) (p < 0.05). None of these treatments affected surface expression of alpha(IIb)beta(3). These studies establish that Rap1b can augment agonist-induced ligand binding to alpha(IIb)beta(3) through effects on integrin affinity, possibly by modulating alpha(IIb)beta(3) interactions with the actin cytoskeleton.

Use of recombinant factor IX in subjects with haemophilia B undergoing surgery

Recombinant human FIX (rFIX) was evaluated in 28 subjects, including 26 with mild, moderate, or severe haemophilia B and two haemophilia B carriers undergoing 36 surgical procedures. Preoperative rFIX dose was highly correlated with postinfusion FIX activity, r=0.61, P=0.0158. Peri- and post-operative estimated blood loss was similar to that expected in non-haemophilic individuals, and haemostasis was rated as excellent or good in 34 of 35 (97.1%) of the operative procedures. Transfusions were required in five of 36 (13.9%) procedures, including one liver transplantation, and three knee and one hip arthroplasties. Adverse events occurred in 15 of 28 (53.6%) subjects, but there were no perioperative haemorrhages, thromboembolic events, coagulation activation, viral transmission, or inhibitor formation. A transient low-responding FIX inhibitor developed in one subject preoperatively, but required no change in treatment and resolved 15 months later. Thus, rFIX was found to be safe and effective in achieving haemostasis in subjects with FIX deficiency undergoing surgery.

Superior mesenteric vein thrombosis with radiologically occult cause: a retrospective study of 43 cases

OBJECTIVE

Our purpose was to examine the clinical presentation, imaging appearance, etiology, and clinical outcome in patients who had acute thrombosis of the superior mesenteric vein with radiologically occult cause.

CONCLUSION

The most common predisposing factors in superior mesenteric vein thrombosis with radiologically occult cause are recent abdominal surgery, infection, and hypercoagulable states. Although no correlation was noted between risk factor and outcome, the presence of bowel wall thickening and mesenteric congestion on CT or MR imaging was associated with the development of bowel ischemia. Prognosis is good in this group of patients, with a mortality of only 7%, although bowel ischemia was noted in 21%.

Gene therapy in hemophilia: clinical trials update

Disorders caused by inborn genetic errors have been a primary target for treatment by gene transfer. Hemophilia A and B have been considered especially important targets because the genes for factor VIII and IX are well characterized, levels of factor VIII and IX do not require complex regulation, small increases in factor level would have significant clinical benefits, good clinical and laboratory tests of efficacy exist, and excellent animal models of hemophilia are available. Four clinical trials of gene transfer in hemophilia, two in hemophilia A and two in hemophilia B, are currently underway or have been completed and two other trials have been approved. The collective interim results from these trials indicate that the current approaches and doses are safe and that low levels of expression are detected. These studies support the continued development of gene transfer as a potential treatment option for hemophilia.

The Malmö International Brother Study (MIBS): further support for genetic predisposition to inhibitor development in hemophilia patients

The issue of factors predisposing for inhibitor development in haemophilia patients is still largely unresolved. In an attempt to address this problem, we initiated a registry in 1996 of siblings with haemophilia and with or without a history of inhibitors. Four hundred and sixty families have accrued, of whom 388 suffer from haemophilia A and 72 haemophilia B. Twenty-five of the brother pairs are twins. The inhibitor incidence in all families with severe haemophilia A was 31.7%. The corresponding figure in the caucasian patients was 27.4%, whereas a higher incidence of inhibitors was reported in the black subjects (55.6%). Twins were reported in six of the 100 inhibitor families, for whom monozygocity was confirmed in three cases. In 32 families (32%), at least two brothers had a history of inhibitors. In 22 (69%) of these families, the inhibitor was also of the same type, i.e. either high- or low-responding. The overall concordance within the severe haemophilia A families was found to be 78.3% (195/249) compared to an expected figure of 68.0% and 58.0% using an inhibitor incidence of 20 and 30%, respectively (P < 0.0001). The corresponding figure for the twins was 88.2% (15/17). Moreover, the risk for inhibitor development in families with a previous inhibitor history was found to be 48% (95% confidence interval [CI] 35-62%), whereas the risk in families with no previous known inhibitor was only 15% (95% CI 11-21%) corresponding to a relative risk of 3.2 (95% CI 2.1-4.9). Immune-tolerance induction was reported in 24 families, of whom 13 siblings were successfully treated. Our data clearly support the concept that a genetic predisposition for inhibitor development exists. However, the markers of this predisposition remain to be elucidated and we believe that the MIBS registry will be useful for this purpose.

Characterization of high-risk HIV-1 seronegative hemophiliacs

Mechanisms that protect most high-risk HIV-1 seronegative (HRSN) persons are not well understood. Among hemophiliacs from the Multicenter Hemophilia Cohort Study who remained HIV-1 seronegative despite a high (94%) risk for acquisition of HIV-1 infection, only 7/43 were homozygous for the protective CCR5 Delta32 polymorphism. Among the remainder, neither CCR5 density nor beta-chemokine production, nor in vitro susceptibility to infection with the HIV-1 isolate JR-FL could distinguish HRSN hemophiliacs from healthy controls. When compared to lymphocytes of healthy controls not at risk for HIV-1 infection, diminished spontaneous lymphocyte proliferation was seen in lymphocytes of HRSN hemophiliacs as well as in lymphocytes of hemophiliacs not at risk for HIV-1 infection. Surprisingly sera/plasmas obtained from high-risk HIV-1 seropositve hemophiliacs prior to seroconversion more often contained alloreactive antibodies than date-matched sera/plasmas obtained from HRSN hemophiliacs. Thus alloreactivity may predispose to acquisition of HIV-1 infection after parenteral exposure.

Issues with the assay of factor VIII activity in plasma and factor VIII concentrates

A review of the literature suggests that assays accurate for the determination of factor VIII in plasma samples may not necessarily retain this accuracy when used for the determination of factor VIII in high-purity factor VII concentrates such as Hemofil M. Review of assay data suggests that it is imperative to obtain maximal activation of the factor VIII in the sample with thrombin when using an assay system of isolated coagulation factors such as the two-stage assay or the various chromogenic substrate assays. Based on a combination of ease and reproducibility of performance and correlation of in vivo and in vitro measurements. it is recommended that the one-stage activated partial thromboplastin time performed with plasma from an individual with severe hemophilia A be used for the measurement of factor VIII potency. Chromogenic substrate assays can be used if care is taken to assure optimal activation of factor VIII by thrombin in the assay and the presence of sufficient factor IXa, phospholipid and calcium ions to stabilize factor VIIIa during the assay process.

Inhibition of CD40 ligand (CD154) in the treatment of factor VIII inhibitors

The development of persistent, high titer inhibitors represents a serious complication of the treatment of patients with severe hemophilia A. Elimination of these inhibitory antibodies is usually attempted through repeated administration of high doses of factor VIII. Such regimens are costly, time-consuming and often fail when the inhibitor is of very high titer or of longstanding duration. A potential alternative approach to inhibit the production of antifactor VIII antibodies is blockade of the T-cell/B-cell collaboration that is required to generate humoral responses. One cognate receptor pair that is required for T-cell-dependent B-cell activation consists of CD40, which is expressed on B-lymphocytes and other antigen presenting cells, and CD40 ligand (CD40L, CD154), which is transiently expressed on activated T-cells. To determine whether blockade of the CD40-CD40L pathway can inhibit the production of anti-factor VIII antibodies, a clinical study has been designed in which patients with hemophilia A and a high titer inhibitor (> 10 BU) receive monthly exposures to factor VIII in the presence of a humanized mouse monoclonal antibody to human CD40L (hu5c8*). Subjects must be between the ages of 5 and 60 years old and be HIV seronegative. To date, three subjects have received at least three doses of hu5c8 at the initial protocol dose of 10 mg/kg. Preliminary results suggest that anti-CD40L inhibition may be effective in blocking anamnestic responses to factor VIII in some patients. It remains to be determined whether this effect will persist and whether patients may eventually become tolerant to factor VIII in the absence of hu5c8 co-administration.

Hemophilia factor VIII therapy. Immunological tolerance. A clinical perspective

Human alloantibodies to factor VIII occur in 15-50% of patients with severe hemophilia A. The development of these inhibitory alloantibodies prevents treatment with replacement factor VIII and places the patient at higher risk for complications from bleeding. Immune tolerance to factor VIII can be achieved in patients with inhibitors through the regular administration of factor VIII. The mechanism by which immune tolerance is achieved is unclear but the regular administration of factor VIII is believed to interrupt the normal immune mechanisms, perhaps by altering antigen presentation and inducing T or B cell anergy. The development of immune tolerance in hemophilia can be seen as a potential model for the development of methods for inducing tolerance to other alloimmune and autoimmune disorders.

Intracellular function in rehydrated lyophilized platelets

This study aimed to evaluate the effect of cross-linking and lyophilization on intracellular signalling processes in rehydrated, lyophilized (RL) platelets, which are under development as a platelet substitute for transfusion. Exposure of RL platelets to thrombin resulted in enhanced phosphorylation of several proteins, including 18 kDa and 42 kDa kinase substrates that were shown to be the substrates of myosin light chain and protein kinase C respectively. Cross-linking and lyophilization depleted the platelets of free cytoplasmic ADP and ATP, but had less effect on protein-bound nucleotides. The surface membrane of RL platelets was found to be permeable to poly dT probes less than approximately 3 kDa in size; larger nucleotide probes and proteins did not penetrate the surface membrane. Taken together, our results indicate that RL platelets retain some of the haemostatic stimulus-response functions of fresh platelets and are capable of feedback amplification in coagulation.