Inhibitor antibodies to factor VIII and factor IX: management

An Update on Laboratory Diagnostics in Haemophilia A and B

Haemophilia A (HA) and B (HB) are X-linked hereditary bleeding disorders caused by lack of activity of coagulation factors VIII (FVIII) or IX (FIX), respectively. Besides conventional products, modern replacement therapies include FVIII or FIX concentrates with an extended half-life (EHL-FVIII/FIX). Two main strategies for measuring plasma FVIII or FIX activity are applied: the one-stage clotting assay (OSCA) and the chromogenic substrate assay (CSA), both calibrated against plasma (FVIII/FIX) standards. Due to the structural modifications of EHL-FVIII/FIX, reagent-dependent assay discrepancies have been described when measuring the activity of these molecules. Assay discrepancies have also been observed in FVIII/FIX gene therapy approaches. On the other hand, nonfactor replacement by the bispecific antibody emicizumab, a FVIIIa-mimicking molecule, artificially shortens activated partial thromboplastin time–based clotting times, making standard OSCAs inapplicable for analysis of samples from patients treated with this drug. In this review, we aim to give an overview on both, the currently applied and future therapies in HA and HB with or without inhibitors and corresponding test systems suitable for accompanying diagnostics.

Platelet-targeted hyperfunctional FIX gene therapy for hemophilia B mice even with preexisting anti-FIX immunity

Gene therapy may lead to a cure for hemophilia B (HB) if it is successful. Data from clinical trials using adeno-associated virus (AAV)-mediated liver-targeted FIX gene therapy are very encouraging. However, this protocol can be applied only to adults who do not have liver disease or anti-AAV antibodies, which occur in 30% to 50% of individuals. Thus, developing a protocol that can be applied to all HB patients is desired. Our previous studies have demonstrated that lentivirus-mediated platelet-specific FIX (2bF9) gene therapy can rescue bleeding diathesis and induce immune tolerance in FIXnull mice, but FIX expression was only ∼2% to 3% in whole blood. To improve the efficacy, we used a codon-optimized hyperfunctional FIX-Padua (2bCoF9R338L) to replace the 2bF9 cassette, resulting in 70% to 122% (35.08-60.77 mU/108 platelets) activity levels in 2bCoF9R338L-transduced FIXnull mice. Importantly, sustained hyperfunctional platelet-FIX expression was achieved in all 2bCoF9R338L-transduced highly immunized recipients with activity levels of 18.00 ± 9.11 and 9.36 ± 12.23 mU/108 platelets in the groups treated with 11 Gy and 6.6 Gy, respectively. The anti-FIX antibody titers declined with time, and immune tolerance was established after 2bCoF9R338L gene therapy. We found that incorporating the proteasome inhibitor bortezomib into preconditioning can help eliminate anti-FIX antibodies. The bleeding phenotype in 2bCoF9R338L-transduced recipients was completely rescued in a tail bleeding test and a needle-induced knee joint injury model once inhibitors dropped to undetectable. The hemostatic efficacy in 2bCoF9R338L-transduced recipients was further confirmed by ROTEM and thrombin generation assay (TGA). Together, our studies suggest that 2bCoF9R338L gene therapy can be a promising protocol for all HB patients, including patients with inhibitors.

Targeted inhibition of activated protein C by a non-active-site inhibitory antibody to treat hemophilia

Activated protein C (APC) is a plasma serine protease with antithrombotic and cytoprotective functions. Based on the hypothesis that specific inhibition of APC’s anticoagulant but not its cytoprotective activity can be beneficial for hemophilia therapy, 2 types of inhibitory monoclonal antibodies (mAbs) are tested: A type I active-site binding mAb and a type II mAb binding to an exosite on APC (required for anticoagulant activity) as shown by X-ray crystallography. Both mAbs increase thrombin generation and promote plasma clotting. Type I blocks all APC activities, whereas type II preserves APC’s cytoprotective function. In normal monkeys, type I causes many adverse effects including animal death. In contrast, type II is well-tolerated in normal monkeys and shows both acute and prophylactic dose-dependent efficacy in hemophilic monkeys. Our data show that the type II mAb can specifically inhibit APC’s anticoagulant function without compromising its cytoprotective function and offers superior therapeutic opportunities for hemophilia.

Activated protein C (APC) is a plasma serine protease with antithrombotic and cytoprotective functions. Here, the authors develop a monoclonal antibody that specifically inhibits APC’s anticoagulant function without compromising its cytoprotective function, and shows efficacy in animal models.

Platelet-Targeted Gene Therapy for Hemophilia

Gene therapy is an attractive approach for disease treatment. Since platelets are abundant cells circulating in blood with the distinctive abilities of storage and delivery and fundamental roles in hemostasis and immunity, they could be a unique target for gene therapy of diseases. Recent studies have demonstrated that ectopic expression of factor VIII (FVIII) in platelets under control of the platelet-specific promoter results in FVIII storage together with its carrier protein von Willebrand factor (VWF) in α-granules and the phenotypic correction of hemophilia A. Importantly, the storage and sequestration of FVIII in platelets appears to effectively restore hemostasis even in the presence of functional-blocking inhibitory antibodies. This review summarizes studies on platelet-specific gene therapy of hemophilia A as well as hemophilia B.

Survey of the anti-factor IX immunoglobulin profiles in patients with hemophilia B using a fluorescence-based immunoassay

Essentials Studies characterizing neutralizing antibodies (inhibitors) in hemophilia B (HB) are lacking. The current study describes anti-factor (F) IX antibody profiles in 37 patients who have HB. Anti-FIX IgG4 levels exhibited a strong positive correlation with Nijmegen-Bethesda results. These data will help to more clearly define, predict, and treat alloantibody formation in HB.

SUMMARY

Background Hemophilia B (HB) is an inherited bleeding disorder caused by the absence or dysfunction of coagulation factor IX (FIX). A subset of patients who have HB develop neutralizing alloantibodies (inhibitors) against FIX after infusion therapy. HB prevalence and the proportion of patients who develop inhibitors are much lower than those for hemophilia A (HA), which makes studies of inhibitors in patients with HB challenging due to the limited availability of samples. As a result, there is a knowledge gap regarding HB inhibitors. Objective Evaluate the largest group of patients with inhibitor-positive HB studied to date to assess the relationship between anti-FIX antibody profiles and inhibitor formation. Methods A fluorescence immunoassay was used to detect anti-FIX antibodies in plasma samples from 37 patients with HB. Results Assessments of antibody profiles showed that anti-FIX IgG1-4 , IgA, and IgE were detected significantly more often in patients with a positive Nijmegen-Bethesda assay (NBA). All NBA-positive samples were positive for IgG4 . Anti-FIX IgG4 demonstrated a strong correlation with the NBA, while correlations were significant, yet more moderate, for anti-FIX IgG1-2 and IgA. Conclusions The anti-FIX antibody profile in HB patients who develop inhibitors is diverse and correlates well with the NBA across immunoglobulin (sub)class, and anti-FIX IgG4 is particularly relevant to functional inhibition. The anti-FIX fluorescence immunoassay may serve as a useful tool to confirm the presence of antibodies in patients who have low positive NBA results and to more clearly define, predict, and treat alloantibody formation against FIX.

Maillard reaction and immunogenicity of protein therapeutics

The recombinant DNA technology enabled the production of a variety of human therapeutic proteins. Accumulated clinical experience, however, indicates that the formation of antibodies against such proteins is a general phenomenon rather than an exception. The immunogenicity of therapeutic proteins results in inefficient therapy and in the development of undesired, sometimes life-threatening, side reactions. The human proteins, designed for clinical application, usually have the same amino acid sequence as their native prototypes and it is not yet fully clear what the reasons for their immunogenicity are. In previous studies we have demonstrated for the first time that interferon-β (IFN-β) pharmaceuticals, used for treatment of patients with multiple sclerosis, do contain advanced glycation end products (AGEs) that contribute to IFN-β immunogenicity. AGEs are the final products of a chemical reaction known as the Maillard reaction or glycation, which implication in protein drugs’ immunogenicity has been overlooked so far. Therefore, the aim of the present article is to provide a comprehensive overview on the Maillard reaction with emphasis on experimental data and theoretical consideration telling us why the Maillard reaction warrants special attention in the context of the well-documented protein drugs’ immunogenicity.

Personalized approaches to the treatment of hemophilia A and B

The recognition that individuals respond differently to the same medication is not new and dates almost to the founding of western medicine. In the last century it came to be recognized that genetic factors influence the heterogeneity of individual responses to medications with respect to both toxicity and effectiveness. Nonetheless, it has been challenging to integrate pharmacogenetic approaches in the routine practice of medicine as the identification of biomarkers is difficult due to the inherent complexity of biological systems. Here, we present potential applications of pharmacogenetics in managing hemophilia A and B. We discuss how predicting and circumventing immunogenicity, an important impediment to treating hemophilia patients, particularly lends itself to a pharmacogenetic approach. In addition, we discuss new trends toward personalizing the management of hemophilia in clinical settings.

High-dose intravenous interferon-beta in multiple sclerosis patients with high-titer neutralizing antibodies (HINABS II) - A pilot study

BACKGROUND

Neutralizing antibodies (NAb) against interferon-beta (IFNβ) affect its treatment efficacy. So far, there are no anti-NAb strategies available.

OBJECTIVES

To investigate if the repeated administration of high-dose IFNβ-1b intravenous in NAb positive multiple sclerosis (MS) patients induces tolerance and establishes IFNβ bioavailability as measured by the induction of myxovirus protein A (MxA).

METHODS

Nine MS patients with NAb titers >500 10-fold reduction units (TRU) received 1500μg IFNβ-1b intravenously once weekly over three months. Blood samples were collected at screening, monthly during the treatment period (before and four hours after IFNβ administration), and at follow-up after 6 months for determination of NAbs and MxA expression.

RESULTS

Median NAb titer at baseline was 1429TRU. NAb titers determined before each infusion did not significantly change over the treatment period and were not different at follow-up compared to baseline. However, NAb titers were significantly decreased four hours after IFNβ infusions (by roughly 50%) and MxA mRNA levels were significantly elevated reaching a median value of 206.

CONCLUSIONS

Weekly intravenous administration of IFNβ in patients with high NAb titers established its bioavailability, but failed to induce tolerance towards IFNβ.

Costs and utilization of hemophilia A and B patients with and without inhibitors

OBJECTIVE

To evaluate the health system costs among patients with hemophilia A and B with and without inhibitors over 5 years.

METHODS

This was a retrospective, observational study utilizing medical and pharmacy electronic medical records and administrative encounters/claims data tracking US patients between 2006-2011. Patients with diagnosis codes for hemophilia A and B were identified. Patients with inhibitors were characterized by utilization of bypassing agents activated prothrombin complex concentrate or factor VIIa on two or more distinct dates. Severity was classified as mild, moderate, or severe based on laboratory tests of clotting factor.

RESULTS

There were 160 hemophilia A patients and 54 hemophilia B patients identified. From this group, seven were designated as patients with inhibitors (five with hemophilia A and two with hemophilia B). Hemophilia A patients without inhibitors reported 65 (41.9%) as being severe, 19 (12.3%) as moderate, and 71 (45.8%) as mild. Hemophilia B patients without inhibitors reported nine (17.3%) had severe, 13 (25.0%) had moderate, and 30 (57.7%) had mild hemophilia. All patients with inhibitors had been hospitalized in the previous 5 years compared to 64 (41.3%) with hemophilia A without inhibitors and 22 (42.3%) with hemophilia B without inhibitors. The median aggregate cost per year (including factor and health resource use) was $325,780 for patients with inhibitors compared to $98,334 for hemophilia A patients without inhibitors and $23,265 for hemophilia B patients without inhibitors.

CONCLUSIONS

The results suggest that, while the frequency of inhibitors within the hemophilia cohort was low, there was a higher frequency of hospitalizations, and the associated median aggregate costs per year were 3-fold higher than those patients without inhibitors. In contrast, hemophilia B patients experience less severe disease and account for lower aggregate yearly costs compared to either patients with hemophilia A or patients with inhibitors.

Recombinant Factor VIIa: clinical applications for an intravenous hemostatic agent with broad-spectrum potential

Recombinant Factor VIIa (NovoSeven, Novo Nordisk) is a unique hemostatic agent with potential for broad-spectrum applications in bleeding patients with congenital and acquired bleeding abnormalities. At present, recombinant Factor VIIa is only approved for the treatment of hemophilia A and B patients who have acquired antibodies to Factors VIII and IX. However, the literature is rapidly expanding indicating that rFVIIa could benefit patients with bleeding due to a variety of etiologies. Unfortunately, the vast majority of these reports are case studies or small-series summaries, and are neither prospective nor controlled. Controlled trials are currently underway in several potential areas of application. While the possibility of thrombotic complications has been a clinical concern, safety data on patients treated to date have not revealed a significant problem. Expansion of the clinical applications for this interesting and important hemostatic agent are hampered by its expense, the limited scope of the US Food and Drug Administration approval for its use, and the absence of an appropriate laboratory monitoring assay.

Sequential therapy with activated prothrombin complex concentrates and recombinant activated factor VII to treat unresponsive bleeding in patients with hemophilia and inhibitors: a single center experience

BACKGROUND

Currently, the greatest challenge in hemophilia treatment is managing hemophilia patients with inhibitors. The two main bypassing agents that are used to treat hemophilia patients with inhibitors are activated prothrombin complex concentrates (APCC) and recombinant factor VIIa (rFVIIa). Hemophilia patients with inhibitors can develop bleeding episodes, that are refractory to monotherapy with either APCC or rFVIIa and thus are often difficult to manage.

METHODS

This report describes a retrospective chart review of four hospitalized patients with severe hemophilia and inhibitors who were treated with sequential therapy of APCC and rFVIIa for refractory bleeding. Sequential therapy was defined as the administration of both rFVIIa and APCC within 12 h.

RESULTS

In 5 episodes experienced by 4 patients with inhibitors, bleeding was not controlled by single bypass treatment, but it was controlled when two agents were sequentially administered. Sequential therapy was administered by alternating one APCC dose to 1 to 2 rFVIIa doses, with dosing intervals ranging from 3 to 6 h. All bleeding episodes were controlled within 12 to 24 h. Sequential therapy was discontinued after 2 to 5 days. No adverse clinical events, such as thrombosis, were observed.

CONCLUSION

Sequential therapy with APCC and rFVIIa was efficacious without adverse events; however, attention on thrombosis is needed. In addition, a prospective clinical trial is needed to provide further evidence for this treatment.

Platelet gene therapy by lentiviral gene delivery to hematopoietic stem cells restores hemostasis and induces humoral immune tolerance in FIX(null) mice

Here, we developed a clinically translatable platelet gene therapy approach for hemophilia B. Platelet-targeted FIX (2bF9) expression was introduced by transplantation of hematopoietic stem cells (HSCs) transduced with 2bF9 lentivirus (LV). Sustained therapeutic levels of platelet-FIX expression were obtained in FIX(null) mice that received 2bF9 LV-transduced HSCs. Approximately 6-39% of the platelets expressed FIX in the transduced recipients, which was sufficient to rescue the bleeding diathesis in FIX(null) mice in tail clipping models. Sequential bone marrow transplantation demonstrated that platelet-FIX expression in the secondary recipients was sustained, leading to phenotypic correction. Notably, none of the transduced recipients developed anti-FIX antibodies after platelet gene therapy. Only one of the nine recipients developed a low titer of inhibitory antibodies (1.6 BU/ml) after challenge with rhFIX. These data suggest that platelet gene therapy can not only restore hemostasis but also induce immune tolerance in hemophilia B mice, indicating that this approach may be a promising strategy for gene therapy of hemophilia B in humans.

Immune tolerance induction for patients with severe hemophilia A: a critical literature review

The development of inhibitors that neutralize the function of clotting factor VIII (FVIII) is currently the most challenging complication associated with the treatment of hemophilia A as it increases the disease-related morbidity and mortality. Immune tolerance induction (ITI) is the only documented strategy to eradicate persistent inhibitors in severe hemophilia A patients. Several studies have been conducted so far to identify patient- and treatment-related factors associated with greater ITI success. The currently available literature on ITI in hemophilia A will be critically reviewed in this article. In particular, we will focus on the role of the type of FVIII product on ITI outcome by analyzing the clinical and experimental data.

Fabry disease, enzyme replacement therapy and the significance of antibody responses

Fabry disease is an X-linked disorder caused by a deficiency of α-galactosidase A. This leads to a progressive accumulation of globotriaosylceramide in tissues throughout the body. Cardiac, renal and neurological manifestations are common and life expectancy is significantly reduced relative to the general population. Management of Fabry disease involves the administration of intravenous enzyme replacement therapy (ERT). Two forms - agalsidase alfa and agalsidase beta - have been licensed in certain jurisdictions and are generally well tolerated; however, some patients develop antibodies to the infused enzyme, which may impair the efficacy and safety of treatment. Agalsidase alfa and agalsidase beta are produced in different systems; this leads to certain differences in post-translational modification that may affect immunogenicity. Immunoglobulin (Ig) G antibodies have frequently been reported in patients with Fabry disease receiving ERT; IgG responses are reported in a greater proportion of patients receiving agalsidase beta than in patients receiving agalsidase alfa. IgE antibodies are less common than IgG antibodies, and have not been observed in patients receiving agalsidase alfa. However, these data are difficult to interpret due to methodological differences in the assessment of seropositivity, and in the doses of enzyme used. The clinical impact of the development of IgG antibodies to ERT in patients with Fabry disease remains unclear, due to lack of data and to the marked heterogeneity of patients both in terms of disease manifestations and response to therapy. Further studies that examine the development of antibodies in patients with Fabry disease and the potential impact of such antibodies on the outcome of ERT are necessary.

Inhibitors of propagation of coagulation (factors VIII, IX and XI): a review of current therapeutic practice

The management of patients with congenital haemophilia who develop alloantibodies against factors of the propagation phase of blood coagulation, commonly known as inhibitors, is the most important challenge facing haemophilia caregivers at present, as this complication not only compromises the efficacy of replacement therapy but also consumes an enormous amount of economic resources. Development of inhibitors further complicates the clinical course of severe haemophilia, with a prevalence of up to 30% in patients with haemophilia A (factor VIII deficiency) and up to 5% in those with haemophilia B (factor IX deficiency) and haemophilia C (factor XI deficiency). While the short-term goal of treatment of patients who develop alloantibodies is the control of bleeding, the eradication of the inhibitor is the main long-term goal. The management of severe bleeding episodes and the eradication of the autoantibody are also the mainstays of treatment of patients with acquired haemophilia, a rare but life-threatening haemorrhagic condition characterized by the development of inhibitory autoantibodies against coagulation factor VIII. The most recent options available for treating patients with congenital haemophilia complicated by inhibitors and acquired haemophilia because of autoantibodies against factor VIII are summarized in this review article.

Current options and new developments in the treatment of haemophilia

Haemophilia A and B are X-linked bleeding disorders due to the inherited deficiency of factor VIII or factor IX, respectively. Of the approximately 1 per 5000-10000 male births affected by haemophilia, 80% are deficient in factor VIII and 20% are deficient in factor IX. Haemophilia is characterized by spontaneous and provoked joint, muscle, gastrointestinal and CNS bleeding leading to major morbidity and even mortality if left untreated or under-treated. The evolution of haemophilia management has been marked by tragedy and triumph over recent decades. Clotting factors and replacement strategies continue to evolve for patients without inhibitors. For patients with an inhibitor, factor replacement for acute bleeding episodes and immune tolerance, immune modulation and extracorporeal methods for inhibitor reduction are the cornerstone of care. In addition, adjuvant therapies such as desmopressin, antifibrinolytics and topical agents also contribute to improved outcomes for patients with and without inhibitors. The future direction of haemophilia care is promising with new longer-acting clotting factors and genetic therapies, including gene transfer and premature termination codon suppressors. With these current and future treatment modalities, the morbidity and mortality rates in patients with haemophilia certainly will continue to improve.

Platelets as delivery systems for disease treatments

Platelets are small, anucleate, discoid shaped blood cells that play a fundamental role in hemostasis. Platelets contain a large number of biologically active molecules within cytoplasmic granules that are critical to normal platelet function. Because platelets circulate in blood through out the body, release biological molecules and mediators on demand and participate in hemostasis as well as many other pathophysiologic processes, targeting expression of proteins of interest to platelets and utilizing platelets as delivery systems for disease treatment would be a logical approach. This paper reviews the genetic therapy for inherited bleeding disorders utilizing platelets as delivery system, with a particular focus on platelet-derived FVIII for hemophilia A treatment.

Thrombin generation and platelet activation induced by rFVIIa (NovoSeven) and NN1731 in a reconstituted cell-based model mimicking haemophilia conditions

Replacement therapy with factor VIII (FVIII) and factor IX (FIX) is routinely used in haemophilia patients with haemophilia A and B, respectively, while recombinant activated FVII (rFVIIa) has proven to induce haemostasis in haemophilia patients with inhibitors. To evaluate the effect of therapeutic intervention in patients with residual factor activities, the effects of increasing concentrations of rFVIIa or NN1731 on thrombin generation and platelet activation were measured in a cell-based model system mimicking severe, moderate and mild haemophilia A or B. Purified monocytes stimulated to express tissue factor and non-activated platelets from peripheral blood of healthy donors were incubated with a mixture of purified human coagulation factors in the absence or presence of increasing concentrations of FVIII or FIX. Sub-samples were analysed for thrombin activity and platelet activation measured as exposure of P-selectin by flow cytometry. Dose-dependent increases in thrombin generation and platelet activation were observed following increasing concentrations of rFVIIa or NN1731 in both haemophilia A- and B-like conditions. At 25 nm rFVIIa, which nears the peak levels in patient plasma after 90 microg kg(-1) intravenous dosing, the effects on maximum thrombin generation rate (maxTG) at 1-10% FVIII were comparable to those at 100% and 200% FVIII in the absence of rFVIIa. Normalization of maxTG required 500 nm rFVIIa and 25 nm NN1731 or 25-100 nm rFVIIa and 5 nm NN1731 in severe or moderate/mild haemophilia A and haemophilia B, respectively. This suggests that NN1731 holds its promise as a future bypassing agent for haemophilia patients with and without inhibitors.

Experience with a third generation recombinant factor VIII concentrate (Advate) for immune tolerance induction in patients with haemophilia A

The development of an inhibitor represents one of the most challenging complications in patients with haemophilia A. Optimal management is immune tolerance induction (ITI), typically through the administration of high doses of factor VIII (FVIII) concentrate. Among 12 patients who underwent ITI using Advate, a third-generation recombinant FVIII product that is free of animal and human protein additives, tolerance was achieved in nine (75%), including seven of 10 patients (70%) with high-titre inhibitors. ITI is ongoing in two patients and not yet successful; immune tolerance failed in the third patient. The median time to success was 4.0 months for group as a whole and for patients with high-titre inhibitors. Treatment was well tolerated, and no adverse events were observed. Advate was found to be equivalent to other FVIII products with regard to both ITI success rates and the incidence of adverse effects when used in these immune tolerance regimens.

Cost and effectiveness of treatments for mild-to-moderate bleeding episodes in haemophilia patients with inhibitors in Korea

First-line treatment for mild-to-moderate bleeding episodes in patients with haemophilia and inhibitors in Korea is currently activated prothrombin complex concentrate (aPCC) with recombinant activated factor VII (rFVIIa) as second-line therapy or as a last resort. The aim of this study was to estimate the cost and effectiveness of aPCC vs. rFVIIa for treating mild-to-moderate bleeds in inhibitor patients from the Korean reimbursement authorities' perspective. Clinical outcomes and resource utilization data (number of doses, average dose, number of outpatient visits, inpatient stays, ambulance transport and concomitant medications) were collected from an observational study involving four Korean paediatric haemophilia centres. Cost-effectiveness was modelled using a decision analysis approach and sensitivity analyses undertaken. rFVIIa was a more effective haemostatic therapy (87.1% efficacy in bleed resolution) than aPCC (64.0%). rFVIIa effected more rapid haemostasis, resolving bleeding in a mean of 6.6 h vs. 25.2 h for aPCC. Fewer rFVIIa doses were required per bleed vs. aPCC (means 1.7 and 2.3). Mean total direct medical costs from bleed initiation to cessation were estimated at Korean Won (KRW)12 460 thousand (US$12 311) for rFVIIa given as first-line therapy and KRW18 304 thousand (US$18 085) for aPCC given as first-line therapy. Sensitivity analyses confirmed the cost-effectiveness of rFVIIa vs. aPCC given as first-line therapy. In Korea, use of rFVIIa as first-line therapy for treatment of mild-to-moderate bleeding episodes in inhibitor patients is both clinically effective and cost-effective compared with initial aPCC treatment. rFVIIa should be considered as the first-line treatment for mild-to-moderate bleeding episodes in patients with haemophilia and inhibitors in Korea.

Single-dose recombinant activated factor VII therapy in hemophilia patients with inhibitors

Recombinant activated factor VII (rFVIIa; NovoSeven, Novo Nordisk, Bagsvaerd, Denmark) is well established as an effective hemostatic agent for the management of hemorrhage in hemophilia patients with inhibitors. Its use in prophylaxis is currently being investigated. On-demand treatment schedules usually involve multiple bolus doses of 90 to 120 microg/kg administered every 2 to 3 hours, but recent evidence from randomized controlled trials suggests that the use of higher single doses is equally safe and effective when used for the home treatment of hemarthroses. Consequently, the use of a single dose of 270 microg/kg rFVIIa for the treatment of bleeds in inhibitor patients has recently been approved by the European Medicines Agency (EMEA). Such high-dose regimens may overcome the rapid clearance rate observed in pediatric patients, and may be more convenient for patients with poor venous access. It also has been suggested that individually tailored single-dose therapies might be beneficial in selected groups of patients, although proper monitoring of such patients is advised. Further research should contribute towards more effective dose optimization of rFVIIa in hemophilic inhibitor patients.

Inhibitor development in haemophilia A: the role of von Willebrand factor/factor VIII concentrates

The presence of inhibitors that neutralize the function of factor VIII (FVIII) decreases the haemostatic efficacy of replacement clotting factor concentrate and increases morbidity among patients with haemophilia A. Certain genetic and environmental variables have been linked to a higher incidence of inhibitors. Conversely, the presence of von Willebrand factor (VWF) in some plasma-derived FVIII products may provide some measure of protection against inhibitor development, although the evidence is not conclusive. Clinical trials are needed to resolve this issue and determine the appropriate role of VWF-containing FVIII concentrates in the treatment of haemophilia A patients.

[A Jehovah's Witness child with hemophilia B and factor IX inhibitors undergoing scoliosis surgery]

PURPOSE

To describe the successful perioperative hemostatic management of a Jehovah's Witness patient with hemophilia B and anaphylactic inhibitors to factor IX, undergoing scoliosis surgery.

CLINICAL FEATURES

A 14 (1/2)-yr-old boy with severe hemophilia B who had a history of anaphylactic inhibitors to factor IX was scheduled to undergo corrective scoliosis surgery. He was initially started on epoetin alfa and iron supplementation to maximize preoperative red cell mass. Additionally, he was placed on a desensitization protocol of recombinant coagulation factor IX (rFIX) and was then treated with activated recombinant coagulation factor VII (rFVIIa) during the postoperative period. Tranexamic acid was given concomitantly. The intraoperative blood loss was approximately 350 mL. The nadir hemoglobin concentration was 111 g.L(-1) on postoperative days one and two. On postoperative day 11, the patient was stable and discharged home with a hemoglobin of 138 g.L(-1). He did not require blood transfusion and no adverse events were observed.

CONCLUSIONS

The use of rFIX, rFVIIa, erythropoetin, iron, and tranexamic acid before, during and after scoliosis surgery may be a viable and safe option for hemophilia patients with inhibitors, who refuse blood products.

Prophylactic treatment of haemophilia patients with inhibitors: clinical experience with recombinant factor VIIa in European Haemophilia Centres

Many patients with haemophilia develop inhibitors to factor VIII and require bypassing agents to provide haemostatic cover for limb- or life-threatening bleeding episodes. Due to the reduced risk of blood-borne pathogen transmission with recombinant products, on-demand recombinant factor VIIa (rFVIIa; NovoSeven is the treatment of choice for children with inhibitors. In haemophiliac patients without inhibitors, primary prophylaxis has been clinical practice for several years. This paper summarises 13 case histories of rFVIIa secondary prophylaxis for haemophilia patients with inhibitors. This was a retrospective survey of adult and paediatric severe haemophilia patients with inhibitors treated with rFVIIa from ten European Haemophilia Centres. There was a wide variation in administered rFVIIa dose, from 200-250 microg kg(-1) per week to 220 microg kg(-1) daily. In many cases, this was lower than the recommended on-demand dose of rFVIIa. In 12/13 cases, prophylaxis with rFVIIa considerably reduced the number of bleeding episodes compared with previous treatment. Eight/nine patients were satisfied or very satisfied with rFVIIa treatment, and in cases reporting subjective quality of life (QoL), all were improved, much improved, or significantly improved. In haemophilia patients with inhibitors, prophylaxis with rFVIIa is highly effective in reducing the number of bleeding episodes and results in good patient compliance and improved QoL. Randomised controlled trials are needed to confirm these findings. Results of a recently completed clinical trial on secondary prophylaxis with rFVIIa in frequently bleeding haemophilia patients with inhibitors are expected in late 2006.

International workshop on immune tolerance induction: consensus recommendations

Although immune tolerance induction (ITI) has been used for 30 years to eliminate inhibitors and restore normal factor pharmacokinetics in patients with hemophilia, there is a paucity of scientific evidence to guide therapeutic decision-making. In an effort to provide direction for physicians and hemophilia treatment center staff members, an international panel of hemophilia opinion leaders met to develop consensus recommendations for ITI in patients with severe and mild hemophilia A and hemophilia B. These recommendations draw on the available published literature and the collective clinical experience of the group and are rated based on the level of supporting evidence.

Postoperative pulmonary thromboembolism possibly associated with recombinant activated factor VII infusion for the treatment of uncontrolled hemorrhage during vertebral instrumentation

We report the successful use of recombinant activated factor VII (rFVIIa) infusion in an 18-year-old man who underwent L3 laminectomy and pedicular screw fixation with severe refractory bleeding secondary to severe coagulopathy, which had remained unresponsive to conventional medical and surgical therapies. However, the patient developed a thromboembolic complication presumably associated with the use of rFVIIa. Although rFVIIa provides a dramatic response in intractable bleeding, it may cause a thromboembolic phenomenon which should be vigilantly considered and promptly treated.

Immune response after neonatal transfer of a human factor IX-expressing retroviral vector in dogs, cats, and mice

INTRODUCTION

Gene therapy could prevent bleeding in hemophilia. However, antibodies could inhibit coagulation, while cytotoxic T lymphocytes could destroy modified cells. The immaturity of the newborn immune system might prevent these immune responses from occurring after neonatal gene therapy.

MATERIALS AND METHODS

Newborn dogs, cats, or mice were injected intravenously with a retroviral vector expressing human Factor IX. Plasma was evaluated for antigen and anti-human Factor IX antibodies. Cytotoxic T lymphocyte responses were evaluated indirectly by analysis of retroviral vector RNA in liver. Lymphocytes were evaluated for cytokine secretion and the ability to suppress an immune response to human Factor IX in mice.

RESULTS AND CONCLUSIONS

Hemophilia B dogs that achieved 942+/-500 ng/ml (19% normal) or 5+/-0.4 ng/ml (0.1% normal) of human Factor IX in plasma only bled 0 or 1.2 times per year, respectively, and were tolerant to infusion of human Factor IX. Normal cats expressed human Factor IX at 118+/-29 ng/ml (2% normal) in plasma without antibody formation. However, plasma human Factor IX disappeared at late times in 1 of 4 cats, which was probably due to a cytotoxic T lymphocyte response that destroyed cells with high expression. C3H mice were tolerant to human Factor IX after neonatal gene therapy, which may involve clonal deletion of human Factor IX-responsive cells. These data demonstrate that neonatal gene therapy does not induce antibodies to human Factor IX in dogs, cats, or mice. The putative cytotoxic T lymphocyte response in one cat requires further study.

Application of current knowledge to the management of bleeding events during immune tolerance induction

The development of inhibitors to factor VIII is the most serious adverse event associated with the treatment of haemophilia A, predisposing patients to uncontrollable haemorrhage, disability and premature death. Eradication of inhibitors via immune tolerance induction (ITI) is effective in the majority of patients, but may require months to years to achieve success. In the interim, the treatment and prevention of acute bleeding episodes are primary foci of care. Regrettably, there is a paucity of information regarding management of bleeding episodes in inhibitor patients undergoing tolerization. Until specific data from ongoing clinical trials are available to provide more guidance in this patient group, it is reasonable and useful to rely on the broader base of medical literature pertaining to patients not being tolerized to deduce strategies for controlling acute and perioperative bleeding episodes in inhibitor patients during ITI.

Gene therapy for hemophilia

PURPOSE OF REVIEW

This review will highlight the progress achieved in the past 2 years on using gene therapy to treat hemophilia in animals and humans.

RECENT FINDINGS

There has been substantial progress in using gene therapy to treat animals with hemophilia. Novel approaches for hemophilia A in mice include expression of Factor VIII in blood cells or platelets derived from ex-vivo transduced hematopoietic stem cells, or in-vivo transfer of transposons expressing Factor VIII into endothelial cells or hepatocytes. Advances in large-animal models include the demonstration that neonatal administration of a retroviral vector expressing canine Factor VIII completely corrected hemophilia A in dogs, and that double-stranded adeno-associated virus vectors resulted in expression of Factor IX that is 28-fold that obtained using single-stranded adeno-associated virus vectors. In humans, one hemophilia B patient achieved 10% of normal activity after liver-directed gene therapy with a single-stranded adeno-associated virus vector expressing human Factor IX. Expression fell at 1 month, however, which was likely due to an immune response to the modified cells.

SUMMARY

Gene therapy has been successful in a patient with hemophilia B, but expression was unstable due to an immune response. Abrogating immune responses is the next major hurdle for achieving long-lasting gene therapy.

Italian guidelines for the diagnosis and treatment of patients with haemophilia and inhibitors

The Italian Association of Haemophilia Centres reviewed and finally approved in November 2004 the new Italian Guidelines for the diagnosis and treatment of patients with clotting factor inhibitors. The recommendations have been based on the identification of levels of clinical evidence derived from the systematic review carried out in 2003 by the School of Health and Related Research, the University of Sheffield, UK, and further integrated by clinical studies published from 2003 to 2004. The Italian guidelines consist of six major domains concerning inhibitor definition, epidemiology, risk factors, diagnosis, inhibitor eradication, management of bleeding episodes, in patients with congenital and acquired coagulation disorders, with 121 statements, 59 synthesis and 54 recommendations. We report here recommendations and open issues concerning the diagnosis and monitoring of inhibitors, inhibitor eradication and the management of bleeding in patients with haemophilia A and B.

High-Dose Recombinant Factor VIIa Therapy in Hemophilia Patients With Inhibitors

Recombinant activated factor VII (rFVIIa; NovoSeven, Novo Nordisk, Bagsvaerd, Denmark) is well established as an effective hemostatic agent for the management and prophylaxis of hemorrhage in hemophilia patients with inhibitors. Treatment schedules usually involve multiple bolus doses of 90 to 120 microg/kg administered every 2 to 3 hours, but recent evidence suggests that the use of higher doses might be justified. Such high-dose regimens may overcome the rapid clearance rate observed in pediatric patients, and may be more convenient for patients with poor venous access. It has been suggested that individually tailored high-dose therapies might be beneficial in selected groups of patients, although careful monitoring of such patients is advised. Thrombelastography has demonstrated considerable success in this regard, allowing accurate assessment of both hemostatic efficacy and individual response to rFVIIa. To date, no safety issues associated with high-dose rFVIIa have been identified. However, it is hoped that further research will support these favorable observations and thus contribute towards more effective dose optimization of rFVIIa in hemophilic inhibitor patients.

Significance of neutralizing antibodies to interferon beta during treatment of multiple sclerosis: expert opinions based on the Proceedings of an International Consensus Conference

On August 30, 2002, an international panel of neurologists who specialize in the treatment of multiple sclerosis (MS) was convened in Paris (France) to discuss the issue of neutralizing antibodies (NAb) to interferon beta (IFN-beta) therapy in patients with MS. The goals of this meeting were to: (i) review the most recent clinical information on NAb, (ii) come to a consensus on the clinical relevance of NAb in the management of patients with MS receiving IFN-beta therapy, and (iii) establish a framework for the development of patient management guidelines based on scientific consensus. The meeting was chaired by Hans-Peter Hartung (Heinrich-Heine University, Düsseldorf, Germany) and Huub Schellekens (Utrecht University, Utrecht, the Netherlands). This article summarizes the opinions of the expert panel on a number of key issues raised at the meeting.