How do some haemophiliacs develop inhibitors?

The case for wider use of recombinant factor VIII concentrates

The introduction of clotting factor concentrates led to major advances in hemophilia care. Rather than simply providing an alternative to plasma-derived concentrates, the introduction in the 1990s of recombinant concentrates added value to replacement therapy particularly with respect to prophylaxis and immune-tolerance induction. While the safety of plasma-derived concentrates has improved considerably, these concentrates may still pose an infectious risk through as-yet unknown pathogens and poor impurity constituent characterization. Recombinant concentrates are increasingly used because of their benefits in pathogen safety, convenience and the potential for unfettered supply. Yet worldwide they remain accessible only to a limited number of patients due to fear of the potential for inhibitor development, overestimation of their costs and underestimation of their benefits. This article reviews the characteristics and properties of recombinant FVIII concentrates to help physicians and patient representatives promote the right of access of patients to the safest products.

Haemophilia in the developing countries: the Iranian experience

INTRODUCTION

Management of haemophilia and inherited bleeding disorders is a major challenge especially in developing countries, because of a shortage or absence of products, the cost and the infrastructural health problems. Development of local expertise which results in an improved outlook and reduction in mortality and morbidity in these countries can be helpful for advocators in other developing countries. However, very little information on demography and organizational models for haemophilia care in developing countries are available in the literature. Our aim is a comprehensive report of haemophilia status and its management in Iran.

MATERIAL AND METHODS

THE MANAGEMENT CENTER OF TRANSPLANTATION AND SPECIAL DISEASES (MCTSD) OF THE MINISTRY OF HEALTH OF IRAN DECIDED TO CARRY OUT A COMPLETE REVIEW AND COMPILATION OF ALL OF THE PUBLISHED OR AVAILABLE DATA ABOUT PATIENTS WITH HAEMOPHILIA (PWH) IN IRAN: their health status, their management planning, organizations, treatment products, facilities and care problems during 2007.

RESULTS

6496 patients with congenital bleeding disorders were registered. Most of them had haemophilia A and B and von Willebrand disease (vWD). However, rare bleeding disorders are seen more than expected. Inhibitor development is 14-28%. There are different data about virological status of PWH. Factor products and facilities are fairly available with more than 1.5 units per capita of inhabitant factor consumption.

CONCLUSIONS

A national formulary based on facilities of the country should be considered and followed by collaboration among the Ministry Of Health, universities and non-governmental organizations.

Polymorphisms in the IL10 but not in the IL1beta and IL4 genes are associated with inhibitor development in patients with hemophilia A

The aim of the Malmö International Brother Study (MIBS) is to evaluate host genetic factors associated with the development of inhibitory antibodies in patients with hemophilia. Factor VIII gene mutations and genetic polymorphisms of the IL1beta, IL4, and IL10 genes, known to influence antibody production in autoimmune diseases, were analyzed in 164 patients (124 with severe, 26 with moderate, and 14 with mild disease) in 78 unrelated families with hemophilia A. Seventy-seven (47%) patients in 54 families had a history of inhibitors (57 high responding, 20 low responding). Inversions were found in 36 families (75 patients). There was no association between the development of inhibitor and the IL1beta Taq I RFLP alleles in exon 5 or the –590 C/T single nucleotide polymorphism (SNP) in the promoter region of IL4. There was, however, a strong association between an allele with 134 bp in one of the CA repeat microsatellites, IL10G, located in the promoter region of the IL10 gene, and the development of inhibitor (odds ratio [OR], 4.4; 95% confidence interval [95% CI], 2.1-9.5; P < .001). The association was consistent in the subgroup of families with severe hemophilia and inversions. IL10 is the first gene located outside the causative factor VIII gene mutation to be associated with inhibitor development.

Effect of factor VIII concentrate on leucocyte cytokine receptor expression in vitro: relevance to inhibitor formation and tolerance induction

Inhibitor formation in haemophilia patients receiving factor VIII (FVIII) concentrate is a serious problem requiring tolerance induction therapy. Inhibitor antibody formation is dependent on interactions between leucocyte cytokines with their corresponding receptors. To investigate this we studied the effect of FVIII on cytokine receptor expression using multiparameter flow cytometry and a whole blood stimulation assay. Upregulation of many cytokine receptors was inhibited by plasma-derived FVIII (pdFVIII) in a dose-dependent manner on T cells, B cells and monocytes although interleukin (IL)-4Ralpha and IL-7Ralpha were upregulated on T cells. The decrease in cytokine receptor upregulation on B cells in the presence of pdFVIII, may result in reduced antibody production. Inhibition of CD132 in the presence of pdFVIII may result in immune tolerance in some recipients of pdFVIII. The immunomodulatory effects of pdFVIII were dose and batch dependent, some being more inhibitory than others. The inhibitory effects of prednisolone with pdFVIII, on cytokine receptor upregulation, were additive. Cytokine receptor expression was not altered in the presence of human recombinant FVIII (rFVIII) concentrate. These findings may explain the reports of less frequent inhibitor antibody formation in some recipients of pdFVIII concentrates. The use of pdFVIII, particularly the more inhibitory batches, may be more suitable than rFVIII for tolerance induction protocols. A clinical study needs to be undertaken to determine the significance of these in vitro findings.

Prophylactic treatment effects on inhibitor risk: experience in one centre

Nowadays, the elective treatment for children with haemophilia is prophylaxis. There is a common consensus that this modality of therapeutic approach is not associated with a higher risk of inhibitor development. We analysed the inhibitor incidence in 50 haemophiliac children and its relationship with mutations, type of clotting factor used and treatment modality. There was a significant correlation between receiving on-demand treatment and an increased incidence of inhibitors, independently of mutations or factor used. We advise putting haemophiliac children under prophylactic treatment as soon as possible, especially if they have mutations associated with high risk of inhibitor development, as prophylaxis is negatively associated with the development of inhibitors.

Prevention of bleeds in hemophilia patients with inhibitors: emerging data and clinical direction

In patients with hemophilia, the development of high-responding inhibitors to factor VIII prevents adequate replacement therapy and results in increased risk of serious bleeding episodes, poor control of joint bleeding, and progressive, debilitating joint disease. Immune tolerance therapy can eradicate inhibitors, but it is not uniformly successful. Emerging data suggest that prophylaxis using activated prothrombin complex concentrates may be effective and safe in reducing the incidence of joint bleeding during immune tolerance therapy and for patients in whom immune tolerance induction fails. However, only controlled clinical trials will ultimately demonstrate whether prophylaxis can prevent joint bleeding and damage, and improve quality of life in patients with inhibitors.

Management of haemophilia and its complications in developing countries

Eighty per cent of people with haemophilia live in developing countries, where technical expertise and health care facilities may be less than optimal. Haemophilia is a relatively rare disease and high-cost, technology-intensive therapy is not a high priority for the governments of developing countries. The rapid spread of transfusion-related viral infections in many developing countries presents further problems for haemophiliacs. However, it is possible to manage haemophiliacs patients with limited resources. Strategies for conserving factor concentrates, include education of doctors and patients, prenatal diagnosis, increasing the use of anti-fibrinolytic agents, physiotherapy, the use of fibrin glue, and simple orthotics and prosthetic measures. These approaches are helpful in the majority of these patients. Meanwhile, with the help of the World Federation of Haemophilia (WFH), all developing countries are gradually improving management skills for this relatively rare but disabling disease. The present review broadly describes the management of various aspects of severe haemophilia in developing countries.

An ELISA assay for the detection of factor VIII antibodies - comparison with the conventional Bethesda assay in a large cohort of haemophilia samples

An enzyme-linked immunosorbent assay (ELISA) has been developed to measure factor VIII antibodies in haemophilia patients. The assay utilizes binding of the antibodies in the plasma to solid phase antigen, i.e. recombinant factor VIII which was subsequently detected by a human polyclonal IgG labelled with the alkaline phosphatase-p-nitrophenyl phosphate substrate system. Comparisons were made with the Bethesda assay for the quantitation of factor VIIII inhibitors. Dose response curves for the reference standards were consistently linear and reproducible. The assay was specific for factor VIII antibodies, showing a negative reaction for antibodies to other coagulation factors, antinuclear factors and antiphospholipid antibodies. Using this method, 312 samples from haemophilia A patients and 31 samples from healthy controls were screened for the presence of inhibitors and compared with the conventional Bethesda assay. Twenty-four cases were found to be positive for inhibitors in both the ELISA and Bethesda assay. Five additional cases were also found to be positive in the ELISA assay, which, however, were negative in Bethesda assay. One patient who was initially positive for factor VIII inhibitors both by the Bethesda assay and ELISA eventually became negative for the Bethesda assay (<0.5 BU/ml) but was still positive for the ELISA assay. The ELISA thus described had a specificity of 97.8% and a sensitivity of 100% when tested against a large cohort of haemophilia A samples.

Successful use of recombinant factor VIIa in a patient with inhibitor secondary to severe factor XI deficiency

Factor XI (FXI) inhibitors are a rare complication of inherited FXI deficiency. We report the successful use of recombinant factor VIIa (FVIIa) in a patient with a high-responding inhibitor undergoing cataract extraction. At the time of surgery there were limited available data on the optimal management of patients with FXI deficiency. A 62-year-old Ashkenazi Jewish woman had a lifelong history of excessive bleeding secondary to severe FXI deficiency (2 U dL-1), and received FXI concentrate (FXI:C) when she underwent a colposuspension procedure. She was subsequently diagnosed with a FXI inhibitor of 16 Bethesda units (BU) when she developed a poor response to FXI:C at the time of total hip replacement. Two months later she was admitted for cataract extraction. The FXI level was < 1 U dL-1 with an inhibitor titre of 48 BU. She received 90 microg kg-1 of FVIIa immediately preoperatively followed by continuous infusion at a rate of 20 microg kg-1 h-1 for 24 h. The cataract extraction was successful and there was no excess bleeding during surgery or in the postoperative period. Mutation analysis of the FXI gene showed that the patient was homozygous for the type II genotype [exon 5, Glu117-->Ter]. The reason for the low prevalence of inhibitor formation in patients with FXI deficiency is unclear but may reflect a number of factors including reporting bias, the rarity of absent circulating FXI:C activity, and the infrequent use of FXI replacement therapy.

Sustained delivery of therapeutic concentrations of human clotting factor IX--a comparison of adenoviral and AAV vectors administered in utero

BACKGROUND

Prenatal somatic gene therapy has been considered for genetic disorders presenting with morbidity at birth. Haemophilia is associated with an increased risk of catastrophic perinatal bleeding complications such as intracranial haemorrhage, which could be prevented by gene transfer in utero. Prenatal gene therapy may be more promising than postnatal treatment, as the fetus may be more amenable to uptake and integration of therapeutic DNA and the immaturity of its immune system may permit life-long immune tolerance of the transgenic protein, thus avoiding the dominant problem in haemophilia treatment, the formation of inhibitory antibodies.

METHODS

Adenovirus serotype 5-derived or AAV serotype 2-derived vectors carrying human clotting factor IX (hfIX) cDNA or a reporter gene were administered intramuscularly, intraperitoneally or intravascularly to late-gestation mouse fetuses. Both vector types were evaluated with respect to the kinetics of hfIX delivery to the systemic circulation and possible immune responses against the vector or the transgene product.

RESULTS

Mice treated in utero by intramuscular injection of an adenoviral vector carrying hfIX cDNA exhibited high-level gene expression at birth and therapeutic--albeit continuously decreasing--plasma concentrations of hfIX over the entire 6 months of the study. Adenoviral vector spread to multiple organs was detected by polymerase chain reaction (PCR). Intramuscular, intraperitoneal or intravascular application of AAV vectors carrying hfIX cDNA led to much lower plasma concentrations of hfIX shortly after birth, which appeared to decline during the first month of life but stabilized in some of the mice at detectable levels. No signs of immune responses were found, either against the different viral vectors or against hfIX.

CONCLUSION

This study demonstrates for the first time that sustained systemic delivery of a therapeutic protein can be achieved by prenatal gene transfer. It thus shows the feasibility of gene therapy in utero and provides a basis for considering this concept as a preventive therapeutic strategy for haemophilia and perhaps also for other plasma protein deficiencies.

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.

Epsilon-aminocaproic acid inhibits the activity of factor VIII inhibitors in patients with severe haemophilia A in vivo and in vitro

Haemophilia patients with inhibitors pose a formidable challenge for patient management. This is particularly problematic in developing countries, where porcine factor VIII, FEIBA, factor VIIa or immunoadsorption column are generally unavailable or unaffordable. Under these circumstances, any effective modality of affordable treatment is welcome. We investigated, both in vivo and in vitro, the effect of epsilon-aminocaproic acid (EACA) on the inhibitory activity of factor VIII inhibitor. It was found that in vitro EACA (final concentration 1.25-5 mg/ml) substantially inhibited the activity of the inhibitors, while the same concentration of EACA had no effect on other immunological reactions like red cell agglutination and immunofluorescence. The inhibitory action of EACA on factor VIII inhibitor was also confirmed in an improvised antigen-binding ELISA system. Further, the inhibitory activity of EACA was confirmed in 2 patients, in whom the inhibitory activity persisted for 15 min following infusion of EACA (100 mg/kg over 10 min). EACA was found to be even more effective in local wound application in patients of haemophilia A with inhibitors. EACA at the concentration cited did not act as an inhibitor of factor VIII inhibitor through occupancy of lysine binding sites. The inhibitory activity of EACA on factor VIII inhibitor was equally seen with recombinant factor VIII also; hence this action cannot be explained by its antifibrinolytic activity.

Immune tolerance therapy for haemophilia

The development of anti-factor VIII and anti-factor IX allo-antibodies in haemophilia A and B, respectively, remains a serious complication of treatment for these two X-linked haemostatic disorders, with major clinical and economic consequences. Treatment of this potentially fatal complication remains one of the greatest challenges facing haematologists at the beginning of the 21st century. Immune tolerance induction (ITI) therapy has been generally accepted as the best available treatment, extinguishing the inhibitor and permitting a resumption of standard dosing schedules. Although there have been several established protocols for ITI therapy developed over the last quarter century, the optimal scheme in terms of safety, clinical efficacy and pharmacoeconomic considerations has yet to be determined.

Phospholipid binding of factor VIII in different therapeutic concentrates

Binding to anionic phospholipid (PL) is essential for the biological function of factor VIII (FVIII). We have developed a method to study the level of PL binding of FVIII in a variety of therapeutic concentrates, using the BIACORETM system which utilizes the Surface Plasmon Resonance (SPR) phenomenon. A HPA sensor chip was employed on to which synthetic phospholipid unilamellar vesicles were adsorbed to form a 3:1 phosphatidylcholine: phosphatidylserine lipid monolayer. Using this surface the interaction of unlabelled FVIII in concentrates was observed from which direct kinetic data (kon, koff and KD values) were obtained in real-time. Marked differences in the binding to PL, as measured by KD values, between different products were observed. These fell into three categories: two recombinant FVIII products showed high affinities for PL with KD values around 0. 05-0.14 nM; four high-purity plasma derived products, two prepared by monoclonal antibody and two prepared by ion-exchange chromatography, had 6-8-fold lower affinities, and two intermediate-purity products had 34-60-fold lower affinities with KD values in the nM region. Measurements of kon and koff values for each product showed that the differences in the KD values expressed were primarily due to the differences in their respective kon values, although the recombinant products showed changes in the koff values. The study showed that the assessment of binding to PL by FVIII in concentrates was possible without prior purification and gave KD values in the range reported previously for other methods. The difference between the products requires further investigation but may be partly due to other proteins present, in particular the content and quality of von Willebrand factor which is known to affect PL binding of FVIII.

Autoimmune factor VIII inhibitors

Dramatic hemorrhage can follow the rare, spontaneous development of inhibitory autoantibodies to factor VIII (FVIII). Diagnosis, which is often delayed, relies on complex, interpretive testing for presence and titer of the inhibitor antibody. Low cross reactivity of the inhibitor to porcine FVIII supports consideration of its therapeutic use. Recombinant activated factor VII has expanded available therapeutic options beyond prothrombin complex concentrates and their activated forms. Use of genetically engineered FVIII molecules has further defined immunodominant epitopes on FVIII and may provide a therapeutic alternative. The optimal region of immunosuppressive therapy remains to be defined. Future laboratory and clinical studies are necessary for advancement of pathophysiologic knowledge and therapeutic options for patients with this uncommon but clinically important disorder.