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

Summary.  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.     

Optimizing therapy with factor VIII/von Willebrand factor concentrates in von Willebrand disease

In von Willebrand disease, the main goals of treatment are to correct the dual defect of haemostasis caused by a reduced or abnormal von Willebrand factor (vWF), i.e. the prolonged bleeding time (BT) and the deficiency of factor VIII coagulant activity (FVIII:C). The synthetic vasopressin analogue, desmopressin (DDAVP), has reduced the need for transfusions in most of the mild forms of von Willebrand disease but DDAVP is ineffective in type 3 and in other severe cases of types 1 and 2 von Willebrand disease. For many years cryoprecipitate has been the mainstay of replacement therapy but, after the introduction of virucidal methods, concentrates containing FVIII/vWF have been considered much safer than cryoprecipitate and proposed in von Willebrand disease management. FVIII/vWF concentrates have been produced and tested by many authors but there is only one report describing four virus-inactivated FVIII/vWF concentrates evaluated in a cross-over randomized trial. According to these in vitro and pharmacokinetic data, the following information can be derived: (a) no FVIII/vWF concentrate had an intact multimeric structure similar to that of normal plasma or of cryoprecipitate; (b) all FVIII/vWF concentrates were equally effective in attaining normal and sustained levels of FVIII:C postinfusion, although peak levels were more delayed in the concentrate devoid of FVIII:C; (c) no FVIII/vWF concentrate consistently normalized the BT in a sustained fashion. On the other hand, clinical haemostasis can be achieved in the management of bleeding episodes and of surgery for most of von Willebrand disease cases regardless of whether the BT is corrected; in the few rare cases with mucosal bleeding not controlled by FVIII/vWF concentrates, infusion of DDAVP or platelet concentrates can be administered in addition.     

von Willebrand factor containing factor VIII concentrates

There are several plasma derived von Wille-brand factors (vWF) containing factor (FVIII) concentrates that can be used in the treatment of von Willebrand disease (vWD). All concentrates are effective in attaining normal postinfusion levels or of FVIII:C but it is difficult to achieve normalization of the bleeding time even with concentrates containing almost all vWF multimers including those of high molecular weight. Haemate P (Centeon) may be considered as the golden standard concentrate available at present. However, the development of more purified vWF concentrates devoid of FVIII:C is the goal for future development.     

Immune tolerance induction with highly purified plasma-derived factor VIII containing von Willebrand factor in hemophilia A patients with high-responding inhibitors

We retrospectively evaluated the efficacy of immune tolerance induction (ITI) in a homogenous cohort of eight patients with constitutive severe hemophilia A with high-responding factor VIII (FVIII) inhibitors using Facteur VIII-LFB/Factane, a highly purified FVIII concentrate containing von Willebrand factor (VWF).     

Characterization of von Willebrand factor in factor VIII concentrates

Commercial concentrates of factor VIII (FVIII) were analyzed in order to 1) determine the effects of viral inactivation on von Willebrand factor (vWF); 2) evaluate the vWF content of the new, immunopurified concentrates; and 3) assess their potential for correcting the long bleeding time of von Willebrand disease (vWD). Included in our study were products that had been treated to inactivate viruses; older, untreated products; and the new, immunopurified concentrates. We measured von Willebrand factor antigen (vWF:Ag), ristocetin cofactor activity (RCoF), and vWF multimeric and subunit composition. A newly developed radioimmunoassay (RIA) was used to quantitate vWF:Ag. The vWF:Ag content varied from 0.083 micrograms/IU FVIII:C for Hemofil M to 32.2 micrograms/IU FVIII:C for Humate-P, whereas pooled normal human plasma (NHP) contained 6.3 micrograms/IU FVIII:C. The RCoF varied from 0.0007 to 2.09 U/IU FVIII:C, with the immunopurified concentrates having the lowest values and Humate-P the highest. The ratio of RCoF to vWF:Ag ranged from 11 to 96 U/mg, as compared to a ratio of 160 for NHP. All of the concentrates lacked the largest vWF multimers, and all had abnormal triplet patterns. Modest differences between some untreated concentrates and their treated counterparts were noted. As expected, the immunopurified concentrates had much lower levels of all vWF activities than the conventionally prepared products. Our data suggest that none of the concentrates have as great a capacity as NHP to correct the prolonged bleeding time of von Willebrand disease.     

Comparative analysis and classification of von Willebrand factor/factor VIII concentrates: impact on treatment of patients with von Willebrand disease

von Willebrand disease (vWD) is a bleeding disorder that results from defects in the quality or quantity of von Willebrand factor (vWF), a glycoprotein essential for normal thrombus formation. vWF circulates in plasma as multimers in sizes ranging up to 20,000 kd. The high molecular weight vWF (HMWvWF) multimers are most essential for primary hemostasis, whereas the lower molecular weight multimers are less functionally active. For many patients, the treatment of choice is factor replacement with a vWF/FVIII concentrate, preferably one with a high content of HMWvWF multimers. Given that the commercially available vWF/FVIII concentrates seem to differ substantially in their biochemical properties as well as in their clinical efficacy, we did a comparative study with 12 vWF/FVIII concentrates to investigate content and activities of FVIII and vWF, as well as the content of HMWvWF multimers. The content of HMWvWF multimers varied considerably among the 12 concentrates. The specific vWF activities, as assessed by ristocetin cofactor activity (vWF:RCo) and collagen-binding activity (vWF:CB), correlated well with the HMWvWF content of the products. Of the products tested, Haemate P/Humate-P had the highest content of HMWvWF multimers (with a multimer pattern closest to that of normal human plasma), the highest specific vWF activities, and the highest values of vWF:RCo and vWF:CB per unit of FVIII:coagulant (C). The goal of bleeding prophylaxis and treatment in type 2, severe type 1, and type 3 vWD patients is to normalize vWF activities (vWF:RCo and vWF:CB) and FVIII:C preferentially by vWF/FVIII concentrates containing the high vWF multimers and a high vWF:RCo/FVIII ratio to achieve normal primary and secondary hemostasis. Based on the present study of a comparative analysis of currently available vWF/FVIII concentrates, a classification of vWF/FVIII products is proposed.     

Alloantibodies to therapeutic factor VIII in hemophilia A: the role of von Willebrand factor in regulating factor VIII immunogenicity

The rising incidence of neutralizing antibodies (inhibitors) against therapeutic factor VIII prompted the conduct of studies to answer the question as to whether this rise is related to the introduction of recombinant factor VIII products. The present article summarizes current opinions and results of non-clinical and clinical studies on the immunogenic potential of recombinant compared to plasma-derived factor VIII concentrates. Numerous studies provided circumstantial evidence that von Willebrand factor, the natural chaperone protein present in plasma-derived factor VIII products, plays an important role in protecting exogenous factor VIII from uptake by antigen presenting cells and from recognition by immune effectors. However, the definite contribution of von Willebrand factor in reducing the inhibitor risk and in the achievement of immune tolerance is still under debate.     

von Willebrand factor in factor VIII concentrates protects against neutralization by factor VIII antibodies of haemophilia A patients

We investigated the neutralization activity of factor VIII (FVIII) antibodies of 12 haemophilia A patients, acquired during treatment with plasma-derived FVIII concentrates. All plasma samples, drawn in a clinically stable situation before any immunotolerance treatment, contained anti-A2 domain and anti-light-chain FVIII antibodies. In nine patients' plasmas, containing relatively high amounts of FVIII light-chain antibodies (53-96%), a higher neutralization activity was found against recombinant FVIII concentrate (Recombinate) than against plasma-derived von Willebrand factor (vWF)-containing concentrate (Haemoctin SDH). No difference in neutralization of the two concentrates was found in two patients' plasmas with almost equal content of FVIII light- and heavy-chain antibodies, or one plasma with predominantly heavy-chain antibodies. These results suggest that haemophilia A patients with relatively high amounts of FVIII light-chain antibodies in plasma might benefit by infusion of FVIII concentrates containing vWF because vWF appears to have some protective effect on FVIII. This hypothesis should be tested by a clinical study.     

Characterization of factor VIII/von Willebrand factor concentrates using a modified method of von Willebrand factor multimer analysis

In order to provide patients with von Willebrand disease a factor VIII (FVIII)/von Willebrand factor (vWF) concentrate of reproducible quality, an SDS-agarose gel electrophoresis method has been established to determine the content of the high molecular weight multimers (band 11 and higher) of vWF. This method has been used to characterize the content of high molecular weight vWF multimers in Humate^® P/Haemate^® P, a commercial FVIII/vWF concentrate. The average content of high molecular weight vWF multimers of 47 batches of Humate^® P/Haemate^® P has been determined to be 84.1% of the corresponding bands in normal human plasma. Use of this multimer analysis method for the characterization of five further commercial products revealed clear differences with respect to the high molecular weight vWF multimer content. Furthermore, there is a linear correlation ( r ² = 0.73) between the content of high molecular weight vWF multimers and the specific activity of vWF (determined as vWF:RCoF/vWF:Ag). The method described here for analysis of the content of high molecular weight vWF multimers is a reliable and reproducible method to characterize this class of factor concentrates with respect to vWF multimer composition.     

Early transfusion of factor VIII/von Willebrand factor concentrates seems to be effective in the treatment of gatrointestinal bleeding in patients with von Willebrand type III disease

The association between gastrointestinal angiodysplasia and von Willebrand disease was reported 30 years ago. The clinical course of patients with von Willebrand disease and angiodysplasia is characterized by numerous admissions to hospital for gastrointestinal bleeding necessitating transfusion with packed red cells, factor VIII and plasma. The management of these patients is problematic. Numerous treatments for the gastrointestinal bleeding have been proposed: surgery, electrocoagulation, laser photocoagulation, sclerotherapy, arteriography with embolization, immunoglobulins, oestrogens, and octreotide, but no treatment modality has been successful in all cases. We report a 66-year-old-female with small bowel angiodysplasia and von Willebrand type III disease in whom prompt administration of factor VIII/vWF concentrates was effective. Education of patients to recognize minimal gastrointestinal bleeding manifestations, periodical clinical visits and early infusion of factor VIII/vWF seems to be fundamental for the success of this therapy. A longer follow-up and the study of other patients are needed to confirm our observation.     

The roles of von Willebrand factor and factor VIII in arterial thrombosis: studies in canine von Willebrand disease and hemophilia A

We have studied the roles of von Willebrand factor (vWF) and factor VIII in arterial thrombosis in four canine phenotypes: normal (n = 6), hemophilia A (n = 11), von Willebrand disease (vWD) (n = 9), and hemophilia A/vWD (n = 1). vWF activity was determined by botrocetin- induced agglutination of fixed human platelets and vWF antigen (vWF:Ag) by Laurell electroimmunoassay and crossed immunoelectrophoresis. Plasma from normal dogs and those with hemophilia A had vWF activity, vWF:Ag, and a full range of vWF:Ag multimers on gel electrophoresis equivalent to normal canine plasma pool. Platelet cytosol contents were isolated by freezing and thawing, triton X-100 solubilization, or sonication of washed platelets with and without protease inhibitors and inhibitors of platelet activation. Washed platelets were also stimulated with calcium ionophore and MgCl2. There was no measurable vWF activity or vWF:Ag in platelet lysates or releasates in any dog regardless of phenotype. All dogs were studied using a standard arterial stenosis and injury procedure to induce arterial thrombosis. Thromboses were detected by cyclic reductions in Doppler blood flow velocity. Vessels were examined by light and scanning electron microscopy. Thrombosis developed in the arteries of normal (9 of 10) and hemophilia A dogs (16 of 16) but in none of the vWD dogs (0 of 10). Infusion of canine vWF cryoprecipitate into vWD dogs markedly shortened bleeding time but did not support thrombosis as seen in dogs with vWF in the plasma and subendothelium. Thrombosis, then, fails to occur when vWF is absent from the plasma and subendothelial compartments or present only in the plasma compartment. These data are consistent with the hypothesis that vWF in the plasma and subendothelium supports thrombosis. Neither plasma FVIII nor platelet vWF is essential for thrombosis in this model.     

Progress in large-scale purification of factor VIII/von Willebrand factor concentrates using ion-exchange chromatography

Background and Objectives We investigated and optimized the parameters of a chromatographic process suitable for industrial scale to obtain a highly purified factor VIII (FVIII)/von Willebrand factor (VWF) concentrate. Materials and Methods Several chromatographic runs were performed on the same production intermediate using different anion-exchange supports. The best matrix was selected and the final product was characterized. Once the chromatographic medium was chosen, the other parameters were evaluated to obtain the highest purified product and to modulate the VWF content in the FVIII/VWF complex. Results Fractogel EMD TMAE was the best support among those tested. It was the only one maintaining good results either with standard or double loading and flow rate conditions with respect to a typical industrial process. The chromatographic recovery of FVIII co-purified with VWF was at least 86% with a specific activity not lower than 140 IU/mg. The FVIII/VWF complex obtained is highly pure and, with the exception of immunoglobulin M (IgM), all investigated contaminant proteins are under the detection limit. Different concentrates characterized by variable FVIII/VWF ratios were purified by varying the chromatographic conditions. Conclusions Several highly purified products, suitable for haemophilia A and von Willebrand disease management, can be obtained, through the same chromatographic process, on an industrial scale.     

ADAMTS13 content in plasma‐derived factor VIII/von Willebrand factor concentrates

Thrombotic thrombocytopenic purpura (TTP) is a microangiopathy syndrome caused by a congenital or acquired deficiency of ADAMTS13, a plasma metalloprotease that cleaves von Willebrand factor (VWF) and thus prevents the formation of platelet‐rich thrombi in the microcirculation. TTP can be fatal if not appropriately and timely treated with the infusion of fresh frozen plasma (FFP) or exchange plasmapheresis, that reverse the process of microangiopathy by removing anti‐ADAMTS13 autoantibodies and replacing functional ADAMTS13. The treatment of TTP with FFP is not free from risks and must be administered in hospitals or clinics, owing to the substantial amount of plasma volume infused or exchanged and the frequent need of catheter application. Moreover, most FFPs are not subjected to treatments to remove or inactivate blood‐borne infectious agents. A number of recent reports indicate that certain plasma‐derived VWF‐factor VIII (FVIII) concentrates are clinically effective in the treatment of congenital TTP. In this study, we measured ADAMTS13 levels in various plasma‐derived VWF‐FVIII concentrates, showing that Koate^®‐DVI (Grifols), contained relatively high amounts of ADAMTS13 and that Alphanate^® (Grifols) was the closest other product in terms of protease content. Koate^®‐DVI contains, on average (five lots tested), 0.091 ± 0.007 Units of ADAMTS13 activity per IU of FVIII. On the basis of this analysis and other reports of VWF‐FVIII concentrate utilization in congenital TTP, potential dosing, and future clinical developments are discussed. Am. J. Hematol. 88:895–898, 2013. © 2013 Wiley Periodicals, Inc.     

In vitro reactivity of factor VIII inhibitors with von Willebrand factor in different commercial factor VIII concentrates

A relevant aspect in the treatment of patients with hemophilia A (HA) presenting inhibitor against factor VIII (FVIII) is the different antigenicity of FVIII used for replacement therapy. The aim of the study was to assess the effect of different products, with variable von Willebrand factor (vWF) concentration, in preventing the binding of inhibitor to FVIII. The reactivity of inhibitors from plasma of 18 patients with HA versus three commercial concentrates containing different amounts of vWF was compared. The results show that increasing amounts of vWF might have a protective effect on the transfused FVIII inactivation.     

Relationships between factor VIII:Ag and factor VIII in recombinant and plasma-derived factor VIII concentrates

A variety of plasma-derived (pd) and recombinant (r) factor VIII (FVIII) concentrates are used to prevent and treat bleeding in severe hemophilia A patients. A significant side effect of FVIII replacement is the development of FVIII neutralizing antibodies (inhibitors) in up to 30% of patients receiving FVIII concentrates. The FVIII protein content (FVIII:Ag) per unit of FVIII:C in FVIII concentrates, and how effectively the FVIII:Ag in FVIII concentrates binds to von Willebrand factor (VWF) may provide information relevant for the survival of FVIII:C in vivo and for estimating the risk for inhibitor development. The FVIII:Ag content of nine r-FVIII and nine pd-FVIII concentrates were quantified in this study using two enzyme-linked immunosorbent assay (ELISA) platforms. The two ELISA platforms were based on the use of a monoclonal anti-(FVIII light chain)-IgG and polyclonal anti-FVIII antibodies as capture antibodies and both ELISAs were equally able to detect > or =0.005 IU of FVIII:Ag. Measured in international units, the r-FVIII concentrates contained significantly higher FVIII:Ag per unit of FVIII:C than the pd-FVIII concentrates. The VWF-binding profiles of the r-FVIII and pd-FVIII concentrates were also determined by gel filtration chromatography. Unlike the plasma-derived products, the r-FVIII concentrates invariably contained a fraction of FVIII:Ag molecules (approximately 20%) which was unable to associate with VWF. Given that VWF regulates both factor VIII proteolysis and survival of FVIII:Ag in vivo, the fraction of FVIII:Ag unable to bind to VWF may have a reduced survival and be more susceptible to proteolytic degradation in vivo. The extent to which the fractions of FVIII:Ag in concentrates able and unable to bind to VWF contribute to inhibitor development in severe FVIII-deficient patients is unknown.     

Pharmacokinetics and hemostatic effect of different factor VIII/von Willebrand factor concentrates in von Willebrand's disease type III

Summary Four different plasma-derived concentrates composed of coagulation factor VIII (FVIII) and von Willebrand factor (vWF) of varying quality (Hemate-P, Behring; Profilate, Alpha; and FVIII-VHP-vWF, C.R.T.S Lille), or almost purified vWF (Facteur Willebrand, C.R.T.S Lille) and one recombinant FVIII concentrate (Recombinate, Baxter) were given, in doses of 30–60 IU VIII:C/kg or 70–110 IU RCof/kg, to five patients with von Willebrand's disease type III, in order to evaluate the role of the vWF in factor FVIII concentrates. All plasma concentrates except Profilate had a multimeric vWF pattern almost similar to that of normal plasma. Bleeding time (b.t.), VIII:C, vWF: Ag, ristocetin cofactor activity, and multimeric pattern of the plasma-vWF were followed for 72 h. Both Duke b.t. and the multimeric pattern in plasma normalized after infusion of Hemate-P, FVIII-VHP-vWF, and Facteur Willebrand and, to a lesser extent, after Profilate. As expected, in response to Recombinate there was no effect on primary hemostasis, and the half-life of FVIII procoagulant activity (VIII:C) was very short. Normalization of the vWF is important not only for improving the primary hemostasis, but also for maintaining the plasma FVIII concentration on a high level, both by reducing the elimination rate of infused FVIII and via a secondary release of endogenous FVIII. If a prompt hemostatic effect is required, we recommend a concentrate containing both FVIII and all vWF multimers, but for prophylactic treatment, pure vWF may be used.     

Continuous factor VIII infusion therapy in patients with haemophilia A undergoing surgical procedures with plasma-derived or recombinant factor VIII concentrates

We describe the experience of a single medical centre with continuous factor VIII (FVIII) infusion therapy in a cohort of patients undergoing elective surgery. Twenty-eight patients had a total of 45 procedures. Intraoperative haemostasis was considered excellent in all 45 cases. FVIII levels were maintained between 46% and 191% of normal (median, 103%) for 2-7 days. Bleeding occurred after five procedures (11%) at times when factor VIII levels were within haemostatic range. No patient required reoperation to control bleeding. There were no cases of sepsis related to continuous infusion of factor VIII. We conclude that continuous infusion: (1) is a safe and effective means of replacement therapy in patients with haemophilia undergoing surgery; (2) provides easier monitoring and more constant coagulation factor levels; and (3) has the potential to decrease the cost of replacement therapy by reducing overall usage of product.