Human recombinant DNA-derived antihemophilic factor in the treatment of previously untreated patients with hemophilia A: final report on a hallmark clinical investigation

BAY 81-8973 Efficacy and Safety in Previously Untreated and Minimally Treated Children with Severe Hemophilia A: The LEOPOLD Kids Trial

INTRODUCTION

 BAY 81-8973, a full-length recombinant factor VIII for hemophilia A treatment, has been extensively evaluated in previously treated patients in the LEOPOLD (Long-Term Efficacy Open-Label Program in Severe Hemophilia A Disease) clinical trials.

AIM

 To assess BAY 81-8973 efficacy and safety when used for bleed prophylaxis and treatment in previously untreated/minimally treated patients (PUPs/MTPs).

METHODS

 In this phase III, multicenter, open-label, uncontrolled study, PUPs/MTPs (<6 years old) with severe hemophilia A received BAY 81-8973 (15-50 IU/kg) at least once weekly as prophylaxis. Primary efficacy endpoint was the annualized bleeding rate (ABR) within 48 hours after prophylaxis infusion. Adverse events and immunogenicity were assessed. Patients who developed inhibitors were offered immune tolerance induction (ITI) treatment in an optional extension phase.

RESULTS

 Fifty-two patients were enrolled, with 43 patients (mean age: 13.6 months) treated. Median (interquartile range) ABR for all bleeds within 48 hours of prophylaxis infusion was 0.0 (0.0-1.8) among patients without inhibitors (n = 20) and 0.0 (0.0-2.2) among all patients. As expected, inhibitors were the most frequent treatment-related adverse event (high titer: 17 [39.5%] patients; low titer: 6 [13.9%] patients). Six of 12 patients who underwent ITI treatment in the extension phase (high titer [n = 5], low titer [n = 1]) achieved a negative inhibitor titer.

CONCLUSION

 BAY 81-8973 was effective for bleed prevention and treatment in PUPs/MTPs. The observed inhibitor rate was strongly influenced by a cluster of inhibitor cases, and consequently, slightly higher than in other PUP/MTP studies. Overall, the BAY 81-8973 benefit-risk profile remains unchanged and supported by ongoing safety surveillance. Immune tolerance can be achieved with BAY 81-8973.

Secondary failure: immune responses to approved protein therapeutics

Recombinant therapeutic proteins are a broad class of biological products used to replace dysfunctional human proteins in individuals with genetic defects (e.g., factor VIII for hemophilia) or, in the case of monoclonal antibodies, bind to disease targets involved in cancers, autoimmune disorders, or other conditions. Unfortunately, immunogenicity (immune response to the drug) remains a key impediment, potentially affecting the safety and efficacy of these therapeutics. Immunogenicity risk is routinely evaluated during the licensure of therapeutic proteins. However, despite eliciting anti-drug immune responses in at least some patients, most protein drugs are nevertheless licensed as they address unmet medical needs. The pre-licensure immunogenicity assessments of therapeutic proteins are the subject of numerous reviews and white papers. However, observation and clinical management of the immunogenicity of approved therapeutic proteins face additional challenges. We survey the immunogenicity of approved therapeutic proteins, discuss the clinical management of immunogenicity, and identify the challenges to establishing clinically relevant immunogenicity assays for use in routine clinical practice.

Immune Responses to Plasma-Derived Versus Recombinant FVIII Products

The most severe side effect of hemophilia treatment is the inhibitor development occurring in 30% of patients, during the earliest stages of treatment with factor (F)VIII concentrates. These catastrophic immune responses rapidly inactivate the infused FVIII, rendering the treatment ineffective. This complication is associated with a substantial morbidity and mortality. The risk factors involved in the onset of the inhibitors are both genetic and environmental. The source of FVIII products, i.e. plasma-derived or recombinant FVIII products, is considered one of the most relevant factors for inhibitor development. Numerous studies in the literature report conflicting data on the different immunogenicity of the products. The SIPPET randomized trial showed an increased in the inhibitor rate in patients using recombinant FVIII products than those receiving plasma-derived products in the first exposure days. The SIPPET randomized trial showed an increase in the inhibitor rate in patients using recombinant FVIII products compared to those treated with plasma-derived products in the first days of exposure. The potential increase in the immunogenicity of recombinant products can be attributed to several factors such as: the different post-translational modification in different cell lines, the presence of protein aggregates, and the role played by the chaperon protein of FVIII, the von Willebrand factor, which modulates the uptake of FVIII by antigen presenting cells (APCs). Furthermore, the presence of non-neutralizing antibodies against FVIII has shown to be in increased inhibitor development as demonstrated in a sub-analysis of the SIPPET study. In addition, the presence of the specific subclasses of the immunoglobulins may also be an important biomarker to indicate whether the inhibitor will evolve into a persistent neutralizing antibody or a transient one that would disappear without any specific treatment. Recently, the availability of novel non-replacement therapies as well as emicizumab, administered by weekly subcutaneous infusion, have significantly changed the quality of life of patients with inhibitors showing a considerable reduction of the annual bleeding rate and in most patients the absence of bleeding. Although, these novel drugs improve patients' quality of life, they do not abolish the need to infuse FVIII during acute bleeding or surgery. Therefore, the issue of immunogenicity against FVIII still remains an important side effect of hemophilia treatment.

Epidemiological Challenges in Rare Bleeding Disorders: FVIII Inhibitor Incidence in Haemophilia A Patients-A Known Issue of Unknown Origin

There is a broad range of factor products approved in Germany for haemophilia A treatment. Since the introduction of recombinant coagulation factor VIII (FVIII) products in the 1990s, there has been substantial debate whether there is a difference in inhibitor incidence between single FVIII products or product classes. Neither haemophilia registries nor clinical studies, including a randomised controlled clinical trial, provided a consistent and definite answer. The reasons were mainly related to methodological challenges in conducting controlled studies in a rare disease. In this analysis, the most relevant epidemiological challenges and main problems were examined, including study bias, potential overlap of individual studies and advanced development of therapy and methods in the course of time. Meta-analyses on two levels showed that therapies using recombinant products resulted in different event rates when compared to plasma-derived products. These results are accompanied by substantial study heterogeneity evidenced by Cochran's Q tests. Only three studies have been identified that meet the standards of current clinical guidance. To finally resolve this ongoing and disputable safety issue of replacement therapy, collaboration among registry owners, academia and regulators must be fostered.

Meta-analysis on incidence of inhibitors in patients with haemophilia A treated with recombinant factor VIII products

: Recent cohort studies showed differences in inhibitor incidence in previously untreated patients (PUPs) with haemophilia A treated with recombinant factor VIII (rFVIII) concentrates. We carried out a systematic literature search and meta-analysis for all randomized clinical trials and observational studies published from 1 January 1988 to 31 August 2015, to assess the incidence of inhibitor development and the relationship with rFVIII product used in PUPs and minimally treated patients (MTPs, ≤5 previous exposure days), with severe haemophilia. The primary outcome measure was development of all inhibitors and high-titre inhibitors. We computed pooled meta-analytic estimates according to the rFVIII product used with the inverse-variance method, assuming a fixed, or a random-effects model if significant between-studies heterogeneity was present. Out of 781 articles, 16 published between 1998 and 2015 were included in the meta-analysis, involving a total of 2094 haemophilia A PUPs or MTPs. The pooled estimate of all inhibitors was 0.27 (95% confidence interval 0.23-0.31). No significant difference in pooled inhibitor incidence across products was found (P = 0.72). Meta-analysis of studies reporting inhibitor hazard ratios with different rFVIII products, adjusted to different risk factors, showed that PUPs/MTPs treated with Advate had a pooled inhibitor hazard ratio estimate of 0.63 (95% confidence interval 0.48-0.83) as compared with Kogenate FS. The overall inhibitor incidence in PUPs/MTPs was 27%. Differences between products were found considering hazard ratios in which potential confounders were taken into account.

BAY 81-8973, a full-length recombinant factor VIII for the treatment of hemophilia A: product review

BAY 81-8973 (Kovaltry^®) is an unmodified, full-length recombinant factor VIII (rFVIII) approved for the prevention and treatment of bleeding episodes in patients with hemophilia A. The amino acid sequence for BAY 81-8973 is identical to that of sucrose-formulated rFVIII (rFVIII-FS; Kogenate^® FS/KOGENATE^®, Bayer), but the two products differ in their manufacturing approaches. The manufacture of BAY 81-8973 includes several modifications and enhancements, such as the introduction of the gene for human heat shock protein 70, a molecular chaperone protein that facilitates folding of proteins; no addition of human- or animal-derived proteins in the cell culture, purification process, or final formulation; and use of a 20-nm filter to remove any potential aggregates and pathogens. BAY 81-8973 was extensively studied in the LEOPOLD clinical development program, which enrolled participants of all age groups (children, adolescents, and adults) with severe hemophilia A. The pharmacokinetic profile of BAY 81-8973 was shown to be noninferior to, and for some variables more favorable than, rFVIII-FS and another commercial full-length rFVIII product. BAY 81-8973 was shown to be efficacious when used for prophylaxis, on-demand treatment, and perioperative hemostasis. The efficacious prophylaxis dose of BAY 81-8973 was approximately 20-40 IU/kg given two or three times per week, which achieved low annualized bleeding rates. Either the one-stage or the chromogenic assay provides accurate measurements for postinfusion monitoring of BAY 81-8973 levels, with no product-specific calibration standard needed. The incidence of treatment-related adverse events was ⩽7% across all LEOPOLD studies, and no previously treated patient developed anti-BAY 81-8973 inhibitors in the completed primary studies.

Safety and effectiveness of room temperature stable recombinant factor VIIa in patients with haemophilia A or B and inhibitors: Results of a multinational, prospective, observational study

INTRODUCTION

A room temperature stable formulation of recombinant activated factor VII (NovoSeven^® ), allowing convenient storage and therefore improved treatment access, has been developed. Bioequivalence to the previous NovoSeven^® was demonstrated in healthy humans, leading to European approval (2008). Although no confirmed cases of neutralising antibodies to rFVIIa in patients with haemophilia A or B have been observed with the original formulation, changes in formulation or storage condition may alter immunogenicity.

AIM

SMART-7™ was designed to investigate the safety of NovoSeven^® in a real-world setting in patients with haemophilia A or B with inhibitors.

METHODS

Study medication was not provided by the sponsor, and treatment was at the discretion of the treating physician, in accordance with the local label. Patient baseline information was collected at enrolment. Information on safety, drug exposure and bleeding episodes was collected and FVII antibody screening was encouraged at baseline and performed at the investigator's discretion.

RESULTS

Fifty-one patients were enrolled and 31 completed the study. Forty-one adverse events (AEs) were reported in 23 patients; 25 AEs in 14 patients were serious. No thromboembolic events were observed. Although four cases of reduced therapeutic response were reported, FVII antibody screening was negative. Forty-eight patients experienced 618 bleeding episodes and 93.4% of 609 evaluated bleeds were stopped by treatment. Of the 538 bleeding episodes treated with NovoSeven^® monotherapy, 94.2% stopped by end of treatment.

CONCLUSION

Data collected during the SMART-7™ study revealed no treatment-related safety issues and no FVII-binding antibodies for patients treated with NovoSeven^® under real-world conditions.

Baby hamster kidney cell-derived recombinant factor VIII: a quarter century of learning and clinical experience

INTRODUCTION

Management and care of individuals with hemophilia A advanced immensely with the introduction of recombinant factor VIII (rFVIII) replacement products. This review provides a historical overview of rFVIII development with a focus on Bayer's rFVIII (with albumin) and sucrose-formulated rFVIII (rFVIII-FS), the only rFVIII products cloned in baby hamster kidney (BHK) cells with >25 years of proven safety and efficacy. Areas covered: We review the advances in rFVIII technology and the efficacy and safety data for BHK-derived rFVIII/rFVIII-FS from clinical trials, investigator-initiated studies, and observational studies. Innovative products with new treatment potentials (eg, BAY 81-8973 and BAY 94-9027) built on this established safety and efficacy profile are also briefly discussed. The literature search strategy included targeted searches (PubMed) with manual article selection and other product-specific searches. Expert commentary: Development of rFVIII products and related improvements in viral safety and manufacturing efficiency have guaranteed an adequate supply of factor products worldwide and increased prophylaxis use. The net effects have been joint health preservation, reduction in morbidity and mortality, and quality-of-life enhancements. Current treatment challenges include lack of adherence to prophylaxis and inhibitor development; extended-half-life rFVIII products and non-FVIII replacement therapies in development may help overcome these challenges.

Analysis of the Japanese subgroup in LEOPOLD II: a phase 2/3 study of BAY 81-8973, a new recombinant factor VIII product

BAY 81-8973, a new full length recombinant FVIII product, has been developed for prophylaxis and on-demand therapy in patients with hemophilia A. LEOPOLD II was a phase 2/3 study comparing prophylaxis versus on-demand treatment with BAY 81-8973. The analysis herein evaluated the clinical profile in Japanese subjects enrolled in LEOPOLD II. The LEOPOLD II was an open-label randomized crossover study. Our analysis evaluated the efficacy using the annualized bleeding rate, safety, and pharmacokinetics in Japanese subjects with severe hemophilia A enrolled in LEOPOLD II. The median annualized bleeding rate was 59.9/year in the on-demand group and 1.9/year in the prophylaxis group for Japanese subjects. There were no study drug-related adverse events in the Japanese subjects. None of the subjects developed FVIII inhibitors. There were no apparent clinical differences in efficacy, safety, and pharmacokinetics between the Japanese and the non-Japanese subjects. Data for the Japanese subjects showed annualized bleeding rates to be remarkably lower in the prophylaxis group compared to the on-demand group and that BAY 81-8973 exhibited a good safety profile and tolerability. These results were similar for the non-Japanese subjects. The results support adoption of BAY 81-8973 for treatment of Japanese subjects with severe hemophilia A.

A close insight to factor VIII inhibitor in the congenital hemophilia A

INTRODUCTION

Hemophilia A (HA) has an X-linked pattern of inheritance and is the most common of the hemorrhagic disorders. HA is caused by a decreased or deficiency of the functional clotting factor VIII (FVIII) and effects 1 in 5000-10,000 male births. The common treatment for hemophilia is replacement therapy by plasma-derived or recombinant FVIII. Approximately 20-30% of people with a severe type of HA develop an inhibitor and this phenomenon is the main challenge in the management of these patients. Genetic factors and environmental determinants contribute to inhibitor development. Here, the roles of various genetic and environmental factors such as the type of FVIII concentrate used, the number of exposure days, and peak treatment time will be discussed in detail. It seems this information is helpful for hematologists.

AREAS COVERED

A literature review was done in January 2016 on PubMed and Scopus using the following keywords:' h(a)emophilia A & factor VIII inhibitor', 'h(a)emophilia A & factor VIII alloantibody', 'h(a)emophilia A & inhibitor'. There was no time limitation; however, there was an English language limitation placed on the articles selected. Expert commentary: Influential genetic and environmental factors in developing inhibitors have been discussed. Most of the risk factors are related to previously untreated patients with hemophili.

Advances in the clinical management of inhibitors in hemophilia A and B

Inhibitors to factor (F)VIII or FIX are the most serious and challenging complication of hemophilia treatment, increasing morbidity and mortality because bleeds no longer respond to standard clotting factor replacement therapy. For patients with high-titer inhibitors, immune tolerance induction achieved through regular factor exposure is the only proven therapy capable of Inhibitor eradication and is almost always indicated for inhibitors of recent onset. Bypassing therapy is used to treat and prevent bleeding, but neither of the two currently available bypassing agents has the predictable hemostatic efficacy of factor replacement in hemophilia patients without inhibitors. Major research efforts are focused on the development of new, more potent therapies for the management of patients with inhibitors.

Clinical advances in hemophilia management

Hemophilia is an excellent example in medicine where clinical translation of basic science discoveries has transformed the gloomy outlook of the disease. This review provides an overview of clinical advances in hemophilia management with a specific focus on the molecular heterogeneity of the disease and progress in management of patients with inhibitors. Novel therapeutics and the emerging ethical issues in the field of hemophilia are also discussed.

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.

Suppression of the immune response to FVIII in hemophilia A mice by transgene modified tolerogenic dendritic cells

Current methods for eradicating clinically significant inhibitory antibodies to human factor VIII (hFVIII) in patients with hemophilia A rely on repeated delivery of high doses of factor concentrates for a minimum of many months. We hypothesize that tolerance can be induced more efficiently and reliably through hFVIII antigen presentation by tolerogenic dendritic cells (tDCs). In this study, we generated tDCs from hemophilia A mice and modified them with a foamy virus vector expressing a bioengineered hFVIII transgene. Naive and preimmunized mice infused with hFVIII expressing tDCs showed suppression of the T cell and inhibitor responses to recombinant hFVIII (rhFVIII). Treatment with hFVIII expressing tDCs was also associated with a higher percentage of splenocytes demonstrating a regulatory T cell phenotype in immunized mice. Furthermore, CD4(+) T cells harvested from recipients of hFVIII expression vector-modified tDCs were able to mediate antigen-specific immune suppression in naive secondary recipients. We also demonstrated a trend for improved suppression of inhibitor formation by coexpressing interleukin-10 (IL-10) and hFVIII from a bicistronic vector. These preclinical results demonstrate the potential for employing vector modified ex vivo generated tDCs to treat high titer inhibitors in patients with hemophilia A.

Review of antihemophilic factor injection for the routine prophylaxis of bleeding episodes and risk of joint damage in severe hemophilia A

Individuals with severe factor VIII deficiency experience recurrent hemorrhages and develop progressive joint damage. Large retrospective, nonrandomized studies of patient cohorts followed over decades show that factor prophylaxis initiated at an early age before the onset of recurrent bleeding reduces the incidence of hemophilic arthropathy. Two recent prospective, multicenter, randomized trials conducted in Europe (the ESPRIT study) and the USA (the Joint Outcome Study) confirm the efficacy of prophylaxis in the prevention of hemarthroses and arthropathy. Regular prophylaxis initiated in early childhood enhances the quality of life for patients with severe hemophilia and reduces the risk of inhibitor development. The substantial costs of such preventative therapy may be offset by the reduced expenditures that the care of degenerative joint disease in adult hemophilia patients would otherwise require.

Evolution of recombinant factor VIII safety: KOGENATE and Kogenate FS/Bayer

The use of factor VIII (FVIII) concentrates in the treatment of hemophilia A has raised important safety issues, historically of pathogen transmission and increasingly of inhibitor development to FVIII treatment. While manufacturing processes of current recombinant FVIII products have been shaped entirely around preventing pathogen transmission, the same modifications that afford a greater margin of safety could affect immunogenicity of the product, consequences of which could only be seen through long-term clinical experience. This review summarizes pathogen safety and inhibitor reports from clinical trials, post-marketing surveillance studies, and study reports on KOGENATE and its successor, Kogenate FS/Bayer. Although KOGENATE and Kogenate FS/Bayer are nearly identical products, subtle manufacturing improvements to address the need for greater margins of safety from a pathogen transmission perspective have also led to a potentially improved immunogenicity profile (15% in previously untreated/minimally treated patients with severe hemophilia A for Kogenate FS/Bayer). Notably, there has been no occurrence of pathogen contamination, and minimal de novo inhibitor formation in previously treated patients throughout the use of both products. Overall, KOGENATE and Kogenate FS/Bayer have a long history of safety in a variety of clinical settings, including treatment of bleeding, surgical management, and prophylaxis therapy.

Suppression of FVIII inhibitor formation in hemophilic mice by delivery of transgene modified apoptotic fibroblasts

The development of inhibitory antibodies to factor VIII (FVIII) is currently the most significant complication of FVIII replacement therapy in the management of patients with severe hemophilia A. Immune tolerance protocols for the eradication of inhibitors require daily delivery of intravenous FVIII for at least 6 months and are unsuccessful in 20-40% of treated patients. We hypothesize that tolerance can be induced more efficiently and reliably by delivery of FVIII antigen within autologous apoptotic cells (ACs). In this study, we demonstrated suppression of the T cell and inhibitor responses to FVIII by infusion of FVIII expression vector modified apoptotic syngeneic fibroblasts in both naive and preimmunized hemophilia A mice. ACs without FVIII antigen exerted modest generalized immune suppression mediated by anti-inflammatory signals. However, FVIII expressing apoptotic syngeneic fibroblasts produced much stronger antigen-specific immune suppression. Mice treated with these fibroblasts generated CD4+ T cells that suppressed the immune response to FVIII after adoptive transfer into naive recipients and antigen-specific CD4+CD25+ regulatory T cells (Tregs) that inhibited the proliferation of FVIII responsive effector T cells in vitro. These preclinical results demonstrate the potential for using FVIII vector modified autologous ACs to treat high-titer inhibitors in patients with hemophilia A.

Risk factors for inhibitor formation in haemophilia: a prevalent case-control study

Inhibitor formation is a major complication of haemophilia treatment. In a prevalent case-control study, we evaluated blood product exposure, genotype and HLA type on haemophilia A inhibitor formation. Product exposure was extracted from medical records. Genotype was determined on stored DNA samples by detection of virtually all mutations-SSCP (DOVAM-S) and subcycling PCR. HLA typing was performed by PCR amplification and exonuclease-released fluorescence. Cases experienced higher intensity factor, 455 vs. 200 U per exposure, P < 0.005, more frequent central nervous system (CNS) bleeding, seven of 20 (35.0%) vs. one of 57 (1.7%), P = 0.001 and more commonly from inhibitor families, seven of 20 (35.0%) vs. zero of 57 (0%), P < 0.001, and African-American, 12 of 63 (19.0%) vs. six of 117 (5.1%), P = 0.015. Among the latter, CNS bleeding was more commonly the initial bleed, 60% vs. 0%, P < 0.001, and survival was shorter, 14 vs. 38 yr, P = 0.025. Inhibitor formation was uncommon in those with missense mutations, two of 65 (3.1%) vs. 31 of 119 (26.0%), P = 0.008, and unrelated to factor VIII immunogenic epitope, P = 0.388, or HLA type, P > 0.100. Genotype was not associated with race. Time to immune tolerance was shorter for titres <120 vs. > or = 120 BU/mL, six vs. 16 months, P < 0.01, but unaffected by tolerizing dose regimen, P > 0.50. Inhibitor formation is associated with high intensity product exposure, CNS bleeding, African-American race and low frequency of missense mutations. The ideal time to initiate prophylaxis to reduce CNS bleeding and inhibitor formation will require prospective studies.

Repeated administration of recombinant human serum albumin caused no serious allergic reactions in patients with liver cirrhosis: a multicenter clinical study

BACKGROUND

We carried out a multicenter study to evaluate the safety of recombinant human serum albumin (rHSA), developed using the methylotrophic yeast Pichia pastoris, during and after repeated administration in patients with liver cirrhosis.

METHODS

rHSA was administered to 423 cirrhosis patients with ascites or edema. rHSA was administered three times over 3 days, and each 3-day treatment course was repeated at least three times with an interval of at least 2 weeks between courses. Adverse drug reactions (ADRs) were monitored during and after repeated rHSA administration. Specific antibody titers against Pichia yeast components were measured before and after treatment. Efficacy was evaluated on the basis of changes in serum albumin level, colloid osmotic pressure, and body weight.

RESULTS

ADRs were observed in 96 of 423 patients (22.7%), with no serious allergy or difference in the incidence of ADRs observed among the first, second, and third administrations. Specific IgE and IgG antibodies were detected before treatment in 19 and 422 patients, respectively. However, allergic ADRs were observed in 14 patients in whom specific IgE antibodies were not detected. No obvious relationship between allergic ADRs and specific IgE or IgG titers was identified. Serum albumin levels and colloid osmotic pressure increased significantly (P < 0.0001), and body weight decreased significantly (P < 0.0001) after rHSA administration.

CONCLUSIONS

rHSA caused no serious allergic reactions even when three treatment courses were administered at intervals of at least 2 weeks.

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.

Immune tolerance therapy utilizing factor VIII/von Willebrand factor concentrate in haemophilia A patients with high titre factor VIII inhibitors

Factor VIII (FVIII) inhibitors remain a serious complication of treatment for patients with haemophilia A. Immune tolerance induction (ITI) can eliminate inhibitors in the majority of patients, but there are major concerns related with this therapy. Investigators have raised the possibility that the use of FVIII/von Willebrand factor (FVIII/VWF) concentrates may improve the success rate of ITI and may shorten the duration of therapy necessary to attain tolerance. This retrospective study describes 25 patients at five institutions in the USA, who were treated with FVIII/VWF concentrate as part of their ITI. These were all patients who were considered poor prognosis because of clinical and laboratory characteristics, which made ITI less likely to be successful or because of a poor response to initial ITI with a monoclonal/recombinant FVIII concentrate. Overall success (complete tolerization) was 32% with another 40% attaining partial tolerization, but not complete tolerization. Of those patients attaining only partial tolerization, two patients ultimately discontinued ITI and had return of their high titre inhibitors. Eight percent of patients failed to attain either partial or complete tolerization and discontinued ITI. Another 24% are continuing with ITI but have titres of >10 BU. This study adds further retrospective data to the information regarding the use of FVIII/VWF concentrate in ITI.

Coagulation factor concentrates: past, present, and future

Clotting factor transfusions are vital for people with diseases such as haemophilia. In the 1970s and 1980s, transfusions with pooled plasma led to a devastatingly high number of recipients becoming infected with blood-borne pathogens such as HIV and hepatitis C. This epidemic triggered the development of virus-free factor concentrates through a combination of improved donor selection and screening, effective virucidal technologies, and recombinant protein expression biotechnology. There is now a wide range of recombinant factor concentrates, and an impressive safety record with respect to pathogen transmission. However, remaining therapeutic challenges include the potential threat of transmission of prions and other pathogens, the formation of inhibitory alloantibodies, and the international disparity that exists in product availability due to differences in licensure status as well as prohibitively high costs. In the future, it is likely that bioengineered recombinant proteins that have been modified to enhance pharmacokinetic properties or reduce immunogenicity, or both, will be used increasingly in clinical practice.

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.

Treatment characteristics and the risk of inhibitor development: a multicenter cohort study among previously untreated patients with severe hemophilia A

CONTEXT

The development of inhibitory antibodies against infused factor (F) VIII is a major complication of treatment of patients with severe hemophilia A.

OBJECTIVE

This study was set up to examine the effects of treatment-related factors on inhibitor development among previously untreated patients with severe hemophilia A.

DESIGN, SETTING AND PATIENTS

In this multicenter cohort study, we combined individual patient data obtained from four recombinant FVIII product registration studies (Kogenate, Kogenate Bayer, Recombinate, ReFacto) that were performed between 1989 and 2001. From the databases we selected all 236 previously untreated patients with severe hemophilia A who were subsequently treated with FVIII on at least 50 days.

MAIN OUTCOME MEASURES

Clinically relevant inhibitor development, defined as the occurrence of at least two positive inhibitor titers and a decreased recovery.

RESULTS

67 patients (28%) developed clinically relevant inhibitors (44 high-titer) at a median of ten exposure days. Age at first exposure was not associated with inhibitor development. Peak treatment moments and surgical procedures were related to an increased inhibitor risk [adjusted relative risk 1.6 (95% confidence interval 1.0-2.6) and 2.7 (95% confidence interval 1.3-5.7), respectively]. A shorter duration between exposure days was associated with an increased risk of inhibitor development. There was a possible association between dosing of FVIII and inhibitor development, which largely disappeared after adjustment for confounding factors.

INTERPRETATION

These findings show that intensive treatment periods are associated with an increased risk of inhibitor development in previously untreated patients with severe hemophilia A. Our results do not support the notion that age at first exposure is associated with the risk of developing inhibitors.

Recombinant versus plasma-derived factor VIII products and the development of inhibitors in previously untreated patients with severe hemophilia A: the CANAL cohort study

It has been suggested that plasma-derived factor VIII products induce fewer inhibitors than recombinant factor VIII products. We investigated the relationship of factor VIII product type and switching between factor VIII products with the risk to develop inhibitors. This multicenter retrospective cohort study included 316 patients with severe hemophilia A born between 1990 and 2000. The outcome was clinically relevant inhibitor development, defined as the occurrence of at least 2 positive inhibitor titers with decreased recovery. The risk of inhibitor development was not clearly lower in plasma-derived compared with recombinant factor VIII products (relative risk [RR], 0.8; 95% confidence interval [CI], 0.5-1.3). Among high-titer inhibitors, the possible reduction in risk was even less pronounced (RR, 0.9; CI, 0.5-1.5). Plasma-derived products with considerable quantities of von Willebrand factor (VWF) carried the same risk for inhibitor development as recombinant factor VIII products (RR, 1.0; CI, 0.6-1.6). Switching between factor VIII products did not increase the risk for inhibitors (RR, 1.1; CI, 0.6-1.8). In conclusion, our findings support neither the notion that plasma-derived factor VIII products with considerable concentrations of VWF confer a lower risk to develop inhibitory antibodies than recombinant factor VIII products, nor that switching between factor VIII product brands increases inhibitor risks in previously untreated patients with severe hemophilia A.

Efficacy, safety and tolerability of recombinant factor VIII (REFACTO�) in patients with haemophilia A: interim data from a postmarketing surveillance study in Germany and Austria

An open-label, multicentre, postmarketing surveillance study conducted in Germany and Austria with recombinant factor VIII (REFACTO) has enrolled 217 patients (mean age 26.3 years) from 38 haemophilia centres during the first 4.8 years. Most patients (188/217; 86.6%) had severe to moderately severe haemophilia A, of whom 153 completed sufficient diary information for the main efficacy analysis. These 153 patients experienced a median of 6.6 (interquartile range 1.4-18.6) bleeding episodes per year. Patients treated with prophylaxis experienced a median of 4.4 (1.1-9.3) bleeds per year, while patients treated on-demand experienced a median of 22.8 (11.3-29.0) bleeds per year. Overall, most physicians (41/43 [95.3%]) were 'very satisfied' or 'satisfied' with the efficacy of REFACTO in the treatment of bleeding episodes. A total of 137 non-serious adverse events have been reported in 52/217 patients (24.0%) to date. In addition, 129 serious adverse events in 87 patients (40%) were reported, including 41 cases of 'less than expected therapeutic effect' (LETE). Of these, 39 LETE cases were reported in one centre; however, patients in this centre experienced considerably fewer bleeding episodes per year than patients outside this centre. Overall, six patients (2.8%) have developed de novo inhibitors, three of which were considered high titre. Four of these patients were at high risk (0-50 exposure days [ED]) of inhibitor formation, one was at intermediate risk (51-100 ED) and one was at low risk (>100 ED). These results emphasize the benefit of postmarketing surveillance and, overall, this study confirms the efficacy, safety and tolerability of REFACTO in the treatment of patients with haemophilia A.

Risk of inhibitors in haemophilia and the type of factor replacement

PURPOSE OF REVIEW

Inhibitors in haemophilia are a serious complication that may render usual replacement therapy ineffective. The risk is greatest in previously untreated children with severe haemophilia A. The role of replacement factor VIII in this group is an important issue.

RECENT FINDINGS

Until now, few clinical studies have correctly taken into account the variety of cofactors involved in inhibitor development: genetic (familial antecedents, ethnicity, F8 and immune response genotypes), and environmental cofactors (age at first infusion, prophylaxis and intensity of treatment). This is a prerequisite to correctly evaluating the putative role of the type of factor replacement. Prospective cohort studies are therefore urgently needed. Depending on the expected inhibitor risk in the reference group, the intensity of the relationship between risk factor and endpoint, the duration of patient follow up, and the design of the study (balanced or unbalanced groups), cohorts including 200-500 previously untreated children should be sufficient to demonstrate an increased intensity of risk of about 2 or more with one product compared with another.

SUMMARY

Aside from clinical studies, fundamental research is essential to test the multiple hypotheses that could explain a difference in inhibitor risk between the currently available factor VIII concentrates in order to develop less immunogenic factor VIII.