Development Of Factor VIII Inhibitors Research Articles

The use of Bacillus subtilis as a cost-effective expression system for production of Cholera Toxin B fused factor VIII epitope regions applicable for inducing oral immune tolerance.

Coagulation factor replacement therapy for the X-linked bleeding disorder Haemophilia, characterized by a deficiency of coagulation protein factor VIII (FVIII), is severely complicated by antibody (inhibitors) formation. The development of FVIII inhibitors drastically alters the quality of life of the patients and is associated with a tremendous increase in morbidity as well as treatment costs. The ultimate goal of inhibitor control is antibody elimination. Immune tolerance induction (ITI) is the only clinically established approach for developing antigen-specific tolerance to FVIII. This work aims to establish a novel cost-effective strategy to produce FVIII molecules in fusion with cholera toxin B (CTB) subunit at the N terminus using the Bacillus subtilis expression system for oral tolerance, as the current clinical immune tolerance protocols are expensive. Regions of B-Domain Deleted (BDD)-FVIII that have potential epitopes were identified by employing Bepipred linear epitope prediction; 2 or more epitopes in each domain were combined and cDNA encoding these regions were fused with CTB and cloned in the Bacillus subtilis expression vector pHT43 and expression analysis was carried out. The expressed CTB-fused FVIII epitope domains showed strong binding affinity towards the CTB-receptor GM1 ganglioside. To conclude, Bacillus subtilis expressing FVIII molecules might be a promising candidate for exploring for the induction of oral immune tolerance.

Management of Severe Hemophilia A: Low-Dose Prophylaxis vs. On-Demand Treatment.

Prophylactic clotting factor infusion regimens to prevent bleeding and joint deformity has become the standard of care in severe hemophilia A patients. To assess low-dose factor prophylaxis in our population as an alternative approach to managing severe hemophilia A. A prospective cohort study that included 68 hemophilia A patients divided into two groups, i.e., Prophylaxis and on-demand. The two groups were compared for annualized bleeding rate (ABR), hospitalization, units of factor VIII (FVIII) infused, or plasma products transfused, i.e., fresh frozen plasma (FFP) and cryoprecipitate (CP), and development of FVIII inhibitors. Of the 68 patients recruited in this study, 25 (36.7%) were in the prophylaxis group, and 43(63.3%) were in the on-demand group. The on-demand group presented a higher median-IQR ABR [8(20-3) vs. 5(10-1.5), p-value 0.024], several hospitalizations (39.7% vs. 0, p-value0.001), and inhibitor development (9.3% vs. 0, p-value 0.289) compared to the prophylaxis group. The prophylaxis approach demonstrated a significant negative correlation of ABR with FVIII prophylaxis (r=-0484, p=value=0.014). Moreover, no hospitalizations or inhibitor development was observed in the prophylaxis group. The estimated annual consumption of FVIII was 328 IU/kg/year in the on-demand group and 1662.6 IU/kg/year in the prophylaxis group. However, a highly significant difference in plasma product utilization was observed between the two groups, i.e., p-value <0.001 and 0.038 for FFP and CP, respectively. Low-dose factor prophylaxis resulted in improved outcomes compared to on-demand treatment in terms of ABR, joint bleeding, hospitalization, and the development of inhibitors. This treatment approach should be adopted as an economically feasible alternative to high-dose Prophylaxis in resource-constrained countries.

Association between interleukin-2 (rs2069762) gene polymorphism and FVIII inhibitor development in Indonesian patients with severe hemophilia A

BACKGROUND Factor VIII (FVIII) inhibitors in hemophilia A (HA) patients render FVIII replacement therapy ineffective. Although its development cause is unclear, it has been classified into therapeutic and genetic-related etiologies. Single nucleotide polymorphisms (SNPs) in several cytokine genes, including interleukin (IL)-2, could increase the risk of FVIII inhibitor development. This study aimed to evaluate the association between IL-2 (rs2069762) gene SNP and FVIII inhibitor development in Indonesian patients with severe HA.&#x0D; METHODS The IL-2 (rs2069762) gene SNP was examined in 119 HA patients. The presence of FVIII inhibitors was quantified using an enzyme-linked immunosorbent assay, with a titer of &lt;0.28 ng/ml considered negative. Patients were divided into two groups: 59 with FVIII inhibitors (positive group) and 60 without inhibitors (negative group). The genotype of the subjects was determined using peripheral blood mononuclear cells and tetra-primer amplification refractory mutation system-polymerase chain reaction.&#x0D; RESULTS There was no association between IL-2 (rs2069762) gene polymorphism and FVIII inhibitor development on genotypes (p = 0.138) and allele frequencies (p = 0.780).&#x0D; CONCLUSIONS IL-2 (rs2069762) gene polymorphism is not a risk factor in the development of FVIII inhibitors in Indonesian patients with severe HA. Thus, further polymorphism studies in other cytokine genes are required to gain a comprehensive understanding of the FVIII inhibitor development.

BAFF rs9514828 gene polymorphism and the risk of the development of inhibitors in children with severe haemophilia A.

Haemophilia A (HA) is an x-linked recessive disease due to deficiency of coagulation factor VIII (FVIII). The development of neutralizing antibodies (inhibitors) against infused FVIII is a major concern. B cell activating factor (BAFF) has been implicated in several autoimmune diseases. We aimed to evaluate the possible association of BAFF rs9514828 gene polymorphism and the risk of the development of FVIII inhibitor in children with severe HA. This cohort study was carried out on 100 newly diagnosed boys with severe HA who were never treated before with FVIII concentrate. Assessment of serum levels of BAFF and BAFF rs9514828 genotyping at first diagnosis was performed and the patients were followed up for the completion of a total of 50 exposure days or the development of inhibitors whichever occurred first. The patients were divided as positive or negative according to the presence or absence of inhibitors. The risk allele for BAFF rs9514828 (T) was significantly more frequent in the inhibitor positive patients than the inhibitor negative patients (P=.003). In addition, CT+TT genotypes were associated with increased risk of FVIII inhibitor development. Receiver operating characteristics (ROC) analysis showed that BAFF levels could predict the development of FVIII inhibitors at a cut-off value of ≥ .92 with a sensitivity of 85.9% and a specificity of 80.2%. BAFF rs9514828 gene polymorphism could be independent risk factor and elevated BAFF levels might be useful prognostic marker for the development of FVIII inhibitor in newly diagnosed children with severe HA.

Characterization of Protein Unable to Bind Von Willebrand Factor in Recombinant Factor VIII Products: Can We Reduce Their Immunogenicity?

Introduction Therapeutic products with blood coagulation factor VIII (FVIII) have a wide range of protein contents per activity unit (or IU/mg, specific activity), available from previous studies (Lin et al, 2004; Butenas et al, 2009) and the prescribing information. The wide range of the specific activities seems to be more pronounced in recombinant FVIII products (rFVIII) compared to plasma-derived FVIII, implying presence of protein with altered structure and biochemical properties. In particular, rFVIII products were reported to contain a protein fraction (FVIII*), unable to bind von Willebrand factor (VWF) without functional activity (Lin et al, 2004;Ofosu et al 2012). Furthermore, FVIII* may represent a risk factor for development of FVIII inhibitors in Hemophilia A patients, as the binding to VWF was shown to reduce FVIII immunogenicity in a tissue culture and mice model systems (Gangadharan et al, 2017; Muczynski et al, 2018). Due to these reasons, FVIII* can be defined as an impurity, which needs to be understood and controlled in rFVIII products. Study objective To develop a methodology to isolate FVIII* from rFVIII samples and to characterize this fraction in various rFVIII products. Experimental design Using immobilized VWF affinity chromatography (IVAC) for analysis of FVIII samples, protein fractions collected from (i) the column flow-through (FVIIIFT, corresponding to FVIII*) and (ii) the column-bound and eluted fraction (FVIIIEL) were characterized using polyacrylamide gel electrophoresis (PAGE) gels followed by silver-staining and immunoblotting, FVIII activity test, surface plasmon resonance, mass spectrometry, and for plasma clearance in mice. Results A robust IVAC methodology was developed. Using this method, we isolated the FVIIIFT and FVIIIEL from all ten third-generation rFVIII products marketed in the USA by study time. These products represent all current pharmaceutical variants of rFVIII including full-size FVIII, B-domain deleted (truncated) FVIII, Fc-fused FVIII, single-chained FVIII, and PEGylated protein, including those with the extended plasma half-life. FVIIIFT was found in all rFVIII products at levels up to 22% of total protein. Compared to FVIIIEL, FVIIIFT had similar pattern of polypeptide bands by PAGE, but lower functional activity, significantly reduced sulfation at Tyr1680 important for VWF binding, moderately decreased interaction with recombinant cluster II of a low-density lipoprotein receptor related protein 1 (a major clearance receptor of FVIII), and approximately 3-times faster clearance in mice (Figure 1). Conclusions Our results show that the FVIII* structure is generally similar to that of the major fraction of rFVIII, while it differs by microheterogeneity in post-translational modifications and possibly local misfolding. The data suggest that upon administration of a rFVIII product in patients, its FVIII* fraction is rapidly removed from the circulation, resulting in a decrease of the effective dosage. Our findings demonstrate a potential of IVAC to control FVIII* fraction in rFVIII products, including its removal from the products during their manufacture. These applications may lead to achieving better quality and efficacy of rFVIII products including reduction of their immunogenicity for improving the care of Hemophilia A. Disclosures No relevant conflicts of interest to declare.

Turoctocog alfa is safe for the treatment of Indian patients with hemophilia A: Guardian 10 trial results

BackgroundHemophilia A is an X chromosome–linked bleeding disorder caused by the deficiency of coagulation factor VIII (FVIII). The majority of the Indian population with hemophilia A use plasma‐derived clotting factors and, in some instances, fresh frozen plasma and cryoprecipitate. Safer and more efficient treatment options are needed for this group of patients. ObjectivesTo assess the safety of turoctocog alfa, a third‐generation recombinant FVIII molecule, for the treatment and prophylaxis of bleeding episodes in previously treated Indian patients with moderate or severe hemophilia A. Patients/MethodsThis single‐country, multicenter, open‐label, nonrandomized trial enrolled 60 patients who received prophylactic treatment with turoctocog alfa for 8 weeks, which corresponded to a minimum of 20 exposure days. Confirmed development of FVIII inhibitors during the 8‐week treatment period was evaluated. Other assessments included frequencies of adverse drug reactions (ARs), serious adverse reactions, drug‐related allergic reactions, and infusion reactions during the 12‐week period after the first treatment; hemostatic effect of turoctocog alfa for the treatment of bleeding episodes; and total annualized dose of turoctocog alfa administered during the 8‐week treatment period. ResultsNo incidence of FVIII inhibitors was detected. No safety concerns such as ARs, serious ARs, or drug‐related allergic reactions were noted. The hemostatic success rate for the treatment of bleeding episodes with turoctocog alfa was 81.6%. ConclusionsThe trial results demonstrated that turoctocog alfa is a safe treatment option for the prophylaxis and treatment of bleeding episodes in previously treated adolescent and adult patients with hemophilia A in the Indian population.

Factor VIII inhibitor development in Egyptian hemophilia patients: does intron 22 inversion mutation play a role?

BackgroundHemophilia A (HA) is an X-linked recessive bleeding disorder characterized by qualitative and quantitative deficiency of factor VIII (FVIII). The development of inhibitor antibodies against FVIII is the most challenging complication of treatment. Mutations in the FVIII gene is one of the genetic factors that leads to development of FVIII inhibitors especially intron 22 inversion (Inv22).ObjectivesThis study was carried out to assess the frequency of Inv22 of FVIII gene in Egyptian patients with hemophilia A and its role as a risk factor for developing inhibitors.Patients and methodsSeventy-two patients with severe HA and 48 patients with moderate HA were enrolled in the current study. All patients were treated on demand with either plasma-derived factor VIII or recombinant factor VIII concentrates. Genotyping of FVIII Inv22 was performed by LD-PCR while the presence and magnitude of inhibitor activity in blood was determined by the Bethesda assay.ResultsAround 23% of all hemophilia cases had positive Inv22. Intron 22 inversion mutation was detected in 6 and 33% of patients with moderate and severe HA respectively. Twenty-one cases (18%) of all hemophilic patients developed inhibitors. Thirty-7% of patients with Inv22 had inhibitor in their blood, almost all, but one, had severe HA. The risk of an inhibitor development during replacement therapy was four folds higher among Inv22 positive cases as compared with mutation negative peers (OR 4.3, 95% CI 1.6–11.9, P = 0.003).ConclusionsThe prevalence of Inv22 of F VIII in Egyptian hemophiliacs is nearly like that of other population. This mutation was more frequently detected among severe hemophilic patients as compared with moderately affected peers. The presence of Inv22 mutation significantly predispose to FVIII inhibitor development.

Low incidence of factor VIII inhibitors in previously untreated patients with severe haemophilia A treated with octanate® : Final report from a prospective study.

Octanate® is a human, plasma-derived, von Willebrand factor-stabilized coagulation factor VIII (FVIII) concentrate with demonstrated haemostatic efficacy in previously treated patients with haemophilia A. This prospective, open-label study aimed to assess the immunogenicity of octanate® in previously untreated patients (PUPs). The study monitored development of FVIII inhibitors in 51 PUPs. Tolerability, viral safety, FVIII recovery and efficacy of octanate® for the prevention and treatment of bleeds and in surgical procedures were also assessed. Five (9.8%) of the 51 patients developed inhibitors during the study, 4 of which (7.8%) were high titre. Three inhibitor cases (5.9%) were considered clinically relevant; 2 were transient inhibitors that disappeared during regular octanate® treatment without a change in dose or treatment frequency. Amongst 45 patients with FVIII:C <1% at baseline and who received ≥20 exposure days (EDs) or had <20 EDs but developed an inhibitor, inhibitor incidence was 11.1% (6.7% clinically relevant). All clinically relevant inhibitors developed within 20EDs of on-demand treatment. No inhibitors developed in PUPs receiving prophylaxis. All patients who developed inhibitors had either intron 22 inversions or large deletions. Irrespective of the reason for administration, haemostatic efficacy was rated as "excellent" in 99.6% of all infusions (4700 of 4717 infusions), and no complications were reported in 23 surgical procedures. Mean incremental in vivo recovery was 2.0%/IU/kg (±0.7) and 1.9%/IU/kg (±0.5) for the first and second assessments, respectively. Tolerability was rated "very good" in 99.9% of infusions. In PUPs with severe haemophilia A, octanate® demonstrated haemostatic efficacy with a low rate of inhibitor development.

The Development of FVIII Inhibitors in Relation to IL10 Gene Polymorphism in Hemophilia A Egyptian Pediatric Patients

ABSTRACTBackground: Development of inhibitors against Factor VIII (FVIII) in hemophilia A patients is a serious complication of therapy. Many cytokines, including interleukin-10 (IL10), may affect inhibitor development; however, literature data are not sufficient to prove this association. The aim of this study was to investigate the relation between FVIII inhibitor formation and IL10-1082A/G polymorphism among Egyptian hemophiliacs. Methods: Patients were screened for FVIII inhibitors using the Bethesda method. IL10-1082A/G polymorphism was detected by polymerase chain reaction–restriction fragment length polymorphism. Results: Six patients (12%) developed inhibitors. No statistically significant difference was found between inhibitor positive and negative patients regarding IL10-1082A/G genotypes, disease severity, or treatment-related variables (type of FVIII received, treatment regimen, age at first exposure to FVIII, and frequency of replacement therapy). Conclusions: FVIII inhibitor formation in this group of Egyptian hemophiliacs was not correlated to IL10-1082A/G polymorphism, disease severity, or any of the treatment variables.

Innovating immune tolerance induction for haemophilia.

Haemophilia A is an X-linked bleeding disorder characterized by a deficiency of coagulation protein factor VIII (FVIII). A challenging complication of therapeutic FVIII infusions is the formation of neutralizing alloantibodies against the FVIII protein defined as inhibitors. The development of FVIII inhibitors drastically alters the quality of life of the patients and is associated with tremendous increases in morbidity as well as treatment costs. Current clinical immune tolerance induction protocols to reverse inhibitors are lengthy, costly and not effective in all patients. Prophylactic protocols to prevent inhibitor formation have not yet been developed in the clinical setting. However, there has been ample progress towards this goal in recent years in preclinical studies using animal models of haemophilia. Here, we review the mechanisms that lead to inhibitor formation against FVIII and two promising new strategies for antigen-specific tolerance induction. CD4+ T cells play an important role in the FVIII-specific B cell response. Immune tolerance can be induced based on transplacental delivery of FVIII domains fused to Fc or on oral delivery of leaf cells from chloroplast transgenic crop plants. Recent literature suggests that prophylactic tolerance induction protocols for FVIII may be feasible in haemophilia A patients.

The role of previously untreated patient studies in understanding the development of FVIII inhibitors.

Development of inhibitors against factor VIII (FVIII), the major complication of haemophilia A treatment today, is influenced by multiple factors. Genetic (F8 mutation, family history, ethnicity, polymorphisms in immune modulating genes) and non-genetic (intensive exposure to FVIII, presence of pro-inflammatory signals as might occur with large bleeds, infections, surgery, or other immune stimulants [e.g. vaccines]) risk factors as well as their complex inter-relationships contribute to the inhibitor risk profile of haemophilia patients, particularly in the previously untreated patient (PUP) population. Studies in PUPs have been fundamental to furthering the understanding of FVIII inhibitor development, as well as discovering previously unappreciated risk factors. The multi-factorial nature of inhibitor development makes it difficult to ascertain the contribution of FVIII products in inhibitor development through individual PUP studies. Sufficiently powered studies of large cohorts may overcome these limitations but interpretations should be conducted cautiously. Proper design and implementation of PUP safety studies will become even more important with the introduction of new molecules, such as extended half-life or human cell-line derived FVIII that propose reduced immunogenicity. Despite these difficulties, carefully performed clinical studies in PUPs may provide important insights into the natural history of the immune response to FVIII and may suggest targets for intervention to reduce immunogenicity.

The IL-10 polarized cytokine pattern in innate and adaptive immunity cells contribute to the development of FVIII inhibitors.

BackgroundHemophilia A (HA) is an X-linked inherited bleeding disorder, resulting from a qualitative or quantitative deficiency of clotting factor VIII (FVIII). Antibodies against FVIII, also called inhibitors, block the procoagulant activity of FVIII; thus, impairing hemostatic activity in patients with HA. The exact mechanism underlying the immunological events behind the development of inhibitors remains unknown. This study aimed to understand immune response to FVIII in patients with HA who were either positive [HAα-FVIII(+)] or negative [HAα-FVIII(−)] for inhibitors.MethodsCytokine profiles [interferon-γ (IFN − γ), tumor necrosis factor-α (TNF-α), interleukin-4 (IL-4), IL-5, and IL-10] of innate and adaptive immune cells present in the peripheral blood of participants were characterized.ResultsPresence of inhibitors was significantly associated with decreased frequencies of TNF-α-positive monocytes and neutrophils, IL-5-positive monocytes, IL-4-positive neutrophils, and increased frequencies of IL-10-positive neutrophils and T cells. T cells from HAα-FVIII(−) patients expressed increased levels of almost all cytokines. In contrast, HAα-FVIII(+) patients showed lower levels of all cytokines in CD4+ and CD8+ T cells, except IL-10. B cells from HAα-FVIII(−) patients expressed increased levels of IL-4 while those from HAα-FVIII(+) patients expressed increased levels of IL-10.ConclusionsThe global cytokine profiles of innate and adaptive immune cells showed an anti-inflammatory/regulatory pattern in HAα-FVIII(+) patients and a mixed pattern, with a bias toward inflammatory cytokine profile, in HAα-FVIII(−) patients. The occurrence of these profiles seems to be associated with presence FVIII inhibitors.

Safety and Prophylactic Efficacy Profiles of ACE910, a Humanized Bispecific Antibody Mimicking the FVIII Cofactor Function, in Japanese Hemophilia A Patients Both without and with FVIII Inhibitors: First-in-Patient Phase 1 Study

Background:Although routine supplementation of exogenous factor VIII (FVIII) effectively prevents bleeding complications in hemophilia A patients, the development of FVIII inhibitors and the need for frequent venous access are still problematic. To overcome these medical problems, a humanized bispecific antibody to factors IXa and X (ACE910) mimicking the FVIII cofactor function has been created.Objectives:To investigate the safety, pharmacokinetic and pharmacodynamic profiles of ACE910 as well as its prophylactic efficacy on bleeding, a first-in-patient open-label phase I study was conducted with once-weekly subcutaneous (SC) administration of ACE910 in Japanese hemophilia A patients both without and with FVIII inhibitors.Methods:In the present study, Japanese patients with severe hemophilia A (FVIII:C <1%, ages 12 to 59 years) were treated with once-weekly SC ACE910 at one of the following dose levels for 12 successive weeks: 0.3 (C-1), 1 (C-2) and 3 mg/kg (C-3). Loading doses of 1 and 3 mg/kg were administered as initial doses to the C-1 and C-2 cohorts, respectively. Prior to the study enrollment, the patients without FVIII inhibitors had received FVIII prophylactic replacement therapy while the patients with FVIII inhibitors had received on-demand therapy and/or prophylactic therapy with bypassing agents. Each cohort included 6 patients (18 patients in total). At least 2 patients without and with FVIII inhibitors were enrolled in each cohort. The annualized bleeding rate (ABR) during 12 weeks receiving ACE910 was calculated, and compared to those demonstrated during 6 months period prior to the study enrollment. In case bleeding event occurred during the course of ACE910 administrations, the patient was treated with on-demand use of FVIII or bypassing agents.Results:The results of the C-1 and C-2 cohorts during 12 weeks receiving ACE910 are shown in this abstract since C-3 cohort is under evaluation. The results from the C-3 cohort will be presented at the time of the meeting.(1) Safety DataIn total, 30 adverse events (AEs) were reported in 10 out of the 12 patients. All AEs were of mild intensity, except for 1 moderate AE in a patient on the C-2 cohort (upper respiratory tract infection). Neither serious adverse events nor laboratory abnormalities to indicate a hypercoagulable state were observed in either cohort. In addition, no AEs related to hypercoagulation were observed including when concomitant on-demand therapy (FVIII or bypassing agents) was given for bleeding. One patient in the C-2 cohort discontinued ACE910 administration due to erythema at the injection site of mild intensity. No anti-ACE910 antibodies were developed during the course of ACE910 administrations.(2) Efficacy DataFour out of 6 patients had FVIII inhibitors in both cohorts. The inhibitor titers of these patients were 3-111 BU/mL. All the patients in both groups had target joints. The ABR prior to the study enrollment in the patients without and with FVIII inhibitors ranged 8.1-77.1 and 18.3-56.8, respectively. During the course of ACE910 administrations the ABR decreased in all patients compared to the ABR prior to the study enrollment. In the C-1 cohort, the ABR decreased by 22.8%-100% and 64.7%-100% in the patients without and with FVIII inhibitors, respectively. In the C-2 cohort, the ABR decreased by 100% and 88.9%-100% in the patients without and with FVIII inhibitors, respectively.(3) Pharmacokinetic and Pharmacodynamic DataThe plasma ACE910 concentration increased in a dose-dependent manner. In all the patients in both cohorts, shortening of APTT and promotion of thrombin generation were observed after the start of ACE910 dosing.Conclusion:The present study is the first to demonstrate that once-weekly SC ACE910 prophylaxis possesses a favorable safety and a promising efficacy profiles in severe hemophilia A patients irrespective of the presence of FVIII inhibitors. Collectively, ACE910 is expected to offer an effective and convenient prophylactic treatment option for hemophilia A, including patients with FVIII inhibitors and/or with venous access difficulty. DisclosuresShima:Chugai Pharmaceutical Co., Ltd.: Consultancy, Honoraria, Membership on an entity’s Board of Directors or advisory committees, Research Funding. Off Label Use: ACE910 clinical phase1 study. Hanabusa:Chugai Pharmaceutical Co., Ltd.: Research Funding. Taki:Chugai Pharmaceutical Co., Ltd.: Research Funding. Matsushita:Chugai Pharmaceutical Co., Ltd.: Research Funding. Sato:Chugai Pharmaceutical Co., Ltd.: Research Funding. Fukutake:Chugai Pharmaceutical Co., Ltd.: Research Funding. Fukazawa:Chugai Pharmaceutical Co., Ltd.: Employment. Maisawa:Chugai Pharmaceutical Co., Ltd.: Employment. Yoneyama:Chugai Pharmaceutical Co., Ltd.: Employment. Nogami:Chugai Pharmaceutical Co., Ltd.: Membership on an entity’s Board of Directors or advisory committees, Research Funding.

Rhesus monkeys and baboons develop clotting factor VIII inhibitors in response to porcine endothelial cells or islets

Xenotransplantation of porcine organs holds promise of solving the human organ donor shortage. The use of α-1,3-galactosyltransferase knockout (GTKO) pig donors mitigates hyperacute rejection, while delayed rejection is currently precipitated by potent immune and hemostatic complications. Previous analysis by our laboratory suggests that clotting factor VIII (FVIII) inhibitors might be elicited by the structurally restricted xenoantibody response which occurs after transplantation of either pig GTKO/hCD55/hCD59/hHT transgenic neonatal islet cell clusters or GTKO endothelial cells. A recombinant xenoantibody was generated using sequences from baboons demonstrating an active xenoantibody response at day 28 after GTKO/hCD55/hCD59/hHT transgenic pig neonatal islet cell cluster transplantation. Rhesus monkeys were immunized with GTKO pig endothelial cells to stimulate an anti-non-Gal xenoantibody response. Serum was collected at days 0 and 7 after immunization. A two-stage chromogenic assay was used to measure FVIII cofactor activity and identify antibodies which inhibit FVIII function. Molecular modeling and molecular dynamics simulations were used to predict antibody structure and the residues which contribute to antibody-FVIII interactions. Competition ELISA was used to verify predictions at the domain structural level. Antibodies that inhibit recombinant human FVIII function are elicited after non-human primates are transplanted with either GTKO pig neonatal islet cell clusters or endothelial cells. There is an apparent increase in inhibitor titer by 15 Bethesda units (Bu) after transplant, where an increase greater than 5 Bu can indicate pathology in humans. Furthermore, competition ELISA verifies the computer modeled prediction that the recombinant xenoantibody, H66K12, binds the C1 domain of FVIII. The development of FVIII inhibitors is a novel illustration of the potential impact the humoral immune response can have on coagulative dysfunction in xenotransplantation. However, the contribution of these antibodies to rejection pathology requires further evaluation because "normal" coagulation parameters after successful xenotransplantation are not fully understood.

Turoctocog alfa for the treatment of hemophilia A

Patients with hemophilia A lack functional coagulation factor VIII (FVIII), causing excessive spontaneous bleeding episodes and bleeding during trauma or surgery. Plasma-derived or synthetic recombinant FVIII is used to control bleeding, but currently available treatments are limited because of patient development of FVIII inhibitors and cross-contamination of human and animal-derived infectious agents. Turoctocog alfa is a recombinant FVIII produced in Chinese hamster ovary cells that has demonstrated good efficacy in thrombin generation and clot formation in preclinical evaluations in murine and canine models of hemophilia A and in patient-derived whole blood. Evaluation in clinical trials in pediatric and adult patients with hemophilia A have demonstrated that the drug has good pharmacokinetic parameters, excellent efficacy in improving annualized bleeding rates, few adverse events and no induction of FVIII inhibitors. The drug is FDA approved as a prophylactic agent and for on-demand treatment to control bleeding including during operative procedures.

Systematic Review of the Role of FVIII Concentrates in Inhibitor Development in Previously Untreated Patients with Severe Hemophilia A: A 2013 Update

Nowadays, patients with hemophilia A receive a high standard of care; therefore, the most challenging complication of factor VIII (FVIII) replacement therapy has become the development of FVIII inhibitors, which render the concentrate infusion ineffective and expose patients to an increased risk of morbidity and mortality. Among environmental risk factors influencing inhibitor development, the type of FVIII products has always drawn the attention of investigators. Conflicting results are reported in the literature concerning rates of inhibitor development after either plasma-derived or recombinant FVIII concentrates. To help elucidate this controversial issue, we have performed a systematic review and meta-analysis of prospective studies evaluating the incidence of inhibitors in previously untreated patients with severe hemophilia A receiving plasma-derived or recombinant FVIII products. The quality of the studies was assessed using the Newcastle-Ottawa Scale (NOS), the STrenghtening the Reporting of OBservational studies in Epidemiology and an ad hoc quality score. Overall, 28 prospective studies, including 1,421 patients with hemophilia A, fulfilled our selection criteria and were included in the systematic review. No statistically significant differences were observed in the inhibitor incidence between plasma-derived and recombinant FVIII concentrates considering all (weighted means: 23%, 95% CI: 15-33% vs. 29%, 95% CI: 26-32%) and high titer (16%, 95% CI: 10-26% vs. 18%, 95% CI: 15-21%) inhibitors. Similarly, no significant differences were found in the inhibitor incidence among the different classes of recombinant products. In conclusion, the results of our meta-analysis show that the different types of FVIII products are not associated with different risks of inhibitor development.

Identification and Multidimensional Optimization of an Asymmetric Bispecific IgG Antibody Mimicking the Function of Factor VIII Cofactor Activity

In hemophilia A, routine prophylaxis with exogenous factor VIII (FVIII) requires frequent intravenous injections and can lead to the development of anti-FVIII alloantibodies (FVIII inhibitors). To overcome these drawbacks, we screened asymmetric bispecific IgG antibodies to factor IXa (FIXa) and factor X (FX), mimicking the FVIII cofactor function. Since the therapeutic potential of the lead bispecific antibody was marginal, FVIII-mimetic activity was improved by modifying its binding properties to FIXa and FX, and the pharmacokinetics was improved by engineering the charge properties of the variable region. Difficulties in manufacturing the bispecific antibody were overcome by identifying a common light chain for the anti-FIXa and anti-FX heavy chains through framework/complementarity determining region shuffling, and by pI engineering of the two heavy chains to facilitate ion exchange chromatographic purification of the bispecific antibody from the mixture of byproducts. Engineering to overcome low solubility and deamidation was also performed. The multidimensionally optimized bispecific antibody hBS910 exhibited potent FVIII-mimetic activity in human FVIII-deficient plasma, and had a half-life of 3 weeks and high subcutaneous bioavailability in cynomolgus monkeys. Importantly, the activity of hBS910 was not affected by FVIII inhibitors, while anti-hBS910 antibodies did not inhibit FVIII activity, allowing the use of hBS910 without considering the development or presence of FVIII inhibitors. Furthermore, hBS910 could be purified on a large manufacturing scale and formulated into a subcutaneously injectable liquid formulation for clinical use. These features of hBS910 enable routine prophylaxis by subcutaneous delivery at a long dosing interval without considering the development or presence of FVIII inhibitors. We expect that hBS910 (investigational drug name: ACE910) will provide significant benefit for severe hemophilia A patients.

Von Willebrand factor – two sides and the edge of a coin

Von Willebrand factor (VWF) has multiple functions in coagulation. It is a clotting protein and its deficiency causes a primary haemostatic bleeding disorder. Excess VWF, particularly high molecular weight multimers can cause thrombosis. There is also a debatable function of protecting factor VIII (FVIII) in circulation with the prevention of development of FVIII inhibitors. This commentary addresses these functions.

Low incidence of factor VIII inhibitors in previously untreated patients during prophylaxis, on-demand treatment and surgical procedures, with Octanate®: interim report from an ongoing prospective clinical study

For patients with haemophilia A (HA), lifelong replacement therapy with factor VIII (FVIII) concentrates is the treatment of choice. Octanate(®) is a plasma-derived, human, von Willebrand factor-stabilized FVIII product with demonstrated haemostatic efficacy in patients with HA. The aim of this ongoing study is to assess the immunogenicity of Octanate(®) in previously untreated patients (PUPs), monitoring for development of FVIII inhibitors. Interim data on 39 PUPs treated for bleeding, prophylactically and for surgical coverage are reported. Two of 39 subjects (5.1%) developed clinically relevant inhibitor titres over the course of the study. Another two displayed inhibitors that disappeared spontaneously without Octanate(®) dose change. All inhibitors developed under on-demand treatment and before exposure day (ED) 50. Remarkably, no inhibitor was observed in PUPs receiving prophylaxis with Octanate(®). Of 39 subjects, 30 had exceeded 50 EDs at the time of this analysis. All inhibitor subjects were found to have large FVIII gene defects, either intron 22-inversions or large deletions. Octanate(®) was well-tolerated and the adverse event profile was consistent with the population studied. The haemostatic efficacy of Octanate(®) in prophylaxis and treatment of bleeding were generally rated as 'excellent', and no complication was reported for surgery. Notable FVIII activity was present in blood at 15 min postadministration, and levels remained high at 1 h. Mean incremental in vivo recovery (IVR) was 2.0 (± 0.6) % IU(-1) kg(-1) . These interim results indicate Octanate(®) to be an efficacious, well-tolerated human FVIII product for management of HA in PUPs, associated with a minimal risk of inhibitors.

Inhibitor Development In Patients with Mild and Moderate Hemophilia A: Results From a Single Centre.

AbstractAbstract 1407The development of factor VIII (FVIII) inhibitors is usually considered uncommon among patients with mild and moderate hemophilia A (HA) and less frequent than in patients with severe HA. We report here the prevalence of FVIII inhibitors and their caracteristics in 167 patients with mild and moderate HA followed in Caen Hemophilia Treatment Centre (Table). FVIII molecular defects were identified by direct sequencing in 167 patients including 30 and 137 with mild and moderate HA, respectively. Following FVIII concentrates infusions, FVIII inhibitors occured in 7.8% of patients (13/167). Fifteen percent (2/13) were low-responding inhibitors. The risk of inhibitor development appeared to be associated with high-risk FVIII genotypes clustered in the A2 and C2 domains, especially p.Arg2150His (50%) and p.Arg593Cys mutations. Interestingly, we described inhibitor development associated with novel missense-mutations (p.Tyr1786Ser, p.Asp115Tyr and -219C>T substitutions in FVIII gene promoter). In addition, high regimen infusion of FVIII concentrates appeared as risk factor for FVIII inhibitors development. Indeed, 60% (8/13) developped FVIII inhibitors following massive infusion of FVIII concentrates associated with FVIII:C levels above 1.2 UI/dL. Inhibitors in mild HA usually cross-react with endogenous factor VIII reducing the circulating basal FVIII:C level and are associated with more bleeding events. Similarly, we observed the evolution of bleeding patterns in our cohort to severe phenotypes. Bleedings were treated with FVIII concentrates and bypassing therapies (activated FVII and activated-prothrombin complex). About 25% (3/13) of these inhibitors disappeared spontaneously. Induction of Immune Tolerance (ITI) protocoles with high doses of FVIII were initiated for 7 high-responding patients with a success rate of 85 % (6/7). However, inhibitors persisted long-term and remained troublesome in 1 of these patients despite of ITI protocole. For two patients, immunosuppressive treatment with corticosteroids was started. Inhibitors disappeared and the levels of FVIII:C became detectable within 6 months. Development of FVIII inhibitors, their disappearance and the efficacy of ITI regimen seem to be different from our experience between patients with mild or moderate HA and severe HA. Disclosures:No relevant conflicts of interest to declare.