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Unmet needs of current hemophilia A treatment include the requirement for frequent intravenous infusions, inhibitor development, and containment of high medical costs. In order to overcome these issues, we produced FVIII which mimics a bispecific antibody against FIXa/FX. ACE910 demonstrated hemostatic effects on both ongoing and spontaneous joint bleeding in the primate acquired hemophilia A model. Recently, a phase 1 study for PK, PD, and the safety of ACE910 was initiated. The t1/2 was approximately 30 days. There were no severe ACE910 related adverse events. Furthermore, bleeding was remarkably decreased by weekly subcutaneous administration in patients with severe hemophilia A, regardless of whether an inhibitor was used. ACE910 has the remarkable advantages of prophylactic efficacy which can be achieved by convenient subcutaneous administrations at a markedly reduced frequency.

Inhibitors are a rare but serious complication of treatment of patients with haemophilia. Phase III clinical trials enrol too few patients to adequately assess new product inhibitor risk. This project explores the feasibility of using a public health surveillance system to conduct national surveillance for inhibitors. Staff at 17 U.S. haemophilia treatment centres (HTC) enrolled patients with haemophilia A and B into this prospective study. HTC staff provided detailed historic data on product use and inhibitors at baseline, and postenrolment patients provided monthly detailed infusion logs. A central laboratory performed inhibitor tests on blood specimens that were collected at baseline, annually, prior to any planned product switch or when clinically indicated. The central laboratory also performed genotyping of all enrolled patients. From January 2006 through June 2012, 1163 patients were enrolled and followed up for 3329 person-years. A total of 3048 inhibitor tests were performed and 23 new factor VIII inhibitors were identified, 61% of which were not clinically apparent. Infusion logs were submitted for 113,205 exposure days. Genotyping revealed 431 distinct mutations causing haemophilia, 151 of which had not previously been reported elsewhere in the world. This study provided critical information about the practical issues that must be addressed to successfully implement national inhibitor surveillance. Centralized testing with routine monitoring and confirmation of locally identified inhibitors will provide valid and representative data with which to evaluate inhibitor incidence and prevalence, monitor trends in occurrence rates and identify potential inhibitor outbreaks associated with products., (© 2013 John Wiley & Sons Ltd.)

Formation of pathogenic antibodies is a major problem in replacement therapies for inherited protein deficiencies. For example, antibodies to coagulation factors ('inhibitors') seriously complicate treatment of haemophilia. While immune tolerance induction (ITI) protocols have been developed, inhibitors against factor IX (FIX) are difficult to eradicate due to anaphylactic reactions and nephrotic syndrome and thus substantially elevate risks for morbidity and mortality. However, hepatic gene transfer with an adeno-associated virus (AAV) serotype 8 vector expressing FIX (at levels of ≥4% of normal) rapidly reversed pre-existing high-titre inhibitors in haemophilia B mice, eliminated antibody production by B cells, desensitized from anaphylaxis (even if protein therapy was resumed) and provided long-term correction. High levels of FIX protein suppressed memory B cells and increased Treg induction, indicating direct and indirect mechanisms of suppression of inhibitor formation. Persistent presence of Treg was required to prevent relapse of antibodies. Together, these data suggest that hepatic gene transfer-based ITI provides a safe and effective alternative to eradicate inhibitors. This strategy may be broadly applicable to reversal of antibodies in different genetic diseases., (© 2013 The Authors. Published by John Wiley and Sons, Ltd on behalf of EMBO.)

Background: Nephrotic syndrome (NS) is a recognized complication of immune tolerance induction (ITI) therapy, a treatment strategy used to treat inhibitors in patients with hemophilia B receiving factor IX concentrate., Case Diagnosis/treatment: We present a 4-year-old boy with hemophilia B and an inhibitor who underwent ITI, and developed NS 19 months into this therapy. A percutaneous renal biopsy was safely performed with factor IX (FIX) concentrate administration both preceding and following the procedure. The patient's inhibitor level had increased to 1.4-1.6 Bethesda Units just prior to the onset of proteinuria. Histology confirmed segmental membranous nephropathy (MGN). The patient was continued on FIX concentrate as ITI and also received 4 weekly doses of rituximab and ongoing immunosuppression with mycophenolate mofetil. This resulted in the complete resolution of his inhibitor and his NS. He continues with a modified ITI regimen and remains inhibitor-free without proteinuria >12 months post-biopsy., Conclusions: Hemophilia B patients undergoing ITI should be regularly screened for NS. At first detection of proteinuria, with proper precautions, a percutaneous kidney biopsy can be performed safely in patients with low levels of inhibitor. Our patient had segmental MGN with complete remission of NS.

Background: As part of a pilot U.S. inhibitor surveillance project initiated at the Centers for Disease Control and Prevention (CDC) in 2006, a centralized inhibitor measurement was instituted., Objective: To validate a modified method for inhibitor measurement suitable for surveillance of treated and untreated patients., Methods/results: In all, 710 subjects with hemophilia A were enrolled; 122 had a history of inhibitor (HI). Nijmegen-Bethesda assay (NBA) results on 50 split specimens shipped on cold packs and frozen were equivalent (r=0.998). Because 55% of 228 initial specimens had factor (F)VIII activity (VIII:C) present, a heat treatment step was added. Heating specimens to 56°C for 30 min and centrifuging removed FVIII, as demonstrated by a reduction of VIII:C and FVIII antigen to <1 U dL(-1) in recently treated patients. Among specimens inhibitor-negative before heating, one of 159 with negative HI and five of 30 with positive HI rose to ≥ 0.5 Nijmegen-Bethesda units (NBU) after heating. Correlation of heated and unheated inhibitor-positive specimens was 0.94 (P=0.0001). The modified method had a coefficient of variation (CV) for a 1 NBU positive control of 10.3% and for the negative control of 9.8%. Based on results on 710 enrollment specimens, a positive CDC inhibitor was defined as ≥ 0.5 NBU. Results were similar when 643 post-enrollment specimens were included. Of 160 enrolled hemophilia B patients, two had HI. All others had NBU ≤ 0.2 at enrollment., Conclusion: The CDC experience demonstrates that this modified NBA can be standardized to be within acceptable limits for clinical tests and can be used for national surveillance., (© 2012 International Society on Thrombosis and Haemostasis.)

Haemophilia B is an X-linked disorder resulting in coagulation factor IX deficiency. Patients with severe deficiency (<1% factor IX activity) may have significant bleeding complications similar to patients with haemophilia A or factor VIII deficiency. The development of inhibitory antibodies to the missing coagulation factor is a major complication in patients with haemophilia. While the incidence of inhibitors in patients with haemophilia A is higher than that in haemophilia B, the occurrence of allergic and or anaphylactic reactions with the development of inhibitors is unique to haemophilia B patients. Since haemophilia B is a rare bleeding disorder and the incidence of inhibitors is an even rarer entity, a registry was established by Dr Indira Warrier under the auspices of the FVIII/FIX subcommittee of the International Society of Thrombosis and Haemostasis, to gather information on the occurrence and characteristics of patients with inhibitors and also the incidence of allergic and anaphylactic reactions in this group of patients. This is the first report from this registry and helps us to gather some insight on haemophilia B patients with inhibitors and complications related to inhibitor development and difficulties with immune tolerance.

Activated recombinant human factor VIIa (rFVIIa) has been used as a hemostatic agent in patients with hemophilia and acquired inhibitors. Other indications for rFVIIa may include liver disease, warfarin sodium (Coumadin) overdose, or trauma. Monitoring patients on this treatment with standard laboratory testing is problematic. Bleeding risk does not correlate well with the prothrombin time (PT) or the activated partial thromboplastin time (aPTT) during therapy with rFVIIa. In addition, there is no identifiable literature on the effect of rFVIIa on assays of inhibitors in this patient group. Monitoring inhibitors may be important during interventions aimed at acutely reducing inhibitor levels, such as during plasma exchange or protein adsorption. We performed factor assays and evaluated inhibitor levels in plasma from 3 patients with deficiencies in FVIII (2 patients) or FIX (1 patient) and inhibitors (titer range, 5.8-17.4 Bethesda units) before and after adding rFVIIa (range, 0.25-8 microg/mL) in vitro. Additionally, we performed assays of factors of both intrinsic and extrinsic systems to determine the impact of rFVIIa on these tests. We found that both factor levels and inhibitor titers from patients with hemophilia A or B could be measured accurately, even in the presence of suprapharmacologic doses of rFVIIa (8 microg/mL). We also obtained accurate measurements for other assays of the intrinsic coagulation system (FXI and FXII) based on the aPTT. Conversely, we found that assays of the extrinsic system based on the PT (FII, FV, and FX) produced results that were unreliable. FVII results were very high but reproducible. These results suggest that assays based on the PT are inaccurate and should be avoided during FVIIa treatment. Conversely, FVIII and FIX levels and inhibitor titers can be accurately monitored in hemophilia patients receiving rFVIIa according to results of aPTT-based coagulation tests.

The haemostatic effect of by-passing agents such as activated prothrombin complex concentrates (aPCC) and recombinant factor VIIa is inadequate in some patients with severe haemophilia and high-responding inhibitors. Theoretically, this could be due to antibody reactivity to procoagulant proteins other than the deficient factor. To evaluate this hypothesis, immunoglobulin (Ig) fractions from six multi-transfused patients (three haemophilia A and three haemophilia B) were purified on protein A sepharose and then subjected to immunoaffinity chromatography on factor IX sepharose and factor VIIa sepharose. All three Ig fractions from the haemophilia B patients, but not commercially available Ig, contained antibodies that bound to both gels. None of the haemophilia A patients had antibodies to factor IX but all three had antibodies towards factor VIIa. The immunoaffinity purified antifactor IX and VIIa antibodies from the haemophilia B patients inhibited thrombin formation in vitro using Feiba as active enzyme, but had no significant effect in the presence of NovoSeven. In contrast, no inhibitory effect was observed with the antifactor VIIa antibodies from the haemophilia A patients. Cross-reactivity to factor IX was seen for the antifactor VIIa antibodies from the patients with haemophilia B. Our findings show that antibody reactivity to other procoagulant factors such as factor VIIa exists in patients with high-responding inhibitors and that these antibodies may have an inhibitory potential that correlates to the amount of active enzyme present. The characterization of the antibody profile may facilitate an optimal treatment with by-passing agents in severe bleeding events.

The development of an inhibitor antibody to factor VIII (or factor IX) in a child with haemophilia presents a major challenge to the paediatric haematologist. This article provides an overview of the incidence of inhibitor development in early childhood (30-52% in boys with severe haemophilia A), genetic risk factors, detection, high titre, low titre and transient inhibitors, and management. Treatment of patients with inhibitors is time-consuming and expensive. One should make every attempt to ensure that the boy's family has an understanding of inhibitors, treatment options, and just what is being recommended for their child and what this involves. Immune tolerance induction is successful in approximately 85% of boys with factor VIII inhibitors, but in only 40-50% of those with factor IX inhibitors. For treatment of bleeding episodes in children with high-titre (> or = 5 Bethesda Units) inhibitors, therapeutic options include activated prothrombin complex concentrates (APCC), rF VIIa, and (for factor VIII inhibitors) porcine factor VIII. The advantages and disadvantages of each are discussed. Although factor IX inhibitors are far less common (occurring in 2-3% of boys with haemophilia B), approximately 50% are accompanied by the occurrence of anaphylaxis or severe allergic reactions to any factor IX-containing product.

Fifteen previously untreated patients (Pups) with severe haemophilia B (factor IX activity < or = 2 U/dl) only treated with one brand of plasma-derived high purity factor IX concentrate (FIX LFB) were studied. Age at first injection varied from 1 to 137 months and follow-up since this first injection from 21 to 86 months (median: 35). Cumulative exposure days (CED) were from 4 to over 100 (median: 26). Among these 15 Pups only one developed an inhibitor. Mutation analysis performed in all patients showed total gene deletion in the patient with inhibitor, partial gene deletion in another one, and missense mutations in 9 families. Mutation was not found in one patient. Actually, according to the data already published, only two patients were at high risk for inhibitor development in our population. Our study, although rather small, confirms the previously reported low incidence of inhibitors in haemophilia B. Large studies on incidence of FIX inhibitors are indeed difficult to perform, due to both the overall small number of severe haemophilia B patients and the low incidence of FIX inhibitors. Consequently, the impact of bias, such as prevalence of different types of gene defects in a given population, is major. Therefore, any study, dealing with incidence of FIX inhibitors in severe haemophilia B should report, for each patient, the type of gene defect.

We have previously described the epitope mapping and functional neutralization of three factor IX inhibitors in hemophilia B (HB-1, 3, and 7) by synthetic peptides (13). However, A concentration of synthetic peptide of about 1000 times the concentration of factor IX in plasma was essential to neutralize the purified antibodies. We now report that substitutional synthetic peptides of epitope are able to neutralize the factor IX inhibitor with a lower concentration. Using two major epitope peptides, 156Val-Asn-Ser-Thr-Glu-Ala-Glu-Thr-Ile164 and 168Ile-Thr-Gln-Ser-Thr-Gln-Ser-Phe-Asn176, we designed changes of antigenicity using the systematic substitution of different amino acids at each residue of the epitope peptides and neutralization rate of factor IX inhibitors by a lower concentration of substitutional synthetic peptides conjugated with bovine serum albumin (BSA). Twenty-five substitutional peptides for HB-1, twenty substitutional peptides for HB-3 and forty-four substitutional peptides for HB-7 reacted stronger than the native sequences. One of the peptides, 1.0 microM of 156Val-Asn-Ser-Thr-Glu-Tyr-Glu-Thr-Ile164 conjugated with BSA, neutralized 26.5% of inhibitor in HB-1's plasma maximally. Our data show that high antigenicity peptides conjugated with BSA ranging in concentration from 0.1 microM to 1.0 microM are able to neutralize factor IX inhibitors in plasma and there is a possibility of peptide neutralization inhibitor therapy.

Six haemophilia B patients were studied while undergoing infusion with factor IX concentrate. All were negative for factor IX antigen (IX:AG) and inhibitor to factor IX coagulant activity (IX:C). One patient showed an atypical response pattern, with prolonged survival of IX:C and IX:Ag. This patient remained under prophylactic treatment and more than 1 year later developed an inhibitor to IX:C of clinical significance. Retrospective study revealed that this patient had significantly higher levels of circulating immune complexes than other haemophilia B patients and in vivo formation of immune complexes containing IX:Ag prior to detection of his inhibitor in conventional clotting assays, suggesting long-term persistence of an occult inhibitor. The inhibitor was shown to be an IgG antibody with both kappa and lambda light chains.

Inhibitors to factor IX in haemophilia B are IgG antibodies. It is of interest to know the subclass type of these antibodies since the biological activity of the four IgG subclasses are different. Subclass identification has been difficult due to the lack of specific antibodies to IgG subclasses. Monoclonal hybridoma antibodies to these subclasses are now available. Here we present the results on the subclass identification of inhibitors from six patients with severe haemophilia B (titres 0.8-800 mu/ml). Plasma from one patient was obtained before inhibitor could be detected by coagulation assays. He had circulating complexes between factor IX and inhibitor. The technique used was crossed immunoelectrophoresis combined with an enzyme-linked immunoassay. This technique allows the subclass determination of both low-titre and high-titre inhibitors. All inhibitors gave a very strong reaction with antibody to IgG4, and four inhibitors also reacted with antibody to IgG1. Three of these inhibitors gave a faint reaction with antibody to IgG2 also, whereas no inhibitor contained any detectable IgG3. The finding of IgG4 as the main subclass is important since IgG4 antibodies do not bind complement. The presence of more than one subclass in the inhibitors demonstrates the heterogeneous nature of the inhibitors. This was demonstrated also at a stage of inhibitor development when the inhibitor could not be detected by coagulation assay.

The few inhibitors to blood coagulation factor IX in patients with Christmas disease (hemophilia B) that have been studied have been shown to belong to the IgG class of immunoglobulins. We report the first case in which a factor IX inhibitor was of the IgA class. Additionally, he appears to be the youngest patient with hemophilia B to have developed an inhibitor. His inhibitor complicated treatment of the patient for several years because of its anamnestic rise following factor IX concentrate administration. It then spontaneously vanished and has not returned in spite of repeated factor IX complex administration.

Two patients with severe hemophilia B complicated with antibodies against factor IX have been treated 13 and 10 times, respectively, with high doses of factor IX concentrate in combination with cyclophosphamide over a period of 10 years. During this treatment a lowering of the anamnestic response was observed over the years. Both patients have now been treated with factor IX and hydrocortisone but no cyclophosphamide in order to find out if real tolerance was induced. One patient received such treatment three times and the other once. Their inhibitor titer following these treatment episodes never exceeded 0.3 U/ml (approximately 0.9 BU/ml) and 0.9 U/ml (approximately 2.7 BU/ml) which is of the same order of magnitude as following the combined treatment (factor IX, hydrocortisone and cyclophosphamide). It is therefore suggested that these patients have been converted from high responders (10-100-fold increase in the inhibitor titer on the original treatment with factor IX and hydrocortisone) into low responders showing a very reasonable inhibitor increase after treatment with factor IX and hydrocortisone but no cyclophosphamide.

Fourteen patients suffering from haemophilia B have been screened for deletions and mutations. None of them produce antibodies against native factor IX. Three patients from the same family were found to have a total deletion of the factor IX gene. Two of the patients, who are cousins, have inherited the same maternal HLA haplotype indicating that postulated immune gene(s) located at the MHC locus might be of importance for the development of antibodies against factor IX. DXS99 is a locus closely linked to the factor IX gene and a recombination event in this family makes it likely that this locus is centromeric to the factor IX gene.

A 37-yr-old hemophiliac with factor IX antibody in high titer required operation for a pseudotumor growing invasively into the bone in his left elbow. Exchange plasma-pheresis was not feasible, mainly because of possible stimulation of factor IX inhibitor. In addition, the patient had antibodies against tissue antigens. The factor IX antibodies were of IgG type and adsorbable to protein-A-agarose. The antibodies were removed by extracorporeal adsorption of the plasma (separated intermittently in a cell centrifuge) to sterile protein-A-Sepharose in columns, operated by a computer. The treated plasma was retransfused. In this manner, a total of 6000 ml of plasma was depleted of antibodies, and the antibody titer, as well as the total immunoglobulin content, decreased to one-fifth of the original values. The remaining antibodies were neutralized by infusion of factor IX concentrate. Conventional substitution therapy, in combination with immunosuppression, was then possible. The operation was performed without complications. No signs of hemolysis, complement activation, or activation of the coagulation system occurred. In principle, the same form of treatment can be used in patients with other forms of antibodies.