Inhibitor-positive Hemophilia Research Articles

The IgG-degrading enzyme, Imlifidase, restores the therapeutic activity of FVIII in inhibitor-positive hemophilia A mice.

Neutralizing anti-factor VIII (FVIII) antibodies, known as FVIII inhibitors, represent a major drawback of replacement therapy in persons with congenital hemophilia A (PwHA), rendering further infusions of FVIII ineffective. FVIII inhibitors can also appear in non-hemophilic individuals causing acquired hemophilia A (AHA). The use of non-FVIII bypassing agents in cases of bleeds or surgery in inhibitor-positive patients is complicated by the lack of reliable biological monitoring and increased thrombotic risk. Imlifidase (IdeS) is an endopeptidase that degrades human immunoglobulin G (IgG); it was recently approved for hyperimmune patients undergoing renal transplants. Here we investigated the ability of IdeS to eliminate FVIII inhibitors in vitro and in a model of inhibitor-positive HA mice. IdeS cleaved anti-FVIII plasma IgG from PwHA and AHA patients, and hydrolyzed recombinant human anti-FVIII IgG independently from their subclass or specificity for the A2, A3, C1 or C2 domains of FVIII. In HA mice passively immunized with recombinant human anti-FVIII IgG, IdeS restored the hemostatic efficacy of FVIII, as evidenced by the correction of the bleeding tendency. Our results provide the proof of concept for the transient removal of FVIII inhibitors by IdeS, thereby opening a therapeutic window for efficient FVIII replacement therapy in inhibitor-positive patients.

Response to standard vs low dose emicizumab in inhibitor positive hemophilia A

Response to standard vs low dose emicizumab in inhibitor positive hemophilia A

Bleeding profile and QOL of children with inhibitor positive hemophilia

Bleeding profile and QOL of children with inhibitor positive hemophilia

Joint health state in relation to different clinical, laboratory, and radiological variables of hemophilia A patients

Abstract Background Haemophilic (HF) arthropathy is a major complication in haemophilia. Collagen factors are responsible for maintaining the integrity of the vessel wall in the joint. Our goal was to assess the haemophilia joint state and its relation to the clinical, laboratory &radiological data. Methods This cross-sectional study included 50 hemophilia A patients recruited from the Pediatric Hematology / Oncology unit, Children’s Hospital, Ain Shams University,Cairo,Egypt. Assessment of joint status clinicallyand radiologically by X-rays& ultrasound was performed. Results 48% of the studied hemophilia A patients had one, 40 % had two target joints or more. The elbow and knee are the most frequently affected joints (46%,62% respectively).There were no significant differences between inhibitor positive and inhibitor negative patients regarding the number of target joints.However, inhibitor positive patients had significantly lower annual bleeding rate; moreover, none of inhibitor positive patients had surgeries done and none were on celecoxib. There were no significant differences between inhibitor positive hemophilia A patients and inhibitor negative regarding US total score, hem QOL, total HJHS and total FISH score. Patients with 2 target joints had significant higher annual bleeding rate, worse quality of life score, higher total HJHS score compared to those with one or without target joints. Conclusion In our study, we argued the lack of significant difference between inhibitor positive and inhibitor negative Hemophilia A patients as regards the occurrence of hemophilic arthropathy. Nevertheless, patients with ≥ 2 target joints had worse annual bleeding rate, quality of life & total HJHS score.

Cost effectiveness of prophylactic treatment with activated prothrombin complex concentrate in a patient with inhibitor-positive hemophilia A

Patients with hemophilia and high titers of inhibitors are hard to treat during bleeding events and consequently are more likely to incur high treatment costs and to experience deterioration in quality of life. We report here the case of a boy with hemophilia A and high titers of inhibitors who responded well to prophylactic activated prothrombin complex concentrate (APCC) treatment. Previously, he had to be hospitalized frequently because of painful bleeding of target joints of the knee and ankle. At the age of 4 years and 3 months, APCC prophylaxis at a dose of 60 U/kg, three times a week, was initiated together with on-demand therapy with recombinant factor VIIa. This reduced the frequency and severity of bleeding and ended the need for hospitalization. This, together with a decreased requirement for bypass agents, APCC treatment significantly reduced the cost of treatment for this patient.

Factor VIII-hydrolyzing IgG in acquired and congenital hemophilia

Anti-factor VIII (FVIII) inhibitory IgG may arise as alloantibodies to therapeutic FVIII in patients with congenital hemophilia A, or as autoantibodies to endogenous FVIII in individuals with acquired hemophilia. We have described FVIII-hydrolyzing IgG both in hemophilia A patients with anti-FVIII IgG and in acquired hemophilia patients. Here, we compared the properties of proteolytic auto- and allo-antibodies. Rates of FVIII hydrolysis differed significantly between the two groups of antibodies. Proline-phenylalanine-arginine-methylcoumarinamide was a surrogate substrate for FVIII-hydrolyzing autoantibodies. Our data suggest that populations of proteolytic anti-FVIII IgG in acquired hemophilia patients are different from that of inhibitor-positive hemophilia A patients.

Quantitation of anti–factor VIII antibodies in human plasma

The presence of antibodies (Abs) in hemophilia A patients can potentially influence the therapeutic qualities of factor VIII (fVIII) administration. Much work has been focused on the presence of inhibitory antibodies, whereas the quantitation of noninhibitory anti-fVIII antibodies has been largely undetermined. Our objective was to develop a sensitive and specific fluorescence-based immunoassay (FLI) for the quantitation of anti-fVIIIAbs in human plasma. Affinity-purified human anti-fVIIIAb, isolated from a hemophilia A subject, was used as a calibrator with a detectability limit of 40 (+/-1.5) pM. The calibrator and the human plasma anti-fVIIIAb were captured on recombinant fVIII (rfVIII)- coupled microspheres and probed with mouse anti-human Ig-R-phycoerythrin. Plasma samples from 150 healthy donors and 39 inhibitor-negative hemophilia A subjects were compared with 4 inhibitor-positive hemophilia A plasma samples with inhibitor titers of 1 BU/mL (94.6 +/- 0.8 nM), 11 BU/mL (214.3 +/- 7.1 nM), 106 BU/mL (2209.4 +/- 84.9 nM), 140 BU/mL (2417.7 +/- 3.8 nM) as measured by the Nijmegen method. We also describe the validation of a mouse anti-human fVIIIAb as a surrogate calibrator. Four healthy individuals (3%) showed detectable anti-fVIIIAb in the range of 0.6 to 6.2 nM, whereas 13 (33%) of the 39 inhibitor-free hemophilia A subjects were positive for anti-fVIIIAb in the range of 0.5 to 20 nM. The method may be useful for therapeutic management of hemophilia A patients.

Quantitation of Non-Inhibitory Anti-Factor VIII Antibodies in human Plasma

Hemophilia A is a clinically heterogeneous bleeding disorder characterized by the absence of functional factor VIII (FVIII). The most severe complication from exposure to exogenous factor VIII therapy is the development of alloantibodies that neutralize the effect of the therapeutic agent. The standard method for quantitation of FVIII inhibitors in human plasma is by the Nijmegen method, a modification of the Bethesda assay. Our objective was to develop a sensitive and specific fluorescence based immunoassay for the quantitation of anti-FVIII antibodies (FVIIIAb) in human plasma. An affinity purified human anti-FVIIIAb isolated from a hemophilia A patient was used as a calibrator, with a detectability limit of 40±1.5pM. The calibrator and the human plasma anti-FVIIIAb were captured on recombinant FVIII coupled microspheres and probed with mouse anti-human Ig conjugated to R-Phycoerythrin. Citrated human plasma samples from 150 healthy donors and 39 inhibitor-negative hemophilia A subjects were studied and compared to 4 inhibitor-positive hemophilia A plasma samples with inhibitor titers of 1BU (94.6±0.08nM), 11BU (214.3±7.1nM), 106BU (2209.4±84.9nM) and 140BU (2417.7±3.8nM) as measured by the Nijmegen method. Among the 150 normal control plasmas, 4 subjects (3%) were determined as positive (anti-FVIIIAb ≥ 40pM) with concentrations in the range of 0.6nM to 1.9nM, well below that of 1BU (94.6±0.08nM) inhibitor-positive sample. Anti-FVIIIAb was also evaluated in seven commercial inhibitor-free plasma samples reported to contain <1% FVIII activity. Two of the seven plasmas were found to contain anti-FVIIIAb with concentrations of 112.9±1.9nM and 71.1±8.5nM. The concentration of the antibody in both samples was within the range of the measured molar concentration of an inhibitor-positive 1BU titer plasma sample. Thirty two inhibitor-negative hemophilia A subjects were also quantitated for anti-FVIIIAb. Eleven of the 32 samples tested positive for anti-FVIIIAb with molar concentrations in the range of 0.6–20nM. The overall prevalence of the non-inhibitory anti-FVIIIAbs in hemophilia A subjects evaluated by our immunoassay (n=39) is approximately 33% relative to healthy donor population in which 3% were determined as positive (≥40pM) for FVIIIAb.

A Case Report of Plasma Exchange, Steroids, Mycophenolate Mofetil and Cyclophosphamide in Acquired Factor VIII Inhibitors

Induction of factor VIII (FVIII) inhibitors sometimes occurs in patients with hemophilia due to frequent supplementation of FVIII. The inhibitor is rarely detected in non-hemophilic patients; however, an association has been described in patients with chronic inflammatory diseases, such as autoimmune diseases (e.g. SLE and rheumatoid arthritis), malignant tumors and drug allergies, and also to pregnant or aged individuals without underlying disease. We report on an 82-year-old patient who was transferred to our hospital after the diagnosis of acquired FVIII inhibitor. On admission the laboratory results showed no detectable FVIII activity (0%, normal range 70-100%), prolongation of coagulation time (APTT 102.4 s), and severe anemia 7.8 g/dL (normal range 12-16 g/dL). On physical examination multiple subcutaneous hematomas were detected and further bleeding in his left pectoralis muscle was observed. Despite extensive investigation no underlying disease was detected. Thirty-six courses of plasma exchange with 360 units of fresh frozen plasma replacement daily were conducted. High dose steroids and mycophenolate mofetil (MMF) were given throughout the course, and cyclophosphamide was administered once. Thirty-four units of erythrocytes were applied during this time. After 36 courses of plasma exchange in combination with high dose steroids, FVIII activity and coagulation time normalized and bleeding could be stopped. The patient was discharged in good health 48 days after admission. Hence, we present a case of severe idiopathic FVIII inhibitor-positive hemophilia successfully treated with the combination of plasma exchange, corticosteroids, cyclophosphamide and MMF.

Antibodies to the FVIII light chain that neutralize FVIII procoagulant activity are present in plasma of nonresponder patients with severe hemophilia A and in normal polyclonal human IgG

AbstractWe have analyzed the properties of anti-factor VIII (FVIII) immunoglobulin (Ig) G recovered by affinity chromatography on FVIII-Sepharose from the IgG fraction of the plasma of healthy individuals and nonresponder patients with hemophilia A. Affinity-purified anti-FVIII antibodies were found to neutralize FVIII activity and to bind to FVIII with an affinity similar to that of anti-FVIII IgG that had been affinity-purified from the plasma of inhibitor-positive hemophilia patients and of patients with anti-FVIII autoimmune disease. The antibodies also exhibited patterns of reactivity with thrombin-digested FVIII similar to those of FVIII inhibitors and preferentially recognized epitopes located in the light chain of FVIII. These observations suggest that FVIII inhibitors occurring in hemophilia A and in patients with anti-FVIII autoimmune disease originate from the expansion of preexisting natural anti-FVIII clones that exhibit FVIII-neutralizing properties.

Antibodies to the FVIII light chain that neutralize FVIII procoagulant activity are present in plasma of nonresponder patients with severe hemophilia A and in normal polyclonal human IgG

We have analyzed the properties of anti-factor VIII (FVIII) immunoglobulin (Ig) G recovered by affinity chromatography on FVIII-Sepharose from the IgG fraction of the plasma of healthy individuals and nonresponder patients with hemophilia A. Affinity-purified anti-FVIII antibodies were found to neutralize FVIII activity and to bind to FVIII with an affinity similar to that of anti-FVIII IgG that had been affinity-purified from the plasma of inhibitor-positive hemophilia patients and of patients with anti-FVIII autoimmune disease. The antibodies also exhibited patterns of reactivity with thrombin-digested FVIII similar to those of FVIII inhibitors and preferentially recognized epitopes located in the light chain of FVIII. These observations suggest that FVIII inhibitors occurring in hemophilia A and in patients with anti-FVIII autoimmune disease originate from the expansion of preexisting natural anti-FVIII clones that exhibit FVIII-neutralizing properties.

T Lymphocyte Proliferative Responses Induced by Recombinant Factor VIII in Hemophilia A Patients with Inhibitors

In this study we sought to determine whether factor VIII-reactive T lymphocytes were present in hemophilia A patients with inhibitor antibodies. Peripheral blood mononuclear cells (MNC) were obtained from 12 severe hemophilia A patients having high titer inhibitors, 4 severe hemophilia A patients without inhibitors and 5 normal male subjects. B cell-depleted MNC were cultured in serum-free medium in the absence or presence of 2 micrograms of recombinant human factor VIII (rFVIII) per ml, and cellular proliferation was assessed after 5 days of culture by measuring 3H-thymidine incorporation. rFVIII induced marked cellular proliferation in cultures of 4 of 12 inhibitor-positive hemophilia patients: fold increase over background (stimulation index, SI) of 7.8 to 23.3. The remaining 8 inhibitor-positive patients, the 4 hemophilia patients without inhibitors and the 5 normal subjects, all had lower proliferative responses to rFVIII, SI range = 1.6 to 6.0. As a group, the inhibitor-positive subjects had significantly higher proliferative responses to rFVIII than did the inhibitor-negative and normal subjects (p < 0.05 by t-test). Cell fractionation experiments showed that T lymphocytes were the rFVIII-responsive cell type, and that monocytes were required for T cell proliferation. Thus, rFVIII-reactive T lymphocytes are present in the peripheral circulation of some inhibitor-positive hemophilia A patients. These T cells may recognize FVIII in an antigen-specific manner and play a central role in the regulation of inhibitor antibody production.