Congenital Hemorrhagic Disorders: New Insights into the Pathophysiology and Treatment of Hemophilia

Safety and efficacy of an anti-human APC antibody for prophylaxis of congenital factor deficiencies in preclinical models

Rebalance of coagulation and anticoagulation to achieve a hemostatic effect has recently gained attention as an alternative therapeutic strategy for hemophilia. We engineered a humanized chimeric antibody, SR604, based on a previously published murine antibody, HAPC1573, which selectively blocks the anticoagulant activity of human activated protein C (APC). SR604 effectively blocked the anticoagulation activities of APC in human plasma deficient in various coagulation factors in vitro with affinities ∼60 times greater than that of HAPC1573. SR604 exhibited prophylactic and therapeutic efficacy in the tail-bleeding and knee-injury models of hemophilia A and B mice expressing human APC (humanized hemophilic mice). SR604 did not interfere with the cytoprotection and endothelial barrier function of APC, nor were there obvious toxicity effects in humanized hemophilic mice. Pharmacokinetic study showed a high bioavailability (106%) of subcutaneously injected SR604 in cynomolgus monkeys. These results demonstrate that SR604 is expected to be a safe and effective therapeutic and/or prophylactic agent with a prolonged half-life for patients with congenital factor deficiencies including hemophilia A and B.

Gene Therapy for Hemophilia A: Where We Stand

Hemophilia A (HA) is a hereditary hemorrhagic disease caused by a deficiency of coagulation factor VIII (FVIII) in blood plasma. Patients with HA usually suffer from spontaneous and recurrent bleeding in joints and muscles, or even intracerebral hemorrhage, which might lead to disability or death. Although the disease is currently manageable via delivery of plasma-derived or recombinant FVIII, this approach is costly, and neutralizing antibodies may be generated in a large portion of patients, which render the regimens ineffective and inaccessible. Given the monogenic nature of HA and that a slight increase in FVIII can remarkably alleviate the phenotypes, HA has been considered to be a suitable target disease for gene therapy. Consequently, the introduction of a functional F8 gene copy into the appropriate target cells via viral or nonviral delivery vectors, including gene correction through genome editing approaches, could ultimately provide an effective therapeutic method for HA patients. In this review, we discuss the recent progress of gene therapy for HA with viral and nonviral delivery vectors, including piggyBac, lentiviral and adeno-associated viral vectors, as well as new raising issues involving liver toxicity, pre-existing neutralizing antibodies of viral approach, and the selection of the target cell type for nonviral delivery.

Unusual olecranon mass with ulnar nerve compressive neuropathy caused by a haemophilic pseudotumour

A 55-year-old man with a history of haemophilia A and bilateral haemophilic arthropathy of the elbows presented with an enlarging left elbow mass and worsening paresthesias in the ulnar distribution of the left hand. The mass, originally thought to be olecranon bursitis and treated as such, was found to be due to a haemophilic pseudotumour. The patient underwent successful excision of the haemophilic pseudotumour with concomitant ulnar nerve decompression and had sustained resolution of the pseudotumour and symptoms at 10 years of follow-up. This case demonstrates the need for consideration of haemophilic pseudotumour in the differential diagnosis for olecranon masses and cubital tunnel compressive neuropathy in patients with haemophilia, and highlights the viability of surgical excision as a therapeutic option for the treatment of haemophilic pseudotumours in the elbow.

Evaluation of Thrombin Generation Assay in Patients With Hemophilia

We evaluated the correlation between thrombin generation (TG) parameters with bleeding symptoms and disease severity in patients with hemophilia. In this cross-sectional study, 59 patients with hemophilia without inhibitors and regardless of their severity were randomly selected from southern Iran and TG assays were conducted. Bleeding score (BS) was calculated by performing a clinical evaluation using Tosetto questionnaire. Only lag time showed a statistically significant correlation with BS ( rs = .316, P = .016). All TG parameters except peak showed association with disease severity ( P < .05). Endogenous thrombin potential showed a significant correlation with factor activity level ( rs = .459, P < .001). Both lag time and start tail showed significant negative correlations with factor activity level ( rs = −0.488, P < .001 and rs= − .289, P < .026, respectively). Although most of the TG parameters evaluated were not significantly correlated with the BS of patients with hemophilia, the majority of TG parameters were significantly associated with factor activity level and disease severity.

Congenital bleeding disorders

Both clinical and basic problems related to the congenital bleeding disorders continue to confront hematologists. On the forefront are efforts to bring genetic correction of the more common bleeding disorders such as hemophilia A to the clinic in a safe and accessible manner. A second issue, particularly for patients with hemophilia, is the development of inhibitors-questions of how they arise and how to prevent and treat these problems that confound otherwise very successful replacement therapy and allow patients to maintain normal lifestyles. A third issue is the continuing question of diagnosis and management of von Willebrand disease, the most common congenital bleeding disorder, especially in individuals who have borderline laboratory values, but have a history of clinical bleeding. In Section I, Dr. Christopher Walsh discusses general principles of effective gene transfer for the hemophilias, specific information about viral vectors and non-viral gene transfer, and alternative target tissues for factor VIII and factor IX production. He highlights information about the immune response to gene transfer and reviews data from the hemophilia gene transfer trials to date. The future prospects for newer methods of therapy such as RNA repair and the use of gene-modified circulating endothelial progenitors are presented as possible alternatives to the more traditional gene therapy approaches. In Section II, Dr. Nigel Key focuses on inhibitor development in patients with hemophilia A. He reviews the progress in our understanding of the risk factors and presents newer information about the immunobiology of inhibitor development. He discusses the natural history of these inhibitors and the screening, laboratory diagnosis, and treatment, including the use of different modalities for the treatment of acute bleeding episodes. Dr. Key also presents information about the eradication of inhibitors by immune tolerance induction and reviews recent information from the international registries regarding the status and success of immune tolerance induction. In Section III, Dr. Margaret Rick discusses the diagnosis, classification, and management of von Willebrand disease. Attention is given to the difficulty of diagnosis in patients with mild bleeding histories and borderline laboratory test results for von Willebrand factor. She presents the value of different laboratory assays for both diagnosis and classification, and she relates the classification of von Willebrand disease to the choice of treatment and to the known genetic mutations. Practical issues of diagnosis and treatment, including clinical cases, will be presented.

Concentrate safety and efficacy

Safety from transmission of infections through plasma-derived clotting factor concentrates is assured by improved donor screening, serological testing of individual donations and direct viral testing of small plasma pools. Modern viral-inactivation techniques are highly effective. Recombinant concentrates stabilized in human albumin are being superaeded by those with other stabilizers. Recently reported discrepancies between estimates of concentrate potency from in vitro assays versus in vivo recovery, depending upon type of assay and reference standard used, are not fully resolved.