Induced tolerance in hemophilia patients with antibodies against IX:C

Advances in bypassing agent therapy for hemophilia patients with inhibitors to close care gaps and improve outcomes

In the past, patients with hemophilia and inhibitors have had less-than-optimal treatment and have experienced more orthopedic complications than patients without inhibitors. Bypassing agents offer the potential to close treatment gaps between inhibitor and noninhibitor patients by helping the former better attain key treatment goals, including: facilitating early initiation of treatment and hemostatic control in hemarthroses; providing effective treatment in serious hemorrhagic episodes; and performance of major surgery. Effective treatment with a bypassing agent minimizes joint and/or muscle damage and potentially can serve as an effective prophylactic agent to minimize the number of hemarthroses experienced per year, thereby mitigating the development of arthropathy. The reported efficacy of the currently available bypassing agents ranges from approximately 50-80% (50-64% in controlled studies) for plasma-derived activated prothrombin complex concentrate (pd-aPCC) and 81-91% (in controlled studies) for recombinant activated factor VII (rFVIIa), including use in major orthopedic surgery. Both bypassing agents have undergone key improvements in their formulation and/or properties in recent years. The nanofiltered, vapor-heated formulation of pd-aPCC has diminished the risk of acquiring blood-borne viral infections and the room temperature stable formulation of rFVIIa allows more convenient storage, increased ease to dissolve and inject, and smaller volumes, thereby increasing overall ease of administration. Use of recommended dosing has been demonstrated to provide effective hemostasis with a minimal number of injections for both agents. In this paper, we review the individual characteristics of pd-aPCC and rFVIIa and discuss clinical data from studies conducted in inhibitor patients that demonstrate the potential benefits of these bypassing agents in this difficult-to-treat population, and underscore the potential opportunities to close the gap in care between inhibitor and noninhibitor hemophilic patients.

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

The diagnostic and treatment strategies related to hemophilia are rapidly evolving. This article focuses on some of the issues of importance. Diagnostic advances in molecular genetics are reviewed by Dr. Ginsburg in Section I, including the current state of knowledge regarding the mutations responsible for hemophilia, with reference to the potential clinical applications of DNA diagnosis and prenatal testing.

Within the area of new therapeutic approaches in hemophilia, recombinant factor VIII and factor IX concentrates, their use and availability are addressed by Dr. Lusher in Section II as well as the use of so-called “primary prophylaxis” with the aim of decreasing long-term hemophilia athropathy. The use of radionuclide synovectomy as replacement for more invasive methods is also reviewed.

Various approaches to the ongoing challenge of the management of hemophilia patients with inhibitors against factor VIII and factor IX are reviewed by Dr. Hedner in Section III, including the principles for immune tolerance induction and the use of recombinant factor VIIa to induce hemostasis in bleeding patients with inhibitors.

In Section IV, gene therapy in hemophilia is reviewed by Dr. High, who focuses on recent developments in the rapidly moving field of gene therapy for hemophilia. Three phase I trials of gene therapy for hemophilia were initiated in 1999, and additional proposed trials are currently in the regulatory review process. Certain aspects of the pathophysiology of hemophilia make it an attractive model for a gene-based approach to treatment. These include latitude in choice of target tissue, a wide therapeutic window, the availability of small and large animal models of the disease, and the ease of determining therapeutic efficacy. Since there is very little published information regarding the ongoing trials, this section reviews the approaches being used, the published pre-clinical data, and considerations affecting clinical trial design in hemophilia gene therapy.

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

The diagnostic and treatment strategies related to hemophilia are rapidly evolving. This article focuses on some of the issues of importance. Diagnostic advances in molecular genetics are reviewed by Dr. Ginsburg in Section I, including the current state of knowledge regarding the mutations responsible for hemophilia, with reference to the potential clinical applications of DNA diagnosis and prenatal testing.

Within the area of new therapeutic approaches in hemophilia, recombinant factor VIII and factor IX concentrates, their use and availability are addressed by Dr. Lusher in Section II as well as the use of so-called “primary prophylaxis” with the aim of decreasing long-term hemophilia athropathy. The use of radionuclide synovectomy as replacement for more invasive methods is also reviewed.

Various approaches to the ongoing challenge of the management of hemophilia patients with inhibitors against factor VIII and factor IX are reviewed by Dr. Hedner in Section III, including the principles for immune tolerance induction and the use of recombinant factor VIIa to induce hemostasis in bleeding patients with inhibitors.

In Section IV, gene therapy in hemophilia is reviewed by Dr. High, who focuses on recent developments in the rapidly moving field of gene therapy for hemophilia. Three phase I trials of gene therapy for hemophilia were initiated in 1999, and additional proposed trials are currently in the regulatory review process. Certain aspects of the pathophysiology of hemophilia make it an attractive model for a gene-based approach to treatment. These include latitude in choice of target tissue, a wide therapeutic window, the availability of small and large animal models of the disease, and the ease of determining therapeutic efficacy. Since there is very little published information regarding the ongoing trials, this section reviews the approaches being used, the published pre-clinical data, and considerations affecting clinical trial design in hemophilia gene therapy.

Disappearance of inhibitor to factor IX in a patient with severe haemophilia B and immunological characterization of the inhibitor

Disappearance of an inhibitor to factor IX in an 11-year-old boy with haemophilia B is described. He had been given a total of 14,200 units of a prothrombin complex concentrate (PCC) before an inhibitor to factor IX developed. He subsequently received four separate infusions of PCC and his inhibitor titre rose in response to the treatment for the following 4 years. No inhibitor is presently detected despite repeated administration of PCC. Immunological characterization of the inhibitor by inhibitor neutralization assays, modified crossed-immunoelectrophoresis and enzyme-linked immunosorbent assay demonstrated that it contained IgG2 and IgG4 heavy chains and kappa and lambda light chains. No large deletion of the factor IX gene in the patient was observed using cDNA (cVII).

IgG subclass identification of inhibitors to factor IX in haemophilia B patients

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.

Induction of split tolerance and clinical cure in high-responding hemophiliacs with factor IX antibodies

An approach to the problem of inducing tolerance in patients with hemophilia complicated by high-responding antibodies is described. Thus, in four patients with severe hemophilia B and high-responding antibodies against factor IX, it has been possible to modify the immune response by giving high doses of intravenous IgG in combination with cyclophosphamide and factor IX, followed by regular factor IX treatment. In three of the patients, the in vivo recovery and half-life of infused factor IX coagulant activity (IX:C) are now normal, while the fourth patient has been converted to a low responder. Hip replacement surgery has been performed successfully in one patient. The tolerant state in these four patients is characterized, and they have all been found to have complexes between factor IX antigen and a "new" antibody without IX:C inhibitory activity. The disappearance rate of the complexed factor IX antigen (i.e., lacking IX:C activity) is considerably prolonged, and the persistence in the circulation of this (probably modified) factor IX molecule may be crucial, since tolerance to factor IX treatment was only induced when immunocomplexes were produced. Since earlier treatment of the patients with cyclophosphamide and factor IX, but without IgG, failed to induce tolerance, it appears to be the IgG that is the prerequisite.

A tumor immunotherapy technique based on modulation of the idiotype anti-idiotype network

In this communication I propose a technique for manipulating the idiotype anti-idiotype network with the aim of enhancing the immune response to tumors. The theoretical basis for this technique follows from Jerne's network theory of the immune system. By tolerizing the host to immunoglobulin bearing idiotypes directed against tumor associated antigens it should be possible to dampen the expected anti-idiotype response to these idiotypes. A reduced anti-idiotype response should result in an increased idiotype response and thus a greater anti-tumor immune response.

Characterisation of the tolerant state in a patient with haemophilia B after removal of high-titre factor IX antibodies

In a patient with severe haemophilia B and antibodies against factor IX in high titre, and known for many years to be a really high responder, it was possible to suppress the secondary antibody response after treatment with high doses of intravenous IgG (Gammonativ, KabiVitrum AB) combined with factor IX and cyclophosphamide. After 2 further treatments, including IgG, a total disappearance of the IX:C inhibitor was noted. The patient now treats himself at home with weekly infusions of only factor IX concentrate. Survival of IX:C is normal, though IX antigen (IX:Ag), as measured with the original antibody in an immunoradiometric assay, persists for at least a week after concentrate infusion. We have not been able to demonstrate an antiidiotypic antibody. Instead the antigenic factor IX material circulates complexed to a 'new' antibody without anticoagulant activity. Theoretically at least, the persistence of such immune complexes may be important for sustaining the patient's tolerance to the anticoagulant antibody's epitope. The initial IgG treatment appears as a crucial factor for induction of tolerance in this case.