[Show abstract][Hide abstract] ABSTRACT: The immune response to factor VIII and the development of inhibitory antibodies is a complex multi-factorial process involving a variety of immune regulatory genes and cells, several of which have the potential to determine risk. A better understanding of the mechanisms involved will increase the likelihood of development of new therapeutic options for patients with hemophilia. This review summarizes genetic and non-genetic risk factors currently under evaluation, and the potential modulative effect of the von Willebrand factor on factor VIII immuno- and antigenicity. In addition, the role of T-regulatory cells in the pathogenicity of inhibitors will be discussed.
[Show abstract][Hide abstract] ABSTRACT: Participants in an international conference on the management of haemophilia patients with inhibitors developed a jointly authored summary of the findings and conclusions of the conference. Current knowledge of the genetic and immunologic mechanisms underlying inhibitor development was briefly summarized. Concerning the purported treatment-related risk factors, conference participants commented on the limitations of the available evidence and the need for more rigorous prospective research in a fully genotyped population. Other clinical considerations discussed included the unproved utility of routine surveillance, the need for assay standardization, the management of acute bleeding and approaches to joint disease prophylaxis and immune tolerance induction (ITI). A number of issues were identified as needing further investigation in larger prospective studies, ideally through international cooperation. Such studies should enroll cohorts that have been scrupulously defined in terms of mutation status and treatment exposure. Finally, conference participants urged their colleagues to participate in the currently ongoing international trials of ITI.
[Show abstract][Hide abstract] ABSTRACT: The development of inhibitor antibodies is perhaps the most serious complication of coagulation factor replacement therapy. A complex interaction of several variables leads to inhibitor formation in congenital haemophilia, while acquired haemophilia represents a failure of the immune tolerance mechanisms that regulate a normal immune response to factor VIII (FVIII). The immune response to FVIII is dependent upon the interaction of different CD4+ T-cell subsets (Th1, Th2 and Th3) specific for FVIII. Failure to activate regulatory CD4+ cells likely plays a crucial role in the development of FVIII inhibitors. Although the basic mechanisms of the immune response to FVIII in the setting of factor replacement therapy are being elucidated, a clear understanding of the relevance of these mechanisms in the context of successful immune tolerance therapy and ultimately gene therapy, awaits further study.
[Show abstract][Hide abstract] ABSTRACT: We present the case of a 61-year-old man with severe haemophilia A and a high-titre factor VIII inhibitor who underwent successful orthotopic liver transplantation (OLT) for hepatocellular carcinoma. Postoperatively, a modest early anamnestic response to FVIII was followed by immunological tolerance to FVIII. This case illustrates the technical feasibility of OLT in some patients with high-titre inhibitors to FVIII, and suggests that immune tolerance may be induced by endogenously produced FVIII from the transplanted organ.
[Show abstract][Hide abstract] ABSTRACT: Severe hemophilia A patients treated with factor (F)VIII may develop antibodies (Ab) that block FVIII function (inhibitors). Autoimmune inhibitors may develop in subjects without congenital hemophilia, and cause acquired hemophilia. Hemophiliacs without inhibitors and healthy subjects may also have small amounts of antiFVIII Ab. FVIII-specific CD4(+) T cells induce antiFVIII Ab synthesis. Here, we have examined their epitope repertoire in hemophilia patients and healthy subjects. We used overlapping synthetic peptides, spanning the sequence of the FVIII A3 domain, to challenge blood CD4(+) T cells in proliferation assays. The epitopes recognized in hemophilia A patients with or without inhibitors, acquired hemophilia patients, or healthy subjects overlapped, yet had characteristic differences. Most members of one or more study groups recognized the sequence regions 1691-1710, 1801-1820, 1831-1850, and 1941-60. In the proposed three-dimensional structure of the A3 domain, these sequences are largely exposed to the solvent and flanked by flexible sequence loops: these are structural features characteristic of 'universal' CD4(+) T epitopes. Hemophilia A patients with inhibitors recognized prominently only the sequence 1801-1820, which overlaps a known inhibitor binding site. This is consistent with the possibility that CD4(+) T cells recognizing epitopes within residues 1801-1820 have a role in inducing inhibitor synthesis. In contrast, CD4(+) T cells sensitized to sequences 1691-1710 and 1941-60, which are recognized by healthy subjects and hemophilia A patients without inhibitors, might curb inhibitor synthesis.
Journal of Thrombosis and Haemostasis 09/2004; 2(8):1385-94. · 5.55 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Approximately 25% of severe hemophilia A patients develop antibodies (Ab) that neutralize the procoagulant function of factor (F)VIII (inhibitors). Autoimmune FVIII inhibitors may develop in individuals without congenital FVIII deficiency and cause acquired hemophilia. Low titers of anti-FVIII Ab may be present in hemophilia A patients without inhibitors and in healthy blood donors. FVIII-specific CD4+ T-cells drive the synthesis of anti-FVIII Ab. We examined the epitope repertoire of CD4+ T-cells from 15 healthy subjects, 10 hemophilia A patients without inhibitors, 11 hemophilia A patients with inhibitors, and six acquired hemophilia patients. Blood CD4+ T-cells were challenged in proliferation assays with a panel 16 overlapping synthetic peptides, spanning the sequence of the FVIII C2 domain. The sequence region 2291-2330 contained the most frequently and strongly recognized peptides in each of the four subject groups. Crystallographic B factor data and the location of these peptides within the three-dimensional structure of the C2 domain confirm that this region has a high degree of solvent exposure and flexibility within the peptide backbone, which are structural features typical of immunodominant universal CD4+ epitopes. Furthermore, this sequence region overlaps inhibitor-binding sites, suggesting that CD4+ T-cells recognizing peptide sequences within this region might be involved in inhibitor synthesis. The sequence regions 2191-2210 (recognized strongly by each study group except hemophilia A patients with inhibitors) and 2241-2290 (recognized primarily by acquired hemophilia patients and healthy subjects) share the same structural features, and also overlap inhibitor-binding sites. Although similar, there appear to be important differences in the CD4+ epitope repertoires of congenital and acquired hemophilia patients.
Journal of Thrombosis and Haemostasis 09/2003; 1(8):1777-84. · 5.55 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Development of antibodies (Ab) that inhibit the procoagulant function of factor VIII (fVIII) seriously complicates the treatment of hemophilia A patients. It also causes acquired hemophilia, a rare yet serious autoimmune disease. The design of effective fVIII-specific tolerizing procedures will require lucidation of the role of the different CD4(+) T cell subsets that drive inhibitor synthesis. To examine the contribution of Th1 and Th2 cells in the anti-fVIII Ab response, we measured the concentration of Th1- and Th2-driven anti-fVIII IgG subclasses in 17 patients with severe hemophilia A and 18 patients with acquired hemophilia. We found that both congenital and acquired hemophilia patients had similar and comparable proportions of Th1- and Th2-induced anti-fVIII Ab, suggesting a more important role of Th1 cells in the immune response to fVIII than previously appreciated. The distribution of anti-fVIII IgG subclasses was stable for periods of up to six months. More intense anti-fVIII Ab responses and higher inhibitor titers correlated with a predominance of Th2-driven subclasses. In contrast, Th1-driven anti-fVIII Ab were predominant in patients who had low anti-fVIII Ab concentrations, even when this was the result of successful immune tolerance or immunosuppressive therapy, which had caused drastic reduction or disappearance of inhibitors. Thus, synthesis of Th2-driven inhibitors occurs when the anti-fVIII Ab response is intense, while Th1 cells may be involved in the long-term maintenance of anti-fVIII Ab synthesis.
Thrombosis and Haemostasis 11/2002; 88(4):568-75. · 5.76 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Porcine factor VIII (pFVIII), which is used to control bleeding in patients with congenital or acquired haemophilia who have high-titre neutralizing antibodies to human FVIII, is not known to increase the risk of arterial or venous thrombosis. We have recently encountered a patient with acquired haemophilia who developed a thrombotic left middle cerebral artery distribution stroke while being treated with pFVIII. To our knowledge, this is the first such reported thrombotic event. We speculate that platelet activation induced by pFVIII may have contributed to thrombosis and suggest that pFVIII be used with caution in elderly patients with pre-existing cardiovascular risk factors.
[Show abstract][Hide abstract] ABSTRACT: The studies we reviewed here have begun to clarify the complex cellular mechanisms involved in the immune response to fVIII, and the circumstances under which fVIII inhibitors develop. Further characterization and comparison of the immune response to fVIII in both hemophilia patients and healthy subjects will help to further elucidate these mechanisms. The murine hemophilia model will hopefully provide further insights into the mechanisms of inhibitor formation, and prove to be a suitable tool for the design and testing of therapeutic strategies aimed at preventing the development of fVIII inhibitors.
Advances in Experimental Medicine and Biology 02/2001; 489:119-34. · 2.01 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Mice genetically deficient in factor VII (fVIII) are a model of hemophilia A. As a first step to reproduce in this mouse model what occurs over time in hemophilia A patients treated with human fVIII (hfVIII), we have investigated the time course and the characteristics of their immune response to hfVIII, after multiple intravenous injections. Anti-hfVIII antibodies appeared after four to five injections. They were IgG1 and to a lesser extent IgG2, indicating that they were induced by both Th2 and Th1 cells. Inhibitors appeared after six injections. CD4+ enriched splenocytes from hfVIII-treated mice proliferated in response to fVIII and secreted IL-10: in a few mice they secreted also IFN-gamma and in one mouse IL-4, but never IL-2. A hfVIII-specific T cell line derived from hfVIII-treated mice secreted both IL-4 and IFN-gamma, suggesting that it included both Th1 and Th2 cells. CD4+ enriched splenocytes of hfIII-treated mice recognized all hfVIII domains. Thus, hemophilic mice develop an immune response to hfVIII administered intravenously similar to that of hemophilia A patients. Their anti-hfVIII antibodies can be inhibitors and belong to IgG subclasses homologous to those of inhibitors in hemophilic patients; their anti-hfVIII CD4+ cells recognize a complex repertoire and both Th1 and Th2 cytokines, and especially IL-10, may drive the antibody synthesis.
Thrombosis and Haemostasis 02/2001; 85(1):125-33. · 5.76 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Antibodies (Ab) that inhibit factor VIII (fVIII) may develop in patients with hemophilia A and rarely in individuals without congenital fVIII deficiency (acquired hemophilia). Synthesis of fVIII inhibitors requires CD4+ T cells. We investigated the proliferative response of blood CD4+ cells from 11 patients with congenital or acquired hemophilia and 12 healthy subjects, to recombinant human fVIII, and to pools of overlapping synthetic peptides spanning the sequences of individual fVIII domains. All patients had CD4+ cells that responded to fVIII. The intensity of the responses fluctuated over time: several patients had brief periods when they did not respond to fVIII. All healthy subjects had transient CD4+ responses to fVIII, that were significantly lower than those of hemophilia patients. Also, healthy subjects responded to fVIII less frequently and for shorter periods than hemophilia patients. All patients and healthy subjects recognized several fVIII domains: the A3 domain was recognized most strongly and frequently. The transient sensitization of CD4+ cells to fVIII in healthy subjects suggests that inadequate tolerization of CD4+ cells to fVIII, due to lack of endogenous fVIII, is an important factor in the development of clinically significant anti-fVIII antibodies in hemophilia A.
Thrombosis and Haemostasis 11/2000; 84(4):643-52. · 5.76 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: These studies have begun to clarify the complex cellular mechanisms involved in the immune response to factor VIII. Although vigorous sensitization of CD4+ cells occurs in healthy subjects, the absence of clinically significant levels of inhibitor antibodies is likely related to the prompt down-regulation of the immune response. It may also be possible that the specific epitope repertoire recognized by CD4+ cells plays a role in the outcome of the immune response to factor VIII. Further characterization and comparison of the CD4+ repertoire in healthy subjects with that of hemophilia patients with and without inhibitors will help clarify which mechanism explains the absence of productive inhibitor synthesis in certain individuals. Also, it might identify CD4+ epitopes recognized by T helper cells that are essential for inhibitor synthesis. Additional studies to further characterize the role of Th1 and Th2 cells in the immune response to factor VIII may also be needed for the design of novel therapeutic strategies aimed at preventing inhibitor development.
Thrombosis and Haemostasis 09/1999; 82(2):509-15. · 5.76 Impact Factor