Inhibitor Formation In Patients Research Articles

Abnormal frequency of the memory B cell subsets and plasmablasts in patients with congenital severe hemophilia A: correlation with “Inhibitor” formation

BackgroundDevelopment of antibodies against infused Factor VIII (FVIII) or "inhibitors" represents a major challenge following FVIII replacement therapy in patients with hemophilia A (HA). Recent studies have shown that certain cellular compartments of the immune system contribute to the production of such antibodies. Herein, we determined the frequency of class-switched CD19+IgD−CD27+/non-class-switched CD19+IgD+CD27+ memory B cell subsets and CD19+CD27hiCD38hi plasmablasts in patients with severe HA and their association with the development of inhibitors in these patients.MethodsThis cross-sectional case–control study enrolled 32 patients with severe HA, including 8 with and 24 without inhibitors, and 24 healthy individuals. The frequencies of the memory B cell subsets and plasmablasts were determined using flow cytometry.ResultsThe frequency of CD19+IgD+CD27+ non-class-switched memory B cells was significantly lower in patients with HA (including both patients with and without inhibitors) than in healthy controls. The percentages of both CD19+IgD−CD27+ class-switched and CD19+IgD+CD27+ non-class-switched memory B cells did not differ significantly between patients with and without inhibitors. HA patients with inhibitors had significantly higher proportions of CD19+CD27hiCD38hi plasmablasts than the control group as well as the inhibitor (-) ones. No significant correlation was observed between the inhibitor levels with the percentages of memory B cell subsets and plasmablasts.ConclusionThis study is the first to demonstrate a dysregulated proportion of CD19+IgD+CD27+ non-class-switched memory B cells and CD19+CD27hiCD38hi plasmablasts in patients with severe HA. Therefore, strategies targeting memory B-cell/plasmablast differentiation may have promising outcomes in the management of inhibitor formation in patients with severe HA.

Altered frequency of FOXP3+ regulatory T cells is associated with development of inhibitors in patients with severe hemophilia A.

The development of anti-factor VIII (FVIII) antibodies or "inhibitors" is a major complication following FVIII replacement therapy in patients with severe hemophilia A (HA), rendering the treatment inefficient. Data on the role of regulatory T cells (Tregs) in inhibitor formation in these patients are rare. Herein, we aimed to investigate whether a difference in the FOXP3+ Tregs is linked to the formation of the inhibitors in severe HA patients. In this cross-sectional study, 32 patients with severe HA (8 patients with inhibitors and 24 without inhibitors) and 24 healthy controls were enrolled. The frequency of FOXP3+ Tregs was determined using multicolor flow cytometry method. Our results showed that the median level of CD4+ CD25+ FOXP3+ Tregs did not significantly differ between HA patients and healthy controls and between HA patients with and without inhibitors (P > 0.05). However, patients with inhibitors had significantly lower amounts of CD4+ CD25- FOXP3+ Tregs compared to those without inhibitors as well as healthy controls (*P = 0.012 and *P = 0.004, respectively). The frequency of CD4+ CD25+ T cells was significantly higher in HA patients who developed inhibitors compared to the inhibitor-negative ones whereas they were lower in inhibitor-negative patients compared to the healthy controls (*P = 0.013 and *P = *0.029, respectively). The percentages of CD4+ CD25+ T cells were positively correlated with the levels of inhibitors in HA patients (r = 0.45, *P = 0.021). Our data demonstrated for the first time that the CD4+ CD25- FOXP3+ Tregs might be implicated in the prevention of inhibitor formation in severe HA patients.

Induction of activated T follicular helper cells is critical for anti-FVIII inhibitor development in hemophilia A mice

AbstractThe development of neutralizing anti-FVIII antibodies (inhibitors) is a major complication of FVIII protein replacement therapy in patients with hemophilia A (HA). Although multiple lines of evidence indicate that the immune response against FVIII is CD4 T-cell–dependent and many FVIII-derived CD4 epitopes have already been discovered, the role of T follicular helper (TFH) cells in FVIII inhibitor development is unknown. TFH cells, a newly identified subset of CD4 T cells, are characterized by expression of the B-cell follicle-homing receptor CXCR5 and PD-1. In this study, we show for the first time that IV FVIII immunization induces activation and accumulation and/or expansion of PD-1+CXCR5+ TFH cells in the spleen of FVIII-deficient (FVIIInull) mice. FVIII inhibitor-producing mice showed increased germinal center (GC) formation and increased GC TFH cells in response to FVIII immunization. Emergence of TFH cells correlated with titers of anti-FVIII inhibitors. Rechallenge with FVIII antigen elicited recall responses of TFH cells. In vitro FVIII restimulation resulted in antigen-specific proliferation of splenic CD4+ T cells from FVIII-primed FVIIInull mice, and the proliferating cells expressed the TFH hallmark transcription factor BCL6. CXCR5+/+ TFH-cell–specific deletion impaired anti-FVIII inhibitor production, confirming the essential role of CXCR5+/+ TFH cells for the generation of FVIII-neutralizing antibodies. Together, our results demonstrate that the induction of activated TFH cells in FVIIInull mice is critical for FVIII inhibitor development, suggesting that inhibition of FVIII-specific TFH-cell activation may be a promising strategy for preventing anti-FVIII inhibitor formation in patients with HA.

Relationship Between Single-Nucleotide Polymorphisms of Tumor Necrosis Factor Alpha, Interleukin-10, Factor II and Factor V with Risk of Inhibitor Development in Patients with Severe Hemophilia A.

About one-fourth of patients with hemophilia A (HA) develop alloantibodies against factor (F) VIII, as the main treatment challenge. Here, we assessed the relationship between interleukin-10 (IL-10), tumor necrosis factor alpha (TNF-α), FII and FV polymorphisms and risk of inhibitor formation in patients with severe HA. We divided 39 patients with severe HA in two groups of case (n: 19) and control (n: 20). Genotyping was performed by multiplex amplification tetra arms refractory mutation systempolymerase chain reaction (ARMS-PCR) and PCR-restriction fragment-length polymorphism (PCR-RFLP). TNFα rs1800629 G>A polymorphism decreased the risk of inhibitor development in codominant and dominant inheritance pattern. Moreover, TNFα rs1800629 A allele, decrease the risk of inhibitor formation, while IL10 rs1800896 A>G, FV rs6025 G>A, and FII rs1799963 G>A polymorphisms were not associated with risk of inhibitor development. It seems that TNFα rs1800629 G>A polymorphism decreased the risk of inhibitor formation in Iranian patients with HA.

Factor VIII products and inhibitor development in previously treated patients with severe or moderately severe hemophilia A: a systematic review

Background Patients with severe hemophiliaA who have been treated extensively with factorVIII products have a low but potentially serious risk of inhibitor development. It is unknown why these patients develop inhibitors, and data on product-related immunogenicity are scarce. Aims To summarize the currently available evidence on the relationship between inhibitor development and recombinant FVIII product type in previously treated patients (PTPs) with severe hemophiliaA. Methods Longitudinal studies were included that reported on denovo inhibitor formation in patients with baseline FVIII activity levels of <0.02IUmL-1 who had been treated with FVIII for at least 50days. Pooled incidence rates of inhibitor development according to product types were calculated with a random intercept Poisson regression model. Results Forty-one independent cohorts were included; 39 patients developed denovo inhibitors during 19157person-years of observation. The overall incidence rate was 2.06 per 1000person-years, with a 95% confidence interval (CI) of 1.06-4.01. According to product type, the pooled incidence rates were 0.99 (95%CI0.37-2.70) per 1000person-years for patients treated with Advate, 5.86 (95%CI0.25-134.92) per 1000person-years for those treated with Kogenate/Helixate, 1.35 (95%CI0.66-2.77) per 1000person-years for those treated with KogenateFS/Helixate NexGen, 12.05 (95%CI1.53-94.78) per 1000person-years for those treated with Refacto, and 4.64 (95%CI0.82-26.43) per 1000person-years for those treated with RefactoAF. Conclusion These results suggest that some products may be associated with increased immunogenicity. However, the low incidence of inhibitors in PTPs and the differences in study design may cause significant variation in estimates of risk.

Assessment of the frequency of regulatory T cells (CD4+CD25+CD127-) in children with hemophilia A: relation to factor VIII inhibitors and disease severity.

A rapidly growing evidence showed that regulatory T cells (Tregs) play a crucial role in tolerance to coagulation factors and may be involved in the pathogenesis of inhibitor formation in patients with hemophilia. We determined the percentage of Tregs (CD4CD25CD127) in 45 children with hemophilia A compared with 45 healthy controls, and assessed their relation to the clinical characteristics of patients and factor VIII (FVIII) inhibitors. Patients were studied stressing on frequency of bleeding attacks, joint pain, history of viral hepatitis, and the received therapy (FVIII precipitate/cryotherapy). FVIII activity and FVIII inhibitors were assessed with flow cytometric analysis of CD4CD25CD127 Tregs. According to residual FVIII activity levels, 30 patients (66.7%) had mild/moderate hemophilia A, whereas 15 (33.3%) patients had severe hemophilia A. The frequency of Tregs was significantly lower among all patients with hemophilia A compared with controls (2.59 ± 1.1 versus 3.73 ± 1.12%; P = 0.002). Tregs were significantly decreased among patients with FVIII inhibitors compared with the inhibitor-negative group (P < 0.001). Patients with hematuria or severe hemophilia A had lower Tregs levels than those without (P = 0.34 and P = 0.011, respectively). A significant positive correlation was found between the percentage of Tregs and FVIII among hemophilia A patients. ROC curve analysis revealed that the cut-off value of Tregs at 1.91% could differentiate patients with and without FVIII inhibitors, with a sensitivity of 100% and a specificity of 91.3%. We suggest that alteration in the frequency of Tregs in young patients with hemophilia A may contribute to inhibitor formation and disease severity.

Interim data on long‐term efficacy, safety and tolerability of a plasma‐derived factor VIII concentrate in 109 patients with severe haemophilia A

The aim of this open-label, multicentre and multinational post-marketing surveillance was to investigate clinical effectiveness, safety and tolerability of a plasma-derived and vWF containing factor VIII product (FVIII/VWF) in patients with severe haemophilia A. Long-term effectiveness, safety and tolerability were investigated in a total of 109 haemophilia A patients treated for prophylaxis or on-demand, as required. Interim data collected until June 2010 are presented. Most patients (99/109; 90.8%) were previously treated patients (PTPs). Mean observation period was 82.6 months. Overall, patients received 105 131 425 IU haemoctin SDH during 68 624 administrations. Each patient was given a mean of 635.4 injections, whereby about half of the administrations were given for treatment of bleeding episodes (46.9%) and the other administrations for prophylactic reasons (53.1%). Patients on prophylaxis had a median of 0.8 bleeding episodes per month. The expected therapeutic effect was reached in 99.3% of treatments. The incidence of clinically relevant inhibitor formation in patients with severe haemophilia (FVIII activity ≤ 1%) was 1.2% for PTPs. One previously untreated patient with severe haemophilia had a clinically relevant transient inhibitor. No treatment related transmissions of hepatitis A, B and C and HIV 1/2 were observed. German patients had a higher extent of exposure and experienced less bleeding episodes than Hungarian patients. In conclusion, haemoctin SDH was effective, safe and well tolerated in long-term prophylaxis and treatment on demand.

Requirements for immune recognition and processing of factor VIII by antigen-presenting cells

Generation of inhibitory antibodies upon repeated FVIII infusion represents a major complication in hemophilia care. Professional antigen presenting cells (APCs) are crucial for orchestration of humoral immune responses. APCs are capable of internalizing soluble as well as particulate antigens through various mechanisms resulting in loading of antigen-derived peptides on MHC class I or II for presentation to T cells. This review highlights how FVIII is recognized and processed by APCs. The significance and contribution of candidate receptors involved in FVIII uptake by APC are discussed. Recent findings defining the repertoire of FVIII peptides presented on MHC class II are addressed. Studies in murine models of hemophilia A suggest that modulation of APC function can reduce inhibitor formation. Based on this we anticipate that modulation of FVIII uptake by APCs may yield novel therapeutic approaches for treatment or prevention of inhibitor formation in patients with hemophilia A.

An analysis of factors affecting the incidence of inhibitor formation in patients with congenital haemophilia in Japan

Studies conducted in European and North American countries have demonstrated that various factors including races affect the frequency of inhibitor formation in haemophilia patients. The present study was undertaken to analyse factors affecting the incidence of inhibitor formation in Japanese haemophilia A and B patients. Analytical data were retrospectively collected from haemophilia A and B patients born after 1988, the year when monoclonal antibody-purified factor VIII products were first marketed in Japan. Various data were collected from 184 patients (153 cases of haemophilia A; 31 cases of haemophilia B). The sample size of haemophilia B cases was too small to reveal any significant differences between the inhibitor formation group and the inhibitor-free group in any of background variables. For patients with haemophilia A, on the other hand, univariate analysis identified the severity of haemophilia and a positive family history of inhibitor development as risk factors for the formation of inhibitors. In analyses of the clotting factor products used, the incidence of inhibitor formation did not differ significantly between the group treated with plasma-derived products (29.7%) and the group treated with recombinant products (25.0%). When background variables were compared, age was higher in the group treated with plasma-derived products but none of the other background variables differed between the two groups. These results suggest that in Japanese haemophilia patients, the type of clotting factor preparations used for therapy has not influenced the incidence of inhibitor formation.

Impact of the Underlying Mutation and the Route of Vector Administration on Immune Responses to Factor IX in Gene Therapy for Hemophilia B

Immune responses to factor IX (F.IX), a major concern in gene therapy for hemophilia, were analyzed for adeno-associated viral (AAV-2) gene transfer to skeletal muscle and liver as a function of the F9 underlying mutation. Vectors identical to those recently used in clinical trials were administered to four lines of hemophilia B mice on a defined genetic background [C3H/HeJ with deletion of endogenous F9 and transgenic for a range of nonfunctional human F.IX (hF.IX) variants]. The strength of the immune response to AAV-encoded F.IX inversely correlated with the degree of conservation of endogenous coding information and levels of endogenous antigen. Null mutation animals developed T- and B-cell responses in both protocols. However, inhibitor titers were considerably higher upon muscle gene transfer (or protein therapy). Transduced muscles of Null mice had strong infiltrates with CD8+ cells, which were much more limited in the liver and not seen for the other mutations. Sustained expression was achieved with liver transduction in mice with crm(-) nonsense and missense mutations, although they still formed antibodies upon muscle gene transfer. Therefore, endogenous expression prevented T-cell responses more effectively than antibody formation, and immune responses varied substantially depending on the protocol and the underlying mutation.

Cumulative analysis of inhibitor formation in patients with haemophilia A treated with sucrose‐formulated recombinant factor VIII

Cumulative analysis of inhibitor formation in patients with haemophilia A treated with sucrose‐formulated recombinant factor VIII

Patients with Severe Factor XI Deficiency Who Have An Inhibitor or IgA Deficiency Can Undergo Uneventful Major Surgery by a Single Infusion of Low Dose Recombinant Factor VIIa and Use of Tranexamic Acid.

Inhibitors to factor XI (FXI) can develop following exposure to plasma products in 33% of patients with severe FXI deficiency who are homozygous for the type II nonsense mutation prevalent in Jews (Salomon et al. Blood 2003; 101:4783). Hemostasis in five such patients was previously achieved during surgery by infusion of recombinant factor VIIa (rFVIIa) and tranexamic acid, but two patients experienced arterial thrombosis following surgery (Schulman et al. Hemophilia 2006; 12:223). Conceivably, the rather high dose of rFVIIa used was responsible for the thrombotic events in these patients. In a previous in vitro study, we showed that low concentrations of rFVIIa can correct thrombin generation in plasma of patients with severe FXI deficiency and an inhibitor to FXI (Livnat et al. J Thromb Hemost 2006; 4:192). In the present study we addressed the question whether low doses of rFVIIa and use of tranexamic would be hemostatically effective and less thrombogenic during and after major surgery in patients with severe FXI deficiency in whom plasma derivatives could not be used. Three patients (two with FXI inhibitor and one with severe IgA deficiency) underwent major surgery managed by a single low dose infusion of rFVIIa and administration of tranexamic acid 1 G q.i.d for 7 days (Table). In patient 1 the infusion was given immediately prior to surgery and in patients 2 and 3 at the end of surgery. Hemostasis was achieved in all patients and no thrombosis occurred.No.Sex/ageFXI (U/dL)FXI inhibitor (B.U)OperationSingle dose rVIIa (uG/Kg)Adverse events1M/62< 0.015.0Laparoscopic cholecystectomy30None2M/61< 0.015.0Transuretheral prostatectomy16None3M/630.020*Parathyroidectomy15None* IgA deficiencyThese observations suggest that a single infusion of low dose rFVIIa and use of tranexamic acid can be a safe modality of treatment in patients with severe FXI deficiency who cannot receive blood products. Furthermore, the protocol outlined here may be used to avoid inhibitor formation in patients with extremely severe FXI deficiency who undergo surgery.

Epidemiology of inhibitor formation with recombinant factor VIII replacement therapy

This article reviews the epidemiology of inhibitor formation in patients receiving recombinant factor VIII (rFVIII) replacement therapy for haemophilia A. Data from pivotal trial programmes, post-marketing surveillance studies, and pharmacovigilance studies for all available rFVIII products were reviewed. To date, no comparative studies have been performed, and in the non-comparative studies, there were differences in the patient population enrolled and study design (including the number of patient exposure days). In the absence of comparative clinical trials, it is not possible to make comparisons between inhibitor data for the various rFVIII products. This review of the epidemiological data shows that across the pivotal trial programmes for rFVIII products, the observed incidence of inhibitors was in the range of 15-32% in previously untreated patients (PUPs) and 0.9-2.9% in previously treated patients (PTPs). High-titre inhibitors (peak >5 BU) were detected in 10-16% of PUPs and 0-2.3% of PTPs. Several initiatives proposed to help standardize collection and interpretation of inhibitor data for patients receiving rFVIII treatment are described. Such standardization would help to clarify the epidemiology of inhibitor formation across FVIII treatments.

Does the Use of Different Factor VIII Products Influence Inhibitor Formation in Patients with Haemaphilia A.

This retrospective study looked at all patients with Haemophilia A who attended Manchester Pendlebury Childrens Hospital for their first and subsequent Factor replacement therapy between January 1980 and May 2005. The aim was to determine :-Does an increased number of different products used influence inhibitor formation.Does using a B domain deleted factor (Refacto) concentrate influence inhibitor formation.Does changing from plasma derived to recombinant factor influence inhibitor formation.A total of 107 patients who received a cumulative total of 65,102 trearment days were identified and the following information was recorded for each patient :-severity of haemophilia (mild, moderate or severe) and baseline factor VIII level, date and age of first product, all types of products used, number of treatment days used of each product, detection of inhibitor and if present date of ocurrence and age of patient. The policy of the unit was to test for inhibitors every six months, pre operatively or when clinically indicated. Thirteen different products were in use during the period of the study :- AHFC(anti haemophilic factor concentrate), Cryoprecipitate, 8Y, 8SM, Alphanate, Replenate, Monoclate P, Helixate, Refacto, Recombinate, Hemophil M, Advate and Haemate P.Only 4 patients out of 107 developed inhibitors and all were exposed to less than 4 products.Inhibitor patient demographicsHaemophilia type and baseline factor VIIINumber of treatment days before inhibitorProducts used with respective treatment daysSevere (<1%)249Cryoprecipitate (128)8Y(121)Severe (1%)75Alphanate(34)8SM(34)Replinate(7)Moderate (2%)39Alphanate(30)Helixate(9)Moderate (2%)18Refacto(2)Helixate(16)A total of 37 patients received 6 or greater factor products. The mean number of treatment days was 1224 (median 1285, SDV 863) and the mean number of factor products used was 6.8 (median 7, SDV 0.81).In severe patients (baseline factor VIII of 2% or less) a total of 31 patients received 4 or greater factor products. The mean number of treatment days was 1512 (median 1501, SDV 776) and the mean number of factor products used was 6.45 (median 6, SDV 1.31). A total of 23 patients received 6 or greater factor products. The mean number of treatment days was 1664 (median 1525, SDV 776) and the mean number of products used was 7.04 (median 7, SDV 0.93).There were 10443 exposure days of Refacto in those patients that did not develop an inhibitor. 69 out of 103 patients were exposed to the product with a mean number of treatment days of 151 (median 43, SDV 237). In the same population 29 out of 43 severe patients (baseline factor VIII of 2% or less) were exposed to the product with a total number of exposure days of 6464 with a mean number of treatment days of 222 (median 241, SDV 241). There were only 2 exposure days of ReFacto in just one of the inhibitor patients.64 patient changed from using plasma to recombinant products. Only one of these patients developed an inhibitor. In this study the number of different factors used, use of a B deleted domain factor and change from plasma derived to recombinant factors did not appear to be factors in the formation of inhibitors.

NO PROTECTIVE EFFECT OF BREASTFEEDING ON INHIBITOR FORMATION IN SEVERE HEMOPHILIA

It has been suggested that breastfeeding may prevent inhibitor formation in patients with hemophilia. In a single-center retrospective cohort study, the authors studied the association between breastfeeding and inhibitor development in 90 severe hemophilia A patients born 1975–2003. Mean follow-up was 13.2 years (standard deviation 8.7). A total of 62% of patients received breastfeeding and 20% developed inhibitors. The inhibitor rate according to breastfeeding was similar: 21% in patients who were breastfed and 18% in others. Patients who were breastfed received their first treatment 0.3 years earlier. After adjustment for age at first treatment, we found no protective effect of breastfeeding on inhibitor formation.

Factor VIII alloantibodies in hemophilia.

The development of an inhibitory response to factor VIII (FVIII) remains a puzzling challenge both for clinicians and scientists, not to mention the difficulties of maintaining hemostasis in patients producing inhibitors. Three main research lines have been explored in recent months. The mechanisms by which an anti-FVIII antibody response is elicited in patients has been examined at both the B- and T-cell levels, with particular emphasis on the generation of specific B- and T-cell clones. The hemophilia A mouse model has served to confirm the main characteristics of the anti-FVIII immune response in terms of T-cell dependency and memorization of the response. Novel strategies for the prevention and downregulation of inhibitors have emerged, with special interest in antigen-specific approaches. Although the ultimate goal, preventing or suppressing inhibitor formation in patients, is not yet achieved, the research activity developed over the past months brings us forward in that direction.

Effect of factor VIII concentrate on antigen-presenting cell (APC)/T-cell interactions in vitro: relevance to inhibitor formation and tolerance induction.

Inhibitor formation in patients with haemophilia receiving factor VIII (FVIII) concentrate is a common problem requiring tolerance induction therapy. Immune tolerance is dependent on defective T cell/antigen-presenting cell (APC) interactions and inhibitor antibody formation is associated with effective T-cell/B-cell interaction. We studied the expression of the cell-surface molecules involved with these interactions using multiparameter flow cytometry and a whole blood stimulation assay-phytohaemaglutinin (PHA) to activate T cells and Escherichia coli lipopolysaccharide (LPS) to activate monocytes and B cells. Up-regulation of T-cell co-stimulatory receptors CD11a, CD40 ligand (CD40L) and CTLA4 were inhibited in a dose-dependent manner by plasma-derived (pd)FVIII, but CD28 was unchanged. Up-regulation of monocyte and B-cell co-stimulatory ligands CD4O, B7-1 (CD80) and B7-2 (CD86) were also inhibited in a dose-dependent manner by pdFVIII, but LFA-3 (CD58) was unchanged. The combined inhibitory effect of prednisolone, an immunosuppressive agent used in several tolerance induction protocols, with pdFVIII on co-stimulatory molecules, was additive. There was no significant alteration in T-cell/APC adhesion or co-stimulatory molecules noted in the presence of recombinant (rh)FVIII concentrate. The inhibitory effect of pdFVIII on molecules involved in interaction between T cells and APCs may result in immune tolerance in recipients of pdFVIII concentrate. The inhibitory effect of pdFVIII on CD40/CD40L up-regulation may result in defective antibody formation. We now provide evidence that the use of pdFVIII, through interfering with APC/T-cell interactions, may be more appropriate than rhFVIII for tolerance induction.

Correlation between factor VIII genotype and inhibitor development in hemophilia A.

The development of neutralizing antibodies, or inhibitors, against infused factor VIII represents a significant complication of treatment for hemophilia A. Although it is likely that both genetic and environmental factors influence whether patients form inhibitors, correlations between types of factor VIII mutations and inhibitor development are becoming apparent. Approximately 20% of all patients with severe hemophilia A generate inhibitors. Of these inhibitor patients, 90% have inversions, large deletions or nonsense mutations of the factor VIII gene that would be predicted to eliminate production of factor VIII antigen. In contrast to patients with severe disease, inhibitor formation in patients with mild/moderate hemophilia A is rare. Inhibitor patients with mild/moderate disease typically have missense mutations that may cause local conformational changes within immunogenic domains of factor VIII and lead to production of dysfunctional antigen. Taken together, hemophilia A patients are predisposed to inhibitor development with mutations causing infused factor VIII to be perceived as either 1) a completely novel antigen or 2) an immunologically altered antigen.

Gene mutations and inhibitor formation in patients with hemophilia B.

The nature of the mutation in the factor IX gene is an important factor in determining whether a patient with hemophilia B will develop an inhibitor. In a series of 62 Swedish families with hemophilia B, including 30 with the severe form, approximately one third of the families exhibiting deletions or nonsense mutations contained one member who developed an inhibitor. The risk for inhibitor development in family members carrying missense mutations was virtually zero.

Tolerance and intolerance to factor VIII: a clinical perspective.

In this chapter I will discuss four aspects of inhibitor formation in patients with hemophilia A: why most patients with hemophilia are and remain tolerant to factor VIII (F.VIII), why some patients who are primarily tolerant to F.VIII get inhibitors later, how many patients get inhibitors, and how we can (re-)induce tolerance in patients with inhibitors.KeywordsFactor VIIIImmune ToleranceRecombinant Factor VIIISevere HemophiliaInhibitor DevelopmentThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.