Immune Tolerance Induction Failure Research Articles

High levels of anti–factor VIII immunoglobulin G4 and immunoglobulin G total are associated with immune tolerance induction failure in people with congenital hemophilia A and high-responding inhibitors

BackgroundImmune tolerance induction (ITI) is the treatment of choice to eradicate neutralizing anti–factor (F)VIII alloantibodies (inhibitors) in people with inherited hemophilia A. However, it is not successful in 10% to 40% of the cases. The biological mechanisms and biomarkers associated with ITI outcome are largely unknown. ObjectivesThe aim of this study was to investigate the association of plasma cytokines (interferon-γ, tumor necrosis factor, interleukin [IL]-2, IL-4, IL-5, IL-6, IL-10, and IL-17A), chemokines (IL-8/CXCL8, RANTES/CCL5, MIG/CXCL9, MCP-1/CCL2, and IP-10/CXCL10), and anti-FVIII immunoglobulin (Ig) G total, IgG1, and IgG4 with ITI outcome. MethodsIn this cross-sectional analysis of the Brazilian Immune Tolerance Study, we assessed plasma levels of anti-FVIII IgGs using an enzyme-linked immunosorbent assay with plasma-derived FVIII and recombinant FVIII as target antigens, immobilized in microplates. ResultsWe assayed 98 plasma samples of moderately severe and severe (FVIII activity, <2%) people with hemophilia A after completion of a first ITI course. Levels of anti–recombinant FVIII IgG total and IgG4 were higher in people with hemophilia A who failed ITI (IgG total optical density [OD], 0.37; IQR, 0.15-0.73; IgG4 OD, 2.19; IQR, 0.80-2.52) than in those who had partial (IgG total OD, 0.03; IQR, 0.00-0.14; IgG4 OD, 0.39; IQR, 0.09-1.11; P < .0001 for both) or complete success (IgG total OD, 0.04; IQR, 0.00-0.07; IgG4 OD, 0.07; IQR, 0.06-0.40; P < .0001 for both). Plasma cytokines, chemokines, and anti-FVIII IgG1 were not associated with ITI outcome. ConclusionOur results show that high levels of plasma anti-FVIII IgG4 and IgG total are associated with ITI failure.

Large Deletion in the Factor VIII Gene Is a Predictor of Immune Tolerance Induction Failure in People with Severe and Moderately-Severe Hemophilia a and High-Responding Inhibitors

Introduction Immune tolerance induction (ITI) is a therapeutic approach to eradicate inhibitors against factor VIII (FVIII) in people with inherited hemophilia A (PwHA). The success of ITI is highly variable, ranging from 60% to 80% across studies. Beyond inhibitor titers, other predictors of ITI outcome are unknown. Deleterious variants in FVIII gene ( F8) are well established risk factors for alloantibodies development in PwHA, although few studies have investigated the role of F8 variants on ITI outcome.Therefore we aimed to comprehensively analyze the association of F8 pathogenic variants on ITI outcome in severe PwHA with high-responding inhibitors. Methods We included severe (FVIII &amp;lt; 1 international units [IU]/dL) and moderately-severe (FVIII 1-2 IU/dL) unrelated PwHA and high-responding inhibitors who completed ITI from a large, admixed population of two well-characterized cohorts - the HEMFIL and the Brazilian Immune Tolerance (BrazIT) studies. We collected socio-demographic, clinical and laboratory data. ITI outcomes were defined according to previous definitions as failure, partial and total successes. Inversions of intron 1 and 22 (Inv22) were detected by polymerase chain reaction (PCR), and high-throughput sequencing approaches were used to unveil the additional F8 variants. The association between F8 pathogenic variants and ITI outcome was adjusted for inhibitor levels. To investigate whether F8 variants associated with inhibitor development were also related to ITI outcome, variants were categorized as “high-risk”, “intermediate-risk”, and “low-risk” categories. These categories for inhibitor development were then compared with the outcomes of ITI (total and partial successes and failure) using data from this study. Results We included158 PwHA, median age 6.6 years at ITI start, 90.5% were severe (Table 1). Inv22 was the most prevalent variant (55.1%) (Table 1). In comparison with Inv22-1, the risk of ITI failure was about 9 times higher (adjusted odds ratio [adjOR] 9.29; 95% confidence interval [95% CI] 1.95-53.70) among carriers of large deletions (Table 2). Conversely, Inv22-2 was associated with favorable ITI outcome in a univariate analysis (OR 0.15; 0.01-0.84), and after adjustment (adjOR 0.32; 95% CI 0.02-1.96) (Table 2). F8 deleterious variants sorted as high-risk and intermediate-risk according to a previously published classification on inhibitor development were associated with failure and successful outcomes, respectively. Conclusion Our study showed that F8 large deletions are independent predictors of ITI failure, and Inv22-2 is likely to be a predictor of successful ITI. We found a correspondence between variants classified as high-risk and intermediate-risk to inhibitor development with ITI failure and success, respectively. We suggest that F8 genotyping should be considered before indication of ITI, as ITI outcome can vary according to individual variant burden.

Levels of Anti-FVIII IgG4 and Total IgG Are Biomarkers of Immune Tolerance Induction Failure in Patients with Inherited Hemophilia a and High-Responding Inhibitors

Background: The development of inhibitors in patients with inherited hemophilia A (PwHA) is an important complication of the treatment with exogenous factor VIII (FVIII), leading to inefficient replacement therapy. Immune tolerance induction (ITI) is the standard treatment to eradicate inhibitors in HA. The immune biology and biomarkers related with ITI outcome are still unclear. Few studies have investigated this, of which most included few PwHA. Furthermore, such studies have not assessed samples in specific time-points, but have rather grouped patients into categories of inhibitors and non-inhibitors. Aims: This study aimed to investigate specific anti-FVIII immunoglobulins IgG1, IgG4 and total IgG as biomarkers of ITI outcome at the completion of ITI. Methods: We included PwHA from 15 hemophilia treatment centers, participants of the Brazilian Immune Tolerance (BrazIT) Cohort Study. Inclusion criteria were severe and moderately-severe (&amp;lt;2% FVIII) PwHA, with high-responding (&amp;gt;5.0BU/mL) inhibitors, who completed a first course of ITI. All patients were treated with the same ITI protocol, i.e., 50 international units (IU)/kilogram (kg) of FVIII. In case ITI titers did not decrease by at least 20% first 3-6 months after inhibitor peak, FVIII was increased to 100 IU/kg daily. We collected socio-demographic, clinical and laboratory data using standardized forms. Outcome of ITI was defined according to published classification as failure, partial and total successes. For this analysis, plasma samples were collected in citrate at completion of ITI and frozen at -80°C until assessment. We measured plasma levels of anti-FVIII IgG1, IgG4 and total IgG in ELISA using immobilized recombinant (r) FVIII (alfaoctocogue, Takeda, USA). Local ethics committees approved this study and all patients/guardians signed informed consent. Results: We included 98 PwHA, median age of 11.0 years (interquartile range [IQR] 7.0-23.0), 94 (95.9%) severe HA (&amp;lt;1%). According to ITI outcome, 40 (40.8%) had ITI failure, 37 (37.8%) had partial success and 21 (21.4%) had total success (Table 1). Levels of total IgG in patients who failed ITI (median optical density [OD], 0.37; IQR 0.15-0.73) were significantly higher when compared to the levels of patients with partial (median OD, 0.03; IQR 0.00-0.14; p&amp;lt;0.0001) and complete (median OD, 0.04; IQR 0.00-0.07; p&amp;lt;0.0001) success. Levels of total IgG anti-FVIII were not different between partial and complete success groups. Levels of anti-FVIII IgG4 were significantly higher in PwHA who failed ITI (median OD, 2.19; IQR 0.74-2.52) compared with those who had partial (median OD, 0.39; IQR 0.09-1.11; p&amp;lt;0.0001) and complete success (median OD, 0.07; IQR 0.06-0.40; p&amp;lt;0.0001). Anti-FVIII IgG4 levels were higher in PwHA presenting partial success compared with those with complete success (p=0.02). Levels of anti-FVIII IgG1 were not different between PwHA who failed ITI (median OD, 0.03; IQR 0.01-0.21), in comparison with the ones who achieved partial success (median OD, 0.03; IQR 0.01-0.08; p=0.35) and achieved complete success (median OD, 0.03; IQR 0.02-0.05; p=0.72) (Table 2). Conclusion: We conclude that anti-FVIII IgG4 and IgG total are good biomarkers of ITI outcome. Levels of IgG4 are associated with ITI outcome in a dose-dependent manner, with failure&amp;gt;partial&amp;gt;complete success. Anti-FVIII IgG1 is not a useful biomarker of ITI outcome. This study was fully supported by Brazilian Governmental grants from Fapemig, CNPq and Ministry of Health of Brazil (Fundo Nacional de Saúde).

Native American Ancestry Is Associated with Successful Immune Tolerance Induction in Admixed Brazilians with Hemophilia a

Immune tolerance induction (ITI) is the treatment of choice for eradicating neutralizing antibodies (inhibitors) against factor VIII (FVIII) in patients with hemophilia A (PwHA). Previous studies have investigated the association of ethnicity with inhibitor development with conflicting results. However, to our concern, studies targeting the role of ethnicity on ITI outcomes are still missing. Since unfavorable ITI response occurs in 30%-40% of these patients, establishing predictors of ITI response is needed. To evaluate genetic determinants of ITI outcome beyond FVIII genotype, we investigated the association of genomic ancestry and ITI response by analyzing the exomes of PwHA from the Brazilian Immune Tolerance Study (Camelo et al. 2021). PwHA were enrolled in 15 hemophilia treatment centers from all Brazilian regions. We collected clinical data and blood samples for DNA extraction. ITI was carried out using a single protocol, regardless of selection based on “good” or “bad” risk of ITI outcome. Inclusion criteria comprised patients with severe and moderately-severe (FVIII&amp;lt;2%) HA with high-responding inhibitors who completed a first course of ITI. Since the characteristics of PwHA who responded with partial and complete success yielded similar results, these groups were analyzed together. Exomes were obtained with high quality using the xGen Exome Research Panel v2 (Illumina). Quality control filters evaluated average coverage and deep coverage, phred score, genomic position, sex, heterozygosity, and duplicated SNPs. In a multiple regression analysis, we used geographic location, inhibitor levels, presence or absence of null mutations (i.e., frameshift, deletions, nonsense, and inversions; Oldenburg et al., 2002), and kinship coefficients as explanatory variables. Inhibitor levels were evaluated as historical inhibitor peak, titer immediately before the start of ITI, and inhibitor peak during ITI. We included 150 PwHA, of whom 136 (91%) had severe (FVIII&amp;lt;1%) HA, median age 0.9 years [IQR, 0.5,1.4] at diagnosis of HA. A total of 44 (29%) PwHA had ITI failure, 60 (40%) had partial success, and 46 (31%) had complete ITI success. Functional annotation showed that most SNPs were intronic (48%) and exonic (29%). We identified 808,706 variants, of which 90,075 were not reported in the dbSNP. Average ancestries of European, African, and Native American were 79.4% [IQR:75.4,83.4], 17.3% [IQR:17.0,17.6), and 3.3% [IQR:2.6,4.0], respectively (Table 1). There was an association between a higher Native American ancestry in patients with successful ITI (2% [IQR:1.95,2.05] ancestry mean) when compared with patients who failed ITI (1% [IQR:0.97,1.03] ancestry mean). A 1% increase in the Native American ancestry proportion was associated with a rise of ~10% in the probability of successful ITI ( odds ratio [OR], 10.43 [95% CI,7.45,13.41], p = 0.040 (Table 2). Neither European nor African ancestry was associated with ITI outcome. In conclusion, Native American ancestry was associated with successful ITI. To our concern, this is the first study to evaluate genomic ancestry as a predictor of ITI response and the first to enroll an admixed population of HA. Identifying ancestry as a predictor of ITI outcome may elicit different therapeutic approaches for inhibitor eradication. However, our findings may not apply to other populations due to a particular characteristic of admixture of the Brazilian population. REFERENCES Camelo, R.M. et al. (2021) ‘Predictors of the outcome of immune tolerance induction in patients with haemophilia A and inhibitors: The Brazilian Immune Tolerance (BRAZIT) study protocol’, PLOS ONE, 16(8). doi:10.1371/journal.pone.0256265. Oldenburg, J., El-Maarri, O. and Schwaab, R. (2002) ‘Inhibitor development in correlation to factor VIII genotypes’, Haemophilia, 8(s2), pp. 23-29. doi:10.1046/j.1351-8216.2001.00134.x.

Prospective Hemophilia Inhibitor PUP Study reveals distinct antibody signatures during FVIII inhibitor eradication.

Factor VIII (FVIII) inhibitor formation is a major clinical concern during replacement therapy in patients with hemophilia A. Immune tolerance induction (ITI) is the only therapeutic approach to attempt inhibitor eradication and establishment of long-term immune tolerance to FVIII. Hemophilia Inhibitor Previously Untreated Patient (PUP) Study (HIPS) was a prospective clinical trial to investigate changes in the immune system of PUPs with severe hemophilia A. Five patients who developed persistent FVIII inhibitors during HIPS entered an ITI extension arm (HIPS-ITI). During HIPS-ITI, inhibitor patients received ITI with the same FVIII product (a single source of recombinant, human full-length FVIII) used in HIPS until successful tolerance, declared failure, or a maximum of 2 years after HIPS-ITI enrollment, whichever came first. Blood samples and clinical data were collected monthly. Longitudinal FVIII-binding antibody signatures, associated binding specificities, and apparent affinities were determined for each patient at each sampling time point. ITI was successful or partially successful in 2 patients and failed in 3. Both groups presented with distinct FVIII-specific antibody signatures. ITI success required the disappearance of FVIII inhibitors, which was associated with the eradication or sustained titer minimization of high-affinity FVIII-specific antibodies, particularly of the immunoglobulin G1 (IgG1) and IgG4 subclasses. In contrast, ITI failure, as reflected by FVIII inhibitor persistence, was associated with persistent high-affinity FVIII-specific antibodies. Interestingly, 1 patient with partial ITI success and 1 patient with ITI failure developed apparent oligoreactive FVIII-binding antibodies during ITI. The explanation of the true nature of these antibodies requires more comprehensive follow-ups in future studies. This trial was registered at www.clinicaltrials.gov as #NCT01652027.

Factor IX antibodies and tolerance in hemophilia B in the Nordic countries – The impact of F9 variants and complications

IntroductionThe development of inhibitory antibodies (inhibitors) in persons with hemophilia B (PwHB) causes significant morbidity. Data on the impact of the F9 variant and immune tolerance induction (ITI) outcome are limited.The aim of this study was to investigate the presence of neutralizing and non-neutralizing antibodies (NNA) in severe hemophilia B (HB) and to evaluate ITI outcome and complications in relation to the pathogenic F9 variant. Materials and methodsPersons with severe HB in the Nordic countries were enrolled and information on F9 variants, inhibitors, ITI and complications were collected. Analyses of anti-FIX antibodies with a fluorescence-immunoassay (xFLI) and an ELISA method were conducted. ResultsSeventy-nine PwHB were enrolled. Null variants were seen in 33 (42 %) PwHB and 12 (15 %) had a current or former inhibitor. Eleven (92 %) of the inhibitor patients had experienced allergic manifestations and three (25 %) nephrotic syndrome. Of 10 PwHB with at least one ITI attempt, eight (80 %) were considered tolerant at enrolment. Immunosuppression was included in seven of eight successful or partially successful attempts. Five PwHB had at least one ITI failure before a successful or partially successful ITI. No NNA could be identified. ConclusionA high proportion of severe F9 gene defects among persons with severe HB in the Nordic countries may explain the observed relatively high prevalence of inhibitors. ITI success was independent of the F9 variant and attained despite allergic manifestations and previous ITI failures. Inclusion of immunosuppression tentatively enhances the chances of ITI success. No NNA were observed.

Longitudinal profiling of anti-factor VIII antibodies in Japanese patients with congenital hemophilia A during factor VIII replacement and immune-tolerance induction therapy.

When patients with hemophilia A develop factor VIII (FVIII) inhibitors, FVIII replacement therapy becomes ineffective. Although immune-tolerance induction (ITI) therapy has been used to eradicate inhibitors, treatment is unsuccessful in approximately 30% of cases. However, the mechanism behind treatment failure remains unclarified. We retrospectively examined the longitudinal profiles of immunoglobulin G (IgG) subclasses and/or the inhibitory activities of FVIII in plasma samples from 14 Japanese patients with congenital hemophilia A during hemostatic, FVIII replacement, and/or ITI therapies. In five patients, an increase in IgG4 was observed simultaneously with a decrease in IgG1 when the patient had a history of relatively high FVIII inhibitor titers, reflecting an apparent change in humoral immunity. In addition, we examined the reactivity and specificity of the patients' anti-FVIII IgG1 and IgG4 to FVIII domains by immunoblotting. Under our experimental conditions, plasma from three patients with historically higher inhibitor titers appeared to have high titers of antibodies against the A2-a2 domain, which did not necessarily correlate with ITI failure. These observations may improve scientific understanding of the immune response to infused FVIII in patients with hemophilia A.

Immune Tolerance Induction in Hemophilia A Patients Using Wilate® —a Canadian 10 Year Study (PREVAIL)

Introduction:Hemophilia A patients with inhibitors experience a higher morbidity, a worse orthopedic condition and a decreased quality of life. In children with severe hemophilia A, attempting to eliminate inhibitors with immune tolerance induction (ITI) is standard of care; however, in adults with longstanding inhibitors ITI has been less extensively studied. Although practical guidelines in adults are scarce there has been an increase in case reports highlighting the success of ITI in patients with long-standing inhibitors.The possibility that the type of factor VIII (FVIII) product used for ITI could influence the likelihood of successful tolerization is the subject of intense debate. It has been postulated that FVIII products containing von Willebrand factor (VWF) may improve the ITI success rate in some patients with inhibitors, especially those with poor prognostic characteristics, i.e., a historical peak inhibitor level >200 BU/mL, an inhibitor level >10 BU/mL at the start of ITI, age >5 years, or >24 months between inhibitor detection and start of ITI.Study RationaleWilate® is the most extensively used plasma-derived FVIII/VWF concentrate for hemophilia A in Canada. Wilate® has been successful in eliminating inhibitors and reducing bleeding in Canadian children and adults who had developed inhibitors during treatment with other FVIII concentrates, including poor-prognosis patients. Wilate® was well tolerated at the high doses required for ITI. Furthermore, anecdotal clinical experience with Wilate® ITI therapy suggest that patients may have less bleeding, which may limit the need for bypassing agents.This research study was designed to evaluate the efficacy of Wilate® in achieving complete or partial ITI success in severe and moderate hemophilia A patients with inhibitors. Secondary objectives are to determine: the time to achieve immune tolerance; bleeding frequency while on Wilate® ITI treatment; quality of life while on Wilate® ITI treatment; joint health while on Wilate® ITI treatment; relapse rate; and time to relapse following successful ITI using Wilate® .Additional optional sub-studies have been incorporated into this study to gain insight into the biology of ITI, including biomarkers that might predict ITI success or failure: genotyping, anti-FVIII antibody characterization including epitope mapping, and thrombin generation.Study ProceduresThis 10-year Canadian study is an open-label, uncontrolled, multi-centre observational trial with both prospective and retrospective cohorts. A total of at least 80 hemophilia A patients with inhibitors will be enrolled into this study.The dose and frequency of ITI treatment will be at the discretion of the treating physician. However, use of risk-determined treatment protocols is recommended. Patients with high-titre inhibitors (defined as one with historical peak titre ≥5 BU/m) who have inhibitor titre ≤10 BU/mL at the start of ITI are “good-risk” for ITI success, and those who have inhibitor titre >10 BU/mL at the start of ITI are “poor-risk”. Patients with high-titre inhibitors who are good-risk should receive 50 IU FVIII/kg BW every other day or 3 times per week; daily treatment may also be considered. Patients with high-titre inhibitors who are poor-risk should receive 100-200 IU FVIII/kg BW daily. Patients with low-titre inhibitors (defined as one with historical peak titre < 5 BU/mL) should receive 50 IU FVIII/kg BW every other day to 3 times per week.For complete success, an individual must achieve the following three criteria: inhibitor titre <0.6 BU (at least 2 separate blood samplings; incremental recovery of FVIII in the normal range (≥66% of normal); FVIII half-life ≥6 hours. For partial success an individual must meet two of the three criteria. In a partial response, one of the three criteria above is met. In a partial failure : none of the three criteria are met, but inhibitor titre has decreased to <5 BU. In a complete failure none of the three criteria are met, and inhibitor titre is still ≥5 BU.ConclusionThis research study aims to evaluate and document data on the success of Wilate ® ITI in hemophilia patients with FVIII-inhibitors. It is the first 10-year study of its kind in a Canadian setting. The results of this study will provide further insights into addressing one of the most serious complications of hemophilia A treatment. DisclosuresMoorehead:Bioverativ: Honoraria; Pfizer: Speakers Bureau; Octapharma: Honoraria; Bayer: Honoraria; Baxalta: Honoraria, Speakers Bureau. Klaassen:Baxalta: Honoraria; Agios Pharmaceuticals: Consultancy; Hoffman-La Roche LTD: Consultancy; Biogen Canada LTD: Consultancy; Amgen: Consultancy; Octapharma: Honoraria. Carcao:Octapharma: Honoraria, Research Funding; Pfizer: Honoraria, Research Funding; Novo Nordisk: Honoraria, Research Funding; Biogen: Honoraria, Research Funding; Baxter: Honoraria, Research Funding; Bayer: Honoraria, Research Funding; CSL Behring: Honoraria, Research Funding; Biotest: Honoraria.

Octanate®: over 20 years of clinical experience in overcoming challenges in haemophilia A treatment.

Treatment of haemophilia A with FVIII replacement has evolved over the past decades to adapt to the needs of patients. octanate®, a plasma-derived, double virus-inactivated, von Willebrand factor (VWF)-containing FVIII concentrate, has been used in clinics worldwide for over 20 years. First licensed in 1998 in Germany, octanate® is approved in over 80 countries for the prevention and treatment of bleeding and for surgical prophylaxis in patients with haemophilia A, and in over 40 countries for immune tolerance induction (ITI). The manufacturing process for octanate® was developed to ensure high viral safety and effectively eliminates both enveloped and nonenveloped viruses. Over the past 20 years, the excellent safety and efficacy of octanate® have been demonstrated in pivotal clinical trials in adult and paediatric previously treated patients (PTPs) for on-demand treatment, prophylaxis and as surgical cover. Importantly, octanate® has displayed low immunogenicity in previously untreated patients (PUPs), with only 9.8% of PUPs developing FVIII inhibitors. octanate® has also shown to be highly effective in inhibitor elimination when used as ITI therapy. In a population of patients with high risk of ITI failure, success was achieved in 79.2% of patients (70.8% complete success), even when using exceptionally stringent success criteria. No relapses were observed. Here we present an overview of the clinical data with octanate® that support its use in a range of patient populations and clinical indications.

Prospective Study of the Immunological Mechanisms of Immune Tolerance Induction in Severe Haemophilia a Patients with Inhibitors: Preliminary Analysis of a Multi-Center Longitudinal Study

BackgroundThe development of an immunogenic response to FVIII and the appearance of neutralizing antibodies - “inhibitors” - against FVIII is the most important adverse event in hemophilia treatment. Immune Tolerance Induction (ITI) via the long-term, intravenous administrations of high-dose FVIII is the only proven strategy to eradicate inhibitors. The success rate is about 60-70% and no formal demonstration of its mechanism of action has been provided yet. Indeed, the mechanisms underlying successful ITI have been unclear, and not much is known about the major factors determinant of success vs. failure.Our aim is to understand the process of activation and immune regulation in response to FVIII in patients undergoing ITI, and comparing the immunological events in patients who successfully eradicate anti-FVIII antibody to those in patients failing to achieve FVIII tolerance.MethodsThis is a multicenter, observational, prospective cohort study enrolling severe HA patients who developed high-titer inhibitors, candidate to ITI. A blood sample has been collected before starting and during the course of ITI, until ITI ends (5 blood samples during the first year, 3 during the second year if ITI treatment is not already ended, plus a final sample 30 days after ITI conclusion). Total PBMCs have been used to establish cell cultures where cells are re-stimulated with the same FVIII used during the ITI or medium alone.To identify candidate genes, key proteins and cell subsets associated to differential outcomes to ITI, immune cells are used for gene expression profiling (Human Inflammation & Immunity Transcriptome Targeted RNA Panel, Qiagen) together with extensive phenotypic characterization of immune cells via the CyTOF (Cytometry by Time Of Flight mass spectrometry) technology. To identify potential biomarkers predictors of ITI outcomes metabolomics analysis and multiplex cytokine arrays are performed in plasma collected at each time point during ITI and in supernatants from cells cultures. Plasma samples, are collected at each time point and stored at -80°C for cytokine determination and metabolomic analysis. Total anti-FVIII antibody (and their isotypes) and inhibitor titer are also determined in plasma samples by Nijmegen methodology in the central laboratory as described previously (1).ResultsCurrently, 18 subjects have been enrolled among 8 Hemophilia Centers. Among these 5 subjects, two patients reached the study endpoint of ITI success by study criteria (negative inhibitor titer, a normal FVIII recovery, a normal FVIII half-life and the absence of anamnesis upon further FVIII exposure) while three were assessed as ITI failure. The analysis of anti-FVIII antibody isotypes revealed the presence of IgG4 as the most relevant component of the total anti-FVIII antibodies. The inhibitor clearance was also accompanied by the disappearance of IgG4 anti-FVIII antibodies in both tolerized patients, while those who failed to eradicate the inhibitor showed a sustained IgG4 anti-FVIII response (Fig. 1). The evaluation of the cytokines in the supernatants from in vitro cultured cells showed a consistent increase in production of pro-inflammatory cytokines in response to FVIII (IL-1β, IL-6, IL-12, IL-17A, IL-15) at all time points only in patients who continued to produce high-titer inhibitors.ConclusionsHere we report an interim analysis of a prospective study of the immunological mechanisms of immune tolerance induction. The preliminary results obtained so far suggest that anti-FVIII IgG4 are a major component of the total anti-FVIII antibodies and their persistence is associated with unfavourable ITI outcome. We expect that the ongoing immune gene expression profiling, immune-phenotypic characterization and determination of soluble marker of activation/regulation of the immune system in supernatants and plasma in this cohort of patients will provide substantial knowledge to increase our current understanding of the complex immunological pathways involved in the development of tolerance to FVIII. Ultimately, this could lead to the discovery of biomarkers of ITI success/failure and to the generation of focused and strategic intervention to modulate the immune system during this treatment.

Immune Tolerance Induction with Simoctocog Alfa (Nuwiq®) in Six Patients with Severe Haemophilia a and FVIII Inhibitors

Introduction and Objective: Inhibitors to coagulation factor VIII (FVIII) are the most serious complication of haemophilia A treatment. Previously untreated patients (PUPs) are at the greatest risk of inhibitors, which generally occur within the first 20 exposure days (ED) to FVIII. Immune tolerance induction (ITI) is the only clinically proven strategy for eradication of inhibitors. We present a case series of six PUPs with severe haemophilia A and inhibitors who underwent ITI with simoctocog alfa (Nuwiq®), a 4th generation human cell-line-derived recombinant FVIII approved for treatment of haemophilia A.Materials and Methods: Six male PUPs with severe haemophilia A who developed FVIII inhibitors after treatment with simoctocog alfa were started on ITI with simoctocog alfa. Primarily, we assessed the success of simoctocog alfa in patients with inhibitors. Success of ITI was determined based on undetectable inhibitor titre (< 0.6 BU/ml), FVIII recovery ≥ 66% and half-life ≥ 6 hours. Secondary objectives were to assess bleeding rate, tolerability and safety in patients with inhibitors treated with simoctocog alfa ITI.Results: The age of the patients at the start of ITI ranged from 8 to 186 months. Four of the patients were Caucasian, and two were African. All patients had a F8 mutation associated with high risk of ITI failure and two patients had an additional risk factor for ITI failure. The number of EDs prior to inhibitor development ranged from 9 to 33, and the peak inhibitor titre ranged from 0.9 to 114 BU. For ITI, five patients were treated with 100 IU/kg simoctocog alfa daily, and one with 90 IU/kg every other day. One patient achieved complete tolerisation and is now on prophylaxis at normal doses, having achieved an undetectable inhibitor titre after 9 months. This was despite an inhibitor titre ≥ 10 BU/mL at ITI start, which is considered a poor prognosis factor for ITI success. Three other patients achieved an undetectable inhibitor titre after 1, 6 and 18 months of ITI, and FVIII recovery has normalised but half-life remains short and they are on weaning doses as the half-life extends. One patient discontinued ITI with simoctocog alfa after 15 months due to an increasing inhibitor level. This patient was 15 years old at ITI start, and older age is associated with poor ITI outcome. Additionally, his haemophilia A was untreated for 15 years, during which time he developed severe arthropathy. One patient, who started ITI 3 months ago, has an ongoing inhibitor titre and continues on ITI with simoctocog alfa.Conclusions: In a case series of six patients treated with simoctocog alfa for ITI, who all had poor prognosis factors for ITI success, four patients (67%) to date have achieved an undetectable inhibitor titre. These data suggest that ITI with simoctocog alfa may be an effective treatment approach in haemophilia A patients with inhibitors. DisclosuresKhair:Shire, SOBI, Pfizer, Roche, Novo Nordisk, Octapharma: Speakers Bureau; shire, SOBI, Pfizer, Roche: Research Funding. Liesner:Roche: Research Funding; Novo Nordisk: Research Funding, Speakers Bureau; Baxalta: Consultancy, Research Funding; Bayer: Consultancy, Research Funding; Octapharma: Consultancy, Other: Clinical study investigator for NuProtect Study (Octapharma sponsored), Research Funding, Speakers Bureau; Sobi: Speakers Bureau. Belyanskaya:Octapharma AG: Employment.

Economic Impact of Immune Tolerance Induction (ITI) with Recombinant Factor VIII Fc Fusion Protein (rFVIIIFc) Compared to Conventional Recombinant Factor VIII (rFVIII)

Introduction:Hemophilia A results from a clotting protein factor VIII (FVIII) deficiency, which leads to the need for the use of exogenous FVIII. Such therapy is effective unless alloantibodies (inhibitors) develop and render FVIII replacement ineffective. Patients with high-titer inhibitors may try to eradicate the presence of these inhibitors by undergoing ITI, an often costly process that requires the prolonged use of frequent doses of FVIII to induce FVIII antigen-specific tolerance. There is no consensus on the best approach to achieve tolerance and no product has been approved by any regulatory agency for ITI treatment in hemophilia A patients with inhibitors. The Fc portion of rFVIIIFc has shown immunomodulatory properties in mice, and chart reviews and case reports suggest that tolerization with rFVIIIFc in first-attempt ITI patients can potentially be achieved rapidly (i.e., ≤18 months) and therefore may possibly offer cost savings compared to conventional rFVIII. This analysis assessed the economic consequences and budget impact of using rFVIIIFc vs. conventional rFVIII for first-attempt immune tolerance induction (ITI) in hemophilia A patients with inhibitors.Methods:A literature-based model was developed to estimate the effect of rFVIIIFc vs conventional rFVIII on drug cost of first-attempt ITI, based on modelled ITI duration and outcome (rates and time to ITI success or failure) for US patients with varying clinical profiles (e.g., historical peak titer, FVIII dose) over a 3-year period. In the model, at any given time after ITI initiation (on either rFVIIIFc or rFVIII), a patient was categorized as ongoing ITI, post-ITI as success, or post-ITI as failure. The duration and outcomes for patients treated with rFVIIIFc ITI were based on observed data for first-attempt ITI patients with varied clinical profiles and ITI regimens from in chart reviews and case reports (n = 9). In the absence of direct head-to-head observations, the duration and outcome of ITI for the exact same patients in a scenario in which they received rFVIII (instead of rFVIIIFc) at the same doses were estimated indirectly using a previously published regression model (Bojke et al. 2009, Value in Health, 12(7), A378-A379) based on data for 113 patients from international and national registries that adjusts for historical and pre-ITI titer levels, time from inhibitor diagnosis to ITI start, and ITI factor dose. To place the cost comparison results in the perspective of a third-party US payer, a budget impact analysis was undertaken on a population of typical hemophilia A patients (after adjusting for patient characteristics) who are embarking on first-attempt ITI in a plan of 10 million insured members. In this analysis, the number of patients starting ITI each year was assumed constant, and patients who successfully eradicated inhibitors with ITI would transition back to FVIII prophylaxis.Results:The model predicted that, compared to rFVIII, rFVIIIFc would result in a reduction in estimated time to ITI success (rFVIIIFc: 9.43 months, rFVIII: 16.80 months), increased success probability at 20 months (rFVIIIFc: 67%, rFVIII: 25%), and lower 3-year per-patient costs (rFVIIIFc: $1,709,000, rFVIII: $3,630,000), respectively. In the budget impact analysis for a US health plan of 10 million insured members, 11.2 patients were expected to be newly diagnosed hemophilia A patients, among whom 1.17 patients were expected to develop inhibitors to FVIII and initiate ITI each year. By year 3, the predicted number of successful ITI patients increased by 23% and the budget savings for the plan were $103,738 per patient per year (for the ~1 patient who started ITI each year) after the inclusion of rFVIIIFc for ITI and subsequent prophylaxis when patients successfully eradicated inhibitors.Conclusions:Based on this mathematical economic model of first-attempt ITI patients, the modeled faster time to tolerization with rFVIIIFc vs. rFVIII, resulted in estimated per-patient and overall budget savings in ITI from a US payer perspective. Current prospective studies (e.g. verITI-8) will provide additional evidence on the efficacy of rFVIIIFc for ITI in Hemophilia A patients with inhibitors. DisclosuresLi:Bioverativ: Employment. Wilson:SOBI: Employment. Botteman:Daiichi Sankyo Incorporated: Research Funding; BMS: Research Funding; Pharmerit International: Employment, Equity Ownership, Research Funding; Celgene: Research Funding; Bioverativ: Consultancy, Other: Provided consulting to Bioverativ, Research Funding. Nicoloso:Bioverativ: Other: an employee of Pharmerit, which provided consulting to Bioverativ. Krishnan:Bioverativ: Employment. Su:Bioverativ: Employment.

Real-World Data of Immune Tolerance Induction Using rFVIIIFc in Subjects With Severe Hemophilia A With Inhibitors at High Risk for ITI Failure

Real-World Data of Immune Tolerance Induction Using rFVIIIFc in Subjects With Severe Hemophilia A With Inhibitors at High Risk for ITI Failure

Recombinant factor VIII Fc fusion protein for immune tolerance induction in patients with severe haemophilia A withinhibitors-A retrospective analysis.

Immune tolerance induction (ITI) is the gold standard for eradication of factor VIII inhibitors in severe haemophilia A; however, it usually requires treatment for extended periods with associated high burden on patients and healthcare resources. Review outcomes of ITI with recombinant factor VIII Fc fusion protein (rFVIIIFc) in patients with severe haemophilia A and high-titre inhibitors. Multicentre retrospective chart review of severe haemophilia A patients treated with rFVIIIFc for ITI. Of 19 patients, 7 were first-time ITI and 12 were rescue ITI. Of 7 first-time patients, 6 had at least 1 high-risk feature for ITI failure. Four of 7 first-time patients were tolerized in a median of 7.8months. The remaining 3 patients continue on rFVIIIFc ITI. Of 12 rescue patients, 7 initially achieved a negative Bethesda titre (≤0.6) in a median of 3.3months, 1 had a decrease in Bethesda titre and continues on rFVIIIFc ITI and 4 have not demonstrated a decrease in Bethesda titre. Of these 4, 3 continue on rFVIIIFc ITI and 1 switched to bypass therapy alone. Two initially responsive patients transitioned to other factors due to recurrence. Overall, 16 of 19 patients remain on rFVIIIFc (prophylaxis or ITI). For those still undergoing ITI, longer follow-up is needed to determine final outcomes. No adverse events reported. Recombinant factor VIII Fc fusion protein demonstrated rapid time to tolerization in high-risk first-time ITI patients. For rescue ITI, rFVIIIFc showed therapeutic benefit in some patients who previously failed ITI with other products. These findings highlight the need to further evaluate the use of rFVIIIFc for ITI.

Anti‐A2 and anti‐A1 domain antibodies are potential predictors of immune tolerance induction outcome in children with hemophilia A

HemophiliaA (HA) is a congenital bleeding disorder resulting from factorVIII deficiency. The most serious complication of HA management is the appearance of inhibitory antibodies (Abs) against injected FVIII concentrates. To eradicate inhibitors, immune tolerance induction (ITI) is usually attempted, but it fails in up to 30% of cases. Currently, no undisputed predictive marker of ITI outcome is available to facilitate the clinical decision. To identify predictive markers of ITI efficacy. The isotypic and epitopic repertoires of inhibitory Abs were analyzed in plasma samples collected before ITI initiation from 15 children with severe HA and high-titer inhibitors, and their levels were compared in the two outcome groups (ITI success [n=7] and ITI failure [n=8]). The predictive value of these candidate biomarkers and of the currently used indicators (inhibitor titer and age at ITI initiation, highest inhibitor titer before ITI, and interval between inhibitor diagnosis and ITI initiation) was then compared by statistical analysis (Wilcoxon test and receiver receiver operating characteristic [ROC] curve analysis). Whereas current indicators seemed to fail in discriminating patients in the two outcome groups (ITI success or failure), anti-A1 and anti-A2 Ab levels before ITI initiation appeared to be good potential predictive markers of ITI outcome (P<0.018). ROC analysis showed that anti-A1 and anti-A2 Abs were the best at discriminating between outcome groups (area under the ROC curve of >0.875). Anti-A1 and anti-A2 Abs could represent new promising tools for the development of ITI outcome prediction tests for children with severe HA.

Immune Tolerance Induction in Severe Hemophilia a Patients Using Wilate®, a Von Willebrand Factor/Factor VIII Concentrate

Introduction: To prevent and treat bleeding episodes, hemophilia A patients undergo factor VIII (FVIII) replacement therapy with either recombinant FVIII (r-FVIII) or plasma-derived FVIII (pd-FVIII). Approximately 32% of patients develop neutralizing antibodies to the FVIII protein rendering FVIII therapy ineffective (Gouw et al. N Engl J Med. 2013; 368:231-239). Development of these neutralizing antibodies, or ‘inhibitors’ is the most serious and challenging complication in the treatment of hemophilia A patients and represents the highest economic burden for a chronic disease (Gringeri et al. Blood 2003; 102:2358-2363). The standard approach for eradicating inhibitors is to tolerize the patient to FVIII through prolonged, daily exposure to high-dose FVIII – a process termed immune tolerance induction (ITI). Although costly, ITI can successfully eliminate inhibitors in a large proportion of low-risk patients, however there are several risk factors that reduce the likelihood of ITI success. For high-risk patients, the choice of drug product (r-FVIII versus pd-FVIII) may be particularly important. Several small studies have demonstrated the superiority of pd-FVIII for ITI, as these products contain the FVIII stabilizing protein, von Willebrand Factor (VWF) (Gringeri et al., Haemophilia 2007; 13:373-379). Wilate® (Octapharma) is a high-purity pd-FVIII complex that contains the two proteins (VWF and FVIII) in a 1:1 ratio. In this retrospective study, we present the patient history and outcome for four severe hemophilia A patients that have undergone ITI with Wilate®. Patients and Methods. All patients presented with severe FVIII deficiency ( Results. ITI with Wilate was found to be well tolerated, with no reported drug-related adverse events. Although 75% of the patients presented with high-risk factors for poor ITI outcome, Wilate ITI reduced inhibitor levels below 5 BU/mL for 3 out of 4 patients. The clinical outcome of Wilate ITI correlated with the presence and number of high-risk factors. Patient 1 did not respond to Wilate, and was considered a failure. This patient had 3 high risk factors for poor ITI outcome including FVIII gene mutation type, peak historical titer >50, and inhibitor titer at ITI onset > 10 BU/mL. Of the three patients that responded to Wilate ITI, patient 4 experienced a CS to Wilate ITI in 4 months. For the remaining 2 patients, Wilate ITI is currently ongoing. Despite the presence of high risk factors, these two patients have thus far achieved a PS with inhibitor levels stable for several months at or below 1 BU/mL. One of these patients (patient 2) presented with 5 high-risk factors, including having failed a previous ITI attempt. The frequency of bleeding episodes were significantly reduced upon commencement of Wilate ITI, allowing for the eventual cessation of FEIBA prophylaxis. Conclusion. Despite the presence of high-risk factors, 3 out of 4 patients (75%) experienced a clinical response to Wilate ITI. The patients experienced improved quality of life. Wilate ITI resulted in a significant reduction in bleed episodes in a high-risk patient. The type of FVIII product to use during ITI has been debated, however, some have observed a higher success rate when plasma-derived FVIII products containing VWF are used. From our experience, we conclude that Wilate for ITI in patients with inhibitors is effective and produces high rates of ITI success in high-risk patients. Disclosures Wu:Bayer: Honoraria, Membership on an entity9s Board of Directors or advisory committees, Research Funding; Baxter: Honoraria; Pfizer: Membership on an entity9s Board of Directors or advisory committees; Biogen Idec: Honoraria, Membership on an entity9s Board of Directors or advisory committees; Novo Nordisk: Honoraria, Membership on an entity9s Board of Directors or advisory committees; Octapharma: Honoraria, Membership on an entity9s Board of Directors or advisory committees; CSL Behring: Honoraria, Membership on an entity9s Board of Directors or advisory committees. Woo:Bayer: Honoraria, Membership on an entity9s Board of Directors or advisory committees; Baxter: Honoraria, Membership on an entity9s Board of Directors or advisory committees; Pfizer: Honoraria, Membership on an entity9s Board of Directors or advisory committees. Crilly:Bayer: Consultancy, Honoraria, Membership on an entity9s Board of Directors or advisory committees; Baxter: Consultancy, Honoraria, Membership on an entity9s Board of Directors or advisory committees; Octapharma: Honoraria, Membership on an entity9s Board of Directors or advisory committees.

When is enough…enough? Developing consensus of definition of failure of immune tolerance induction in patients with haemophilia and inhibitors.

Immune tolerance induction (ITI) is the preferred management of haemophilia A patients who develop high titre inhibitors against factor VIII. However, the optimal ITI regimen, predictors of ITI outcome and definitions of successful and unsuccessful ITI remain unclear. The aim of this project was to develop a consensus on the definition of ITI treatment failure for Australian clinical practice using a modified Delphi approach. Three consecutive surveys were distributed to the directors of 17 haemophilia treatment centres in Australia. Participants were asked to rate their agreement with definitions of ITI treatment failure generated from a literature review. Thirty-five statements regarding ITI achieved consensus (majority agree or strongly agree) during the three survey rounds. After round 3, four statements achieved majority disagreement, and for two statements no consensus was reached. Our study demonstrates that clinicians in Australia necessitate an arbitrary time to assess ITI failure, but that clinical outcomes of ITI are important in assessing response. Assessment over any 3- to 6-month period without a 20% reduction in inhibitor titre is suggestive of failure, but a reduction in bleeding phenotype alone may be sufficient to continue ITI. Overall, a period of 3 or 5 years of ITI may be required to determine response to ITI. Documentation of improvement in clinical measures, supported by the laboratory features of factor VIII inhibitor levels and pharmacokinetics, is essential in assessing the success of failure of ITI in these patients.

Immune Tolerance Induction (ITI) in Adults with Congenital Hemophilia: A Multicenter Experience

AbstractAbstract 1123 IntroductionMost inhibitors developing in adulthood are low titer inhibitors [Eckhardt 2012], however high titer inhibitors have been described [Kruse-Jarres 2010, Hay 2011]. The role of ITI in the management of adult inhibitors has not been established. Two large registries have suggested that age at ITI initiation could be a predictor of success. The North American ITI registry showed a trend toward a younger age in the ITI success group [DiMichele 2002], while the International ITI group showed a more definitive difference, where patients receiving ITI at age > 20 years had a 40 % success rate compared to a much higher success rate of 70 t0 78% in younger individuals [Mariani 2001]. Prospective therapy trials in an adult congenital hemophilia inhibitor population are difficult to conduct, as the number of patients is limited. The aim of the this multicenter retrospective review was to document our experience in the management of adult hemophilia inhibitor patients with ITI MethodsTwelve hemophilia treatment centers which are part of the Globally Emerging Hemophilia Expert Panel (GEHEP) with centers in Canada, Europe, South Africa and the US, who collectively look after over 3000 hemophilia patients, participated in this study. Each center obtained ethics approval prior to data collection. Retrospective record review was undertaken at each center to identify congenital hemophilia patients treated with ITI as an adult (started at ≥ 17 years of age)and who completed the treatment course between 1980 and 2012. The treatment course was defined as any of the accepted ITI regimens. Treatment success was defined as inhibitor eradication or >66% factor recovery. ResultsOf 21 patients who received ITI as an adult, 71% had partial (<5BU and FVIII was able to be reinstated) or complete success. All patients had hemophilia A and most were severe (One patient in the ITI failure group had a level of 2% and in the success group, one had a level of 1% and on of 3%). Of the 13 patients achieving complete success, 38% relapsed (mean follow up of 9.4 years, range 3 months to 29 years). Age at start of ITI did not seem to be a predictor of success: mean age in the success group was 32.0 years (range 17 –55) and in the failure group was 33.5 years (range 22 – 57). All patients in the failure group were white, where 3 patients in the success group were non-white. The success group included one low responding inhibitor and had an overall lower peak inhibitors (mean 89.75 BU, range 3 – 270 BU) than the failure group (mean 353.8 BU, range 89–600 BU). Fifty percent of the failure patients had received a prior ITI attempt, where only 8% of the success group had. More patients in the failure group had received plasma derived factor VIII product for their ITI (83%) than in the success group (69%) but dosing was not significantly different (mean of 416 units/kg/week in failure group, 455 U/kg/week in success group). Overall, patient who failed stayed on ITI slightly longer (mean 20 months) than the patients who succeeded (mean 16 months). ConclusionIn this limited series of adult inhibitor hemophilia patients treated with ITI, the success rate was high and comparable to that obtained in the pediatric population. Age at start of ITI did not seem to be a predictor of success, but prior ITI and historical peak inhibitor were negative predictors. Prospective clinical studies are required to expand on these preliminary findings. Disclosures:Kruse-Jarres:Bayer: Administrative and meeting support Other, Honoraria, Research Funding.

Immune tolerance induction with a high purity von Willebrand factor/VIII complex concentrate in haemophilia A patients with inhibitors at high risk of a poor response

Immune tolerance induction (ITI) is effective in approximately 70% of haemophilia patients with inhibitors. Poor prognostic factors are age >6 years, ITI started >1 year from inhibitor development, inhibitor peaks >200 BU, inhibitor titre >10 BU when ITI is started and previously failed ITI. The objective of this study was to identify the effectiveness in ITI of a high purity von Willebrand factor/factor VIII (VWF/FVIII) complex concentrate in inhibitor patients at high risk of failure. Patients with severe or moderate haemophilia A and high responding inhibitors who had at least one poor prognostic factor for ITI failure were prospectively followed-up. Success was defined by undetectable inhibitor, recovery and half life >66% of expected values. ITI dose regimens were chosen by each haemophilia centre. Seventeen haemophiliacs (16 severe, one moderate), aged 4-54 years (median 23) were followed-up for 6-71 months. Poor prognostic factors were delayed-onset ITI (n = 16), age >6 years (n = 16), previously failed ITI (n = 4), inhibitor peak >200 BU (n = 2) and inhibitor >10 BU when ITI was started (n = 4). Complete success was obtained in nine patients (53%) after 4-30 months of treatment (median 24), including two of four patients who had previously failed ITI. Seven patients achieved a partial success, with sustained low inhibitor titres (median 1.5 BU, range 1.1-2.8) but abnormal recovery and/or half-life, while the remaining patient withdrew ITI after 12 months when the inhibitor titer was still 70 BU. These findings suggest that high purity VWF/FVIII complex concentrates are effective in ITI, even in patients at high risk of failure.

Immune Tolerance Induction in 28 Children with Hemophilia Awith Inhibitors.

Aim: To study the characteristics, treatment, and outcome of patients with hemophilia with inhibitors who have undergone immune tolerance induction (ITI) at the Children's Hospital of Michigan over the past 14 years.Methods: In compliance with local IRB regulations, patient charts and laboratory databases were reviewed and salient data extracted. 28 boys underwent 29 attempts at immune tolerance induction.Results:Hemophilia A26 boys with severe hemophilia A with inhibitors underwent 27 trials of ITI. In this cohort of 26 patients the average age at which patients developed an inhibitor was 22 months and the average age at start of ITI was 5 years 4 months (range 2 months to 17 years 5 months). The average number of exposure days prior to inhibitor development was 10 (1–47). The average time between development of an inhibitor and initiation of ITI was 43 months, with no difference between those who successfully completed ITI and those who did not. Six patients had low titer inhibitors (0.8–6.5 BU) and successfully completed ITI using a modified low dose ITI regimen of factor infusions 3–7 times per week. 20 of the patients with high titer inhibitors (6.4–1280 BU) were treated with daily infusions of 50–200 units/kg/d of factor VIII (FVIII) products. For ITI, 4 patients received high purity plasma derived FVIII (PD-FVIII) and 21 received recombinant FVIII (rFVIII) and one received both. In patients who became tolerized to FVIII, the average time to achieve an inhibitor titer of 0 Bethesda Units (BU) was 211 days. In those who were unable to achieve tolerance, the average length of the trial was 263 days. 21 of the ITI trials employed a central venous catheter and in 5 patients ITI was stopped after removal of the line because of recurrent infections. 14 boys received FEIBA, rFVIIa, or porcine FVIII for bleeding episodes during ITI; 8 of them failed ITI and one is still on therapy. Seven trials of ITI were in Caucasian patients (26 %), 17 in African American (AA) (63 %), and 3 in Middle Eastern patients (11 %). 19 patients achieved complete tolerance (73 %), 6 patients failed (23 %), one failed twice, and one patient continues on therapy. All but 2 patients who successfully completed ITI went on prophylaxis with FVIII. All patients who successfully completed ITI have maintained tolerance with a mean follow-up of 101 months (range 7–168).Table I:Hemophilia AFailed ITISuccessful ITINumber of trials*7 (23 %)19 (73 %)African Americans7 (41 %)10 (59 %)Non-AA010 (100 %)Historical Peak Titer (mean)345 BU47 BUTiter at Start of ITI (mean)62 BU5 BUPeak Titer on ITI (mean)168 BU46 BUAge at inhibitor development (mean)26 months12 monthsITI with PD-FVIII14ITI with rFVIII715*One still ongoingHemophilia BDuring this time period, 2 boys with severe hemophilia B underwent ITI. Both had severe allergic reactions at the time of inhibitor development; both underwent desensitization successfully but both failed ITI. Both started ITI with plasma derived factor nine at age 15 months. One developed nephrotic syndrome while on ITI.Conclusions:Most patients with Hemophilia A were able to achieve and maintain tolerance (73%). Higher titer inhibitors, hemophilia B, younger age at development of inhibitor, AA race and treatment of bleeds with bypass agents or porcine factor while on ITI were risk factors for ITI failures. Loss of central venous access with recurrent infections was also a common reason for ITI failure.