Immune Tolerance Treatment Research Articles

Extended Half-Life Coagulation Factors: A New Era in the Management of Hemophilia Patients

Despite effective factor replacement and various treatment schedules, there remain several challenges and unmet needs in the prophylactic treatment of hemophilia limiting its adoption and thereby posing an increased risk of spontaneous bleeding. In this regard, extended half-life (EHL) recombinant factor VIII (rFVIII) and factor IX (rFIX) products promise optimal prophylaxis by decreasing the dose frequency, increasing the compliance, and improving the quality of life without compromising safety and efficacy. EHL products might lead to higher trough levels without increasing infusion frequency, or could facilitate the ability to maintain trough levels while reducing infusion frequency. This paper aims to provide a comprehensive review of the rationale for developing EHL coagulation factors and their utility in the management of hemophilia, with special emphasis on optimal techniques for half-life extension and criteria for defining EHL coagulation factors, as well as indications, efficacy, and safety issues of the currently available EHL-rFVIII and EHL-rFIX products. Potential impacts of these factors on quality of life, health economics, and immune tolerance treatment will also be discussed alongside the challenges in pharmacokinetic-driven prophylaxis and difficulties in monitoring the EHL products with laboratory assays.

Treatment of Surgical Brain Injury by Immune Tolerance Induced by Peripheral Intravenous Injection of Biotargeting Nanoparticles Loaded With Brain Antigens.

Once excessive, neurological disorders associated with inflammatory conditions will inevitably cause secondary inflammatory damage to brain tissue. Immunosuppressive therapy can reduce the inflammatory state, but resulting infections can expose the patient to greater risk. Using specific immune tolerance organs or tissues from the body, brain antigen immune tolerance treatment can create a minimal immune response to the brain antigens that does not excessively affect the body's immunity. However, commonly used immune tolerance treatment approaches, such as those involving the nasal, gastrointestinal mucosa, thymus or liver portal vein injections, affect the clinical conversion of the therapy due to uncertain drug absorption, or inconvenient routes of administration. If hepatic portal intravenous injections of brain antigens could be replaced by normal peripheral venous infusion, the convenience of immune tolerance treatment could certainly be greatly increased. We attempted to encapsulate brain antigens with minimally immunogenic nanomaterials, to control the sizes of nanoparticles within the range of liver Kupffer cell phagocytosis and to coat the antigens with a coating material that had an affinity for liver cells. We injected these liver drug-loaded nanomaterials via peripheral intravenous injection. With the use of microparticles with liver characteristics, the brain antigens were transported into the liver out of the detection of immune armies in the blood. This approach has been demonstrated in rat models of surgical brain injury. It has been proven that the immune tolerance of brain antigens can be accomplished by peripheral intravenous infusion to achieve the effect of treating brain trauma after operations, which simplifies the clinical operation and could elicit substantial improvements in the future.

Analysis of allogeneic hematopoietic stem cell transplantation with high-dose cyclophosphamide-induced immune tolerance for severe aplastic anemia

The study was aimed to explore the efficacy and safety of allo-HSCT with high-dose cyclophosphamide-induced immune tolerance for SAA. In the present study, 20 cases (12 male, 8 female; average age=17.8years) received reduced-intensity conditioning allo-HSCT from August 2012 to August 2014 in the Beijing Military Region General Hospital. All were HLA mismatched and received CSA; 11 received ATG-intensive immune therapy. Donors underwent mobilization with cell colony-stimulating factor. The modified preconditioning regimen included reduced-strength fludarabine combined with Busulfex and cytarabine, cyclophosphamide. Cyclophosphamide (50mg/kg/d) induced immune tolerance 3days after transplantation and was combined with immunosuppressive agents, including CSA, MTX, and FK506, for GVHD prophylaxis and the management of observed toxicity, GVHD and DFS. Hematopoietic reconstitution was achieved in 17 cases and engraftment after a second transplantation in an additional three cases. The average times to engraftment were 17.4 and 21.3days, respectively, with neutrophils ≥0.5×109/L and platelets ≥20×109/L. Engraftment was confirmed by the evidence of 100% donor hematopoiesis; T lymphocyte subset counts also increased significantly after transplantation. During follow-up monitoring to April 2015 (median duration=17.7months), three patients died of complications, while the other 17 showed disease-free survival (DFS rate=85%; longest DFS period=32months). Reduced-intensity allo-HSCT with high-dose cyclophosphamide-induced immune tolerance treatment is effective for SAA and can be the key technology extensively used in clinic, but its efficacy needs to be confirmed further with prospective randomized study with increased sample size.

Long-Term Treatment and Transfusion of Normal Blood Components Following Tolerance Induction in Patients with Anti-IgA Anaphylactic Reactions

Background: In general, patients with significant anti-Ig-A do not tolerate intravenous (i.v.) administration of normal blood products. Here, we present our experiences in the induction of immune tolerance (IIT) and long-term treatment in a series of such patients affected in such a way. The question whether blood components from IgA-deficient donors are required will be discussed. Methods: Ten adult patients (4 females and 6 males; age ranging from 36 to 75 years) with anti-IgA were included in this study. All patients required long-term treatment with blood components. One patient had IgA deficiency and paroxysmal nocturnal hemoglobinuria (PNH), and all other patients had common variable immunodeficiency (CVID). The particle gel immunoassay was used for the detection of anti-IgA. Immune tolerance to IgA was induced by controlled subcutaneous (s.c.) and/or i.v. infusions of IgG preparations. Results: Prior to IIT, anti-IgA was detectable in plasma samples of all patients and significantly diminished or abolished by controlled s.c. and/or i.v. infusions of IgG. Multiple transfusions with normal blood components could be repeatedly performed with the patient suffering from PNH without any complications. As long as i.v. IgG (IVIgG) infusions were consequently administered as individually required (intervals 2-8 weeks), none of the patients developed reactions during observation (up to 10 years). However, interruption of treatment and re-exposure to IVIgG resulted in adverse reactions. Conclusion: Patients with significant anti-IgA can be safely desensitized and tolerate long-term IgG substitutions independent of the IgA concentration of the used blood component.

The expanding role of prophylaxis with recombinant activated factor VII.

The expanding role of prophylaxis with recombinant activated factor VII.

The between-Laboratory Variation of Factor VIII Inhibitor Testing: The Experience of the External Quality Assessment Program of the ECAT Foundation

The detection and quantification of factor VIII (FVIII) inhibitors is clinically important both for the identification of hemophilia A patients with inhibitors and for the management of immune tolerance treatment. Only limited data are available on the between-laboratory variation of FVIII inhibitor testing. This report describes the evaluation of the results of the large-scale external quality assessment program of the European Concerted Action on Thrombosis Foundation. This study includes the results of six different surveys for the period 2006 to 2008 with 100 to 170 participating laboratories. The overall between-laboratory variation ranged from 28% to 52% with a slightly lower variation for the Nijmegen assay (approximately 39%) on average than for the Bethesda assay (approximately 45%). The use of buffered normal pooled plasma as FVIII source showed better performance compared with the use of nonbuffered pooled plasma; likewise the use of FVIII-deficient plasma compared with the use of imidazole buffer. However, the combination of both was essential for lowest between-laboratory variation. The Nijmegen assay also showed better performance with respect to specificity and sensitivity than the Bethesda assay, although the results for neither were entirely satisfactory. In general, it can be concluded that the measurement of FVIII inhibitory antibodies with the Nijmegen assay should be favored over the use of the Bethesda assay. However, further improvement of the laboratory test for FVIII inhibitors is urgently needed.

Prophylaxis with recombinant factor VIIa for the management of bleeding episodes during immune tolerance treatment in a boy with severe haemophilia A and high‐response inhibitors

Prophylaxis with recombinant factor VIIa for the management of bleeding episodes during immune tolerance treatment in a boy with severe haemophilia A and high‐response inhibitors

Treatment of an Adult Patient with Hemophilia A and High Titer Inhibitor with Rituximab and Prednisone.

Development of inhibitors is a serious complication in hemophilia A patients (factor VIII deficiency) who receive plasma-derived or recombinant products. It occurs in about 20–30% of patients with severe or moderate hemophilia A. The presence of a high titer inhibitor (titer > 5BU), is associated with increased morbidity and mortality, complicates disease management, and increases cost of treatment. Treatments used for the management of acute bleeds include high doses of human FVIII, porcine FVIII, prothrombin complex concentrates, FVIII bypassing activity (FEIBA), and recombinant VIIa (rVIIa)). The induction of immune tolerance (IT)with daily high doses of FVIII has been reported to eradicate the inhibitor in 60–80% of patients; although it is a very costly procedure, the response appears to be dependent on the level of the inhibitor with patients with low inhibitor titer (<10 BU) responding better to IT treatment. To rapidly reduce/eradicate the alloimmune factor VIII antibodies immunomodulatory agents, including immunoglobulin, corticosteroids, cyclophosphamide, azathioprine, and plasmapheresis have been used. Rituximab, an anti-CD20 monoclonal antibody, eliminates circulating B cells and has been shown to reduce/eradicate alloimmune factor VIII antibodies in children with severe hemophilia A. We report the clinical course and response to rituximab treatment in a 24 year old male with moderate hemophilia A and high titer inhibitor. The patient presented with a massive retroperitoneal bleed with Hb 6.4g/dL and an inhibitor titer of 41 BU reaching a maximum of 111 BU over the next four weeks. For the acute bleeding episode, he received FEIBA and rVIIa. For the treatment of inhibitor, he was given rituximab 375 mg/m2 × 4 together with prednisone 1 mg/Kg daily. Prednisone was slowly tapered off over the next several weeks. Three months later, his inhibitor titer had decreased to 35 BU and remained below 15 BU for the next 30 weeks. The course of this patient's response suggests that rituximab in combination with prednisone may rapidly reduce inhibitor titer in adult patients with hemophilia and high titer inhibitor. It is possible the rituximab therapy may replace IT therapy or be used as an adjunct to IT therapy. Also, the combination of rituximab and prednisone treatment may reduce/prevent the exposure of young patients to cytotoxic chemotherapy. Randomized clinical trials will be required to determine whether the combination of rituximab and prednisone is a better option compared to cytoxan and prednisone to reduce/eradicate inhibitors in young adult hemophilia patients with high titer inhibitor. [Display omitted]

Immune Tolerance Resulting in a Dramatic Clinical Improvement in a High-Responding Inhibitor Hemophilia A Patient Using Immunosuppression with Mycofenolate Mofetil and a Factor VIII Concentrate Containing Von Willebrand Factor.

A 40 year-old Caucasian patient with severe familial hemophilia A (FVIII <1%) related to an intron 22 inversion developed at the age of 2 a high-responding inhibitor. His elder brother also suffers from hemophilia A with high-responding inhibitor. Until 2000, the patient had been treated either using activated prothrombin complex concentrates (Autoplex® and Feiba®) or factor VIII (FVIII) concentrates of human (1983) and porcine origin (1992), resulting respectively in an inhibitor level rise at 360 Bethesda Units (BU) and 1800 BU. Between 2000 and 2003, the patient received exclusively recombinant activated Factor VII (NovoSeven®), and his inhibitor levels stabilized at a plateau of 15–20 BU. Between 2000 and 2003, several life or function threatening bleeding episodes occurred, such as hematomas of the iliopsoas muscles, spinal cord hematoma with transient paraplegia. Furthermore, due to hemarthroses the patient was confined to a wheelchair. Given the major impact of the inhibitor on the patient's functional prognosis, life expectancy and quality of life, immune tolerance (IT) treatment was initiated, despite the high risk of failure (initiation 36 years after inhibitor onset, historical peak titer at 1800 BU, persistence of a plateau of 15–20 BU despite the absence of any stimulation with FVIII within the 3 last years). It started with an immunosuppressive drug, mycofenolate mofetil (Cellcept®) first given in may 2003 (no effect alone on inhibitor titer) and then in November 2003, infusions of a FVIII concentrate rich in von Willebrand factor, Factane® (LFB, Les Ulis, France) using 12,000 IU/day (150 IU/kg) of FVIII. The inhibitor peaked at 520 BU on D19 and was 0.5 BU by May 2004. Thus, the FVIII dosage was progressively reduced to 7000 IU/day. In July 2005, 24 hours after a 7000 IU FVIII infusion, inhibitor level was 0.7 BU, the residual FVIII level was 0.04IU/ml with a recovery of FVIIIc of 1.37%/IU/kg infused and a half-life of 4.9 hours. No significant change in the immunophenotype of peripheral blood lymphocytes was observed during this course. The patient's quality of life was dramatically improved, with no hospitalization required and no bleeding episode observed within the 16 last months. The patient can now stand and has returned to his previous social activities.These preliminary results show that this IT treatment, performed despite a high theoretical risk of failure, resulted in this patient in a dramatic clinical improvement, even though biological criteria of success have not yet been achieved. The respective roles of the type of FVIII concentrate, and of immunosuppression remain to be assessed, as well as the cost/benefit analysis on a longer follow-up period.

Prophylactic Use of rFVIIa in a Young Hemophilia A Patient with Factor VIII Inhibitor.

The prevention of bleeding by prophylaxis regimen particularly for joint rehabilitation, could be considered a more effective treatment for hemophilia patients. In hemophiliacs with factor VIII inhibitor (F VIII inh) prophylaxis is not generally proposed because the bypassing agents for these patients may be less effective than F VIII concentrates. We report the regimen and results of a 6 months rFVIIa (Recombinant factor VIIa) prophylaxis, in a young hemophilia A patient (4 years old), with F VIII inh and immune tolerance induction (ITI) treatment and compared, with rFVIIa, the on demand treatment results for the 6 months prior to prophylaxis. After 2 years of a high dose regimen ITI, the FVIII inh titer was less than 50 BU and the immune tolerance treatment remains on going. Due to the development of a right knee target joint the rFVIIa prophylaxis was decided as an active rehabilitation approach to prevent the development of chronic arthropathy as well as to improve the quality of life of the child. During the 6 months period, prior to the initiation of rFVIIa prophylaxis 22 bleeds occurred i.e., 9 right knee hemarthrosis and 13 other joint bleedings and hematoma including elbow, wrist, ankle, foot, arm and chest. These bleeds were all treated with rFVIIa with a dose ranging from 100 to 200 μg/kg depending on the severity of the episodes and the duration of treatment ranged from 1 to 8 days. After 6 recurrent right knee hemarthrosis, a lavage of the joint was performed and prophylaxis with rFVIIa was subsequently initiated. A 120 μg/kg rFVIIa injection was performed 3 times a week concomitantly with the ITI treatment infusion and just before the physiotherapy course. During the 6 months of prophylaxis regimen we observed 9 bleeds with 3 major post traumatic bleedings which were treated by one 200 μg/kg/day rFVIIa injection which was resolved in one to three days. This prophylaxis treatment was effective for the arthropathy evolution and permitted the patient to return to school on a regular basis compared to the previous year. The total dose of on demand rFVIIa treatment used before prophylaxis was 458 mg/6 months. This amount decreased by 25% during the six months of prophylaxis with rFVIIa to reach 343 mg. The results of this significant observation led us to conclude that rFVIIa could be effectively used as prophylactic treatment in patients with FVIII inh and administered safely via a portacath device even in cases of high doses, as demonstrated in this young patient. This prevention approach resulted in a decrease of bleeding episodes, injections, and a significant improvement in the quality of life.

A healthy hemophilic patient without arthropathy: from concept to clinical reality.

Hemophilia is characterized by joint hemorrhage with subsequent development of arthropathy. During the past 40 to 50 years, factor VIII concentrates have been developed that enable effective treatment of bleeding. However, the development of dosing, including the implementation of prophylaxis, has been hampered by concentrate transmission of blood-borne diseases. Since the advent of viral reducing procedures that were applied to plasma-derived products and the implementation of recombinant DNA technology into the manufacturing procedure, concentrates can be considered as safe today, and hemophilic care can be more focused on the treatment modalities as such. Thus, prophylaxis is being improved and made available to more patients. Studies are in progress in order to give more scientific evidence behind its use. Magnetic resonance imaging (MRI) seems promising in scaling early arthropathy and may be a tool in the future, superior to plain X-ray and orthopedic examination, to follow patients on prophylaxis, especially children. The development of inhibitors is the most severe threat to the health of hemophiliacs today and in the future. Much has been done to elucidate genetic factors predisposing for inhibitors, and the reactivity of inhibitors with the factor VIII molecule has also been investigated. More has to be done, however, and there are still many open issues regarding immune tolerance treatment and treatment of acute bleeding in inhibitor patients. Hemophilic care has come far in order to restore health for the hemophilic population. The treatment is effective in the prevention of joint disease and the inhibitor problem is handled better now. Side effects have been reduced to a minimum. In addition, carrier and prenatal diagnosis add important contributions to improve life for the patient and his family. The next important step for the future is gene therapy, and early clinical studies are already in progress.

Immune tolerance induction in hemophilia A: a review.

In this article, a comparative analysis of the data stemming from the studies conducted in the field of immune tolerance treatment (ITT) of hemophilia A was attempted. Comparisons are difficult because previous studies differ in many respects, including the dosage of factor (F) VIII, the number of FVIII administrations per day, the association with immunosuppressive drugs (prednisone, cyclophosphamide), and, most importantly, the definition of success in terms of the reacquisition of tolerance. However, a number of variables consistently influenced outcome: the inhibitor titer, either the maximum one or the one assayed before immune tolerance (IT) start and age. As to the FVIII dose, results are contrasting, even though the overall impression is that high dosages are associated with higher success rates. Treatment duration analyses appear to be fairly consistent in all the studies, with 1 year as the crucial time period useful in predicting outcome. Preliminary data suggest that concentrates containing von Willebrand factor may increase the success rate and allow patients refractory to IT procedures carried out with ultrapure or recombinant concentrates to become tolerant in the end. These data need to be formally confirmed in trials that compare the different brands. In the studies published so far, a common language and widely accepted definitions of the variables have emerged, which are important in setting up the controlled trials and improving the comparison among published data.

Epitope specificity of anti-FVIII antibodies during immune tolerance therapy with factor VIII preparation containing von Willebrand factor

The study aimed at characterizing the putative changes in the epitope specificity of anti-FVIII antibodies during a successful immune tolerance treatment of the haemophilia A patient with the factor VIII (FVIII) preparation containing the von Willebrand factor (VWF). At the beginning of treatment, anti-FVIII inhibitory antibodies recognizing predominantly the light chain of FVIII were prevalent and persisted throughout the treatment. More detailed characterization of the FVIII antibody epitope specificity by using GST-fusion proteins corresponding to different FVIII domains revealed the prevalence of C1-domain-specific antibodies, while a remarkably lower amount of antibodies were targeted at the C2 and the a3 domains of the FVIII light chain and towards the A2 and the A1 domain of the FVIII heavy chain. The epitope specificity of antibodies remained rather unchanged throughout treatment except the elevated level of C2-domain-specific FVIII antibodies after a temporary interruption of treatment. The patient's antibodies were unable to interfere with the FVIII binding to VWF or to phospholipids, but inhibited FXa generation and the binding of FX to FVIII on the phospholipid monolayer. Thus, a unique pattern of the epitope specificity of FVIII antibodies and the mechanism to inhibit FVIII:C activity by FVIII-light-chain-specific antibodies were characterized.

Safety and efficacy of KOGENATE® Bayer in previously untreated patients (PUPs) and minimally treated patients (MTPs)

Safety and efficacy of KOGENATE Bayer (Kogenate FS), a second-generation full-length recombinant factor VIII formulated with sucrose as stabilizer and produced without the addition of human albumin during purification and the final formulation, was assessed in a prospective, international clinical trial including 31 previously untreated patients (PUPs) and minimally treated patients (MTPs) with severe haemophilia A in home therapy and surgery. Factor VIII inhibitor development was monitored and mutation type profiles were analysed. As of 30 June 2000, the patients received a total of 2.729 infusions (mean 88; range 6-274) for bleeding episodes, surgery or prophylactic treatment. No unexpected drug-related adverse events were observed. Four patients developed an inhibitor after 3-12 exposure days (EDs). One patient successfully underwent immune tolerance treatment; inhibitors in two patients disappeared spontaneously with on-demand treatment, while the inhibitor titre remains low in one patient. Twenty-nine patients (93%) with more than 20 EDs can be regarded as at low risk for inhibitor development. In conclusion, KOGENATE Bayer is efficacious and well-tolerated for treatment of children with severe haemophilia A. The incidence of inhibitor formation is not different to that observed with other recombinant or plasma-derived products.

Immune tolerance treatment in haemophilia patients with inhibitors: the Spanish Registry.

We present a retrospective study of immune tolerance treatment (ITT) carried out in 42 Spanish haemophiliac patients. Most of the patients were high responders (39/42), with a median maximum titre of 67 Bethesda units (BU) (range 6-2984). The median inhibitor titre at the start the ITT was 11 BU (range 1-256 BU) and the median age of the patients was 7 years (range 0-57). The mean factor dosage was 140 IU kg bodyweight(-1) day(-1) (range 25-500). In most of the ITTs, plasma-derived factor concentrate of intermediate and high purity was used. The inhibitor was eradicated in 26/38 (68%) of the patients who completed the treatment and two patients changed their status from high to low responders. Multivariate logistic regression analysis showed that three significant variables were associated with the highest probability of success: (i) the use of low factor doses for ITT (< or = 100 IU kg(-1) day(-1); P = 0.0106; 95% CI 0.000289-0.342); (ii) a titre of < 10 BU at start of ITT (P = 0.0286; 95% CI 0.00253-0.7189) and (iii) a lower maximum titre (P = 0.0214; 95% CI 0.98-0.9994).

Immune tolerance induction in haemophilia A patients with high‐responding inhibitors to factor VIII: experience at a single institution

Inhibitor antibodies to transfused factor VIII pose significant challenges in the management of haemophilia A patients. The main concern is the inefficacy of replacement therapy in patients with high‐titre antibodies, who have a shorter life‐span and a greater morbidity compared to subjects without inhibitors. The ultimate goal in treating these patients is to eliminate the inhibitor antibody entirely, allowing the recommencement of specific replacement therapy. The results of an immune tolerance regimen based on pharmacokinetic parameters are reported here. In 12 high‐responder haemophilia A patients immune tolerance induction (ITI) was attempted with daily administration of factor VIII concentrates of very high purity, either plasma‐derived or produced by recombinant‐DNA technology. Patients were given 100 IU kg–1 day–1 until the inhibitor was shown to be absent by at least two negative assays 1 month apart, with normal recovery of infused factor VIII and normal half‐life (&gt; 6 h), as assessed after a 3‐day washout period. After the patient was judged to be inhibitor‐free, immune tolerance treatment was continued with unmodified factor VIII doses for 2 months. Doses were thereafter gradually reduced and finally, regular prophylaxis by administration of 25 IU kg–1 three times weekly was instituted. Immune tolerance was achieved in 10 of the 12 patients (including six of seven with long‐standing inhibitors) within a median time of 8 months. Outcome of immune tolerance was not influenced by age at start of ITI nor by the interval between inhibitor development and ITI. The success rate and the inhibitor disappearance time of our immune tolerance regimen, utilizing high‐purity factor VIII, agrees with those reported by other investigators.

Immune tolerance induction in haemophilia A patients with high-responding inhibitors to factor VIII: experience at a single institution.

Inhibitor antibodies to transfused factor VIII pose significant challenges in the management of haemophilia A patients. The main concern is the inefficacy of replacement therapy in patients with high-titre antibodies, who have a shorter life-span and a greater morbidity compared to subjects without inhibitors. The ultimate goal in treating these patients is to eliminate the inhibitor antibody entirely, allowing the recommencement of specific replacement therapy. The results of an immune tolerance regimen based on pharmacokinetic parameters are reported here. In 12 high-responder haemophilia A patients immune tolerance induction (ITI) was attempted with daily administration of factor VIII concentrates of very high purity, either plasma-derived or produced by recombinant-DNA technology. Patients were given 100 IU kg(-1) day(-1) until the inhibitor was shown to be absent by at least two negative assays 1 month apart, with normal recovery of infused factor VIII and normal half-life (> 6 h), as assessed after a 3-day washout period. After the patient was judged to be inhibitor-free, immune tolerance treatment was continued with unmodified factor VIII doses for 2 months. Doses were thereafter gradually reduced and finally, regular prophylaxis by administration of 25 IU kg(-1) three times weekly was instituted. Immune tolerance was achieved in 10 of the 12 patients (including six of seven with long-standing inhibitors) within a median time of 8 months. Outcome of immune tolerance was not influenced by age at start of ITI nor by the interval between inhibitor development and ITI. The success rate and the inhibitor disappearance time of our immune tolerance regimen, utilizing high-purity factor VIII, agrees with those reported by other investigators.

Successful Immune Tolerance Treatment with Monoclonal or Recombinant Factor VIII Concentrates in High Responding Inhibitor Patients

AbstractVery high purity factor VIII (FVI1I) concentrates (plasma‐derived or produced by recombinant‐DNA technology) were used to achieve immune tolerance in five patients with high‐responding inhibitors to FVIII. The mean time required for inhibitor disappearance was 5 months. Four out of five patients showed normalisation of the half‐life of infused FVIII after 8–18 months of treatment with 100 IU FVIII/kg body weight administered once daily. Highly purified FVIII products thus appear to be suitable for achieving immune tolerance without negative effects on endogenous von Willebrand factor levels and activity.

Successful Immune Tolerance Treatment with Monoclonal or Recombinant Factor VIII Concentrates in High Responding Inhibitor Patients

Very high purity factor VIII (FVIII) concentrates (plasma–derived or produced by recombinant–DNA technology) were used to achieve immune tolerance in five patients with high–responding inhibitors to FVIII. The mean time required for inhibitor disappearance was 5 months. Four out of five patients showed normalisation of the half–life of infused FVIII after 8–18 months of treatment with 100 IU FVIII/kg body weight administered once daily. Highly purified FVIII products thus appear to be suitable for achieving immune tolerance without negative effects on endogenous von Willebrand factor levels and activity.