Rituximab and immune tolerance in severe hemophilia A: a consecutive national cohort

Pre-Clinical In-Vitro Studies on Parameters Governing Immune Complex Formation

The success of biotherapeutics is often challenged by the undesirable events of immunogenicity in patients, characterized by the formation of anti-drug antibodies (ADA). Under specific conditions, the ADAs recognizing the biotherapeutic can trigger the formation of immune complexes (ICs), followed by cascades of subsequent effects on various cell types. Hereby, the connection between the characteristics of ICs and their downstream impact is still not well understood. Factors governing the formation of ICs and the characteristics of these IC species were assessed systematically in vitro. Classic analytical methodologies such as SEC-MALS and SV-AUC, and the state-of-the-art technology mass photometry were applied for the characterization. The study demonstrates a clear interplay between (1) the absolute concentration of the involved components, (2) their molar ratios, (3) structural features of the biologic, (4) and of its endogenous target. This surrogate study design and the associated analytical tool-box is readily applicable to most biotherapeutics and provides valuable insights into mechanisms of IC formation prior to FIH studies. The applicability is versatile—from the detection of candidates with immunogenicity risks during developability assessment to evaluation of the impact of degraded or post-translationally modified biotherapeutics on the formation of ICs.

B cell-activating factor modulates the factor VIII immune response in hemophilia A

Inhibitors of factor VIII (FVIII) remain the most challenging complication of FVIII protein replacement therapy in hemophilia A (HA). Understanding the mechanisms that guide FVIII-specific B cell development could help identify therapeutic targets. The B cell-activating factor (BAFF) cytokine family is a key regulator of B cell differentiation in normal homeostasis and immune disorders. Thus, we used patient samples and mouse models to investigate the potential role of BAFF in modulating FVIII inhibitors. BAFF levels were elevated in pediatric and adult HA inhibitor patients and decreased to levels similar to those of noninhibitor controls after successful immune tolerance induction (ITI). Moreover, elevations in BAFF levels were seen in patients who failed to achieve FVIII tolerance with anti-CD20 antibody-mediated B cell depletion. In naive HA mice, prophylactic anti-BAFF antibody therapy prior to FVIII immunization prevented inhibitor formation and this tolerance was maintained despite FVIII exposure after immune reconstitution. In preimmunized HA mice, combination therapy with anti-CD20 and anti-BAFF antibodies dramatically reduced FVIII inhibitors via inhibition of FVIII-specific plasma cells. Our data suggest that BAFF may regulate the generation and maintenance of FVIII inhibitors and/or anti-FVIII B cells. Finally, anti-CD20/anti-BAFF combination therapy may be clinically useful for ITI.

On the road to eliminating long-lived plasma cells-"are we there yet?"

Central to protective humoral immunity is the activation of B cells and their terminal differentiation into antibody-secreting plasma cells. Long-lived plasma cells (LLPC) may survive for years to decades. Such long-lived plasma cells are also responsible for producing pathogenic antibodies that cause a variety of challenges such as autoimmunity, allograft rejection, and drug neutralization. Up to now, various therapeutic strategies aimed at durably eliminating pathogenic antibodies have failed, in large part due to their inability to efficiently target LLPCs. Several antibody-based therapies have recently gained regulatory approval or are in clinical phases of development for the treatment of multiple myeloma, a malignancy of plasma cells. We discuss the exciting potential of using these emerging cancer immunotherapies to solve the antibody problem.

Current status of haemophilia inhibitor management in mainland China: a haemophilia treatment centres survey on treatment preferences and real-world clinical practices

To investigate the current experience and expertise for haemophilia inhibitor patient management in haemophilia treatment centres (HTCs) in mainland China. Questionnaires were distributed to 'tertiary tier A' hospital HTCs across China to collect information on treatment preferences for bleeding control, prophylaxis and inhibitor eradication, as well as their regimens in real-world clinical practice. Of 40 questionnaires distributed, 39 were returned. In all, 38 were analysable for treatment preferences and 34 for actual clinical practice. For haemostatic treatment, 76·3% (29/38) HTCs preferred activated recombinant human Factor VII (rFVIIa). In clinical practice, the most widely used by-pass agent was prothrombin complex concentrate (26 HTCs). Although 65·8% (25/38) of HTCs believed prophylaxis treatment was necessary, it was prescribed in only 12. Similarly, 65·8% (25/38) of HTCs believed immune tolerance induction (ITI) therapy was necessary but only 14·8% (92/622) of patients in 19 HTCs received low-dose ITI treatment. HTCs in relatively economically developed cities (with higher-than-average per-capita gross domestic product) had better access to haemostatic treatment, coagulation testing and were more likely to provide prophylaxis and ITI in practice. The present survey showed there were gaps in haemophilia inhibitor care between the HTC physicians' preferences and their actual clinical practice. More specific care guidelines, education and clinical decision support tools are needed to guide clinical practice.

Low-dose immune tolerance induction alone or with immunosuppressants according to prognostic risk factors in Chinese children with hemophilia A inhibitors

BACKGROUND

In developing countries, children with hemophilia A (HA) with high-titer inhibitor and poor immune tolerance induction (ITI) prognostic risk(s) cannot afford the recommended high- or intermediate-dose ITI.

OBJECTIVES

To determine the efficacy of low-dose ITI (plasma-derived factor VIII [FVIII]/von Willebrand factor at 50 FVIII IU/kg every other day) by itself (ITI-alone) or combined with immunosuppressants rituximab and prednisone (ITI-IS) in children with HA with high-titer inhibitor.

METHODS

All enrolled patients had pre-ITI inhibitor ≥10 BU. We used ITI-alone if inhibitor titer was <40 BU pre-ITI and during ITI, and ITI-IS if titer was ≥100 BU (historic) or ≥40 BU (pre- or during ITI) or if the patient was nonresponsive on ITI-alone.

RESULTS

Fifty-six children were analyzable, with median historic peak inhibitor titer 48.0 BU and followed for median 31.4 months. Overall, 35 (62.5%) achieved phase 2 success with negative inhibitor and normal FVIII recovery. The phase 2 success rate was 95% for the 20 patients receiving ITI-alone. For the 36 patients receiving ITI-IS, the phase 2 success rate was 44.4%, but would increase to 63.6% if the 14 patients with historic peak inhibitor titer ≥100 BU (and having phase 2 success rate of only 14.3%) were excluded. One patient developed repeated infection after IS treatment. Relapse occurred in 11.4% (4/35) patients with phase 2 success associated with rapid ITI dose reduction or irregular post-ITI FVIII prophylaxis. Our strategy reduced the cost from high-dose ITI by 74% to 90%.

CONCLUSION

The use of low-dose ITI with or without immunosuppressants according to ITI prognostic risk(s) is a clinically and economically feasible strategy for eradicating inhibitors in children with HA, particularly for those with historic peak inhibitor titer <100 BU.

Clinical Care of Bone Health in Patients on the Immune Tolerance Induction's Protocols With an Immunosuppressive Agent for Inhibitor Eradication in Hemophilia

Nowadays, the development of factor VIII and IX inhibitors in patients with hemophilia is considered as the most challenging in the treatment of hemophilia. Immune tolerance induction (ITI) therapy is an approach for eradication of inhibitors. Some ITI protocols are routinely in use for the eradication of inhibitors in patients with hemophilia. Moreover, such a therapeutic regimen may facilitate the tendency to reduced bone density in patients with inhibitor. This study scheduled to investigate whether that predisposing role of ITI protocols with an immunosuppressive agent has considered or not. By a literature review, published ITI protocols in hemophilia with inhibitors were evaluated. Among them, 51 papers found and studied thoroughly. None of them had performed the bone mineral examination in patients with hemophilia and inhibitor under treatment. Since there are 2 coexisting facilitating factors in these protocols, considering the bone mineral density study for patients with inhibitor who are undergoing ITI protocols with an immunosuppressive agent is recommended.

Real-world evidence on health resource use among patients with haemophilia and inhibitor exhibiting severe bleeding episodes

OBJECTIVE

This study aimed to explore real-world evidence on health resource use (HRU) spending on patients with haemophilia and inhibitor.

MATERIALS AND METHODS

Medical records from 1990 to 2019 of patients with haemophilia and inhibitor from three comprehensive haemophilia treatment centres were retrospectively retrieved.

RESULTS

In all, 31 patients with haemophilia (A = 30, B = 1) and inhibitor ≥5 BU were included. The mean initial inhibitor of 95.4 BU was detected at the mean age of 6.7 years. The mean number of annual hospitalisations was 3.9. A total of 795 bleeding episodes (major =125, minor =670) were evaluated. The treatment included bypassing agents or plasma exchange before administering high-dose factor VIII concentrate and intervention or surgery. Six patients succumbed to bleeding at the mean age of 17.2 years. Nineteen surviving patients experienced multiple morbidity except six patients with successful and partially successful immune tolerance induction (ITI). The mean (SD) annual total medical consumption for episodic treatment and successful ITI per patient with haemophilia A were 30,804 (81,332) USD and 55,531 (100,566) USD, respectively. Only episodic treatment was paid by the government budget for limited amounts of bypassing agents.

CONCLUSION

Management for patients with haemophilia and inhibitor exhibiting severe bleeding is challenging for medical personnel in countries having limited resources over decades. The real-world data will be used to negotiate with the government to increase budget for adequate bypassing agents or nonreplacement therapy and to include ITI in the national haemophilia treatment.

Rituximab for treating inhibitors in people with inherited severe hemophilia

BACKGROUND

Hemophilia A and B are inherited coagulation disorders characterized by a reduced or absent level of factor VIII or factor IX respectively. The severe form is characterized by a factor level less than 0.01 international units (IU) per milliliter. The development of inhibitors in hemophilia is the main complication of treatment, because the presence of these antibodies, reduces or even nullifies the efficacy of replacement therapy, making it very difficult to control the bleeding. People with inhibitors continue to have significantly higher risks of morbidity and mortality, with considerable treatment costs. Given the wide 'off-label' use of rituximab for treating people with hemophilia and inhibitors, its efficacy and safety need to be evaluated. This is an update of a previously published Cochrane Review.

OBJECTIVES

To assess the efficacy and safety of rituximab for treating inhibitors in people with inherited severe hemophilia A or B.

SEARCH METHODS

We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group's Coagulopathies Trials Register, complied from electronic database searches and handsearching of journals and conference abstract books. We searched the reference lists of relevant articles and reviews and also searched for ongoing or unpublished studies. We also undertook further searches of other bibliographic databases and trial registries. Date of last search of the Cochrane Cystic Fibrosis and Genetic Disorders Group's Coagulopathies Trials Register: 19 March 2020.

SELECTION CRITERIA

Randomized controlled trials and controlled clinical trials investigating the efficacy and safety of rituximab for treating inhibitors in people with hemophilia.

DATA COLLECTION AND ANALYSIS

No randomized controlled trials matching the selection criteria were eligible for inclusion.

MAIN RESULTS

No randomized controlled trials on rituximab for treating inhibitors in people with hemophilia were identified.

AUTHORS' CONCLUSIONS

We were unable to identify any relevant trials on the efficacy and safety of rituximab for treating inhibitors in people with hemophilia. The research evidence available is from case reports and case series. Randomized controlled trials are needed to evaluate the efficacy and safety of rituximab for this condition. However, prior to the publication of any possible future randomized controlled trials, meta-analysis of case reports and case series may provide some evidence.

Combined anti-CD20 and mTOR inhibition with factor VIII for immune tolerance induction in hemophilia A patients with refractory inhibitors

BACKGROUND

Hemophilia A (HA) inhibitor patients that fail traditional immune tolerance induction (ITI) have increased morbidity and mortality. Preclinical studies support factor VIII (FVIII) tolerance induction with a combined approach of anti-CD20 mediated transient B cell depletion and rapamycin mediated regulatory T cell (Treg) induction.

METHODS

Two refractory HA inhibitor patients were treated with rituximab, rapamycin, and FVIII ITI. Their clinical course, anti-FVIII immunoglobulins, cytokines, and select lymphocytes were followed.

RESULTS

One patient achieved complete and the other partial FVIII tolerance; both had marked annualized bleeding rate improvement. FVIII-specific immunoglobulins, but not total Treg counts, correlated with tolerance induction. IL-6 and IL-21 correlation with complete tolerance induction may support that down-regulation of T effectors and IgG4 production, respectively, contribute to the pathogenesis of tolerance induction.

CONCLUSIONS

This regimen may be considered to induce FVIII tolerance in HA patients with refractory inhibitors. Further characterization of the FVIII-specific immune response is necessary to clarify the mechanism of immune tolerance.

Low-dose immune tolerance induction for children with hemophilia A with poor-risk high-titer inhibitors: A pilot study in China

BACKGROUND

Immune tolerance induction (ITI) therapy is currently unaffordable in China. Management of hemophilia A children with high-titer inhibitor is therefore a challenge.

AIM

To describe the ITI strategy using plasma-derived factor VIII/von Willebrand factor concentrate (pdFVIII/VWF) +/- immunosuppression and to report its efficacy in children with hemophilia A having poor-risk status for ITI success.

METHODS

A prospective pilot study on children with hemophilia A having poor-risk status (all with at least inhibitor titer > 10 BU pre-ITI initiation). Patients received ~50 IU/kg FVIII every other day using domestic intermediate purity pdFVIII/VWF products, either alone or in combination with rituximab +/- prednisone.

RESULTS

Sixteen patients with median age 2.9 (range, 2.2-13.2) years and median pre-ITI inhibitor titer 30.7 (range, 10.4-128) BU were enrolled. Analysis at median 14.7 (range, 12.4-22.6) months' follow-up showed a total response rate of 87.5%. This included success (achieving inhibitor < 0.6 BU) in 13 patients (81.3%) in a median of 8.8 (range, 3.2-11.8) months, and partial success (achieving inhibitor < 5 BU but > 0.6BU) in 1 (6.3%). Compared to the pre-ITI period, the mean bleeds/month during ITI was 0.51 (64.0% reduction), and joint bleeds/month was 0.34 (64.3% reduction). This low-dose ITI strategy cost less by 70% to 87% than that for the high-dose FVIII regimen. No severe adverse events were observed.

CONCLUSION

This low-dose ITI strategy of pdFVIII/VWF +/- immunosuppression achieved relatively satisfactory outcomes in children with hemophilia A inhibitor having poor-risk status. This low-dose regimen showed economic advantages and is therefore suitable for using in China. However, further study in a larger cohort with a longer follow-up time is needed.

Hemophilia A with inhibitor: Immune tolerance induction (ITI) in the mirror of time

Inhibitor (neutralizing antibodies) development remains the most significant complication in patients with severe congenital hemophilia A receiving exogenous factor VIII (FVIII). Although our understanding of the pathophysiology of inhibitor development has advanced, the knowledge gained has not yet translated into a robust decline in incidence, with the overall risk remaining at ∼30%. Immune Tolerance Induction (ITI) is the only current method to successfully eradicate an inhibitor and achieve long-term tolerance. Although current practice utilizes a wide variety of ITI regimens, identification of an optimal regimen has not emerged. Over the last decade, the number of replacement products available in hemophilia has greatly expanded. The cumulative evidence with each product for use in ITI is often lacking. Most recently emicizumab, a humanized monoclonal bi-specific antibody that substitutes for the scaffolding effect of FVIIIa was approved; this agent prevents bleeding in both inhibitor and non-inhibitor patients. The use of emicizumab will bring about a new era in care that will require clinicians to challenge current practice paradigms including use and administration of ITI. This review will summarize the main clinical ITI data and practices for patients with severe congenital hemophilia A with inhibitors (CHAwI) over the last four decades and will highlight current studies in the field, with attention to open questions.

Inhibitors in haemophilia A and B: Management of bleeds, inhibitor eradication and strategies for difficult-to-treat patients

The standard therapy for patients with haemophilia is prophylactic treatment with replacement factor VIII (FVIII) or factor IX (FIX). Patients who develop inhibitors against FVIII/FIX face an increased risk of bleeding, and the likelihood of early development of progressive arthropathy, alongside higher treatment-related costs. Bypassing agents can be used to prevent and control bleeding, as well as the recently licensed prophylaxis, emicizumab, but their efficacy is less predictable than that of factor replacement therapy. Antibody eradication, by way of immune tolerance induction (ITI), is still the preferred management strategy for treating patients with inhibitors. This approach is successful in most patients, but some are difficult to tolerise and/or are unresponsive to ITI, and they represent the most complicated patients to treat. However, there are limited clinical data and guidelines available to help guide physicians in formulating the next treatment steps in these patients. This review summarises currently available treatment options for patients with inhibitors, focussing on ITI regimens and those ITI strategies that may be used in difficult-to-treat patients. Some alternative, non-ITI approaches for inhibitor management, are also proposed.

Rituximab for treating inhibitors in people with inherited severe hemophilia

BACKGROUND

Hemophilia A and B are inherited coagulation disorders characterized by a reduced or absent level of factor VIII or factor IX respectively. The severe form is characterized by a factor level less than 0.01 international units (IU) per milliliter. The development of inhibitors in hemophilia is the main complication of treatment, because the presence of these antibodies, reduces or even nullifies the efficacy of replacement therapy, making it very difficult to control the bleeding. People with inhibitors continue to have significantly higher risks of morbidity and mortality, with considerable treatment costs. Given the wide 'off-label' use of rituximab for treating people with hemophilia and inhibitors, its efficacy and safety need to be evaluated. This is an update of a previously published Cochrane Review.

OBJECTIVES

To assess the efficacy and safety of rituximab for treating inhibitors in people with inherited severe hemophilia A or B.

SEARCH METHODS

We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group's Coagulopathies Trials Register, complied from electronic database searches and handsearching of journals and conference abstract books. We searched the reference lists of relevant articles and reviews and also searched for ongoing or unpublished studies. We also undertook further searches of other bibliographic databases and trial registries.Date of last search of the Cochrane Cystic Fibrosis and Genetic Disorders Group's Coagulopathies Trials Register: 16 February 2017.

SELECTION CRITERIA

Randomized controlled trials and controlled clinical trials investigating the efficacy and safety of rituximab for treating inhibitors in people with hemophilia.

DATA COLLECTION AND ANALYSIS

No randomized controlled trials matching the selection criteria were eligible for inclusion.

MAIN RESULTS

No randomized controlled trials on rituximab for treating inhibitors in people with hemophilia were identified.

AUTHORS' CONCLUSIONS

We were unable to identify any relevant trials on the efficacy and safety of rituximab for treating inhibitors in people with hemophilia. The research evidence available is from case reports and case series. Randomized controlled trials are needed to evaluate the efficacy and safety of rituximab for this condition. However, prior to the publication of any possible future randomized controlled trials, meta-analysis of case reports and case series may provide some evidence.

Achievements, challenges and unmet needs for haemophilia patients with inhibitors: Report from a symposium in Paris, France on 20 November 2014

Over the past 20 years, there have been many advances in haemophilia treatment that have allowed patients to take greater control of their disease. However, the development of factor VIII (FVIII) inhibitors is the greatest complication of the disease and a challenge in the treatment of haemophilia making management of bleeding episodes difficult and surgical procedures very challenging. A meeting to discuss the unmet needs of haemophilia patients with inhibitors was held in Paris on 20 November 2014. Topics discussed were genetic and non-genetic risk factors for the development of inhibitors, immunological aspects of inhibitor development, FVIII products and inhibitor development, generation and functional properties of engineered antigen-specific T regulatory cells, suppression of immune responses to FVIII, prophylaxis in haemophilia patients with inhibitors, epitope mapping of FVIII inhibitors, current controversies in immune tolerance induction therapy, surgery in haemophilia patients with inhibitors and future perspectives for the treatment of haemophilia patients with inhibitors. A summary of the key points discussed is presented in this paper.

Combination therapy for inhibitor reversal in haemophilia A using monoclonal anti-CD20 and rapamycin

Development of antibodies (inhibitors) against coagulation factor VIII (FVIII) is a major complication of intravenous replacement therapy in haemophilia A (HA). Current immune tolerance induction (ITI) regimens are not universally effective. Rituximab, a B cell-depleting antibody against CD20, has shown mixed results for inhibitor reversal in patients. This study aims to develop a combinatorial therapy for inhibitor reversal in HA, using anti-murine CD20 (anti-mCD20) antibody and rapamycin, which targets both B and T cell responses. Additionally, it extensively characterises the role of the IgG backbone in B cell depletion by anti-CD20 antibodies. For this, inhibitors were generated in BALB/c-HA mice by weekly IV injection of FVIII. Subsequently, anti-mCD20 (18B12) with IgG2a or IgG1 backbone was injected IV in two doses three weeks apart and B cell depletion and recovery was characterised. Rapamycin was administered orally 3x/week (for 1 month) while continuing FVIII injections. Altering the IgG backbone of anti-mCD20 from IgG2a to IgG1 reduced overall depletion of B cells (including memory B cells), and marginal zone, B-10, and B-1b cells were specifically unaffected. While neither antibody was effective alone, in combination with rapamycin, anti-mCD20 IgG2a but not IgG1 was able to reverse inhibitors in HA mice. This regimen was particularly effective for starting titres of ~10 BU. Although IgG1 anti-mCD20 spared potentially tolerogenic B cell subsets, IgG2a directed sustained hyporesponsiveness when administered in conjunction with rapamycin. This regimen represents a promising treatment for inhibitor reversal in HA, as both of these compounds have been extensively used in human patients.

Inhibitor recurrence after immune tolerance induction: a multicenter retrospective cohort study

BACKGROUND

Immune tolerance induction (ITI) in patients with congenital hemophilia A is successful in up to 70%. Although there is growing understanding of predictors of response to ITI, the probability and predictors of inhibitor recurrence after successful ITI are not well understood.

OBJECTIVES

To determine the association of clinical characteristics, particularly adherence to factor VIII (FVIII) prophylaxis after ITI, with inhibitor recurrence in patients with hemophilia A who were considered tolerant after ITI.

METHODS

In this multicenter retrospective cohort study, 64 subjects with FVIII level < 2% who were considered successfully tolerant after ITI were analyzed to estimate the cumulative probability of inhibitor recurrence using the Kaplan-Meier method. The association of clinical characteristics with inhibitor recurrence was assessed using logistic regression.

RESULTS

A recurrent inhibitor titer ≥ 0.6 BU mL(-1) occurred at least once in 19 (29.7%) and more than once in 12 (18.8%). The probability of any recurrent inhibitor at 1 and 5 years was 12.8% and 32.5%, respectively. Having a recurrent inhibitor was associated with having received immune modulation during ITI (odds ratio [OR] 3.8, 95% confidence interval [CI] 1.2-22.4) and FVIII recovery of < 85% at the end of ITI (OR 2.6, 95% CI 1.3-5.9) but was not associated with adherence to post-ITI prophylactic FVIII infusion (OR 0.5, 95% CI 0.06-4.3).

CONCLUSIONS

The use of immune modulation therapy during ITI and lower FVIII recovery at the end of ITI appear to be associated with an increased risk of inhibitor recurrence after successful ITI. Adherence to post-ITI prophylactic FVIII infusions is not a major determinant of recurrence.

Advances in the clinical management of inhibitors in hemophilia A and B

Inhibitors to factor (F)VIII or FIX are the most serious and challenging complication of hemophilia treatment, increasing morbidity and mortality because bleeds no longer respond to standard clotting factor replacement therapy. For patients with high-titer inhibitors, immune tolerance induction achieved through regular factor exposure is the only proven therapy capable of Inhibitor eradication and is almost always indicated for inhibitors of recent onset. Bypassing therapy is used to treat and prevent bleeding, but neither of the two currently available bypassing agents has the predictable hemostatic efficacy of factor replacement in hemophilia patients without inhibitors. Major research efforts are focused on the development of new, more potent therapies for the management of patients with inhibitors.

The anti-CD20 monoclonal antibody rituximab to treat acquired haemophilia A

BACKGROUND

Acquired haemophilia A (AHA) is a rare bleeding disorder caused by the development of specific autoantibodies against naturally occurring factor VIII (FVIII). Although about half of cases are idiopathic, AHA may be associated with several non-neoplastic conditions, autoimmune disorders, as well as haematological malignancies, such as chronic lymphocytic leukaemia and lymphoma. The long-term suppression of inhibitors is one of the mainstays of the treatment of AHA. Apart from standard immunosuppressive treatments, rituximab has been proven to be effective in AHA.

MATERIALS AND METHODS

The aim of this review is to provide a systematic description of data available in the literature on this topic. To do so, we performed a search using the indexed online database Medline/PubMed, without temporal limits, matching the words "rituximab" and "acquired h(a)emophilia". Furthermore, additional published studies were identified in the reference list of the publications found in PubMed.

RESULTS

The review of the literature confirms that rituximab may be a safe and useful treatment for AHA.

DISCUSSION

Although rituximab is not a standard therapy for AHA, it may be useful in resistant cases. However, the definitive place of this monoclonal antibody in the therapeutic strategy for AHA (first or second-line, alone or in combination with other drugs) remains to be determined more precisely and warrants further investigation.

Immunosuppressive agents in the treatment of inhibitors in congenital haemophilia A and B--a systematic literature review

The development of inhibitory antibodies to factor VIII (FVIII) or factor IX (FIX) in patients with haemophilia is a serious complication of treatment with coagulation factor concentrates. Antibodies develop in 10-15% of haemophilia A and in up to 5% of haemophilia B patients. Several strategies have been developed over the years to facilitate the eradication of inhibitors and reduce the cost. These include plasmapheresis and/or extracorporeal protein A absorption to remove the inhibitor from the plasma, and immunosuppression and/or immune modulation to suppress the production of inhibitory antibodies. Different immunosuppressive (IS) agents have been described with varying success. To evaluate the outcome of these agents, we performed a systematic literature review using the PubMed database. The total number of articles identified was 345; 299 papers were excluded leaving 46 papers to be included in the study. No randomised studies were identified, only case reports and case series. The most frequently used agents in the 46 case reports and cohort studies identified were cyclophosphamide and rituximab. All cases exposed to cyclophosphamide, rituximab and other IS agents had a complete success rate of 40-44%, 40-63% and 33-56%, respectively. However, the definition of success was not consistent among the studies. In conclusion, our review of the literature indicates that IS agents in combination with FVIII or FIX could be an option and may be cost-effective in many patients. The risk of adverse events seems to be relatively low. To fully explore the effect of IS agents, randomised studies are warranted.

Rituximab for treating inhibitors in people with inherited severe hemophilia

BACKGROUND

Hemophilia A and B are inherited coagulation disorders characterized by a reduced or absent level of factor VIII or factor IX respectively. The severe form is characterized by a factor level less than 0.01 international units (IU) per milliliter. The development of inhibitors in hemophilia is the main complication of treatment, because the presence of these antibodies, reduces or even nullifies the efficacy of replacement therapy, making it very difficult to control the bleeding. People with inhibitors continue to have significantly higher risks of morbidity and mortality, with considerable treatment costs. Given the wide 'off-label' use of rituximab for treating people with hemophilia and inhibitors, its efficacy and safety need to be evaluated.

OBJECTIVES

To assess the efficacy and safety of rituximab for treating inhibitors in people with inherited severe hemophilia A or B.

SEARCH METHODS

We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group's Coagulopathies Trials Register, complied from electronic database searches and handsearching of journals and conference abstract books. We searched the reference lists of relevant articles and reviews and also searched for ongoing or unpublished studies.Date of last search: 27 January 2015.

SELECTION CRITERIA

Randomized controlled trials and controlled clinical trials investigating the efficacy and safety of rituximab for treating inhibitors in people with hemophilia.

DATA COLLECTION AND ANALYSIS

No randomized controlled trials matching the selection criteria were eligible for inclusion.

MAIN RESULTS

No randomized controlled trials on rituximab for treating inhibitors in people with hemophilia were identified.

AUTHORS' CONCLUSIONS

We were unable to identify any relevant trials on the efficacy and safety of rituximab for treating inhibitors in people with hemophilia. The research evidence available is from case reports and case series. Randomized controlled trials are needed to evaluate the efficacy and safety of rituximab for this condition. However, prior to the publication of any possible future randomized controlled trials, meta-analysis of case reports and case series may provide some evidence.

Immune tolerance induction using a factor VIII/von Willebrand factor concentrate (BIOSTATE), with or without immunosuppression, in Australian paediatric severe haemophilia A patients with high titre inhibitors: a multicentre, retrospective study

INTRODUCTION

It has been postulated that factor VIII (FVIII) products containing von Willebrand factor (VWF) may improve immune tolerance induction (ITI) success rate in patients with haemophilia A and poor prognostic factors.

MATERIALS AND METHODS

We conducted a retrospective cohort analysis of a FVIII/VWF concentrate (BIOSTATE) for ITI in paediatric patients with severe haemophilia A (SHA) and inhibitors, from January 2003 to December 2011 at 3 paediatric-only Haemophilia Treatment Centres in Australia. Response to ITI was assessed at or before 33 months and at completion of ITI. Fifteen male patients with SHA were included in the analysis.

RESULTS

BIOSTATE was used for primary ITI in 8 patients (2 years, range 1.1-11.5 years) and for salvage ITI in 7 patients (9.9 years, range 1.1-15.4). At the end of the observation period there were 11 patients who achieved a complete response with BIOSTATE after a median duration of 21 months (range 5-85 months); a partial response was achieved in 2 patients in whom ITI is ongoing. Therefore, the overall response rate was 86.6%. Two patients were deemed treatment failures: one due to non-compliance after 18 months of ITI and another in whom a partial response had not been achieved after 22 months of ITI.

CONCLUSION

BIOSTATE was well-tolerated and effective when used for primary or salvage ITI in this cohort of paediatric patients with SHA and a high-level inhibitor.

Rituximab for treatment of inhibitors in haemophilia A. A Phase II study

The development of antibodies against infused factor VIII (FVIII) in patients with haemophilia A is a serious complication leading to poorly controlled bleeding and increased morbidity. No treatment has been proven to reduce high titre antibodies in patients who fail immune tolerance induction or are not candidates for it. The Rituximab for the Treatment of Inhibitors in Congenital Hemophilia A (RICH) study was a phase II trial to assess whether rituximab can reduce anamnestic FVIII antibody (inhibitor) titres. Male subjects with severe congenital haemophilia A and an inhibitor titre ≥5 Bethesda Units/ml (BU) following a FVIII challenge infusion received rituximab 375 mg/m² weekly for weeks 1 through 4. Post-rituximab inhibitor titres were measured monthly from week 6 through week 22 to assess treatment response. Of 16 subjects who received at least one dose of rituximab, three (18.8%) met the criteria for a major response, defined as a fall in inhibitor titre to <5 BU, persisting after FVIII re-challenge. One subject had a minor response, defined as a fall in inhibitor titre to <5 BU, increasing to 5-10 BU after FVIII re-challenge, but <50% of the original peak inhibitor titre. Rituximab is useful in lowering inhibitor levels in patients, but its effect as a solo treatment strategy is modest. Future studies are indicated to determine the role of rituximab as an adjunctive therapy in immune tolerisation strategies.

Inhibitor eradication with rituximab in haemophilia: where do we stand?

Rituximab is a humanized chimeric anti-CD20 monoclonal antibody initially developed for the treatment of some haematological malignancies. Thanks to its ability to rapidly and specifically deplete B cells, it has also been used in a variety of autoimmune disorders, haematological or not. In this context, during the last decade several small case series have documented successful inhibitor eradication with rituximab, alone or in combination with other immunosuppressive agents, in patients with acquired haemophilia A refractory to standard therapy. In addition, a number of investigators have recently used this agent in patients with congenital haemophilia A or B and alloantibodies refractory to first-line treatment. This article critically reviews the current knowledge on the use of rituximab in acquired haemophilia or congenital haemophilia complicated by alloantibodies, also providing treatment algorithms for the management of these conditions.

B-Cell Depletion is Protective Against Anti-AAV Capsid Immune Response: A Human Subject Case Study

Gene therapy strategies for congenital myopathies may require repeat administration of adeno-associated viral (AAV) vectors due to aspects of the clinical application, such as: (i) administration of doses below therapeutic efficacy in patients enrolled in early phase clinical trials; (ii) progressive reduction of the therapeutic gene expression over time as a result of increasing muscle mass in patients treated at a young age; and (iii) a possibly faster depletion of pathogenic myofibers in this patient population. Immune response triggered by the first vector administration, and to subsequent doses, represents a major obstacle for successful gene transfer in young patients. Anti-capsid and anti-transgene product related humoral and cell-mediated responses have been previously observed in all preclinical models and human subjects who received gene therapy or enzyme replacement therapy (ERT) for congenital myopathies. Immune responses may result in reduced efficacy of the gene transfer over time and/or may preclude for the possibility of re-administration of the same vector. In this study, we evaluated the immune response of a Pompe patient dosed with an AAV1-GAA vector after receiving Rituximab and Sirolimus to modulate reactions against ERT. A key finding of this single subject case report is the observation that B-cell ablation with rituximab prior to AAV vector exposure results in non-responsiveness to both capsid and transgene, therefore allowing the possibility of repeat administration in the future. This observation is significant for future gene therapy studies and establishes a clinically relevant approach to blocking immune responses to AAV vectors.

Inhibitors in childhood hemophilia A: genetic and treatment-related risk factors for development and eradication

The development of neutralizing antibodies remains a serious complication of hemophilia replacement therapy. Factor VIII inhibiting antibodies (inhibitors) occur commonly following replacement therapy in hemophilia A, creating a significant burden of clinical disease. This article will review our current understanding of risk factors and their known impact on inhibitor development in previously untreated or minimally treated children with severe and mild hemophilia A. It will also explore how the most recently elucidated immunology of inhibitor development might hold important clues to more effective inhibitor eradication and prevention in this heavily impacted patient population.

Factor X inhibitor: a fulminant presentation and fatal course of a rare syndrome in a 59-year-old male

Factor X inhibitors are rare. The few cases documented in the literature have occurred after viral prodromes, in association with cancer, or after exposure to antibiotics. Acquired factor X deficiencies are also rare and their etiology is largely unknown. We report a new case of a factor X inhibitor and review prior cases of both factor X inhibitors and non-amyloidosis-related acquired factor X deficiencies.

Bortezomib in the rapid reduction of high sustained antibody titers in disorders treated with therapeutic protein: lessons learned from Pompe disease

PURPOSE

High sustained antibody titers complicate many disorders treated with a therapeutic protein, including those treated with enzyme replacement therapy, such as Pompe disease. Although enzyme replacement therapy with alglucosidase alfa (Myozyme) in Pompe disease has improved the prognosis of this otherwise lethal disorder, patients who develop high sustained antibody titers to alglucosidase alfa enter a prolonged phase of clinical decline resulting in death despite continued enzyme replacement therapy. Clinically effective immune-tolerance induction strategies have yet to be described in the setting of an entrenched immune response characterized by high sustained antibody titers, wherein antibody-producing plasma cells play an especially prominent role.

METHODS

We treated three patients with infantile Pompe disease experiencing marked clinical decline due to high sustained antibody titers. To target the plasma cell source of high sustained antibody titers, a regimen based on bortezomib (Velcade) was used in combination with rituximab, methotrexate, and intravenous immunoglobulin.

RESULTS

The treatment regimen was well tolerated, with no obvious side effects. Patient 1 had a 2,048-fold, and patients 2 and 3 each had a 64-fold, reduction in anti-alglucosidase alfa antibody titer, with concomitant sustained clinical improvement.

CONCLUSION

The addition of bortezomib to immunomodulatory regimens is an effective and safe treatment strategy in infantile Pompe disease, with potentially broader clinical implications.

Transient B cell depletion or improved transgene expression by codon optimization promote tolerance to factor VIII in gene therapy

The major complication in the treatment of hemophilia A is the development of neutralizing antibodies (inhibitors) against factor VIII (FVIII). The current method for eradicating inhibitors, termed immune tolerance induction (ITI), is costly and protracted. Clinical protocols that prevent rather than treat inhibitors are not yet established. Liver-directed gene therapy hopes to achieve long-term correction of the disease while also inducing immune tolerance. We sought to investigate the use of adeno-associated viral (serotype 8) gene transfer to induce tolerance to human B domain deleted FVIII in hemophilia A mice. We administered an AAV8 vector with either human B domain deleted FVIII or a codon-optimized transgene, both under a liver-specific promoter to two strains of hemophilia A mice. Protein therapy or gene therapy was given either alone or in conjunction with anti-CD20 antibody-mediated B cell depletion. Gene therapy with a low-expressing vector resulted in sustained near-therapeutic expression. However, supplementary protein therapy revealed that gene transfer had sensitized mice to hFVIII in a high-responder strain but not in mice of a low-responding strain. This heightened response was ameliorated when gene therapy was delivered with anti-murine CD20 treatment. Transient B cell depletion prevented inhibitor formation in protein therapy, but failed to achieve a sustained hypo-responsiveness. Importantly, use of a codon-optimized hFVIII transgene resulted in sustained therapeutic expression and tolerance without a need for B cell depletion. Therefore, anti-CD20 may be beneficial in preventing vector-induced immune priming to FVIII, but higher levels of liver-restricted expression are preferred for tolerance.

The literature on inhibitors: articles that influence my management of patients with hemophilia A and high-titer inhibitors

High-titer inhibitors represent the greatest management challenge faced by clinicians who treat patients with hemophilia A, as bleeding episodes no longer respond to standard factor VIII replacement therapy. Over the last seven decades, major strides have been made in inhibitor treatment. This article focuses on the seminal clinical observations and studies that provided the foundation for these advances in hemophilia care.

Immunogenicity to therapeutic proteins: impact on PK/PD and efficacy

The development of therapeutic proteins requires the understanding of the relationship between the dose, exposure, efficacy, and toxicity of these molecules. Several intrinsic and extrinsic factors contribute to the challenges for measuring therapeutic proteins in a precise and accurate manner. In addition, induction of an immune response to therapeutic protein results in additional complexities in the analysis of the pharmacokinetic profile, toxicity, safety, and efficacy of this class of molecules. Assessment of immunogenicity of therapeutic proteins is a required aspect of regulatory filings for a licensing application and for the safe and efficacious use of these compounds. A systematic strategy and well-defined criteria for measuring anti-drug antibodies (ADA) have been established, to a large extent, through coordinated efforts. These recommendations are based on risk assessment and include the determination of ADA content (concentration/titer), affinity, immunoglobulin isotype/subtype, and neutralization capacity. This manuscript reviews the requirements necessary for understanding the nature of an ADA response in order to discern the impact of immunogenicity on pharmacokinetics/pharmacodynamics and efficacy.

What is the Evidence for the Use of Immunomodulatory Agents to Eradicate Inhibitory Antibodies in Patients with Severe Hemophilia A Who Have Previously Failed to Respond to Immune Tolerance Induction?

An 18-year-old man has severe hemophilia A that has been complicated by a high-titer inhibitory antibody (peak 170 BU/mL). He had previously failed a trial of immune tolerance induction (ITI) using daily high-dose (100 units/kg/d) factor VIII (FVIII) for 20 months and would like to know if immunomodulatory agents, with or without another course of ITI, might eradicate the inhibitor.

Current Controversies in the Formation and Treatment of Alloantibodies to Factor VIII in Congenital Hemophilia A

Hemophilia A is a rare bleeding disorder treated with numerous factor VIII (FVIII)–containing replacement concentrates. This treatment approach has led to the formation of alloantibodies that neutralize the FVIII activity (inhibitors) conveyed by these commercially available concentrates in ∼ 25% of patients with severe hemophilia A (FVIII activity < 1% of normal). This phenomenon significantly complicates the treatment of these patients and compromises the effectiveness and efficiency of these products to reverse or prevent bleeding complications. Studying the population with alloantibody inhibitors is imperative but difficult due to the overall small number of individuals affected and the heterogeneity within this limited group. Furthermore, few randomized clinical trials have been conducted to answer pertinent questions so many controversies persist. This article focuses on the conflicting data on the variables associated with alloantibody FVIII inhibitor development with a particular emphasis on age and intensity of first treatment, the role of primary prophylaxis regimens in modulating this phenomenon, and the degree of purity of FVIII product as a potential contributing risk factor. The optimal dosing regimen and type of FVIII replacement product that should be used to achieve the highest success rate in immune tolerance induction (ITI) protocols are also discussed, as well as whether the addition of immunomodulatory agents, especially rituximab, to ITI regimens enhances the durability of ITI and the eradication of alloantibody FVIII inhibitors.

Clinical advances in hemophilia management

Hemophilia is an excellent example in medicine where clinical translation of basic science discoveries has transformed the gloomy outlook of the disease. This review provides an overview of clinical advances in hemophilia management with a specific focus on the molecular heterogeneity of the disease and progress in management of patients with inhibitors. Novel therapeutics and the emerging ethical issues in the field of hemophilia are also discussed.

Immune tolerance induction in haemophilia: evidence and the way forward

Given the inhibitor-associated morbidity resulting from limited effective treatment options, antibody eradication is the ultimate goal of inhibitor management. The only clinically proven strategy for achieving antigen-specific tolerance to factor VIII is immune tolerance induction (ITI). First reported over 30 years ago, much of our current knowledge about ITI in haemophilia A and B was derived from small cohort studies and retrospective national and international ITI registries. More recently, prospective randomised ITI trials have been designed and initiated to answer outstanding questions related to the optimisation of current therapeutic strategy in haemophilia A. However, due to the low incidence of inhibitor development in haemophilia B compared to haemophilia A, there are few comparable data from which to develop a useful evidence-based approach to the prevention and eradication of FIX inhibitors. The lack of an effective strategy is particularly problematic given the even greater morbidity associated with the almost unique occurrence of allergic and anaphylactic reactions that often herald FIX antibody development, and further complicates attempts to eradicate FIX inhibitors. Ultimately, successful inhibitor prevention and eradication strategies for both diseases will emerge from the clinical translation of our evolving knowledge of immune stimulation and tolerance. This paper will discuss our current understanding of immune tolerance outcome and outcome predictors for haemophilia A and B; it will also review the current consensus recommendations for ITI, as well as the emerging scientific body of immunological knowledge that may significantly impact the therapeutic and preventative strategies of the future.

Genetic polymorphisms and the impact of a higher clopidogrel dose regimen on active metabolite exposure and antiplatelet response in healthy subjects

A double-blind crossover study was conducted in four CYP2C19 genotype-defined metabolizer groups to assess whether increase in clopidogrel dosing can overcome reduced pharmacodynamic response in CYP2C19 poor metabolizers (PMs). Ten healthy subjects in each of four metabolizer groups were randomized to a clopidogrel regimen of a 300-mg loading dose (LD) and a 75-mg/day maintenance dose (MD) for 4 days followed by 600-mg LD and 150 mg/day MD, or vice versa. The exposure levels of clopidogrel's active metabolite H4 (clopi-H4) in PMs were 71% lower on the 75-mg/day regimen and 64% lower on the 150-mg/day regimen than the corresponding exposure levels in extensive metabolizers (EMs). In PMs, the maximal platelet aggregation (MPA) induced by adenosine diphosphate (ADP) 5 µmol/l was 10.5% lower on the 75-mg/day regimen and 7.9% lower on the 150-mg/day regimen than the corresponding values in EMs. PMs who were on the clopidogrel regimen of 600-mg LD/150 mg/day MD showed clopi-H4 exposure and MPA levels similar to those in EMs who were on the regimen of 300-mg LD/75 mg/day MD. In a pooled analysis evaluating CYP1A2, CYP2B6, CYP2C9, CYP2C19, CYP3A5, CYP2D6, ABCB1, and P2RY12 polymorphisms (N = 396 healthy subjects), only CYP2C19 had a significant impact on antiplatelet response. In healthy CYP2C19 PMs, a clopidogrel regimen of 600-mg LD/150 mg/day MD largely overcomes diminished clopi-H4 exposure and antiplatelet response, as assessed by MPA levels.