Incidence of development of factor VIII and factor IX inhibitors in haemophiliacs

Comprehensive domain-specific analysis and immunoglobulin G profiling of anti-factor VIII antibodies using a bead-based multiplex immunoassay

BACKGROUND

Antibodies against factor (F)VIII are a major complication in the treatment of patients with severe hemophilia A. The Nijmegen-Bethesda assay (NBA) is the gold standard for detection of neutralizing antibodies (inhibitors), whereas both inhibitors and nonneutralizing antibodies can be detected by immunoassays such as enzyme-linked immunosorbent assay (ELISA) and multiplex bead-based assays.

OBJECTIVES

Evaluation of an in-house Luminex bead-based assay (LumiTope) compared with a commercially available ELISA and NBA.

METHODS

The LumiTope method comprised full-length and B-domain-deleted FVIII as well as 9 purified FVIII single or multidomains. The respective proteins were coupled to magnetic beads to detect domain-specific immunoglobulin (IgG; IgG1-4) anti-FVIII antibodies in a large cohort of patients with hemophilia A with and without inhibitors.

RESULTS

Overall, LumiTope assay had a high sensitivity (94.9%) and specificity (91.2%), particularly in patients with low-titer inhibitors compared with ELISA (sensitivity of 72.2% vs 27.7%). IgG4 was the most abundant IgG subclass in NBA-positive patients. NBA-positive and -negative patients showed different domain profiles. Patients with genetic variants in the heavy chain predominantly exhibited antibodies specific to this chain, while those with a light-chain variant showed a more diverse distribution of antibody specificities. Patients with an intron 22 inversion resembled those with a light-chain defect, with a majority of antibodies targeting the light chain.

CONCLUSION

LumiTope assay provides a sensitive and specific method for not only detection but also domain specification of anti-FVIII-antibodies. Implementation of bead-based assays could improve antibody detection, profiling, and comparability of results and complement NBA.

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

BACKGROUND

Development of antibodies against infused Factor VIII (FVIII) or "inhibitors" represents a major challenge following FVIII replacement therapy in patients with hemophilia A (HA). Recent studies have shown that certain cellular compartments of the immune system contribute to the production of such antibodies. Herein, we determined the frequency of class-switched CD19+IgD-CD27+/non-class-switched CD19+IgD+CD27+ memory B cell subsets and CD19+CD27hiCD38hi plasmablasts in patients with severe HA and their association with the development of inhibitors in these patients.

METHODS

This cross-sectional case-control study enrolled 32 patients with severe HA, including 8 with and 24 without inhibitors, and 24 healthy individuals. The frequencies of the memory B cell subsets and plasmablasts were determined using flow cytometry.

RESULTS

The frequency of CD19+IgD+CD27+ non-class-switched memory B cells was significantly lower in patients with HA (including both patients with and without inhibitors) than in healthy controls. The percentages of both CD19+IgD-CD27+ class-switched and CD19+IgD+CD27+ non-class-switched memory B cells did not differ significantly between patients with and without inhibitors. HA patients with inhibitors had significantly higher proportions of CD19+CD27hiCD38hi plasmablasts than the control group as well as the inhibitor (-) ones. No significant correlation was observed between the inhibitor levels with the percentages of memory B cell subsets and plasmablasts.

CONCLUSION

This study is the first to demonstrate a dysregulated proportion of CD19+IgD+CD27+ non-class-switched memory B cells and CD19+CD27hiCD38hi plasmablasts in patients with severe HA. Therefore, strategies targeting memory B-cell/plasmablast differentiation may have promising outcomes in the management of inhibitor formation in patients with severe HA.

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

INTRODUCTION

The development of anti-factor VIII (FVIII) antibodies or "inhibitors" is a major complication following FVIII replacement therapy in patients with severe hemophilia A (HA), rendering the treatment inefficient. Data on the role of regulatory T cells (Tregs) in inhibitor formation in these patients are rare. Herein, we aimed to investigate whether a difference in the FOXP3+ Tregs is linked to the formation of the inhibitors in severe HA patients.

METHODS

In this cross-sectional study, 32 patients with severe HA (8 patients with inhibitors and 24 without inhibitors) and 24 healthy controls were enrolled. The frequency of FOXP3+ Tregs was determined using multicolor flow cytometry method.

RESULTS

Our results showed that the median level of CD4+ CD25+ FOXP3+ Tregs did not significantly differ between HA patients and healthy controls and between HA patients with and without inhibitors (P > 0.05). However, patients with inhibitors had significantly lower amounts of CD4+ CD25- FOXP3+ Tregs compared to those without inhibitors as well as healthy controls (*P = 0.012 and *P = 0.004, respectively). The frequency of CD4+ CD25+ T cells was significantly higher in HA patients who developed inhibitors compared to the inhibitor-negative ones whereas they were lower in inhibitor-negative patients compared to the healthy controls (*P = 0.013 and *P = *0.029, respectively). The percentages of CD4+ CD25+ T cells were positively correlated with the levels of inhibitors in HA patients (r = 0.45, *P = 0.021).

CONCLUSION

Our data demonstrated for the first time that the CD4+ CD25- FOXP3+ Tregs might be implicated in the prevention of inhibitor formation in severe HA patients.

Strength training program for an athlete with hemophilia A and an inhibitor while taking a new prophylactic drug treatment: a case report

BACKGROUND

Currently, patients with hemophilia and inhibitor are being offered therapy, including a tissue factor pathway inhibitor (TFPI). The new prophylactic drug treatment may allow for new opportunities for other interventions and overall improvement in quality of life. This case report assessed the safety and effects of a strength training program in a patient with an inhibitor on a specific new study drug.

DESCRIPTION

A 20-year-old patient with severe hemophilia A with an inhibitor participated in a 6-week strength training program. The strengthening program consisted of 7 exercises involving limb and trunk muscles. A qualitative assessment of movement patterns was performed using the Functional Movement Test. Dynamic balance was measured by the Y-Balance Test, whereby the power of lower extremities was measured by Counter Movement Jump. The Quality of Life Index was done by survey to assess the perceived overall quality of the patient's life. The exercise fatigue after each training was measured with the Borg scale.

OUTCOMES

After the intervention during treatment with the new drug, the patient's quality of life increased, especially in terms of health and function (from 15.6 to 29.1 points), also, the power of the lower limbs increased. There were no bleeding episodes during the intervention and after a 3-month follow-up.

CONCLUSION

The proposed program during the application of the new prophylactic treatment seems to be effective in improving quality of life and increasing lower limb power in a hemophilic patient with an inhibitor. However, randomized clinical trials are needed to confirm the results.

Successful living donor liver transplantation in a patient with hemophilia A and factor VIII inhibitor: a case report with perioperative recommendations

Liver transplantation in patients with end-stage liver disease and coexisting hemophilia A has been described. Controversy exists over perioperative management of patients with factor VIII inhibitor predisposing patients to hemorrhage. We describe the case of a 58-year-old man with a history of hemophilia A and factor VIII inhibitor, eradicated with rituximab prior to living donor liver transplantation without recurrence of inhibitor. We also provide perioperative management recommendations from our successful multidisciplinary approach.

Emicizumab prophylaxis in haemophilia A with inhibitors: Three years follow-up from the UK Haemophilia Centre Doctors' Organisation (UKHCDO)

INTRODUCTION

The UK National Haemophilia Database (NHD) collects data from all UK persons with haemophilia A with inhibitors (PwHA-I). It is well-placed to investigate patient selection, clinical outcomes, drug safety and other issues not addressed in clinical trials of emicizumab.

AIMS

To determine safety, bleeding outcomes and early effects on joint health of emicizumab prophylaxis in a large, unselected cohort using national registry and patient reported Haemtrack (HT) data between 01 January 2018 and 30 September 2021.

METHODS

Prospectively collected bleeding outcomes were analysed in people with ≥6 months emicizumab HT data and compared with previous treatment if available. Change in paired Haemophilia Joint Health Scores (HJHS) were analysed in a subgroup. Adverse events (AEs) reports were collected and adjudicated centrally.

RESULTS

This analysis includes 117 PwHA-I. Mean annualised bleeding rate (ABR) was .32 (95% CI, .18; .39) over a median 42 months treatment with emicizumab. Within-person comparison (n = 74) demonstrated an 89% reduction in ABR after switching to emicizumab and an increase in zero treated bleed rate from 45 to 88% (p < .01). In a subgroup of 37 people, total HJHS improved in 36%, remained stable in 46% and deteriorated in 18%, with a median (IQR) within-person change of -2.0 (-9, 1.5) (p = .04). Three arterial thrombotic events were reported, two possibly drug related. Other AEs were generally non-severe and usually limited to early treatment, included cutaneous reactions (3.6%), headaches (1.4%), nausea (2.8%) and arthralgia (1.4%).

CONCLUSIONS

Emicizumab prophylaxis is associated with sustained low bleeding rates and was generally well-tolerated in people with haemophilia A and inhibitors.

BAY 81-8973 Efficacy and Safety in Previously Untreated and Minimally Treated Children with Severe Hemophilia A: The LEOPOLD Kids Trial

INTRODUCTION

 BAY 81-8973, a full-length recombinant factor VIII for hemophilia A treatment, has been extensively evaluated in previously treated patients in the LEOPOLD (Long-Term Efficacy Open-Label Program in Severe Hemophilia A Disease) clinical trials.

AIM

 To assess BAY 81-8973 efficacy and safety when used for bleed prophylaxis and treatment in previously untreated/minimally treated patients (PUPs/MTPs).

METHODS

 In this phase III, multicenter, open-label, uncontrolled study, PUPs/MTPs (<6 years old) with severe hemophilia A received BAY 81-8973 (15-50 IU/kg) at least once weekly as prophylaxis. Primary efficacy endpoint was the annualized bleeding rate (ABR) within 48 hours after prophylaxis infusion. Adverse events and immunogenicity were assessed. Patients who developed inhibitors were offered immune tolerance induction (ITI) treatment in an optional extension phase.

RESULTS

 Fifty-two patients were enrolled, with 43 patients (mean age: 13.6 months) treated. Median (interquartile range) ABR for all bleeds within 48 hours of prophylaxis infusion was 0.0 (0.0-1.8) among patients without inhibitors (n = 20) and 0.0 (0.0-2.2) among all patients. As expected, inhibitors were the most frequent treatment-related adverse event (high titer: 17 [39.5%] patients; low titer: 6 [13.9%] patients). Six of 12 patients who underwent ITI treatment in the extension phase (high titer [n = 5], low titer [n = 1]) achieved a negative inhibitor titer.

CONCLUSION

 BAY 81-8973 was effective for bleed prevention and treatment in PUPs/MTPs. The observed inhibitor rate was strongly influenced by a cluster of inhibitor cases, and consequently, slightly higher than in other PUP/MTP studies. Overall, the BAY 81-8973 benefit-risk profile remains unchanged and supported by ongoing safety surveillance. Immune tolerance can be achieved with BAY 81-8973.

Until programmed death do us tolerant

Healthy individuals are generally immunologically tolerant to proteins derived from one's self (termed self proteins). However, patients with monogenic clotting disorders, like hemophilia A (HemA), lack central tolerance to the absent self protein. Thus, when exposed to replacement therapy, such as procoagulant factor VIII, they may mount an immune response against the very self protein that is missing. In the current issue of the JCI, Becker-Gotot, Meissner, et al. present data on a possible mechanism for tolerance to factor VIII in healthy individuals and the immune response in patients, involving a role of PD-1 and T regulatory cells. The findings suggest that treatment with PD-1- and PD-1L-specific reagents may induce tolerance in patients with autoimmune disease, especially those with HemA who also possess inhibiting antibodies.

Immune tolerance against infused FVIII in hemophilia A is mediated by PD-L1+ Tregs

A major complication of hemophilia A therapy is the development of alloantibodies (inhibitors) that neutralize intravenously administered coagulation factor VIII (FVIII). Immune tolerance induction therapy (ITI) by repetitive FVIII injection can eradicate inhibitors, and thereby reduce morbidity and treatment costs. However, ITI success is difficult to predict and the underlying immunological mechanisms are unknown. Here, we demonstrated that immune tolerance against FVIII under nonhemophilic conditions was maintained by programmed death (PD) ligand 1-expressing (PD-L1-expressing) regulatory T cells (Tregs) that ligated PD-1 on FVIII-specific B cells, causing them to undergo apoptosis. FVIII-deficient mice injected with FVIII lacked such Tregs and developed inhibitors. Using an ITI mouse model, we found that repetitive FVIII injection induced FVIII-specific PD-L1+ Tregs and reengaged removal of inhibitor-forming B cells. We also demonstrated the existence of FVIII-specific Tregs in humans and showed that such Tregs upregulated PD-L1 in patients with hemophilia after successful ITI. Simultaneously, FVIII-specific B cells upregulated PD-1 and became killable by Tregs. In summary, we showed that PD-1-mediated B cell tolerance against FVIII operated in healthy individuals and in patients with hemophilia A without inhibitors, and that ITI reengaged this mechanism. These findings may impact monitoring of ITI success and treatment of patients with hemophilia A.

Engineering a Therapeutic Protein to Enhance the Study of Anti-Drug Immunity

The development of anti-drug antibodies represents a significant barrier to the utilization of protein-based therapies for a wide variety of diseases. While the rate of antibody formation can vary depending on the therapeutic employed and the target patient population receiving the drug, the antigen-specific immune response underlying the development of anti-drug antibodies often remains difficult to define. This is especially true for patients with hemophilia A who, following exposure, develop antibodies against the coagulation factor, factor VIII (FVIII). Models capable of studying this response in an antigen-specific manner have been lacking. To overcome this challenge, we engineered FVIII to contain a peptide (323-339) from the model antigen ovalbumin (OVA), a very common tool used to study antigen-specific immunity. FVIII with an OVA peptide (FVIII-OVA) retained clotting activity and possessed the ability to activate CD4 T cells specific to OVA323-339 in vitro. When compared to FVIII alone, FVIII-OVA also exhibited a similar level of immunogenicity, suggesting that the presence of OVA323-339 does not substantially alter the anti-FVIII immune response. Intriguingly, while little CD4 T cell response could be observed following exposure to FVIII-OVA alone, inclusion of anti-FVIII antibodies, recently shown to favorably modulate anti-FVIII immune responses, significantly enhanced CD4 T cell activation following FVIII-OVA exposure. These results demonstrate that model antigens can be incorporated into a therapeutic protein to study antigen-specific responses and more specifically that the CD4 T cell response to FVIII-OVA can be augmented by pre-existing anti-FVIII antibodies.

How to manage bleeding disorders in aging patients needing surgery

With improvements in medical care, the life expectancy of patients with bleeding disorders is approaching that of the general population. A growing population of older adult patients with bleeding disorders is at risk of age-related comorbidities and in need of various elective and emergent age-related procedures. The increased risk of thrombosis and volume overload in older adults complicates perioperative hemostatic management. Furthermore, antithrombotic treatment such as antiplatelet or anticoagulant therapy, which is frequently required for various cardiovascular interventions, requires a meticulous individualized approach. Evidence-based guidelines for the management of aging patients with bleeding disorders are lacking, largely due to the underrepresentation of older adult patients in clinical trials as well as the rarity of many such bleeding disorders. We discuss the current guidelines and recommendations in the perioperative hemostatic management of older adult patients with hemophilia and von Willebrand disease as well as other rare bleeding disorders. The optimal management of these patients is often complex and requires a thorough multidisciplinary and individualized approach involving hematologists, surgeons, anesthesiologists, and the specialists treating the underlying disorder.

Phage display broadly identifies inhibitor-reactive regions in von Willebrand factor

BACKGROUND

Correction of von Willebrand factor (VWF) deficiency with replacement products containing VWF can lead to the development of anti-VWF alloantibodies (i.e., VWF inhibitors) in patients with severe von Willebrand disease (VWD).

OBJECTIVE

Locate inhibitor-reactive regions within VWF using phage display.

METHODS

We screened a phage library displaying random, overlapping fragments covering the full-length VWF protein sequence for binding to a commercial anti-VWF antibody or to immunoglobulins from three type 3 VWD patients who developed VWF inhibitors in response to treatment with plasma-derived VWF. Immunoreactive phage clones were identified and quantified by next-generation DNA sequencing (NGS).

RESULTS

Next-generation DNA sequencing markedly increased the number of phages analyzed for locating immunoreactive regions within VWF following a single round of selection and identified regions not recognized in previous reports using standard phage display methods. Extending this approach to characterize VWF inhibitors from three type 3 VWD patients (including two siblings homozygous for the same VWF gene deletion) revealed patterns of immunoreactivity distinct from the commercial antibody and between unrelated patients, though with notable areas of overlap. Alloantibody reactivity against the VWF propeptide is consistent with incomplete removal of the propeptide from plasma-derived VWF replacement products.

CONCLUSION

These results demonstrate the utility of phage display and NGS to characterize diverse anti-VWF antibody reactivities.

Eptacog Beta for Bleeding Treatment and Prevention in Congenital Hemophilia A and B With Inhibitors: A Review of Clinical Data and Implications for Clinical Practice

OBJECTIVE

To review the pharmacology, dosing and administration, safety, clinical efficacy, and role of eptacog beta in the treatment of congenital hemophilia with inhibitors.

DATA SOURCES

A literature search of PubMed (1966 to August 2021) was conducted using the keywords eptacog beta, recombinant FVII, and hemophilia.

STUDY SELECTION AND DATA EXTRACTION

All relevant published articles and prescribing information on eptacog beta for the treatment of congenital hemophilia with inhibitors were reviewed.

DATA SYNTHESIS

Eptacog beta is a novel recombinant activated factor VII (rVIIa) product that demonstrated efficacy in controlling bleeding and associated pain in patients with hemophilia A or B with inhibitors. Eptacog beta has limited Food and Drug Administration-approved and off-label indications compared with other bypassing agents (BPAs; activated prothrombin complex concentrates [aPCC; eptacog alfa]). Eptacog beta costs less than eptacog alfa, but still more than aPCCs.

RELEVANCE TO PATIENT CARE AND CLINICAL PRACTICE

This review provides insight into the role of eptacog beta for treatment of congenital hemophilia with inhibitors and reviews important health system formulary considerations for available BPAs.

CONCLUSIONS

Eptacog beta is more cost-effective than eptacog alfa and, as such, may become the preferred rVIIa formulary product. However, eptacog alfa availability remains necessary for the treatment of disorders where eptacog beta has limited data. aPCC should remain the first-line BPA for the treatment of bleeding in patients with inhibitors with no contraindications to use because of its equivocal efficacy and safety and in light of the magnitude of cost savings associated with this strategy.

Risk factors for antibody formation in children with hemophilia: methodological aspects and clinical characteristics of the HEMFIL cohort study

Up to 35% of patients with hemophilia A and 5% with hemophilia B develop neutralizing antibodies which can inhibit the therapeutic activity of factor replacement (inhibitors). Despite the clinical relevance of antifactor VIII and IX neutralizing antibodies, there is still a major gap on the knowledge of risk factors for their development. Furthermore, most of the studies on risk factors for inhibitor development come from Caucasian and Afro-American populations. The HEMFIL is a Brazilian prospective cohort study of previously untreated children with hemophilia, which primary aim is to identify new risk factors related to inhibitor development. This manuscript aims at describing the study design and its methodology. After the diagnosis, children are followed up to 75 exposure days or to inhibitor development. Standardized forms and blood samples are collected to describe clinical characteristics and to perform the measurement of immunological and genetic biomarkers at three time points; Inclusion time (T0), at inhibitor development or at 75 exposure days without inhibitors (T1) and after immune tolerance induction for patients in whom it is indicated and performed (T2). Currently, 120 children have been included, of whom, 95 have completed the follow-up. For severe/moderately severe hemophilia A, the cumulative incidence of inhibitors at 75 exposure days was 35% (95% confidence interval, 26-46%). The inclusion of additional patients and a longer follow-up will allow the analysis of risk factors for inhibitor development.

Recent Advances in the Treatment of Hemophilia: A Review

Progress in hemophilia therapy has been remarkable in the first 20 years of the third millennium, but the innovation began with the description the fractionation of plasma in 1946. The first concentrates followed the discovery of FVIII in the cryoprecipitate of frozen plasma and FIX in the supernatant in the early 1960s, which led to the initial attempts at replacement therapy. Unfortunately, the lack of screening methods for viral pathogens resulted in people with hemophilia (PWH) receiving concentrates contaminated by hepatitis A virus, hepatitis C virus, and human immunodeficiency virus, as these concentrates were made from large industrial pools of plasma derived from thousands of donors. Fortunately, by 1985, viral screening methods and proper virucidal techniques were developed that made concentrates safe. Increasingly pure products followed the introduction of chromatography steps with monoclonal antibodies in the production process. The problem of immunogenicity of exogenously administered concentrates has not yet had a complete solution. The development of alloantibodies against FVIII in about 25-35% of PWH is the most serious adverse effect of replacement therapy. The next major advance followed the cloning of the F8 gene and later the F9 genes, which paved the way to produce concentrates of factors obtained by the recombinant DNA technology. The injected FVIII and FIX molecules had a relatively short circulating half-life in the plasma of people with hemophilia A and B, approximately 12 and 18 hours, respectively. The ability to prolong the plasma half-life and extend the interval between injections followed the application of methods to conjugate the factor molecule with the fragment crystallizable of IgG1 or albumin or by adding polyethylene glycol, which has led to an increase in the half-life of concentrates, especially for rFIX. The next frontier in hemophilia therapy is the application of durable and potentially curative therapies such as with gene addition therapy. Experiments in hemophilia B have demonstrated durable responses. Unfortunately, the results with gene therapy for hemophilia A have not been as remarkable and the durability must still be demonstrated. Nonetheless, the long-term safety, predictability, durability, and efficacy of gene therapy for hemophilia A and B remain an open question. At present, only healthy adult PWH have been enrolled in gene therapy clinical trials. The application of gene therapy to children and those with pre-existing antibodies against the delivery vector must also be studied before this therapy becomes widespread.

Non-Human Glycans Can Regulate Anti-FVIII Antibody Formation in Mice

Recombinant Factor VIII (FVIII) products represent a life-saving intervention for patients with hemophilia A. However, patients can develop antibodies against FVIII that prevent FVIII function and directly increase morbidity and mortality. The development of anti-FVIII antibodies varies depending on the type of recombinant product employed, with previous studies suggesting that 2nd generation baby hamster kidney (BHK)-derived FVIII products display greater immunogenicity than 3rd generation Chinese hamster ovary (CHO)-derived FVIII. However, the underlying mechanisms responsible for these differences remain incompletely understood. Our results demonstrate that BHK cells express higher levels of the non-human carbohydrate a1-3 galactose (aGal) than CHO cells, suggesting that aGal incorporation onto FVIII may result in anti-aGal antibody recognition that could positively influence the development of anti-FVIII antibodies. Consistent with this, BHK-derived FVIII exhibits increased levels of aGal, which corresponds to increased reactivity with anti-aGal antibodies. Infusion of BHK-derived, but not CHO-derived, FVIII into aGal knock out mice, which spontaneously generate anti-aGal antibodies, results in significantly higher anti-FVIII antibody formation, suggesting that the increased levels of aGal on BHK-derived FVIII can influence immunogenicity. These results suggest that post-translational modifications of recombinant FVIII products with non-human carbohydrates may influence the development of anti-FVIII antibodies.

Natural history study of factor IX deficiency with focus on treatment and complications (B-Natural)

INTRODUCTION

Haemophilia B (HB) is less well studied than haemophilia A (HA); despite similarities between the two inherited bleeding disorders, important differences remain that require further research.

AIM

B-Natural is a multi-centre, prospective, observational study of HB, designed to increase understanding of clinical manifestations, treatment, quality-of-life (QoL), inhibitor development, immune tolerance induction (ITI) outcome, renal function and create a biorepository for future investigations.

METHODS

Participants include sibling pairs/groups without a current/history of inhibitors and singletons or siblings with a current/history of inhibitors followed for six months. Demographics, medical, social history and treatment were recorded. A physical examination including joint range of motion (ROM) was performed; QoL was assessed. Samples were collected for F9 gene mutation, HLA typing, non-inhibitory antibodies and renal function testing.

RESULTS

Twenty-four centres enrolled 224 individuals from 107 families including 29 with current/history of inhibitors. Of these, 68, 30.4%, had severe (<1% FIX level of normal); 114, 50.9%, moderate (1%-5%); and 42, 18.8%, mild (>5-<40%) disease. At enrolment, 53.1% had 50 + exposure days to exogenous FIX. Comparison of joint scores showed significant (P < .05) differences between those with severe (with/without inhibitors), and those with moderate/mild disease. The majority with severe disease, 80.0% with current/history of inhibitors and 64.3% of those without, were treated with prophylaxis.

CONCLUSION

B-Natural provides data supporting an increased understanding of HB and its impact throughout life. The need for optimal disease control to normalize physical and psychosocial outcomes is underscored, and further analyses will contribute to an increased understanding of critical issues in HB.

Origins, Development, Current Challenges and Future Directions with Activated Prothrombin Complex Concentrate for the Treatment of Patients with Congenital Haemophilia with Inhibitors

Congenital haemophilia A (HA) is caused by deficiency of coagulation factor VIII (FVIII) activity, leading to spontaneous or traumatic bleeding events. While FVIII replacement therapy can treat and prevent bleeds, approximately 30% of patients with severe HA develop inhibitor antibodies that render FVIII replacement therapy ineffective. The bypassing agents (BPAs), activated prothrombin complex concentrate (aPCC) and recombinant activated FVII, first approved in 1977 and 1996, respectively, act to generate thrombin independent of pathways that involve factors IX and VIII. Both may be used in patients with congenital haemophilia and inhibitors (PwHIs) for the treatment and prevention of acute bleeds and quickly became standard of care. However, individual patients respond differently to different agents. While both agents are approved for on-demand treatment and perioperative management for patients with congenital haemophilia with inhibitors, aPCC is currently the only BPA approved worldwide for prophylaxis in PwHI. Non-factor therapies (NFTs) have a mechanism of action distinct from BPAs and have reported higher efficacy rates as prophylactic regimens. Nonetheless, treatment challenges remain with NFTs, particularly regarding the potential for synergistic action on thrombin generation with concomitant use of other haemostatic agents, such as BPAs, for the treatment of breakthrough bleeds and in perioperative management. Concomitant use of NFTs with other haemostatic agents could increase the risk of adverse events such as thromboembolic events or thrombotic microangiopathy. This review focuses on the origins, development and on-going role of aPCC in the evolving treatment landscape in the management of PwHI.

Assessing the Performance of Extended Half-Life Coagulation Factor VIII, FC Fusion Protein by Using Chromogenic and One-Stage Assays in Saudi Hemophilia A Patients

Background

The one-stage assay is the most common method to measure factor VIII activity (FVIII : C) in hemophilia A patients. The chromogenic assay is another two-stage test involving purified coagulation factors followed by factor Xa-specific chromogenic substrate.

Aim

This study aimed to assess the discrepancy and correlation between the chromogenic and one-stage assays in measuring FVIII : C levels in hemophilia patients receiving Extended Half-Life Elocta® as a recombinant extended half-life coagulation factor.

Methods

We performed a study comparing the measurements of FVIII : C levels by the chromogenic versus the one-stage assays at different drug levels. Data of FVIII : C levels, dosage, and the time interval from administration to measurement were retrieved from the hospital records. The correlation, mean differences, and discrepancy between the two assays were calculated. The linear regression analysis was used to predict the time interval till reaching 1% FVIII : C.

Results

Fourteen patients with 56 samples were included in the study. Of them, 13 patients were receiving Elocta® as a prophylactic, while one was receiving Elocta® on demand. One-third of these samples showed a discrepancy between the chromogenic and one-stage assays. The two assays were well correlated. Mean differences were significant at the individual and the time interval level. The time since the last Elocta® injection could significantly predict FVIII : C levels (β = 0.366, P < 0.001).

Conclusion

Our findings suggested a significant difference between both methods; the FVIII : C levels measured by the one-stage assay were less than those estimated by the chromogenic assay. However, the measurements of FVIII levels by the two assays were well correlated but discrepant in one-third of the samples. The levels of FVIII : C reach 1% after 5.4 days since the last Elocta® administration.

Synergistic Effect of Bypassing Agents and Sequence Identical Analogue of Emicizumab and Fibrin Clot Structure in the In Vitro Model of Hemophilia A

Development of inhibitors to factor VIII (FVIII) occurs in approximately 30% of severe hemophilia A (HA) patients. These patients are treated with bypassing agents (activated prothrombin complex concentrate [aPCC] and recombinant activated FVII-rFVIIa). Recently, a bispecific FIX/FIXa- and FX/FXa-directed antibody (emicizumab) has been approved for the treatment of HA patients with inhibitors. However, the data from clinical studies imply that coadministration of emicizumab and bypassing agents, especially aPCC, could have a thrombotic effect.

This study was aimed to address the question of potential hypercoagulability of emicizumab and bypassing agents' coadministration, we have investigated fibrin clot formation and structure in the in vitro model of severe HA after adding sequence-identical analogue (SIA) of emicizumab and bypassing agents.

Combined overall hemostasis potential (OHP) and fibrin clot turbidity assay was performed in FVIII-deficient plasma after addition of different concentrations of SIA, rFVIIa, and aPCC. Pooled normal plasma was used as control. The fibrin clots were analyzed by scanning electron microscopy (SEM).

OHP and turbidity parameters improved with the addition of aPCC, while therapeutic concentrations of rFVIIa did not show substantial improvement. SIA alone and in combination with rFVIIa or low aPCC concentration improved OHP and turbidity parameters and stabilized fibrin network, while in combination with higher concentrations of aPCC expressed hypercoagulable pattern and generated denser clots.

Our in vitro model suggests that combination of SIA and aPCC could potentially be prothrombotic, due to hypercoagulable changes in fibrin clot turbidity and morphology. Additionally, combination of SIA and rFVIIa leads to the formation of stable clots similar to normal fibrin clots.

Spontaneous subepithelial hemorrhage of renal pelvis and ureter (Antopol-Goldman lesion) in hemophilia A patient with inhibitor: Case report and review of the literature

INTRODUCTION

The Antopol-Goldman lesion (AGL), which expresses subepithelial hemorrhage in the renal pelvis, was first defined by Antopol and Goldman in 1948. The objective of this study is to report the first case of AGL in patients with congenital hemophilia and review the relevant literature.

PATIENT CONCERNS

A 32-year-old male patient diagnosed with congenital hemophilia A (FVIII = %4) with high responding inhibitors (7.4 BU) was admitted to our emergency department with gross hematuria and sudden onset flank pain.

DIAGNOSIS

Abdominal computed tomography (CT-scan) presented a hyperdense lesion in the left ureteropelvic junction with Hounsfield Units of 56 compatibles with hemorrhage.

INTERVENTIONS

The patient was given 4500 IU of factor eight inhibitor bypass activity (FEIBA) intravenously twice daily for 5 days. Subsequently, 4500 IU of FEIBA was administrated once a day for 2 days.

OUTCOMES

The patient's complaints disappeared on the fourth day of treatment. Macroscopic and microscopic hematuria was not seen in the following days. Follow-up CT was done 3 months after discharge and showed normal left renal pelvis without hyperdenosis. Follow-up CT was performed 3 months after discharge and presented normal left renal pelvis with no hyperdense lesion.

CONCLUSION

Although very rare, AGL should be kept in mind in the differential diagnosis of renal pelvic hemorrhage. In the patient who has an underlying history of coagulopathy nephrectomy can be avoided when there is awareness of AGL.

Fc Gamma Receptors and Complement Component 3 Facilitate Anti-fVIII Antibody Formation

Anti-factor VIII (fVIII) alloantibodies, which can develop in patients with hemophilia A, limit the therapeutic options and increase morbidity and mortality of these patients. However, the factors that influence anti-fVIII antibody development remain incompletely understood. Recent studies suggest that Fc gamma receptors (FcγRs) may facilitate recognition and uptake of fVIII by recently developed or pre-existing naturally occurring anti-fVIII antibodies, providing a mechanism whereby the immune system may recognize fVIII following infusion. However, the role of FcγRs in anti-fVIII antibody formation remains unknown. In order to define the influence of FcγRs on the development of anti-fVIII antibodies, fVIII was injected into WT or FcγR knockout recipients, followed by evaluation of anti-fVIII antibodies. Anti-fVIII antibodies were readily observed following fVIII injection into FcγR knockouts, with similar anti-fVIII antibody levels occurring in FcγR knockouts as detected in WT mice injected in parallel. As antibodies can also fix complement, providing a potential mechanism whereby anti-fVIII antibodies may influence anti-fVIII antibody formation independent of FcγRs, fVIII was also injected into complement component 3 (C3) knockout recipients in parallel. Similar to FcγR knockouts, C3 knockout recipients developed a robust response to fVIII, which was likewise similar to that observed in WT recipients. As FcγRs or C3 may compensate for each other in recipients only deficient in FcγRs or C3 alone, we generated mice deficient in both FcγRs and C3 to test for potential antibody effector redundancy in anti-fVIII antibody formation. Infusion of fVIII into FcγRs and C3 (FcγR × C3) double knockouts likewise induced anti-fVIII antibodies. However, unlike individual knockouts, anti-fVIII antibodies in FcγRs × C3 knockouts were initially lower than WT recipients, although anti-fVIII antibodies increased to WT levels following additional fVIII exposure. In contrast, infusion of RBCs expressing distinct alloantigens into FcγRs, C3 or FcγR × C3 knockout recipients either failed to change anti-RBC levels when compared to WT recipients or actually increased antibody responses, depending on the target antigen. Taken together, these results suggest FcγRs and C3 can differentially impact antibody formation following exposure to distinct alloantigens and that FcγRs and C3 work in concert to facilitate early anti-fVIII antibody formation.

Immunogenicity of Protein Therapeutics: A Lymph Node Perspective

The continuous development of molecular biology and protein engineering technologies enables the expansion of the breadth and complexity of protein therapeutics for in vivo administration. However, the immunogenicity and associated in vivo development of antibodies against therapeutics are a major restriction factor for their usage. The B cell follicular and particularly germinal center areas in secondary lymphoid organs are the anatomical sites where the development of antibody responses against pathogens and immunogens takes place. A growing body of data has revealed the importance of the orchestrated function of highly differentiated adaptive immunity cells, including follicular helper CD4 T cells and germinal center B cells, for the optimal generation of these antibody responses. Understanding the cellular and molecular mechanisms mediating the antibody responses against therapeutics could lead to novel strategies to reduce their immunogenicity and increase their efficacy.

Treatment of Hemophilia A Using Factor VIII Messenger RNA Lipid Nanoparticles

Hemophilia A (HemA) patients are currently treated with costly and inconvenient replacement therapy of short-lived factor VIII (FVIII) protein. Development of lipid nanoparticle (LNP)-encapsulated mRNA encoding FVIII can change this paradigm. LNP technology constitutes a biocompatible and scalable system to efficiently package and deliver mRNA to the target site. Mice intravenously infused with the luciferase mRNA LNPs showed luminescence signals predominantly in the liver 4 h after injection. Repeated injections of LNPs did not induce elevation of liver transaminases. We next injected LNPs carrying mRNAs encoding different variants of human FVIII (F8 LNPs) into HemA mice. A single injection of B domain-deleted F8 LNPs using different dosing regimens achieved a wide range of therapeutic activities rapidly, which can be beneficial for various usages in hemophilia treatment. The expression slowly declined yet remained above therapeutic levels up to 5–7 days post-injection. Furthermore, routine repeated injections of F8 LNPs in immunodeficient mice produced consistent expression of FVIII over time. In conclusion, F8 LNP treatment produced rapid and prolonged duration of FVIII expression that could be applied to prophylactic treatment and potentially various other treatment options. Our study showed potential for a safe and effective platform of new mRNA therapies for HemA.

Investigating the influence of LCT rs3754689 polymorphism on inhibitor development in Iranian and Afghan patients with severe hemophilia A

: Development of alloantibodies against factor VIII (FVIII) in patients with severe hemophilia A is the main complication of FVIII replacement therapy. There are many studies indicating several genetic factors associated with inhibitor development. A recent study showed that there is a correlation between the risk of inhibitor development and LCT rs3754689 polymorphism among Italian hemophilia A patients. The aim of this study was to speculate whether LCT rs3754689 polymorphism is correlated to inhibitor development in Afghan and Iranian patients. In addition, we assessed the association of F8 gene mutations and inhibitor development in Iranian patients. This case-control study was conducted on 33 severe hemophilia A patients with inhibitor and 119 samples without inhibitor. Genotyping was performed by Sanger sequencing, inverse and multiplex PCR. According to the obtained data, we found a significant correlation between LCT rs3754689 polymorphism and the risk of inhibitor development in Afghan patients (observed risk, 0.11; 95% confidence interval, 0.01-0.88; P = 0.012). Among Iranian patients, rs3754689 polymorphism showed no significant association with inhibitor development against FVIII (P > 0.05). However, we found a significant correlation between the risk of inhibitor formation and large deletions and nonsense mutations in F8 gene among Iranian patients (observed risk, 7.25; 95% confidence interval, 1.93-27.18; P = 0.003). Lack of association of rs3754689 polymorphism in Iranian population shows the various effects of genetic markers in different populations. More studies in different ethnicities or larger sample sizes are recommended.

Plant cell-made protein antigens for induction of Oral tolerance

The gut associated lymphoid tissue has effective mechanisms in place to maintain tolerance to food antigens. These can be exploited to induce antigen-specific tolerance for the prevention and treatment of autoimmune diseases and severe allergies and to prevent serious immune responses in protein replacement therapies for genetic diseases. An oral tolerance approach for the prevention of peanut allergy in infants proved highly efficacious and advances in treatment of peanut allergy have brought forth an oral immunotherapy drug that is currently awaiting FDA approval. Several other protein antigens made in plant cells are in clinical development. Plant cell-made proteins are protected in the stomach from acids and enzymes after their oral delivery because of bioencapsulation within plant cell wall, but are released to the immune system upon digestion by gut microbes. Utilization of fusion protein technologies facilitates their delivery to the immune system, oral tolerance induction at low antigen doses, resulting in efficient induction of FoxP3⁺ and latency-associated peptide (LAP)⁺ regulatory T cells that express immune suppressive cytokines such as IL-10. LAP and IL-10 expression represent potential biomarkers for plant-based oral tolerance. Efficacy studies in hemophilia dogs support clinical development of oral delivery of bioencapsulated antigens to prevent anti-drug antibody formation. Production of clinical grade materials in cGMP facilities, stability of antigens in lyophilized plant cells for several years when stored at ambient temperature, efficacy of oral delivery of human doses in large animal models and lack of toxicity augur well for clinical advancement of this novel drug delivery concept.

Safety of recombinant coagulation factors in treating hemophilia

INTRODUCTION

During the last decade, new FVIII/IX concentrates have been developed for the treatment of patients affected by hemophilia A/B. Significant progress has been achieved regarding their half-life, but the old issue of immunogenicity and new concerns about safety need to be addressed.

AREAS COVERED

After the implementation of virucidal methods, both plasma-derived and recombinant clotting factor concentrates achieved a very safe profile. The development of anti-FVIII antibodies is the major adverse event of replacement therapy with both FVIII concentrates. Furthermore, the new extended half-life concentrates, protein fused or pegylated, raised some concerns about their side effects.

EXPERT OPINION

The treatment of hemophilia A with inhibitors by induction of immunotolerance and using by-passing concentrates, improved the quality of life of patients but did not allow them to have a life expectancy like that of patients without inhibitors. The new humanized monoclonal antibody (MAb) ACE910, mimicking FVIII function, seems to be able to reduce the bleedings of hemophilia A patients with inhibitors. The post-marketing surveillance will clarify if the adverse events observed during the phase III clinical trials and compassionate use were due to the association with a Prothrombin activated complex concentrate or to the prothrombotic effect of the drug itself.

New therapies using nonfactor products for patients with hemophilia and inhibitors

Regular prophylaxis with factor VIII (FVIII) or FIX products to prevent bleeding in patients with severe hemophilia A (HA) and HB, respectively, results in marked suppression of the onset of arthropathy and contributes greatly to improvements in quality of life. Some issues remain with the use of clotting factor replacement therapy, however. The need for multiple IV infusions is associated with a substantial mental and physical burden, and the hemostatic effect of bypassing agents (BPAs) in patients with inhibitor is inconsistent. The development of subcutaneous products with prolonged hemostatic efficiency, irrespective of the presence of inhibitors, has been a longtime wish for patients. A new class of therapeutic agents that act by enhancing coagulation (emicizumab) and inhibiting anticoagulant pathways (fitusiran and concizumab) have been established, and clinical trials using these nonfactor products are ongoing. The current findings have demonstrated that prophylaxis by nonfactor products supports marked reductions of bleeding episodes in hemophilia patients with or without inhibitor. Emicizumab has already been approved for use internationally. Some concerns are evident, however. Thrombotic microangiopathy and thromboembolism have occurred in 5 emicizumab-treated patients receiving repeated infusions of activated prothrombin complex concentrates, and a sinus vein thrombosis has occurred in a fitusiran-treated patient receiving repeated infusions of FVIII product. Moreover, reliable techniques to monitor hemostatic function in patients receiving nonfactor products with concomitant BPA or FVIII/FIX therapies require further assessment. These novel therapeutic agents have promising hemostatic properties, although wider experience in hemophilia centers is warranted to establish appropriate therapeutic strategies.

The effect of emicizumab prophylaxis on health-related outcomes in persons with haemophilia A with inhibitors: HAVEN 1 Study

INTRODUCTION

Persons with haemophilia A (PwHA) with inhibitors to factor VIII often experience decreased health-related outcomes. In HAVEN 1 (NCT02622321), there was a statistically significant reduction in bleeding with emicizumab prophylaxis versus no prophylaxis.

AIM

Describe health-related outcomes in PwHA with inhibitors in HAVEN 1.

METHODS

PwHA with inhibitors aged ≥12 years previously on episodic bypassing agents (BPAs) were randomized to emicizumab prophylaxis (Arm A; n = 35) or no prophylaxis (Arm B; n = 18); participants previously on BPA prophylaxis received emicizumab prophylaxis (Arm C; n = 49). Health-related outcomes assessed at baseline and monthly thereafter: Haemophilia Quality of Life Questionnaire for Adults (Haem-A-QoL), Haemophilia-specific Quality of Life Questionnaire for Children Short Form (Haemo-QoL SF), EuroQol 5-Dimensions 5-Levels (EQ-5D-5L) index utility score (IUS) and visual analogue scale (EQ-VAS) and work/school days. Days hospitalized also recorded.

RESULTS

At week 25, differences (ANCOVA) in adjusted mean scores (95% confidence interval) favoured Arm A versus B for Haem-A-QoL "Total" score (14.0 [5.6, 22.5]; P = 0.002) and "Physical Health" (21.6 [7.9, 35.2]; P = 0.003); EQ-VAS (-9.7 [-17.6, -1.82]; P = 0.017); and IUS (-0.16 [-0.25, -0.07]; P = 0.001); mean scores are comparable in Arms A and C. Throughout the study, a greater proportion of participants on emicizumab prophylaxis than no prophylaxis exceeded questionnaire-specific responder thresholds. Mean proportion of missed work days and number of days hospitalized were lower with emicizumab prophylaxis than no prophylaxis.

CONCLUSIONS

In PwHA with inhibitors, emicizumab prophylaxis was associated with substantial and meaningful improvements in health-related outcomes.

Identification of serpins specific for activated protein C using a lysate-based screening assay

Activated protein C (APC) is a powerful anticoagulant enzyme that proteolytically inactivates the cofactors of the Xase and prothrombinase complexes, factors VIIIa and Va. A common mutation in factor V, fV_Leiden, confers resistance to APC leading to an increased risk of thrombosis in the normal population. However, when coinherited with haemophilia, fV_Leiden reduces bleeding severity, suggesting that inhibition of APC may be a useful strategy for treatment of haemophilia. We previously reported on serpins that were rationally designed for improved specificity for APC over other coagulation serine proteases. Based on structural differences in the substrate binding pockets to either side of the P1 Arg, we mutated the P2 and P1' residues to Lys. Although this approach achieved APC specificity, it resulted in a reduction in the rate of APC inhibition relative to the parent containing only the P1 Arg. Here we conduct site-specific random mutagenesis at the P2 and P1' positions to determine if improvements could be made in the rate of APC inhibition. In addition to our original Lys mutations, we found that Arg and Gln also confer specificity for APC. However, in all cases specificity for APC resulted in a reduction in inhibition rate.

Epitope mapping via selection of anti-FVIII antibody-specific phagepresented peptide ligands that mimic the antibody binding sites

The most serious complication in today’s treatment of congenital haemophilia A is the development of neutralising antibodies (inhibitors) against factor VIII (FVIII). Although FVIII inhibitors can be eliminated by immune tolerance induction (ITI) based on repeated administration of high doses of FVIII, 20–30% of patients fail to become tolerant. Persistence of FVIII inhibitors is associated with increased morbidity and mortality. Data from recent studies provide evidence for a potential association between ITI outcome and epitope specificity of FVIII inhibitors. Nevertheless the determination of epitopes and their clinical relevance has not yet been established. In this study a general strategy for the identification of anti-FVIII antibody epitopes in haemophilia A patient plasma was to be demonstrated. Phage-displayed peptide libraries were screened against anti-FVIII antibodies to isolate specific peptides. Peptide specificity was confirmed by FVIII-sensitive ELISA binding. Peptide residues essential for antibody binding were identified by mutational analysis and epitopes were predicted via FVIII homology search. The proposed mapping strategy was validated for the monoclonal murine antibody (mAb) 2–76. Binding studies with FVIII variants confirmed the location of the predicted epitope at the level of individual amino acids. In addition, anti-FVIII antibody-specific peptide ligands were selected for 10 haemophilia A patients with FVIII inhibitors. Detailed epitope mapping for three of them showed binding sites on the A2, A3 and C2 domains. Precise epitope mapping of anti-FVIII antibodies using antibody-specific peptide ligands can be a useful approach to identify antigenic sites on FVIII.

Prospective surveillance study of haemophilia A patients switching from moroctocog alfa or other factor VIII products to moroctocog alfa albumin-free cell culture (AF-CC) in usual care settings

This prospective, open-label, postauthorisation safety surveillance study assessed clinically significant inhibitor development in patients with severe haemophilia A transitioning from moroctocog alfa or other factor VIII (FVIII) replacement products to reformulated moroctocog alfa (AF-CC). Males aged12 years with severe haemophilia A (FVIII:C) < 1 IU/dl), > 150 exposure days (EDs) to recombinant or plasma-derived FVIII products, and no detectable inhibitor at screening were enrolled. Primary end point was the incidence of clinically significant FVIII inhibitor development. Secondary end points included annualised bleeding rate (ABR), less-than-expected therapeutic effect (LETE), and FVIII recovery. Patients were assigned to one of two cohorts based on whether they were transitioning to moroctocog alfa (AF-CC) from moroctocog alfa (cohort 1; n=146) or from another recombinant or plasma-derived FVIII product (cohort 2; n=62). Mean number of EDs on study was 94 (range, 1–139). Six positive FVIII inhibitor results, as determined by local laboratories, were reported in four patients; none were confirmed by a central laboratory, no inhibitor-related clinical manifestations were reported, and all anti-FVIII antibody assays were negative. Median ABRs were 23.4 and 3.4 in patients categorised at baseline as following on-demand and prophylactic regimens, respectively; 86.5 % of bleeding episodes resolved after one infusion. LETE incidence was 0.06 % and 0.19 % in the on-demand and prophylaxis settings, respectively. FVIII recovery remained constant throughout the study. No new safety concerns were identified. This study found no increased risk of clinically significant FVIII inhibitor development in patients transitioning from moroctocog alfa or other FVIII replacement products to moroctocog alfa (AF-CC).

Prevalence and epitope specificity of non-neutralising antibodies in a large cohort of haemophilia A patients without inhibitors

Antibodies (inhibitors and non-neutralising antibodies [NNA]) directed against factor VIII (FVIII) remain the main iatrogenic complication in haemophilia A (HA) patients. Inhibitors reduce FVIII procoagulant properties, whereas NNA are directed against non-functional epitopes. NNA are poorly studied and their prevalence, epitope specificity and physiopathology inadequately defined. The aim of this study was first to evaluate NNA prevalence in a French retrospective multicentric series of 210 patients without inhibitors, then to determine their epitope specificity (against the heavy chain [HC] or the light chain [LC] of FVIII) and particularly to assess the prevalence of anti-B domain NNA using specifically designed x-MAP assays. NNA occurred in 18.1% of patients (38/210) and their prevalence was not influenced by the severity of the disease. Among the 38 patients with NNA, 73.7% had anti-FVIII Abs against the HC, 13.2% against the LC and 13.2% had anti-FVIII Abs against both chains. There is thus a clear immuno-dominance of the HC of FVIII in the epitope profile of NNA, whatever the severity of HA. The proportion of NNA that recognised the B domain was 18.4% (n=7/38). A multivariate analysis did not highlight differences in NNA occurrence between patients treated with recombinant FVIII or with plasma-derived FVIII (19.6% vs. 14.9%, p=0.53).

Complement C3 is a novel modulator of the anti-factor VIII immune response

Development of neutralizing antibodies against therapeutic Factor VIII (FVIII) is the most serious complication of the treatment of hemophilia A. There is growing evidence to show the multifactorial origin of the anti-FVIII immune response, combining both genetic and environmental factors. While a role for the complement system on innate as well as adaptive immunity has been documented, the implication of complement activation on the onset of the anti-FVIII immune response is unknown. Here, using in vitro assays for FVIII endocytosis by human monocyte-derived dendritic cells and presentation to T cells, as well as in vivo complement depletion in FVIII-deficient mice, we show a novel role for complement C3 in enhancing the immune response against therapeutic FVIII. In vitro, complement C3 and its cleavage product C3b enhanced FVIII endocytosis by dendritic cells and presentation to a FVIII-specific CD4⁺ T-cell hybridoma. The C1 domain of FVIII had previously been shown to play an important role in FVIII endocytosis, and alanine substitutions of the K2092, F2093 and R2090 C1 residues drastically reduce FVIII uptake in vitro. Interestingly, complement activation rescued the endocytosis of the FVIII C1 domain triple mutant. In a mouse model of severe hemophilia A, transient complement C3 depletion by humanized cobra venom factor, which does not generate anaphylatoxin C5a, significantly reduced the primary anti-FVIII immune response, but did not affect anti-FVIII recall immune responses. Taken together, our results suggest an important adjuvant role for the complement cascade in the initiation of the immune response to therapeutic FVIII.

Simoctocog alfa for the treatment of hemophilia A

INTRODUCTION

Hemophilia A is the most frequent inherited bleeding disorder and most challenging coagulation disorder. To combat this, a number of new improved rFVIII/IX concentrates have recently been approved. Some of them are derived from protein fusion biotechnology or pegylation to extend their half-life (HL). However, prophylaxis has become a standard of care to prevent arthropathy in hemophiliacs though the need of frequent venipunctures is a major obstacle to primary prophylaxis. The new Extended Half-Life (EHL) rFIX concentrates allow increased intervals, while the improved HL of new rFVIII was moderate. rFVIII Simoctocog alfa is produced in Human Embryonic Kidney (HEK) cells and the post-translational modifications performed by HEK cells are very similar to those occurring in the native FVIII. Areas covered: Herein, the author provides a review of simoctocog alfa with its contents including information on simoctocog alfa's manufacturing, clinical trials, safety and tolerability. They also give their expert opinion and future perspectives on this therapy. Expert opinion: An important advantage of simoctocog alfa is the possibility to omit at least 30% of venipunctures with prophylaxis. Consequently, the standard three times weekly bolus administrations may be reduced to twice weekly, meaning approximately 50 fewer venipunctures per year. This may be particularly helpful to children.

Marginal zone B cells are critical to factor VIII inhibitor formation in mice with hemophilia A

Although factor VIII (FVIII) replacement therapy can be lifesaving for patients with hemophilia A, neutralizing alloantibodies to FVIII, known as inhibitors, develop in a significant number of patients and actively block FVIII activity, making bleeding difficult to control and prevent. Although a variety of downstream immune factors likely regulate inhibitor formation, the identification and subsequent targeting of key initiators in inhibitor development may provide an attractive approach to prevent inhibitor formation before amplification of the FVIII immune response occurs. As the initial steps in FVIII inhibitor development remain incompletely understood, we sought to define early regulators of FVIII inhibitor formation. Our results demonstrate that FVIII localizes in the marginal sinus of the spleen of FVIII-deficient mice shortly after injection, with significant colocalization with marginal zone (MZ) B cells. FVIII not only colocalizes with MZ B cells, but specific removal of MZ B cells also completely prevented inhibitor development following FVIII infusion. Subsequent rechallenge with FVIII following MZ B-cell reconstitution resulted in a primary antibody response, demonstrating that MZ B-cell depletion did not result in FVIII tolerance. Although recipient exposure to the viral-like adjuvant polyinosinic:polycytidylic acid enhanced anti-FVIII antibody formation, MZ B-cell depletion continued to display similar effectiveness in preventing inhibitor formation following FVIII infusion in this inflammatory setting. These data strongly suggest that MZ B cells play a critical role in initiating FVIII inhibitor formation and suggest a potential strategy to prevent anti-FVIII alloantibody formation in patients with hemophilia A.

Anti-FcγRIIB (CD32) Antibodies Differentially Modulate Murine FVIII-Specific Recall Response in vitro

Fc gamma receptors (FcγRs) for IgG regulate adaptive immune responses by modulating activating and inhibitory signalling pathways within immune cells. Data from a haemophilia A mouse model demonstrate that genetic deletion or blockade of the inhibitory FcγR (CD32) suppresses the formation of antibody-secreting cells (ASCs) in vitro. Mechanisms preventing the FVIII-specific recall response, however, remain unclear. Here, the potential role of CD32 inhibition was studied by differentially modulating receptor activity with selected anti-CD32 monoclonal antibodies (mAbs). Splenocytes from immunized FVIII^-/- mice were restimulated with FVIII in the absence or presence of different anti-CD32 mAbs over 6 days. At day 6, cytokine release was quantified from cell culture supernatant and the formation of FVIII-specific ASCs assessed. Binding of FVIII-containing immune complexes (F8-ICs) to bone marrow-derived dendritic cells (BMdDCs) was also investigated. The antagonistic CD32 mAb AT128 suppressed the formation of FVIII-specific ASCs and reduced secretion of IFN-γ and IL-10. In contrast, the agonistic mAbs AT130-2 and AT130-5, and their F(ab')₂ fragments, allowed the formation of FVIII-specific ASCs, even though the full IgG of AT130-2 reduced binding of F8-ICs to CD32. Data suggest that an inhibitory signal is transmitted when F8-ICs bind to CD32 and that this signal is required during memory B cell (MBC) activation to support formation of FVIII-specific ASCs. If the inhibitory signal is lacking due to CD32 deletion or blockade with antagonistic anti-CD32 mAbs, FVIII-specific T cell stimulation and ASC formation are suppressed, whereas agonistic stimulation of CD32 restores T cell stimulation and ASC formation.

CD32 inhibition and high dose of rhFVIII suppress murine FVIII-specific recall response by distinct mechanisms in vitro

Development of neutralising antibodies (inhibitors) against factor VIII (FVIII) is a frequent and severe complication of replacement therapy in haemophilia A. Previous data from haemophilia A mouse model demonstrates that both CD32 inhibition and high doses of rhFVIII prevent the differentiation of FVIII-specific memory B cells (MBCs) into antibody secreting cells (ASCs). Here, cellular targets responsible for the suppression of ASC formation by means of CD32 inhibition and high dose of rhFVIII were analysed. We investigated apoptosis on FVIII-specific MBCs using a pan caspases inhibitor, and screened for defects in rhFVIII presentation by analysing T cell release of Th1- and Th2-cytokines in vitro. Although high dose of rhFVIII suppressed ASC formation, cytokine response was not affected. Upon re-stimulation of splenocytes with high dose of rhFVIII, prevention of apoptosis fully restored the FVIII-specific recall response. In contrast, genetic deletion or inhibition of CD32 significantly altered Th1- and Th2-response. CD32 blockade and inhibition of apoptosis resulted in a partial rescue of FVIII-specific ASCs. Normal cytokine secretion could not be restored. In conclusion, suppression of FVIII-specific recall response by CD32 and high doses of rhFVIII is mediated by distinct mechanisms. High dose of rhFVIII induces apoptosis in FVIII-specific MBCs but does not influence FVIII-specific T cell response. CD32 blockade, however, may suppress the FVIII-specific recall response by two ways: i) increasing apoptosis of FVIII-specific MBCs and ii) disturbing FVIII-specific T cell response by modulating presentation of rhFVIII to CD4⁺ T cells in vitro.

Targeting factor VIII expression to platelets for hemophilia A gene therapy does not induce an apparent thrombotic risk in mice

Essentials Platelet-Factor (F) VIII gene therapy is a promising treatment in hemophilia A. This study aims to evaluate if platelet-FVIII expression would increase the risk for thrombosis. Targeting FVIII expression to platelets does not induce or elevate thrombosis risk. Platelets expressing FVIII are neither hyper-activated nor hyper-responsive.

SUMMARY

Background Targeting factor (F) VIII expression to platelets is a promising gene therapy approach for hemophilia A, and is successful even in the presence of inhibitors. It is well known that platelets play important roles not only in hemostasis, but also in thrombosis and inflammation. Objective To evaluate whether platelet-FVIII expression might increase thrombotic risk and thereby compromise the safety of this approach. Methods In this study, platelet-FVIII-expressing transgenic mice were examined either in steady-state conditions or under prothrombotic conditions induced by inflammation or the FV Leiden mutation. Native whole blood thrombin generation assay, rotational thromboelastometry analysis and ferric chloride-induced vessel injury were used to evaluate the hemostatic properties. Various parameters associated with thrombosis risk, including D-dimer, thrombin-antithrombin complexes, fibrinogen, tissue fibrin deposition, platelet activation status and activatability, and platelet-leukocyte aggregates, were assessed. Results We generated a new line of transgenic mice that expressed 30-fold higher levels of platelet-expressed FVIII than are therapeutically required to restore hemostasis in hemophilic mice. Under both steady-state conditions and prothrombotic conditions induced by lipopolysaccharide-mediated inflammation or the FV Leiden mutation, supratherapeutic levels of platelet-expressed FVIII did not appear to be thrombogenic. Furthermore, FVIII-expressing platelets were neither hyperactivated nor hyperactivatable upon agonist activation. Conclusion We conclude that, in mice, more than 30-fold higher levels of platelet-expressed FVIII than are required for therapeutic efficacy in hemophilia A are not associated with a thrombotic predilection.

F376A/M388A-solulin, a new promising antifibrinolytic for severe haemophilia A

INTRODUCTION

Haemophilia is a major bleeding disorder due to a deficiency of procoagulant factor VIII (type A) or IX (type B). The treatment is substitutive and based on infusion of factor concentrates. Main limitations of this therapy are cost, short factor half-life and the development of inhibitors (up to 30% of severe HA patients). An important aggravating factor of haemophilia is due to a premature fibrinolysis, directing attention to the therapeutic potential of suitable antifibrinolytics. Thrombomodulin (TM) is a key player of the coagulation cascade by activating protein C (an inhibitor of thrombin generation, thus antagonizing coagulation) and of the fibrinolytic cascade by activating thrombin activatable fibrinolysis inhibitor TAFI (thus reducing fibrinolysis). Solulin is a soluble form of TM that shows both capabilities.

AIM

Here, we developed a new generation of solulin variants (F376A-, M388A- and F376A/M388A-solulin) with a decreased ability to activate protein C and a conserved capacity to activate TAFI.

METHODS

We produced and characterized solulin variants in vitro. In addition, F376A/M388A-solulin was tested ex vivo, using blood samples of haemophilic A patients, with thromboelastography.

RESULTS

The solulin variants (F376A, M388A and the double-mutant F376A/M388A) lost their abilities to activate protein C but are still capable to activate TAFI. Thrombelastography showed increased clot firmness and stability, that, as opposed to wild-type solulin, was maintained even at high concentrations of F376A/M388A-solulin (100 nm).

CONCLUSION

In sum, these results open new opportunities for the development of specific medication for haemophilic patients.