Advances in bypassing agent therapy for hemophilia patients with inhibitors to close care gaps and improve outcomes

AAV mediated genome engineering with a bypass coagulation factor alleviates the bleeding phenotype in a murine model of hemophilia B

It is crucial to develop a long-term therapy that targets hemophilia A and B, including inhibitor-positive patients. We have developed an Adeno-associated virus (AAV) based strategy to integrate the bypass coagulation factor, activated FVII (murine, mFVIIa) gene into the Rosa26 locus using Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/Cas9 mediated gene-editing. AAV vectors designed for expression of guide RNA (AAV8-gRNA), Cas9 (AAV2 neddylation mutant-Cas9), and mFVIIa (AAV8-mFVIIa) flanked by homology arms of the target locus were validated in vitro. Hemophilia B mice were administered with AAV carrying gRNA, Cas9 (1 × 1011 vgs/mouse), and mFVIIa with homology arms (2 × 1011 vgs/mouse) with appropriate controls. Functional rescue was documented with suitable coagulation assays at various time points. The data from the T7 endonuclease assay revealed a cleavage efficiency of 20-42 %. Further, DNA sequencing confirmed the targeted integration of mFVIIa into the safe-harbor Rosa26 locus. The prothrombin time (PT) assay revealed a significant reduction in PT in mice that received the gene-editing vectors (22 %), and a 13 % decline in mice that received only the AAV-FVIIa when compared to mock treated mice, 8 weeks after vector administration. Furthermore, FVIIa activity in mice that received triple gene-editing vectors was higher (122.5mIU/mL vs 28.8mIU/mL) than the mock group up to 15 weeks post vector administration. A hemostatic challenge by tail clip assay revealed that hemophilia B mice injected with only FVIIa or the gene-editing vectors had significant reduction in blood loss. In conclusion, AAV based gene-editing facilitates sustained expression of coagulation FVIIa and phenotypic rescue in hemophilia B mice.

Acquired Hemophilia A: Bleeding Pattern and Hemostatic Therapeutic Strategies

Acquired Hemophilia A (AHA) is a rare autoimmune disorder characterized by the onset of a sudden and unexpected bleeding episode in a patient with no personal or family history of bleeding diathesis, and with a typical laboratory feature, i.e., a prolonged activated partial thromboplastin time that is not otherwise explained. This bleeding disorder is caused by autoantibodies directed against the coagulation factor VIII (FVIII). AHA is idiopathic in 50% of cases and is secondary to well-defined diseases in the remaining 50%. AHA affects elderly patients although it has also been observed in the post-partum period. Bleeding manifestations are heterogeneous, ranging from mild to life-threatening bleeds involving limbs and organs. Severe bleeding with a significant decrease in hemoglobin levels must be promptly and adequately treated in order to avoid a worsening of the hemorrhages and their complications. According to international recommendations, the bypass agents (i.e., activated prothrombin complex concentrate and activated recombinant factor VII) and the replacement therapy with recombinant porcine FVIII are considered as the first-line therapy for bleeding control, due to their proven clinical efficacy. Plasma-derived or recombinant FVIII concentrates could be used as second-line treatments. Emicizumab may represent a valid and interesting therapeutic option for prophylaxis of bleeding recurrences.

Determinants of successful immune tolerance induction in hemophilia A: systematic review and meta-analysis

Background

Immune tolerance induction (ITI) aims to eradicate anti-factor VIII (FVIII) antibodies (inhibitors) in persons with hemophilia A. However, this burdensome treatment fails in 10% to 40%. To estimate the chance of ITI success in clinical decision making, it is important to identify the predictors of ITI success.

Objectives

We performed a systematic review and meta-analysis to summarize the current evidence on determinants of ITI outcome in persons with hemophilia A.

Methods

A literature search was conducted to identify randomized controlled trials, cohort, or case-control studies reporting on the predictors for ITI outcome in persons with hemophilia A. The main outcome was ITI success. Methodological quality was assessed using an adapted Joanna Briggs Institute checklist, rating as high if ≥11 of 13 criteria were met. Pooled odds ratios (ORs) for ITI success were calculated for each determinant. ITI success was defined as negative inhibitor titer (<0.6 BU/mL), FVIII recovery ≥66% of expected, and FVIII half-life ≥6 hours in 16 (59.3%) studies.

Results

We included 27 studies, involving 1,734 participants. Methodological quality of 6 (22.2%) studies (418 participants) was rated as high. Twenty different determinants were assessed. Historical peak titer ≤100 BU/mL (compared with >100 BU/mL, OR, 1.7; 95% CI, 1.4-2.1), pre-ITI titer ≤10 BU/mL (compared with >10 BU/mL, OR, 1.8; 95% CI, 1.4-2.3), and peak titer during ITI ≤100 BU/mL (compared with >100 BU/mL, OR, 2.7; 95% CI, 1.9-3.8) were associated with a higher chance of ITI success.

Conclusion

Our results suggest that determinants related to the inhibitor titer are associated with ITI success.

Safety evaluation of emicizumab prophylaxis in individuals with haemophilia A

INTRODUCTION

Emicizumab is a bispecific-humanized monoclonal antibody that improves hemostasis by bridging activated factor IX and factor X to substitute for the function of missing activated FVIII. It is an alternative to prophylaxis with factor VIII replacement and is associated with improved outcomes in individuals with hemophilia A with and without inhibitors.

AREAS COVERED

Emicizumab is efficacious in reducing bleeding events when compared to on-demand treatment and factor-based prophylaxis. Except for the few thrombotic microangiopathy and thrombotic event cases mainly seen in the HAVEN 1 trial, emicizumab has an overall excellent safety profile with minimal side effects.

EXPERT OPINION

Knowledge gaps include the efficacy and safety of emicizumab in younger age groups and those with mild or moderate hemophilia A. Future directions for research include exploring the risk of inhibitor recurrence in patients with a history of high titer inhibitor who have been successfully tolerized, who switch from factor prophylaxis to emicizumab, as well as conducting 'real world studies' to evaluate the patient's perception of emicizumab in regard to ease and tolerability in order to optimize individualized treatment plans.

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.

Outcomes in children with hemophilia A with inhibitors: Results from a noninterventional study

BACKGROUND

Data regarding management of pediatric persons with hemophilia A (PwHA) with factor VIII (FVIII) inhibitors are limited. This prospective noninterventional study (NCT02476942) evaluated annualized bleeding rates (ABRs), safety, and health-related quality of life (HRQoL) in pediatric PwHA with FVIII inhibitors.

PROCEDURE

PwHA aged <12 years with current FVIII inhibitors and high-titer inhibitor history were enrolled. Participants remained on usual treatment; no interventions were applied. Outcomes included ABR, safety, and HRQoL.

RESULTS

Twenty-four PwHA aged 2-11 years (median 7.5) were enrolled and monitored for 8.7-44.1 weeks (median 23.4). In the episodic (n = 10) and prophylactic (n = 14) groups, respectively, 121 of 185 (65.4%) and 101 of 186 (54.3%) bleeds were treated using activated prothrombin complex concentrate (aPCC) and/or recombinant activated FVII (rFVIIa). ABRs (95% confidence interval) were 19.4 (13.2-28.4) and 18.5 (14.2-24.0) for treated bleeds, and 32.7 (20.5-52.2) and 33.1 (22.4-48.9) for all bleeds, respectively. Most prophylactic group participants (92.9%) were prescribed aPCC; 50% adhered to their prescribed treatment regimen. Adherence to prophylactic rFVIIa was not assessed. Serious adverse events included hemarthrosis (12.5%) and mouth hemorrhage (12.5%); the most common nonserious adverse event was viral upper respiratory tract infection (12.5%). HRQoL showed functional impairment at baseline; scores remained stable throughout, with little intergroup variation.

CONCLUSIONS

ABRs remained high in pediatric PwHA with inhibitors receiving standard treatment. This study demonstrates the need for more effective treatments, with reduced treatment burden, to prevent bleeds, increase prophylaxis adherence, and improve patient outcomes.

The changing face of immune tolerance induction in haemophilia A with the advent of emicizumab

INTRODUCTION

As a result of the new treatment paradigm that the haemophilia community will face with the availability of novel (non-factor) therapies, an updated consensus on ITI recommendations and inhibitor management strategies is needed.

AIM

The Future of Immunotolerance Treatment (FIT) group was established to contemplate, determine and recommend the best management options for patients with haemophilia A and inhibitors.

DISCUSSION AND CONCLUSIONS

Despite the considerable success of emicizumab in the management of inhibitor patients, the FIT group still sees the importance of eradicating inhibitors. However, the availability of emicizumab and other non-factor therapies in the future might impact greatly on how ITI is undertaken. Theoretically, concomitant use of emicizumab and FVIII might allow emicizumab to effectively prevent bleeding with lower dose ITI regimens. This might allow for the greater adoption of low-dose/low-frequency FVIII ITI regimens, which may result in a reduced need for central venous access devices while still maintaining a reasonable likelihood of ITI success. The FIT group proposes a new management algorithm for current ITI (without emicizumab) and a hypothetical new approach with the availability of emicizumab. As there are no published data regarding the concomitant use of emicizumab and FVIII for ITI, the FIT Expert group encourages the undertaking of properly conducted prospective studies to explore these approaches further.

Sequential bypassing agents during major orthopedic surgery: a new approach to hemostasis

Sequential bypassing agents may be a safe and effective treatment during major orthopedic surgery in hemophilia patients with inhibitors.

The role of recombinant activated factor VII in the haematological management of elective orthopaedic surgery in haemophilia A patients with inhibitors

The clinical profile and expectations of haemophilic patients with inhibitors have changed over the last three decades, mainly because of the prolongation of life-expectancy, often resulting in an increase of the orthopaedic burden. Recombinant activated factor VII (rFVIIa) is the most frequently used bypassing agent in haemophilia patients with inhibitors during elective orthopaedic surgery. For nearly 30 years, rFVIIa has been successfully used to control haemostasis in several major and minor surgical procedures. Clinical trials, case series, reports and surveys were progressively aimed at optimising rFVIIa usage in very demanding conditions managed in highly specialised centres. Recommendations from consensus opinions and guidelines have been provided on the basis of this clinical experience.