Recombinant porcine factor VIII: Lessons from the past and place in the management of hemophilia A with inhibitors in 2021

Cross-reacting antiporcine factor VIII inhibitors in patients with acquired hemophilia A

•Recombinant porcine factor VIII (rpFVIII) is a hemostatic treatment for bleeding in acquired hemophilia A.•The efficacy of rpFVIII can be negatively affected by cross-reacting anti-human FVIII antibodies.•In this cohort, 52% of patients with acquired hemophilia A had baseline cross-reacting antibodies.•Cross-reacting antibodies were associated with decreased FVIII activity levels post-rpFVIII infusion.

Immunogenicity of Therapeutic Biological Modalities - Lessons from Hemophilia A Therapies

The introduction and development of biologics such as therapeutic proteins, gene-, and cell-based therapy have revolutionized the scope of treatment for many diseases. However, a significant portion of the patients develop unwanted immune reactions against these novel biological modalities, referred to as immunogenicity, and no longer benefit from the treatments. In the current review, using Hemophilia A (HA) therapy as an example, we will discuss the immunogenicity issue of multiple biological modalities. Currently, the number of therapeutic modalities that are approved or recently explored to treat HA, a hereditary bleeding disorder, is increasing rapidly. These include, but are not limited to, recombinant factor VIII proteins, PEGylated FVIII, FVIII Fc fusion protein, bispecific monoclonal antibodies, gene replacement therapy, gene editing therapy, and cell-based therapy. They offer the patients a broader range of more advanced and effective treatment options, yet immunogenicity remains the most critical complication in the management of this disorder. Recent advances in strategies to manage and mitigate immunogenicity will also be reviewed.

From a bispecific monoclonal antibody to gene therapy: A new era in the treatment of hemophilia A

The treatment of hemophilia A has progressed amazingly in recent years. Emicizumab, a bispecific-humanized monoclonal antibody, is able to improve coagulation by bridging activated factor IX and factor X. Emicizumab is administered subcutaneously and much less often compared to factor VIII products. It has low immunogenicity, does not require dose adjustment, and can be administered regardless of the presence of factor VIII inhibitors. Thrombin generation assays but not factor VIII activity are indicated to guide and monitor the treatment. Emicizumab has enabled the conversion of patients with severe forms into patients with milder forms of hemophilia A. It has reduced the number of bleeding episodes compared to both on-demand and prophylactic substitution therapy and has an excellent safety profile. Gene therapy can elevate factor VIII plasma levels for many years after a single treatment course, could offer long-term protection from bleeding episodes, and minimize or eliminate the need for substitutive treatment with factor VIII concentrates. Gene therapy can provoke an immune response, manifested by an increase in common liver enzymes, that require immunotherapy. Long term monitoring is necessary to identify possible adverse effects. Future objectives are: the development of an ideal viral vector, the possibility of its re-administration, the use of gene therapy in hemophiliac children, and determining whether it can be successfully used to induce immune tolerance to factor VIII ceteri paribus. The future will determine the place of each type of treatment and group of patients for which it is indicated.

Structural insights into blood coagulation factor VIII: Procoagulant complexes, membrane binding, and antibody inhibition

Advances in structural studies of blood coagulation factor VIII (FVIII) have provided unique insight into FVIII biochemistry. Atomic detail models of the B domain-deleted FVIII structure alone and in complex with its circulatory partner, von Willebrand factor (VWF), provide a structure-based rationale for hemophilia A-associated mutations which impair FVIII stability and increase FVIII clearance rates. In this review, we discuss the findings from these studies and their implications toward the design of a recombinant FVIII with improved circulatory half-life. Additionally, we highlight recent structural studies of FVIII bound to inhibitory antibodies that have refined our understanding of FVIII binding to activated platelet membranes and formation of the intrinsic tenase complex. The combination of bioengineering and structural efforts to understand FVIII biochemistry will improve therapeutics for treating hemophilia A, either through FVIII replacement therapeutics, immune tolerance induction, or gene therapy approaches.

Inhibitors: Diagnostic challenges, unknowns of inhibitor development, treatment of bleeding and surgery, and insights into diagnosis and treatment in China

Factor (F) VIII inhibitors develop in around 30% of previously untreated patients (PUPs) with severe haemophilia, to a lesser extend in moderate and mild haemophilia A and in up to 10% in severe haemophilia B. Diagnostic challenges and questions remain including access to high quality testing, the role for functional inhibitor testing and binding antibody testing, and the adaptations needed in the presence of non-factor replacement therapy. Despite significant gains in knowledge there are still many unanswered questions underlying the immunologic mechanisms of inhibitor development and tolerance. Therapeutic options include eradication of inhibitors using immune tolerance induction therapy (ITI), prophylaxis with bypassing agents (i.e., recombinant activated factor VII /rFVIIa or activated prothrombin complex concentrate/aPCC) or non-factor replacement therapies (e.g., emicizumab) and treatment of bleeds or coverage of surgeries/invasive procedure. Recently a haemophilia centre capacity building program was launched in China to further develop the infrastructure and support needed to improve the diagnosis of haemophilia, detection of inhibitors, and continue to improve the care of patients with haemophilia and inhibitors.