Porcine factor VIII provides clinical benefit to patients with high levels of inhibitors to human and porcine factor VIII

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

The most serious complication of factor VIII (FVIII) replacement therapy is the occurrence of anti-FVIII alloantibodies that can strongly reduce or abolish the effect of human FVIII products. Bypassing agents to control bleeding episodes are recommended for these patients, but their efficacy is difficult to predict and monitor. FVIII products derived from porcine plasma had an important role in the treatment of hemophilia A for 50 years, from 1954 to 2004. Indeed, porcine FVIII could achieve hemostasis in patients in whom human FVIII products were ineffective. A recombinant porcine FVIII product is now available. This highly purified protein has the same biochemical and hemostatic properties, but much lower risks of infection and toxicity compared with plasma-derived porcine FVIII. The product is licensed in the United States and Europe for the treatment of acquired hemophilia A. However, this recombinant molecule could also be of clinical interest for people with inherited hemophilia A and inhibitors, particularly for the management of bleeding episodes in people receiving emicizumab as prophylactic treatment in the absence of anti-porcine FVIII antibodies.

Optimization of storage conditions for diluted working solutions of porcine factor VIII and performance of the Bethesda assay for the determination of antiporcine FVIII inhibitor titres

The use of porcine factor VIII (FVIII) (Hyate:C, Ipsen) has proven to be very successful in treating patients with FVIII inhibitors. The best way to predict the usefulness of porcine FVIII therapy, and/or to estimate the appropriate treatment dose in a given patient, is to measure the patient inhibitor titre against porcine FVIII with the Bethesda assay, using porcine FVIII as the source of FVIII in the assay. The goals of the present study were to (1) find the optimal storage temperature, diluent and concentration for a working solution of porcine FVIII to be used as the source of FVIII for the porcine Bethesda assay, (2) assess the reliability of the labelled FVIII units in the preparation of such working solutions of porcine FVIII and (3) compare the inhibitor titres determined by the Bethesda assay using both porcine and human standard reference curves for measuring residual FVIII. The results of the present study demonstrate that a ready-to-use working solution of 1 U mL(-1) of Hyate:C diluted in human FVIII deficient plasma, either containing or deficient in von Willebrand factor antigen, is stable for up to 12 months, at -20 degrees C. The preparation of the 1 U mL(-1) working solution could be reliably calculated based on the units indicated on the vial label. Finally, using the human standard curve yields similar results to using the porcine standard curve for measuring any titre of allo- or auto-antibody against FVIII in the Bethesda assay, using Hyate:C as the source of FVIII. These findings are of practical value when performing a porcine FVIII-based Bethesda assay.

Transfusion-sparing hemostatic agents

A variety of agents are available to improve hemostasis and reduce blood loss in multiple clinical settings. These agents are most commonly used to reduce bleeding when an underlying hemostatic defect is present. Some new agents offer the potential to decrease blood loss even in the absence of an obvious underlying hemostatic defect. The authors discuss the use of a variety of products to reduce bleeding and minimize transfusion of blood products in the setting of clotting factor deficiency or inhibition, platelet deficiency and/or dysfunction, increased fibrinolysis, therapeutic anticoagulation, and coagulopathies caused by dilution and consumption in the setting of trauma and surgery. The authors primarily focus on the available pharmaceuticals.

Platelet activation and hypercoagulability following treatment with porcine factor VIII (HYATE:C)

Activation of platelets and coagulation in vivo was studied in nine patients with hemophilia A and inhibitors to human Factor VIII, prior to and following treatment with porcine Factor VIII (PFVIII; HYATE:C). In addition, six hemophiliac patients were similarly studied after treatment with recombinant Factor VIII (rFVIII). Platelet activation was also examined in vitro using porcine von Willebrand factor (PvWF)-enriched and PvWF-depleted fractions obtained by fractionation of PFVIII. Coagulation was assessed by measuring the concentrations of plasma prothrombin fragment 1+2 concentrations (prothrombinase generation) and Factor Xa-ATIII. Patients treated with PFVIII had significantly increased numbers of circulating platelets expressing CD62 and CD63 (markers of platelet activation) and annexin V (marker of platelet procoagulant activity) compared to patients treated with rFVIII; the former patients also demonstrated an increase in plasma coagulability after therapy. In in vitro experiments it was observed that the platelet-activating and procoagulant capacity of PFVIII resided in the PvWF-enriched fraction, and the same was true for the plasma hypercoagulability following exposure of platelets to PFVIII. These results support the hypothesis that PFVIII-induced platelet activation provides a mechanism for enhancing hemostasis, separate from, and additional to, that due to increased circulating Factor VIII, and it is due to residual PvWF in the PFVIII preparation.

Porcine factor VIII in the treatment of high-titre inhibitor patients

Development of an inhibitor against factor VIII (FVIII) is an important complication of haemophilia. It occurs in approximately 25-30% of patients with haemophilia A [1]. FVIII inhibitors may also occur as autoantibodies. The latter occur in non-haemophiliacs and, although rare (occurring in approximately one per million of the population), are frequently associated with life-threatening bleeding. Inhibitors are considered low level if they are < 5 Bethesda Units (BU) or high level if they are > 10 BU. The former usually remain low and rarely give anamnestic response, the latter do so frequently. Despite various approaches to their management, the presence of inhibitors remains a major cause of morbidity and mortality. The effectiveness of porcine FVIII (pFVIII) in treating patients with both auto- and alloantibodies to FVIII has been well demonstrated when adequate circulating levels of FVIII are obtained [2--10]. However, pFVIII therapy may give rise to antibodies to the pFVIII and the utility of this treatment in the presence of high levels of porcine antibody is less well recognized and understood. Nonetheless, pFVIII under these circumstances may be useful in a select group of patients where management is difficult.