Porcine factor VIII

Efficacy and safety of recombinant porcine factor VIII in Japanese patients with acquired hemophilia A

Acquired hemophilia A (AHA) is a rare bleeding disorder caused by autoantibodies inhibiting human factor VIII (hFVIII). This phase II/III open-label study evaluated the safety and efficacy of recombinant porcine factor VIII (rpFVIII, susoctocog alfa) in adults with AHA and severe bleeding episodes in Japan (NCT04580407). The initial rpFVIII dose was 200 U/kg, with subsequent doses based on clinical measures including plasma FVIII activity. The primary efficacy endpoint was the proportion of severe bleeding episodes with a positive response to rpFVIII therapy 24 h after treatment initiation. Five patients were eligible for, and completed, rpFVIII treatment (age group: 60s-80s; median hFVIII inhibitor: 52 BU/mL; porcine FVIII [pFVIII] inhibitor: 3/5 patients). The median (range) total dose/patient was 548.4 (198-1803) U/kg with a median 3.0 infusions/patient. All patients responded positively to rpFVIII therapy at 24 h regardless of baseline pFVIII inhibitor status. rpFVIII treatment was well tolerated with no adverse events of special interest such as thromboembolic events or de novo pFVIII inhibitors. This study supports the use of rpFVIII as a novel therapy in the clinical management of patients with AHA in Japan. rpFVIII was approved for treating bleeding episodes in adults with AHA in Japan in 2024.

Analytical Performance of Different Laboratory Methods for Measuring Susoctocog-Alfa

Recombinant porcine factor VIII (rpFVIII) is indicated for treating bleeding episodes in acquired haemophilia A, but there are few data regarding laboratory methods to adequately monitor treatment. This study involving three Italian laboratories aimed to evaluate the analytical performance of different assays for measuring rpFVIII. Five spiked rpFVIII samples (0.5–1.5 IU/mL) were analysed on three days, in triplicate, with eleven combinations of reagents (Werfen, Boston, MA, USA: SynthasIL and SynthaFax for one-stage assay, Chromogenix Coamatic FVIII for chromogenic assay), FVIII depleted plasmas (with or without von Willebrand factor—VWF) and calibrators (HemosIL human calibrator plasma, porcine calibrator diluted in FVIII deficient plasma with or without VWF). The assays were performed on ACL TOP analysers (Werfen, Boston, MA, USA). Intra- and inter-assay and inter-laboratory Coefficient of Variation (CV%) were calculated together with percentage of recovery (% recovery) on the expected value. The results showed that the reagent combinations reaching satisfactory analytical performance are: SynthasIL/human calibrator/deficient plasma+VWF (total recovery 99.4%, inter-laboratory CV 4.04%), SynthasIL/porcine calibrator/deficient plasma+VWF (total recovery 111%, inter-laboratory CV 2.75%) and Chromogenic/ porcine calibrator/deficient plasma+VWF (total recovery 96.6%, inter-laboratory CV 8.32%). This study highlights that the use of porcine standard (when available) and FVIII deficient plasma with VWF should be recommended.

Acquired Haemophilia A: An Intriguing Disease

Abstract. Acquired Haemophilia A is a rare acquired bleeding disorder caused by Factor VIII autoantibodies, which neutralise FVIII activity. These inhibitors differ from alloantibodies against FVIII, which can occur in congenital Haemophilia A after repeated exposures to plasma-derived or recombinant FVIII products. In most cases, the disease occurs suddenly in subjects without a personal or familiar history of bleedings, with symptoms that may be mild, moderate, or severe. However, only laboratory alterations are present in ~ 30% of patients. The incidence varies from 1 to 4 cases per million/year; more than 80% of patients are elderly, males and females are similarly affected. There is a small peak of incidence related to pregnancy in young women aged 20–40 years. The disease may be underdiagnosed in the elderly. The diagnostic algorithm is based on an isolated prolonged activated partial thromboplastin time, normal thrombin time, absence of Lupus Anticoagulant, and a mixing test that reveals the presence of an inhibitor: the finding of reduced FVIII activity and the detection of neutralising autoantibodies against FVIII lead to the diagnosis. The disease is idiopathic in 44%–63% of cases, while in the others etiological factors are present. Bleeding prevention and treatment are based on therapeutic tools as by-passing agents, recombinant porcine FVIII concentrate or, in a limited number of cases, FVIII concentrates and desmopressin. As soon as the diagnosis has been made, immunosuppressive therapy must be started to eradicate the inhibitor. Better knowledge of the disease, optimal management of bleeding and eradication of the inhibitor have significantly reduced morbidity and mortality in most patients.

International recommendations on the diagnosis and treatment of acquired hemophilia A

Acquired hemophilia A (AHA), a rare bleeding disorder caused by neutralizing autoantibodies against coagulation factor VIII (FVIII), occurs in both men and women without a previous history of bleeding. Patients typically present with an isolated prolonged activated partial thromboplastin time due to FVIII deficiency. Neutralizing antibodies (inhibitors) are detected using the Nijmegen-modified Bethesda assay. Approximately 10% of patients do not present with bleeding and, therefore, a prolonged activated partial thromboplastin time should never be ignored prior to invasive procedures. Control of acute bleeding and prevention of injuries that may provoke bleeding are top priorities in patients with AHA. We recommend treatment with bypassing agents, including recombinant activated factor VII, activated prothrombin complex concentrate, or recombinant porcine FVIII in bleeding patients. Autoantibody eradication can be achieved with immunosuppressive therapy, including corticosteroids, cyclophosphamide and rituximab, or combinations thereof. The median time to remission is 5 weeks, with considerable interindividual variation. FVIII activity at presentation, inhibitor titer and autoantibody isotype are prognostic markers for remission and survival. Comparative clinical studies to support treatment recommendations for AHA do not exist; therefore, we provide practical consensus guidance based on recent registry findings and the authors' clinical experience in treating patients with AHA.

Cross-reacting inhibitors against recombinant porcine factor VIII in acquired hemophilia A: Data from the GTH-AH 01/2010 Study

BACKGROUND

Recombinant porcine factor VIII (rpFVIII, OBI-1, susoctocog alfa) is used for the treatment of acute bleeds in patients with acquired hemophilia A (AHA). Inhibitors in AHA can sometimes cross-react with rpFVIII.

OBJECTIVES

To assess the frequency, strength, and determinants of cross-reactivity.

PATIENTS/METHODS

Baseline samples from 70 patients of the prospective, observational cohort study GTH-AH 01/2010 were assessed for anti-human FVIII and anti-rpFVIII inhibitors using modified Nijmegen-Bethesda assays, as well as anti-human FVIII domain reactivity using enzyme-linked immunoassay (ELISA).

RESULTS

Anti-human FVIII inhibitors were present in all samples ranging between 0.7 and 3891 Bethesda Units (BU)/mL. Inhibitors from 31 of 70 patients (44%) partially inhibited rpFVIII with anti-rpFVIII titers ranging between 0.5 and 471 BU/mL. Anti-rpFVIII titers were ≤5 BU in most patients. Patients with cross-reacting inhibitors, as compared to patients without, had significantly higher anti-human FVIII titers (27.8 versus 5.4 BU/mL) and lower baseline FVIII activity (<1 versus 2.6 IU/dL). The ratio between anti-rpFVIII to anti-human titers was highest for inhibitors involving the C1 domain. Cross-reactivity was very rare, if inhibitors reacted only with the C2 domain of FVIII (6%). An anti-human FVIII titer of >100 BU/mL predicted cross-reactivity with 97% likelihood, whereas an anti-human FVIII titer of <3.8 BU/mL predicted absent cross-reactivity with 90% likelihood.

CONCLUSION

Cross-reacting inhibitors should be considered when choosing a treatment for bleeding patients with AHA. Cross-reactivity is frequent in patients with anti-human FVIII titers of >100 BU/mL.

Acquired Hemophilia of Unknown Etiology in an Elderly Man: Case Report

BACKGROUND Acquired hemophilia is a rare but potentially dangerous bleeding disorder caused by autoantibodies against coagulation factors. It affects 1 to 1.5 per 1 million people each year. While 50% of cases could be idiopathic, other causes include malignancies, diabetes, pregnancy, infection, and autoimmune disorders. CASE REPORT We report a case of a 90-year-old male who developed a spontaneous hematoma on the dorsum of his right hand, with no prior history of trauma or any other mucosal bleeding. His activated partial thromboplastin time (aPTT) was found to be prolonged (>180 seconds) with a very low level of factor VIII (0.1%). CONCLUSIONS As workups did not identify the source, including malignancy and autoimmune diseases, of his acquired hemophilia, it is believed to be idiopathic. He was started on intravenous recombinant factor VIIa (NovoSeven) to control the bleeding in combination with an immunosuppressive therapy of cyclophosphamide and prednisolone. In approximately 10% of patients with acquired hemophilia, underlying malignancy, such as squamous cell cancer, chronic lymphocytic leukemia, non-Hodgkin lymphoma, and multiple myeloma can present and commonly develop in elderly patients. Therefore, patients diagnosed with idiopathic acquired hemophilia should be given long-term follow up.

Novel assays in the coagulation laboratory: a clinical and laboratory perspective

The ability to monitor Factor VIII (FVIII) and Factor IX (FIX) levels is integral to the clinical management of hemophilia A and B patients, respectively. Factor activity levels are checked during regular follow-up, post-infusion of factor concentrates, during pre- and post-operative assessments, and when the presence of an inhibitor is suspected. However, the ability to accurately and reproducibly measure factor activity levels with standard coagulation assays has been challenging due to the emergence of recombinant factor concentrates with extended half-lives. Similarly, special considerations must be given to the type of inhibitor assay used in patients with acquired hemophilia receiving recombinant porcine FVIII replacement. Alternative approaches to achieve hemostasis with clotting factor mimetics and interference of endogenous anticoagulants lack standardized assays for monitoring hemostatic efficacy. Laboratory assays measuring dynamic clotting parameters such as thrombin generation or whole blood viscoelasticity may provide a way forward, but have yet to enter routine clinical use. This review highlights the role of specialized coagulation assays in an era where multiple new hemostatic therapeutics for hemophilia are available, and underscores the need for clear communication between bedside and laboratory clinicians.

Review of recombinant anti-haemophilic porcine sequence factor VIII in adults with acquired haemophilia A

Acquired haemophilia A (AHA) is a rare, serious bleeding disorder most often encountered in elderly patients. The mainstay of haemostatic management is with bypassing agents (BPAs) including recombinant activated factor VII (rFVIIa) and activated prothrombin complex concentrates (aPCCs). Their major limitation is incomplete efficacy, potential risk for thrombosis and the lack of routine laboratory assays for monitoring treatment response. Plasma-derived porcine FVIII (pd-pFVIII, Hyate C^®), first used in the 1950s for the management of congenital haemophilia, has sufficient sequence homology to be haemostatic in humans, but the lack of complete homology facilitates efficacy even in the presence of human allo- and autoantibodies against human FVIII (hFVIII). In a small phase II/III study, recombinant porcine FVIII (rpFVIII, Obizur^®, OBI-1, susoctocog alfa) was shown to be safe and effective for the management of bleeding episodes in patients with AHA with anti-porcine FVIII (anti-pFVIII) antibody levels of 20 BU/ml or less. Treatment outcome was judged on clinical response and FVIII levels after an initial fixed dose of 200 IU/kg. The rise in FVIII levels showed considerable inter-individual variability and was significantly influenced by the presence of anti-pFVIII antibodies. Based on the baseline levels of anti-pFVIII antibodies and response to treatment, three potential patient groups were identifiable. In the first group, the absence of cross-reacting antibodies was associated with supra-therapeutic FVIII levels, fewer infusions and lower rpFVIII utilization per treatment episode. The second group had patients with low levels of cross-reacting anti-pFVIII antibodies (0.8-5 BU/ml) with near-normal response to rpFVIII. The last group had higher titres of anti-pFVIII antibody (10-30 BU/ml) associated with lower FVIII levels, more infusions and higher consumption of rpFVIII. We propose a new treatment algorithm for the haemostatic management of AHA that includes the potential first-line clinical use of rpFVIII that takes into account availability of anti-pFVIII antibody results, titre of anti-pFVIII antibodies and severity of bleeding episode.

Alternative therapies for the management of inhibitors

The development of inhibitors to factor VIII (FVIII) or factor IX (FIX) remains a major treatment complication encountered in the treatment of haemophilia. Not all patients with even the same severity and genotype develop inhibitors suggesting an underlying mechanism of tolerance against FVIII- or FIX-related immunity. One mechanism may be central tolerance observed in patients in whom the FVIII mutation enables some production of the protein. The other is a peripheral tolerance mechanism which may be evident in patients with null mutation. Recently, recombinant porcine FVIII (rpFVIII, Obixur, OBI-1, BAX801) has been developed for the haemostatic treatment of both congenital haemophilia with inhibitor (CHAWI) and acquired haemophilia A (AHA). In 28 subjects with AHA with life-/limb-threatening bleeding, rpFVIII reduced or stopped bleeding in all patients within 24 h. The cross-reactivity of anti-human FVIII antibodies to rpFVIII remains around 30-50%. Recently, new therapeutics based on the quite novel concepts have been developed and clinical studies are ongoing. These are humanized asymmetric antibody mimicking FVIIIa function by maintaining a suitable interaction between FIXa and FX (Emicizumab, ACE910), and small interfering RNAs (siRNA, ALN-AT3) suppress liver production of AT through post-transcriptional gene silencing and a humanized anti-TFPI monoclonal antibody (Concizumab). Their main advantages are longer half-life, subcutaneous applicability and efficacy irrespective of the presence of inhibitors which will make it easier to initiate more effective treatment especially early childhood.

Porcine recombinant factor VIII: an additional weapon to handle anti-factor VIII antibodies

This review focuses on the use of recombinant porcine factor VIII (FVIII) for the treatment of bleeding episodes in patients with severe haemophilia A complicated by inhibitors and in those with acquired haemophilia A due to the onset of anti-FVIII autoantibodies. We present the main characteristics of recombinant porcine factor VIII (FVIII) and provide a summary of the published results of the clinical studies of this novel recombinant FVIII. There is a special emphasis on how the use of recombinant porcine factor VIII (FVIII) is expected to improve the clinical management of these patients.

Xenotransfusion of anemic cats with blood compatibility issues: pre- and posttransfusion laboratory diagnostic and crossmatching studies

BACKGROUND

Finding compatible feline blood donors can be challenging. Canine blood has been occasionally used when compatible feline blood was not available in emergency situations.

OBJECTIVES

The study goals were to describe the effects of xenotransfusion in 2 anemic cats receiving canine blood because of discordant blood types and acute transfusion reaction, respectively, and to report in vitro heterotyping and crossmatching results between canine and feline blood samples.

MATERIAL AND METHODS

Blood samples from patients and other cats and dogs were typed, crossmatched, and assessed for alloantibodies using gel, card, and immunochromatographic strip techniques.

RESULTS

Cat 1 was found to have type AB blood. Cat 2, which experienced an acute transfusion reaction, had type A blood. Neither had detectable alloantibodies against feline RBC. Both cats transiently improved after transfusion with canine blood; however, acute intravascular hemolysis occurred and the PCV rapidly declined. Blood typing post xenotransfusion with DEA 1 strips revealed a positive control band that was absent in feline blood, thus allowing for the identification of transfused canine RBC. Longitudinal assessment revealed that canine RBC could no longer be detected 4 days after xenotransfusion. Major crossmatching (feline plasma with canine RBC) resulted in both positive and negative reactions, depending on the cat. Minor crossmatching results showed mostly incompatibility.

CONCLUSION

While both cats survived xenotransfusion, the positive control band on the DEA 1 strip revealed that transfused canine RBC were short-lived and intravascular hemolysis occurred. Crossmatch results between cats and dogs showed varied incompatibilities and may not predict transfusion reactions.

New products for the treatment of haemophilia

Current developments in haemophilia therapy are directed at two therapeutic targets: reduction of injection frequency and reduction or bypassing of inhibitors. A variety of new molecules addressing these aims are now completing clinical trials and are ready to enter clinical use. First amongst these are modified Factor VIII (FVIII) and Factor IX (FIX) molecules with extended half-lives. FIX modifications have achieved 5-fold prolongation of half-life whilst effects on FVIII have been more modest, at less than two-fold. We now face the problem of integrating these into clinical practice. Other approaches have generated chemically modified FVIII molecules with altered activation profiles. An alternative way of correcting the haemophilia defect is to reduce the activity of natural anticoagulants in an attempt to restore the balance of haemostasis. These methods are also giving promising results but, as with all new approaches, it will be some while before they all find their place in practice.

Industrial production of clotting factors: Challenges of expression, and choice of host cells

The development of recombinant forms of blood coagulation factors as safer alternatives to plasma derived factors marked a major advance in the treatment of common coagulation disorders. These are complex proteins, mostly enzymes or co-enzymes, involving multiple post-translational modifications, and therefore are difficult to express. This article reviews the nature of the expression challenges for the industrial production of these factors, vis-à-vis the translational and post-translational bottlenecks, as well as the choice of host cell lines for high-fidelity production. For achieving high productivities of vitamin K dependent proteins, which include factors II (prothrombin), VII, IX and X, and protein C, host cell limitation of γ-glutamyl carboxylation is a major bottleneck. Despite progress in addressing this, involvement of yet unidentified protein(s) impedes a complete cell engineering solution. Human factor VIII expresses at very low levels due to limitations at several steps in the protein secretion pathway. Protein and cell engineering, vector improvement and alternate host cells promise improvement in the productivity. Production of Von Willebrand factor is constrained by its large size, complex structure, and the need for extensive glycosylation and disulfide-bonded oligomerization. All the licensed therapeutic factors are produced in CHO, BHK or HEK293 cells. While HEK293 is a recent adoption, BHK cells appear to be disfavored.

Acquired hemophilia A: emerging treatment options

Acquired hemophilia A is a rare autoimmune disorder caused by an autoantibody (inhibitor) to factor VIII (FVIII) that interferes with its coagulant function and predisposes to severe, potentially life-threatening hemorrhage. Disease management focuses on controlling bleeding, primarily with the use of bypassing therapy and recombinant porcine FVIII, and permanently eradicating the autoantibody using various immunosuppressants. Treatment challenges include delayed diagnosis, difficulty achieving hemostasis and durable remissions, and complications associated with the use of hemostatic and immunosuppressive therapy in a primarily older patient population.

Recombinant B domain deleted porcine factor VIII for the treatment of bleeding episodes in adults with acquired hemophilia A

Hemophilia A is an inherited deficiency of clotting factor VIII (FVIII) often complicated by inhibitor development (CHAWI) in which neutralizing antibodies block the therapeutic benefit of replacement therapy. Inhibitors to FVIII can also be seen in an auto-immune disease known as acquired hemophilia A (AHA). 'Bypassing' therapies have been shown to provide hemostasis but dosing must be done empirically because current assays cannot measure objective markers of treatment efficacy and safety. A recombinant porcine sequence factor VIII (r-pFVIII) has been developed for the management of AHA. Preclinical, Phase I and Phase II clinical research studies in CHAWI subjects showed therapeutic potential and safety of this agent. A Phase II/III study in AHA with serious bleeding episodes shows a positive response in all subjects after administration. Based on current preclinical and clinical trial data, r-pFVIII should become the first line of treatment in the management of hemorrhage in patients with AHA.

The 1.7 Å X-ray crystal structure of the porcine factor VIII C2 domain and binding analysis to anti-human C2 domain antibodies and phospholipid surfaces

The factor VIII C2 domain is essential for binding to activated platelet surfaces as well as the cofactor activity of factor VIII in blood coagulation. Inhibitory antibodies against the C2 domain commonly develop following factor VIII replacement therapy for hemophilia A patients, or they may spontaneously arise in cases of acquired hemophilia. Porcine factor VIII is an effective therapeutic for hemophilia patients with inhibitor due to its low cross-reactivity; however, the molecular basis for this behavior is poorly understood. In this study, the X-ray crystal structure of the porcine factor VIII C2 domain was determined, and superposition of the human and porcine C2 domains demonstrates that most surface-exposed differences cluster on the face harboring the "non-classical" antibody epitopes. Furthermore, antibody-binding results illustrate that the "classical" 3E6 antibody can bind both the human and porcine C2 domains, although the inhibitory titer to human factor VIII is 41 Bethesda Units (BU)/mg IgG versus 0.8 BU/mg IgG to porcine factor VIII, while the non-classical G99 antibody does not bind to the porcine C2 domain nor inhibit porcine factor VIII activity. Further structural analysis of differences between the electrostatic surface potentials suggest that the C2 domain binds to the negatively charged phospholipid surfaces of activated platelets primarily through the 3E6 epitope region. In contrast, the G99 face, which contains residue 2227, should be distal to the membrane surface. Phospholipid binding assays indicate that both porcine and human factor VIII C2 domains bind with comparable affinities, and the human K2227A and K2227E mutants bind to phospholipid surfaces with similar affinities as well. Lastly, the G99 IgG bound to PS-immobilized factor VIII C2 domain with an apparent dissociation constant of 15.5 nM, whereas 3E6 antibody binding to PS-bound C2 domain was not observed.