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 (R)), 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 (R), 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.