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

This was a phase II/III, multicenter, prospective, open-label, non-controlled study to evaluate the efficacy and safety of rpFVIII for the treatment of severe bleeding episodes in Japanese patients with AHA (ClinicalTrials.gov ID: NCT04580407). The study protocol, informed consent form, and all amendments were reviewed and approved by the local institutional review boards of each investigator site before study initiation. The study was conducted in accordance with the Declaration of Helsinki and the principles and guidelines described in the study protocol. Informed consent was received from all patients in this study.

Eligible patients included men and women aged at least 18 years who were suspected of having, or had previously received, an AHA diagnosis (based on clinical evaluation and laboratory testing) and who presented with a severe bleeding episode (e.g., threatening vital organ function, requiring a blood transfusion, compromising muscle viability or neurovascular integrity, or affecting a major joint). Once a diagnosis of AHA had been confirmed, patients were able to start treatment with rpFVIII. Prior treatment with rFVIIa, aPCC, and pd-FVIIa/FX was not an exclusion criterion, provided that a washout period was allowed (3 h, 6 h, or 8 h, respectively) before the initial rpFVIII infusion.

rpFVIII was administered at an initial dose of 200 U/kg. The need for additional doses was determined by the investigator based on clinical bleeding status (reviewed every 6–12 h as per expert consensus recommendations) [26] and clinical laboratory evaluation (FVIII:C [measured with a one-stage clotting assay using the World Health Organization hFVIII plasma standard], activated partial thromboplastin clotting time [aPTT], hemoglobin [Hgb] and hematocrit [Hct] at 30 min, 8 h, 16 h, and 24 h after the first infusion, then every 12 h until 72 h, and then every 24 h until the end of infusion/study). If additional doses of rpFVIII were administered, FVIII:C, aPTT, Hgb, and Hct were also measured at each subsequent dose until 24 h after the dose was administered. Additional doses of rpFVIII were administered as frequently as every 4–12 h with dose and frequency determined based on the post-infusion FVIII:C result and the target FVIII:C. For bleeds of particular clinical concern (e.g., severe mucosal, intracranial, retro- or intra-abdominal, genitourinary, neck, traumatic, or postoperative bleeds), the target trough FVIII:C was at least 80% for the first 24 h. For all other severe bleeding episodes (e.g., joint, muscle, soft tissue) in the first 24 h and all bleeding episodes after the first 24 h, the target trough FVIII:C was at least 50%. The dose of rpFVIII could not exceed 800 U/kg every 4 h. Treatment with rpFVIII was continued until bleeding was successfully controlled, until the investigator concluded a lack of efficacy, or until the patient withdrew from the study.

The primary efficacy endpoint was the proportion of severe bleeding episodes with a demonstrated positive response to rpFVIII therapy at 24 h after the initiation of treatment using a well-defined four-point ordinal scale (Supplementary Table S1). A positive response was defined as effective or partially effective assessment of efficacy. Control of bleeding was evaluated based on obvious blood loss (external blood loss and bodily fluids), hematology results, blood transfusion and blood component requirements, physical or technological examination of the bleeding site, neurological examination, and imaging studies. Patients who experienced a therapeutic response to rpFVIII were eligible for treatment with rpFVIII for any subsequent major bleeding episode but outcomes for these bleeding episodes were not part of the primary efficacy analysis. Re-bleeding was considered to have occurred if there was bleeding from a previously successfully controlled site within 2 weeks of the last dose of rpFVIII. In this case, the event was recorded as an adverse event (AE) and treated appropriately. Key secondary efficacy endpoints included: the overall proportion of severe bleeding episodes successfully controlled with rpFVIII therapy; the proportion of bleeding episodes responsive to rpFVIII therapy at 30 min, 8 h, and 16 h after the initiation of therapy, and every 14 days until the end of the study (90 days after the final dose of rpFVIII for initial bleeding, to cover the average time to remission of AHA [3, 27] including resolution of other bleeding besides initial bleeding); and the frequency, total dose, and total number of infusions of rpFVIII required to successfully control qualified bleeding episodes.

Safety endpoints included AEs, serious adverse events (SAEs), clinical laboratory measurements, vital signs, and the presence of anti-BHK cell antibodies. AEs of special interest included hypersensitivity reactions, the development of de novo inhibitors to pFVIII, anamnestic reactions with an increase of inhibitor titer to pFVIII and/or hFVIII, and thromboembolic events.

The planned total sample size for this study was five patients, which was based on feasibility considerations given the low incidence of AHA in Japan. The primary efficacy endpoint was calculated as the proportion of patients with a positive response to rpFVIII therapy at 24 h post-treatment and the corresponding exact two-sided Clopper–Pearson 95% confidence intervals (CIs). Patients who had hemostatic response and stopped treatment because bleeding was controlled were assumed to be responders at the 24-h assessment time point.

In total, six patients signed the informed consent form, and five patients were eligible to receive treatment. Of the five patients who entered the study treatment period, all patients completed rpFVIII treatment for the initial qualified bleeding episode. One patient (patient 3) discontinued the study owing to the need to receive prophylactic treatment with emicizumab. Three men and two women were included in the study. All patients were aged in their 60s to 80s, and the median (range) weight was 51.7 (46.7–65.7) kg (Table 1). Four patients received a diagnosis of AHA at this admission and one patient received a diagnosis 33 months previously. The median (range) hFVIII inhibitor concentration at baseline was 52.0 (7–150) Bethesda units (BU)/mL. Three out of five (60%) patients had detectable pFVIII inhibitors at baseline and the median (range) pFVIII inhibitor titer for all five patients was 0.9 (0.0–9.3) BU/mL. Three patients had a history of rFVIIa treatment, and one patient had a history of pd-FVIIa/FX treatment in the 6-month period before receiving rpFVIII. All patients used immunosuppressive medicine concomitantly (prednisolone was used by three patients for AHA, by one patient for multiple uses, and by one patient for systemic lupus erythematous as a comorbidity; Supplementary Table S2). No patient received a blood transfusion in this study or in the 6 months before the study started.

All five patients (100%, 95% CI 47.8–100.0) were assessed by the investigators to have achieved the primary efficacy endpoint (severe bleeding episodes with a positive response to rpFVIII therapy at 24 h after the initiation of treatment; Table 2).

The proportion of patients who had a response to rpFVIII therapy at designated assessment time points after the initiation of therapy is summarized in Table 2. Four out of five patients showed a positive response at 30 min after the initial dose of rpFVIII. All patients whose responses were assessed showed a positive response to rpFVIII at 8 h, 16 h, and 24 h after the initial dose, at all assessed follow-up visits, and at the end of study visit. No patient experienced a re-bleed in this study. Overall, all five patients were assessed by the investigator to have successfully controlled their severe bleeding episode with rpFVIII treatment in this study.

Total dose, frequency of infusions, and total number of infusions of rpFVIII required to control severe bleeding episodes successfully are summarized in Table 3. The median (range) total dose of rpFVIII per patient was 548.4 (198–1803) U/kg. Individual patient responses to treatment and dosage information are shown in Table 4. One patient received one infusion and four patients received three infusions of rpFVIII. The median number of total infusions per patient was 3.0 infusions and the median (range) number of infusions was 1.5 (1–3) infusions/day. Compliance for rpFVIII dosing was 100% in all five patients.

Individual patient inhibitor titers against hFVIII and pFVIII throughout the study are shown in Fig. 1. Although three patients had detectable pFVIII inhibitors before the initial dose, all five patients were assessed to have a positive response to rpFVIII at 24 h after initiation of treatment and achieved eventual control of the bleeding episode. No patient developed de novo pFVIII inhibitors or anamnestic reactions with an increase of inhibitor titers against pFVIII and/or hFVIII. One patient (patient 2) did develop an increase of inhibitor titers against pFVIII and hFVIII from baseline, but as this occurred 42 days after the end of the rpFVIII infusion, it was not considered an anamnestic reaction to rpFVIII. This patient was taking prednisolone (Supplementary Table S2) at a lower dose (15 mg) than that recommended by the Japanese AHA guidelines for their weight (46.7 kg) [10], which may have reduced the efficacy of the prednisolone and resulted in an increase in hFVIII inhibitor titers. These inhibitors may have cross-reacted with pFVIII and caused a similar increase in the pFVIII inhibitor titer. The two patients in whom pFVIII inhibitors were not detected at baseline did not develop pFVIII inhibitors after initiation of treatment.

Individual patient plots of FVIII:C and aPTT with rpFVIII dosing information over the study are shown in Fig. 2 and summarized in Table 4. Overall, FVIII:C increased following each rpFVIII infusion, although the increase was variable between patients. For example, one patient received a single infusion of rpFVIII 198 U/kg, and immediately had FVIII:C exceeding 300%. The FVIII:C in this patient remained over 50% during the 24 h period that followed (Fig. 2d). In contrast, another patient had FVIII:C of approximately 10% immediately after their first dose, which then fell to 1% by 6 h after the first infusion. This patient had pFVIII inhibitors at baseline, and subsequently received two further infusions at the maximum possible dose (800 U/kg and 803 U/kg) (Fig. 2b). Overall, the median (range) duration of rpFVIII treatment was 1.0 (1–5) days. The patient who received the single infusion had a 1-day treatment duration, while of the four patients who received three infusions, three patients received second and third infusions within approximately 24 h following the initial dose of rpFVIII (Fig. 2a–c), and one patient received second and third infusions on day 3 and day 5, respectively (Fig. 2e). After each infusion, aPTT tended to shorten as FVIII:C increased. In patients with pFVIII inhibitors at baseline (Fig. 2a–c), the increase in FVIII:C after the first infusion of rpFVIII was smaller than the increase seen in patients without pFVIII inhibitors (Fig. 2d and e). For four out of five patients, the maximum FVIII:C recorded in the 24 h following the first infusion was at least 50%, even for patients with pFVIII inhibitors at baseline.

In total, 49 AEs were reported in five patients, most of which were mild to moderate in severity. Two severe AEs (urinary tract infection and subcutaneous hemorrhage) were reported in one patient, with neither AE considered related to rpFVIII treatment. AEs by system organ class reported in at least three patients were skin and subcutaneous tissue disorders (reported in four patients) and gastrointestinal disorders (reported in three patients).

Five SAEs were reported in two patients in this study. Patient 2 experienced three SAEs (subcutaneous hemorrhage, hemorrhagic diathesis, and urinary tract infection), which were considered by the investigator to be unrelated to rpFVIII treatment. Patient 3 experienced two SAEs (cryoglobulinemia and central hypothyroidism), which were both considered by the investigator to be related to rpFVIII treatment because a causal relationship could not be completely denied. The sponsor considered it unlikely that both events were related to rpFVIII because the patient had a medical history of autoimmune disease (seronegative arthritis) (Supplementary Table S3) and there was no compelling evidence that directly linked the study medication to the events. This patient had to discontinue the study because treatment with emicizumab was required. Their condition deteriorated, and the patient died of general debility 3 months later. No other AEs (serious or nonserious) were considered by the investigator to be related to rpFVIII treatment. There were no reports from the investigators of hypersensitivity reactions or thromboembolic events, and no patient developed anti-BHK antibodies. There were also no clinically significant changes in laboratory parameters or vital signs throughout the study. The sponsor classified one AE of erythema as an AE of special interest (hypersensitivity reactions), but this was not considered related to the study drug. No deaths or AEs leading to study drug discontinuation were reported during the AE collection period in this study.