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Introduction: FLT180a (verbrinacogene setparvovec) is an investigational, liver-directed AAV gene therapy for the treatment of patients with hemophilia B (HB). FLT180a consists of a novel, potent, engineered capsid (AAVS3) containing an expression cassette encoding a Factor IX (FIX) gain-of-function protein variant ('Padua'; FIX-R338L). The B-AMAZE study was designed to identify a dose of FLT180a that maintains FIX activity within the normal range (50-150%) and thereby protect patients with severe HB from spontaneous and traumatic bleeds. Methods: B-AMAZE was a multicentre, open-label Phase 1/2 clinical trial (NCT03369444; sponsored by UCL) that evaluated FLT180a dose levels using an escalating/descending adaptive design in patients with severe (FIX activity Results: Ten HB patients received a single dose of FLT180a. Four FLT180a doses ranging from 3.84e11 vg/kg to 1.28e12 vg/kg were assessed. As of the data cut-off date, all patients have been followed for ≥16 months. FLT180a demonstrated a favorable safety profile, without evidence of inhibitors against FIX, infusion-related or allergic reactions. The most common treatment-related adverse event was transient elevation in alanine aminotransferase. An event of AV fistula thrombosis occurred in a 67-year-old patient who received the highest dose of 1.28e12 vg/kg (total dose of 1.15e14 vg) and had supranormal FIX levels; this patient was treated with anticoagulants. While these FIX levels demonstrate the potency of our proprietary AAVS3 capsid, this dose will not be used in future hemophilia studies. At Week 26 after FLT180a administration, a dose-response relationship was observed with mean FIX activity of 45.0%, 35.5%, 141.5%, and 175.5% for 3.84e11, 6.4e11, 8.32e11, and 1.28e12 vg/kg doses, respectively (Table); FIX activity levels ≥50% were achieved in 7 of 8 patients treated with the three highest doses. One patient (Patient 4) who received 6.4e11 vg/kg lost transgene expression early due to transaminitis and resumed routine factor prophylaxis. The 8.32e11 vg/kg cohort received an extended immune management regimen (9-18 weeks) with prophylactic tacrolimus in addition to prednisolone to prevent breakthrough vector-related transaminitis. However, after cessation of the immune management regimen, transaminitis with concomitant reductions in FIX activity was observed in all patients in the 8.32e11 vg/kg cohort. The combination of prophylactic tacrolimus and prednisolone appeared to have suppressed immune-mediated transaminitis while administered, but recurrence of transaminitis developed soon after cessation. This unique and previously unreported observation suggests that the longer-duration prophylactic immune management regimen may have prevented tolerization to the vector because this was not observed in earlier cohorts where a brief course of tacrolimus was given reactively for breakthrough transaminitis. All patients (including the 8.32e11 vg/kg cohort) have achieved steady state. Patients in the earliest cohort who received the lowest dose (3.84e11 vg/kg) have shown stable FIX activity for >3 years. There were no spontaneous bleeds that required FIX supplementation in patients who maintained FIX activity above 50%; Patient 4 in the 6.4e11 vg/kg cohort experienced two bleeds (cause unknown) after he lost transgene expression, which were treated with exogenous FIX. One patient received exogenous FIX for treatment of a traumatic bleed, but his FIX activity level was 57% at the time of the event. Additional efficacy and safety results with >3.5 years of follow-up will be presented. Conclusions: B-AMAZE is the first HB gene therapy study to achieve normal levels of FIX activity using relatively low vector doses. Results suggest that a dose of 7.7e11 vg/kg, coupled with a short course of prophylactic immune management, has the potential to achieve durable FIX activity in the normal range (50-150%) and thereby prevent spontaneous bleeds and normalize hemostasis in the event of traumatic bleeds. Figure 1 Figure 1. Disclosures Chowdary: Sanofi: Honoraria; Roche: Honoraria; CSL Behring: Honoraria, Research Funding; Freeline: Honoraria, Research Funding; Novo Nordisk: Honoraria, Research Funding; Pfizer: Honoraria, Research Funding; SOBI: Honoraria, Research Funding; Takeda: Honoraria, Research Funding; Boehringer Ingelheim: Honoraria; Chugai: Honoraria; Spark: Honoraria; Bayer: Honoraria, Research Funding. Shapiro: Roche: Honoraria; CSL Bering: Honoraria; Takeda: Honoraria, Speakers Bureau; Pfizer: Consultancy, Speakers Bureau. Makris: Freeline: Consultancy. Dolan: Takeda: Speakers Bureau; Roche-Chugai: Speakers Bureau; Spark Therapeutics: Speakers Bureau; Octapharma: Speakers Bureau; CSL: Speakers Bureau; Biomarin: Speakers Bureau; Bayer: Research Funding, Speakers Bureau; Novo Nordisk: Research Funding, Speakers Bureau; Pfizer: Research Funding. Tuddenham: Freeline: Consultancy, Current holder of individual stocks in a privately-held company. Long: Freeline: Current Employment. Krop: Freeline: Current Employment. Nathwani: Freeline: Current holder of individual stocks in a privately-held company, Other: Board of directors.

The effect of recombinant factor VIII (rFVIII) brand on inhibitor development was investigated in all 407 severe hemophilia A previously untreated patients born in the United Kingdom (UK) between 1 January 2000 and 31 December 2011. Eighty-eight (22%) had been in the RODIN study. Information was extracted from the National Haemophilia Database. Because exposure days (EDs) were not known for some patients, time from first treatment was used as a surrogate for rFVIII exposure. An inhibitor developed in 118 (29%) patients, 60 high and 58 low titer, after a median (interquartile range) of 7.8 (3.3-13.5) months from first exposure and 16 (9-30) EDs. Of 128 patients treated with Kogenate Bayer/Helixate NexGen, 45 (35.2%, 95% confidence interval [CI] 27.4-43.8) developed an inhibitor compared with 42/172 (24.4%, 95% CI 18.6% to 31.4%) with Advate (P = .04). The adjusted hazard ratio (HR) (95% CI) for Kogenate Bayer/Helixate NexGen compared with Advate was 2.14 (1.12-4.10) (P = .02) for high titer and 1.75 (1.11-2.76) (P = .02) for all inhibitors. When excluding UK-RODIN patients, the adjusted HR (95% CI) for high-titer inhibitors was 2.00 (0.93-4.34) (P = .08). ReFacto AF was associated with a higher incidence of all, but not high-titer, inhibitors than Advate. These results will help inform debate around the relative immunogenicity and use of rFVIII brands.

Abstract 1226 The performance and utility of a condensed bleeding score (Bowman et al, J Thromb Haemost., 2008;6:2062) in relation to the diagnosis of a congenital bleeding disorder in new referrals to a regional haemostasis clinic over an 8 month period is presented. Between November 2010 and June 2011, 50 patients over the age of 16 (median age, 31 years; range, 16–79), including 32 females, were referred for investigation of a possible congenital bleeding disorder following detection of abnormal coagulation results and/or presentation with a bleeding history. A bleeding score was performed as part of their initial assessment. 12(24%) patients were from local referral and 38(76%) patients were referred from other hospitals in the region for further investigation of a suspected bleeding disorder. Basic coagulation tests (activated partial thromboplastin time (APTT), prothrombin time Clauss fibrinogen and platelet count) were normal in the referred patients from other centres. 50% (6/12) of the local referrals were for investigation of a prolonged APTT detected on routine coagulation screening prior to major surgery. The median bleeding score was 6 with a range of −1 to 14 (Table 1). The presence of a congenital bleeding disorder was confirmed in 31 of the 50 patients (62%), including 19/31 (61%) of the female patients and 12/31(39%) of the males. Correlation of an abnormal bleeding score (score ≥ 4) with diagnosis of a congenital bleeding disorder was only seen for diagnosis of type 1 Von Willebrand Disease (VWD) (Table 2). Analysis of the cases with low scores and abnormal results identified two groups of patients; firstly, those who had not yet had a significant haemostatic challenge, and secondly, those in whom the abnormal coagulation results were explained by a non-haemostatically significant reduction in a coagulation factor level (e.g. FVII, 15%; dysfibrinogenaemia; F XII deficiency). These clinically insignificant laboratory abnormalities explain the discrepancy between the number of patients with abnormal laboratory tests (35) and the number of patients diagnosed with a congenital bleeding disorder (31).Table 1Bleeding score (range)Number of patients with normal lab resultsNumber of patients with abnormal lab results−1 to +1382–44105–74128–102311–1422Total1535Table 2DiagnosisNumber of patientsMedian bleeding scoreAge rangeType 1 VWD116 (4–10)17–51Type 2 VWD48 (5–13)17–36Factor XI123 (1–8)17–76Platelet function defect46 (2–9)17–57 Compared to previous reports the range of scores found with this assessment tool was narrow and could not exclude patients from further laboratory assessment. However the condensed bleeding score has only been validated prospectively for the diagnosis of type 1 VWD and all patients in this cohort who were diagnosed with type 1 VWD had an abnormal bleeding score (≥ 4). This observation supports the role of this scoring system in the assessment of patients for type 1 VWD. The use of the condensed bleeding score in assessing patients with suspected factor XI deficiency is difficult due to the lack of a phenotypic relationship between residual factor XI activity and a bleeding tendency. Furthermore, although factor XI deficiency is a rare congenital bleeding disorder in our cohort of patients 12/31(39%) were diagnosed with factor XI deficiency. This may explain the overall lack of correlation between bleeding score and diagnosis of a congenital bleeding disorder. Patients who have an abnormal bleeding score but normal laboratory tests need consideration of further investigations before concluding they are normal. The possibility of an acquired bleeding disorder should be considered. A thorough drug history is also important as one of the patients with a bleeding score of 14 was taking a non-steroidal anti-inflammatory drug. The use of the condensed bleeding score in the detection of congenital bleeding disorders other than type 1 VWD requires further validation in a larger number of patients. Disclosures: No relevant conflicts of interest to declare.

3489 Poster Board III-426 Introduction- Inherited bleeding disorders comprise a heterogeneous group of diseases that reflect abnormalities of coagulation proteins, platelets and blood vessels. Intracranial haemorrhage (ICH) is an unusual but life-threatening complication of such disorders. A 10-year retrospective study was conducted to investigate the episodes of ICH in patients with an inherited bleeding disorder who where followed by a regional haemophilia comprehensive care center in the UK. Methods- All cases of ICH occurring in patients with an inherited bleeding disorder which presented between 1999 and 2009 were retrospectively identified using the haemophilia centre database. Case notes were reviewed and aetiology, clinical features, radiological findings, management and outcome of ICH in this population were studied. Results- Of 640 patients registered with an inherited bleeding disorder in haemophilia centre database, a total of 10 ICHs in 9 patients were identified. Age of patients ranged from 5 months to 72 years with a higher number of males (M:F = 7:2). Diagnosis included: Severe haemophilia A (3 patients); Mild haemophilia A (1 patient); Severe haemophilia B (1 patient); Type 2A von Willebrand disease (VWD) (1 patient); Type 3 VWD (1 patient); Congenital afibrinogenemia (1 patient); Severe factor V deficiency (1 patient). Two of the patients with severe haemophilia A had inhibitors, one of whom was receiving immune tolerance therapy at the time of the ICH. 7 of ICHs were spontaneous and 3 were trauma-related. ICH was the first significant bleeding event in 2 patients- one with severe haemophilia A, aged 5 months, and one with severe haemophilia B, aged 6 months. Type of ICHs were 7 subdural, 1 subarachnoid and 2 subdural with intracerebral. All patients were symptomatic. Common presenting features were headache (6 patients), vomiting (5 patients), limb paralysis (3 patients), cranial nerve palsy (3 patients) and seizures (2 patients). None had systemic bleeding concurrent to the ICH. Initial diagnostic modality was CT scan without contrast for all patients. The two patients with severe haemophilia A and inhibitors were initially treated with recombinant factor VIIa. The remaining patients with haemophilia were treated with factor VIII/IX concentrate. The patient with severe haemophilia B required surgical evacuation. The patients with severe haemophilia A/B without inhibitors were commenced on long-term prophylaxis with factor replacement therapy following their ICH. The patient with congenital afibrinogenemia was initially treated with fibrinogen concentrate, repeated CT scan on day ten showed significant expansion of hematoma, surgical evacuation was done and he was commenced on long-term prophylaxis. The patient with factor V deficiency received prothrombin complex concentrate (octaplex). The two patients with VWD were treated with haemate P, the patient with type 2A VWD received prophylaxis for 4 weeks. The patient with type 3 VWD died within an hour of admission despite haemate P treatment. Six patients had long-term morbidity including limb weakness, seizure, ventriculoperitoneal shunt and developmental delay. These results are summarized in [Table 1][1]. Conclusions- ICH can occur in patients with a severe inherited bleeding disorder and can result in substantial morbidity and mortality. ICH can also occur in patients with a mild inherited bleeding disorder following trauma. There is no reliable predictor for intracranial bleeding which could aid decision-making in terms of prophylactic therapy to prevent ICH. CT scan is an appropriate initial diagnostic modality. It is important to educate patients and parents about symptoms to allow early diagnosis. Treatment should be administered rapidly to control bleeding in order to limit adverse outcomes. | Age | Sex | Diagnosis | Type of ICH | Spontaneous or traumatic | Long term morbidity/mortality | |:----:| --- | -------------------------- | --------------------- | ------------------------ | -------------------------------------- | | 5Mo | M | Severe Haemophilia A | SDH | Spontaneous | Developmental delay, VP shunt | | 3Y | M | Severe Haemophilia A | SAH | Spontaneous | Limb weakness | | 48Y | M | Severe Haemophilia A | SDH | Spontaneous | Seizure | | 20Y | M | Mild Haemophilia A | SDH and Intracerebral | Traumatic | Nil | | 6Mo | M | Severe Haemophilia B | SDH | Spontaneous | Developmental delay, Seizure, VP shunt | | 37Y | M | Congenital afibrinogenemia | SDH | Spontaneous | Limb weakness | | 72Y | M | Type 2A VWD | SDH and Intracerebral | Spontaneous | Nil | | 19Y | F | Type 3 VWD | SDH | Traumatic | Died | | 53 Y | F | Severe factor V deficiency | SDH | Traumatic | Limb weakness | Table 1 Disclosures: No relevant conflicts of interest to declare. [1]: #T1

The optimal duration of anticoagulation following a venous thromboembolism (VTE) is influenced by the site of the event and the presence of risk factors. After anticoagulation is discontinued, approximately 10% of patients will have a recurrent event. At present, there is no accurate method of identifying this group of patients, in whom the benefits of reanticoagulation may outweigh the bleeding risks. In 2006, Palaretti et al reported the use of a single qualitative d-dimer measurement, 4 weeks after stopping anticoagulation for a spontaneous VTE, to identify patients at increased risk of a recurrent VTE. Our observational study investigates whether serial quantitative d-dimer measurements, after the discontinuation of anticoagulation for VTE, are of use in identifying patients at higher risk of VTE recurrence. We followed an unselected group of patients attending a hospital based Thrombosis Clinic in whom anticoagulation for VTE was stopped. Over a 2 year period from July 2005 to July 2007, anticoagulation was discontinued in 216 patients (112 females, 104 males) after a median period of 6 months’ treatment (range 2–324 months). The patients ranged in age from 16–88 years, with a mean age of 54 years. Of the group, 146 had been anticoagulated for a deep vein thrombosis (DVT), 59 for pulmonary embolism (PE) +/− DVT, and 11 had been anticoagulated for VTE at other sites. Major risk factors for VTE (recent surgical procedure, malignancy, pregnancy) were present at diagnosis in 80 patients. Minor risk factors (minor trauma, prolonged travel or immobility, hormone therapy) were present in 61 patients, while no risk factors were identified in 69 patients. Presence of risk factors was unknown in the remaining 6 patients. After discontinuation of their anticoagulation, patients were followed up in the Thrombosis Clinic for a median of 14.5 months (range 0–41 months). D-dimer measurements were recorded at the point of stopping anticoagulation, 4 weeks later, and then on subsequent clinic visits. Quantitative d-dimer results were obtained using an automated latex immunoassay (Instrumentation Laboratories, d-dimers HS) on an ACL TOP CTS analyser. Recurrence of VTE occurred in 23 of the 216 (10.7%) patients. D-dimer results off anticoagulation were available in 207 patients. Forty six patients had repeatedly high d-dimer measurements (> 300ng/ml) off anticoagulation. D-dimers remained within the normal range in 112 patients. In 33 patients, d-dimers were initially normal, but subsequently became high, while the opposite was true in 16 patients, where initially high d-dimers later fell into the normal range. Of the recurrences, 8 occurred in the group who had repeatedly high d-dimers after anticoagulation was stopped (17.4%), whilst only 3 recurrences occurred in patients whose d-dimers were consistently normal (2.7%). In the group whose d-dimers were initially normal, but subsequently became high during follow up, there were 6 recurrences (18.2%). There was 1 recurrence in the group whose d-dimers were initially high, but then became normal. In the 9 patients in whom serial d-dimer results were not available, 5 recurrent VTE were observed: 4 of these occurred within 4 weeks of the patient stopping anticoagulation. After statistical analysis of the data, taking into account the nature of the original event, age, gender and d-dimer measurements, a high d-dimer off anticoagulation was the only significant independent variable predicting for recurrence of VTE (Chi-square 13.1 p