We have previously shown that a single portal vein infusion of a recombinant adeno-associated viral vector (rAAV) expressing canine Factor IX (F.IX) resulted in long-term expression of therapeutic levels of F.IX in dogs with severe hemophilia B. We carried out a phase 1/2 dose-escalation clinical study to extend this approach to humans with severe hemophilia B. rAAV-2 vector expressing human F.IX was infused through the hepatic artery into seven subjects. The data show that: (i) vector infusion at doses up to 2 x 10(12) vg/kg was not associated with acute or long-lasting toxicity; (ii) therapeutic levels of F.IX were achieved at the highest dose tested; (iii) duration of expression at therapeutic levels was limited to a period of approximately 8 weeks; (iv) a gradual decline in F.IX was accompanied by a transient asymptomatic elevation of liver transaminases that resolved without treatment. Further studies suggested that destruction of transduced hepatocytes by cell-mediated immunity targeting antigens of the AAV capsid caused both the decline in F.IX and the transient transaminitis. We conclude that rAAV-2 vectors can transduce human hepatocytes in vivo to result in therapeutically relevant levels of F.IX, but that future studies in humans may require immunomodulation to achieve long-term expression.

Over-anticoagulation is a common problem with warfarin therapy and can lead to major or life-threatening bleeding. The goal of urgent warfarin reversal is to elevate or replace vitamin K-dependent clotting factors. In the United States, fresh frozen plasma (FFP) is considered the standard of care for warfarin reversal. Prothrombin complex concentrates (PCCs) offer an alternative to FFP for rapidly replacing deficient clotting factors and correcting the international normalized ratio (INR). However, few prospective clinical trials have been conducted to evaluate the effectiveness of these concentrates relative to other treatment modalities. A review of the published literature over the last 30 years found that PCCs offer a rapid and specific method for replacing vitamin K-dependent clotting factors and restoring normal hemostasis in the context of overcoagulation. In those studies in which PCCs were compared with FFP, PCCs were found more effective in shortening the time to INR correction and were associated with a low risk of thrombotic adverse events. Evidence-based treatment guidelines are needed to optimize the use of PCCs for warfarin reversal. Am. J. Hematol. 83:137-143, 2008. V

The therapeutic efficacy of prothrombin-complex concentrates in patients with hemophilia and inhibitors (antibodies) to factor VIII has been increasingly debated. We therefore entered 51 hemophiliacs with factor VIII inhibitors into a double-blind randomized crossover study to compare two commercial prothrombin-complex concentrates (Konyne and Proplex) and an albumin placebo. Acute hemarthrosis of the elbow, knee, or ankle was treated with a single dose of a test preparation and assessed six hours later with objective and subjective criteria. In all measurements the concentrates were significantly more effective than the placebo. The data indicate that although prothrombin-complex concentrates, when used in a single dose, are only partially effective in the treatment of joint hemorrhage in hemophiliacs with inhibitors, their continued use for acute hemarthrosis is justified in the absence of any other effective and readily available therapy for this disorder.

Summary. Background: When life-threatening bleeding occurs in patients on warfarin, timely reversal becomes imperative. In the USA, warfarin effect is commonly reversed with fresh frozen plasma (FFP). The use of FFP is complicated by delays in correction, volume overload and often, inadequate correction. Objective: Evaluate the feasibility and efficacy of a protocol for rapid administration of prothrombin complex concentrate (PCC) in the setting of the urgent need for reversal of warfarin. Methods/patients: We instituted a policy for rapid delivery and administration of PCC. Appropriate patients received 25-50 U kg )1 of PCC. The prothrombin time (PT)/International Normalized Ratios (INR) was recorded before and immediately after dosing, and 24 h postdosing. Patients requiring surgical interventions were cleared for the operating room (OR) immediately. Fifty-eight patients were treated, with a median age of 75.5 years (range 26-92). Results: The median INR on presentation was 3.8 (1.4-52.8). Immediately following PCC administration the median INR was 1.3 (0.9-5.7), only two patients with INRs exceeding 2.0. The benefit was maintained at 24 h with a median INR of 1.5 (1.1-3.4). Four patients experienced thrombotic events during their hospitalization, (two deep vein thrombosis, two non-q-wave myocardial infarction) although none was attributed to PPC therapy. Conclusions: PCC administration is an effective treatment modality for the correction of warfarin anticoagulation in the urgent setting. Advantages over FFP include more timely correction, absence of volume overload and potentially more complete correction. Broader use of PCC in this setting appears to be appropriate.

In view of uncontrolled observations and anecdotal reports suggesting that the activated PCC, Autoplex, was much more effective than standard (non-activated) PCC in controlling bleeding in hemophiliacs with inhibitors, a controlled double-blind study was designed to compare the effectiveness of Autoplex and Proplex. Acute hemarthrosis was chosen for study as this common but non-life-threatening lesion lends itself well to controlled study. A single dose of “unknown” product (Autoplex 75 FECU/kg; Autoplex 50 FECU/kg; or Proplex 75 FIX U/kg) was given, and effectiveness was judged at 6 hr. By all criteria of efficacy, there were no significant differences between the products. It is noteworthy that a single dose of PCC was judged effective in 50% of episodes, a figure that is consistent with other published clinical trials. In this model, no additional benefit was derived from using the activated PCC, Autoplex, in either dosage.