Long-term safety and efficacy of lentiviral hematopoietic stem/progenitor cell gene therapy for Wiskott-Aldrich syndrome.

Patients with Wiskott-Aldrich syndrome (WAS) lacking a human leukocyte antigen-matched donor may benefit from gene therapy through the provision of gene-corrected, autologous hematopoietic stem/progenitor cells. Here, we present comprehensive, long-term follow-up results (median follow-up, 7.6 years) (phase I/II trial no. NCT02333760 ) for eight patients with WAS having undergone phase I/II lentiviral vector-based gene therapy trials (nos. NCT01347346 and NCT01347242 ), with a focus on thrombocytopenia and autoimmunity. Primary outcomes of the long-term study were to establish clinical and biological safety, efficacy and tolerability by evaluating the incidence and type of serious adverse events and clinical status and biological parameters including lentiviral genomic integration sites in different cell subpopulations from 3 years to 15 years after gene therapy. Secondary outcomes included monitoring the need for additional treatment and T cell repertoire diversity. An interim analysis shows that the study meets the primary outcome criteria tested given that the gene-corrected cells engrafted stably, and no serious treatment-associated adverse events occurred. Overall, severe infections and eczema resolved. Autoimmune disorders and bleeding episodes were significantly less frequent, despite only partial correction of the platelet compartment. The results suggest that lentiviral gene therapy provides sustained clinical benefits for patients with WAS.

Partial versus complete factor VIII inhibition in a mouse model of venous thrombosis.

INTRODUCTION: Partial inhibition of Factor VIII (FVIII) may provide antithrombotic efficacy whilst avoiding excessive anticoagulation. MATERIALS AND METHODS: We studied the anticoagulant effects of a partial (TB-402) and a complete (BO2C11) FVIII-inhibiting monoclonal antibody (MAb) on FVIII, aPTT, thrombin generation and fibrin deposition in a flow chamber model. The antithrombotic efficacy of TB-402 and BO2C11 was compared in a mouse model of venous thrombosis. RESULTS: Both in vitro and ex vivo, the maximally achievable FVIII inhibition by TB-402 was about 25 to 30%. The degree of inhibition reached a plateau in vitro at 0.316 µg/mL and ex vivo after administering 0.1mg/kg and higher doses. BO2C11 strongly inhibited FVIII:C, up to 91% at 100 µg/mL in vitro, and by 88% ex vivo 1 hour after administering 1mg/kg to the mice. Whereas BO2C11 also markedly prolonged the aPTT and completely inhibited thrombin generation in vitro and ex vivo, the effect of TB-402 on the aPTT and on thrombin generation was limited. Similarly, in a dynamic flow chamber model, TB-402 and BO2C11 inhibited tissue factor-induced human fibrin deposition by 40% and 76%, respectively. In a mouse model of FeCl(3)-induced venous thrombosis, TB-402 (1mg/kg) inhibited thrombus formation to the same extent as BO2C11 (2mg/kg) and enoxaparin (5mg/kg), with a mean (±SD) occlusion time of 51 ± 13 minutes for TB-402, compared to 28 ± 6 minutes for the controls, 51 ± 13 minutes for BO2C11 and 55 ± 11 minutes for enoxaparin. CONCLUSIONS: In this mouse model of venular thrombosis, partial FVIII inhibition yielded similar antithrombotic effects as nearly complete FVIII inhibition. These preclinical data are indicative of a therapeutic potential of partial FVIII inhibition in the management of venous thromboembolism.

Mitogen-activated protein kinases in hemostasis and thrombosis.

The mitogen-activated protein (MAP) kinases ERK2, p38 and JNK1 are present in platelets and are activated by various stimuli, such as thrombin, collagen, von Willebrand factor (VWF) and ADP. Until recently, MAP kinases were only studied in the conventional model of agonist-induced platelet aggregation mediated by fibrinogen and integrin alphaIIbbeta3. However, this approach is likely to be too limited for a physiological understanding of platelet MAP kinases and their signaling pathways. Recent studies with varying blood-flow conditions and animal models of thrombosis have provided deeper insight into the role of MAP kinases in thrombus formation and the dependence of these kinases on shear conditions. This review summarizes and discusses the physiological functions of these kinases in hemostasis and thrombosis as revealed by various technical approaches.