This study will seek to determine the safety, tolerability, kinetics and efficacy of a single IV infusion of ZS801.~Hemophilia B is a genetic bleeding disorder resulting in the lack of ability to produce blood-clotting factor IX (FIX). Individuals with hemophilia B suffer repeated bleeding events, which can cause chronic joint disease and sometimes leads to death due to the inability for blood to clot efficiently. The current treatment is intravenous infusion of FIX protein products, either prophylactically or in response to bleeding.~ZS801 is an adeno-associated viral (AAV) vector designed to drive expression of the human factor IX (hFIX) transgene and raise circulating levels of endogenous FIX.~Dose-escalation phase: 16 patients will be enrolled sequentially every 3 weeks or more between cohorts and administered with single infusion of ZS801. Dose escalation may occur based on the safety and FIX activity on steady state. The dose levels are as follows: 2.0×10^12vg/kg, 5.0×10^12vg/kg, 1.0×10^13vg/kg.~Dose-expansion phase: 5 patients will be enrolled and be administrated of ZS801.~Subjects will provide informed consent and then undergo screening assessments up to 6-8 weeks prior administration of ZS801. All subjects will undergo 52 weeks safety and efficacy observation.
A non-randomized, open-label, dose-escalation, phase I/II study to evaluate the safety, tolerability, kinetics and efficacy of a single intravenous infusion of ZS801 in hemophilia B subjects with endogenous FIX ≤2%.