Time course of expression and immune response against hF.IX after systemic administration of hF.IX LVs. The plasma levels of human clotting factor IX were monitored after tail-vein injection of LVs expressing hF.IX from the CMV and ALB promoters and vehicle (PBS) into adult C57BL/6 (A) and BALB/c (B) mice. For the ALB LVs, 2 different amounts of vector were injected: 20 μg (ALB I) and 40 μg (ALB II) p24 vector equivalents. Means + SD, n = 4, are shown. (C-G) ELISA immunoassay was performed on the plasma to detect anti-hF.IX antibodies. Absorbance of the indicated dilutions are shown as mean ± SD, n = 4, for panels C-E, and for individual mice for panels F-G. (H) The vector DNA content was measured in the liver and spleen of C57BL/6 LV-injected mice 25 weeks after injection. Means + SD, n = 3, are shown.