Plasma hFIX:Ag concentrations in mice after prenatal intravascular injection. At 16 days' gestation, fetal hemophilic mice (A-B) or outbred normal MF1 mice (C) were injected intravascularly with hFIX adenovirus (A) or hFIX lentivirus (B-C). Monthly blood samples were collected into citrate buffer for plasma analysis of hFIX concentrations. Open symbols indicate sampling times for FIX:C assay (A-B) or liver biopsy and blood collection for liver enzyme analysis (C). Labels T1-T6 correlate hFIX:Ag with immunohistochemistry shown in Figure 2. The arrows indicate the time at which hemophilic mice were immune challenged with hFIX in adjuvant. Dashed lines indicate approximate equivalences to percentages of normal human hFIX:Ag plasma levels.