Continuous expression of mFVIIa-VEAY in hemophilia B mice with inhibitors. (A) Scheme for generating anti–human FIX inhibitory antibodies in HB mice. Downward arrows indicate injection of complete or incomplete Freund adjuvant (CFA and IFA, respectively) complexed with 20 μg of hFIX or administration of AAV-expressing mFVIIa-VEAY. Upwards arrows indicate collection of tail blood to assay Bethesda titer and total anti-hFIX IgG. Timepoints A-C are indicated. (B) Bethesda titers of HB mice before administration of AAV-mFVIIa-VEAY. (C) Total anti-hFIX IgG in HB mice prior (timepoints A-C) and after administration of AAV-mFVIIa-VEAY. *P < .05 vs timepoint A. Nonsignificant (NS) differences are indicated. (D) aPTT in HB mice with inhibitors to hFIX after administration of AAV-mFVIIa-VEAY. *P < .05 vs baseline (week 0). A gray box indicates the range in hemostatically normal mice using human FIX–deficient plasma (32.1 ± 2.4 seconds, n = 10). All data shown as average ± 1 SD.