FVIII activity and inhibitor analysis. Plasma was collected from each animal prior to and following vector administration at each time point indicated. Chromogenic bioassay analysis was carried out on the samples to determine FVIII activity. The results were compared against pooled human plasma and reported in units of human FVIII activity. A Bethesda assay was employed to establish inhibitor titers for dog D. (A) FVIII activity (solid line, left) and inhibitor analysis (dashed line, right) of HD-CMV-cFVIII–treated dog. The anti–FVIII antibody response showed cross-reactivity with both canine and human plasma. The titer of anti–canine FVIII inhibitors are reported here. (B) FVIII activity of dogs treated with HD-HNF-cFVIII.