Coagulation testing and antibody studies in dog E35. (A) Canine F.IX antigen levels as a function of time after injection. F.IX level peaked 2 weeks after injection and rapidly declined to undetectable. Arrows denote time points at which cyclophosphamide was administered. (B) WBCT as a function of time after injection. The WBCT fell into the normal range by day 6 and began to prolong again by day 15. By day 23 it had returned to the baseline of more than 60 minutes. (C) Bethesda titer as a function of time. An inhibitory antibody of 8.2 BU was first detected at day 27, and persisted for the remainder of the animal's lifespan. (D) Anti–F.IX antibody measured by subclass as a function of time. IgG2 was first detected at high levels (2225 ng/mL) on day 15 after vector injection, prior to appearance of inhibitory antibody or to infusion of canine plasma. IgG1 rose gradually beginning about 35 days after vector injection and continued to rise throughout the course of the experiment.