rhFIX antigen level in tolerized hemophilia B dogs. The level of rhFIX antigen is shown from just before initiation of maintenance through day 475 in the 5 tolerized hemophilia B dogs. Maintenance with subcutaneous rhFIX was started at day 112 as described in Table 1 and adjusted to 82.6 IU/kg twice weekly at day 178. All samples were drawn just prior to the next dose. Error bars indicate SD.