Assessment of the bleeding phenotype in 2bCoF9R338L-transduced rhFIX-primed recipients. The tail bleeding test and the needle-induced joint injury were performed on recipients at least 6 months after HSCT once their inhibitor titers dropped to undetectable. ROTEM and nWB-TGA were performed on blood drawn from the vena cava (terminal experiment). For the tail bleeding test, the tail tip was transected using a 1.6-mm diameter template. Animals were monitored hourly, and bleeding time was recorded. Fifty-microliter blood samples were collected for blood counts before and after the test. Hemoglobin levels before the test were defined as 100%. For the knee joint injury, a G30 × 1/2 needle was used to induce injury in the right knee, leaving the left knee uninjured as an intra-animal control. The diameter of the knee joint was measured using a digital micro caliper before and 48 hours after injury. The diameter of the knee joint before the injury was defined as 1. (A) Bleeding time from the tail bleeding test. (B) The percentage of hemoglobin remaining after the tail bleeding test. (C) The needle-induced knee joint injury. (D) ROTEM analysis of whole blood. (E) TGA analysis of whole blood. WT and FIX^null mice served as controls. Data are presented as mean ± SD except for panel B, which are presented in a box and whisker plot. *P < .05; **P < .01; ***P < .001; ****P < .0001.