Administration of MAPC1591, and not MPC1609, reduces joint bleeding, joint edema, and synovitis in hemophilia A mice following needle puncture joint injury. A single dose of control IgG, MPC1609, or MAPC1591 (1 mg/kg) was administered to FVIII^−/− mice ip. Twenty-four hours later, joint bleeding was induced with a needle puncture. Mice were monitored for 14 days to assess changes in the joint diameter and to determine the VBS. (A) Knee joint diameter, before the injury and alternate days for 2 weeks following the injury, was measured using electronic calipers. The diameter of the knee joint before the injury was subtracted from the diameter following the injury, and the differences in the knee joint diameter were plotted as the percentage change in joint diameter. (B) Joint bleeding was evaluated by physical examination of knee joints and assigning an arbitrary score (0 to 3; 0, normal knee and absence of blood; 1, normal knee, and presence of blood; 2, distended but not a tense knee, and presence of blood; 3, tense and distended knee, and presence of blood). (C) Photographs of representative knee joints at the end of 14 days after the injury. Mice were euthanized, and the hind limbs were photographed after removing overlying skin. UN, an uninjured knee. (D) Synovitis score. Synovitis scores were assigned as described in “Materials and methods,” and the maximum synovitis score was 11. *Statistically significant difference in the data between mice administered with control IgG and mice administered MAPC 1591. #Statistically significant difference in the data between mice administered with MPC1609 and mice administered with MAPC1591. Data were plotted as ± standard error of the mean (SEM; n = 7 to 8 mice per group). *,#P < .05; **,##P < .01; ***P < .001; ****P < .0001.