Histology of normal dog muscle 8 weeks after direct intramuscular injection of AAV-CMV-canine F.IX. (A) Anatomy of dog hindlimb, showing sites of biopsy. (B) Immunofluorescence staining for canine F.IX at injection site. (C) Hematoxylin and eosin staining of same site, showing normal histology. Vacuoles within muscle fibers are due to freeze artifact. (D) Immunofluorescence staining of uninjected muscle in same limb. For all panels, original magnification ×100.