Evidence of F.IXprotein in subject Fmuscle. (A) Western blot for human F.IX on protein extracted from tissue removed at bedside on patient expiry (top half) and at autopsy (bottom half); A indicates autopsy; R, right leg; L, left leg; F.IX, Benefix recombinant hF.IX control. (B) H&E stain of patient-injected muscle showing normal histology. (C-D) F.IX IHC of strongly F.IX-positive (C, same sample boxed in red from panel A) and very weakly positive (D, same sample boxed in black from panel A) tissue sections of injected patient muscle. (C-F) Magnification: ×20; red stars indicate F.IX-expressing muscle fibers; and white stars, no F.IX production. (E-F) F.IX IF of strongly F.IX-positive (E, same sample boxed in red from panel A) and very weakly positive (F, same sample boxed in black from panel A) sections of injected patient muscle.