Contribution of circulating AC133⁺ stem cells to the replenishment of the satellite cell pool in dystrophic muscles. (A–C) After injection into dystrophic muscle, a few human nuclear lamin A/C–positive cells were distributed near the capillary network (arrows) and regenerating myofibers, identified by a centrally located nucleus (blue after DAPI staining). Double-staining with antibodies against human nuclear lamin A/C (A) and M-cadherin (B) shows that some donor cells express markers typical of satellite cells both outside and underneath (arrowheads) the basal lamina (identified by laminin staining in green). These cells appear pink in the merged image (C) of A and B. (D) Note the presence of several donor lamin A/C (red) cells and M-cadherin (green) double-positive cells (arrowheads) with nuclei localized at the periphery of the fibers under the sarcolemma. (E) We injected a PKH26-labeled AC133 population intramuscularly and sorted PKH26 cells from muscle-derived cells of three scid/mdx mice injected 21 days before. The gated area shown in the top left screen of E corresponds to the sorted population of PKH26-labeled injected cells (inset) that had been stained with anti–M-cadherin (5% of the total PKH26-sorted cells) and resulted in mostly CD34– cells. Few of these cells expressed bright fluorescence such as that of nondividing cells (arrows in inset of E). (F) Expression of endothelial and myogenic markers within three injected TA muscles (M1, M2, and M3) 45 days after injection of AC133⁺ cells isolated from the blood was also demonstrated by RT-PCR. +, positive control; –, negative control.