Participation of stem cells from human cord blood in skeletal muscle regeneration of SCID mice

Objective In this report, we demonstrate the participation of human cord blood (HUCB) stem cells in the skeletal muscle regeneration of SCID (severe combined immunodeficient) mice. Materials and Methods The HUCB cells were labeled with the PKH26 fluorescent marker or recognized by an anti-HLA-ABC or anti-β-2-microglobulin antibody. The HUCB cells were implanted directly into the damaged mouse muscle. The regeneration process and the implanted HUCB cells were traced each day after the damage, throughout a period of 7 days, and additionally at day 30 with the use of flow cytometry and confocal microscopy. Results The PKH26-labeled cells isolated from the regenerating muscle were positive for the anti-HLA-ABC antibody. The percentage of the PKH26+ and HLA-ABC+ cells decreased from day 1 to day 5. In the regenerating muscle, the percentage of the HLA-ABC+ cells increased, as measured on days 7 and 30. Moreover, myofibers containing fragments of the PKH26-labeled sarcolemma were noticed. Labeling with the anti-human β2-microglobulin antibody showed the presence of positive cells and myofibers at day 7 of the regeneration, suggesting fusion of human and mouse cells. Conclusions We suggest that the HUCB cells implanted into the damaged muscle are present there for at least 30 days and that they participate in the muscle regeneration. Moreover, our study shows that the implanted HUCB cells form human muscle precursor cells residing in the repaired mouse muscle. We suggest that the HUCB cell circulation after transplantation depends on SDF-1 (stromal-derived factor-1) expression in regenerating muscle.