Fig. 3. Regenerating muscles of SP-transplanted mice contain a population of GFP⁺/CD45^–/Sca-1⁺ cells. (A) Analysis of muscle mononuclear cells 5 days post-CTX of both transplant types revealed a large population of infiltrating immune cells (upper right quadrant) as well as a smaller population of muscle-resident CD45⁺ cells (upper left quadrant). SP-transplanted mice also contained a population of donor-derived cells that have lost CD45 (lower right quadrant). (B) 14 days after CTX damage, the percentages of GFP⁺/CD45^– and GFP^–/CD45⁺ populations (in both transplant types), as well as GFP⁺CD45^– cells from the SP-transplanted mice, were reduced. In WBM transplants, the percentage of GFP⁺/CD45^– cells was stable. (C) Comparing the abundance of this population of donor-derived CD45^– cells across the two transplant types, SP-transplanted mice contained significantly more GFP⁺/CD45^– cells than did their WBM-transplanted counterparts 5 days after damage (P=0.1, Wilcoxon ranksum test, n=4). We believe that these donor-derived cells are not an inflammatory population because the cells do not express the hematopoietic marker CD45. Analysis carried out 14 days post-CTX did not show any significant difference between the two transplant types. (D) GFP⁺/CD45^– cells isolated from SP-transplanted mice sacrificed 5 days post-CTX were analyzed for Sca-1 expression and were 97.3% positive for this marker.