Effect of human MSCs on the engraftment of human hematopoietic cells. (A) BM cells obtained from the MSC-injected or noninjected tibia from the same mouse were examined by flow cytometry at 6 weeks after transplantation. Representative flow cytometric profiles are shown. The relative frequencies of each population are shown at the corner of the respective quadrants. The numbers in parentheses indicate the proportion of CD45⁺ cells positive for each marker. (B) Percentages of human CD45⁺ cells in the right (injected) and the left (noninjected) tibia of the MSC-injected (MSC) and control mice (CT). (C) Absolute numbers of CD34⁺ cells in the right and the left tibia of the MSC-injected and control mice. Each white circle represents one mouse. Values obtained from the same mouse are connected with lines. (D) Distribution of clonogenic progenitors into the right and the left tibia of the MSC-injected and control mice. The proportions of clonogenic cells present in the respective tibia over the total number of clonogenic cells recovered from both tibiae of each mouse are shown (n = 3). ^*P < .05 and ^**P < .01 relative to the noninjected (left) tibia. (E) Secondary transplantation. BM cells obtained separately from the MSC-injected or noninjected tibia from the same mouse were transplanted into separate secondary hosts. Human cell engraftment was analyzed by CD45 expression at 6 weeks after transplantation. Results of 2 pairs of secondary host are shown. Numbers in parentheses above each flow cytometric profile show the percentage of CD45 cells in the BM cells of primary host. The relative frequencies of CD45 cells in secondary hosts are shown in each profile.