In vivo localization of CD34⁺ cells and their interaction with HMRCs after IBMT of CD34⁺CD38^- or CD34⁺CD38⁺ populations together with human MSCs. (A) Sorting profiles of CD34⁺CD38⁺ and CD34⁺CD38^- populations. The relative frequencies of each population are shown in the corner of the respective quadrants. (B) At 1 or 3 weeks after IBMT, bone sections were stained with an anti-CD34 antibody and examined for counting. Eighteen slides from 3 mice for each group were counted to obtain the proportion of CD34⁺ cells localized to the endosteum (endosteal area) at the both time points. CD34⁺ cells in the endosteal area were further categorized into cells attaching to bone-lining osteoblasts (with osteoblasts) and cells interacting with HMRCs (with HMRCs). The proportions of CD34⁺ cells in each category are shown. At 1 week after IBMT, the proportions of CD34⁺ cells both in the endosteal area and in contact with HMRCs were not different between the 2 groups. At 3 weeks after IBMT, the SRC-enriched CD34⁺CD38^--transplanted group had the higher proportions of CD34⁺ cells in the endosteal area as well as those interacting with HMRCs. At the both time points examined, the proportion of CD34⁺ cells interacted with osteoblasts was higher in the SRC-enriched CD34⁺CD38^--transplanted group. Bars represent the CD34⁺CD38^--transplanted group (▪) and the CD34⁺CD38⁺-transplanted group (□). ^*P < .001, ^**P < .005, and ^***P < .05 relative to the CD34⁺CD38⁺ group.