In Vivo Imaging of Hematopoietic Stem Cell Engraftment in the Mouse Tibia Bone

Abstract 1286

A fundamental question in stem cell biology is where stem cells reside and how stem cell niches control stem cell activity. Although the hematopoietic stem/progenitor cell (HSPC) is well characterized, our current knowledge of where and how transplanted HSPCs become engrafted is very limited. HSPC transplantation is now routinely done in clinics to correct a variety of bone marrow deficiencies. Considering its extensive use, understanding the HSPC engraftment process has now become critical if we are to improve the treatment strategies. A key to understanding HSPC engraftment is to be able to observe the process in vivo. We aimed to visualize fluorescent HSCs in the mouse tibia bone directly by grinding one side of the tibia until the bone was sufficiently thin for direct observation. By making a “window” into the tibia bone, we were able to observe the early engraftment process of a single HSC forming a colony in real time with high resolution. The Sca-1+, c-Kit+, Lin- (SKL) cells preferred to lodge and proliferate mainly on the osteoblastic niche. In contrast, further purified SKL, CD48-, CD150+ population (SLAM-SKL) was mostly observed in the perivascular niche. When mice were co-transplanted with DsRed+ SKL and GFP+ SLAM-SKL populations, SKL cells were 5–7 times more than SLAM-SKL cells in the bone marrow at Day 7. However, contribution of each population to the blood circulation at the same time was similar, which suggests that the SLAM-SKL cells engrafted in the perivascular niche can produce blood much quicker. We were not only able to observe the engrafted cells but also visualize donor derived cells circulating in the bone marrow in real time. Our study shows a novel technique to understand and highlight the dynamic process of the stem cell engraftment in complex microenvironment of the bone marrow.