Early association of transplanted LSKCD34⁻ hematopoietic cells with vascularized structures. (Left panel) At 24 hours after irradiation at 10 Gy, C57BL/6 recipient mice were transplanted with 1000 LSKCD34⁻ CFSE-labeled cells. One, 3, 5, and 15 hours after transplantation, videos of the hematopoietic reconstitution were performed on the femurs of 3 different mice. Pictures taken over time are representative of the very few frames of the femoral head that contain single cells. Scale bar represents 50 μm. White arrows indicate individual cells, and the fluorescence intensity of these single cells is shown. (Right panel) At the time of irradiation, 30 μg of fluorescent anti–PECAM-1 or anti-IgG isotype antibodies was injected into recipient mice; and 24 hours later, these mice were transplanted with 1000 LSKCD34⁻ CFSE-labeled cells. Five hours after transplantation, videos of the hematopoietic reconstitution were performed on the femurs of 3 different mice. Pictures obtained with the fluorescent anti–PECAM-1 antibodies and the LSKCD34⁻ CFSE-labeled cells represent selected frames (from 349 and 359) of the femoral head. The top window represents a 2-fold enlargement of the indicated femoral area showing CFSE-labeled hematopoietic cells in the vicinity of PECAM-1⁺ cells.