Tissue distribution of MSCs transplanted into NOD/SCID mice. (A-B) Frequency and distribution of fluorescence-labeled MSCs in murine organs. MSCs were labeled with the vital dye PKH-26 or CFSE and intravenously injected. At 2, 6, or 24 hours after transplantation with 1 × 106 MSCs, mice were killed, organs were minced, and single-cell suspensions were prepared. (A) The incidence of labeled cells was determined by flow cytometry by determination of the number of fluorescing cells per 100 000 cells, including non-transplanted controls. (B) Absolute numbers of MSCs homed per organ were determined as described in “Materials and methods.” Values are means ± SD from 4 (2 hours, 6 hours) or 8 (24 hours) mice. (C) Microscopic analysis of transplanted PKH-labeled MSCs. Cryosections from lung, liver, and spleen were derived from organs of mice given transplants 24 hours after transplantation of 5 × 106 PKH+ MSCs. ECs and vessels were stained with fluorescence-labeled anti-CD31 antibody (green), transplanted prelabeled MSCs were visualized by their PKH fluorescence (red; indicated by arrowheads), and nuclei were stained by DAPI (blue). Original magnification, × 200. MSCs used for these experiments were from passages 6 or 7.
