Dependence of expansion on initial plating density. (A) Expansion as a function of plating density for passage 3 mMSCs from Bl/6 mice. Cultures were counted every 3 days. Fold increase of cells was determined by total cell number recovered divided by the initial cell number plated. (B) The fold increase in cell number after 12 days of culture for mMSC from 5 different mouse strains. (C) t-CFU assays of the 12-day cultures after initial plating at increasing densities. (D) t-CFU and sc-CFU assays of Bl/6 mMSCs. Data are expressed as the mean ± SE, n = 3to5.