Proliferation of pluripotent and committed progenitors in the presence of FTY720. (A) Effect of FTY720 on week-5 cobblestone area formation by mobilized Lin^- progenitor cells. Lin-cells (5 × 10³) were cultured with 1 × 10⁴ single MS-5 or FBMD-1 cells with or without 100 nM FTY720. The effect of the immunomodulator on proliferation of multipotent progenitors was highest in cultures containing MS-5 cells, which are known to produce large amounts of SDF-1. Data represent the mean plus or minus SEM of 4 independent experiments. ^**P < .01. (B) Effect of FTY720 on colony formation by mobilized Lin^- progenitor cells. Colony-forming efficiency was analyzed by standard semisolid culture in methylcellulose medium supplemented with growth factors and the designated concentrations of FTY720. Only at concentrations of FTY720 more than or equal to one μM was the proliferative capacity of lineage-committed progenitors impaired. Data represent the mean plus or minus SEM of 3 independent experiments. □: BFU-E; ▵: CFU-Mix; ○: CFU-GM; •: total colonies.