SDF-1 enhances the survival of human thymocyte precursors.

(A) Purified CD34⁺ thymic precursor cells were cultured in triplicate for 48 hours in serum-free medium alone (control) or containing rhSDF-1α protein. Annexin V, bcl-2, and bax expression (open histograms) measured by flow cytometry in the thymocytes harvested from control and rhSDF-1α–treated cellular suspensions is shown. Background staining is shown by isotype-matched control antibody (solid histograms). Data are representative results from 3 independent experiments. MFI is shown for bcl-2 staining. (B) Determination of CD34⁺ thymic cell viability after culture for 48 hours in serum-free medium alone (indicated by 1) or supplemented with either rhSDF-1α (2), IL-7 (3), SCF (4), flt3-ligand (5), or a combination of rhSDF-1α plus IL-7 (6), SCF (7) or flt3-ligand (8). Percentage of viable cells was determined by staining with annexin V and propidium iodide. Viable cells were defined as annexin V negative and propidium iodide negative. Data represent the means ± SD of 4 independent experiments, including 3 cultures per point. Asterisks refer to the statistical significance differences between control and the different treatments. *P ≤ .05; **P ≤ .01.