Blockade of SDF-1/CXCR4 signaling arrests human thymocyte development.

SCID fetal thymic lobes seeded with highly purified CD34⁺human thymic precursors were organ cultured for 18 days in the absence (control) or presence of neutralizing anti–SDF-1α antibodies or blocking anti-CXCR4 mAbs. Cells were triple labeled as described in “Materials and methods” with antihuman CD45-FITC, anti–CD4-PerCp, anti–CD3-PE, or anti–CD8-PE. Dot plots show CD4 versus CD8 or CD3 expression on gated human CD45-FITC⁺ cells. Data are representative of 4 independent experiments.