Mouse SCF effectively supports human mast cell development in vitro. Human cord blood CD34⁺ cells were cultured with suboptimal (10 ng/mL) and optimal (100 ng/mL) doses of recombinant SCF. The number of mast cells (C) after 6 weeks of culture was assessed in terms of the total number of the viable cells (A) and the Kit⁺ percentage (B) determined by flow cytometric analysis. Bar graphs display mean ± SD values from 3 independent experiments.