Combination of SCF and TPO stimulates neutrophilic cell production by CD34⁺ cord blood cells in serum-deprived liquid culture. (A) CD34⁺ cord blood cells (2 × 10⁴) were plated per well containing serum-deprived liquid culture medium supplemented with SCF, TPO, G-CSF, or GM-CSF, alone or in combination. Half of the cells and culture medium were replaced weekly with fresh medium containing growth factor(s). Numbers of viable cells were serially counted. (B) The cultured cells were processed for staining with POX. The results shown are from one representative experiment of three. Similar results were obtained in the other two experiments. SCF (○), TPO (◊), G-CSF (▵), GM-CSF (□), SCF + TPO (•), SCF + G-CSF (▴), SCF + GM-CSF (▪).