Dose-dependence of induced differentiation by ATRA or Vit D3 in antisense RB-transfected and mock-transfected U-937 cells. Cells (0.2 × 10⁶ /mL) of (▪) the antisense transfected clone A1 and (□) mock-transfected clone M6 were incubated with ATRA (A) at concentrations ranging from 0 to 10 μmol/L or Vit D3 (B) at concentrations ranging from 0 to 100 nmol/L for 4 days followed by an NBT-reducing test. It was not possible to use higher concentrations of inducer due to toxic effects. Two hundred cells from each clone were counted and the percentage of cells containing reduced NBT was determined. Results shown are from one representative experiment.