Effects of ATRA or Vit D3 on NBT-reducing capability of antisense RB-transfected and mock-transfected clones. Cells at an initial concentration of 0.2 × 10⁶ cells/mL were incubated with (A) ATRA (1 μmol/L) or (B) Vit D3 (0.1 μmol/L) for 4 days followed by an NBT-reducing test. Two hundred cells from each clone were counted on a cytospin slide and the percentage of cells containing reduced NBT was determined. Results shown are (A) from one representative experiment and (B) mean values from three separate experiments, bars ± SEM.