Effect of MPA on pRb phosphorylation. Immunoblot analysis of pRb in resting peripheral blood T lymphocytes (lane 1), T lymphocytes stimulated with IL-2/PHA-L alone (lane 2) or in combination with 1 μmol/L MPA (lane 3), 1 μmol/L MPA plus 50 μmol/L guanosine and 100 μmol/L 8-aminoguanosine (lane 4), 250 μmol/L hydroxyurea (lane 5), 10 μmol/L ara-C (lane 6), and 1 μg/mL aphidicolin (lane 7). Cells were harvested after 24 hours of treatment and drugs were added at time 0.