Low doses of Peg IFN-α 2a and Nutlin-3 increase p53 activity. Western blotting demonstrated that the phospho-p53 level in PV CD34⁺ cells from 2 individual patients (PV1 and PV2) was increased after treatment with low doses of Nutlin-3 combined with Peg IFN-α 2a. The p21 protein level was also increased by combination drug therapy.