Abstract: This invention is based on the finding that expression of an exogenous nucleic acid encoding a polypeptide having human T-cell leukemia virus type I (HTLV-1) Tax activity in p53 null cells results in a sensitization of those cells to DNA damaging agents. Therefore, the present invention is directed to a method of inducing cell death in p53 null cells, enhancing susceptibility to such DNA damaging agents, and the selective cell killing of p53 null cells. It has been found that retroviral vectors, and particularly lentiviral vectors, are suitable for the present invention to permit the transient expression of the HTLV-1 Tax protein in the p53 null cells, which sensitizes the cells.