The next cycle will consist of high-dose single agent thiotepa. Hematopoietic stem cells mobilized and collected during the previous cyclophosphamide cycle and transduced with the retroviral vectors will be reinfused following treatment with thiotepa to augment recovery of bone marrow function. After recovery, intensification with natural product chemotherapy will be administered, consisting of four cycles of paclitaxel given as a 24-hour infusion followed by four cycles of single agent doxorubicin. Peripheral blood mononuclear cells will be monitored following each cycle of paclitaxel and doxorubicin for the presence of the MDRI and NeoR transgenes. The ration of the levels of MDRI to NeoR transgenes in peripheral blood will determine whether in vivo expansion of the PBPCs containing the selectable MDRI marker has been achieved.