After an initial harvest of filgrastim (G-CSF)-mobilized autologous peripheral blood stem cells (PBSC) for transplantation, patients receive one additional dose of G-CSF and undergo one additional apheresis. The CD34+ cells are cultured in the presence of recombinant human thrombopoietin, interleukin-3, and flt3 ligand to expand megakaryocytes. Patients then undergo treatment with high-dose chemotherapy (and, in some cases, total body irradiation) followed by reinfusion of the conventional PBSC harvest and the ex vivo expanded megakaryocytes.