One-half of the cells to be reinfused will be transduced with a retroviral vector containing the gene for the multidrug resistance protein (MDRI in vector G1MD) and the other half will be transduced with a vector containing the neomycin resistance gene (NeoR in vector G1Na.40). Both of these vectors have previously been approved by the Recombinant DNA Advisory Committee for PBPC transduction in Medicine Branch protocols.