Human purine nucleoside phosphorylase and adenosine deaminase: gene transfer into cultured cells and murine hematopoietic stem cells by using recombinant amphotropic retroviruses - Mclvor, RS; Johnson, MJ; Miller, AD; Pitts, S; Williams, SR; Valerio, D; Martin, DW, Jr; Verma, IM (Mol Cell Biol, 1987)