PRESELECTION OF TRANSDUCED MURINE HEMATOPOIETIC STEM-CELL POPULATIONSLEADS TO INCREASED LONG-TERM STABILITY AND EXPRESSION OF THE HUMAN MULTIPLE-DRUG RESISTANCE GENE

We have been using the human multiple drug resistance (MDR) gene to tr ansduce murine hematopoietic cells via retro troviruses as a model sys tem for potential human gene therapy. In this paper, we show that tran splantation of MDR-transduced midgestational fetal liver cells (FLCs) into lethally irradiated mice leads to the continued presence and expr ession of the human MDR gene in the short-lived granulocyte-macrophage s of recipients' peripheral blood (PB) for up to 12 months, We have al so shown the ability of this retroviral system to efficiently transduc e several murine FLC subpopulations enriched for hematopoietic stem ce lls (FL-HSCs) both (1) short-term by MDR-polymerase chain reaction ana lysis of individual day 12 colony-forming unit-spleen and (2) long-ter m by in vivo maintenance of MDR and expression of its product, p-glyco protein, up to 1 year in PB. More highly enriched FL-HSC subpopulation s show the greatest number of circulating granulocyte-macrophage cells expressing MDR long-term. These studies also show that preselection b y fluorescence-activated cell sorting of MDR-transduced and -expressin g cells before transplant significantly increases the percentage of ci rculating granulocyte-macrophage cells that express MDR at all time po ints analyzed posttransplant as compared with unsorted cells transduce d in the same manner (P<.01). These results have potentially significa nt implications for future human gene therapy trials. (C) 1995 by The American Society of Hematology.