Preselection of transduced murine hematopoietic stem cell populations leads 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 transduce murine hematopoietic cells via retroviruses as a model system for potential human gene therapy. In this paper, we show that transplantation of MDR-transduced midgestational fetal liver cells (FLCs) into lethally irradiated mice leads to the continued presence and expression of the human MDR gene in the short-lived granulocyte-macrophages of recipients' peripheral blood (PB) for up to 12 months. We have also shown the ability of this retroviral system to efficiently transduce several murine FLC subpopulations enriched for hematopoietic stem cells (FL-HSCs) both (1) short-term by MDR-polymerase chain reaction analysis of individual day 12 colony-forming unit-spleen and (2) long-term by in vivo maintenance of MDR and expression of its product, p-glycoprotein, up to 1 year in PB. More highly enriched FL-HSC subpopulations show the greatest number of circulating granulocyte-macrophage cells expressing MDR long-term. These studies also show that preselection by fluorescence-activated cell sorting of MDR-transduced and -expressing cells before transplant significantly increases the percentage of circulating granulocyte-macrophage cells that express MDR at all time points analyzed posttransplant as compared with unsorted cells transduced in the same manner (P < .01). These results have potentially significant implications for future human gene therapy trials.