MURINE HEMATOPOIETIC RECONSTITUTION AFTER TAGGING AND SELECTION OF RETROVIRALLY TRANSDUCED BONE-MARROW CELLS

A major problem facing the effective treatment of patients with cancer is how to get the specific antitumor agent into every tumor cell. In this report we describe the use of a strategy that, by using retrovira l vectors encoding a truncated human CD5 cDNA, allows the selection of only the infected cells, and we show the ability to obtain, before bo ne marrow transplantation, a population of 5-fluouraci-treated murine bone marrow cells that are 100% marked. This marked population of bone marrow cells is able to reconstitute the hematopoietic system in leth ally irradiated mice, indicating that the surface marker lacks deleter ious effects on the functionality of bone marrow cells, No gross abnor malities in hematopoiesis were detected in mice repopulated with CD5-e xpressing cells. Nevertheless, a significant proportion of the hematop oietic cells no longer expresses the surface marker CD5 in the 9-month -old recipient mice. This transcriptional inactivity of the proviral l ong terminal repeat (LTR) was accompanied by de novo methylation of th e proviral sequences. Our results show that the use of the CD5 as a re trovirally encoded marker enables the rapid, efficient, and nontoxic s election in vitro of infected primary cells, which can entirely recons titute the hematopoietic system in mice. These results should now grea tly enhance the power of studies aimed at addressing questions such as generation of cancer-negative hematopoiesis.