LONG-TERM EXPRESSION OF THE GENE ENCODING GREEN FLUORESCENT PROTEIN IN MURINE HEMATOPOIETIC CELLS USING RETROVIRAL GENE TRANSFER1

BACKGROUND: A major goal in retroviral-based gene therapy is to establish methods that allow for selection and tracking of transduced cell populations. Green fluorescent protein (GFP) may be useful for gene therapy applications because it is a naturally fluorescent protein that can be detected using conventional flow cytometers facilitating rapid analysis and purification of transduced cell populations. However, it is unknown whether GFP can be stably expressed in vivo, particularly in multiple bone marrow-derived cell lineages. METHODS: A murine retrovirus carrying the gene encoding GFP was used to infect murine bone marrow cells (BMCs). These studies were conducted to (1) directly determine whether GFP could be used as a marker of BMC transduction, (2) determine whether GFP is capable of being expressed in multiple bone marrow-derived hematopoietic cell lineages, and (3) determine whether GFP could be used to follow the fate of transduced cells in vivo. RESULTS: Infection of BMCs with retroviruses carrying the gene encoding GFP resulted in a fluorescent signal in viable transduced cells that was detectable by flow cytometry. Expression of GFP was detected in multiple bone marrow-derived cell lineages after transduction, including stem cell antigen-positive (Sca-1+), lineage marker-negative (Lin-) cells. Using GFP as a selectable marker, we were able to enrich for transduced cells by cell sorting. Mice reconstituted with enriched populations of GFP+ cells showed a significant increase in the percentage of cells expressing GFP in the periphery when compared with mice reconstituted with unenriched transduced bone marrow. CONCLUSIONS: These data indicate that GFP can be used to select for transduced BMCs in vitro, expressed in multiple bone marrow-derived cell lineages, used to select transduced cells, and follow the fate of transduced cells long-term in vivo.