Transcriptional targeting of retroviral vectors to the erythroblastic progeny of transduced hematopoietic stem cells

Targeted expression to specific tissues or cell lineages is a necessary fea ture of a gene therapy vector for many clinical applications, such as corre ction of hemoglobinopathies or thalassemias by transplantation of genetical ly modified hematopoietic stem cells. We developed retroviral vectors in wh ich the constitutive viral enhancer in the U3 region of the 3' LTR is repla ced by an autoregulatory enhancer of the erythroid-specific GATA-1 transcri ption factor gene. The replaced enhancer is propagated to the 5' LTR upon i ntegration into the target cell genome. The modified vectors were used to t ransduce human hematopoietic cell lines, cord blood-derived CD34(+) stem/pr ogenitor cells, and murine bone marrow repopulating stem cells. The express ion of appropriate reporter genes (Delta LNGFR, EGFP) was analyzed in the d ifferentiated progeny of transduced stem cells in vitro, in liquid culture as well as in clonogenic assay, and in vivo, after bone marrow transplantat ion in lethally irradiated mice. The GATA-1 autoregulatory enhancer effecti vely restricts the expression of the LTR-driven proviral transcription unit to the erythroblastic progeny of both human progenitors and mouse-repopula ting stem cells, Packaging of viral particles, integration into the target genome, and stability of the integrated provirus are not affected by the LT R modification. Enhancer replacement is therefore an effective strategy to target expression of a retroviral transgene to a specific progeny of transd uced hematopoietic stem cells. (C) 1999 by The American Society of Hematolo gy.