Abstract
Targeting transgene expression to specific hematopoietic cell lineages could contribute to the safety of retroviral vectors in gene therapeutic applications. Chronic granulomatous disease (CGD), a defect of phagocytic cells, can be managed by gene therapy, using retroviral vectors with targeted expression to myeloid cells. In this context, we analyzed the myelospecificity of the human miR223 promoter, which is known to be strongly upregulated during myeloid differentiation, to drive myeloid-restricted expression of p47(phox) and gp91(phox) in mouse models of CGD and in primary patient-derived cells. The miR223 promoter restricted the expression of p47(phox), gp91(phox), and green fluorescent protein (GFP) within self-inactivating (SIN) gamma- and lentiviral vectors to granulocytes and macrophages, with only marginal expression in lymphocytes or hematopoietic stem and progenitor cells. Furthermore, gene transfer into primary CD34+ cells derived from a p47(phox) patient followed by ex vivo differentiation to neutrophils resulted in restoration of Escherichia coli killing activity by miR223 promoter-mediated p47(phox) expression. These results indicate that the miR223 promoter as an internal promoter within SIN gene therapy vectors is able to efficiently correct the CGD phenotype with negligible activity in hematopoietic progenitors, thereby limiting the risk of insertional oncogenesis and development of clonal dominance.