Human miR223 Promoter as a Novel Myelo-Specific Promoter for Chronic Granulomatous Disease Gene Therapy

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.

Brendel and colleagues evaluate the properties of a DNA fragment derived from the human miR223 regulatory region as an internal promoter within self-inactivating (SIN) retroviral vectors for the gene therapy of chronic granulomatous disease (CGD). They show that miR223-driven expression of gp91^phox or p47^phox efficiently corrects the CGD phenotype in mouse models. Importantly, the miR223-driven vector leads to negligible transgene expression in hematopoietic progenitors, which may reduce the risk of insertional oncogenesis and development of clonal dominance that is sometimes observed with SIN retroviral vectors.