Gene therapy of apolipoprotein E-deficient mice using a novel macrophage-specific retroviral vector

The use of retroviral gene transfer into hematopoietic stem cells for human gene therapy has been hampered by the absence of retroviral vectors that can generate long-lasting, lineage-specific gene expression. We developed self-inactivating retroviral vectors that incorporate gene-regulatory elements from the macrophage-restricted human CD68 gene. Through the transplantation of transduced murine hematopoietic stem cells (HSCs), we show that a vector incorporating a 342-base pair (bp) fragment of 5' flanking sequence from the CD68 gene, in addition to the CD68 first intron, was able to direct macrophage-specific expression of an enhanced green fluorescent protein (EGFP) reporter gene in inflammatory cell exudates and lymphoid organs in vivo. Levels of EGFP expression generated by this vector were greater than those generated by a standard Moloney murine leukemia retroviral vector, and they were stable for at least a year after transplantation of transduced HSCs. To evaluate the ability of this vector to generate therapeutically useful levels of gene expression, we transplanted apolipoprotein E (ApoE)-deficient HSCs transduced with a virus encoding ApoE into ApoE-deficient mice. Macrophages from these mice expressed levels of ApoE that were comparable to those from wild-type mice, and vector-driven expression of ApoE in macrophages was sufficient to reverse both hypercholesterolemia and atherosclerotic lesion development. The future application of this retroviral vector should provide a powerful tool to further elucidate macrophage function and for human gene therapy.