(485be) Targeted Gene Delivery to Hematopoietic Stem Cells

Hematopoietic stem cells (HSCs) are often used as targets for therapy because of their self-renewal and multi-lineage differentiation capabilities. Although HSCs only represent a small fraction of cells in the bone marrow they can fully reconstitute all blood cell elements including cells integral to the immune system such as B cells, T cells and dendritic cells. A system to deliver genes specifically to HSCs would be a powerful tool for engineering novel therapies for the hematopoietic system. To circumvent the need for specific targeting, current strategies depend upon direct injection to a localized site with cell-specific promoters/enhancers or, ex vivo isolation, purification, and transduction. The c-KIT receptor (CD117) is a precise marker in the bone marrow for hematopoietic progenitor cells and can serve as a unique molecular determinant to differentiate between cell types that can be targeted for gene therapy. We report herein a targeted lentivector that harnesses the natural ligand?receptor recognition mechanism for targeted modification of c-KIT receptor-expressing cells. For targeting, we incorporate membrane-bound human stem cell factor (hSCF), and for fusion, a Sindbis virus-derived fusogenic molecule (FM) onto the lentiviral surface. These engineered vectors can recognize cells expressing CD117, resulting in efficient targeted transduction of cells in an SCF-receptor dependent manner in vitro, and in vivo in xenografted mouse models. Development of a high titer lentivector to cKIT receptor-specific cells is an attractive tool for stem cell engineering for targeted differentiation and expansion and could potentially ensure therapeutic effects in the desired cells while limiting side effects caused by gene expression in non-target cells.