Gene transfer into murine hematopoietic stem cells and bone marrow stromal cells

The use of recombinant retroviral vectors to transfer genetic sequences into hematopoietic stem cells (HSC) is one approach to somatic gene therapy. Two limitations of such retroviral vectors are the degree of efficiency of transfer into the reconstituting hematopoietic stem cells and the loss of reconstituting ability of hematopoietic stem cells when manipulated in vitro during infection and selection. We have investigated the effects on the efficiency of gene transfer of prestimulation of hematopoietic stem cells by growth factors prior to infection. Prestimulation of bone marrow cells in WEHI-3b-conditioned media improved the efficiency of gene transfer into CFU-S stem cells. The majority of animals transplanted with bone marrow infected after prestimulation with a simplified retrovirus, Zip PGK ADA, demonstrated long-term and stable expression of human adenosine deaminase (ADA) after full hematopoietic reconstitution. In separate experiments, retroviral vectors have been used to transfer the SV40 large T antigen sequences into stromal cells making up the hematopoietic microenvironment. Stromal cells expressing large T antigen are immortalized, and some support the maintenance of day 12 CFU-S (CFU-S12) and reconstituting hematopoietic stem cells in vitro for up to 4 weeks. Such immortalized stromal cell lines provide an in vitro hematopoietic microenvironment which may allow prolonged in vitro manipulations during infection and selection of hematopoietic stem cells without loss of reconstituting ability. We are using immortalized stromal cell lines resistant to deoxycoformycin (dCF) to select transduced murine HSC containing human ADA in vitro. The use of recombinant retroviral vectors provides a promising approach to correction of human diseases involving bone marrow cells.