Analysis of gene transfer efficiency of retrovirus producer cell transplantation for in situ gene transfer to hematopoietic cells

Retronectin enhances lentivirus-mediated gene delivery into hematopoietic progenitor cells

Genetic modification of hematopoietic stem cells holds great promise in the treatment of hematopoietic disorders. However, clinical application of gene delivery has been limited, in part, by low gene transfer efficiency. To overcome this problem, we investigated the effect of retronectin (RN) on lentiviral-mediated gene delivery into hematopoietic progenitor cells (HPCs) derived from bone marrow both in vitro and in vivo. RN has been shown to enhance transduction by promoting colocalization of lentivirus and target cells. We found that RN enhanced lentiviral transfer of the VENUS transgene into cultured c-Kit(+) Lin(-) HPCs. As a complementary approach, in vivo gene delivery was performed by subjecting mice to intra-bone marrow injection of lentivirus or a mixture of RN and lentivirus. We found that co-injection with RN increased the number of VENUS-expressing c-Kit(+) Lin(-) HPCs in bone marrow by 2-fold. Further analysis of VENUS expression in colony-forming cells from the bone marrow of these animals revealed that RN increased gene delivery among these cells by 4-fold. In conclusion, RN is effective in enhancing lentivirus-mediated gene delivery into HPCs.

In vivo gene transfer into adult stem cells in unconditioned mice by in situ delivery of a lentiviral vector

The potential of in vivo lentivirus-mediated bone marrow stem cell gene transfer by bone cavity injection, which could take full advantage of any source of stem cells present there, has not been previously explored. Such an approach may avoid several difficulties encountered by ex vivo hematopoietic stem cell (HSC) gene transfer. We sought to determine if efficient gene transfer could be achieved in HSC and mesenchymal stem/progenitor cells (MSC) by intrafemoral injection of a lentivirus vector in mice. Four months after injection, up to 12% GFP-expressing cells were observed in myeloid and lymphoid subpopulations. Significant transduction efficiencies were seen in Lin(-)c-kit(+)Sca1(+) HSC/progenitors and CFU with multilineage potential, which were also confirmed by duplex PCR analysis of progenitor-derived colonies. Four months after secondary BMT, we observed 8.1 to 15% vector(+) CFU in all recipients. Integration analysis by LAM-PCR demonstrated that multiple transduced clones contributed to hematopoiesis in these animals. We also showed that GFP-expressing MSC retained multilineage differentiation potential, with 2.9 to 8.8% GFP-containing CFU-fibroblasts detected in both injected and BMT recipients. Our data provide evidence that adult stem cells in bone marrow can be efficiently transduced "in situ" by in vivo vector administration without preconditioning. This approach could lead to a novel application for treatment of human diseases.

From leading role to the backstage: Mesenchymal stem cells as packaging cell lines for in situ production of viral vectors

Gene therapy is based on the genetic manipulation of target cells. The genetic information required to genetically engineer these cells can be delivered through non-viral or viral vectors that present different biologic properties. The production of viral vectors for gene therapy depends on the nature of the cells transfected with plasmids containing the genetic information for recombinant viral assemblage. These so-called packaging cell lines (PCL) can be injected into the target organ, for the in situ transduction of target cells. There have been recent reports about the capacity of mesenchymal stem cells (MSCs) to target tumor cells. Different research groups, including our own, have isolated these MSCs, but they have not yet been studied as potential PCL to produce viral vectors. We propose here that a MSC packaging cell line could be employed for in situ gene therapy of solid tumors. The tropism of MSCs for tumor cells may render this PCL more efficient in that microenvironment, producing viral vectors for longer periods of time, shifting MSCs from target cell to the backstage level of viral gene therapy.