Human adult bone marrow contains both hematopoietic stem cells that generat
e cells of all hematopoietic lineages and human mesenchymal stem cells (hMS
Cs), which support hematopoiesis and contribute to the regeneration of mult
iple connective tissues. The goal of the current study was to demonstrate t
hat transduced hMSCs maintain transgene expression after stem cell differen
tiation in vitro and in vivo. We have introduced genes into cultured hMSCs
by retroviral vector transfer and demonstrated long-term in vitro and in vi
vo expression of human interleukin 3 (hIL-3) and green fluorescent protein
(GFP). Protocols were developed to achieve transduction efficiencies of 80-
90% in these stem cells. In vitro expression of hIL-3 averaged 350 ng/10(6)
cells/24 h over 17 passages (>6 months) and GFP expression was stable over
the same time period. Transduced hMSCs were able to differentiate into oste
ogenic, adipogenic, and chondrogenic lineages and maintained transgene expr
ession after differentiation. Parallel studies were performed in vivo using
NOD/SCID mice. Human MSCs expressing hIL-3 were cultured on several matric
es and then delivered by subcutaneous, intravenous, and intraperitoneal rou
tes. Sampling of peripheral blood demonstrated that systemic hIL-3 expressi
on was maintained in the range of 100-800 pg/ml over a period of 3 months.
These results illustrate the ability of hMSCs to express genes of therapeut
ic potential and demonstrate their potential clinical utility as cellular v
ehicles for systemic gene delivery.