Sustained and promoter dependent bone morphogenetic protein expression by rat mesenchymal stem cells after BMP-2 transgene electrotransfer.

Transplantation of mesenchymal stem cells (MSCs) with electrotransferred bone morphogenetic protein-2 (BMP-2) transgene is an attractive therapeutic modality for the treatment of large bone defects: it provides both stem cells with the ability to form bone and an effective bone inducer while avoiding viral gene transfer. The objective of the present study was to determine the influence of the promoter driving the human BMP-2 gene on the level and duration of BMP-2 expression after transgene electrotransfer into rat MSCs. Cytomegalovirus, elongation factor-1α, glyceraldehyde 3-phosphate dehydrogenase, and beta-actin promoters resulted in a BMP-2 secretion rate increase of 11-, 78-, 66- and 36-fold over respective controls, respectively. In contrast, the osteocalcin promoter had predictable weak activity in undifferentiated MSCs but induced the strongest BMP-2 secretion rates in osteoblastically-differentiated MSCs. Regardless of the promoter driving the transgene, a plateau of maximal BMP-2 secretion persisted for at least 21 d after the hBMP-2 gene electrotransfer. The present study demonstrates the feasibility of gene electrotransfer for efficient BMP-2 transgene delivery into MSCs and for a three-week sustained BMP-2 expression. It also provides the first in vitro evidence for a safe alternative to viral methods that permit efficient BMP-2 gene delivery and expression in MSCs but raise safety concerns that are critical when considering clinical applications.