EFFICIENCY OF A HIGH-TITER RETROVIRAL VECTOR FOR GENE-TRANSFER INTO SKELETAL MYOBLASTS

Background: Genetic transformation of skeletal myoblasts for myocardia l repair is dependent on an efficient gene transfer system that integr ates the genes of interest into the genome of the target cell and its progeny. The aim of this investigation was to evaluate the use of a ne w retrovirally based gene transfer system for this purpose, Methods: M FGnlslacZ retroviral vector, packaged in high-titer, split-genome pack aging cell line (FLYA4) was used to transduce the skeletal myoblast ce ll line L6. L6 cells, cultured in 10% fetal calf serum, were transduce d with the MFGnlslacZ vector by means of filtered supernatant from FLY A4 cells, Transduced L6 cells were divided into four groups. Group I c ells were fixed as myoblasts 3 days after transduction. Group II cells were allowed to differentiate into myotubes. Group III cells were spl it every 3 days for 4 months. Group IV cells were split as in group II I but then allowed to differentiate into myotubes. All samples were fi xed and stained for beta-galactosidase activity. The effects on gene t ransfer of transforming growth factor-beta, insulin-like growth factor -I, and platelet-derived growth factor were determined by spectrophoto metric assay of beta-galactosidase activity in cells transduced in the presence or absence of serum with 0 to 200 ng/ml of each growth facto r. Results: Morphometric analysis showed that 66.3% +/- 3% to 69.6% +/ - 6% of cells in groups I to IV expressed the lacZ reporter gene. In t he presence of serum, transforming growth factor-beta significantly in hibited gene transfer, whereas insulin-like growth factor-I and platel et-derived growth factor significantly enhanced gene transfer. In abse nce of serum, however, only platelet-derived growth factor enhanced re trovirally mediated gene transfer into skeletal myoblasts. Conclusion: MFG retroviral vectors packaged in FLYA4 cells are efficient in gene transfer into skeletal myoblasts and result in transgenic expression t hat is maintained after repeated cell division, differentiation, or bo th. Platelet-derived growth factor enhances retrovirally mediated gene transfer into skeletal myoblasts.