TARGETED EXPRESSION OF TRANSFORMING GROWTH-FACTOR-BETA-1 IN INTRACARDIAC GRAFTS PROMOTES VASCULAR ENDOTHELIAL-CELL DNA-SYNTHESIS

Intracardiac grafts comprised of genetically modified skeletal myoblas ts were assessed for their ability to effect longterm delivery of reco mbinant transforming growth factor-beta (TGF-beta) to the heart. C2C12 myoblasts were stably transfected with a construct comprised of an in ducible metallothionein promoter fused to a modified TGF-beta 1 cDNA. When cultured in medium supplemented with zinc sulfate, cells carrying this transgene constitutively secrete active TGF-beta 1. These geneti cally modified myoblasts were used to produce intracardiac grafts in s yngeneic C3Heb/FeJ hosts. Viable grafts were observed as long as three months after implantation, and immunohistological analyses of mice ma intained on water supplemented with zinc sulfate revealed the presence of grafted cells which stably expressed TGF-beta 1. Regions of appare nt neovascularization, as evidenced by tritiated thymidine incorporati on into vascular endothelial cells, were observed in the myocardium wh ich bordered grafts expressing TGF-beta 1. The extent of vascular endo thelial cell DNA synthesis could be modulated by altering dietary zinc . Similar effects on the vascular endothelial cells were not seen in m ice with grafts comprised of nontransfected cells. This study indicate s that genetically modified skeletal myoblast grafts can be used to ef fect the local, long-term delivery of recombinant molecules to the hea rt.