GENETICALLY-MODIFIED HUMAN EP OVEREXPRESSING PDGF-A DIRECTS THE DEVELOPMENT OF A CELLULAR AND VASCULAR COLLECTIVE TISSUE STROMA WHEN TRANSPLANTED TO ATHYMIC MICE - IMPLICATIONS FOR THE USE OF GENETICALLY-MODIFIED KERATINOCYTES TO MODULATE DERMAL REGENERATION

We investigated the hypothesis that keratinocyte-produced platelet-der ived growth factor-AA (PDGF-AA) is involved in epidermal-dermal intera ctions and that PDGF-AA is an important mediator of the temporal and s patial events of tissue repair. Retroviral-mediated gene transfer was used to introduce the gene encoding human PDGF-A into cultures of huma n diploid keratinocytes, Genetic modification boosted the endogenous i n vitro level of PDGF-AA secretion by over 300 fold. When PDGF-secreti ng cells were transplanted as epithelial sheets to athymic mice, modif ied keratinocytes underwent terminal differentiation and generated a s tratified epithelium comparable to unmodified cells. Seven days after grafting the newly synthesized connective tissue layer subjacent to th e PDGF-A-modified grafts was significantly thicker, was rich in mononu clear cells and fibroblasts, and had increased numbers of blood vessel s when compared to control grafts of unmodified cells. These results s uggest that PDGF-AA secreted by the epidermis is an important mediator of epithelial-mesenchymal interactions and helps to promote growth an d vascularization of the underlying dermal tissue. Further, these data demonstrate the feasibility of using genetically modified cells to mo dulate tissue regeneration.