Growth factor delivery from genetically modified skin grafts

Summary form only given. Keratinocytes of the epidermis can be cultured in vitro and have been used as part of a skin substitute for the treatment of defects of the skin such as burns and ulcers. Cultured cells are often combined with various biomaterials to create a composite skin graft. Our goal is to enhance the therapeutic effectiveness of these tissue-engineered skin grafts by genetic modification of the cells. We used retroviral-mediated gene transfer to genetically modify diploid human keratinocytes to express keratinocyte growth factor (KGF), a paracrine mediator of epithelial cell growth and wound healing. Modified keratinocytes secreted high levels of KGF in vitro. To examine the direct effects of KGF on the morphogenesis of the epidermis, we generated skin equivalents in vitro by seeding human keratinocytes on the papillary surface of acellular dermis and raising them up to the air liquid interface. The epidermis of those grafts with cells expressing KGF were significantly thicker, with more basal cells, increased proliferation and delayed differentiation compared to the epidermis formed by control unmodified cells. To investigate the effects in vivo, we transplanted these grafts to full-thickness wounds on athymic mice. At 1 & 6 weeks after transplantation, both grafts formed a stratified and differentiated epidermis, however, the epidermis of grafts of KGF expressing cells was significantly thicker with evidence of suprabasal proliferation. Expression of the hyperproliferative keratin, K16, persisted in grafts of KGF cells and early revascularization of the acellular dermis of these grafts Was enhanced. Composite grafts with genetically modified allogeneic cells may be useful for tissue repair and may offer certain advantages over more conventional means of wound healing growth factor delivery.