GENETICALLY-MODIFIED SKIN TO TREAT DISEASE - POTENTIAL AND LIMITATIONS

Molecular definition of disease at the level of the gene and advances in recombinant DNA technology suggest that many diseases are amenable to correction by genes not bearing the defective elements that result in disease. Many questions must be answered before this therapy can be used to correct chronic diseases. These questions fall into safety an d efficacy categories. Experience with transplanting cellular elements of skin or skin substitutes (defined as skin that possess the cell ty pes and a dermal structure to develop into a functioning skin) to athy mic rodents is considerable and is seen as a system where these questi ons can be answered. This paper reviews these questions and presents o ur early analysis of genetically modified cells in skin substitutes in vivo and in vitro. Experimental data demonstrate that both a matrix o f woven nylon, housing a fibroblast generated collage, and dead dermis can be utilized to shuttle genetically modified human fibroblasts fro m the laboratory to an in vivo setting. Genetically modified fibroblas ts do not migrate from the shuttle to the surrounding tissue. The surv ival of significant numbers, similar to 70%, of genetically modified f ibroblasts for at least 6 weeks in these shuttles, supports this gener al approach as having clinical utility. It is also concluded that skin substitute systems can be used to generate a genetically modified ski n in vitro that has the capacity to develop into functional skin in vi vo. Further, as genetically modified keratinocytes differentiate there is increased production by the transgene, supporting the concept that keratinocytes have true potential as shuttles for therapeutic genes. This work demonstrates that transplantation of systems containing gene tically modified cells of the skin can be used to experimentally defin e many aspects of gene therapy using skin before this technology is ta ken to the clinic. Examples include determining the effect of gene tra nsduction and expression on structure and function of the genetically modified skin as well as on distant skin and an assessment of the tran slational capacity of the transgene as function of time and cell numbe r.