Engineering autologous dermo-epidermal skin composites in vitro

Extensive skin loss may result from burns, soft tissue trauma, various skin diseases, and from removal of giant naevi. Taken together, these conditions still represent a significant clinical problem. Although most of these patients survive today, and although various skin transplantation techniques finally allow restoration of skin integrity, the functional and cosmetic results are far from ideal. This is mainly due to disfiguring and often disabling hypertrophic scarring and keloid formation which is a consistent and lifelong sequel after large scale skin transplantation, particularly in children. Thus, an autologous dermo-epidermal skin substitute (consisting of cultured human keratinocytes, endothelial cells, myoepithelial cells and fibroblasts) which is timely available, easily transplantable and that yields functional and cosmetic long-term results with minimal or even no scarring would be an optimal solution to repair large skin defects.

Our goal is to develop autologous dermo-epidermal skin composites (full thickness skin analogues) that can be used clinically to cover skin defects of any origin in one single surgical intervention. To achieve that, these composites have to fulfill the following criteria:
a) the dermo-epidermal graft serves as a skin analogue both morphologically and functionally
b) it contains an intact stem cell compartment
c) it is rapidly and sufficiently vascularized after grafting
d) it has adequate mechanical properties for transplantation, in particular is has developed a robust dermo-epidermal junction

We are currently testing different types of biodegradable matrices which serve as dermal templates with regard to being populated by endothelial cells and fibroblasts. Additionally, we are creating genetically engineered allogeneic fibroblasts overexpressing and releasing biologically active molecules, such as certain members of the Wnt, Notch and Hedgehog families, which are thought to be implicated in the maintenance of the stem cell compartment. This gene transfer approach is deliberately designed to bring about the transient expression of the "therapeutic" gene. The transient character of this strategy results from the fact that the genetically manipulated fibroblasts are allogenic and hence will be eliminated by the immune system within 3-4 weeks.
Some of the cultured dermo-epidermal composites have already been transplanted onto immuno-incompetent rats to study take, engraftment, as well as early and late functional and cosmetic results.
As soon as a cultured skin substitute performs successfully in the animal model, a clinical pilot study will be envisioned.