EB

The epidermolysis bullosa (EB) consortium consisted of three expertise centers (Groningen, Freiburg, Madrid) for the hereditary disease EB, which is characterized by blistering of the skin and mucosae following minor friction or trauma. The disease severity of EB varies from limited blisters in the skin to a lethal form involving internal epithelial lining. The management of EB is mainly supportive with symptomatic treatment, since currently no cure exists. In 1997, patches of unaffected skin were discovered on the hands and upper arms in a patient with EB. This natural correction was named “Revertant Mosaicism (RM)”. In 2009, in a subset of Dutch patients RM was identified in 35% of the patients. However, only 2 revertant EB cases had been identified outside the Netherlands. Therefore, in aim 1 the knowledge from Groningen in identifying RM would be shared with the other two centers in order to identify more patients with RM. Further, to increase the awareness among (geno)dermatologists, a symposium would be organised in the frame of this grant (aim 2). RM attests to the feasibility of cell therapy using the patient’s own naturally corrected cells for autotransplantation, and thereby circumvents the restrictions of genetic modification. Before a start could be made for successful cell therapy, optimal growth and selection conditions needed to be identified (aim 3). The revertant keratinocytes would be subsequently used to generate a skin equivalent (aim 4) and tested in a skin-humanized mouse model suitable to test revertant cell therapy (aim 5).

Aim 1: Examining of individuals in Madrid and Freiburg led to the identification of more patients with RM. The patients were specifically interviewed relating to skin areas where blistering did not occur. Even when the patients were not aware of having such areas, careful clinical examination revealed in Freiburg and Madrid putative revertant patches in 19 and 4 patients with different subtypes of EB, respectively. Several publications have described the underlying correction mechanism in these patients.
Aim 2: The first symposium on “Natural Gene Therapy of the Skin” was held prior to the 41st annual meeting of the European Society for Dermatological Research on Wednesday 7 September 2011 in Barcelona. The programme consisted of a variety of invited speakers: from the occurrence of mosaicism in plants, animal models to study mosaicism, to natural gene therapy in hematological disorders and of course, natural gene therapy in the skin. The symposium had more than 90 participants. A summary of the symposium was published in “Experimental Dermatology”.
Aim 3-5: The naturally corrected revertant keratinocytes provide an opportunity for autologous cell therapy. In one patient we sought to locally treat EB by transplantation of revertant skin. Persistent ulcers (> 1 year) in the patient with non-Herlitz junctional EB caused by mutations in the LAMB3 gene were treated by transplantation of 73 3-mm split-thickness biopsy specimens from one of his revertant patches. All transplanted biopsy specimens were accepted and complete re-epithelialization occurred within 14 days. During 18 months of follow-up, the patient never experienced blisters or wounds in the grafted area, nor in the healed donor sites. This case demonstrated that phenotypical and genotypical correction of skin in patients with RM by expansion of revertant skin might be a promising therapeutic option for cutaneous manifestations of EB. A limitation of this technique of punch grafting is however, the limited expansion of revertant skin.
Another technique that was investigated is revertant cell therapy by using the patient’s revertant cells for skin graft production. In the three different centers, keratinocytes and fibroblasts were cultured of revertant skin areas of several patients. From a patient with EB due to mutations in the COL17A1 gene a 6-mm punch biopsy was taken of a revertant patch of the forearm. Subsequently, keratinocytes were cultured for several passages. Our data demonstrated that after a marked decrease during in-vitro expansion on plastic, the percentage of revertant keratinocytes stabilizes during skin equivalent production and remains stable in-vivo. Further, we showed long-term survival of revertant keratinocytes because of transplantation of revertant epidermal stem cells, thereby demonstrating the feasibility of revertant cell therapy for patients with EB.