Translating the combination of gene therapy and tissue engineering for treating recessive dystrophic epidermolysis bullosa

The combination of gene therapy and tissue engineering is one of the most promising strategies for the treatment of recessive dystrophic epidermolysis bullosa (RDEB). RDEB is a rare genetic disease characterised by mutations in the COL7A1 gene, encoding type VII collagen (COLVII), which forms anchoring fibrils at the dermal-epidermal junction of the skin. This disease causes severe blistering and only palliative treatments are offered. In this study, the base of a strategy combining gene therapy and a tissue-engineered skin substitute (TES), which would be suitable for the permanent closure of skin wounds, was set-up. As a high transduction efficiency into fibroblasts and/or keratinocytes seems to be a prerequisite for a robust and sustained correction of RDEB, different envelope pseudotyped retroviral vectors and the transduction enhancer EF-C were tested. When green fluorescent protein (GFP) was used as a reporter gene to evaluate the retroviral-mediated gene transfer, the fibroblast infection efficiency was 30 % higher with the Ampho pseudotyped vector as compared with the other pseudotypes. At least a 3.1-fold and a 1.3-fold increased transduction were obtained in fibroblasts and keratinocytes, respectively, with EF-C as compared with polybrene. A continuous and intense deposit of haemagglutinin (HA)-COLVII was observed at the dermal-epidermal junction of self-assembled TESs made of cells transduced with a HA-tagged COL7A1 vector. Furthermore, HA-tagged basal epidermal cells expressing keratin 19 were observed in TESs, suggesting stem cell transduction. This approach could be a valuable therapeutic option to further develop, in order to improve the long-term life quality of RDEB patients.

Generation of a high-titer packaging cell line for the production of retroviral vectors in suspension and serum-free media

Several patients with severe combined immunodeficiency-X1 disease and adenosine deaminase deficiency have been cured by retroviral-mediated gene therapy. Despite the earlier success, the production of retroviral vectors for clinical gene therapy is cumbersome, costly and lacks safety features because of the adherent nature of packaging cells and the necessity to supplement the culture media with bovine serum. The aim of this study was to generate a retrovirus packaging cell line that could be used for the production of large clinical batch vectors. Bicistronic vectors containing an internal ribosomal entry site followed by a selection gene were used to express Moloney murine leukemia gag-pol and amphotropic envelope viral proteins in HEK293 cells. The candidate clone (293GP-A2) that was selected as the packaging cell line could release recombinant green fluorescent protein retroviruses at 4x10(7) infectious viral particles per ml. Similar titers were achieved after these cells were adapted to grow in suspension and serum-free media. Furthermore, using the same culture conditions viral titers proved to be stable for a 3-month culture period. The 293GP-A2 packaging cell line has the potential to be cultured in bioreactors, opening the possibility for large-scale use of retroviral vectors in late stage clinical trials.