TRANSPOSMART

Type 3 von Willebrand disease, which has a prevalence below five per million, is caused by the absence of the haemostatic protein von Willebrand factor, leading to a severe bleeding disorder. Since the disease treatment requires high blood levels of von Willebrand factor, a therapeutic approach ensuring highly efficient and prolonged in vivo production of the missing protein would be of particular benefit for the patients in terms of health, comfort of life and cost. 
Liver is an optimal organ for the secretion and systemic distribution of a therapeutic transgene product and has been shown to efficiently express the functional transgene von Willebrand factor. The TranspoSMART consortium will assemble and fine-tune “cutting edge” gene therapy tools, in particular non-viral vectors in order to produce a high and sustained level of therapeutic protein secretion by the liver. The Transposmart approach offers an optimal strategy to deliver and express the von Willebrand factor-encoding gene in the liver, for blood secretion. 

By using a physical technique and an optimized “miniplasmid” free of antibiotic resistance gene (pFAR), we could obtain a level of production of von Willebrandt Factor higher than the physiological level. Blood circulating von Willebrandt Factor was stable for several weeks. Identical results were obtained by using a viral vector, called “recombinant adenovirus”. In both cases, genomic integration of the von Willebrandt therapeutic gene was obtained by using an innovative technology: the Sleeping Beauty transposon. Another advanced molecular tool, the use of “S-MAR matrix attachment regions” did not show any decisive advantage for the in vivo expression of the von Willebrandt Factor.
These results led to a clear advances, because in a mouse model of von Willebrand disease, we could observe that, although supra-physiological level of circulating von Willebrandt Factor was observed, little improvement in clotting efficiency was observed. We could clearly demonstrate that this resulted from the fact that liver produced low-molecular-weight non mature von Willebrandt Factor, which was devoid of clotting activity. This fundamental result indicates that the vascular endothelium, which has the capacity to process the von Willebrandt Factor into high multimeric molecular weight form, is the optimal target tissue for a gene therapy of von Willebrandt Factor deficiency, whereas the liver is not. Our reseaarch is now targeting gene delivery to the vascular endothelium.
On the other hand, the very important secretion of an exogenous protein observed with our pFAR miniplasmid / Sleeping Beauty Transposon technological platform points to the general use of this platform for a number