The general scheme of gene-based differentiation toward pancreatic endocrine cells would be to transfect stem cells, in a stepwise fashion, with candidate pro-endodermal, pro-pancreatic, and pro-endocrine expression vectors. However, a conventional strategy for transfection/antibiotic selection of clones would be extremely difficult to reduce to practice, as every step would require the selection of clones containing the appropriate integration. Since ES cells tend to progressively stop dividing after the initiation of differentiation, repeating this process for each one of the subsequent genes would be nearly impossible. As for the use of viruses to deliver these genes, we have already stated the problems that will likely stand in the way of the development of clinical therapies. Read the rest of this entry »