Use of Human Embryonic Stem Cells in Therapy

Pluripotent stem cells (PSCs) are defined by their potential of unlimited self-renewal and the ability to differentiate – both in vitro and in vivo – into all cell types of endodermal, mesodermal and ectodermal origins, rendering them a promising applicability in cell replacement therapies. These characteristics also make PSCs powerful tools for studying the molecular mechanisms underlying cellular differentiation, as well as for accessing the biological effects of pharmaceutical compounds on the normal embryo development, and also on virtually any differentiated cell type. PSCs can be obtained from early stage embryos – usually from the inner cell mass of blastocysts – and adapted for propagation in culture in the laboratory, thus resulting in the establishment of an Embryonic Stem Cell (ESC) line. They can also be artificially obtained in the laboratory through the use of techniques that induce the reprogramming of somatic, differentiated cell types (i.e. dermal fibroblasts) into undifferentiated, pluripotent stem cells (Induced Pluripotent Stem Cells – iPSCs). In this chapter we discuss the potential advantages and disadvantages of the use of these two PSC types in regenerative medicine, and give an overview of the current status of cell therapy studies and clinical trials in humans. We also comment on a more recently developed alternative source of cells for use in therapy – the direct reprogrammed cells – and finally, we discuss the potential applications of PSCs and directly reprogrammed cells in drug screening assays.