Advances in RNA Viral Vector Technology to Reprogram Somatic Cells: The Paramyxovirus Wave

Ethical issues are a significant barrier to the use of embryonic stem cells in patients due to their origin: human embryos. To further the development of stem cells in a patient application, alternative sources of cells were sought. A process referred to as reprogramming was established to create induced pluripotent stem cells from somatic cells, resolving the ethical issues, and vectors were developed to deliver the reprogramming factors to generate induced pluripotent stem cells. Early viral vectors used integrating retroviruses and lentiviruses as delivery vehicles for the transcription factors required to initiate reprogramming. However, because of the inherent risk associated with vectors that integrate into the host genome, non-integrating approaches were explored. The development of non-integrating viral vectors offers a safer alternative, and these modern vectors are reliable, efficient, and easy to use to achieve induced pluripotent stem cells suitable for direct patient application in the growing field of individualized medicine. This review summarizes all the RNA viral vectors in the field of reprogramming with a special focus on the emerging delivery vectors based on non-integrating  Paramyxoviruses, Sendai and measles viruses. We discuss their design and evolution towards being safe and efficient reprogramming vectors in generating induced pluripotent stem cells from somatic cells.