What are iPS Cells?
An induced pluripotent Stem cell (or iPS cell) is an adult cell that has been reprogrammed to behave like an embryonic Stem cell (or ES cell). But what can it be used for?
Embryonic stem cells
When an ovum is fertilized, the egg divides, and within a short space of time cells are formed that have the potential to develop into all the tissues of the body. These cells are called embryonic stem cells and are known as pluripotent cells. Pluripotency is the ability to generate all different cell types. As they mature, ES cells gradually lose their differentiation potential and develop a functional specialization. For example, a lymphocyte will tackle infections, whereas a pancreatic cell will be capable of producing insulin – for the rest of its life. Until recently, it was believed to be impossible for a cell to return to a state of immaturity and recover its differentiation potential. ES cells exist in vast numbers during the early stages of embryonic development. At birth, stem cells can also be found in the umbilical cord blood, but in small numbers, and their differentiation potential is already limited. Similarly, stem cells are present in most adult tissues, but in minute quantities, and they are not easily accessible. Moreover, their differentiation potential is restricted to the cell types of the tissue in which they are found: for example, a neural Stem cell can only generate neural cells (neurons, oligodendrocytes and astrocytes), whereas a hematopoietic Stem cell can only develop into blood cells: red blood cells, lymphocytes, macrophages, etc. These cells are multipotent rather than pluripotent. The sources of stem cells are therefore extremely limited, and with regard to embryonic stem cells, are also fraught with ethical issues. These natural sources therefore impose a limitation to the potential industrial applications for stem cells.
Induced pluripotent stem cells
In 2006, the team of Professor Shinya Yamanaka at Kyoto University demonstrated that it is possible to reprogram a mature adult cell to give it back the properties of an embryonic stem cell. In order for this adult cell to return to a state of immaturity and be able to differentiate into all cell types, you just need it to express four genes (not normally expressed in adult cells). These cells are termed induced pluripotent stem cells, or iPS cells. This discovery is revolutionary, even if its applications will involve a great deal more work. Professor Yamanaka’s discovery offers the scientific community access to an unlimited source of pluripotent stem cells, for adult tissues and with no associated ethical issues. This potential, together with the possibility of deriving stem cells from any individual, offers tremendous therapeutic applications, from drug screening to regenerative medicine.
Genome engineering to control iPS cells
Because iPS cells have only been discovered very recently, science has yet to devise methods for controlling their behavior and differentiation pathways as well as their fate when they are reinjected in a complete organism. Before iPS cells can be applied, it is vital to be able to fully control them and to make them completely secure, while retaining their beneficial properties. If iPS cells are to become the cellular tools of the future, Genome engineering technologies, which enable the targeted and controlled modifications to the genomes of all species, will play an essential role and may open the road to a complete new approach to repair medicine.