Induced pluripotent stem cells
Reprogramming an adult cell back to a pluripotent state — and why it changed the field's constraints.
In 2006, Yamanaka's group showed that introducing four transcription factors could revert an adult somatic cell to a pluripotent state, capable of forming any cell type in the body. Induced pluripotent stem cells (iPSCs) removed at a stroke two constraints on the field: the ethical objections attached to embryonic sources, and the immunological problem of using another person's cells — iPSCs can be made from the patient.
Their advantage over MSCs is breadth. MSCs are multipotent, limited to a family of lineages; iPSCs are pluripotent. That same property is the risk: cells that can become anything can form teratomas, so incomplete differentiation before implantation is a genuine safety concern rather than a theoretical one.
For bone and dental applications iPSCs remain less used than MSCs, partly because accessible adult sources already exist and partly because manufacturing is demanding — a translation problem more than a biological one. See Translation in regenerative medicine.
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