The most well-known type of pluripotent stem cell is the embryonic stem cell.

Induced pluripotent stem cells were first generated by Shinya Yamanaka's team at Kyoto University, Japan, in 2006.

They hypothesized that genes important to embryonic stem cell (ESC) function might be able to induce an embryonic state in adult cells.

They chose twenty-four genes previously identified as important in ESCs and used retroviruses to deliver these genes to mouse fibroblasts.

The fibroblasts were engineered so that any cells reactivating the ESC-specific gene, Fbx15, could be isolated using antibiotic selection.

Upon delivery of all twenty-four factors, ESC-like colonies emerged that reactivated the Fbx15 reporter and could propagate indefinitely.

To identify the genes necessary for reprogramming, the researchers removed one factor at a time from the pool of twenty-four.

However, considerable advances have been made in improving the efficiency and the time it takes to obtain i PSCs.

Upon introduction of reprogramming factors, cells begin to form colonies that resemble pluripotent stem cells, which can be isolated based on their morphology, conditions that select for their growth, or through expression of surface markers or reporter genes.

i PSCs are typically derived by introducing products of specific sets of pluripotency-associated genes, or “reprogramming factors”, into a given cell type.