Induced pluripotent stem cells, commonly abbreviated as iPS cells or iPSCs are a type of pluripotent stem cell artificially derived from a non-pluripotent cell, typically an adult somatic cell, by inducing a "forced" expression of specific genes. iPSCs were first produced in 2006 from mouse cells and in 2007 from human cells. This has been cited as an important advance in stem cell research, as it may allow researchers to obtain pluripotent stem cells, which are important in research and potentially have therapeutic uses, without the controversial use of embryos. They may also be less prone to immune rejection than embryonic stem cells because of the fact that they are derived entirely from the patient. Induced pluripotent stem cells were first generated by Shinya Yamanaka's team at Kyoto University, Japan in 2006. Yamanaka used genes that had been identified as particularly important in embryonic stem cells (ESCs), and used retroviruses to transfect mouse fibroblasts with a selection of those genes. Eventually, four key pluripotency genes essential for the production of pluripotent stem cells were isolated; Oct-3/4, SOX2, c-Myc, and Klf4. In November 2007, a milestone was achieved by creating iPSCs from adult human cells; two independent research teams' studies were released - one in Science by James Thomson at University of Wisconsin–Madison and another in Cell by Shinya Yamanaka and colleagues at Kyoto University, Japan. With the same principle used earlier in mouse models, Yamanaka had successfully transformed human fibroblasts into pluripotent stem cells using the same four pivotal genes: Oct3/4, Sox2, Klf4, and c-Myc with a retroviral system. Thomson and colleagues used OCT4, SOX2, NANOG, and a different gene LIN28 using a lentiviral system.