cells grew in culture and demonstrated pluripotent characteristics, as demonstrated by the ability to form teratomas, differentiate in vitro, and form embryoid bodies. Martin referred to these cells as ES cells. It is now known that the feeder cells provide leukemia inhibitory factor (LIF) and serum provides bone morphogenetic proteins (BMPs) that are necessary to prevent ES cells from differentiating. These factors are extremely important for the efficiency of deriving ES cells. Furthermore, it has been demonstrated that different mouse strains have different efficiencies for isolating ES cells. Current uses for mouse ES cells include the generation of transgenic mice, including knockout mice. For human treatment, there is a need for patient specific pluripotent cells. Generation of human ES cells is more difficult and faces ethical issues. So, in addition to human ES cell research, many groups are focused on the generation of induced pluripotent stem cells (iPS cells). Potential methods for new cell line derivation On August 23, 2006, the online edition of Nature scientific journal published a letter by Dr. Robert Lanza (medical director of Advanced Cell Technology in Worcester, MA) stating that his team had found a way to extract embryonic stem cells without destroying the actual embryo. This technical achievement would potentially enable scientists to work with new lines of embryonic stem cells derived using public funding in the US, where federal funding was at the time limited to research using embryonic stem cell lines derived prior to August 2001. In March, 2009, the limitation was lifted. Human embryonic stem cells have also been derived by somatic cell nuclear transfer (SCNT). This approach has also sometimes been referred to as "therapeutic cloning" because SCNT bears similarity to other kinds of cloning in that nuclei are transferred from a somatic cell into an enucleated zygote. However, in this case SCNT was used to produce embryonic stem cell lines in a lab, not living organisms via a pregnancy. The "therapeutic" part of the name is included because of the hope that SCNT produced embryonic stem cells could have clinical utility. Induced pluripotent stem cells The iPS cell technology was pioneered by Shinya Yamanaka's lab in Kyoto, Japan, who showed in 2006 that the introduction of four specific genes encoding transcription factors could convert adult cells into pluripotent stem cells. He was awarded the 2012 Nobel Prize along with Sir John Gurdon "for the discovery that mature cells can