Stem cells are the special cells that can turn into any kind of cell in the body. Embryos have them, and use them during development. This has lead to controversy as collecting stem cells needed destroying an embryo. Now we can take cells from an adult, and turn them into pluripotent stem cells by reprogramming them.
This can be done by turning on genes that are active in stem cells, and turning off genes that are active in whatever type of cell they are. Scientists also introduce proteins that are important during embryonic development.
Hopefully this will allow stem cell research in the United States to catch up with the rest of the world.