An ambitious EC-funded research initiative on epigenetics advancing towards systems biology

Response written by: Elphège Nora, PhD - postdoctoral researcher in Edith Heard's laboratory, Institut Curie

Each cell of the body produces molecules known as proteins. The structure of proteins is directly encoded by the cells' genes. In humans, genes are very similar from one individual to another but there are not completely identical. This means that the proteins produced by my cells are very similar, but not completely identical to yours.
In our blood some special cells, called the cells of the immune system, have the amazing ability to probe the proteins that are on the outside of almost all the other cells of the body. At the beginning of their life some very important immune cells are trained to become aggressive whenever they meet proteins encoded by foreign genes. Then immune cells migrate through the blood vessels and can reach almost every part of the body, where they meet many other cells. As you can see—not much happens to your immune cells when they meet other cells from your body. However, upon encountering a foreign cell that has foreign proteins because of its foreign genes, your immune cells will become aggressive toward that foreign cell and simply kill it.

Normally this is a good thing, because in most cases these foreign cells are parasites that made their way in our body, such as pathogenic microorganisms. But the problem is that a tissue graft [http://www.merriam-webster.com/dictionary/graft] is, by definition, also made up of foreign cells. In order to prevent the immune system from systematically destroying the graft, doctors typically prescribe drugs that tamper with the action of the immune system so that grafted patients can tolerate the foreign cells in their body. The goal is to tamper with the action of the immune system, but not prevent it from acting completely otherwise grafted patients would not be able to fight against pathogenic microorganisms. Thus, a fine balance has to be reached, and sometime the immune system is still too strong despite of the drugs—and will end up destroying the transplanted tissue.