These play a vital role in development and can lead to disease if dysfunctional. The study of these mechanisms is especially significant with respect to embryonic stem cell research and therapeutic cloning. Embryonic stem cells are pluripotent, meaning they can develop into almost any kind of body cell. The aim of Professor Jaenisch's research is to create custom-tailored embryonic stem cells to treat diseases which until now have not been treatable or could only be treated inadequately. "Research still has a long way to go to achieve this goal," Professor Jaenisch said. "It would be premature to say that clinical application is imminent."

The research of Professor Jaenisch and his team includes working with stem cells which originate from human embryonic cells created by in vitro fertilization. In his view, they are not suitable for therapeutic purposes because they would be rejected by the recipient's immune system.

That is why researchers, by means of cell nucleus transfer technology, are attempting to engineer embryonic stem cells that the immune system does not attack. To achieve this, researchers remove the nucleus of the oocyte and replace it with the nucleus of a body cell, for example of a skin cell. The idea is that the embryonic stem cells thus cultured in a petri dish will be given back to the donor of the body cells for therapeutic purposes without provoking an auto-immune response. Professor Jaenisch: "The goal is to do without human oocytes in the future."

It was Rudolf Jaenisch who succeeded in demonstrating for the first time that a genetic defect in mice can be corrected by means of therapeutic cloning. But before therapeutic cloning for humans can be considered seriously, research must still answer a number of questions. Professor Jaenisch and his team want to understand how the oocyte reprograms the body cell inserted into it, turning it into an embryonic stem cell- in other words, they want to find out what makes a stem cell a stem cell.; Source: Max-Delbrück-Centrum für Molekulare Medizin