Stem Cell Research Challenges

Ideally, scientists would like to be able to grow a particular type of cell in the laboratory and then inject it into a patient, where it would replace diseased tissue. But stem cells are not yet being used to treat disease because scientists still haven't learned how to direct a stem cell to differentiate into a specific tissue or cell type (brain vs. liver, for example) and to control that differentiation once the cells are injected into a person.

Scientists have not yet reached the stage where they can get stem cells to differentiate reliably.

Take the example of diabetes. To treat diabetics, scientists must not only create insulin-producing cells, but they must be able to regulate how those cells produce insulin once they are in the body.

In nature, stem cells are triggered to differentiate by internal and external cues. The internal cues are genes inside each cell, which are like a series of instructions that dictate how it should function. The external cues are chemicals released by other cells or contact with other cells, either of which may change the way the stem cell functions.

Scientists do know that turning genes on and off is crucial to the process of differentiation, so they have been experimenting by inserting certain genes into the culture dish and then using those genes to try to coax stem cells to differentiate into specific types of cells. But some sort of signal is needed to actually trigger the stem cells to differentiate. Scientists are still searching for that signal.

Photo courtesy University of Wisconsin Board of Regents Differentiation success: Derived from human embryonic stem cells, precursor neural cells grow in a lab dish and generate mature neurons (red) and glial cells (green), in the lab of University of Wisconsin at Madison stem-cell researcher and neurodevelopmental biologist Su-Chun Zhang.

Photo courtesy University of Wisconsin Board of Regents After transplantation into the brains of young mice, the neural precursor cells give rise to functioning neurons (red in A) and astrocytes (red in B), a star-shaped cell of the brain and spinal cord.

And there are other obstacles standing in the way of stem cell use. One is the problem of rejection. If a patient is injected with stem cells taken from a donated embryo, his or her immune system may see the cells as foreign invaders and launch an attack against them. Using adult stem cells could overcome this problem somewhat, since stem cells taken from the patient would not be rejected by his or her immune system. But adult stem cells are less flexible than embryonic stem cells and are harder to manipulate in the lab.

Next, let's examine how stem cells could potentially treat diseases.