In stem cell therapy researchers grow stem cells in a lab. These stem cells are manipulated to specialize into specific types of cells, such as heart muscle cells, blood cells or nerve cells. The specialized cells can then be implanted into a person. For example, if the person has heart disease, the cells could be injected into the heart muscle. The healthy transplanted heart cells could then contribute to repairing defective heart muscle. Researchers have already shown that adult bone marrow cells guided to become heart-like cells can repair heart tissue in people, and more research is ongoing.
Researchers have discovered ways to direct stem cells to become specific types of cells, such as directing embryonic stem cells to become heart cells. Embryonic stem cells also could grow irregularly or specialize in different cell types spontaneously. Researchers study how to control the growth and differentiation of embryonic stem cells. Embryonic stem cells also might trigger an immune response in which the recipients body attacks the stem cells as foreign invaders, or simply fail to function normally, with unknown consequences. Researchers continue to study how to avoid these possible complications.
Therapeutic cloning, also called somatic cell nuclear transfer, is a technique to create versatile stem cells independent of fertilized eggs. In this technique, the nucleus, which contains the genetic material, is removed from an unfertilized egg. The nucleus is also removed from a somatic cell of a donor. This donor nucleus is then injected into the egg, replacing the nucleus that was removed, a process called nuclear transfer. The egg is allowed to divide and soon forms a blastocyst. This process creates a line of stem cells that is genetically identical to the donors - in essence, a clone. Some researchers believe that stem cells derived from therapeutic cloning may offer benefits over those from fertilized eggs because cloned cells are less likely to be rejected once transplanted back into the donor and may allow researchers to see exactly how a disease develops.