What are stem cell lines and why do researchers want to use them?

A stem cell line is a group of cells that all descend from a single original stem cell and is grown in a lab. Cells in a stem cell line keep growing but don't differentiate into specialized cells. Ideally, they remain free of genetic defects and continue to create more stem cells. Clusters of cells can be taken from a stem cell line and frozen for storage or shared with other researchers.

What is stem cell therapy (regenerative medicine), and how does it work?

Stem cell therapy, also known as regenerative medicine, promotes the reparative response of diseased, dysfunctional or injured tissue using stem cells or their derivatives. It is the next chapter of organ transplantation and uses cells instead of donor organs, which are limited in supply.

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.

Have stem cells already been used to treat diseases?

Yes, doctors have performed stem cell transplants, also known as bone marrow transplants. In stem cell transplants, stem cells replace cells damaged by chemotherapy or disease or as a way for the donor's immune system to fight some types of cancer and blood-related diseases, such as leukemia. These transplants use adult stem cells or umbilical cord blood.

Researchers are testing adult stem cells to treat other conditions, including a number of degenerative diseases such as heart failure.

What are the potential problems with using embryonic stem cells in humans?

To be useful in people, researchers must be certain that stem cells will differentiate into the specific cell types desired.

Researchers have discovered ways to direct stem cells to become specific types of cells, such as directing embryonic stem cells to become heart cells. Research is ongoing in this area.

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 recipient's 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.

What is therapeutic cloning, and what benefits might it offer?

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 donor's — 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.

Has therapeutic cloning in people been successful?

No. Researchers haven't been able to successfully perform therapeutic cloning with humans despite success in a number of other species.

However, in recent studies, researchers have created human pluripotent stem cells by modifying the therapeutic cloning process. Researchers continue to study the potential of therapeutic cloning in people.

Mar. 23, 2013 See more In-depth