Early Stem Cells

What is an early stem cell?

Often called embryonic stem cells, early stem cells are found in the earliest human cellular formations. In normal human reproductive development early stem cells become all the cells of the body, making them pluripotent. When extracted from the inner cell mass of a blastocyst, early stem cells grow easily in cell culture and can multiply into many stem cell lines that can be maintained for a long period of time. Early human stem cells are thought to be an important source of potentially all types of clinically relevant cells that could become replacement tissue (e.g., organs) in the future or be used to treat and prevent disease.

What is a blastocyst?

A blastocyst is a thin-walled hollow sphere made up of an outer layer of cells, a fluid filled cavity, and an inner cell mass containing pluripotent stem cells. Also called the blastula, the blastocyst develops after cleavage and prior to implantation at approximately five days. Further reproductive development occurs only if the blastocyst is successfully implanted in the uterus.

How big is a blastocyst?

A blastocyst is a microscopic group of cells - smaller than Roosevelt's eye on the face of a U.S. dime. At day five when stem cells can be harvested, a blastocyst is approximately 0.1 to 0.2 millimeters (0.0039 to 0.0079 inches) in size.

Where do stem cells come from?

Early stem cells are found in the inner cell mass of the blastocyst. Once the inner cell mass is removed from the blastocyst, the stem cells are placed in a culture dish where they grow and replicate over time. In normal reproductive development, the inner cell mass becomes all the tissues of the body and the yolk sac.

What is the primary source of blastocysts for research?

The primary sources of blastocysts for use in stem cell research are pre-embryos created by the in vitro fertilization process and donated by consenting adults once they are no longer needed for reproductive purposes.

What is Somatic Cell Nuclear Transfer (SCNT)?

Somatic cell nuclear transfer (SCNT) is a laboratory procedure that produces a blastocyst from an unfertilized egg and an ordinary adult somatic cell (e.g., from a single skin cell).

When were early human stem cells first isolated from IVF-blastocysts?

Early human stem cells were first isolated in 1998 by Dr. James Thomson and his research team at the University of Wisconsin. For more information on Dr. Thomson's research please visit his web site at the University of Wisconsin. Between 1998 and 2001, approximately 78 early stem cell lines have been created using IVF-blastocysts globally. For a table with information on the 78 stem cell lines, click here.

How many unwanted pre-embryos are there in the United States?

According to a survey conducted in 2003, there are approximately 400,000 unwanted pre-embryos in the United States. (Source: Hoffman, D.I., et al. 2003. Cryopreserved embryos in the United States and their availability for research. Fertility and Sterility 79: 1063-1069.) These pre-embryos are no longer needed for fertility purposes and remain frozen or will be destroyed.

How does SCNT work?

SCNT substitutes the nucleus of a somatic cell (which contains all the genetic information of the patient) for the nucleus of a donated egg that has not been fertilized. In cell culture, this customized egg is then coaxed with an electronic or chemical catalyst to develop into a zygote as if it had been fertilized. The zygote begins cell division and develops into a ball of cells called the morula and then into the blastocyst at approximately five days. The inner cell mass of the blastocyst is then removed to generate a pluripotent stem cell line. After the inner cell mass is removed, the blastocyst is no longer capable of further development.

When can we expect results from SCNT?

The SCNT methodology is still in its infancy. Researchers hypothesize that when the genetic information from the cells of a patient is used, the pluripotent stem cells will be able to make customized tissue that will not be rejected by the patient. SCNT researchers contend that the knowledge gained about developmental biology via the SCNT methodology will allow future researchers to create individualized pluripotent stem cell lines without needing fertilized eggs as sources.

Can SCNT be used to clone humans?

The purpose of SCNT is to find cures and therapies to treat human disease. SCNT awakens the natural capacity for self-repair that resides in a person's genes. While SCNT has been the technique used to clone animals like "Dolly" the sheep, there is no evidence that it could also successfully clone a human due to the increased complexity of the human organism.

Blastocysts produced by a fertilized egg (IVF) and SCNT are considered by many to be fundamentally different, and no SCNT-blastocysts should ever be implanted in a uterus. There is no conception of new life via SCNT.

For more information about SCNT, please visit:

• National Academies of Science, Commission on Life Sciences. 2002. Stem Cells and the Future of Regenerative Medicine.
• National Institutes of Health Stem Cell Basics
• Missouri Coalition for Life Saving Cures