Embryonic stem cells are primarily obtained from two sources: existing human embryos and embryos created through somatic cell nuclear transfer (SCNT), a type of cloning.
Here's a more detailed breakdown:
1. From Existing Human Embryos:
- Source: These embryos are typically those that are created during in vitro fertilization (IVF) procedures. When couples undergo IVF to conceive, multiple eggs are often fertilized to increase the chances of a successful pregnancy. Embryos that are not implanted may be donated for research purposes, including the derivation of embryonic stem cells.
- Process: Embryonic stem cells are extracted from the inner cell mass of a blastocyst, which is an early-stage embryo approximately 5-7 days after fertilization. The extraction process destroys the embryo.
- Ethical Considerations: The use of existing human embryos raises ethical concerns for some, as it involves the destruction of a potential human life.
2. From Embryos Created Through Somatic Cell Nuclear Transfer (SCNT):
- Source: SCNT, also known as therapeutic cloning, involves creating an embryo in the lab using a patient's own cells. This process starts by taking an egg cell and removing its nucleus (which contains the genetic material). The nucleus is then replaced with the nucleus from a somatic cell (any cell other than a sperm or egg cell) from the individual.
- Process: The reconstructed egg is then stimulated to divide and develop into a blastocyst. Similar to the process with IVF embryos, embryonic stem cells are extracted from the inner cell mass of the blastocyst, destroying the embryo in the process.
- Benefit: The stem cells derived from SCNT are genetically matched to the patient, which significantly reduces the risk of rejection if these cells are used in future therapies.
- Ethical Considerations: Similar to using existing embryos, the creation and destruction of embryos via SCNT raise ethical concerns.
In summary, embryonic stem cells are obtained by isolating them from the inner cell mass of a blastocyst, either derived from surplus IVF embryos or created through somatic cell nuclear transfer. Both methods involve the destruction of the embryo.