Deriving Human Embryonic Stem Cell Lines without Destroying the Embryo
by Anthony Tuan Nguyen
Every human being begins as a single stem cell. This stem cell has the power of virtually unlimited division and proliferation until it differentiates into a specialized cell, such as a muscle cell. Since human embryonic stem (hES) cells can be cultured to yield different tissues and organs, many scientists believe they hold great promise for regenerative medicine. Diseases such as muscular dystrophy, Parkinson's disease, heart disease, and vision and hearing loss might be treated by transplanting cells generated from hES cells.
The current approach of harvesting hES cells, however, entails the destruction of the extracted embryo. In light of this and other moral issues, in August 2001, President George W. Bush discontinued federal funding of all research on future stem cell lines. Published this August in the journal Nature, Dr. Christopher Scott, Executive Director of the Stanford Program on Stem Cells in Society, examined the ethical issues of a new technique for deriving hES cell lines. The Lanza Method
Dr. Robert Lanza of Advanced Cell Technology, a biotechnology company in Alameda, California, and his research team developed a new method for deriving hES cells, potentially without destroying the human embryo. They used a technique called preimplantation genetic diagnosis (PGD), which is usually used for the early identification of genetic defects in embryos created through in vitro fertilization (IVF). PGD involves the biopsy of only one of an early-stage embryo's eight cells (blastomeres) for genetic inspection, allowing the remaining cells to mature into a fetus.
Lanza claims that the extracted cell from PGD can also be used to produce a functional stem cell line, thereby preserving the human embryo. Lanza cited PGD as the proper method of extracting the potential hES cell, but multiple blastomeres were extracted from each embryo and cultured in isolation to increase the chances of yielding stable hES cell lines. Consequently, no embryos survived into human beings in the study. Previously, Lanza's team had derived embryonic stem cell lines from single mouse blastomeres, and those single-blastomere-biopsied embryos were allowed to develop into live mice.
The Moral Controversy
Interestingly, Lanza and his collaborators have seemingly escalated the debate over the ethics of stem cell research. According to Scott, several issues still remain. ÒThose who believe a two-day old, eight-celled embryo is a person will object to the procedure on at least three counts," Scott explains. "First, if an embryo is a person and has rights, then we shouldn't tread on these rights, including taking material from it to use for research." There does not exist a definitive boundary between cell mass and live fetus. Therefore, can we perform PGD on the embryo and much less extract a stem cell line without its consent? Why should we be able to use an embryo for organ regeneration when fully-developed humans are asked for their consent in organ donation?
Furthermore, "Because we know identical twins can form at this stage of human development, they say that removing a single cell to make a cell line is possibly killing a twin," adds Scott. In the eight-cell embryos, it is unknown which cells are designated to differentiate into the fetus or into the trophectoderm (external supporting tissue). The triggering mechanism that causes cells to differentiate into specific tissue has yet to be determined. Moreover, it is has not been shown it is impossible for separated blastomeres to develop into human beings. Nonetheless, the Lanza method can bypass lengthy legal red tape because the embryoÕs parents can give consent for both PGD and stem cell extraction concurrently.
As for the third issue, Scott says, "It's not proven beyond a doubt that the biopsy procedure doesn't harm the embryo." To this date, thousands of children have been born after undergoing PGD and lead normal lives. However, according to Scott, Ò[This fact] seems to suggest the procedure is relatively safe. But long-term effects of PGD may appear later in life.Ó Because of the novelty of PGD, these children are only in their teens and possibly have not manifested harmful side effects from PGD.
Uncertain Future for Stem CellsMillions of sick people around the world can potentially benefit from embryonic stem cell research, and public funding can support more rapid development of new stem cell technology. Yet, the ethical question remains: are the lives of millions outweighed by the inherent rights endowed upon a human embryo?
Scott remarks, "The embryo biopsy technique wouldn't cause such a big stir if we had government funding for research with frozen IVF embryos.Ó Although President Bush vetoed a bill for the funding of stem cell lines derived from discarded embryos, Congress narrowly missed the margin to override his veto. Apparently, the decision to federally fund stem cell research lies in the hands of voters.
Fact box: Dr. James Thomson of the University of Wisconsin was the first to successfully isolate a human embryonic stem cell line in 1998. His paper entitled ÒEmbryonic Stem Cell Lines Derived from Human BlastocystsÓ was published in Science.