According to researchers, existing stem cell lines could accrue genetic abnormalities over time and new stem cell lines will likely be needed. Dr. Burt Vogels, chairman of a key stem cell research committee of the National Research Council and Institute of Medicine said that every time a cell divide in a tissue culture it accumulates mutations. In aggregate those mutations may cause certain problems too.
Stem cells are unspecialized cells that can become any cell type with specialized functions. They can be gleaned from several sources, such as placenta, umbilical cords and adult cells, but scientists say those derived from human embryos are most useful for therapeutic and research applications. If implanted in a patient, they could grow cells afresh, offering cures for intractable diseases like Parkinson's disease, Alzheimer's and diabetes.
One issues is that many of the existing lines were "cultured with animal cells and serum" creating the fear that pathogens in mice or cows could be transmitted to humans if the stem cells are used for therapeutic applications.
Another problem is that patient's immune system may attack the newly introduced stem cells. One way of sidestepping the problem is through a process known as somatic cell nuclear transfer or SCNT. That procedure, also known as therapeutic cloning, involves taking DNA from a cell belonging to a patient and inserting it into an egg whose nucleus has been removed. When the cell divides, it produces stem cells that can be put in the patient without causing an immune response.
But some lawmakers would like to see so-called therapeutic cloning -- which, unlike reproductive cloning, will never result in a birth -- outlawed. A proposed measure, would outlaw the act of therapeutically cloning a human embryo. It would also ban the importation of products derived from therapeutic cloning.
Vogels said such a ban could mean that regenerative medical applications will never occur and people with terrible diseases won't be healed. He also said that since much biomedical research is international, it's likely most useful lines and reagents will be developed outside the U.S..Therefore, a ban on importation would also curtail important research.