Reaching the point where society can reap the potential benefits of stem cells will take time. Researchers face a number of major challenges as they study stem cells.
Technical hurdles
Controlling stem cells isn't easy. Both adult and embryonic stem cells present challenges. Though stem cells exist in adult tissue, they're not present in great numbers, so they can be hard to find and to extract for growth. They also may be difficult to grow into large batches of unspecialized cells in the laboratory — a necessary step if they're to serve as replacement cells in disease treatment. And their ability to transform into different kinds of cells appears to be limited.
Working with embryonic stem cells has its challenges, too. Though they're easier to grow into batches of unspecialized cells, scientists need to better understand how these cells reproduce in the laboratory, and how to reliably trigger them to differentiate into the specific types of cells needed. Concerns that transplanted stem cells may not work in conjunction with the tissue of the person receiving them also exist. Transplanted cells could "overgrow," as happens in many cancers. And a person's immune system may reject the cells as foreign, because cells derived from embryonic or fetal tissue are genetically different from mature tissue. Ethical questions
Because of the technical limitations involved in using adult stem cells, embryonic stem cells are generally more appealing to stem cell researchers. But the use of embryonic stem cells gives rise to ethical questions.
Embryonic stem cells are derived from embryos created outside of a woman's body (in vitro) — using donated eggs fertilized in a laboratory — not from eggs fertilized inside a woman's body. Gathering embryonic stem cells requires destroying the embryo. Some people believe this process represents a destruction of human life, and feel that it shouldn't be done for research purposes. Others disagree, suggesting that an embryo doesn't have the same rank as a fetus. Some believe it's OK to use embryos for research if they're not being created specifically for research, but instead exist as unused byproducts of an in vitro fertilization procedure for infertile couples.
