Your life began at conception as a single cell known as the zygote, or fertilized egg. That tiny new cell contained your complete human signature, your very own DNA, never to be duplicated. Even more amazing, you were a master stem cell, or “source” cell, with the ability to multiply and eventually transform into all the cell types and tissues that make up the human body.
About one day after fertilization, the egg divides for the first time into an exact cell copy of itself. Early along the way, a clump of about 100 cells (a blastocyst) is formed. This tiny cell mass then separates into two groups: An inner cell mass (the embryo), and an outer ring of cells which are the life support system (placenta).
It is at this early stage, while they are still unassigned or “unspecialized” that resarchers harvest embryonic stem cells from the inner cell mass of the embryo, which is killed in the harvesting process. It is then the researchers task to try to mimic nature by cultivating and engineering those cells to specialize and take over for sick cells in a patient’s body. If they are not harvested, embryonic stem cells live on and begin to differentiate naturally, forming three distinctive germ layers (or cell lines) within a later embryo. From those germ layers the cells further redefine themselves into more than 200 kinds of specialized adult cells that make up the nerve, muscle, skin, bone, cartilage, blood and other tissues or your body. What, then, is an adult stem cell?
Think of an adult stem cell as a multi-purpose, spare part. It is a unique cell, yet uncommitted, that is found in a specialized tissue (muscle, bone, heart, brain, etc.) From its natural embryonic development an adult stem cell retains its ability to multiply and to renew itself as a healthy replacement for any of the damaged cell types that make up the particular tissue where it was found. Because they are taken from a patient’s own tissue sample, transplanted adult stem cells are not likely to be rejected by the immune system. And morally, adult stem cells can be acquired without killing or harming any individual.
A rich source of adult stem cells happens to be the placenta and umbilical cord usually considered medical waste following a baby’s delivery. Umbilical cord cells are not yet committed and can morph into specialized, healthy cells. They are available from public storage banks which provide the ability to search for matches, and are less likely to be rejected by a host. Plus, they can be obtained for half the cost of a bone-marrow transplant with no risk to the donor. (See how to donate umbilical cord cells below.)
Adult stem cells show us their amazing healing capacity all the time: How adult stem cells do what they do, we’re not really sure. Cell turnover is constant in nearly all tissues and organs of the body. We take for granted how quickly wounds heal and skin begins to repair itself immediately after an injury. When a portion of a liver is removed surgically, the organ can regenerate up to 50% of its mass within weeks. And in our blood streams, stem cells replace our red blood cells at a rate of 350 million per minute.
Are they even more versatile than we thought? Until recently, it was thought that adult stem cells were already too locked-in or specialized to their host tissue to be successful repairing another tissue or organ type. But experiments transplanting adult bone marrow stem cells into other organs such as the heart and brain show their ability to adapt and become cell mates with totally different types of tissues in the host patient’s body.
In November, 2007, separate teams of scientists from Japan and the U.S. claimed to have used gene technology to successfully reprogram adult stem cells back to a primitive embryonic-like state from which they can be transplanted and morph into heart, nerve or other human tissue. No embryos are destroyed in the process. Many hurdles and lab experiments remain before the proper controls are in place and clinical trials on humans begin. The new reprogramming technology is something any scientist with basic technology in molecular and cell biology can do and puts ethical stem cell research back on the fast track
Crossing the moral line. Stem cell work is a rigorous process. It involves hunting the elusive stem cell, then removing, cultivating and finally replacing it into a patient’s body. Scientists argue that cells harvested from embryos are more accessible and offer greater potential since they have not yet begun to specialize. Once a stem cell is isolated, it can be used to create a cell line from which are produced other cells just like itself, so there's no need to ever have to isolate that cell type again. Cell lines give the scientist a way to mass-produce stem cells as a commodity that can be grown indefinitely in the laboratory, then frozen, stored and distributed to other researchers, or for use in patients.
But before embryonic stem cells are ready for use in human patients, researchers must overcome elusive problems of immune rejection. They must decipher the mysterious chemical signals that instruct an embryonic cell and prove they can recreate those signals. They must guarantee that a laboratory engineered stem cell will choose the right path to a particular tissue specialty, or they risk facing horrifying prospects like creating a tumor or a tooth in a patient’s brain or heart – a result already achieved in mice. So far, embryonic cell trials remain at the animal level, while adult stem cell research has an impressive forty year history with stunning results on human patients. It's clear we need not cross the moral line to cure a condition by destroying an early life.
Still, scientists not concerned with the moral issue want to clone human embryos to increase the supply of embryonic stem cells for research even though the embryos are destroyed in the process. It’s scientific fact that a cloned embryo is no less a human being than one produced normally via sexual fertilization. Consider: In the case of identical twins, the first twin is created naturally when the egg is fertilized. Later, the egg splits (no one knows why) creating the second twin, which is a “clone.” Is the second twin not a human being?
It's no longer just "embryonic vs. adult." Computer-driven science is taking us into a whole new universe of biomedical exploration, revealing countless ways that our cells communicate with one another. Some scientists believe the secret of engineering stem cells may be in using gene therapies, adding or replacing genes to cells to define their specialty in the body. There is increasing evidence stem cells respond to certain chemical signals that can summon them to an injured site without the need for transplantation. We are finding answers to cells' mysteries that could not even be envisioned just a few years ago. The moral and political debate over embryonic vs. adult stem cell research is a drag on the scientific effort. The many promising alternatives to the prospect of an embryonic holocaust should be enough to end the debate, even within secular scientific circles.