Stem cell research has been a hot national topic for several years now (perhaps most notably since President Bush's 2001 suspension of federal funding for researching/gathering new embryonic stem cells lines), yet few understand the science of this complex issue.
There is a reason for the stem cell furor. Scientists believe that stem cells--particularly the extremely versatile embryonic stem cells--hold the key to treating and curing myriad diseases. Among the diseases scientists hope to treat are neurological disorders like Parkinson's and Alzheimer's, and diseases of the organs and bones, including cardiac diseases, and skin grafts for burn victims. Scientists hope research might yield cells for insulin production in diabetics, cartilage growth for treating arthritis and treatment for traumatic injuries like spinal cord injuries, balancing those high hopes for embryonic stem cells however is weighty opposition to the research. Opponents say that research on embryonic stem cells--typically taken from fertilized eggs destined for disposal from fertility clinics--is unethical, and the presented dilemma is that of technological advancement versus simple humanity. Characterizing the research as immoral and the embryos as equivalent to human beings usually has a religious justification. Accepting the view of embryonic stem cell research as destruction of human life, President Bush has not only suspended federal funding for embryonic stem cell research, but also "supports legislative efforts to ... prohibit the production of human embryos solely to be destroyed in medical research." Thus federal funding is eliminated and the science is on its way to being criminalized.
As a result, scientists are looking to alternative stem cell sources. Researchers prize embryonic stem cells in particular for their versatility--because they are unassigned cells that can potentially transform themselves into some 200 types of tissue. But with federal funding for embryonic stem cell research gone, the 60 existing lines limited in research potential and legislation on the move to ban the research, scientists have few options left in stem cell research: adult stem cells and more promisingly, stem cells from umbilical cord blood.
To understand the differences among stem cell sources--embryonic, adult and cord blood--and their respective potentials and limitations, we need to know what stem cells are. Stem cells are the body's basic building blocks that develop into every kind of tissue in the body--bone, muscle, organs, blood, etc. Embryonic stem cells are the most versatile and can become any kind of tissue. Adult stem cells, those formed and retained by the body for tissue repair and maintenance, are found in the brain, bone marrow, muscle and fat. These stem cells do not have the versatility of non-adult stem cells; adult stem cells are already assigned to their function. That is, adult skin stem cells can't become blood stem cells and vice versa. Adult stem cells do not possess the elasticity of either embryonic or cord blood stem cells. Inverse to the practicality of embryonic stem cells, though, is the raging moral debate. Embryonic stem cells carry some sticky political issues that, for the most part, do not affect research with adult or cord blood stem cells.
Somewhere between the controversial but versatile embryonic and noncontroversial but limited adult stem cells is another scientific hope: umbilical cord blood stem cells. Cord blood research does not give rise to the same ethical squeamishness as embryonic stem cells, yet cord blood contains far more versatile stem cells than those stem cells extracted from adult tissue. In addition, there has been a lot of relatively unrestricted research on umbilical cord stem cells, and stem cell therapies derived from the research are currently in use. Accordingly, much has been made of the potential of stem cells derived from umbilical cord blood. Proponents of cord blood stem cell research have suggested cord blood as the morally painless alternative to the ethical quagmire existing around embryonic stem cell research. So what is the difference between stem cells derived from cord blood versus embryos?
First, there's the method of collection. While embryonic stem cells are taken from fertilized eggs, which are destroyed in the process and thereby creating controversy, umbilical cord blood stem cells are donated after a typical live birth. Thus, ethical questions that arise with the former do not arise with the latter. To get the stem cells, blood remaining in the umbilical cord can be collected in a short, noninvasive and noncontroversial procedure. And if not collected for stem cells, cord blood is simply disposed of as medical waste. Cord blood can be stored in a private cord blood bank, or donated, much in the manner of giving blood. It costs donors nothing to donate cord blood. However, the technology hasn't reached all regions and it can be difficult to find a place set up to take cord blood donations. (Thirteen states have participating hospitals but Idaho is not yet one of them.)
Besides the method of collection, however, there are other differences between embryonic and cord blood stem cells. Umbilical cord blood stem cells are a particular kind: blood-forming or "hematopoietic" stem cells. (In contrast to the unassigned nature of embryonic stem cells.) Hematopoietic stem cells are found in blood or bone marrow. Umbilical cord blood stem cells, like those from bone marrow, are used in the treatment of many diseases, although not yet in neurological diseases such as Parkinson's. The inability to use cord blood stem cells in the treatment of neurological diseases is frustrating for scientists because there is promising research indicating the possible effectiveness of embryonic stem cells in the treatment of neurological disorders through therapeutic cloning. Researchers must also deal with the fact that cord blood stem cells, unlike embryonic stem cells, cannot proliferate or differentiate into other cell types under lab conditions; also stem cells are difficult to discern from other cells in blood or bone marrow. So while cord blood stem cells are the only stem cells understood enough to be used in cell therapy, their uses are definitely limited.
Cord blood stem cells do have life-saving technological applications that are being used now, not just theoretical potential. A notable example of such an application is evident in the treatment of inborn errors of metabolism, like Sanfilippo Syndrome. Mucopolysacchrides are long chains of sugar molecules that the body uses to build connective tissues. Children who have Sanfilippo Syndrome, an extremely rare mucopolysaccharide disorder caused by a recessive gene, are missing heparan sulfate, an enzyme essential in breaking down used mucopolysacchrides. Incompletely broken down mucopolysacchrides remain stored in cells in the body, causing advancing damage. The disorder doesn't usually manifest in infants, but rather symptoms appear as increasing damage occurs. Affecting different people in different ways, the progress of the syndrome varies among individuals. However, changes tend to be gradual as the disorder moves through three main stages. During preschool years, children with Sanfilippo show a lack of development when compared to other children of the same age. Language and cognitive function will then go, and finally motor function as well.
Annabelle Green is a 2-year-old in Boise with Sanfilippo Syndrome. Earlier this spring, Annabelle and her family flew to Duke University in North Carolina so the toddler could undergo experimental treatment for Sanfilippo. Annabelle's treating physician at Duke is Dr. Joanne Kurtzberg, a pioneer researcher in cord blood transplantation and a leader in stem cell research and transplantation in children. Annabelle is only the 12th child to receive the cord blood transplant treatment for Sanfilippo. There is about a 50 percent survival rate for patients; five of the first 11 patients have died. However, Annabelle was diagnosed much earlier than Sanfilippo children usually are (as the syndrome doesn't usually manifest enough to be detected until brain damage is already extensive), and doctors are optimistic. (Currently, she is recovering quite well and the family hopes to be back in Boise soon.) Although a 50/50 rate of survival may seem dismal, the number actually represents a vast improvement. Three and a half years ago, prior to starting treatment of Sanfilippo Syndrome with cord blood transplants, that survival rate was zero. There is no other treatment. Without the cord blood transplant, children afflicted with the syndrome will suffer profound brain damage as well as joint, tissue and sensorydeterioration with a life expectancy of 10 to 15 years, half of that in a vegetative state.
As with any other transplant, there is the danger of rejection in cord blood transplantation (a risk scientists believe would not exist in this same procedure with embryonic stem cells). In addition, Graft Versus Host Disease (GVHD), a common transplant complication, is less severe with cord blood than with bone marrow transplants. And though it takes cord blood longer than bone marrow to graft after a transplant, studies suggest that ultimately cord blood is more effective at regenerating the body's store of blood stem cells.
Christine Barrietua, Annabelle's grandmother, wants people to understand the treatment that her granddaughter is receiving. The stem cells Annabelle received are from donated cord blood--that is, umbilical cord blood donated from a live birth. This research, Barrietua stresses, is different from embryonic stem cell research, which some do not realize. Their family has been approached by confused strangers expressing pity that an embryo had to be destroyed so Annabelle could be treated. When people heard "stem cells," they incorrectly associated the term with "embryonic stem cells." Even in Annabelle's case, whose vital stem cell transplant is of the "noncontroversial" cord blood variety, controversy attends nevertheless. In the court of public opinion, often all stem cell research is commingled with reproductive politics.