Last time, I looked at the different categories of stem cells. This post looks at the different sources for those cells along with their availability as well as any potential pro’s or con’s in acquiring them, and comparisons between the different sources.

First I will look at multipotent adult stem cells. Adult stem cells can be extracted either from bone marrow or the peripheral system. Both resources have their benefits and negative sides. Bone marrow is a very rich source for stem cells but destruction of bone marrow results in the process. Peripheral stem cells, on the other hand, can be harvested without destruction to bone marrow, but the process takes longer. Adult stem cells are superior to embryonic and umbilical cord blood cells because they are plentiful, always an exact match DNA so the body’s immune system will never reject them, and they have shown promising results. The potential for adult stem cells to develop from one tissue into cells of another tissue is great, though no adult cell has been shown to be pluripotent.

Umbilical cord stem cells, like bone marrow, are a second very rich source of stem cells. Umbilical cord blood cells were discovered in 2005 by scientists at Kingston University in England, named as such because they originate in umbilical cord blood. Umbilical Cord cells can be used not only by the infant, but also by the mother and fathers. While the more distant the relationship, the more likely it is that the cord cells will be rejected by an individual’s immune system, there are numerous common cell types, so matching cells is a possibility where there are numerous donors. The benefits and potential of umbilical cord cells are very exciting and it would be hard to overemphasize their flexibility and desirability. Not only can they be used among many people (assuming there are successful matches in cells types), umbilical cells can be donated and stored, just like blood; compared to adult cells and embryonic cells, the umbilical is the richest for stem cells; and even when there is not an exact DNA match between donor and recipient, scientists have developed processes to improve the transfer of cells, reducing the risk of the recipient’s immune system rejecting the donation. Furthermore, it has been suggested that these stem cells “have the ability to differentiate into more cell types than adult stem cells, opening up greater possibilities for cell-based therapies.” Cord cells continue to show great potential, highlighted in a recent 2007 discovery made by researchers led by Dr. Anthony Atala, who claimed that a new type of stem cell had been found in amniotic fluid. Cells of this type are of great interest for they could potentially prove to be an alternative to embryonic cells.

Embryonic stem cells were first discovered in 1998 by James Thompson of the University of Wisconsin-Madison. Doing research, he was able to isolate cells from the inner mass of early embryos, and developed the first embryonic stem cell lines. Embryonic cells are pluripotent stem cells because they have the potential to develop into all or nearly all of the tissues in the body. Because of their ability to develop into so many different kinds of cells, many scientists believe that embryonic stem cells have potential to treat Parkinson’s patients by replacing destroyed dopamine-secreting neurons in a Parkinson’s patient’s brain; diabetics by transplanting insulin-producing pancreatic beta cells; and heart disease by infusing cardiac muscle cells in a heart damaged by myocardial infarction, among many others.
However, even with this vast amount of purported potential, of all the research to date, embryonic stem cells have probably generated the most controversy. Embryonic stem cells are cells which are extracted directly from an embryo before its cells begin to differentiate. This is the stage at which the embryo is referred to as a blastocyst. Conveniently, the cells from a blastocyst can be kept alive indefinitely and continue to double every two to three days. However, extracting cells from an embryo requires its destruction, and this is where controversy comes in over the issue of embryonic cells. There are many people who believe that a human embryo is no different than an adult human in terms of whether or not it is seen as being a living human being, having differences that only include things such as size and level of development. Consequently, the destruction of an embryo can also be seen as the killing of very young, though less developed human life. On the other side of the issue are people who hold that the embryos, the tiny blastocysts, really have no human qualities at all and therefore have no ethical problems in abstracting embryonic cells at the expense of the embryo.

Stem cell research, along with many other issues of bioethics, are very hot topics in today’s public arena, not the least of which has to do with the government legislation and oversight of these matters. Because of the vast amount of controversy over the ethicality of embryonic research, in August of 2001, President George W. Bush announced his decision to limit Federal funding for embryonic research to only those fifteen currently existing stem cell lines. There are other stem cell lines available for research; however, they do not have the assistance of federal funding. President Bush allowed for federally funded research on existing lines, but did not want the sponsor the creation and destruction of more embryos for research because of what many see are questionable ethics that surround that process.

As technology and research continue to advance, more questions, debates, and discoveries will arise from stem cell research, and our society will be faced with more excitement, disappointment and ethical questions at every turn. Science and values will, and already have, come in to conflict, and as responsible, thoughtful individuals in our society, we have to be ready to answer tough questions. What is the purpose of medicine? What is the job of a doctor? What is life? Is it ever right to take one life to save another? In the midst of it all, stem cell research is positive. Even with the questions surrounding embryonic stem cells, adult cells are available, the research for them does receive federal funding, and they have resulted in therapeutic treatments for numbers of diseases. Thanks to the discovery of the multipotent cord blood cells, it is at least a conceivable possibility that they could be found to be as effective as embryonic stem cells, and they have the benefit of being without ethical controversy, also having in their favor the fact that they are very readily available. Time will tell what further results can be gained from the continuance of stem cell research, but enough is known already to be assured that this is a promising field of research with very bright horizons of discovery ahead of us.

This post will be in two parts, containing excerpts from a paper that I wrote for my biology class this summer. It is a general overview of stem cell research. Part I will a very brief history of stem cell research and a look at the four categories of stem cells. In Part II I will look at the three main sources of stem cells.

History
Stem cell research as we know it today first came about in the mid 1800’s with the discovery that cells were the basic building blocks of life and that some cells had the ability to generate other cells. Stem cells are best understood when contrasted with another kind of cells known as “differentiated cells.” Differentiated cells are cells that are created for a particular function, (.e. heart muscle or blood cell) and do not have the ability to generate other kinds of cells. Stem cells, on the other hand, are undifferentiated cells meaning that the have the ability to mature, or differentiate, into different kinds of cells.
It was not until the early 1900’s that it was discovered that some cells had the ability to generate blood cells, and in 1968, the first bone marrow transplant was successfully performed. Other notable events in the history of stem cell research include the 1978 discovery of stem cells in human cord blood, discoveries in the 1908’s of in vitro and embryonic stem cells created from rodents, and cloned lamb cells in 1997.

Categories of Stem Cells
Stem cells can be classified into four general categories, based on their ability to differentiate. Totipotent cells are found in embryos and each of these cells can form a complete organism (i.g. identical twins). Pluripotent cells are found in the undifferentiated cell mass of the blastocyst and can form over 200 different cell types in the human body. And finally, multipotent stem cells are derived from fetal tissue, cord blood, and adult stem cells. Their ability to differentiate is more limited than embryonic stem cells, but already have successes in cell-based therapies. The final category contains unipotent stem cells, which can only produce one type of cell but have the property of self-renewal, distinguishing them from non-stem cells. Within these four categories, there are three main sources for obtaining stem cells: adults, cord, and embryonic cells which I will look at next time.