What are stem cells?
The human body is composed of billions of cells, each of which is one of roughly 200 types. You have skin cells, blood cells (of which 200 billion are created on a daily basis), brain cells, and so on. However, foetuses do not have all of these different types of cells - instead the foetus has a number of stem cells, which under different conditions grow into different types of cells, until one has another member of the voting public(although everybody has stem cells in them, as they are continually generated by the body). The study of stem cells dates back to the 1960s, following research made by two Canadian scientists, Ernest A. McCulloch and James E. Till. This study went largely unnoticed for years due to the difficulties involved in acquiring and maintaining these cells outside of the human body. However in 1998, a research team led by James Thomson from the University of Wisconsin-Madison found a way to isolate and grow stem cells separately from the human body. Because stem cells reproduce to create more stem cells (as well as different types of cells), an established culture can be split up and grown into more cultures, allowing multiple researchers the chance to run any number of experiments.
This is, however, only part of the story - there are four different types of stem cells, and each type determines the use of the cells it produces.
- Totipotent stem cells are created by the fusion of a sperm and egg, and are also created by the first few divisions of the egg. These cells can grow into any type of cell.
- Pluripotent stem cells are the next generation of totipotent cells, and can also grow into any type of cell, with the exception of totipotent cells.
- Multipotent stem cells can grow into any type of a family of cells (e.g. red blood cells, platelets, white blood cells, but not neurons)
- Progenitor or unipotent stem cells can only produce one type of cell, but can reproduce themselves.
In other words, totipotent cells can be any type of cell, including those required to develop a foetus, while pluripotent cells can be any type of cell except that required for foetal development
. These cells develop into multipotent cells of different types, which then create all the different variations on that type.
Where do stem cells come from?
One of the best sources for stem cells, especially the particularly important totipotent and pluripotent stem cells, is of course from human embryos - normally surplus frozen embryos left as a by-product of In-Vitro Fertilisation. Typically, an In-Vitro Fertilisation procedure leaves about sixteen surplus embryos, and couples are given the option of either discarding these embryos, donating them to another couple trying to have a baby, donating the embryos for research or keeping the embryos frozen. For emotional reasons, few give the embryos away for adoption, and because freezing the embryos is expensive, most couples choose to have the embryos discarded. While researchers argue that these embryos are ideal candidates for study, various groups have opposed this, often with the argument that destroying human embryos (which is what happens with the extraction of the stem cells) constitutes murder.
Stem cells can also be extracted from adults without harm to the subject, although this procedure is very difficult and yields relatively few cells which can only be changed into a small variety of different cell types (in other words, the cells are usually multipotent instead of totipotent or pluripotent). In addition, the cells themselves are usually damaged in some way due to the normal effects of aging and exposure to the radiation, including ultraviolet radiation, that every person experiences. However, recent research has shown that adult stem cells may be more versatile than previously thought, in that they can change into different cell types entirely.
Another source of multipotent stem cells (although not pluripotent or totipotent cells) is umbilical cord blood, which is usually discarded during the birth process.
Therapeutic cloning is another very emotional topic, which has unfortunately been subject to some falsehoods. In therapeutic cloning, DNA from an individual patient is inserted into an egg, which is then subjected to various stimuli that cause it to divide, creating pluripotent stem cells which are then harvested. This eliminates the possibility that the egg could ever grow into a person. However, many people have taken this to mean that a cloned human could be grown by such methods, causing further outcry. The advantage of this method is that scientists can create stem cells that are individually matched to each patient, limiting the chances of rejection.
What are stem cells used for?
Stem cells have been in use for thirty years, with adult bone marrow stem cells being used to treat patients with leukemia or lymphoma. Because chemotherapy kills stem cells along with cancerous cells, the stem cells are often removed before chemotherapy and replaced afterwards. Furthermore, stem cells have also been used to treat cancer more directly. Researchers at Harvard injected specially engineered stem cells into the brain of a rat with brain cancer, along with a non-toxic substance. Within a few days the stem cells had converted the substance into a cancer-killing agent, and reduced the tumour by eighty percent. Stem cells have also been used in skin grafts, to regenerate muscle damage, and to repair hearts. Blindness and missing teeth have also been treated with stem cell research.
In addition, the study of how stem cells develop sheds much more light on the development of the foetus, a relatively unknown process. As more is learned, new techniques for identifying and curing various diseases and defects in the womb become available.
The true advantage of stem cells, however, is that any part of the body can be regrown or repaired, with an increasingly smaller chance of rejection. With enough research, entire body parts could be replaced, including arms or legs as well as internal organs such as kidneys or livers. Pending further research on how the brain works, people could theoretically be made immortal, as the process of aging is slowed or reversed.
It is difficult to believe that stem cells have become such an important and emotional topic of late. For the sake of something so small that it cannot be seen with the naked eye, protests have been held, advertisements have been sponsored by various groups, books have been written, and politicians have declaimed at length (although some might say that politicians will do that for just about anything). The purpose of this writeup is to provide information on a sensitive issue in a completely unbiased way. Please note also that I am not a biologist, and that if this is the only article you read before deciding to replace Granny's kidney in your basement lab, you're an idiot. Thank you.
Thanks go to Doyle for helping me fact-check this W/U.