| Stem cells are primal cells common to all multi-cellular | | | | vitro culture conditions can alter the behavior of cells, |
| organisms that retain the ability to renew themselves | | | | making it unclear whether the cells will behave in a |
| through cell division and can differentiate into a wide | | | | similar manner in vivo. Considerable debate exists |
| range of specialized cell types. Research in the human | | | | whether some proposed adult cell populations are |
| stem cell field grew out of findings by Canadian | | | | truly stem cells. |
| scientists Ernest A. McCulloch and James E. Till in the | | | | • Totipotent stem cells are produced from |
| 1960s. | | | | the fusion of an egg and sperm cell. Cells produced |
| A stem cell is a primitive type of cell that can be | | | | by the first few divisions of the fertilized egg are |
| coaxed into developing into most of the 220 types | | | | also totipotent. These cells can differentiate into |
| of cells found in the human body (e.g. blood cells, | | | | embryonic and extraembryonic cell types. |
| heart cells, brain cells, etc). Some researchers regard | | | | • Pluripotent stem cells are the descendants |
| them as offering the greatest potential for the | | | | of totipotent cells and can differentiate into cells |
| alleviation of human suffering since the development | | | | derived from the three germ layers. |
| of antibiotics. Over 100 million Americans and two | | | | • Multipotent stem cells can produce only |
| billion other humans worldwide suffer from diseases | | | | cells of a closely related family of cells. |
| that may eventually be treated more effectively with | | | | • Unipotent cells can produce only one cell |
| stem cells or even cured. These include heart disease, | | | | type, but have the property of self-renewal which |
| diabetes, and certain types of cancer. | | | | distinguishes them from non-stem cells. |
| Stem cells can be extracted from very young human | | | | Treatments |
| embryos -- typically from surplus frozen embryos left | | | | Medical researchers believe that stem cell therapy |
| over from in-vitro fertilization (IVF) procedures at | | | | has the potential to radically change the treatment of |
| fertility clinics. A couple undergoing IVF is faced with | | | | human disease. A number of adult stem cell therapies |
| four alternatives for their 16 or so surplus embryos: | | | | already exist, particularly bone marrow transplants |
| There are very few parents willing to give their | | | | that are used to treat leukaemia. In the future, |
| embryos to another couple for a variety of emotional | | | | medical researchers anticipate being able to use |
| reasons. There are very few couples willing to | | | | technologies derived from stem cell research to treat |
| receive them for emotional reasons and because | | | | a wider variety of diseases including cancer, |
| thawed embryos have such a low chance of starting | | | | parkinson's disease, spinal cord injuries, and muscle |
| a pregnancy. Preservation can be expensive. | | | | damage, amongst a number of other impairments |
| Stem cell properties | | | | and conditions. However, there still exists a great deal |
| These properties can be illustrated in vitro, using | | | | of social and scientific uncertainty surrounding stem |
| methods such as clonogenic assays, where the | | | | cell research, which could possibly be overcome |
| progeny of single cell is characterized. However, in | | | | through public debate and future research. |