At the most basic level, the promise that stem cells hold is also the source of the controversy over them. The idea that replacement parts for our bodies might one day be as easy to create as ordering prescription medication from the local drugstore is breathtaking. But if these same cells can only work their magic through the destruction of human embryos, then cure and curse will be one and the same to many people. To those who see a human being’s life as starting from the moment of fertilization, regenerative medicine via stem cells is nothing more than high-tech cannibalism. There is an alternative, imperfect though it may be. In recent years, scientists have discovered that similar kinds of cells can be found outside the holy sphere of the human embryo’s blastocyst. These "adult" stem cells can be found in the blood, the pockets of our bone marrow, the umbilical cord, under the dermis of the skin, and, just perhaps, buried deep in the brain.
Adult stem cells (ASCs) are the technology of choice among those who morally object to the use of embryonic stem cells. At a May 2005 White House press conference, President Bush reaffirmed his opposition to funding embryonic stem cell research outside of the existing stem cell lines, but praised the use of "alternative sources" of stem cells. (Potten et al 2006) The ones mentioned in the above paragraph, such as stem cells from bone marrow and umbilical cord blood, are classic examples of ASCs. "With the right policies and the right techniques," Bush asserted, "we can pursue scientific progress while still fulfilling our moral duties." (Potten et al 2006) But is this indeed the case, or is it wishful thinking? As with many complex subjects, there is no clear-cut answer.
The degree to which adult stem cells can be put to use often depends on who is being interviewed. However, if one sticks as closely as possible to what has been reliably reproduced in multiple laboratories over time, some hard facts do become available. That is, at least as "hard" as the facts can be, before the technology advances yet further and changes reality yet again. A fair number of therapies involving adult stem cells are in human clinical trials at present, and the number continues to grow. It is likely that these therapies will make their appearance at the local hospital or health clinic long before embryonic stem cells can even begin to make it to human trials. At the third annual meeting of the International Society for Stem Cell Research, held in 2005, the clear majority of the presentations dealt with therapies related to adult stem cells. (Holland et al 2006) Clearly, the interest—and, not coincidentally, the private sector venture capital—lies in ASCs for now.
There is simply no tool as powerful as the embryonic stem cell (ESC). In possesses, in the words of one researcher, "the potential to address every single disease or condition that our species is heir to." (Holland et al 2006) This is because embryonic stem cells, which are extracted from the fifth day of the embryo’s blastocyst formation, have such a high degree of developmental plasticity that they are capable of becoming any type of cell in the body. It is medical fact that ESCs are incredibly pluripotent. (Humber 2004) However, a second look must be taken when advocates of embryonic stem cells claim that the cells can be grown in infinite numbers.