STEM CELL RESEARCH

Stem Cell Research

Stem Cell Research

Introduction

The human body is composed of a vast number of cells, on the order of 1013 to 1014. These are grouped, based on functional and morphological characteristics into various types of tissue composed of similar cells. Yet, for all humans, there was a time when there was but one cell.

Stem cell research is often confused with cloning as both involve the use of embryonic stem cells. While reproductive and therapeutic cloning only involve the use of embryos, stem cell research involves the use of adult stems cells, stem cells from fetuses, umbilical cord blood cells, and amniotic fluid, along with embryonic stem cells, to find cures for a variety of degenerative diseases. This cell was the product of syngamy (fertilization): the union of egg and sperm. This one cell divided and, in response to internal and environmental cues, various cells arising from these divisions became what we call stem cells (Snow, 2003). Stem cells are distinguished by their ability to proliferate indefinitely and their ability to give rise to numerous more specialized cell types. In contrast, differentiated cells have a limited ability to renew themselves and are limited in the types of cells they may differentiate into (Humber, 2004).

While stem cells may be classified according to their level of plasticity, a more functional method of classification is by source. Generally speaking, when classified by source, all stem cells within a classification will have comparable plasticities. Two classes of stem cells are already apparent. Those destined to form the cells of the maternal environment are termed human placental stem cells (hPSCs). Most of the remaining cells are human embryonic stem cells (hESCs).

As development progresses, cell specialization occurs and stem cells of diminished plasticity (typically termed multi-potent) become the norm. At various stages of development these are termed human fetal stem cells (hFSCs) and human adult stem cells (hASCs). At later stages of differentiation (diminished plasticity), it is common to refer to the stem cells by the limited types of specialized cells they can give rise to. Hence, hematopoietic stem cells from bone marrow and umbilical cord blood give rise to the various blood cells and neural stem cells give rise to various cells of the nervous system (Holm, 2006).

hASCs are acquired from willing adult donors, particularly marrow donors. Also, cord blood can be collected at the time of birth and stored for future use or research. Human fetal stem cells are collected from abortuses (Holland, 2006). A more complicated picture arises when hESCs are considered. Such cells are clearly taken from embryos (specifically the inner cell mass), but unlike with hASCs, it is not currently possible to obtain hESCs in significant quantities and maintain the viability of the embryo. Also, unlike adults who exist independent of any research need, embryos can arise in a number of ways. A large number of embryos remain frozen as so-called supernumeracy embryos created as part of in vitro fertilization (IVF). In some jurisdictions, it is legal to use ...