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STEM CELL RESEARCH
Embryonic stem cells (ES cells) are stem cells
derived from the inner cell mass of an early stage embryo known as a
blastocyst. Human embryos reach the blastocyst stage 4-5 days post
fertilization, at which time they consist of 50-150 cells.
ES cells are pluripotent. This means they are able to differentiate into
all derivatives of the three primary germ layers: ectoderm, endoderm,
and mesoderm. These include each of the more than 220 cell types in the
adult body. Pluripotency distinguishes ES cells from multipotent
progenitor cells found in the adult; these only form a limited number of
cell types. When given no stimuli for differentiation, (i.e. when grown
in vitro), ES cells maintain pluripotency through multiple cell
divisions. The presence of pluripotent adult stem cells remains a
subject of scientific debate.
Because of their plasticity and potentially unlimited capacity for
self-renewal, ES cell therapies have been proposed for regenerative
medicine and tissue replacement after injury or disease. To date, no
approved medical treatments have been derived from embryonic stem cell
research. This is not unusual for a new medical research field; in this
case, the first human embryonic stem cell line was only reported in
1998. Besides the ethical problems of stem cell therapy (see stem cell
controversy), there is a technical problem of graft-versus-host disease
associated with allogeneic stem cell transplantion. However, these
problems associated with histocompatibility may be solved using
autologous donor adult stem cells or via therapeutic cloning.
There is widespread controversy over stem cell research due to the
techniques used in the creation and usage of embryonic stem cells.
Embryonic stem cell research is particularly controversial because, with
the present state of technology, starting an embryonic stem cell line
requires the destruction of a human embryo and/or therapeutic cloning.
Some opponents of the research also argue that this practice is a
slippery slope to reproductive cloning and tantamount to the
instrumentalization of a potential human being. Contrarily, medical
researchers in the field argue that it is necessary to pursue embryonic
stem cell research because the resultant technologies are expected to
have significant medical potential, and that the embryos used for
research are only those slated for destruction anyway. The ensuing
debate has prompted authorities around the world to seek regulatory
frameworks and highlighted the fact that embryonic stem cell research
represents a social and ethical challenge. |
What
is a stem cell?
Research history and
developments
Isolation and in vitro culture
Production of male gametes
Contamination by reagents used in cell culture
Reducing donor-host rejection
Potential method for new cell line derivation
Stem cell therapies
Controversy of
Embryonic stem cell research
Arguments for cell research state these reasons:
Arguments against embryonic stem cell research
Stem cells without embryonic destruction
Patents covering human
stem cell research
International policy
context
US policy debate
Origins of policy debate in the U.S.
Congressional response
References |