stem cell

Embryonic cell that can develop into different tissues. Stem cells are used in medical research but their use is ethically controversial as the donor embryo is destroyed. Stem cells differ from other types of cells in that they are unspecialized cells that can reproduce themselves for long periods of time using cell division, but are capable of changing themselves into almost any type of specialist cell given the correct stimulus. Scientists have postulated that stem cell research could lead to cures for a wide range of medical conditions, from heart ailments to Parkinson's disease to growing replacement body parts.

There are three basic kinds of stem cell, which are known as totipotent, pluripotent, and multipotent. Totipotent stem cells form when a fertilized egg first divides, and can form a complete organism by forming all the necessary tissues, such as bone, muscle, or nerve tissue, and also form the placenta. Pluripotent stem cells form as part of the blastocyst and can form most kinds of tissue, but are not able to generate the whole organism. Multipotent cells are generated by an embryo and give rise to only specific kinds of cells.

Examples of the types of specialist cell into which stem cells can develop are the cells that operate in the beating of the heart and the cells in the pancreas capable of producing insulin.

Recent research Different countries have different guidelines relating to the use of embryonic stem cells (ESCs). In the UK proposals were put forward in 2000 to allow researchers to harvest ESCs. In the USA medical guidelines are more restrictive.

Australian medical researchers claimed in 2001 to have shown that adult stem cells could develop into different tissue types. Previously it was thought that only stem cells from embryos had this ability, but this was proved otherwise in experiments involving the extraction of stem cells from the brains of adult mice. The discovery could lead to self-repair of damaged brains or spinal cords, avoiding the need to use stem cells taken from human embryos.

In 2002 a team of scientists at the University of Minnesota, USA, announced the finding of a stem cell, present in the bone marrow of adults, that could potentially develop into every tissue in the human body. These stem cells were called multipotent adult progenitor cells, or MAPCs.

In 2003 human embryonic stem cells were grown into a cell line for the first time in the UK. To generate the stem-cell line, the research team at King's College, London used embryos that had been discarded from genetic screening tests in fertility treatments. An ESC line is a series of cells that are generated from a single embryo and which are maintained in their original primitive state in a laboratory. Stem-cell lines can be used to create a wide range of specialist stem cells, which could potentially result in new treatments for diseases.

In February 2004, scientists at Seoul National University, South Korea, reported the cloning of 30 human embryos. The aim of their research was to grow the embryos to obtain embryonic stem cells as an alternative to using natural embryos for the same task. This procedure removes some of the moral implications of destroying natural embryos to collect stem cells.

Also in 2004, stem cells from fat were used for the first time to heal an injury. Stem cells harvested from the belly fat of a mouse manufactured bone cells that healed 4-mm/.15-in fractures in mouse skulls. The fat stem cells filled the fractures up to 90% compared with 10% in untreated cases.

In 2005 scientists developed a stem-cell line from cloned human cells for the first time. A team of researchers at Seoul National University, South Korea produced patient-specific embryonic stem-cell lines from 11 human donors. The genetic sequences of stem cell lines are identical to the cells of the donor patient. Some of the donors were suffering from diseases such as diabetes. A possible application of this research is to stimulate the stem cells to grow into human cells to provide clues to the disease specific to the cell donor.