Stem cells are stirring up great excitement in medical research. What are they and why are scientists so intrigued by them?
Most of the 300 trillion cells that make up the human body are fully specialised for particular functions in organs such as the heart or the brain, or in tissues like muscle, fat and bone. Others play a supply or defensive role in the blood or immune system. Each cell type has a specific lifespan and function, which is dependent on the desired activity of the cell. Some cells are replaced, others live for the duration of a person’s life. For example blood cells only live for up to a few months, and are replaced at a rate of several billion each day. Where as brain cells, may last a lifetime. Stem cells are the foundation of normal growth and development of any organism and serve as a biological repair system for the body.
Stem cells are found in the early embryo, the fetus, placenta, umbilical cord, and in many different tissues of the adult body. Stem cells are often divided into two groups: adult stem cells and embryonic stem cells.
Under certain conditions, stem cells can be induced to become other types of cells, for example blood cells, muscle cells or neurons. Stem cells occurring in the various structures at differing stages of growth and development herald different levels of potential, which continues to be a central theme of enquiry within the stem cell community. Adult stem cells are derived from, or resident in, fetal or adult tissue, and can usually only give rise to the cells of that tissue, thus they are considered multipotent. Embryonic stem cells, derived from a small group of cells within the very early embryo, and their new counterpart induced pluripotent stem (iPS) cells are considered pluripotent as they can become every type of cell in the body.
At the stage of an early embryo, primitive stem cells begin the process of tissue and organ development. These cells have the potential and material to create any type of tissue or structure in the body. They can theoretically divide without limit to replenish damaged or diseased cells. The division of cells throughout the life of the organism is fundamental to the development, growth and maintenance of tissues and structures within the body, but is most obvious in the rapid growth phase of a developing foetus. Controlling this differentiation process is one of the biggest challenges in stem cell research.
The ability of stem cells to replace damaged or diseased cells and the significant potential to induce stem cells to develop into different cells underlies the degree of interest and levels of investment in this field of enquiry. The potential for stem cells as a treatment for a number of serious diseases and injuries offers hope to millions of patients and clinicians worldwide, but there is much scientists are yet to discover and confirm before many of these hoped-for treatments become a reality. In the short term, stem cell technology is likely to result in a number of products and tools for basic research and possibly drug discovery before the development of cell-based therapies.
The above image shows Cardiac Progenitor Cells in Adult Hearts (image courtesy of Corey Heffernan)