Discovery of Stem Cell

Ernest McCulloch and James Till, respectively a cellular biologist and a biophysicist, discovered the existence of stem cells in the early 1960’s in experiments with mice and bone marrow. Their discoveries led to successful treatments of cancer, among other illnesses, with bone marrow transplants. The two have been called the fathers of the stem cell field.

The work that laid the foundation for ES cell discovery was the study of teratocarcinomas, complex tumors containing a mix of specialized cell types as well as a population of unspecialized cells. These unspecialized cells are called embryonal carcinoma (EC) cells. The latter were shown to be pluripotent and could give rise to various cell types both in vitro and in vivo. It was therefore natural to consider using these cells for therapeutic purposes. However, EC ells never seemed ideal for this purpose because they had an abnormal number of chromosomes and originated from tumors. Careful study of the induction of teratocarcinomas in experimental animals, as well as an understanding of the biology of EC cells and early embryos, led scientists to the discovery of ES cells in the early 1980s. The demonstration that ES cells contained the normal number of chromosomes and were truly pluripotential has influenced many scientific disciplines.

Stem cells have generated more excitement, scrutiny and controversy than any other area of recent scientific study. The first stem cells, which were discovered half a century ago, were isolated from blood. Now, scientists around the globe are researching various types of stem cells for their potential to regenerate lost tissue and revolutionize medicine.

Embryonic stem (ES) cells are derived from the embryo when it exists as a blastocyst. They have the ability to develop into all the different cell types found in the body. Actually, when a sperm fertilizes an egg, the resulting single cell begins to divide and multiply at a rate much faster than that observed in somatic cells. Scientists refer to these cells as totipotent stem cells. These primordial embryonic cells have the potential to grow into a complete mammal. Within days of fertilization, these new and dividing cells form a hollow sphere, called a blastocyst. Stem cells arising in the inner mass of the blastocyst are called the ES cells. The ES cells are considered pluripotent - they can divide indefinitely and blossom into all the various tissue types of the human body, but they have the lost the totipotent ability to grow into a separate being. After roughly 14 days, ES cells divide to give rise to what will eventually develop into the spine. At this stage, the stem cells within the embryo are considered multipotent. These cells can grow into some tissues, but not all tissues. Those destined to become bone or blood, for example, may not be able to form stomach or skin.

By definition, stem cells have two important characteristics that distinguish them from other types of cells. First, they are unspecialized cells that renew themselves for long periods of time through cell division of at least one daughter cell. Secondly, under certain physiological or experimental conditions, they can be induced to differentiate. This means that they can divide into cells with special functions, such as the beating cells of the heart muscle or the insulin-producing cells of the pancreas.

Stem cells differ from other kinds of cells in the body. All stem cells, regardless of their source, have three general properties: they are capable of dividing and renewing themselves for long periods; they are unspecialized; they can choose to become one of the many different types of cells present in the body based on signals from their environments.

Due to these discovery , a whole new field in medicine is being dedicated to the study of stem cells called stem cell bioengineering whose ultimate objective is to be able to understand and possibly control stem cell differentiation and lineage commitment in vitro. If this can be achieved, a multitude of therapeutic applications can be envisioned. One potential application is the generation of neurons for the treatment of Alzheimer’s disease, spinal cord injuries, or Parkinson’s disease. The production of heart muscle cells for heart attack survivors may also be possible. The generation of insulin-secreting pancreatic islet cells for the treatment of type-1 diabetes, and even the generation of hair follicle stem cells of certain types of baldness, have been considered. Stem cells could also be useful for a number of tissue engineering applications such as the production of complete organs including livers, kidneys, eyes, hearts, or even parts of the brain. This represents a considerably greater challenge, beyond the generation of specialized cell types, and will require considerable time and effort to develop. Other areas that would benefit from a better understanding and control of stem cell proliferation in vitro are drug testing, cancer research, and fundamental research on embryonic development.