Stem Cells

Stem cells are undifferentiated (unspecialized) cells that are capable of renewing themselves through cell division. Stem cells also have the capability of differentiating into more specialized cells. There are two major types of stem cells: adult or tissue-specific stem cells (i.e. neural, hematopoietic, & mesenchymal stem cells) and pluripotent stem cells (ES & iPS cells).

Tissue Specific Stem Cells

Tissue-specific stem cells exist throughout the fetal and adult body and are found in a range of tissues. Tissue-specific stem cells maintain portions of the adult body by providing an internal repair system in response to damage caused by disease, aging, or injury. However, tissue-specific stem cells only differentiate into a limited number of cell types.

ES and iPS Cells

In contrast, pluripotent stem cells are capable of differentiating into all the cell types of the adult organism. Pluripotent stem cells provide a unique model system to study human development and disease as these cells are capable of perpetual growth in vitro. ES cells are derived from the inner cell mass (ICM) of a pre-implantation embryo at the blastocyst stage. ES cells are highly sought after for biological research as they are capable of making many cell types that can then be used in the research and treatment of human diseases.

Recently, embryonic-like stem cells have been produced from adult cells such as fibroblasts formed from a simple skin biopsy of any human patient. The adult cells are "induced" back to an embryonic state through the addition of vectors, which cause the cell to express embryonic genes. Thus, these cells are known as induced pluripotent stem (iPS) cells. Like ES cells, iPS cells can be differentiated into any cell in the body, and are therefore considered pluripotent. iPS cells can be derived from patients with specific disorders, such as Parkinson's or cardiovascular disease, and used in research. The iPS cells allow for a direct assessment of the mechanisms by which specific genetic mutations contribute to disease and allow for the formation of functional cells for autologous, cell-based therapy.