The National Stem Cell Foundation defines stem cells as the body’s “master cells.”
They are the building blocks of all organs, tissues, blood, and the immune system. In many instances they serve as an internal repair system, regenerating to replace lost or damaged cells for the life of a person.
Stem cells generate all the cells and structures of the human body from conception to end of life. There are three broad categories of stem cells and multiple tissue-specific stem cell types.
ADULT STEM CELLS
All cells of the living human body are adult stem cells. Stem cells found in amniotic fluid, placenta, and cord blood represent the earliest stage of adult stem cells and are routinely collected and “banked” for potential use. Many adult stem cell types are considered “multipotent” or capable of developing into most cells and tissues of the body. Tissue specific stem cells are capable of replacing only the tissue or organs in which they live.
INDUCED PLURIPOTENT STEM CELLS (iPS Cells)
An iPS cell is an adult stem cell, most often a skin cell, which has been reprogrammed to revert back to a pluripotent state. iPS cells are readily in use as tools for drug development and disease modeling. They are also in widespread research and clinical trial use to induce the production of missing cells that will halt or reverse catastrophic and currently incurable degenerative diseases. Because they are collected directly from the affected patient, there is no risk of transplant rejection.
EMBRYONIC STEM CELLS
Embryonic stem cells are collected from in vitro fertilization clinics when donated to research. In vitro fertilization involves the joining of egg and sperm in a laboratory dish and freezing the resulting earliest stage embryo for future implantation. Embryonic stem cells are considered pluripotent as they are capable of developing into all the cells and tissues of the body. The 2006 discovery that adult skin cells could be reprogrammed to behave like pluripotent stem cells largely leap frogged the use of embryonic cells for clinical development.
MESENCHYMAL STEM CELLS
Mesenchymal stem cells (MSCs) are multipotent stem cells that can differentiate into a variety of cell types, including bone cells (osteoblasts), cartilage cells (chondrocytes), muscle cells (myocytes) and fat cells that give rise to marrow adipose tissue (adipocytes).
Neural Stem Cells:
Neural Stem Cell (NSCs): Multipotent cells which are able to self-renew and proliferate without limit, to produce progeny. Neural stem cells have the potential to give rise to offspring cells that grow and differentiate into neurons and glial cells.
Epithelial Stem Cells:
Epithelial stem cells maintain tissues throughout adult life and are tightly regulated by their microenvironmental niche to balance cell production and loss. These stem cells have been studied extensively as signal-receiving cells, responding to cues from other cell types and mechanical stimuli.
Hematopoietic Stem Cells (Blood Stem Cells):
Hematopoietic stem cells (HSCs) reside in bone marrow (BM) and produce all cells required to replenish the blood and immune systems; this process is tightly regulated to maintain a steady number of leukocytes, platelets, and red cells in the blood.
Skin Stem Cells:
Skin stem cells are multipotent adult stem cells present in adult skin, which can self-renew and differentiate into different cell lineages of the skin. Skin stem cells are active during skin renewal, which occurs throughout life, and in skin repair after injury.
They are responsible for constant renewal (regeneration) of your skin, and for healing wounds. So far, scientists have identified several different types of skin stem cell: Epidermal stem cells are responsible for everyday regeneration of the different layers of the epidermis.