Adult stem cells are specialized cells within the body that contribute to its ongoing maintenance and repair. They play a role in replacing cells lost due to normal processes, injury, or disease. The ability to obtain adult stem cells from various tissues allows for their investigation and potential use in regenerative applications.
What Are Adult Stem Cells?
Adult stem cells, also known as somatic stem cells, are undifferentiated cells found throughout the body after development. They possess two main characteristics: the ability to self-renew, meaning they can divide to create more stem cells, and the ability to differentiate into specialized cell types. This differentiation potential is typically multipotent, allowing them to form several cell types within their tissue of origin.
These cells function as an internal repair system, continually generating replacements for cells that are lost or damaged. Adult stem cells reside in various tissues, including bone marrow, fat, and skin, acting to maintain tissue homeostasis. Unlike embryonic stem cells, which can become any cell type in the body and are derived from early-stage embryos, adult stem cells are found in developed organisms and have a more restricted differentiation capacity.
Collecting Stem Cells from Bone Marrow
Bone marrow collection is an established method for obtaining adult stem cells. This procedure typically takes place in an operating room under general anesthesia. Needles are carefully inserted through the skin, usually into the back of the pelvic bone, to aspirate the liquid marrow. Multiple punctures may be necessary to collect a sufficient quantity of stem cells, with the entire collection often taking about 60 to 90 minutes.
After the bone marrow collection, donors are monitored in a recovery area. Recovery times vary, but most donors can return to their usual activities within a few days to a couple of weeks. Common post-procedure effects include soreness, bruising, or mild pain in the lower back or hip area where the aspiration occurred. Fatigue and muscle aches are also possible, but these side effects typically resolve with rest and over-the-counter pain relievers. The body naturally replenishes the donated marrow within a few weeks.
Collecting Stem Cells from Peripheral Blood
Peripheral blood stem cell (PBSC) collection has become a common method, often preferred for its less invasive nature compared to bone marrow aspiration. This process begins with the administration of growth factor medications, such as granulocyte colony-stimulating factor (G-CSF), through daily subcutaneous injections for several days. G-CSF works by stimulating the bone marrow to produce more stem cells and encourages them to move into the bloodstream.
Once enough stem cells have mobilized into the peripheral blood, usually after four to five days of injections, the collection proceeds via a process called apheresis. This outpatient procedure is similar to blood donation: blood is drawn from one arm, passed through a machine that separates and collects the stem cells, and returns the remaining blood components to the donor through the other arm. This collection typically takes between four to eight hours and may require one or two sessions to obtain the necessary quantity of cells.
The G-CSF injections can cause temporary side effects, including bone or muscle aches, headache, fatigue, and nausea. These flu-like symptoms are usually mild to moderate and subside shortly after the injections cease. The apheresis procedure itself has few direct side effects, though some donors might experience tingling sensations or lightheadedness. The main advantage of this method is avoiding the need for general anesthesia and a surgical procedure.
Collecting Stem Cells from Adipose Tissue
Adipose (fat) tissue is an abundant source of adult stem cells, desirable for its accessibility and the high concentration of mesenchymal stem cells (MSCs) it contains. The process typically involves a minimally invasive, liposuction-like procedure, often performed under local anesthesia. A small incision is made, usually in areas like the abdomen or lower back, and a thin tube called a cannula is inserted to extract fat.
The aspirated fat tissue is then processed to isolate the stem cells. This often involves washing the tissue to remove impurities, followed by enzymatic digestion to release the cells from the fat matrix. The resulting solution is then centrifuged, which separates the stromal vascular fraction (SVF), rich in stem cells, from other components. This concentrated stem cell sample is then ready for various applications.
Adipose-derived stem cells offer several advantages, including ease of collection with low donor discomfort and a shorter recovery time compared to bone marrow harvesting. These cells also maintain their proliferative capacity and can differentiate into multiple cell types, making them versatile for regenerative purposes.
Less Common Adult Stem Cell Sources
Beyond bone marrow, peripheral blood, and adipose tissue, adult stem cells can be isolated from several other tissues. These methods are generally less common or still undergoing extensive research.
Dental pulp, found within teeth, is a source of mesenchymal stem cells that can be collected from extracted adult teeth, such as wisdom teeth, or even deciduous (baby) teeth. The process involves isolating the pulp and then culturing the stem cells. Hair follicles also contain adult stem cells, specifically in the bulge region, and can be obtained through a punch biopsy or even depilation, with ongoing studies exploring their use in hair regeneration.
Skin contains adult stem cells and fibroblasts that can be used for regenerative purposes. These cells are typically acquired through a small skin biopsy, often from an area not exposed to the sun. The collected tissue is then processed to extract and expand the cells in a laboratory setting before potential application. Other emerging sources include menstrual blood, umbilical cord tissue, and amniotic fluid.