Stem cells are unique cells with the ability to self-renew, dividing to create more copies of themselves. They also differentiate, transforming into various specialized cell types throughout the body. This versatility makes stem cells fundamental to biological processes, supporting tissue maintenance and repair. Their potential to regenerate damaged cells offers promise for medical advancements.
Natural Sources of Stem Cells
Stem cells are naturally found in different locations within the body. Adult stem cells reside in various mature tissues, acting as an internal repair system. These include bone marrow, adipose (fat) tissue, peripheral blood, and dental pulp. Adult stem cells are typically multipotent or unipotent, differentiating into a limited range of cell types specific to their tissue of origin.
Embryonic stem cells, in contrast, originate from the inner cell mass of an early-stage embryo at the blastocyst stage. These cells are pluripotent, developing into almost any cell type in the body, but not placental tissue. This broad differentiation potential distinguishes them from adult stem cells. Induced pluripotent stem cells (iPSCs) are not found naturally but are engineered by reprogramming adult cells to behave like embryonic stem cells.
How Adult Stem Cells Are Collected
The collection of adult stem cells involves several distinct medical procedures. Bone marrow aspiration draws stem cells directly from the bone marrow, most commonly from the hip bone (iliac crest), under general anesthesia. This procedure typically involves inserting a needle multiple times to extract marrow, a rich source of hematopoietic stem cells. It is considered a surgical procedure that can cause discomfort at the collection site.
Peripheral blood stem cell collection, also known as apheresis, is a less invasive method. Donors often receive growth factor injections for several days to mobilize stem cells from the bone marrow into the bloodstream. Once mobilized, blood is drawn from one arm and passed through an apheresis machine, which separates the stem cells before returning the remaining blood to the other arm. This outpatient procedure may need to be repeated over several days to collect sufficient cells.
Adipose tissue-derived stem cells are obtained from fat tissue, typically through liposuction. This method offers an abundant source of mesenchymal stem cells. Umbilical cord blood collection is a non-invasive process performed immediately after birth. Blood remaining in the umbilical cord and placenta is collected, providing a valuable source of hematopoietic stem cells without risk to the mother or baby.
How Embryonic Stem Cells Are Obtained
Embryonic stem cells are derived from the inner cell mass of a blastocyst, typically a human embryo 5 to 7 days old. These are generally “surplus” embryos created for in vitro fertilization (IVF) treatments, no longer needed for reproduction. With informed consent, these embryos can be used for research.
The process involves culturing the donated embryo until it reaches the blastocyst stage. The inner cell mass is then isolated. These cells are subsequently cultured to establish stable embryonic stem cell lines. The use of human embryos for research raises complex ethical considerations, often debated between potential medical advancements and concerns regarding the moral status of the early embryo.
How Induced Pluripotent Stem Cells Are Created
Induced pluripotent stem cells (iPSCs) are engineered in a laboratory, not collected from existing biological sources. This process involves reprogramming specialized adult somatic cells, such as skin or blood cells, into a pluripotent state. This reprogramming allows them to behave similarly to embryonic stem cells.
Creating iPSCs involves introducing specific “reprogramming factors” into adult cells. These factors, typically a combination of genes or proteins, are often delivered using viral vectors. Their introduction triggers epigenetic changes within the cells, leading to their transformation into iPSCs.
An advantage of iPSCs is that they can be generated from an individual’s own cells, making them patient-specific and potentially reducing immune rejection in therapeutic applications. This method also bypasses many ethical concerns associated with embryonic stem cells. iPSCs hold potential for disease modeling, drug discovery, and various applications in regenerative medicine.