Células madres, or stem cells, are the body’s raw building blocks. They are unique cells capable of two things no other cell can do: copying themselves indefinitely and transforming into specialized cell types like muscle, nerve, or blood cells. Every tissue in your body traces back to stem cells that divided and matured during development, and some remain in your body throughout life to repair damage and replace worn-out cells.
How Stem Cells Work
A stem cell’s power comes from two core abilities. The first is self-renewal: a stem cell can divide and produce a perfect copy of itself, maintaining a steady supply. The second is differentiation: under the right signals, it can mature into a specialized cell with a specific job, like carrying oxygen or transmitting nerve impulses.
When a stem cell divides, it often produces two different daughter cells. One stays a stem cell, keeping the reserve intact. The other migrates away from its home environment, called a niche, and begins the process of specializing. This is how your bone marrow continuously produces billions of fresh blood cells every day, and how your skin replaces itself roughly every two to three weeks.
Types Based on Potency
Not all stem cells are equally flexible. Scientists classify them by how many different cell types they can become, a property called potency.
- Totipotent: These can become any cell in the body plus the tissues that support a pregnancy, like the placenta. The only undisputed totipotent cell is the fertilized egg, or zygote.
- Pluripotent: These can become any cell type in the adult body (nerve, muscle, liver, blood) but cannot form placental tissue. Embryonic stem cells fall into this category.
- Multipotent: These can produce several related cell types within a single family. Blood-forming stem cells in your bone marrow, for example, generate red blood cells, white blood cells, and platelets, but they cannot become brain or liver cells.
Where Stem Cells Come From
There are three main sources scientists and doctors work with, each with distinct advantages and limitations.
Embryonic stem cells are harvested from donated embryonic tissue, typically from embryos created during fertility treatments that are no longer needed. Because they are pluripotent, they can become virtually any cell type. Their supply is limited, though, and their use raises ethical questions for some people.
Adult stem cells exist in small numbers in tissues throughout your body, including bone marrow, fat, and the brain. They are already partially specialized, which means they are multipotent rather than pluripotent. A bone marrow stem cell, for instance, excels at making blood cells but cannot readily become a heart cell. The advantage is that they can be taken directly from a patient.
Induced pluripotent stem cells (iPSCs) are a newer innovation. Scientists take ordinary adult cells from skin, blood, or even urine and reprogram them in a lab to behave like embryonic stem cells. Because iPSCs carry the patient’s own genetic code, they offer a perfectly personalized model of that individual’s biology. This makes them useful for studying how a disease develops in a specific person and for testing whether a therapy will help or harm that patient. They also sidestep many of the ethical concerns tied to embryonic stem cell research.
Currently Approved Medical Uses
Despite the excitement around stem cells, only one type of stem cell therapy is routinely approved by the U.S. Food and Drug Administration: blood stem cell transplantation, commonly known as a bone marrow transplant. It is used to treat cancers and disorders that affect the blood and immune system, including leukemia, lymphoma, and sickle cell disease.
In this procedure, cells can come from two sources. An autologous transplant uses the patient’s own stem cells, collected and stored before intensive treatment. Because the cells are genetically identical to the patient, the body does not reject them. An allogeneic transplant uses cells from a matched donor. This carries a higher risk of complications because the donor’s immune cells can attack the patient’s tissues, a reaction called graft-versus-host disease. However, those same donor immune cells can also attack remaining cancer cells, which sometimes gives allogeneic transplants a survival advantage in aggressive diseases.
Research in Progress
Scientists are actively testing stem cell approaches for conditions that currently have no cure. Neurodegenerative diseases are a major focus. In ALS, which destroys the nerve cells that control movement, early animal experiments using transplanted stem cells showed a decrease in disease symptoms. Researchers are also exploring whether stem cells derived from iPSCs could replace damaged nerve tissue in multiple sclerosis, though that work is still in its initial stages.
Diabetes, heart disease, spinal cord injuries, and Parkinson’s disease are all areas where clinical trials are underway. The goal in most of these studies is regenerative medicine: using stem cells to rebuild or replace tissue the body cannot repair on its own. Results so far are promising enough to sustain large-scale research, but no stem cell treatment for these conditions has yet passed the bar for regulatory approval.
Risks of Unproven Treatments
Hundreds of clinics around the world market stem cell injections for arthritis, back pain, autism, chronic fatigue, heart disease, and many other conditions. The FDA has issued direct consumer warnings about these products. None of these treatments have been approved for orthopedic conditions like osteoarthritis, tendonitis, or disc disease. None have been approved for neurological disorders including Alzheimer’s, Parkinson’s, ALS, or stroke. None have been approved for heart disease, lung disease, macular degeneration, chronic pain, or autism.
The risks are real. Patients at unregulated clinics have suffered serious bacterial infections, paralysis, and permanent bilateral vision loss. There are also theoretical concerns about cancer: laboratory studies have documented cases where stem cells became genetically unstable and transformed into cells that promote tumor growth. While no cancers have been confirmed in formal clinical trials using carefully controlled stem cell preparations, the products sold at many commercial clinics are not characterized or tested to that standard.
If a clinic claims stem cells can cure a condition not on the FDA’s approved list, that is a red flag. Legitimate stem cell therapies go through rigorous clinical trials before reaching patients, and the vast majority of the treatments advertised online have not completed that process.