I’ve been lecturing on stem cells as a professor here at UC Davis School of Medicine for many years so I can answer common questions such as “What are stem cells?”. The medical students ask many great questions. They are always interested in clinical applications. The goal of today’s article is to help you have a much clearer understanding of stem cells.
You might also enjoy our Stem Cell Channel on YouTube.
The short answer is that stem cells are undifferentiated cells with power to make other kinds of cells. Most cells cannot do that as they can only make more of themselves. What this means is that stem cells can be used to make specialized cells. These include neurons, heart cells, and more. Such cells are used in research or in the clinic in the future. Bone marrow transplantation is the best example of a proven stem cell therapy.
What’s in this article?
What are stem cells?
Stem cells are defined as undifferentiated cells, which can become one or more other kinds of cells.
The human body contains hundreds of different types of cells that are important for our daily health. These cells are responsible for keeping our bodies running each day such as making our hearts beat, brains think, kidneys clean our blood, replace our skin cells as they shed off, and so on. The unique job of stem cells is to make all these other types of cells. They are the suppliers of new cells. When stem cells divide they can make more of themselves or more of other types of cells. For example, stem cells in skin can make more of themselves or they can make differentiated cells of the skin that have specific jobs of their own such as making the melanin pigment.
Why are stem cells important?
When we get injured or sick, our cells also are injured or killed. When this happens, stem cells become active. Stem cells have the job of fixing our injured tissues and of replacing other cells when they routinely die. In this way our stem cells keep us healthy and prevent us from prematurely aging. Stem cells are like our own army of microscopic doctors.
Stem cells come in many different forms. Scientists think that every organ of our body has its own specific type of stem cells. For example, our blood is made from blood (also known as hematopoietic) stem cells. However, stem cells are also present from the earliest stages of human development, and when scientists grow these, they are called “embryonic stem cells”.
Stem cells likely also play roles in aging. I proposed a stem cell theory of aging in my book. I’ve included an illustration from it by my student Taylor Seamount above.
Types of stem cells
The reason scientists are excited about embryonic stem cells is that the natural job of embryonic stem cells is to build every organ and tissue in our bodies during human development.
What this means is that embryonic stem cells, unlike adult stem cells, can be coaxed into potentially forming almost any other of the hundreds of types of human cells.
For example, while a blood stem cell can only make blood, an embryonic stem cell can make blood, bone, skin, brain, and so on.
In addition, embryonic stem cells are programmed by nature to build tissues and even organs, while adult stem cells are not.
What this means is that embryonic stem cells have a greater natural capacity to fix diseased organs.
Embryonic stem cells are made from leftover embryos from fertility treatments that are only a few days old, that were made in a dish in a laboratory, and that would otherwise be thrown away.
These embryos have 100 or less cells in the case of human ES cells.
In rarer instances ES cells can be made by somatic cell nuclear transfer.
This “cloning” process involves moving nuclei from one cell to another.
What are iPS cells?
Scientists and doctors are excited about this new type of stem cell called induced pluripotent stem cells or “iPS” cells. We are excited about these cells because iPS cells have almost all the same properties as embryonic stem cells, but are not made from an embryo. (Note you can watch a video about all you need to know about embryonic stem cells above on our YouTUbe channel.)
Thus, there are no ethical concerns with iPS cells. In addition, iPS cells are made from a patient’s own non-stem cells, meaning that iPS cells could be given back to a patient without risk of immune rejection, an important issue with any stem cell transplant.
Future of stem cell therapies
Because by nature stem cells have the job of replacing sick or old cells, scientists have conceived the idea of using stem cells as therapies for patients with a wide variety of medical conditions. The idea here is that by giving a sick patient stem cells or differentiated cells made from stem cells, we can make use of the stem cells’ natural ability to heal to make the patient healthy again.
For example, if a patient has a heart attack, by giving that patient a transplant of stem cells as a therapy our goal is to have the transplanted stem cells repair the damage to the heart. The natural populations of stem cells that we all possess have only a limited capacity to fix injuries to our bodies. Going back to the example of the heart, the heart’s own stem cells are just not up to the task of fixing the damage from a heart attack, but a transplant of millions of stem cells would be far more powerful.
Stem cells for heart disease or other conditions?
Therefore by giving patients transplants of stem cells we boost the body’s ability to heal beyond the capabilities of the limited number of naturally occurring stem cells. I still see some challenges before stem cell therapies become more common including safety, as stem cells can potentially form tumors, and immune rejection. Even so, stem cells are likely to transform medicine and in perhaps just one or two decades most of us will know someone, perhaps even ourselves, who has had a stem cell transplant. Stem cells hold promise to treat most of the major diseases that people face including cancer, heart disease, Parkinson’s Disease, Multiple Sclerosis, Stroke, Huntington’s Disease, spinal cord injury, and many more.
Risks of stem cells
Currently, there are few stem cell transplants available that are proven by scientists to be both safe and effective. The best example is bone marrow transplantation. However, clinics are selling many unproven stem cell treatments around the world. Often these treatments get a lot of attention in the media. Frequently celebrities such as sports stars buy these treatments. Generally, scientists and doctors in the stem cell field caution patients against such treatments. Why? It is unclear whether these treatments actually work and whether they are safe. Patients have died from such treatments. While it is reasonable to consider all options when facing a potentially incurable condition or disease, we recommend caution. One should only consider such treatments as a last resort and only after talking with your personal physician.
The FDA has even issued warnings about stem cells, which are worth a read.
This post is part of our SCOPE stem cells not lost in translation project. It’s all about educational outreach. You can learn more about the project and read the other 34 languages on that page. As of 2022, I updated this English language page extensively beyond the translated versions.