Stem Cells For Dummies
Scientists use various types of stem cells in the lab to gain a better understanding of how normal human development works and to look for new methods of treating a wide range of devastating human ailments. Stem cells in the bone marrow, for example, are routinely used to treat leukemia and other blood disorders, and similar techniques are being tested for other diseases involving problems with the immune system. As yet, no one has developed a safe and effective treatment using human embryonic stem cells, because the science itself is still young. But many researchers expect to see several such treatments enter clinical trials (and eventually the market) at an ever-increasing pace.
What Are Stem Cells?
You’ve probably heard about stem cells in the news and may wonder exactly what that scientific term means. Stem cells are the body’s master cells. Stem cells can renew themselves (a process called self-renewal), and they can also make a variety of other kinds of cells.
Stem cells are either embryonic stem cells or adult stem cells. In the lab, embryonic stem cells keep reproducing themselves until they’re coaxed into creating specific types of cells. In the body, these cells eventually disappear, so a human adult body no longer contains cells that can generate any kind of cell — at least not in the normal course of things. (Scientists can manipulate adult cells to become other types of cells.)
The main difference between embryonic and adult stem cells is their type of potency. Here’s a breakdown of the differences:
Embryonic stem cells: Embryonic stem cells are derived from three- to five-day-old embryos that are created for fertilization treatments but aren’t going to be used to try to start a pregnancy; in other words, these blastocysts have never been implanted in a woman’s uterus and will be discarded if they aren’t used for research. IVF doctors culture a fertilized IVF embryo in a culture dish until it develops to the blastocyst stage. Researchers extract the inner cell mass, which is then used to derive embryonic stem cells.
Embryonic stem cells are pluripotent, meaning they can give rise to any type of cell in the fully developed body. (Embryonic stem cells can’t create the placenta or umbilical cord tissues, but they appear to be able to generate any other type of cell.)
Adult stem cells: So-called adult stem cells are really stem cells in specific tissues whose job seems to be replenishing their particular tissues — or specific parts of their tissues — as needed. Adult stem cells also renew themselves periodically to ensure that a pool of stem cells is always available to generate specific cell types. So far, scientists have verified stem cell caches in several tissues, including bone marrow, the brain, fatty tissue (called adipose tissue), the liver, the reproductive system (both male and female), skeletal muscles, skin, and teeth.
Adult stem cells are generally multipotent, able to give rise to several kinds of cells in their home tissues. However, in their normal environments, adult stem cells don’t seem to generate cell types outside their particular tissues. Liver stem cells, for example, don’t generate heart cells, and brain stem cells don’t generate kidney cells.
Stem cell researchers have developed a technique for reprogramming adult cells in the lab to get them to act more like embryonic stem cells. These reprogrammed cells are called induced pluripotent stem cells (iPS cells), and they can be made from adult cells in the skin, fatty tissue, and other sources.
Explore Current Stem Cell Treatments
Scientists have been working with human adult stem cells — the stem cells found in specific tissues — for more than 40 years, compared to only a dozen years for human embryonic stem cells. As a result, the only stem cell treatments that have been proven to work well so far involve tissue stem cells, mainly those found in bone marrow and skin.
Researchers are sketching out all kinds of possible uses for stem cells on the drawing boards, and some of these potential uses are in or preparing to enter clinical trials — experiments to see whether these treatments really work in people. So far, though, the only proven stem cell therapies are for burns and blood disorders; everything else is experimental or theoretical, at least for the moment (no matter what you may read in ads or marketing brochures).
Transplanting bone marrow
Bone marrow transplants have been used since the 1950s to treat leukemia and other blood disorders. Bone marrow is the spongy material found in the center of your bones. Bone marrow, which resides mainly in the large bones like the hip bone and shoulder blade, holds caches of hematopoietic (blood-forming) stem cells that can give rise to all the cell types in the blood:
Red blood cells, which pick up oxygen from the lungs and distribute it to the body’s tissues, and take carbon dioxide and other waste products from the tissues and return them to the lungs for expulsion.
White blood cells, which roam through the bloodstream looking for and attacking foreign invaders like bacteria.
Platelets, which induce the blood to clot.
Doctors use bone marrow transplants to replace the blood and immune systems of patients with certain blood cancers or other disorders. Transplanted blood-forming stem cells home in to the bone marrow and, once settled, begin rebuilding the patient’s supply of blood cells. Depending on the disease and the method used to harvest blood-forming stem cells, the stem cells begin producing new blood cells within 10 days to 6 weeks.
Healing burns with skin grafts
Skin grafts have been used for centuries, although no one knew exactly why they worked until fairly recently. Skin is particularly rich in stem cells because so much skin is lost through normal wear and tear; you shed thousands, or even millions, of dead skin cells every day. In mild cuts and burns, these stem cells work to repair the damaged tissue. In severe burns, though, the stem cells in the burn area are destroyed, so doctors have to take skin from an undamaged area.
The main obstacle in skin grafts is that, currently, only the burn patient’s own skin works reliably. If doctors try to use skin from another person, the patient’s immune system eventually rejects the graft. Scientists are working on ways to grow skin that’s genetically compatible with the patient so that, even if the patient doesn’t have enough undamaged skin to use, the burns can still be treated effectively.
Stem Cell Research for Patient Treatment Plans
Stem cell scientists use stem cells to understand normal cell physiology, cell function, and development, as well as the mechanisms and progression of various diseases. Scientists hope to use this valuable stem cell research to develop future treatments for diseases. For example:
Scientists can create stem cells with the genetic changes that cause Alzheimer’s and study what happens to individual cells and how those events affect other cells. Discovering the inner workings of normal development and disease progression gives scientists a basis to identify key pathways or elements that are broken or misused in disease.
When scientists can identify exactly what goes wrong in a particular disease, researchers can then begin testing drugs to see which ones, if any, fix the problem or prevent further damage. They also can experiment with different types of cells and different genetic combinations to see whether certain cells can provide help to damaged cells.
Scientists also can use stem cells to generate tissues for study, testing, and possible therapies. For example, some labs are working on growing replacement skin to treat burns; other labs are working on growing pancreatic cells to treat diabetes.
If researchers can figure out reliable ways to grow tissues that are specific to a particular patient, those methods could be used to help tens of thousands of people who need tissue transplants but can’t find a suitable donor. Eventually, scientists hope to be able to grow entire organs in the lab — if they can figure out the right structure and combination of different cell and tissue types and get them to work the way they’re supposed to in the body.