Meriam-Webster defines stem cells as: an unspecialized cell that gives rise to differentiated cells. This means the can turn into any cells the body is in need of . Their almost limitless potential has made stem cells a significant focus of medical research. Imagine having the ability to return memory to an Alzheimer’s patient, replace skin that was lost during a terrible accident or enable a wheelchair-bound person to walk again. But before scientists can use stem cells for medical purposes, they must first learn how to harness their power.
They can’t treat disease until they learn how to manipulate stem cells to get them to develop into specific tissues or organs. A stem cell is essentially the building block of the human body. The stem cells inside an embryo will eventually give rise to every cell, organ and tissue in the fetus’s body. Unlike a regular cell, which can only replicate to create more of its own kind of cell, a stem cell is pluripotent. When it divides, it can make any one of the 220 different cells in the human body. Stem cells also have the capability to self-renew — they can reproduce themselves many times over.
There are two types of stem cells: embryonic stem cells and adult stem cells. Embryonic stem cells come from an embryo — the mass of cells in the earliest stage of human development that, if implanted in a woman’s womb, will eventually grow into a fetus. When the embryo is between three and five days old, it contains stem cells, which are busily working to create the various organs and tissues that will make up the fetus. Adults also have stem cells in the heart, brain, bone marrow, lungs and other organs. They are our built-in repair kits, regenerating cells damaged by disease, injury and everyday wear and tear.
Adult stem cells were once believed to be more limited than stem cells, only giving rise to the same type of tissue from which they originated. But new research suggests that adult stem cells may have the potential to generate other types of cells, as well. For example, liver cells may be coaxed to produce insulin, which is normally made by the pancreas. This capability is known as plasticity or transdifferentiation In the early 1980s, scientists learned how to pull embryonic stem cells from a mouse and grow them in a laboratory. In 1998, they first reproduced human embryonic stem cells in a lab.
Photo courtesy University of Wisconsin Board of Regents Culture trays containing human embryonic stems cells being stored in heat-controlled storage and studied by developmental biologist James Thomson’s research lab at the University of Wisconsin in Madison Where do researchers get human embryos? Embryos can either be made via reproduction — merging sperm and egg — or by cloning. Researchers aren’t likely to create an embryo with sperm and egg, but many use fertilized embryos from fertility clinics. Sometimes, couples who are trying to have a baby create several fertilized embryos and don’t implant them all.
They may donate the ones that are left over to science. Another way to create an embryo is via a technique called therapeutic cloning. This technique merges a cell (from the patient who needs the stem cell therapy) with a donor egg. The nucleus is removed from the egg and replaced with the nucleus of the patient’s cell.. This egg is stimulated to divide either chemically or with electricity, and the resulting embryo carries the patient’s genetic material, which significantly reduces the risk that his or her body will reject the stem cells once they are implanted.
Both methods — using existing fertilized embryos and creating new embryos specifically for research purposes — are controversial. But before we get into the controversy, let’s find out how scientists get stem cell to replicate in a laboratory setting in order to study them. An embryo that has developed for three to five days is called a blastocyst. A blastocyst is a mass of about 100 or so cells. The stem cells are the inner cells of the blastocyst. They will ultimately develop into every cell, tissue and organ in the body.
Photo courtesy Michael Vernon, West Virginia University Blastocyst Scientists remove stem cells from the blastocyst and culture them (grow them in a nutrient-rich solution) in a Petri dish in the laboratory. After the cells have replicated several times and are becoming too numerous for the culture dish, they are removed and placed into several other dishes. In just a few months, several stem cells can become millions of stem cells. Embryonic stem cells that have been cultured for several months without differentiating are referred to as a stem cell line. Cell lines can be frozen and shared between laboratories. Photo courtesy University of Wisconsin Board of Regents
Microscopic 5x view of a colony of undifferentiated human embryonic stems cells being studied in developmental biologist James Thomson’s research lab at the University of Wisconsin in Madison: The embryonic stem cell colonies are the rounded, dense masses of cells. The flat, elongated cells are fibroblasts used as “feeder cells. ” Adult stem cells are much harder for scientists to work with because they are more difficult to extract and culture than their embryonic counterparts. Stem cells not only are hard to find in adult tissue, but scientists also have difficulty getting them to replicate in the laboratory.
But even embryonic stem cells, which can be grown effectively in the lab, are not easy to control. Scientists are still struggling to get them to grow into specific tissue types. Adult stem cells are much harder for scientists to work with because they are more difficult to extract and culture than their embryonic counterparts. Stem cells not only are hard to find in adult tissue, but scientists also have difficulty getting them to replicate in the laboratory. But even embryonic stem cells, which can be grown effectively in the lab, are not easy to control.
Scientists are still struggling to get them to grow into specific tissue types. Ideally, scientists would like to be able to grow a particular type of cell in the laboratory and then inject it into a patient, where it would replace diseased tissue. But stem cells are not yet being used to treat disease because scientists still haven’t learned how to direct a stem cell to differentiate into a specific tissue or cell type (brain vs. liver, for example) and to control that differentiation once the cells are injected into a person.