Where Do Stem Cells Come From?

From Early Controversy to Current Frontiers in Science

Stem cells are specialized cells that have the potential to develop into not one but many different types of cell. They are unlike any other cell for three specific reasons:

  • They are unspecialized, meaning they have no specific function in the body.
  • They have the capacity to become specialized cells such as brain cells, muscle cells, and blood cells.
  • They can divide and renew continually over a long period of time.

    Currently, blood stem cells are the only type regularly used for treatment. In cases of leukemia or lymphoma, this type of cell is used in a procedure we commonly refer to as a bone marrow transplant. For this purpose, only adult stems cells are used.

    When it comes to stem cell research, the cells may come from any number of different sources, including adult donors, embryos, or genetically altered human cells.

    Stem Cells in Bone Marrow Transplants

    The cells of the bone marrow produce all of your healthy blood cells, including red blood cells, white blood cells, and platelets. Hematopoietic stem cells are those found in bone marrow that serves as the "parent" for all of these different types of cells.

    Hematopoietic stem cells are transplanted into a person with cancer to help replenish bone marrow. The procedure is often used when high dose chemotherapy effectively destroys the existing stem cells in a person’s bone marrow.

    To remedy this, donated stem cells are injected into a vein and eventually settle in the bone marrow where they start producing healthy, new blood cells.

    Peripheral Blood Stem Cell Transplants

    Years ago, the only source for hematopoietic stem cells were those taken from bone marrow. It was soon after discovered that many of these cells were circulating freely in the bloodstream.

    In time, scientists learned how to harvest these cells from circulating blood and to transplant them directly into a donor.

    This type of transplant— known as a peripheral blood stem cell transplant, or PBSCT — has become the more common procedure, although both methods are still used. PBSCT is far less invasive and doesn’t require the removal of marrow from the hip bone.

    Somatic Stem Cells

    Adult stem cells, called somatic stem cells, are derived from a human donor. Hematopoietic stem cells are the most widely known example. Scientists have found somatic stem cells in more tissues than was once imagined, including the brain, skeletal muscle, skin, teeth, heart, gut, liver, ovarian cells, and testis.

    Embryonic Stem Cells

    Embryonic stem cells are controversial since they are derived from human embryos that have either been destroyed or harvested for science. Embryonic stem cells were first grown in a laboratory in 1998 for reproductive purposes. Today, they are used primarily for research into treatments or cures for cancers, blindness, juvenile diabetes, Parkinson’s, spinal cord injuries, and genetic disorders of the immune system.

    Embryonic stem cells are pluripotent, meaning they are able to grow into the three types of germ cell layers that make up the human body (ectoderm, mesoderm, endoderm).

    In other words, they can develop into each of the more than 200 cell types if specified to do so.

    Induced Pluripotent Stem Cells

    Induced pluripotent stem cells, or iPSCs, are somatic stem cells that have been genetically reprogrammed to be more like embryonic stem cells. iPSCs usually start out as skin or blood cells which then undergo genetic programming.

    iPSCs were first developed in 2006 and pose one major advantage over somatic and embryonic stem cells: they can be made in a patient-matched manner. What this means is that a lab can tailor-make a pluripotent stem cell line individualized from a person’s own cells or tissues.

    Sources:

    Simara, P.; Motl, J.; and Kaufman, D. “Pluripotent Stem Cells and Gene Therapy.” Transl Res. 2013; 161(4):284-292.

    Al-Shamekh, S. and Goldberg, J. “Retinal Repair with Induced Pluripotent Stem Cells.” Transl Res. 2014; 163(4):377-386.

    Finkbeiner, S. and Spence, J. “A Gutsy Task: Generating Intestinal Tissue from Human Pluripotent Stem Cells.” Digestive Diseases and Sciences. 2013; 58(5):1176-1184.

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