Programs: Science and Policy
Recent Embryonic Stem Cell Progress
AAAS has compiled a list of peer-reviewed and recommended findings that demonstrate some achievements in embryonic stem cell research. This is a sampling of the current data and not reflective of the breadth and scope of all embryonic stem cell research.
The use of embryonic stem cells in the laboratory setting has evolved considerably in recent years. Embryonic stem cells are relatively difficult to grow in cell culture (outside of the body). Initially, human embryonic stem cells had to be grown in the presence of animal growth serum and mouse feeder cells. A problem is that animal products could harbor viruses or other problematic agents and render the stem cells useless for human therapies. Two years ago, a new culture media absent of all animal products and animal cells was developed and human embryonic cells were successfully grown (Bio of Repro 70:837-45, 2004). More recently, new human embryonic stem cells lines were developed that have never been grown in the presence of animal products (Nature Biotech 24:185-7, 2006) which could allow these cells to be used in potential therapy. Other cell culture advances include the use of defined media conditions to maintain human embryonic stem cell proliferation (and therefore repress differentiation) or direct the cells toward specific types of differentiation (PNAS 103(18):6907-12, 2005 and PLOS Medicine 2:0554-60, 2005).
Advancements have also been made in the generation of new cell lines. Researchers were able to develop embryonic stem cells lines from human embryos with known genetic diseases (such as myotonic dystrophy, beta-thalassaemia, and Fanconi anaemia); these cell lines can be used to better understand the a specific disease (Reproductive BioMedicine Online 10(1):105-110 2005). Another research team was able to develop an embryonic stem cell line from a single cell biopsy that is routinely taken from human embryos for diagnostic purposes; this technique may circumvent some of the ethical issues surrounding the use of human embryos in research (Nature 444(7118):481-5 2006).
The use of somatic cells (all adult cells except for the sex cells) in combination with embryonic stem cells is a useful yet controversial technology. One scientific team has developed a technique involving the fusion of somatic cells with preexisting embryonic stem cell lines. The fusion caused the somatic cells to undergo genetic reprogramming and resulted in cells with developmental characteristics similar to human embryonic cells. This approach could allow for the creation of patient-specific stem cells (Science 309:1369-73, 2005).
Researchers were able to generate neurons from monkey embryonic stem cells and then transplant them into monkeys with Parkinson's disease. The transplanted cells were functional and diminished the symptoms of Parkinson's disease (J Clin Invest 115:102-109, 2005). Other scientists have been able to produce these same dopaminergic neurons from human embryonic stem cells in culture (PNAS 101(34): 12543-48, 2004). More recently, scientists demonstrated that human embryonic stem cells can be injected into developing mouse brain to form functional neural cells (PNAS 102(51):18644-48). Together, these finding suggest that embryonic stem cells have the capacity to form functioning neurons and can be successfully transplanted into brain.
Research on spinal cord regeneration has been extensive; many scientists have demonstrated that embryonic stem cells can be treated with growth factors to produce functioning nerve cells in culture (Nat Biotechnol 23(2):215-21, 2005). Paralyzed mice and rats received transplants with neurons derived from embryonic stem cells; these transplants resulted in positive therapeutic outcomes including recovery from paralysis (Cell 110:385-397, Ann Neurol 60:32-44, 2006, and Ann Neurol 60:22-34, 2006). Other researchers have developed oligodendrocytes (the protective cells surrounding spinal cord nerves) from human embryonic stem cells and recovered motor function in rats with recent spinal injuries (J Neuroscience 25:4694-4705, 2006).
The ability of embryonic stem cells to form germ cells (the primitive cells in the embryo that mature into sperm or eggs) is important in demonstrating their totipotentiality (the ability to generate any tissue in the body). Researchers have reported that mouse embryonic stem cells can be treated in culture to develop both male and female germ cells and are therefore totipotent (Science 300:1251-56 2003, Nature 427(6970):148-54 2004 , and PNAS 100(20):11457-62 2003).
Research has focused on deriving a use for embryonic stem cells in the treatment of diabetes (the disease whereby pancreatic cells fail to secrete insulin). Mouse embryonic stem cells have been successfully differentiated into pancreas cells that secrete insulin in a culture system (Stem Cells 22:1205-1217, 2004). Later studies have demonstrated that human embryonic stem cells could be cotransplanted with embryonic mouse pancreas cells in culture to form insulin producing cells as well (Diabetes 54:2867-74, 2005).
Mouse embryonic stem cells have been used to study liver-based genetic defects such as hemophilia A and B. Researchers differentiated mouse embryonic stem cells in culture and then injected these cells into the liver of diseased mice. This treatment reversed a form of hemophilia in mice that is similar to hemophilia B in humans (PNAS 102: 2958-63, 2005)
Most research and subsequent treatment of hematopoietic (blood cell) disorders involves adult stem cells isolated from bone marrow. For the past few decades, treatments for blood diseases, such as leukemia, have utilized bone marrow stem cells. Some research has been dedicated to the potential use of embryonic stem cells in other blood disorders. Recently, a team of researchers differentiated human embryonic stem cells into hematopoietic cells and through a series of treatments in sheep were able to develop a long term bone marrow transplantation (Blood 107(5): 2180-3, 2006).
Updated July 13, 2007