Research Briefs: Stem Cells

Progress is ongoing in coaxing stem cells along specific paths, altering their genes and understanding the immune response to stem cell transplantation

Article Highlights:
  • Scientists have coaxed stem cells into becoming astrocytes, a type of nervous-system support cell; and converted skin cells to nerve cells without first taking them through a stem cell stage.
  • A new strategy for correcting genetic defects in stem cells has been developed.
  • The immune system may not tolerate transplants involving induced pluripotent stem cells, even if the donor and recipient have the same genetic background.
  • The National Institutes of Health can fund research involving human embryonic stem cells, with some restrictions.
by Margaret Wahl on June 13, 2011 - 2:23pm

Stem cells are a hot topic these days in medicine, science and law, although the term has multiple meanings and it's easy to get confused.

In short, stem cells are cells at an early stage of development from which specialized cells, such as muscle or nerve cells, can develop (in other words, from which these specialized cells "stem").

Different kinds of stem cells are referred to as:

  • totipotent, meaning they can become any other kind of cell;
  • pluripotent, meaning they can become many (but not all) kinds of cells;
  • embryonic, meaning they're taken from human or animal embryos, which are multicellular organisms at a very early stage of development;
  • fetal, meaning they're taken from human or animal fetuses, organisms at a later stage of development than the embryo stage;
  • adult, meaning taken from a fully developed animal or human of any age (muscle satellite cells are one example); and
  • induced, meaning the cells were converted back into stem cells after having matured into other types of cells.

Human embryonic stem cells have been the subject of much controversy over the last several years, because of ethical and other concerns about their use. They're extremely important for research but are unlikely to be used directly as therapeutic cells, mainly because it can be difficult to control their developmental fate.

Popular alternatives now in development as potential therapies for neuromuscular and other diseases are:

  • induced pluripotent stem cells, which are cells taken from mature organisms and then converted back to pluripotent stem cells, after which they can be coaxed along specific developmental lines in the laboratory; and
  • adult stem cells, which are immature cells found in fully developed animals and humans that have the potential to develop into specific cell types, such as the satellite cells found in muscle tissue that can become muscle cells under certain circumstances.

For more about stem cells in general, see Stem Cell Information from the U.S. National Institutes of Health (NIH).

Here are some recent developments in the field.

Astrocytes in a dish

Researchers at the University of Wisconsin-Madison and Fudan University Shanghai Medical School in Shanghai, China, have generated immature human astrocytes from human pluripotent stem cells.

Astrocytes are "support cells" in the nervous system, where they help maintain motor neurons, which control voluntary muscle function, and other types of nerve cells. Motor neurons are the cells that are affected in amyotrophic lateral sclerosis (ALS) and spinal muscular atrophy (SMA).

These "astrocytes in a dish" may become useful for understanding the roles of astrocytes in disease processes and in developing new treatments for neurological disorders.

The scientific paper was published online May 22, 2011, in Nature Biotechnology. See also Human brain's most ubiquitous cell cultivated in lab dish.

Skin cells converted directly to neurons

Scientists at Stanford (Calif.) University School of Medicine have converted human skin cells directly into functional nerve cells (neurons) by adding four proteins to them. The new approach is significant, because the researchers did not first convert the mature skin cells back into stem cells (i.e., did not create induced pluripotent stem cells). The new, four-protein strategy may make it easier and possibly safer to generate neurons for research or therapeutic purposes.

The scientific paper was published online in Nature on May 26, 2011. See also: Scientists turn human skin cells directly into neurons, skipping iPS [induced pluripotent stem cell] stage.

New genetic correction strategy is applied to stem cells

A new approach for correcting genetic errors in stem cells has been developed by investigators at the Salk Institute for Biological Studies in La Jolla, Calif.; the Scripps Research Institute, also in La Jolla; the University of California-San Diego; and the Center for Regenerative Medicine in Barcelona, Spain.

The strategy, based on a concept known as homologous recombination, can swap out one section of a gene for another, potentially altering large portions of a gene. The phenomenon can be compared to the "find-and-replace" command found in word-processing programs. The replacement section is delivered via a viral transporter.

Using this new strategy, the researchers corrected mutations in the lamin A/C gene in human induced pluripotent stem cells and human adult stem cells. Mutations in this gene can result in one form of Emery-Dreifuss muscular dystrophy (EDMD), one form of congenital muscular dystrophy (CMD), the type 1B form of limb-girdle muscular dystrophy (LGMD), and one form of Charcot-Marie-Tooth disease (CMT), as well as some non-neuromuscular conditions.

One way of employing this approach would be to create induced pluripotent stem cells from an individual’s own cells (such as skin cells), thereby creating stem cellsthat are a genetic match for the individual. Then the stem cells would be corrected with homologous recombination and ultimately transplanted into the individual as a disease treatment.

The findings were published June 3, 2011, in Cell Stem Cell. See also: Editing scrambled genes in human stem cells may help realize the promise of combined stem cell-gene therapy.

A cautionary note sounded about induced pluripotent stem cells

Scientists at the University of California-San Diego have conducted experiments in mice that showed that induced pluripotent stem cells can be rejected by the immune system, even if the donor and recipient have exactly the same genetic makeup, as was the case with the laboratory mice.

Induced pluripotent stem cells made from a patient's own cells are being considered as a possible therapeutic strategy to treat many diseases.

It had previously been widely believed that this type of stem cell would be accepted by a recipient's immune system if the original cell came from the recipient or from an organism with identical genes to the recipient.

The new findings sound a cautionary note about the immune system's tolerance of such a cell transplantation strategy, even without any genetic correction having been performed on the cells. The findings imply that immunosuppressant medications might be needed for people receiving transplants of induced pluripotent stem cells.

The scientific paper was published online May 13, 2011, in Nature. See also Study Finds Therapies Using Induced Pluripotent Stem Cells Could Encounter Immune Rejection Problems.

NIH allowed to fund research using human embryonic cells

A decision reached by the U.S. Court of Appeals for the District of Columbia on April 29, 2011, has for now allowed the U.S. National Institutes of Health to fund research involving human embryonic stem cells, with some restrictions. The decision invalidates a temporary injunction against such funding.

Human embryonic stem cells are cells at their earliest and most flexible stage. Their use in research has been disputed on ethical grounds.

It is unlikely that embryonic stem cells would be used directly as therapeutic agents, not only because of ethical concerns, but because of the difficulty in obtaining embryos and the danger that an embryonic cell might not become the desired type of mature cell after transplantation into the body.

However, embryonic stem cells are considered important research tools for learning about both normal human development and genetic diseases.

See also: Human Embryonic Stem-Cell Research Under Siege — Battle Won but Not the War.

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