Batista et al. Nature.
Key to scientific progress is the ability to test new treatments in animals that represent the human disease of interest or in cells in the laboratory that represent the human disease. The better these test systems represent the human disease, the more likely it is that approaches successful in the test systems will actually work in the clinical trials. An example of test systems not being truly representative of human diseases are the animal models of cancer. Literally thousands of drugs, vaccines and other approaches have been demonstrated to cure cancer in mice, but when tested in humans do not work.
Stem cells are now being used to create in vitro (in the lab) models of human diseases. One way in which this is occurring is by creating stem cells from skin or other adult tissues of people with diseases. Specifically, the process of generating iPS cells allows for creation of cells that resemble embryonic stem cells from practically any adult tissue. Thus if one wanted to study drugs that affect lung function in patients with cystic fibrosis, one could take a small skin sample of a cystic fibrosis patient, generate iPS cells, and use these cells in vitro to create human lung tissue that would be similar to the lung of the original cystic fibrosis patient. This way one could take the artificially generated tissue and test drugs on it. Prior to the creation of iPS cells, something like this would have required taking out lung specimens from cystic fibrosis patients, something which would definitely not be ethical !
In the study discussed today (Batista et al. Telomere shortening and loss of self-renewal in dyskeratosis congenita induced pluripotent stem cells. Nature. 2011 May 22) investigators studied the rare disease dyskeratosis congenita. This condition is associated with accelerated aging.
The study demonstrated that iPS cells from dyskeratosis congenita patients possess the exact same biochemical defects characteristic of the disease and when patients with different severity of the disease were used to generate iPS cells, the more advanced the disease was, the less telomerase activity was found in the cells.
Mimicking Human Diseases in Cells: iPS Cells Used to Create Model of Extremely Rare Condition Dyskeratosis Congenita
Killing of the iPS Field?
Zhao et al. Nature.
Embryonic stem cells are associated with numerous ethical dilemmas. The creation of equivalents of ES cells through retrodifferentiation led to a new area of research that does not require destruction of life. Specifically, it was discovered that any adult cell can be transfected with several genes, which results in the cell taking the phenotype and function of cells that appear to be very similar to embryonic stem cells. These cells can give rise to any tissue that embryonic stem cells give rise to, and unfortunately, like embryonic stem cells for teratomas (tumors). We made a video to explain this http://www.youtube.com/watch?v=_RLlUdJLy74.
One of the most exciting medical properties of iPS cells is that they can be made from a donor and theoretically the cells and their differentiated offspring should not be rejected by the donor. This would allow for generation of compatible cells, without the need for immune suppression. However, a recent study suggests that this may not be the case.
In the study (Zhao et al. Immunogenicity of induced pluripotent stem cells. Nature. 2011 May 13) investigators assessed the ability of embryonic stem cells and induced pluripotent stem cells (iPS) to stimulate immune responses using inbred, genetically identical mice. They found that embryonic stem cells (ESCs) derived from C57BL/6 (B6) mice can efficiently form teratomas (an aggressive type of tumor) in B6 mice (syngeneic) without any evident immune rejection. However, when allogeneic ESCs from 129/SvJ mice where transplanted into B6 mice, they were rapidly rejected by the B6 immune system. This by itself is interesting because transplantation of adult stem cells, mesenchymal stem cells, does not lead to rejection when transplanted between mouse strains.
When B6 mouse embryonic fibroblasts (MEFs) were reprogrammed into iPSCs by either retroviral approach (ViPSCs) or a novel episomal approach (EiPSCs) that causes no genomic integration and transplanted into B6 mice rejection was observed. Specifically, the retrovirally-generated iPS cells were more immunogenic than those generated by the novel episomal method. Rejection of both types of iPS cells was characterized by T cell infiltration.
Global gene expression analysis of teratomas formed by B6 ESCs and EiPSCs demonstrated that several iPS genes were expressed that contributed to immunogenicity. According to the authors “these findings indicate that, in contrast to derivatives of ESCs, abnormal gene expression in some cells differentiated from iPSCs can induce T-cell-dependent immune response in syngeneic recipients.”
UW Researchers Make Stem Cell Breakthrough
Seung Park, Badger Herald
Researchers at the University of Wisconsin have made a breakthrough in stem cell research. Igor Slukvin headed the team that has successfully reprogrammed bone marrow cells into induced pluripotent stem cells (iPSCs). “This is important because blood banks have huge amounts of samples of bone marrow,” he said. “You can select as many types of cells as you want and make stem cells out of them.”
This regression was a major accomplishment, as reprogramming a cell is similar to an adult human reversing development and becoming a child again, according to Timothy Kamp, an associate professor of medicine. “When our organs develop, it’s a one-way street as you go from a precursor stem cell which grows and forms specialized tissues for various systems,” Kamp said. “As these cells grow progressively more specialized, they can’t go back and return to being a stem cell.” Obviously, this problem has been overcome, the concept behind the reprogramming comes from a set of DNA binding proteins that regulate gene expression.
Slukvin also took cells from a patient with chronic myeloid leukemia and generated transgene-free iPSCs from their bone marrow. These cells show a unique translocation of a chromosome while also maintaining the pluripotency of an embryonic stem cell. The implication of this being that the disease can now be followed, as they have regressed back into stem cells, the redevelopment of the disease will be able to be observed.
Using Stem Cells to Study Alcohol Dependence
One of the major advancements in the area of stem cell research has been the establishment of techniques for "retro-differentiating" of old cells into younger cells. Perhaps one of the best examples of this is the discovery by the Japanese group of Yamanaka the skin cells can be coaxed to take the resemblance of embryonic stem cells by transfection with 4 genes. These cells, called inducible pluripotent stem (iPS) cells have numerous applications in many fields.
From a therapeutic perspective, iPS cells allow for the first time the possibility of "reprogramming" adult cells into younger cells, thus opening the door to autologous stem cell therapy for tissue regeneration. In other words, the therapeutic dream of iPS is for one day to be able to take patient skin cells, transform them into stem cells, and then have a large supply of young cells that can be used for repairing any organ of the body.
The other major area in which iPS cells have made a major contribution is in the field of basic research/drug development. Currently when scientists develop new drugs the drugs are tested in human cancer cells that resemble the tissue that the scientist is interested in. So if someone was developing a drug to stimulate pancreatic cells to produce more insulin, the drug initially would be tested on insulinoma cells. If the drug has some positive effects it is then tested in animals, and if successful, in humans.
There are several problems with this model. The first is that many times the cancer cell lines that resemble healthy tissue do not resemble it well. This causes a lot of drugs that appear to work in cells not to work in animals. To some extent this problem is addressed by using cells derived from humans that are not cancerous. The drawback with this is that human cells are expensive and
possess great variability.
Since iPS cells are capable of generating human cells that are "younger", and since they can be created from skin of people with various diseases, the use of iPS cells to generate cells for drug testing has become very popular. For example, if someone wants to study the effects of drugs on ALS, neurons from ALS patients can be easily created from iPS cells in larger quantities than can be extracted from cadaver sources. Dr. Stormy Chamberlain from the UConn Health Center is performing work using iPS cells to develop an in vitro model of alcoholism. Specifically, skin cells will be extracted from alcoholic and non-alcoholic patients. iPS cells will be generated from these skin cells, and then converted into neurons in tissue culture. The neurons will be assessed for abnormalities that are specific to the alcoholic patients.
A collaborator, Dr. Jonathan Covault stated "As proof of principle, we have used skin cells from six subjects to generate pluripotent stem cells, and we have successfully created neural cultures from three of these to develop mature neurons," says Covault. "Going forward, we will compare neurons derived from healthy subjects with those from alcohol-dependent patients. We’ll be evaluating their ability to support electrical signaling and form neuron-to-neuron connections, as well as their pattern of chemical and gene expression responses to single and repeated exposures to alcohol."
