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- Growing induced Pluripotent Stem Cells (iPSC) without Animal Products:
Ideally, stem cells used to treat human beings will be grown without exposure to animal products such as the mouse embryonic fibroblasts (MEFs) or bovine serum used in standard stem cell culture. Previously, scientists developed xeno-free (animal-free) culture systems for human embryonic stem cells (hESCs) by using serum replacement with fibronectin matrix or human fibroblast feeder layers. Building on this knowledge, privately-funded scientists have now developed a xeno-free derivation and culture system for human induced pluripotent stem cells (iPSCs). The scientists eliminated animal products from each step of the process, including the viral particles used for reprogramming. iPSCs generated and grown under these xeno-free conditions demonstrate expected characteristics of pluripotent cells, including the ability to form teratomas and generate cells characteristic of all three germ layers. This work may one day help scientists develop standardized animal-free human stem cell therapies. Stem Cells Dev. Epub ahead of print; laboratory of J.B. Cibelli. 2009 Dec 23.
- Lack of diversity in most commonly-used hESC lines: Privately-funded researchers examined the genetic ancestry of the most commonly-used hESC lines by comparing the genotypes of hESC lines to reference datasets from the HapMap and Human Genome Diversity Projects. They found that the majority of the hESC lines cluster with (or are most similar to) individuals of European and Middle Eastern origin. Two of the lines clustered with data from East Asians, and none clustered with data from individuals of African ancestry. If hESC studies are to improve human health, it is important that they accurately represent the genetic variations common to the population. Accordingly, the authors propose that derivation of new hESC lines should emphasize underrepresented populations, N Engl J Med 362(2):183-185, 2010. Epub 2009 Dec.; laboratory of S.J. Morrison.
- New hematopoietic stem cell (HSC) transplant protocol reverses sickle cell anemia in adults:
Individuals with sickle cell disease, also known as sickle cell anemia, carry an abnormal gene for the oxygen-carrying protein called hemoglobin found in red blood cells (RBCs). The abnormal hemoglobin causes RBCs to collapse into a sickle, or C-shape, and become stiff and sticky. Clumps of these abnormal RBCs block blood flow and can cause severe pain, organ damage from lack of oxygen, and stroke. Individuals with sickle cell disease often develop anemia because sickle cells die off quickly and bone marrow does not make new RBCs fast enough. Scientists have been able to cure children with severe sickle cell disease by using myeloablative conditioning, which destroys the child’s own diseased bone marrow, combined with hematopoietic stem cell (HSC, found in bone marrow) transplantation. However, scientists have not been able to cure adults with severe sickle cell disease because adults cannot tolerate the toxicity of myeloablative conditioning plus the HSC transplant procedure. Attempts to cure adults using less toxic non-myeloablative conditioning plus HSC transplant have not been successful – adults either destroy the transplanted bone marrow stem cells or develop severe graft versus host disease (GVHD). NIH intramural researchers tested a new protocol using a drug, sirolimus, to attempt to induce immune system tolerance of transplanted HSCs under non-myeloablative conditions. Ten adults with severe sickle cell disease were transplanted under the new protocol. All of the treated individuals survived, and the treatment reversed the disease in 9 of them. If these results can be repeated on a larger scale, this new method of inducing tolerance to transplants may one day be available to cure adults with severe sickle cell disease. Hsieh et al, NEJM 361: 2309-2317; laboratories of G.P. Rodgers, J.D. Powell, and J.F. Tisdale. 2009 Dec 10.
- Adult stem cells may provide a new weapon against AIDS:
Although anti-viral drugs help individuals with HIV to manage their symptoms, new options are needed. Privately-funded scientists have reprogrammed bone marrow stem cells into "killer" T-cells with anti-HIV receptors. The new HIV-specific "killer" T-cells recognized and killed cells that had gobbled up HIV and displayed the HIV proteins on their surfaces (HIV antigen-presenting cells) in a humanized mouse model of HIV (an immune-compromised mouse with human fetal thymus and liver). This strategy may help scientists find a way to re-establish immune control of HIV and other diseases that outwit the human immune system. PLoS One. 4(12): e8208, 2009; laboratory of J.A. Zack. 2009 Dec 7.
- iPSCs may help treat human age-related macular degeneration:
Retinal pigment epithelium (RPE) is a supporting cell layer critical to the survival and function of rods and cones in the retina of the eye. Scientists have previously demonstrated that RPE cells derived from human embryonic stem cells (hESCs) improve vision when transplanted to a rat model of age-related macular degeneration (AMD). Now scientists supported by the United Kingdom have tested whether RPE cells derived from induced pluripotent stem cells (iPSCs) have the same capabilities. When iPSC-derived RPEs were transplanted into the same rat AMD model, they preserved retinal integrity and vision if given before degeneration began. However, iPSC-derived RPE cells don’t survive as long as hESC-derived RPE cells. The scientists propose that the noted improvements in vision may result from either:
Thus, even if human iPSC-derived RPE cells don't survive long term, these cells may still prove to be a useful therapy for human RPE. Carr et al. PLoS One. 4(12): e-8152, 2009; laboratory of P.J. Coffey. 2009 Dec 3.
- The transplanted cells' ability to attract the host inflammatory response; the host phagocytes may help replace the debris-removing function of lost RPE cells.
- The transplanted cells may have a neuroprotective effect on host RPE cells.
- New techniques improve utility of iPSCs:
- In the original technique for generating induced pluripotent stem cells (iPSCs), the reprogramming factors are carried into the adult cells using inactivated viruses that integrate at random into the host DNA. This is dangerous because of the possibility that the virus will interrupt or otherwise damage the normal function of a critical gene in the host cell. NIH-supported scientists report progress towards using a single virus to introduce the reprogramming genes (thus reducing the number of insertions) and the ability to control where the virus actually inserts. These changes move us a bit further toward improving the utility of iPSCs for treating humans. Carey et al. Nature Methods Advance Online Publication; Stadtfeld et al. Nature Methods Advance Online Publication; laboratories of R. Jaenisch and K. Hochedlinger. 2009 Dec 13.
- It can also be difficult for scientists to accurately identify which adult cells have been fully reprogrammed, and which are only partially reprogrammed. NIH-supported researchers now report development of a live cell imaging technique that enables scientists to sort partially and fully reprogrammed iPSCs. Chan et al. Nature Biotechnology 27: 1033-1038; laboratories of G.Q. Daley and T.L. Schlaeger. 2009 Nov.
- French researchers generate skin from hESCs
Keratinocytes are skin cells that make up approximately 95% of the outer layer of human skin, or epidermis. The epidermis is maintained and repaired by division of the keratinocyte stem cells. Acute burn victims are susceptible to infection and dehydration during their typical 3-week wait for expansion of their own (autologous) skin grafts. A new human embryonic stem cell (hESC) culturing technique developed in France mirrors the 40-day development of the epidermis in human embryos. The new culturing technique coaxes hESCs to generate keratinocyte stem cells (k-hESCs) that rapidly expand. K-hESCs derived this way may fulfill a critical window of need for severe burn victims awaiting autologous grafts. If they prove to be stable over the long term, k-hESC allografts may also help individuals with chronic genetic skin conditions where autologous grafts are not possible. Lancet 374: 1745-1753, 2009; laboratory of G. Waksman.
- NIH-Funded Scientists Generate Haploid Human Gametes from Human Embryonic Stem Cells
In the developing embryo, human primordial germ cells divide to produce either sperm or eggs (gametes). Some birth defects and many forms of human infertility are thought to arise from problems with early gamete development. However, scientists have been unable to study early gamete development because it takes place before the human embryo is 2 weeks old. Now, NIH-funded scientists have identified 3 genes whose expression can be manipulated to drive human embryonic stem cells (hESCs) into becoming human primordial germ cells and then dividing to become haploid gametes. Although scientists have previously reported their ability to generate primordial germ cells, this laboratory is the first to report achievement of later stages of meiosis and development of haploid gametes. The ability to generate and study these cells in the laboratory will help scientists learn more about the cause of some birth defects, and to identify germ cell errors responsible for many forms of infertility. Nature 462:222–225; laboratory of R. Reijo Pera. 2009 Nov12.
- Comparison of hESCs, iPSCs, and Adult Cells
The advent of induced pluripotent stem cell (iPSC) technology has led many to question the continuing need for research on human embryonic stem cells (hESCs). However, the differences and similarities between iPSCs and hESCs have not been adequately explored to determine which may be more suitable for the future treatment of human disease. Epigenetic regulation of genes can change whether they are on or off without changing the DNA itself, and plays an important role in determining a cell’s characteristics. Scientists studying epigenetic regulation have typically focused on small cytosine and guanine-rich regions of DNA ("CpG islands") believed to contain most of the alterations involved in gene activity states. NIH-funded scientists performed a genome-wide analysis of the epigenetic state of iPSC lines, their parent fibroblast cell lines, and several other cell types, including hESCs. There were several major findings from this work. 1) The differentially methylated regions (DMRs) identified by comparing iPSCs and fibroblasts were predominantly located in CpG island "shores" rather than in the islands themselves and were closely associated with genes that are important for pluripotency and developmental processes. 2) The methylation pattern of iPSCs and hESCs, while highly similar, were not completely equal, and may indicate that iPSCs occupy a potentially "aberrant state" between fully differentiated tissue (fibroblasts) and hESCs. 3) The DMRs involved in the epigenetic reprogramming to the pluripotent state greatly overlap with those in normal tissue development and aberrant programming of cancer. Future research will need to explore whether the noted differences between iPSCs, hESCs, and normal and cancerous tissues impact the potential clinical usefulness and practicality of customized reprogramming. Nat Genet 41(12):1350-1353, 2009; laboratories of G.Q. Daley and A.P. Feinberg.
- hESC Derivatives Help Spinal-Cord-Injured Rats Regain Mobility
Individuals who suffer spinal cord injuries (SCI) lose not only the nerve cells in the spinal cord, but also the supporting cells that insulate the spinal cord with myelin. Researchers supported in part by the Geron Corporation tested the ability of GRNOPC1, a proprietary hESC-derived population containing myelinating oligodendrocyte progenitor cells (OPCs), to restore mobility to rats with cervical spinal cord injuries. An earlier study demonstrated that injected OPCs enhanced remyelination and improved mobility in rats with thoracic SCI, but only in those rats injected at 7 days following injury, i.e., acute SCI. This study tested the same procedure in rats treated 7 days following cervical SCI. As in the earlier study, the OPCs migrated to the lesion site and enhanced remyelination, and treated rats demonstrated improved mobility. This report is being used to provide pre-clinical safety and efficacy data as the basis for approval of a clinical trial using Geron's OPCs to help individuals with acute injuries in either the cervical or thoracic spinal cord. Stem Cells 28(1):152-163 , 2010. Epub 2009 Oct 28; laboratory of H.S. Keirstead.
- Induced Pluripotent Stem Cells Able to Produce Live Mice
In the field of animal stem cell research, a stem cell's ability to produce a live mouse in a tetraploid complementation assay is the gold standard test for pluripotency. Until recently, only mouse embryonic stem cells had demonstrated this ability. Now, two groups of scientists in China report that they have reprogrammed adult mouse cells using the four pluripotency genes reported in the first mouse iPSC publication (see Scientists Reprogram Adult Mouse Skin Cells by Adding Defined Factors) and generated iPSC-derived embryos that survived gestation and were born alive after tetraploid complementation. One laboratory also demonstrated that an iPSC-generated male mouse was capable of impregnating a female and passing on its iPSC-derived characteristics. This research is an important demonstration that iPSCs are truly pluripotent. Nature 461(7260):86–90, laboratory of Q. Zhou, 2009 Sep 3; Cell Stem Cell 52:135–138, laboratory of S. Gao, 2009 July 23.
- Cancer-destroying Cells Generated from Human Embryonic Stem Cells
Natural Killer, or NK cells, are a specialized type of white blood cells that continuously patrol the body, eliminating cells that have become abnormal, such as cancer cells. In healthy individuals, NK cells eliminate cancerous cells before they can cause problems. In some individuals, however, their native NK cells are unable to eliminate all cancerous cells. NK cells generated from umbilical cord blood (UCB-NK cells) are already being used to treat individuals with cancer, but they are neither consistent nor efficient in destroying cancer cells. NIH-supported scientists at the University of Minnesota hope to generate a more potent version of NK cells for use in cancer therapies, and developed a way to coax human embryonic stem cells (hESCs) to differentiate into NK cells. The scientists studied mice with human cancers to compare the cancer-destroying ability of hESC-derived NKs to the abilities of UCB-NK cells. They found that hESC-derived NKs were better than UCB-NKs at destroying both leukemia (blood cancer) and solid tumors, such as breast and prostate cancer. The hESC-derived NK cells not only destroyed human cancers in mice, but also protected them from recurrence and metastasis. Further studies will address whether other hESC lines are capable of generating such potent NK cells. This research marks an important advance for scientists working to understand how NK cells work and how they may be used to attack and destroy human cancers. Blood 113(24):6094-6101. Epub 2009 Apr 13; laboratory of D.S. Kaufman. 2009 Jun 11.
- Human Corneal Stem Cells Repair Defective Corneas in Mice
The cornea helps to protect the eye from environmental irritants and serves as the eye's outermost lens, contributing between 65—75 percent of the eye's total focusing power. In most cases, scratches on the cornea caused by irritants or trauma can be repaired by the cornea's own stem cells. However, deeper scratches can cause corneal scarring, resulting in a haze on the cornea that can greatly impair vision. In this case, the cornea is unable to repair itself, and a corneal transplant may be needed. As with most transplant organs, corneas are in low supply. NIH-supported scientists transplanted stem cells from the adult human corneal stroma (cells that make up the transparent cornea) into the eyes of mice that exhibit corneal cloudiness. These mice's eyes lack the ability to produce a protein called lumican, which organizes the cornea's collagen in order to make it transparent. After injection of the human cornea stromal stem cells, the transparency of the treated corneas was comparable to those in mice with normal corneas. Treated mice did not reject the transplanted human cells. The scientists will now try to reproduce this result in animals with cornea scarring. If successful, the scientists may be able to develop a potential stem cell therapy for cornea scarring in humans. Stem Cells epub 2009; laboratory of J. Funderburgh.
Another Safety Improvement for Generating Induced Pluripotent Stem Cells (iPSCs)
Scientists funded by the Juvenile Diabetes Research Foundation, the United Kingdom, and Canada reprogrammed mouse and human fibroblasts without using potentially dangerous viruses. For both types of fibroblasts, the reprogramming genes and an inducible transcription factor (can be used to turn expression on and off) were carried into the cells by naked DNA sequences. The naked DNA carriers also contained marking sequences that are targeted and "cut out" by specific enzymes. Using these special carriers, the scientists were able to insert reprogramming genes, turn them on for a specific period of time, and then remove the reprogramming genes and the transcription factor by adding the specific enzyme that zeroes in on and cuts out its targets. This method has several benefits: temporary expression of the reprogramming genes, the ability to remove inserted DNA after reprogramming is accomplished, use of a single carrier for all four reprogramming genes, and carriers' seeming increased resistantance to "silencing," or being inactivated (which could explain the higher efficiency as compared to other non-viral carriers).
This method has some potential drawbacks. Insertion of the reprogramming factors is random and could still temporarily interfere with an important gene. Part of the carrier DNA is often left behind even after removal. The DNA cuts made at the DNA removal site are not always repaired correctly. The PiggyBac method used for some of the experiments employs a transposon, or "jumping gene." Jumping genes are known to cause human diseases such as muscular dystrophy or hemophilia, as well as increase susceptibility to cancer. The bottom line: These methods are another step toward improving our ability to reprogram cells and increasing our understanding of reprogramming. However, these methods could still pose a danger to human health if derivatives of these cells are used to treat humans. The cells generated by this method are a valuable research tool and provide useful means to screen drugs and establish human disease models in culture. Nature advance online publication; laboratory of A. Nagy; Nature advance online publication; laboratory of K. Woltjen. 2009 Mar 6.
- Induced Pluripotent Stem Cell–Derived Working Heart Muscle Cells
Heart transplants are done as a life-saving measure for end-stage heart failure when medical treatment and less drastic surgery have failed. Fortunately, most heart transplant recipients (about 90 percent) can come close to resuming their normal daily activities; however, donor hearts are in short supply. NIH-supported scientists have been able to grow heart muscle cells (cardiomyocytes) from induced pluripotent stem cells (iPSCs). They compared cardiomyocytes derived from iPSCs with cardiomyocytes derived from human embryonic stem cells (hESCs). All cardiomyocytes in the study were derived using an embryoid body (EB) method. Both iPSC- and hESC-derived cardiomyocytes showed a reduction in gene expression for OCT4 and NANOG (known to regulate pluripotency) as they differentiated. However, pluripotency gene expression was more variable in iPSC-derived cardiomyocytes. Both types of cardiomyocytes demonstrated heart muscle–specific characteristics, such as organized bands of contraction proteins, and electrical activity that causes them to spontaneously contract. Overall, the iPSC-derived cardiomyocytes are very similar to hESC-derived cardiomyocytes. Due to the short supply of donor hearts for transplantation, these iPSC-derived cardiomyocytes may one day provide an important treatment for the substantial number of people with heart disease. By reprogramming their own skin cells into cardiomyocytes for repairing their heart muscle, patients can avoid the immune-suppressing drugs that accompany traditional heart transplant. Scientists also hope that the derived cardiomyocytes will be useful for testing potential drugs and for understanding the underlying cause of heart disease. Circulation Research advance online publication; laboratory of T. Kamp. 2009 Feb 12.