However, to test the drugs properly, the conditions must be equal when comparing the effects of two drugs. To achieve this goal, researchers need to gain full control of the differentiation process to generate pure populations of differentiated cells.
One of the biggest fears of professional sportsmen is getting an injury, which most often signifies the end of their professional career. This applies especially to tendon injuries, which, due to current treatment options focusing either on conservative or surgical treatment, often do not provide acceptable outcomes.
Problems with the tendons start with their regeneration capabilities. Instead of functionally regenerating after an injury, tendons merely heal by forming scar tissues that lack the functionality of healthy tissues. Factors that may cause this failed healing response include hypervascularization, deposition of calcific materials, pain, or swelling [ 84 ].
Additionally, in addition to problems with tendons, there is a high probability of acquiring a pathological condition of joints called osteoarthritis OA [ 85 ]. OA is common due to the avascular nature of articular cartilage and its low regenerative capabilities [ 86 ]. Although arthroplasty is currently a common procedure in treating OA, it is not ideal for younger patients because they can outlive the implant and will require several surgical procedures in the future.
These are situations where stem cell therapy can help by stopping the onset of OA [ 87 ]. However, these procedures are not well developed, and the long-term maintenance of hyaline cartilage requires further research. Osteonecrosis of the femoral hip ONFH is a refractory disease associated with the collapse of the femoral head and risk of hip arthroplasty in younger populations [ 88 ].
Although total hip arthroplasty THA is clinically successful, it is not ideal for young patients, mostly due to the limited lifetime of the prosthesis. An increasing number of clinical studies have evaluated the therapeutic effect of stem cells on ONFH. Most of the authors demonstrated positive outcomes, with reduced pain, improved function, or avoidance of THA [ 89 , 90 , 91 ]. Ageing is a reversible epigenetic process.
The first cell rejuvenation study was published in [ 92 ]. Cells from aged individuals have different transcriptional signatures, high levels of oxidative stress, dysfunctional mitochondria, and shorter telomeres than in young cells [ 93 ]. There is a hypothesis that when human or mouse adult somatic cells are reprogrammed to iPSCs, their epigenetic age is virtually reset to zero [ 94 ].
In their study, Ocampo et al. Their procedure revealed that these genes can also be used for effective regenerative treatment [ 97 ]. The main challenge of their method was the need to employ an approach that does not use transgenic animals and does not require an indefinitely long application.
The first clinical approach would be preventive, focused on stopping or slowing the ageing rate. Later, progressive rejuvenation of old individuals can be attempted. In the future, this method may raise some ethical issues, such as overpopulation, leading to lower availability of food and energy.
For now, it is important to learn how to implement cell reprogramming technology in non-transgenic elder animals and humans to erase marks of ageing without removing the epigenetic marks of cell identity. Stem cells can be induced to become a specific cell type that is required to repair damaged or destroyed tissues Fig. Currently, when the need for transplantable tissues and organs outweighs the possible supply, stem cells appear to be a perfect solution for the problem.
The most common conditions that benefit from such therapy are macular degenerations [ 98 ], strokes [ 99 ], osteoarthritis [ 89 , 90 ], neurodegenerative diseases, and diabetes [ ]. Due to this technique, it can become possible to generate healthy heart muscle cells and later transplant them to patients with heart disease. Stem cell experiments on animals. These experiments are one of the many procedures that proved stem cells to be a crucial factor in future regenerative medicine.
In the case of type 1 diabetes, insulin-producing cells in the pancreas are destroyed due to an autoimmunological reaction. As an alternative to transplantation therapy, it can be possible to induce stem cells to differentiate into insulin-producing cells [ ]. They can be stored in a tissue bank to be an essential source of human tissue used for medical examination.
The problem with conventional differentiated tissue cells held in the laboratory is that their propagation features diminish after time. This does not occur in iPSCs. The umbilical cord is known to be rich in mesenchymal stem cells. Due to its cryopreservation immediately after birth, its stem cells can be successfully stored and used in therapies to prevent the future life-threatening diseases of a given patient.
Stem cells of human exfoliated deciduous teeth SHED found in exfoliated deciduous teeth has the ability to develop into more types of body tissues than other stem cells [ ] Table 1. Techniques of their collection, isolation, and storage are simple and non-invasive. Among the advantages of banking, SHED cells are:.
Guaranteed donor-match autologous transplant that causes no immune reaction and rejection of cells [ ]. Not subject to the same ethical concerns as embryonic stem cells [ ]. In contrast to cord blood stem cells, SHED cells are able to regenerate into solid tissues such as connective, neural, dental, or bone tissue [ , ]. In , two researchers, Katsuhiko Hayashi et al. They succeeded in delivering healthy and fertile pups in infertile mice. The experiment was also successful for female mice, where iPSCs formed fully functional eggs.
Young adults at risk of losing their spermatogonial stem cells SSC , mostly cancer patients, are the main target group that can benefit from testicular tissue cryopreservation and autotransplantation. Effective freezing methods for adult and pre-pubertal testicular tissue are available [ ]. Qiuwan et al. For now, reaching successful infertility treatments in humans appears to be only a matter of time, but there are several challenges to overcome. First, the process needs to have high efficiency; second, the chances of forming tumours instead of eggs or sperm must be maximally reduced.
The last barrier is how to mature human sperm and eggs in the lab without transplanting them to in vivo conditions, which could cause either a tumour risk or an invasive procedure. In neuroscience, the discovery of neural stem cells NSCs has nullified the previous idea that adult CNS were not capable of neurogenesis [ , ].
Neural stem cells are capable of improving cognitive function in preclinical rodent models of AD [ , , ].
Awe et al. PD is an ideal disease for iPSC-based cell therapy [ ]. Although the results were not uniform, they showed that therapies with pure stem cells are an important and achievable therapy.
Teeth represent a very challenging material for regenerative medicine. They are difficult to recreate because of their function in aspects such as articulation, mastication, or aesthetics due to their complicated structure. Currently, there is a chance for stem cells to become more widely used than synthetic materials.
Teeth have a large advantage of being the most natural and non-invasive source of stem cells. For now, without the use of stem cells, the most common periodontological treatments are either growth factors, grafts, or surgery.
For example, there are stem cells in periodontal ligament [ , ], which are capable of differentiating into osteoblasts or cementoblasts, and their functions were also assessed in neural cells [ ]. Tissue engineering is a successful method for treating periodontal diseases.
Stem cells of the root apical areas are able to recreate periodontal ligament. One of the possible methods of tissue engineering in periodontology is gene therapy performed using adenoviruses-containing growth factors [ ]. As a result of animal studies, dentin regeneration is an effective process that results in the formation of dentin bridges [ ].
Enamel is more difficult to regenerate than dentin. After the differentiation of ameloblastoma cells into the enamel, the former is destroyed, and reparation is impossible. Medical studies have succeeded in differentiating bone marrow stem cells into ameloblastoma [ ].
Healthy dental tissue has a high amount of regular stem cells, although this number is reduced when tissue is either traumatized or inflamed [ ]. There are several dental stem cell groups that can be isolated Fig. Localization of stem cells in dental tissues.
Periodontal ligaments stem cells are located in the periodontal ligament. Apical papilla consists of stem cells from the apical papilla SCAP. These were the first dental stem cells isolated from the human dental pulp, which were [ ] located inside dental pulp Table 2. They have osteogenic and chondrogenic potential. Mesenchymal stem cells MSCs of the dental pulp, when isolated, appear highly clonogenic; they can be isolated from adult tissue e. MSCs differentiate into odontoblast-like cells and osteoblasts to form dentin and bone.
Their best source locations are the third molars [ ]. DPSCs are the most useful dental source of tissue engineering due to their easy surgical accessibility, cryopreservation possibility, increased production of dentin tissues compared to non-dental stem cells, and their anti-inflammatory abilities.
These cells have the potential to be a source for maxillofacial and orthopaedic reconstructions or reconstructions even beyond the oral cavity. DPSCs are able to generate all structures of the developed tooth [ ]. In particular, beneficial results in the use of DPSCs may be achieved when combined with other new therapies, such as periodontal tissue photobiomodulation laser stimulation , which is an efficient technique in the stimulation of proliferation and differentiation into distinct cell types [ ].
DPSCs can be induced to form neural cells to help treat neurological deficits. Stem cells of human exfoliated deciduous teeth SHED have a faster rate of proliferation than DPSCs and differentiate into an even greater number of cells, e. SHED do not undergo the same ethical concerns as embryonic stem cells. DPSCs alone were tested and successfully applied for alveolar bone and mandible reconstruction [ ]. These cells are used in periodontal ligament or cementum tissue regeneration.
PDLSCs exist both on the root and alveolar bone surfaces; however, on the latter, these cells have better differentiation abilities than on the former [ ]. PDLSCs have become the first treatment for periodontal regeneration therapy because of their safety and efficiency [ , ]. These cells are mesenchymal structures located within immature roots. They are isolated from human immature permanent apical papilla.
SCAP are the source of odontoblasts and cause apexogenesis. These stem cells can be induced in vitro to form odontoblast-like cells, neuron-like cells, or adipocytes. These cells are loose connective tissues surrounding the developing tooth germ. DFCs contain cells that can differentiate into cementoblasts, osteoblasts, and periodontal ligament cells [ , ]. Additionally, these cells proliferate after even more than 30 passages [ ]. DFCs are most commonly extracted from the sac of a third molar.
When DFCs are combined with a treated dentin matrix, they can form a root-like tissue with a pulp-dentin complex and eventually form tooth roots [ ]. Dental pulp stem cells can differentiate into odontoblasts. There are few methods that enable the regeneration of the pulp. The first is an ex vivo method. Proper stem cells are grown on a scaffold before they are implanted into the root channel [ ]. The second is an in vivo method.
This method focuses on injecting stem cells into disinfected root channels after the opening of the in vivo apex. Additionally, the use of a scaffold is necessary to prevent the movement of cells towards other tissues.
For now, only pulp-like structures have been created successfully. Methods of placing stem cells into the root channel constitute are either soft scaffolding [ ] or the application of stem cells in apexogenesis or apexification. Immature teeth are the best source [ ]. Nerve and blood vessel network regeneration are extremely vital to keep pulp tissue healthy.
The potential of dental stem cells is mainly regarding the regeneration of damaged dentin and pulp or the repair of any perforations; in the future, it appears to be even possible to generate the whole tooth. Such an immense success would lead to the gradual replacement of implant treatments.
Mandibulary and maxillary defects can be one of the most complicated dental problems for stem cells to address. In , it was reported that it is possible to grow teeth from stem cells obtained extra-orally, e.
Pluripotent stem cells derived from human urine were induced and generated tooth-like structures. The physical properties of the structures were similar to natural ones except for hardness [ ]. Nonetheless, it appears to be a very promising technique because it is non-invasive and relatively low-cost, and somatic cells can be used instead of embryonic cells. More importantly, stem cells derived from urine did not form any tumours, and the use of autologous cells reduces the chances of rejection [ ].
Over recent years, graphene and its derivatives have been increasingly used as scaffold materials to mediate stem cell growth and differentiation [ ]. Both graphene and graphene oxide GO represent high in-plane stiffness [ ]. Because graphene has carbon and aromatic network, it works either covalently or non-covalently with biomolecules; in addition to its superior mechanical properties, graphene offers versatile chemistry.
Graphene exhibits biocompatibility with cells and their proper adhesion. It also tested positively for enhancing the proliferation or differentiation of stem cells [ ]. After positive experiments, graphene revealed great potential as a scaffold and guide for specific lineages of stem cell differentiation [ ]. Graphene has been successfully used in the transplantation of hMSCs and their guided differentiation to specific cells.
The acceleration skills of graphene differentiation and division were also investigated. It was discovered that graphene can serve as a platform with increased adhesion for both growth factors and differentiation chemicals. Extracellular vesicles EVs can be released by virtually every cell of an organism, including stem cells [ ], and are involved in intercellular communication through the delivery of their mRNAs, lipids, and proteins.
As Oh et al. IncRNAs can bind to specific loci and create epigenetic regulators, which leads to the formation of epigenetic modifications in recipient cells. Because of this feature, exosomes are believed to be implicated in cell-to-cell communication and the progression of diseases such as cancer [ ]. Recently, many studies have also shown the therapeutic use of exosomes derived from stem cells, e.
In intrinsic skin ageing, on the other hand, the loss of elasticity is a characteristic feature. The skin dermis consists of fibroblasts, which are responsible for the synthesis of crucial skin elements, such as procollagen or elastic fibres. These elements form either basic framework extracellular matrix constituents of the skin dermis or play a major role in tissue elasticity.
Fibroblast efficiency and abundance decrease with ageing [ ]. Huh et al. It was discovered that, in addition to the induction of fibroblast physiology, hAFSC transplantation also improved diseases in cases of renal pathology, various cancers, or stroke [ , ].
Oh [ ] also presented another option for the treatment of skin wounds, either caused by physical damage or due to diabetic ulcers. Induced pluripotent stem cell-conditioned medium iPSC-CM without any animal-derived components induced dermal fibroblast proliferation and migration. During the crucial step of proliferation, fibroblasts migrate and increase in number, indicating that it is a critical step in skin repair, and factors such as iPSC-CM that impact it can improve the whole cutaneous wound healing process.
Paracrine actions performed by iPSCs are also important for this therapeutic effect [ ]. Bae et al. It was also demonstrated that iPSC factors can enhance skin wound healing in vivo and in vitro when Zhou et al. Peng et al. However, the research article points out that the procedure was accomplished only on in vitro acquired retina. Although stem cells appear to be an ideal solution for medicine, there are still many obstacles that need to be overcome in the future. One of the first problems is ethical concern.
The most common pluripotent stem cells are ESCs. Therapies concerning their use at the beginning were, and still are, the source of ethical conflicts. The reason behind it started when, in , scientists discovered the possibility of removing ESCs from human embryos. Stem cell therapy appeared to be very effective in treating many, even previously incurable, diseases. The problem was that when scientists isolated ESCs in the lab, the embryo, which had potential for becoming a human, was destroyed Fig.
Because of this, scientists, seeing a large potential in this treatment method, focused their efforts on making it possible to isolate stem cells without endangering their source—the embryo. Use of inner cell mass pluripotent stem cells and their stimulation to differentiate into desired cell types. For now, while hESCs still remain an ethically debatable source of cells, they are potentially powerful tools to be used for therapeutic applications of tissue regeneration.
Because of the complexity of stem cell control systems, there is still much to be learned through observations in vitro. For stem cells to become a popular and widely accessible procedure, tumour risk must be assessed.
New cells need to have the ability to fully replace lost or malfunctioning natural cells. Additionally, there is a concern about the possibility of obtaining stem cells without the risk of morbidity or pain for either the patient or the donor. Uncontrolled proliferation and differentiation of cells after implementation must also be assessed before its use in a wide variety of regenerative procedures on living patients [ ]. One of the arguments that limit the use of iPSCs is their infamous role in tumourigenicity.
There is a risk that the expression of oncogenes may increase when cells are being reprogrammed. In , a technique was discovered that allowed scientists to remove oncogenes after a cell achieved pluripotency, although it is not efficient yet and takes a longer amount of time.
The process of reprogramming may be enhanced by deletion of the tumour suppressor gene p53, but this gene also acts as a key regulator of cancer, which makes it impossible to remove in order to avoid more mutations in the reprogrammed cell.
The low efficiency of the process is another problem, which is progressively becoming reduced with each year. The use of transcription factors creates a risk of genomic insertion and further mutation of the target cell genome. For now, the only ethically acceptable operation is an injection of hESCs into mouse embryos in the case of pluripotency evaluation [ ].
Pioneering scientific and medical advances always have to be carefully policed in order to make sure they are both ethical and safe. Because stem cell therapy already has a large impact on many aspects of life, it should not be treated differently. Currently, there are several challenges concerning stem cells. First, the most important one is about fully understanding the mechanism by which stem cells function first in animal models.
This step cannot be avoided. For the widespread, global acceptance of the procedure, fear of the unknown is the greatest challenge to overcome. The efficiency of stem cell-directed differentiation must be improved to make stem cells more reliable and trustworthy for a regular patient. The scale of the procedure is another challenge. Future stem cell therapies may be a significant obstacle. Transplanting new, fully functional organs made by stem cell therapy would require the creation of millions of working and biologically accurate cooperating cells.
Bringing such complicated procedures into general, widespread regenerative medicine will require interdisciplinary and international collaboration. Immunological rejection is a major barrier to successful stem cell transplantation. With certain types of stem cells and procedures, the immune system may recognize transplanted cells as foreign bodies, triggering an immune reaction resulting in transplant or cell rejection.
Further development and versatility of stem cells may cause reduction of treatment costs for people suffering from currently incurable diseases.
When facing certain organ failure, instead of undergoing extraordinarily expensive drug treatment, the patient would be able to utilize stem cell therapy. The effect of a successful operation would be immediate, and the patient would avoid chronic pharmacological treatment and its inevitable side effects. Although these challenges facing stem cell science can be overwhelming, the field is making great advances each day.
Stem cell therapy is already available for treating several diseases and conditions. Their impact on future medicine appears to be significant. After several decades of experiments, stem cell therapy is becoming a magnificent game changer for medicine.
With each experiment, the capabilities of stem cells are growing, although there are still many obstacles to overcome. Regardless, the influence of stem cells in regenerative medicine and transplantology is immense. Currently, untreatable neurodegenerative diseases have the possibility of becoming treatable with stem cell therapy.
Tissue banks are becoming increasingly popular, as they gather cells that are the source of regenerative medicine in a struggle against present and future diseases. With stem cell therapy and all its regenerative benefits, we are better able to prolong human life than at any time in history. Embryonic stem cells derived from morulae, inner cell mass, and blastocysts of mink: comparisons of their pluripotencies.
Embryo Dev. Stem cell therapy in treatment of different diseases. Acta Medica Iranica. Quality guidelines for clinical-grade human induced pluripotent stem cell lines. Regenerative Med. Amps K, Andrews PW, et al. Screening ethnically diverse human embryonic stem cells identifies a chromosome 20 minimal amplicon conferring growth advantage.
Google Scholar. Amit M, Itskovitz-Eldor J. Atlas of human pluripotent stem cells: derivation and culturing. New York: Humana Press; Feeder-independent culture of human embryonic stem cells. Nat Methods. Kang MI. Transitional CpG methylation between promoters and retroelements of tissue-specific genes during human mesenchymal cell differentiation. Cell Biochem.
Quality control during manufacture of a stem cell therapeutic. BioProcess Int. Bloushtain-Qimron N. Epigenetic patterns of embryonic and adult stem cells. Cell Cycle. Brindley DA. What cell therapies are available right now? What about the therapies that are available overseas?
Why does it take so long to create new therapies? How do scientists get stem cells to specialize into different cell types? How do scientists test stem cell therapies? Can't stem cell therapies increase the chances of a tumor? Is there a risk of immune rejection with stem cells? How do scientists grow stem cells in the right conditions? When most people think about about stem cells treating disease they think of a stem cell transplant.
In a stem cell transplant, stem cells are first specialized into the necessary adult cell type. Then, those mature cells replace tissue that is damaged by disease or injury. This type of treatment could be used to:. Any of these would have a significant impact on human health without transplanting a single cell. Given that researchers may be able to study all cell types they have the potential to make breakthroughs in any disease. CIRM has created disease pages for many of the major diseases being targeted by stem cell scientists.
You can find those disease pages here. You can also sort our complete list of CIRM awards to see what we've funded in different disease areas.
While there are a growing number of potential therapies being tested in clinical trials there are only a few stem cell therapies that have so far been approved by the FDA. Two therapies that CIRM provided early funding for have been approved.
Those are:. Right now the most commonly used stem cell-based therapy is bone marrow transplantation. Blood-forming stem cells in the bone marrow were the first stem cells to be identified and were the first to be used in the clinic.
Adult stem cells. These stem cells are found in small numbers in most adult tissues, such as bone marrow or fat.
Compared with embryonic stem cells, adult stem cells have a more limited ability to give rise to various cells of the body. Until recently, researchers thought adult stem cells could create only similar types of cells. For instance, researchers thought that stem cells residing in the bone marrow could give rise only to blood cells. However, emerging evidence suggests that adult stem cells may be able to create various types of cells.
For instance, bone marrow stem cells may be able to create bone or heart muscle cells. This research has led to early-stage clinical trials to test usefulness and safety in people. For example, adult stem cells are currently being tested in people with neurological or heart disease.
Adult cells altered to have properties of embryonic stem cells induced pluripotent stem cells. Scientists have successfully transformed regular adult cells into stem cells using genetic reprogramming. By altering the genes in the adult cells, researchers can reprogram the cells to act similarly to embryonic stem cells. This new technique may allow researchers to use reprogrammed cells instead of embryonic stem cells and prevent immune system rejection of the new stem cells.
However, scientists don't yet know whether using altered adult cells will cause adverse effects in humans. Researchers have been able to take regular connective tissue cells and reprogram them to become functional heart cells.
In studies, animals with heart failure that were injected with new heart cells experienced improved heart function and survival time. Perinatal stem cells. Researchers have discovered stem cells in amniotic fluid as well as umbilical cord blood. These stem cells also have the ability to change into specialized cells. Amniotic fluid fills the sac that surrounds and protects a developing fetus in the uterus.
Researchers have identified stem cells in samples of amniotic fluid drawn from pregnant women to test for abnormalities — a procedure called amniocentesis. Embryonic stem cells are obtained from early-stage embryos — a group of cells that forms when a woman's egg is fertilized with a man's sperm in an in vitro fertilization clinic. Because human embryonic stem cells are extracted from human embryos, several questions and issues have been raised about the ethics of embryonic stem cell research.
The National Institutes of Health created guidelines for human stem cell research in The guidelines define embryonic stem cells and how they may be used in research, and include recommendations for the donation of embryonic stem cells. Also, the guidelines state embryonic stem cells from embryos created by in vitro fertilization can be used only when the embryo is no longer needed.
The embryos being used in embryonic stem cell research come from eggs that were fertilized at in vitro fertilization clinics but never implanted in a woman's uterus.
The stem cells are donated with informed consent from donors. The stem cells can live and grow in special solutions in test tubes or petri dishes in laboratories. Although research into adult stem cells is promising, adult stem cells may not be as versatile and durable as are embryonic stem cells. Adult stem cells may not be able to be manipulated to produce all cell types, which limits how adult stem cells can be used to treat diseases.
Adult stem cells also are more likely to contain abnormalities due to environmental hazards, such as toxins, or from errors acquired by the cells during replication. However, researchers have found that adult stem cells are more adaptable than was first thought.
A stem cell line is a group of cells that all descend from a single original stem cell and are grown in a lab. Cells in a stem cell line keep growing but don't differentiate into specialized cells. Ideally, they remain free of genetic defects and continue to create more stem cells.
Clusters of cells can be taken from a stem cell line and frozen for storage or shared with other researchers. Stem cell therapy, also known as regenerative medicine, promotes the repair response of diseased, dysfunctional or injured tissue using stem cells or their derivatives.
It is the next chapter in organ transplantation and uses cells instead of donor organs, which are limited in supply. However, there are still problems with accessibility, low frequency e.
Nevertheless, there are several ongoing phase I trials using bone marrow and skeletal satellite cells for the treatment of human heart failure 64 , despite unconvincing or contradictory evidence for a correct in situ transdifferentiation of these adult stem cells implanted in the heart of animal models So far, there are few examples of ES cell-based therapy using animal models of diseases that have provided encouraging and promising results. As illustrated in Figure 3 , these are a rat model of spinal cord injury, b mouse model of Parkinson's disease, c myocardial infarction MI in mice and rats, and d diabetes in mouse.
We will describe them and discuss the limitations of the present achievements. The absence of spontaneous axonal regeneration in the adult mammalian central nervous system causes devastating functional consequences in patients with spinal cord injuries. During the past decade, several attempts have been made to find a strategy to repair injured spinal cords in experimental animals, which could provide a novel therapeutic approach in humans.
Very interesting results have been achieved recently in a rat model of spinal cord injury When a heterogeneous population of differentiating ES cells i. More recently, Wichterle et al. Furthermore, it has been shown that ES cells, when transplanted into adult rat spinal cord after chemical demyelination or in myelin-deficient mutant mice, differentiated into mature oligodendrocytes, produced myelin, and myelinated host axons PD is characterized by the selective and gradual loss of dopaminergic neurons in the substantia nigra of the midbrain with a subsequent reduction in striatal dopamine.
The loss of this group of neurons is responsible for most PD symptoms i. PD has been treated with grafts of fetal cells, but the limited access of these cells and their poor survival restrict wider application of this approach. ES cells may be particularly valuable for circumventing this problem, as they can proliferate and maintain their developmental potential in culture.
Dopaminergic neurons have been efficiently derived from ES cells in vitro Bjorklund et al. If a large number of ES cells are implanted into the brain, they grow into every cell type and form teratomas in all cases, eventually killing their host More recently, Kim et al. The use of neuron-selective media were reported to increase the fraction of neuronal cells, and this type of optimization may be fundamental for the safe production of selected phenotypes Whether a similar outcome will soon be demonstrated for hES cells will depend on the development of safe strategies that will allow immunotolerance and avoid tumorigenic risks.
Chronic congestive heart failure CHF is a common consequence of heart muscle or valve damage and represents a major cause of cardiovascular morbidity and mortality in developed countries. When heart muscle is damaged by injury or decreased blood flow ischemia , functional contracting cardiomyocytes are replaced with nonfunctional scar tissue.
In fact, cardiomyocyte withdrawal from the cell cycle in the early neonatal period renders the adult heart incapable to regenerate after injury. Therefore, the use of a cell therapy approach to replace lost cardiomyocytes with new engraftable ones would represent an invaluable, low-invasiveness technique for the treatment of heart failure as an alternative to whole heart transplantation. The way in which hES cells could be used to treat heart disease has already been tested in mice and rats.
Mouse ES cells, when cultivated as embryoid bodies, are able to differentiate in vitro into cardiomyocytes of ventricle-, atrium-, and pacemaker-like cell types characterized by developmentally controlled expression of cardiac-specific genes, structural proteins, sarcomeric proteins 74 , 75 , and ion channels 8 , 76 , Clearly, the purity of differentiated ES-derived cardiomyocyte culture is a key issue to avoid the potential formation of teratomas, which would disrupting heart contractility.
Klug et al. On differentiation, only cardiac-committed cells expressing the antibiotic resistance gene can survive when treated with neomycin. Similarly, cardiomyocytes with a ventricular phenotype have been selected using the ventricular-specific myosin light chain isoform 2v promoter controlling the expression of green fluorescent protein 49 , So far, however, no study has investigated the engraftment of specific subpopulations of ES-derived cardiomyocytes, such as ventricular, atrial, or pacemaker cells.
Whether these approaches can generate sufficient numbers of cardiac cells suited for myocardial repair in vivo remains to be established. Ideally, understanding how to control cardiomyocyte differentiation would maximize proliferation of cardiac progenitors cells in culture while impeding their terminal differentiation, which should be undergone after transplantation.
Several animal models of MI using coronary ligation in rats or cryoinjury in mice have been used to test the implantation of fetal-, embryo-, or ES-derived cardiomyocytes by direct injection into heart muscle 78— Li et al. Transplantation of stage E12 to E15 embryonic cardiomyocytes into MI or cryoinjured hearts attenuated left ventricular dilatation, infarct thinning, and myocardial dysfunction 79 , Recently, Min et al. Although implanted cells survived and integrated the myocardium, which was associated with considerable improvement of global cardiac function, still many grafts remained isolated and did not differentiate into an adult phenotype The results published so far indicate that ES cell transplantation is a feasible approach to improve ventricular function in the infarcted failing heart.
However, despite encouraging beneficial effects on heart function and remodeling, the mechanism behind these results remains to be demonstrated. Benefits may be associated with enhanced angiogenesis via the release of angiogenic factors such as VEGF.
Several key issues still need to be addressed including the extent to which cell engraftment affects cardiac function actively i. Importantly, the possibility that some ES cells not committed to cardiac lineage could form deleterious teratomas with time has not yet been ruled out.
Lack or defect of insulin produces diabetes mellitus, a devastating disease suffered by million people in the world. Transplantation of insulin-producing cells could be a cure for type 1 and some cases of type 2 diabetes. Mouse and human ES cells can produce insulin-secreting cells in culture 32 , Lumelsky et al. When implanted subcutaneously in diabetic mice, these cells, although able to vascularize and remain immunoreactive to insulin, could not reverse high blood sugar levels in mice with symptoms of diabetes This may not be surprising considering the inappropriate site of implantation and the insufficient amount of insulin produced.
Nonetheless, grafted animals were able to maintain their body weight and survive for longer periods. This protection might take the form of tolerization, cell encapsulation, or cell engineering with immunoprotective genes.
The derivation of hES cells is a fundamental discovery that holds promise for three major areas of biomedicine: a transplantation medicine, b pharmaceutical research and development, and c human developmental biology. The availability of hES cells opens extraordinary opportunities for tissue transplantation.
Examples of cells for transplantation therapies include heart muscle cells for use in repairing the tissue damage inflicted by heart attacks, blood-forming cells for use in bone marrow transplantation procedures for cancer patients, and nerve cells for use in treating patients with spinal cord injury, stroke, Parkinson's or Alzheimer's diseases, and diabetes. Frailty is a major problem in geriatric medicine 87— Its pathogenesis involves neuronal and muscle cell failure as well as decreased cardiovascular function 90 , The availability of hES cells represents a tremendous potential to reverse frailty and prevent functional decline.
Human embryonic stem cells also represent a new technology for pharmaceutical research and development. Until now, the only cell lines available for this work were either animal or abnormal transformed human cells. Permanent, stable sources for normal human differentiated cells may be developed for drug screening and testing, drug toxicology studies, as well as new drug target identification 92— In addition, hES cells may also allow the creation of in vivo models of human disease for drug development as a superior alternative to current mouse models.
Finally, unraveling the biology of hES cells as they differentiate into functional cell types in vitro offers a unique platform to understand the mechanisms of human embryonic development, tissue differentiation, and repair. Until now, early genetic events in human embryology have been largely inaccessible to direct observation. Research with hES cells may lead to the discovery of novel genes that fundamentally control tissue differentiation, and may facilitate a molecular understanding of how specific human tissues and organs develop without conducting research on human embryos or fetuses.
These gene products could result in the development of therapeutic drugs and proteins with potential applications in wound healing, stroke, heart attack, spinal cord injury, and brain degenerative diseases. Successful use of any stem cell-based therapy will eventually depend on our ability to isolate specific cell types in large numbers that will differentiate to a fully functional state, as well as on the challenging demonstration of their in vivo function.
To this end, it is crucial to pursue basic research on human ES cell biology to ensure better understanding of basic principles and what genes and proteins are essential for hES developmental progression.
This comprehension does not only specifically involve the transplantation of ES cell-derived cells but will also help the development of new therapeutic strategies to improve the transdifferentiation and expansion of adult stem cells, such as umbilical cord blood cells or bone marrow cells.
Many hurdles not only technical but also ethical have to be cleared before the research reaches a point where clinical trials can begin. Examples of mouse embryonic stem ES cell clones, which are propagated in an undifferentiated state by culturing them over mitomycin-inactivated mouse embryonic fibroblasts as feeder cells and in the presence of the cytokine LIF leukemia inhibitory factor panel a. Some cell lines are feeder cell-independent such as the CGR8 line 49 panel b.
Every 2 days, cells are dissociated by trypsinization. Undifferentiated ES cells can be expanded in the presence of LIF, or their differentiation can be initiated by removing LIF and by forming three-dimensional structures called embryoid bodies EB containing the three embryonic derivatives.
Possible methods for the selection of a suited cell lineage include the insertion into embryonic stem ES cells of transgenes i. Upon differentiation, the expression of the transgene is dictated by the tissue-specific promoter, allowing the selection of the desired cell type, i.
Examples of applications of mouse embryonic stem cells to repair or replace diseased tissues in animal models of human diseases. Address correspondence to Marisa E. E-mail: marisa. Shapiro SS, et al.
Embryonic stem cell lines derived from human blastocysts. Smith AG. Embryo-derived stem cells: of mice and men. Annu Rev Cell Dev Biol. Martin GR. Isolation of a pluripotent cell line from early mouse embryos cultured in medium conditioned by teratocarcinoma stem cells.
Establishment in culture of pluripotential cells from mouse embryos. Donaldson DD, et al. Inhibition of pluripotential embryonic stem cell differentiation by purified polypeptides.
0コメント