stem-cell therapy stem-cell therapy stem-cell therapy is the use of stem cells to treat or prevent a disease or condition. as of 2016, the only established therapy using stem cells is hematopoietic stem cell transplantation. this usually takes the form of a bone-marrow transplantation, but the cells can also be derived from umbilical cord blood. research is underway to develop various sources for stem cells as well as to apply stem-cell treatments for neurodegenerative diseases and conditions such as diabetes and heart disease. this article is about the medical therapy. for the cell type, see stem cell. stem-cell therapy has become controversial following developments such as the ability of scientists to isolate and culture embryonic stem cells, to create stem cells using somatic cell nuclear transfer and their use of techniques to create induced pluripotent stem cells. this controversy is often related to abortion politics and to human cloning. additionally, efforts to market treatments based on transplant of stored umbilical cord blood have been controversial. medical uses further information: hematopoietic stem cell transplantation for over 30 years, hematopoietic stem cell transplantation (hsct) has been used to treat people with conditions such as leukaemia and lymphoma; this is the only widely practiced form of stem-cell therapy. during chemotherapy, most growing cells are killed by the cytotoxic agents. these agents, however, cannot discriminate between the leukaemia or neoplastic cells, and the hematopoietic stem cells within the bone marrow. this is the side effect of conventional chemotherapy strategies that the stem-cell transplant attempts to reverse; a donor's healthy bone marrow reintroduces functional stem cells to replace the cells lost in the host's body during treatment. the transplanted cells also generate an immune response that helps to kill off the cancer cells; this process can go too far, however, leading to graft vs host disease, the most serious side effect of this treatment. another stem-cell therapy, called prochymal, was conditionally approved in canada in 2012 for the management of acute graft-vs-host disease in children who are unresponsive to steroids. it is an allogenic stem therapy based on mesenchymal stem cells (mscs) derived from the bone marrow of adult donors. mscs are purified from the marrow, cultured and packaged, with up to 10,000 doses derived from a single donor. the doses are stored frozen until needed. the fda has approved five hematopoietic stem-cell products derived from umbilical-cord blood, for the treatment of blood and immunological diseases. in 2014, the european medicines agency recommended approval of limbal stem cells for people with severe limbal stem cell deficiency due to burns in the eye. research diseases and conditions where stem cell treatment is promising or emerging stem cells are being studied for a number of reasons. the molecules and exosomes released from stem cells are also being studied in an effort to make medications. in addition to the functions of the cells themselves, paracrine soluble factors produced by stem cells, known as the stem cell secretome, have been found to be another mechanism by which stem cell-based therapies mediate their effects in degenerative, autoimmune, and inflammatory diseases. stem cell expansion to be used for research or treatment applications, large numbers of high-quality stem cells are needed. thus, it is necessary to develop culture systems which produce pure populations of tissue-specific stem-cells in vitro without the loss of stem-cell potential. two main approaches are taken for this purpose: two-dimensional and three-dimensional cell culture. cell culture in two dimensions has been routinely performed in thousands of laboratories worldwide for the past four decades. in two-dimensional platforms, cells are typically exposed to a solid, rigid flat surface on the basal side and to liquid at the apical surface. inhabiting such a two-dimensional rigid substrate requires a dramatic adaption for the surviving cells because they lack the extracellular matrix that is unique to each cell type and which may alter cell metabolism and reduce its functionality. three-dimensional cell culture systems may create a biomimicking microenvironment for stem cells, resembling their native three-dimensional extracellular matrix (ecm). advanced biomaterials have significantly contributed to three-dimensional cell culture systems in recent decades, and more unique and complex biomaterials have been proposed for improving stem-cell proliferation and controlled differentiation. among them, nanostructured biomaterials are of particular interest because they have the advantage of a high surface-to-volume ratio, and they mimic the physical and biological features of natural ecm at the nanoscale. neurodegeneration research has been conducted on the effects of stem cells on animal models of brain degeneration, such as in parkinson's disease, amyotrophic lateral sclerosis, and alzheimer's disease. preliminary studies related to multiple sclerosis have been conducted, and a 2020 phase 2 trial found significantly improved outcomes for mesenchymal stem cell treated patients compared to those receiving a sham treatment. in january 2021 the fda approved the first clinical trial for an investigational stem cell therapy to restore lost brain cells in people with advanced parkinson's disease. healthy adult brains contain neural stem cells, which divide to maintain general stem-cell numbers, or become progenitor cells. in healthy adult laboratory animals, progenitor cells migrate within the brain and function primarily to maintain neuron populations for olfaction (the sense of smell). pharmacological activation of endogenous neural stem cells has been reported to induce neuroprotection and behavioral recovery in adult rat models of neurological disorder. brain and spinal cord injury stroke and traumatic brain injury lead to cell death, characterized by a loss of neurons and oligodendrocytes within the brain. clinical and animal studies have been conducted into the use of stem cells in cases of spinal cord injury. frailty syndrome a small-scale study on individuals 60 year or older with aging frailty showed, after intravenous treatment with mesenchymal stem cells (msc) from healthy young donors, showed significant improvements in physical performance measures. msc helps with the blockade of inflammation by decreasing it, causing the effects of frailty to reverse. heart stem cells are studied in people with severe heart disease. the work by bodo-eckehard strauer was discredited by identifying hundreds of factual contradictions. among several clinical trials reporting that adult stem cell therapy is safe and effective, actual evidence of benefit has been reported from only a few studies. some preliminary clinical trials achieved only modest improvements in heart function following use of bone marrow stem cell therapy. stem-cell therapy for treatment of myocardial infarction usually makes use of autologous bone-marrow stem cells, but other types of adult stem cells may be used, such as adipose-derived stem cells. possible mechanisms of recovery include: generation of heart muscle cells stimulating growth of new blood vessels to repopulate damaged heart tissue secretion of growth factors criticisms in 2013, studies of autologous bone-marrow stem cells on ventricular function were found to contain "hundreds" of discrepancies. critics report that of 48 reports, just five underlying trials seemed to be used, and that in many cases whether they were randomized or merely observational accepter-versus-rejecter, was contradictory between reports of the same trial. one pair of reports of identical baseline characteristics and final results, was presented in two publications as, respectively, a 578-patient randomized trial and as a 391-subject observational study. other reports required (impossible) negative standard deviations in subsets of people, or contained fractional subjects, negative nyha classes. overall, many more people were reported as having receiving stem cells in trials, than the number of stem cells processed in the hospital's laboratory during that time. a university investigation, closed in 2012 without reporting, was reopened in july 2013. in 2014, a meta-analysis on stem cell therapy using bone-marrow stem cells for heart disease revealed discrepancies in published clinical trial reports, whereby studies with a higher number of discrepancies showed an increase in effect sizes. another meta-analysis based on the intra-subject data of 12 randomized trials was unable to find any significant benefits of stem cell therapy on primary endpoints, such as major adverse events or increase in heart function measures, concluding there was no benefit. the time trial, which used a randomized, double-blind, placebo-controlled trial design, concluded that "bone marrow mononuclear cells administration did not improve recovery of lv function over 2 years" in people who had a myocardial infarction. accordingly, the boost-2 trial conducted in 10 medical centers in germany and norway reported that the trial result "does not support the use of nucleated bmcs in patients with stemi and moderately reduced lvef". furthermore, the trial also did not meet any other secondary mri endpoints, leading to a conclusion that intracoronary bone marrow stem cell therapy does not offer a functional or clinical benefit. blood-cell formation the specificity of the human immune-cell repertoire is what allows the human body to defend itself from rapidly adapting antigens. however, the immune system is vulnerable to degradation upon the pathogenesis of disease, and because of the critical role that it plays in overall defense, its degradation is often fatal to the organism as a whole. diseases of hematopoietic cells are diagnosed and classified via a subspecialty of pathology known as hematopathology. the specificity of the immune cells is what allows recognition of foreign antigens, causing further challenges in the treatment of immune disease. identical matches between donor and recipient must be made for successful transplantation treatments, but matches are uncommon, even between first-degree relatives. research using both hematopoietic adult stem cells and embryonic stem cells has provided insight into the possible mechanisms and methods of treatment for many of these ailments. fully mature human red blood cells may be generated ex vivo by hematopoietic stem cells (hscs), which are precursors of red blood cells. in this process, hscs are grown together with stromal cells, creating an environment that mimics the conditions of bone marrow, the natural site of red-blood-cell growth. erythropoietin, a growth factor, is added, coaxing the stem cells to complete terminal differentiation into red blood cells. further research into this technique should have potential benefits to gene therapy, blood transfusion, and topical medicine. regrowing teeth in 2004, scientists at king's college london discovered a way to cultivate a complete tooth in mice and were able to grow bioengineered teeth stand-alone in the laboratory. researchers are confident that the tooth regeneration technology can be used to grow live teeth in people. in theory, stem cells taken from the patient could be coaxed in the lab turning into a tooth bud which, when implanted in the gums, will give rise to a new tooth, and would be expected to be grown in a time over three weeks. it will fuse with the jawbone and release chemicals that encourage nerves and blood vessels to connect with it. the process is similar to what happens when humans grow their original adult teeth. many challenges remain, however, before stem cells could be a choice for the replacement of missing teeth in the future. cochlear hair cell regrowth heller has reported success in re-growing cochlea hair cells with the use of embryonic stem cells. in a 2019 review that looked at hearing regeneration and regenerative medicine, stem cell-derived otic progenitors have the potential to greatly improve hearing. blindness and vision impairment since 2003, researchers have successfully transplanted corneal stem cells into damaged eyes to restore vision. "sheets of retinal cells used by the team are harvested from aborted fetuses, which some people find objectionable." when these sheets are transplanted over the damaged cornea, the stem cells stimulate renewed repair, eventually restore vision. the latest such development was in june 2005, when researchers at the queen victoria hospital of sussex, england were able to restore the sight of forty people using the same technique. the group, led by sheraz daya, was able to successfully use adult stem cells obtained from the patient, a relative, or even a cadaver. further rounds of trials are ongoing. pancreatic beta cells people with type 1 diabetes lose the function of insulin-producing beta cells within the pancreas. in recent experiments, scientists have been able to coax embryonic stem cell to turn into beta cells in the lab. in theory if the beta cell is transplanted successfully, they will be able to replace malfunctioning ones in a diabetic patient. mesenchymal stem cells being injected into knee of patient orthopedics use of mesenchymal stem cells (mscs) derived from adult stem cells is under preliminary research for potential orthopedic applications in bone and muscle trauma, cartilage repair, osteoarthritis, intervertebral disc surgery, rotator cuff surgery, and