Bone marrow transplant is the most widely used stem cell therapy, but some therapies derived from umbilical cord blood are also in use. Research is underway to develop various sources for stem cells, and to apply stem cell treatments for neurodegenerative diseases and conditions, diabetes, heart disease, and other conditions. With the ability of scientists to isolate and culture embryonic stem cells, and with scientists' growing ability to create stem cells using somatic cell nuclear transfer and techniques to create induced pluripotent stem cells, controversy has crept in, both related to abortion politics and to human cloning. Additionally, efforts to market treatments based on transplant of stored umbilical cord blood have proven controversial.

For along time, bone-marrow have been used to treat cancer patients with conditions such as leukaemia and lymphoma; this is the only form of stem cell therapy that is widely practiced. 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. It is this 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 Holoclar, a treatment involving stem cells, for use in the European Union. Holoclar is used for people with severe limbal stem cell deficiency due to burns in the eye.

Research has been conducted to learn whether stem cells may be used to treat brain degeneration, such as in Parkinson's, Amyotrophic lateral sclerosis, and Alzheimer's disease.

Healthy adult brains contain neural stem cells which divide to maintain general stem cell numbers, or become progenitor cells. In healthy adult 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. A small clinical trial was underway in Scotland in 2013, in which stem cells were injected into the brains of stroke patients. Clinical and animal studies have been conducted into the use of stem cells in cases of spinal cord injury.

References:

Androutsellis-Theotokis, A., Leker R.R., Soldner, F. 2006. "Notch signalling regulates stem cell numbers in vitro and in vivo". Nature 442 (7104): 823–6. doi:10.1038/nature04940. PMID 16799564.

Androutsellis-Theotokis, A., Rueger, M.A., Mkhikian, H., Korb, E., McKay, R.D. 2008. "Signaling pathways controlling neural stem cells slow progressive brain disease". Cold Spring Harb. Symp. Quant. Biol. 73: 403–10. doi:10.1101/sqb.2008.73.018. PMID 19022746.

Androutsellis-Theotokis. A., Rueger, M.A., Park ,D.M. 2009. "Targeting neural precursors in the adult brain rescues injured dopamine neurons". Proc. Natl. Acad. Sci. U.S.A. 106 (32): 13570–5. doi:10.1073/pnas.0905125106. PMC 2714762. PMID 19628689.

Cummings, B.J., Uchida, N., Tamaki, S.J. 2005. "Human neural stem cells differentiate and promote locomotor recovery in spinal cord-injured mice". Proc. Natl. Acad. Sci. U.S.A. 102 (39): 14069–74. doi:10.1073/pnas.0507063102. PMC 1216836. PMID 16172374.

Ghosh, Pallab. 2013. Stroke patients see signs of recovery in stem cell trial BBC News health, Retrieved 27 may 2013

Kan, K.S., Kim, S.W., Oh, Y.H. 2005. "A 37-year-old spinal cord-injured female patient, transplanted of multipotent stem cells from human UC blood, with improved sensory perception and mobility, both functionally and morphologically: a case study". Cytotherapy 7 (4): 368–73. doi:10.1080/14653240500238160. PMID 16162459.

Karanes, C., Nelson, G.O., Chitphakdithai, P., Agura, E., Ballen, K.K., Bolan, C.D., Porter, D.L., Uberti, J.P., King, R.J., Confer, D.L.2008. "Twenty years of unrelated donor hematopoietic cell transplantation for adult recipients facilitated by the National Marrow Donor Program". Biology of Blood and Marrow Transplantation 14 (9 Suppl): 8–15. doi:10.1016/j.bbmt.2008.06.006. PMID 18721775.

Malard, F., Mohty, M. New Insight for the Diagnosis of Gastrointestinal Acute Graft-versus-Host Disease. Mediators Inflamm. 2014;2014:701013. PMID 24733964.

Rosemann, A. Why regenerative stem cell medicine progresses slower than expected. J Cell Biochem. 2014 Dec;115(12):2073-6. PMID 25079695.

Vastag, B. 2001. "Stem cells step closer to the clinic: paralysis partially reversed in rats with ALS-like disease". JAMA 285 (13): 1691–3. doi:10.1001/jama.285.13.1691. PMID 11277806.