This article is about the medical therapy. For the cell type, see Stem cell.

Stem cell therapy is an intervention strategy that introduces new adult stem cells into damaged tissue in order to treat disease or injury. Many medical researchers believe that stem cell treatments have the potential to change the face of human disease and alleviate suffering.[1] The ability of stem cells to self-renew and give rise to subsequent generations with variable degrees of differentiation capacities,[2] offers significant potential for generation of tissues that can potentially replace diseased and damaged areas in the body, with minimal risk of rejection and side effects.

A number of stem cell therapies exist, but most are at experimental stages, costly or controversial,[3] with the notable exception of bone-marrow transplantation.[citation needed] Medical researchers anticipate that adult and embryonic stem cells will soon be able to treat cancer, Type 1 diabetes mellitus, Parkinson's disease, Huntington's disease, Celiac disease, cardiac failure, muscle damage and neurological disorders, and many others.[4] Nevertheless, before stem cell therapeutics can be applied in the clinical setting, more research is necessary to understand stem cell behavior upon transplantation as well as the mechanisms of stem cell interaction with the diseased/injured microenvironment.[4]

For over 30 years, bone-marrow, and more recently, umbilical-cord blood stem cells, have been used to treat cancer patients with conditions such as leukemia and lymphoma.[5][6] 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.

Stroke and traumatic brain injury lead to cell death, characterized by a loss of neurons and oligodendrocytes within the brain. 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). In pregnancy and after injury, this system appears to be regulated by growth factors and can increase the rate at which new brain matter is formed.[citation needed] Although the reparative process appears to initiate following trauma to the brain, substantial recovery is rarely observed in adults, suggesting a lack of robustness.[7]

Stem cells may also be used to treat brain degeneration, such as in Parkinson's and Alzheimer's disease.[8][9]

Pharmacological activation of an endogenous population of neural stem cells / neural precursor cells by soluble factors has been reported to induce powerful neuroprotection and behavioral recovery in adult rat models of neurological disorder through a signal transduction pathway involving the phosphorylation of STAT3 on the serine residue and subsequent Hes3 expression increase (STAT3-Ser/Hes3 Signaling Axis).[10][11][12]

Stem cell technology gives hope of effective treatment for a variety of malignant and non-malignant diseases through the rapid developing field that combines the efforts of cell biologists, geneticists and clinicians. Stem cells are defined as totipotent progenitor cells capable of self-renewal and multi-lineage differentiation. Stem cells survive well and show steady division in culture which then causes them the ideal targets for vitro manipulation. Research into solid tissue stem cells has not made the same progress as haematopoietic stem cells because of the difficulty of reproducing the necessary and precise 3D arrangements and tight cell-cell and cell-extracellular matrix interactions that exist in solid organs. Yet, the ability of tissue stem cells to assimilate into the tissue cytoarchitecture under the control of the host microenvironment and developmental cues, makes them ideal for cell replacement therapy. [3] [13]

The development of gene therapy strategies for treatment of intra-cranial tumours offers much promise, and has shown to be successful in the treatment of some dogs;[14] although research in this area is still at an early stage. Using conventional techniques, brain cancer is difficult to treat because it spreads so rapidly. Researchers at the Harvard Medical School transplanted human neural stem cells into the brain of rodents that received intracranial tumours. Within days, the cells migrated into the cancerous area and produced cytosine deaminase, an enzyme that converts a non-toxic pro-drug into a chemotheraputic agent. As a result, the injected substance was able to reduce the tumor mass by 81 percent. The stem cells neither differentiated nor turned tumorigenic.[15]

Some researchers believe that the key to finding a cure for cancer is to inhibit proliferation of cancer stem cells. Accordingly, current cancer treatments are designed to kill cancer cells. However, conventional chemotherapy treatments cannot discriminate between cancerous cells and others. Stem cell therapies may serve as potential treatments for cancer.[16] Research on treating lymphoma using adult stem cells is underway and has had human trials. Essentially, chemotherapy is used to completely destroy the patients own lymphocytes, and stem cells injected, eventually replacing the immune system of the patient with that of the healthy donor.

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