[1] Unlike embryonic stem cells, the use of human adult stem cells in research and therapy is not considered to be controversial, as they are derived from adult tissue samples rather than human embryos designated for scientific research.

It can be induced by modifying the growth medium when stem cells are cultured in vitro or by transplanting them to an organ of the body different from the one they were originally isolated from.

More recent findings suggest that pluripotent stem cells may reside in blood and adult tissues in a dormant state.

[13][14][15][16] Stem cell function becomes impaired with age, and this contributes to progressive deterioration of tissue maintenance and repair.

Adult stem cell research has been focused on uncovering the general molecular mechanisms that control their self-renewal and differentiation.

MSCs have been isolated from the placenta, adipose tissue, lung, bone marrow and blood, Wharton's jelly from the umbilical cord,[30] and teeth (perivascular niche of dental pulp and periodontal ligament).

[31] MSCs are attractive for clinical therapy due to their ability to differentiate, provide trophic support, and modulate innate immune response.

The mesenchymal stem cells thus alter the outcome of the immune response by changing the cytokine secretion of dendritic and T-cell subsets.

The existence of stem cells in the adult brain has been postulated following the discovery that the process of neurogenesis, the birth of new neurons, continues into adulthood in rats.

Normally, adult neurogenesis is restricted to two areas of the brain – the subventricular zone, which lines the lateral ventricles, and the dentate gyrus of the hippocampal formation.

[37] Although the generation of new neurons in the hippocampus is well established, the presence of true self-renewing stem cells there has been debated.

[38] Under certain circumstances, such as following tissue damage in ischemia, neurogenesis can be induced in other brain regions, including the neocortex.

This means they can be easily obtained from all individuals, including older patients who might be most in need of stem cell therapies.

[55] Adult stem cell treatments have been used for many years to successfully treat leukemia and related bone/blood cancers utilizing bone marrow transplants.

[59] Research has shown that CD34+ hematopoietic Stem Cells are relatively more numerous in men than in women of reproductive age group among spinal cord Injury victims.

[62] Centeno et al. have reported high-field MRI evidence of increased cartilage and meniscus volume in individual human clinical subjects as well as a large n=227 safety study.

[66] The therapeutic potential of adult stem cells is the focus of much scientific research, due to their ability to be harvested from the parent body that is females during the delivery.

[70][71] Additionally, cues from the immediate environment (including how stiff or porous the surrounding structure/extracellular matrix is) can alter or enhance the fate and differentiation of the stem cells.

[78][79] A great deal of adult stem cell research has focused on investigating their capacity to divide or self-renew indefinitely, and their differentiation potential.

There is now a hypothesis that stem cells reside in many adult tissues and that these unique reservoirs of cells not only are responsible for the normal reparative and regenerative processes but are also considered to be a prime target for genetic and epigenetic changes, culminating in many abnormal conditions including cancer.

This complicates the design of drugs, for instance, neural stem cell-targeted therapies for the treatment of clinical depression.

[85] Due to their multipotency, capacity to release growth factors, and immunomodulatory abilities, stem cell-based therapies have become a viable tool for the treatment of both acute and delayed phases of stroke.

By inducing neurogenesis, angiogenesis, and synaptogenesis as well as activating endogenous restorative processes through the generation of cytokines and trophic factors, this transdifferentiation can form cells with a neural lineage.