Mesenchymal Stem Cells: The ‘Other’ Bone Marrow Stem Cells

No treatments using MSCs are yet available. However, several possibilities for their use in the clinic are currently being explored.

Bone and cartilage repairThe ability of MSCs to differentiate into bone cells called osteoblasts has led to their use in early clinical trials investigating the safety of potential bone repair methods. These studies are looking at possible treatments for localized skeletal defects (damage at a particular place in the bone).

Other research is focussed on using MSCs to repair cartilage. Cartilage covers the ends of bones and allows one bone to slide over another at the joints. It can be damaged by a sudden injury like a fall, or over a long period by a condition like osteoarthritis, a very painful disease of the joints. Cartilage does not repair itself well after damage. The best treatment available for severe cartilage damage is surgery to replace the damaged joint with an artificial one. Because MSCs can differentiate into cartilage cells called chondrocytes, scientists hope MSCs could be injected into patients to repair and maintain the cartilage in their joints. Researchers are also investigating the possibility that transplanted MSCs may release substances that will tell the patients own cells to repair the damage.

Many hurdles remain before this kind of treatment can become a reality. For example, when MSCs are transplanted, most of them are rapidly removed from the body. Researchers are working on new techniques for transplanting the cells, such as developing three-dimensional structures or scaffolds that mimic the conditions in the part of the body where the cells are needed. These scaffolds will hold the cells and encourage them to differentiate into the desired cell type.

Heart and blood vessel repairSome studies in mice suggest that MSCs can promote formation of new blood vessels in a process called neovascularisation. MSCs do not make new blood vessel cells themselves, but they may help with neovascularisation in a number of ways. For example, they may release proteins that stimulate the growth of other cells called endothelial precursors cells that will develop to form the inner layer of blood vessels. They may also "guide" the assembly of new blood vessels from preexisting endothelial cells (those that line the blood vessel). Such studies on animals have led researchers to hope that MSCs may provide a way to repair the blood vessel damage linked to heart attacks or diseases such as critical limb ischaemia. A number of early stage clinical trials using MSCs in patients are currently underway but it is not yet clear whether the treatments will be effective.

Inflammatory and autoimmune diseasesSeveral claims have been made that MSCs are able to avoid detection by the immune system and can be transplanted from one patient to another without risk of immune rejection by the body. However, these claims have not been confirmed by other studies. MSCs are rejected like any other "non-self" cell type. It has also been suggested that MSCs may be able to slow down the multiplication of immune cells in the body to reduce inflammation and help treat transplant rejection or autoimmune diseases. Again, this has yet to be proven and much more evidence is needed to establish whether MSCs could really be used for this kind of application.

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Mesenchymal Stem Cells: The 'Other' Bone Marrow Stem Cells