Bone marrow transplants
Bone marrow transplants have been used successfully for treatments of different blood diseases for more than 40 years and have significantly improved the prognosis of many previously incurable diseases. Human blood stem cells reside in the bone marrow inside virtually all bones of the body. The renewal capacity of the bone marrow is astonishing with blood stem cells producing around 500 billion new blood cells, that is red and white blood cells and platelets, every day. Thus, a small amount of transplanted bone marrow is able to effectively replace blood cells, that are defective or have been lost due to disease.
Bone marrow transplants are frequently used in the treatment of lukemia, in other words blood cancer, and other severe forms of cancer. The white blood cells of the lukemia patient are destroyed by chemotherapy or radiation therapy, leading also to the destruction of healthy blood cells. The patient receives a bone marrow transplant containing blood stem cells, that replace the sick and destroyed blood cells. The bone marrow usually originates from a suitable anonymous donor found through the international stem cell registry. Sometimes, a bone marrow transplant from a relative can also be used. A bone marrow donation will not even momentarily affect the ability of the donor’s bone marrow to produce new blood cells due to the very small amount of the donated bone marrow. It’s also possible to retrieve blood stem cells from the circulation, placental blood or cord blood. In these cases, the amount of blood stem cells is much smaller. Many leukemia patients, especially children, recover fully thanks to stem cell transplants. Blood stem cells are also used to treat other blood diseases and immune deficiencies.
The skin contains two types of stem cells that renew the skin and the body hair. Human skin renews approximately once a month when the stem cells residing in the deep layer of the skin gradually produce new skin cells and old skin cells shed off. In the 1970’s, scientists learned to culture human skin cells in the laboratory, leading to the development of skin transplant methods. It however took many years before the role of skin stem cells in the success of skin transplants was understood; the skin was able to renew due to the stem cells present in the transplant.
During a skin transplant, the patient’s own healthy skin from other parts of the body is usually used since the body rarely rejects its own skin transplant. The transplant can be taken from many parts of the body but usually the site is chosen so that the skin resembles that of the injured area as closely as possible. Nowadays it’s possible to grow new skin in the laboratory for months of time and once the skin is transplanted it’s able to renew the patient’s skin for decades without any signs of cancer-causing changes. Skin transplants are used a lot for burn injuries but also for treatment of wounds that are difficult to heal or result from a large surgery. In 2017, a team of Italian scientists was able fort the first time to perform a near whole-body skin transplantation using transplants that originated from the patient’s own gene-corrected skin cells. They were thereby able to save the life of the patient, a young boy, who suffered from a life-threatening skin disease.
Stem cell treatments for the eyes
In 2015 the EU approved a stem cell based therapy for treating eye injuries of the cornea. The cornea is normally renewed by its own stem cells called limbal stem cells. If the limbal stem cells are injured, for example following a chemical accident, it can lead to blindness. Corneal transplants, that have been grown from limbal stem cells in the laboratory, can be used to repair this kind of injury.
Retinis pigmentosa is a condition where the retinas of the eyes gradually are destroyed, leading to loss of vision. Using stem cells, it’s possible to generate cells that can support the retina and halt the progression of the disease, possibly even leading to partial restoration of lost vision. Both embryonic stem cells and iPS cells have been used in experimental treatments with promising outcome. The amount of transplanted cells is small and the cells are well differentiated, which diminishes the risk of the transplanted cells causing tumours, thereby increasing the safety of the treatment.
MSC, Mesenchymal stem/stromal cells
So-called mesenchymal stem cells (MSC) originate from the bone marrow and can generate bone, cartilage and fat cells. Mesenchymal stromal cells, that are isolated from connective or fat tissue, are also sometimes referred to as MSC. There are thus different kinds of cells that are called MSC and their ability to generate bone or cartilage tissue depends on their origin as well as handling of them in the laboratory. MSC’s have not been shown to be able to generate other specialized cells apart from bone, cartilage and fat cells.
Scientists are looking into the possibilities to use MSC’s in treatments of bone and cartilage injuries. In the laboratory, MSC’s are able to generate cartilage tissue, but attempts to get these cells to repair arthritis of the knees in humans have had conflicting outcome. These treatments are not approved for example by the US Food and Drug Administration, FDA, or by the European Medicines Agency, EMA. However, the EMA has approved treatments that rely on cartilage cells, not MSC’s, for arthritis treatments.
MSC’s are also known to be able to reduce inflammation and much of the benefits that have been reported for experimental treatments using MSC’s are thought to be a result of the anti-inflammatory, not cartilage-renewing, properties of MSC’s. In Finland, the usage of adipose tissue transplants in treatments for perianal fistulas associated with Crohn’s disease was recently approved. Mesenchymal stromal cells in the transplants have an evident local anti-inflammatory effect. The possibility to use MSC’s in other serious inflammatory diseases is being investigated.