Types of Stem Cell

 

Ever since modern medicine discovered stem cells and their potential to regenerate to different kinds of cells, the topic had never left the lime light. Stem cells can be thought of as primitive, "unspecialized" cells that are able to divide and become specialized cells of the body such as liver cells, muscle cells, blood cells, and other cells with specific functions. Stem cells are referred to as "undifferentiated" cells because they have not yet committed to a developmental path that will form a specific tissue or organ.

In the past, only 2 kinds of stem cells had been noted, the embryonic stem cells and tissue stem cells, however, recently, a 3^rd kind of stem cell,  the induced pluripotent stem cells is also turning heads and getting its share of popularity.

Embryonic stem cells

Embryonic stem cells are derived from a four- or five-day-old human embryo that is in the blastocyst phase of development. The embryos are usually extras that have been created in IVF (in vitro fertilization) clinics where several eggs are fertilized in a test tube, but only one is implanted into a woman.

Embryonic stem cells (ESCs) cells have unlimited potential to produce specialised cells of the body, which suggests enormous possibilities for disease research and for providing new therapies. Recently, human ESCs that meet the strict quality requirements for use in patients have been produced. These ‘clinical grade’ human ESCs have been approved for use in a very small number of early clinical trials.

Recently, Human embryonic stem cells (ESCs) has been approved for researches to Improve our understanding of how the body develops from a fertilized egg; this can also provide insights into how our adult tissues are maintained and repaired in health; understand how diseases occur and develop; a number of diseases, such as cancer or birth defects, are the result of problems in the process of differentiation from stem cells to more specialized cells; Search for and test potential new drugs by studying cells in the laboratory; develop future cell-based therapies for currently untreatable diseases.

Tissue Stem Cells

Different organs and tissues in our body have their own stem cells that help them repair and regenerate in cases of diseases and trauma.

Blood Stem Cells

Blood stem cells had been used for treating several diseases for some time now. Bone marrow transplants are able to replace a patient’s diseased blood system for life due to the repair property of blood stem cells. Thousands, even millions of patients actually benefit from this kind of treatment every year, although the chance of complication is still possible especially with blood like in instances where the donor’s immune cells attack the patient’s tissues (graft-versus-host disease or GVHD) and of course, there is always a risk of infection during  treatment because the patient’s own bone marrow cells must be killed with chemotherapy before the transplant can take place.

Skin Stem Cells

Skin stem cells have been used since the 1980s to grow sheets of new skin in the lab for severe burn patients. However, the new skin has no hair follicles, sweat glands or sebaceous (oil) glands, so the technique is far from perfect and further research is still underway to improve the results. Currently, the technique is mainly used to save the lives of patients who have third degree burns over very large areas of their bodies and is only carried out in a few clinical centers as the procedure is quiet extensive.

Cord Blood Stem Cells

Cord blood stem cells can be harvested from the umbilical cord of a baby after birth. The cells can be frozen (‘cryopreserved’) in cell banks and are currently used to treat children with cancerous blood disorders such as leukaemia, as well as genetic blood diseases like Fanconi anaemia. In early 2013, cord blood has also been used to treat a 2 year old boy with cerebral palsy.

Treatment of adults has so far been more challenging but adults have been successfully treated with double cord transplants. The most commonly held view is that success in adults is restricted by the number of cells that can be obtained from one umbilical cord, but immune response may also play a role. One advantage of cord blood transplants is that they are less to be rejected by the immune system than bone marrow transplant. Nevertheless, cord blood must still be matched to the patient to be successful.

Mesenchymal Stem Cells

Mesenchymal stem cells (MSCs) are found in the bone marrow and are responsible for bone and cartilage repair. They also produce fat cells. Early research suggested that MSCs could differentiate into many other types of cells but it is now clear that this is not the case. MSCs, like all tissue stem cells, are not pluripotent but multipotent – they can make a limited number of types of cells, but NOT all types of cells of the body. Claims have also been made that MSCs can be obtained from a wide variety of tissues in addition to bone marrow. These claims have not been confirmed and scientists are still debating the exact nature of cells obtained from these other tissues. Several claims had also been made that MSCs can avoid detection by the immune system and that MSCs taken from one person can be transplanted into another with little or no risk of rejection by the body, however, it’s validity is still in question as trails are still being conducted.

Adipose-Derived Stem Cells (Most Popular type of Mesenchymal Stem Cell)

Adipose tissue is an abundant, accessible, and replenishable source of adult stem cells that can be isolated from liposuction waste tissue by collagenase digestion and differential centrifugation. These adipose-derived adult stem (ADAS) cells are multipotent, differentiating along the adipocyte, chondrocyte, myocyte, neuronal, and osteoblast lineages, and can serve in other capacities, such as providing hematopoietic support and gene transfer. ADAS cells have potential applications for the repair and regeneration of acute and chronically damaged tissues. Additional pre-clinical safety and efficacy studies will be needed before the promise of these cells can be fully realized.

Stem Cells in the Eyes

Clinical studies in patients have shown that tissue stem cells taken from an area of the eye called the limbus can be used to repair damage to the cornea – the transparent layer at the front of the eye. If the cornea is severely damaged, for example by a chemical burn, limbal stem cells can be taken from the patient, multiplied in the lab and transplanted back onto the patient’s damaged eye(s) to restore sight. However, this can only help patients who have some undamaged limbal stem cells remaining in one of their eyes. The treatment has been shown to be safe and effective in early stage trials. Further studies with larger numbers of patients are now being carried out for this type of treatment to be approved by regulatory authorities for widespread use in Europe.

Induced Pluripotent Stem Cells

The most recent breakthrough in stem cell research is the discovery that specialized adult cells can be ‘reprogrammed’ (through experimentation) into cells that behave like embryonic stem cells, termed induced pluripotent stem cells(iPSCs). The generation of iPSCs has huge implications for disease research and drug development. For example, researchers have generated brain cells from iPSCs made from skin samples belonging to patients with neurological disorders such as Down’s syndrome or Parkinson’s disease. These lab-grown brain cells show signs of the patients’ diseases. This has implications for understanding how the diseases actually happen – researchers can watch the process in a dish – and for searching for and testing new drugs. Such studies give a taste of the wide range of disease research being carried out around the world using iPSCs.

The discovery of iPSCs also raised hopes that cells could be made from a patient’s own skin in order to treat their disease, avoiding the risk of immune rejection. However, use of iPSCs in cell therapy is theoretical at the moment and no clinical trials are being conducted yet as the focus of researches surrounding these stem cells is mainly to point out how problems occur first so medications or preventive measures can be developed.

Since the technology is still very new and the reprogramming process is not yet well understood, scientists still need to find ways to produce the new cells safely and effectively Current techniques involve genetic modification, which can sometimes result in the cells forming tumors. The cells must also be shown to completely and reproducibly differentiate into the required types of specialized cells to meet standards suitable for use in patients.