Types of Cells

The body is made up of about 200 different kinds of specialised cells such as muscle cells, nerve cells, fat cells and skin cells.

All specialised cells originate from stem cells. A stem cell is a cell that is not yet specialised. The process of specialisation is called differentiation and once the differentiation pathway of a stem cell has been decided, it can no longer become another type of cell. A stem cell that can become every type of cell in the body is called pluripotent whilst a stem cell that can become only some types of cells is called multipotent. Stem cells are found in the early embryo, the fetus, placenta, umbilical cord, and in many different tissues of the adult body.

Stem cells are often divided into two groups: tissue specific stem cells (often referred to as adult stem cells) and pluripotent stem cells (including embryonic stem cells and induced pluripotent stem cells). Tissue specific stem cells are derived from, or resident in, fetal or adult tissue, and can usually only give rise to the cells of that tissue, thus they are considered multipotent. Embryonic stem cells, derived from a small group of cells within the very early embryo, and their new counterpart induced pluripotent stem (iPS) cells are considered pluripotent as they can become every type of cell in the body.

Tissue Specific Stem Cells

Tissue specific stem cells are undifferentiated cells found in the tissues and organs of the body. They are capable of self-renewal. Their differentiation is mainly restricted to forming the cell types of that tissue or organ. The chief role of tissue specific stem cells is to maintain and repair the tissue in which they are found. Skin stem cells, for example, give rise to new skin cells, ensuring that old or damaged skin cells are replenished.

It now appears that all tissues probably contain adult stem cells. Most tissues contain only tiny numbers of stem cells. The exception is bone marrow and umbilical cord blood which contains relatively high numbers of stem cells. In each tissue, adult stem cells are used to produce new mature cells as old ones die in the natural processes of ageing. They may also be activated by disease or injury.

Due to their small numbers isolation of adult stem cells is difficult but they have been successfully isolated from the brain, bone marrow, blood, muscle, skin, lung, pancreas and liver. To date the majority of research has been carried out on haematopoietic stem cells isolated from bone marrow and umbilical cord blood and on mesenchymal stem cells which can also be sourced from the bone marrow and some other tissues. Mesenchymal stem cells are the stem cells that form our fat, muscle, bone and cartilage and they can also differentiate into nerve cells.

Haematopoietic stem cells are the stem cells from which all blood cells and many of the cells of our adult immune system are derived. These are the stem cells with the longest history of clinical use in treating disorders such as leukaemia via bone marrow transplants. There has recently been much interest in whether haematopoietic stem cells can be caused to differentiate into non blood cells, such as heart muscle cells or even nerve cells.

Mesenchymal stem cells can be found in the bone marrow but are also found in several other sites in the body such as the placenta. Mesenchymal stem cells are particularly interesting to researchers because in addition to their capacity to differentiate into the multiple cell types listed above, they also have anti-inflammatory and immune-suppressing properties. This means that mesenchymal stem cells could be useful as therapies for diseases caused by immune attack on specific tissues.

Umbilical cord blood stem cells are a type of tissue specific stem cell. Blood can be collected from the umbilical cord of a newborn baby shortly after birth. This blood is rich in haematopoietic stem cells that can be used to generate blood cells and cells of the immune system. Cord blood stem cells may be used to treat a range of blood disorders and immune system conditions such as leukaemia, anaemia and autoimmune diseases. Once collected, cord blood can be stored in a cord blood bank for future use as a potential source of stem cells for transplant.

How to Increase Stem Cell Survival

Even if stem cells have an intrinsic capacity to create new tissue, they are unlikely to do so if the recipient environment is not conducive to regeneration.

Increasing Stem Cell Survival by Preconditioning

Survival of injected stem cells is influenced by the recipient environment. For instance, Laflamme et al., injected human mesenchymal stem cells (hMSCs) into areas of rat peri-infarct and normal myocardium. After 28 days, 90% of labeled hMSCs were found in the normal myocardium, whereas in the infarcted myocardium only 18% of injected human cells were detectable. Ischemia is thought to create an inhospitable environment by inducing local expression of inflammatory cytokines that promote cell apoptosis. Alternatively, cell survival can be enhanced by inhibition of local inflammation. Adenosine in addition to its well known cardiac effects is a potent natural anti-inflammatory agent. Patel et al showed that in canine myocardial infarction, an adenosine agonist reduced infarct size by 16% when given at the time of coronary reperfusion. In continuation of attempts to improve cell survival, Pons et al showed that injection of vascular endothelial growth factor to an MI heart increased MSCs survival by 2.9 fold in ischemic myocardium and improved therapeutic effects of MSCs for treatment of MI.1 The timing of therapies to reduce ischemia-induced cell apoptosis appears to be critical. For instance, when the large randomized, placebo-controlled AMISTAD-2 trial1 was subjected to adenosine infusion as an adjuvant to thrombolytic reperfusion therapy, within the first 3.2 hours onset of evolving MI, infarct size was reduced 14% more compared with therapy after that cut-point

Promotion of Cell Growth and Differentiation

Many factors that promote growth and differentiation are also anti-apoptotic. For instance, growth factor, G-CSF1, not only substantially inhibits apoptosis, but also promotes cell proliferation. Bartunek et al., pretreated MSCs with fibroblast growth factor (FGF) to induce a 10% increase in regional wall thickening of the infarcted territory in the chronic dog MI model.1 lipopolysaccharide2 is also one of the other pro-proliferative factors that have been tested.

What Can Patients do to Increase Cell Survival?

Anything that improves general health, immune status and circulation will improve the effectiveness of stem cell treatment.

A. Exercise – Has been shown to increase the number of stem cells in the circulation. A vigorous circulation is essential for cell growth.

B. Diet – Everything that you eat will have an impact on cell survival. Fruit and vegetables rich in antioxidants and phytonutrients will actively support an optimal environment for cell growth. Saturated fats and high GI carbohydrates have been shown to be inflamatory and have a negative effect.

C. Supplements – There are many supplements that look very promising. These include:-

• Resveratrol
• Carnatine
• Colostrum
• Fish Oil
• Vitamins, Minerals and Antioxidants