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STEMCELLS RESOLVE ISSUE OVER RETINAL TISSUE

Dr B.S. Chidamber is a vitreo-retinal surgeon and head of the department of Ophthalmology, Welcare Hospital. He has pioneered in starting Vitreo-Retinal centres in various places at Manipal Hospital in Bangalore, India, at Al Nahda Hospital in the Sultanate of Oman and now at Welcare Hospital, Dubai.

What are the different kinds of stem cells and can you elaborate on each of these?

There are many different cells encompassed by the term stem cells. For example Totipotent cells contain the genetic information needed to create all the cells of the body including the placenta. Human embryo has this capacity only in the first few divisions of a fertilized egg. After 3 to 4 divisions these cells become increasingly specialised. As this next stage is reached these cells are called as Pluripotent cells. These cells are also highly versatile and can give rise to any cell type, except the placenta or other supportive tissue of the uterus.

At the next stage, cells become Multipotent stem cells and can give rise to several other cell types. These types are of a limited number. A multipotent cell is hematopoietic cell — blood stem cells that can develop into several types of blood cells but cannot develop into brain cells. At the end of the long chain of cell divisions that make up the embryo are the 'terminally differentiated cells' that are considered to be permanently committed to a specific function.

What are the properties of stem cells?

Stem cells have different properties, functions and living environments. Different stem cells exist at various time points during an individual's lifespan, from conception to old age. Stem cells can routinely be found in embryos, fetuses and in adults. They have the capacity to extensively multiply long-term, produce more identical stem cells by a procedure called "self-renewal". While stem cells themselves are unspecialised, they can produce cells, such as retinal photoreceptors or other characteristic cells of the body. These cells adopt specialised shapes and functions. Such specialisation is called 'terminal differentiation'.

Towards cure of what diseases are stem cells being used in modern day research?

Diabetes, Alzheimer's disease, Parkinson's disease, Spinal paralysis, Strokes, Leukemia, Bone cartilage regeneration, Traumatic nerve injuries, Skin, Hair re-growth are some of the conditions for which it is being tried.

Can you explain stem cells with particular emphasis on the eyes?

In the eye, it has been used to re-grow retinal tissue and cornea. The retina can be compared to the film of a camera. As the film in a camera captures images similarly the retina captures images and conveys it to the brain via the optic nerve in the form of electrical impulses. The retina or the light sensitive layer can be compared to a wet tissue paper in its thickness, has 1.5 million cells and 10 different cellular layers. The central 5mm is the most critical area called the macula, which enables one to see fine vision, perception of colour, depth of vision etc. The rest of the retina aids in the field of vision. The ravages of retinal diseases like Age related Macula degeneration, Diabetic retinopathy, Retinitis pigmentosa are few of the cases where the photoreceptor cells are destroyed, culminating in blindness. Retinal receptors are also destroyed in many intrinsic abnormalities (genetic disorders), or due to death of supportive cells in the retinal pigment epithelium resulting in poor vision or blindness.

Some other parts of the body can cope with similar cell death, because other existing cells in the tissue can divide in a regulated way to new cells that replenish the remaining stock. Unfortunately, this is not the case for mature retinal photoreceptor cells. About 10,000 cells per eye — have retinal stem cells, this number is not adequate to cope with the extent of damage. These way stem cells might be very handy for the purpose of transplant and try recovering the ailing retina of its photoreceptors thus restoring sight.

What kind of research has been done on this subject in recent times?

Pioneering work by Dr Derek Van der Kooy and Dr Martin Friedlander has shown excellent results in mice. Stem cells harvested, were taken and injected into the cavity of the eye (vitreous hum our). The stem cells migrated to the damage or degenerated area. The diseased retina seems to chemically attract these cells via an unknown code. Normal vascular and neuronal structures of the retina were restored in this area. This eye responded to light. The fellow diseased eye, which was used as a control did not show respocce to light. These early fascinating results have tremendous clinical applications.

Besides, work by Dr Michael Young, PhD, and his colleagues from Boston, showed in mice that neuronal stem cells did not induce an immune response though the brain cells did possess antigens when transplanted. It's not far off when this technology can be used to prevent and treat blinding disorders in humans.

How safe is stem cell therapy?

There are risks and side effects associated with stem cell therapy. Human testing is still awaited. Unspecialised stem cells, especially embryonic stem cells have a potential to cause tumours. As with any transplant procedures, there is always a possibility of the cells acting as a vector for infectious diseases. Most of these are being overcome with further research. The need for tissue typing before and immunosuppressive drugs after transplant may be needed.

How bright does the future appear with regard to Stem cell therapy?

Looking at the various procedures being tried, it goes to show the complex interaction required to generate the perception of vision. With the breakthrough just round the corner it is a matter of time, for this riddle to be answered. Now that the human genome has been mapped, the genetic bases of various diseases are being studied. 'Genetic Engineering' combined with stem cell transplant, would become a reality to treat these sight-threatening disorders.

In this era of scientific development and research, the relentless search for new techniques, will keep the hopes of millions of blind people alive that they can enjoy the gift of sight one day.