Throughout the world, many researchers are pursuing a variety of ways to repair or replace neurons and other cells in the brain. These experimental treatments are still being worked out in animal models and cannot, at the present time be considered as therapies for human beings. At least not yet. Some of these treatments have been discussed in previous future medicine articles (see: Trophic Factors, Engineered Antibodies and Small Molecules and RNA). In this article cell and gene therapy will be briefly discussed.

Cell Therapy: Neuronal Stem Cells

Embryonic neuronal stem cells, which are unspecialized cells that give rise to cells with specific functions, have been identified by scientists in the brain and spinal cord of embryonic and adult mice. These cells are able to continually produce all three major cell types found in the brain:

• Neurons: the cells responsible for signal transmission.
• Astrocytes: the cells that protect and nourish the neurons.
• Oligodendrocytes: the cells that surround the axons (the long branch of the neuron that conducts the signal away from the cell body) and allow them to conduct their signals efficiently.

The production abilities of these stem cells could one day be used to replace brain cells that have succumbed to disease. A more limited type of stem cell has been discovered in the adult nervous system in various kinds of tissue. This raises the possibility that these adult stem cells could be pharmacologically directed to replace damaged neurons.

Gene Therapy: the Trojan Horse Approach

A variety of viruses that are being studied by scientists could eventually be used to carry therapeutic genes to the brain unnoticeably (hence ‘Trojan horse’) in order to counteract nervous system diseases. The viruses include the herpes simplex type 1 virus (HSV), adenovirus, lentovirus, adeno-associated virus, and other viruses that are primarily attracted to neuronal cells. All of these viruses have been found to be modifiable to the point that they can carry new genes to cells in tissue cultures and rodent central nervous systems. Recently, HSV and adenovirus vectors have also been evaluated in early stage human trials for treating brain tumors.

So, to conclude this Future Medicine series, it can be stated that these potential therapies are all in their early developmental stages and some difficulties still have to be overcome before they can be applied to human beings. Yet, they will certainly be further developed in the next few years and show great potential in treating diseases that, at present, are very difficult to properly treat.