Transplanting cells involves a plethora of different aspect that have to be take in account in preclinical and clinical trials.
The first aspect that should be considered is if the pathology induces the dead of brain cells or rather causes, at the first step the change of cells interaction. A further aspect to be taken in account concerns the possibility of systemic transplantation only when it is known that the BBB is open. Another aspect from the disease side that should be considered is if the pathology induces an inflammatory response, in this case the role of the transplanted cells should be not only substitutional but also anti-inflammatory, likely many stem cells have this feature.
Stem cells used
On these basis the choice of the cells to be used in the transplantation approach can be very wide.
Many different type of stem cells have a potential therapeutic role for the treatment of neurological diseases (Table 2). We can divide the approach in two big branches in function of the role that the transplanted cells are supposed to exert: substitutional and trophic.
In the early age of the stem cells transplantation in neurological diseases the substitutional role was hypothesized and hoped. Many scientific works in animal models have shown that the cells homing in the nervous tissue were not sufficient to exert any effect or to justify any physiological outcome (Pluchino et al., 2003;Bottai et al., 2008;Pluchino et al., 2009;Bottai et al., 2010;Cusimano et al., 2012;Nizzardo et al., 2013).
If the therapeutical approach is performed when the neurological impairment is already wide it is very difficult to be able to reconstitute the tissue and, a fortiori, to rebuild the damaged neural circuits. Indeed, the injury at the level of the spinal cord involves the lost of motor-neurons with long axons that are surrounded by myelin sheets. In these cases the transplanted cells have to reconstitute not only the neurons but also the glia; moreover, they should be able to extend their process in the appropriate direction in order to exert their therapeutic action.
With the actual knowledge it is unlikely that this task could be achieved; however, the combination of transplanting therapies and bio-engineering (constructing scaffolds) could be a new venue for transplantation research in finely structured tissues.
Different type of stem cells used for the treatment of neurological diseases
In a physiological point of view we can divide stem cells in embryonic, fetal and adult cells (Table 2). The difference is the origin, the proliferation and differentiation capability, the telomeres stability.
Embryonic stem cells and induced pluripotent stem cells.
Since the early 80’s (Evans and Kaufman, 1981) it has well known that the ESCs possess high proliferation and differentiation capability and were able to generate a whole mouse (Nagy et al., 1993). In the late nineties it was also demonstrated the possibility to produce...