**6. Conclusion**

In this chapter, we introduced the current application of stem cells in ALS (summarized in Figure 1). There are three points we should keep in mind about this topic. First, stem cell therapy design should be aimed at neuroprotection rather than motor neuron replacement. Motor neuron replacement is technically difficult to achieve. Also, in theory it will not bring much improvement to the patients because the evidence shows that glial cells are the actual determinant of ALS disease progression. Secondly, combining stem cell transplantation and growth factor delivery provides the best result in slowing disease progression and prolonging survival, as the two greatly complement each other. Finally, we are now convinced that injections of stem cells in multiple sites are needed in order to alleviate symptoms of ALS. There should be at least one injection that focuses on protecting cell bodies of motor neurons and another that aims to maintain neuromuscular connections. To sum up, stem cell applications have made a lot of contributions to ALS research and have great potential to bring breakthroughs to the field in the near future.

Fig. 1. Schematic illustration of possible stem cell interventions for ALS therapies. These could include: (1) Motor neuron replacement, differentiation of neural progenitor cells to motor neurons and projection to the periphery; (2) Differentiation and replacement of dysfunctional astrocytes; (3) Modulation of immunological environment around the degenerating motor neuron; (4) Trophic/growth factor delivery via stem cells to provide neuroprotective support for the endogenous populations; (5) Local delivery of growth factors to support neuromuscular junctions and axon integrity.
