The brain has extremely limited capabilities to repair itself, but new strategies are emerging to improve the brain’s ability to regenerate lost neurons and to facilitate the incorporation of implanted stem cells into brain circuitry. There are currently at least eight private and three public companies developing neuroregeneration cell transplant therapies. More than $450 million in venture funding has been invested in companies working on cell replacement and stem cell therapies for brain and spinal cord disorders.

There are significant challenges to overcome when considering the use of implanted cells for neurological diseases. For example, inducing a cell to differentiate into a skin cell or a liver cell is likely to be easier than inducing it to form precise connections with another area of the brain. The chemical signals for forming the appropriate connections in the brain may be present only during certain times of development. Additionally, the character and connections of these new cells must be stable. Despite these complexities, stem cell therapies offer the potential for outright cures to some
neurological diseases.

Recently, we have seen progress in bringing these treatments into human trials. A California company has been in clinical testing of fetal stem cells to treat Batten’s disease since 2005 and expects to complete their Phase I study in early 2009. In December 2008, they received FDA approval to begin trials in a second disorder, Pelizaeus–Merzbacher disease (PMD), a fatal brain disorder that affects mainly young children. In February 2009, the first embryonic stem cell trial for spinal cord injury treatment was also approved. These are slow and precautious steps, centering on untreatable disorders, but cell-based therapeutic candidates for amyotrophic lateral sclerosis, Parkinson’s disease, Alzheimer’s disease, and stroke will soon follow.