Parkinson’s disease is a degenerative disease of the central nervous system. It results from the death of motor neurons that produce dopamine, a hormone that transmits signals from one neuron to the next. The lack of dopamine means that neurons cannot talk to each other and the major effects are related to control of bodily movements. Two main routes for proposed therapy have been to identify what kills the motor neurons and stop the killing from happening (many research efforts are focused on this in laboratories across the world) or, alternatively, to supply new dopamine-producing neurons to replace the ones that have been killed.
The goal for cell therapists has typically been the latter – can a sufficient number of dopamine-producing neurons be made to replace the dying neurons? Typically, when a certain cell population is lacking, scientists and physicians turn to cell donors, as in the case of bone marrow transplantations or blood donors, which have saved countless numbers of lives over the past decades. However, things are not as simple with neurons as they do not have a readily accessible donor tissue. This is why the discovery of induced pluripotent stem cells in 2006 was so massive. It gave cell therapists a new avenue to explore – normal mature skin cells could be re-programmed backwards into a pluripotent state where they could make essentially all types of cells again. This meant that researchers could imagine taking the skin cells of a person and growing them into whatever cell type they needed without worrying about the complications of immune rejection. Of course the process of creating the specific cell type of interest from these iPS cells is difficult and each cell type takes years to figure out – but it appears that the group of Ole Isacson at Harvard has successfully leveraged this progress in the case of dopamine-producing neurons to scale the therapy up to monkeys.
In this study, Penelope Hallett and colleagues derived iPS cells from two cynomolgus monkeys and then grew these cells in defined conditions to promote the growth of midbrain-like dopamine neurons (basically, cells that do not quite have all the characteristics of the normal dopamine neurons, but importantly, could make dopamine). They next transplanted these cells back into the monkeys to see if the cells could alleviate the disease symptoms. In one of the two animals, the response was quite remarkable with improvements in motor function observed in both the area of the transplantation as well as the opposite side of the brain. Increased motor activity was observed and importantly, because the cells were derived from iPSCs from the same monkey, there was no need for immunosuppression.
One of the other potential concerns of such a therapy would be the longevity of the graft – the ideal scenario would have a one-time transplant that would last a patient’s lifetime. The researchers in this study showed that the iPS-derived neurons lasted for up to two years but have not yet looked at later time points. This is a very promising timeline for future studies and hopefully will pave the way for safety trials and eventually clinical trials in patients with Parkinson’s.
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