Here is an example of ongoing work on stem cell transplants for the treatment of Parkinson's disease, in which the proximate cause of the condition is an accelerated age-related loss of a small but vital population of dopamine-generating neurons in the brain. Similar transplant therapies have been tested in a number of species, and in human patients over the past decade, but there is a great variety of possible cell sources and methodologies of treatment. Progress towards a standardized therapy emerging from all of this has been frustratingly slow.
Human parthenogenetic stem cells, derived from unfertilized oocytes, can be used to generate unlimited supply of neural stem cells for transplantation. Researchers testing the potential of cell therapy for treating Parkinson's disease (PD) has found that grafting human parthenogenetic stem cell-derived neural stem cells (hpNSCs) into non-human primates modeled with PD promoted behavioral recovery, increased dopamine concentrations in the brain, and induced the expression of beneficial genes and pathways when compared to control animals not transplanted with stem cells.
The researchers also reported that the intracerebral injection and transplantation of hpNSCs was "safe and well-tolerated" for the two transplantation test animal groups with moderate to severe PD symptoms. "Previous clinical studies have shown that grafted fetal neural tissue can achieve considerable biochemical and clinical improvements in PD, however the source of fetal tissue is limited and may sometimes be ethically controversial. Human parthenogenetic stem cells offer a good alternative because they can be derived without destroying potentially viable human embryos and can be used to generate an unlimited supply of neural cells for transplantation."
PD is characterized by a profound loss of function of the brain's basal ganglia, resulting in a loss of dopamine neurons. Experiments using stem cells have offered benefits in pre-clinical studies, but have also provided "a wide variety of patient outcomes." This study used hpNSCs because the cells demonstrate characteristics of human embryonic stem cells, but are not sourced from viable embryos, which may be destroyed in the process. Previous studies with hpNSCs had shown that the cells could also be "chemically directed" to differentiate into multipotent neural stem cells and were able to be frozen for future use. While the study was designed to determine whether the test animals showed greater improvement than the control group, researchers added that a longer outcome period than 12 months may have demonstrated continued improvement and divergence from controls.