A potential approach to treating Parkinson’s disease has emerged in an animal study.

Researchers from Kyoto University reported promising results from a trial that entailed implanting induced pluripotent (iPS) stem cells into the brains of monkeys who had a version of the neurodegenerative disorder caused by a neuron-killing toxin.

Pluripotent stem cells have the ability to form any cell type in the body, which is a feature scientists believe could help replace dead neurons that produce dopamine, also known as dopaminergic (DA) neurons in people diagnosed with Parkinson’s, according to Nature. The iPS variety are made by coaxing adult cells into an embryonic-like state, but are not associated with the same ethical concerns as their actual embryonic counterparts.

Here’s how this experiment worked.

The scientists were able to morph iPS cells derived from healthy patients as well as individuals with Parkinson’s into dopamine-producing neurons, which were then transplanted into the brains of the macaque monkeys used as test subjects.

The success of the trial was determined based on metrics including the quality of the cells, as well as certain genes that yielded different expression levels like Dlk1.

"Dlk1 is one of the predictive markers of cell quality for DA neurons made from embryonic stem cells and transplanted into rat. We found Dlk1 in DA neurons transplanted into monkey. We are investigating Dlk1 to evaluate the quality of the cells for clinical applications,” said Tetsuhiro Kikuchi, a neurosurgeon who participated in this study, in a statement.

The new brain cells survived for at least two years and established connections with the monkey’s brain cells.

There was also no sign that the transplanted cells developed into tumors or evoked an immune response that could not be dealt with via immune-suppressing drugs.

Next, the team hopes to start clinical trials by the end of next year. Successfully refining this manufacturing process when it comes to these cells could ultimately yield treatments for Parkinson’s that can address the underlying cause of the condition instead of just the symptoms.

Results from this study appeared in the journal Nature Communications.