Two small studies published recently in Nature offer early, but important validation that stem cell treatments for Parkinson’s disease are viable.

They also are a step toward a future where stem cells can be used not just to treat, but ideally to repair or prevent damage to the brain. Getting there will take incredible coordination and a continued commitment to understanding the drivers of neurodegenerative diseases; we can’t fix what we don’t know is broken.

The treatments, one originally developed by a team at Memorial Sloan Kettering Cancer Center in New York and the other by researchers in Kyoto, Japan, are the culmination of decades of work to figure out how to turn stem cells into functional therapies for Parkinson’s. (To be clear, these stem cells are designed in a lab and are not the same as the dubious therapies sold in stem cell clinics — none of which are FDA-approved.)

Parkinson’s disease is marked by a loss of neurons that make dopamine, a chemical messenger involved in movement and coordination. By the time someone shows signs of the disease such as a hand tremor or muscle stiffness, they have already lost anywhere from 60 to 80% of those nerve cells in the part of the brain that controls movement.

Since the 1990s, researchers have imagined using stem cells to replace those lost neurons. Finally, it seems, they are figuring out the right set of cues to prompt stem cells to turn into dopamine-producing nerve cells. Moreover, these two experiments, which together tested separate therapies across 18 patients, offered hints that those cells, once implanted in the brain, might work as intended.

The main goal of both studies was to ensure the stem cells were safe, well tolerated and feasible as a therapeutic. So far, so good. There was one small caveat: Because the treatments were made with donor stem cells rather than the patient’s own cells, (an “off the shelf” approach that could make them easier to commercialize), participants initially had to take immunosuppressants to keep their bodies from rejecting the therapy, and some experienced mild to moderate side effects related to those drugs.

Even better, the cells settled right into their environment and seemed to be functional even after people stopped taking immunosuppressants. Once implanted, a relatively straightforward procedure where millions of cells are carefully distributed in a part of the brain, the young nerve cells need to mature and form the right connections to their neighbors before they can start shipping out dopamine. That process takes many months, but the hope is that once that network is in place, these cells could be functional for many years, perhaps even for the rest of a Parkinson’s patient’s life.

Using an imaging technique that lights up the endings of the nerve cells that make dopamine, the researchers showed that people continued to produce more of the neurotransmitter than before the transplant. And both research groups also found promising, but preliminary signs that the approach could improve motor symptoms and potentially quality of life for some patients.

Of course, much more work is needed to prove these treatments work. Researchers must affirm their safety in larger studies and better understand whether these cells remain functional for the long term and can make a meaningful difference in patients’ lives. To that end, BlueRock Therapeutics, a subsidiary of Bayer AG that licensed Memorial Sloan Kettering’s stem cell technology related to Parkinson’s, has begun a Phase 3 trial to test its treatment in roughly 100 people. Multiple other, earlier studies are underway to test other stem cell approaches in Parkinson’s.

Eventually, Parkinson’s patients will have to decide if they even want these therapies. In the years it has taken researchers to get to this promising stage, better ways of delivering dopamine precursors to the brain or treating the movement symptoms of Parkinson’s using deep brain stimulation have emerged.

Regardless, this is an important advance, perhaps even more so for the promise it holds for other brain diseases. Proving that stem cells can be safely implanted in the brain is a step toward researchers’ ultimate dream of designing therapies that go beyond symptoms and can actually fix the brain or even protect it from future damage.

“This is a proof of concept that we can repair parts of the brain, to give it new life and function, which opens the door to other neurological disorders,” says Viviane Tabar, a stem cell biologist and neurosurgeon at Memorial Sloan Kettering Cancer Center.

Designing those therapies is by now the easy part, says Lorenz Studer, director of MSK’s Center for Stem Cell Biology. “Things are going to go much more quickly, from an engineering perspective.”

But, Studer cautions, understanding the right way to apply those tools — in other words, knowing what support cell or nerve cell to deliver into the brain — continues to be a challenge.

There’s a huge amount of work ahead, but this proof of concept in Parkinson’s should be motivation to keep pushing — both at the basic biology and at driving stem cell treatments forward.

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This column reflects the personal views of the author and does not necessarily reflect the opinion of the editorial board or Bloomberg LP and its owners.

Lisa Jarvis is a Bloomberg Opinion columnist covering biotech, health care and the pharmaceutical industry. Previously, she was executive editor of Chemical & Engineering News.

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