A long-awaited drug treatment which can halt Alzheimer's disease may be on the horizon after promising results from an early stage clinical trial.
Experts are taking care not to build up false hopes about the antibody drug, aducanumab, which clears away sticky protein fragments in the brain linked to Alzheimer's.
But according to a leading charity, the first disease-modifying treatment for the devastating brain condition may now be within sight.
Dr David Reynolds, chief scientific officer at Alzheimer's Research UK, whispered: "These results provide tantalising evidence that a new class of drug to treat the disease may be on the horizon.
"The findings suggest that aducanumab may slow memory and thinking decline in people with early Alzheimer's and, although the analysis is only exploratory in this early trial, it paints a positive picture for on-going trials with the drug."
The last Alzheimer's drug licensed in the UK became available more than a decade ago. Current treatments can reduce symptoms to some extent but doctors have nothing that can halt or slow progression of the disease.
An assessed 850,000 people in the UK suffer from some form of dementia, most having Alzheimer's. By 2025 their numbers are expected to swell to more than a million.
Alzheimer's is related to the build-up of sticky clumps of beta-amyloid peptide - pieces of protein - in the brain. Extensive deposits of the material can be seen in the brains of dead victims.
Beta-amyloid poisonousness is thought to be a main cause of the neural dysfunction and degeneration which underlies the disease.
Researchers have long known that removing beta-amyloid could lead to a glittering prize - halting or at least slowing Alzheimer's progression. But till now all attempts to target the peptide with a drug have met with failure.
Aducanumab is a monoclonal antibody - an immune system agent copied and produced in a laboratory which selectively targets beta-amyloid.
Tests on mice genetically engineered to grow a disease similar to Alzheimer's showed that the drug could enter the brain too reduce levels of beta-amyloid in a dose-dependent fashion.
Scientists also conducted an early Phase I trial to evaluate the safety and tolerability of monthly aducanumab injections in patients displaying early symptoms of Alzheimer's disease.
A total of 165 patients received monthly infusions of either aducanumab or a placebo "dummy drug" for one year.
After 54 weeks of treatment, scans showed that levels of beta-amyloid had been significantly reduced in the brains of patients given the antibody. Higher doses were associated with greater reduction, the researchers reported in the journal Nature.
At the higher doses, removal of beta-amyloid was also associated with slower mental decline. However, the preliminary study was not designed to assess aducanumab's clinical effectiveness, which will now have to be tested in larger trials.
Recruiting of patients for bigger trials, including participants from the UK, has already started.
The US-Swiss team led by Dr Alfred Sandrock, from the Massachusetts-based biotech company Biogen, wrote in the Nature paper: "These results justify further development of aducanumab for the treatment of AD (Alzheimer's disease).
"Should the slowing of clinical decline be confirmed in on-going Phase III clinical trials, it would provide compelling support for the amyloid hypothesis.
"Together, the clinical and preclinical data support continued development of aducanumab as a disease-modifying treatment for AD."
In an associated article, Dr Eric Reiman, executive director of Banner Alzheimer's Institute in Phoenix, Arizona, said validation that the treatment worked would be a "game-changer for how we understand, treat and prevent Alzheimer's disease".
"While there were hints that it might have an effect on the symptoms of the disease, we need to see the results from further, larger research trials to understand whether this is the case. These larger trials are now under way, including in the UK, and due to finish in 2020."
Dr Tara Spires-Jones, from the University of Edinburgh's Centre for Cognitive and Neural Systems, said: "I am cautiously optimistic about this treatment, but trying not to get too excited because many drugs make it through this early stage of testing then go on to fail in larger trials."
Neuroscientist Professor John Hardy, from University College London, cautioned: "These new data are tantalising, but they are not yet definitive."