A blood product that stopped Alzheimer's disease from worsening for three years in some patients is being hailed as an unexpected medical breakthrough.
Experts were surprised by the results because the drug, designed to boost the immune system rather than treat Alzheimer's, stabilised the incurable brain disease that typically worsens in a matter of months.
Although the strongest benefit was in just four patients, doctors hope a bigger trial that will include the US, Australia and England will confirm the drug's promising results.
The phase-two trial of the drug, made by pharmaceutical giant Baxter International, was presented by a team from New York's Weill Cornell Medical College at an Alzheimer's Association international conference in Vancouver this week.
Known generically as intravenous immunoglobulin, or IVIg, the therapy is made from natural antibodies taken from healthy blood donors and is usually used to fight infections in patients with weakened immune systems.
It is thought to work against Alzheimer's by clearing toxic proteins called beta amyloid from the brain.
All 11 patients given the drug for three years showed improvements in thinking abilities, memory and daily functioning.
The four patients given the most effective dose showed no decline.
Scientists say the study is too small to show whether the drug will prove effective against Alzheimer's on a wider scale but to have the disease stabilise in four patients treated for three years with the same dose was an unexpected but positive finding.
Neuroscientist Bryce Vissel, from Sydney's Garvan Institute of Medical Research, said the drug showed real promise.
"It's potentially very exciting as a treatment for this devastating disease where there is a progressive decline and the projected number of people to get it is outrageously high," he said.
"Because it's an approved drug already, we know it's safe so it doesn't have to go through all the safety trials."
Dr Vissel said that in simple terms, Alzheimer's was almost like an autoimmune disease of the brain, which helped explain why the immune system drug appeared to be so effective.
Having a bigger trial in Australia was good news for local patients.
"To see four patients have three years without further progression is pretty exciting and offers real hope to people who are pretty scared about this disease," he said.