(Corrects name of vaccine in para 9 to ACI-24 from ACI-35)
* AC Immune starts world's first trial of anti-pTau vaccine
* Drug targets build-up of tau protein in brain cells
* CEO says open to further partnering deals
* Exploring all options for the company, including IPO
ZURICH, Jan 9 (Reuters) - AC Immune, a privately held biotech company based in Switzerland, has launched the world's first trial of a vaccine against a protein believed to cause Alzheimer's after securing funding from private investors.
Its ACI-35 vaccine aims to stimulate the immune system to produce antibodies which target the tau protein that forms twisted fibres and tangles inside the brain.
Many scientists believe tau is an important cause of Alzheimer's, alongside another protein known as amyloid, that has been the main focus of drug development efforts so far.
Although there is still no treatment that can effectively modify the disease or slow its progression, a number of big pharma companies - including Roche, Eli Lilly, Merck & Co and Johnson & Johnson - are pursuing a variety of approaches to get to the root cause.
AC Immune's most advanced Alzheimer's drug is the anti-Abeta antibody crenezumab which it licensed to Roche's subsidiary Genentech in 2006. Results of a Phase II trial of crenezumab are expected in the first half of this year and will be crucial for the company's next steps.
"At the moment we are keeping all options open," Chief Executive Andrea Pfeifer said in a telephone interview, adding that the company would consider an initial public offering in the United States as an option.
Earlier on Thursday, AC Immune said it had completed a fourth round of financing, raising 20 million Swiss francs ($22 million) from existing investors.
The funds will enable the company to start Phase I clinical trials with ACI-35 earlier than expected and Pfeifer said the company would be open for a partner to advance it into later-stage trials that are costlier and require more patients.
AC Immune has a further vaccine ACI-24 in Phase I/IIa clinical trials to prevent and clear amyloid plaques, another hallmark of the fatal brain-wasting disease.
Despite the company having a promising number of drugs in development for the disease, Pfeifer said it was difficult to predict when one could be on the market.
"I would say however that in the next three to five years there should be a medication for Alzheimer's out there and hopefully it could be one of ours," she said.
Over the past 15 years more than 100 experimental Alzheimer's drugs have failed in tests. Industry analysts believe that the prize for a truly effective drug could be a market worth $10 billion in annual sales. ($1 = 0.9090 Swiss francs) (Reporting by Caroline Copley; Editing by Catherine Evans)