ACI-35 is an investigational anti-tau vaccine being developed by Acimmune as a possible treatment of Alzheimer’s disease. In 2015, Acimmune outlicensed the vaccine to Janssen Pharmaceuticals.

How ACI-35 works

Alzheimer’s disease, a neurodegenerative disorder, results in a slow decline in memory and thinking abilities as it progresses. Its symptoms are thought to be caused by protein plaques and tangles responsible for the death of nerve cells and tissue loss in the brain. Tangles result from the build-up of a protein called tau. These tau protein tangles deprive cells of essential nutrients and eventually kill them.

ACI-35 is a liposome-based vaccine consisting of a synthetic peptide antigen (a molecule capable of inducing an immune response) and a liposomal anchor, to mimic the pathological shape of the tau protein. In this way, it activates the immune system to produce antibodies that selectively target the misfolded and pathogenic forms of the tau protein.

ACI-35 in clinical trials

The safety and efficacy of ACI-35 were first tested in 2013 in a preclinical study on a mouse model of tauopathy, a condition that results from the pathological aggregation of tau protein in the brain. Results were published in the scientific journal Plos One, showing that the vaccine produced a rapid and robust immune response against the tau protein. Researchers also verified that long-term vaccination appeared to be safe, reducing tauopathy in the brain of the mice without leading to neuroinflammation or other adverse effects.

A placebo-controlled Phase 1b trial (ISRCTN13033912) was then launched to evaluate the safety, tolerability, and immunogenicity of ACI-35 in patients with mild to moderate Alzheimer’s disease. It compared low, medium, and high doses of ACI-35 to placebo, given as an injection, in 24 patients for a period of six months. After the initial dosing regimen, patients underwent a subsequent booster shot, followed by a six-month safety observation period. The trial finished in June 2017, but results had not been published as of February 2018.

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