Swiss biopharmaceutical company AC Immune SA has announced positive interim results from the Phase II trial of its Parkinson’s disease (PD) treatment, ACI-7104.056.

The data offer early evidence that targeting the underlying pathology of PD with a therapeutic vaccine could slow the progression of the debilitating movement disorder. The candidate is an active immunotherapy designed to stimulate the patient’s own immune system to produce antibodies against pathological forms of alpha-synuclein (a-syn), a protein that forms toxic clumps known as Lewy bodies in the brains of people with PD.

Following the news, the company’s stock is currently trading at $3.39, up 21.5% from market close on 10 December. AC Immune reported cash reserves of CHF 108.5 million ($136 million) as of September 30.

A First-of-its-Kind Approach Shows Potential

According to the company, this is the first time an active immunotherapy has generated data suggesting a potential slowing of PD progression. The interim analysis from the placebo-controlled, and biomarker-based VacSYn Phase II trial (NCT06015841) involved 34 patients with early-stage PD, with participants treated for at least 12 months.

“The interim Phase II data shows the potential of our ACI-7104.056 active immunotherapy to slow the progression of Parkinson’s disease,” said Dr. Andrea Pfeifer, CEO of AC Immune.

A core finding from the interim analysis was a 100% responder rate for immunogenicity. All participants receiving the therapy developed robust antibody responses against the target a-syn antigen, with antibody levels in the blood over 500-fold higher than those in the placebo group. Critically, these antibodies successfully crossed the blood-brain barrier, with significantly elevated levels also detected in the cerebrospinal fluid (CSF).

The therapy’s potential disease-modifying effect is supported by the stabilization of key disease biomarkers in the treatment arm, as detailed in the accompanying investor presentation:

• Total a-syn levels in the CSF stabilized in treated patients but decreased in the placebo group, a sign that the therapy may be engaging and clearing the pathological protein from the brain.
• Levels of neurofilament light chain (NfL), a marker of neuronal damage, remained stable in the treatment group but increased in the placebo group, suggesting a potential slowing of neurodegeneration.
• Trends toward stabilization were also observed in plasma GFAP (a marker of neuroinflammation) and in DaT-SPECT imaging, which measures the integrity of dopamine-producing neurons.

Clinical Measures and Safety Profile

Early clinical assessments also hinted at a beneficial effect. Scores on the motor examination section (Part III) of the standard MDS-UPDRS rating scale suggested a trend toward stabilization in the active treatment group at 74 weeks, whereas the placebo group showed the expected worsening. This difference was more pronounced when assessing patients in the medication “OFF” state.

The treatment demonstrated a favorable safety profile to date. No clinically relevant or serious adverse events were considered related to the study drug. The most common side effects were transient injection site reactions, headaches, and fatigue.

Based on these promising interim results, AC Immune plans to engage with regulatory authorities to discuss a clinical development plan aimed at potential registration. Final data from this part of the study is expected in mid-2026.

AC Immune’s pipeline includes several active immunotherapy and small molecule programs targeting proteins implicated in Alzheimer’s and Parkinson’s diseases.