LAUSANNE, Switzerland — September 23, 2026
AC Immune SA reported positive safety and immunogenicity results through Week 100 from Part 1 of the Phase 2 VacSYn trial of ACI-7104 in patients with early-stage Parkinson’s disease (PD). The randomized, double-blind, placebo-controlled study met all Part 1 primary endpoints for safety, tolerability and immunogenicity. The analysis included all 34 randomized patients, with 25 receiving ACI-7104 and nine receiving placebo. AC Immune said the results support continued development of ACI-7104 as an active immunotherapy targeting alpha-synuclein (α-syn) in early PD.
ACI-7104 Demonstrates Strong Immunogenicity and CSF Penetration
ACI-7104 was generally safe and well tolerated through Week 100, while demonstrating a 100% antibody response rate against the PD01 immunizing α-syn target antigen after three immunizations. The company also reported antibody reactivity against aggregated forms of α-synuclein, which are associated with Parkinson’s disease pathology. Robust antibody penetration into cerebrospinal fluid (CSF) was observed in all patients, providing evidence that treatment-induced antibodies reached the central nervous system. AC Immune said the immune response was strong and boostable, with preferential binding to aggregated α-syn species.
Exploratory Analyses Show Signals of Target Engagement
Part 1 was not designed to evaluate biomarker or clinical efficacy outcomes, but AC Immune conducted exploratory analyses of CSF biomarkers and clinical measures of disease activity. A signal in total α-synuclein levels in CSF provided preliminary evidence consistent with target engagement, while exploratory correlation analyses identified trends between antibody levels and measures of disease activity. Because the Part 1 sample size was limited and these analyses were exploratory, the findings do not establish clinical efficacy. The company said the observations provide a basis for further investigation in the next stage of development.
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VacSYn Advances Toward Part 2 and FDA Discussions
The VacSYn program is continuing in a two-year Part 1 extension while preparations advance for Part 2, which is intended to provide evidence of clinical activity and support a potential Phase 3 development decision. AC Immune is consolidating the final Part 2 design and plans to submit it to the FDA for review, with regulatory discussions expected in early 2027. ACI-7104 is an optimized formulation of AC Immune’s clinically validated anti-α-syn active immunotherapy approach, designed to generate target-specific antibodies against pathological oligomeric α-syn. The company is evaluating the program as part of its broader pipeline of therapies targeting misfolded proteins and pathways involved in neurodegenerative diseases.
Source :AC Immune,, press release
