AC Immune SA (NASDAQ:ACIU), a clinical-stage biopharmaceutical company developing targeted therapeutics for neurodegenerative diseases, today announced positive safety and immunogenicity results through week-100 in Part 1 of VacSYn, its randomized, double-blind, placebo-controlled Phase 2 trial of ACI-7104 in patients with early-stage Parkinson’s disease (PD). The study is being conducted in two parts with the aim for Part 1 being to show safety, tolerability and immunogenicity while Part 2 is designed to provide evidence of clinical activity as the basis for a Phase 3 decision. The Part 1 data reported today includes results from all 34 patients randomized into the study (25 patients receiving ACI-7104 and nine receiving placebo).

The primary endpoints for Part 1 of the VacSYn trial of ACI-7104 were safety, tolerability and immunogenicity, all of which were met. ACI-7104 was generally safe and well-tolerated and shown to be strongly immunogenic, with 100% of patients developing antibodies against the immunizing a-syn target antigen PD01 after three immunizations. Antibody reactivity against the aggregated species of a-syn was also demonstrated. Robust antibody penetration into the cerebrospinal fluid (CSF) was observed in all patients.

Part 1 of VacSYn was not designed for biomarker or clinical outcomes evaluation; however, additional exploratory analyses included monitoring the impact of ACI-7104 treatment on certain biomarkers (such as total a-syn and Neurofilament Light chain in the CSF), as well as clinical measures of disease activity. A signal was observed for total a-syn in the CSF, providing preliminary evidence consistent with target engagement. Exploratory correlation analyses identified trends suggesting an association between immunogenicity (antibody levels) and disease activity measures. While the sample size in Part 1 was limited, these observations provide a clear basis for further investigation.

The VacSYn trial of ACI-7104 in early-stage Parkinson’s disease continues in Part 1 (2-year extension) and is advancing toward the initiation of Part 2 (expansion). The final design of Part 2 is being consolidated and will be submitted to the FDA for review, with meetings expected early in 2027.