AC Immune posts 100% antibody response in Parkinson’s trial
The 34-patient Part 1 focused on safety, tolerability and immunogenicity; Part 2 is designed to provide evidence of clinical activity.
Rhea-AI Filing Summary
AC Immune SA reported safety and immunogenicity results through week 100 in Part 1 of its Phase 2 VacSYn trial of ACI-7104 in early-stage Parkinson’s disease. All primary endpoints—safety, tolerability and immunogenicity—were met; the study included 34 patients, with 25 receiving ACI-7104 and nine receiving placebo. The company reported a 100% antibody response after three immunizations and antibody penetration into cerebrospinal fluid.
Exploratory analyses found a signal in total α-synuclein in cerebrospinal fluid, described as preliminary evidence consistent with target engagement. Part 1 was not designed to evaluate biomarkers or clinical outcomes. The trial continues in a two-year extension, and Part 2 is advancing toward initiation; its design is being consolidated for FDA review, with meetings expected in early 2027.
Positive
- VacSYn Part 1 met all three primary endpoints through week 100.
Negative
- None.
Filing Explained
AC Immune says Part 2 is intended to test clinical activity and provide evidence for a Phase 3 decision; its design is still being consolidated for FDA review, with discussions expected in early 2027.
Key Figures
Key Terms
immunogenicity medical
cerebrospinal fluid medical
target engagement medical
aggregated species medical
FAQ
AI-generated questions and answers. How Rhea-AI works. Not financial advice.
What did ACIU report about the VacSYn Phase 2 trial?
How many patients were in ACIU’s VacSYn Part 1?
What antibody response did ACI-7104 produce in ACIU’s trial?
Did ACIU report target engagement in the VacSYn trial?
What is next for ACIU’s ACI-7104 trial?
AI-generated analysis. How Rhea-AI works. Not financial advice.
UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549
FORM 6-K
REPORT OF FOREIGN PRIVATE ISSUER PURSUANT TO RULE 13a-16 OR 15d-16 UNDER THE SECURITIES EXCHANGE ACT OF 1934
For the month of September, 2026
Commission file number: 001-37891
AC IMMUNE SA
(Exact Name of Registrant as Specified in Its Charter)
EPFL Innovation Park
Building B
1015 Lausanne, Switzerland
(Address of Principal Executive Offices)
Indicate by check mark whether the registrant files or will file annual reports under cover of Form 20-F or Form 40-F.
Form 20-F ☒ Form 40-F ☐
On September 23, 2026, AC Immune SA issued a press release announcing 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). A copy of the press release is attached as Exhibit 99.1 to this Report on Form 6-K.
This Report on Form 6-K (excluding Exhibit 99.1) shall be deemed to be incorporated by reference into the registration statements on Form F-3 (File Nos. 333-227016, 333-249655 and 333-277940) and Form S-8 (File Nos. 333-213865, 333-216539 and 333-233019) of AC Immune SA and to be a part thereof from the date on which this report is filed, to the extent not superseded by documents or reports subsequently filed or furnished.
EXHIBIT INDEX
Exhibit | | Description |
99.1 | | Press Release dated September 23, 2026 |
SIGNATURE
Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.
| AC IMMUNE SA | |
| | |
| By: | /s/ Martin Zuegel |
| | Name: Martin Zuegel |
| | Title: Interim Chief Executive Officer |
| | |
| | |
| By: | /s/ Christopher Roberts |
| | Name: Christopher Roberts |
| | Title: Chief Financial Officer |
| | |
Date: September 23, 2026 | | |
Exhibit 99.1
PRESS RELEASE
AC Immune Reports Positive Safety & Immunogenicity at week-100 in Part 1 of VacSYn Phase 2 Trial of ACI-7104
Lausanne, Switzerland, September 23, 2026 – 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.
Martin Zügel, Interim CEO of AC Immune SA, commented: “The results from the complete data set at week-100 in Part 1 are encouraging, with all primary endpoints met, strong immunogenicity demonstrated, and a 100% response rate. This program is one of our strongest active immunotherapies, with ACI-7104-induced antibodies demonstrating preferential binding to aggregated a-syn species. We will now refine our approach to the next development steps in the program and discuss our plans with regulators before embarking on an expanded Phase 2 trial designed to provide evidence of clinical activity as the basis for entry into Phase 3.”
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Exhibit 99.1
PRESS RELEASE
Günther Staffler, Executive Vice President, Development at AC Immune SA, commented: “We are pleased to have observed strong and boostable immune responses, with significant antibody penetration into the CSF and signals for target engagement. Together with the favorable safety profile through week-100, and exploratory correlations between antibody titers and disease activity measures, we are confident that these results provide a strong foundation for the continued development of ACI-7104 into Part 2.”
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Ends
For further information, please contact:
SVP, Investor Relations & Corporate Communications | |
International Media Optimum Strategic Communications |
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About VacSYn
VacSYn (ClinicalTrials.gov: NCT06015841) is an adaptive, randomized, double-blind, placebo-controlled, and biomarker-based Phase 2 study in patients with early PD, consisting of two parts. Part 1 includes 34 patients randomized 3:1 to receive ACI-7104 or placebo, respectively. The results reported
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Exhibit 99.1
PRESS RELEASE
today include data from all participants 100 weeks since initiation of treatment. 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 and support a Phase 3 decision.
About ACI-7104
ACI-7104.056 is an optimized formulation of its clinically validated anti-a-syn predecessor active immunotherapy that generated a target-specific antibody response against pathological oligomeric a-syn to inhibit spreading and downstream neurodegeneration in early Parkinson’s disease. The accumulation of alpha-synuclein protein aggregates has been shown to cause inflammatory stress in cells and contribute to the degeneration of neurons in the brain. It has been known to play a key role in the development of neurodegenerative diseases such as Parkinson’s Disease.
About AC Immune SA
AC Immune (NASDAQ: ACIU) is a clinical-stage biopharmaceutical company developing a pipeline of products, including both active immunotherapies and small molecules, targeting key misfolded proteins and pathways for the treatment of multiple neurodegenerative diseases. The company has a growing focus on its wholly owned proprietary clinical-stage programs, including: ACI-7104, an active immunotherapy targeting α-synuclein (α-syn) in Parkinson's disease; and ACI-19764, a small molecule inhibitor of the NLRP3 inflammasome. In addition, an early-stage small molecule development program targeting intracellular a-syn is advancing towards the clinic.
ACIU has a strong track record of securing strategic partnerships with leading global pharmaceutical companies, resulting in substantial non-dilutive funding and >$4.5 billion in potential milestone payments, plus royalties from sales. ACIU’s pharma-partnered programs, all in Alzheimer’s disease, include: a collaboration on ACI-24, an active immunotherapy targeting Abeta; a collaboration on ACI-35 targeting phospho-Tau; and a collaboration developing brain-penetrant small molecule drugs targeting intracellular pathologic Tau.
All trademarks used or mentioned in this release are protected by law. The information on our website and any other websites referenced herein is expressly not incorporated by reference into, and does not constitute a part of, this press release.
Forward looking statements
This press release contains statements that constitute “forward-looking statements” within the meaning of Section 27A of the Securities Act of 1933 and Section 21E of the Securities Exchange Act of 1934. Forward-looking statements are statements other than historical fact and may include statements that address future operating, financial or business performance or AC Immune’s strategies or expectations. In some cases, you can identify these statements by forward-looking words such as “may,” “might,” “will,” “should,” “expects,” “plans,” “anticipates,” “believes,” “estimates,” “predicts,” “projects,” “potential,” “outlook” or “continue,” and other comparable terminology. Forward-looking statements are based on management’s current expectations and beliefs and involve significant risks and uncertainties that could cause actual results, developments and business decisions to differ materially from those contemplated by these statements. These risks and uncertainties include those described under the captions “Item 3.
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Exhibit 99.1
PRESS RELEASE
Key Information – Risk Factors” and “Item 5. Operating and Financial Review and Prospects” in AC Immune’s Annual Report on Form 20-F and other filings with the Securities and Exchange Commission. Forward-looking statements speak only as of the date they are made, and AC Immune does not undertake any obligation to update them in light of new information, future developments or otherwise, except as may be required under applicable law. All forward-looking statements are qualified in their entirety by this cautionary statement.
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