AC Immune Reports Positive Safety & Immunogenicity at week-100 in Part 1 of VacSYn Phase 2 Trial of ACI-7104
Week-100 Part 1 data show ACI-7104 met safety and immunogenicity endpoints, supporting AC Immune’s progression toward an expanded Phase 2.
Rhea-AI Summary
AC Immune (ACIU) reported that all primary endpoints were met at week-100 in Part 1 of VacSYn, its randomized, double-blind, placebo-controlled Phase 2 trial of active immunotherapy ACI-7104 in early Parkinson’s disease.
The 34‑patient cohort (25 on ACI‑7104, nine on placebo) showed that ACI‑7104 was generally safe and well tolerated and strongly immunogenic, with a 100% antibody response rate after three immunizations against the α‑syn target antigen PD01. Antibody reactivity against aggregated α‑syn species and robust antibody penetration into cerebrospinal fluid (CSF) were observed in all treated patients. Exploratory analyses showed a signal in total α‑syn in CSF, consistent with target engagement, and trends linking antibody levels with disease activity measures. Part 1 (two‑year extension) continues, while the Part 2 expansion design is being finalized for FDA review, with meetings expected in early 2027.
Positive
- All primary endpoints met for safety, tolerability and immunogenicity in Part 1 of the Phase 2 VacSYn trial
- 100% antibody response rate against the α-syn target antigen PD01 after three ACI-7104 immunizations in treated patients
- Robust antibody penetration into cerebrospinal fluid observed in all ACI-7104-treated patients
- Biomarker signal in total α-syn in CSF provides preliminary evidence consistent with target engagement
- Favorable safety profile maintained through week-100 in early-stage Parkinson’s disease patients
- Development advancing with Part 2 Phase 2 expansion design being finalized for FDA review and meetings planned for early 2027
Negative
- None.
News Explained
Part 1 met its safety, tolerability and immunogenicity endpoints, but was not designed to evaluate clinical outcomes; the planned Part 2 expansion is intended to test clinical activity and support a Phase 3 decision.
Key Figures
- Immunogenicity response rate
- 100%
- Patients developed antibodies against PD01 after three immunizations
- Part 1 participants
- 34 patients
- 25 received ACI-7104 and nine received placebo
- Part 1 extension
- 2 years
- VacSYn Part 1 extension
- FDA meeting timing
- Early 2027
- Meetings expected to discuss the future development path
Previous Clinical trial Reports
-
76-week interim VacSYn data showed safety and a 100% immunogenicity responder rate.
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Key Terms
immunogenicity medical
cerebrospinal fluid medical
placebo-controlled technical
double-blind technical
AI-generated analysis. How Rhea-AI works. Not financial advice.
- All primary endpoints of the study were met, with ACI-7104 shown to be generally safe and well tolerated
- Strong immunogenicity demonstrated, with
100% response rate after three immunizations - Clear antibody penetration into the cerebrospinal fluid (CSF) and signals for target engagement
- Discussions with FDA regarding future development path planned for early 2027
- AC Immune to host webcast & conference call today at 10:00am EDT / 16:00 CEST details below
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
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
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.”
Conference call details:
Participants may call the following numbers, 10 – 15 minutes before conference start
Switzerland / Europe: +41 (0) 58 310 50 00
United Kingdom: +44 (0) 203 059 58 63
United States: +1 (1) 631 570 56 13
HD Web Phone™: Click Here
Other international numbers available HERE
Webcast link: https://event.choruscall.com/mediaframe/webcast.html?webcastid=lUHjSJWK
A live and archived webcast will also be accessible in the Investors section of the Company's website at https://www.acimmune.com/.
Ends
For further information, please contact:
| SVP, Investor Relations & Corporate Communications Gary Waanders, Ph.D., MBA AC Immune Phone: +41 21 345 91 91 Email: gary.waanders@acimmune.com | |
| International Media Optimum Strategic Communications Nick Bastin, Joshua Evans, Aoife Minihan, Ben Cowe Phone: +44 (0) 20 4566 8543 Email: acimmune@optimumcomms.com | |
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 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 >
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. 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.
Attachment
FAQ
AI-generated questions and answers. How Rhea-AI works. Not financial advice.
What is the design and purpose of the VacSYn Phase 2 trial?
VacSYn (NCT06015841) is an adaptive, randomized, double-blind, placebo-controlled, biomarker-based Phase 2 study in patients with early Parkinson’s disease, conducted in two parts. Part 1 includes 34 patients randomized 3:1 to receive ACI-7104 or placebo and aims to assess safety, tolerability and immunogenicity. Part 2 is designed to provide evidence of clinical activity and support a Phase 3 decision.
What exploratory biomarker and clinical findings were observed in Part 1?
Part 1 was not designed for formal biomarker or clinical outcomes evaluation, but exploratory analyses monitored biomarkers such as total α-syn and Neurofilament Light chain in CSF, plus clinical disease activity measures. A signal was seen in total α-syn in CSF, consistent with target engagement, and correlation analyses identified trends suggesting an association between antibody levels and disease activity measures.
What are the next development steps for ACI-7104 in Parkinson’s disease?
The Part 1 two-year extension continues and the design of the Part 2 expansion is being consolidated. The company plans to submit the final Part 2 design to the FDA and expects meetings with the agency in early 2027 to discuss the future development path and the Phase 2 expansion intended to provide evidence of clinical activity for a Phase 3 decision.
How can investors and stakeholders access the VacSYn results webcast?
A conference call and webcast are scheduled for today at 10:00am EDT / 16:00 CEST. Participants can join by phone using regional numbers for Switzerland/Europe (+41 (0) 58 310 50 00), the United Kingdom (+44 (0) 203 059 58 63), or the United States (+1 (1) 631 570 56 13), or via the HD Web Phone link provided. A live and archived webcast will also be accessible in the Investors section of AC Immune’s website at https://www.acimmune.com/.