AC Immune Positive Interim Phase 2 Data on ACI-7104.056 Support Potential Slowing of Progression of Parkinson's Disease Results show, for the first time, that targeting underlying a-syn pathology with an ac

AC Immune Positive Interim Phase 2 Data on ACI-7104.056

Potential Slowing of Progression of Parkinson's Disease

Lausanne, Switzerland, December 11, 2025 -- AC Immune SA (NASDAQ:

ACIU), a clinical-stage biopharmaceutical company pioneering precision therapeutics for neurodegenerative diseases, today announced positive

interim safety and efficacy results from the Phase 2 VacSYn trial of its wholly-owned anti-alpha-synuclein (a-syn) active immunotherapy

ACI-7104.056 in early Parkinson's disease (PD).

The results show, for the first time, that targeting a-syn pathology

with an active immunotherapy could potentially slow the rate of progression of PD. Disease-related biomarker results, including a-syn

CSF levels and neurofilament light (NfL), suggest stabilization of PD pathology. Plasma glial fibrillary acidic protein (GFAP) and dopamine

transporter (DaT) SPECT imaging show trends toward disease modification. In addition, total scores on Part III of the Movement Disorder

Society-Unified Parkinson's Disease Rating Scale (MDS-UPDRS) are suggestive of a trend for stabilization.

Dr. Andrea Pfeifer, CEO of AC Immune SA, commented: "The

interim Phase 2 data shows the potential of our ACI-7104.056 active immunotherapy to slow the progression of Parkinson's disease

and hold the promise of a tremendous step forward for millions of patients. The consistent signs of efficacy, combined with the continuing

strong safety record, underline ACI-7104.056's potential to transform PD treatment and are a strong basis for accelerating development.

We will discuss ACI-7104.056 with the regulators to establish a clinical development plan towards registration."

Werner Poewe, MD, emeritus Professor of Neurology at Innsbruck Medical

University and a leading expert in Parkinson's disease, commented: "The remarkable consistency of the trends observed

across multiple disease-related biomarkers and on clinical assessments in the treatment arm are very promising. Importantly, clinical

and biomarker outcomes provide signals that the immunological response elicited by ACI-7104 may be associated with beneficial effects

on PD progression. Overall, these findings are highly encouraging and fully support further development of the program. If further substantiated

the current data would have major implications for future PD therapy. For the first time, we are seeing signals that targeting the underlying

pathology of Parkinson's with active immunotherapy could slow disease progression."

VacSYn (ClinicalTrials.gov: NCT06015841)

is an adaptive, 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-7104.056 or placebo, respectively. All participants in this interim analysis have been treated

for at least 12 months (i.e. 48 weeks), with 20 participants treated for up to 18 months (i.e. 74 weeks).

Interim results showed all target criteria for immunogenicity were

The stabilization of disease-relevant biomarkers in the central nervous

system (CNS), suggests slowing of Parkinson's disease pathology, with potential disease modification.

Clinical measures of motor symptoms also suggest a trend for stabilization

of disease in the active arm of the study.

Interim results from weeks 50 and 76 continue to demonstrate that ACI-7105.056

is generally safe and well-tolerated enabling a positive benefit/risk ratio. No clinically relevant or serious adverse events (AEs) considered

related to the study drug have been reported to date. The most common AEs were transient injection site reactions (56%), headaches (15%)

Based on these promising interim results, AC Immune aims to seek regulatory

feedback on an ACI-7104.056 clinical development plan to potentially accelerate towards registration. Final data from Part 1 of the VacSYn

trial are expected in mid-2026.

AC Immune management will host a conference call and webcast today

at 9:00am ET / 15:00 CET to provide an overview of the data, followed by a Q&A session.

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) 207 107 06 13

United States: +1 (1) 631 570 56 13

Other international numbers available HERE

Webcast Link: https://event.choruscall.com/mediaframe/webcast.html?webcastid=6bsnwXCG

A live and archived webcast will also be accessible in the Investors

section of the Company's website at https://www.acimmune.com/.

ACI-7104.056 is an optimized formulation of its clinically validated

anti-a-syn predecessor active immunotherapy which 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.

AC Immune SA is a clinical-stage biopharmaceutical company and a global

leader in precision prevention for neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, and NeuroOrphan

indications driven by misfolded proteins. The Company's two clinically validated technology platforms, SupraAntigen

and Morphomer , fuel its pipeline of first- and best-in-class assets, which currently features a range of therapeutic and

diagnostic programs, including candidates in Phase 2 and Phase 3 development. AC Immune has a strong track record of securing strategic

partnerships with leading global pharmaceutical companies, resulting in substantial non-dilutive funding to advance its proprietary programs

and >$4.5 billion in potential milestone payments plus royalties.

SupraAntigen is a registered trademark of AC Immune

SA in the following territories: AU, EU, CH, GB, JP, RU, SG and USA. Morphomer is a registered trademark of AC Immune

SA in CA, CN, CH, EU, GB, JP, KR, NO, RU and SG.

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.

For further information, please contact:

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.