ACI-7104 VacSYn Phase 2

The research record

This is the project's file for this landmark, as written and checked. Sources are listed at the end; anything not yet confirmed is marked "Not yet verified".

Who

AC Immune SA (Switzerland), which bought the PD01 vaccine programme from AFFiRiS in an all-stock deal valued at US$58.7 million in July 2021. Trial NCT06015841.

What happened

• Design. VacSYn is an adaptive, randomised, double-blind, placebo-controlled Phase 2 in early Parkinson's. Part 1 tests safety, tolerability and antibody response; Part 2 is meant to give evidence of clinical effect for a Phase 3 decision. The drug is ACI-7104.056, which the company calls an optimised formulation of PD01 (a peptide joined to a carrier protein, with an adjuvant to boost the immune response).
• Part 1. Started 24 July 2023. 34 people were randomised, 25 to vaccine and 9 to placebo.
• Result (23 September 2026, company release). Safety and tolerability, antibody response and the other primary measures were met at week 100. 100% of vaccinated people made antibodies to the PD01 antigen after three injections, and antibodies reached spinal fluid in all. Total alpha-synuclein in spinal fluid showed a signal the company calls preliminary evidence of target engagement. No motor or other clinical scores were reported; the company says the sample was too small to judge them. An earlier December 2025 company interim release reported on 20 people at 18 months (via Alzforum).
• Next. The company plans to submit a Part 2 expansion (up to 150 people) to the FDA, with meetings expected in early 2027. Registry (updated 1 October 2026): active, not recruiting; estimated primary completion June 2028; no results posted.

Why it moved us toward a cure

If an antibody made by the body slows spread of synuclein, it would be a cheaper, longer-lasting alternative to infusions like prasinezumab (landmark 63). This trial builds on the human safety data from PD01A (landmark 324) and the original mouse idea (landmark 103). Another vaccine, UB-312, had weak brain exposure (landmark 183).

Outcome

Pending. Safety and immune response are shown; efficacy is open. The registry's estimated primary completion is June 2028.

Sources

• AC Immune release, 23 Sep 2026
• ClinicalTrials.gov NCT06015841 (API v2, read 19 Oct 2026)
• AC Immune acquisition, Biopharma-Reporter, 27 Jul 2021 · MedCity News · Alzforum
• Not yet verified: doses; the structure of the carrier; the December 2025 interim figures (Alzforum, press release not read); what the registry's estimated enrolment of 150 covers; any peer-reviewed report.