AC Immune SA (ACIU) released interim data Thursday from its Phase 2 VacSYn trial that could represent a meaningful step forward in treating Parkinson's disease. The trial tested ACI-7104.056, an active immunotherapy targeting alpha-synuclein, a protein that accumulates abnormally in early Parkinson's patients.
Here's what makes this interesting: the results suggest that targeting this protein with immunotherapy might actually slow disease progression, which would be a first for this treatment approach. The data showed stabilization of disease-related biomarkers, including alpha-synuclein levels in cerebrospinal fluid and neurofilament light.
Why Biomarker Stabilization Matters
Elevated neurofilament light levels signal ongoing neuronal damage or neurodegeneration in Parkinson's disease. When you see those levels stabilize rather than climb, it suggests the treatment might be slowing neuronal damage. The stabilization of these disease-relevant biomarkers in the central nervous system points toward actual disease modification, not just symptom management.
Additional markers showed encouraging trends. Plasma glial fibrillary acidic protein and dopamine transporter SPECT imaging both trended toward disease modification, adding weight to the biomarker story.
Impressive Antibody Response
The immunotherapy generated a robust antibody response against the target antigen with a 100% responder rate. At week 76, two weeks after the sixth immunization, antibody titers in serum were over 500-fold higher than the placebo group.
The antibody responses to both the immunizing peptide and the native alpha-synuclein peptide got boosted after each dose from the second through sixth immunization. The placebo group showed no detectable signal. Importantly, the titers against the target antigen increased with successive immunizations, demonstrating that ACI-7104.056 generates antibodies capable of crossing the blood-brain barrier. In cerebrospinal fluid, average IgG antibody levels were over 500-fold higher than placebo.
Motor Symptoms Show Stabilization
Clinical measurements of motor symptoms also suggested a stabilization trend in the active treatment arm. The total MDS-UPDRS Part III score at week 74 showed the ACIU treatment group didn't demonstrate meaningful progression in the mean total score or change from baseline, while the placebo arm showed the expected increase in mean total score consistent with normal disease progression.
When researchers stratified the MDS-UPDRS Part III score by levodopa ON/OFF state, the difference in change from baseline scores between active treatment and placebo groups became even more pronounced.
Safety Profile Remains Strong
Interim results from weeks 50 and 76 continue showing that ACI-7105.056 is generally safe and well-tolerated. The company expects final data from Part 1 of the VacSYn trial in mid-2026.
AC Immune stock jumped 12.43% to $3.14 on Thursday following the announcement.