Target engagement and immunogenicity of an active immunotherapeutic targeting pathological α-synuclein: a phase 1 placebo-controlled trial

Abstract

Investigational therapeutics that target toxic species of α-synuclein (αSyn) aim to slow down or halt disease progression in patients with Parkinson's disease (PD). Here this 44-week, randomized, placebo-controlled, double-blind, single-center phase 1 study investigated safety, tolerability and immunogenicity of UB-312, an active immunotherapeutic targeting pathological αSyn, in patients with PD. The primary outcome measures were adverse event frequency and change in anti-αSyn antibody titers in blood and cerebrospinal fluid (CSF). Exploratory outcomes were changes in clinical scales and biomarker-based target engagement as measured by seed amplification assays. Twenty patients were randomized 7:3 (UB-312:placebo) into 300/100/100 μg or 300/300/300 μg (weeks 1, 5 and 13) intramuscular prime-boost dose groups. Safety was similar across groups; adverse events were mostly mild and transient. Two patients experienced three serious adverse events in total, one possibly treatment related; all resolved without sequalae. Anti-αSyn antibodies in serum from 12/13 and CSF from 5/13 patients who received three UB-312 doses confirmed immunogenicity. Mean serum titers (in log-dilution factor) increased from baseline by 1.398 and 1.354, and peaked at week 29 at 2.520 and 2.133, for 300/100/100 μg and 300/300/300 μg, respectively. CSF titers were 0 at baseline and were 0.182 and 0.032 at week 21, respectively. Exploratory analyses showed no statistical differences in clinical scales but a significant reduction of αSyn seeds in CSF of a subset of UB-312-treated patients. These data support further UB-312 development. ClinicalTrials.gov: NCT04075318 .

Fig. 1. Patient disposition.

Enrolled patients were randomized to placebo (n = 6), UB-312 300/100/100 μg (n = 7) and UB-312 300/300/300 μg (n = 7) treatment groups. The PP population comprised 20 participants up to week 13 and 19 thereafter.

Fig. 2. Epitope-specific anti-αSyn antibody titers in blood and CSF.

UB-312 or placebo were administered at weeks 1, 5 and 13. a, Serum antibody titers increased predominantly after the third vaccination. The definition of seroconversion was met in 12/13 participants receiving all three doses (5/6 in the 300/100/100 μg group and 7/7 in the 300/300/300 μg group). Increases were more pronounced in the 300/100/100 μg treatment group compared with the 300/300/300 μg treatment group. Samples were analyzed in duplicate and data are expressed as logDF mean + s.d. b, CSF antibody titers were more pronounced in the 300/100/100 μg treatment group compared with the 300/300/300 μg cohort; levels were detectable in 4/6 and 1/7 participants, respectively. Samples were analyzed in duplicate and data are expressed as logDF mean + s.d. Numbers per group: placebo, n = 6; 300/100/100 μg, n = 7 up to week 13 and thereafter n = 6 until week 45; 300/300/300 μg, n = 7. logDF, log-dilution factor.

Fig. 3. Evaluation of αSyn seeds in CSF and MDS–UPDRS scores in patients with PD with and without CSF titers.

a, CSF samples collected before treatment (baseline) were serially diluted and tested in the αSyn-SAA (n = 20). Data presented are maximal dilution factor achieved before losing the signal in the αSyn-SAA; the bar represents median ± 95% CI. b, Maximum fluorescence (%CFB, mean ± s.e.m.) in CSF samples collected at baseline, week 21 and week 45 in patients treated with placebo (n = 6), UB-312 300/100/100 μg (n = 6, one patient provided CSF only at baseline and is excluded) or UB-312 300/300/300 μg (n = 6, one individual who was αSyn-SAA negative at baseline is excluded) showed a significant difference between placebo and 300/100/100 μg (two-way ANOVA, time × treatment interaction, P = 0.0343). c, A comparison of the maximum fluorescence (%CFB, mean ± s.e.m.) in CSF samples collected at baseline, week 21 and week 45 showed a significant difference (two-way ANOVA, time × treatment interaction, P = 0.0037) between individuals with (n = 5) versus without (n = 13) detectable antibody titers. d, Maximum fluorescence at EoS (%CFB means of three technical replicates per individual; bar represents median ± 95% CI) shows a significant between-group difference (two-tailed unpaired t-test, P = 0.0094). e, A comparison in CFB (mean ± s.e.m.) in MDS–UPDRS-II score showed a significant difference (unpaired t-test, time × group interaction, P = 0.016) between patients with (n = 5) versus without (n = 13) detectable CSF antibody titers. The subcomponent that showed the greatest difference in this change was ‘Getting out of bed, getting out of a car or standing up from a low chair’ (Supplementary Table 1). A two-way ANOVA with a mixed-effect model was followed by within-group analysis per Benjamini, Krieger and Yekitieli. f, A comparison in the CFB (mean ± s.e.m.) in MDS–UPDRS-III score between patients with (n = 5) versus without (n = 13) detectable CSF antibody titers. A two-way ANOVA was used as per e. In a–f, *P < 0.05 and **P < 0.01. CI, confidence interval.

Fig. 4. Levels of pS129-αSyn in the CSF of patients with detectable CSF antibodies after immunization with UB-312.

CSF samples were analyzed in duplicate using immunomagnetic reduction as described in the methods, in patients with (n = 5) and without (n = 13) detectable CSF antibody titers. Data are expressed as percent CFB, mean ± s.e.m. A Bonferroni multiple comparisons test confirmed a significant difference between groups at EoS, *P = 0.0154.

Extended Data Fig. 1. UB-312 derived antibodies preferentially bind aggregated αSyn and alter the kinetics of αSyn aggregation in the SAA.

(a) Dot blot analyses indicate that IgG fractions and affinity purified antibodies collected from healthy volunteers post-immunization (week 17) preferentially bind aggregates of αSyn derived from patients with MSA or PD, as well as to aggregates of recombinant αSyn. (b) Post-immunization IgG fractions spiked into a buffer containing seeds delay the aggregation of αSyn. Data are means ± SEM. Samples were run in triplicate (c) Post-immunization IgG fractions spiked into a CSF sample from a patient with PD delay the aggregation of αSyn. Data are means ± SEM. Samples were run in duplicate. αSyn-SAA, alpha-synuclein seed amplification assay; Ab, antibody; CSF, cerebrospinal fluid; IgG, immunoglobulin G; MSA, multiple system atrophy; SEM, standard error of the mean; PD, Parkinson’s disease.