Evaluating the Efficacy, Safety, Pharmacokinetics, and Pharmacodynamics of BIIB054 in Participants With Parkinson's Disease
Evaluating the Efficacy, Safety, Pharmacokinetics, and Pharmacodynamics of BIIB054 in Participants With Parkinson's Disease
The primary objective of the study is to evaluate the clinical efficacy of BIIB054 via dose
 response using the change from baseline in Movement Disorder Society-Unified Parkinson's
 Disease Rating Scale (MDS-UPDRS) Total Score.

 The secondary objectives of the study are to evaluate the dose-related safety of BIIB054, to
 evaluate the clinical efficacy of BIIB054 via MDS-UPDRS total score, to assess the
 pharmacokinetic (PK) profile of BIIB054, to evaluate the clinical efficacy of BIIB054 based
 on MDS-UPDRS subparts, to evaluate the pharmacodynamic effects of BIIB054 on the integrity of
 nigrostriatal dopaminergic nerve terminals and to evaluate the immunogenicity of BIIB054.
Inclusion Criteria

 -  Diagnosed with Parkinson's disease (PD) within a maximum of 3 years prior to
 Screening.

 -  Score of ≤2.5 on the Modified Hoehn and Yahr Scale.

 -  Has not received any medication for the treatment of the motor symptoms of PD for at
 least 12 weeks prior to Day 1 and, in the opinion of the Investigator, is not expected
 to require PD treatment for at least 6 months following Day 1. Maximum total duration
 of prior PD regimens should not exceed 30 days. Stable (at least 8 weeks) dosages of
 medications that are used to treat conditions other than PD tremor are allowed.
 Further guidance will be provided by the study's Medical Monitor on a case by case
 basis.

 -  Screening dopamine transporter (DaT)/ single-photon emission computed tomography
 (SPECT) results consistent with neurodegenerative Parkinsonism (central reading).

 -  All women of childbearing potential and all men must practice highly effective
 contraception during the study and for 6 months after their last dose of study
 treatment.

 Exclusion Criteria:

 -  Presence of freezing of gait.

 -  Montreal cognitive assessment (MOCA) score <23 or other significant cognitive
 impairment or clinical dementia that, in the opinion of the Investigator, would
 interfere with study evaluation.

 -  History of or screening brain magnetic resonance imaging (MRI) scan indicative of
 clinically significant abnormality, as read by central reader.

 -  History of severe allergic or anaphylactic reactions, or history of hypersensitivity
 to BIIB054 or any of the inactive ingredients in the drug product or to radioligands
 or iodine used in the study.

 -  Participation in any active immunotherapy study targeting alpha-synuclein.

 -  Use of allowed medications not previously specified at doses that have not been stable
 for at least 8 weeks before Day 1, and/or that are not expected to remain stable for
 the duration of the study.

 -  Clinically significant abnormal laboratory test values at Screening, as determined by
 the Investigator.

 -  Blood donation (1 unit or more) within 8 weeks before Day 1 (must also refrain from
 donating blood for the duration of the study).

 NOTE : Other protocol defined Inclusion/Exclusion criteria may apply