The purpose of the study is to evaluate the safety and tolerability after administration of multiple doses and the pharmacokinetics (PK) of single and multiple doses of UCB0599 in healthy study participants and participants with Parkinson's Disease (PD).

Inclusion Criteria:

• Participant must be 40 to 80 years of age inclusive, at the time of signing the informed consent
• Study participant with Parkinson's disease (PD) must have a clinical diagnosis of PD. The following diagnostic criteria must be met: Bradykinesia AND at least ONE of the following: muscular rigidity or resting tremor
• Study participant with PD must have a historic brain image (magnetic resonance imaging (MRI) or computerized tomography (CT) obtained at any point from the time of clinical diagnosis to the time of Screening that does not show any brain abnormalities that could cause symptomatic Parkinsonism
• Study participant must have a Hoehn and Yahr Stage: 1 to 3
• Study participant must be either untreated, or treated with a stable regimen (at least 4 weeks prior to Baseline Visit) of antiparkinsonian drugs and is expected to remain on this regimen for the duration of the study
• Body weight >50 kg (110 lbs) and body mass index (BMI) within the range 18 to 32 kg/m^2 (inclusive)

Exclusion Criteria:

• Study participant has a known hypersensitivity to any components of the study medication or comparative drugs as stated in this protocol
• Study participant has a known relevant allergy, a pre-existing history of a relevant allergic condition, or a predisposition for an allergic reaction (ie, total immunoglobulin E [IgE] value above normal range at Screening); this study participant's inclusion should be discussed with the Medical Monitor
• Study participant has a history of levodopa-induced motor fluctuations or dyskinesia expected to interfere with his/her ability to participate in the study
• Study participant has ongoing significant inflammatory gastrointestinal disorders and/or clinical signs of significant gastrointestinal problems at Screening
• Study participant has a historic brain scan (MRI scan or CT scan) or an MRI scan performed at Screening indicative of a clinically significant abnormality
• Study participant has a diagnosis of a significant Central nervous system (CNS) disease other than PD or history of epilepsy or seizure disorder other than febrile seizures as a child
• Abnormalities in lumbar spine previously known or determined by a screening lumbar x-ray (if conducted)
• History of clinically significant back pain, back pathology, and/or back injury (for example, degenerative disease, spinal deformity, or spinal surgery) that may predispose participant to complications or technical difficulty with lumbar puncture
• Evidence or history of significant active bleeding or coagulation disorder or use of drugs that affect coagulation or platelet function within 14 days prior to lumbar catheter insertion
• Current or chronic history of liver disease, or known hepatic or biliary abnormalities (with the exception of Gilbert's syndrome or asymptomatic gallstones)
• Study participant has a history or present condition of respiratory or cardiovascular disorders at Screening (eg, cardiac insufficiency, coronary heart disease, uncontrolled hypertension, arrhythmia, tachyarrhythmia, or myocardial infarction) which is considered clinically significant by the Investigator
• Study participant has medical history or current diagnosis of diabetes
• Study participant has clinical significant electrocardiogram (ECG) abnormality at Screening, in the opinion of the Investigator
• Study participant has had prior treatment with an investigational vaccine for PD (including active immunization or passive immunotherapy with monoclonal antibodies)
• Study participant has had prior surgical treatment of PD involving intracranial surgery or implantation of a device (including deep brain stimulation) or duodopa

Due to the small sample size in this trial, IPD cannot be adequately anonymized i.e., there is a reasonable likelihood that individual participants could be re-identified. For this reason, data from this trial cannot be shared.