Inclusion Criteria:
1. Men and women aged ≥55 years.
2. Subject is willing and able to provide written informed consent.
3. Probable DLB by consensus criteria (McKeith et al, 2017; McKeith et al, 2020).
4. MoCA score ≥18 OR CDR global score (CDR-GS) ≤ 1.0 during Screening.
5. If the patient is currently receiving cholinesterase inhibitor and/or memantine therapy, the patient must have received such therapy for greater than 3 months and on a stable dose for at least 6 weeks at the time of enrollment. Except for reducing the dose for tolerability reasons, the dose of cholinesterase inhibitor may not be modified during the study. If the patient is not currently receiving such therapy, but received such therapy previously, that therapy must have been discontinued at least 3 months prior to enrollment.
6. Normal or corrected eyesight and auditory abilities, sufficient to perform all aspects of the cognitive and functional assessments.
7. No history of learning difficulties that may interfere with their ability to complete the cognitive tests.
8. Received vaccination for SARS-CoV-19 unless medical contraindications prevent being vaccinated or has a history of natural infection.
9. Must have reliable informant or caregiver.
Exclusion Criteria:
1. Diagnosis of any other ongoing central nervous system (CNS) condition other than DLB, including, but not limited to, post-stroke dementia, vascular dementia, Alzheimer's disease (AD), Frontotemporal dementia (FTD), or Parkinson's disease (PD).
2. Ongoing major and active psychiatric disorder and/or other concurrent medical condition that, in the opinion of the Investigator, might compromise safety and/or compliance with study requirements.
3. Suicidality, defined as active suicidal thoughts within 6 months before Screening or at Baseline, defined as answering yes to items 4 or 5 on the Columbia-Suicide Severity Rating Scale (C-SSRS), or history of suicide attempt in previous 2 years, or, in the Investigator's opinion, at serious risk of suicide.
4. Diagnosis of alcohol or drug abuse within the previous 2 years.
5. Poorly controlled clinically significant medical illness, such as hypertension (blood pressure \>180 mmHg systolic or 100 mmHg diastolic); myocardial infarction within 6 months; uncompensated congestive heart failure or other significant cardiovascular, pulmonary, renal, liver, infectious disease, immune disorder, or metabolic/endocrine disorders or other disease that would interfere with assessment of drug safety.
6. Aspartate aminotransferase (AST) or alanine aminotransferase (ALT) \>2 × the upper limit of normal (ULN), total bilirubin \>1.5 × ULN, and/or International Normalized Ratio (INR) \>1.5. If patient is taking blood thinners (e.g., warfarin), and has no known liver issues, INR \>3.
7. Positive screen for human immunodeficiency virus, hepatitis B surface antigen (HbsAg), antibody (anti-HbS), hepatitis C virus (HCV) antibody or evidence of latent or active tuberculosis, active opportunistic or life-threatening infections.
8. Participated in a study of an investigational drug less than 6 weeks or 5 half-lives of an investigational drug, whichever is longer, before enrollment in this study.
9. Receipt of a live vaccine, with the exception of influenza, within 4 weeks before starting study drug treatment.
10. History of previous neurosurgery to the brain within the past five years.
11. If male with female partner(s) of child-bearing potential, unwilling or unable to adhere to contraception requirements specified in the protocol.
12. If female who has not has not reached menopause \>1 year previously or has not had a hysterectomy or bilateral oophorectomy/salpingo-oophorectomy, has a positive pregnancy test result during Screening and/or is unwilling or unable to adhere to the contraception requirements specified in the protocol.
13. If female, currently pregnant or breastfeeding.
