• Clinical Dementia Rating Scale-Sum of Boxes (CDR-SB) [ Time Frame: 16 weeks ]
  Change in Clinical Dementia Rating Scale-Sum of Boxes (CDR-SB) score based on semi-quantitative scoring of each domain (box) evaluating cognitive impairment in milder and more progressive forms of dementia, in neflamapimod-treated subjects compared to placebo-recipients. The domain (box) scores will be calculated for a Sum of Boxes score. Secondary efficacy endpoints will utilize the same analysis method and model as the primary endpoint.
• Mini-Mental State Examination (MMSE) [ Time Frame: 16 weeks ]
  Change in Mini-Mental State Examination (MMSE) with respect to orientation, memory, concentration, language, and praxis (scores ranging from 0 to 30 with lower scores indicating greater cognitive impairment), in neflamapimod-treated subjects compared to placebo-recipients. Secondary efficacy endpoints will utilize the same analysis method and model as the primary endpoint.
• Neuropsychiatric Inventory (NPI-10) [ Time Frame: 16 weeks ]
  Change in Neuropsychiatric Inventory (NPI-10) domains, specifically depression (dysphoria), anxiety, hallucinations, and agitation/aggression, in neflamapimod-treated subjects compared to placebo-recipients. Responses indicating subject has a problem with a particular sub-domain lead to questions of the caregiver rating the frequency of the symptoms on a 4-point scale, severity on a 3-point scale, and the distress the symptoms cause them on a 5-point scale. Secondary efficacy endpoints will utilize the same analysis method and model as the primary endpoint.
• International Shopping List Test (ISLT) [ Time Frame: 16 weeks ]
  Change in International Shopping List Test (ISLT) immediate and delayed recall and recognition will be used to assess episodic memory in neflamapimod-treated subjects compared to placebo-recipients. Secondary efficacy endpoints will utilize the same analysis method as the primary endpoint.
• Timed Up and Go Test (TUG) [ Time Frame: 16 weeks ]
  Change in Timed Up and Go Test (TUG) to assess mobility (score of >15 seconds indicates subject has increased risk of falls) in neflamapimod-treated subjects compared to placebo-recipients. Secondary efficacy endpoints will utilize the same analysis method and model as the primary endpoint.
• Quantitative Electroencephalogram (qEEG) [ Time Frame: 16 weeks ]
  Change in quantitative electroencephalogram (qEEG) parameters (all waveforms, with particular focus on relative alpha and theta power) with the subject awake in accordance with the 10-20 International System of Electrode placement will be evaluated as a potential biomarker for DLB. Slowing of the dominant frequency band by qEEG over posterior aspects of the brain has been recognized to be prominent in DLB, and various patterns have been identified to differentiate DLB from AD. EEG will be analyzed at an academic center (VU Medical Center, Amsterdam), who will develop the specific parameters during the conduct of the study, and they will specify the analytic approach in the Statistical Analysis Plan (SAP) that will be implemented prior to the completion of subject enrollment.

• Experimental: Neflamapimod
  40 mg capsules administered orally, BID or TID with food for 16 weeks; subjects will follow the BID regimen if weighing <80 kg or the TID regimen if weighing ≥80 kg
  Intervention: Drug: Neflamapimod
• Placebo Comparator: Placebo
  40 mg matching placebo capsules administered orally, BID or TID with food for 16 weeks; subjects will follow the BID regimen if weighing <80 kg or the TID regimen if weighing ≥80 kg
  Intervention: Drug: Neflamapimod

Inclusion Criteria:

1. Men and women aged ≥55 years.
2. Subject or subject's legally authorized representative is willing and able to provide written informed consent.
3. Probable DLB and identified cognitive deficits, according to current consensus criteria (McKeith et al, 2017), specifically one core clinical feature and a positive DaTscan. If a negative DaTscan, but the subject has historical PSG-verified RBD, the subject would also qualify.
4. MMSE score of 15-28, inclusive, during Screening.
5. Currently receiving cholinesterase inhibitor therapy, having received such therapy for greater than 3 months and on a stable dose for at least 6 weeks at the time of randomization. Except for reducing the dose for tolerability reasons, the dose of cholinesterase inhibitor may not be modified during the study.
6. Normal or corrected eye sight 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. 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), or Parkinson's disease (PD).
2. 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 C-SSRS, or history of suicide attempt in previous 2 years, or, in the Investigator's opinion, at serious risk of suicide.
3. 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.
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.
7. Known human immunodeficiency virus, hepatitis B, or active hepatitis C virus infection.
8. Participated in a study of an investigational drug less than 3 months or 5 half-lives of an investigational drug, whichever is longer, before enrollment in this study.
9. History of previous neurosurgery to the brain.
10. If male with female partner(s) of child-bearing potential, unwilling or unable to adhere to contraception requirements specified in the protocol.
11. 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.