The purpose of this study is to assess the safety, tolerability, pharmacokinetics (PK) and pharmacodynamics of MK-2214 in adults with mild cognitive impairment (MCI) or mild-to-moderate Alzheimer's Disease (AD). The primary hypothesis (Part 1) is that at a generally well tolerated dose level, the true geometric mean concentration at Day 85 of MK-2214 in cerebrospinal fluid is >0.3 nanomolar (nM).

Inclusion Criteria:

• Participant is in overall good health based on medical history and laboratory safety tests
• BMI between 18.5 and 35 kg/m^2

Part 1 (MCI and Mild to Moderate AD) Only:

• History of cognitive and functional decline with gradual onset and slow progression for at least one year before Screening
• Have an Mini-Mental State Examination (MMSE) >12 at the prestudy visit
• Modified Hachinski Ischemic Score (MHIS) score <4 at the prestudy visit

Exclusion Criteria:

• Based on clinical interview and Columbia-Suicide Severity Rating Scale (C-SSRS), has reported suicidal ideation with intent, with or without a plan or method
• History of unstable or poorly controlled endocrine, gastrointestinal (GI), cardiovascular, hematological, hepatic, renal, respiratory, or genitourinary abnormalities or diseases
• History of clinically significant active neurological disease (except for AD or MCI for participants in Part 1)
• History of clinically significant active autoimmune disease requiring ongoing systemic immunosuppressant therapy
• History of cancer (malignancy)
• History of significant multiple and/or severe allergies (eg, food, drug, latex allergy), or has had an anaphylactic reaction or significant intolerability to prescription or nonprescription drugs or food
• Positive test(s) for Hepatitis B Surface Antigen (HBsAg), hepatitis C antibodies or human immunodeficiency virus (HIV)
• Has had a major surgery and/or donated or lost 1 unit of blood (approximately 500 mL) within 4 weeks prior to the prestudy visit
• Has a contraindication to lumbar dural puncture, such as coagulopathy, concomitant anticoagulation beyond low dose aspirin, thrombocytopenia, or other factors that could preclude safe lumbar puncture
• Currently receiving or has received aducanumab or another anti-amyloid therapy within the last 6 months
• Has a history of receiving biological therapy within 3 months or 5 half-lives (whichever is longer) or any human immunoglobulin preparation within the last year
• Has received any non-live vaccine starting from 14 days prior to first study intervention or is scheduled to receive any non-live vaccine through 14 days following the final dose of study intervention. Exception: COVID-19 and influenza vaccines may be administered
• Is receiving systemic immunosuppression, including corticosteroids exceeding physiologic replacement doses

https://trialstransparency.msdclinicaltrials.com/pdf/ProcedureAccessClinicalTrialData.pdf