A Study of MK-2214 in Adults With Mild Cognitive Impairment or Mild-to-Moderate Alzheimer's Disease (MK-2214-002)

Inclusion Criteria:

• Participant is in overall good health based on medical history and laboratory safetytests

• 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 progressionfor 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), hasreported 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 genitourinaryabnormalities or diseases

• History of clinically significant active neurological disease (except for AD or MCIfor participants in Part 1)

• History of clinically significant active autoimmune disease requiring ongoingsystemic immunosuppressant therapy

• History of cancer (malignancy)

• History of significant multiple and/or severe allergies (eg, food, drug, latexallergy), or has had an anaphylactic reaction or significant intolerability toprescription or nonprescription drugs or food

• Positive test(s) for Hepatitis B Surface Antigen (HBsAg), hepatitis C antibodies orhuman immunodeficiency virus (HIV)

• Has had a major surgery and/or donated or lost 1 unit of blood (approximately 500mL) within 4 weeks prior to the prestudy visit

• Has a contraindication to lumbar dural puncture, such as coagulopathy, concomitantanticoagulation beyond low dose aspirin, thrombocytopenia, or other factors thatcould preclude safe lumbar puncture

• Currently receiving or has received aducanumab or another anti-amyloid therapywithin 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 studyintervention or is scheduled to receive any non-live vaccine through 14 daysfollowing the final dose of study intervention. Exception: COVID-19 and influenzavaccines may be administered

• Is receiving systemic immunosuppression, including corticosteroids exceedingphysiologic replacement doses