A Study to Assess the Safety, Tolerability, Pharmacokinetics, Immunogenicity, and Pharmacodynamics of E2025 in Healthy Participants

Inclusion criteria

• Non-smoking, male or female age greater than or equal to (>=) 18 years and less than or equal to (<=) 55 years old at the time of informed consent. Females must be of nonchildbearing potential
• Body weight >=50 kilogram (kg) and a Body Mass Index (BMI) >=18 and less than (<) 30 kilogram per square meter (kg/m^2) at Screening

Exclusion criteria

• Females who are breastfeeding or pregnant at Screening or Baseline; Females of childbearing potential.
• Males who have not had a successful vasectomy (confirmed azoospermia) if their female partners are of childbearing potential and are not willing to use a highly effective contraceptive method throughout the study period or for 203 days after their partner's study drug administration.
• Clinically significant illness that requires medical treatment within 8 weeks or a clinically significant infection that requires medical treatment within 4 weeks of dosing
• Evidence of disease that may influence the outcome of the study within 4 weeks before dosing; example, psychiatric disorders and disorders of the gastrointestinal tract, liver, kidney, respiratory system, endocrine system, hematological system, neurological system, or cardiovascular system, or participants who have a congenital abnormality in metabolism
• Any clinically abnormal symptom or organ impairment found by medical history at Screening, and physical examinations, vital signs, ECG finding, or laboratory test results that require medical treatment at Screening
• A prolonged QT/QTc interval (QTcF >450 millisecond [ms]). A history of risk factors for torsade de pointes or the use of concomitant medications that prolonged the QT/QTc interval
• Persistent systolic blood pressure (BP) greater than 130 millimeter of mercury (mmHg) or diastolic BP greater than 85 mmHg at Screening or Baseline; Heart rate less than 50 or more than 100 beats per minute at Screening or Baseline
• Any lifetime history of suicidal ideation or any lifetime history of suicidal behavior as indicated by the Columbia-suicide Severity Rating Scale (C-SSRS) or equivalent scale or via interview with a psychiatrist
• Any lifetime history of psychiatric disease (including but not limited to depression or other mood disorders, bipolar disorder, psychotic disorders, including schizophrenia, panic attacks, anxiety disorders); any current psychiatric symptoms as indicated by a standard screening tool.
• Known history of clinically significant drug allergy; known history of food allergies or presently experiencing significant seasonal or perennial allergy at Screening
• Any history of hypersensitivity reaction to a foreign protein, with clinical features not limited to nasal or conjunctival symptoms such as in allergic rhinitis
• Known to be human immunodeficiency virus positive and/or active viral hepatitis (hepatitis B core antibody [HBcAb], hepatitis B viral protein [HBcAg], hepatitis B surface antigen [HBsAg], hepatitis C virus antibody [HCVAb]) as demonstrated by positive serology at Screening
• History of drug or alcohol dependency or abuse within the 2 years before Screening, or a positive urine drug test or breath alcohol test at Screening or Baseline
• Currently enrolled in another clinical study or used any investigational drug or device within 28 days (or 5*the half-life, whichever is longer) preceding informed consent
• Receipt of blood products within 4 weeks, or donation of blood within 8 weeks, or donation of plasma within 1 week of dosing
• Exposure to any biologic drug within 90 days or at least 5 half-lives (whichever is longer), or within 4 weeks for vaccines, before Screening, with the exception of flu (7 days before dosing) and COVID-19 vaccination (14 days before dosing until after the Follow-up visit).
• Any contraindication to continuous CSF sampling via indwelling lumbar catheter or via lumbar puncture (LP)
• Participants identified at risk for hemorrhage.
• Inadequate venous access that would interfere with study drug administration or obtaining blood samples
• Participants who contravene the restrictions on concomitant medications, food, beverages, physical activities, and others as defined in the protocol