The primary objective of this study is to evaluate the safety and tolerability of single subcutaneous (SC) doses of ALXN2230 in healthy participants.

Part A of this study is expected to enroll approximately 40 participants (30 on ALXN2230 and 10 on placebo) across 5 cohorts and Part B is expected to enroll approximately 8 participants (6 on ALXN2230 and 2 on placebo) in 1 cohort.

Inclusion Criteria:

• Participants who are overtly healthy as determined by medical evaluation including medical history, physical examination, laboratory tests, and cardiac monitoring.
• Baseline immunoglobulin G (IgG) concentrations ≥ 1000 milligrams per deciliter (mg/dL) and ≤ 1600 mg/dL at Screening.
• Antibody titers for Tetanus toxoid (≥ 0.1 International Units per milliliter (IU/mL)) at Screening.
• Nonsmokers and not using any nicotine-containing products. A nonsmoker is defined as an individual who has abstained from smoking for at least 1 year prior to Screening.
• BMI within the range 18 to 32 kilograms per square meter (kg/m2), inclusive; with body weight ≥ 50 kilograms (kg).

Exclusion Criteria:

• History or presence of cardiovascular, respiratory, hepatic, renal, gastrointestinal, endocrinological, hematological, or neurological disorders capable of significantly altering the absorption, metabolism, or elimination of drugs; constituting a risk when taking the study intervention; or interfering with the interpretation of data.
• Abnormal blood pressure (BP) (resting BP not to exceed 140/80 mmHg and no less than 90/60 mmHg).
• Participants who have history of allergy or hypersensitivity to excipients in ALXN2230.
• History of unexplained, recurrent infection, or infection requiring treatment with systemic antibiotics within 90 days prior to dosing on Day 1.
• Pregnant or breastfeeding females are excluded from the clinical study.
• Participants with known clinically relevant immunological disorders.
• Lymphoma, leukemia, breast cancer or any malignancy within the past 5 years except for basal cell or squamous epithelial carcinomas of the skin that have been resected with no evidence of metastatic disease for 5 years.
• ALT > 1.0 × upper limit of normal (ULN)
• TBIL > 1.0 × ULN
• Current or chronic history of liver disease or known hepatic or biliary abnormalities (with exception for Gilbert's syndrome).
• QTc > 450 millisecond (msec) for male participants or > 470 msec for female participants.
• Significant blood loss (including blood donation [> 500 mL]) or had a transfusion of any blood product within 12 weeks prior to dosing or plan 1 within 4 weeks after the end of the study.

Additional inclusion/exclusion criteria may apply, per protocol.

Alexion has a public commitment to allow requests for access to study data and will be supplying a CSR synopsis and plain language summaries.