This is a study to determine the safety and pharmacokinetics of CDX-0159 administered subcutaneously in healthy subjects.

CDX-0159 is a humanized monoclonal antibody that binds to a protein called KIT that is expressed on mast cells.

The study will evaluate the safety, pharmacokinetics, and pharmacodynamics of CDX-0159 administered subcutaneously in healthy subjects.

Key Inclusion Criteria:

• An informed consent signed and dated by the subject.
• Healthy volunteer aged 18-55.
• In generally good health and without significant medical conditions based on physical exam, ECG, and laboratory test results.
• Body mass index (BMI) ≥ 18.5 kg/m2 to ≤ 35 kg/m2
• No medication other than mild analgesics, vitamins and mineral supplements or, oral contraceptives.
• Both males and females of child bearing potential must agree to use a medically accepted contraceptive regimen during study and up to 150 days afterwards.
• Not a current smoker, vaper, or regular user of any nicotine or cannabinoid containing products
• Willing to follow all study rules

Key Exclusion Criteria:

• Women who are pregnant or nursing
• History of anaphylaxis or systemic reactions to food or other triggers
• Autoimmune disorders requiring more than topical medication
• Vaccination with live vaccines within 4 months prior to screening visit (subjects must agree to avoid live vaccination during the study and 4 months after).
• Positive urine test for alcohol and drugs of abuse.

Other Protocol defined inclusion and exclusion criteria could apply.