This is a study to determine the safety of CDX-622 in healthy participants.

CDX-622 is a bispecific antibody that binds to stem cell factor (SCF) and thymic stromal lymphopoietin (TSLP).

This study will evaluate the safety, pharmacokinetics, and Pharmacodynamics of IV single ascending doses (Part 1), IV multiple ascending doses (Part 2), and subcutaneous (SC) single ascending doses (Part 3) of CDX-622 in healthy participants.

Key Inclusion Criteria:

• An informed consent signed and dated by the participant.
• 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 kg/m2 to ≤ 32 kg/m2.
• No course of medication, whether prescribed or over the counter, in the 4 weeks before study drug administration.
• Both males and females of childbearing potential must agree to use a medically accepted contraceptive regimen during study and up to 150 days afterwards.
• Not a current smoker (or regular user of any nicotine containing product).
• Willing to follow all study rules.

Key Exclusion Criteria:

• Women who are pregnant or nursing.
• History of anaphylaxis, food allergies, or allergies (chronic or seasonal) requiring prescription medication.
• History of asthma requiring the use of inhaled medication within the past 5 years.
• Vaccination within 4 weeks prior to study drug administration (subjects must agree to avoid vaccination during the study).
• Blood donation (excluding plasma donation) of approximately 500 mL within 56 days prior to Screening.
• Positive urine test for alcohol and drugs of abuse.

Additional protocol defined inclusion and exclusion criteria could apply.