This is a phase 1, single dose, randomized, open-label, parallel-group study to evaluate the pharmacokinetics (PK), safety, tolerability and immunogenicity of ZL-1503 and to explore its PD biomarkers following a single subcutaneous (SC) or intravenous (IV) administration in healthy volunteers.

Inclusion Criteria:

• Healthy male and female volunteers, 18-65 years of age
• Body mass index (BMI) between ≥ 18.5 and < 32.5 kg/m2
• Negative pregnancy tests for women of childbearing potential.

Exclusion Criteria:

• Significant health issues, such as positive tests for human immunodeficiency virus (HIV), hepatitis C virus (HCV), hepatitis B surface antigen (HBsAg), active tuberculosis, immunodeficiencies or autoimmune diseases.
• History of major metabolic, liver, kidney, hematologic or other significant disorders.
• Abnormal Electrocardiogram (ECG) findings
• Clinically relevant abnormal lab results, including low blood counts, or abnormal liver and kidney function.
• History of drug abuse or addiction within 6 months prior to screening
• Current smoker or use of any nicotine or tobacco containing products within the last 6 months prior to dosing.
• Donated >500mL blood within 2 months of dosing.