Healthy Participants Randomized, Double-blind, Placebo-controlled, Phase Ⅰ

This first-in-human (FIH), randomized, double-blind, placebo-controlled Phase 1 study is designed to evaluate the safety, tolerability, pharmacokinetics (PK), pharmacodynamics (PD), and immunogenicity of BY002 (an investigational, bispecific tandem VHH antibody targeting the CGRP receptor) in healthy adult subjects. This Phase 1 study consists of two parts: a Single Ascending Dose (SAD) study and a Multiple Ascending Dose (MAD) study. Furthermore, both the SAD and MAD studies incorporate a capsaicin challenge test to assess the inhibitory effect of BY002 on capsaicin-induced elevation of dermal blood flow (DBF), serving as a PD marker for CGRP receptor antagonism.

Inclusion criteria

• 1. Male or female aged ≥18 years at the time of signing the Informed Consent Form (ICF).

• At screening, body mass index (BMI) between 18 and 30 kg/m² (inclusive), with weight ≥50.0 kg for males and ≥45.0 kg for females.

• Good health status determined by screening examinations. Good health status is defined as: absence of clinically relevant abnormalities or psychiatric diseases that, in the investigator's judgment, could compromise participant safety, affect the scientific validity of the study, expose the participant to unacceptable risk, or interfere with their compliance with study procedures and restrictions.

• Male participants and their partners of childbearing potential must agree to use highly effective contraception during the study and for at least 12 weeks after the last dose. Male participants must refrain from donating sperm during this period. Female participants must not be pregnant or lactating. Women of childbearing potential (WOCBP) must have a negative pregnancy test at screening and be willing to use highly effective contraception throughout the study and for at least 12 weeks after the last dose. Female participants must avoid donating eggs during this period.

• Participants who, after capsaicin challenge during screening, meet the criteria specified in the Capsaicin Challenge Test Operating Manual (applicable only to participants undergoing the capsaicin challenge test).

• Provide written informed consent before any study-related procedures are performed.

Exclusion criteria

• 1. Individuals with a history or current presence of clinically significant cardiovascular (e.g., hypertension), pulmonary, gastrointestinal, hepatic, renal, metabolic, hematological, neurological, musculoskeletal, rheumatologic, psychiatric, systemic, ocular, reproductive, otorhinolaryngological, dermatological, or infectious diseases, or acute disease signs, unless deemed not clinically significant by the investigator and sponsor.

• Individuals who have donated blood (≥400 mL) or experienced significant blood loss (≥400 mL), donated ≥2 units of blood components, or received a blood transfusion within 2 months prior to the first dose of investigational drug; or who plan to donate blood during the study.

• Individuals with allergic constitution (defined as a clear history of allergy to two or more drugs, or to two or more common foods, or to common inhaled/contact irritants such as pollen, dust mites, pet dander, mold, etc.), or a known history of allergic reactions to any therapeutic protein drugs (including monoclonal antibodies, fusion proteins, recombinant enzymes, cytokines, peptide hormones, blood products, vaccines, etc.).

• Participants who are known to be allergic to any component of the investigational drug product or to capsaicin (applicable only to participants undergoing the capsaicin challenge test), or who have other contraindications.

• Alcohol abuse or frequent alcohol consumption within 6 months prior to screening, defined as weekly alcohol intake exceeding 14 units (1 unit = 360 mL of beer, 45 mL of 40% spirits, or 150 mL of wine), or unwillingness to abstain from alcohol and any alcohol-containing products during the study; or a positive alcohol breath test.

• History of drug abuse within 12 months prior to screening, or positive urine drug screen result.

• Smokers (defined as consuming more than 5 cigarettes or equivalent products per week), or those who cannot discontinue the use of any tobacco products during the study period.

• The investigator determines that the participant's skin characteristics are unsuitable for capsaicin skin challenge (applicable only to participants undergoing the capsaicin challenge test).

• Participants for whom venous blood collection is difficult.

• Individuals who, as judged by the investigator, have clinically significant abnormalities in physical examination, vital signs, ECG, clinical laboratory tests (hematology, blood biochemistry, urinalysis, coagulation function), or chest X-ray at screening.

• Individuals with a QT interval corrected using Fridericia's formula (QTcF) >450 ms for male participants or >470 ms for female participants on the screening electrocardiogram (ECG).

• Positive result in any of the following tests: Hepatitis B surface antigen (HBsAg), anti-hepatitis C virus (anti-HCV) antibody, anti-human immunodeficiency virus antibody (anti-HIV Ab), and specific antibody to Treponema pallidum (TP-Ab).

• Individuals who have used any prescription medication, over-the-counter (OTC) drugs, traditional Chinese patent medicines, Chinese herbal medicines, vitamins, or dietary supplements within 14 days prior to the first dose or within 5 elimination half-lives or pharmacodynamic half-lives (whichever is longer) that may interfere with the study assessments.

• Receipt of any vaccine within 2 weeks prior to the first dose of the investigational drug.

• Individuals who have enrolled in or participated in any clinical trial containing investigational drugs or other medical research within 1 month prior to the first dose, or within 5 elimination half-lives (whichever is longer).

• Individuals deemed by the investigator to be likely noncompliant during the study period, or unable to cooperate due to language barriers or intellectual disability, or otherwise unsuitable for participation in the trial.