First-in-Human Study Testing a New Antibody Treatment for Tick-Borne Encephalitis in Healthy Volunteers.

Inclusion Criteria: * Adults aged 18 to \<55 years * Good general health (medical history, physical exam, normal labs) * Written informed consent provided * Ability to read and understand local language * Contraception requirements : Women of childbearing potential: negative pregnancy test, surgically sterile, postmenopausal, or using highly effective contraception for 3 months post-infusion. Men: surgically sterile or using highly effective contraception (self or partner) and abstain from sperm donation for 3 months post-infusion. Exclusion Criteria: * BMI \<19 or \>30 * Infections: HIV, active hepatitis B (HBsAg), active hepatitis C * Prior participation in investigational study within 30 days * History of hypersensitivity to monoclonal antibodies * Recent surgery or unresolved adverse events * Active autoimmune disease requiring systemic treatment * Recent use of immunosuppressive agents or immunoglobulins * Immunodeficiency diagnosis * Significant cardiovascular events within 6 months * Live/attenuated vaccines within 28 days * Major surgery within 28 days * Pregnancy or breastfeeding * Professional or private link with the research team * Any condition judged by the investigator to interfere with safety or study results