A First-In-Human Study With a Single Dose UCB4019 in Healthy Volunteers

Inclusion Criteria: * Good physical and mental health * At least 18 and less than 65 years of age * Female subjects of childbearing potential must agree to use a highly effective method of birth control, during the study and for a period of 3 months after their last dose of study drug Exclusion Criteria: * Total Immunoglobulin G \<7 g/L or \>16 g/L at the Screening Visit * Absolute neutrophil count \<1.5x10\^9/L and/or lymphocyte count \<1.0x10\^9/L * Known viral hepatitis, has a positive test for Hepatitis B surface antigen or is Hepatitis C virus antibody positive * Positive test to Human Immunodeficiency Virus (HIV) 1/2 antibodies * Past medical history or family history of primary immunodeficiency * Evidence of latent/active Tuberculosis (TB) * Active infection or a serious infection within 6 weeks before the first dose of IMP * Renal impairment * Hepatic impairment * Vaccination within 6 weeks before the Screening Visit or intent to have a vaccination before Day 43 of the Safety Follow-up Period * Subject is splenectomized * received any IMP or experimental procedure within 90 days before the first dose of IMP * received UCB7665 in a clinical study