A Study of YKST02 in Participants With Primary IgA Nephropathy

Inclusion Criteria: * Diagnosis of primary IgA nephropathy (IgAN) * Proteinuria above a protocol-defined threshold at screening * Receiving stable standard-of-care therapy for IgAN for an adequate duration prior to enrollment, unless contraindicated or not tolerated * Women of childbearing potential must have a negative pregnancy test prior to study drug administration and agree to use effective contraception; male participants must agree to use effective contraception * Able to understand the study procedures and provide written informed consent Exclusion Criteria: * Secondary IgA nephropathy (e.g., associated with liver disease, autoimmune disorders, infections, or other systemic conditions) * Other clinically significant renal diseases unrelated to IgAN (e.g., diabetic nephropathy, lupus nephritis, vasculitis) * Nephrotic syndrome considered unsuitable for study participation * Rapidly progressive glomerulonephritis or rapidly declining renal function * Estimated glomerular filtration rate (eGFR) \<45 mL/min/1.73 m² * Immunodeficiency or low immunoglobulin G (IgG) levels below normal * Clinically significant abnormal laboratory findings (e.g., hematologic, hepatic, or coagulation abnormalities) * Requirement for systemic corticosteroids for concomitant conditions * Use of immunosuppressive, targeted, or biologic therapies within a defined period prior to screening or anticipated use during the study * Prior treatment with B-cell-depleting or other targeted biologic therapies within a defined period * History of demyelinating disorders (e.g., multiple sclerosis) * Clinically significant cardiovascular or cerebrovascular disease within 6 months prior to screening * History of organ transplantation or planned transplantation during the study * Current dialysis or anticipated need for dialysis during the study * Major surgery within 4 weeks prior to screening or planned during the study * Active infection requiring systemic therapy, recent serious infection, or chronic/recurrent infections * Known active hepatitis B, hepatitis C, or human immunodeficiency virus (HIV) infection * Active or untreated latent tuberculosis * History of splenectomy * Uncontrolled comorbidities (e.g., poorly controlled hypertension or diabetes) * Malignancy within the past 5 years, except adequately treated non-invasive cancers * Known hypersensitivity to YKST02 or its components * Receipt of another investigational product within 4 weeks or 5 half-lives (whichever is longer) prior to screening * Receipt of live or attenuated vaccines within 4 weeks prior to screening or planned during the study * Any condition that, in the investigator's judgment, would make the participant unsuitable for the study