Study of YKST02 Alone or in Combination With YK012 in Patients With Active or Refractory Systemic Lupus Erythematosus

Inclusion Criteria: * Diagnosed with systemic lupus erythematosus (SLE) according to the 2019 EULAR/ACR classification criteria, with active disease defined as SLEDAI-2K ≥6 at screening, and considered to have inadequate response, intolerance, or ineligibility to standard therapy. * Have received standard therapy for SLE for at least 12 weeks prior to screening (including corticosteroids and at least one immunosuppressant and/or biologic agent), or are intolerant to or unsuitable for such therapies. * Receiving stable background therapy prior to enrollment, including stable doses of corticosteroids (within 2 weeks prior to enrollment), and/or antimalarial agents or one immunosuppressant (within 4 weeks prior to enrollment). * Positive for at least one lupus-related autoantibody at screening (e.g., anti-dsDNA, antinuclear antibody, or anti-Smith antibody). * Able and willing to provide written informed consent and comply with study procedures. Exclusion Criteria: * Known hypersensitivity to monoclonal antibodies, immunoglobulins, or any component of the study drug. * Prior treatment with B cell-depleting therapies, B cell-targeting biologics, or other biologic or targeted therapies within protocol-defined washout periods. * Receipt of intravenous immunoglobulin or plasma exchange within protocol-defined washout periods. * Receipt of live or attenuated vaccines within 4 weeks prior to enrollment. * Presence of other active autoimmune diseases or inflammatory conditions (except secondary Sjögren's syndrome) that may interfere with assessment of SLE disease activity. * History of major organ transplantation. * History of malignancy within the past 5 years (except adequately treated low-risk cancers). * Clinically significant or uncontrolled cardiovascular, cerebrovascular, neurological, hepatic, renal, hematologic, or metabolic diseases. * Active or uncontrolled infections, including tuberculosis (active or untreated latent), hepatitis B or C, human immunodeficiency virus (HIV), or other clinically significant infections. * Active or severe neuropsychiatric conditions that may interfere with study participation. * Uncontrolled hypertension or clinically significant electrocardiogram abnormalities (including prolonged QT interval). * Clinically significant abnormal laboratory findings at screening (e.g., severe cytopenias, impaired liver or renal function, or coagulation abnormalities). * Recent major surgery or planned surgery during the study period. * Recent use of investigational agents or participation in another clinical study within 4 weeks prior to enrollment. * Pregnant or breastfeeding women, or women of childbearing potential unwilling to use effective contraception during the study and for an appropriate period after the last dose. * Any other condition that, in the opinion of the investigator, would make the participant unsuitable for the study.