This Phase 1, open label, dose escalation study evaluates the safety, tolerability, pharmacokinetics, pharmacodynamics, and preliminary clinical activity of HB2198, a tetravalent bispecific anti CD19/CD20 antibody, in adults with moderately to severely active systemic lupus erythematosus (SLE), including lupus nephritis and extra renal lupus. Approximately 30 participants will receive two intravenous doses of HB2198 and be followed for 12 months to assess safety, B cell depletion, disease activity, immunologic biomarkers, and renal outcomes.