A 23-year-old female was admitted with recurrent arthralgia for over a year and edema for 1 month. Physical examination: BP 150/90 mmHg, marked facial and lower extremity edema, knee joint swelling and mild tenderness. Lab findings: Hb 78g/L, WBC 3.0×10⁹/L, PLT 50×10⁹/L, urine protein (++++), RBC 10-20/HPF, WBC 5-10/HPF, 24-hour urinary protein quantification 5.6g (non-selective proteinuria), ALT 50U, A/G=30/40g/L, serum IgG 22g/L. After evaluation, she was diagnosed with diffuse proliferative lupus nephritis. In addition to prednisone and anticoagulation therapy, which of the following should be added?