Inclusion Criteria:
* Voluntarily sign the informed consent form and be able to complete the trial according to the protocol;
* The age range is between 18 and 75 years old (including the critical value, subject to the day of signing the informed consent form), regardless of gender;
* Diagnosed with primary (idiopathic) membranous nephropathy by renal biopsy before or during screening;
* Two separate 24-hour urine protein tests performed during screening show elevated results, meeting the protocol-specified criteria:
* Estimated glomerular filtration rate (eGFR) calculated using the CKD-EPI formula (Levey, et al., 2009) ≥40 mL/min/1.73m²;
* If the patient is taking angiotensin-converting enzyme inhibitors (ACEi), angiotensin II receptor blockers (ARB), sodium-glucose cotransporter 2 (SGLT-2) inhibitors, or finerenone, the medication dose must remain stable for at least 4 weeks before screening (adherence to medication \>50% of this period is considered stable).
* Women of childbearing potential (WOCBP) must have a negative pregnancy test at screening and prior to the first administration of investigational product (Day 1 \[D1\], with an allowable time window of -7 days). Women of childbearing potential and male patients must agree to use effective contraception from the date of signing the informed consent form until 6 months after the last dose of investigational product.
Women of childbearing potential are defined as all women who have reached menarche and have not undergone sterilization procedures (e.g., hysterectomy, bilateral tubal ligation, or bilateral oophorectomy) and are not postmenopausal. Postmenopausal women are defined as women with ≥12 consecutive months of amenorrhea without an alternative identifiable cause; OR women with irregular menstrual cycles receiving hormone replacement therapy (HRT) whose serum follicle-stimulating hormone (FSH) level is \>35 mIU/mL.
Women using oral, implantable, or injectable contraceptives, or contraceptive methods such as intrauterine devices, diaphragms, condoms, and spermicides; or women practicing abstinence or whose sexual partner has undergone sterilization (e.g., vasectomy) shall still be classified as women of childbearing potential.
Exclusion Criteria:
* Secondary membranous nephropathy (e.g., due to malignancy, systemic autoimmune diseases, infection, medications, etc.).
* Concurrent other types of glomerulonephritis (e.g., IgA nephropathy), or renal pathological lesions including interstitial nephritis, glomerulosclerosis, etc., involving \>50% of renal tissue that may affect prognosis.
* Patients with type 1 diabetes mellitus, or type 2 diabetes mellitus complicated with diabetic nephropathy (patients with type 2 diabetes must provide a renal biopsy report obtained within 1 year prior to screening).
* History of severe hypersensitivity to rituximab or other human-mouse chimeric antibodies (e.g., anaphylactic shock and angioedema), or known hypersensitivity to any ingredient or excipient of the investigational product.
* Patients judged by the investigator to have prior resistance to cyclosporine or cyclophosphamide, or resistance (lack of response) to anti-CD20 therapy or any other B-cell depleting therapy.
* Prior receipt of any of the following therapeutic agents for membranous nephropathy:
① Glucocorticoids at conventional doses (oral, intravenous, intramuscular, etc.) within 1 month before screening (exception: glucocorticoid dose equivalent to prednisone \<1.0 mg/kg/day administered for ≤7 days is not an exclusion criterion); pulse glucocorticoid therapy within 3 months before screening (methylprednisolone ≥250 mg/day for ≥3 consecutive days).
② Immunosuppressants including mycophenolate mofetil, tacrolimus, cyclosporine, tripterygium wilfordii, etc., within 1 month before screening (if administered for ≤7 days, screening may be performed after drug discontinuation).
③ Alkylating agents (e.g., cyclophosphamide, chlorambucil, etc.) or traditional Chinese medicines with unknown ingredients within 6 months before screening.
④ Any anti-CD20 therapy within 9 months before screening, or any other B-cell depleting therapy or targeted therapy inhibiting antibody production (e.g., belimumab, etc.) within 6 months before screening.
* The 24-hour urine protein or urine protein-creatinine ratio (UPCR) at screening or baseline decreased by \>50% compared with the 24-hour urine protein or UPCR level within 6 months prior to randomization, and the investigator assesses a trend of spontaneous remission.
* Any abnormal laboratory result at screening as follows:
1. Hepatic impairment defined as AST or ALT \> 2× upper limit of normal (ULN), or total bilirubin \>1.5×ULN.
2. Without growth factor support or blood transfusion: total white blood cell count \<3.0×10⁹/L, absolute neutrophil count \<1.5×10⁹/L, platelet count \<75×10⁹/L, or hemoglobin \<90 g/L.
* Virology test results at screening:
1. Positive hepatitis B surface antigen (HBsAg).
2. Negative HBsAg but positive hepatitis B core antibody, with further HBV DNA level exceeding the upper reference limit of the local hospital.
3. Patients with positive hepatitis C virus (HCV) antibody and positive HCV RNA.
4. Positive human immunodeficiency virus (HIV) serology.
* Suspected active tuberculosis based on medical history or tuberculosis screening.
* Patients with known active bacterial, viral, fungal, mycobacterial, parasitic or other infections (excluding superficial onychomycosis) within 4 weeks before the baseline visit; or history of any major systemic infection requiring intravenous antibiotic therapy or hospitalization, or severe chronic/recurrent infection.
* Other severe diseases that may preclude participation in this trial, such as uncontrolled diabetes; severe cardiac dysfunction (NYHA class II or higher); acute coronary syndrome within the previous 6 months; coronary revascularization including stent implantation, coronary artery bypass grafting, and other cardiac or great vessel surgery within the previous 6 months; severe arrhythmias including frequent ventricular premature beats, ventricular tachycardia, rapid atrial fibrillation/flutter, severe bradycardia; uncontrolled hypertension (\>150/100 mmHg); severe respiratory diseases (e.g., history of obstructive lung disease and bronchospasm), etc.
* History of malignant neoplasm within the past 5 years or active malignancy at present (except for cutaneous squamous cell carcinoma, basal cell carcinoma, and cervical carcinoma in situ that have been successfully treated with no evidence of recurrence).
* Patients who received live/attenuated vaccines within 4 weeks before the baseline visit, or plan to receive live vaccines during the study period.
* History of organ/tissue transplantation or stem cell transplantation. 16. Patients who underwent any major surgical procedure within 12 weeks before the baseline visit or plan to undergo major surgery during the study.
* History of clinically significant drug abuse or alcohol abuse within 6 months before the baseline visit, as judged by the investigator.
* Pregnant or lactating women.
* Participation in another clinical drug trial, where the time from last study drug administration to screening is less than 30 days or 5 half-lives of the prior investigational product (whichever is longer); or plan to participate in another clinical drug trial during this study.
* Any other condition or symptom that, in the opinion of the investigator, renders the subject unsuitable for participation in this study.
