Inclusion Criteria:
1. Voluntary signing of informed consent.
2. Age ≥ 18 years, no gender restriction.
3. Histologically confirmed follicular lymphoma (grades 1-3a), CD20 positive by immunohistochemistry.
4. No prior systemic treatment for FL.
5. Ann Arbor stage III/IV, or stage II with bulky disease (bulky disease defined as a tumor diameter ≥ 7 cm).
6. Presence of measurable lesions.
7. Meeting any of the following criteria:
1. B symptoms: unexplained fever \>38°C, night sweats, unexplained weight loss \>10% in the last 6 months.
2. Abnormal signs: splenomegaly, pleural effusion, ascites, etc.
3. Major organ damage: involvement of major organs leading to organ dysfunction.
4. Hematologic involvement: cytopenia \[WBC \< 1.0 × 10⁹/L and/or PLT \< 100 × 10⁹/L\]; leukemia-like manifestations (malignant cells \> 5.0 × 10⁹/L); elevated LDH levels; HGB \< 120 g/L; β2-microglobulin ≥ 3 mg/L.
5. Bulky disease: involvement of ≥ 3 tumors with each diameter ≥ 3 cm, or any lymph node or extranodal tumor with diameter ≥ 7 cm (for Ann Arbor stage III-IV patients).
6. Tumor enlargement of 20%-30% within 2-3 months, or approximately 50% enlargement within 6 months.
8. Eastern Cooperative Oncology Group (ECOG) performance status of 0, 1, or 2.
9. Expected survival of \> 6 months.
Exclusion Criteria:
1. History of allergy to any component of monoclonal antibodies or investigational drugs.
2. Central nervous system involvement.
3. History of previous malignant tumors.
4. Clinically significant cardiac or pulmonary diseases.
5. Infection requiring intravenous antibiotic treatment or hospitalization within 4 weeks prior to enrollment; or infection requiring oral antibiotics within 2 weeks prior to enrollment; or symptoms related to an infection within 1 week prior to enrollment.
6. Major surgery within 4 weeks prior to enrollment.
7. Vaccination with live vaccines within 4 weeks prior to enrollment or planned live vaccination during the study.
8. HIV antibody positive.
9. Active syphilis infection, TP antibody positive, and anti-TP treatment within the last 2 years.
10. Hepatitis C virus (HCV) antibody positive with HCV RNA quantitative test result exceeding the detection limit; Hepatitis B surface antigen (HBsAg) positive or Hepatitis B core antibody (HBcAb) positive, with Hepatitis B virus DNA quantitative test result exceeding the detection limit (for patients with HBsAg or HBcAb positive status, regardless of HBV-DNA detection, oral entecavir or other antiviral therapy must be initiated prior to enrollment and continued according to the physician's instructions during the trial).
11. Pregnant or breastfeeding women, or planning to become pregnant during the study.
12. Investigator determines the patient is unsuitable for enrollment or may not be able to complete the trial for other reasons.
