This phase III trial aims to compare the efficacy and safety of MIL62 combined lenalidomide and lenalidomide alone to treat patient diagnosed with Follicular Lymphoma (FL) and refractory to rituximab. The study randomized patients with a 1:1 ratio to receive either MIL62 plus lenalidomide or lenalidomide.

Inclusion Criteria:

1. Adult patients, >=18 years of age;
2. Patients with either histologically documented CD20-positive FL, WHO grade 1, 2 or 3a
3. Evidence of refractory to rituximab
4. Eastern Cooperative Oncology Group (ECOG) performance status of 0, 1 or 2
5. At least one bi-dimensionally measurable nodal or tumor lesion defined by CT scan as: greatest transverse diameter > 1.5 cm and a short axis ≥ 10mm
6. Adequate hematologic function
7. Life expectancy >5 years
8. Able and willing to provide written informed consent and to comply with the study protocol

Exclusion Criteria:

1. Evidence of refractory to lenalinomide
2. Central nervous system lymphoma
3. Patients with progressive multifocalleukoencephalopathy (PML)
4. Prior use of any antibody therapy(except for Rituximab ) within 3 months of study start
5. Prior use of any anti-cancer vaccine
6. Prior administration of radiotherapy 42 days prior to study entry
7. Prior administration of chemotherapy 28 days prior to study entry
8. History of prior malignancy within the last 3 years, with the exception of curatively treated basal or squamous cell carcinoma of the skin and low-grade in situ carcinoma of the cervix
9. History of severe allergic or anaphylactic reactions to monoclonal antibody therapy
10. Known hypersensitivity to thalidomide or lenalidomide
11. Regular treatment with corticosteroids prior to the start of cycle 1, unless administered for indications other than NHL at a dose equivalent to < 20 mg/day prednisone
12. Any serious active disease or co-morbid medical condition (such as New York Heart Association Class II or IV cardiac disease, severe arrhythmia, myocardial infarction within the last 6 months, unstable arrhythmias, or unstable angina) or pulmonary disease (including obstructive pulmonary disease and history of bronchospasm or other according to investigator's decision)
13. Infection with human immunodeficiency virus (HIV), hepatitis B or hepatitis C(including HBsAg,HBcAb positive with abnormal HBV DAN or HCV RNA )
14. Pregnant or lactating females