Inclusion Criteria:

• ≥ 18 years of age.
• Biopsy proven Focal Segmental Glomerulosclerosis (FSGS) lesion
• Foot process effacement ≥ 80% on electron microscopy.
• Presence of nephrotic syndrome (proteinuria > 3.5g/24hrs and serum albumin < 3.5 g/dl) prior to initiation of immunosuppressive therapy.
• Resistant or dependent on therapy, including corticosteroids or calcineurin inhibitors or who have failed rituximab. Patient who have contraindication to or refuse to take high dose corticosteroids are allowed. 

Exclusion Criteria:

• Genetic or secondary forms of FSGS.
• Hepatitis B, C or HIV positive.
• Pregnant or breast-feeding.
• Active infection.
• Kidney transplant.
• Anemia with Hgb < 8.0 g/dL.
• Thrombocytopenia with platelet count < 100’000.
• Any other disease, metabolic dysfunction, physical examination finding, or clinical laboratory finding giving reasonable suspicion of a disease or condition that contraindicates the use of an investigational drug or that may affect the interpretation of the results or render the patient at high risk from treatment complication.
• Patients who have received cyclophosphamide in the last 6 months.
• Patients who received rituximab previously with CD20 count of < 5 cells/microliter  at the time of enrollment.
• For women who are not postmenopausal (≥ 12 months of non-therapy-induced amenorrhea) or surgically sterile (absence of ovaries and/or uterus): agreement to remain abstinent or use two adequate methods of contraception, including at least one method with a failure rate of less than (<) 1 percent (%) per year, during the treatment period and for at least 18 months after the last dose of study drug.
• For men: agreement to remain abstinent or use two adequate methods for contraception, including at least one method with failure rate of less than 1% per year during the treatment period and for at least 6 months (180 days) after the last dose of drug.