The purpose of this study is to evaluate the safety and tolerability of two dosing regimens of FG-3019 administered over 12 weeks in patients with diabetic nephropathy and proteinuria on background angiotensin converting enzyme inhibitor (ACEi) and/or angiotensin II receptor antagonist (ARB) therapy.

Inclusion Criteria:

1. Age 18-80 years, inclusive
2. Diagnosis of type 1 or type 2 diabetes according to American Diabetes Association (ADA) criteria
3. First morning urinary ACR >0.200 g/g
4. Receiving stable doses of ACEi and/or ARB therapy prior to Screening
5. Estimated glomerular filtration rate of ≥20 and <90 mL/min/1.73 m2
6. Willingness to maintain ACEi and/or ARB therapy, and any additional anti-hypertensive therapies to control blood pressure, at a stable dose
7. Maintenance of all additional antihypertensive medications, insulin, oral hypoglycemic agents, and cholesterol-lowering medications prior to randomization

Exclusion Criteria:

1. Female subjects who are pregnant or breastfeeding
2. Organ transplant recipient, previous dialysis, or non-diabetic renal disease other than benign cysts or anatomical variants
3. Any history of New York Heart Association (NYHA) class III/IV heart failure (HF)
4. Screening electrocardiogram showing acute, clinically significant findings including but not limited to ST depression
5. Recent history of serious heart problems (e.g. coronary artery bypass graft, cerebrovascular accident, or myocardial infarction)
6. History of cancer in the past 5 years, possibly excluding non-melanomatous skin cancer, localized bladder cancer, or in situ cervical cancer.
7. History of allergic or anaphylactic reaction to human, humanized, chimeric or murine monoclonal antibodies
8. Participation in other studies of investigational drugs at the time of Screening AND receipt of an investigational drug within 42 days prior to Screening
9. Aspartate aminotransferase (AST) or alanine aminotransferase (ALT) >2.5 times the upper limit of normal
10. Hemoglobin <10 g/dL
11. Positive for HIV (IgG) antibody