Inclusion Criteria:

• Signed Informed Consent Form
• Age ≥ 18 years
• History of histologically confirmed CD20+ follicular NHL Grade 1, 2, or 3a
• Progression of disease following the most recent treatment with rituximab-containing therapy that resulted in stable disease or a partial or complete response lasting ≥ 6 months
• Measurable disease
• Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1
• For subjects of reproductive potential (males and females), use of a reliable means of contraception (e.g., contraceptive pill, intrauterine device [IUD], physical barrier throughout the trial and for 1 year following their final exposure to study treatment).
• Life expectancy of > 3 months

Exclusion Criteria:

• Prior radiotherapy to a measurable, metastatic lesion(s) to be used to measure response unless that lesion shows unequivocal progression at baseline
• Radiation therapy to a peripheral lesion within 14 days prior to Day 1; Radiation therapy to a thoracic, abdominal, or pelvic field within 28 days prior to Day 1
• Chemotherapy, hormonal therapy, radiotherapy, or immunotherapy within 4 weeks prior to Day 1
• Patients who have received radioimmunotherapy for relapsed or refractory, follicular NHL are eligible for the study if they received this therapy at least 1 year prior to Day 1, they have adequate bone marrow function, and they have no evidence of myelodysplastic syndrome on bone marrow aspirate/biopsy
• Prior treatment with Apo2L/TRAIL or an agonist antibody to DR4 or DR5
• Concurrent systemic corticosteroid therapy
• Evidence of clinically detectable ascites on Day 1
• Other invasive malignancies within 5 years prior to Day 1
• History or evidence upon physical examination of CNS disease within 1 year prior to study entry
• Active infection requiring parenteral antibiotics on Day 1
• Major surgical procedure, open biopsy, or significant traumatic injury within 28 days prior to Day 1 or anticipation of need for major surgical procedure during the course of the study and fine needle aspirations within 7 days prior to Day 1
• Pregnancy or lactation
• Serious nonhealing wound, ulcer, or bone fracture
• Current or recent participation in another experimental drug study
• Clinically significant cardiovascular disease
• Known positive test result for HIV, hepatitis B surface antigen (sAg), hepatitis B IgG or IgM core antibody, or hepatitis C antibody
• Known sensitivity to murine or human antibodies
• History of other disease, metabolic dysfunction, physical examination finding, or clinical laboratory finding giving reasonable suspicion of a disease or condition that contraindicates use of an investigational drug or that might affect interpretation of the results of the study or render the subject at high risk from treatment complications