Key Inclusion Criteria:

Key Inclusion Criteria:

• Aged >= 18 years old at the time of informed consent.
• Histologically confirmed follicular Grade 1-3a NHL.
• Relapsed or progressive disease after at least 1 prior chemotherapy requiring treatment.
• Bidimensionally measurable disease with at least 1 lesion >= 2.0 cm in a single dimension.
• Acceptable hematologic, hepatic, and renal function parameters.
• Recovered fully from any significant toxicity associated with prior surgery, radiation treatments, chemotherapy, biological therapy, autologous bone marrow or stem cell transplant, or investigational drugs.

Key Exclusion Criteria:

• Follicular lymphoma Grade 3b.
• Rituximab refractory or refractory to anti-CD20 radioimmunotherapy (no response to prior rituximab or prior rituximab-containing regimen, or a response with a TTP of less than 6 months).
• Cancer radiotherapy, biological therapy, or chemotherapy within 3 weeks prior to Study Day 1 (6 weeks if nitrosourea or mitomycin C).
• Prior lymphoma vaccine therapy within 12 months prior to Study Day 1.
• Prior antibody therapy for lymphoma (including radioimmunotherapy) within 6 months prior to Study Day 1.
• Autologous bone marrow or stem cell transplant within 6 months prior to Study Day 1.
• Prior allogeneic transplant.
• Transfusion-dependent subjects.
• Another primary malignancy requiring active treatment (except hormonal therapy).
• Serious nonmalignant disease (e.g., congestive heart failure, hydronephrosis); active uncontrolled bacterial, viral, or fungal infections; or other conditions, which would compromise protocol objectives in the opinion of the Investigator and/or the Sponsor.
• New York Heart Association Class III or IV cardiac disease or myocardial infarction within 6 months prior to Study Day 1.