This is an open-label, multicenter Phase Ib study designed to evaluate the safety, pharmacokinetics, and preliminary efficacy of SGN-40 when combined with rituximab in patients with relapsed CD20-positive, follicular or marginal zone NHL who have received at least one prior rituximab-containing regimen.

Inclusion Criteria:

• Documented history of histologically confirmed CD20-positive, follicular NHL or marginal zone NHL
• At least one previous treatment with rituxan monotherapy or a rituximab-containing regimen
• Measurable disease
• Either fresh or archived tumor specimen must be available for central confirmation of diagnosis and correlative studies
• Life expectancy of > 3 months
• For patients of reproductive potential, use of a reliable means of contraception

Exclusion Criteria:

• Chemotherapy or radiotherapy within 28 days of Day 1
• Prior treatment with a monoclonal antibody directed against CD40
• Radioimmunotherapy or immunotherapy with a monoclonal antibody other than rituximab within 3 months of Day 1
• Prior treatment with an investigational drug within 28 days of Day 1
• Prior allogeneic bone marrow transplant
• Prior autologous hematopoietic stem cell transplant within 12 weeks of Day 1
• Concurrent systemic corticosteroid therapy
• Prior anaphylactoid or other serious reaction to rituximab that resulted in hospitalization or discontinuation of therapy, or both
• Evidence of clinically detectable ascites on Day 1
• Other invasive malignancies within 3 years prior to Day 1 except for adequately treated basal cell or squamous cell skin cancer, in situ carcinoma of the cervix, in situ breast cancer, in situ prostate cancer, or other cancer of which the patient has been disease-free for at least 3 years
• History or evidence on physical examination of CNS disease
• Active infection requiring parenteral antibiotics within 14 days of Day 1
• Major surgical procedure (excluding lymph node biopsy) or significant traumatic injury within 28 days prior to Day 1
• Pregnancy (positive pregnancy test) or lactation
• Serious, nonhealing wound, ulcer, or bone fracture
• Clinically significant cardiovascular disease, congestive heart failure, serious cardiac arrhythmia requiring medication within 1 year prior to Day 1. Grade II or greater peripheral vascular disease at study entry.
• Known human immunodeficiency virus (HIV) infection
• Known serious medical conditions, including cirrhosis, hepatitis C infection, and chronic obstructive or chronic restrictive pulmonary disease