Inclusion Criteria:

• Male or female, >18 years old
• Histological diagnosis of CD20+ B-cell NHL, with DLBCL or other aggressive lymphomas by WHO lymphoma criteria including mantle cell lymphoma and transformed follicular lymphoma.
• Failed at least one prior standard treatment regimen for NHL
• If DLBCL, either received, ineligible for or refused high-dose chemotherapy with stem cell transplant
• Measurable NHL disease by CT, with at least one lesion >1.5 cm in one dimension
• Adequate performance status (>70 Karnofsky scale, 0-1 ECOG)* with an estimated life expectancy of at least 6 months
• Laboratory parameters:
  • Adequate hematology (Hemoglobin ≥ 10 g/dL, ANC ≥ 1.5 ´ 109/L, platelets ≥100 x 109/L) without ongoing transfusional support
  • Adequate renal and liver function (creatinine and bilirubin ≤ 1.5 x IULN; AST and ALT ≤ 2.5 x IULN)
• Otherwise,
• 3 months beyond any prior rituximab or veltuzumab treatment, 12 weeks beyond autologous stem cell transplant and 4 weeks beyond chemotherapy, other experimental treatments, or any radiation therapy to the index lesion(s).
• Screened for hepatitis B (no time limit) and negative by tests included in NCCN guidelines (hepatitis B surface antigen/antibodies, core antigen/antibodies, hepatitis B e-antigen).
• Patients of childbearing potential must be willing to practice birth control during the study until at least 12 weeks after last veltuzumab infusion; women of childbearing potential must have a negative urine or serum pregnancy test to enter the study.
• Ability to provide signed, informed consent

Exclusion Criteria:

• Pregnant or lactating women. Women of childbearing potential are required to have a negative pregnancy test
• NCI CTC Grade 3 or 4 infusion reaction to prior anti-CD20 antibodies (rituximab, veltuzumab, etc.)
• A known anti-antibody response to prior antiCD20 antibodies (HACA positive, HAHA positive, etc)
• Prior radioimmunotherapy, including Zevalin or Bexxar.
• Prior high-dose chemotherapy with peripheral blood stem cell transplant.
• Prior therapy with other human or humanized monoclonal antibodies, unless HAHA tested and negative
• Primary CNS lymphoma, HIV lymphoma or transformed lymphoma, or presence of symptomatic CNS metastases or carcinomatous meningitis.
• Rituximab or veltuzumab resistant, defined as having progressed during or within 6 months of any prior rituximab or veltuzumab treatment.
• Bulky disease by CT, defined as any single mass >10 cm in its greatest diameter
• Bone marrow involvement ≥25%
• Prior external beam radiation therapy to >30% bone marrow.
• Pleural effusion with positive cytology for lymphoma
• Patients known to be HIV positive, hepatitis B positive, or hepatitis C positive
• Known autoimmune disease or presence of autoimmune phenomena.
• Evidence of infection or requiring antibiotics within 7 days.
• Use of systemic corticosteroids within 2 weeks, except low dose regimens (prednisone, <20 mg/day, or equivalent) which may continue if unchanged.
• Prior malignancies (other than non-melanoma skin cancer or carcinoma in situ of the cervix) unless disease free for 5 years.
• Prior malignancy with less than a 5-year disease-free interval, excluding nonmelanoma skin cancers and carcinoma in situ of the cervix.
• Other concurrent medical or psychiatric conditions that, in the Investigator's opinion, may be likely to confound study interpretation or prevent completion of study procedures and follow-up examinations