Autologous peripheral blood stem cell transplantation combined with high dose chemotherapy is the treatment of choice given to patients with diffuse large-B cell lymphoma (DLBCL) following relapse of the disease. Although many people are cured of their lymphoma with this therapy, the disease comes back in a certain proportion of patients. The purpose of this study is to test the safety and effectiveness of the monoclonal antibody, CT-011, in patients with DLBCL who have received autologous peripheral blood stem cell transplantation. All final eligible patients will receive an IV infusion of CT-011 on Day 1 (30 to 90 days post autologous PBSCT). Treatment will be repeated every 42 days for a total of three courses with treatment visits on Days 1, 43, and 85. Follow-up for safety and clinical outcome will be conducted throughout the study till 18 months post autologous PBSCT. Approximately 70 patients will participate in this study.

Inclusion Criteria:

1. Patient's age is 18 years or older, both genders.
2. Confirmed Diffuse Large B-cell Lymphoma, transformed follicular lymphoma, diffuse mixed cell lymphoma or primary mediastinal large cell lymphoma with B-cell lineage.
3. The lymphoma is chemosensitive.
4. The lymphoma did not progress since pre-transplant chemotherapy.
5. ECOG performance status 0-1.

Exclusion Criteria:

1. Serious other illness.
2. Active autoimmune disease.
3. Type 1 diabetes.
4. Known immune deficiency.
5. Clinical evidence of primary or secondary brain or spinal cord involvement by lymphoma.
6. Active bacterial, fungal, or viral infection.
7. Positive HIV, Hepatitis B surface antigen plus viremia, or Hepatitis C antibody plus viremia.
8. Pregnant or nursing (positive pregnancy test).
9. Other concurrent clinical study or investigational therapy.