The purpose of this study is to see at what dose MDX-1342, a monoclonal antibody, is safe and tolerable for patients with chronic lymphocytic leukemia (CLL). Information on any responses that patients may have to the drug will also be collected.

Chronic lymphocytic leukemia (CLL) is a monoclonal hematopoietic disorder characterized by a progressive expansions of lymphocytes of B-cell lineage. These small, mature-appearing lymphocytes accumulate in the blood, bone marrow, lymph nodes, and spleen. CLL is a common leukemia in the wester world and accounts for 25% to 30% of adult leukemias. CD19,an integral membrane protein, is expressed by pro-B cells and functions as a co-stimulatory molecule that regulates mature B-cell activation and enhances B-cell proliferation. MDX-1342, a fully human monoclonal antibody, has demonstrated to specifically bind to human CD19 antigen with high affinity. Therefore, it is theorized that MDX-1342 will block activation of B cell stimulation, decreasing the number of cancerous B cell clones.

Inclusion Criteria:

• relapsed/refractory CD19-positive CLL
• At least 28 days since prior treatment for CLL
• ECOG PS 0-2
• Screening laboratory values must be met

Exclusion Criteria:

• No prior anti-CD19 antibody tx
• No active, uncontrolled infection
• No prior allogeneic bone marrow transplant
• No autoimmune disease