Polypeptides and antibodies derived from chronic lymphocytic Leukemia cells and uses thereof

A method for treating chronic lymphocytic leukemia (CLL), said method comprising administering to a patient suffering from CLL an antibody, or an antigen-binding fragment thereof, that binds to OX-2/CD200 and comprises a light chain CDR1 having the sequence set forth in residues 26-36 of SEQ ID NO:209;

• a light chain CDR2 having the sequence set forth in residues 52-58 of SEQ ID NO:209;
• a light chain CDR3 having the sequence set forth in residues 91-99 of SEQ ID NO:209;
• a heavy chain CDR1 having the sequence set forth in SEQ ID NO:149;
• a heavy chain CDR2 having the sequence set forth in SEQ ID NO:174;
• and a heavy chain CDR3 having the sequence set forth in SEQ ID NO:195, wherein the patient's CLL has been identified as overexpressing OX-2/CD200 three to six-fold as compared to normal peripheral blood mononuclear cells.