FcγRIIB specific antibodies and methods of use thereof

A method of treating cancer in a patient having a cancer characterized by a cancer antigen, said method comprising administering to said patient a therapeutically effective amount of a humanized antibody or an antigen-binding fragment thereof that specifically binds to the extracellular domain of native human FcγRIIB with a greater affinity than said antibody binds to the extracellular domain of native human FcγRIIA, wherein said humanized antibody or said antigen-binding fragment thereof possesses CDR1, CDR2 and CDR3 from an antibody heavy chain, and CDR1, CDR2 and CDR3 from an antibody light chain, and wherein said humanized antibody or fragment thereof comprises:

• (1) a polypeptide comprising the amino acid sequence of SEQ ID NO. 1 (CDR1 of the heavy chain of humanized antibody 2B6), SEQ ID NO. 2 (CDR2 of the heavy chain of humanized antibody 2B6), and SEQ ID NO. 3 (CDR3 of the heavy chain of humanized antibody 2B6);
• or
• (2) a polypeptide comprising the amino acid sequence of SEQ ID NO. 8 (CDR1 of the light chain of humanized antibody 2B6), SEQ ID NO. 11 (CDR2 of the light chain of humanized antibody 2B6), and SEQ ID NO. 12 (CDR3 of the light chain of humanized antibody 2B6);
• or
• (3) a polypeptide comprising the amino acid sequence of SEQ ID NO. 29 (CDR1 of the heavy chain of humanized antibody 3H7), SEQ ID NO. 30 (CDR2 of the heavy chain of humanized antibody 3H7), and SEQ ID NO. 31 (CDR3 of the heavy chain of humanized antibody 3H7);
• or
• (4) a polypeptide comprising the amino acid sequence of SEQ ID NO. 38 (CDR1 of the light chain of humanized antibody 3H7), SEQ ID NO. 39 (CDR2 of the light chain of humanized antibody 3H7), and SEQ ID NO. 40 (CDR3 of the light chain of humanized antibody 3H7);
• and wherein the administered antibody reduces the population of cancer cells expressing FcγRIIB.