Abstract: The present invention relates to antibodies or fragments thereof that specifically bind the extracellular domain of Fc?RIIB, particularly human Fc?RIIB, and block the Fc binding site of human Fc?RIIB. The invention provides methods of treating cancer and/or regulating immune complex mediated cell activation by administering the antibodies of the invention to enhance an immune response. The invention also provides methods of breaking tolerance to an antigen by administering an antigen-antibody complex and an antibody of the invention.

Abstract: The present invention relates to antibodies or fragments thereof that specifically bind Fc?RIIB, particularly human Fc?RIIB, with greater affinity than said antibodies or fragments thereof bind Fc?RIIA, particularly human Fc?RIIA. The present invention also provides the use of an anti-Fc?RIIB antibody or an antigen-binding fragment thereof, as a single agent therapy for the treatment, prevention, management, or amelioration of a cancer, preferably a B-cell malignancy, particularly, B-cell chronic lymphocytic leukemia or non-Hodgkin's lymphoma, an autoimmune disorder, an inflammatory disorder, an IgE-mediated allergic disorder, or one or more symptoms thereof. The invention provides methods of enhancing the therapeutic effect of therapeutic antibodies by administering the antibodies of the invention to enhance the effector function of the therapeutic antibodies. The invention also provides methods of enhancing efficacy of a vaccine composition by administering the antibodies of the invention.

Abstract: The present invention relates to antibodies or fragments thereof that specifically bind Fc?RIIB, particularly human Fc?RIIB, with greater affinity than said antibodies or fragments thereof bind Fc?RIIA, particularly human Fc?RIIA. The invention provides methods of enhancing the therapeutic effect of therapeutic antibodies by administering the antibodies of the invention to enhance the effector function of the therapeutic antibodies. The invention also provides methods of enhancing efficacy of a vaccine composition by administering the antibodies of the invention.