The present invention relates to antibodies or fragments thereof that specifically bind Fc³RIIB, particularly human Fc³RIIB, with greater affinity than said antibodies or fragments thereof bind Fc³RIIA, particularly human Fc³RIIA. The present invention also provides the use of an anti-Fc³RIIB 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.
