The present invention relates to molecules having a variant Fc region, wherein said variant Fc region comprises at least one amino acid modification relative to a wild-type Fc region. These modified molecules confer an effector function to a molecule, where the parent molecule does not detectably exhibit this effector function. In one embodiment, the variant Fc region binds FcγRIIIA and/or FcγRIIA with a greater affinity, relative to a comparable molecule comprising the wild-type Fc region. The molecules of the invention have particular utility in treatment, prevention or management of a disease or disorder, in a sub-population of patients, wherein the target antigen is expressed at low levels in the target cell population.
