The present invention relates to Fc region-containing polypeptides that exhibit improved 
effector function due to alterations of the extent of 
fucosylation, and to methods of using such polypeptides for treating or preventing 
cancer and other diseases. The Fc region-containing polypeptides of the present invention are preferably immunoglobulins (e.g., antibodies), in which the Fc region comprises at least one 
amino acid substitution relative to the corresponding 
amino acid sequence of a 
wild type Fc region, and which is sufficient to attenuate post-translational 
fucosylation and mediate improved binding to an activating 
Fc receptor and reduced binding to an inhibitory 
Fc receptor. The methods of the invention are particularly useful in preventing, treating, or ameliorating one or more symptoms associated with a 
disease, disorder, or infection where either an enhanced 
efficacy of 
effector cell function mediated by FcγR is desired (e.g., 
cancer, infectious 
disease) or an inhibited 
effector cell response mediated by FcγR is desired (e.g., 
inflammation, 
autoimmune disease).