The present invention provides humanized monoclonal antibodies, bi-specific antibodies, antibody conjugates, and fusion proteins that bind to the chemokine receptor CCR4. This antibody is derived from CCR4- IgG1 and recognizes the same epitope. This antibody contains either an IgG4 or a stabilized IgG4 in order to improve binding efficiency and reduce in vivo Fab arm exchange. Binding of the antibodies disclosed herein to CCR4 inhibits ligand-mediated activities and is used to treat symptoms of cancer.