The present invention relates to combination therapy involving two or more Fc region-containing antigen-binding polypeptides, such as antibodies, wherein the polypeptides have been modified such that hetero-oligomerization between the polypeptides is strongly favored over homo-oligomerization when the polypeptides are bound to their corresponding target antigens. The invention also relates to polypeptides, compositions, kits and devices suitable for use in the combination therapy of the invention.