The invention relates to combination therapy involving two or more antibodies, wherein the Fc regions of the two antibodies have been modified such that hetero-oligomerization between the antibodies is strongly favored over self-oligomerization when antibodies are bound to their corresponding target antigens and such that hetero-oligomerization-independent effector functions of one or both antibodies are eliminated or strongly reduced. The invention also relates to antibodies, compositions, and kits suitable for use in the combination therapy of the invention.