This invention relates to an antibody which is modified version of a therapeutic antibody with affinity for a cell-surface antigen, the antibody having reduced affinity for the antigen compared with the therapeutic antibody as a result of a modification or modifications to the antibody molecule, wherein the antibody is capable of inducing immunological tolerance to the therapeutic antibody. The invention further relates to a method of inducing immunological tolerance to a therapeutic antibody, comprising administering to a patient an antibody which is a modified version of the therapeutic antibody and which has reduced affinity for the antigen as compared with the therapeutic antibody.