The variable region of the B cell receptor (BCR), known as the idiotype, is a patient-specific tumour surface marker on lymphoma cells. To therapeutically target idiotypes, Torchia et al. created antibody-like molecules termed peptibodies comprised of a short synthetic patient-specific idiotype-binding peptide covalently linked to the amino-terminus of a recombinant immunoglobulin G crystallizable fragment (IgG Fc). The peptibodies crosslink idiotypes on human lymphoma cells, triggering BCR signalling and inducing apoptosis, resulting in complete clearance of human lymphoma in mouse xenograft models.