Design and application of diabodies, triabodies and tetrabodies for cancertargeting

Multivalent recombinant antibody fragments provide high binding avidity and unique specificity to a wide range of target antigens and haptens. This re view describes the design and expression of diabodies, triabodies and tetra bodies using examples of scFv molecules that target viruses (influenza neur aminidase) and cancer (Ep-CAM; epithelial cell adhesion molecule). We discu ss the preferred choice of linker length between V-domains to direct the fo rmation of either diabodies (60 kDa), triabodies (90 kDa) or tetrabodies (1 20 kDa), each with size, flexibility and valency suited to different applic ations for in vivo imaging and therapy. The increased binding valency of th ese scFv multimers results in high avidity (low off-rates). A particular ad vantage for tumour targeting is that molecules of 60-100 kDa have increased tumour penetration and fast clearance rates compared to the parent Ig (150 kDa). We highlight a number of cancer-targeting scFv multimers that have r ecently successfully undergone pre-clinical trials for in vivo stability an d efficacy. We also review the design of multi-specific Fv modules suited t o cross-link two or more different target antigens. These bi- and tri-speci fic multimers can be formed by association of different scFv molecules and, in the first examples, have been designed as cross-linking reagents for T- cell recruitment into tumours (immunotherapy), viral retargeting (gene ther apy) and as red blood cell agglutination reagents (immunodiagnostics). (C) 2001 Elsevier Science B.V. All rights reserved.