Structure of VB22B sc(Fv)2 minibody. A noncovalent (55 kDa) “diabody” (middle of figure) can be generated by taking the VH and VL regions of a whole anti-Mpl monoclonal IgG (left) and coupling them via a 5-amino acid linker (GGGGS). VB22B sc(Fv)2 is made by binding one VH and one VL fragment together with a 15-amino acid linker [(GGGGS)3] and then binding 2 of these constructs together with the same 15-amino acid linker (middle). Both the diabody and the VB22Bsc(Fv)2 bind and activate the TPO receptor (right). Illustration by Paulette Dennis.