a, Configuration of the trispecific antibody (left), and the crystal structures modeled using the crystal structure of anti-CD28supxCD3mid CODV-Fab and the anti-CD38VH1 Fab model (right), color-coded by parental antibody. Dark shades (purple or green) denote heavy-chain peptides, while light shades denote light-chain peptides. Fv, variable fragment. b, Model of the trispecific antibody bound to the cell-surface membrane CD28 dimer. CD28 residues 135–152 are modeled as a random coil extending from the last visible electron density of the COOH terminus of CD28. The CD28 dimer is depicted in red. Trispecific antibody is shown in surface representation, with a side view from the membrane (top) and at 90° of rotation (bottom).