Advanced structural and bispecific antibody engineering vector systems. Features core-hinge stabilized IgG4 backbones (S228P, S228P/L235E) to prevent Fab-arm exchange, as well as complete multi-vector expression platforms utilizing dsFab interchain disulfide locks, CrossMab domain swapping, and Knobs-into-Holes (KiH) heterodimerization technologies for error-free bispecific assembly.