US Patent 9815909 Readily isolated bispecific antibodies with native immunoglobulin format

The invention relates to antigen-binding proteins or antibodies having heterodimers of heavy chains, i.e., two immunoglobulin heavy chains that differ by at least one or two amino acid(s) that allows for isolation of the antigen-binding protein based on a differential affinity of an immunoglobulin heavy chain and a modified/mutated immunoglobulin heavy chain toward an affinity reagent. The invention also relates antigen-binding proteins, including bispecific antibodies, having IgG CH1 regions with different affinities with respect to affinity reagent(s) that allows rapid isolation by differential binding of the IgG regions to the affinity reagent(s).