Effect of allotypic variation of human IgG1 on the thermal stability of disulfide-linked knobs-into-holes mutants of the Fc for stable bispecific antibody design.

BACKGROUND: Disulfide-linked knobs-into-holes (dKiH) mutation is a well-validated antibody engineering technique to force heterodimer formation of different Fcs for efficient production of bispecific antibodies. An artificial disulfide bond is created between mutated cysteine residues in CH3 domain of human IgG1 Fc whose positions are 354 of the "knob" and 349 of the "hole" heavy chains. The disulfide bond is located adjacent to the exposed loop with allotypic variations at positions 356 and 358. Effects of the variation on the biophysical property of the Fc protein with dKiH mutations have not been reported. METHODS: We produced dKiH Fc proteins of high purity by affinity-tag fusion to the hole chain and IdeS treatment, which enabled removal of mispaired side products. Thermal stability was analyzed in a differential scanning calorimetry instrument. RESULTS: We firstly analyzed the effect of the difference in allotypes of the Fcs on the thermal stability of the heterodimeric Fc. We observed different melting profiles of the two allotypes (G1m1 and nG1m1) showing slightly higher melting temperature of G1m1 than nG1m1. Additionally, we showed different characteristics among heterodimers with different combinations of the allotypes in knob and hole chains. CONCLUSION: Allotypic variations affected melting profiles of dKiH Fc proteins possibly with larger contribution of variations adjacent to the disulfide linkage.