Half molecule exchange is the process whereby two IgG4 molecules exchange a heavy chain-light chain unit to form a new IgG4 entity with specificity towards two different antigens. While this unique property of IgG4 molecules confers anti-inflammatory properties in nature, it is not a desirable feature for a therapeutic mAb. Engineering of the IgG4 hinge region making it resemble that of an IgG1 is sufficient to dramatically reduce half molecule exchange in vitro and in vivo. The S228P modification of the hinge confers pharmaceutical properties to IgG4 equivalent to those of standard IgG1, while retaining the inability to trigger ADCC and CDC. Application of the molecular precepts underlying half molecule exchange between IgG4 molecules to IgG1 scaffolds offers the possibility to produce bispecific antibodies in vitro.
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