Hybrid IgG4/IgG4 Fc antibodies form upon ‘Fab-arm’ exchange as demonstrated by SDS-PAGE or size-exclusion chromatography

Human IgG4 antibodies are dynamic molecules that in vivo exchange half-molecules to become bispecific antibodies. Here we show that IgG4 antibodies and IgG4 Fc fragments similarly exchange resulting in hybrid antibodies (a single Fab + Fc) with a molecular weight of ca. 100 kDa. These antibodies can be separated from IgG4 and IgG4 Fc using size-exclusion chromatography and non-reducing SDS-PAGE. This method does not rely on a cross-linking immunoassay with its potential for false-positive results due to aggregation and it unambiguously demonstrates that the ‘Fab-arm’ exchange process depends entirely on the Fc part (hinge + CH2 + CH3).