High-Throughput IgG Reformatting and Expression Using Hybrid Secretion Signals and InTag Positive Selection Technology.

We have previously published protocols for high-throughput IgG reformatting and expression, that enable rapid reformatting of phage-displayed antibody Fab fragments into a single dual expression vector for full IgG expression in Expi293F cells (Chen et al. Nucleic Acids Res 42:e26, 2014; Chen et al. Methods in Molecular Biology, vol 1701, 2018). However, when working with phage clones from a naïve library containing highly diverse N-terminal sequences, where the 5' PCR primers bind, the PCR step can become cumbersome. To overcome this limitation, we have investigated and found that the C-terminal 7 amino acid residues of the human antibody VH1 secretion signal can be replaced with those from ompA or pelB bacterial signals to form hybrid signal sequences that can drive strong IgG expression in Expi293F cells. The use of such hybrid signals allows any Fab fragment in the library to be amplified and cloned into the IgG expression vector using only a single 5' PCR primer targeting the bacterial secretion signal of the light or heavy chain, thus dramatically simplifying the IgG reformatting workflow.