Table 5.

The advantages and disadvantages of major site-specific conjugation methods for payloads other than synthetic cytotoxins.

Methods Targeting Different Sites	Technical Categories	Advantages	Disadvantages
Cys-mediated conjugation	Specific amino acids	Well investigated No special reagent or enzyme required Broad range of DAR (2 to 6) Process scalable	Potential instability in vivo, depending on the site engineered with Cys
Conjugation through Gln295 in deglycosylated Ab using mTG	Specific amino acids	High stability High selectivity	Special enzyme required DAR limited to 2
Conjugation through introduced unnatural amino acid (pAcF)	Unnatural amino acid	High selectivity Process scalable Extensively investigated	Special reagent required Cell line engineering required
Modification (GlcNAc) using transglycosidase	Glycan	High stability High selectivity Applicable for high DAR (>2) No genetic engineering required	Special reagent and enzyme required
Modification using co-expressed FGE (Cys in LCTPSR)	Short peptide tag	High stability High selectivity	Immunogenicity in human unknown with introduced peptide
Conjugation using SrtA-mediated transpeptidation	Short peptide tag	High stability High selectivity	Special enzyme required Immunogenicity in human unknown with introduced peptide