Table 1.

The four categories of the site-specific antibody–drug conjugation.

Techniques	Conjugation Sites	Genetic Engineering	Metabolic Labeling	Chemo-Enzymatic Modification	Selective References
Specific amino acids	C (Cys), Q (Gln)	+	−	±	[14,15,16,17,18,19,20,21,22,23]
Unnatural amino acids	pAcF, pAMF, Sec, etc.	+	+	±	[24,25,26,27,28]
Glycans	Sialic acid, GalNAc, GlcNAc, Gal, Fuc, etc.	−	±	+	[29,30,31,32,33,34,35]
Short peptide tags	LLQG, LCTPSR, etc.	+	−	+	[36,37,38,39,40,41,42]