Therapeutic MABs are large immunoglobulin proteins (usually IgG) comprising several polypeptide chains. They may require further modification such as by glycosylation, conjugation with another molecule, or for a fragment to be extracted.

Conjugation with a PEG polymer (eg certolizumab pegol) can help delay clearance from the body and extend the MAB’s half-life.⁴

Conjugation with a cytotoxic agent such as ozogamicin, monomethyl auristatin E (MMAE and named vedotin as the conjugate) or maleimidocaproyl monomethyl auristatin F (mcMMAF/mafodotin), uses the MAB to deliver the cytotoxic drug to specific receptors that are expressed on cancerous cells. MMAE’s toxicity is such that a MAB is needed to target it at the active site in order to keep the dose low.⁴

Using a MAB fragment can reduce exposure to extraneous peptide material, while improving target specificity. Being smaller also promotes better tissue or tumour penetration/distribution than the unmodified antibody.