A Review of Methodologies for the Detection, Quantitation, and Localization of Free Cysteine in Recombinant Proteins: A Focus on Therapeutic Monoclonal Antibodies

Abstract

Free-cysteine residues in recombinant biotherapeutics such as monoclonal antibodies can arise from incorrect cellular processing of disulfide bonds during synthesis or by reduction of disulfide bonds during the harvest and purification stage of manufacture. Free cysteines can affect potency, induce aggregation, and decrease the stability of therapeutic proteins, and the levels and positions of free cysteines in proteins are closely monitored by both manufacturers and regulators to ensure safety and efficacy. This review summarizes the latest methodologies for the detection and quantification of free cysteines.