The accelerated blood clearance (ABC) phenomenon: clinical challenge and approaches to manage.

Despite the clinical introduction of an increasing number of polyethylene glycol (PEG)-conjugated substances, PEG has been named as the cause of an unexpected immunogenic response known as the "accelerated blood clearance (ABC) phenomenon." This phenomenon has been extensively observed during the repeated administration of PEG-conjugated substances and PEGylated nanocarriers including PEGylated liposomes, PEGylated nanoparticles, PEGylated micelles, etc., resulting in the increased clearance and reduced efficacy of PEG-conjugated substances/PEGylated nanocarriers. In this review, therefore, we focused on the possible mechanisms underlying the induction of such a phenomenon and emphasized the factors affecting its magnitude. In addition, the clinical implications of the ABC phenomenon on the therapeutic efficacy of PEG-conjugated substances/PEGylated nanocarriers, along with the new approaches that can be applied to manage and/or abrogate the induction of the ABC phenomenon, are also discussed.