Hemocompatibility testing for nanomedicines and biologicals: predictive assays for complement mediated infusion reactions

Infusion, or hypersensitivity reactions (HSRs) are frequent side effects of i.v. administered nanomedicines and biologicals. These, mostly mild and well tolerated, but occasionally severe or fatal allergic reactions represent a hemo-incompatibility due to activation of the complement (C) system. This review details the HSRs caused by marketed nanomedicines (liposomal drugs, micellar systems, polymer-conjugates of proteins, imaging agents, drug carrier nanosystems) and antibody therapeutics (mAbs), pointing out the remarkable similarity of clinical symptoms and difference from true (IgE-mediated) allergy. Beside the essentials, such as terminology, prevalence, risk factors and molecular and cellular mechanism of C activation-related pseudoallergy (CARPA) caused by the above agents, the paper highlights the biological rationale of these reactions, i.e., misinterpretation of nanoparticulate drugs by the immune system as pathogenic viruses, and C activation being an inherent function of mAbs. The public, as well as regulatory agencies are increasingly aware of the safety risks of possibly severe adverse immune reaction of drugs in the above categories, expressing need for new and appropriate immune toxicity tests in the preclinical stage. Here we outline and comment on the available methods for C activation and CARPA testing in vitro and in vivo, namely, the ELISA of C cleavage products (C3a, C5a, C4d, Bb, SC5b-9), the hemolytic (CH50) C assay, FACS measurement of basophil leukocyte activation, a – potentially – multiplex bead assay for C activation byproducts, the porcine assay of nanoparticle-induced cardiopulmonary distress and other CARPA tests in animals. The proven parallelisms between C activation and HSRs in vivo provide rationale for using these tests as predictors of infusion hypersensitivity, and the review suggests a decision tree for their use.