Detection of drug specific circulating immune complexes from in vivo cynomolgus monkey serum samples.

BACKGROUND Administration of a biotherapeutic can result in the formation of anti-drug antibodies (ADAs). The resulting ADA can potentially form immune complexes (ICs) with the drug leading to altered pharmacokinetic (PK) profiles and/or adverse events. Furthermore the presence of such complexes may interfere with accurate PK assessment, and/or detection of ADA in immunogenicity assays. Here, we present two assays to detect the presence of drug-ADA immune complexes in cynomolgus monkeys. RESULTS Serum samples were analyzed for IC formation in vivo. 8/8 tested animals were positive for drug specific IC. Depending on the time point tested 4/8 or 7/8 animals tested positive for ADA during drug dosing. All 8 animals were confirmed positive for ADA during the washout phase, indicating drug interference in the bridging assay. Relative amount of IC over time was determined and its correlation with PK and ADA was then assessed. Multivariate data analysis demonstrates good correlation between signals obtained from the anti-drug and FcγRIIIa based capture assays, although due to its biological characteristic FcγRIIIa based assay captured only a subset of drug specific IC. In one animal IC remained in circulation even when the drug levels decreased below detection limit. CONCLUSION Results from this study indicate the presence of IC during administration of an immunogenic biotherapeutic. Potential application of these assays includes detection of ADA in an IC during high drug levels. The results on the kinetics of IC formation during ADA response can complement the understanding of PK and ADA profiles. Moreover, the presence of IC indicates possible ADA interference in standard PK assays and potential underestimation of total drug exposure in toxicology studies. In addition this study also highlights the need to understand downstream in vivo consequences of drug-ADA IC as no animals under investigation developed adverse events.