Efficient clearence of A beta protofibrils in A beta PP-transgenic mice treated with a brain-penetrating bifunctional antibody

Background: Amyloid-beta (A beta) immunotherapy is one of the most promising disease-modifying strategies for Alzheimer's disease (AD) Despite recent progress targeting aggregated forms of A beta, low antibody brain penetrance remains a challenge In the piesent study, we used transferrin receptor (TfR)-mediated transcytosis to facilitate brain uptake of our previously developed A beta protofibril-selective mAb158, with the aim of increasing the efficacy of immunotherapy directed toward soluble A beta protofibills. Methods: A beta protein precursor (A beta PP)-transgenic mice (tg-ArcSwe) were given a single dose of mAb158, modified for TfR-mediated transcytosis (RmAb158-scFvSDB), in companson with an equimolar dose or a tenfold higher dose of unmodified recombinant mAb158 (RmAb158) Soluble A beta protofibrills and total A beta in the brain were measured by enzyme-linked immunosorbent assay (ELISA) Brain distribution of radiolabeled antibodies was visualized by positron emission tomography (PET) and ex vivo autoiadiography. Results: ELISA analysis of Tris-buffered saline brain extracts demonstrated a 40% reduction of soluble A beta protofibrils in both RmAb158-scFv8D3- and high-dose RmAb158-treated mice, whereas there was no A beta protofibril reduction in mice treated with a low dose of RmAb158. Further, ex vivo autoradiography and PET imaging revealed diffeient brain distribution patterns of RmAb158-scFv8D3 and RmAb158, suggesting that these antibodies may affect A beta levels by different mechanisms. Conclusions: With a combination of biochemical and imaging analyses, this study demonstrates that antibodies engineered to be transported across the blood brain barrier can be used to increase the efficacy of A beta immunotherapy. This strategy may allow for decreased antibody doses and thereby reduced side effects and treatment costs