Gantenerumab: a novel human anti-Aß antibody demonstrates sustained cerebral amyloid-ß binding and elicits cell-mediated removal of human amyloid-ß.

The amyloid-ß lowering capacity of anti-Aß antibodies has been demonstrated in transgenic models of Alzheimer's disease (AD) and in AD patients. While the mechanism of immunotherapeutic amyloid-ß removal is controversial, antibody-mediated sequestration of peripheral Aß versus microglial phagocytic activity and disassembly of cerebral amyloid (or a combination thereof) has been proposed. For successful Aß immunotherapy, we hypothesized that high affinity antibody binding to amyloid-ß plaques and recruitment of brain effector cells is required for most efficient amyloid clearance. Here we report the generation of a novel fully human anti-Aß antibody, gantenerumab, optimized in vitro for binding with sub-nanomolar affinity to a conformational epitope expressed on amyloid-ß fibrils using HuCAL(®) phage display technologies. In peptide maps, both N-terminal and central portions of Aß were recognized by gantenerumab. Remarkably, a novel orientation of N-terminal Aß bound to the complementarity determining regions was identified by x-ray analysis of a gantenerumab Fab-Aß(1-11) complex. In functional assays gantenerumab induced cellular phagocytosis of human amyloid-ß deposits in AD brain slices when co-cultured with primary human macrophages and neutralized oligomeric Aß42-mediated inhibitory effects on long-term potentiation in rat brain. In APP751(swedish)xPS2(N141I) transgenic mice, gantenerumab showed sustained binding to cerebral amyloid-ß and, upon chronic treatment, significantly reduced small amyloid-ß plaques by recruiting microglia and prevented new plaque formation. Unlike other Aß antibodies, gantenerumab did not alter plasma Aß suggesting undisturbed systemic clearance of soluble Aß. These studies demonstrated that gantenerumab preferentially interacts with aggregated Aß in the brain and lowers amyloid-ß by eliciting effector cell-mediated clearance.

The human combinatorial antibody library HuCAL GOLD combines diversification of all six CDRs according to the natural immune system with a novel display method for efficient selection of high-affinity antibodies.

This article describes the generation of the Human Combinatorial Antibody Library HuCAL GOLD. HuCAL GOLD is a synthetic human Fab library based on the HuCAL concept with all six complementarity-determining regions (CDRs) diversified according to the sequence and length variability of naturally rearranged human antibodies. The human antibody repertoire was analyzed in-depth, and individual CDR libraries were designed and generated for each CDR and each antibody family. Trinucleotide mixtures were used to synthesize the CDR libraries in order to ensure a high quality within HuCAL GOLD, and a beta-lactamase selection system was employed to eliminate frame-shifted clones after successive cloning of the CDR libraries. With these methods, a large, high-quality library with more than 10 billion functional Fab fragments was achieved. By using CysDisplay, the antibody fragments are displayed on the tip of the phage via a disulfide bridge between the phage coat protein pIII and the heavy chain of the antibody fragment. Efficient elution of specific phages is possible by adding reducing agents. HuCAL GOLD was challenged with a variety of different antigens and proved to be a reliable source of high-affinity human antibodies with best affinities in the picomolar range, thus functioning as an excellent source of antibodies for research, diagnostic, and therapeutic applications. Furthermore, the data presented in this article demonstrate that CysDisplay is a robust and broadly applicable display technology even for high-throughput applications.