A new class of monoclonal A beta antibodies selectively targets and triggers deposition of A beta protofibrils

Aggregation and accumulation of amyloid-beta peptide ( A beta) are a critical trigger for the onset of Alzheimer's disease (AD). While the plaques are the most outstanding A beta pathological feature, much of the recent research emphasis has been on soluble A beta species because of their diffusible, proinflammatory, and toxic properties. The focus on soluble aggregated A beta species has also increased the interest in antibodies that are selective for different A beta conformations. In the current study, we developed and characterized a new class of monoclonal antibodies (referred to as mAbSL) that are selective for A beta protofibrils. Cloning and sequencing of the heavy and light chain variable regions for multiple antibodies identified sequence characteristics that may impart the conformational selectivity by the antibodies. Transfection of FreeStyle 293F cells with the plasmids permitted in-house expression and purification of mAbSL antibodies along with non-conformation-selective A beta monoclonal antibodies (A beta mAbs). Several of the purified mAbSL antibodies demonstrated significant affinity and selectivity for A beta 42 protofibrils compared with A beta 42 monomers and A beta 42 fibrils. Competition ELISA assays assessing the best overall antibody, mAbSL 113, yielded affinity constants of 7 nM for the antibody-A beta 42 protofibril interaction, while the affinity for either A beta 42 monomers or A beta 42 fibrils was roughly 80 times higher. mAbSL 113 significantly inhibited A beta 42 monomer aggregation by a unique mechanism compared with the inhibition displayed by A beta mAb 513. A beta 42 protofibril dynamics were also markedly altered in the presence of mAbSL 113, whereby insoluble complex formation and protofibril deposition were stimulated by the antibody at low substoichiometric molar ratios. As the field contemplates the therapeutic effectiveness of A beta conformation-selective antibodies, the findings presented here demonstrate new information on a monoclonal antibody that selectively targets A beta protofibrils and impacts A beta dynamics.