Selection and structural characterization of anti-TREM2 scFvs that reduce levels of shed ectodomain

Aleksandra Szykowska,Yu Chen,Thomas B Smith,Charlotta Preger,Jingjing Yang,Dongming Qian,Shubhashish M Mukhopadhyay,Edvard Wigren,Stephen J Neame,Susanne Gräslund,Helena Persson,Peter J Atkinson,Elena Di Daniel,Emma Mead,John Wang,John B Davis,Nicola A Burgess-Brown,Alex N Bullock

doi:10.1016/j.str.2021.06.010

Abstract

SummaryMutations in TREM2, a receptor expressed by microglia in the brain, are associated with an increased risk of neurodegeneration, including Alzheimer's disease. Numerous studies support a role for TREM2 in sensing damaging stimuli and triggering signaling cascades necessary for neuroprotection. Despite its significant role, ligands and regulators of TREM2 activation, and the mechanisms governing TREM2-dependent responses and its cleavage from the membrane, remain poorly characterized. Here, we present phage display generated antibody single-chain variable fragments (scFvs) to human TREM2 immunoglobulin-like domain. Co-crystal structures revealed the binding of two scFvs to an epitope on the TREM2 domain distal to the putative ligand-binding site. Enhanced functional activity was observed for oligomeric scFv species, which inhibited the production of soluble TREM2 in a HEK293 cell model. We hope that detailed characterization of their epitopes and properties will facilitate the use of these renewable binders as structural and functional biology tools for TREM2 research.

Highlights

Late-onset Alzheimer’s disease (LOAD) is the most common type of dementia, characterized by accumulation of extracellular amyloid-b (Ab) aggregates and intracellular neurofibrillary tangles of hyper-phosphorylated tau, with a long prodromal phase followed by cognitive decline
Among the genes identified by genome-wide association studies (GWAS) is TREM2 (Triggering Receptor Expressed on Myeloid cells), which encodes a single transmembrane receptor expressed in myeloid-derived cells, including microglia in the central nervous system (CNS) (Guerreiro et al, 2013)
Phage display selection of anti-TREM2 scFvs To facilitate the development of renewable antibody binders against TREM2, we performed phage display selections using the SciLifeLib synthetic library of human scFvs constructed and designed as reported previously (Preger et al, 2020; Sa€ll et al, 2016)

Summary

Introduction

Late-onset Alzheimer’s disease (LOAD) is the most common type of dementia, characterized by accumulation of extracellular amyloid-b (Ab) aggregates and intracellular neurofibrillary tangles of hyper-phosphorylated tau, with a long prodromal phase followed by cognitive decline. After some late-stage clinical trials targeting Ab failed to meet their desired endpoints and several large genome-wide association studies (GWAS) linked genes coding for components of the immune response to AD, neuro-inflammation has become an area of intense research for therapeutics (Block et al, 2007; Lambert et al, 2013). Homozygous loss-of-function mutations in TREM2, or the associated adaptor protein DAP12, were previously identified to cause aggressive earlyonset dementia in Nasu-Hakola disease (Paloneva et al, 2003).

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