Enhancing protective microglial activities with a dual function TREM2 antibody to the stalk region

• Main Authors: Kai Schlepckow, Kathryn M Monroe, Gernot Kleinberger, Ludovico Cantuti‐Castelvetri, Samira Parhizkar, Dan Xia, Michael Willem, Georg Werner, Nadine Pettkus, Bettina Brunner, Alice Sülzen, Brigitte Nuscher, Heike Hampel, Xianyuan Xiang, Regina Feederle, Sabina Tahirovic, Joshua I Park, Rachel Prorok, Cathal Mahon, Chun‐Chi Liang, Ju Shi, Do Jin Kim, Hanna Sabelström, Fen Huang, Gilbert Di Paolo, Mikael Simons, Joseph W Lewcock, Christian Haass
• Format: Article
• Language: English
• Published: Wiley 2020-04-01
• Series: EMBO Molecular Medicine
• Subjects: Alzheimer's disease; amyloid β‐peptide; microglia; therapeutic antibody; TREM2
• Online Access: https://doi.org/10.15252/emmm.201911227
• ISSN: 1757-4676; 1757-4684

Abstract Triggering receptor expressed on myeloid cells 2 (TREM2) is essential for the transition of homeostatic microglia to a disease‐associated microglial state. To enhance TREM2 activity, we sought to selectively increase the full‐length protein on the cell surface via reducing its proteolytic shedding by A Disintegrin And Metalloproteinase (i.e., α‐secretase) 10/17. We screened a panel of monoclonal antibodies against TREM2, with the aim to selectively compete for α‐secretase‐mediated shedding. Monoclonal antibody 4D9, which has a stalk region epitope close to the cleavage site, demonstrated dual mechanisms of action by stabilizing TREM2 on the cell surface and reducing its shedding, and concomitantly activating phospho‐SYK signaling. 4D9 stimulated survival of macrophages and increased microglial uptake of myelin debris and amyloid β‐peptide in vitro. In vivo target engagement was demonstrated in cerebrospinal fluid, where nearly all soluble TREM2 was 4D9‐bound. Moreover, in a mouse model for Alzheimer's disease‐related pathology, 4D9 reduced amyloidogenesis, enhanced microglial TREM2 expression, and reduced a homeostatic marker, suggesting a protective function by driving microglia toward a disease‐associated state.