TREM2 (Triggering Receptor Expressed on Myeloid Cells 2) modulator therapy represents one of the most promising approaches for treating Alzheimer's disease (AD) by targeting microglial function. Unlike approaches that directly target amyloid-beta or tau, TREM2 modulators aim to restore the phagocytic and protective functions of microglia, the brain's immune cells.
TREM2 is a cell-surface receptor expressed primarily on microglia in the central nervous system. It plays a critical role in microglial survival, proliferation, phagocytosis, and the formation of disease-associated microglia (DAM) [1]. Rare coding variants in TREM2 (particularly R47H) increase Alzheimer's disease risk by approximately 3-fold, comparable to the effect of APOE4 [2]. This genetic evidence strongly supports TREM2 as a therapeutic target.
The fundamental therapeutic rationale is that enhancing TREM2 signaling could restore microglial function, leading to improved clearance of pathological proteins, reduced neuroinflammation, and ultimately slower disease progression.
TREM2 is a type I transmembrane receptor consisting of:
TREM2 signals through association with DAP12 (TYROBP), an adaptor protein containing an immunoreceptor tyrosine-based activation motif (ITAM). Upon ligand binding, DAP12 becomes phosphorylated and activates SYK, which initiates downstream signaling cascades [3].
TREM2 undergoes proteolytic cleavage by ADAM10 and ADAM17 at the extracellular domain, releasing a soluble fragment (sTREM2) into the cerebrospinal fluid (CSF) and blood. sTREM2 has emerged as an important biomarker and potential therapeutic agent:
The ratio of sTREM2 to membrane-bound TREM2 provides important diagnostic information about microglial activation status.
TREM2 signaling intersects with CSF1R (Colony Stimulating Factor 1 Receptor) pathways, which are crucial for microglial survival and proliferation:
The majority of drug development programs focus on TREM2 agonism based on the following rationale:
Agonists aim to:
Some researchers argue that TREM2 antagonism could be beneficial:
Current clinical evidence predominantly supports agonism, but the debate continues and may be resolved with data from ongoing clinical trials.
The 5xFAD mouse model (bearing 5 familial AD mutations) has been extensively used to study TREM2:
Similar findings have been observed in APP/PS1 mice:
| Study | Model | Intervention | Key Findings |
|---|---|---|---|
| Wang et al., 2016 | 5xFAD | TREM2 overexpression | Enhanced plaque clearance, improved cognition |
| Lee et al., 2018 | APP/PS1 | Anti-TREM2 antibody | Reduced synaptic loss, altered plaque morphology |
| Shi et al., 2019 | 5xFAD | TREM2 agonism | Promoted microglial metabolic fitness |
| Schlepckow et al., 2020 | 5xFAD | sTREM2 | Protective effects via receptor competition |
AL002 is a humanized anti-TREM2 monoclonal antibody designed to act as an agonist:
JNJ-7524 is another anti-TREM2 antibody in development:
Several other companies have TREM2 programs at various stages:
While antibody-based approaches dominate, small molecule TREM2 modulators are also being explored:
Most small molecule programs remain in discovery stages, focusing on:
Cerebrospinal fluid sTREM2 is a validated biomarker for:
| Biomarker | Matrix | Utility |
|---|---|---|
| sTREM2 | CSF | Target engagement, disease staging |
| TREM2 expression | PET | Microglial activation imaging |
| CSF cytokines | CSF | Inflammation monitoring |
| Amyloid/tau | CSF/PET | Patient stratification |
The INVOKE-2 Phase 2 trial (AL002, Alector/AbbVie) evaluating TREM2 agonist therapy for Alzheimer's disease did not meet its primary endpoints. This failure, published in Nature Medicine in October 2025 [8], has significant implications for the TREM2 therapeutic approach:
This failure highlights the complexity of targeting microglial function in AD and suggests that TREM2 modulation may need to be combined with other therapeutic approaches.
| Trial | Agent | Phase | Status | NCT Number |
|---|---|---|---|---|
| INVOKE-2 | AL002 | Phase 2 | Failed (2025) | NCT04592874 |
| AL002 Phase 1 | AL002 | Phase 1 | Completed | NCT03822208 |
| JNJ-7524 | JNJ-7524 | Phase 1 | Recruiting | NCT05659095 |
Primary endpoints in ongoing trials include:
Based on preclinical and early clinical data:
Clinical trials implement comprehensive safety monitoring:
Emerging strategies include:
Future developments may enable:
Guerreiro et al. TREM2 variants in Alzheimer's disease (2013). 2013. ↩︎
Jonsson et al. TREM2 and Alzheimer's disease (2013). 2013. ↩︎
Wang et al. TREM2 in amyloid pathology (2015). 2015. ↩︎
Suarez-Calvet et al. sTREM2 as biomarker (2016). 2016. ↩︎
Mancuso et al. CSF1R and TREM2 in neurodegeneration (2019). 2019. ↩︎
Schlepckow et al. TREM2 agonism in 5xFAD mice (2020). 2020. ↩︎
Lee et al. Anti-TREM2 antibody in APP/PS1 mice (2018). 2018. ↩︎
Rethinking TREM2 as a target for Alzheimer's disease after the INVOKE-2 trial failure (2025). 2025. ↩︎