TREM2 Therapeutic Strategy Post-INVOKE-2

Sanofi/Vigil VG-3927 is the first oral small molecule TREM2 modulator, working as a molecular glue that stabilizes TREM2 and prevents shedding. Phase 1 showed dose-dependent CSF sTREM2 reduction. Oral dosing solves the BBB penetration problem that limited antibody approaches (AL002 had only 0.17-0.28% CSF entry). Sanofi paid ~$470M for this asset after INVOKE-2 failure, signaling strong conviction.

CSF sTREM2 levels follow a dynamic trajectory in AD, peaking during early symptomatic disease. Rather than constant TREM2 agonism, a precision approach would activate TREM2 only during the therapeutic window when microglial phagocytosis is beneficial (pre-plaque and early plaque stages) and withdraw when chronic activation becomes neurotoxic. sTREM2 could serve as both patient selection biomarker and treatment monitoring tool.

Given that TREM2 monotherapy (AL002) failed and anti-amyloid monotherapy (lecanemab, donanemab) shows modest benefit, combining TREM2-mediated microglial activation with amyloid clearance could be synergistic. TREM2 activation enhances phagocytic capacity while anti-amyloid antibodies provide substrate. This addresses the lesson that AD multifactorial etiology may require multi-target approaches. No combination trial exists yet.

The protective PLCG2-P522R variant reduces AD risk by activating downstream TREM2 signaling components directly, bypassing TREM2 itself. Targeting PLCγ2 could achieve TREM2-like microglial activation without the receptor-level complexity. This is supported by genetic evidence and provides an alternative if TREM2-level interventions continue to fail.

Next-generation TREM2 antibody engineering combining: (1) biparatopic binding for enhanced receptor clustering and signaling (Biogen 2025 approach), (2) anti-transferrin receptor shuttle for BBB penetration (learning from DNL919 toxicity by using safer shuttle designs like M07-TFN), and (3) effectorless Fc to avoid ARIA. Preclinical M07-TFN showed 30-fold p-SYK activation and strong BBB translocation in human models.

Novartis VHB937 binds the IgSF domain of TREM2 (different from AL002) and stabilizes TREM2 on the cell surface rather than directly agonizing it. This produces opposite biomarker changes vs AL002: increased surface TREM2, reduced proinflammatory markers (SPP1, sCSF1R, CCL3). Phase 2 currently recruiting (n=407). The key insight is that how you activate TREM2 matters as much as whether you activate it.