Triggering receptor expressed on myeloid cells 2 (TREM2) is an immune receptor expressed on the surface of microglia, macrophages, dendritic cells, and osteoclasts. The R47H TREM2 variant is a significant risk factor for late-onset Alzheimer's disease (AD), and the molecular basis of R47H TREM2 loss of function is an emerging area of TREM2 biology. Here, we report three high-resolution structures of the extracellular ligand-binding domains (ECDs) of R47H TREM2, apo-WT, and phosphatidylserine (PS)-bound WT TREM2 at 1.8, 2.2, and 2.2 Å, respectively. The structures reveal that Arg plays a critical role in maintaining the structural features of the complementarity-determining region 2 (CDR2) loop and the putative positive ligand-interacting surface (PLIS), stabilizing conformations capable of ligand interaction. This is exemplified in the PS-bound structure, in which the CDR2 loop and PLIS drive critical interactions with PS via surfaces that are disrupted in the variant. Together with and characterization, our structural findings elucidate the molecular mechanism underlying loss of ligand binding, putative oligomerization, and functional activity of R47H TREM2. They also help unravel how decreased and stability of TREM2 contribute to loss of function in disease.

Triggering receptor expressed on myeloid cells 2 (TREM2) sustains microglia response to brain injury stimuli including apoptotic cells, myelin damage, and amyloid β (Aβ). Alzheimer’s disease (AD) risk is associated with the TREM2R47H variant, which impairs ligand binding and consequently microglia responses to Aβ pathology. Here, we show that TREM2 engagement by the mAb hT2AB as surrogate ligand activates microglia in 5XFAD transgenic mice that accumulate Aβ and express either the common TREM2 variant (TREM2CV) or TREM2R47H. scRNA-seq of microglia from TREM2CV-5XFAD mice treated once with control hIgG1 exposed four distinct trajectories of microglia activation leading to disease-associated (DAM), interferon-responsive (IFN-R), cycling (Cyc-M), and MHC-II expressing (MHC-II) microglia types. All of these were underrepresented in TREM2R47H-5XFAD mice, suggesting that TREM2 ligand engagement is required for microglia activation trajectories. Moreover, Cyc-M and IFN-R microglia were more abundant in female than male TREM2CV-5XFAD mice, likely due to greater Aβ load in female 5XFAD mice. A single systemic injection of hT2AB replenished Cyc-M, IFN-R, and MHC-II pools in TREM2R47H-5XFAD mice. In TREM2CV-5XFAD mice, however, hT2AB brought the representation of male Cyc-M and IFN-R microglia closer to that of females, in which these trajectories had already reached maximum capacity. Moreover, hT2AB induced shifts in gene expression patterns in all microglial pools without affecting representation. Repeated treatment with a murinized hT2AB version over 10 d increased chemokines brain content in TREM2R47H-5XFAD mice, consistent with microglia expansion. Thus, the impact of hT2AB on microglia is shaped by the extent of TREM2 endogenous ligand engagement and basal microglia activation.

β-Site amyloid precursor protein cleaving enzyme 1 (BACE1) is an aspartyl protease that plays a key role in the production of amyloid β (Aβ) in the brain and has been extensively pursued as a target for the treatment of Alzheimer's disease (AD). BACE2, an aspartyl protease that is structurally related to BACE1, has been recently reported to be involved in melanosome maturation and pigmentation. Herein, we describe the development of a series of cyclopropylthiazines as potent and orally efficacious BACE1 inhibitors. Lead optimization led to the identification of 20, a molecule with biochemical IC 50 BACE2/BACE1 ratio of 47. Administration of 20 resulted in no skin/fur color change in a 13-day mouse hypopigmentation study and demonstrated robust and sustained reduction of CSF and brain Aβ 40 levels in rat and monkey pharmacodynamic models. On the basis of a compelling data package, 20 (AM-6494) was advanced to preclinical development.

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Background PF-04236921 is a fully human monoclonal antibody that binds with high affinity to the human interleukin-6 (IL6) ligand, and neutralizes its activity. It is a new subcutaneous (SC) biological therapy in development for inflammatory diseases. Objectives To evaluate the safety, tolerability, pharmacokinetics (PK), and pharmacodynamics (PD) of PF-04236921 following single intravenous (IV) doses and single SC doses in healthy adult volunteers (HVs). Methods The first in human Study B0151001 was conducted in 48 HVs who, in ascending IV dose cohorts, were randomly assigned to receive PF-04236921 (7, 22, 44, 118, 284, 500, and 700 mg) or placebo. Adverse events (AEs) were monitored throughout the study. Serum samples were collected to measure PF-04236921 concentrations, C-reactive protein (CRP), total IL6 as a target biomarker, and antibodies to PF-04236921. Subjects were followed until their serum levels of PF-04236921 were undectable. Non-compartmental analysis and population PK modeling were performed to characterize the PK of PF-04236921. Population PK/PD modeling was conducted to characterize the CRP response. A single SC dose of PF-04236921 (200 mg) was administered to 10 HVs in Study B0151004 with similar assessments. Results Overall, PF-04236921 was generally well tolerated. There was no apparent increase in the frequency or distribution of AEs including infections or laboratory abnormalities with increasing dose. Expected minor elevations in serum lipids, and transient reductions in circulating neutrophil counts were observed, but were not associated with infections or other adverse events. Three serious AEs in two subjects were reported in Study B0151001. No serious AEs were reported in Study B0151004. No antidrug antibodies to PF-04236921 or injection site reactions were observed. Following IV administrations, exposure (Cmax and AUC(0,∞)) increased approximately dose-proportionally. Terminal half-life in HVs was approximately 51 days. Comparison of dose-normalized exposure suggested SC bioavailability is >90%. A two-compartment model adequately described the PK of PF-04236921 following IV administration. Population estimates for the clearance (CL), the central volume of distribution (V1), the inter-compartmental clearance (Q) and the peripheral volume of distribution (V2) were 0.00416 L hr-1, 3.23 l, 0.0215 L hr-1 and 3.72 L hr-1, respectively. Compared with placebo subjects, a sustained decrease from baseline in CRP and an increase in total IL-6 were observed in treated dose groups. An inhibitory indirect response PD model described the relationship between PF-04236921 concentrations and CRP suppression in HVs with a population estimate of EC50 of 422 ng/ml. Conclusions PF-04236921 is being developed as an IL6 inhibitor for inflammatory diseases. PF-04236921 demonstrated a well-tolerated safety profile, no positive antibodies to PF-04236921 in HVs and desirable PK and PD properties supporting sustained target inhibition. Phase 2 studies using the SC formulation of PF-04236921 are currently ongoi...