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The spread of prion‐like protein aggregates is a common driver of pathogenesis in various neurodegenerative diseases, including Alzheimer's disease (AD) and related Tauopathies. Tau pathologies exhibit a clear progressive spreading pattern that correlates with disease severity. Clinical observation combined with complementary experimental studies has shown that Tau preformed fibrils (PFF) are prion‐like seeds that propagate pathology by entering cells and templating misfolding and aggregation of endogenous Tau. While several cell surface receptors of Tau are known, they are not specific to the fibrillar form of Tau. Moreover, the underlying cellular mechanisms of Tau PFF spreading remain poorly understood. Here, it is shown that the lymphocyte‐activation gene 3 (Lag3) is a cell surface receptor that binds to PFF but not the monomer of Tau. Deletion of Lag3 or inhibition of Lag3 in primary cortical neurons significantly reduces the internalization of Tau PFF and subsequent Tau propagation and neuron‐to‐neuron transmission. Propagation of Tau pathology and behavioral deficits induced by injection of Tau PFF in the hippocampus and overlying cortex are attenuated in mice lacking Lag3 selectively in neurons. These results identify neuronal Lag3 as a receptor of pathologic Tau in the brain，and for AD and related Tauopathies, a therapeutic target. [ABSTRACT FROM AUTHOR]

Regulatory T cells ([T.sub.reg] cells) have a crucial role in the immune system by preventing autoimmunity, limiting immunopathology, and maintaining immune homeostasis (1). However, they also represent a major barrier to effective anti-tumour immunity and sterilizing immunity to chronic viral infections1. The transcription factor Foxp3 has a major role in the development and programming of [T.sub.reg] cells (2,3). The relative stability of [T.sub.reg] cells at inflammatory disease sites has been a highly contentious subject (4-6). There is considerable interest in identifying pathways that control the stability of [T.sub.reg] cells as many immune-mediated diseases are characterized by either exacerbated or limited [T.sub.reg]-cell function. Here we show that the immune-cell-expressed ligand semaphorin-4a (Sema4a) and the [T.sub.reg]-cell-expressed receptor neuropilin-1 (Nrp1) interact both in vitro, to potentiate [T.sub.reg]-cell function and survival, and in vivo, at inflammatory sites. Using mice with a [T.sub.reg]-cell-restricted deletion of Nrp1, we show that Nrp1 is dispensable for suppression of autoimmunity and maintenance of immune homeostasis, but is required by [T.sub.reg] cells to limit anti-tumour immune responses and to cure established inflammatory colitis. Sema4a ligation of Nrp1 restrained Akt phosphorylation cellularly and at the immunologic synapse by phosphatase and tensin homologue (PTEN), which increased nuclear localization of the transcription factor Foxo3a. The Nrp1-induced transcriptome promoted [T.sub.reg]-cell stability by enhancing quiescence and survival factors while inhibiting programs that promote differentiation. Importantly, this Nrp1-dependent molecular program is evident in intra-tumoral [T.sub.reg] cells. Our data support a model in which [T.sub.reg]-cell stability can be subverted in certain inflammatory sites, but is maintained by a Sema4a-Nrp1 axis, highlighting this pathway as a potential therapeutic target that could limit [T.sub.reg]-cell-mediated tumour-induced tolerance without inducing autoimmunity., It was suggested initially that [T.sub.reg]-cell-mediated suppression was contact-dependent, and soluble factors were insufficient, as purified [T.sub.reg] cells failed to suppress across a permeable transwell membrane (3,7). However, we have [...]

Author(s): Lauren W. Collison [1]; Creg J. Workman [1]; Timothy T. Kuo [3]; Kelli Boyd [2]; Yao Wang [1]; Kate M. Vignali [1]; Richard Cross [1]; David Sehy [4]; Richard [...]

Tight control of T-cell proliferation and effector function is essential to ensure an effective but appropriate immune response. Here, we reveal that this is controlled by the metalloprotease-mediated cleavage of LAG-3, a negative regulatory protein expressed by all activated T cells. We show that LAG-3 cleavage is mediated by two transmembrane metalloproteases, ADAM10 and ADAM17, with the activity of both modulated by two distinct T-cell receptor (TCR) signaling-dependent mechanisms. ADAM10 mediates constitutive LAG-3 cleavage but increases ∼12-fold following T-cell activation, whereas LAG-3 shedding by ADAM17 is induced by TCR signaling in a PKCθ-dependent manner. LAG-3 must be cleaved from the cell surface to allow for normal T-cell activation as noncleavable LAG-3 mutants prevented proliferation and cytokine production. Lastly, ADAM10 knockdown reduced wild-type but not LAG-3−/− T-cell proliferation. These data demonstrate that LAG-3 must be cleaved to allow efficient T-cell proliferation and cytokine production and establish a novel paradigm in which T-cell expansion and function are regulated by metalloprotease cleavage with LAG-3 as its sole molecular target. [ABSTRACT FROM AUTHOR]

The T cell receptor (TCR)-CD3 complex is composed of a genetically diverse αβTCR heterodimer associated noncovalently with the invariant CD3 dimers CD3εγ, CD3εδ, and CD3ζζ. The TCR mediates peptide-MHC recognition, whereas the CD3 molecules transduce activation signals to the T cell. Although much is known about downstream T cell signaling pathways, the mechanism whereby TCR engagement by peptide-MHC initiates signaling is poorly understood. A key to solving this problem is defining the spatial organization of the TCR-CD3 complex and the interactions between its subunits. We have applied solution NMR methods to identify the docking site for CD3 on the β chain of a human autoimmune TCR. We demonstrate a low affinity but highly specific interaction between the extracellular domains of CD3 and the TCR constant β (Cβ) domain that requires both CD3εγ and CD3εδ subunits. The mainly hydrophilic docking site, comprising 9-11 solvent-accessible Cβ residues, is relatively small (~400 Ų), consistent with the weak interaction between TCR and CD3 extracellular domains, and devoid of glycosylation sites. The docking site is centered on the αA and αB helices of Cβ, which are located at the base of the TCR. This positions CD3εγ and CD3εδ between the TCR and the T cell membrane, permitting us to distinguish among several possible models of TCR-CD3 association. We further correlate structural results from NMR with mutational data on TCR-CD3 interactions from cell-based assays. [ABSTRACT FROM AUTHOR]

Inhibitory receptors on immune cells are pivotal regulators of immune escape in cancer. Among these inhibitory receptors, CTLA-4 (targeted clinically by ipilimumab) serves as a dominant off-switch while other receptors such as PD-1 and LAG-3 seem to serve more subtle rheostat functions. However, the extent of synergy and cooperative interactions between inhibitory pathways in cancer remain largely unexplored. Here, we reveal extensive coexpression of PD-1 and LAG-3 on tumor-infiltrating CD4+ and CD8+ T cells in three distinct transplantable tumors. Dual anti-LAG-3/anti-PD-1 antibody treatment cured most mice of established tumors that were largely resistant to single antibody treatment. Despite minimal immunopathologic sequelae in PD-1 and LAG-3 single knockout mice, dual knockout mice abrogated self-tolerance with resultant autoimmune infiltrates in multiple organs, leading to eventual lethality. However, Lag3-/-Pdcd1-/- mice showed markedly increased survival from and clearance of multiple transplantable tumors. Together, these results define a strong synergy between the PD-1 and LAG-3 inhibitory pathways in tolerance to both self and tumor antigens. In addition, they argue strongly that dual blockade of these molecules represents a promising combinatorial strategy for cancer. [ABSTRACT FROM AUTHOR]

CD4 + T cells share common developmental pathways with CD8 + T cells, and upon maturation, CD4 + T conventional T (Tconv) cells lack phenotypic markers that distinguish these cells from FoxP3 + T regulatory cells. We developed a tamoxifen-inducible ThPOK CreERT2.hCD2 line with Frt sites inserted on either side of the CreERT2-hCD2 cassette, and a Foxp3 Ametrine-FlpO strain, expressing Ametrine and FlpO in Foxp3 + cells. Breeding these mice resulted in a CD4conv iCreERT2-hCD2 line that allows for the specific manipulation of a gene in CD4 + Tconv cells. As FlpO removes the CreERT2-hCD2 cassette, CD4 + Treg cells are spared from Cre activity, which we refer to as allele conditioning. Comparison with an E8I iCreERT2.GFP mouse that enables inducible targeting of CD8 + T cells, and deletion of two inhibitory receptors, PD-1 and LAG-3, in a melanoma model, support the fidelity of these lines. These engineered mouse strains present a resource for the temporal manipulation of genes in CD4 + T cells and CD4 + Tconv cells., Competing Interests: Declaration of interests D.A.A.V. is a cofounder and stockholder in Novasenta, Tizona, Trishula, and Potenza; a stockholder in Oncorus, Werewolf, and Apeximmune; has patents licensed and royalties in Astellas and BMS; is a scientific advisory board member of Tizona, Werewolf, F-Star, Bicara, and Apeximmune; a consultant to Astellas, BMS, Almirall, Incyte, G1 Therapeutics; and has received research funding from BMS, Astellas, and Novasenta. A.H.S. has patents/pending royalties on the PD-1 pathway from Roche and Novartis. A.H.S. is on the advisory boards of Surface Oncology, Elstar, SQZ Biotechnologies, Elpiscience, Selecta, Bicara, and Monopteros; consults for Novartis; and has received research funding from Novartis, Roche, Quark, Merck, and AbbVie that is unrelated to this project. E.J.W. has consulting agreements with and/or is on the scientific advisory boards of Merck, Elstar, Janssen, Related Sciences, Synthekine, and Surface Oncology; is a founder of Surface Oncology and Arsenal Biosciences; and has a patent licensing agreement on the PD-1 pathway with Roche/Genentech., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Regulatory T (Treg) cells are crucial for immune homeostasis, but they also contribute to tumor immune evasion by promoting a suppressive tumor microenvironment (TME). Mice with Treg cell-restricted Neuropilin-1 deficiency show tumor resistance while maintaining peripheral immune homeostasis, thereby providing a controlled system to interrogate the impact of intratumoral Treg cells on the TME. Using this and other genetic models, we showed that Treg cells shaped the transcriptional landscape across multiple tumor-infiltrating immune cell types. Treg cells suppressed CD8 + T cell secretion of interferon-γ (IFNγ), which would otherwise block the activation of sterol regulatory element-binding protein 1 (SREBP1)-mediated fatty acid synthesis in immunosuppressive (M2-like) tumor-associated macrophages (TAMs). Thus, Treg cells indirectly but selectively sustained M2-like TAM metabolic fitness, mitochondrial integrity, and survival. SREBP1 inhibition augmented the efficacy of immune checkpoint blockade, suggesting that targeting Treg cells or their modulation of lipid metabolism in M2-like TAMs could improve cancer immunotherapy., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Regulatory T cells (T regs ) are a barrier to anti-tumor immunity. Neuropilin-1 (Nrp1) is required to maintain intratumoral T reg stability and function but is dispensable for peripheral immune tolerance. T reg -restricted Nrp1 deletion results in profound tumor resistance due to T reg functional fragility. Thus, identifying the basis for Nrp1 dependency and the key drivers of T reg fragility could help to improve immunotherapy for human cancer. We show that a high percentage of intratumoral NRP1 + T regs correlates with poor prognosis in melanoma and head and neck squamous cell carcinoma. Using a mouse model of melanoma where Nrp1-deficient (Nrp1 -/- ) and wild-type (Nrp1 +/+ ) T regs can be assessed in a competitive environment, we find that a high proportion of intratumoral Nrp1 -/- T regs produce interferon-γ (IFNγ), which drives the fragility of surrounding wild-type T regs , boosts anti-tumor immunity, and facilitates tumor clearance. We also show that IFNγ-induced T reg fragility is required for response to anti-PD1, suggesting that cancer therapies promoting T reg fragility may be efficacious., (Copyright © 2017 Elsevier Inc. All rights reserved.)