Cholesterol inhibits TCR signaling by directly restricting TCR-CD3 core tunnel motility

Structures of human γδ T cell receptor-CD3 complex

Gamma delta (γδ) T cells, a unique T cell subgroup, are crucial in various immune responses and immunopathology1-3. The γδ T cell receptor (TCR), which is generated by γδ T cells, recognizes a diverse range of antigens independently of the major histocompatibility complex2. The γδ TCR associates with CD3 subunits, initiating T cell activation and holding great potential in immunotherapy4. Here we report the structures of two prototypical human Vγ9Vδ2 and Vγ5Vδ1 TCR-CD3 complexes5,6, revealing two distinct assembly mechanisms that depend on Vγ usage. The Vγ9Vδ2 TCR-CD3 complex is monomeric, with considerable conformational flexibility in the TCRγ-TCRδ extracellular domain and connecting peptides. The length of the connecting peptides regulates the ligand association and T cell activation. A cholesterol-like molecule wedges into the transmembrane region, exerting an inhibitory role in TCR signalling. The Vγ5Vδ1 TCR-CD3 complex displays a dimeric architecture, whereby two protomers nestle back to back through the Vγ5 domains of the TCR extracellular domains. Our biochemical and biophysical assays further corroborate the dimeric structure. Importantly, the dimeric form of the Vγ5Vδ1 TCR is essential for T cell activation. These findings reveal organizing principles of the γδ TCR-CD3 complex, providing insights into the unique properties of γδ TCR and facilitating immunotherapeutic interventions.

The resting and ligand-bound states of the membrane-embedded human T-cell receptor-CD3 complex

The T-cell receptor (TCR) is central to the ligand-dependent activation of T lymphocytes and as such orchestrates both adaptive and pathologic immune processes. However, major questions remain regarding the structure and function of the human TCR. Here, we present cryogenic electron microscopy structures for the unliganded and HLA-bound human TCR-CD3 complex in nanodiscs that provide a native-like lipid environment. The unliganded structures reveal two related conformations that are distinct from its structure in detergent. These new "closed and compacted" conformations afford insights into the interactions between the TCR-CD3 and the membrane, including conserved surface patches that make extensive outer leaflet contact, and suggest novel conformational regulation by glycans. We show that the closed/compacted conformations, not the extended one previously reported in detergent, represent the unliganded resting state for the TCR-CD3 in vivo, underscoring the importance of structural interrogation of membrane proteins in native-like environments. By contrast, the structure of the HLA-bound complex in nanodiscs is in an open and extended conformation, showing that physiologic ligand binding is sufficient to induce substantial conformational change in the TCR-CD3 complex. We use conformation-locking disulfide mutants to show that ectodomain opening is necessary for maximal ligand-dependent TCR-CD3 activation, demonstrating that TCR-intrinsic conformational change is necessary for full TCR-CD3 activation and opening numerous avenues for immunoreceptor engineering.

The recent advancement of TCR-T cell therapies for cancer treatment

Adoptive cell therapies involve infusing engineered immune cells into cancer patients to recognize and eliminate tumor cells. Adoptive cell therapy, as a form of living drug, has undergone explosive growth over the past decade. The recognition of tumor antigens by the T-cell receptor (TCR) is one of the natural mechanisms that the immune system used to eliminate tumor cells. TCR-T cell therapy, which involves introducing exogenous TCRs into patients' T cells, is a novel cell therapy strategy. TCR-T cell therapy can target the entire proteome of cancer cells. Engineering T cells with exogenous TCRs to help patients combat cancer has achieved success in clinical trials, particularly in treating solid tumors. In this review, we examine the progress of TCR-T cell therapy over the past five years. This includes the discovery of new tumor antigens, protein engineering techniques for TCR, reprogramming strategies for TCR-T cell therapy, clinical studies on TCR-T cell therapy, and the advancement of TCR-T cell therapy in China. We also propose several potential directions for the future development of TCR-T cell therapy.

Transient hydroxycholesterol treatment restrains TCR signaling to promote long-term immunity

T cell receptor (TCR) plays a fundamental role in adaptive immunity, and TCR-T cell therapy holds great promise for treating solid tumors and other diseases. However, there is a noticeable absence of chemical tools tuning TCR activity. In our study, we screened natural sterols for their regulatory effects on T cell function and identified 7-alpha-hydroxycholesterol (7a-HC) as a potent inhibitor of TCR signaling. Mechanistically, 7a-HC promoted membrane binding of CD3ε cytoplasmic domain, a crucial signaling component of the TCR-CD3 complex, through alterations in membrane physicochemical properties. Enhanced CD3ε membrane binding impeded the condensation between CD3ε and the key kinase Lck, thereby inhibiting Lck-mediated TCR phosphorylation. Transient treatments of TCR-T cells with 7a-HC resulted in reduced signaling strength, increased memory cell populations, and superior long-term antitumor functions. This study unveils a chemical regulation of TCR signaling, which can be exploited to enhance the long-term efficacy of TCR-T cell therapy.

Immunometabolism of CD8+ T cell differentiation in cancer

CD8+ cytotoxic T lymphocytes (CTLs) are central mediators of tumor immunity and immunotherapies. Upon tumor antigen recognition, CTLs differentiate from naive/memory-like toward terminally exhausted populations with more limited function against tumors. Such differentiation is regulated by both immune signals, including T cell receptors (TCRs), co-stimulation, and cytokines, and metabolism-associated processes. These immune signals shape the metabolic landscape via signaling, transcriptional and post-transcriptional mechanisms, while metabolic processes in turn exert spatiotemporal effects to modulate the strength and duration of immune signaling. Here, we review the bidirectional regulation between immune signals and metabolic processes, including nutrient uptake and intracellular metabolic pathways, in shaping CTL differentiation and exhaustion. We also discuss the mechanisms underlying how specific nutrient sources and metabolite-mediated signaling events orchestrate CTL biology. Understanding how metabolic programs and their interplay with immune signals instruct CTL differentiation and exhaustion is crucial to uncover tumor-immune interactions and design novel immunotherapies.

The CD4 transmembrane GGXXG and juxtamembrane (C/F)CV+C motifs mediate pMHCII-specific signaling independently of CD4-LCK interactions

CD4+ T cell activation is driven by five-module receptor complexes. The T cell receptor (TCR) is the receptor module that binds composite surfaces of peptide antigens embedded within MHCII molecules (pMHCII). It associates with three signaling modules (CD3γε, CD3δε, and CD3ζζ) to form TCR-CD3 complexes. CD4 is the coreceptor module. It reciprocally associates with TCR-CD3-pMHCII assemblies on the outside of a CD4+ T cells and with the Src kinase, LCK, on the inside. Previously, we reported that the CD4 transmembrane GGXXG and cytoplasmic juxtamembrane (C/F)CV+C motifs found in eutherian (placental mammal) CD4 have constituent residues that evolved under purifying selection (Lee et al., 2022). Expressing mutants of these motifs together in T cell hybridomas increased CD4-LCK association but reduced CD3ζ, ZAP70, and PLCγ1 phosphorylation levels, as well as IL-2 production, in response to agonist pMHCII. Because these mutants preferentially localized CD4-LCK pairs to non-raft membrane fractions, one explanation for our results was that they impaired proximal signaling by sequestering LCK away from TCR-CD3. An alternative hypothesis is that the mutations directly impacted signaling because the motifs normally play an LCK-independent role in signaling. The goal of this study was to discriminate between these possibilities. Using T cell hybridomas, our results indicate that: intracellular CD4-LCK interactions are not necessary for pMHCII-specific signal initiation; the GGXXG and (C/F)CV+C motifs are key determinants of CD4-mediated pMHCII-specific signal amplification; the GGXXG and (C/F)CV+C motifs exert their functions independently of direct CD4-LCK association. These data provide a mechanistic explanation for why residues within these motifs are under purifying selection in jawed vertebrates. The results are also important to consider for biomimetic engineering of synthetic receptors.

How the immune mousetrap works: Structural evidence for the immunomodulatory action of a peptide from influenza NS1 protein

One of the critical stages of the T-cell immune response is the dimerization of the intramembrane domains of T-cell receptors (TCR). Structural similarities between the immunosuppressive domains of viral proteins and the transmembrane domains of TCR have led several authors to hypothesize the mechanism of immune response suppression by highly pathogenic viruses: viral proteins embed themselves in the membrane and act on the intramembrane domain of the TCRalpha subunit, hindering its functional oligomerization. It has also been suggested that this mechanism is used by influenza A virus in NS1-mediated immunosuppression. We have shown that the peptide corresponding to the primary structure of the potential immunosuppressive domain of NS1 protein (G51) can reduce concanavalin A-induced proliferation of PBMC cells, as well as in vitro, G51 can affect the oligomerization of the core peptide corresponding to the intramembrane domain of TCR, using AFM and small-angle neutron scattering. The results obtained using in cellulo and in vitro model systems suggest the presence of functional interaction between the NS1 fragment and the intramembrane domain of the TCR alpha subunit. We have proposed a possible scheme for such interaction obtained by computer modeling. This suggests the existence of another NS1-mediated mechanism of immunosuppression in influenza.

T cell cholesterol transport is a metabolic checkpoint that links intestinal immune responses to dietary lipid absorption

The intrinsic pathways that control membrane organization in immune cells and the impact of such pathways on cellular function are not well defined. Here we report that the non-vesicular cholesterol transporter Aster-A links plasma membrane (PM) cholesterol availability in T cells to immune signaling and systemic metabolism. Aster-A is recruited to the PM during T-cell receptor (TCR) activation, where it facilitates the removal of newly generated "accessible" membrane cholesterol. Loss of Aster-A leads to excess PM cholesterol accumulation, resulting in enhanced TCR nano-clustering and signaling, and Th17 cytokine production. Finally, we show that the mucosal Th17 response is restrained by PM cholesterol remodeling. Ablation of Aster-A in T cells leads to enhanced IL-22 production, reduced intestinal fatty acid absorption, and resistance to diet-induced obesity. These findings delineate a multi-tiered regulatory scheme linking immune cell lipid flux to nutrient absorption and systemic physiology.

Nutrients: Signal 4 in T cell immunity

T cells are integral in mediating adaptive immunity to infection, autoimmunity, and cancer. Upon immune challenge, T cells exit from a quiescent state, followed by clonal expansion and effector differentiation. These processes are shaped by three established immune signals, namely antigen stimulation (Signal 1), costimulation (Signal 2), and cytokines (Signal 3). Emerging findings reveal that nutrients, including glucose, amino acids, and lipids, are crucial regulators of T cell responses and interplay with Signals 1-3, highlighting nutrients as Signal 4 to license T cell immunity. Here, we first summarize the functional importance of Signal 4 and the underlying mechanisms of nutrient transport, sensing, and signaling in orchestrating T cell activation and quiescence exit. We also discuss the roles of nutrients in programming T cell differentiation and functional fitness and how nutrients can be targeted to improve disease therapy. Understanding how T cells respond to Signal 4 nutrients in microenvironments will provide insights into context-dependent functions of adaptive immunity and therapeutic interventions.

T-cell virtuosity in ''knowing thyself"

Major Histocompatibility Complex (MHC) I and II and the αβ T-cell antigen receptor (TCRαβ) govern fundamental traits of adaptive immunity. They form a membrane-borne ligand-receptor system weighing host proteome integrity to detect contamination by nonself proteins. MHC-I and -II exhibit the "MHC-fold", which is able to bind a large assortment of short peptides as proxies for self and nonself proteins. The ensuing varying surfaces are mandatory ligands for Ig-like TCRαβ highly mutable binding sites. Conserved molecular signatures guide TCRαβ ligand binding sites to focus on the MHC-fold (MHC-restriction) while leaving many opportunities for its most hypervariable determinants to contact the peptide. This riveting molecular strategy affords many options for binding energy compatible with specific recognition and signalling aimed to eradicated microbial pathogens and cancer cells. While the molecular foundations of αβ T-cell adaptive immunity are largely understood, uncertainty persists on how peptide-MHC binding induces the TCRαβ signals that instruct cell-fate decisions. Solving this mystery is another milestone for understanding αβ T-cells' self/nonself discrimination. Recent developments revealing the innermost links between TCRαβ structural dynamics and signalling modality should help dissipate this long-sought-after enigma.

Metabolic waypoints during T cell differentiation

This Review explores the interplay between T cell activation and cell metabolism and highlights how metabolites serve two pivotal functions in shaping the immune response. Traditionally, T cell activation has been characterized by T cell antigen receptor-major histocompatibility complex interaction (signal 1), co-stimulation (signal 2) and cytokine signaling (signal 3). However, recent research has unveiled the critical role of metabolites in this process. Firstly, metabolites act as signal propagators that aid in the transmission of core activation signals, such as specific lipid species that are crucial at the immune synapse. Secondly, metabolites also function as unique signals that influence immune differentiation pathways, such as amino acid-induced mTORC1 signaling. Metabolites also play a substantial role in epigenetic remodeling, by directly modifying histones, altering gene expression and influencing T cell behavior. This Review discusses how T cells integrate nutrient sensing with activating stimuli to shape their differentiation and sensitivity to metabolites. We underscore the integration of immunological and metabolic inputs in T cell function and suggest that metabolite availability is a fundamental determinant of adaptive immune responses.

Stress-Induced Immunosuppression Inhibits Regional Immune Responses in Chicken Adipose Tissue Partially through Suppressing T Cells by Up-Regulating Steroid Metabolism

Lipid metabolism plays an important role in maintaining lipid homeostasis and regulating immune functions. However, the regulations and mechanisms of lipid metabolism on the regional immune function of avian adipose tissue (AT) have not been reported. In this study, qRT-PCR was used to investigate the changes and relationships of different lipid metabolism pathways in chicken AT during stress-induced immunosuppression (SIIS) inhibiting immune response to Newcastle disease virus vaccine, then the miRNA regulation patterns of 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) gene and its potential applications were further identified. The results showed that AT actively responded to SIIS, and ATGL, CPT1A and HMGCR were all the key genes involved in the processes of SIIS inhibiting the immune responses. SIIS significantly inhibited the natural and specific immune phases of the primary immune response and the initiation phase of the secondary immune response in AT by suppressing T cells by up-regulating steroid anabolism. Moreover, steroid metabolism could play dual roles in regulating the regional immune functions of AT. The miR-29a/c-3p-HMGCR network was a potential regulation mechanism of steroid metabolism in AT, and serum circulating miR-29a/c-3p had the potential as molecular markers. The study can provide valuable references for an in-depth investigation of the regional immune functions regulated by lipid metabolism in AT.

The CD4 transmembrane GGXXG and juxtamembrane (C/F)CV+C motifs mediate pMHCII-specific signaling independently of CD4-LCK interactions

CD4+ T cell activation is driven by 5-module receptor complexes. The T cell receptor (TCR) is the receptor module that binds composite surfaces of peptide antigens embedded within MHCII molecules (pMHCII). It associates with three signaling modules (CD3γε, CD3δε, and CD3ζζ) to form TCR-CD3 complexes. CD4 is the coreceptor module. It reciprocally associates with TCR-CD3-pMHCII assemblies on the outside of a CD4+ T cells and with the Src kinase, LCK, on the inside. Previously, we reported that the CD4 transmembrane GGXXG and cytoplasmic juxtamembrane (C/F)CV+C motifs found in eutherian (placental mammal) CD4 have constituent residues that evolved under purifying selection (Lee, et al., 2022). Expressing mutants of these motifs together in T cell hybridomas increased CD4-LCK association but reduced CD3ζ, ZAP70, and PLCγ1 phosphorylation levels, as well as IL-2 production, in response to agonist pMHCII. Because these mutants preferentially localized CD4-LCK pairs to non-raft membrane fractions, one explanation for our results was that they impaired proximal signaling by sequestering LCK away from TCR-CD3. An alternative hypothesis is that the mutations directly impacted signaling because the motifs normally play an LCK-independent role in signaling. The goal of this study was to discriminate between these possibilities. Using T cell hybridomas, our results indicate that: intracellular CD4-LCK interactions are not necessary for pMHCII-specific signal initiation; the GGXXG and (C/F)CV+C motifs are key determinants of CD4-mediated pMHCII-specific signal amplification; the GGXXG and (C/F)CV+C motifs exert their functions independently of direct CD4-LCK association. These data provide a mechanistic explanation for why residues within these motifs are under purifying selection in jawed vertebrates. The results are also important to consider for biomimetic engineering of synthetic receptors.

Cholesterol, Eukaryotic Lipid Domains, and an Evolutionary Perspective of Transmembrane Signaling

Transmembrane signaling is essential for complex life forms. Communication across a bilayer lipid barrier is elaborately organized to convey precision and to fine-tune strength. Looking back, the steps that it has taken to enable this seemingly mundane errand are breathtaking, and with our survivorship bias, Darwinian. While this review is to discuss eukaryotic membranes in biological functions for coherence and theoretical footing, we are obliged to follow the evolution of the biological membrane through time. Such a visit is necessary for our hypothesis that constraints posited on cellular functions are mainly via the biomembrane, and relaxation thereof in favor of a coordinating membrane environment is the molecular basis for the development of highly specialized cellular activities, among them transmembrane signaling. We discuss the obligatory paths that have led to eukaryotic membrane formation, its intrinsic ability to signal, and how it set up the platform for later integration of protein-based receptor activation.

Allosteric inhibition of the T cell receptor by a designed membrane ligand

The T cell receptor (TCR) is a complex molecular machine that directs the activation of T cells, allowing the immune system to fight pathogens and cancer cells. Despite decades of investigation, the molecular mechanism of TCR activation is still controversial. One of the leading activation hypotheses is the allosteric model. This model posits that binding of pMHC at the extracellular domain triggers a dynamic change in the transmembrane (TM) domain of the TCR subunits, which leads to signaling at the cytoplasmic side. We sought to test this hypothesis by creating a TM ligand for TCR. Previously we described a method to create a soluble peptide capable of inserting into membranes and binding to the TM domain of the receptor tyrosine kinase EphA2 (Alves et al., eLife, 2018). Here, we show that the approach is generalizable to complex membrane receptors, by designing a TM ligand for TCR. We observed that the designed peptide caused a reduction of Lck phosphorylation of TCR at the CD3ζ subunit in T cells. As a result, in the presence of this peptide inhibitor of TCR (PITCR), the proximal signaling cascade downstream of TCR activation was significantly dampened. Co-localization and co-immunoprecipitation in diisobutylene maleic acid (DIBMA) native nanodiscs confirmed that PITCR was able to bind to the TCR. AlphaFold-Multimer predicted that PITCR binds to the TM region of TCR, where it interacts with the two CD3ζ subunits. Our results additionally indicate that PITCR disrupts the allosteric changes in the compactness of the TM bundle that occur upon TCR activation, lending support to the allosteric TCR activation model. The TCR inhibition achieved by PITCR might be useful to treat inflammatory and autoimmune diseases and to prevent organ transplant rejection, as in these conditions aberrant activation of TCR contributes to disease.

Cholesterol metabolism in T-cell aging: Accomplices or victims

Aging has a significant impact on the function and metabolism of T cells. Cholesterol, the most important sterol in mammals, is known as the "gold of the body" because it maintains membrane fluidity, rigidity, and signal transduction while also serving as a precursor of oxysterols, bile acids, and steroid hormones. Cholesterol homeostasis is primarily controlled by uptake, biosynthesis, efflux, and regulatory mechanisms. Previous studies have suggested that there are reciprocal interactions between cholesterol metabolism and T lymphocytes. Here, we will summarize the most recent advances in the effects of cholesterol and its derivatives on T-cell aging. We will furthermore discuss interventions that might be used to help older individuals with immune deficiencies or diminishing immune competence.

A dynamic biomimetic model of the membrane-bound CD4-CD3-TCR complex during pMHC disengagement

The coordinated (dis)engagement of the membrane-bound T cell receptor (TCR)-CD3-CD4 complex from the peptide-major histocompatibility complex (pMHC) is fundamental to TCR signal transduction and T cell effector function. As such, an atomic-scale understanding would not only enhance our basic understanding of the adaptive immune response but would also accelerate the rational design of TCRs for immunotherapy. In this study, we explore the impact of the CD4 coreceptor on the TCR-pMHC (dis)engagement by constructing a molecular-level biomimetic model of the CD3-TCR-pMHC and CD4-CD3-TCR-pMHC complexes within a lipid bilayer. After allowing the system complexes to equilibrate (engage), we use steered molecular dynamics to dissociate (disengage) the pMHC. We find that 1) the CD4 confines the pMHC closer to the T cell by 1.8 nm at equilibrium; 2) CD4 confinement shifts the TCR along the MHC binding groove engaging a different set of amino acids and enhancing the TCR-pMHC bond lifetime; 3) the CD4 translocates under load increasing the interaction strength between the CD4-pMHC, CD4-TCR, and CD4-CD3; and 4) upon dissociation, the CD3-TCR complex undergoes structural oscillation and increased energetic fluctuation between the CD3-TCR and CD3-lipids. These atomic-level simulations provide mechanistic insight on how the CD4 coreceptor impacts TCR-pMHC (dis)engagement. More specifically, our results provide further support (enhanced bond lifetime) for a force-dependent kinetic proofreading model and identify an alternate set of amino acids in the TCR that dominate the TCR-pMHC interaction and could thus impact the design of TCRs for immunotherapy.

Decoding the crosstalk between mevalonate metabolism and T cell function

The mevalonate pathway is an essential metabolic pathway in T cells regulating development, proliferation, survival, differentiation, and effector functions. The mevalonate pathway is a complex, branched pathway composed of many enzymes that ultimately generate cholesterol and nonsterol isoprenoids. T cells must tightly control metabolic flux through the branches of the mevalonate pathway to ensure sufficient isoprenoids and cholesterol are available to meet cellular demands. Unbalanced metabolite flux through the sterol or the nonsterol isoprenoid branch is metabolically inefficient and can have deleterious consequences for T cell fate and function. Accordingly, there is tight regulatory control over metabolic flux through the branches of this essential lipid synthetic pathway. In this review we provide an overview of how the branches of the mevalonate pathway are regulated in T cells and discuss our current understanding of the relationship between mevalonate metabolism, cholesterol homeostasis and T cell function.

Self-programmed dynamics of T cell receptor condensation

A common event upon receptor-ligand engagement is the formation of receptor clusters on the cell surface, in which signaling molecules are specifically recruited or excluded to form signaling hubs to regulate cellular events. These clusters are often transient and can be disassembled to terminate signaling. Despite the general relevance of dynamic receptor clustering in cell signaling, the regulatory mechanism underlying the dynamics is still poorly understood. As a major antigen receptor in the immune system, T cell receptors (TCR) form spatiotemporally dynamic clusters to mediate robust yet temporal signaling to induce adaptive immune responses. Here we identify a phase separation mechanism controlling dynamic TCR clustering and signaling. The TCR signaling component CD3ε chain can condensate with Lck kinase through phase separation to form TCR signalosomes for active antigen signaling. Lck-mediated CD3ε phosphorylation, however, switched its binding preference to Csk, a functional suppressor of Lck, to cause the dissolvement of TCR signalosomes. Modulating TCR/Lck condensation by targeting CD3ε interactions with Lck or Csk directly affects T cell activation and function, highlighting the importance of the phase separation mechanism. The self-programmed condensation and dissolvement is thus a built-in mechanism of TCR signaling and might be relevant to other receptors.

HECT, UBA and WWE domain containing 1 represses cholesterol efflux during CD4+ T cell activation in Sjögren's syndrome

Introduction: Sjögren's syndrome (SS) is a chronic autoimmune disorder characterized by exocrine gland dysfunction, leading to loss of salivary function. Histological analysis of salivary glands from SS patients reveals a high infiltration of immune cells, particularly activated CD4⁺ T cells. Thus, interventions targeting abnormal activation of CD4⁺ T cells may provide promising therapeutic strategies for SS. Here, we demonstrate that Hect, uba, and wwe domain containing 1 (HUWE1), a member of the eukaryotic Hect E3 ubiquitin ligase family, plays a critical role in CD4⁺ T-cell activation and SS pathophysiology. Methods: In the context of HUWE1 inhibition, we investigated the impact of the HUWE1 inhibitor BI8626 and sh-Huwe1 on CD4⁺ T cells in mice, focusing on the assessment of activation levels, proliferation capacity, and cholesterol abundance. Furthermore, we examined the therapeutic potential of BI8626 in NOD/ShiLtj mice and evaluated its efficacy as a treatment strategy. Results: Inhibition of HUWE1 reduces ABCA1 ubiquitination and promotes cholesterol efflux, decreasing intracellular cholesterol and reducing the expression of phosphorylated ZAP-70, CD25, and other activation markers, culminating in the suppressed proliferation of CD4⁺ T cells. Moreover, pharmacological inhibition of HUWE1 significantly reduces CD4⁺ T-cell infiltration in the submandibular glands and improves salivary flow rate in NOD/ShiLtj mice. Conclusion: These findings suggest that HUWE1 may regulate CD4⁺ T-cell activation and SS development by modulating ABCA1-mediated cholesterol efflux and presents a promising target for SS treatment.

An elevated preoperative cholesterol-to-lymphocyte ratio predicts unfavourable outcomes in colorectal cancer liver metastasis patients receiving simultaneous resections: a retrospective study

BACKGROUND

To explore the clinical prognostic utility of the preoperative cholesterol-to-lymphocyte ratio (CLR) in outcomes for colorectal cancer liver metastasis (CRLM) patients receiving simultaneous resection of the primary lesion and liver metastases.

METHODS

A total of 444 CRLM patients receiving simultaneous resections were enrolled. The optimal cut-off value for CLR was determined using the highest Youden's index. Patients were divided into the CLR < 3.06 group and the CLR≥3.06 group. Propensity score matching analysis (PSM) and the inverse probability of treatment weighting (IPTW) method were conducted to eliminate bias between the two groups. The outcomes included short-term outcomes and long-term outcomes. Kaplan-Meier curves and log-rank tests were used to analyse progression-free survival (PFS) and overall survival (OS).

RESULTS

In the short-term outcome analysis, after 1:1 PSM, 137 patients were distributed to the CLR < 3.06 group and CLR≥3.06 group. No significant difference was noted between the two groups (P > 0.1). Compared with patients with CLR < 3.06, patients with CLR≥3.06 had comparable operation times (320.0 [272.5-421.0] vs. 360.0 [292.5-434.5], P = 0.088), blood loss (200.0 [100.0-400.0] vs. 200.0 [150.0-450.0], P = 0.831), postoperative complication rates (50.4% vs. 46.7%, P = 0.546) and postoperative ICU rates (5.8% vs. 11.7%, P = 0.087). In the long-term outcome analysis, Kaplan-Meier analysis showed that compared with patients with CLR < 3.06, patients with CLR≥3.06 had worse PFS (P = 0.005, median: 10.2 months vs. 13.0 months) and OS (P = 0.002, median: 41.0 months vs. 70.9 months). IPTW-adjusted Kaplan-Meier analysis showed that the CLR≥3.06 group had worse PFS (P = 0.027) and OS (P = 0.010) than the CLR < 3.06 group. In the IPTW-adjusted Cox proportional hazards regression analysis, CLR≥3.06 was an independent factor for PFS (HR = 1.376, 95% CI 1.097-1.726, P = 0.006) and OS (HR = 1.723, 95% CI 1.218-2.439, P = 0.002). IPTW-adjusted Cox proportional hazards regression analysis including postoperative complications, operation time, intraoperative blood loss, intraoperative blood transfusion and postoperative chemotherapy revealed that CLR≥3.06 was an independent factor for PFS (HR = 1.617, 95% CI 1.252-2.090, P < 0.001) and OS (HR = 1.823, 95% CI 1.258-2.643, P = 0.002).

CONCLUSIONS

The preoperative CLR level predicts unfavourable outcomes in CRLM patients receiving simultaneous resection of the primary lesion and liver metastases and should be taken into consideration when developing treatment and monitoring strategies.

Sulfotransferase 2B1b, Sterol Sulfonation, and Disease

The primary function of human sulfotransferase 2B1b (SULT2B1b) is to sulfonate cholesterol and closely related sterols. SULT2B1b sterols perform a number of essential cellular functions. Many are signaling molecules whose activities are redefined by sulfonation-allosteric properties are switched "on" or "off," agonists are transformed into antagonists, and vice versa. Sterol sulfonation is tightly coupled to cholesterol homeostasis, and sulfonation imbalances are causally linked to cholesterol-related diseases including certain cancers, Alzheimer disease, and recessive X-linked ichthyosis-an orphan skin disease. Numerous studies link SULT2B1b activity to disease-relevant molecular processes. Here, these multifaceted processes are integrated into metabolic maps that highlight their interdependence and how their actions are regulated and coordinated by SULT2B1b oxysterol sulfonation. The maps help explain why SULT2B1b inhibition arrests the growth of certain cancers and make the novel prediction that SULT2B1b inhibition will suppress production of amyloid β (Aβ) plaques and tau fibrils while simultaneously stimulating Aβ plaque phagocytosis. SULT2B1b harbors a sterol-selective allosteric site whose structure is discussed as a template for creating inhibitors to regulate SULT2B1b and its associated biology. SIGNIFICANCE STATEMENT: Human sulfotransferase 2B1b (SULT2B1b) produces sterol-sulfate signaling molecules that maintain the homeostasis of otherwise pro-disease processes in cancer, Alzheimer disease, and X-linked ichthyosis-an orphan skin disease. The functions of sterol sulfates in each disease are considered and codified into metabolic maps that explain the interdependencies of the sterol-regulated networks and their coordinate regulation by SULT2B1b. The structure of the SULT2B1b sterol-sensing allosteric site is discussed as a means of controlling sterol sulfate biology.

Structural analysis of cancer-relevant TCR-CD3 and peptide-MHC complexes by cryoEM

The recognition of antigenic peptide-MHC (pMHC) molecules by T-cell receptors (TCR) initiates the T-cell mediated immune response. Structural characterization is key for understanding the specificity of TCR-pMHC interactions and informing the development of therapeutics. Despite the rapid rise of single particle cryoelectron microscopy (cryoEM), x-ray crystallography has remained the preferred method for structure determination of TCR-pMHC complexes. Here, we report cryoEM structures of two distinct full-length α/β TCR-CD3 complexes bound to their pMHC ligand, the cancer-testis antigen HLA-A2/MAGEA4 (230-239). We also determined cryoEM structures of pMHCs containing MAGEA4 (230-239) peptide and the closely related MAGEA8 (232-241) peptide in the absence of TCR, which provided a structural explanation for the MAGEA4 preference displayed by the TCRs. These findings provide insights into the TCR recognition of a clinically relevant cancer antigen and demonstrate the utility of cryoEM for high-resolution structural analysis of TCR-pMHC interactions.

Structure and mechanism of immunoreceptors: New horizons in T cell and B cell receptor biology and beyond

Immunoreceptors, also named non-catalytic tyrosine-phosphorylated receptors, are a large class of leukocyte cell-surface proteins critically involved in innate and adaptive immune responses. Their most characteristic defining feature is a shared signal transduction machinery where binding events of cell surface-anchored ligands to the small extracellular receptor domains are translated into phosphorylation of conserved tyrosine-containing cytosolic sequence motifs initiating downstream signal transduction cascades. Despite their central importance to immunology, the molecular mechanism of how ligand binding activates the receptors and results in robust intracellular signaling has remained enigmatic. Recent breakthroughs in our understanding of the architecture and triggering mechanism of immunoreceptors come from cryogenic electron microscopy studies of the B cell and T cell antigen receptors.

Promise of dostarlimab in cancer therapy: Advancements and cross-talk considerations

In recent years, immunotherapy for cancer treatment using monoclonal antibodies has shown clinical success, particularly with programmed cell death protein 1 (PD-1) and its ligand programmed death-ligand 1 (PD-L1). Dostarlimab, an immune checkpoint inhibitor, interacts with adaptive immunity by binding to human PD-1, inhibiting PD-L1 and PD-L2 interactions, and cross-talk with adaptive immunity. Recent clinical trials have shown that dostarlimab is effective in treating mismatch repair deficiency (dMMR) in endometrial cancer patients, leading to its approval in the United States and the European Union in 2021. This article provides a comprehensive overview of dostarlimab, its therapeutic ability, and the different indications for which it is being used. Dostarlimab could serve as a potential alternative to many cancer treatments that frequently have severe consequences on patients' quality of life. Teaser The comprehensive story behind dostarlimab is how it cured all 18 cancer patients who took part in the experimental clinical trial, ultimately leading to its approval by the US FDA.

Regional immunity of chicken adipose tissue responds to secondary immunity induced by Newcastle disease vaccine via promoting immune activation and weakening lipid metabolism

Adipose tissue (AT) is considered as a regional immune organ and plays an important role in the anti-infection immune response. However, the function and mechanism of chicken AT in response to secondary immune response remain poorly understood. Here, we used mRNA and microRNA (miRNA) sequencing technology to survey the transcriptomic landscape of chicken abdominal adipose tissue (AAT) during the first and second immunization with Newcastle disease virus (NDV) vaccine, and carried out bioinformatics analysis, such as Gene Ontology (GO) terms and Kyoto Encyclopedia of Genes and Genomes (KEGG) functional enrichment analysis, protein-protein interaction (PPI) analysis, and miRNA-mRNA integrated analysis. The results indicated that chicken AAT actively responded to the secondary immune response. DNA replication and cytoskeleton regulation as the regulatory functions of immune activation changed significantly, and weakened lipid metabolism was an effective strategy for the secondary immunity. Mechanically, the regulatory network between the differentially expressed miRNAs (DEMs) and their targeted differentially expressed genes (DEGs), such as miR-206/miR-499-5p-nuclear receptor subfamily 4 group A member 3 (NR4A3)/methylsterol monooxygenase 1 (MSMO1) pathway, was one of the potential key mechanisms by which AAT responded to the secondary immune response. In conclusion, regional immunity of chicken AT responds to secondary immunity by promoting immune activation and weakening lipid metabolism, and this study can instruct future research on antiviral strategy.

A concerted mechanism involving ACAT and SREBPs by which oxysterols deplete accessible cholesterol to restrict microbial infection

Most of the cholesterol in the plasma membranes (PMs) of animal cells is sequestered through interactions with phospholipids and transmembrane domains of proteins. However, as cholesterol concentration rises above the PM's sequestration capacity, a new pool of cholesterol, called accessible cholesterol, emerges. The transport of accessible cholesterol between the PM and the endoplasmic reticulum (ER) is critical to maintain cholesterol homeostasis. This pathway has also been implicated in the suppression of both bacterial and viral pathogens by immunomodulatory oxysterols. Here, we describe a mechanism of depletion of accessible cholesterol from PMs by the oxysterol 25-hydroxycholesterol (25HC). We show that 25HC-mediated activation of acyl coenzyme A: cholesterol acyltransferase (ACAT) in the ER creates an imbalance in the equilibrium distribution of accessible cholesterol between the ER and PM. This imbalance triggers the rapid internalization of accessible cholesterol from the PM, and this depletion is sustained for long periods of time through 25HC-mediated suppression of SREBPs and continued activation of ACAT. In support of a physiological role for this mechanism, 25HC failed to suppress Zika virus and human coronavirus infection in ACAT-deficient cells, and Listeria monocytogenes infection in ACAT-deficient cells and mice. We propose that selective depletion of accessible PM cholesterol triggered by ACAT activation and sustained through SREBP suppression underpins the immunological activities of 25HC and a functionally related class of oxysterols.

Enhancing the Antitumor Immunity of T Cells by Engineering the Lipid-Regulatory Site of the TCR/CD3 Complex

The engagement of the T-cell receptor (TCR) by a specific peptide-MHC ligand initiates transmembrane signaling to induce T-cell activation, a key step in most adaptive immune responses. Previous studies have indicated that TCR signaling is tightly regulated by cholesterol and its sulfate metabolite, cholesterol sulfate (CS), on the membrane. Here, we report a novel mechanism by which CS modulates TCR signaling through a conformational change of CD3 subunits. We found that the negatively charged CS interacted with the positively charged cytoplasmic domain of CD3ε (CD3εCD) to enhance its binding to the cell membrane and induce a stable secondary structure. This secondary structure suppressed the release of CD3εCD from the membrane in the presence of Ca2+, which in turn inhibited TCR phosphorylation and signaling. When a point mutation (I/A) was introduced to the intracellular immunoreceptor tyrosine-based activation motifs (YxxI-x6-8-YxxL) of CD3ε subunit, it reduced the stability of the secondary structure and regained sensitivity to Ca2+, which abolished CS-mediated inhibition and enhanced the signaling of the TCR complex. Notably, the I/A mutation could be applied to both murine and human TCR-T cell therapy to improve the antitumor efficacy. Our study reveals insights into the regulatory mechanism of TCR signaling and provides a strategy to functionally engineer the TCR/CD3 complex for T cell-based cancer immunotherapy.

Antigen receptor structure and signaling

The key to mounting an immune response is that the host cells must be coordinated to generate an appropriate immune response against the pathogenic invaders. Antigen receptors recognize specific molecular structures and recruit adaptors through their effector domains, triggering trans-membrane transduction signaling pathway to exert immune response. The T cell antigen receptor (TCR) and B cell antigen receptor (BCR) are the primary determinant of immune responses to antigens. Their structure determines the mode of signaling and signal transduction determines cell fate, leading to changes at the molecular and cellular level. Studies of antigen receptor structure and signaling revealed the basis of immune response triggering, providing clues to antigen receptor priming and a foundation for the rational design of immunotherapies. In recent years, the increased research on the structure of antigen receptors has greatly contributed to the understanding of immune response, different immune-related diseases and even tumors. In this review, we describe in detail the current view and advances of the antigen structure and signaling.

Lipids for CD8+ TILs: Beneficial or harmful?

Lipids and lipid metabolism play crucial roles in regulating T cell function and are tightly related to the establishment of immune memory. It is reported that tumor-infiltrating CD8+T lymphocytes (CD8+TILs) burn fats to restore their impaired effector function due to the lack of glucose. Conversely, fatty acids (FAs) and cholesterol in the tumor microenvironment (TME) drive the CD8+ TILs dysfunction. The origin of dysfunctional CD8+ TILs shares important features with memory T cell’s precursor, but whether lipids and/or lipid metabolism reprogramming directly influence the memory plasticity of dysfunctional CD8+ TILs remains elusive. It is necessary to understand the interplay between cellular lipid metabolism and dysfunction of CD8+ TILs in the case of targeting T cell’s metabolism to synergize cancer immunotherapy. Therefore, in this review, we summarize the latest research on CD8+ TILs lipid metabolism, evaluate the impacts of lipids in the TME to CD8+ TILs, and highlight the significance of promoting memory phenotype cell formation by targeting CD8+ T cells lipid metabolism to provide longer duration of cancer immunotherapy efficacy.

Cryo-electron Microscopic Analysis of Single-Pass Transmembrane Receptors

Single-pass transmembrane receptors (SPTMRs) represent a diverse group of integral membrane proteins that are involved in many essential cellular processes, including signal transduction, cell adhesion, and transmembrane transport of materials. Dysregulation of the SPTMRs is linked with many human diseases. Despite extensive efforts in past decades, the mechanisms of action of the SPTMRs remain incompletely understood. One major hurdle is the lack of structures of the full-length SPTMRs in different functional states. Such structural information is difficult to obtain by traditional structural biology methods such as X-ray crystallography and nuclear magnetic resonance (NMR). The recent rapid development of single-particle cryo-electron microscopy (cryo-EM) has led to an exponential surge in the number of high-resolution structures of integral membrane proteins, including SPTMRs. Cryo-EM structures of SPTMRs solved in the past few years have tremendously improved our understanding of how SPTMRs function. In this review, we will highlight these progresses in the structural studies of SPTMRs by single-particle cryo-EM, analyze important structural details of each protein involved, and discuss their implications on the underlying mechanisms. Finally, we also briefly discuss remaining challenges and exciting opportunities in the field.

A Cysteine Residue within the Kinase Domain of Zap70 Regulates Lck Activity and Proximal TCR Signaling

Alterations in both the expression and function of the non-receptor tyrosine kinase Zap70 are associated with numerous human diseases including immunodeficiency, autoimmunity, and leukemia. Zap70 propagates the TCR signal by phosphorylating two important adaptor molecules, LAT and SLP76, which orchestrate the assembly of the signaling complex, leading to the activation of PLCγ1 and further downstream pathways. These events are crucial to drive T-cell development and T-cell activation. Recently, it has been proposed that C564, located in the kinase domain of Zap70, is palmitoylated. A non-palmitoylable C564R Zap70 mutant, which has been reported in a patient suffering from immunodeficiency, is incapable of propagating TCR signaling and activating T cells. The lack of palmitoylation was suggested as the cause of this human disease. Here, we confirm that Zap70^C564R is signaling defective, but surprisingly, the defective Zap70 function does not appear to be due to a loss in palmitoylation. We engineered a C564A mutant of Zap70 which, similarly to Zap70^C564R, is non-palmitoylatable. However, this mutant was capable of propagating TCR signaling. Moreover, Zap70^C564A enhanced the activity of Lck and increased its proximity to the TCR. Accordingly, Zap70-deficient P116 T cells expressing Zap70^C564A displayed the hyperphosphorylation of TCR-ζ and Zap70 (Y319), two well-known Lck substrates. Collectively, these data indicate that C564 is important for the regulation of Lck activity and proximal TCR signaling, but not for the palmitoylation of Zap70.

Structure of a fully assembled tumor-specific T cell receptor ligated by pMHC

The T cell receptor (TCR) expressed by T lymphocytes initiates protective immune responses to pathogens and tumors. To explore the structural basis of how TCR signaling is initiated when the receptor binds to peptide-loaded major histocompatibility complex (pMHC) molecules, we used cryogenic electron microscopy to determine the structure of a tumor-reactive TCRαβ/CD3δγε2ζ2 complex bound to a melanoma-specific human class I pMHC at 3.08 Å resolution. The antigen-bound complex comprises 11 subunits stabilized by multivalent interactions across three structural layers, with clustered membrane-proximal cystines stabilizing the CD3-εδ and CD3-εγ heterodimers. Extra density sandwiched between transmembrane helices reveals the involvement of sterol lipids in TCR assembly. The geometry of the pMHC/TCR complex suggests that efficient TCR scanning of pMHC requires accurate pre-positioning of T cell and antigen-presenting cell membranes. Comparisons of the ligand-bound and unliganded receptors, along with molecular dynamics simulations, indicate that TCRs can be triggered in the absence of spontaneous structural rearrangements.

Enhancing and inhibitory motifs regulate CD4 activity

CD4⁺ T cells use T cell receptor (TCR)–CD3 complexes, and CD4, to respond to peptide antigens within MHCII molecules (pMHCII). We report here that, through ~435 million years of evolution in jawed vertebrates, purifying selection has shaped motifs in the extracellular, transmembrane, and intracellular domains of eutherian CD4 that enhance pMHCII responses, and covary with residues in an intracellular motif that inhibits responses. Importantly, while CD4 interactions with the Src kinase, Lck, are viewed as key to pMHCII responses, our data indicate that CD4–Lck interactions derive their importance from the counterbalancing activity of the inhibitory motif, as well as motifs that direct CD4–Lck pairs to specific membrane compartments. These results have implications for the evolution and function of complex transmembrane receptors and for biomimetic engineering.

A T cell resilience model associated with response to immunotherapy in multiple tumor types

Despite breakthroughs in cancer immunotherapy, most tumor-reactive T cells cannot persist in solid tumors due to an immunosuppressive environment. We developed Tres (tumor-resilient T cell), a computational model utilizing single-cell transcriptomic data to identify signatures of T cells that are resilient to immunosuppressive signals, such as transforming growth factor-β1, tumor necrosis factor-related apoptosis-inducing ligand and prostaglandin E2. Tres reliably predicts clinical responses to immunotherapy in melanoma, lung cancer, triple-negative breast cancer and B cell malignancies using bulk T cell transcriptomic data from pre-treatment tumors from patients who received immune-checkpoint inhibitors (n = 38), infusion products for chimeric antigen receptor T cell therapies (n = 34) and pre-manufacture samples for chimeric antigen receptor T cell or tumor-infiltrating lymphocyte therapies (n = 84). Further, Tres identified FIBP, whose functions are largely unknown, as the top negative marker of tumor-resilient T cells across many solid tumor types. FIBP knockouts in murine and human donor CD8⁺ T cells significantly enhanced T cell-mediated cancer killing in in vitro co-cultures. Further, Fibp knockout in murine T cells potentiated the in vivo efficacy of adoptive cell transfer in the B16 tumor model. Fibp knockout T cells exhibit reduced cholesterol metabolism, which inhibits effector T cell function. These results demonstrate the utility of Tres in identifying biomarkers of T cell effectiveness and potential therapeutic targets for immunotherapies in solid tumors.