Molecular features underlying differential SHP1/SHP2 binding of immune checkpoint receptors

Development of a Peptide Inhibitor Targeting the C-SH2 Domain of the SHP2 Phosphatase

Src homology 2 (SH2) domain-containing phosphatase 2 (SHP2) mediates important signal transduction upon cell surface receptor stimulation, regulating multiple cellular functions. In addition to the catalytically active phosphotyrosine (pTyr) phosphatase domain, SHP2 contains two regulatory pTyr-binding domains: the N-SH2 and C-SH2 domains. While the role of the N-SH2 domain is well understood, the role of the C-SH2 domain is less clear. To support studies on the involvement of the domains in SHP2 function, herein, the development of a peptide inhibitor containing a nonhydrolysable pTyr mimetic, which selectively binds to the C-SH2 domain of SHP2 and blocks its protein-protein interactions, is described. Incorporation of the pTyr mimetic l-O-malonyltyrosine (l-OMT) results in robust binding affinity to the C-SH2 domain, while the widely used pTyr mimetic phosphonodifluoromethyl phenylalanine (F2Pmp) abolishes binding, showing that this mimetic is not a general binder of SH2 domains, which challenges existing notions. The C-SH2 inhibitor peptide (CSIP) is stable, selective, cell permeable, and noncytotoxic. CSIP enriches the toolbox of inhibitors with different modes of action targeting SHP2, and will support studies to better understand SHP2 regulation and interactions, which can ultimately inform new drug discovery efforts.

TIM-3 teams up with PD-1 in cancer immunotherapy: mechanisms and perspectives

Immunotherapy using immune checkpoint inhibitors (ICIs) has become a prominent strategy for cancer treatment over the past ten years. However, the efficacy of ICIs remains limited, with certain cancers exhibiting resistance to these therapeutic approaches. Consequently, several immune checkpoint proteins are presently being thoroughly screened and assessed in both preclinical and clinical studies. Among these candidates, T cell immunoglobulin and mucin-domain containing-3 (TIM-3) is considered a promising target. TIM-3 exhibits multiple immunosuppressive effects on various types of immune cells. Given its differential expression levels at distinct stages of T cell dysfunction in the tumor microenvironment (TME), TIM-3, along with programmed cell death protein 1 (PD-1), serves as indicators of T cell exhaustion. Moreover, it is crucial to carefully evaluate the impact of TIM-3 and PD-1 expression in cancer cells on the efficacy of immunotherapy. To increase the effectiveness of anti-TIM-3 and anti-PD-1 therapies, it is proposed to combine the inhibition of TIM-3, PD-1, and programmed death-ligand 1 (PD-L1). The efficacy of TIM-3 inhibition in conjunction with PD-1/PD-L1 inhibitors is being evaluated in a number of ongoing clinical trials for patients with various cancers. This study systematically investigates the fundamental biology of TIM-3 and PD-1, as well as the detailed mechanisms through which TIM-3 and PD-1/PD-L1 axis contribute to cancer immune evasion. Additionally, this article provides a thorough analysis of ongoing clinical trials evaluating the synergistic effects of combining PD-1/PD-L1 and TIM-3 inhibitors in anti-cancer treatment, along with an overview of the current status of TIM-3 and PD-1 antibodies.

SHP2 regulates the HIF-1 signaling pathway in the decidual human endometrial stromal cells†

The decidual endometrial stromal cells play a critical role in the establishment of uterine receptivity and pregnancy in human. Our previous studies demonstrate that protein tyrosine phosphatase 2 SHP2 is highly expressed in decidualized cells and governs the decidualization progress. However, the role and mechanism of SHP2 in the function of decidual cells remain unclear. Here, we screened proteins interacting with SHP2 in decidual hTERT-immortalized human endometrial stromal cells (T-HESCs) and identified Hypoxia-inducible factor-1 (HIF-1) signaling pathway as a potential SHP2-mediated signaling pathway through proximity-dependent biotinylation (BioID) analysis. Immunoprecipitation (Co-IP) revealed an interaction between SHP2 and HIF-1α, which colocalized to the nucleus in decidual cells. Furthermore, the SHP2 expression correlated with the transcriptional activation of HIF-1α and its downstream genes Beta-enolase (Eno3), Pyruvate kinase 2 (Pkm2), Aldolase C (Aldoc), and Facilitative glucose transporter 1 (Glut1). Knockdown or inhibition of SHP2 significantly reduced the mRNA and protein levels of HIF-1α and its downstream genes, as well as lactate production in decidual cells. We also established a hypoxia model of T-HESCs and 293 T cells and found that hypoxic treatment induced the expression of SHP2 and HIF-1α, which colocalized in the nucleus. SHP2 forced-expression rescued the inhibitory effects of SHP2 deficiency on HIF-1α expression and lactate production. Finally, SHP2 binds to the promoter regions of HIF-1α and its target genes (Eno3, Pkm2, Aldoc, and Glut1). Collectively, our results suggest that SHP2 influences the function of decidual cells by HIF-1α signaling and provide a novel function mechanism of decidual stromal cells.

Dys-regulated phosphatidylserine externalization as a cell intrinsic immune escape mechanism in cancer

The negatively charged aminophospholipid, phosphatidylserine (PS), is typically restricted to the inner leaflet of the plasma membrane under normal, healthy physiological conditions. PS is irreversibly externalized during apoptosis, where it serves as a signal for elimination by efferocytosis. PS is also reversibly and transiently externalized during cell activation such as platelet and immune cell activation. These events associated with physiological PS externalization are tightly controlled by the regulated activation of flippases and scramblases. Indeed, improper regulation of PS externalization results in thrombotic diseases such as Scott Syndrome, a defect in coagulation and thrombin production, and in the case of efferocytosis, can result in autoimmunity such as systemic lupus erythematosus (SLE) when PS-mediated apoptosis and efferocytosis fails. The physiological regulation of PS is also perturbed in cancer and during viral infection, whereby PS becomes persistently exposed on the surface of such stressed and diseased cells, which can lead to chronic thrombosis and chronic immune evasion. In this review, we summarize evidence for the dysregulation of PS with a main focus on cancer biology and the pathogenic mechanisms for immune evasion and signaling by PS, as well as the discussion of new therapeutic strategies aimed to target externalized PS. We posit that chronic PS externalization is a universal and agnostic marker for diseased tissues, and in cancer, likely reflects a cell intrinsic form of immune escape. The continued development of new therapeutic strategies for targeting PS also provides rationale for their co-utility as adjuvants and with immune checkpoint therapeutics.

Genotype-driven sensitivity of mice to tick-borne encephalitis virus correlates with differential host responses in peripheral macrophages and brain

BACKGROUND

Tick-borne encephalitis (TBE) is the most common tick-borne viral infection in Eurasia. Outcomes range from asymptomatic infection to fatal encephalitis, with host genetics likely playing a role. BALB/c mice have intermediate susceptibility to TBE virus (TBEV) and STS mice are highly resistant, whereas the recombinant congenic strain CcS-11, which carries 12.5% of the STS genome on the BALB/c background, is more susceptible than BALB/c mice. In the present study, we employed these genetically distinct mouse models to investigate the host response to TBEV infection in both peripheral macrophages, one of the initial target cell populations, and the brain, the terminal target organ of the virus.

METHODS

TBEV growth and the production of key cytokines and chemokines were measured and compared in macrophages derived from BALB/c, CcS-11, and STS mice. In addition, brains from these TBEV-infected mouse strains underwent in-depth transcriptomic analysis.

RESULTS

Virus production in BALB/c and CcS-11 macrophages exhibited similar kinetics 24 and 48 h post-infection (hpi), but CcS-11 macrophages yielded significantly higher titers 72 hpi. Macrophages from both sensitive strains demonstrated elevated chemokine and proinflammatory cytokine production upon infection, whereas the resistant strain, STS, showed no cytokine/chemokine activation. Transcriptomic analysis of brain tissue demonstrated that the genetic background of the mouse strains dictated their transcriptional response to infection. The resistant strain exhibited a more robust cell-mediated immune response, whereas both sensitive strains showed a less effective cell-mediated response but increased cytokine signaling and signs of demyelination, with loss of oligodendrocytes.

CONCLUSIONS

Our findings suggest that variations in susceptibility linked to host genetic background correspond with distinct host responses, both in the periphery upon virus entry into the organism and in the brain, the target organ of the virus. These results provide insights into the influence of host genetics on the clinical trajectory of TBE.

Target therapy of TIGIT; a novel approach of immunotherapy for the treatment of colorectal cancer

The T cell immunoglobulin and immunoreceptor tyrosine-based inhibitory motif domain (TIGIT), a newly discovered checkpoint, is characterized by its elevated expression on CD4 + T cells, CD8 + T cells, natural killer (NK) cells, regulatory T cells (Tregs), and tumor-infiltrating lymphocytes (TILs). Research to date has been shown that TIGIT has been linked to exhaustion of NK cell both and T cells in numerous cancers. CD155, being the specific ligand of TIGIT in humans, emerges as a key target for immunotherapy owing to its crucial interaction with TIGIT. Furthermore, numerous studies have demonstrated that the combination of TIGIT with other immune checkpoint inhibitors (ICIs) and/or traditional treatments elicits a potent antitumor response in colorectal cancer (CRC). This review provides an overview of the structure, function, and signaling pathways associated with TIGIT across multiple immune system cell types. Additionally, focusing on the role of TIGIT in the progression of CRC, this study reviewed various studies exploring TIGIT-based immunotherapy in CRC.

Inhibitory immune checkpoints suppress the surveillance of senescent cells promoting their accumulation with aging and in age-related diseases

The accumulation of pro-inflammatory senescent cells within tissues is a common hallmark of the aging process and many age-related diseases. This modification has been called the senescence-associated secretory phenotype (SASP) and observed in cultured cells and in cells isolated from aged tissues. Currently, there is a debate whether the accumulation of senescent cells within tissues should be attributed to increased generation of senescent cells or to a defect in their elimination from aging tissues. Emerging studies have revealed that senescent cells display an increased expression of several inhibitory immune checkpoint ligands, especially those of the programmed cell death protein-1 (PD-1) ligand-1 (PD-L1) proteins. It is known that the PD-L1 ligands, especially those of cancer cells, target the PD-1 receptor of cytotoxic CD8+ T and natural killer (NK) cells disturbing their functions, e.g., evoking a decline in their cytotoxic activity and promoting their exhaustion and even apoptosis. An increase in the level of the PD-L1 protein in senescent cells was able to suppress their immune surveillance and inhibit their elimination by cytotoxic CD8+ T and NK cells. Senescent cells are known to express ligands for several inhibitory immune checkpoint receptors, i.e., PD-1, LILRB4, NKG2A, TIM-3, and SIRPα receptors. Here, I will briefly describe those pathways and examine whether these inhibitory checkpoints could be involved in the immune evasion of senescent cells with aging and age-related diseases. It seems plausible that an enhanced inhibitory checkpoint signaling can prevent the elimination of senescent cells from tissues and thus promote the aging process.

An Imaging-Based Assay to Measure the Location of PD-1 at the Immune Synapse for Testing the Binding Efficacy of Anti-PD-1 and Anti-PD-L1 Antibodies

PD-1 is an immune checkpoint on T cells. Antibodies to PD-1 or its ligand PD-L1 are gaining popularity as a leading immunotherapy approach. In the US, 40% of all cancer patients will be treated with anti-PD-1 or anti-PD-L1 antibodies but, unfortunately, only 30% will respond, and many will develop immune-related adverse events. There are nine FDA-approved anti-PD-1/PD-L1 antibodies, and approximately 100 are in different stages of clinical development. It is a clinical challenge to choose the correct antibody for a given patient, and this is critical in advanced malignancies, which often do not permit a second-line intervention. To resolve that, an in vitro assay to compare the performance of the different anti-PD-1/PD-L1 antibodies is not only a critical tool for research purposes but also a possible tool for personalized medicine. There are some assays describing the binding affinity and function of anti-PD-1/PD-L1 antibodies. However, a significant limitation of existing assays is that they need to consider the location of PD-1 in the immune synapse, the interface between the T cell and tumor cells, and, therefore, ignore a critical component in its biology. To address this, we developed and validated an imaging-based assay to quantify and compare the ability of different anti-PD-1/PD-L1 antibodies to remove PD-1 from the immune synapse. We correlated that with the same antibodies' ability to increase cytokine secretion from the targeted cells. The strong correlation between PD-1 location and its function in vitro and in vivo within the antibody treatment setting validates this assay's usability, which is easily recordable and straightforward. Key features • Live-cell imaging quantifies and compares how anti-PD-1 and anti-PD-L1 antibodies disrupt PD-1 localization, causing the removal of PD-1 during immune synapse formation. • Hao et al. [1] validated the protocol, and the findings were extended to a live confocal microscopy method. • It requires a Zeiss LSM 900 confocal microscope and appropriate imaging software and is optimized for the latest version of Zen Blue. • Anti-PD-1 antibodies are commonly used in cancer therapies, and this protocol optimizes the analysis of their effectiveness.

Discovery of JAB-3312, a Potent SHP2 Allosteric Inhibitor for Cancer Treatment

As an oncogenic phosphatase, SHP2 acts as a converging node in the RTK-RAS-MAPK signaling pathway in cancer cells and suppresses antitumor immunity by passing signals downstream of PD-1. Here, we utilized the extra druggable pocket outside the previously identified SHP2 allosteric tunnel site by the (6,5 fused), 6 spirocyclic system. The optimized compound, JAB-3312, exhibited a SHP2 binding Kd of 0.37 nM, SHP2 enzymatic IC50 of 1.9 nM, KYSE-520 antiproliferative IC50 of 7.4 nM and p-ERK inhibitory IC50 of 0.23 nM. For JAB-3312, an oral dose of 1.0 mg/kg QD was sufficient to achieve 95% TGI in KYSE-520 xenograft model of mouse. JAB-3312 was well-tolerated in animal models, and a close correlation was observed between the plasma concentration of JAB-3312 and the p-ERK inhibition in tumors. Currently, JAB-3312 is undergoing clinical trials as a potential anticancer agent.

BTLA and PD-1 signals attenuate TCR-mediated transcriptomic changes

T cell co-inhibitory immune checkpoints, such as PD-1 or BTLA, are bona fide targets in cancer therapy. We used a human T cell reporter line to measure transcriptomic changes mediated by PD-1- and BTLA-induced signaling. T cell receptor (TCR)-complex stimulation resulted in the upregulation of a large number of genes but also in repression of a similar number of genes. PD-1 and BTLA signals attenuated transcriptomic changes mediated by TCR-complex signaling: upregulated genes tended to be suppressed and the expression of a significant number of downregulated genes was higher during PD-1 or BTLA signaling. BTLA was a significantly stronger attenuator of TCR-complex-induced transcriptome changes than PD-1. A strong overlap between genes that were regulated indicated quantitative rather than qualitative differences between these receptors. In line with their function as attenuators of TCR-complex-mediated changes, we found strongly regulated genes to be prime targets of PD-1 and BTLA signaling.

The Toxoplasma secreted effector TgWIP modulates dendritic cell motility by activating host tyrosine phosphatases Shp1 and Shp2

The obligate intracellular parasite Toxoplasma gondii causes life-threatening toxoplasmosis to immunocompromised individuals. The pathogenesis of Toxoplasma relies on its swift dissemination to the central nervous system through a 'Trojan Horse' mechanism using infected leukocytes as carriers. Previous work found TgWIP, a protein secreted from Toxoplasma, played a role in altering the actin cytoskeleton and promoting cell migration in infected dendritic cells (DCs). However, the mechanism behind these changes was unknown. Here, we report that TgWIP harbors two SH2-binding motifs that interact with tyrosine phosphatases Shp1 and Shp2, leading to phosphatase activation. DCs infected with Toxoplasma exhibited hypermigration, accompanying enhanced F-actin stress fibers and increased membrane protrusions such as filopodia and pseudopodia. By contrast, these phenotypes were abrogated in DCs infected with Toxoplasma expressing a mutant TgWIP lacking the SH2-binding motifs. We further demonstrated that the Rho-associated kinase (Rock) is involved in the induction of these phenotypes, in a TgWIP-Shp1/2 dependent manner. Collectively, the data uncover a molecular mechanism by which TgWIP modulates the migration dynamics of infected DCs in vitro.

Genetically Engineered CLDN18.2 CAR-T Cells Expressing Synthetic PD1/CD28 Fusion Receptors Produced Using a Lentiviral Vector

This study aimed to develop synthetic Claudin18.2 (CLDN18.2) chimeric antigen receptor (CAR)-T (CAR-T) cells as a treatment for advanced gastric cancer using lentiviral vector genetic engineering technology that targets the CLDN18.2 antigen and simultaneously overcomes the immunosuppressive environment caused by programmed cell death protein 1 (PD-1). Synthetic CAR T cells are a promising approach in cancer immunotherapy but face many challenges in solid tumors. One of the major problems is immunosuppression caused by PD-1. CLDN18.2, a gastric-specific membrane protein, is considered a potential therapeutic target for gastric and other cancers. In our study, CLDN18.2 CAR was a second-generation CAR with inducible T-cell costimulatory (CD278), and CLDN18.2-PD1/CD28 CAR was a third-generation CAR, wherein the synthetic PD1/CD28 chimeric-switch receptor (CSR) was added to the second-generation CAR. In vitro, we detected the secretion levels of different cytokines and the killing ability of CAR-T cells. We found that the secretion of cytokines such as interferon-gamma (IFN-γ) and tumor necrosis factor-alpha (TNF-α) secreted by three types of CAR-T cells was increased, and the killing ability against CLDN18.2-positive GC cells was enhanced. In vivo, we established a xenograft GC model and observed the antitumor effects and off-target toxicity of CAR-T cells. These results support that synthetic anti-CLDN18.2 CAR-T cells have antitumor effect and anti-CLDN18.2-PD1/CD28 CAR could provide a promising design strategy to improve the efficacy of CAR-T cells in advanced gastric cancer.

The Toxoplasma secreted effector TgWIP modulates dendritic cell motility by activating host tyrosine phosphatases Shp1 and Shp2

The obligate intracellular parasite Toxoplasma gondii causes life-threatening toxoplasmosis to immunocompromised individuals. The pathogenesis of Toxoplasma relies on its swift dissemination to the central nervous system through a 'Trojan Horse' mechanism using infected leukocytes as carriers. Previous work found TgWIP, a protein secreted from Toxoplasma, played a role in altering the actin cytoskeleton and promoting cell migration in infected dendritic cells (DCs). However, the mechanism behind these changes was unknown. Here, we report that TgWIP harbors two SH2-binding motifs that interact with tyrosine phosphatases Shp1 and Shp2, leading to phosphatase activation. DCs infected with Toxoplasma exhibited hypermigration, accompanying enhanced F-actin stress fibers and increased membrane protrusions such as filopodia and pseudopodia. By contrast, these phenotypes were abrogated in DCs infected with Toxoplasma expressing a mutant TgWIP lacking the SH2-binding motifs. We further demonstrated that the Rho-associated kinase (Rock) is involved in the induction of these phenotypes, in a TgWIP-Shp1/2 dependent manner. Collectively, the data uncover a molecular mechanism by which TgWIP modulates the migration dynamics of infected DCs in vitro.

Folding and Binding Kinetics of the Tandem of SH2 Domains from SHP2

The SH2 domains of SHP2 play a crucial role in determining the function of the SHP2 protein. While the folding and binding properties of the isolated NSH2 and CSH2 domains have been extensively studied, there is limited information about the tandem SH2 domains. This study aims to elucidate the folding and binding kinetics of the NSH2-CSH2 tandem domains of SHP2 through rapid kinetic experiments, complementing existing data on the isolated domains. The results indicate that while the domains generally fold and unfold independently, acidic pH conditions induce complex scenarios involving the formation of a misfolded intermediate. Furthermore, a comparison of the binding kinetics of isolated NSH2 and CSH2 domains with the NSH2-CSH2 tandem domains, using peptides that mimic specific portions of Gab2, suggests a dynamic interplay between NSH2 and CSH2 in binding Gab2 that modulate the microscopic association rate constant of the binding reaction. These findings, discussed in the context of previous research on the NSH2 and CSH2 domains, enhance our understanding of the function of the SH2 domain tandem of SHP2.

The BTLA-HVEM axis restricts CAR T cell efficacy in cancer

The efficacy of T cell-based immunotherapies is limited by immunosuppressive pressures in the tumor microenvironment. Here we show a predominant role for the interaction between BTLA on effector T cells and HVEM (TNFRSF14) on immunosuppressive tumor microenvironment cells, namely regulatory T cells. High BTLA expression in chimeric antigen receptor (CAR) T cells correlated with poor clinical response to treatment. Therefore, we deleted BTLA in CAR T cells and show improved tumor control and persistence in models of lymphoma and solid malignancies. Mechanistically, BTLA inhibits CAR T cells via recruitment of tyrosine phosphatases SHP-1 and SHP-2, upon trans engagement with HVEM. BTLA knockout thus promotes CAR signaling and subsequently enhances effector function. Overall, these data indicate that the BTLA-HVEM axis is a crucial immune checkpoint in CAR T cell immunotherapy and warrants the use of strategies to overcome this barrier.

Agonistic anti-DCIR antibody inhibits ITAM-mediated inflammatory signaling and promotes immune resolution

DC inhibitory receptor (DCIR) is a C-type lectin receptor selectively expressed on myeloid cells, including monocytes, macrophages, DCs, and neutrophils. Its role in immune regulation has been implicated in murine models and human genome-wide association studies, suggesting defective DCIR function associates with increased susceptibility to autoimmune diseases such as rheumatoid arthritis, lupus, and Sjögren's syndrome. However, little is known about the mechanisms underlying DCIR activation to dampen inflammation. Here, we developed anti-DCIR agonistic antibodies that promote phosphorylation on DCIR's immunoreceptor tyrosine-based inhibitory motifs and recruitment of SH2 containing protein tyrosine phosphatase-2 for reducing inflammation. We also explored the inflammation resolution by depleting DCIR+ cells with antibodies. Utilizing a human DCIR-knock-in mouse model, we validated the antiinflammatory properties of the agonistic anti-DCIR antibody in experimental peritonitis and colitis. These findings provide critical evidence for targeting DCIR to develop transformative therapies for inflammatory diseases.

Cross-Talks between Raf Kinase Inhibitor Protein and Programmed Cell Death Ligand 1 Expressions in Cancer: Role in Immune Evasion and Therapeutic Implications

Innovations in cancer immunotherapy have resulted in the development of several novel immunotherapeutic strategies that can disrupt immunosuppression. One key advancement lies in immune checkpoint inhibitors (ICIs), which have shown significant clinical efficacy and increased survival rates in patients with various therapy-resistant cancers. This immune intervention consists of monoclonal antibodies directed against inhibitory receptors (e.g., PD-1) on cytotoxic CD8 T cells or against corresponding ligands (e.g., PD-L1/PD-L2) overexpressed on cancer cells and other cells in the tumor microenvironment (TME). However, not all cancer cells respond-there are still poor clinical responses, immune-related adverse effects, adaptive resistance, and vulnerability to ICIs in a subset of patients with cancer. This challenge showcases the heterogeneity of cancer, emphasizing the existence of additional immunoregulatory mechanisms in many patients. Therefore, it is essential to investigate PD-L1's interaction with other oncogenic genes and pathways to further advance targeted therapies and address resistance mechanisms. Accordingly, our aim was to investigate the mechanisms governing PD-L1 expression in tumor cells, given its correlation with immune evasion, to uncover novel mechanisms for decreasing PD-L1 expression and restoring anti-tumor immune responses. Numerous studies have demonstrated that the upregulation of Raf Kinase Inhibitor Protein (RKIP) in many cancers contributes to the suppression of key hyperactive pathways observed in malignant cells, alongside its broadening involvement in immune responses and the modulation of the TME. We, therefore, hypothesized that the role of PD-L1 in cancer immune surveillance may be inversely correlated with the low expression level of the tumor suppressor Raf Kinase Inhibitor Protein (RKIP) expression in cancer cells. This hypothesis was investigated and we found several signaling cross-talk pathways between the regulations of both RKIP and PD-L1 expressions. These pathways and regulatory factors include the MAPK and JAK/STAT pathways, GSK3β, cytokines IFN-γ and IL-1β, Sox2, and transcription factors YY1 and NFκB. The pathways that upregulated PD-L1 were inhibitory for RKIP expression and vice versa. Bioinformatic analyses in various human cancers demonstrated the inverse relationship between PD-L1 and RKIP expressions and their prognostic roles. Therefore, we suspect that the direct upregulation of RKIP and/or the use of targeted RKIP inducers in combination with ICIs could result in a more targeted anti-tumor immune response-addressing the therapeutic challenges related to PD-1/PD-L1 monotherapy alone.

Probing the Immunoreceptor Tyrosine-Based Inhibition Motif Interaction Protein Partners with Proteomics

Phosphorylation of tyrosine is the basic mode of protein function and signal transduction in organisms. This process is regulated by protein tyrosine kinases (PTKs) and protein tyrosinases (PTPs). Immunoreceptor tyrosine-based inhibition motif (ITIM) has been considered as regulating the PTP activity through the interaction with the partner proteins in the cell signal pathway. The ITIM sequences need to be phosphorylated first to active the downstream signaling proteins. To explore potential regulatory mechanisms, the ITIM sequences of two transmembrane immunoglobulin proteins, myelin P0 protein-related protein (PZR) and programmed death 1 (PD-1), were analyzed to investigate their interaction with proteins involved in regulatory pathways. We discovered that phosphorylated ITIM sequences can selectively interact with the tyrosine phosphatase SHP2. Specifically, PZR-N-ITIM (pY) may be critical in the interaction between the ITIM and SH2 domains of SHP2, while PD1-C-ITSM (pY) may play a key role in the interaction between the ITIM and SH2 domains of SHP2. Quite a few proteins were identified containing the SH2 domain, exhibiting phosphorylation-mediated interaction with PZR-ITIM. In this study, 14 proteins with SH2 structural domains were identified by GO analysis on 339 proteins associated to the affinity pull-down of PZR-N-ITIM (pY). Through the SH2 domains, these proteins may interact with PZR-ITIM in a phosphorylation-dependent manner.

Anti-Tumor Potential of Post-Translational Modifications of PD-1

Programmed cell death protein-1 (PD-1) is a vital immune checkpoint molecule. The location, stability, and protein-protein interaction of PD-1 are significantly influenced by post-translational modification (PTM) of proteins. The biological information of PD-1, including its gene and protein structures and the PD-1/PD-L1 signaling pathway, was briefly reviewed in this review. Additionally, recent research on PD-1 post-translational modification, including the study of ubiquitination, glycosylation, phosphorylation, and palmitoylation, was summarized, and research strategies for PD-1 PTM drugs were concluded. At present, only a part of PD-1/PD-L1 treated patients (35-45%) are benefited from immunotherapies, and novel strategies targeting PTM of PD-1/PD-L1 may be important for anti-PD-1/PD-L1 non-responders (poor responders).

A high-throughput two-cell assay for interrogating inhibitory signaling pathways in T cells

The recent success of immunotherapies relying on manipulation of T-cell activation highlights the value of characterising the mediators of immune checkpoint signaling. CRISPR/Cas9 is a popular approach for interrogating signaling pathways; however, the lack of appropriate assays for studying inhibitory signaling in T cells is limiting the use of large-scale perturbation-based approaches. Here, we adapted an existing Jurkat cell-based transcriptional reporter assay to study both activatory and inhibitory (PD-1-mediated) T-cell signaling using CRISPR-based genome screening in arrayed and pooled formats. We targeted 64 SH2 domain-containing proteins expressed by Jurkat T cells in an arrayed screen, in which individual targets could be assessed independently, showing that arrays can be used to study mediators of both activatory and inhibitory signaling. Pooled screens succeeded in simultaneously identifying many of the known mediators of proximal activating and inhibitory T-cell signaling, including SHP2 and PD-1, confirming the utility of the method. Altogether, the data suggested that SHP2 is the major PD-1-specific, SH2 family mediator of inhibitory signaling. These approaches should allow the systematic analysis of signaling pathways in T cells.

BTLA contributes to acute-on-chronic liver failure infection and mortality through CD4+ T-cell exhaustion

B- and T-lymphocyte attenuator (BTLA) levels are increased in patients with hepatitis B virus-related acute-on-chronic liver failure (HBV-ACLF). This condition is characterized by susceptibility to infection and T-cell immune exhaustion. However, whether BTLA can induce T-cell immune exhaustion and increase the risk of infection remains unclear. Here, we report that BTLA levels are significantly increased in the circulating and intrahepatic CD4+ T cells from patients with HBV-ACLF, and are positively correlated with disease severity, prognosis, and infection complications. BTLA levels were upregulated by the IL-6 and TNF signaling pathways. Antibody crosslinking of BTLA activated the PI3K-Akt pathway to inhibit the activation, proliferation, and cytokine production of CD4+ T cells while promoting their apoptosis. In contrast, BTLA knockdown promoted their activation and proliferation. BTLA-/- ACLF mice exhibited increased cytokine secretion, and reduced mortality and bacterial burden. The administration of a neutralizing anti-BTLA antibody reduced Klebsiella pneumoniae load and mortality in mice with ACLF. These data may help elucidate HBV-ACLF pathogenesis and aid in identifying novel drug targets.

Dissecting the Ability of Siglecs To Antagonize Fcγ Receptors

Fcγ receptors (FcγRs) play key roles in the effector function of IgG, but their inappropriate activation plays a role in several disease etiologies. Therefore, it is critical to better understand how FcγRs are regulated. Numerous studies suggest that sialic acid-binding immunoglobulin-type lectins (Siglecs), a family of immunomodulatory receptors, modulate FcγR activity; however, it is unclear of the circumstances in which Siglecs can antagonize FcγRs and which Siglecs have this ability. Using liposomes displaying selective ligands to coengage FcγRs with a specific Siglec, we explore the ability of Siglec-3, Siglec-5, Siglec-7, and Siglec-9 to antagonize signaling downstream of FcγRs. We demonstrate that Siglec-3 and Siglec-9 can fully inhibit FcγR activation in U937 cells when coengaged with FcγRs. Cells expressing Siglec mutants reveal differential roles for the immunomodulatory tyrosine-based inhibitory motif (ITIM) and immunomodulatory tyrosine-based switch motif (ITSM) in this inhibition. Imaging flow cytometry enabled visualization of SHP-1 recruitment to Siglec-3 in an ITIM-dependent manner, while SHP-2 recruitment is more ITSM-dependent. Conversely, both cytosolic motifs of Siglec-9 contribute to SHP-1/2 recruitment. Siglec-7 poorly antagonizes FcγR activation for two reasons: masking by cis ligands and differences in its ITIM and ITSM. A chimera of the Siglec-3 extracellular domains and Siglec-5 cytosolic tail strongly inhibits FcγR when coengaged, providing evidence that Siglec-5 is more like Siglec-3 and Siglec-9 in its ability to antagonize FcγRs. Additionally, Siglec-3 and Siglec-9 inhibited FcγRs when coengaged by cells displaying ligands for both the Siglec and FcγRs. These results suggest a role for Siglecs in mediating FcγR inhibition in the context of an immunological synapse, which has important relevance to the effectiveness of immunotherapies.

Molecular Imaging of PD-1 Unveils Unknown Characteristics of PD-1 Itself by Visualizing "PD-1 Microclusters"

Programmed cell death-1 (PD-1) is one of the most famous coinhibitory receptors that are expressed on effector T cells to regulate their function. The PD-1 ligands, PD-L1 and PD-L2, are expressed by various cells throughout the body at steady state and their expression was further regulated within different pathological conditions such as tumor-bearing and chronic inflammatory diseases. In recent years, immune checkpoint inhibitor (ICI) therapies with anti-PD-1 or anti-PD-L1 has become a standard treatment for various malignancies and has shown remarkable antitumor effects. Since the discovery of PD-1 in 1992, a huge number of studies have been conducted to elucidate the function of PD-1. Herein, this paper provides an overview of PD-1 biological findings and sheds some light on the current technology for molecular imaging of PD-1.

Consideration of SHP-1 as a Molecular Target for Tumor Therapy

Abnormal activation of receptor tyrosine kinases (RTKs) contributes to tumorigenesis, while protein tyrosine phosphatases (PTPs) contribute to tumor control. One of the most representative PTPs is Src homology region 2 (SH2) domain-containing phosphatase 1 (SHP-1), which is associated with either an increased or decreased survival rate depending on the cancer type. Hypermethylation in the promoter region of PTPN6, the gene for the SHP-1 protein, is a representative epigenetic regulation mechanism that suppresses the expression of SHP-1 in tumor cells. SHP-1 comprises two SH2 domains (N-SH2 and C-SH2) and a catalytic PTP domain. Intramolecular interactions between the N-SH2 and PTP domains inhibit SHP-1 activity. Opening of the PTP domain by a conformational change in SHP-1 increases enzymatic activity and contributes to a tumor control phenotype by inhibiting the activation of the Janus kinase/signal transducer and activator of transcription (JAK/STAT3) pathway. Although various compounds that increase SHP-1 activation or expression have been proposed as tumor therapeutics, except sorafenib and its derivatives, few candidates have demonstrated clinical significance. In some cancers, SHP-1 expression and activation contribute to a tumorigenic phenotype by inducing a tumor-friendly microenvironment. Therefore, developing anticancer drugs targeting SHP-1 must consider the effect of SHP-1 on both cell biological mechanisms of SHP-1 in tumor cells and the tumor microenvironment according to the target cancer type. Furthermore, the use of combination therapies should be considered.

Protein tyrosine phosphatases as emerging targets for cancer immunotherapy

Contemporary strategies in cancer immunotherapy, despite remarkable success, remain constrained by inherent limitations such as suboptimal patient responses, the emergence of drug resistance, and the manifestation of pronounced adverse effects. Consequently, the need for alternative strategies for immunotherapy becomes clear. Protein tyrosine phosphatases (PTPs) wield a pivotal regulatory influence over an array of essential cellular processes. Substantial research has underscored the potential in targeting PTPs to modulate the immune responses and/or regulate antigen presentation, thereby presenting a novel paradigm for cancer immunotherapy. In this review, we focus on recent advances in genetic and biological validation of several PTPs as emerging targets for immunotherapy. We also highlight recent development of small molecule inhibitors and degraders targeting these PTPs as novel cancer immunotherapeutic agents.

PD-1 and PD-L1: architects of immune symphony and immunotherapy breakthroughs in cancer treatment

PD-1 (Programmed Cell Death Protein-1) and PD-L1 (Programmed Cell Death Ligand-1) play a crucial role in regulating the immune system and preventing autoimmunity. Cancer cells can manipulate this system, allowing them to escape immune detection and promote tumor growth. Therapies targeting the PD-1/PD-L1 pathway have transformed cancer treatment and have demonstrated significant effectiveness against various cancer types. This study delves into the structure and signaling dynamics of PD-1 and its ligands PD-L1/PD-L2, the diverse PD-1/PD-L1 inhibitors and their efficacy, and the resistance observed in some patients. Furthermore, this study explored the challenges associated with the PD-1/PD-L1 inhibitor treatment approach. Recent advancements in the combination of immunotherapy with chemotherapy, radiation, and surgical procedures to enhance patient outcomes have also been highlighted. Overall, this study offers an in-depth overview of the significance of PD-1/PD-L1 in cancer immunotherapy and its future implications in oncology.

6-Mercaptopurine potently inhibits recruitment of SHP2 by phosphorylated PD-1 to inhibit PD-1 signalling and enhance T cell function

Antibody inhibitors that block PD-1/PD-L1 interaction have been approved for oncological clinics, yielding impressive treatment effects. Small molecules inhibiting PD-1 signalling are at various stages of development, given that small molecular drugs are expected to outperform protein drugs in several ways. Currently, a significant portion of these small molecular inhibitors achieve this purpose by binding to a limited region of the PD-L1 protein, thereby limiting the choice of chemical structures. Alternative strategies for developing small-molecular PD-1 inhibitors are urgently needed to broaden the choice of chemical structures. Here, we report that 6-mercaptopurine (6-MP) inhibits PD-1 signalling, activates T cell function in vitro and in vivo and shrinks tumours by activating cytotoxic T cells. Mechanistically, 6-MP potently inhibited PD-1 signalling by blocking the recruitment of SHP2 by PD-1. Considering that 6-MP is a chemotherapeutic agent already approved by the FDA for childhood leukaemia, our work revealed a novel anti-tumour mechanism for this drug and suggests that 6-MP warrants further clinical evaluation for other tumour types.

CTLA4 depletes T cell endogenous and trogocytosed B7 ligands via cis-endocytosis

CD28 and CTLA4 are T cell coreceptors that competitively engage B7 ligands CD80 and CD86 to control adaptive immune responses. While the role of CTLA4 in restraining CD28 costimulatory signaling is well-established, the mechanism has remained unclear. Here, we report that human T cells acquire antigen-presenting-cell (APC)-derived B7 ligands and major histocompatibility complex (MHC) via trogocytosis through CD28:B7 binding. Acquired MHC and B7 enabled T cells to autostimulate, and this process was limited cell-intrinsically by CTLA4, which depletes B7 ligands trogocytosed or endogenously expressed by T cells through cis-endocytosis. Extending this model to the previously proposed extrinsic function of CTLA4 in human regulatory T cells (Treg), we show that blockade of either CD28 or CTLA4 attenuates Treg-mediated depletion of APC B7, indicating that trogocytosis and CTLA4-mediated cis-endocytosis work together to deplete B7 from APCs. Our study establishes CTLA4 as a cell-intrinsic molecular sink that limits B7 availability on the surface of T cells, with implications for CTLA4-targeted therapy.

cis-B7:CD28 interactions at invaginated synaptic membranes provide CD28 co-stimulation and promote CD8+ T cell function and anti-tumor immunity

B7 ligands (CD80 and CD86), expressed by professional antigen-presenting cells (APCs), activate the main co-stimulatory receptor CD28 on T cells in trans. However, in peripheral tissues, APCs expressing B7 ligands are relatively scarce. This raises the questions of whether and how CD28 co-stimulation occurs in peripheral tissues. Here, we report that CD8+ T cells displayed B7 ligands that interacted with CD28 in cis at membrane invaginations of the immunological synapse as a result of membrane remodeling driven by phosphoinositide-3-kinase (PI3K) and sorting-nexin-9 (SNX9). cis-B7:CD28 interactions triggered CD28 signaling through protein kinase C theta (PKCθ) and promoted CD8+ T cell survival, migration, and cytokine production. In mouse tumor models, loss of T cell-intrinsic cis-B7:CD28 interactions decreased intratumoral T cells and accelerated tumor growth. Thus, B7 ligands on CD8+ T cells can evoke cell-autonomous CD28 co-stimulation in cis in peripheral tissues, suggesting cis-signaling as a general mechanism for boosting T cell functionality.

Evaluation of therapeutic PD-1 antibodies by an advanced single-molecule imaging system detecting human PD-1 microclusters

With recent advances in immune checkpoint inhibitors (ICIs), immunotherapy has become the standard treatment for various malignant tumors. Their indications and dosages have been determined empirically, taking individually conducted clinical trials into consideration, but without a standard method to evaluate them. Here we establish an advanced imaging system to visualize human PD-1 microclusters, in which a minimal T cell receptor (TCR) signaling unit co-localizes with the inhibitory co-receptor PD-1 in vitro. In these microclusters PD-1 dephosphorylates both the TCR/CD3 complex and its downstream signaling molecules via the recruitment of a phosphatase, SHP2, upon stimulation with the ligand hPD-L1. In this system, blocking antibodies for hPD-1-hPD-L1 binding inhibits hPD-1 microcluster formation, and each therapeutic antibody (pembrolizumab, nivolumab, durvalumab and atezolizumab) is characterized by a proprietary optimal concentration and combinatorial efficiency enhancement. We propose that our imaging system could digitally evaluate PD-1-mediated T cell suppression to evaluate their clinical usefulness and to develop the most suitable combinations among ICIs or between ICIs and conventional cancer treatments.

Exploration of T cell immune responses by expression of a dominant-negative SHP1 and SHP2

SHP1 and SHP2 are SH2 domain-containing proteins which have inhibitory phosphatase activity when recruited to phosphorylated ITIMs and ITSMs on inhibitory immune receptors. Consequently, SHP1 and SHP2 are key proteins in the transmission of inhibitory signals within T cells, constituting an important point of convergence for diverse inhibitory receptors. Therefore, SHP1 and SHP2 inhibition may represent a strategy for preventing immunosuppression of T cells mediated by cancers hence improving immunotherapies directed against these malignancies. Both SHP1 and SHP2 contain dual SH2 domains responsible for localization to the endodomain of inhibitory receptors and a protein tyrosine phosphatase domain which dephosphorylates and thus inhibits key mediators of T cell activation. We explored the interaction of the isolated SH2 domains of SHP1 and SHP2 to inhibitory motifs from PD1 and identified strong binding of both SH2 domains from SHP2 and more moderate binding in the case of SHP1. We next explored whether a truncated form of SHP1/2 comprising only of SH2 domains (dSHP1/2) could act in a dominant negative fashion by preventing docking of the wild type proteins. When co-expressed with CARs we found that dSHP2 but not dSHP1 could alleviate immunosuppression mediated by PD1. We next explored the capacity of dSHP2 to bind with other inhibitory receptors and observed several potential interactions. In vivo we observed that the expression of PDL1 on tumor cells impaired the ability of CAR T cells to mediate tumor rejection and this effect was partially reversed by the co-expression of dSHP2 albeit at the cost of reduced CAR T cell proliferation. Modulation of SHP1 and SHP2 activity in engineered T cells through the expression of these truncated variants may enhance T cell activity and hence efficacy in the context of cancer immunotherapy.

Application of the Nicoya OpenSPR to Studies of Biomolecular Binding: A Review of the Literature from 2016 to 2022

The Nicoya OpenSPR is a benchtop surface plasmon resonance (SPR) instrument. As with other optical biosensor instruments, it is suitable for the label-free interaction analysis of a diverse set of biomolecules, including proteins, peptides, antibodies, nucleic acids, lipids, viruses, and hormones/cytokines. Supported assays include affinity/kinetics characterization, concentration analysis, yes/no assessment of binding, competition studies, and epitope mapping. OpenSPR exploits localized SPR detection in a benchtop platform and can be connected with an autosampler (XT) to perform automated analysis over an extended time period. In this review article, we provide a comprehensive survey of the 200 peer-reviewed papers published between 2016 and 2022 that use the OpenSPR platform. We highlight the range of biomolecular analytes and interactions that have been investigated using the platform, provide an overview on the most common applications for the instrument, and point out some representative research that highlights the flexibility and utility of the instrument.

New Targets for Antiviral Therapy: Inhibitory Receptors and Immune Checkpoints on Myeloid Cells

Immune homeostasis is achieved by balancing the activating and inhibitory signal transduction pathways mediated via cell surface receptors. Activation allows the host to mount an immune response to endogenous and exogenous antigens; suppressive modulation via inhibitory signaling protects the host from excessive inflammatory damage. The checkpoint regulation of myeloid cells during immune homeostasis raised their profile as important cellular targets for treating allergy, cancer and infectious disease. This review focuses on the structure and signaling of inhibitory receptors on myeloid cells, with particular attention placed on how the interplay between viruses and these receptors regulates antiviral immunity. The status of targeting inhibitory receptors on myeloid cells as a new therapeutic approach for antiviral treatment will be analyzed.

TIGIT-CD226-PVR axis: advancing immune checkpoint blockade for cancer immunotherapy

Recent advances in understanding the roles of immune checkpoints in allowing tumors to circumvent the immune system have led to successful therapeutic strategies that have fundamentally changed oncology practice. Thus far, immunotherapies against only two checkpoint targets have been approved, CTLA-4 and PD-L1/PD-1. Antibody blockade of these targets enhances the function of antitumor T cells at least in part by relieving inhibition of the T cell costimulatory receptor CD28. These successes have stimulated considerable interest in identifying other pathways that may bte targeted alone or together with existing immunotherapies. One such immune checkpoint axis is comprised of members of the PVR/nectin family that includes the inhibitory receptor T cell immunoreceptor with Ig and immunoreceptor tyrosine-based inhibitory domains (TIGIT). Interestingly, TIGIT acts to regulate the activity of a second costimulatory receptor CD226 that works in parallel to CD28. There are currently over two dozen TIGIT-directed blocking antibodies in various phases of clinical development, testament to the promise of modulating this pathway to enhance antitumor immune responses. In this review, we discuss the role of TIGIT as a checkpoint inhibitor, its interplay with the activating counter-receptor CD226, and its status as the next advance in cancer immunotherapy.

Immune Checkpoint Receptors Signaling in T Cells

The characterization of the receptors negatively modulating lymphocyte function is rapidly advancing, driven by success in tumor immunotherapy. As a result, the number of immune checkpoint receptors characterized from a functional perspective and targeted by innovative drugs continues to expand. This review focuses on the less explored area of the signaling mechanisms of these receptors, of those expressed in T cells. Studies conducted mainly on PD-1, CTLA-4, and BTLA have evidenced that the extracellular parts of some of the receptors act as decoy receptors for activating ligands, but in all instances, the tyrosine phosphorylation of their cytoplasmatic tail drives a crucial inhibitory signal. This negative signal is mediated by a few key signal transducers, such as tyrosine phosphatase, inositol phosphatase, and diacylglycerol kinase, which allows them to counteract TCR-mediated activation. The characterization of these signaling pathways is of great interest in the development of therapies for counteracting tumor-infiltrating lymphocyte exhaustion/anergy independently from the receptors involved.