PD-1 and BTLA regulate T cell signaling differentially and only partially through SHP1 and SHP2

The pathogenic T42A mutation in SHP2 rewires the interaction specificity of its N-terminal regulatory domain

Mutations in the tyrosine phosphatase Src homology-2 domain-containing protein tyrosine phosphatase-2 (SHP2) are associated with a variety of human diseases. Most mutations in SHP2 increase its basal catalytic activity by disrupting autoinhibitory interactions between its phosphatase domain and N-terminal SH2 (phosphotyrosine recognition) domain. By contrast, some disease-associated mutations located in the ligand-binding pockets of the N- or C-terminal SH2 domains do not increase basal activity and likely exert their pathogenicity through alternative mechanisms. We lack a molecular understanding of how these SH2 mutations impact SHP2 structure, activity, and signaling. Here, we characterize five SHP2 SH2 domain ligand-binding pocket mutants through a combination of high-throughput biochemical screens, biophysical and biochemical measurements, and molecular dynamics simulations. We show that while some of these mutations alter binding affinity to phosphorylation sites, the T42A mutation in the N-SH2 domain is unique in that it also substantially alters ligand-binding specificity, despite being 8 to 10 Å from the specificity-determining region of the SH2 domain. This mutation exerts its effect on sequence specificity by remodeling the phosphotyrosine-binding pocket, altering the mode of engagement of both the phosphotyrosine and surrounding residues on the ligand. The functional consequence of this altered specificity is that the T42A mutant has biased sensitivity toward a subset of activating ligands and enhances downstream signaling. Our study highlights an example of a nuanced mechanism of action for a disease-associated mutation, characterized by a change in protein-protein interaction specificity that alters enzyme activation.

The Immune Checkpoint BTLA in Oral Cancer: Expression Analysis and Its Correlation to Other Immune Modulators

In oral squamous cell carcinoma (OSCC) tissues, an immunotolerant situation triggered by immune checkpoints (ICPs) can be observed. Immune checkpoint inhibitors (ICIs) against the PD1/PD-L axis are used with impressive success. However, the response rate is low and the development of acquired resistance to ICI treatment can be observed. Therefore, new treatment strategies especially involving immunological combination therapies need to be developed. The novel negative immune checkpoint BTLA has been suggested as a potential biomarker and target for antibody-based immunotherapy. Moreover, improved response rates could be displayed for tumor patients when antibodies directed against BTLA were used in combination with anti-PD1/PD-L1 therapies. The aim of the study was to check whether the immune checkpoint BTLA is overexpressed in OSCC tissues compared to healthy oral mucosa (NOM) and could be a potential diagnostic biomarker and immunological target in OSCC. In addition, correlation analyses with the expression of other checkpoints should clarify more precisely whether combination therapies are potentially useful for the treatment of OSCC. A total of 207 tissue samples divided into 2 groups were included in the study. The test group comprised 102 tissue samples of OSCC. Oral mucosal tissue from 105 healthy volunteers (NOM) served as the control group. The expression of two isoforms of BTLA (BTLA-1/2), as well as PD1, PD-L1/2 and CD96 was analyzed by RT-qPCR. Additionally, BTLA and CD96 proteins were detected by IHC. Expression levels were compared between the two groups, the relative differences were calculated, and statistical relevance was determined. Furthermore, the expression rates of the immune checkpoints were correlated to each other. BTLA expression was significantly increased in OSCC compared to NOM (pBTLA_1 = 0.003; pBTLA_2 = 0.0001, pIHC = 0.003). The expression of PD1, its ligands PD-L1 and PD-L2, as well as CD96, were also significantly increased in OSCC (p ≤ 0.001). There was a strong positive correlation between BTLA expression and that of the other checkpoints (p < 0.001; ρ ≥ 0.5). BTLA is overexpressed in OSCC and appears to be a relevant local immune checkpoint in OSCC. Thus, antibodies directed against BTLA could be potential candidates for immunotherapies, especially in combination with ICI against the PD1/PD-L axis and CD96.

PD1 inhibits PKCθ-dependent phosphorylation of cytoskeleton-related proteins and immune synapse formation

ABSTRACT

The inhibitory surface receptor programmed cell death protein 1 (PD1) is a major target for antibody-based cancer immunotherapies. Nevertheless, a substantial number of patients fail to respond to the treatment or experience adverse effects. An improved understanding of intracellular pathways targeted by PD1 is thus needed to develop better predictive and prognostic biomarkers. Here, via unbiased phosphoproteome analysis of primary human T cells, we demonstrate that PD1 triggering inhibited the phosphorylation and physical association with protein kinase Cθ (PKCθ) of a variety of cytoskeleton-related proteins. PD1 blocked activation and recruitment of PKCθ to the forming immune synapse (IS) in a Src homology-2 domain-containing phosphatase-1/2 (SHP1/SHP2)-dependent manner. Consequently, PD1 engagement led to impaired synaptic phosphorylation of cytoskeleton-related proteins and formation of smaller IS. T-cell receptor induced phosphorylation of the PKCθ substrate and binding partner vimentin was long-lasting and it could be durably inhibited by PD1 triggering. Vimentin phosphorylation in intratumoral T cells also inversely correlated with the levels of the PD1 ligand, PDL1, in human lung carcinoma. Thus, PKCθ and its substrate vimentin represent important targets of PD1-mediated T-cell inhibition, and low levels of vimentin phosphorylation may serve as a biomarker for the activation of the PD1 pathway.

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.

Protein tyrosine phosphatases: emerging role in cancer therapy resistance

BACKGROUND

Tyrosine phosphorylation of intracellular proteins is a post-translational modification that plays a regulatory role in signal transduction during cellular events. Dephosphorylation of signal transduction proteins caused by protein tyrosine phosphatases (PTPs) contributed their role as a convergent node to mediate cross-talk between signaling pathways. In the context of cancer, PTP-mediated pathways have been identified as signaling hubs that enabled cancer cells to mitigate stress induced by clinical therapy. This is achieved by the promotion of constitutive activation of growth-stimulatory signaling pathways or modulation of the immune-suppressive tumor microenvironment. Preclinical evidences suggested that anticancer drugs will release their greatest therapeutic potency when combined with PTP inhibitors, reversing drug resistance that was responsible for clinical failures during cancer therapy.

AREAS COVERED

This review aimed to elaborate recent insights that supported the involvement of PTP-mediated pathways in the development of resistance to targeted therapy and immune-checkpoint therapy.

EXPERT OPINION

This review proposed the notion of PTP inhibition in anticancer combination therapy as a potential strategy in clinic to achieve long-term tumor regression. Ongoing clinical trials are currently underway to assess the safety and efficacy of combination therapy in advanced-stage tumors.

THEMIS promotes T cell development and maintenance by rising the signaling threshold of the inhibitory receptor BTLA

The current paradigm about the function of T cell immune checkpoints is that these receptors switch on inhibitory signals upon cognate ligand interaction. We here revisit this simple switch model and provide evidence that the T cell lineage protein THEMIS enhances the signaling threshold at which the immune checkpoint BTLA (B- and T-lymphocyte attenuator) represses T cell responses. THEMIS is recruited to the cytoplasmic domain of BTLA and blocks its signaling capacity by promoting/stabilizing the oxidation of the catalytic cysteine of the tyrosine phosphatase SHP-1. In contrast, THEMIS has no detectable effect on signaling pathways regulated by PD-1 (Programmed cell death protein 1), which depend mainly on the tyrosine phosphatase SHP-2. BTLA inhibitory signaling is tuned according to the THEMIS expression level, making CD8+ T cells more resistant to BTLA-mediated inhibition than CD4+ T cells. In the absence of THEMIS, the signaling capacity of BTLA is exacerbated, which results in the attenuation of signals driven by the T cell antigen receptor and by receptors for IL-2 and IL-15, consequently hampering thymocyte positive selection and peripheral CD8+ T cell maintenance. By characterizing the pivotal role of THEMIS in restricting the transmission of BTLA signals, our study suggests that immune checkpoint operability is conditioned by intracellular signal attenuators.

The pathogenic T42A mutation in SHP2 rewires the interaction specificity of its N-terminal regulatory domain

Mutations in the tyrosine phosphatase SHP2 are associated with a variety of human diseases. Most mutations in SHP2 increase its basal catalytic activity by disrupting auto-inhibitory interactions between its phosphatase domain and N-terminal SH2 (phosphotyrosine recognition) domain. By contrast, some disease-associated mutations located in the ligand-binding pockets of the N- or C-terminal SH2 domains do not increase basal activity and likely exert their pathogenicity through alternative mechanisms. We lack a molecular understanding of how these SH2 mutations impact SHP2 structure, activity, and signaling. Here, we characterize five SHP2 SH2 domain ligand-binding pocket mutants through a combination of high-throughput biochemical screens, biophysical and biochemical measurements, and molecular dynamics simulations. We show that, while some of these mutations alter binding affinity to phosphorylation sites, the T42A mutation in the N-SH2 domain is unique in that it also substantially alters ligand-binding specificity, despite being 8-10 Å from the specificity-determining region of the SH2 domain. This mutation exerts its effect on sequence specificity by remodeling the phosphotyrosine binding pocket, altering the mode of engagement of both the phosphotyrosine and surrounding residues on the ligand. The functional consequence of this altered specificity is that the T42A mutant has biased sensitivity toward a subset of activating ligands and enhances downstream signaling. Our study highlights an example of a nuanced mechanism of action for a disease-associated mutation, characterized by a change in protein-protein interaction specificity that alters enzyme activation.

PD-1-mediated inhibition of T cell activation: Mechanisms and strategies for cancer combination immunotherapy

The programmed cell death 1 (PD-1) immune checkpoint of co-inhibitory signaling plays crucial roles in controlling the magnitude and duration of T cell activation to limit tissue damage and maintain self-tolerance. Cancer cells hijack the co-inhibitory pathway and escape immune surveillance by overexpressing the PD-1 ligand PD-L1. Immune checkpoint inhibitors, such as PD-1 blocking antibody have been approved for tumor immunotherapy. However, not all patients can benefit from PD-1 monotherapy. Combination immunotherapy based on PD-1 axis blockade substantially improves clinical anti-tumor efficacy. In this review, we briefly summarize the current progress on the mechanisms of PD-1-mediated inhibition of T cell activation and strategies for cancer combination immunotherapy.

Blockade of BTLA alone or in combination with PD-1 restores the activation and proliferation of CD8+ T cells during in vitro infection with NCP BVDV

Bovine viral diarrhea virus (BVDV) infection can result in typical peripheral blood lymphopenia and immune dysfunction. However, the molecular mechanism underlying the onset of lymphopenia remains unclear. B and T lymphocyte attenuator (BTLA) is a novel immune checkpoint molecule that primarily inhibits activation and proliferation of T cells. Blockade of BTLA with antibodies can boost the proliferation and anti-viral immune functions of T cells. Nonetheless, the immunomodulatory effects of BTLA in CD8+ T cells during BVDV infection remain unknown. Therefore, BTLA expression was measured in bovine peripheral blood CD8+ T cells infected with BVDV in vitro. Furthermore, the effects of BTLA or PD-1 blockade on CD8+ T cell activation, proliferation, and anti-viral immunological activities were investigated, as well as expression of signaling molecules downstream of BTLA, both alone and in combination. The results demonstrated that BTLA and PD-1 mRNA and protein levels were considerably increased in CD8+ T cells infected with cytopathic and non-cytopathic (NCP) BVDV. Surprisingly, as compared to blockade of either BTLA or PD-1, blockade of both dramatically increased proliferation and expression of CD25 and p-EKR of CD8+ T cells infected with NCP BVDV. Furthermore, blockade of BTLA, but not PD-1, had no effect on BVDV replication or IFN-γ expression. These findings confirmed the immunomodulatory roles of BTLA during BVDV infection, as well as the synergistic role of BTLA and PD-1 in NCP BVDV infection, thereby providing new insights to promote activation and the anti-viral immunological activities of CD8+ T cells.

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.

A Systematic Review of the Advances in the Study of T Lymphocyte Suppressor Receptors in HBV Infection: Potential Therapeutic Targets

Background: HBV-specific T lymphocytes are pivotal in eliminating the hepatitis B virus (HBV) and regulating intrahepatic inflammatory reactions. Effective T cell responses curtail HBV infection; however, compromised immunity can result in persistent infection. Beyond the acute phase, the continued presence of antigens and inflammation leads to the increased expression of various inhibitory receptors, such as PD-1, CTLA-4, Tim-3, LAG3, 2B4, CD160, BTLA, and TIGIT. This escalates the dysfunction of and diminishes the immune and proliferative abilities of T cells. Methods: In this study, we reviewed English-language literature from PubMed, Web of Science, and Scopus up to 9 July 2023. This paper aims to elucidate the inhibitory effects of these receptors on HBV-specific T lymphocytes and how immune function can be rejuvenated by obstructing the inhibitory receptor signaling pathway in chronic HBV patients. We also summarize the latest insights into related anti-HBV immunotherapy. Result: From 66 reviewed reports, we deduced that immunotherapy targeting inhibitory receptors on T cells is a reliable method to rejuvenate T cell immune responses in chronic HBV patients. However, comprehensive combination therapy strategies are essential for a functional cure. Conclusions: Targeting T cell suppressor receptors and combining immunotherapy with antiviral treatments may offer a promising approach towards achieving a functional cure, urging future research to prioritize effective combination therapeutic strategies for chronic HBV infection.

Antibody agonists trigger immune receptor signaling through local exclusion of receptor-type protein tyrosine phosphatases

Antibodies can block immune receptor engagement or trigger the receptor machinery to initiate signaling. We hypothesized that antibody agonists trigger signaling by sterically excluding large receptor-type protein tyrosine phosphatases (RPTPs) such as CD45 from sites of receptor engagement. An agonist targeting the costimulatory receptor CD28 produced signals that depended on antibody immobilization and were sensitive to the sizes of the receptor, the RPTPs, and the antibody itself. Although both the agonist and a non-agonistic anti-CD28 antibody locally excluded CD45, the agonistic antibody was more effective. An anti-PD-1 antibody that bound membrane proximally excluded CD45, triggered Src homology 2 domain-containing phosphatase 2 recruitment, and suppressed systemic lupus erythematosus and delayed-type hypersensitivity in experimental models. Paradoxically, nivolumab and pembrolizumab, anti-PD-1-blocking antibodies used clinically, also excluded CD45 and were agonistic in certain settings. Reducing these agonistic effects using antibody engineering improved PD-1 blockade. These findings establish a framework for developing new and improved therapies for autoimmunity and cancer.

SHP-1 Regulates CD8+ T Cell Effector Function but Plays a Subtle Role with SHP-2 in T Cell Exhaustion Due to a Stage-Specific Nonredundant Functional Relay

SHP-1 (Src homology region 2 domain-containing phosphatase 1) is a well-known negative regulator of T cells, whereas its close homolog SHP-2 is the long-recognized main signaling mediator of the PD-1 inhibitory pathway. However, recent studies have challenged the requirement of SHP-2 in PD-1 signaling, and follow-up studies further questioned the alternative idea that SHP-1 may replace SHP-2 in its absence. In this study, we systematically investigate the role of SHP-1 alone or jointly with SHP-2 in CD8+ T cells in a series of gene knockout mice. We show that although SHP-1 negatively regulates CD8+ T cell effector function during acute lymphocytic choriomeningitis virus (LCMV) infection, it is dispensable for CD8+ T cell exhaustion during chronic LCMV infection. Moreover, in contrast to the mortality of PD-1 knockout mice upon chronic LCMV infection, mice double deficient for SHP-1 and SHP-2 in CD8+ T cells survived without immunopathology. Importantly, CD8+ T cells lacking both phosphatases still differentiate into exhausted cells and respond to PD-1 blockade. Finally, we found that SHP-1 and SHP-2 suppressed effector CD8+ T cell expansion at the early and late stages, respectively, during chronic LCMV infection.

BTLA biology in cancer: from bench discoveries to clinical potentials

Immune checkpoints play a critical role in maintaining the delicate balance of immune activation in order to prevent potential harm caused by excessive activation, autoimmunity, or tissue damage. B and T lymphocyte attenuator (BTLA) is one of crucial checkpoint, regulating stimulatory and inhibitory signals in immune responses. Its interaction with the herpes virus entry mediator (HVEM) plays an essential role in negatively regulating immune responses, thereby preserving immune homeostasis. In cancer, abnormal cells evade immune surveillance by exploiting checkpoints like BTLA. Upregulated BTLA expression is linked to impaired anti-tumor immunity and unfavorable disease outcomes. In preclinical studies, BTLA-targeted therapies have shown improved treatment outcomes and enhanced antitumor immunity. This review aims to provide an in-depth understanding of BTLA's biology, its role in various cancers, and its potential as a prognostic factor. Additionally, it explores the latest research on BTLA blockade in cancer immunotherapy, offering hope for more effective cancer treatments.

Using CombiCells, a platform for titration and combinatorial display of cell surface ligands, to study T-cell antigen sensitivity modulation by accessory receptors

Understanding cellular decisions due to receptor-ligand interactions at cell-cell interfaces has been hampered by the difficulty of independently varying the surface density of multiple different ligands. Here, we express the synthetic binder protein SpyCatcher, designed to form spontaneous covalent bonds with interactors carrying a Spytag, on the cell surface. Using this, we show that addition of different concentrations and combinations of native Spytag-fused ligands allows for the combinatorial display of ligands on cells within minutes. We use this combinatorial display of cell surface ligands-called CombiCells-to assess T cell antigen sensitivity and the impact of T cell co-stimulation and co-inhibition receptors. We find that the T cell receptor (TCR) displayed greater sensitivity to peptides on major-histocompatibility complexes (pMHC) than synthetic chimeric antigen receptor (CARs) and bi-specific T cell engager (BiTEs) display to their target antigen, CD19. While TCR sensitivity was greatly enhanced by CD2/CD58 interactions, CAR sensitivity was primarily but more modestly enhanced by LFA-1/ICAM-1 interactions. Lastly, we show that PD-1/PD-L1 engagement inhibited T cell activation triggered solely by TCR/pMHC interactions, as well as the amplified activation induced by CD2 and CD28 co-stimulation. The ability to easily produce cells with different concentrations and combinations of ligands should accelerate the study of receptor-ligand interactions at cell-cell interfaces.

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 signaling negatively regulates the common cytokine receptor γ chain via MARCH5-mediated ubiquitination and degradation to suppress anti-tumor immunity

Combination therapy with PD-1 blockade and IL-2 substantially improves anti-tumor efficacy comparing to monotherapy. The underlying mechanisms responsible for the synergistic effects of the combination therapy remain enigmatic. Here we show that PD-1 ligation results in BATF-dependent transcriptional induction of the membrane-associated E3 ubiquitin ligase MARCH5, which mediates K27-linked polyubiquitination and lysosomal degradation of the common cytokine receptor γ chain (γc). PD-1 ligation also activates SHP2, which dephosphorylates γcY357, leading to impairment of γc family cytokine-triggered signaling. Conversely, PD-1 blockade restores γc level and activity, thereby sensitizing CD8+ T cells to IL-2. We also identified Pitavastatin Calcium as an inhibitor of MARCH5, which combined with PD-1 blockade and IL-2 significantly improves the efficacy of anti-tumor immunotherapy in mice. Our findings uncover the mechanisms by which PD-1 signaling antagonizes γc family cytokine-triggered immune activation and demonstrate that the underlying mechanisms can be exploited for increased efficacy of combination immunotherapy of cancer.

PD-1 inhibits T cell actin remodeling at the immunological synapse independently of its signaling motifs

Engagement of the receptor programmed cell death molecule 1 (PD-1) by its ligands PD-L1 and PD-L2 inhibits T cell-mediated immune responses. Blocking such signaling provides the clinical effects of PD-1-targeted immunotherapy. Here, we investigated the mechanisms underlying PD-1-mediated inhibition. Because dynamic actin remodeling is crucial for T cell functions, we characterized the effects of PD-1 engagement on actin remodeling at the immunological synapse, the interface between a T cell and an antigen-presenting cell (APC) or target cell. We used microscopy to analyze the formation of immunological synapses between PD-1+ Jurkat cells or primary human CD8+ cytotoxic T cells and APCs that presented T cell-activating antibodies and were either positive or negative for PD-L1. PD-1 binding to PD-L1 inhibited T cell spreading induced by antibody-mediated activation, which was characterized by the absence of the F-actin-dense distal lamellipodial network at the immunological synapse and the Arp2/3 complex, which mediates branched actin formation. PD-1-induced inhibition of actin remodeling also prevented the characteristic deformation of T cells that contact APCs and the release of cytotoxic granules. We showed that the effects of PD-1 on actin remodeling did not require its tyrosine-based signaling motifs, which are thought to mediate the co-inhibitory effects of PD-1. Our study highlights a previously unappreciated mechanism of PD-1-mediated suppression of T cell activity, which depends on the regulation of actin cytoskeleton dynamics in a signaling motif-independent manner.

Small molecule inhibitors for cancer immunotherapy and associated biomarkers - the current status

Following the success of cancer immunotherapy using large molecules against immune checkpoint inhibitors, the concept of using small molecules to interfere with intracellular negative regulators of anti-tumor immune responses has emerged in recent years. The main targets for small molecule drugs currently include enzymes of negative feedback loops in signaling pathways of immune cells and proteins that promote immunosuppressive signals within the tumor microenvironment. In the adaptive immune system, negative regulators of T cell receptor signaling (MAP4K1, DGKα/ζ, CBL-B, PTPN2, PTPN22, SHP1), co-receptor signaling (CBL-B) and cytokine signaling (PTPN2) have been preclinically validated as promising targets and initial clinical trials with small molecule inhibitors are underway. To enhance innate anti-tumor immune responses, inhibitory immunomodulation of cGAS/STING has been in the focus, and inhibitors of ENPP1 and TREX1 have reached the clinic. In addition, immunosuppressive signals via adenosine can be counteracted by CD39 and CD73 inhibition, while suppression via intratumoral immunosuppressive prostaglandin E can be targeted by EP2/EP4 antagonists. Here, we present the status of the most promising small molecule drug candidates for cancer immunotherapy, all residing relatively early in development, and the potential of relevant biomarkers.

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.

B- and T-lymphocyte attenuator could be a new player in accelerated atherosclerosis associated with chronic kidney disease

BACKGROUND

In chronic kidney disease (CKD), cardiovascular morbi-mortality is higher than in general population. Atherosclerotic cardiovascular disease is accelerated in CKD, but specific CKD-related risk factors for atherosclerosis are unknown.

METHODS

CKD patients from the NEFRONA study were used. We performed mRNA array from blood of patients free from atheroma plaque at baseline, with (n=10) and without (n=10) de novo atherosclerotic plaque development 2 years later. Selected mRNA candidates were validated in a bigger sample (n=148). Validated candidates were investigated in vivo in an experimental model of CKD-accelerated atherosclerosis, and in vitro in murine macrophages.

RESULTS

mRNA array analysis showed 92 up-regulated and 67 down-regulated mRNAs in samples from CKD patients with de novo plaque development. The functional analysis pointed to a paramount role of the immune response. The validation in a bigger sample confirmed that B- and T-lymphocyte co-inhibitory molecule (BTLA) down-regulation was associated with de novo plaque presence after 2 years. However, BTLA down-regulation was not found to be associated with atherosclerotic progression in patients with plaque already present at baseline. In a model of CKD-accelerated atherosclerosis, mRNA and protein expression levels of BTLA were significantly decreased in blood samples and atheroma plaques. Plaques from animals with CKD were bigger, had more infiltration of inflammatory cells, higher expression of IL6 and IL17 and less presence of collagen than plaques from control animals. Incubation of macrophages with rat uremic serum decreased BTLA expression.

CONCLUSIONS

BTLA could be a potential biomarker or therapeutic target for atherosclerosis incidence in CKD patients.

Protein Kinase C at the Crossroad of Mutations, Cancer, Targeted Therapy and Immune Response

The frequent PKC dysregulations observed in many tumors have made these enzymes natural targets for anticancer applications. Nevertheless, this considerable interest in the development of PKC modulators has not led to the expected therapeutic benefits, likely due to the complex biological activities regulated by PKC isoenzymes, often playing ambiguous and protective functions, further driven by the occurrence of mutations. The structure, regulation and functions of PKCs have been extensively covered in other publications. Herein, we focused on PKC alterations mostly associated with complete functional loss. We also addressed the modest yet encouraging results obtained targeting PKC in selected malignancies and the more frequent negative clinical outcomes. The reported observations advocate the need for more selective molecules and a better understanding of the involved pathways. Furthermore, we underlined the most relevant immune mechanisms controlled by PKC isoforms potentially impacting the immune checkpoint inhibitor blockade-mediated immune recovery. We believe that a comprehensive examination of the molecular features of the tumor microenvironment might improve clinical outcomes by tailoring PKC modulation. This approach can be further supported by the identification of potential response biomarkers, which may indicate patients who may benefit from the manipulation of distinctive PKC isoforms.

Comprehensive Review: Unveiling the Pro-Oncogenic Roles of IL-1ß and PD-1/PD-L1 in NSCLC Development and Targeting Their Pathways for Clinical Management

In the past decade, targeted therapies for solid tumors, including non-small cell lung cancer (NSCLC), have advanced significantly, offering tailored treatment options for patients. However, individuals without targetable mutations pose a clinical challenge, as they may not respond to standard treatments like immune-checkpoint inhibitors (ICIs) and novel targeted therapies. While the mechanism of action of ICIs seems promising, the lack of a robust response limits their widespread use. Although the expression levels of programmed death ligand 1 (PD-L1) on tumor cells are used to predict ICI response, identifying new biomarkers, particularly those associated with the tumor microenvironment (TME), is crucial to address this unmet need. Recently, inflammatory cytokines such as interleukin-1 beta (IL-1β) have emerged as a key area of focus and hold significant potential implications for future clinical practice. Combinatorial approaches of IL-1β inhibitors and ICIs may provide a potential therapeutic modality for NSCLC patients without targetable mutations. Recent advancements in our understanding of the intricate relationship between inflammation and oncogenesis, particularly involving the IL-1β/PD-1/PD-L1 pathway, have shed light on their application in lung cancer development and clinical outcomes of patients. Targeting these pathways in cancers like NSCLC holds immense potential to revolutionize cancer treatment, particularly for patients lacking targetable genetic mutations. However, despite these promising prospects, there remain certain aspects of this pathway that require further investigation, particularly regarding treatment resistance. Therefore, the objective of this review is to delve into the role of IL-1β in NSCLC, its participation in inflammatory pathways, and its intricate crosstalk with the PD-1/PD-L1 pathway. Additionally, we aim to explore the potential of IL-1β as a therapeutic target for NSCLC treatment.

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.

Thymic expression of immune checkpoint molecules and their implication for response to immunotherapies

The thymus is responsible for generating a diverse T cell repertoire that is tolerant to self, but capable of responding to various immunologic insults, including cancer. Checkpoint blockade has changed the face of cancer treatment by targeting inhibitory molecules, which are known to regulate peripheral T cell responses. However, these inhibitory molecules and their ligands are expressed during T cell development in the thymus. In this review, we describe the underappreciated role of checkpoint molecule expression during the formation of the T cell repertoire and detail the importance of inhibitory molecules in regulating T cell lineage commitment. Understanding how these molecules function in the thymus may inform therapeutic strategies for better patient outcomes.

Targeting RNA N6-methyladenosine to synergize with immune checkpoint therapy

Cancer immunotherapy, especially immune checkpoint therapy, has revolutionized therapeutic options by reactivating the host immune system. However, the efficacy varies, and only a small portion of patients develop sustained antitumor responses. Hence, illustrating novel strategies that improve the clinical outcome of immune checkpoint therapy is urgently needed. N6-methyladenosine (m⁶A) has been proved to be an efficient and dynamic posttranscriptional modification process. It is involved in numerous RNA processing, such as splicing, trafficking, translation and degradation. Compelling evidence emphasizes the paramount role of m⁶A modification in the regulation of immune response. These findings may provide a foundation for the rational combination of targeting m⁶A modification and immune checkpoints in cancer treatment. In the present review, we summarize the current landscape of m⁶A modification in RNA biology, and highlight the latest findings on the complex mechanisms by which m⁶A modification governs immune checkpoint molecules. Furthermore, given the critical role of m⁶A modification in antitumor immunity, we discuss the clinical significance of targeting m⁶A modification to improve the efficacy of immune checkpoint therapy for cancer control.

Drastic transformation of visceral adipose tissue and peripheral CD4 T cells in obesity

Obesity has a pronounced effect on the immune response in systemic organs that results in not only insulin resistance but also altered immune responses to infectious diseases and malignant tumors. Obesity-associated microenvironmental changes alter transcriptional expression and metabolism in T cells, leading to alterations in T-cell differentiation, proliferation, function, and survival. Adipokines, cytokines, and lipids derived from obese visceral adipose tissue (VAT) may also contribute to the systemic T-cell phenotype, resulting in obesity-specific pathogenesis. VAT T cells, which have multiple roles in regulating homeostasis and energy utilization and defending against pathogens, are most susceptible to obesity. In particular, many studies have shown that CD4 T cells are deeply involved in the homeostasis of VAT endocrine and metabolic functions and in obesity-related chronic inflammation. In obesity, macrophages and adipocytes in VAT function as antigen-presenting cells and contribute to the obesity-specific CD4 T-cell response by inducing CD4 T-cell proliferation and differentiation into inflammatory effectors via interactions between major histocompatibility complex class II and T-cell receptors. When obesity persists, prolonged stimulation by leptin and circulating free fatty acids, repetitive antigen stimulation, activating stress responses, and hypoxia induce exhaustion of CD4 T cells in VAT. T-cell exhaustion is characterized by restricted effector function, persistent expression of inhibitory receptors, and a transcriptional state distinct from functional effector and memory T cells. Moreover, obesity causes thymic regression, which may result in homeostatic proliferation of obesity-specific T-cell subsets due to changes in T-cell metabolism and gene expression in VAT. In addition to causing T-cell exhaustion, obesity also accelerates cellular senescence of CD4 T cells. Senescent CD4 T cells secrete osteopontin, which causes further VAT inflammation. The obesity-associated transformation of CD4 T cells remains a negative legacy even after weight loss, causing treatment resistance of obesity-related conditions. This review discusses the marked transformation of CD4 T cells in VAT and systemic organs as a consequence of obesity-related microenvironmental changes.

The effect of combining PD-1 agonist and low-dose Interleukin-2 on treating systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease involving multiple organs. It is often called "immortal cancer" due to the difficulties in disease treatment. As the cornerstone of immune regulation, the programmed cell death protein 1 (PD-1) has been extensively studied in the context of chronic inflammation due to its ability of regulating immune response and immunosuppression. Recently, more and more studies on rheumatic immune related complications have also focused on PD-1 and proposed that the use of PD-1 agonist could inhibit the activation of lymphocytes and alleviate SLE disease activity. In this review, we summarized the role of PD-1 in SLE, implicating its potential application as a biomarker to predict SLE disease activity; we also proposed that the combination of PD-1 agonist and low-dose IL-2 may have better therapeutic efficacy, shining light on a new direction for developing specific treatment approaches.

Inborn errors of immunity associated with defects of self-tolerance checkpoints: The CD28 family

One of the causes of inborn errors of immunity is immune dysregulation. The inability of the immune system to regulate the extent of its activity has several deleterious effects, including autoimmunity, recurrent infections, and malignancy. In recent years, many proteins in the CD28 family - CD28, ICOS, CTLA-4, PD-1, and BTLA - have come into the focus of several research areas for their consequential role in the upregulation or downregulation of the immune response. In this review, we will discuss the structure and function of these proteins, as well as provide an overview of the clinical picture of patients with genetic defects.

PD-1/LAG-3 bispecific antibody potentiates T cell activation and increases antitumor efficacy

Several clinical studies demonstrate that there exist other immune checkpoints overexpressed in some PD-1 inhibitor-resistant tumor patients. Among them, Lymphocyte-activation gene 3 (LAG-3) is one of the important immune checkpoint molecules and has been clinically demonstrated to have synergistic anti-tumor effects in combination with PD-1 antibody. In this study, we designed a novel 'knob-in-hole' PD-1/LAG-3 bispecific antibody (BsAb) YG-003D3. In conclusion, the BsAb maintained the similar affinity and thermal stability to the parental antibody, and the BsAb structure can be independent of each other in the process of double-target recognition, and the recognition activity will not be affected. Moreover, the BsAb can not only target PD-1 and LAG-3 on single cell simultaneously, but also bridge the two kinds of cells expressing PD-1 and LAG-3, so as to release the 'brake system of immune checkpoints' and activate immune cells to exert anti-tumor effects more effectively. Especially in the PBMCs activation assay, YG-003D3 induced stronger IFN-γ, IL-6, and TNF-α secretion compared to anti-PD-1 or anti-LAG-3 single drug group or even combined drug group. In the tumor killing experiment of PBMC in vitro, YG-003D3 has a better ability to activate PBMC to kill tumor cells than anti-PD-1 or anti-LAG-3 single drug group or even combined drug group, and the killing rate is as high as 20%. In a humanized PD-1/LAG-3 transgenic mouse subcutaneous tumor-bearing model, YG-003D3 showed good anti-tumor activity, even better than that of the combination group at the same molar concentration. Further studies have shown that YG-003D3 could significantly alter the proportion of immune cells in the tumor microenvironment. In particular, the proportion of CD45⁺, CD3⁺ T, CD8⁺ T cells in tumor tissue and the proportion of CD3⁺ T, CD8⁺ T, CD4⁺ T cells in peripheral blood were significantly increased. These results suggest that YG-003D3 exerts a potent antitumor effect by activating the body 's immune system. In summary, the BsAb YG-003D3 has good anti-tumor activity, which is expected to become a novel drug candidate for cancer immunotherapy.

Concomitant deletion of Ptpn6 and Ptpn11 in T cells fails to improve anticancer responses

Anticancer T cells acquire a dysfunctional state characterized by poor effector function and expression of inhibitory receptors, such as PD-1. Blockade of PD-1 leads to T cell reinvigoration and is increasingly applied as an effective anticancer treatment. Recent work challenged the commonly held view that the phosphatase PTPN11 (known as SHP-2) is essential for PD-1 signaling in T cells, suggesting functional redundancy with the homologous phosphatase PTPN6 (SHP-1). Therefore, we investigated the effect of concomitant Ptpn6 and Ptpn11 deletion in T cells on their ability to mount antitumour responses. In vivo data show that neither sustained nor acute Ptpn6/11 deletion improves T cell-mediated tumor control. Sustained loss of Ptpn6/11 also impairs the therapeutic effects of anti-PD1 treatment. In vitro results show that Ptpn6/11-deleted CD8+ T cells exhibit impaired expansion due to a survival defect and proteomics analyses reveal substantial alterations, including in apoptosis-related pathways. These data indicate that concomitant ablation of Ptpn6/11 in polyclonal T cells fails to improve their anticancer properties, implying that caution shall be taken when considering their inhibition for immunotherapeutic approaches.

Effect of pembrolizumab on T lymphocyte subsets in patients with advanced oral cancer and its therapeutic effect

BACKGROUND

The aim of this study is to investigate changes of peripheral blood lymphocyte subsets before and after treatment with pembrolizumab for advanced oral cancer and its clinical sig-nificance.

METHODS

32 patients with advanced oral cancer who received pembrolizumab treatment were selected as observation group, 30 healthy people during the same period were selected as control group. Before treatment and in cycles 1, 2, 3 and 4 after treatment, fluid cytometry was used to detect changes in levels of lymphocyte subsets in peripheral blood of patients.

RESULTS

CD3+, CD4+, CD4+/CD8 + indexes of patients with advanced oral cancer before treatment were significantly lower than those in control group (P < .05), CD8 + level was significantly increased (P < .05); After 1 cycle of pembrolizumab treatment, there was no significant difference in changes of lymphocyte subsets compared with before immunotherapy; After 2 and 3 cycles of treatment, CD3+, CD4+, CD4+/CD8 + values were higher than before the treatment (P > .05), CD8 + index was slightly lower than before treatment (P < .05); After fourth cycle of treatment, CD3+, CD4+, CD4+/CD8 + values were significantly improved compared to before treatment (P < .05), CD8 + index was significantly lower than before treatment (P < .05); In treatment process of patients with stable disease (SD)/partial response (PR), the CD3+, CD4+, CD4+/CD8 + values of fourth cycles were higher than before treatment (P < .05), CD8 + index was lower than before treatment (P < .05); During treatment of progressive disease (PD) patients, changes of lymphocyte subsets in fourth cycles were not significantly different from those before treatment (P > .05). This article shows through analysis that expression of programmed cell death ligand 1 (PD-L1) and pathological types have no obvious influence on effect of immunotherapy. Multi-factor analysis shows that it is more meaningful to observe the changes of CD3+, CD4 + and CD8 + at the same time to predict effect of immunotherapy.

CONCLUSION

Pembrolizumab can regulate changes of T lymphocyte subsets in patients with advanced oral cancer, improve immune status of patients, there is no obvious adverse reaction. Monitoring changes of lymphocyte subsets during treatment can predict effect of immunotherapy.

Harnessing the immune system by targeting immune checkpoints: Providing new hope for Oncotherapy

With the goal of harnessing the host’s immune system to provide long-lasting remission and cures for various cancers, the advent of immunotherapy revolutionized the cancer therapy field. Among the current immunotherapeutic strategies, immune checkpoint blockades have greatly improved the overall survival rates in certain patient populations. Of note, CTLA4 and PD-1/PD-L1 are two major non-redundant immune checkpoints implicated in promoting cancer immune evasion, and ultimately lead to relapse. Antibodies or inhibitors targeting these two c+heckpoints have achieved some encouraging clinical outcomes. Further, beyond the canonical immune checkpoints, more inhibitory checkpoints have been identified. Herein, we will summarize recent progress in immune checkpoint blockade therapies, with a specific focus on key pre-clinical and clinical results of new immune checkpoint therapies for cancer. Given the crucial roles of immune checkpoint blockade in oncotherapy, drugs targeting checkpoint molecules expressed by both cancer and immune cells are in clinical trials, which will be comprehensively summarized in this review. Taken together, investigating combinatorial therapies targeting immune checkpoints expressed by cancer cells and immune cells will greatly improve immunotherapies that enhance host elimination of tumors.

A comprehensive review of SHP2 and its role in cancer

Src homology 2-containing protein tyrosine phosphatase 2 (SHP2) is a non-receptor protein tyrosine phosphatase ubiquitously expressed mainly in the cytoplasm of several tissues. SHP2 modulates diverse cell signaling events that control metabolism, cell growth, differentiation, cell migration, transcription and oncogenic transformation. It interacts with diverse molecules in the cell, and regulates key signaling events including RAS/ERK, PI3K/AKT, JAK/STAT and PD-1 pathways downstream of several receptor tyrosine kinases (RTKs) upon stimulation by growth factors and cytokines. SHP2 acts as both a phosphatase and a scaffold, and plays prominently oncogenic functions but can be tumor suppressor in a context-dependent manner. It typically acts as a positive regulator of RTKs signaling with some inhibitory functions reported as well. SHP2 expression and activity is regulated by such factors as allosteric autoinhibition, microRNAs, ubiquitination and SUMOylation. Dysregulation of SHP2 expression or activity causes many developmental diseases, and hematological and solid tumors. Moreover, upregulated SHP2 expression or activity also decreases sensitivity of cancer cells to anticancer drugs. SHP2 is now considered as a compelling anticancer drug target and several classes of SHP2 inhibitors with different mode of action are developed with some already in clinical trial phases. Moreover, novel SHP2 substrates and functions are rapidly growing both in cell and cancer. In view of this, we comprehensively and thoroughly reviewed literatures about SHP2 regulatory mechanisms, substrates and binding partners, biological functions, roles in human cancers, and different classes of small molecule inhibitors target this oncoprotein in cancer.

Tumor accomplice: T cell exhaustion induced by chronic inflammation

The development and response to treatment of tumor are modulated by inflammation, and chronic inflammation promotes tumor progression and therapy resistance. This article summarizes the dynamic evolution of inflammation from acute to chronic in the process of tumor development, and its effect on T cells from activation to the promotion of exhaustion. We review the mechanisms by which inflammatory cells and inflammatory cytokines regulate T cell exhaustion and methods for targeting chronic inflammation to improve the efficacy of immunotherapy. It is great significance to refer to the specific state of inflammation and T cells at different stages of tumor development for accurate clinical decision-making of immunotherapy and improving the efficiency of tumor immunotherapy.

The Features of Checkpoint Receptor—Ligand Interaction in Cancer and the Therapeutic Effectiveness of Their Inhibition

To date, certain problems have been identified in cancer immunotherapy using the inhibition of immune checkpoints (ICs). Despite the excellent effect of cancer therapy in some cases when blocking the PD-L1 (programmed death-ligand 1) ligand and the immune cell receptors PD-1 (programmed cell death protein 1) and CTLA4 (cytotoxic T-lymphocyte-associated protein 4) with antibodies, the proportion of patients responding to such therapy is still far from desirable. This situation has stimulated the exploration of additional receptors and ligands as targets for immunotherapy. In our article, based on the analysis of the available data, the TIM-3 (T-cell immunoglobulin and mucin domain-3), LAG-3 (lymphocyte-activation gene 3), TIGIT (T-cell immunoreceptor with Ig and immunoreceptor tyrosine-based inhibitory motif (ITIM) domains), VISTA (V-domain Ig suppressor of T-cell activation), and BTLA (B- and T-lymphocyte attenuator) receptors and their ligands are comprehensively considered. Data on the relationship between receptor expression and the clinical characteristics of tumors are presented and are analyzed together with the results of preclinical and clinical studies on the therapeutic efficacy of their blocking. Such a comprehensive analysis makes it possible to assess the prospects of receptors of this series as targets for anticancer therapy. The expression of the LAG-3 receptor shows the most unambiguous relationship with the clinical characteristics of cancer. Its inhibition is the most effective of the analyzed series in terms of the antitumor response. The expression of TIGIT and BTLA correlates well with clinical characteristics and demonstrates antitumor efficacy in preclinical and clinical studies, which indicates their high promise as targets for anticancer therapy. At the same time, the relationship of VISTA and TIM-3 expression with the clinical characteristics of the tumor is contradictory, and the results on the antitumor effectiveness of their inhibition are inconsistent.

Immune checkpoint modulators in cancer immunotherapy: recent advances and emerging concepts

The discovery of immune checkpoint inhibitors (ICIs) has now been universally acknowledged as a significant breakthrough in tumor therapy after the targeted treatment of checkpoint molecules: anti-programmed cell death protein 1/programmed cell death ligand 1 (PD-1/PD-L1) and anti-cytotoxic T lymphocyte-associated antigen-4 (CTLA-4) on several cancer types achieved satisfying results. However, there are still quite a lot of patients suffering from severe side effects and ineffective treatment outcomes. Although the current ICI therapy is far from satisfying, a series of novel immune checkpoint molecules with remarkable preclinical and clinical benefits are being widely investigated, like the V-domain Ig suppressor of T cell activation (VISTA), which can also be called PD-1 homolog (PD-1H), and ectonucleotidases: CD39, CD73, and CD38, which belong to the ribosyl cyclase family, etc. In this review, we systematically summarized and discussed these molecules' biological structures, molecular features, and the corresponding targeted drugs, aiming to help the in-depth understanding of immune checkpoint molecules and promote the clinical practice of ICI therapy.

Immune checkpoint modulators in cancer immunotherapy: recent advances and emerging concepts

The discovery of immune checkpoint inhibitors (ICIs) has now been universally acknowledged as a significant breakthrough in tumor therapy after the targeted treatment of checkpoint molecules: anti-programmed cell death protein 1/programmed cell death ligand 1 (PD-1/PD-L1) and anti-cytotoxic T lymphocyte-associated antigen-4 (CTLA-4) on several cancer types achieved satisfying results. However, there are still quite a lot of patients suffering from severe side effects and ineffective treatment outcomes. Although the current ICI therapy is far from satisfying, a series of novel immune checkpoint molecules with remarkable preclinical and clinical benefits are being widely investigated, like the V-domain Ig suppressor of T cell activation (VISTA), which can also be called PD-1 homolog (PD-1H), and ectonucleotidases: CD39, CD73, and CD38, which belong to the ribosyl cyclase family, etc. In this review, we systematically summarized and discussed these molecules' biological structures, molecular features, and the corresponding targeted drugs, aiming to help the in-depth understanding of immune checkpoint molecules and promote the clinical practice of ICI therapy.

Targeting SHP2 phosphatase in hematological malignancies

INTRODUCTION

Src homology-2-containing protein tyrosine phosphatase 2 (SHP2) is a ubiquitously expressed, non-receptor protein tyrosine phosphatase encoded by the PTPN11 gene. Gain-of-function (GOF) mutations in PTPN11 are associated with the development of various hematological malignancies and Noonan syndrome with multiple lentigines (NS-ML). Preclinical studies performed with allosteric SHP2 inhibitors and combination treatments of SHP2 inhibitors with inhibitors of downstream regulators (such as MEK, ERK, and PD-1/PD-L1) demonstrate improved antitumor benefits. However, the development of novel SHP2 inhibitors is necessary to improve the therapeutic strategies for hematological malignancies and tackle drug resistance and disease relapse.

AREAS COVERED

This review examines the structure of SHP2, its function in various signaling cascades, the consequences of constitutive activation of SHP2 and potential therapeutic strategies to treat SHP2-driven hematological malignancies.

EXPERT OPINION

While SHP2 inhibitors have exhibited promise in preclinical trials, numerous challenges remain in translation to the clinic, including drug resistance. Although PROTAC-based SHP2 degraders show better efficacy than SHP2 inhibitors, novel strategies need to be designed to improve SHP2-specific therapies in hematologic malignancies. Genome-wide CRISPR screening should also be used to identify molecules that confer resistance to SHP2 inhibitors. Targeting these molecules together with SHP2 can increase the target specificity and reduce drug resistance.

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.

Mechanistic convergence of the TIGIT and PD-1 inhibitory pathways necessitates co-blockade to optimize anti-tumor CD8+ T cell responses

Dual blockade of the PD-1 and TIGIT coinhibitory receptors on T cells shows promising early results in cancer patients. Here, we studied the mechanisms whereby PD-1 and/or TIGIT blockade modulate anti-tumor CD8⁺ T cells. Although PD-1 and TIGIT are thought to regulate different costimulatory receptors (CD28 and CD226), effectiveness of PD-1 or TIGIT inhibition in preclinical tumor models was reduced in the absence of CD226. CD226 expression associated with clinical benefit in patients with non-small cell lung carcinoma (NSCLC) treated with anti-PD-L1 antibody atezolizumab. CD226 and CD28 were co-expressed on NSCLC infiltrating CD8⁺ T cells poised for expansion. Mechanistically, PD-1 inhibited phosphorylation of both CD226 and CD28 via its ITIM-containing intracellular domain (ICD); TIGIT's ICD was dispensable, with TIGIT restricting CD226 co-stimulation by blocking interaction with their common ligand PVR (CD155). Thus, full restoration of CD226 signaling, and optimal anti-tumor CD8⁺ T cell responses, requires blockade of TIGIT and PD-1, providing a mechanistic rationale for combinatorial targeting in the clinic.

Clinical Significance of BTLA and HVEM Expression on Circulating CD4+ T and CD8+ T Cells in Chronic Hepatitis B Virus Infection

In this study, B and T lymphocyte attenuator (BTLA) and herpesvirus entry mediator (HVEM) expression on the surface of circulating CD4⁺ T and CD8⁺ T cells of patients with chronic hepatitis B (CHB) was investigated to explore their relationship with hepatitis B virus (HBV) clinical parameters. Both BTLA and HVEM were significantly upregulated on CD4⁺ T and CD8⁺ T cells of CHB patients compared with healthy controls (p < 0.01). Intriguingly, in CHB patients, the percentage of BTLA expression was positively correlated with that of HVEM (CD4⁺ T cells: r = 0.5461, p < 0.001 and CD8⁺ T cells: r = 0.4206, p < 0.01). Moreover, the percentage of BTLA expression was positively correlated with the levels of aspartate aminotransferase (AST) (CD4⁺ T cells: r = 0.3136, p < 0.05 and CD8⁺ T cells: r = 0.3159, p < 0.05) and alanine aminotransaminase (ALT) (CD4⁺ T cells: r = 0.3177, p < 0.05 and CD8⁺ T cells: r = 0.3311, p < 0.05). At the same time, the percentage of HVEM expression was also positively correlated with AST levels (CD4⁺ T cells: r = 0.3721, p < 0.05 and CD8⁺ T cells: r = 0.3325, p < 0.05) and ALT (CD4⁺ T cells: r = 0.3689, p < 0.05 and CD8⁺ T cells: r = 0.3476, p < 0.05). However, the percentage of BTLA and HVEM expression did not show significant relevance to HBV viral load. Further study demonstrated that BTLA inhibitory signaling could significantly inhibit T cell proliferation, activation, and cytokine production under optimal T cell receptor signaling (p < 0.05). Thereby, our findings indicate that the increased BTLA and HVEM expression on the surface of CD4⁺ and CD8⁺ T cells might represent a certain clinical significance and be involved in CHB progression during T cell exhaustion.

Glioma targeted therapy: insight into future of molecular approaches

Gliomas are the common type of brain tumors originating from glial cells. Epidemiologically, gliomas occur among all ages, more often seen in adults, which males are more susceptible than females. According to the fifth edition of the WHO Classification of Tumors of the Central Nervous System (WHO CNS5), standard of care and prognosis of gliomas can be dramatically different. Generally, circumscribed gliomas are usually benign and recommended to early complete resection, with chemotherapy if necessary. Diffuse gliomas and other high-grade gliomas according to their molecule subtype are slightly intractable, with necessity of chemotherapy. However, for glioblastoma, feasible resection followed by radiotherapy plus temozolomide chemotherapy define the current standard of care. Here, we discuss novel feasible or potential targets for treatment of gliomas, especially IDH-wild type glioblastoma. Classic targets such as the p53 and retinoblastoma (RB) pathway and epidermal growth factor receptor (EGFR) gene alteration have met failure due to complex regulatory network. There is ever-increasing interest in immunotherapy (immune checkpoint molecule, tumor associated macrophage, dendritic cell vaccine, CAR-T), tumor microenvironment, and combination of several efficacious methods. With many targeted therapy options emerging, biomarkers guiding the prescription of a particular targeted therapy are also attractive. More pre-clinical and clinical trials are urgently needed to explore and evaluate the feasibility of targeted therapy with the corresponding biomarkers for effective personalized treatment options.

Immune Checkpoint Gene Expression Profiling Identifies Programmed Cell Death Ligand-1 Centered Immunologic Subtypes of Oral and Squamous Cell Carcinoma With Favorable Survival

Objective

This study aimed to identify the programmed death ligand-1 (PDL1, also termed as CD274) and its positively correlated immune checkpoint genes (ICGs) and to determine the immune subtypes of CD274-centered ICG combinations in oral and squamous cell carcinoma (OSCC).

Materials and Methods

Firstly, the 95 ICGs obtained via literature reviews were identified in the Cancer Genome Atlas (TCGA) database in relation to OSCC, and such 88 ICG expression profiles were extracted. ICGs positively correlated with CD274 were utilized for subsequent analysis. The relationship between ICGs positively correlated with CD274 and immunotherapy biomarkers (tumor mutation burden (TMB), and adaptive immune resistance pathway genes) was investigated, and the relationships of these genes with OSCC clinical features were explored. The prognostic values of CD274 and its positively correlated ICGs and also their associated gene pairs were revealed using the survival analysis.

Results

Eight ICGs, including CTLA4, ICOS, TNFRSF4, CD27, B- and T-lymphocyte attenuator (BTLA), ADORA2A, CD40LG, and CD28, were found to be positively correlated with CD274. Among the eight ICGs, seven ICGs (CTLA4, ICOS, TNFRSF4, CD27, BTLA, CD40LG, and CD28) were significantly negatively correlated with TMB. The majority of the adaptive immune resistance pathway genes were positively correlated with ICGs positively correlated with CD274. The survival analysis utilizing the TCGA-OSCC data showed that, although CD274 was not significantly associated with overall survival (OS), the majority of ICGs positively correlated with CD274 (BTLA, CD27, CTLA4, CD40LG, CD28, ICOS, and TNFRSF4) were significantly correlated with OS, whereby their low-expression predicted a favorable prognosis. The survival analysis based on the gene pair subtypes showed that the combination subtypes of CD274_low/BTLA_low, CD274_low/CD27_low, CD274_low/CTLA4_low, CD8A_high/BTLA_low, CD8A_high/CD27_low, and CD8A_high/CTLA4_low predicted favorable OS.

Conclusion

The results in this study provide a theoretical basis for prognostic immune subtyping of OSCC and highlight the importance of developing future immunotherapeutic strategies for treating oral cancer.

The changes in peripheral blood Th17 and Treg ratios in Hashimoto's thyroiditis are accompanied by differential PD-1/PD-L1 expression

OBJECTIVE

The aim of this study was to analyze the percentages of T helper 17 cells (Th17s) and T regulatory cells (Tregs) in autoimmune Hashimoto's thyroiditis (HT), and the expression of the checkpoint molecules programmed death receptor 1/programmed death ligand 1 (PD-1/PD-L1) on these cells.

METHODS

This is a case-control study involving 53 initially diagnosed HT patients (HT group) and 21 normal controls (NC group). The peripheral blood mononuclear cells from the individuals of the two groups were isolated and restimulated ex vivo; the percentage of Th17s, Tregs, PD-1⁺ Th17s, PD-L1⁺ Th17s, PD-1⁺ Tregs, and PD-L1⁺ Tregs was assessed by flow cytometric analysis.

RESULTS

(1) The percentage of Th17s in the peripheral blood of the HT group was significantly higher than that of the NC group [(6.38 ± 1.32)% versus (3.12 ± 0.66)%; t = 14.110, P < 0.001], while the percentage of peripheral blood Tregs was significantly lower [(3.82 ± 1.48)% versus (5.61 ± 1.60)%; t = -4.599, P < 0.001]. (2) HT patients' Th17s expressed PD-1 at a significantly lower frequency than their counterparts in the NC [(6.46 ± 2.77)% versus (18.51 ± 3.96)%; t = -14.842, P < 0.001], while no difference was observed for PD-L1 between the two groups. (3) In contrast, both PD-1 and PD-L1 were expressed at significantly higher frequency on HT patients' Tregs than on NC [respectively: (17.01 ± 3.04)% versus (10.23 ± 2.77)%; t = 8.850, P < 0.001 for PD-1; (16.60 ± 9.58)% versus (11.36 ± 10.14)%; t = 2.089, P < 0.005, for PD-L1].

CONCLUSION

(1) The increased percentage of Th17s and decreased percentage of PD-1⁺ Th17s in the HT group suggest that a loss of control on Th17 activity through the checkpoint inhibitory axis PD-1/PD-L1 may participate in disease pathogenesis. (2) While the decreased percentage of Tregs in HT patients may explain a lack of regulatory functions able to prevent the autoimmune destruction of the thyroid, the significance of the increased frequency of Tregs expressing PD-1 and PD-L1, previously reported to boost Tregs differentiation, remains to be established. Elucidating this apparent contradiction may reveal important mechanisms underlying HT pathogenesis.

Unleashing T cell responses to cancer through removal of intracellular checkpoints

In a new study, researchers identified protein tyrosine phosphatase PTP1B as an inhibitor of cytokine receptor signalling and demonstrated that blocking activity or expression of this enzyme unleashes T cell responses to cancer.

High BTLA Expression Likely Contributes to Contraction of the Regulatory T Cell Subset in Lupus Disease

B and T lymphocyte attenuator (BTLA) is a co-inhibitory receptor that is expressed by lymphoid cells and regulates the immune response. Consistent with an inhibitory role for BTLA, the disease is exacerbated in BTLA-deficient lupus mice. We recently demonstrated that the BTLA pathway is altered in CD4⁺ T cells from lupus patients. In the present work, we aimed at delineating the expression pattern of BTLA on CD4⁺ T cell subsets suspected to play a key role in lupus pathogenesis, such as circulating follicular helper T cells (cT_FH) and regulatory T cells (Tregs). We did not detect significant ex vivo variations of BTLA expression on total CD4⁺ T cells (naive and memory), cT_FH or T_FH subsets between lupus patients and healthy controls. However, we interestingly observed that BTLA expression is significantly increased on activated Tregs, but not resting Tregs, from lupus patients, especially those displaying an active disease. Moreover, it correlates with the diminution of the Tregs frequency observed in these patients. We also showed that both BTLA mRNA and protein expression remain low after TCR stimulation of activated Tregs sorted from healthy donors and evidenced a similar dynamic of BTLA and HVEM expression profile by human Tregs and effector CD4⁺ T cells upon T cell activation than the one previously described in mice. Finally, we observed that the HVEM/BTLA ratio is significantly lower in Tregs from lupus patients compared to healthy controls, whereas ex vivo effector CD4⁺ T cells express higher BTLA levels. Our data suggest that an altered expression of BTLA and HVEM could be involved in an impaired regulation of autoreactive T cells in lupus. These results provide a better understanding of the BTLA involvement in lupus pathogenesis and confirm that BTLA should be considered as an interesting target for the development of new therapeutic strategies.

Myeloid antigen-presenting cell niches sustain antitumor T cells and license PD-1 blockade via CD28 costimulation

The mechanisms regulating exhaustion of tumor-infiltrating lymphocytes (TIL) and responsiveness to PD-1 blockade remain partly unknown. In human ovarian cancer, we show that tumor-specific CD8+ TIL accumulate in tumor islets, where they engage antigen and upregulate PD-1, which restrains their functions. Intraepithelial PD-1+CD8+ TIL can be, however, polyfunctional. PD-1+ TIL indeed exhibit a continuum of exhaustion states, with variable levels of CD28 costimulation, which is provided by antigen-presenting cells (APC) in intraepithelial tumor myeloid niches. CD28 costimulation is associated with improved effector fitness of exhausted CD8+ TIL and is required for their activation upon PD-1 blockade, which also requires tumor myeloid APC. Exhausted TIL lacking proper CD28 costimulation in situ fail to respond to PD-1 blockade, and their response may be rescued by local CTLA-4 blockade and tumor APC stimulation via CD40L.

The importance of immune checkpoints in immune monitoring: A future paradigm shift in the treatment of cancer

The growth and development of cancer are directly correlated to the suppression of the immune system. A major breakthrough in cancer immunotherapy depends on various mechanisms to detect immunosuppressive factors that inhibit anti-tumor immune responses. Immune checkpoints are expressed on many immune cells such as T-cells, regulatory B cells (Bregs), dendritic cells (DCs), natural killer cells (NKs), regulatory T (Tregs), M2-type macrophages, and myeloid-derived suppressor cells (MDSCs). Immune inhibitory molecules, including CTLA-4, TIM-3, TIGIT, PD-1, and LAG-3, normally inhibit immune responses via negatively regulating immune cell signaling pathways to prevent immune injury. However, the up-regulation of inhibitory immune checkpoints during tumor progression on immune cells suppresses anti-tumor immune responses and promotes immune escape in cancer. It has recently been indicated that cancer cells can up-regulate various pathways of the immune checkpoints. Therefore, targeting immune inhibitory molecules through antibodies or miRNAs is a promising therapeutic strategy and shows favorable results. Immune checkpoint inhibitors (ICIs) are introduced as a new immunotherapy strategy that enhance immune cell-induced antitumor responses in many patients. In this review, we highlighted the function of each immune checkpoint on different immune cells and therapeutic strategies aimed at using monoclonal antibodies and miRNAs against inhibitory receptors. We also discussed current challenges and future strategies for maximizing these FDA-approved immunosuppressants' effectiveness and clinical success in cancer treatment.