Affinity purification mass spectrometry analysis of PD-1 uncovers SAP as a new checkpoint inhibitor

Synergistic blockade of SHP-2 and A2AR signal pathways with targeted nanoparticles restores anti-tumor immunity of CD8+ T cells

Anti-PD-1/PD-L1-based immune checkpoint blockade targeting T cell immunoregulatory proteins has revolutionized cancer treatment. However, only a limited number of patients benefit from this therapy due to the therapeutic resistance and inhibitory pathways other than PD-1 in T cells. Here, we report a new strategy to restore and enhance effector T cell functions through nanoparticle-induced synergistic target of immune checkpoints. SHP099, an allosteric inhibitor for Src-homology domain-containing protein tyrosine phosphatase-2 (SHP2), and CPI-444, a selected inhibitor for adenosine A2AR receptor, were co-encapsulated in a T cell-targeting nanoparticle (SCNP/αCD8). SCNP/αCD8 nanoparticles showed preferable internalization by CD8+ T cells and efficiently blocked SHP2 and A2AR signaling pathways. The simultaneous blockade thus enhanced proliferation, cytokine secretion, cytotoxic function and antitumor activity of CD8+ T cells and significantly inhibited tumor growth in the mouse model. The enhanced anti-tumor immunity in vivo is also ascribed to improved infiltration of effector CD8+ T cells in tumor tissues. These findings suggest that concurrent blockade of A2AR and SHP2 immune checkpoint signaling pathways with small molecule inhibitors offers a promising alternative strategy to enhance T cell functions for enhanced cancer immunotherapy.

Efficacy of neoadjuvant PD-1/PD-L1 inhibitor in resectable NSCLC: a meta-analysis based on randomized controlled trials

BACKGROUND

The efficacy of neoadjuvant immunotherapy in resectable non-small-cell lung cancer (NSCLC) is controversial. The aim of this study is to explore the efficacy of additional PD-1/PD-L1 inhibitors in the neoadjuvant treatment of resctable NSCLC.

METHODS

Data sources included Cochrane Library, Embase, Web of Science, and PubMed from beginning of the database creation to May 2024. The primary outcomes of the study included event-free survival (EFS), overall survival (OS), pathological complete response (pCR), major pathological response (MPR).

RESULTS

Seven RCTs, including 2929 patients, were included in the analysis. The results showed that the experimental group had significantly higher rates of pCR (RR = 5.9, p < 0.001) and MPR (RR = 2.88, p < 0.001) compared to the control group. OS (HR = 0.57) and EFS (HR = 0.58) was also significantly improved in the experimental group. Subgroup analysis of EFS revealed that the benefit was higher in the East (HR = 0.56) than in the West (HR = 0.70). Additionally, the benefit seemed to rise with PD-L1 tumor cell proportion score (TPS) (TPS < 1%, HR = 0.76; 1% < TPS < 49%, HR = 0.56; TPS ≥ 50%, HR = 0.38). The benefit degree seemed to be higher in the III period patients (HR = 0.75) than I-II period patients (HR = 0.52). It is important to emphasize that smokers (HR = 0.54, p < 0.001) benefited from neoadjuvant immunotherapy but nonsmokers (HR = 0.68, p = 0.055) did not.

CONCLUSION

Neoadjuvant PD-1/PD-L1 inhibitor combined with chemotherapy can significantly improve the short-term and long-term prognosis of patients with resectable NSCLC. Moreover, the efficacy of this treatment regimen may be affected by different clinicopathological characteristics of patients.

PD-1 endocytosis unleashes the cytolytic potential of checkpoint blockade in tumor immunity

PD-1 immune checkpoint blockade (ICB) is a key cancer treatment. While blocking PD-1 binding to ligand is known, the role of internalization in enhancing ICB efficacy is less explored. Our study reveals that PD-1 internalization helps unlock ICB's full potential in cancer immunotherapy. Anti-PD-1 induces 50%-60% surface PD-1 internalization from human and mouse cells, leaving low to intermediate levels of resistant receptors. Complexes then appear in early and late endosomes. Both CD4 and CD8 T cells, especially CD8+ effectors, are affected. Nivolumab outperforms pembrolizumab in human T cells, while PD-1 internalization requires crosslinking by bivalent antibody. While mono- and bivalent anti-PD-1 inhibit tumor growth with CD8 tumor-infiltrating cells expressing increased granzyme B, bivalent antibody is more effective where the combination of steric blockade and endocytosis induces greater CD8+ T cell tumor infiltration and the expression of the cytolytic pore protein, perforin. Our findings highlight an ICB mechanism that combines steric blockade and PD-1 endocytosis for optimal checkpoint immunotherapy.

Role of the Crosstalk B:Neoplastic T Follicular Helper Cells in the Pathobiology of Nodal T Follicular Helper Cell Lymphomas

Angioimmunoblastic T-cell lymphoma (AITL), the most common form of peripheral T-cell lymphoma, originates from follicular helper T (Tfh) cells and is notably resistant to current treatments. The disease progression and maintenance, at least in early stages, are driven by a complex interplay between neoplastic Tfh and clusters of B-cells within the tumor microenvironment, mirroring the functional crosstalk observed inside germinal centers. This interaction is further complicated by recurrent mutations, such as TET2 and DNMT3A, which are present in both Tfh cells and B-cells. These findings suggest that the symbiotic relationship between these 2 cell types could represent a therapeutic vulnerability. This review examines the key components and signaling mechanisms involved in the synapses between B-cells and Tfh cells, emphasizing their significant role in the pathobiology of AITL and potential as therapeutic targets.

Changing the location of proteins on the cell surface is a promising strategy for modulating T cell functions

Targeting immune receptors on T cells is a common strategy to treat cancer and autoimmunity. Frequently, this is accomplished through monoclonal antibodies targeting the ligand binding sites of stimulatory or inhibitory co-receptors. Blocking ligand binding prevents downstream signalling and modulates specific T cell functions. Since 1985, the FDA has approved over 100 monoclonal antibodies against immune receptors. This therapeutic approach significantly improved the care of patients with numerous immune-related conditions; however, many patients are unresponsive, and some develop immune-related adverse events. One reason for that is the lack of consideration for the localization of these receptors on the cell surface of the immune cells in the context of the immune synapse. In addition to blocking ligand binding, changing the location of these receptors on the cell surface within the different compartments of the immunological synapse could serve as an alternative, efficient, and safer approach to treating these patients. This review discusses the potential therapeutic advantages of altering proteins' localization within the immune synapse and summarizes published work in this field. It also discusses the novel use of bispecific antibodies to induce the clustering of receptors on the cell surface. It presents the rationale for developing novel antibodies, targeting the organization of signalling receptor complexes on the cell surface. This approach offers an innovative and emerging technology to treat cancer patients resistant to current immunotherapies.

Exclusion of PD-1 from the immune synapse: A novel strategy to modulate T cell function

Targeting immune checkpoint receptors on T cells is a common cancer treatment strategy. Frequently, this is accomplished through antibodies targeting the ligand of inhibitory co-receptors. Blocking the immune checkpoint PD-1 binding to its ligands PD-L1 and PD-L2 prevents downstream signaling and enhances anti-tumor T cell responses. This approach improves cancer patients' outcomes. However, only one-third of the patients respond to these treatments. To better understand the mechanism of anti-PD-1 antibodies, we explored the location of PD-1 within the immune synapse. Surprisingly, we discovered that anti-PD-1 antibodies, besides blocking the interaction between PD-1 and its ligands, also removed PD-1 from the synapse. We demonstrated a correlation between removing PD-1 from the synapse by anti-PD-1 antibodies and the extent of T cell activation. Interestingly, a short version of the anti-PD-1 antibody, F(ab')2, failed to remove PD-1 from the synapse and activate T cells. Using the syngeneic tumor model, we showed a superior anti-tumor effect of the anti-PD-1 antibody over the shorter version of the same antibody. Our data indicate that anti-PD-1 antibodies activate T cells by removing PD-1 from the synapse, and changing the location of PD-1 or other immune receptors within the immune synapse could serve as an alternative, efficient approach to treat cancer.

In vitro T cell responses to PD-1 blockade are reduced by IFN-α but do not predict therapy response in melanoma patients

PD-1 blockade therapy has revolutionized melanoma treatment, but still not all patients benefit and pre-treatment identification of those patients is difficult. Increased expression of inflammatory markers such as interleukin (IL)-6 in blood of patients correlates with poor treatment response. We set out to study the effect of inflammatory cytokines on PD-1 blockade in vitro. For this, we studied the effect of IL-6 and type I interferon (IFN) in vitro on human T cells in a mixed leukocyte reaction (MLR) in the absence or presence of PD-1 blockade. While IL-6 reduced IFN-γ secretion by T cells in both the presence and absence of PD-1 blockade, IFN-α specifically reduced the IFN-γ secretion only in the presence of PD-1 blockade. IFN-α reduced T cell proliferation independent of PD-1 blockade and reduced the percentage of cells producing IFN-γ only in the presence of PD-1 blockade. Next we determined the type I IFN score in a cohort of 22 melanoma patients treated with nivolumab. In this cohort, we did not find a correlation between clinical response and type I IFN score, nor between clinical response and IFN-γ secretion in vitro in a MLR in the presence of PD-1 blockade. We conclude that IFN-α reduces the effectiveness of PD-1 blockade in vitro, but that in this cohort, type I IFN score in vivo, nor IFN-γ secretion in vitro in a MLR in the presence of PD-1 blockade correlated to decreased therapy responses in patients.

PD-L1 blockade in mitigating severe acute pancreatitis induced pancreatic damage through modulation of immune cell apoptosis

Acute pancreatitis (AP) is a prevalent gastrointestinal disorder. The immune response plays a crucial role in AP progression. However, the impact of immune regulatory checkpoint PD-L1 on severe acute pancreatitis (SAP) remains uncertain. Hence, this study aimed to examine the influence of PD-L1 on SAP. We assessed PD-L1 expression in neutrophils and monocytes obtained from SAP patients. We induced SAP in C57BL/6J mice, PD-L1 gene-deficient mice, and PD-L1 humanized mice using intraperitoneal injections of cerulein plus lipopolysaccharide. Prior to the initial cerulein injection, a PD-L1 inhibitor was administered. Pancreatic tissues were collected for morphological and immunohistochemical evaluation, and serum levels of amylase, lipase, and cytokines were measured. Flow cytometry analysis was performed using peripheral blood cells. The expression of PD-L1 in neutrophils and monocytes was significantly higher in SAP patients compared to healthy individuals. Likewise, the expression of PD-L1 in inflammatory cells in the peripheral blood of SAP-induced C57BL/6J mice was notably higher than in the control group. In mice with PD-L1 deficiency, SAP model exhibited lower pancreatic pathology scores, amylase, lipase, and cytokine levels compared to wild-type mice. PD-L1 deletion resulted in reduced neutrophil apoptosis, leading to an earlier peak in neutrophil apoptosis. Furthermore, it decreased early monocyte apoptosis and diminished the peak of T lymphocyte apoptosis. Within the SAP model, administration of a PD-L1 inhibitor reduced pancreatic pathology scores, amylase, lipase, and cytokine levels in both C57BL/6J mice and PD-L1 humanized mice. These findings suggest that inhibiting PD-L1 expression can alleviate the severity of SAP.

Proteomics from compartment-specific APEX2 labeling in Mycobacterium tuberculosis reveals Type VII secretion substrates in the cell wall

The cell wall of mycobacteria plays a key role in interactions with the environment. Its ability to act as a selective filter is crucial to bacterial survival. Proteins in the cell wall enable this function by mediating the import and export of diverse metabolites, from ions to lipids to proteins. Identifying cell wall proteins is an important step in assigning function, especially as many mycobacterial proteins lack functionally characterized homologues. Current methods for protein localization have inherent limitations that reduce accuracy. Here we showed that although chemical labeling of live cells did not exclusively label surface proteins, protein tagging by the engineered peroxidase APEX2 within live Mycobacterium tuberculosis accurately identified the cytosolic and cell wall proteomes. Our data indicate that substrates of the virulence-associated Type VII ESX secretion system are exposed to the periplasm, providing insight into the currently unknown mechanism by which these proteins cross the mycobacterial cell envelope.

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.

Exclusion of PD-1 from the immune synapse: a novel strategy to modulate T cell function

Targeting immune checkpoint receptors on T cells is a common cancer treatment strategy. Frequently, this is accomplished through antibodies targeting the ligand of inhibitory co-receptors. Blocking the immune checkpoint PD-1 binding to its ligands PD-L1 and PD-L2 prevents downstream signaling and enhances anti-tumor T cell responses. This approach improved cancer patients' outcome. However, only one-third of the patients respond to these treatments. To better understand the mechanism of anti-PD-1 antibodies, we explored the location of PD-1 within the immune synapse. Surprisingly, we discovered that anti-PD-1 antibodies, besides blocking the interaction between PD-1 and its ligands, also removed PD-1 from the synapse. We demonstrated a correlation between removing PD-1 from the synapse by anti-PD-1 antibodies and the extent of T cell activation. Interestingly, a short version of the anti-PD-1 antibody, F(ab') 2 , failed to remove PD-1 from the synapse and activate T cells. Using syngeneic tumor model, we showed a superior anti-tumor effect to anti-PD-1 antibody over the shorter version of the antibody. Our data indicates that anti-PD-1 antibodies activate T cells by removing PD-1 away from the synapse and changing the location of PD-1 or other immune receptors within immune synapse could serve as an alternative, efficient approach to treat cancer.

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.

Bispecific antibody targeting TGF-β and PD-L1 for synergistic cancer immunotherapy

The PD-1/PD-L1 signaling pathway plays a crucial role in cancer immune evasion, and the use of anti-PD-1/PD-L1 antibodies represents a significant milestone in cancer immunotherapy. However, the low response rate observed in unselected patients and the development of therapeutic resistance remain major obstacles to their clinical application. Accumulating studies showed that overexpressed TGF-β is another immunosuppressive factor apart from traditional immune checkpoints. Actually, the effects of PD-1 and TGF-β pathways are independent and interactive, which work together contributing to the immune evasion of cancer cell. It has been verified that blocking TGF-β and PD-L1 simultaneously could enhance the efficacy of PD-L1 monoclonal antibody and overcome its treatment resistance. Based on the bispecific antibody or fusion protein technology, multiple bispecific and bifunctional antibodies have been developed. In the preclinical and clinical studies, these updated antibodies exhibited potent anti-tumor activity, superior to anti-PD-1/PD-L1 monotherapies. In the review, we summarized the advances of bispecific antibodies targeting TGF-β and PD-L1 in cancer immunotherapy. We believe these next-generation immune checkpoint inhibitors would substantially alter the cancer treatment paradigm, especially in anti-PD-1/PD-L1-resistant patients.

Experiment-guided molecular simulations define a heterogeneous structural ensemble for the PTPN11 tandem SH2 domains

SHP2 plays an important role in regulating cellular processes, and its pathogenic mutations cause developmental disorders and are linked to cancer. SHP2 is a multidomain protein, comprising two SH2 domains arranged in tandem, a catalytic PTP domain, and a disordered C-terminal tail. SHP2 is activated upon binding two linked phosphopeptides to its SH2 domains, and the peptide orientation and spacing between binding sites are critical for enzymatic activation. For decades, the tandem SH2 has been extensively studied to identify the relative orientation of the two SH2 domains that most effectively binds effectors. So far, neither crystallography nor experiments in solution have provided conclusive results. Using experiment-guided molecular simulations, we determine the heterogeneous structural ensemble of the tandem SH2 in solution in agreement with experimental data from small-angle X-ray scattering and NMR residual dipolar couplings. In the solution ensemble, N-SH2 adopts different orientations and positions relative to C-SH2. We suggest that the intrinsic structural plasticity of the tandem SH2 allows SHP2 to respond to external stimuli and is essential for its functional activity.

SLAM-family receptors come of age as a potential molecular target in cancer immunotherapy

The signaling lymphocytic activation molecule (SLAM) family receptors were discovered in immune cells for the first time. The SLAM-family receptors are a significant player in cytotoxicity, humoral immune responses, autoimmune diseases, lymphocyte development, cell survival, and cell adhesion. There is growing evidence that SLAM-family receptors have been involved in cancer progression and heralded as a novel immune checkpoint on T cells. Previous studies have reported the role of SLAMs in tumor immunity in various cancers, including chronic lymphocytic leukemia, lymphoma, multiple myeloma, acute myeloid leukemia, hepatocellular carcinoma, head and neck squamous cell carcinoma, pancreas, lung, and melanoma. Evidence has deciphered that the SLAM-family receptors may be targeted for cancer immunotherapy. However, our understanding in this regard is not complete. This review will discuss the role of SLAM-family receptors in cancer immunotherapy. It will also provide an update on recent advances in SLAM-based targeted immunotherapies.

Targeting protein phosphatases in cancer immunotherapy and autoimmune disorders

Protein phosphatases act as key regulators of multiple important cellular processes and are attractive therapeutic targets for various diseases. Although extensive effort has been dedicated to phosphatase-targeted drug discovery, early expeditions for competitive phosphatase inhibitors were plagued by druggability issues, leading to the stigmatization of phosphatases as difficult targets. Despite challenges, persistent efforts have led to the identification of several drug-like, non-competitive modulators of some of these enzymes - including SH2 domain-containing protein tyrosine phosphatase 2, protein tyrosine phosphatase 1B, vascular endothelial protein tyrosine phosphatase and protein phosphatase 1 - reigniting interest in therapeutic targeting of phosphatases. Here, we discuss recent progress in phosphatase drug discovery, with emphasis on the development of selective modulators that exhibit biological activity. The roles and regulation of protein phosphatases in immune cells and their potential as powerful targets for immuno-oncology and autoimmunity indications are assessed.

Cell wall proteomics in live Mycobacterium tuberculosis uncovers exposure of ESX substrates to the periplasm

The cell wall of mycobacteria plays a key role in interactions with the environment and its ability to act as a selective filter is crucial to bacterial survival. Proteins in the cell wall enable this function by mediating the import and export of diverse metabolites from ions to lipids to proteins. Accurately identifying cell wall proteins is an important step in assigning function, especially as many mycobacterial proteins lack functionally characterized homologues. Current methods for protein localization have inherent limitations that reduce accuracy. Here we showed that protein tagging by the engineered peroxidase APEX2 within live Mycobacterium tuberculosis enabled the accurate identification of the cytosolic and cell wall proteomes. Our data indicate that substrates of the virulence-associated Type VII ESX secretion system are exposed to the Mtb periplasm, providing insight into the currently unknown mechanism by which these proteins cross the mycobacterial cell envelope.

Current studies and future promises of PD-1 signal inhibitors in cervical cancer therapy

PD-1 (Programmed cell death-1) is a receptor that inhibits the activation of T cells and is an important target for cancer immunotherapy. PD-1 expression stays high on antigen-specific T cells that have been stimulated for a long time, making them less responsive to stimuli. Consequently, there has been a recent surge in the number of researchers focusing on how the PD-1 axis delivers inhibitory signals to uncover new therapeutic targets. As an inhibitory signaling mechanism, the PD-1 axis controls immunological responses. Blocking the PD-1 axis has been shown to have long-lasting effects on various cancers, demonstrating the crucial role of PD-1 in blocking anti-tumor immunity. Despite this role, most patients do not respond to PD-1 monotherapy, and some have experienced adverse events. Many challenges remain regarding the PD-1 signaling axis to be addressed. In this review, we outline the most recent research and prospects of PD-1 signal inhibitors to enhance cervical cancer therapy.

Wiskott-Aldrich syndrome protein interacts and inhibits diacylglycerol kinase alpha promoting IL-2 induction

Background

Phosphorylation of diacylglycerol by diacylglycerol-kinases represents a major inhibitory event constraining T cell activation upon antigen engagement. Efficient TCR signalling requires the inhibition of the alpha isoform of diacylglycerol kinase, DGKα, by an unidentified signalling pathway triggered by the protein adaptor SAP. We previously demonstrated that, in SAP absence, excessive DGKα activity makes the T cells resistant to restimulation-induced cell death (RICD), an apoptotic program counteracting excessive T cell clonal expansion.

Results

Herein, we report that the Wiskott-Aldrich syndrome protein (WASp) inhibits DGKα through a specific interaction of the DGKα recoverin homology domain with the WH1 domain of WASp. Indeed, WASp is necessary and sufficient for DGKα inhibition, and this WASp function is independent of ARP2/3 activity. The adaptor protein NCK-1 and the small G protein CDC42 connect WASp-mediated DGKα inhibition to SAP and the TCR signalosome. In primary human T cells, this new signalling pathway is necessary for a full response in terms of IL-2 production, while minimally affecting TCR signalling and restimulation-induced cell death. Conversely, in T cells made resistant to RICD by SAP silencing, the enhanced DAG signalling due to DGKα inhibition is sufficient to restore apoptosis sensitivity.

Conclusion

We discover a novel signalling pathway where, upon strong TCR activation, the complex between WASp and DGKα blocks DGKα activity, allowing a full cytokine response.

Allosteric inhibition of SHP2 rescues functional T-cell abnormalities in SAP deficiency

BACKGROUND

X-linked lymphoproliferative disease (XLP) is a primary immunodeficiency arising from SH2D1A mutations leading to loss of SLAM-associated protein (SAP). SAP is an intracellular adaptor protein that binds to SLAM family receptors and is expressed in specific lymphoid lineages. In T cells, SAP relays activatory signals from the T-cell receptor but in its absence SH2 containing protein tyrosine phosphase-1 (SHP1), SH2 containing protein tyrosine phosphase-2 (SHP2), and SH2 containing inositol 5'-phosphatase proteins (SHIP) induce T-cell inhibitory signals leading to abnormal T-cell responses. This results in severe clinical manifestations including immune dysregulation, dysgammaglobulinemia, lymphoma, and hemophagocytic lymphohistiocytosis. Current treatment relies on supportive therapies including immunoglobulin replacement and symptom-directed therapy, with hematopoietic stem cell transplant offering the only curative option.

OBJECTIVES

As most XLP symptoms are due to defective T-cell function, this study investigated whether inhibition of SHP2 can restore cellular function in the absence of SAP.

METHODS

Healthy donor and XLP patient T cells were activated with anti-CD3/CD28 in T-cell media supplemented with a SHP2 inhibitor (RMC-4550 in vitro for 24 hours) and functional assays were performed to assess follicular T_H (T_FH) cell function, CD8 cytotoxicity, and sensitivity to restimulation-induced cell death. Additionally, SAP-deficient (SAP^y/-) mice were treated with RMC-4550 before T-cell mediated challenge with 4-hydroxy-3-nitrophenylacetly conjugated chicken gammaglobulin and subsequent assessment of humoral immunity analyzing T_FH cell population, germinal center formation, and antigen-dependent immunoglobulin secretion.

RESULTS

This study shows that the use of RMC-4550 restores T-cell function in XLP patient cells and a SAP^y/- model, demonstrating restoration of T_FH cell function through immunoglobulin and cytokine secretion analysis alongside rescue of cytotoxicity and restimulation-induced cell death.

CONCLUSIONS

These data suggest that SHP2 inhibitors could offer a novel and effective targeted treatment approach for patients with XLP.

The depths of PD-1 function within the tumor microenvironment beyond CD8+ T cells

Programmed cell death-1 (PD-1; CD279) is a cell surface receptor that is expressed in both innate and adaptive immune cells. The role of PD-1 in adaptive immune cells, specifically in CD8+ T cells, has been thoroughly investigated but its significance in other immune cells is yet to be well established. This review will address the role of PD-1 based therapies in enhancing non-CD8+ T cell immune responses within cancer. Specifically, the expression and function of PD-1 in non-CD8+ immune cell compartments such as CD4+ T helper cell subsets, myeloid cells and innate lymphoid cells (ILCs) will be discussed. By understanding the immune cell specific function of PD-1 within tissue resident innate and adaptive immune cells, it will be possible to stratify patients for PD-1 based therapies for both immunogeneic and non-immunogeneic neoplastic disorders. With this knowledge from fundamental and translational studies, PD-1 based therapies can be utilized to enhance T cell independent immune responses in cancers.

Combination Approaches to Target PD-1 Signaling in Cancer

Cancer remains the second leading cause of death in the US, accounting for 25% of all deaths nationwide. Immunotherapy techniques bolster the immune cells' ability to target malignant cancer cells and have brought immense improvements in the field of cancer treatments. One important inhibitory protein in T cells, programmed cell death protein 1 (PD-1), has become an invaluable target for cancer immunotherapy. While anti-PD-1 antibody therapy is extremely successful in some patients, in others it fails or even causes further complications, including cancer hyper-progression and immune-related adverse events. Along with countless translational studies of the PD-1 signaling pathway, there are currently close to 5,000 clinical trials for antibodies against PD-1 and its ligand, PD-L1, around 80% of which investigate combinations with other therapies. Nevertheless, more work is needed to better understand the PD-1 signaling pathway and to facilitate new and improved evidence-based combination strategies. In this work, we consolidate recent discoveries of PD-1 signaling mediators and their therapeutic potential in combination with anti-PD-1/PD-L1 agents. We focus on the phosphatases SHP2 and PTPN2; the kinases ITK, VRK2, GSK-3, and CDK4/6; and the signaling adaptor protein PAG. We discuss their biology both in cancer cells and T cells, with a focus on their role in relation to PD-1 to determine their potential in therapeutic combinations. The literature discussed here was obtained from a search of the published literature and ClinicalTrials.gov with the following key terms: checkpoint inhibition, cancer immunotherapy, PD-1, PD-L1, SHP2, PTPN2, ITK, VRK2, CDK4/6, GSK-3, and PAG. Together, we find that all of these proteins are logical and promising targets for combination therapy, and that with a deeper mechanistic understanding they have potential to improve the response rate and decrease adverse events when thoughtfully used in combination with checkpoint inhibitors.

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.

Quantifying the contribution of transcription factor activity, mutations and microRNAs to CD274 expression in cancer patients

Immune checkpoint inhibitors targeting the programmed cell death protein 1 (PD-1)/programmed cell death protein ligand 1 (PD-L1) axis have been remarkably successful in inducing tumor remissions in several human cancers, yet a substantial number of patients do not respond to treatment. Because this may be partially due to the mechanisms giving rise to high PD-L1 expression within a patient, it is highly relevant to fully understand these mechanisms. In this study, we conduct a bioinformatic analysis to quantify the relative importance of transcription factor (TF) activity, microRNAs (miRNAs) and mutations in determining PD-L1 (CD274) expression at mRNA level based on data from the Cancer Genome Atlas. To predict individual CD274 levels based on TF activity, we developed multiple linear regression models by taking the expression of target genes of the TFs known to directly target PD-L1 as independent variables. This analysis showed that IRF1, STAT1, NFKB and BRD4 are the most important regulators of CD274 expression, explaining its mRNA levels in 90–98% of the patients. Because the remaining patients had high CD274 levels independent of these TFs, we next investigated whether mutations associated with increased CD274 mRNA levels, and low levels of miRNAs associated with negative regulation of CD274 expression could cause high CD274 levels in these patients. We found that mutations or miRNAs offered an explanation for high CD274 levels in 81–100% of the underpredicted patients. Thus, CD274 expression is largely explained by TF activity, and the remaining unexplained cases can largely be explained by mutations or low miRNA abundance.

Cryo-EM structures reveal high-resolution mechanism of a DNA polymerase sliding clamp loader

Sliding clamps are ring-shaped protein complexes that are integral to the DNA replication machinery of all life. Sliding clamps are opened and installed onto DNA by clamp loader AAA+ ATPase complexes. However, how a clamp loader opens and closes the sliding clamp around DNA is still unknown. Here, we describe structures of the Saccharomyces cerevisiae clamp loader Replication Factor C (RFC) bound to its cognate sliding clamp Proliferating Cell Nuclear Antigen (PCNA) en route to successful loading. RFC first binds to PCNA in a dynamic, closed conformation that blocks both ATPase activity and DNA binding. RFC then opens the PCNA ring through a large-scale 'crab-claw' expansion of both RFC and PCNA that explains how RFC prefers initial binding of PCNA over DNA. Next, the open RFC:PCNA complex binds DNA and interrogates the primer-template junction using a surprising base-flipping mechanism. Our structures indicate that initial PCNA opening and subsequent closure around DNA do not require ATP hydrolysis, but are driven by binding energy. ATP hydrolysis, which is necessary for RFC release, is triggered by interactions with both PCNA and DNA, explaining RFC's switch-like ATPase activity. Our work reveals how a AAA+ machine undergoes dramatic conformational changes for achieving binding preference and substrate remodeling.

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

A large number of inhibitory receptors recruit SHP1 and/or SHP2, tandem-SH2-containing phosphatases through phosphotyrosine-based motifs immunoreceptor tyrosine-based inhibitory motif (ITIM) and immunoreceptor tyrosine-based switch motif (ITSM). Despite the similarity, these receptors exhibit differential effector binding specificities, as exemplified by the immune checkpoint receptors PD-1 and BTLA, which preferentially recruit SHP2 and SHP1, respectively. The molecular basis by which structurally similar receptors discriminate SHP1 and SHP2 is unclear. Here, we provide evidence that human PD-1 and BTLA optimally bind to SHP1 and SHP2 via a bivalent, parallel mode that involves both SH2 domains of SHP1 or SHP2. PD-1 mainly uses its ITSM to prefer SHP2 over SHP1 via their C-terminal SH2 domains (cSH2): swapping SHP1-cSH2 with SHP2-cSH2 enabled PD-1:SHP1 association in T cells. In contrast, BTLA primarily utilizes its ITIM to prefer SHP1 over SHP2 via their N-terminal SH2 domains (nSH2). The ITIM of PD-1, however, appeared to be de-emphasized due to a glycine at pY+1 position. Substitution of this glycine with alanine, a residue conserved in BTLA and several SHP1-recruiting receptors, was sufficient to induce PD-1:SHP1 interaction in T cells. Finally, structural simulation and mutagenesis screening showed that SHP1 recruitment activity exhibits a bell-shaped dependence on the molecular volume of the pY+1 residue of ITIM. Collectively, we provide a molecular interpretation of the SHP1/SHP2-binding specificities of PD-1 and BTLA, with implications for the mechanisms of a large family of therapeutically relevant receptors.

PD-1-induced proliferating T cells exhibit a distinct transcriptional signature

Ligation of the inhibitory receptor PD-1 on T cells results in the inhibition of numerous cellular functions. Despite the overtly inhibitory outcome of PD-1 signalling, there are additionally a collection of functions that are activated. We have observed that CD4+ T cells stimulated through the T-cell receptor and PD-1 primarily do not proliferate; however, there is a population of cells that proliferates more than T-cell receptor stimulation alone. These highly proliferating cells could potentially be associated with PD-1-blockade unresponsiveness in patients. In this study, we have performed RNA sequencing and found that following PD-1 ligation proliferating and non-proliferating T cells have distinct transcriptional signatures. Remarkably, the proliferating cells showed an enrichment of genes associated with an activated state despite PD-1 signalling. Additionally, circulating follicular helper T cells were significantly more prevalent in the non-proliferating population, demonstrated by enrichment of the associated genes CXCR5, CCR7, TCF7, BCL6 and PRDM1 and validated at the protein level. Translationally, we also show that there are more follicular helper T cells in patients that respond favourably to PD-1 blockade. Overall, the presence of transcriptionally and functionally distinct T cell populations responsive to PD-1 ligation may provide insights into the clinical differences observed following therapeutic PD-1 blockade.

The PD-1 Interactome

T cell activation is a fine-tuned process that involves T cell receptor and costimulation signals. To prevent undue activation of T cells, inhibitory molecules including PD-1 (programmed death 1) are induced and function as brakes for T cell signaling. In a steady state, the interaction of PD-1 with its ligands PD-L1 (B7-H1, CD274) and PD-L2 (B7-DC, CD273) maintains peripheral immune tolerance. However, the expression of PD-L1 on tumor cells and interaction with PD-1 on T cells dampen anti-tumor immunity. Therapeutic inhibitors of the PD-1 pathway have revolutionized tumor immunotherapy. Unfortunately, the majority of patients do not develop sustained anti-tumor responses. However, the knowledge about unique PD-1 interactions and their role in mediating PD-1 inhibitory signals is currently limited. Advances in the mechanistic understanding of the molecular and signaling integration of the PD-1 pathway could unleash the great potential in tumor immunotherapy by allowing the development of combinatorial approaches that target not only PD-1 and its ligands but also its unique downstream signal mediators. In this review, the current advances in understanding the mechanisms of extracellular and intracellular PD-1 interactions and their significance in potential future therapeutic approaches are discussed.

SHP2 inhibition diminishes KRASG12C cycling and promotes tumor microenvironment remodeling

KRAS is the most frequently mutated human oncogene, and KRAS inhibition has been a longtime goal. Recently, inhibitors were developed that bind KRASG12C-GDP and react with Cys-12 (G12C-Is). Using new affinity reagents to monitor KRASG12C activation and inhibitor engagement, we found that an SHP2 inhibitor (SHP2-I) increases KRAS-GDP occupancy, enhancing G12C-I efficacy. The SHP2-I abrogated RTK feedback signaling and adaptive resistance to G12C-Is in vitro, in xenografts, and in syngeneic KRASG12C-mutant pancreatic ductal adenocarcinoma (PDAC) and non-small cell lung cancer (NSCLC). SHP2-I/G12C-I combination evoked favorable but tumor site-specific changes in the immune microenvironment, decreasing myeloid suppressor cells, increasing CD8+ T cells, and sensitizing tumors to PD-1 blockade. Experiments using cells expressing inhibitor-resistant SHP2 showed that SHP2 inhibition in PDAC cells is required for PDAC regression and remodeling of the immune microenvironment but revealed direct inhibitory effects on tumor angiogenesis and vascularity. Our results demonstrate that SHP2-I/G12C-I combinations confer a substantial survival benefit in PDAC and NSCLC and identify additional potential combination strategies.

SHP2 Targets ITK Downstream of PD-1 to Inhibit T Cell Function

PD-1 is a critical therapeutic target in cancer immunotherapy and antibodies blocking PD-1 are approved for multiple types of malignancies. The phosphatase SHP2 is the main effector mediating PD-1 downstream signaling and accordingly attempts have been made to target this enzyme as an alternative approach to treat immunogenic tumors. Unfortunately, small molecule inhibitors of SHP2 do not work as expected, suggesting that the role of SHP2 in T cells is more complex than initially hypothesized. To better understand the perplexing role of SHP2 in T cells, we performed interactome mapping of SAP, an adapter protein that is associated with SHP2 downstream signaling. Using genetic and pharmacological approaches, we discovered that SHP2 dephosphorylates ITK specifically downstream of PD-1 and that this event was associated with PD-1 inhibitory cellular functions. This study suggests that ITK is a unique target in this pathway, and since ITK is a SHP2-dependent specific mediator of PD-1 signaling, the combination of ITK inhibitors with PD-1 blockade may improve upon PD-1 monotherapy in the treatment of cancer.

In Vitro Assays to Study PD-1 Biology in Human T Cells

Our understanding of programmed cell death 1 (PD-1) biology is limited due to technical difficulties in establishing reproducible, yet simple, in vitro assays to study PD-1 signaling in primary human T cells. The protocols in this article were refined to test the consequences of PD-1 ligation on short-term T cell signaling, long-term T cell function, and the structural consequences of PD-1 ligation with PD-1 ligands. Basic Protocol 1 addresses the need for a robust and reproducible short-term assay to examine the signaling cascade triggered by PD-1. We describe a phospho flow cytometry method to determine how PD-1 ligation alters the level of CD3ζ phosphorylation on Tyr¹⁴² , which can be easily applied to other proximal signaling proteins. Basic Protocol 2 describes a plate-bound assay that is useful to examine the long-term consequences of PD-1 ligation such as cytokine production and T cell proliferation. Complementary to that, Basic Protocol 3 describes an in vitro superantigen-based assay to evaluate T cell responses to therapeutic agents targeting the PD-1/PD-L axis, as well as immune synapse formation in the presence of PD-1 engagement. Finally, in Basic Protocol 4 we outline a tetramer-based method useful to interrogate the quality of PD-1/PD-L interactions. These protocols can be easily adapted for mouse studies and other inhibitory receptors. They provide a valuable resource to investigate PD-1 signaling in T cells and the functional consequences of various PD-1-based therapeutics on T cell responses. © 2020 Wiley Periodicals LLC. Basic Protocol 1: PD-1 crosslinking assay to determine CD3ζ phosphorylation in primary human T cells Basic Protocol 2: Plate-based ligand binding assay to study PD-1 function in human T cells Support Protocol 1: T cell proliferation assay in the presence of PD-1 ligation Basic Protocol 3: In vitro APC/T cell co-culture system to evaluate therapeutic interventions targeting the PD-1/PD-L1 axis Support Protocol 2: Microscopy-based approach to evaluate the consequences of PD-1 ligation on immune synapse formation Basic Protocol 4: Tetramer-based approach to study PD-1/PD-L1 interactions.

Transmembrane adaptor protein PAG is a mediator of PD-1 inhibitory signaling in human T cells

The inhibitory receptor PD-1 is expressed on T cells to inhibit select functions when ligated. The complete signaling mechanism downstream of PD-1 has yet to be uncovered. Here, we discovered phosphoprotein associated with glycosphingolipid-enriched microdomains 1 (PAG) is phosphorylated following PD-1 ligation and associate this with inhibitory T cell function. Clinical cohort analysis correlates low PAG expression with increased survival from numerous tumor types. PAG knockdown in T cells prevents PD-1-mediated inhibition of cytokine secretion, cell adhesion, CD69 expression, and ERK204/187 phosphorylation, and enhances phosphorylation of SRC527 following PD-1 ligation. PAG overexpression rescues these effects. In vivo, PAG contributes greatly to the growth of two murine tumors, MC38 and B16, and limits T cell presence within the tumor. Moreover, PAG deletion sensitizes tumors to PD-1 blockade. Here PAG is established as a critical mediator of PD-1 signaling and as a potential target to enhance T cell activation in tumors.

Diacylglycerol Kinase alpha in X Linked Lymphoproliferative Disease Type 1

Diacylglycerol kinases are intracellular enzymes that control the balance between the secondary messengers diacylglycerol and phosphatidic acid. DGKα and DGKζ are the prominent isoforms that restrain the intensity of T cell receptor signalling by metabolizing PLCγ generated diacylglycerol. Thus, their activity must be tightly controlled to grant cellular homeostasis and refine immune responses. DGKα is specifically inhibited by strong T cell activating signals to allow for full diacylglycerol signalling which mediates T cell response. In X-linked lymphoproliferative disease 1, deficiency of the adaptor protein SAP results in altered T cell receptor signalling, due in part to persistent DGKα activity. This activity constrains diacylglycerol levels, attenuating downstream pathways such as PKCθ and Ras/MAPK and decreasing T cell restimulation induced cell death. This is a form of apoptosis triggered by prolonged T cell activation that is indeed defective in CD8⁺ cells of X-linked lymphoproliferative disease type 1 patients. Accordingly, inhibition or downregulation of DGKα activity restores in vitro a correct diacylglycerol dependent signal transduction, cytokines production and restimulation induced apoptosis. In animal disease models, DGKα inhibitors limit CD8⁺ expansion and immune-mediated tissue damage, suggesting the possibility of using inhibitors of diacylglycerol kinase as a new therapeutic approach.

Phosphotyrosine couples peptide binding and SHP2 activation via a dynamic allosteric network

SHP2 is a ubiquitous protein tyrosine phosphatase, whose activity is regulated by phosphotyrosine (pY)-containing peptides generated in response to extracellular stimuli. Its crystal structure reveals a closed, auto-inhibited conformation in which the N-terminal Src homology 2 (N-SH2) domain occludes the catalytic site of the phosphatase (PTP) domain. High-affinity mono-phosphorylated peptides promote catalytic activity by binding to N-SH2 and disrupting the interaction with the PTP. The mechanism behind this process is not entirely clear, especially because N-SH2 is incapable of accommodating complete peptide binding when SHP2 is in the auto-inhibited state. Here, we show that pY performs an essential role in this process; in addition to its contribution to overall peptide-binding energy, pY-recognition leads to enhanced dynamics of the N-SH2 EF and BG loops via an allosteric communication network, which destabilizes the N-SH2-PTP interaction surface and simultaneously generates a fully accessible binding pocket for the C-terminal half of the phosphopeptide. Subsequently, full binding of the phosphopeptide is associated with the stabilization of activated SHP2. We demonstrate that this allosteric network exists only in N-SH2, which is directly involved in the regulation of SHP2 activity, while the C-terminal SH2 domain (C-SH2) functions primarily to recruit high-affinity bidentate phosphopeptides.

SLAM Associated Protein Signaling in T Cells: Tilting the Balance Toward Autoimmunity

T cell activation is the result of the integration of signals across the T cell receptor and adjacent co-receptors. The signaling lymphocyte activation molecules (SLAM) family are transmembrane co-receptors that modulate antigen driven T cell responses. Signal transduction downstream of the SLAM receptor is mediated by the adaptor protein SLAM Associated Protein (SAP), a small intracellular protein with a single SH2 binding domain that can recruit tyrosine kinases as well as shield phosphorylated sites from dephosphorylation. Balanced SLAM-SAP signaling within T cells is required for healthy immunity, with deficiency or overexpression prompting autoimmune diseases. Better understanding of the molecular pathways involved in the intracellular signaling downstream of SLAM could provide treatment targets for these autoimmune diseases.

Mitochondrial STAT3 regulates antioxidant gene expression through complex I-derived NAD in triple negative breast cancer

Signal transducer and activator of transcription 3 (STAT3) is a transcription factor with roles in inflammation and tumorigenicity. A fraction of STAT3 localizes in mitochondria, where it augments tumorigenesis via regulation of mitochondrial functions, including modulation of respiration and redox status. We show a novel mechanism for mitochondrial STAT3 regulation of redox homeostasis in triple‐negative breast cancer cells. Loss of STAT3 diminished complex I dehydrogenase activity and impaired NAD+ regeneration, leading to impaired expression of glutathione biosynthetic genes and other antioxidant genes. Expressing mitochondrially restricted STAT3 or replenishment of the cellular NAD pool restored antioxidant gene expression, as did complementation of the NADH dehydrogenase activity by expression of the STAT3‐independent yeast dehydrogenase, NDI1. These NAD‐regulated processes contributed to malignant phenotypes by promoting clonal cell growth and migration. Proximity interaction and protein pull‐down assays identified three components of complex I that associated with mitochondrial STAT3, providing a potential mechanistic basis for how mitochondrial STAT3 affects complex I activity. Our data document a novel mechanism through which mitochondrial STAT3 indirectly controls antioxidant gene regulation through a retrograde NAD+ signal that is modulated by complex I dehydrogenase activity.

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

Blockade antibodies of the immunoinhibitory receptor PD-1 can stimulate the anti-tumor activity of T cells, but clinical benefit is limited to a fraction of patients. Evidence suggests that BTLA, a receptor structurally related to PD-1, may contribute to resistance to PD-1 targeted therapy, but how BTLA and PD-1 differ in their mechanisms is debated. Here, we compared the abilities of BTLA and PD-1 to recruit effector molecules and to regulate T cell signaling. While PD-1 selectively recruited SHP2 over the stronger phosphatase SHP1, BTLA preferentially recruited SHP1 to more efficiently suppress T cell signaling. Contrary to the dominant view that PD-1 and BTLA signal exclusively through SHP1/2, we found that in SHP1/2 double-deficient primary T cells, PD-1 and BTLA still potently inhibited cell proliferation and cytokine production, albeit more transiently than in wild type T cells. Thus, PD-1 and BTLA can suppress T cell signaling through a mechanism independent of both SHP1 and SHP2.

VRK2 inhibition synergizes with PD-1 blockade to improve T cell responses

Therapeutic programmed cell death protein 1 (PD-1) blockade enhances T cell mediated anti-tumor immunity but many patients do not respond and a significant proportion develops inflammatory toxicities. To develop better therapeutics and to understand the signaling pathways downstream of PD-1 we performed phosphoproteomic analysis of PD-1 and identified vaccinia related kinase 2 (VRK2) as a key mediator of PD-1 signaling. Using genetic and pharmacological approaches, we discovered that VRK2 is required for PD-1-induced phosphorylation of the protein p21 activated kinase 2 (PAK2), and for the inhibition of IL-2, IL-8, and IFN-γ secretion. Moving into in vivo syngeneic tumor models, pharmacologic inhibition of VRK2 in combination with PD-1 blockade enhanced tumor clearance through T cell activation. This study suggests that VRK2 is a unique therapeutic target and that combination of VRK2 inhibitors with PD-1 blockade may improve cancer immunotherapy.

Checkpoint Molecules in Rheumatology-or the Benefits of Being Exhausted

PURPOSE OF REVIEW

This review will focus on the most common co-inhibitory molecules, emphasizing the importance of these in relation to rheumatic disease.

RECENT FINDINGS

Checkpoint molecules are pivotal in determining the outcome of antigen activation. Checkpoint molecules consist of co-stimulatory and co-inhibitory molecules, where the first activates and the latter inhibits the antigen presentation process. Studies show that increased activity of co-inhibitory molecules is associated with a good prognosis in rheumatic diseases. Opposite, when cancer patients are treated with antibodies blocking the inhibitory pathways, autoimmune diseases, including arthritis, develop as immune-related adverse events (IrAE). This emphasizes the importance of these pathways in autoimmune disease. Co-inhibitory molecules are becoming increasingly interesting as future treatment targets in rheumatic conditions. Treatments with antibodies blocking these pathways result in IrAE, often manifesting as autoimmune rheumatic diseases. Therefore, a need to get acquainted with these molecules is growing so we can cope with future challenges in rheumatic diseases.

Potential role of diacylglycerol kinases in immune-mediated diseases

The mechanism promoting exacerbated immune responses in allergy and autoimmunity as well as those blunting the immune control of cancer cells are of primary interest in medicine. Diacylglycerol kinases (DGKs) are key modulators of signal transduction, which blunt diacylglycerol (DAG) signals and produce phosphatidic acid (PA). By modulating lipid second messengers, DGK modulate the activity of downstream signaling proteins, vesicle trafficking and membrane shape. The biological role of the DGK α and ζ isoforms in immune cells differentiation and effector function was subjected to in deep investigations. DGK α and ζ resulted in negatively regulating synergistic way basal and receptor induced DAG signals in T cells as well as leukocytes. In this way, they contributed to keep under control the immune response but also downmodulate immune response against tumors. Alteration in DGKα activity is also implicated in the pathogenesis of genetic perturbations of the immune function such as the X-linked lymphoproliferative disease 1 and localized juvenile periodontitis. These findings suggested a participation of DGK to the pathogenetic mechanisms underlying several immune-mediated diseases and prompted several researches aiming to target DGK with pharmacologic and molecular strategies. Those findings are discussed inhere together with experimental applications in tumors as well as in other immune-mediated diseases such as asthma.

Identification of Radil as a Ras binding partner and putative activator

Ras genes are among the most frequently mutated oncogenes in human malignancies. To date, there are no successful anticancer drugs in the clinic that target Ras proteins or their pathways. Therefore, it is imperative to identify and characterize new components that regulate Ras activity or mediate its downstream signaling. To this end, we used a combination of affinity-pulldown and mass spectrometry to search for proteins that are physically associated with KRas. One of the top hits was Radil, a gene product with a Ras-association domain. Radil is known to be a downstream effector of Rap1, inhibiting RhoA signaling to regulate cell adhesion and migration. We demonstrate that Radil interacted with all three isoforms of Ras including HRas, NRas, and KRas, although it exhibited the strongest interaction with KRas. Moreover, Radil interacts with GTP-bound Ras more efficiently, suggesting a possibility that Radil may be involved in Ras activation. Supporting this, ectopic expression of Radil led to transient activation of mitogen-activated protein kinase kinase and extracellular signal-regulated kinase; Radil knockdown resulted in weakened activation of Ras downstream signaling components, which was coupled with decreased cell proliferation and invasion, and reduced expression of mesenchymal cell markers. Moreover, Radil knockdown greatly reduced the number of adhesion foci and depolymerized actin filaments, molecular processes that facilitate cancer cell migration. Taken together, our present studies strongly suggest that Radil is an important player for regulating Ras signaling, cell adhesion, and the epithelial–mesenchymal transition and may provide new directions for Ras-related anticancer drug development.

Allosteric SHP2 inhibitors in cancer: Targeting the intersection of RAS, resistance, and the immune microenvironment

The nonreceptor protein tyrosine phosphatase SHP2 (encoded by PTPN11) integrates growth and differentiation signals from receptor tyrosine kinases (RTKs) into the RAS/mitogen-activated protein kinase (MAPK) cascade. Considered 'undruggable' over three decades, SHP2 is now a potentially druggable target with the advent of allosteric SHP2 inhibitors. These agents hold promise for improving patient outcomes, showing efficacy in preclinical cancer models, where SHP2 is critical for either oncogenic signaling or resistance to current targeted agents. SHP2 inhibition may also produce immunomodulatory effects in certain tumor microenvironment cells to help cultivate antitumor immune responses. The first generation of allosteric SHP2 inhibitors is under clinical evaluation to determine safety, appropriate tolerability management, and antitumor efficacy, investigations that will dictate future clinical applications.

Immunoaffinity microflow liquid chromatography/tandem mass spectrometry for the quantitation of PD1 and PD-L1 in human tumor tissues

RATIONALE

High tumor expression of programmed cell death protein (PD1) and programmed death-ligand 1 (PD-L1) is thought to be associated with positive clinical outcomes after treatment with anti-PD1 or anti-PD-L1 agents. Several sensitive methods based on immunohistochemistry, ligand binding assay (LBA), and liquid chromatography/mass spectrometry involving the measurement of PD1 and PD-L1 expression have been reported. Here, we expand on the characterization of different tumor types using a highly specific, sensitive, and robust immunoaffinity liquid chromatography/tandem mass spectrometry (IA-LC/MS/MS)-based method for the simultaneous quantitation of PD1 and PD-L1 in tumor tissues.

METHODS

Human tumor tissue samples were homogenized using a Precellys Evolution homogenizer. The samples were incubated with anti-PD1 and anti-PD-L1 capture polyclonal antibodies, which were bound to magnetic beads. Following enrichment, samples were digested with trypsin. A Waters iKEY HSS T3 1.8 um (150 μm × 100 mm) column with a gradient flow rate of 3 μL/min was used for chromatographic separation, and a Waters TQ-S triple quadrupole mass spectrometer was used for detection. Selected reaction monitoring (SRM) transitions with unit resolution for precursor/product ion masses were optimized for PD1 and PD-L1 surrogate peptides.

RESULTS

The surrogate peptides LAAFPEDR for PD1 and FTVTVPK for PD-L1 yielded the most intense SRM transitions at m/z 459.7 > 516.2 and m/z 396.2 > 543.3, respectively, and thus were selected for the quantitation of PD1 and PD-L1. The lower limit of quantitation for PD1 and PD-L1 was 0.062 ng/mL with an assay range up to 10 ng/mL. Using this method, human PD1 and PD-L1 were detected and quantified from four different types of tumor tissues. The data show that PD1 expression level was highly correlated with that of PD-L1 in all tumor tissues analyzed here.

CONCLUSIONS

A highly specific and sensitive immunoaffinity microflow LC/MS/MS method for the simultaneous quantification of PD1 and PD-L1 in tumor tissues was developed and implemented. This method combines the advantage of immuno-capture for analyte enrichment with the high specificity of detection of multiple surrogate peptides by LC/MS/MS. The quantification of PD1 and PD-L1 co-expression in tumor could help evaluate their role in assessing tumor type selection and patient stratification.

Immune checkpoint molecules in natural killer cells as potential targets for cancer immunotherapy

Recent studies have demonstrated the potential of natural killer (NK) cells in immunotherapy to treat multiple types of cancer. NK cells are innate lymphoid cells that play essential roles in tumor surveillance and control that efficiently kill the tumor and do not require the major histocompatibility complex. The discovery of the NK's potential as a promising therapeutic target for cancer is a relief to oncologists as they face the challenge of increased chemo-resistant cancers. NK cells show great potential against solid and hematologic tumors and have progressively shown promise as a therapeutic target for cancer immunotherapy. The effector role of these cells is reliant on the balance of inhibitory and activating signals. Understanding the role of various immune checkpoint molecules in the exhaustion and impairment of NK cells when their inhibitory receptors are excessively expressed is particularly important in cancer immunotherapy studies and clinical implementation. Emerging immune checkpoint receptors and molecules have been found to mediate NK cell dysfunction in the tumor microenvironment; this has brought up the need to explore further additional NK cell-related immune checkpoints that may be exploited to enhance the immune response to refractory cancers. Accordingly, this review will focus on the recent findings concerning the roles of immune checkpoint molecules and receptors in the regulation of NK cell function, as well as their potential application in tumor immunotherapy.

The Extrinsic and Intrinsic Roles of PD-L1 and Its Receptor PD-1: Implications for Immunotherapy Treatment

Programmed death-ligand 1 (PD-L1) is an immune checkpoint inhibitor that binds to its receptor PD-1 expressed by T cells and other immune cells to regulate immune responses; ultimately preventing exacerbated activation and autoimmunity. Many tumors exploit this mechanism by overexpressing PD-L1 which often correlates with poor prognosis. Some tumors have also recently been shown to express PD-1. On tumors, PD-L1 binding to PD-1 on immune cells promotes immune evasion and tumor progression, primarily by inhibition of cytotoxic T lymphocyte effector function. PD-1/PD-L1-targeted therapy has revolutionized the cancer therapy landscape and has become the first-line treatment for some cancers, due to their ability to promote durable anti-tumor immune responses in select patients with advanced cancers. Despite this clinical success, some patients have shown to be unresponsive, hyperprogressive or develop resistance to PD-1/PD-L1-targeted therapy. The exact mechanisms for this are still unclear. This review will discuss the current status of PD-1/PD-L1-targeted therapy, oncogenic expression of PD-L1, the new and emerging tumor-intrinisic roles of PD-L1 and its receptor PD-1 and how they may contribute to tumor progression and immunotherapy responses as shown in different oncology models.

1H, 13C, 15N chemical shift assignments of SHP2 SH2 domains in complex with PD-1 immune-tyrosine motifs

Inhibition of immune checkpoint receptor Programmed Death-1 (PD-1) via monoclonal antibodies is an established anticancer immunotherapeutic approach. This treatment has been largely successful; however, its high cost demands equally effective, more affordable alternatives. To date, the development of drugs targeting downstream players in the PD-1-dependent signaling pathway has been hampered by our poor understanding of the molecular details of the intermolecular interactions involved in the pathway. Activation of PD-1 leads to phosphorylation of two signaling motifs located in its cytoplasmic domain, the immune tyrosine inhibitory motif (ITIM) and immune tyrosine switch motif (ITSM), which recruit and activate protein tyrosine phosphatase SHP2. This interaction is mediated by the two Src homology 2 (SH2) domains of SHP2, termed N-SH2 and C-SH2, which recognize phosphotyrosines pY223 and pY248 of ITIM and ITSM, respectively. SHP2 then propagates the inhibitory signal, ultimately leading to suppression of T cell functionality. In order to facilitate mechanistic structural studies of this signaling pathway, we report the resonance assignments of the complexes formed by the signaling motifs of PD-1 and the SH2 domains of SHP2.

Structure of the human clamp loader reveals an autoinhibited conformation of a substrate-bound AAA+ switch

DNA replication requires the sliding clamp, a ring-shaped protein complex that encircles DNA, where it acts as an essential cofactor for DNA polymerases and other proteins. The sliding clamp needs to be opened and installed onto DNA by a clamp loader ATPase of the AAA+ family. The human clamp loader replication factor C (RFC) and sliding clamp proliferating cell nuclear antigen (PCNA) are both essential and play critical roles in several diseases. Despite decades of study, no structure of human RFC has been resolved. Here, we report the structure of human RFC bound to PCNA by cryogenic electron microscopy to an overall resolution of ∼3.4 Å. The active sites of RFC are fully bound to adenosine 5'-triphosphate (ATP) analogs, which is expected to induce opening of the sliding clamp. However, we observe the complex in a conformation before PCNA opening, with the clamp loader ATPase modules forming an overtwisted spiral that is incapable of binding DNA or hydrolyzing ATP. The autoinhibited conformation observed here has many similarities to a previous yeast RFC:PCNA crystal structure, suggesting that eukaryotic clamp loaders adopt a similar autoinhibited state early on in clamp loading. Our results point to a "limited change/induced fit" mechanism in which the clamp first opens, followed by DNA binding, inducing opening of the loader to release autoinhibition. The proposed change from an overtwisted to an active conformation reveals an additional regulatory mechanism for AAA+ ATPases. Finally, our structural analysis of disease mutations leads to a mechanistic explanation for the role of RFC in human health.

Revisiting the PD-1 pathway

Programmed Death-1 (PD-1; CD279) is an inhibitory receptor induced in activated T cells. PD-1 engagement by its ligands, PD-L1 and PD-L2, maintains peripheral tolerance but also compromises anti-tumor immunity. Blocking antibodies against PD-1 or its ligands have revolutionized cancer immunotherapy. However, only a fraction of patients develop durable antitumor responses. Clinical outcomes have reached a plateau without substantial advances by combinatorial approaches. Thus, great interest has recently emerged to investigate, in depth, the mechanisms by which the PD-1 pathway transmits inhibitory signals with the goal to identify molecular targets for improvement of the therapeutic success. These efforts have revealed unpredictable dimensions of the pathway and uncovered novel mechanisms involved in PD-1 and PD-L1 regulation and function. Here, we provide an overview of the recent advances on the mechanistic aspects of the PD-1 pathway and discuss the implications of these new discoveries and the gaps that remain to be filled.