Inducible costimulator facilitates T-dependent B cell activation by augmenting IL-4 translation

Helios characterized circulating follicular helper T cells with enhanced functional phenotypes and was increased in patients with systemic lupus erythematosus

Helios was related to the immunosuppressive capacity and stability of regulatory T cells. However, the significance of Helios in follicular help T (TFH) and follicular regulatory T (TFR) cells is unclear. This research aimed to clarify the significance of Helios (IKZF2) in TFH and TFR cells and its clinical value in systemic lupus erythematosus (SLE). IKZF2 mRNA in different cell subsets was analyzed. Helios+ percentages in TFH and TFR cells were identified in the peripheral blood of 75 SLE patients and 62 HCs (healthy controls). PD-1 and ICOS expression were compared between Helios+ and Helios- cells. The capacity of TFH cells to secrete IL-21 and TFR cells to secrete IL-10 was measured. Correlation analysis and receiver operating characteristic (ROC) curve analysis were conducted to assess the clinical significance of Helios-related TFH and TFR cell subsets in SLE. There was Helios expression in TFH and TFR cells. PD-1 and ICOS were lower in Helios+ TFR than in Helios- TFR. ICOS was increased in Helios+ TFH cells compared with Helios- TFH cells, and ICOS in Helios+ TFH cells was downregulated in SLE. Helios+ TFH cells secreted more IL-21 than Helios- TFH cells, and Helios+ TFH cells from SLE patients had a stronger IL-21 secretion than HCs. Helios+ TFH percentages were negatively correlated with C3 and C4 and positively related to CRP and SLEDAI, and the AUC of Helios+ TFH to distinguish SLE from HC was 0.7959. Helios characterizes circulating TFH cells with enhanced function. Increased Helios+ TFH cells could reflect the autoimmune status of SLE.

Altered Phenotypes of Colonic and Peripheral Blood Follicular Helper and Follicular Cytotoxic T Cells in Mice with DSS-Induced Colitis

Background

Follicular helper T (Tfh), follicular regulatory T (Tfr), and follicular cytotoxic T (Tfc) cells play important roles in autoimmune diseases. Nevertheless, their changes of functional phenotypes in ulcerative colitis (UC), most importantly, their changes in colon tissue as the target-organ, have not been explored.

Methods

DSS-colitis was induced in Balb/c mice and lymphocytes were collected from spleen, mesenteric lymph nodes, peripheral blood and colon. Tfh, Tfr, and Tfc cells were analyzed using flow cytometry based on their CD4+CXCR5+FOXP3-Tfh, CD4+CXCR5+FOXP3+Tfr and CD8+CXCR5+Tfc expressions. Various functional characterization markers including CD44, CD62L, TIGIT, CD226, PD-1, ICOS, Helios, CTLA-4 and Bcl6 were analyzed in the T cell subsets of the organs.

Results

Tfh and Tfr cells in the colon were significantly increased in DSS-colitis mice. Additionally, the proportions of Tfr and Tfc cells in the peripheral blood were also increased, while Tfc cell proportions in the colon were decreased. The proportion of naïve cells in the Tfh, Tfr and Tfc cells in the colon and peripheral blood decreased, while the proportion of effector memory T cells increased. The TIGIT+CD226-Tfh and Tfc cells were upregulated in the colon of DSS-colitis mice. The PD-1+, ICOS+ and PD-1+ICOS+ Tfh cells were increased in both the colonic and peripheral blood Tfh and Tfc of DSS-colitis mice. The Bcl6+ proportions in the Tfh and Tfr were increased in the colon of DSS-colitis mice.

Conclusion

The colonic and peripheral blood Tfh and Tfc cells of DSS-colitis mice have a significantly activated T cell phenotype, which may play a significant role in the pathogenesis of UC.

The role of eIF4F-driven mRNA translation in regulating the tumour microenvironment

Cells can rapidly adjust their proteomes in dynamic environments by regulating mRNA translation. There is mounting evidence that dysregulation of mRNA translation supports the survival and adaptation of cancer cells, which has stimulated clinical interest in targeting elements of the translation machinery and, in particular, components of the eukaryotic initiation factor 4F (eIF4F) complex such as eIF4E. However, the effect of targeting mRNA translation on infiltrating immune cells and stromal cells in the tumour microenvironment (TME) has, until recently, remained unexplored. In this Perspective article, we discuss how eIF4F-sensitive mRNA translation controls the phenotypes of key non-transformed cells in the TME, with an emphasis on the underlying therapeutic implications of targeting eIF4F in cancer. As eIF4F-targeting agents are in clinical trials, we propose that a broader understanding of their effect on gene expression in the TME will reveal unappreciated therapeutic vulnerabilities that could be used to improve the efficacy of existing cancer therapies.

Metabolic modulation of immune checkpoints and novel therapeutic strategies in cancer

Cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4) or programmed death-1 (PD-1)/programmed death-ligand 1 (PD-L1)-based immune checkpoint inhibitors (ICIs) have led to significant improvements in the overall survival of patients with certain cancers and are expected to benefit patients by achieving complete, long-lasting remissions and cure. However, some patients who receive ICIs either fail treatment or eventually develop immunotherapy resistance. The existence of such patients necessitates a deeper understanding of cancer progression, specifically nutrient regulation in the tumor microenvironment (TME), which includes both metabolic cross-talk between metabolites and tumor cells, and intracellular metabolism in immune and cancer cells. Here we review the features and behaviors of the TME and discuss the recently identified major immune checkpoints. We comprehensively and systematically summarize the metabolic modulation of tumor immunity and immune checkpoints in the TME, including glycolysis, amino acid metabolism, lipid metabolism, and other metabolic pathways, and further discuss the potential metabolism-based therapeutic strategies tested in preclinical and clinical settings. These findings will help to determine the existence of a link or crosstalk between tumor metabolism and immunotherapy, which will provide an important insight into cancer treatment and cancer research.

Inflammatory Cytokine-Neutralizing Antibody Treatment Prevented Increases in Follicular Helper T Cells and Follicular Regulatory T Cells in a Mouse Model of Arthritis

Background

Follicular T helper (TFH) and follicular regulatory T (TFR) cells play important roles in humoral immunity. Nevertheless, their significance in rheumatoid arthritis (RA) pathogenesis has not been fully elucidated. As an important treatment strategy, the effect of inflammatory factor-neutralizing antibodies on TFH and TFR in RA remains unclear.

Methods

We used the collagen-induced arthritis (CIA) mouse model to illustrate the quantity and functional changes in TFH and TFR cells. The changes of plasmablast, TFH and TFR cells in the spleen and peripheral blood of CIA mice were analyzed by flow cytometry. The levels of TFH and TFR and their functional subsets in the spleen after anti-inflammatory antibody treatment were analyzed and compared. The functional changes of TFH and TFR in CIA mice before and after treatment were detected by in vitro culture experiments.

Results

Plasmablast levels were increased in CIA spleen and peripheral blood and both TFH and TFR cell levels were upregulated. TFH and TFR cells were decreased significantly after the anti-inflammatory antibody treatment. TIGIT⁺ and TIGIT⁺CD226⁻ TFH cells in CIA mouse spleen were elevated and PD-1 and ICOS expression on spleen TFH and TFR cells was increased. Both the ability of TFH cells to secrete IL-21 and aid B cells and the ability of TFR cells to secrete IL-10 and inhibit TFH cells were enhanced in the CIA mice. After antibody treatment, the cell subsets and functions were recovered.

Conclusion

Germinal center TFH and TFR cells were increased and their functions were enhanced. With inflammatory factor-neutralizing antibody treatment, TFH and TFR subsets and their functions returned to normal. These findings provide important information on the dynamics of humoral immune-related cell subsets in RA and the effects of treatment on them.

Sirolimus therapy restores the PD-1+ICOS+Tfh:CD45RA-Foxp3high activated Tfr cell balance in primary Sjögren's syndrome

BACKGROUND

Primary Sjögren's syndrome (pSS) is a common chronic autoimmune disease characterized by lymphocytic infiltration of salivary and lacrimal glands. The current study was performed to investigate the roles of follicular helper T (Tfh) and follicular regulatory T (Tfr) subsets in patients with pSS, and to evaluate the effects of sirolimus on these cells.

METHODS

Levels of circulating Tfh and Tfr subsets in 58 pSS patients and 26 healthy controls (HC) were determined by flow cytometry. These T cell subsets were also analyzed in 12 patients before and after treatment with sirolimus. Clinical features and correlations with follicular T cells were analyzed systematically. The discriminative ability of the cells and ratios was evaluated based on the area under the receiver operating characteristic curves.

RESULTS

Patients with pSS had higher percentage and absolute number of PD-1+ICOS+Tfh cells, while lower percentage and absolute number of Tfr, activated regulatory T (aTreg) cells, and CD45RA-Foxp3^high activated Tfr cells. Furthermore, increased number of PD-1+ICOS+Tfh cells was associated with B cells, while decreased numbers of Tfr and their subsets was strongly associated with aTreg cells in pSS patients. Also, the higher proportion of PD-1+ICOS+Tfh cells was positively correlated with higher level of autoantibodies, ESR, IgG, cytokines (IL-2, IL-4, IL-10, IL-17, IFN-γ, TNF-α, IL-21 and sIL-2αR), and disease activity. Unexpectedly, the elevated PD-1+ICOS+Tfh:CD45RA-Foxp3^high activated Tfr ratio had the greatest ability to discriminate between pSS and HC, and sirolimus therapy restored the PD-1+ICOS+Tfh cells:CD45RA-Foxp3^high activated Tfr ratio, and controlled disease activity.

CONCLUSION

The novel ratio of PD-1+ICOS+Tfh to CD45RA-Foxp3^high activated Tfr cells can effectively discriminate the pSS patients from controls, and Tfr cell subsets may resemble Treg cell lineages. Furthermore, the PD-1+ICOS+Tfh cells can be used as a biomarker of disease activity and to verify the therapeutic effects of sirolimus in pSS.

Follicular Helper CD4+ T Cells, Follicular Regulatory CD4+ T Cells, and Inducible Costimulator and Their Roles in Multiple Sclerosis and Experimental Autoimmune Encephalomyelitis

Follicular helper CD4+ T (TFH) cells are a specialized subset of effector T cells that play a central role in orchestrating adaptive immunity. TFH cells mainly promote germinal center (GC) formation, provide help to B cells for immunoglobulin affinity maturation and class-switch recombination of B cells, and facilitate production of long-lived plasma cells and memory B cells. TFH cells express the nuclear transcriptional repressor B cell lymphoma 6 (Bcl-6), the chemokine (C-X-C motif) receptor 5 (CXCR5), the CD28 family members programmed cell death protein-1 (PD-1) and inducible costimulator (ICOS) and are also responsible for the secretion of interleukin-21 (IL-21) and IL-4. Follicular regulatory CD4+ T (TFR) cells, as a regulatory counterpart of TFH cells, participate in the regulation of GC reactions. TFR cells not only express markers of TFH cells but also express markers of regulatory T (Treg) cells containing FOXP3, glucocorticoid-induced tumor necrosis factor receptor (GITR), cytotoxic T lymphocyte antigen 4 (CTLA-4), and IL-10, hence owing to the dual characteristic of TFH cells and Treg cells. ICOS, expressed on activated CD4+ effector T cells, participates in T cell activation, differentiation, and effector process. The expression of ICOS is highest on TFH and TFR cells, indicating it as a key regulator of humoral immunity. Multiple sclerosis (MS) is a severe autoimmune disease that affects the central nervous system and results in disability, mediated by autoreactive T cells with evolving evidence of a remarkable contribution from humoral responses. This review summarizes recent advances regarding TFH cells, TFR cells, and ICOS, as well as their functional characteristics in relation to MS.

Increased circulating PD-1hiCXCR5- peripheral helper T cells are associated with disease severity of active ulcerative colitis patients

PURPOSE

A recently identified population of T cells, phenotypically CD4⁺PD-1^hiCXCR5^-, has been firstly termed as peripheral helper T cells (Tph) and found to be pathogenic in autoimmune diseases. However, the potential role of Tph in ulcerative colitis (UC) remains unclear. We aim to investigate the changes of circulating Tph in UC patients and their potential significance in the pathogenesis of UC.

METHODS

Totally 68 UC patients and 34 age- and sex-matched healthy controls were enrolled. Circulating Tph and B cell subsets were analyzed by flow cytometry. Expressions of inducible T-cell co-stimulator (ICOS) on Tph cells were analyzed. Serum IL-4, IL-10, IL-12 and IL-21 were detected using ELISA. Correlation analyses were conducted between Tph cells and disease severity, functional B cell subsets and serum cytokines.

RESULTS

Both the frequency and absolute number of Tph were significantly increased in active UC patients and ICOS levels in Tph cells were also elevated, compared with remission UC patients and healthy controls. Tph and ICOS expression were significantly positively correlated with Mayo score and serum CRP in active UC patients, and were significantly decreased when achieving remission after treatment. Tph levels were correlated with new memory B cells, plasmablasts, serum IL-4 and IL-21. Meanwhile, serum IL-10 showed negative correlation while IL-12 exhibited positive correlation with circulating Tph cells in UC patients.

CONCLUSIONS

Circulating Tph cells are elevated in active UC patients and are associated with the disease activity, which may contribute to the pathogenesis of UC.

Resisting Resistance to Immune Checkpoint Therapy: A Systematic Review

The treatment landscape in oncology has witnessed a major revolution with the introduction of checkpoint inhibitors: anti-PD1, anti-PDL1 and anti-CTLA-4. These agents enhance the immune response towards cancer cells instead of targeting the tumor itself, contrary to standard chemotherapy. Although long-lasting durable responses have been observed with immune checkpoints inhibitors, the response rate remains relatively low in many cases. Some patients respond in the beginning but then eventually develop acquired resistance to treatment and progress. Other patients having primary resistance never respond. Multiple studies have been conducted to further elucidate these variations in response in different tumor types and different individuals. This paper provides an overview of the mechanisms of resistance to immune checkpoint inhibitors and highlights the possible therapeutic approaches under investigation aiming to overcome such resistance in order to improve the clinical outcomes of cancer patients.

Controlling TIME: How MNK Kinases Function to Shape Tumor Immunity

A number of studies have clearly established the oncogenic role for MAPK-interacting protein kinases (MNK) in human malignancies. Modulation of MNK activity affects translation of mRNAs involved in cancer development, progression, and resistance to therapies. As a result, there are ongoing efforts to develop and evaluate MNK inhibitors for cancer treatment. However, it is important to recognize that MNK activity also plays an important role in regulating the innate and adaptive immune systems. A better understanding of the role of MNK kinases and MNK-mediated signals in regulating the immune system could help mitigate undesired side effects while maximizing therapeutic efficacy of MNK inhibitors. Here, we provide a systematic review on the function of MNK kinases and their substrates in immune cells.

Activated inducible co-stimulator-positive programmed cell death 1-positive follicular helper T cells indicate disease activity and severity in ulcerative colitis patients

Inducible co-stimulator-positive (ICOS) and programmed cell death 1-positive (PD-1) are important markers for follicular helper T cells (Tfh); however, their roles and clinical values in ulcerative colitis (UC) remain unknown. In this study, we recruited 68 UC patients and 34 healthy controls. Circulating ICOS⁺ , PD-1⁺ and ICOS⁺ PD-1⁺ Tfh subsets were analyzed by flow cytometry. Twelve active UC patients achieving remission after treatment with 5-aminosalicylic acid were followed-up and Tfh subset changes were analyzed. Serum immunoglobulin (Ig)G, C-reactive protein (CRP), interleukin (IL)-4 and IL-21 levels and B cell subsets were analyzed and Mayo scores were calculated. Correlation analyses were performed between Tfh subsets and the clinical indicators. Receiver operating characteristic (ROC) curves were generated to evaluate the efficiency of Tfh subsets for disease monitoring. We found that levels of ICOS⁺ , PD-1⁺ and ICOS⁺ PD-1⁺ Tfh cells were significantly increased in active UC and significantly decreased when achieving clinical remission. Activated ICOS⁺ PD-1⁺ Tfh cells were positively correlated with serum CRP and Mayo scores. Furthermore, ICOS⁺ PD-1⁺ Tfh cells were significantly correlated with circulating new memory B cells and plasmablasts, as well as serum IgG, IL-4 and IL-21. ROC analyses showed that when ICOS⁺ PD-1⁺ Tfh cells were used in combination with PD-1⁺ Tfh cells, the diagnostic efficacy in distinguishing active UC from stable remission patients was higher than that of any one used alone, with area under curve (AUC) value 0·931. Our findings suggest that increased ICOS⁺ PD-1⁺ Tfh cells are associated with the activation of B cells in the pathogenesis of UC, and may be a potential biomarker for UC disease monitoring.

Active Tonic mTORC1 Signals Shape Baseline Translation in Naive T Cells

Naive CD4⁺ T cells are an example of dynamic cell homeostasis: T cells need to avoid autoreactivity while constantly seeing self-peptides, yet they must be primed to react to foreign antigens during infection. The instructive signals that balance this primed yet quiescent state are unknown. Interactions with self-peptides result in membrane-proximal, tonic signals in resting T cells. Here we reveal selective and robust tonic mTORC1 signals in CD4⁺ T cells that influence T cell fate decisions. We find that the Ras exchange factor Rasgrp1 is necessary to generate tonic mTORC1 signals. Genome-wide ribosome profiling of resting, primary CD4⁺ T cells uncovers a baseline translational landscape rich in mTOR targets linked to mitochondria, oxidative phosphorylation, and splicing. Aberrantly increased tonic mTORC1 signals from a Rasgrp1^Anaef allele result in immunopathology with spontaneous appearance of T peripheral helper cells, follicular helper T cells, and anti-nuclear antibodies that are preceded by subtle alterations in the translational landscape.

Myers et al. evaluate a mouse model of autoimmunity, Rasgrp1^Anaef. They find that T cells with the Rasgrp1^Anaef allele exhibit altered signaling from Rasgrp1 to the mTORC1 pathway in the basal state. They show that increased basal Rasgrp1^Anaef-mTORC1 signals lead to an altered translational landscape in T cells and immunopathology.

Cell Intrinsic and Systemic Metabolism in Tumor Immunity and Immunotherapy

Immune checkpoint inhibitor (ICI) therapy has shown extraordinary promise at treating cancers otherwise resistant to treatment. However, for ICI therapy to be effective, it must overcome the metabolic limitations of the tumor microenvironment. Tumor metabolism has long been understood to be highly dysregulated, with potent immunosuppressive effects. Moreover, T cell activation and longevity within the tumor microenvironment are intimately tied to T cell metabolism and are required for the long-term efficacy of ICI therapy. We discuss in this review the intersection of metabolic competition in the tumor microenvironment, T cell activation and metabolism, the roles of tumor cell metabolism in immune evasion, and the impact of host metabolism in determining immune surveillance and ICI therapy outcomes. We also discussed the effects of obesity and calorie restriction—two important systemic metabolic perturbations that impact intrinsic metabolic pathways in T cells as well as cancer cells.

mTOR and other effector kinase signals that impact T cell function and activity

T cells play important roles in autoimmune diseases and cancer. Following the cloning of the T cell receptor (TCR), the race was on to map signaling proteins that contributed to T cell activation downstream of the TCR as well as co-stimulatory molecules such as CD28. We term this "canonical TCR signaling" here. More recently, it has been appreciated that T cells need to accommodate increased metabolic needs that stem from T cell activation in order to function properly. A central role herein has emerged for mechanistic/mammalian target of rapamycin (mTOR). In this review we briefly cover canonical TCR signaling to set the stage for discussion on mTOR signaling, mRNA translation, and metabolic adaptation in T cells. We also discuss the role of mTOR in follicular helper T cells, regulatory T cells, and other T cell subsets. Our lab recently uncovered that "tonic signals", which pass through proximal TCR signaling components, are robustly and selectively transduced to mTOR to promote baseline translation of various mRNA targets. We discuss insights on (tonic) mTOR signaling in the context of T cell function in autoimmune diseases such as lupus as well as in cancer immunotherapy through CAR-T cell or checkpoint blockade approaches.

Colony-Stimulating Factor 1 Receptor (CSF1R) Activates AKT/mTOR Signaling and Promotes T-Cell Lymphoma Viability

PURPOSE

Peripheral T-cell lymphomas are clinically aggressive and usually fatal, as few complete or durable remissions are achieved with currently available therapies. Recent evidence supports a critical role for lymphoma-associated macrophages during T-cell lymphoma progression, but the specific signals involved in the cross-talk between malignant T cells and their microenvironment are poorly understood. Colony-stimulator factor 1 receptor (CSF1R, CD115) is required for the homeostatic survival of tissue-resident macrophages. Interestingly, its aberrant expression has been reported in a subset of tumors. In this article, we evaluated its expression and oncogenic role in T-cell lymphomas.

EXPERIMENTAL DESIGN

Loss-of-function studies, including pharmacologic inhibition with a clinically available tyrosine kinase inhibitor, pexidartinib, were performed in multiple in vitro and in vivo models. In addition, proteomic and genomic screenings were performed to discover signaling pathways that are activated downstream of CSF1R signaling.

RESULTS

We observed that CSF1R is aberrantly expressed in many T-cell lymphomas, including a significant number of peripheral and cutaneous T-cell lymphomas. Colony-stimulating factor 1 (CSF1), in an autocrine or paracrine-dependent manner, leads to CSF1R autophosphorylation and activation in malignant T cells. Furthermore, CSF1R signaling was associated with significant changes in gene expression and in the phosphoproteome, implicating PI3K/AKT/mTOR in CSF1R-mediated T-cell lymphoma growth. We also demonstrated that inhibition of CSF1R in vivo and in vitro models is associated with decreased T-cell lymphoma growth.

CONCLUSIONS

Collectively, these findings implicate CSF1R in T-cell lymphomagenesis and have significant therapeutic implications.

Beyond PD-1/PD-L1 Inhibition: What the Future Holds for Breast Cancer Immunotherapy

Cancer immunotherapy has altered the management of human malignancies, improving outcomes in an expanding list of diseases. Breast cancer - presumably due to its perceived low immunogenicity - is a late addition to this list. Furthermore, most of the focus has been on the triple negative subtype because of its higher tumor mutational load and lymphocyte-enriched stroma, although emerging data show promise on the other breast cancer subtypes as well. To this point the clinical use of immunotherapy is limited to the inhibition of two immune checkpoints, Programmed Cell Death Protein 1 (PD-1) and Cytotoxic T-lymphocyte-associated Protein 4 (CTLA-4). Consistent with the complexity of the regulation of the tumor - host interactions and their lack of reliance on a single regulatory pathway, combinatory approaches have shown improved efficacy albeit at the cost of increased toxicity. Beyond those two checkpoints though, a large number of co-stimulatory or co-inhibitory molecules play major roles on tumor evasion from immunosurveillance. These molecules likely represent future targets of immunotherapy provided that the promise shown in early data is translated into improved patient survival in randomized trials. The biological role, prognostic and predictive implications regarding breast cancer and early clinical efforts on exploiting these immune-related therapeutic targets are herein reviewed.

A Blood Pact: the Significance and Implications of eIF4E on Lymphocytic Leukemia

Elevated levels of eukaryotic initiation factor 4E (eIF4E) are implicated in neoplasia, with cumulative evidence pointing to its role in the etiopathogenesis of hematological diseases. As a node of convergence for several oncogenic signaling pathways, eIF4E has attracted a great deal of interest from biologists and clinicians whose efforts have been targeting this translation factor and its biological circuits in the battle against leukemia. The role of eIF4E in myeloid leukemia has been ascertained and drugs targeting its functions have found their place in clinical trials. Little is known, however, about the pertinence of eIF4E to the biology of lymphocytic leukemia and a paucity of literature is available in this regard that prospectively evaluates the topic to guide practice in hematological cancer. A comprehensive analysis on the significance of eIF4E translation factor in the clinical picture of leukemia arises, therefore, as a compelling need. This review presents aspects of eIF4E involvement in the realm of the lymphoblastic leukemia status; translational control of immunological function via eIF4E and the state-of-the-art in drugs will also be outlined.

Next generation immune-checkpoints for cancer therapy

The discovery and clinical application of immune-checkpoint inhibitors has dramatically improved the treatments, outcomes and therapeutic concepts in multiple tumor settings. This breakthrough was mainly based on monoclonal antibodies blocking the inhibitory molecule CTLA-4 and or the PD-1/PD-L1 axis, with the aim of counteracting major tumor immune evasion mechanisms. Even acknowledging these important successes, not all the patients benefit from these treatments. Translational and clinical research efforts are ongoing to explore the potentialities of a new generation of immune-modulatory molecules to extend current clinical applications and contrast the unsolved issues of resistance and disease relapse that still affects a considerable rate of patients. New immune-checkpoints, with either stimulatory or inhibitory functions are emerging with key roles in regulating T cell response but also affecting other crucial effectors belonging to the innate immune response (e.g., natural killer). Their therapeutic exploitation, either alone or in strategical combinations, is providing important preclinical results, holding promises currently explored in initial clinical trials. The first results point toward favorable safety profiles with selective hints of activity in challenging settings. Important issues regarding the dose, schedule and rational combinations remain open and data from the clinical studies are needed. Here we provide an overview of the main emerging stimulatory or inhibitory immune-checkpoints exploitable in cancer treatment, briefly reporting their biological function, preclinical activity and preliminary clinical data.

ICOS Signaling Controls Induction and Maintenance of Collagen-Induced Arthritis

ICOS is a key costimulatory receptor facilitating differentiation and function of follicular helper T cells and inflammatory T cells. Rheumatoid arthritis patients were shown to have elevated levels of ICOS⁺ T cells in the synovial fluid, suggesting a potential role of ICOS-mediated T cell costimulation in autoimmune joint inflammation. In this study, using ICOS knockout and knockin mouse models, we found that ICOS signaling is required for the induction and maintenance of collagen-induced arthritis (CIA), a murine model of rheumatoid arthritis. For the initiation of CIA, the Tyr¹⁸¹-based SH2-binding motif of ICOS that is known to activate PI3K was critical for Ab production and expansion of inflammatory T cells. Furthermore, we found that Tyr¹⁸¹-dependent ICOS signaling is important for maintenance of CIA in an Ab-independent manner. Importantly, we found that a small molecule inhibitor of glycolysis, 3-bromopyruvate, ameliorates established CIA, suggesting an overlap between ICOS signaling, PI3K signaling, and glucose metabolism. Thus, we identified ICOS as a key costimulatory pathway that controls induction and maintenance of CIA and provide evidence that T cell glycolytic pathways can be potential therapeutic targets for rheumatoid arthritis.

Emerging targets in cancer immunotherapy

The first generation of immune checkpoint inhibitors (anti-CTLA-4 and anti-PD-1/PD-L1) targeted natural immune homeostasis pathways, co-opted by cancers, to drive anti-tumor immune responses. These agents led to unprecedented results in patients with previously incurable metastatic disease and may become first-line therapies for some advanced cancers. However, these agents are efficacious in only a minority of patients. Newer strategies are becoming available that target additional immunomodulatory mechanisms to activate patients' own anti-tumor immune responses. Herein, we present a succinct summary of emerging immune targets with reported pre-clinical efficacy that have progressed to active investigation in clinical trials. These emerging targets include co-inhibitory and co-stimulatory markers of the innate and adaptive immune system. In this review, we discuss: 1) T lymphocyte markers: Lymphocyte Activation Gene 3 [LAG-3], T-cell Immunoglobulin- and Mucin-domain-containing molecule 3 [TIM-3], V-domain containing Ig Suppressor of T cell Activation [VISTA], T cell ImmunoGlobulin and ITIM domain [TIGIT], B7-H3, Inducible T-cell Co-stimulator [ICOS/ICOS-L], CD27/CD70, and Glucocorticoid-Induced TNF Receptor [GITR]; 2) macrophage markers: CD47/Signal-Regulatory Protein alpha [SIRPα] and Indoleamine-2,3-Dioxygenase [IDO]; and 3) natural killer cell markers: CD94/NKG2A and the Killer Immunoglobulin-like receptor [KIR] family. Finally, we briefly highlight combination strategies and potential biomarkers of response and resistance to these cancer immunotherapies.

Impact of immunosuppressive drugs on circulating Tfh cells in kidney transplant recipients: A pilot study

BACKGROUND

T follicular helper cells (Tfh) are recently revealed to be vital in antibody-mediated rejection (AMR) in kidney transplant recipients (KTRs). However, the impact of immunosuppressive drugs on Tfh cells is not fully understood. The purpose of this study was to investigate the variation of Tfh cells phenotypically and functionally in KTRs treated with different immunosuppression regimens.

METHODS

We recruited 26 KTRs treated with tacrolimus (TAC) -based regimen, 13 with sirolimus (SRL) -based regimen and 10 healthy controls (HC) in this study. The percentage and absolute number of circulating Tfh cells and the co-expression of Tfh related molecules including inducible costimulatory molecule (ICOS), programmed cell death protein 1 (PD-1), interleukin-21 (IL-21) and signal transducer and activator of transcription 3 (STAT3) were analyzed by flow cytometry, while serum IL-6 was detected by electrochemiluminescence immunoassay.

RESULTS

The percentage and absolute number of Tfh cells and the co-expression of PD-1, STAT3 in Tfh cells were significantly higher in TAC group than that in SRL group. While no difference was found in regard to IL-21 and ICOS co-expressed with Tfh cells among three groups. Multiple linear regression analysis results showed that pre-transplant PRA level was the significant confounder affecting the absolute numbers of Tfh and CD4+CXCR5+PD-1+ T cells. In addition, correlation analysis showed that CD4+CXCR5+STAT3+ T cells were positively correlated to Tfh cells.

CONCLUSIONS

Our study indicates that sirolimus can suppress the quantity of Tfh cells more significantly than tacrolimus. The higher level of circulating Tfh cells in tacrolimus group might be related to STAT3 signaling.

Posttranscriptional and Translational Control of Gene Regulation in CD4+ T Cell Subsets

The immune system is under strict regulatory control to ensure homeostasis of inflammatory responses, lying dormant when not needed but quick to act when called upon. Small changes in gene expression can lead to drastic changes in lineage commitment, cellular function, and immunity. Conventional assessment of these changes centered on the analysis of mRNA levels through a variety of methodologies, including microarrays. However, mRNA synthesis does not always correlate directly to protein synthesis and downstream functional activity. Work conducted in recent years has begun to shed light on the various posttranscriptional changes that occur in response to a dynamic external environment that a given cell type encounters. We provide a critical review of key posttranscriptional mechanisms (i.e., microRNA) and translational mechanisms of regulation of gene expression in the immune system, with a particular emphasis on these regulatory processes in various CD4(+) T cell subsets.

Attenuation of AMPK signaling by ROQUIN promotes T follicular helper cell formation

T follicular helper cells (Tfh) are critical for the longevity and quality of antibody-mediated protection against infection. Yet few signaling pathways have been identified to be unique solely to Tfh development. ROQUIN is a post-transcriptional repressor of T cells, acting through its ROQ domain to destabilize mRNA targets important for Th1, Th17, and Tfh biology. Here, we report that ROQUIN has a paradoxical function on Tfh differentiation mediated by its RING domain: mice with a T cell-specific deletion of the ROQUIN RING domain have unchanged Th1, Th2, Th17, and Tregs during a T-dependent response but show a profoundly defective antigen-specific Tfh compartment. ROQUIN RING signaling directly antagonized the catalytic α1 subunit of adenosine monophosphate-activated protein kinase (AMPK), a central stress-responsive regulator of cellular metabolism and mTOR signaling, which is known to facilitate T-dependent humoral immunity. We therefore unexpectedly uncover a ROQUIN–AMPK metabolic signaling nexus essential for selectively promoting Tfh responses.

DOI:http://dx.doi.org/10.7554/eLife.08698.001

The immune system protects the body from invading microbes like bacteria and viruses. Upon recognizing the presence of these microbes, cells in the immune system are activated to destroy the foreign threat and clear it from the body.

A type of immune cell called T follicular helper cells (or Tfh for short) are formed during an infection and are essential for coordinating other immune cells to produce high-quality antibody proteins that attack the microbes. Without Tfh cells, life-long production of these protective antibodies is severely crippled, which can cause common variable immune deficiency and other serious immunodeficiency diseases. On the other hand, the body must also avoid generating excessive numbers of Tfh cells, which can lead to the production of antibodies that attack healthy cells of the body.

ROQUIN is a protein that inhibits the formation of Tfh cells and other types of active T cells. A region on the protein called the ROQ domain destabilizes particular molecules of ribonucleic acid (RNA) that are required for these specialist T cells to form and work properly. ROQUIN belongs to a large family of enzymes that have a so-called RING domain, which is a feature that enables these enzymes to attach tags onto specific target proteins to modify their activity or stability. However, it was not known whether the RING domain of ROQUIN was active.

Ramiscal et al. now address this question in mice. Unexpectedly, the experiments show that the RING domain is required to promote the formation of Tfh cells, but not other types of active T cells. This domain allows ROQUIN to repress an enzyme called AMPK, which normally blocks cell growth by regulating cell metabolism. The findings suggest that the different roles of the ROQ and RING domains allow ROQUIN to fine-tune the numbers of Tfh cells so that they remain within a safe range. In the future, these findings may aid the development of vaccines that are more efficient at generating protective Tfh cells to prevent infectious diseases.

DOI:http://dx.doi.org/10.7554/eLife.08698.002

Impaired Phenotype and Function of T Follicular Helper Cells in HIV-1-Infected Children Receiving ART

T follicular helper (Tfh) cells are important components in development of specific humoral immune responses; whether the number and biology of Tfh cells is impaired in HIV-1-infected children is not yet studied.The frequency, phenotype, and function of Tfh cells and B cells were determined in blood of HIV-1-infected children receiving antiretroviral therapy (ART) and age-matched controls. Flow cytometry was used to characterize the frequency of Tfh cells and B cell subsets. Cytokine expression was measured after in vitro activation of Tfh cells.A reduced frequency of memory Tfh cells (P < 0.001) was identified in HIV-1-infected children and, on these cells, a reduced expression of programmed death-1 (PD-1) and inducible T cell costimulator (ICOS) (P < 0.001 and P < 0.01). Upon activation, the capacity of Tfh cells to express IL-4, an important cytokine for B cell function, was impaired in HIV-1-infected children.B cell subpopulations in HIV-1-infected children displayed significant differences from the control group: the frequency of resting memory (RM) B cells was reduced (P < 0.01) whereas the frequency of exhausted memory B cells increased (P < 0.001). Interestingly, the decline of RM cells correlated with the reduction of memory Tfh cells (P = 0.02).Our study shows that function and phenotype of Tfh cells, pivotal cells for establishment of adaptive B cell responses, are impaired during HIV-1 infection in children. A consistent reduction of memory Tfh cells is associated with declined frequencies of RM B cells, creating a novel link between dysfunctional features of these cell types, major players in establishment of humoral immunity.

Retroviral vectors elevate coexpressed protein levels in trans through cap-dependent translation

Retroviruses cause immunodeficiency and cancer but also are used as vectors for the expression of heterologous genes. Nevertheless, optimal translation of introduced genes often is not achieved. Here we show that transfection into mammalian cells of lentiviral or gammaretroviral vectors, including those with specific shRNAs, increased expression of a cotransfected gene relative to standard plasmid vectors. Levels of most endogenous cellular proteins were unchanged. Transfer of lentiviral vector sequences into a standard plasmid conferred the ability to give increased expression of cotransfected genes (superinduction). Superinduction by the retroviral vector was not dependent on the cell type or species, the type of reporter gene, or the method of transfection. No differences were detected in the IFN, unfolded protein, or stress responses in the presence of retroviral vectors. RT-PCRs revealed that RNA levels of cotransfected genes were unchanged during superinduction, yet Western blotting, pulse labeling, and the use of bicistronic vectors showed increased cap-dependent translation of cointroduced genes. Expression of the mammalian target of rapamycin (mTOR) kinase target 4E-BP1, but not the mTOR inhibitor Torin 1, preferentially inhibited superinduction relative to basal protein expression. Furthermore, transcription of lentiviral vector sequences from a doxycycline-inducible promoter eliminated superinduction, consistent with a DNA-triggered event. Thus, retroviral DNA increased translation of cointroduced genes in trans by an mTOR-independent signaling mechanism. Our experiments have broad applications for the design of retroviral vectors for transfections, DNA vaccines, and gene therapy.

Life of T follicular helper cells

Antibodies are powerful defense tools against pathogens but may cause autoimmune diseases when erroneously directed toward self-antigens. Thus, antibody producing cells are carefully selected, refined, and expanded in a highly regulated microenvironment (germinal center) in the peripheral lymphoid organs. A subset of T cells termed T follicular helper cells (Tfh) play a central role in instructing B cells to form a repertoire of antibody producing cells that provide life-long supply of high affinity, pathogen-specific antibodies. Therefore, understanding how Tfh cells arise and how they facilitate B cell selection and differentiation during germinal center reaction is critical to improve vaccines and better treat autoimmune diseases. In this review, I will summarise recent findings on molecular and cellular mechanisms underlying Tfh generation and function with an emphasis on T cell costimulation.

IL-4-secreting secondary T follicular helper (Tfh) cells arise from memory T cells, not persisting Tfh cells, through a B cell-dependent mechanism

Humoral immunity requires cross-talk between T follicular helper (Tfh) cells and B cells. Nevertheless, a detailed understanding of this intercellular interaction during secondary immune responses is lacking. We examined this by focusing on the response to a soluble, unadjuvanted, pathogen-derived Ag (soluble extract of Schistosoma mansoni egg [SEA]) that induces type 2 immunity. We found that activated Tfh cells persisted for long periods within germinal centers following primary immunization. However, the magnitude of the secondary response did not appear to depend on pre-existing Tfh cells. Instead, Tfh cell populations expanded through a process that was dependent on memory T cells recruited into the reactive LN, as well as the participation of B cells. We found that, during the secondary response, IL-4 was critical for the expansion of a population of plasmablasts that correlated with increased SEA-specific IgG1 titers. Additionally, following immunization with SEA (but not with an Ag that induced type 1 immunity), IL-4 and IL-21 were coproduced by individual Tfh cells, revealing a potential mechanism through which appropriate class-switching can be coupled to plasmablast proliferation to enforce type 2 immunity. Our findings demonstrate a pivotal role for IL-4 in the interplay between T and B cells during a secondary Th2 response and have significant implications for vaccine design.

The CD28-B7 Family in Anti-Tumor Immunity: Emerging Concepts in Cancer Immunotherapy

The interactions between B7 molecules and CD28-family receptors are crucial in the regulation of adaptive cellular immunity. In cancer, the aberrant expression of co-inhibitory B7 molecules has been attributed to reduced anti-tumor immunity and cancer immune evasion, prompting the development of cancer therapeutics that can restore T cell function. Murine tumor models have provided significant support for the targeting of multiple immune checkpoints involving CTLA-4, PD-1, ICOS, B7-H3 and B7-H4 during tumor growth, and clinical studies investigating the therapeutic effects of CTLA-4 and PD-1 blockade have shown exceptionally promising results in patients with advanced melanoma and other cancers. The expression pattern of co-inhibitory B7 ligands in the tumor microenvironment has also been largely correlated with poor patient prognosis, and recent evidence suggests that the presence of several B7 molecules may predict the responsiveness of immunotherapies that rely on pre-existing tumor-associated immune responses. While monotherapies blocking T cell co-inhibition have beneficial effects in reducing tumor burden, combinatorial immunotherapy targeting multiple immune checkpoints involved in various stages of the anti-tumor response has led to the most substantial impact on tumor reduction. In this review, we will examine the contributions of B7- and CD28-family members in the context of cancer development, and discuss the implications of current human findings in cancer immunotherapy.