Ablation of Transcription Factor IRF4 Promotes Transplant Acceptance by Driving Allogenic CD4+ T Cell Dysfunction

Total plasma cfDNA methylation in pediatric kidney transplant recipients provides insight into acute allograft rejection pathophysiology

Cell-free DNA (cfDNA) is a marker of organ injury and immune response. DNA methylation is an epigenetic regulator of gene expression. Here, we elucidate total plasma cfDNA methylation from kidney transplant recipients in presence versus absence of rejection. In doing so, we exploit cfDNA as a real-time biomarker to define molecular pathways of rejection. Twenty plasma cfDNA samples from pediatric kidney transplant recipients were collected at allograft biopsy. Differentially methylated cytosine residues (>20 % methylation difference, q-value <0.05) were identified in presence (N = 7) versus absence (N = 9) of acute rejection. Separate analyses were performed comparing borderline rejection (N = 4) to rejection and non-rejection. In rejection versus non-rejection, there were 1269 differentially methylated genes corresponding to 533 pathways. These numbers were 4-13× greater than comparisons against borderline samples. Enriched pathways between rejection and non-rejection samples were related to immune cell/inflammatory response, lipid metabolism, and tryptophan-kynurenine metabolism, suggesting differential methylation of these pathways contributes to rejection.

Inhibition of interferon regulatory factor 4 orchestrates T cell dysfunction, extending mouse cardiac allograft survival

BACKGROUND

T cell dysfunction, which includes exhaustion, anergy, and senescence, is a distinct T cell differentiation state that occurs after antigen exposure. Although T cell dysfunction has been a cornerstone of cancer immunotherapy, its potential in transplant research, while not yet as extensively explored, is attracting growing interest. Interferon regulatory factor 4 (IRF4) has been shown to play a pivotal role in inducing T cell dysfunction.

METHODS

A novel ultra-low-dose combination of Trametinib and Rapamycin, targeting IRF4 inhibition, was employed to investigate T cell proliferation, apoptosis, cytokine secretion, expression of T-cell dysfunction-associated molecules, effects of mitogen-activated protein kinase (MAPK) and mammalian target of rapamycin (mTOR) signaling pathways, and allograft survival in both in vitro and BALB/c to C57BL/6 mouse cardiac transplantation models.

RESULTS

In vitro , blockade of IRF4 in T cells effectively inhibited T cell proliferation, increased apoptosis, and significantly upregulated the expression of programmed cell death protein 1 (PD-1), Helios, CD160, and cytotoxic T lymphocyte-associated antigen (CTLA-4), markers of T cell dysfunction. Furthermore, it suppressed the secretion of pro-inflammatory cytokines interferon (IFN)-γ and interleukin (IL)-17. Combining ultra-low-dose Trametinib (0.1 mg·kg -1 ·day -1 ) and Rapamycin (0.1 mg·kg -1 ·day -1 ) demonstrably extended graft survival, with 4 out of 5 mice exceeding 100 days post-transplantation. Moreover, analysis of grafts at day 7 confirmed sustained IFN regulatory factor 4 (IRF4) inhibition, enhanced PD-1 expression, and suppressed IFN-γ secretion, reinforcing the in vivo efficacy of this IRF4-targeting approach. The combination of Trametinib and Rapamycin synergistically inhibited the MAPK and mTOR signaling network, leading to a more pronounced suppression of IRF4 expression.

CONCLUSIONS

Targeting IRF4, a key regulator of T cell dysfunction, presents a promising avenue for inducing transplant immune tolerance. In this study, we demonstrate that a novel ultra-low-dose combination of Trametinib and Rapamycin synergistically suppresses the MAPK and mTOR signaling network, leading to profound IRF4 inhibition, promoting allograft acceptance, and offering a potential new therapeutic strategy for improved transplant outcomes. However, further research is necessary to elucidate the underlying pharmacological mechanisms and facilitate translation to clinical practice.

Transient Anti-TCRβ mAb Treatment Induces CD4 + T Cell Exhaustion and Prolongs Survival in a Mouse Model of Systemic Lupus Erythematosus

T cells play a critical role in the pathogenesis of systemic lupus erythematosus (SLE). Chronic T cell receptor (TCR) signalling induces T cell exhaustion, characterised by reduced capacity to induce tissue damage. Here, we investigated the therapeutic potential of the anti-TCRβ (H57-597) monoclonal antibody (mAb) in a mouse model of SLE. Four-month-old MRL/lpr mice exhibiting SLE phenotypes received 5 weekly doses of anti-TCRβ mAb or phosphate-buffered saline (PBS) vehicle control. Subsequently, mouse survival was monitored daily. On day 1 post the final dose of treatment, SLE pathogenesis was determined using histological staining and spot urine test. T and B cell states in the brain, kidney, and secondary lymphoid organs were determined by flow cytometry. Transient treatment of anti-TCRβ mAb significantly prolonged the survival of MRL/lpr mice. Accordingly, MRL/lpr mice in the anti-TCRβ mAb group exhibited decreased proteinuria scores and minimal renal pathological damage compared to the PBS control group. Flow cytometric analysis revealed that anti-TCRβ mAb treatment resulted in a reduction in the frequencies of CD4+ T cells and CD138+B220lo/- plasma cells, plus an increase in Foxp3+ regulatory T cell frequency. Furthermore, CD4+ T cells from anti-TCRβ mAb treated mice exhibited elevated expression levels of PD-1 and TIM-3, with reduced IFN-γ production, indicative of an exhaustion-like phenotype. Therefore, transient administration of anti-TCRβ mAb treatment induces an exhaustion-like phenotype in CD4+ T cells, resulting in prolonged survival of MRL/lpr mice. Inducing autoreactive T-cell exhaustion holds promise as an attractive therapeutic approach for SLE.

Apex1 safeguards genomic stability to ensure a cytopathic T cell fate in autoimmune disease models

T cells have a remarkable capacity to clonally expand, a process that is intricately linked to their effector activities. As vigorously proliferating T cell also incur substantial DNA lesions, how the dividing T cells safeguard their genomic integrity to allow the generation of T effector cells remains largely unknown. Here we report the identification of the apurinic/apyrimidinic endonuclease-1 (Apex1) as an indispensable molecule for the induction of cytopathic T effectors in mouse models. We demonstrate that conditional deletion of Apex1 in T cells resulted in a remarkable accumulation of baseless DNA sites in the genome of proliferating T cells, which further led to genomic instability and apoptotic cell death. Consequently, Apex1-deleted T cells failed to acquire any effector features after activation and failed to mediate autoimmune diseases and allergic tissue damages. Detailed mutational analyses pinpointed the importance of its endonuclease domain in the generation of T effector cells. We provide further evidence that inhibiting the base repair activities of Apex1 with chemical inhibitors similarly abrogated the induction of autoimmune diseases. Collectively, our study suggests that Apex1 serves as a gatekeeper for the generation of cytopathic T cells and that therapeutically targeting Apex1 may have important clinical implications in the treatment of autoimmune diseases.

IRF4 impedes human CD8 T cell function and promotes cell proliferation and PD-1 expression

Human CD8 tumor-infiltrating lymphocytes (TILs) with impaired effector functions and PD-1 expression are categorized as exhausted. However, the exhaustion-like features reported in TILs might stem from their activation rather than the consequence of T cell exhaustion itself. Using CRISPR-Cas9 and lentiviral overexpression in CD8 T cells from non-cancerous donors, we show that the T cell receptor (TCR)-induced transcription factor interferon regulatory factor 4 (IRF4) promotes cell proliferation and PD-1 expression and hampers effector functions and expression of nuclear factor κB (NF-κB)-regulated genes. While CD8 TILs with impaired interferon γ (IFNγ) production exhibit activation markers IRF4 and CD137 and exhaustion markers thymocyte selection associated high mobility group box (TOX) and PD-1, activated T cells in patients with COVID-19 do not demonstrate elevated levels of TOX and PD-1. These results confirm that IRF4+ TILs are exhausted rather than solely activated. Our study indicates, however, that PD-1 expression, low IFNγ production, and active cycling in TILs are all influenced by IRF4 upregulation after T cell activation.

MEK1/2-PKM2 Pathway Modulates the Immunometabolic Reprogramming of Proinflammatory Allograft-infiltrating Macrophages During Heart Transplant Rejection

BACKGROUND

Emerging evidence has highlighted the role of macrophages in heart transplant rejection (HTR). However, the molecular signals modulating the immunometabolic phenotype of allograft-infiltrating macrophages (AIMs) during HTR remain unknown.

METHODS

We analyzed single-cell RNA sequencing data from cardiac graft-infiltrating immunocytes to characterize the activation patterns and metabolic features of AIMs. We used flow cytometry to determine iNOS and PKM2 expression and MEK/ERK signaling activation levels in AIMs. We then generated macrophage-specific Mek1/2 knockout mice to determine the role of the MEK1/2-PKM2 pathway in the proinflammatory phenotype and glycolytic capacity of AIMs during HTR.

RESULTS

Single-cell RNA sequencing analysis showed that AIMs had a significantly elevated proinflammatory and glycolytic phenotype. Flow cytometry analysis verified that iNOS and PKM2 expressions were significantly upregulated in AIMs. Moreover, MEK/ERK signaling was activated in AIMs and positively correlated with proinflammatory and glycolytic signatures. Macrophage-specific Mek1/2 deletion significantly protected chronic cardiac allograft rejection and inhibited the proinflammatory phenotype and glycolytic capacity of AIMs. Mek1/2 ablation also reduced the proinflammatory phenotype and glycolytic capacity of lipopolysaccharides + interferon-γ-stimulated macrophages. Mek1/2 ablation impaired nuclear translocation and PKM2 expression in macrophages. PKM2 overexpression partially restored the proinflammatory phenotype and glycolytic capacity of Mek1/2 -deficient macrophages. Moreover, trametinib, an Food and Drug Administration-approved MEK1/2 inhibitor, ameliorated chronic cardiac allograft rejection.

CONCLUSIONS

These findings suggest that the MEK1/2-PKM2 pathway is essential for immunometabolic reprogramming of proinflammatory AIMs, implying that it may be a promising therapeutic target in clinical heart transplantation.

Targeted depletion of PD-1-expressing cells induces immune tolerance through peripheral clonal deletion

Thymic negative selection of the T cell receptor (TCR) repertoire is essential for establishing self-tolerance and acquired allograft tolerance following organ transplantation. However, it is unclear whether and how peripheral clonal deletion of alloreactive T cells induces transplantation tolerance. Here, we establish that programmed cell death protein 1 (PD-1) is a hallmark of alloreactive T cells and is associated with clonal expansion after alloantigen encounter. Moreover, we found that diphtheria toxin receptor (DTR)-mediated ablation of PD-1+ cells reshaped the TCR repertoire through peripheral clonal deletion of alloreactive T cells and promoted tolerance in mouse transplantation models. In addition, by using PD-1-specific depleting antibodies, we found that antibody-mediated depletion of PD-1+ cells prevented heart transplant rejection and the development of experimental autoimmune encephalomyelitis (EAE) in humanized PD-1 mice. Thus, these data suggest that PD-1 is an attractive target for peripheral clonal deletion and induction of immune tolerance.

Dissecting the immune discrepancies in mouse liver allograft tolerance and heart/kidney allograft rejection

The liver is the most tolerogenic of transplanted organs. However, the mechanisms underlying liver transplant tolerance are not well understood. The comparison between liver transplantation tolerance and heart/kidney transplantation rejection will deepen our understanding of tolerance and rejection in solid organs. Here, we built a mouse model of liver, heart and kidney allograft and performed single-cell RNA sequencing of 66,393 cells to describe the cell composition and immune cell interactions at the early stage of tolerance or rejection. We also performed bulk RNA-seq of mouse liver allografts from Day 7 to Day 60 post-transplantation to map the dynamic transcriptional variation in spontaneous tolerance. The transcriptome of lymphocytes and myeloid cells were characterized and compared in three types of organ allografts. Cell-cell interaction networks reveal the coordinated function of Kupffer cells, macrophages and their associated metabolic processes, including insulin receptor signalling and oxidative phosphorylation in tolerance induction. Cd11b+ dendritic cells (DCs) in liver allografts were found to inhibit cytotoxic T cells by secreting anti-inflammatory cytokines such as Il10. In summary, we profiled single-cell transcriptome analysis of mouse solid organ allografts. We characterized the immune microenvironment of mouse organ allografts in the acute rejection state (heart, kidney) and tolerance state (liver).

CD4+ T cell immunity is dependent on an intrinsic stem-like program

CD4+ T cells are central to various immune responses, but the molecular programs that drive and maintain CD4+ T cell immunity are not entirely clear. Here we identify a stem-like program that governs the CD4+ T cell response in transplantation models. Single-cell-transcriptomic analysis revealed that naive alloantigen-specific CD4+ T cells develop into TCF1hi effector precursor (TEP) cells and TCF1-CXCR6+ effectors in transplant recipients. The TCF1-CXCR6+CD4+ effectors lose proliferation capacity and do not reject allografts upon adoptive transfer into secondary hosts. By contrast, the TCF1hiCD4+ TEP cells have dual features of self-renewal and effector differentiation potential, and allograft rejection depends on continuous replenishment of TCF1-CXCR6+ effectors from TCF1hiCD4+ TEP cells. Mechanistically, TCF1 sustains the CD4+ TEP cell population, whereas the transcription factor IRF4 and the glycolytic enzyme LDHA govern the effector differentiation potential of CD4+ TEP cells. Deletion of IRF4 or LDHA in T cells induces transplant acceptance. These findings unravel a stem-like program that controls the self-renewal capacity and effector differentiation potential of CD4+ TEP cells and have implications for T cell-related immunotherapies.

Interferon regulatory factor 4 plays a pivotal role in the development of aGVHD-associated colitis

Interferon regulatory factor 4 (IRF4) is a master transcription factor that regulates T helper cell (Th) differentiation. It interacts with the Basic leucine zipper transcription factor, ATF-like (BATF), depletion of which in CD4+ T cells abrogates acute graft-versus-host disease (aGVHD)-induced colitis. Here, we investigated the immune-regulatory role of Irf4 in a mouse model of MHC-mismatched bone marrow transplantation. We found that recipients of allogenic Irf4-/- CD4+ T cells developed less GVHD-related symptoms. Transcriptome analysis of re-isolated donor Irf4-/- CD4+ T helper (Th) cells, revealed gene expression profiles consistent with loss of effector T helper cell signatures and enrichment of a regulatory T cell (Treg) gene expression signature. In line with these findings, we observed a high expression of the transcription factor BTB and CNC homolog 2; (BACH2) in Irf4-/- T cells, which is associated with the formation of Treg cells and suppression of Th subset differentiation. We also found an association between BACH2 expression and Treg differentiation in patients with intestinal GVHD. Finally, our results indicate that IRF4 and BACH2 act as counterparts in Th cell polarization and immune homeostasis during GVHD. In conclusion, targeting the BACH2/IRF4-axis could help to develop novel therapeutic approaches against GVHD.

The OX40-TRAF6 axis promotes CTLA-4 degradation to augment antitumor CD8+ T-cell immunity

Immune checkpoint blockade (ICB), including anti-cytotoxic T-lymphocyte associated protein 4 (CTLA-4), benefits only a limited number of patients with cancer. Understanding the in-depth regulatory mechanism of CTLA-4 protein stability and its functional significance may help identify ICB resistance mechanisms and assist in the development of novel immunotherapeutic modalities to improve ICB efficacy. Here, we identified that TNF receptor-associated factor 6 (TRAF6) mediates Lys63-linked ubiquitination and subsequent lysosomal degradation of CTLA-4. Moreover, by using TRAF6-deficient mice and retroviral overexpression experiments, we demonstrated that TRAF6 promotes CTLA-4 degradation in a T-cell-intrinsic manner, which is dependent on the RING domain of TRAF6. This intrinsic regulatory mechanism contributes to CD8+ T-cell-mediated antitumor immunity in vivo. Additionally, by using an OX40 agonist, we demonstrated that the OX40-TRAF6 axis is responsible for CTLA-4 degradation, thereby controlling antitumor immunity in both tumor-bearing mice and patients with cancer. Overall, our findings demonstrate that the OX40-TRAF6 axis promotes CTLA-4 degradation and is a potential therapeutic target for the improvement of T-cell-based immunotherapies.

The transcription factor IRF4 determines the anti-tumor immunity of CD8+ T cells

Understanding the factors that regulate T cell infiltration and functional states in solid tumors is crucial for advancing cancer immunotherapies. Here, we discovered that the expression of interferon regulatory factor 4 (IRF4) was a critical T cell intrinsic requirement for effective anti-tumor immunity. Mice with T-cell-specific ablation of IRF4 showed significantly reduced T cell tumor infiltration and function, resulting in accelerated growth of subcutaneous syngeneic tumors and allowing the growth of allogeneic tumors. Additionally, engineered overexpression of IRF4 in anti-tumor CD8+ T cells that were adoptively transferred significantly promoted their tumor infiltration and transition from a naive/memory-like cell state into effector T cell states. As a result, IRF4-engineered anti-tumor T cells exhibited significantly improved anti-tumor efficacy, and inhibited tumor growth either alone or in combination with PD-L1 blockade. These findings identify IRF4 as a crucial cell-intrinsic driver of T cell infiltration and function in tumors, emphasizing the potential of IRF4-engineering as an immunotherapeutic approach.

Immune Checkpoints in Solid Organ Transplantation

Allogenic graft acceptance is only achieved by life-long immunosuppression, which comes at the cost of significant toxicity. Clinicians face the challenge of adapting the patients' treatments over long periods to lower the risks associated with these toxicities, permanently leveraging the risk of excessive versus insufficient immunosuppression. A major goal and challenge in the field of solid organ transplantation (SOT) is to attain a state of stable immune tolerance specifically towards the grafted organ. The immune system is equipped with a set of inhibitory co-receptors known as immune checkpoints (ICs), which physiologically regulate numerous effector functions. Insufficient regulation through these ICs can lead to autoimmunity and/or immune-mediated toxicity, while excessive expression of ICs induces stable hypo-responsiveness, especially in T cells, a state sometimes referred to as exhaustion. IC blockade has emerged in the last decade as a powerful therapeutic tool against cancer. The opposite action, i.e., subverting IC for the benefit of establishing a state of specific hypo-responsiveness against auto- or allo-antigens, is still in its infancy. In this review, we will summarize the available literature on the role of ICs in SOT and the relevance of ICs with graft acceptance. We will also discuss the possible influence of current immunosuppressive medications on IC functions.

Immune Regulation of the Liver Through the PCSK9/CD36 Pathway During Heart Transplant Rejection

BACKGROUND

PCSK9 (proprotein convertase subtilisin/kexin 9), which is mainly secreted by the liver, is not only a therapeutic target for hyperlipidemia and cardiovascular disease, but also has been implicated in the immune regulation of infections and tumors. However, the role of PCSK9 and the liver in heart transplant rejection (HTR) and the underlying mechanisms remain unclear.

METHODS

We assessed serum PCSK9 expression in both murine and human recipients during HTR and investigated the effect of PCSK9 ablation on HTR by using global knockout mice and a neutralizing antibody. Moreover, we performed multiorgan histological and transcriptome analyses, and multiomics and single-cell RNA-sequencing studies of the liver during HTR, as well. We further used hepatocyte-specific Pcsk9 knockout mice to investigate whether the liver regulated HTR through PCSK9. Last, we explored the regulatory effect of the PCSK9/CD36 pathway on the phenotype and function of macrophages in vitro and in vivo.

RESULTS

Here, we report that murine and human recipients have high serum PCSK9 levels during HTR. PCSK9 ablation prolonged cardiac allograft survival and attenuated the infiltration of inflammatory cells in the graft and the expansion of alloreactive T cells in the spleen. Next, we demonstrated that PCSK9 was mainly produced and significantly upregulated in the recipient liver, which also showed a series of signaling changes, including changes in the TNF-α (tumor necrosis factor α) and IFN-γ (interferon γ) signaling pathways and the bile acid and fatty acid metabolism pathways. We found mechanistically that TNF-α and IFN-γ synergistically promoted PCSK9 expression in hepatocytes through the transcription factor SREBP2 (sterol regulatory element binding protein 2). Moreover, in vitro and in vivo studies indicated that PCSK9 inhibited CD36 expression and fatty acid uptake by macrophages and strengthened the proinflammatory phenotype, which facilitated their ability to promote proliferation and IFN-γ production by donor-reactive T cells. Last, we found that the protective effect of PCSK9 ablation against HTR is dependent on the CD36 pathway in the recipient.

CONCLUSIONS

This study reveals a novel mechanism for immune regulation by the liver through the PCSK9/CD36 pathway during HTR, which influences the phenotype and function of macrophages and suggests that the modulation of this pathway may be a potential therapeutic target to prevent HTR.

Antigen-specific B cells direct T follicular-like helper cells into lymphoid follicles to mediate Mycobacterium tuberculosis control

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb), is a global cause of death. Granuloma-associated lymphoid tissue (GrALT) correlates with protection during TB, but the mechanisms of protection are not understood. During TB, the transcription factor IRF4 in T cells but not B cells is required for the generation of the TH1 and TH17 subsets of helper T cells and follicular helper T (TFH)-like cellular responses. A population of IRF4+ T cells coexpress the transcription factor BCL6 during Mtb infection, and deletion of Bcl6 (Bcl6fl/fl) in CD4+ T cells (CD4cre) resulted in reduction of TFH-like cells, impaired localization within GrALT and increased Mtb burden. In contrast, the absence of germinal center B cells, MHC class II expression on B cells, antibody-producing plasma cells or interleukin-10-expressing B cells, did not increase Mtb susceptibility. Indeed, antigen-specific B cells enhance cytokine production and strategically localize TFH-like cells within GrALT via interactions between programmed cell death 1 (PD-1) and its ligand PD-L1 and mediate Mtb control in both mice and macaques.

Small-molecule BCL6 inhibitor protects chronic cardiac transplant rejection and inhibits T follicular helper cell expansion and humoral response

Background: B cell lymphoma 6 (BCL6) is an important transcription factor of T follicular helper (Tfh) cells, which regulate the humoral response by supporting the maturation of germinal center B cells and plasma cells. The aim of this study is to investigate the expansion of T follicular helper cells and the effect of the BCL6 inhibitor FX1 in acute and chronic cardiac transplant rejection models.

Methods: A mouse model of acute and chronic cardiac transplant rejection was established. Splenocytes were collected at different time points after transplantation for CXCR5+PD-1+ and CXCR5+BCL6+ Tfh cells detection by flow cytometry (FCM). Next, we treated the cardiac transplant with BCL6 inhibitor FX1 and the survival of grafts was recorded. The hematoxylin and eosin, Elastica van Gieson, and Masson staining of cardiac grafts was performed for the pathological analysis. Furthermore, the proportion and number of CD4+ T cells, effector CD4+ T cells (CD44+CD62L−), proliferating CD4+ T cells (Ki67+), and Tfh cells in the spleen were detected by FCM. The cells related to humoral response (plasma cells, germinal center B cells, IgG1+ B cells) and donor-specific antibody were also detected.

Results: We found that the Tfh cells were significantly increased in the recipient mice on day 14 post transplantation. During the acute cardiac transplant rejection, even the BCL6 inhibitor FX1 did not prolong the survival or attenuate the immune response of cardiac graft, the expansion of Tfh cell expansion inhibit. During the chronic cardiac transplant rejection, FX1 prolonged survival of cardiac graft, and prevented occlusion and fibrosis of vascular in cardiac grafts. FX1 also decreased the proportion and number of splenic CD4+ T cells, effector CD4+ T cells, proliferating CD4+ T cells, and Tfh cells in mice with chronic rejection. Moreover, FX1 also inhibited the proportion and number of splenic plasma cells, germinal center B cells, IgG1+ B cells, and the donor-specific antibody in recipient mice.

Conclusion: We found BCL6 inhibitor FX1 protects chronic cardiac transplant rejection and inhibits the expansion of Tfh cells and the humoral response, which suggest that BCL6 is a potential therapeutic target of the treatment for chronic cardiac transplant rejection.

IRF4 International Consortium. A multimorphic mutation in IRF4 causes human autosomal dominant combined immunodeficiency

Interferon regulatory factor 4 (IRF4) is a transcription factor (TF) and key regulator of immune cell development and function. We report a recurrent heterozygous mutation in IRF4, p.T95R, causing an autosomal dominant combined immunodeficiency (CID) in seven patients from six unrelated families. The patients exhibited profound susceptibility to opportunistic infections, notably Pneumocystis jirovecii, and presented with agammaglobulinemia. Patients' B cells showed impaired maturation, decreased immunoglobulin isotype switching, and defective plasma cell differentiation, whereas their T cells contained reduced TH17 and TFH populations and exhibited decreased cytokine production. A knock-in mouse model of heterozygous T95R showed a severe defect in antibody production both at the steady state and after immunization with different types of antigens, consistent with the CID observed in these patients. The IRF4T95R variant maps to the TF's DNA binding domain, alters its canonical DNA binding specificities, and results in a simultaneous multimorphic combination of loss, gain, and new functions for IRF4. IRF4T95R behaved as a gain-of-function hypermorph by binding to DNA with higher affinity than IRF4WT. Despite this increased affinity for DNA, the transcriptional activity on IRF4 canonical genes was reduced, showcasing a hypomorphic activity of IRF4T95R. Simultaneously, IRF4T95R functions as a neomorph by binding to noncanonical DNA sites to alter the gene expression profile, including the transcription of genes exclusively induced by IRF4T95R but not by IRF4WT. This previously undescribed multimorphic IRF4 pathophysiology disrupts normal lymphocyte biology, causing human disease.

Immunogenomic correlates of immune-related adverse events for anti-programmed cell death 1 therapy

Despite impressive antitumor efficacy of programmed cell death 1 (PD-1) inhibitors, this inhibition can induce mild to severe autoimmune toxicities, termed immune-related adverse events (irAEs). Yet, predictive pretreatment biomarkers for irAEs development across cancer types remain elusive. We first assessed cellular and molecular factors. To determine factors predicting the risk of irAEs for anti-PD-1 immunotherapy across multiple cancer types, an integrative analysis of cellular and molecular factors from 9104 patients across 21 cancer types and 4865522 postmarketing adverse event reports retrieved from adverse event reporting system was then performed. Accuracy of predictions was quantified as Pearson correlation coefficient determined using leave-one-out cross-validation. Independent validation sets included small cell lung cancer and melanoma cohorts. Out of 4865522 eligible adverse events reports, 10412 cases received anti-PD-1 monotherapy, of which, 2997 (28.78%) exhibited at least one irAE. Among established immunogenomic factors, dendritic cells (DC) abundance showed the strongest correlation with irAEs risk, followed by tumor mutational burden (TMB). Further predictive accuracy was achieved by DC and TMB in combination with CD4⁺ naive T-cells abundance, and then validated in the small cell lung cancer cohort. Additionally, global screening of multiomics data identified 11 novel predictors of irAEs. Of these, IRF4 showed the highest correlation. Best predictive performance was observed in the IRF4 - TCL1A - SHC-pY317 trivariate model. Associations of IRF4 and TCL1A expression with irAEs development were verified in the melanoma cohort receiving immune checkpoint inhibitors. Collectively, pretreatment cellular and molecular irAEs-associated features as well as their combinations are identified regardless of cancer types. These findings may deepen our knowledge of irAEs pathogenesis and, ultimately, aid in early detection of high-risk patients and management of irAEs.

Reduced Satb1 expression predisposes CD4+ T conventional cells to Treg suppression and promotes transplant survival

Limiting CD4+ T cell responses is important to prevent solid organ transplant rejection. In a mouse model of costimulation blockade-dependent cardiac allograft tolerance, we previously reported that alloreactive CD4+ conventional T cells (Tconvs) develop dysfunction, losing proliferative capacity. In parallel, induction of transplantation tolerance is dependent on the presence of regulatory T cells (Tregs). Whether susceptibility of CD4+ Tconvs to Treg suppression is modulated during tolerance induction is unknown. We found that alloreactive Tconvs from transplant tolerant mice had augmented sensitivity to Treg suppression when compared with memory T cells from rejector mice and expressed a transcriptional profile distinct from these memory T cells, including down-regulated expression of the transcription factor Special AT-rich sequence-binding protein 1 (Satb1). Mechanistically, Satb1 deficiency in CD4+ T cells limited their expression of CD25 and IL-2, and addition of Tregs, which express higher levels of CD25 than Satb1-deficient Tconvs and successfully competed for IL-2, resulted in greater suppression of Satb1-deficient than wild-type Tconvs in vitro. In vivo, Satb1-deficient Tconvs were more susceptible to Treg suppression, resulting in significantly prolonged skin allograft survival. Overall, our study reveals that transplantation tolerance is associated with Tconvs' susceptibility to Treg suppression, via modulated expression of Tconv-intrinsic Satb1. Targeting Satb1 in the context of Treg-sparing immunosuppressive therapies might be exploited to improve transplant outcomes.

Activation and regulation of alloreactive T cell immunity in solid organ transplantation

Transplantation is the only curative treatment for patients with kidney failure but it poses unique immunological challenges that must be overcome to prevent allograft rejection and ensure long-term graft survival. Alloreactive T cells are important contributors to graft rejection, and a clearer understanding of the mechanisms by which these cells recognize donor antigens - through direct, indirect or semi-direct pathways - will facilitate their therapeutic targeting. Post-T cell priming rejection responses can also be modified by targeting pathways that regulate T cell trafficking, survival cytokines or innate immune activation. Moreover, the quantity and quality of donor-reactive memory T cells crucially shape alloimmune responses. Of note, many fundamental concepts in transplant immunology have been derived from models of infection. However, the programmed differentiation of allograft-specific T cell responses is probably distinct from that of pathogen-elicited responses, owing to the dearth of pathogen-derived innate immune activation in the transplantation setting. Understanding the fundamental (and potentially unique) immunological pathways that lead to allograft rejection is therefore a prerequisite for the rational development of therapeutics that promote transplantation tolerance.

Long-range phasing of dynamic, tissue-specific and allele-specific regulatory elements

Epigenomic maps identify gene regulatory elements by their chromatin state. However, prevailing short-read sequencing methods cannot effectively distinguish alleles, evaluate the interdependence of elements in a locus or capture single-molecule dynamics. Here, we apply targeted nanopore sequencing to profile chromatin accessibility and DNA methylation on contiguous ~100-kb DNA molecules that span loci relevant to development, immunity and imprinting. We detect promoters, enhancers, insulators and transcription factor footprints on single molecules based on exogenous GpC methylation. We infer relationships among dynamic elements within immune loci, and order successive remodeling events during T cell stimulation. Finally, we phase primary sequence and regulatory elements across the H19/IGF2 locus, uncovering primate-specific features. These include a segmental duplication that stabilizes the imprinting control region and a noncanonical enhancer that drives biallelic IGF2 expression in specific contexts. Our study advances emerging strategies for phasing gene regulatory landscapes and reveals a mechanism that overrides IGF2 imprinting in human cells.

METTL3 inhibition reduces N6 -methyladenosine levels and prevents allogeneic CD4+ T-cell responses

Alloreactive CD4+ T cells play a central role in allograft rejection. However, the post-transcriptional regulation of the effector program in alloreactive CD4+ T cells remains unclear. N6 -methyladenosine (m6 A) RNA modification is involved in various physiological and pathological processes. Herein, we investigated whether m6 A methylation plays a role in the allogeneic T-cell effector program. m6 A levels of CD4+ T cells from spleens, draining lymph nodes and skin allografts were determined in a skin transplantation model. The effects of a METTL3 inhibitor (STM2457) on CD4+ T-cell characteristics including proliferation, cell cycle, cell apoptosis and effector differentiation were determined after stimulation of polyclonal and alloantigen-specific (TEa; CD4+ T cells specific for I-Eα52-68 ) CD4+ T cells with α-CD3/α-CD28 monoclonal antibodies and cognate CB6F1 alloantigen, respectively. We found that graft-infiltrating CD4+ T cells expressed high m6 A levels. Administration of STM2457 reduced m6 A levels, inhibited T-cell proliferation and suppressed effector differentiation of polyclonal CD4+ T cells. Alloreactive TEa cells challenged with 40 μm STM2457 exhibited deficits in T-cell proliferation and T helper type 1 cell differentiation, a cell cycle arrest in the G0 phase and elevated cell apoptosis. Moreover, these impaired T-cell responses were associated with the diminished expression levels of transcription factors Ki-67, c-Myc and T-bet. Therefore, METTL3 inhibition reduces the expression of several key transcriptional factors for the T-cell effector program and suppresses alloreactive CD4+ T-cell effector function and differentiation. Targeting m6 A-related enzymes and molecular machinery in CD4+ T cells represents an attractive therapeutic approach to prevent allograft rejection.

Single-Cell RNA sequencing reveals immune cell dynamics and local intercellular communication in acute murine cardiac allograft rejection

Rationale: Transplant rejection is a major impediment to long-term allograft survival, in which the actions of immune cells are of fundamental importance. However, the immune cell dynamics and local intercellular communication of acute cardiac allograft rejection are not completely clear.

Methods: Here we performed single-cell RNA sequencing on CD45⁺ immune cells isolated from cardiac grafts and spleens in a model of murine heterotopic heart transplantation. Moreover, we applied unsupervised clustering, functional enrichment analysis, cell trajectory construction and intercellular communication analysis to explore the immune cell dynamics and local intercellular communication of acute cardiac allograft rejection at single-cell level. The effect of CXCR3 antagonist and neutralizing antibody against its ligand on allograft rejection and T cell function was evaluated in murine heart transplantation model.

Results: We presented the immune cell landscape of acute murine cardiac allograft rejection at single-cell resolution, and uncovered the functional characteristics and differentiation trajectory of several alloreactive cell subpopulations, including Mki67^hi CTLs, Ccl5^hi CTLs, activated Tregs and alloreactive B cells. We demonstrated local intercellular communication and revealed the upregulation of CXCR3 and its ligands in cardiac allografts. Finally, CXCR3 blockade significantly suppressed acute cardiac allograft rejection and inhibited the alloreactive T cell function.

Conclusions: These results provide a new insight into the immune cell dynamics and local intercellular communication of acute cardiac allograft rejection, and suggest CXCR3 pathway may serve as a potential therapeutic target for transplant rejection.

Suppression of FOXP3 expression by the AP-1 family transcription factor BATF3 requires partnering with IRF4

FOXP3 is the lineage-defining transcription factor for Tregs, a cell type critical to immune tolerance, but the mechanisms that control FOXP3 expression in Tregs remain incompletely defined, particularly as it relates to signals downstream of TCR and CD28 signaling. Herein, we studied the role of IRF4 and BATF3, two transcription factors upregulated upon T cell activation, to the conversion of conventional CD4+ T cells to FOXP3+ T cells (iTregs) in vitro. We found that IRF4 must partner with BATF3 to bind to a regulatory region in the Foxp3 locus where they cooperatively repress FOXP3 expression and iTreg induction. In addition, we found that interactions of these transcription factors are necessary for glycolytic reprogramming of activated T cells that is antagonistic to FOXP3 expression and stability. As a result, Irf4 KO iTregs show increased demethylation of the critical CNS2 region in the Foxp3 locus. Together, our findings provide important insights how BATF3 and IRF4 interactions integrate activating signals to control CD4+ cell fate decisions and govern Foxp3 expression.

B-cell response in solid organ transplantation

The transcriptional regulation of B-cell response to antigen stimulation is complex and involves an intricate network of dynamic signals from cytokines and transcription factors propagated from T-cell interaction. Long-term alloimmunity, in the setting of organ transplantation, is dependent on this B-cell response, which does not appear to be halted by current immunosuppressive regimens which are targeted at T cells. There is emerging evidence that shows that B cells have a diverse response to solid organ transplantation that extends beyond plasma cell antibody production. In this review, we discuss the mechanistic pathways of B-cell activation and differentiation as they relate to the transcriptional regulation of germinal center B cells, plasma cells, and memory B cells in the setting of solid organ transplantation.

Construction and analysis of a ceRNA network and patterns of immune infiltration in chronic rhinosinusitis with nasal polyps: based on data mining and experimental verification

Recent studies have revealed the significant role of the competing endogenous RNA (ceRNA) network in human diseases. However, systematic analysis of the ceRNA mechanism in chronic rhinosinusitis with nasal polyps (CRSwNP) is limited. In this study, we constructed a competitive endogenous RNA (ceRNA) network and identified a potential regulatory axis in CRSwNP based on bioinformatics analysis and experimental verification. We obtained lncRNA, miRNA, and mRNA expression profiles from the Gene Expression Omnibus. After analysis of CRSwNP patients and the control groups, we identified 565 DE-lncRNAs, 23 DE-miRNAs, and 1799 DE-mRNAs by the DESeq2 R package or limma R package. Enrichment analysis of 1799 DE-mRNAs showed that CRSwNP was associated with inflammation and immunity. Moreover, we identified 21 lncRNAs, 8 miRNAs and 8 mRNAs to construct the lncRNA-miRNA-mRNA ceRNA network. A potential MIAT/miR-125a/IRF4 axis was determined according to the degree and positive correlation between a lncRNA and its competitive endogenous mRNAs. The GSEA results suggested that IRF4 may be involved in immune cell infiltration. The validation of another dataset confirmed that MIAT and IRF4 were differentially expressed between the CRSwNP and control groups. The area under the ROC curve (AUC) of MIAT and IRF4 was 0.944. The CIBERSORT analysis revealed that eosinophils and M2 macrophages may be involved in the CRSwNP process. MIAT was correlated with dendritic cells and M2 macrophages, and IRF4 was correlated with dendritic cells. Finally, to validate the key genes, we performed in-silico validation using another dataset and experimental validation using immunohistochemistry, immunofluorescence, and Western blot. In summary, the constructed novel MIAT/miR-125a/IRF4 axis may play a critical role in the development and progression of CRSwNP. We believe that the ceRNA network and immune cell infiltration could offer further insight into novel molecular therapeutic targets for CRSwNP.

Ablation of BATF Alleviates Transplant Rejection via Abrogating the Effector Differentiation and Memory Responses of CD8+ T Cells

Allogeneic CD8⁺ T cells are prominently involved in allograft rejection, but how their effector differentiation and function are regulated at a transcriptional level is not fully understood. Herein, we identified the basic leucine zipper ATF-like transcription factor (BATF) as a key transcription factor that drives the effector program of allogeneic CD8⁺ T cells. We found that BATF is highly expressed in graft-infiltrating CD8⁺ T cells, and its ablation in CD8⁺ T cells significantly prolonged skin allograft survival in a fully MHC-mismatched transplantation model. To investigate how BATF dictates allogeneic CD8⁺ T cell response, BATF^-/- and wild-type (WT) CD8⁺ T cells were mixed in a 1:1 ratio and adoptively transferred into B6.Rag1^-/- mice 1 day prior to skin transplantation. Compared with WT CD8⁺ T cells at the peak of rejection response, BATF^-/- CD8⁺ T cells displayed a dysfunctional phenotype, evident by their failure to differentiate into CD127^-KLRG1⁺ terminal effectors, impaired proliferative capacity and production of pro-inflammatory cytokines/cytotoxic molecules, and diminished capacity to infiltrate allografts. In association with the failure of effector differentiation, BATF^-/- CD8⁺ T cells largely retained TCF1 expression and expressed significantly low levels of T-bet, TOX, and Ki67. At the memory phase, BATF-deficient CD8⁺ T cells displayed impaired effector differentiation upon allogeneic antigen re-stimulation. Therefore, BATF is a critical transcriptional determinant that governs the terminal differentiation and memory responses of allogeneic CD8⁺ T cells in the transplantation setting. Targeting BATF in CD8⁺ T cells may be an attractive therapeutic approach to promote transplant acceptance.

CD39 and CD326 Are Bona Fide Markers of Murine and Human Plasma Cells and Identify a Bone Marrow Specific Plasma Cell Subpopulation in Lupus

Antibody-secreting cells (ASCs) contribute to immunity through production of antibodies and cytokines. Identification of specific markers of ASC would allow selective targeting of these cells in several disease contexts. Here, we performed an unbiased, large-scale protein screening, and identified twelve new molecules that are specifically expressed by murine ASCs. Expression of these markers, particularly CD39, CD81, CD130, and CD326, is stable and offers an improved resolution for ASC identification. We accessed their expression in germ-free conditions and in T cell deficient mice, showing that at least in part their expression is controlled by microbial- and T cell-derived signals. Further analysis of lupus mice revealed the presence of a subpopulation of LAG-3– plasma cells, co-expressing high amounts of CD39 and CD326 in the bone marrow. This population was IgM+ and correlated with IgM anti-dsDNA autoantibodies in sera. Importantly, we found that CD39, CD81, CD130, and CD326 are also expressed by human peripheral blood and bone marrow ASCs. Our data provide innovative insights into ASC biology and function in mice and human, and identify an intriguing BM specific CD39++CD326++ ASC subpopulation in autoimmunity.

Genetically targeting the BATF family transcription factors BATF and BATF3 in the mouse abrogates effector T cell activities and enables long-term heart allograft survival

T cells must be activated and become effectors first before executing allograft rejection, a process that is regulated by diverse signals and transcription factors. In this study, we studied the basic leucine zipper ATF-like transcription factor (BATF) family members in regulating T cell activities in a heart transplant model and found that mice deficient for both BATF and BATF3 (Batf-/- Batf3-/- mice) spontaneously accept the heart allografts long-term without tolerizing therapies. Similarly, adoptive transfer of wild type T cells into Rag1-/- hosts induced prompt rejection of heart and skin allografts, whereas the Batf-/- Batf3-/- T cells failed to do so. Analyses of graft-infiltrating cells showed that Batf-/- Batf3-/- T cells infiltrate the graft but fail to acquire an effector phenotype (CD44high KLRG1+ ). Co-transfer experiments in a T cell receptor transgenic TEa model revealed that the Batf-/- Batf3-/- T cells fail to expand in vivo, retain a quiescent phenotype (CD62L+ CD127+ ), and unable to produce effector cytokines to alloantigen stimulation, which contrasted sharply to that of wild type T cells. Together, our data demonstrate that the BATF and BATF3 are critical regulators of T effector functions, thus making them attractive targets for therapeutic interventions in transplant settings.

In vivo genome-wide CRISPR screens identify SOCS1 as intrinsic checkpoint of CD4+ TH1 cell response

[Figure: see text].

Identification of HIV-1-specific cascaded microRNA-mRNA regulatory relationships by parallel mRNA and microRNA expression profiling with AIDS patients after antiviral treatment

BACKGROUND

The pathogenesis of human immunodeficiency virus 1 (HIV-1) infection is so complex that have not been clearly defined, despite intensive efforts have been made by many researchers. MicroRNA (miRNA) as regulation factor in various human diseases may influence the course of HIV-1 infection by targeting mRNAs. Thus, studies combining transcription of posttranscriptional miRNA regulation are required.

METHODS

With the purpose of identifying cascaded miRNA-mRNA regulatory relationships related to HIV infection in gene level, the parallel miRNA, and mRNA expression profiles were analyzed to select differential expressed miRNAs and mRNAs. Then, miRNA-mRNA interactions were predicted using 3 data sources and Pearson correlation coefficient was calculated based on the gene expression level for accuracy improvement. Furthermore, the calculation of the regulatory impact factors was conducted to reveal crucial regulators in HIV-1 infection. To give further insight into these transcription factor (TF) regulators, the differentially co-expression analysis was conducted to identify differentially co-expressed links and differential co-expressed genes and the co-expression gene modules were identified using a threshold-based hierarchical clustering method, then modules were combined into a miRNA-TF-mRNA network.

RESULTS

A total of 69,126 differentially co-expressed links and 626 differential co-expressed genes were identified. Functional enrichment analysis indicated that these co-expressed genes were significantly involved in immune response and apoptosis. Moreover, according to regulatory impact factors, 5 most influential TFs and miRNA in HIV-1 infection were identified and miRNA-TF-mRNA regulatory networks were built during the computing process.

CONCLUSIONS

In our study, a set of integrated methods was generated to identify important regulators and miRNA-TF-mRNA interactions. Parallel profiling analysis of the miRNAs and mRNAs expression of HIV/acquired immunodeficiency syndrome (AIDS) patients after antiretroviral therapy indicated that some regulators have wide impact on gene regulation and that these regulatory elements may bear significant implications on the underlying molecular mechanism and pathogenesis of AIDS occurrence.

CD4 T-Cell Exhaustion: Does It Exist and What Are Its Roles in Cancer?

In chronic infections and in cancer, persistent antigen stimulation under suboptimal conditions can lead to the induction of T-cell exhaustion. Exhausted T cells are characterized by an increased expression of inhibitory markers and a progressive and hierarchical loss of function. Although cancer-induced exhaustion in CD8 T cells has been well-characterized and identified as a therapeutic target (i.e., via checkpoint inhibition), in-depth analyses of exhaustion in other immune cell types, including CD4 T cells, is wanting. While perhaps attributable to the contextual discovery of exhaustion amidst chronic viral infection, the lack of thorough inquiry into CD4 T-cell exhaustion is particularly surprising given their important role in orchestrating immune responses through T-helper and direct cytotoxic functions. Current work suggests that CD4 T-cell exhaustion may indeed be prevalent, and as CD4 T cells have been implicated in various disease pathologies, such exhaustion is likely to be clinically relevant. Defining phenotypic exhaustion in the various CD4 T-cell subsets and how it influences immune responses and disease severity will be crucial to understanding collective immune dysfunction in a variety of pathologies. In this review, we will discuss mechanistic and clinical evidence for CD4 T-cell exhaustion in cancer. Further insight into the derivation and manifestation of exhaustive processes in CD4 T cells could reveal novel therapeutic targets to abrogate CD4 T-cell exhaustion in cancer and induce a robust antitumor immune response.

Functional roles of graft-infiltrating lymphocytes during early-phase post-transplantation in mouse cardiac transplantation models

Immunological behavior of graft-infiltrating lymphocytes (GILs) determines the graft fate (i.e., rejection or acceptance). Nevertheless, the functional alloreactivity and the phenotype of GILs at various times during the early post-transplantation phase have not been fully elucidated. We examined the immunological activities of early-phase GILs using a murine model of cardiac transplantation. GILs from 120-h allografts, but not 72-h allografts, showed robust activation and produced proinflammatory cytokines. In particular, a significant increase in CD69⁺ T-bet⁺ Nur77⁺ T cells was detected in 120-h allografts. Furthermore, isolated GILs were used to reconstitute BALB/c Rag2^-/- γc^-/- (BRG) mice. BRG mice reconstituted with 120-h GILs displayed donor-specific immune reactivity and rejected donor strain cardiac allografts; conversely, 72-h GILs exhibited weak anti-donor reactivity and did not reject allografts. These findings were confirmed by re-transplantation of cardiac allografts into BRG mice at 72-h post-transplantation. Re-transplanted allografts continued to function for >100 days, despite the presence of CD3⁺ GILs. In conclusion, the immunological behavior of GILs considerably differs over time during the early post-transplantation phase. A better understanding of the functional role of early-phase GILs may clarify the fate determination process in the graft-site microenvironment.

Current Status of and Opinions on Heart Transplantation in China

The purpose of this review is to provide a comprehensive update on recent advances in heart transplantation in China. Despite advances in pharmacologic and device treatment of chronic heart failure, long-term morbidity and mortality remain high, and many patients progress to endstage heart failure. Heart transplantation has become standard treatment for selected patients with end-stage heart failure, though challenges still exist. However, multiple advances over the past few years will improve the survival and quality-of-life of heart transplant recipients. This article elaborates on the specific characteristics of heart transplantation in China, the current issues, development trends, and related experiences with heart transplantation in Wuhan Union Hospital.

IRF4 is Correlated with the Conversion to a Th17-Like Phenotype in Regulatory T Cells from the Malignant Pleural Effusion

Background

RORγt⁺Foxp3⁺ (Th17-like) Tregs are a plastic Treg subset implicated in immune-related diseases; however, the mechanism of Treg phenotypic transformation in malignant pleural effusion (MPE) has not been elucidated.

Methods

The percentage of CD4⁺CD25⁺Foxp3⁺Helios⁺ and RORγt⁺Foxp3⁺ Tregs from peripheral blood and pleural effusion mononuclear cells were measured. The level of interferon regulatory factor 4 (IRF4) mRNA expression was detected by quantitative real-time reverse transcription polymerase chain reaction. The effects of IRF4 on the induction of Tregs from patients with non-small cell lung cancer (NSCLC) were evaluated in vitro. Correlation assays between IRF4 expression and the frequency of RORγt⁺Foxp3⁺ Tregs were performed.

Results

The frequency of CD4⁺CD25⁺Foxp3⁺Helios⁺ Tregs and CD4⁺RORγt⁺ Th17 cells was both increased in the MPE of NSCLC patients. The group of double-positive Foxp3⁺RORγt⁺ Treg phenotype were identified in the pleural effusion. A significant increase in the frequency of Foxp3⁺RORγt⁺ Tregs was found in MPE compared with the non-malignant pleural effusion (NPE). Compared to NPE, the relative level of IRF4 expression was increased in the MPE. IRF4 expression was positively associated with the frequency of Foxp3⁺RORγt⁺ Tregs in the PE. In vitro, the level of Helios mRNA and protein expression was reduced in induced Tregs following IRF4 over-expression. Additionally, the level of RORγt protein expression was substantially increased. However, ectopic Helios expression in induced Tregs reversed the effects induced by enhanced IRF4 expression.

Conclusion

IRF4 may serve as a potential molecule that promotes the conversion of regulatory T cells from MPE to a Th17-like phenotype by modulating Helios.

Schrödinger's T Cells: Molecular Insights Into Stemness and Exhaustion

T cell stemness and exhaustion coexist as two key contrasting phenomena during chronic antigen stimulation, such as infection, transplant, cancer, and autoimmunity. T cell exhaustion refers to the progressive loss of effector function caused by chronic antigen exposure. Exhausted T (T_EX) cells highly express multiple inhibitory receptors and exhibit severe defects in cell proliferation and cytokine production. The term T cell stemness describes the stem cell-like behaviors of T cells, including self-renewal, multipotency, and functional persistence. It is well accepted that naïve and some memory T cell subsets have stem cell-like properties. When investigating the exhaustive differentiation of T cells in chronic infection and cancer, recent studies highlighted the stemness of "precursors of exhausted" T (T_PEX) cells prior to their terminal differentiation to T_EX cells. Clinically successful checkpoint blockades for cancer treatment appear to invigorate antitumor T_PEX cells but not T_EX cells. Here we discuss the transcriptional and epigenetic regulations of T cell stemness and exhaustion, with a focus on how systems immunology was and will be utilized to define the molecular basis underlying the transition of T_PEX to T_EX cells. We suggest a "stepwise model" of T cell stemness and exhaustion, in which loss of stemness and exhaustion progression are gradual multi-step processes. We provide perspectives on the research needed to define T cell stemness and exhaustion in the transplantation setting, in which allogenic T cells are also chronically exposed to alloantigens. A better understanding of T cell stemness and exhaustion will shed light on developing novel strategies for immunotherapies.

Aspirin Attenuates Cardiac Allograft Rejection by Inhibiting the Maturation of Dendritic Cells via the NF-κB Signaling Pathway

Background: Dendritic cells (DCs) serve as an important part of the immune system and play a dual role in immune response. Mature DCs can initiate immune response, while immature or semi-mature DCs induce immune hyporesponsiveness or tolerance. Previous studies have shown that aspirin can effectively inhibit the maturation of DCs. However, the protective effect of aspirin on acute cardiac allograft rejection has not been studied. The aim of this study was to elucidate the effect of aspirin exert on allograft rejection. Methods: The model of MHC-mismatched (BALB/c to B6 mice) heterotopic heart transplantation was established and administered intraperitoneal injection with aspirin. The severity of allograft rejection, transcriptional levels of cytokines, and characteristics of immune cells were assessed. Bone marrow-derived dendritic cells (BMDCs) were generated with or without aspirin. The function of DCs was determined via mixed lymphocyte reaction (MLR). The signaling pathway of DCs was detected by Western blotting. Results: Aspirin significantly prolonged the survival of cardiac allograft in mouse, inhibited the production of pro-inflammatory cytokines and the differentiation of effector T cells (Th1 and Th17), as well as promoted the regulatory T cells (Treg). The maturation of DCs in the spleen was obviously suppressed with aspirin treatment. In vitro, aspirin decreased the activation of NF-κB signaling of DCs, as well as impeded MHCII and co-stimulatory molecules (CD80, CD86, and CD40) expression on DCs. Moreover, both the pro-inflammatory cytokines and function of DCs were suppressed by aspirin. Conclusion: Aspirin inhibits the maturation of DCs through the NF-κB signaling pathway and attenuates acute cardiac allograft rejection.

Immunological exhaustion: How to make a disparate concept operational?

In this essay, we show that 3 distinct approaches to immunological exhaustion coexist and that they only partially overlap, generating potential misunderstandings. Exploring cases ranging from viral infections to cancer, we propose that it is crucial, for experimental and therapeutic purposes, to clarify these approaches and their interconnections so as to make the concept of exhaustion genuinely operational.

Ablation of Survivin in T Cells Attenuates Acute Allograft Rejection after Murine Heterotopic Heart Transplantation by Inducing Apoptosis

Although studies in oncology have well explored the pharmacological effects of Birc5, little is known about its role in allogeneic T-cell responses. Therefore, the present study used a mouse model of acute heart allograft rejection to investigate the protective effect and mechanism of conditional knockout of Birc5 in T cells. Survivin (encoded by Birc5) was up-regulated in T cells activated in vivo and in vitro. Deletion of Birc5 in T cells attenuated acute heart allograft rejection by reducing the ratio of effector to naive T cells and Th1 to Tregs. In addition, deletion of Birc5 had no noticeable effect on proliferation but on apoptosis and the secretion of IFN-γ. The results revealed a significant increase in the percentage of Annexin V positive CD4⁺ T cells in the Birc5^-/- group, compared to the WT. Moreover, there was significant increase in early apoptotic alloreactive T cells in Birc5^-/- mice and this was partly mediated by caspase-3. Furthermore, treatment with YM155 inhibited acute heart allograft rejection in vivo and increased T-cell apoptosis in healthy human PBMCs in vitro. The results highlight a potential therapeutic target for the prevention and treatment of acute transplant rejection.

Arsenic Trioxide Combining Leflunomide Activates Nrf2-ARE-HO-1 Signaling Pathway and Protects Heart Xenografts

OBJECTIVE

To investigate the molecular mechanisms underlying the effects of arsenic trioxide (As₂O₃) in combination with leflunomide on the hamster-to-rat heart xenotransplant.

METHODS

Transplantation of LVG hamster hearts to Lewis rats was performed by anastomosis of vessels in the neck using end-to-end anastomosis with a non-suture cuff technique. Four groups of recipient rats (n=6 in each) were treated with normal saline (control), As₂O₃ [5 mg/(kg·day) intraperitoneally], leflunomide [5 mg/(kg·d) orally], or leflunomide [5 mg/(kg·d)+As₂O₃ [5 mg/(kg·d)] in combination. Donor hearts and/or rat spleens were harvested and analyzed 4 days after transplantation. Quantitative reverse-transcription polymerase chain reaction and Western blot analysis were performed to detect the expression of the nuclear factor erythroid-derived factor 2-related factor (Nrf2) and its target gene heme oxygenase-1 (HO-1), Treg cell marker fork-head Box P3 (FOXP3), apoptosis-associated proteins Bcl-2, Bax, and cleaved caspase-3. Immunohistochemical staining was used to detect the levels of inflammatory natural killer cell and macrophage infiltration, intercellular cell adhesion molecule-1 (ICAM-1) and complement C3.

RESULTS

Expression of Nrf2-ARE-HO-1 signaling pathway was upregulated in heart xenografts in rats treated with As₂O₃ plus leflunomide compared with control rats or rats treated with either drug alone (P<0.01), and this was accompanied by an increased Treg cells in the recipient rat spleen (P<0.01). In contrast, the expressions of Bax, cleaved caspase-3, ICAM-1, and complement C3, and infiltration of inflammatory cells in the xenografts were inhibited by As₂O₃ plus leflunomide treatment (P<0.01).

CONCLUSION

Combination treatment with As₂O₃ and leflunomide protected hamster heart-xenografts in recipient rats.

Transgenic Expression of a Mutant Ribonuclease Regnase-1 in T Cells Disturbs T Cell Development and Functions

Regnase-1 is an RNA-binding protein with ribonuclease activities, and once induced it controls diverse immune responses by degrading mRNAs that encode inflammatory cytokines and costimulatory molecules, thus exerting potent anti-inflammatory functions. However, Regnase-1 is extremely sensitive to degradation by proteases and therefore short-lived. Here, we constructed a mutant Regnase-1 that is resistant to degradation and expressed this mutant in vivo as a transgene specifically in T cells. We found that the mutant Regnase-1 transgenic mice exhibited profound lymphopenia in the periphery despite grossly normal spleen and lymph nodes, and spontaneously accepted skin allografts without any treatment. Mechanistic studies showed that in the transgenic mice thymic T cell development was disrupted, such that most of the developing thymocytes were arrested at the double positive stage, with few mature CD4⁺ and CD8⁺ T cells in the thymus and periphery. Our findings suggest that interfering with the dynamic Regnase-1 expression in T cells disrupts T cell development and functions and further studies are warranted to uncover the mechanisms involved.

IRF4 ablation in B cells abrogates allogeneic B cell responses and prevents chronic transplant rejection

BACKGOUND

B cells contribute to chronic transplant rejection by producing donor-specific antibodies and promoting T cell response, but how these processes are regulated at the transcriptional level remains unclear. Herein, we investigate the role of transcription factor interferon regulatory factor 4 (IRF4) in controlling B cell response during chronic transplant rejection.

METHODS

We generated the Irf4^gfp reporter mice to determine IRF4 expression in B cell lineage. We then used mice with B cell-specific IRF4 deletion to define the role of IRF4 in B cell response after NP-KLH immunization or allogeneic heart transplantation. In particular, graft survival and histology, as well as B and T cell responses, were evaluated after transplantation.

RESULTS

IRF4 is dynamically expressed at different stages of B cell development and is absent in germinal center (GC) B cells. However, IRF4 ablation in the B cell lineage primarily eliminates GC B cells in both naïve and NP-KLH immunized mice. In the transplantation setting, IRF4 functions intrinsically in B cells and governs allogeneic B cell responses at multiple levels, including GC B cell generation, plasma cell differentiation, donor-specific antibody production, and support of T cell response. B cell-specific IRF4 deletion combined with transient CTLA4-Ig treatment abrogates acute and chronic cardiac allograft rejection in naïve recipient mice but not in donor skin-sensitized recipients.

CONCLUSIONS

B cells require IRF4 to mediate chronic transplant rejection. IRF4 ablation in B cells abrogates allogeneic B cell responses and may also inhibit the ability of B cells to prime allogenic T cells. Targeting IRF4 in B cells represents a potential therapeutic strategy for eliminating chronic transplant rejection.

From the Immune Profile to the Immunoscore: Signatures for Improving Postsurgical Prognostic Prediction of Pancreatic Neuroendocrine Tumors

OBJECTIVE

Immune infiltration plays an important role in tumor development and progression and shows promising prognostic value in numerous tumors. In this study, we aimed to identify the role of immune infiltration in pancreatic neuroendocrine tumors (Pan-NETs) and to establish an Immunoscore system to improve the prediction of postsurgical recurrence-free survival.

METHODS

To derive transcriptional signatures and deconvolute specific immune populations, two GEO datasets containing 158 Pan-NET patients were reanalyzed to summarize the immune infiltration landscape and identify immune-related signatures. Using real-time reverse transcription-polymerase chain reaction, immunofluorescence and immunochemistry methods, candidate signatures were further detected. The least absolute shrinkage and selection operator (LASSO) logistic regression model used statistically significant survival predicators in the training cohort (n=125) to build an Immunoscore system. The prognostic and predictive accuracy was validated in an external independent cohort of 77 patients.

RESULTS

The immune infiltration profile in Pan-NETs showed significant heterogeneity, among which accumulated immune cells, T lymphocytes and macrophages were predominant. Fourteen statistically significant immune-related signatures were further identified in the screening cohort. The Immunoscore system for Pan-NETs (ISpnet) consisting of six immune features (CCL19, IL-16, CD163, IRF4, CD8PT and CD8IT) was constructed to classify patients as high and low risk in the training cohort (cutoff value = 2.14). Low-risk patients demonstrated longer 5-year recurrence-free survival (HR, 0.061; 95% CI, 0.026 to 0.14; p < 0.0001), with fewer recurrences and better prognoses. To predict the individual risk of recurrence, a nomogram incorporating both immune signatures and clinicopathological characteristics was developed.

CONCLUSION

Our model, ISpnet, captures immune feature-associated prognostic indicators in Pan-NETs and represents the first immune feature-based score for the postsurgical prognostic prediction. The nomogram based on the ISpnet and independent clinical risk factors might facilitate decision-making regarding early recurrence risk monitoring, identify high-risk patients in need of adjuvant therapy, and provide auxiliary guidance for patients with Pan-NETs that may benefit from immunotherapy in clinical trials.

T reg-specific insulin receptor deletion prevents diet-induced and age-associated metabolic syndrome

Adipose tissue (AT) regulatory T cells (T regs) control inflammation and metabolism. Diet-induced obesity causes hyperinsulinemia and diminishes visceral AT (VAT) T reg number and function, but whether these two phenomena were mechanistically linked was unknown. Using a T reg–specific insulin receptor (Insr) deletion model, we found that diet-induced T reg dysfunction is driven by T reg–intrinsic insulin signaling. Compared with Foxp3^cre mice, after 13 wk of high-fat diet, Foxp3^creInsr^fl/fl mice exhibited improved glucose tolerance and insulin sensitivity, effects associated with lower AT inflammation and increased numbers of ST2⁺ T regs in brown AT, but not VAT. Similarly, Foxp3^creInsr^fl/fl mice were protected from the metabolic effects of aging, but surprisingly had reduced VAT T regs and increased VAT inflammation compared with Foxp3^cre mice. Thus, in both diet- and aging-associated hyperinsulinemia, excessive Insr signaling in T regs leads to undesirable metabolic outcomes. Ablation of Insr signaling in T regs represents a novel approach to mitigate the detrimental effects of hyperinsulinemia on immunoregulation of metabolic syndrome.

The Role of T Cell Receptor Signaling in the Development of Type 1 Diabetes

T cell receptor (TCR) signaling influences multiple aspects of CD4⁺ and CD8⁺ T cell immunobiology including thymic development, peripheral homeostasis, effector subset differentiation/function, and memory formation. Additional T cell signaling cues triggered by co-stimulatory molecules and cytokines also affect TCR signaling duration, as well as accessory pathways that further shape a T cell response. Type 1 diabetes (T1D) is a T cell-driven autoimmune disease targeting the insulin producing β cells in the pancreas. Evidence indicates that dysregulated TCR signaling events in T1D impact the efficacy of central and peripheral tolerance-inducing mechanisms. In this review, we will discuss how the strength and nature of TCR signaling events influence the development of self-reactive T cells and drive the progression of T1D through effects on T cell gene expression, lineage commitment, and maintenance of pathogenic anti-self T cell effector function.

The Next-Generation Immune Checkpoint LAG-3 and Its Therapeutic Potential in Oncology: Third Time's a Charm

The blockade of immune checkpoints (ICPs), such as cytotoxic T lymphocyte associated protein-4 (CTLA-4) and programmed death-1 (PD-1) and its ligand (PD-L1), has propelled the field of immuno-oncology into its current era. Drugs targeting these ICPs have improved clinical outcome in a number of patients with solid and hematological cancers. Nonetheless, some patients have no benefit from these ICP-blocking therapies. This observation has instigated research into alternative pathways that are responsible for the escape of cancer cells from anti-cancer immune responses. From this research, a number of molecules have emerged as promising therapeutic targets, including lymphocyte activating gene-3 (LAG-3), a next-generation ICP. We will review the current knowledge on the biological activity of LAG-3 and linked herewith its expression on activated immune cells. Moreover, we will discuss the prognostic value of LAG-3 and how LAG-3 expression in tumors can be monitored, which is an aspect that is of utmost importance, as the blockade of LAG-3 is actively pursued in clinical trials.

CD4+ T cell exhaustion leads to adoptive transfer therapy failure which can be prevented by immune checkpoint blockade

Cytotoxic CD8⁺ T cell exhaustion is one of the mechanisms underlying the tumor immune escape. The paradigm-shifting immune checkpoint therapy can mitigate CD8⁺ T lymphocyte exhaustion, reinvigorate the anticancer immunity, and achieve durable tumor regression for some patients. Emerging evidence indicates that CD4⁺ T lymphocytes also have a critical role in anticancer immunity, either by directly applying cytotoxicity toward cancer cells or as a helper to augment CD8⁺ T cell cytotoxicity. Whether anticancer CD4⁺ T lymphocytes undergo exhaustion during immunotherapy of solid tumors remains unknown. Here we report that melanoma antigen TRP-1/gp75-specific CD4⁺ T lymphocytes exhibit an exhaustion phenotype after being adoptively transferred into mice bearing large subcutaneous melanoma. Exhaustion of these CD4⁺ T lymphocytes is accompanied with reduced cytokine release and increased expression of inhibitory receptors, resulting in loss of tumor control. Importantly, we demonstrate that PD-L1 immune checkpoint blockade can prevent exhaustion, induce proliferation of the CD4⁺ T lymphocytes, and consequently prevent tumor recurrence. Therefore, when encountering an excessive amount of tumor antigens, tumor-reactive CD4⁺ T lymphocytes also enter the exhaustion state, which can be prevented by immune checkpoint blockade. Our results highlight the importance of tumor-specific CD4⁺ T lymphocytes in antitumor immunity and suggest that the current immune checkpoint blockade therapy may achieve durable anticancer efficacy by rejuvenating both tumor antigen-specific CD8⁺ T lymphocytes and CD4⁺ T lymphocytes.

Adoptive CD8+ T cell therapy generates immunological memory to inhibit melanoma metastasis

Adoptive T cell therapy has emerged as a promising treatment for cancer. However, it is unknown whether adoptively transferred anti-tumor T cells can form immunological memory and provide continuous protection against cancer metastasis. Herein, we used TCR transgenic Pmel-1 CD8⁺ T cells as a model to investigate whether early transferred Pmel-1 CD8⁺ T cells can generate immunological memory to prevent later melanoma metastasis. Upon stimulation with the cognate melanoma-associated hgp100 antigen, in vitro cultured Pmel-1 CD8⁺ T cells developed into effector T (Teff) cells that exhibited potent cytotoxic activity against B16F10 melanoma cells. Next, B16F10 melanoma cells were intravenously injected into C57BL/6 (B6) mice to establish experimental lung metastasis. In vitro generated Pmel-1 Teff cells were adoptively transferred into the mice on the same day of or three weeks prior to B16F10 cell inoculation. We found that adoptive Pmel-1 Teff cell therapy significantly inhibited the B16F10 lung metastasis and prolonged the animal survival. Importantly, Pmel-1 Teff cells transferred three weeks prior to tumor inoculation were as potent as the Pmel-1 Teff cells transferred on the same day in inhibiting melanoma metastasis. Hence, our results suggest that adoptive CD8⁺ Teff cell therapy generates immunological memory that continuously protect against melanoma metastasis.

Tissue distribution and developmental changes of interferon regulatory factors in chickens and effects of infectious bursal disease virus infection

Interferon regulatory factors (IRFs) are a family of transcription factors that play a role in a variety of biological processes including immune regulation of interferon and expression of inflammatory cytokines. However, the data on IRFs are rather limited in chickens. In the present study, qRT-PCR was used to study the tissue distribution of IRFs in chickens at D15 (the 15th day of raising) and developmental changes of all chIRFs (Chicken interferon regulatory factors) in BF from E15 (the 15th day of incubation) to D15. The effects of IBDV infection with chickens on the transcriptional level of chIRFs were also investigated. The results showed: (1) chIRF1 mRNA was expressed much more abundantly in intestinal tract, chIRF2, chIRF6, chIRF7, chIRF8 and chIRF10 distributed mainly in liver or/and kidney. The expression of chIRF5 was mainly in spleen and chIRF4 distributed uniquely abundantly in BF. (2) The mRNA expression levels of chIRF5, chIRF7, chIRF8 and chIRF10 was low before hatching of chicken and at D1 and increased significantly from D5 till to the experiment end and the fold change of chIRF5 at D10 and chIRF7 at D5 reached 41.0-fold and 15.7-fold compared to that of E15, respectively (P < 0.05). ChIRF4 mRNA level was always high during the whole experiment except for E15 and it was 11.9-fold at the highest time point than that of E15 (the lowest time point). (3) When chicken was infected with IBDV, the expression levels of chIRF2, chIRF7 and chIRF10 mRNA had the tendency of increasing first and then decreasing but they peaked at 1dpi, 2 dpi, and 3dpi, respectively. The expression of chIRF5 mRNA was suppressed obviously during the whole experiment stage in IBDV-infected chicken. And chIRF4 expression was up-regulated transitorily at 1dpi and then was suppressed on a very low level till to the experiment end. Conclusion: The chIRFs were constitutively expressed in different tissues examined and has tissue-specific expression. Of them, chIRF2, chIRF4, chIRF5, chIRF7, chIRF8 and chIRF10 were related closely with the development or immune response of BF, and when chicken was infected with IBDV, some of them were activated, earlier or later on, some of them were suppressed. These findings would help to sieve out a few antiviral chIRF candidate gene to improve the host's innate immune and provide a foundation of the further exploiting a new vaccine adjuvant.

LAG-3: from molecular functions to clinical applications

To prevent the destruction of tissues owing to excessive and/or inappropriate immune responses, immune cells are under strict check by various regulatory mechanisms at multiple points. Inhibitory coreceptors, including programmed cell death 1 (PD-1) and cytotoxic T lymphocyte antigen 4 (CTLA-4), serve as critical checkpoints in restricting immune responses against self-tissues and tumor cells. Immune checkpoint inhibitors that block PD-1 and CTLA-4 pathways significantly improved the outcomes of patients with diverse cancer types and have revolutionized cancer treatment. However, response rates to such therapies are rather limited, and immune-related adverse events are also observed in a substantial patient population, leading to the urgent need for novel therapeutics with higher efficacy and lower toxicity. In addition to PD-1 and CTLA-4, a variety of stimulatory and inhibitory coreceptors are involved in the regulation of T cell activation. Such coreceptors are listed as potential drug targets, and the competition to develop novel immunotherapies targeting these coreceptors has been very fierce. Among such coreceptors, lymphocyte activation gene-3 (LAG-3) is expected as the foremost target next to PD-1 in the development of cancer therapy, and multiple clinical trials testing the efficacy of LAG-3-targeted therapy are underway. LAG-3 is a type I transmembrane protein with structural similarities to CD4. Accumulating evidence indicates that LAG-3 is an inhibitory coreceptor and plays pivotal roles in autoimmunity, tumor immunity, and anti-infection immunity. In this review, we summarize the current understanding of LAG-3, ranging from its discovery to clinical application.