Treg-mediated Immune Suppression Research Articles

Establishment of an in vitro evaluation method for immunomodulatory functions of yeast strains.

Saccharomyces cerevisiae, a widely studied yeast known for its industrial applications, is increasingly recognized for its potential in immunomodulation. This study aimed to systematically analyze and compare the immune-modulating properties of various S. cerevisiae strains under controlled experimental conditions. Three essential signals crucial for immune response activation were evaluated to elucidate the immunological responses elicited by these strains, i.e., dendritic cells (DC) cytokine secretion profiles, maturation status, and T cell polarization. Analysis of DC cytokine secretion profiles and maturation status revealed that all tested yeast strains induced DC activation, characterized by significant IL-6 secretion and modest IL-10 induction, as well as upregulation of MHC II molecules. Additionally, strain-specific effects were observed, particularly, strain AJM109 and Y1383 uniquely enhanced CD86 and PD-L1 expression, respectively, suggesting differential impacts on DC co-stimulatory signaling. Furthermore, strain Y1383 showed a unique capacity to support Treg-mediated immune suppression, demonstrating its potential in immune tolerance induction. These findings underscore the complexity of S. cerevisiae-based immune modulation and emphasize the importance of standardized evaluation methods to distinguish their specific immunological effects.

Abstract 2485: A combined mregDC and Treg signature associates with antitumor efficacy of CCR4 antagonist tivumecirnon FLX475

Abstract Cancers evade immune surveillance through multiple mechanisms including the recruitment of immunosuppressive regulatory T cells (Treg). Tivumecirnon (formerly known as FLX475), a small molecule oral CCR4 antagonist under clinical evaluation, blocks the binding of CCR4 to its ligands CCL17 and CCL22 and thereby reduces Treg infiltration into the tumor microenvironment (TME). This relieves Treg-mediated immune suppression resulting in increased antitumor immunity. Our clinical study (NCT03674567) demonstrated that tivumecirnon can block the local accumulation of Treg in the TME and has clinical activity as monotherapy as well as in combination with pembrolizumab. In both mouse and human tumors, we identified a subset of tumor infiltrating dendritic cells (DC) producing high levels of CCL22, previously identified as mregDC, suggesting a potential role in the CCR4-dependent recruitment of Treg. To study the role of mregDC in the recruitment of Treg, non-clinical studies were performed. CD45+ immune cells from the TME of MB49 tumor bearing mice treated with tivumecirnon or vehicle and were analyzed by flow cytometry, scRNA-seq and CITE-seq. We confirmed that mregDC cells are the primary producer of CCL22 in the TME and that tivumecirnon treatment reduced the number of Treg cells in the TME and increased the percentage of IFN gamma and granzyme B expressing CD4+ T cells. Based on these findings we interrogated tumor biopsies from patients from our clinical study prior to (n = 33), and after approximately 6 weeks of treatment (n = 22, pre/post-treatment paired samples) with tivumecirnon +/- pembrolizumab. We performed RNAseq and compared to published biopsy data from anti-PD-1 treated patients. We found that higher mregDC + Treg signature levels at baseline significantly (p < 0.001) associated with response to tivumecirnon and pembrolizumab therapy. Importantly, analysis of published datasets revealed that higher baseline mregDC and Treg levels are not associated with response to anti-PD-1 monotherapy. Analysis of TCGA gene expression data demonstrated a positive correlation with mregDC and Treg cells across human tumor types, indicating a previously unknown relationship between these cell types. Further application of this mregDC and Treg signature to the TCGA dataset identified a subset of cancer types resistant to prior treatments that could potentially benefit from combinatorial treatment with tivumecirnon. Overall, this study demonstrated that inhibition of the CCR4 pathway using tivumecirnon can disrupt the immunosuppressive mregDC – Treg axis leading to enhanced antitumor activity. Furthermore, the levels of mregDC and Treg may be used as a biomarker for selection of patients more likely to respond to tivumecirnon in combination with anti-PD-1. Additional studies are required to confirm these results Citation Format: Adam Grant, Juraj Adamik, Jingtao Qiu, Jacob Wert, Molly Grandcolas, Scott Jacobson, Rakesh K. Goyal, William Ho, Shoji Ikeda, Marvin Au, Damian Trujillo, Michael Chisamore, Denise de Almeida Nagata, Mohsen S. Ghomi, Dirk G. Brockstedt, Paul D. Kassner, George Katibah. A combined mregDC and Treg signature associates with antitumor efficacy of CCR4 antagonist tivumecirnon FLX475 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2485.

Mitochondrial-Targeting Nanotrapper Captured Copper Ions to Alleviate Tumor Hypoxia for Amplified Photoimmunotherapy in Breast Cancer.

Hypoxia is a pervasive feature of solid tumors, which significantly limits the therapeutic effect of photodynamic therapy (PDT) and further influences the immunotherapy efficiency in breast cancer. However, the transient alleviation of tumor hypoxia fails to address the underlying issue of increased oxygen consumption, resulting from the rapid proliferation of tumor cells. At present, studies have found that the reduction of the oxygen consumption rate (OCR) by cytochrome C oxidase (COX) inhibition that induced oxidative phosphorylation (OXHPOS) suppression was able to solve the proposed problem. Herein, we developed a specific mitochondrial-targeting nanotrapper (I@MSN-Im-PEG), which exhibited good copper chelating ability to inhibit COX for reducing the OCR. The results proved that the nanotrapper significantly alleviated the hypoxic tumor microenvironment by copper chelation in mitochondria and enhanced the PDT effect in vitro and in vivo. Meanwhile, the nanotrapper improved photoimmunotherapy through both enhancing PDT-induced immunogenetic cell death (ICD) effects and reversing Treg-mediated immune suppression on 4T1 tumor-bearing mice. The mitochondrial-targeting nanotrapper provided a novel and efficacious strategy to enhance the PDT effect and amplify photoimmunotherapy in breast cancer.

CTLA-4 Blockade Results in the Enrichment of Proliferative CD56 dimCD16 + NK Cells Following Infusion of Haploidentical Donor Memory-like Natural Killer Cells Plus IL-15 Superagonist in a Phase 1 Trial

Introduction Regulatory T cells (Tregs) blunt anti-tumor responses of major immune effector cells including CD8 T cells and natural killer (NK) cells. Tregs constitutively express CTLA-4 and thus the use of ipilimumab, a CTLA-4 blocker can potentially overcome the Treg-mediated immune suppression. We (and others) have shown that a brief activation of conventional NK cells with the cytokine combination IL-12, IL-15, and IL-18 generates cytokine-induced memory-like (CIML) NK cells which exhibit enhanced anti-tumor responses, have a longer half-life (up to 90 vs ~12 days of conventional NK cells), and show promising activity in several early phase clinical trials. N-803 is an IL-15 super-agonist with a long half-life that preferentially activates and expands NK and CD8+ T cells without affecting Tregs, making it an ideal cytokine for combining with adoptive immunotherapy. In the current study, we hypothesized the use of ipilimumab (IPI) will abrogate Treg-mediated inhibition and thus allow enhanced proliferation, activation, and anti-tumor responses of the adoptively transferred CIML NK cells.To address this, we conducted a phase 1 trial of HLA-haploidentical CIML NK cells in combination with IPI and N-803 in patients with advanced head and neck cancer (HNC). Using flow cytometry and CITE-Seq on the banked peripheral blood samples, we performed an in-depth characterization of NK cells expanded following IPI pre-exposure and compared it to those who did not receive IPI. Methods We enrolled 10 patients with refractory HNC regardless of human papillomavirus (HPV) status who had prior platinum and immunotherapy (NCT04290546). All patients received lymphodepletion with fludarabine (25 mg/m 2 x 5 days) and cyclophosphamide (60 mg/kg x 2 days) during days -6 to -2 prior to haploidentical CIML NK cell infusion on day 0 (5-10 x 10 6 cells/kg=dose level 0) followed by N-803 (15 mcg/kg subcutaneously) starting on day +1 every 21-days for 4-doses. In cohort 2, patients received IPI (3 mg/kg) on day -7, no ipilimumab was given to the first 6 patients treated on the lead-in safety cohort 1. Flow cytometry using a custom NK cell panel was performed on samples collected on days +7, +14, +21, +28, +42, and +60 after CIML NK cell infusion. FlowSOM clustering was performed on NK cell markers. UMAP clustering was applied to CITE sequencing data acquired from samples collected on day +7 and day +28, and well-defined markers genes for each cluster were used to identify cell populations. NK cell function (cytotoxicity, IFNg, and CD107a) was assessed using flow-cytometry based assays. Results The median age of the patients was 58, 90% were men and 80% had oropharyngeal primaries. Mild CRS (grade 2 or lower) was observed in 60% of patients. No neurotoxicity or graft-versus-host disease was observed. Maximal expansion of NK cells occurred on day +7 following CIML NK cell infusion in 9/10 of patients. The single patient without NK cell expansion was found to have a donor-specific anti-HLA antibody. Day +7 NK cells exhibited upregulation of IFNg expression following cytokine restimulation as compared to resting NK cells. Tumor regression was observed in 50% of treated patients at day +30 based on RECIST v1.1 criteria. Patients who had tumor regression had an expansion of CD56 dimCD16 + NK cell clusters by day +14. IPI treated patients were noted to have a relative enrichment of CD16 + NK cell metaclusters at day +14 compared to no IPI patients (Figure 1A). At the time of maximal NK cell expansion, CITEseq defined NK cell clusters were dominant in both IPI and no IPI patients, but the proliferative gene sets were enriched in the IPI treated patient (Figure 1B). IPI exposure had no effect on the distribution of regulatory T cells or CD8 + T cell populations at day +28 compared to the no IPI patients. Conclusions The use of donor-derived CIML NK cells is safe and associated with tumor regression in patients with advanced HNC. The use of IPI was associated with the preferential expansion of CD16 + NK cell clusters that had enrichment of proliferative gene sets. Tumor regression was associated with CD56 dimCD16 + NK cell expansion. Further work is required to elucidate the mechanism by which IPI exposure is associated with the expansion of specific subsets of CIML NK cells.

Inhibition of TCR-MHC-II interactions abrogates Treg-mediated immune suppression and augments anti-tumor immunity.

Abstract CD4 +Foxp3 +Tregs play a non-redundant role in controlling autoimmunity. Continuous TCR signaling and the availability of exogenous IL-2 from CD4 +effectors regulate the size of the Treg pool and their suppressive function in the steady state. Homeostatic proliferation of Tregs and memory phenotype (MP) CD4 +Foxp3 −T cells depends on CD80/CD86-CD28 signaling. Acute blockade of TCR-MHC-II interactions in vivo by anti-MHC-II mAb significantly enhances memory phenotype (MP) Treg, CD4 +, and CD8 +T cell expansion by a CD28-dependent pathway. IL-15 trans presentation by APC also contributes to Treg, MP CD4 +and MP CD8 +proliferation following blockade of TCR-MHC-II interaction by a CD122-dependent pathway. Combined CD28 activation and IL-15 stimulation together with IL-2 deprivation secondary to MHCII-TCR blockade result in decreased expression of CD25, but enhancement of Foxp3 expression by Treg. In addition, Treg exhibit decreased pAKT/NFAT signaling, but enhanced pSTAT5/mTOR signaling. Mice transplanted with several different transplantable tumors manifest enhanced tumor immunity in the presence of MHCII-TCR inhibition. Our results demonstrate that in the absence of TCR-MHC-II interactions, Treg proliferate, but lose their identity and manifest disabled suppressor function resulting in enhanced innate and adaptive immunity against cancer progression. This work was supported by the Intramural Research Program of NIAID, NIH. This work was supported by the Intramural Research Program of NIAID, NIH.

Acidity-mediated induction of FoxP3+ regulatory T cells.

Glucose limitation and increased lactic acid levels are consequences of the elevated glycolytic activity of tumor cells, and constitute a metabolic barrier for the function of tumor infiltrating effector immune cells. The immune-suppressive functions of regulatory T cells (Tregs) are unobstructed in lactic-acid rich environments. However, the impact of lactic acid on the induction of Tregs remains unknown. We observed increased TGFβ-mediated induction of Forkhead box P3+ (FoxP3+ ) cells in the presence of extracellular lactic acid, in a glycolysis-independent, acidity-dependent manner. These CD4+ FoxP3+ cells expressed Treg-associated markers, including increased expression of CD39, and were capable of exerting suppressive functions. Corroborating these results in vivo, we observed that neutralizing the tumor pH by systemic administration of sodium bicarbonate (NaBi) decreased Treg abundance. We conclude that acidity augments Treg induction and propose that therapeutic targeting of acidity in the tumor microenvironment (TME) might reduce Treg-mediated immune suppression within tumors.

IL1R2 increases regulatory T cell population in the tumor microenvironment by enhancing MHC-II expression on cancer-associated fibroblasts

BackgroundRegulatory T cells (Treg) are an integral part of the tumor immune tolerance. Carcinoma-associated fibroblasts (CAFs) is a pivotal driver for accumulation of Treg cells in the tumor microenvironment (TME)....

Regulatory T cells: Their role in triple-negative breast cancer progression and metastasis.

Triple-negative breast cancer (TNBC) is an aggressive and immunogenic subtype of breast cancer. This tumorigenicity is independent of hormonal or HER2 pathways because of a lack of respective receptor expression. TNBC is extremely prone to drug resistance and early recurrence because of T-regulatory cell (Treg) infiltration into the tumor microenvironment (TME) in addition to other mechanisms like genomic instability. Tumor-infiltrating Tregs interact with both tumor and stromal cells as well as extracellular matrix components in the TME and induce an immune-suppressive phenotype. Hence, treatment of TNBC with conventional therapies remains challenging. Understanding the protective mechanism of Tregs in shielding TNBC from antitumor immune responses in the TME will pave the way for developing novel, immune-based therapeutics. The current review focuses on the role of tumor-infiltrating Tregs in tumor progression and metabolic reprogramming of the TME. The authors have extended their focus to oncotargeting Treg-mediated immune suppression in breast cancer. Because of its potential role in the TME, modulating Treg activity may provide a novel strategic intervention to combat TNBC. Both under laboratory conditions and in clinical trials, currently available anticancer drugs and natural therapeutics as potential agents for targeting Tregs are explored.

Treg-expressed CTLA-4 depletes CD80/CD86 by trogocytosis, releasing free PD-L1 on antigen-presenting cells

Foxp3-expressing CD4+CD25+ regulatory T cells (Tregs) constitutively and highly express the immune checkpoint receptor cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4), whose Treg-specific deficiency causes severe systemic autoimmunity. As a key mechanism of Treg-mediated suppression, Treg-expressed CTLA-4 down-regulates the expression of CD80/CD86 costimulatory molecules on antigen-presenting cells (APCs). Here, we show that Treg-expressed CTLA-4 facilitated Treg-APC conjugation and immune synapse formation. The immune synapses thus formed provided a stable platform whereby Tregs were able to deplete CD80/CD86 molecules on APCs by extracting them via CTLA-4-dependent trogocytosis. The depletion occurred even with Tregs solely expressing a mutant CTLA-4 form lacking the cytoplasmic portion required for its endocytosis. The CTLA-4-dependent trogocytosis of CD80/CD86 also accelerated in vitro and in vivo passive transfer of other membrane proteins and lipid molecules from APCs to Tregs without their significant reduction on the APC surface. Furthermore, CD80 down-regulation or blockade by Treg-expressed membrane CTLA-4 or soluble CTLA-4-immunoglobulin (CTLA-4-Ig), respectively, disrupted cis-CD80/programmed death ligand-1 (PD-L1) heterodimers and increased free PD-L1 on dendritic cells (DCs), expanding a phenotypically distinct population of CD80lo free PD-L1hi DCs. Thus, Tregs are able to inhibit the T cell stimulatory activity of APCs by reducing their CD80/CD86 expression via CTLA-4-dependent trogocytosis. This CD80/CD86 reduction on APCs is able to exert dual suppressive effects on T cell immune responses by limiting CD80/CD86 costimulation to naïve T cells and by increasing free PD-L1 available for the inhibition of programmed death-1 (PD-1)-expressing effector T cells. Blockade of CTLA-4 and PD-1/PD-L1 in combination may therefore synergistically hinder Treg-mediated immune suppression, thereby effectively enhancing immune responses, including tumor immunity.

Treg-expressed CTLA-4 depletes CD80/CD86 by trogocytosis, releasing free PD-L1 on antigen-presenting cells

Abstract Foxp3-expressing CD4+CD25+ regulatory T cells (Tregs) are engaged in the maintenance of immunological self-tolerance and homeostasis. They constitutively and highly express the immune checkpoint receptor CTLA-4, whose Treg-specific deficiency causes severe systemic autoimmunity. As a key mechanism of Treg-mediated suppression, CTLA-4 downregulates the expression of CD80/CD86 costimulatory ligands on antigen-presenting cells (APCs). Here we showed that CTLA-4 facilitated the immune synapse formation and conjugation of Tregs and APCs. These conjugates thus provided stable platforms whereby Tregs were able to deplete CD80/CD86 proteins on APCs by uptaking them via CTLA-4-dependent trogocytosis. The depletion occurred even with Tregs expressing a mutant CTLA-4 lacking the cytoplasmic portion required for its endocytosis. The CTLA-4-dependent trogocytosis of CD80/CD86 also accelerated in vitro and in vivo passive transfer of other membrane proteins and lipid molecules from APCs to Tregs without their significant reduction on the APC surface. Furthermore, CD80 downregulation or blockade by the Treg-expressed membrane CTLA-4 or its solubilized form, respectively, disrupted cis-CD80/PD-L1 heterodimers and increased free PD-L1 on dendritic cells. Taken together, Tregs can exert dual suppressive effects on T-cell immune responses by converting highly stimulatory (CD80highfree PD-L1low) DCs to non-stimulatory/inhibitory (CD80lowfree PD-L1high) DCs via CTLA-4-dependent trogocytosis. Immune checkpoint blockade therapies with the combination of anti-CTLA-4 and anti-PD-1/PD-L1 antibodies may therefore synergistically hinder Treg-mediated immune suppression, thereby effectively enhancing tumor immunity.

High-dose per Fraction Radiotherapy Induces Both Antitumor Immunity and Immunosuppressive Responses in Prostate Tumors.

The use of high-dose per fraction radiotherapy delivered as stereotactic body radiotherapy is a standard of care for prostate cancer. It is hypothesized that high-dose radiotherapy may enhance or suppress tumor-reactive immunity. The objective of this study was to assess both antitumor and immunosuppressive effects induced by high-dose radiotherapy in prostate cancer coclinical models, and ultimately, to test whether a combination of radiotherapy with targeted immunotherapy can enhance antitumor immunity. We studied the effects of high-dose per fraction radiotherapy with and without anti-Gr-1 using syngeneic murine allograft prostate cancer models. The dynamic change of immune populations, including tumor-infiltrating lymphocytes (TIL), T regulatory cells (Treg), and myeloid-derived suppressive cells (MDSC), was evaluated using flow cytometry and IHC. Coclinical prostate cancer models demonstrated that high-dose per fraction radiotherapy induced a rapid increase of tumor-infiltrating MDSCs and a subsequent rise of CD8 TILs and circulating CD8 T effector memory cells. These radiation-induced CD8 TILs were more functionally potent than those from nonirradiated controls. While systemic depletion of MDSCs by anti-Gr-1 effectively prevented MDSC tumor infiltration, it did not enhance radiotherapy-induced antitumor immunity due to a compensatory expansion of Treg-mediated immune suppression. In allograft prostate cancer models, high-dose radiotherapy induced an early rise of MDSCs, followed by a transient increase of functionally active CD8 TILs. However, systemic depletion of MDSC did not augment the antitumor efficacy of high-dose radiotherapy due to a compensatory Treg response, indicating blocking both MDSCs and Tregs might be necessary to enhance radiotherapy-induced antitumor immunity.

Beyond T-Cells: Functional Characterization of CTLA-4 Expression in Immune and Non-Immune Cell Types.

The immune response consists of a finely-tuned program, the activation of which must be coupled with inhibitory mechanisms whenever initiated. This ensures tight control of beneficial anti-pathogen and anti-tumor responses while preserving tissue integrity, promoting tissue repair, and safeguarding against autoimmunity. A cogent example of this binary response is in the mobilization of co-stimulatory and co-inhibitory signaling in regulating the strength and type of a T-cell response. Of particular importance is the costimulatory molecule CD28 which is countered by CTLA-4. While the role of CD28 in the immune response has been thoroughly elucidated, many aspects of CTLA-4 biology remain controversial. The expression of CD28 is largely constrained to constitutive expression in T-cells and as such, teasing out its function has been somewhat simplified by a limited and specific expression profile. The expression of CTLA-4, on the other hand, while reported predominantly in T-cells, has also been described on a diverse repertoire of cells within both lymphoid and myeloid lineages as well as on the surface of tumors. Nonetheless, the function of CTLA-4 has been mostly described within the context of T-cell biology. The focus on T-cell biology may be a direct result of the high degree of amino acid sequence homology and the co-expression pattern of CD28 and CTLA-4, which initially led to the discovery of CTLA-4 as a counter receptor to CD28 (for which a T-cell-activating role had already been described). Furthermore, observations of the outsized role of CTLA-4 in Treg-mediated immune suppression and the striking phenotype of T-cell hyperproliferation and resultant disease in CTLA-4−/− mice contribute to an appropriate T-cell-centric focus in the study of CTLA-4. Complete elucidation of CTLA-4 biology, however, may require a more nuanced understanding of its role in a context other than that of T-cells. This makes particular sense in light of the remarkable, yet limited utility of anti-CTLA-4 antibodies in the treatment of cancers and of CTLA-4-Ig in autoimmune disorders like rheumatoid arthritis. By fully deducing the biology of CTLA-4-regulated immune homeostasis, bottlenecks that hinder the widespread applicability of CTLA-4-based immunotherapies can be resolved.

Targeting ANXA1 abrogates Treg-mediated immune suppression in triple-negative breast cancer

BackgroundRegulatory T (Treg) cells play a negative role in anti-tumor immunity against triple-negative breast cancer, so it is of great significance to find the potential therapeutic target of Treg cells.MethodsFirst,...

Control of regulatory T-cell differentiation and function by T-cell receptor signalling and Foxp3 transcription factor complexes.

The transcription factor Foxp3 controls the differentiation and function of regulatory T-cells (Treg). Studies in the past decades identified numerous Foxp3-interacting protein partners. However, it is still not clear how Foxp3 produces the Treg-type transcriptomic landscape through cooperating with its partners. Here I show the current understanding of how Foxp3 transcription factor complexes regulate the differentiation, maintenance and functional maturation of Treg. Importantly, T-cell receptor (TCR) signalling plays central roles in Treg differentiation and Foxp3-mediated gene regulation. Differentiating Treg will have recognized their cognate antigens and received TCR signals before initiating Foxp3 transcription, which is triggered by TCR-induced transcription factors including NFAT, AP-1 and NF-κB. Once expressed, Foxp3 seizes TCR signal-induced transcriptional and epigenetic mechanisms through interacting with AML1/Runx1 and NFAT. Thus, Foxp3 modifies gene expression dynamics of TCR-induced genes, which constitute cardinal mechanisms for Treg-mediated immune suppression. Next, I discuss the following key topics, proposing new mechanistic models for Foxp3-mediated gene regulation: (i) how Foxp3 transcription is induced and maintained by the Foxp3-inducing enhanceosome and the Foxp3 autoregulatory transcription factor complex; (ii) molecular mechanisms for effector Treg differentiation (i.e. Treg maturation); (iii) how Foxp3 activates or represses its target genes through recruiting coactivators and corepressors; (iv) the 'decision-making' Foxp3-containing transcription factor complex for Th17 and Treg differentiation; and (v) the roles of post-translational modification in Foxp3 regulation. Thus, this article provides cutting-edge understanding of molecular biology of Foxp3 and Treg, integrating findings by biochemical and genomic studies.

Abstract A100: Downregulation of type 1 interferon receptor (IFNAR1) regulates the balance of regulatory T cells (Tregs) and cytotoxic T lymphocytes (CTLs) in tumor microenvironment

Abstract Solid tumors are infiltrated by not only CD8+ effector T cells (CTLs) exerting tumoricidal function, but also by regulatory T cells (Tregs), which are a key barrier to antitumor immunity (1). In the tumor microenvironment, the type 1 interferon (IFN) signaling is downregulated due to proteolytic degradation of IFNAR1 (2). Reduced IFNAR1 levels in tumor stroma are important for establishing the immune privileged niche to support tumor development and progression (3). IFN pathway plays complex and controversial roles in regulating immune responses ([4-7). In this study, we show that loss of IFNAR1 leads to changes in the activities of Tregs and CTLs. Genetic stabilization of IFNAR1 (Ifnar1S526A, SA) recruits more CTLs in the tumor microenvironment; however, it does not change the frequency of Tregs. In addition, in SA tumor tissues, the CTLs appear to exhibit a greater tumoricidal activity. Furthermore, we find that SA Treg lost their inhibitory function and SA CTLs are resistant to Treg-mediated immune suppression. In all, we discuss putative mechanisms underlying these phenotypes that IFN pathway regulates the balance of Treg and CTL activities in the tumor microenvironment. Citation Format: Hongru Zhang, Jun Gui, Angelica Ortiz, Serge Fuchs. Downregulation of type 1 interferon receptor (IFNAR1) regulates the balance of regulatory T cells (Tregs) and cytotoxic T lymphocytes (CTLs) in tumor microenvironment [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2019 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(3 Suppl):Abstract nr A100.

CHARACTERISTIC GUT MICROBIOME COMPOSITION IN ALZHEIMER’S DISEASE SUGGESTS THE POSSIBILITY OF HIGH POTENCY IN ENHANCING COLONIC TREG CELLS ABUNDANCE CLOSELY RELATED TO PROGRESSIVE COGNITIVE DYSFUNCTION

Recent study in transgenic APPPS1 mouse model of Alzheimer's disease (AD) strongly indicates involvement of gut microbiome (GMB) in the amyloid pathology. However, there have been few comprehensive surveys of GMB composition including the bacterial species level in humans with AD. To investigate the characteristics of GMB composition in AD, we performed bacterial 16S ribosomal RNA gene sequencing of DNA isolated from fecal samples in AD patients (n=65) with dementia, and age- and gender-matched cognitively normal control patients (n=41). GMB analysis revealed that AD patients has significantly increased alpha diversity (chao1: p=0.049 and shannon's index: p=0.004) and significantly different composition in weighted Unifrac analysis (PERMANOVA: R2=0.022, p=0.037), compared to control. We observed significantly increased relative abundance of Verrucomicrobia at the phylum level, and markedly higher abundance of Clostridium (13.0±1.1>7.0±0.8, p=2.2E-05) and Blautia (10.0±0.9>5.6±0.7, p=0.0002) which are the predominant genera of Clostridia clusters IV, XIVa, and XVIII inducing colonic regulatory T (Treg) cells essential for maintaining immune tolerance and immuno homeostasis, and higher abundance of Roseburia (2.5±0.3>1.9±0.3, p=0.033), but significantly lower abundance of Lactobacillus (2.0±0.7<4.9±1.5, p=0.031) at the the genus level in AD patients compared to control. The additional abundance of Clostridium and Blautia genus significantly negatively related to progressive decrease of cognitive function (r=−0.418, p<0.01, n=104). From the analysis of operational taxonomic units which showed significantly different abundance between AD and control patients (relative abundance≧0.1%), twenty best-hit bacterial species were identified. Fifteen of these species fall within the Clostridia clusters IV (n=5), XIVa (n=9), and XVIII (n=1) enhancing Treg cells abundance, and seventeen belong to the species producing short-chain fatty acids which regulates the differentiation and expansion of colonic Treg cells: eleven species producing acetate which is rerouted into butyrate, four butyrate-producing species, and two propionate-producing species. Recent evidence in transgenic 5xFAD mouse model indicates that Treg-mediated systemic immune suppression is involved in the pathogenesis of AD. Present GMB analysis in AD patients suggests the possibility of high potency in enhancing colonic Treg cells abundance closely related to progressive decline in cognitive function.

Interleukin-4 Supports the Suppressive Immune Responses Elicited by Regulatory T Cells.

Interleukin-4 (IL-4) has been considered as one of the tolerogenic cytokines in many autoimmune animal models and clinical settings. Despite its role in antagonizing pathogenic Th1 responses, little is known about whether IL-4 possesses functions that affect regulatory T cells (Tregs). Tregs are specialized cells responsible for the maintenance of peripheral tolerance through their immune modulatory capabilities. Interestingly, it has been suggested that IL-4 supplement at a high concentration protects responder T cells (Tresps) from Treg-mediated immune suppression. In addition, such supplement also impedes TGF-β-induced Treg differentiation in vitro. However, these phenomena may contradict the tolerogenic role of IL-4, and the effects of IL-4 on Tregs are therefore needed to be further elucidated. In this study, we utilized IL-4 knockout (KO) mice to validate the role of IL-4 on Treg-mediated immune suppression. Although IL-4 KO and control animals harbor similar frequencies of Tregs, Tregs from IL-4 KO mice weakly suppressed autologous Tresp activation. In addition, IL-4 deprivation impaired the ability of Tregs to modulate immune response, whereas IL-4 supplementation reinforced IL-4 KO Tregs in their function in suppressing Tresps. Finally, the presence of IL-4 was associated with increased cell survival and granzyme expression of Tregs. These results suggest the essential role of IL-4 in supporting Treg-mediated immune suppression, which may benefit the development of therapeutic strategies for autoimmune diseases.

Characterization of MK-4166, a Clinical Agonistic Antibody That Targets Human GITR and Inhibits the Generation and Suppressive Effects of T Regulatory Cells.

GITR is a T-cell costimulatory receptor that enhances cellular and humoral immunity. The agonist anti-mouse GITR antibody DTA-1 has demonstrated efficacy in murine models of cancer primarily by attenuation of Treg-mediated immune suppression, but the translatability to human GITR biology has not been fully explored. Here, we report the potential utility of MK-4166, a humanized GITR mAb selected to bind to an epitope analogous to the DTA-1 epitope, which enhances the proliferation of both naïve and tumor-infiltrating T lymphocytes (TIL). We also investigated the role of GITR agonism in human antitumor immune responses and report here the preclinical characterization and toxicity assessment of MK-4166, which is currently being evaluated in a phase I clinical study. Expression of human GITR was comparable with that of mouse GITR in tumor-infiltrating Tregs despite being drastically lower in other human TILs and in many human peripheral blood populations. MK-4166 decreased induction and suppressive effects of Tregsin vitro In human TIL cultures, MK-4166 induced phosphorylation of NFκB and increased expression of dual specificity phosphatase 6 (DUSP6), indicating that MK-4166 activated downstream NFκB and Erk signaling pathways. Furthermore, MK-4166 downregulated FOXP3 mRNA in human tumor infiltrating Tregs, suggesting that, in addition to enhancing the activation of TILs, MK-4166 may attenuate the Treg-mediated suppressive tumor microenvironment. Cancer Res; 77(16); 4378-88. ©2017 AACR.

Abstract NG03: Marine omega-3 polyunsaturated fatty acid and colorectal cancer prevention and treatment

Abstract NG03: Marine omega-3 polyunsaturated fatty acid and colorectal cancer prevention and treatment

CXCL13-producing TFH cells link immune suppression and adaptive memory in human breast cancer.

T follicular helper cells (TFH cells) are important regulators of antigen-specific B cell responses. The B cell chemoattractant CXCL13 has recently been linked with TFH cell infiltration and improved survival in human cancer. Although human TFH cells can produce CXCL13, their immune functions are currently unknown. This study presents data from human breast cancer, advocating a role for tumor-infiltrating CXCL13-producing (CXCR5-) TFH cells, here named TFHX13 cells, in promoting local memory B cell differentiation. TFHX13 cells potentially trigger tertiary lymphoid structure formation and thereby generate germinal center B cell responses at the tumor site. Follicular DCs are not potent CXCL13 producers in breast tumor tissues. We used the TFH cell markers PD-1 and ICOS to identify distinct effector and regulatory CD4+ T cell subpopulations in breast tumors. TFHX13 cells are an important component of the PD-1hiICOSint effector subpopulation and coexpanded with PD-1intICOShiFOXP3hi Tregs. IL2 deprivation induces CXCL13 expression in vitro with a synergistic effect from TGFβ1, providing insight into TFHX13 cell differentiation in response to Treg accumulation, similar to conventional TFH cell responses. Our data suggest that human TFHX13 cell differentiation may be a key factor in converting Treg-mediated immune suppression to de novo activation of adaptive antitumor humoral responses in the chronic inflammatory breast cancer microenvironment.