A senescence-mimicking (senomimetic) VEGFR TKI side-effect primes tumor immune responses via IFN/STING signaling

Tyrosine kinase inhibitors (TKIs) that block the vascular endothelial growth factor receptors (VEGFRs) disrupt tumor angiogenesis but also have many unexpected side-effects that impact tumor cells directly. This includes the induction of molecular markers associated with senescence, a form of cellular aging that typically involves growth arrest. We have shown that VEGFR TKIs can hijack these aging programs by transiently inducting senescence-markers (SMs) in tumor cells to activate senescence-associated secretory programs that fuel drug resistance. Here we show that these same senescence-mimicking ('senomimetic') VEGFR TKI effects drive an enhanced immunogenic signaling that, in turn, can alter tumor response to immunotherapy. Using a live-cell sorting method to detect beta-galactosidase, a commonly used SM, we found that subpopulations of SM-expressing (SM+) tumor cells have heightened interferon (IFN) signaling and increased expression of IFN-stimulated genes (ISGs). These ISG increases were under the control of the STimulator of INterferon Gene (STING) signaling pathway, which we found could be directly activated by several VEGFR TKIs. TKI-induced SM+ cells could stimulate or suppress CD8 T-cell activation depending on host:tumor cell contact while tumors grown from SM+ cells were more sensitive to PD-L1 inhibition in vivo, suggesting that offsetting immune-suppressive functions of SM+ cells can improve TKI efficacy overall. Our findings may explain why some (but not all) VEGFR TKIs improve outcomes when combined with immunotherapy and suggest that exploiting senomimetic drug side-effects may help identify TKIs that uniquely 'prime' tumors for enhanced sensitivity to PD-L1 targeted agents.

Neurotrophic factor Neuritin modulates T cell electrical and metabolic state for the balance of tolerance and immunity

The adaptive T cell response is accompanied by continuous rewiring of the T cell's electric and metabolic state. Ion channels and nutrient transporters integrate bioelectric and biochemical signals from the environment, setting cellular electric and metabolic states. Divergent electric and metabolic states contribute to T cell immunity or tolerance. Here, we report that neuritin (Nrn1) contributes to tolerance development by modulating regulatory and effector T cell function. Nrn1 expression in regulatory T cells promotes its expansion and suppression function, while expression in the T effector cell dampens its inflammatory response. Nrn1 deficiency causes dysregulation of ion channel and nutrient transporter expression in Treg and effector T cells, resulting in divergent metabolic outcomes and impacting autoimmune disease progression and recovery. These findings identify a novel immune function of the neurotrophic factor Nrn1 in regulating the T cell metabolic state in a cell context-dependent manner and modulating the outcome of an immune response.

Neoadjuvant therapy in non-small cell lung cancer: basis, promise, and challenges

Introduction

Survival rates for early-stage non-small cell lung cancer (NSCLC) remain poor despite the decade-long established standard of surgical resection and systemic adjuvant therapy. Realizing this, researchers are exploring novel therapeutic targets and deploying neoadjuvant therapies to predict and improve clinical and pathological outcomes in lung cancer patients. Neoadjuvant therapy is also increasingly being used to downstage disease to allow for resection with a curative intent. In this review, we aim to summarize the current and developing landscape of using neoadjuvant therapy in the management of NSCLC.

Methods

The PubMed.gov and the ClinicalTrials.gov databases were searched on 15 January 2023, to identify published research studies and trials relevant to this review. One hundred and seven published articles and seventeen ongoing clinical trials were selected, and relevant findings and information was reviewed.

Results & Discussion

Neoadjuvant therapy, proven through clinical trials and meta-analyses, exhibits safety and efficacy comparable to or sometimes surpassing adjuvant therapy. By attacking micro-metastases early and reducing tumor burden, it allows for effective downstaging of disease, allowing for curative surgical resection attempts. Research into neoadjuvant therapy has necessitated the development of surrogate endpoints such as major pathologic response (MPR) and pathologic complete response (pCR) allowing for shorter duration clinical trials. Novel chemotherapy, immunotherapy, and targeted therapy agents are being tested at a furious rate, paving the way for a future of personalized systemic therapy in NSCLC. However, challenges remain that prevent further mainstream adoption of preoperative (Neoadjuvant) therapy. These include the risk of delaying curative surgical resection in scenarios of adverse events or treatment resistance. Also, the predictive value of surrogate markers of disease cure still needs robust verification. Finally, the body of published data is still limited compared to adjuvant therapy. Addressing these concerns with more large scale randomized controlled trials is needed.

Skeletal muscle index is associated with long term outcomes after lobectomy for non-small cell lung cancer

BACKGROUND

Skeletal muscle indices have been associated with improved peri-operative outcomes after surgical resection of non-small-cell lung cancer (NSCLC). However, it is unclear if these indices can predict long term cancer specific outcomes.

METHODS

NSCLC patients undergoing lobectomy at our institute between 2009-2015 were included in this analysis (N = 492). Preoperative CT scans were used to quantify skeletal muscle index (SMI) at L4 using sliceOmatic software. Cox proportional modelling was performed for overall (OS) and recurrence free survival (RFS).

RESULTS

For all patients, median SMI was 45.7 cm2/m2 (IQR, 40-53.8). SMI was negatively associated with age (R = -0.2; p < 0.05) and positively associated with BMI (R = 0.46; P < 0.05). No association with either OS or RFS was seen with univariate cox modelling. However, multivariable modelling for SMI with patient age, gender, race, smoking status, DLCO and FEV1 (% predicted), American Society of Anesthesiology (ASA) score, tumor histology and stage, and postoperative neoadjuvant therapy showed improved OS (HR = 0.97; P = 0.0005) and RFS (HR = 0.97; P = 0.01) with SMI. Using sex specific median SMI as cutoff, a lower SMI was associated with poor OS (HR = 1.65, P = 0.001) and RFS (HR = 1.47, P = 0.03).

CONCLUSIONS

SMI is associated with improved outcomes after resection of NSCLC. Further studies are needed to understand the biological basis of this observation. This study provides additional rationale for designing and implementation of rehabilitation trials after surgical resection, to gain durable oncologic benefit.

Immunoprofiling bronchoalveolar lavage cells reveals multifaceted smoking-associated immune dysfunction

Background

Bronchoalveolar lavage (BAL) is an underutilised tool in the search for pulmonary disease biomarkers. While leukocytes with effector and suppressor function play important roles in airway immunity and tumours, it remains unclear if frequencies and phenotypes of BAL leukocytes can be useful parameters in lung cancer studies and clinical trials. We therefore explored the utility of BAL leukocytes as a source of biomarkers interrogating the impact of smoking, a major lung cancer risk determinant, on pulmonary immunity.

Methods

In this "test case" observational study, BAL samples from 119 donors undergoing lung cancer screening and biopsy procedures were evaluated by conventional and spectral flow cytometry to exemplify the comprehensive immune analyses possible with this biospecimen. Proportions of major leukocyte populations and phenotypic markers levels were found. Multivariate linear rank sum analysis considering age, sex, cancer diagnosis and smoking status was performed.

Results

Significantly increased frequencies of myeloid-derived suppressor cells and PD-L1-expressing macrophages were found in current and former smokers compared to never-smokers. While cytotoxic CD8 T-cells and conventional CD4 helper T-cell frequencies were significantly reduced in current and former smokers, expression of immune checkpoints PD-1 and LAG-3 as well as Tregs proportions were increased. Lastly, the cellularity, viability and stability of several immune readouts under cryostorage suggested BAL samples are useful for correlative end-points in clinical trials.

Conclusions

Smoking is associated with heightened markers of immune dysfunction, readily assayable in BAL, that may reflect a permissive environment for cancer development and progression in the airway.

Abstract 73: Blockade of p38 MAPK reduces the tumor-induced immune suppressive microenvironment in metastatic breast cancer

The ability of CD8+ T cells to mount an anti-tumor immune response is compromised by immune suppression in the tumor microenvironment (TME). Tumor Associated Macrophages (TAMs) and Myeloid Derived Suppressor Cells (MDSCs) are a major part of this immune suppressive network. Targeting these populations remains challenging. Previously, we have reported that pharmacological and genetic blockade of p38 MAPK impeded the expansion and mobilization of monocytic and granulocytic MDSCs in mouse mammary carcinoma models. We also found that blockade of p38 or depletion of MDSCs reduced tumor growth and metastasis while enhancing the levels of CD8+ T cells in the primary tumors. In the present study, we asked whether CD8+ T cells contribute to the anti-metastatic activity of p38 inhibitor (p38i) and how p38 blockade affects the functional status of T cells and MDSCs. By using the mouse mammary carcinoma 4T1 model, we found that depletion of CD8+ T cells negated the effects of p38i on tumor growth and metastasis, indicating that CD8+ T cells contribute to the anti-tumor and anti-metastatic effects of p38 blockade. Next, we examined whether p38i exhibits a direct effect on T cells. The results of the T cell proliferation in vitro assays revealed that p38 blockade did not have a direct impact on T cell proliferation in response to αCD3/αCD28 stimulation. To determine the effect of p38 blockade on T cells in vivo, we performed single cell RNA-seq on the 4T1 tumor models treated with p38i and the 4T1 model with p38α (Mapk14) knockout (p38ko). This study revealed that p38 blockade by p38i or by inactivation of p38 in tumor cells decreased the amount of exhausted T cells and increased Th1 cells in the TME, indicating a positive effect on T cell functions. Furthermore, we observed a significant decrease in inflammatory signaling in granulocytes and monocytes upon p38 blockade. Our previous study showed that p38i did not affect generation of MDSCs in vitro in response to G-CSF & GM-CSF. To determine whether p38i alters MDSCs in vivo, we assessed MDSC gene signature in monocytic and granulocytic MDSCs isolated from spleens of tumor-bearing mice subjected to p38 blockade. This work revealed that the MDSC gene signature was reduced in both p38i and p38ko groups compared to tumor bearing mice treated with vehicle-control. These results indicated a reduction in the MDSC generation in the in vivo model. Our study revealed that blockade of p38 reduces tumor induced immune suppression and may enhance anti-tumor immune response in metastatic breast cancer.

Citation Format: Priyanka Rajan, Justin Zonneville, Robert Zollo, Mackenzie Honikel, Sofija Raudins, Sean Colligan, Brian Morreale, Mohammed Alruwaili, Mohammed Alqarni, Scott Olejniczak, Joseph Barbi, Scott Abrams, Andrei Bakin. Blockade of p38 MAPK reduces the tumor-induced immune suppressive microenvironment in metastatic breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 73.

Aging augments obesity-induced thymic involution and peripheral T cell exhaustion altering the "obesity paradox"

Introduction

The incidence of obesity, a condition characterized by systemic chronic inflammation, has reached pandemic proportions and is a poor prognostic factor in many pathologic states. However, its role on immune parameters has been diverse and at times contradictory. We have previously demonstrated that obesity can result in what has been called the "obesity paradox" which results in increased T cell exhaustion, but also greater efficacy of immune checkpoint blockade in cancer treatment.

Methods

The role of obesity, particularly in the context of aging, has not been robustly explored using preclinical models. We therefore evaluated how age impacts the immune environment on T cell development and function using diet-induced obese (DIO) mice.

Results

We observed that DIO mice initially displayed greater thymopoiesis but then developed greater thymic involution over time compared to their lean counterparts. Both aging and obesity resulted in increased T cell memory conversion combined with increased expression of T cell exhaustion markers and Treg expansion. This increased T cell immunosuppression with age then resulted in a loss of anti-tumor efficacy by immune checkpoint inhibitors (ICIs) in older DIO mice compared to the younger DIO counterparts.

Discussion

These results suggest that both aging and obesity contribute to T cell dysfunction resulting in increased thymic involution. This combined with increased T cell exhaustion and immunosuppressive parameters affects immunotherapy efficacy reducing the advantage of obesity in cancer immunotherapy responses.

Inhibiting the biogenesis of myeloid-derived suppressor cells enhances immunotherapy efficacy against mammary tumor progression

While immune checkpoint inhibitors (ICIs) have transformed the therapeutic landscape in oncology, they are effective in select subsets of patients. Efficacy may be limited by tumor-driven immune suppression, of which 1 key mechanism is the development of myeloid-derived suppressor cells (MDSCs). A fundamental gap in MDSC therapeutics is the lack of approaches that target MDSC biogenesis. We hypothesized that targeting MDSC biogenesis would mitigate MDSC burden and bolster tumor responses to ICIs. We tested a class of agents, dihydroorotate dehydrogenase (DHODH) inhibitors, that have been previously shown to restore the terminal differentiation of leukemic myeloid progenitors. DHODH inhibitors have demonstrated preclinical safety and are under clinical study for hematologic malignancies. Using mouse models of mammary cancer that elicit robust MDSC responses, we demonstrated that the DHODH inhibitor brequinar (a) suppressed MDSC production from early-stage myeloid progenitors, which was accompanied by enhanced myeloid maturation; (b) augmented the antitumor and antimetastatic activities of programmed cell death 1-based (PD-1-based) ICI therapy in ICI-resistant mammary cancer models; and (c) acted in concert with PD-1 blockade through modulation of MDSC and CD8+ T cell responses. Moreover, brequinar facilitated myeloid maturation and inhibited immune-suppressive features in human bone marrow culture systems. These findings advance the concept of MDSC differentiation therapy in immuno-oncology.

Identification of patient characteristics associated with survival benefit from metformin treatment in patients with stage I non-small cell lung cancer

BACKGROUND

Non-small cell lung cancer (NSCLC) continues to be a major cause of cancer deaths. Previous investigation has suggested that metformin use can contribute to improved outcomes in NSCLC patients. However, this association is not uniform in all analyzed cohorts, implying that patient characteristics might lead to disparate results. Identification of patient characteristics that affect the association of metformin use with clinical benefit might clarify the drug's effect on lung cancer outcomes and lead to more rational design of clinical trials of metformin's utility as an intervention. In this study, we examined the association of metformin use with long-term mortality benefit in patients with NSCLC and the possible modulation of this benefit by body mass index (BMI) and smoking status, controlling for other clinical covariates.

METHODS

This was a retrospective cohort study in which we analyzed data from the Veterans Affairs (VA) Tumor Registry in the United States. Data from all patients with stage I NSCLC from 2000 to 2016 were extracted from a national database, the Corporate Data Warehouse that captures data from all patients, primarily male, who underwent treatment through the VA health system in the United States. Metformin use was measured according to metformin prescriptions dispensed to patients in the VA health system. The association of metformin use with overall survival (OS) after diagnosis of stage I NSCLC was examined. Patients were further stratified according to BMI and smoking status (previous vs current) to examine the association of metformin use with OS across these strata.

RESULTS

Metformin use was associated with improved survival in patients with stage I NSCLC (average hazard ratio, 0.82; P < .001). An interaction between the effect of metformin use and BMI on OS was observed (χ2 = 3268.42; P < .001) with a greater benefit of metformin use observed in patients as BMI increased. Similarly, an interaction between smoking status and metformin use on OS was also observed (χ2 = 2997.05; P < .001) with a greater benefit of metformin use observed in previous smokers compared with current smokers.

CONCLUSIONS

In this large retrospective study, we showed that a survival benefit is enjoyed by users of metformin in a robust stage I NSCLC patient population treated in the VA health system. Metformin use was associated with an 18% improved OS. This association was stronger in patients with a higher BMI and in previous smokers. These observations deserve further mechanistic study and can help rational design of clinical trials with metformin in patients with lung cancer.

Altered acetyl-CoA metabolism presents a new potential immunotherapy target in the obese lung microenvironment

Contrary to the "obesity paradox," which arises from retrospective studies relying on body mass index to define obesity, epidemiologic evidence suggests central or visceral obesity is associated with a higher risk for the development of lung cancer. About 60% of individuals at high risk for developing lung cancer or those already with early-stage disease are either overweight or obese. Findings from resected patient tumors and mouse lung tumor models show obesity dampens immune activity in the tumor microenvironment (TME) encouraging disease progression. In line with this, we have observed a marked, obesity-specific enhancement in the presence and phenotype of immunosuppressive regulatory T (Treg) cells in murine tumors as well as the airways of both humans and mice. Leveraging direct metabolomic measurements and robust inferred analyses from RNA-sequencing data, we here demonstrate for the first time that visceral adiposity alters the lung microenvironment via dysregulated acetyl-CoA metabolism in a direction that facilitates immune suppression and lung carcinogenesis.

Abstract 2082: Obesity dependent benefits of metformin for improved anti-tumor immunity and outcomes in non-small cell lung cancer

Metformin, the widely used and studied diabetes drug, has been reported to have anti-cancer effects. However, in retrospective clinical studies, the survival benefit associated with metformin use in cancer patients is often modest. Consequently, the design and conduct of sufficiently powered prospective clinical trials aimed at exploring this drug’s anti-tumor potential are hampered by the absence of predictive biomarkers. Testing the notion that specific patient characteristics such as obesity may impact the relative potency of metformin’s effects on lung cancer survival, we analyzed the patient outcomes of 756 non-small cell lung cancer (NSCLC) cases with early- (stage I/II, n = 490) or late-stage disease (stage III/IV, n = 266) that either did or did not use metformin (n = 121 and 635, respectively) while not receiving neoadjuvant therapy. We found that metformin use is associated with improved overall and recurrence free survival only in overweight and obese patients defined by a body mass index (BMI) greater than 25 kg/m2. Corroborative findings obtained from immunocompetent mouse lung cancer models aligned with these observations. In these studies, despite supporting accelerated growth of both primary and metastatic tumors compared to their normal weight counterparts, animals subjected to diet induced obesity (DIO) experienced significantly reduced tumor development upon metformin treatment. In contrast, the drug had little-to-no effect on tumor burden in normal weight controls. Furthermore, while flow cytometric evaluation of obese mouse-derived tumors identified several previously described mediators of immune dysfunction previously described in animals with DIO (e.g., widespread up-regulation of the immune checkpoint factors PD-1 and Lag3, elevated suppressor cell proportions and activity), metformin treatment was associated with their reversal specifically in the tumors of obese mice. Interestingly, the drug had little effect on the tumor immune contexture of normal weight mice, and gene expression analysis failed to reveal considerable alterations in canonical cancer pathways. Thus, our preclinical and clinical studies suggest that the anti-diabetic drug metformin has an anti-cancer effect in NSCLC that is restricted to overweight individuals and reflects its potential to direct favorable, context-specific immune reprogramming. This work also provides the rationale for using high BMI as a predictive biomarker of the anti-cancer effect of metformin in lung cancer.

Citation Format: Joseph Barbi, Randall J. Smith, Robert Zollo, Stephanie N. Sass, Deschana Washington, Cara Petrucci, Aravind Srinivasan, Eric Kannisto, Santosh Patnaik, Sai Sai Yendamuri. Obesity dependent benefits of metformin for improved anti-tumor immunity and outcomes in non-small cell lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2082.

The neurotrophic factor Neuritin regulates T cell anergy and T regulatory cell function

T cell activation and tolerance are tightly regulated to ensure effective elimination of foreign antigen while maintaining immune tolerance to self-antigens. Development of T cell anergy and regulatory T cell (Treg) mediated suppression both contribute to the establishment of immune tolerance. Here, we show that neuritin (Nrn1), a conserved GPI-anchored surface molecule important for the development, survival and function of neurons, is highly expressed in anergic and Treg cells. Nrn1 deficient CD4 cells are resistant to Treg cell mediated suppression, display defective anergy induction, and have reduced peripheral Treg generation. Nrn1 deficient Foxp3+ Treg cells exhibit reduced control of inflammatory colitis. Moreover, upon induction of experimental autoimmune encephalomyelitis (EAE), Nrn1 deficient mice develop non-remitting disease and have increased spinal cord inflammatory infiltrates. These in vivo findings underscore the importance of Nrn1 in immune tolerance. Recently, Nrn1 was identified as an accessory component of the ionotropic AMPA receptor (AMPAR) complex in neurons. AMPARs mediate glutamate dependent cation flux and regulate cell membrane potential. Cell membrane potential can impact nutrient uptake, calcium influx, cell size, proliferation and survival. In vitro analysis reveals that Nrn1 deficient Treg cells exhibit reduced proliferation and survival, associated with higher membrane potential, reduced nutrient sensitivity, reduced glycolysis and mTOR activation. AMPAR blockade can correct proliferation defect in Nrn1 deficient Treg cells. These findings reveal Nrn1 as an important regulator of immune tolerance functioning through the modulation of glutamate activated AMPAR.

Obesity-Specific Association of Statin Use and Reduced Risk of Recurrence of Early Stage NSCLC

Introduction

Statins, used for their lipid-lowering activity, have anti-inflammatory and anticancer properties as well. We evaluated this potential benefit of statin use in patients with NSCLC.

Methods

All 613 patients with pathologic stage 1 or 2 NSCLC who had lobectomy without neoadjuvant therapy at our institution during 2008 to 2015 were included. Association between presurgery statin use and overall survival and recurrence-free survival (RFS) was analyzed using Cox proportional hazards regression. Association of statin use with tumor transcriptome was evaluated in another 350 lung cancer cases.

Results

Univariable analyses did not reveal a statistically significant association of statin use with either overall survival or RFS, with hazard ratio equals to 1.19 and 0.70 (Wald p = 0.28 and 0.09), respectively. In subgroup analyses, significantly improved RFS was found in statin users, but only in overweight/obese patients (body mass index [BMI] > 25; n = 422), with univariable and multivariable hazard ratio of 0.49 and 0.46 (p = 0.005 and 0.002), respectively, but not in patients with BMI less than or equal to 25 (n = 191; univariable p = 0.21). Transcriptomes of tumor statin users had high expression of tumoricidal genes such as granzyme A and interferon-γ compared with those of nonusers among high- but not low-BMI patients with lung cancer.

Conclusions

Our study suggests that statins may improve the outcome of early stage NSCLC but only in overweight or obese patients. This benefit may stem from a favorable reprogramming of the antitumor immune response that statins perpetrate specifically in the obese.

Abstract 3195: Hijacked senescence secretomes as 'immune primers' of antiangiogenic TKI efficacy

VEGF receptor tyrosine kinase inhibitors (VEGFR TKIs) and immune checkpoint inhibitors (ICIs) are approved together as a treatment regimen for multiple metastatic cancers, yet the mechanistic basis for this combinatory benefit remains unclear. Previously we have shown that resistance to VEGFR TKI treatment can transiently hijack the secretory machinery typically associated with senescence - the process of cellular aging. Here we report that these senescence-associated secretory programs can also drive immune cell activation, potentially ‘priming' the tumor for PD-1 pathway inhibition. Using a novel live-cell sorting method based on C12FDG - a substrate for senescence-associated beta-galactosidase activity - we isolated senescence-marker (SM) expressing VEGFR TKI-treated cells for transcriptomic analysis. SM+ cell populations were enriched for senescence, immune, and interferon secretory processes, with a unique gene signature validated using published preclinical and clinical datasets. Notably, SM+ cells were found to be more sensitive to CD8 T-cell mediated tumor inhibition in vivo and ex vivo and be sensitive to PD-L1 blockade and inhibitors of mTOR, a key secretory regulator. Together, these results suggest VEGFR TKI controlled secretory programs contributing to resistance can simultaneously prime the tumor microenvironment for immune cell activation, providing an explanation for improved effects of antiangiogenic and immunotherapy combinations in patients.

Citation Format: Melissa Dolan, Yuhao Shi, James W. Hill, Michalis Mastri, Cristina Vaghi, Joseph Barbi, Sebastien Benzekry, John M. Ebos. Hijacked senescence secretomes as 'immune primers' of antiangiogenic TKI efficacy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 3195.

Hypoxia-inducible factor 1: A link between metabolism and T cell differentiation and a potential therapeutic target

Naïve T cells activated by antigen-presenting cells (APC) can be differentiated into at least four major types of T-helper (T_H) cells: T_H1, T_H2, T_H17 and inducible regulatory T cells (iTreg) based on their unique cytokine production profiles and characteristic functions.¹ T_H1 produce interferon-γ (IFNγ) and are important for protective immune responses to intracellular viral, bacterial and parasitic infection. T_H2 cells produce interleukin-4 (IL-4), IL-5, IL-23 and are critical for controlling extracellular parasites such as helminthes. T_H17 cells are responsible for expelling extracellular bacteria and fungi through secretion of IL-17a, IL-17f and IL-22.² These cells however are perhaps better known for their propensity to drive autoimmune responses. Tregs including naturally occurring regulatory T cells (nTreg) play important roles in the suppressive control of both innate and adaptive immunity in vivo.^3,4

The deubiquitinase USP44 promotes Treg function during inflammation by preventing FOXP3 degradation

The transcription factor forkhead box P3 (FOXP3) is essential for the development of regulatory T cells (Tregs) and their function in immune homeostasis. Previous studies have shown that in natural Tregs (nTregs), FOXP3 can be regulated by polyubiquitination and deubiquitination. However, the molecular players active in this pathway, especially those modulating FOXP3 by deubiquitination in the distinct induced Treg (iTreg) lineage, remain unclear. Here, we identify the ubiquitin-specific peptidase 44 (USP44) as a novel deubiquitinase for FOXP3. USP44 interacts with and stabilizes FOXP3 by removing K48-linked ubiquitin modifications. Notably, TGF-β induces USP44 expression during iTreg differentiation. USP44 co-operates with USP7 to stabilize and deubiquitinate FOXP3. Tregs genetically lacking USP44 are less effective than their wild-type counterparts, both in vitro and in multiple in vivo models of inflammatory disease and cancer. These findings suggest that USP44 plays an important role in the post-translational regulation of Treg function and is thus a potential therapeutic target for tolerance-breaking anti-cancer immunotherapy.

Augmentation of IFN-γ+ CD8+ T cell responses correlates with survival of HCC patients on sorafenib therapy

BACKGROUNDSorafenib has been shown to reduce the extent of immunosuppression in patients with hepatocellular carcinoma (HCC). The rationale of this investigation was to identify biomarkers that can predict treatment efficacy of sorafenib in HCC patients and to unravel the mechanism by which sorafenib impedes immune suppression mediated by distinct immunosuppressive cell subsets.METHODSWith informed consent, blood samples were collected from 30 patients with advanced HCC, at baseline and 2 time points after initiation of sorafenib treatment. The frequency of PD-1+ T cells, ERK2 phosphorylation on flt-3+ Tregs and MDSCs, and T effector cell function were quantified by using flow cytometry.RESULTSElevated levels of CD8+Ki67+ T cells producing IFN-γ were associated with improved progression-free survival and overall survival (OS). High frequencies of these T cells were correlated with significantly reduced risk of death over time. Patients with an increased pretreatment T effector/Treg ratio showed significant improvement in OS. ERK+flt-3+ Tregs and MDSCs were significantly decreased after sorafenib therapy. Increased numbers of baseline flt-3+p-ERK+ MDSCs were associated with survival benefit of patients.CONCLUSIONA high baseline CD4+ T effector/Treg ratio is a potential biomarker of prognostic significance in HCC. CD8+Ki67+ T cells producing IFN-γ are a key biomarker of response to sorafenib therapy resulting in survival benefit. The immune modulation resulted from sorafenib-mediated blockade of signaling through the VEGF/VEGFR/flt-3 pathway, affecting ERK phosphorylation. These insights may help identify patients who likely would benefit from VEGFR antagonism and inform efforts to improve the efficacy of sorafenib in combination with immunotherapy.TRIAL REGISTRATIONNCT02072486.FUNDINGNational Comprehensive Cancer Network Oncology Research Program from general research support provided by Bayer US LLC (NCCNSORA0002), National Cancer Institute grant P30CA016056, and pilot funds from Roswell Park Alliance Foundation.

Body Mass Index Influences the Salutary Effects of Metformin on Survival After Lobectomy for Stage I NSCLC

INTRODUCTION

Metformin, a common medication used in the treatment of diabetes mellitus is known to have anticancer effects. We hypothesized that the salutary effect of metformin on the survival of patients with stage I NSCLC is influenced by body mass index (BMI).

METHODS

Patients undergoing lobectomy for stage I NSCLC without neoadjuvant therapy were included. Univariate and multivariate survival analyses to examine the association between metformin use and overall survival (OS), disease-specific survival (DSS), and recurrence-free survival were performed, stratified by BMI (>25 kg/m² and ≤25 kg/m²). Expression of immune checkpoints in patients on metformin and not was performed in a separate cohort of 205 patients with advanced disease.

RESULTS

Four hundred thirty-four stage I patients (including 74 metformin users) were deemed eligible for analysis. Univariate and multivariate analysis revealed an association between metformin use and OS (hazard ratio [HR] = 0.52; p = 0.04) as well as DSS (HR = 0.21; p = 0.04) but not recurrence-free survival (HR = 0.67; p = 0.33) in high-BMI patients only. In a separate cohort of 205 patients with tumors of all stages (including 35 metformin users), downregulation of immune checkpoint gene expression (programmed cell death 1, cytotoxic T-lymphocyte associated protein 4, B and T lymphocyte associated, CD27 molecule, lymphocyte activating 3, and inducible T cell costimulator) in metformin users was seen only in high-BMI patients, with upregulation of these genes seen in low-BMI patients with metformin use.

CONCLUSIONS

Metformin use may be associated with better OS and DSS only in high-BMI patients. This hypothesis is supported by gene expression data of immune checkpoint genes in metformin users using a separate cohort of advanced-stage tumors. Further studies examining the interaction of BMI with metformin in NSCLC are worthwhile.

TRAF6 directs FOXP3 localization and facilitates regulatory T-cell function through K63-linked ubiquitination

Regulatory T cells (Tregs) are crucial mediators of immune control. The characteristic gene expression and suppressive functions of Tregs depend considerably on the stable expression and activity of the transcription factor FOXP3. Transcriptional regulation of the Foxp3 gene has been studied in depth, but both the expression and function of this factor are also modulated at the protein level. However, the molecular players involved in posttranslational FOXP3 regulation are just beginning to be elucidated. Here, we found that TRAF6‐deficient Tregs were dysfunctional in vivo; mice with Treg‐restricted deletion of TRAF6 were resistant to implanted tumors and displayed enhanced anti‐tumor immunity. We further determined that FOXP3 undergoes K63‐linked ubiquitination at lysine 262 mediated by the E3 ligase TRAF6. In the absence of TRAF6 activity or upon mutation of the ubiquitination site, FOXP3 displayed aberrant, perinuclear accumulation and disrupted regulatory function. Thus, K63‐linked ubiquitination by TRAF6 ensures proper localization of FOXP3 and facilitates the transcription factor's gene‐regulating activity in Tregs. These results implicate TRAF6 as a key posttranslational, Treg‐stabilizing regulator that may be targeted in novel tolerance‐breaking therapies.

YAP Is Essential for Treg-Mediated Suppression of Antitumor Immunity

Regulatory T cells (Treg) are critical for maintaining self-tolerance and immune homeostasis, but their suppressive function can impede effective antitumor immune responses. FOXP3 is a transcription factor expressed in Tregs that is required for their function. However, the pathways and microenvironmental cues governing FOXP3 expression and Treg function are not completely understood. Herein, we report that YAP, a coactivator of the Hippo pathway, is highly expressed in Tregs and bolsters FOXP3 expression and Treg function in vitro and in vivo. This potentiation stemmed from YAP-dependent upregulation of activin signaling, which amplifies TGFβ/SMAD activation in Tregs. YAP deficiency resulted in dysfunctional Tregs unable to suppress antitumor immunity or promote tumor growth in mice. Chemical YAP antagonism and knockout or blockade of the YAP-regulated activin receptor similarly improved antitumor immunity. Thus, we identify YAP as an unexpected amplifier of a Treg-reinforcing pathway with significant potential as an anticancer immunotherapeutic target.Significance: Tregs suppress antitumor immunity, and pathways supporting their function can be novel immunotherapy targets. Here, the selective expression of YAP by Tregs, its importance for their function, and its unexpected enhancement of pro-Treg Activin/SMAD signaling are reported, as are validations of potential cancer-fighting antagonists of YAP and its regulatory targets. Cancer Discov; 8(8); 1026-43. ©2018 AACR.This article is highlighted in the In This Issue feature, p. 899.

MicroRNA-17 Modulates Regulatory T Cell Function by Targeting Co-regulators of the Foxp3 Transcription Factor

Regulatory T (Treg) cells are important in maintaining self-tolerance and immune homeostasis. The Treg cell transcription factor Foxp3 works in concert with other co-regulatory molecules, including Eos, to determine the transcriptional signature and characteristic suppressive phenotype of Treg cells. Here, we report that the inflammatory cytokine interleukin-6 (IL-6) actively repressed Eos expression through microRNA-17 (miR-17). miR-17 expression increased in Treg cells in the presence of IL-6, and its expression negatively correlated with that of Eos. Treg cell suppressive activity was diminished upon overexpression of miR-17 in vitro and in vivo, which was mitigated upon co-expression of an Eos mutant lacking miR-17 target sites. Also, RNAi of miR-17 resulted in enhanced suppressive activity. Ectopic expression of miR-17 imparted effector-T-cell-like characteristics to Treg cells via the de-repression of genes encoding effector cytokines. Thus, miR-17 provides a potent layer of Treg cell control through targeting Eos and additional Foxp3 co-regulators.

Ubiquitin-dependent regulation of Foxp3 and Treg function

Regulatory T (Treg) cells are crucial enforcers of immune homeostasis. Their characteristic suppressive function largely arises from an equally unique pattern of gene expression. A complex network of factors and processes contribute to this 'signature' Treg gene expression landscape. Many of these alter the level and activity of the Treg-defining transcription factor Foxp3. As stable expression of Foxp3 is important for the ability of Treg cells to successfully prevent excessive or inappropriate immune activation, uncovering the mechanisms regulating Foxp3 level is required for the understanding and therapeutic exploitation of Tregs. While transcriptional regulation of the Foxp3 gene has been studied in depth, additional regulatory layers exist controlling the expression and activity of this key transcription factor. These include less-defined mechanisms active at the post-translational level. These pathways are just beginning to be elucidated. Here, we summarize emerging evidence for distinct, post-translationally active, ubiquitin-dependent pathways capable of controlling the activation and expression of Foxp3 and the function of Tregs. These pathways offer untapped opportunities for therapeutic fine-tuning of Tregs and their all-important restraint of the immune system.

Hypoxia-inducible factors in T lymphocyte differentiation and function. A Review in the Theme: Cellular Responses to Hypoxia

Low oxygen concentrations or hypoxia is a trait common to inflamed tissues. Therefore it is not surprising that pathways of hypoxic stress response, largely governed by hypoxia-inducible factors (HIF), are highly relevant to the proper function of immune cells. HIF expression and stabilization in immune cells can be triggered not only by hypoxia, but also by a variety of stimuli and pathological stresses associated with leukocyte activation and inflammation. In addition to its role as a sensor of oxygen scarcity, HIF is also a major regulator of immune cell metabolic function. Rapid progress is being made in elucidating the roles played by HIF in diverse aspects of both innate and adaptive immunity. Here we discuss a number of breakthroughs that have shed light on how HIF expression and activity impact the differentiation and function of diverse T cell populations. The insights gained from these findings may serve as the foundation for future therapies aimed at fine-tuning the immune response.

Treg functional stability and its responsiveness to the microenvironment

Regulatory T cells (Tregs) prevent autoimmunity and tissue damage resulting from excessive or unnecessary immune activation through their suppressive function. While their importance for proper immune control is undeniable, the stability of the Treg lineage has recently become a controversial topic. Many reports have shown dramatic loss of the signature Treg transcription factor Forkhead box protein 3 (Foxp3) and Treg function under various inflammatory conditions. Other recent studies demonstrate that most Tregs are extremely resilient in their expression of Foxp3 and the retention of suppressive function. While this debate is unlikely to be settled in the immediate future, improved understanding of the considerable heterogeneity within the Foxp3(+) Treg population and how Treg subsets respond to ranging environmental cues may be keys to reconciliation. In this review, we discuss the diverse mechanisms responsible for the observed stability or instability of Foxp3(+) Treg identity and function. These include transcriptional and epigenetic programs, transcript targeting, and posttranslational modifications that appear responsive to numerous elements of the microenvironment. These mechanisms for Treg functional modulation add to the discussion of Treg stability.

Ubiquitous points of control over regulatory T cells

Posttranslational modification by ubiquitin tagging is crucial for regulating the stability, activity and cellular localization of many target proteins involved in processes including DNA repair, cell cycle progression, protein quality control, and signal transduction. It has long been appreciated that ubiquitin-mediated events are important for certain signaling pathways leading to leukocyte activation and the stimulation of effector function. Now it is clear that the activities of molecules and pathways central to immune regulation are also modified and controlled by ubiquitin tagging. Among the mechanisms of immune control, regulatory T cells (or Tregs) are themselves particularly sensitive to such regulation. E3 ligases and deubiquitinases both influence Tregs through their effects on the signaling pathways pertinent to these cells or through the direct, posttranslational regulation of Foxp3. In this review, we will summarize and discuss several examples of ubiquitin-mediated control over multiple aspects of Treg biology including the generation, function and phenotypic fidelity of these cells. Fully explored and exploited, these potential opportunities for Treg modulation may lead to novel immunotherapies for both positive and negative fine-tuning of immune restraint.

The ubiquitin ligase Stub1 negatively modulates regulatory T cell suppressive activity by promoting degradation of the transcription factor Foxp3

Regulatory T (Treg) cells suppress inflammatory immune responses and autoimmunity caused by self-reactive T cells. The key Treg cell transcription factor Foxp3 is downregulated during inflammation to allow for the acquisition of effector T cell-like functions. Here, we demonstrate that stress signals elicited by proinflammatory cytokines and lipopolysaccharides lead to the degradation of Foxp3 through the action of the E3 ubiquitin ligase Stub1. Stub1 interacted with Foxp3 to promote its K48-linked polyubiquitination in an Hsp70-dependent manner. Knockdown of endogenous Stub1 or Hsp70 prevented Foxp3 degradation. Furthermore, the overexpression of Stub1 in Treg cells abrogated their ability to suppress inflammatory immune responses in vitro and in vivo and conferred a T-helper-1-cell-like phenotype. Our results demonstrate the critical role of the stress-activated Stub1-Hsp70 complex in promoting Treg cell inactivation, thus providing a potential therapeutic target for the intervention against autoimmune disease, infection, and cancer.

Stabilization of the transcription factor Foxp3 by the deubiquitinase USP7 increases Treg-cell-suppressive capacity

Stable Foxp3 expression is required for the development of functional regulatory T (Treg) cells. Here, we demonstrate that the expression of the transcription factor Foxp3 can be regulated through the polyubiquitination of multiple lysine residues, resulting in proteasome-mediated degradation. Expression of the deubiquitinase (DUB) USP7 was found to be upregulated and active in Treg cells, being associated with Foxp3 in the nucleus. Ectopic expression of USP7 decreased Foxp3 polyubiquitination and increased Foxp3 expression. Conversely, either treatment with DUB inhibitor or USP7 knockdown decreased endogenous Foxp3 protein expression and decreased Treg-cell-mediated suppression in vitro. Furthermore, in a murine adoptive-transfer-induced colitis model, either inhibition of DUB activity or USP7 knockdown in Treg cells abrogated their ability to resolve inflammation in vivo. Our data reveal a molecular mechanism in which rapid temporal control of Foxp3 expression in Treg cells can be regulated by USP7, thereby modulating Treg cell numbers and function.

Pentalinon andrieuxii root extract is effective in the topical treatment of cutaneous leishmaniasis caused by Leishmania mexicana

Cutaneous leishmaniasis (CL) manifests as localized skin lesions, which lead to significant tissue destruction and disfigurement. In the Yucatan Peninsula, Mayan traditional healers use Pentalinon andrieuxii Muell.-Arg. (Apocynaceae) roots for the topical treatment of CL. Here, we studied the effect of P. andrieuxii root hexane extract (PARE) on the parasites and host cells in vitro and examined its efficacy in the topical treatment of CL caused by Leishmania mexicana. PARE exhibited potent antiparasitic activity in vitro against promastigotes as well as amastigotes residing in macrophages. Electron microscopy of PARE-treated parasites revealed direct membrane damage. PARE also activated nuclear factor kappaB and enhanced interferon-γ receptor and MHC class II expression and TNF-α production in macrophages. In addition, PARE induced production of the Th1 promoting cytokine IL-12 in dendritic cells as well as enhanced expression of the co-stimulatory molecules CD40, CD80, and CD86. In vivo studies showed that L. mexicana-infected mice treated by topical application of PARE resulted in the significant reduction in lesion size and parasite burden compared to controls. These findings indicate that PARE could be used as an alternative therapy for the topical treatment of CL.

Metabolic control of the Treg/Th17 axis

The interplay of the immune system with other aspects of physiology is continually being revealed and in some cases studied in considerable mechanistic detail. A prime example is the influence of metabolic cues on immune responses. It is well appreciated that upon activation, T cells take on a metabolic profile profoundly distinct from that of their quiescent and anergic counterparts; however, a number of recent breakthroughs have greatly expanded our knowledge of how aspects of cellular metabolism can shape a T-cell response. Particularly important are findings that certain environmental cues can tilt the delicate balance between inflammation and immune tolerance by skewing T-cell fate decisions toward either the T-helper 17 (Th17) or T-regulatory (Treg) cell lineage. Recognizing the unappreciated immune-modifying potential of metabolic factors and particularly those involved in the generation of these functionally opposing T-cell subsets will likely add new and potent therapies to our repertoire for treating immune mediated pathologies. In this review, we summarize and discuss recent findings linking certain metabolic pathways, enzymes, and by-products to shifts in the balance between Th17 and Treg cell populations. These advances highlight numerous opportunities for immune modulation.

Neuritin promotes the expansion and persistence of regulatory T cells in vitro and in vivo. (P1051)

Regulatory T cells (Tregs) represent a major force for immune control and the prevention of excessive or self-directed responses. These cells are marked by expression of the transcription factor Foxp3 and their ability to suppress leukocyte activation. Deficits in Treg function or numbers result in immune mediated pathologies, reflecting their importance as a layer of immune regulation. However the factors and mechanisms responsible for maintaining these cells are incompletely understood. Here, we report that a GPI-anchored molecule known as neuritin is highly and uniquely expressed by Treg and this molecule potently drives expansion and persistence of the ‘Treg-pool’. Transgenic expression of neuritin by Tregs enhanced their division in vitro while treatment with anti-neuritin antibody stunted Treg proliferation. Further suggesting a role in maintaining the Treg population, neuritin transgenic mice displayed expedited recovery in the EAE model of autoimmune disease accompanied by elevated frequencies of Foxp3+ Tregs. Conversely, antibody mediated neuritin blockade prolonged disease and stunted proliferation of Foxp3+ cells during EAE. Further dissection of neuritin activity revealed the involvement of paradoxically enhanced IL-2 production by this Treg specific factor. In all these findings strongly implicate neuritin as a Treg derived factor responsible for the persistence of these cells and their control of immune responses.

Glucose-independent glutamine metabolism via TCA cycling for proliferation and survival in B cells

Because MYC plays a causal role in many human cancers, including those with hypoxic and nutrient-poor tumor microenvironments, we have determined the metabolic responses of a MYC-inducible human Burkitt lymphoma model P493 cell line to aerobic and hypoxic conditions, and to glucose deprivation, using stable isotope-resolved metabolomics. Using [U-(13)C]-glucose as the tracer, both glucose consumption and lactate production were increased by MYC expression and hypoxia. Using [U-(13)C,(15)N]-glutamine as the tracer, glutamine import and metabolism through the TCA cycle persisted under hypoxia, and glutamine contributed significantly to citrate carbons. Under glucose deprivation, glutamine-derived fumarate, malate, and citrate were significantly increased. Their (13)C-labeling patterns demonstrate an alternative energy-generating glutaminolysis pathway involving a glucose-independent TCA cycle. The essential role of glutamine metabolism in cell survival and proliferation under hypoxia and glucose deficiency makes them susceptible to the glutaminase inhibitor BPTES and hence could be targeted for cancer therapy.

Mammalian antimicrobial peptide influences control of cutaneous Leishmania infection

Cathelicidin-type antimicrobial peptides (CAMP) are important mediators of innate immunity against microbial pathogens acting through direct interaction with and disruption of microbial membranes and indirectly through modulation of host cell migration and activation. Using a mouse knock-out model in CAMP we studied the role of this host peptide in control of dissemination of cutaneous infection by the parasitic protozoan Leishmania. The presence of pronounced host inflammatory infiltration in lesions and lymph nodes of infected animals was CAMP-dependent. Lack of CAMP expression was associated with higher levels of IL-10 receptor expression in bone marrow, splenic and lymph node macrophages as well as higher anti-inflammatory IL-10 production by bone marrow macrophages and spleen cells but reduced production of the pro-inflammatory cytokines IL-12 and IFN-γ by lymph nodes. Unlike wild-type mice, local lesions were exacerbated and parasites were found largely disseminated in CAMP knockouts. Infection of CAMP knockouts with parasite mutants lacking the surface metalloprotease virulence determinant resulted in more robust disseminated infection than in control animals suggesting that CAMP activity is negatively regulated by parasite surface proteolytic activity. This correlated with the ability of the protease to degrade CAMP in vitro and co-localization of CAMP with parasites within macrophages. Our results highlight the interplay of antimicrobial peptides and Leishmania that influence the host immune response and the outcome of infection.

Eos mediates Foxp3-dependent gene silencing in CD4+ regulatory T cells. (138.20)

CD4+ regulatory T cells (Tregs) maintain immunological self-tolerance and immune homeostasis by suppressing aberrant or excessive immune responses. The core genetic program of Tregs and their ability to suppress pathologic immune responses depends on the transcription factor Foxp3. Despite progress in understanding mechanisms of Foxp3-dependent gene activation, the molecular mechanism of Foxp3-dependent gene repression remains largely unknown. Here we identify Eos, a zinc-finger transcription factor of the Ikaros family, as a critical mediator of Foxp3-dependent gene silencing in Tregs. By qRT-PCR analysis we found that Eos is highly expressed in the CD4+CD25+ and CD4+Foxp3+ population of T cells. Additionally, Eos interacts directly with Foxp3 and induces chromatin modifications that result in gene silencing in Tregs. Silencing of Eos in Tregs abrogates their ability to suppress naïve T cell proliferation in vitro. Furthermore, Tregs with Eos knockdown fail to protect recipient Rag2-/- mice from severe colitis when co-transferred with naïve (CD4+CD25- CD62Lhigh ) T cells. Eos silencing in Tregs also endows these cells with partial effector function. These results demonstrate the critical role that Eos plays in Treg programming. They also raise the possibility that the interaction between Foxp3 and Eos may be a therapeutic target for controlling pathological immune responses in which excessive Treg activity plays an important role such as cancer and chronic infections.

Eos mediates Foxp3-dependent gene silencing in CD4+ regulatory T cells

CD4+ regulatory T cells (Tregs) maintain immunological self-tolerance and immune homeostasis by suppressing aberrant or excessive immune responses. The core genetic program of Tregs and their ability to suppress pathologic immune responses depends on the transcription factor Foxp3. Despite progress in understanding mechanisms of Foxp3-dependent gene activation, the molecular mechanism of Foxp3-dependent gene repression remains largely unknown. We identified Eos, a zinc-finger transcription factor of the Ikaros family, as a critical mediator of Foxp3-dependent gene silencing in Tregs. Eos interacts directly with Foxp3 and induces chromatin modifications that result in gene silencing in Tregs. Silencing of Eos in Tregs abrogates their ability to suppress immune responses and endows them with partial effector function, thus demonstrating the critical role that Eos plays in Treg programming.

Signal transducer and activator of transcription 1 in T cells plays an indispensable role in immunity to Leishmania major by mediating Th1 cell homing to the site of infection

The signal transducer and activator of transcription 1 (STAT1) signaling pathway mediates the biological functions of IFN-gamma. We have previously shown that the STAT1 pathway is indispensable for host resistance against Leishmania major infection. In this study, we examined the role of STAT1 in lymphocytes and specifically CD4(+) and CD8(+) T cells in mediating immunity against L. major by transferring T cells from wild-type (WT) and STAT1(-/-) C57BL/6 mice into Rag2(-/-) C57BL/6 mice. Rag2(-/-) mice reconstituted with unfractionated STAT1(-/-) splenocytes (B cells and T cells) failed to mount an efficient Th1 response after L. major infection, produced more IL-4, and developed large lesions full of parasites. In contrast, Rag2(-/-) mice reconstituted with WT (STAT1(+/+)) splenocytes mounted a Th1 response and developed self-resolving lesions. Studies using Rag2(-/-) recipients that received a combination of purified CD4(+) and CD8(+) T cells from WT or STAT1(-/-) mice revealed that STAT1 deficiency in CD4(+) T cells, but not in CD8(+) T cells, leads to development of chronic, nonhealing lesions and systemic dissemination of parasites into the spleen after L. major infection. Further studies using Rag2(-/-) recipients of WT Thy1.1(+) and STAT1(-/-) Thy1.2(+) T cells showed that STAT1 in CD4(+) T cells was not required for Th1 differentiation during L. major infection. However, it was critical for up-regulation of CXCR3 on CD4(+) T cells and their migration to the regional lymph node and the cutaneous site of infection. Together, these studies indicate that the STAT1 pathway in CD4(+) T cells plays a critical role in immunity against L. major by controlling the migration of Th1 cells to the site of infection rather than their generation. Further, they reveal an essential role for CD4(+) T cell STAT1 in preventing systemic dissemination of L. major infection.

Selective deficiency of STAT1 in CD4+ T cells enhances susceptibility to Leishmania major infection not by preventing induction of Th1 response, but by impairing CD4+ T cell homing (44.26)

We previously reported that STAT1 signaling is indispensable for host resistance against Leishmania major. In this study, we examined the role of STAT1 in lymphocytes as well as CD4+ versus CD8+ T cells in mediating immunity to L. major by performing adoptive transfers of T cells from WT and STAT1-/- C57BL/6 mice to Rag2-/- C57BL/6 mice. Rag2-/- mice reconstituted with STAT1-/- splenocytes (B cells and T cells) failed to mount an efficient Th1 response following L. major infection, produced more IL-4 and developed large lesions full of parasites. In contrast, Rag2-/- mice reconstituted with WT (STAT1+/+) splenocytes mounted a Th1 response and developed self-resolving lesions. Studies using Rag2-/- recipients that received a combination of purified CD4+ and CD8+ T cells from WT or STAT1-/- mice revealed that STAT1 in CD4+, but not CD8+ T cells was indispensable for immunity against L. major. Further studies using Thy1.1+ congenic recipients receiving WT or STAT1 Thy1.2+ CD4+ cells showed that STAT1 in CD4+ T cells was not required for Th1 differentiation and IFN-γ production during L. major infection, but was critical for migration to regional lymph nodes and the cutaneous site of infection. Together these studies indicate that STAT1 signaling in CD4+ T cells plays a critical role in immunity against L. major by controlling migration of Th1 cells to the site of infection rather than their generation.

Research Support: NIH

The chemokine receptor CXCR3 is required for optimal murine resistance against Toxoplasma gondii (129.30)

CXC chemokine receptor 3 (CXCR3) plays a critical role in recruitment of neutrophils, natural killer cells and T cells to sites of inflammation. Since these cell types are all critical in control of Toxoplasma gondii infection we hypothesized that CXCR3 is critical for immunity against T. gondii. To test this hypothesis we compared the course of T. gondii (ME49) infection in WT and CXCR3-/- mice on a C57BL/6 background. Following ME49 challenge, CXCR3-/- mice developed high brain parasite loads and succumbed to infection significantly faster than WT mice. T. gondii antigen-stimulated splenocytes from CXCR3-/- mice produced significantly more IFN-γ than WT splenocytes, but serum levels of this cytokine were lower in the former. Flow cytometry also revealed that CXCR3-/- mice recruit fewer leukocytes into the brain than WT mice early during infection. Finally, adoptive transfer studies involving Rag2-/- mice reconstituted with CXCR3-/- or WT lymphocytes revealed that CXCR3 expression on T cells was critical for effective immunity against ME49. Taken together, these results show that CXCR3 is critical for immunity against T. gondii. Furthermore, they suggest that increased susceptibility of CXCR3-/- mice is due to impaired leukocyte trafficking - most likely CXCR3 expressing T cells - into infection sites and not due to impairments in type I CD4+ T cell responses.

Support: NIH

Macrophages contribute to pathogenesis of visceral leishmaniasis via a STAT1-dependent mechanism (131.10)

We previously reported that STAT1-/- mice on a susceptible BALB/c background were highly resistant to visceral leishmaniasis (VL) and developed minimal organ pathology compared with wild-type (WT) controls, despite mounting a poor Th1 response. We also found that STAT1 in non-T cells (i.e. macrophages and neutrophils) mediated susceptibility and pathology. The objective of this study was to determine whether macrophages are involved in the pathogenesis of VL cause by Leishmania donovani and to determine the role of STAT1 in phagocytes in mediating disease susceptibility. Depletion of monocytes and macrophages using clodronate-containing liposomes both prior to and after L. donovani infection impaired Th1 development in WT BALB/c mice, but rendered them highly resistant to infection and minimized liver pathology. This phenotype was strikingly similar to that seen in infected STAT1-/- mice. Further in vivo studies using an airpouch model demonstrated that both macrophages and neutrophils of STAT1-/- mice had significant impairments in parasite uptake compared with WT controls. Taken together, these results demonstrate that macrophages are involved in the pathogenesis of VL, and that STAT1 signaling may mediate disease susceptibility by facilitating parasite uptake into host phagocytes.

Support: NIH

T cells from Leishmania major-susceptible BALB/c mice have a defect in efficiently up-regulating CXCR3 upon activation

Genetic background influences the outcome of Leishmania major infection. C57BL/6 mice mount a Th1 response and resolve infection. In contrast, BALB/c mice mount a Th2 response and develop chronic lesions. This susceptible phenotype is seen even though BALB/c mice generate IFN-gamma-producing T cells at proportions similar to C57BL/6 mice in their lymph nodes (LN) early after infection. We had previously shown that chemokine receptor CXCR3 mediates immunity against L. major by recruiting IFN-gamma-producing T cells to the lesions of C57BL/6 mice. Therefore, we hypothesized that IFN-gamma-secreting T cells in BALB/c mice are unable to confer protection because they may be defective in up-regulating CXCR3. To test this hypothesis, we analyzed kinetics of CXCR3-expressing T cells in the LN and lesions of BALB/c and C57BL/6 mice during L. major infection. Additionally, we compared the ability of T cells from BALB/c and C57BL/6 mice to up-regulate CXCR3 upon activation. We found that resolution of L. major infection in C57BL/6 mice was associated with an increase in the proportion of CXCR3(+) T cells in regional LN and lesions, whereas disease progression in BALB/c mice was associated with a decrease in these populations. Anti-CD3/CD28-activated T cells from naive BALB/c but not C57BL/6 mice were defective in up-regulating CXCR3. Impaired induction of CXCR3 on BALB/c T cells was not due to lack of IFN-gamma and was mediated partially by IL-10 but not IL-4 or IL-13. We propose that defective CXCR3 up-regulation on T cells in BALB/c mice may contribute to L. major susceptibility.

Macrophage migration inhibitory factor (MIF) is critical for the host resistance against Toxoplasma gondii

Macrophage migration inhibitory factor (MIF) exerts either a protective or a deleterious role in the immune response to different pathogens. We analyzed herein the role of MIF in the host control of toxoplasmosis using MIF(-/-) mice backcrossed to either the BALB/c or the C57BL/6 genetic backgrounds. Both, wild-type (WT) BALB/c and MIF(-/-) BALB/c mice were susceptible to infection with highly virulent RH as well as moderately virulent ME49 strains of T. gondii. MIF(-/-) mice, however, showed greater liver damage and more brain cysts, produced less proinflammatory cytokines, and succumbed significantly faster than WT mice. Bone marrow-derived dendritic cells (BMDCs) from MIF(-/-) mice produced less interleukin-1beta, interleukin-12, and tumor necrosis factor-alpha than WT BMDCs after stimulation with soluble Toxoplasma antigen (STAg). Similar observations were made in CD11c(+) low-density cells isolated from the spleens of MIF(-/-) mice challenged with STAg. MIF(-/-) C57BL/6 mice succumbed to ME49 infection faster than their WT counterparts. C57BL/6 mice that succumbed to infection with the ME49 strain produced less MIF than resistant BALB/c mice similarly infected. Interestingly, an analysis of brains from patients with cerebral toxoplasmosis showed low levels of MIF expression. Together, these findings demonstrate that MIF plays a critical role in mediating host resistance against T. gondii.

Role of phosphatidylinositol-3-kinase-gamma (PI3Kgamma)-mediated pathway in 17beta-estradiol-induced killing of L. mexicana in macrophages from C57BL/6 mice

We recently demonstrated that 17beta-estradiol (E2) enhances killing of Leishmania mexicana in macrophages from both male and female DBA/2 mouse by increasing nitric oxide (NO) production. Here, we analyzed the effect of E2 on leishmanicidal activity and cytokine production by bone marrow-derived macrophages (BMDMs) from male and female C57BL/6 mice in vitro, specifically examining the role of phosphatidylinositol-3-kinase-gamma (PI3Kgamma) in E2-induced parasite killing. Unlike its effect on macrophages from both male and female DBA/2 mice, E2 only increased leishmanicidal activity in macrophages from female C57BL/6 mice, which was evident by a significant reduction in both infection rates and infection levels compared to sham controls. E2-treated BMDMs from female C57BL/6 mice expressed higher levels of interferon-gammaRalpha, and also produced more interleukin (IL)-12, IL-6 and NO than both the sham controls and E2-treated male-derived macrophages. Sham-treated BMDMs from female PI3Kgamma-/- C57BL/6 mice displayed lower infection rates and infection levels compared to sham-treated wild-type (WT) macrophages. However E2, unlike its effect on macrophages from female WT C57BL/6 mice, failed to reduce infection rates and infection levels in BMDMs from female PI3Kgamma-/- mice. Interestingly, E2-treated BMDMs from female C57BL/6 mice produced significant amounts of inflammatory cytokines and NO in levels comparable to those observed in sham-treated PI3Kgamma-deficient macrophages as well as E2-treated macrophages from WT mice. These findings show that E2 exerts a distinct effect on leishmanicidal activity of macrophages from male versus female C57BL/6 mice. In addition, they suggest that PI3Kgamma is not required for E2-induced cytokine and NO production in L. mexicana-infected macrophages from female C57BL/6 mice but it may be involved in parasite clearance from these cells.

Lack of CXCR3 delays the development of hepatic inflammation but does not impair resistance to Leishmania donovani

CXC chemokine receptor 3 (CXCR3) ligands CXCL9 and CXCL10 are produced at high levels in mice and humans infected with Leishmania donovani, but their contribution to host resistance against L. donovani is not clear. Here, using CXCR3(-/-) mice, we demonstrate that, although CXCR3 regulates early immune cell trafficking and hepatic inflammation during L. donovani infection, it is not essential for immunity against L. donovani, unlike L. major. CXCR3(-/-) C57BL/6 mice show a delayed onset of hepatic inflammation and granuloma formation after L. donovani infection. However, they mount an efficient T helper cell type 1 response, recruit T cells to the liver, and control parasite growth as efficiently as do CXCR3(+/+) C57BL/6 mice.