A cell-level discriminative neural network model for diagnosis of blood cancers

MOTIVATION

Precise identification of cancer cells in patient samples is essential for accurate diagnosis and clinical monitoring but has been a significant challenge in machine learning approaches for cancer precision medicine. In most scenarios, training data are only available with disease annotation at the subject or sample level. Traditional approaches separate the classification process into multiple steps that are optimized independently. Recent methods either focus on predicting sample-level diagnosis without identifying individual pathologic cells or are less effective for identifying heterogeneous cancer cell phenotypes.

RESULTS

We developed a generalized end-to-end differentiable model, the Cell Scoring Neural Network (CSNN), which takes sample-level training data and predicts the diagnosis of the testing samples and the identity of the diagnostic cells in the sample, simultaneously. The cell-level density differences between samples are linked to the sample diagnosis, which allows the probabilities of individual cells being diagnostic to be calculated using backpropagation. We applied CSNN to two independent clinical flow cytometry datasets for leukemia diagnosis. In both qualitative and quantitative assessments, CSNN outperformed preexisting neural network modeling approaches for both cancer diagnosis and cell-level classification. Post hoc decision trees and 2D dot plots were generated for interpretation of the identified cancer cells, showing that the identified cell phenotypes match the cancer endotypes observed clinically in patient cohorts. Independent data clustering analysis confirmed the identified cancer cell populations.

AVAILABILITY AND IMPLEMENTATION

The source code of CSNN and datasets used in the experiments are publicly available on GitHub (http://github.com/erobl/csnn). Raw FCS files can be downloaded from FlowRepository (ID: FR-FCM-Z6YK).

CTLA4 depletes T cell endogenous and trogocytosed B7 ligands via cis-endocytosis

CD28 and CTLA4 are T cell coreceptors that competitively engage B7 ligands CD80 and CD86 to control adaptive immune responses. While the role of CTLA4 in restraining CD28 costimulatory signaling is well-established, the mechanism has remained unclear. Here, we report that human T cells acquire antigen-presenting-cell (APC)-derived B7 ligands and major histocompatibility complex (MHC) via trogocytosis through CD28:B7 binding. Acquired MHC and B7 enabled T cells to autostimulate, and this process was limited cell-intrinsically by CTLA4, which depletes B7 ligands trogocytosed or endogenously expressed by T cells through cis-endocytosis. Extending this model to the previously proposed extrinsic function of CTLA4 in human regulatory T cells (Treg), we show that blockade of either CD28 or CTLA4 attenuates Treg-mediated depletion of APC B7, indicating that trogocytosis and CTLA4-mediated cis-endocytosis work together to deplete B7 from APCs. Our study establishes CTLA4 as a cell-intrinsic molecular sink that limits B7 availability on the surface of T cells, with implications for CTLA4-targeted therapy.

Dual receptor T cells mediate effective antitumor immune responses via increased recognition of tumor antigens

BACKGROUND

Discovery that ~16% of T cells naturally co-express two T-cell receptor (TCR) clonotypes prompts examining the role of dual TCR cells in immune functions.

METHODS

Using TCRα-reporter transgenic mice, enabling unambiguous identification of single-TCR and dual-TCR cells, we tested the role of dual TCR cells in antitumor immune responses against immune-responsive syngeneic 6727 sarcoma and immune-resistant B16F10 melanoma.

RESULTS

Dual TCR cells were specifically increased among tumor-infiltrating lymphocytes (TILs) in both models, indicating selective advantage in antitumor responses. Phenotype and single-cell gene expression analyses identified dual TCR are predominant during the effective antitumor response, demonstrating selectively increased activation in the TIL compartment and skewing toward an effector memory phenotype. Absence of dual TCR cells impaired immune response to B16F10 but not 6727, suggesting that dual TCR cells may be more influential in responses against poorly immunogenic tumors. Dual TCR cells demonstrated an advantage in recognition of B16F10-derived neoantigens in vitro, providing a mechanistic basis for their antitumor reactivity.

CONCLUSIONS

These results discover an unrecognized role for dual TCR cells in protective immune function and identify these cells and their TCRs as a potential resource for antitumor immunotherapy.

cis-B7:CD28 interactions at invaginated synaptic membranes provide CD28 co-stimulation and promote CD8+ T cell function and anti-tumor immunity

B7 ligands (CD80 and CD86), expressed by professional antigen-presenting cells (APCs), activate the main co-stimulatory receptor CD28 on T cells in trans. However, in peripheral tissues, APCs expressing B7 ligands are relatively scarce. This raises the questions of whether and how CD28 co-stimulation occurs in peripheral tissues. Here, we report that CD8⁺ T cells displayed B7 ligands that interacted with CD28 in cis at membrane invaginations of the immunological synapse as a result of membrane remodeling driven by phosphoinositide-3-kinase (PI3K) and sorting-nexin-9 (SNX9). cis-B7:CD28 interactions triggered CD28 signaling through protein kinase C theta (PKCθ) and promoted CD8⁺ T cell survival, migration, and cytokine production. In mouse tumor models, loss of T cell-intrinsic cis-B7:CD28 interactions decreased intratumoral T cells and accelerated tumor growth. Thus, B7 ligands on CD8⁺ T cells can evoke cell-autonomous CD28 co-stimulation in cis in peripheral tissues, suggesting cis-signaling as a general mechanism for boosting T cell functionality.

Abstract 606: Cis-B7:CD28 interactions at invaginated synaptic membranes activate CD28 and promote T cell function

Absence of adequate CD28 costimulation is a common feature of dysfunctional T cells in cancer. However, although augmentation of CD28 signaling is well known to be essential for restoring dysfunctional T cell immune responses upon immune checkpoint blockade treatment, it is unclear how CD28 in tumor-infiltrated T cells is activated in the absence of corresponding ligands on cancer. In current dogma, the T cell CD28 can be activated in trans by CD80 (B7-1) or CD86 (B7-2) expressed on professional antigen presenting cells (APCs) enriched in secondary lymphoid organs. Notably, besides professional APCs, B7 ligands are also displayed by T cells, but their functions are unclear. Here we report that B7 ligands expressed on T cells interact with CD28 in cis at membrane invaginations of the immunological synapse, as a result of phosphoinositide-3-kinase (PI3K) mediated membrane remodeling. Cis-B7:CD28 interactions triggered CD28 signaling through protein-kinase-C-theta (PKCθ) and promoted T cell survival, migration and cytokine production. In a B7 deficient tumor model grafted with primed CD8+ T cells, blockade of T cell intrinsic B7:CD28 interactions accelerated tumor growth and decreased intratumoral T cells. Thus, B7 ligands on T cells can evoke cell autonomous CD28 costimulation in cis in peripheral tissues, suggesting cis-signaling as a general mechanism for boosting T cell functionality.

Citation Format: Yunlong Zhao, Christine Caron, Ya-Yuan Chan, Calvin K. Lee, Xiaozheng Xu, Jack D. Bui, Enfu Hui. Cis-B7:CD28 interactions at invaginated synaptic membranes activate CD28 and promote T cell function [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 606.

A cell-level discriminative neural network model for diagnosis of blood cancers

Motivation

Precise identification of cancer cells in patient samples is essential for accurate diagnosis and clinical monitoring but has been a significant challenge in machine learning approaches for cancer precision medicine. In most scenarios, training data are only available with disease annotation at the subject or sample level. Traditional approaches separate the classification process into multiple steps that are optimized independently. Recent methods either focus on predicting sample-level diagnosis without identifying individual pathologic cells or are less effective for identifying heterogeneous cancer cell phenotypes.

Results

We developed a generalized end-to-end differentiable model, the Cell Scoring Neural Network (CSNN), which takes the available sample-level training data and predicts both the diagnosis of the testing samples and the identity of the diagnostic cells in the sample, simultaneously. The cell-level density differences between samples are linked to the sample diagnosis, which allows the probabilities of individual cells being diagnostic to be calculated using backpropagation. We applied CSNN to two independent clinical flow cytometry datasets for leukemia diagnosis. In both qualitative and quantitative assessments, CSNN outperformed preexisting neural network modeling approaches for both cancer diagnosis and cell-level classification. Post hoc decision trees and 2D dot plots were generated for interpretation of the identified cancer cells, showing that the identified cell phenotypes match the cancer endotypes observed clinically in patient cohorts. Independent data clustering analysis confirmed the identified cancer cell populations.

Availability

The source code of CSNN and datasets used in the experiments are publicly available on GitHub and FlowRepository.

Contact

Edgar E. Robles: roblesee@uci.edu and Yu Qian: mqian@jcvi.org.

Supplementary information

Supplementary data are available on GitHub and at Bioinformatics online.

SnapShot: Cancer immunoediting

In the tumor microenvironment, immune cells and tumor cells interact in a process called cancer immunoediting, giving rise to changes in gene expression, metabolism, mutational burden, and cellularity in the tumor. This SnapShot compares endogenous versus therapy-induced cancer immunoediting and outlines the molecular and cellular characteristics of interactions that result in complete tumor regression versus tumor escape and progression. To view this SnapShot, open or download the PDF.

Lymphatic-preserving treatment sequencing with immune checkpoint inhibition unleashes cDC1-dependent antitumor immunity in HNSCC

Despite the promise of immune checkpoint inhibition (ICI), therapeutic responses remain limited. This raises the possibility that standard of care treatments delivered in concert may compromise the tumor response. To address this, we employ tobacco-signature head and neck squamous cell carcinoma murine models in which we map tumor-draining lymphatics and develop models for regional lymphablation with surgery or radiation. We find that lymphablation eliminates the tumor ICI response, worsening overall survival and repolarizing the tumor- and peripheral-immune compartments. Mechanistically, within tumor-draining lymphatics, we observe an upregulation of conventional type I dendritic cells and type I interferon signaling and show that both are necessary for the ICI response and lost with lymphablation. Ultimately, we provide a mechanistic understanding of how standard oncologic therapies targeting regional lymphatics impact the tumor response to immune-oncology therapy in order to define rational, lymphatic-preserving treatment sequences that mobilize systemic antitumor immunity, achieve optimal tumor responses, control regional metastatic disease, and confer durable antitumor immunity.

Monomethyl auristatin antibody and peptide drug conjugates for trimodal cancer chemo-radio-immunotherapy

Locally advanced cancers remain therapeutically challenging to eradicate. The most successful treatments continue to combine decades old non-targeted chemotherapies with radiotherapy that unfortunately increase normal tissue damage in the irradiated field and have systemic toxicities precluding further treatment intensification. Therefore, alternative molecularly guided systemic therapies are needed to improve patient outcomes when applied with radiotherapy. In this work, we report a trimodal precision cytotoxic chemo-radio-immunotherapy paradigm using spatially targeted auristatin warheads. Tumor-directed antibodies and peptides conjugated to radiosensitizing monomethyl auristatin E (MMAE) specifically produce CD8 T cell dependent durable tumor control of irradiated tumors and immunologic memory. In combination with ionizing radiation, MMAE sculpts the tumor immune infiltrate to potentiate immune checkpoint inhibition. Here, we report therapeutic synergies of targeted cytotoxic auristatin radiosensitization to stimulate anti-tumor immune responses providing a rationale for clinical translational of auristatin antibody drug conjugates with radio-immunotherapy combinations to improve tumor control.

AMC-070: Lenalidomide Is Safe and Effective in HIV-Associated Kaposi Sarcoma

PURPOSE

Kaposi sarcoma (KS), an endothelial cell tumor associated with KS herpesvirus (KSHV), remains among the most common malignancies occurring with HIV infection (HIV-KS). As an oral anti-inflammatory, antiangiogenic, and immunomodulatory agent, lenalidomide is potentially an attractive alternative to standard chemotherapy for KS.

EXPERIMENTAL DESIGN

The primary objectives of this phase I/II trial were to determine the maximum tolerated dose (MTD) and response rates for lenalidomide in HIV-KS. Secondary objectives included correlating response with natural killer (NK) and T-cell subsets, plasma cytokines, viral copy number, and KSHV gene expression in biopsies. Four dose levels of oral lenalidomide taken 21 consecutive days of 28-day cycles were evaluated in adults with HIV-KS on antiretroviral therapy with controlled viremia.

RESULTS

Fifteen and 23 participants enrolled in phases I and II, respectively, 76% of whom had received prior KS therapy. The MTD was not reached, declaring 25 mg as the recommended phase II dose (RP2D). The most frequent adverse events were neutropenia, fatigue, leukopenia, and diarrhea. Of the 25 evaluable participants receiving RP2D, 60% responded. Correlative studies performed in a subset of participants demonstrated a significant increase in proportions of blood T cells with T-regulatory phenotype, and plasma cytokines trended toward a less inflammatory pattern. Clinical response was associated with loss of KSHV transcription.

CONCLUSIONS

Lenalidomide is active in HIV-KS. The most common adverse events were manageable. With 60% of participants receiving RP2D obtaining a partial response and <10% discontinuing due to adverse events, the response and tolerability to lenalidomide support its use in HIV-KS. See related commentary by Henry and Maki, p. 2485.

Cancer-cell-secreted extracellular vesicles suppress insulin secretion through miR-122 to impair systemic glucose homeostasis and contribute to tumour growth

Epidemiological studies demonstrate an association between breast cancer (BC) and systemic dysregulation of glucose metabolism. However, how BC influences glucose homeostasis remains unknown. We show that BC-derived extracellular vesicles (EVs) suppress pancreatic insulin secretion to impair glucose homeostasis. EV-encapsulated miR-122 targets PKM in β-cells to suppress glycolysis and ATP-dependent insulin exocytosis. Mice receiving high-miR-122 EVs or bearing BC tumours exhibit suppressed insulin secretion, enhanced endogenous glucose production, impaired glucose tolerance and fasting hyperglycaemia. These effects contribute to tumour growth and are abolished by inhibiting EV secretion or miR-122, restoring PKM in β-cells or supplementing insulin. Compared with non-cancer controls, patients with BC have higher levels of circulating EV-encapsulated miR-122 and fasting glucose concentrations but lower fasting insulin; miR-122 levels are positively associated with glucose and negatively associated with insulin. Therefore, EV-mediated impairment of whole-body glycaemic control may contribute to tumour progression and incidence of type 2 diabetes in some patients with BC.

Intratumoral immunotherapy using platelet-cloaked nanoparticles enhances antitumor immunity in solid tumors

Intratumoral immunotherapy is an emerging modality for the treatment of solid tumors. Toll-like receptor (TLR) agonists have shown promise for eliciting immune responses, but systemic administration often results in the development of adverse side effects. Herein, we investigate whether localized delivery of the TLR agonist, resiquimod (R848), via platelet membrane-coated nanoparticles (PNP-R848) elicits antitumor responses. The membrane coating provides a means of enhancing interactions with the tumor microenvironment, thereby maximizing the activity of R848. Intratumoral administration of PNP-R848 strongly enhances local immune activation and leads to complete tumor regression in a colorectal tumor model, while providing protection against repeated tumor re-challenges. Moreover, treatment of an aggressive breast cancer model with intratumoral PNP-R848 delays tumor growth and inhibits lung metastasis. Our findings highlight the promise of locally delivering immunostimulatory payloads using biomimetic nanocarriers, which possess advantages such as enhanced biocompatibility and natural targeting affinities.

Evaluation of IL-17D in Host Immunity to Group A Streptococcus Infection

IL-17D is a cytokine that belongs to the IL-17 family and is conserved in vertebrates and invertebrates. In contrast to IL-17A and IL-17F, which are expressed in Th17 cells, IL-17D is expressed broadly in nonimmune cells. IL-17D can promote immune responses to cancer and viruses in part by inducing chemokines and recruiting innate immune cells such as NK cells. Although bacterial infection can induce IL-17D in fish and invertebrates, the role of mammalian IL-17D in antibacterial immunity has not been established. To determine whether IL-17D has a role in mediating host defense against bacterial infections, we studied i.p. infection by group A Streptococcus (GAS) in wild-type (WT) and Il17d ^-/- mice. Compared with WT animals, mice deficient in IL-17D experienced decreased survival, had greater weight loss, and showed increased bacterial burden in the kidney and peritoneal cavity following GAS challenge. In WT animals, IL-17D transcript was induced by GAS infection and correlated to increased levels of chemokine CCL2 and greater neutrophil recruitment. Of note, GAS-mediated IL-17D induction in nonimmune cells required live bacteria, suggesting that processes beyond recognition of pathogen-associated molecular patterns were required for IL-17D induction. Based on our results, we propose a model in which nonimmune cells can discriminate between nonviable and viable GAS cells, responding only to the latter by inducing IL-17D.

Heterogeneity and clonal relationships of adaptive immune cells in ulcerative colitis revealed by single-cell analyses

Inflammatory bowel disease (IBD) encompasses a spectrum of gastrointestinal disorders driven by dysregulated immune responses against gut microbiota. We integrated single-cell RNA and antigen receptor sequencing to elucidate key components, cellular states, and clonal relationships of the peripheral and gastrointestinal mucosal immune systems in health and ulcerative colitis (UC). UC was associated with an increase in IgG1⁺ plasma cells in colonic tissue, increased colonic regulatory T cells characterized by elevated expression of the transcription factor ZEB2, and an enrichment of a γδ T cell subset in the peripheral blood. Moreover, we observed heterogeneity in CD8⁺ tissue-resident memory T (T_RM) cells in colonic tissue, with four transcriptionally distinct states of differentiation observed across health and disease. In the setting of UC, there was a marked shift of clonally related CD8⁺ T_RM cells toward an inflammatory state, mediated, in part, by increased expression of the T-box transcription factor Eomesodermin. Together, these results provide a detailed atlas of transcriptional changes occurring in adaptive immune cells in the context of UC and suggest a role for CD8⁺ T_RM cells in IBD.

Novel computational analytics of clinical flow cytometry data identifies difficult-to-resolve leukemia cells for precision diagnosis

Motivation

Diagnosis of leukemia relies on accurate identification of leukemic cell populations. Flow cytometry (FCM) is a primary diagnostic assay routinely used in clinical practice. The assay workflows consist of multiple manual gating steps performed by technicians, followed by interpretation by hematopathologists. Challenges to this process include technical variability in manual gating, difficulty in identification of the atypical leukemic cells, and the growing number of antigens used for diagnosis.

Methods

Instead of conducting ad hoc analysis of individual samples, our proposed computational approach leverages preexisting clinical FCM data to improve robustness of the computational identification of leukemic cells. Instead of separating cell population identification and sample classification into two steps, our machine learning classification method optimizes them simultaneously, producing gating locations that are recognizable to hematopathologists.

Results

Our study consists of 10-color FCM data from blood or bone marrow samples of 129 random subjects for chronic lymphocytic leukemia (CLL) diagnosis. Our initial automated gating analysis rendered an accuracy of 89% matched the diagnosis of the hematopathologist. In the remaining cases with discrepant results, the misclassified CLL cells had atypical molecular phenotypes, making them difficult to identify. In our improved pipeline, we demonstrate that these atypical types of CLL cells can be clearly captured using a non-linear embedding dimensionality reduction step.

Conclusion

The results demonstrate the power of a novel computational analysis pipeline for improving the identification of aberrant leukemia cells for precision diagnosis.

Machine Learning of Discriminative Gate Locations for Clinical Diagnosis

High-throughput single-cell cytometry technologies have significantly improved our understanding of cellular phenotypes to support translational research and the clinical diagnosis of hematological and immunological diseases. However, subjective and ad hoc manual gating analysis does not adequately handle the increasing volume and heterogeneity of cytometry data for optimal diagnosis. Prior work has shown that machine learning can be applied to classify cytometry samples effectively. However, many of the machine learning classification results are either difficult to interpret without using characteristics of cell populations to make the classification, or suboptimal due to the use of inaccurate cell population characteristics derived from gating boundaries. To date, little has been done to optimize both the gating boundaries and the diagnostic accuracy simultaneously. In this work, we describe a fully discriminative machine learning approach that can simultaneously learn feature representations (e.g., combinations of coordinates of gating boundaries) and classifier parameters for optimizing clinical diagnosis from cytometry measurements. The approach starts from an initial gating position and then refines the position of the gating boundaries by gradient descent until a set of globally-optimized gates across different samples are achieved. The learning procedure is constrained by regularization terms encoding domain knowledge that encourage the algorithm to seek interpretable results. We evaluate the proposed approach using both simulated and real data, producing classification results on par with those generated via human expertise, in terms of both the positions of the gating boundaries and the diagnostic accuracy. © 2019 The Authors. Cytometry Part A published by Wiley Periodicals, Inc. on behalf of International Society for Advancement of Cytometry.

PD-L1:CD80 Cis-Heterodimer Triggers the Co-stimulatory Receptor CD28 While Repressing the Inhibitory PD-1 and CTLA-4 Pathways

Combined immunotherapy targeting the immune checkpoint receptors cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) and programmed cell death 1 (PD-1), or CTLA-4 and the PD-1 ligand (PD-L1) exhibits superior anti-tumor responses compared with single-agent therapy. Here, we examined the molecular basis for this synergy. Using reconstitution assays with fluorescence readouts, we found that PD-L1 and the CTLA-4 ligand CD80 heterodimerize in cis but not trans. Quantitative biochemistry and cell biology assays revealed that PD-L1:CD80 cis-heterodimerization inhibited both PD-L1:PD-1 and CD80:CTLA-4 interactions through distinct mechanisms but preserved the ability of CD80 to activate the T cell co-stimulatory receptor CD28. Furthermore, PD-L1 expression on antigen-presenting cells (APCs) prevented CTLA-4-mediated trans-endocytosis of CD80. Atezolizumab (anti-PD-L1), but not anti-PD-1, reduced cell surface expression of CD80 on APCs, and this effect was negated by co-blockade of CTLA-4 with ipilimumab (anti-CTLA-4). Thus, PD-L1 exerts an immunostimulatory effect by repressing the CTLA-4 axis; this has implications to the synergy of anti-PD-L1 and anti-CTLA-4 combination therapy.

Isoflurane Impacts Murine Melanoma Growth in a Sex-Specific, Immune-Dependent Manner: A Brief Report

The impact of volatile anesthetics on cancer progression has been observed for decades, but sex differences have not been described. Male and female immune systems vary considerably, and the immune system plays an important role in limiting cancer growth. Currently, mouse models describing the impact of volatile anesthetics on cancer growth are limited to same-sex models. In this brief report, we describe a sex-specific impact of isoflurane on melanoma growth observed in wild-type but not in immune-deficient mice. Future experimental designs related to anesthesia and cancer should evaluate the biological variable of sex in a systematic manner.

IL-17D promotes anti-bacterial immunity in Group A Streptococcus infection

Interleukin (IL)-17D is a cytokine in the IL-17 family that is conserved in vertebrates and invertebrates. In contrast to IL-17A, which is expressed in T cells, IL-17D is expressed broadly in non-immune cells. IL-17D can promote immune responses to cancer and viruses in part by inducing chemokines that recruit natural killer cells and neutrophils. Although bacterial infection can induce IL-17D in other species, the role of mammalian IL-17D in anti-bacterial immunity has not been determined. In order to ascertain whether IL-17D has a role in mediating immunity against bacterial infections, we studied intraperitoneal infection by Group A Streptococcus (GAS) S. pyogenes in wild-type (WT) and IL-17D-deficient mice. We found that there was more weight loss and decreased survival in mice deficient in IL-17D compared to WT animals after GAS infection. In addition, IL-17D deficient animals had increased bacterial burden in the kidney and peritoneal cavity after GAS infection compared to WT animals. In WT animals, IL-17D transcript could be induced by GAS infection, correlating with increased levels of the chemokine CCL2 and neutrophil recruitment. Notably, GAS-mediated induction of IL-17D seemed to require live bacteria, indicating that pattern recognition did not mediate induction of IL-17D. Altogether, our results demonstrate a role for IL-17D in sensing replicating bacteria and inducing immune responses important in clearing bacteria in distant organs.

Immuno-oncological Efficacy of RXDX-106, a Novel TAM (TYRO3, AXL, MER) Family Small-Molecule Kinase Inhibitor

Expression of the TAM (TYRO3, AXL, MER) family of receptor tyrosine kinases (RTK) has been associated with cancer progression, metastasis, and drug resistance. In immune cells, TAM RTKs can dampen inflammation in favor of homeostatic wound-healing responses, thus potentially contributing to the evasion of cancer cells from immune surveillance. Here we characterize the small-molecule RXDX-106 as a selective and potent pan-TAM RTK inhibitor with slow dissociation kinetics and significant antitumor activity in multiple syngeneic tumor models. Expression of AXL and MER on both immune and tumor cells increased during tumor progression. Tumor growth inhibition (TGI) following treatment with RXDX-106 was observed in wild-type mice and was abrogated in immunodeficient mice, suggesting that the antitumor activity of RXDX-106 is, in part, due to the presence of immune cells. RXDX-106-mediated TGI was associated with increased tumor-infiltrating leukocytes, M1-polarized intratumoral macrophages, and activation of natural killer cells. RXDX-106 proportionally increased intratumoral CD8⁺ T cells and T-cell function as indicated by both IFNγ production and LCK phosphorylation (pY393). RXDX-106 exhibited its effects via direct actions on TAM RTKs expressed on intratumoral macrophages and dendritic cells, leading to indirect activation of other immune cells in the tumor. RXDX-106 also potentiated the effects of an immune checkpoint inhibitor, α-PD-1 Ab, resulting in enhanced antitumor efficacy and survival. Collectively, these results demonstrate the capacity of RXDX-106 to inhibit tumor growth and progression and suggest it may serve as an effective therapy against multiple tumor types. SIGNIFICANCE: The pan-TAM small-molecule kinase inhibitor RXDX-106 activates both innate and adaptive immunity to inhibit tumor growth and progression, indicating its clinical potential to treat a wide variety of cancers.

Identification and editing of stem-like cells in methylcholanthrene-induced sarcomas

The cancer stem cell (CSC) paradigm posits that specific cells within a tumor, so-called CSC-like cells, have differing levels of tumorigenicity and chemoresistance. Original studies of CSCs identified them in human cancers and utilized mouse xenograft models to define the cancer initiating properties of these cells, thereby hampering the understanding of how immunity could affect CSCs. Indeed, few studies have characterized CSCs in the context of cancer immunoediting, and it is currently not clear how immunity could impact on the levels or stem-like behavior of CSCs. Using the well-studied 3'methylcholanthrene (MCA) model of primary sarcoma formation, we have defined a CSC-like population within MCA-induced sarcomas as expressing high levels of stem cell antigen-1 (Sca-1) and low levels of CD90. These Sca-1⁺CD90^- CSC-like cells had higher tumor initiating ability, could spontaneously give rise to Sca-1-negative cells, and formed more sarcospheres than corresponding non-CSC-like cells. Moreover, when examining MCA-induced sarcomas that were in the equilibrium phase of cancer growth, higher levels of CSC-like cells were found compared to MCA-induced sarcomas in the escape phase of cancer progression. Notably, CSC-like cells also emerged during escape from anti-PD-1 or anti-CTLA4 therapy, thus suggesting that CSC-like cells could evade immune therapy. Finally, we demonstrate that paradoxically, interferon (IFN)-γ produced in vivo by immune cells could promote the emergence of CSC-like cells. Our findings define the existence of a Sca1⁺CD90^- CSC-like population in the MCA-sarcoma model capable of differentiation, tumorsphere formation, and increased tumor initiation in vivo. These cells may also act as mediators of immune resistance during cancer immunoediting and immune therapy.

Siglec-7 engagement by GBS β-protein suppresses pyroptotic cell death of natural killer cells

Natural killer (NK) cells are innate immune lymphocytes that recognize and destroy abnormal host cells, such as tumor cells or those infected by viral pathogens. To safely accomplish these functions, NK cells display activating receptors that detect stress molecules or viral ligands displayed at the cell surface, balanced by inhibitory receptors that bind to self-molecules. To date, such activating and inhibitory receptors on NK cells are not known to recognize bacterial determinants. Moreover, NK cell responses to direct interactions with extracellular bacteria are poorly explored. In this study, we observed the human neonatal pathogen group B Streptococcus (GBS) can directly engage human NK cells. The interaction was mediated through the B6N segment of streptococcal β-protein, binding to the inhibitory receptor Siglec-7 via its amino-terminal V-set domain. Unlike classical Siglec binding, the interaction is also independent of its sialic acid recognition property. In contrast to WT GBS, mutants lacking β-protein induced efficient pyroptosis of NK cells through the NLRP3 inflammasome, with production and secretion of the proinflammatory cytokine IL-1β and dissemination of the cytotoxic molecule granzyme B. We postulate that GBS evolved β-protein engagement of inhibitory human Siglec-7 to suppress the pyroptotic response of NK cells and thereby block recruitment of a broader innate immune response, i.e., by "silencing the sentinel."

Interleukin-17D and Nrf2 mediate initial innate immune cell recruitment and restrict MCMV infection

Innate immune cells quickly infiltrate the site of pathogen entry and not only stave off infection but also initiate antigen presentation and promote adaptive immunity. The recruitment of innate leukocytes has been well studied in the context of extracellular bacterial and fungal infection but less during viral infections. We have recently shown that the understudied cytokine Interleukin (IL)-17D can mediate neutrophil, natural killer (NK) cell and monocyte infiltration in sterile inflammation and cancer. Herein, we show that early immune cell accumulation at the peritoneal site of infection by mouse cytomegalovirus (MCMV) is mediated by IL-17D. Mice deficient in IL-17D or the transcription factor Nuclear factor (erythroid-derived 2)-like 2 (Nrf2), an inducer of IL-17D, featured an early decreased number of innate immune cells at the point of viral entry and were more susceptible to MCMV infection. Interestingly, we were able to artificially induce innate leukocyte infiltration by applying the Nrf2 activator tert-butylhydroquinone (tBHQ), which rendered mice less susceptible to MCMV infection. Our results implicate the Nrf2/IL-17D axis as a sensor of viral infection and suggest therapeutic benefit in boosting this pathway to promote innate antiviral responses.

Cell-cell fusion as a mechanism of DNA exchange in cancer

Cell-cell fusion is a common biological phenomenon involved in both healthy and disease conditions. Fusion occurs when two or more cells combine their plasma membranes and become a single hybrid cell that retains certain genetic information from each parent cell. Here, using a Cre-loxP-based method initially developed to investigate extracellular vesicle targeting, we found that cancer cells spontaneously and rapidly deliver DNA to non-cancer cells in vitro via a cell-cell fusion event. We found that B16 melanoma cells and progressor and regressor fibrosarcomas were capable of spontaneously fusing with immune cells (macrophages) and non-immune cells (fibroblasts) in vitro, with varying degrees of efficiency. Further analysis of hybrid clones resulting from fusion between B16 melanoma cells and mouse embryonic fibroblasts showed that these cells were aneuploid and possessed enhanced clonal diversity and chemoresistance compared to non-hybrid melanoma cells. We also observed cell-cell fusion to occur in vivo between melanoma cells and non-cancer cells of both hematopoietic and non-hematopoietic origin. These findings suggest that cell-cell fusion occurs in murine cancer models and show that this mechanism has the potential to cause massive genomic alterations that are observed in cancer. Furthermore, these findings somewhat contradict recent publications suggesting that the Cre-loxP method measures only extracellular vesicle-mediated intercellular communication.

Cell death-inducing reagents activate cancer immune surveillance via inducing Interleukin-17D in macrophages

We have previously established a role for the cytokine IL-17D during cancer immune surveillance in that its cancer-intrinsic expression recruits NK cells into the tumor microenvironment, thereby leading to cancer regression. We additionally showed that the transcription factor Nrf2 regulates IL-17D and can itself be induced by the chemical tBHQ. Here, we sought to investigate what other endogenous or exogenous signals induce IL-17D not only in cancer cells but also in macrophages that are abundant in the tumor microenvironment. By testing different agonists in vitro, we found that all reagents that led to increased cell death (such as chemotherapy) also induced IL-17D. This effect was moderate in cancer cells but more profound in macrophages and depended on Nrf2. Interestingly, the expression of IL-17D correlated with type I Interferon expression, suggesting that these molecules function in the same pathway. Additionally, the only reagent that induced IL-17D without leading to cell death was poly (dA:dT), a nucleic acid known to induce intracellular DNA sensing pathways such as the Absent in melanoma (AIM)2 or the cGAS/Stimulator of IFNs (STING) pathway. This suggests that ectopic nucleic acids (likely resulting from cell death) are inducers of IL-17D. Remarkably, co-injecting bone marrow-derived macrophages (BMDMs) that had induced IL-17D together with cancer cells increased the number of NK cells in tumors and decreased cancer growth. This effect was dependent on IL-17D because it was abolished if IL-17D deficient BMDMs were injected. We hypothesize that the IL-17D pathway evolved to sense ectopic DNA, likely present due to cell death, and that boosting this pathway in cancer cells or macrophages could serve as cancer immune therapy.

Integrin Activation Controls Regulatory T Cell-Mediated Peripheral Tolerance

Maintenance of the regulatory T (Treg) cell pool is essential for peripheral tolerance and prevention of autoimmunity. Integrins, heterodimeric transmembrane proteins consisting of α and β subunits that mediate cell-to-cell and cell-to-extracellular matrix interactions, play an important role in facilitating Treg cell contact-mediated suppression. In this article, we show that integrin activation plays an essential, previously unappreciated role in maintaining murine Treg cell function. Treg cell-specific loss of talin, a β integrin-binding protein, or expression of talin(L325R), a mutant that selectively abrogates integrin activation, resulted in lethal systemic autoimmunity. This dysfunction could be attributed, in part, to a global dysregulation of the Treg cell transcriptome. Activation of integrin α₄β₁ led to increased suppressive capacity of the Treg cell pool, suggesting that modulating integrin activation on Treg cells may be a useful therapeutic strategy for autoimmune and inflammatory disorders. Taken together, these results reveal a critical role for integrin-mediated signals in controlling peripheral tolerance by virtue of maintaining Treg cell function.

Mechanisms regulating immune surveillance of cellular stress in cancer

The purpose of this review is to explore immune-mediated mechanisms of stress surveillance in cancer, with particular emphasis on the idea that all cancers have classical hallmarks (Hanahan and Weinberg in Cell 100:57-70, 67; Cell 144:646-674, 68) that could be interrelated. We postulate that hallmarks of cancer associated with cellular stress pathways (Luo et al. in Cell 136:823-837, 101) including oxidative stress, proteotoxic stress, mitotic stress, DNA damage, and metabolic stress could define and modulate the inflammatory component of cancer. As such, the overarching goal of this review is to define the types of cellular stress that cancer cells undergo, and then to explore mechanisms by which immune cells recognize, respond to, and are affected by each stress response.

Cell-cell fusion as a mechanism of DNA exchange in cancer

Cell-cell fusion describes the process by which two cells combine their plasma membranes and become a single cell, possessing and retaining certain genetic information from each parent cell. Here, using a Cre-loxP-based method initially developed to investigate extracellular vesicle targeting, we found that cancer cells spontaneously and rapidly deliver DNA to non-cancer cells in vitro via a cell-cell fusion event. The resulting hybrid cells were aneuploid and possessed enhanced clonal diversity and chemoresistance compared to non-hybrid cancer cells. We also observed cell-cell fusion to occur in vivo between melanoma cells and non-cancer cells of both hematopoietic and non-hematopoietic lineages. These findings suggest that cell-cell fusion occurs during the natural progression of cancer and show that this mechanism has the potential to cause massive genomic alterations that are observed in cancer. Furthermore, these findings somewhat contradict recent publications suggesting that the Cre-loxP method measures only extracellular vesicle-mediated intercellular communication.

Downregulation of 26S proteasome catalytic activity promotes epithelial-mesenchymal transition

The epithelial-mesenchymal transition (EMT) endows carcinoma cells with phenotypic plasticity that can facilitate the formation of cancer stem cells (CSCs) and contribute to the metastatic cascade. While there is substantial support for the role of EMT in driving cancer cell dissemination, less is known about the intracellular molecular mechanisms that govern formation of CSCs via EMT. Here we show that β2 and β5 proteasome subunit activity is downregulated during EMT in immortalized human mammary epithelial cells. Moreover, selective proteasome inhibition enabled mammary epithelial cells to acquire certain morphologic and functional characteristics reminiscent of cancer stem cells, including CD44 expression, self-renewal, and tumor formation. Transcriptomic analyses suggested that proteasome-inhibited cells share gene expression signatures with cells that have undergone EMT, in part, through modulation of the TGF-β signaling pathway. These findings suggest that selective downregulation of proteasome activity in mammary epithelial cells can initiate the EMT program and acquisition of a cancer stem cell-like phenotype. As proteasome inhibitors become increasingly used in cancer treatment, our findings highlight a potential risk of these therapeutic strategies and suggest a possible mechanism by which carcinoma cells may escape from proteasome inhibitor-based therapy.

The Next Frontier: Head and Neck Cancer Immunoprevention

Restoring T cell-mediated antitumor immunity by targeting immune checkpoint inhibitors in head and neck squamous cell carcinoma (HNSCC) results in immunomodulation and durable remissions. However, the overall response rate to these immunotherapies in HNSCC is only approximately 20%. This raises the possibility that immunologic intervention earlier in the HNSCC continuum, such as in oral premalignant lesions (OPL) could elicit an increased therapeutic response. New experimental studies suggest that immune therapies can be used for HNSCC prevention rather than therapy. Given the current excitement for precision medicine, these findings support the future development of multimodality approaches for preventive immune oncology. Cancer Prev Res; 10(12); 681-3. ©2017 AACRSee related article by Jin Wang, et al., p. 684.

Innate sensing of cancer's non-immunologic hallmarks

A cancer mass consists of a complex composition of cancer cells, stromal cells, endothelial cells and also immune cells, which can represent more than half of the cellularity of a solid cancer. These immune cells become activated when they sense cancer antigens and stress ligands. Innate immune cells also detect various aspects of cellular stress that characterize a growing tumor mass. These key hallmarks of cellular stress are also detected by the cancer cell itself. In this review, we highlight studies that show that the cancer cell itself could be considered an 'innate cell' that senses and reacts to non-immunologic hallmarks of cancer, including displaced nucleic acids, proteotoxic stress, oxidative stress, and metabolic alterations.

Proteasome activity regulates CD8+ T lymphocyte metabolism and fate specification

During an immune response, CD8+ T lymphocytes can undergo asymmetric division, giving rise to daughter cells that exhibit distinct tendencies to adopt terminal effector and memory cell fates. Here we show that "pre-effector" and "pre-memory" cells resulting from the first CD8+ T cell division in vivo exhibited low and high rates of endogenous proteasome activity, respectively. Pharmacologic reduction of proteasome activity in CD8+ T cells early during differentiation resulted in acquisition of terminal effector cell characteristics, whereas enhancement of proteasome activity conferred attributes of memory lymphocytes. Transcriptomic and proteomic analyses revealed that modulating proteasome activity in CD8+ T cells affected cellular metabolism. These metabolic changes were mediated, in part, through differential expression of Myc, a transcription factor that controls glycolysis and metabolic reprogramming. Taken together, these results demonstrate that proteasome activity is an important regulator of CD8+ T cell fate and raise the possibility that increasing proteasome activity may be a useful therapeutic strategy to enhance the generation of memory lymphocytes.

Abstract 4805: The role of exosomes in fibrosarcoma progression

Among pediatric cancers, sarcomas, especially those with large tumor burdens and metastatic disease, often result in poor outcome. Thus, new treatments are urgently needed to inhibit tumor progression, prevent metastasis, and improve overall survival.

To understand the mechanisms driving sarcoma progression, we employed two mouse fibrosarcoma cell lines that display different growth phenotypes when transplanted into syngeneic immune competent mice. Progressor fibrosarcomas evade detection by the immune system and develop large tumor burdens, while regressor fibrosarcomas regress shortly after a period of limited tumor growth. This difference in the growth phenotype is mediated in part by immune cells, but the mechanisms by which progressor and regressor cells influence immune cell activity are not fully elucidated.

Our research has focused on exosomes, 50-100 nm secreted nanovesicles, that contain bioactive cargoes and have emerged as mediators of intercellular communication between various cells. Here, we hypothesize that fibrosarcoma exosomes determine the aggressiveness of the disease by either educating tumor cells themselves or altering interactions with host cells.

To investigate the role of fibrosarcoma exosomes, we first educated regressor tumor cells with progressor exosomes for 3 weeks in vitro, and vice versa. Upon in vivo inoculation, progressor cells conditioned with regressor cell-derived exosomes grew significantly slower compared to untreated progressor cells. In contrast, regressor cells educated with progressor exosomes did not regress and overgrew significantly compared to untreated regressor cells. These results indicate that exosomes have an ability to reprogram a tumor phenotype.

To determine if fibrosarcoma exosomes specifically impact the host, we evaluated whether conditioning naïve mice with progressor exosomes alters in vivo growth of regressor tumor cells injected after three weeks of education. Twenty percent of regressor tumors continued to grow following progressor exosome education, while all tumors regressed in the control PBS group. These data suggest that exosomes also play an important role in the interaction with the host cells influencing tumor growth and disease progression.

Next, to determine which exosomal cargo may mediate these effects, we sought to characterize the proteome of exosomes from progressor and regressor cells using mass spectrometry. We found basigin, also known as CD147, a transmembrane embryonic glycoprotein reported to regulate cell proliferation, tumor migration and metastasis as one of the candidate proteins highly expressed in progressor-derived exosomes.

We conclude that exosomes derived from fibrosarcoma progresssors and regressors can alter the tumor phenotype both directly and indirectly. Exosomal cargo, such as basigin, may mediate the aggressive behavior of tumor cells, making it a potential therapeutic target to inhibit fibrosarcoma progression.

Citation Format: Miho Nakajima, Stephen C. Searles, Ayuko Hoshino, Katherine M. Offer, Candia M. Kenific, Jack D. Bui, David C. Lyden. The role of exosomes in fibrosarcoma progression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4805. doi:10.1158/1538-7445.AM2017-4805

Abstract 1961: Downregulation of proteasome activity promotes epithelial-mesenchymal transition

The epithelial-mesenchymal transition (EMT) is a developmental program that is aberrantly activated in cancer cells, producing an invasive phenotype that can lead to metastases. Inducers of EMT are largely known and have been widely studied. However, the mechanisms that regulate the link between extracellular stimuli and EMT phenotypes remain poorly understood. Preliminary evidence from our laboratory suggests that downregulation of proteasome activity may be responsible, in part, for driving EMT. Using immortalized human mammary epithelial (HMLE) cells as a model, we show that (1) EMT is associated with decreased proteasome activity and increased polyubiquitinated substrates, (2) pharmacologic inhibition of proteasome activity leads to increased EMT phenotypes and functionality, and (3) pharmacologic inhibition of proteasome activity leads to increased EMT via stabilization of the TGF-β signaling pathway. Together, these data suggest that proteasome activity may be an unappreciated regulator of EMT.

Citation Format: Daniel A. Garcia, Asoka Banno, Eric D. Van Baarsel, Patrick J. Metz, Christella E. Widjaja, Stephanie H. Kim, Jack D. Bui, Jing Yang, John T. Chang. Downregulation of proteasome activity promotes epithelial-mesenchymal transition [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1961. doi:10.1158/1538-7445.AM2017-1961

Exosomal MEK1 delays tumor growth by promoting anti-tumor immunity

Exosomes mediate intercellular communication and regulation in many processes, including cancer-immune cell interactions. Exosomes are small (~100 nm) membrane vesicles that arise from the late endosomal pathway and contain bioactive molecules that are transferred to and affect the function of target cells. Tumor-derived exosomes are important regulators of anti-tumor immunity and have been shown to exert stimulatory and inhibitory effects on immune cells, depending on the experimental setting. Using a proteomic approach, we found that exosomes derived from tumors that undergo immune rejection (“regressors”) contain different proteins than exosomes from progressively growing tumors (“progressors”). Specifically, the signaling molecule MAP2K1 (“MEK1”) is highly enriched in regressor compared to progressor exosomes, leading us to hypothesize that exosomal MEK1 stimulates anti-tumor immunity and inhibits tumor progression. We found that forced expression of MEK1 in progressor exosomes delays tumor growth and increases anti-tumor immune cell infiltration, and that MEK1-hi exosomes are sufficient to delay tumor growth, but MEK1-low exosomes are not. Moreover, we found that MEK1 protein can be physically transferred from tumor cells to macrophages via exosomes, and that MEK1-hi exosomes induce pro-inflammatory cytokine production in macrophages, but MEK1-low exosomes do not. We propose that tumor-derived MEK1 is transferred to macrophages via exosomes, which enhances their anti-tumoricidal effector function and delays tumor growth. This cell extrinsic, anti-tumor activity of MEK1 contrasts with the known oncogenic properties of MEK1 and could limit the efficacy of MEK1 inhibitors currently in clinical trials.

The Nrf2/Interleukin-17D axis as a novel target for cancer immune therapy

The oxidative stress-sensing transcription factor Nrf2 has been studied by cancer researchers as a double-edged sword that can either promote or inhibit cancer. Previous findings have shown that Nrf2 can act as a tumor suppressor by detoxifying carcinogens. Paradoxically, when cancer cells express Nrf2, they are protected from oxidative stress and certain chemotherapies, thus explaining why some cancer cells constitutively activate Nrf2 as a tumor promoter. We recently found that the cytokine Interleukin (IL)-17D mediates the recruitment of natural killer (NK) cells to tumor sites, thereby leading to tumor rejection. Here, we show that Nrf2 induced IL-17D in primary tumors and tumor cell lines. Moreover, the known Nrf2-activator tBHQ induced Nrf2 and IL-17D simultaneously, without creating harmful oxidative stress. Applying a tBHQ-containing skin cream to established tumors led to NK cell-mediated tumor regression, and this depended on IL-17D and Nrf2. We propose that the use of tBHQ or other Nrf2 activators can intiate a tumor surveillance pathway involving IL-17D and NK cells, thus mediating cancer regression and bearing potential for cancer immune therapy.

The ancient cytokine IL-17D is regulated by Nrf2 and mediates tumor and virus surveillance

Early stage immune responses can dictate the severity and outcome of inflammatory processes such as tumor growth and viral infection. Cytokines such as the interleukin 17 (IL-17) family and cellular stress defense (e.g., anti-oxidant) pathways have evolved early and regulate disease surveillance in vertebrates and invertebrates as far back as Caenorhabditis elegans. Our group has recently found a new role for nuclear factor erythroid-derived 2-like 2 (Nrf2) in regulating early anti-cancer immune responses by inducing IL-17D and recruiting natural killer (NK) cells. In this Cytokine Stimulus, we discuss recent findings that encourage boosting the Nrf2/IL-17D/NK cell axis for the treatment of cancer and viral infection.

Immunosurveillance and immunoediting in MMTV-PyMT-induced mammary oncogenesis

Evidence of cancer immunosurveillance and immunoediting processes has been primarily demonstrated in mouse models of chemically induced oncogenesis. Although these models are very tractable, they are characterized by high mutational loads that represent a minority of human cancers. In this study, we sought to determine whether cancer immunosurveillance and immunoediting could be demonstrated in a more clinically relevant oncogene-induced model of carcinogenesis, the MMTV-PyMT (PyMT) mammary carcinoma model. This model system in the FVB/NJ strain background was previously used to demonstrate that adaptive immunity had no role in limiting primary cancer formation and in fact promoted metastasis, thus calling into question whether cancer immunosurveillance operated in preventing the development of breast cancer. Our current study in the C57BL/6 strain backgrounds provides a different conclusion, as we report here the existence of an adaptive immunosurveillance of PyMT mammary carcinomas using two independent models of immune deficiency. PyMT mice bred onto a Rag1^-/- background or immune suppressed by chronic tacrolimus therapy both demonstrated accelerated development of mammary carcinomas. By generating a bank of cell lines from these animals, we further show that a subset of PyMT cell lines had delayed growth after transplantation into wild-type (WT) syngeneic, but not immune-deficient hosts. This reduced growth rate in immunocompetent animals was characterized by an increase in immune cell infiltration and tissue differentiation. Furthermore, loss of the immune cell infiltration that characterized immunoediting of slow growing cell lines, changed them into fast growing variants capable of progressing in the immunocompetent model. In conclusion, our study provides evidence that immunosurveillance and immunoediting of PyMT-derived cell lines modulate tumor progression in this oncogene-induced model of cancer.

Molecular Programming of Tumor-Infiltrating CD8+ T Cells and IL15 Resistance

Despite clinical potential and recent advances, durable immunotherapeutic ablation of solid tumors is not routinely achieved. IL15 expands natural killer cell (NK), natural killer T cell (NKT) and CD8(+) T-cell numbers and engages the cytotoxic program, and thus is under evaluation for potentiation of cancer immunotherapy. We found that short-term therapy with IL15 bound to soluble IL15 receptor α-Fc (IL15cx; a form of IL15 with increased half-life and activity) was ineffective in the treatment of autochthonous PyMT murine mammary tumors, despite abundant CD8(+) T-cell infiltration. Probing of this poor responsiveness revealed that IL15cx only weakly activated intratumoral CD8(+) T cells, even though cells in the lung and spleen were activated and dramatically expanded. Tumor-infiltrating CD8(+) T cells exhibited cell-extrinsic and cell-intrinsic resistance to IL15. Our data showed that in the case of persistent viral or tumor antigen, single-agent systemic IL15cx treatment primarily expanded antigen-irrelevant or extratumoral CD8(+) T cells. We identified exhaustion, tissue-resident memory, and tumor-specific molecules expressed in tumor-infiltrating CD8(+) T cells, which may allow therapeutic targeting or programming of specific subsets to evade loss of function and cytokine resistance, and, in turn, increase the efficacy of IL2/15 adjuvant cytokine therapy. Cancer Immunol Res; 4(9); 799-811. ©2016 AACR.

Nrf2 Induces IL-17D to Mediate Tumor and Virus Surveillance

Cells undergoing xenobiotic or oxidative stress activate the transcription factor nuclear factor erythroid-derived 2-like 2 (Nrf2), which initiates an intrinsic "stress surveillance" pathway. We recently found that the cytokine IL-17D effects a form of extrinsic stress surveillance by inducing antitumor immunity, but how IL-17D is regulated remains unknown. Here, we show that Nrf2 induced IL-17D in cancer cell lines. Moreover, both Nrf2 and IL-17D were induced in primary tumors as well as during viral infection in vivo. Expression of IL-17D in tumors and virally infected cells is essential for optimal protection of the host as il17d(-/-) mice experienced a higher incidence of tumors and exacerbated viral infections compared to wild-type (WT) animals. Moreover, activating Nrf2 to induce IL-17D in established tumors led to natural killer cell-dependent tumor regression. These data demonstrate that Nrf2 can initiate both intrinsic and extrinsic stress surveillance pathways and highlight the use of Nrf2 agonists as immune therapies for cancer and infection.

Nrf2 induces IL-17D to mediate tumor and virus surveillance

Cells undergoing xenobiotic or oxidative stress activate the transcription factor Nrf2, which initiates an intrinsic “stress surveillance” pathway involving detoxifying enzymes. We recently found that the cytokine IL-17D effects a form of extrinsic stress surveillance by inducing antitumor immunity, but how IL-17D is regulated remains unknown. Here, we show that Nrf2 induced IL-17D directly in primary tumors as well as during viral infection in vivo. Expression of IL-17D in tumors and virally infected cells is essential for optimal protection of the host as il17d−/− mice experienced a higher incidence of tumors and exacerbated viral infections compared to WT animals. Moreover, activating Nrf2 to induce IL-17D in established tumors led to NK cell-dependent tumor regression. These data demonstrate that Nrf2 can initiate both intrinsic and extrinsic stress surveillance pathways and highlight the use of Nrf2 agonists as immune therapies for cancer and infection.

Integrin activation controls regulatory T cell identity and stability

Maintenance of the regulatory T (Treg) cell pool is essential for peripheral tolerance and prevention of autoimmunity. Integrins, heterodimeric transmembrane proteins consisting of α and β subunits that mediate cell-cell and cell-extracellular matrix interactions, have been shown to play an important role in facilitating cell contact-mediated suppression by Treg cells. Here we show that integrin activation plays an essential, previously unappreciated role in maintaining the stability of the Treg cell pool. Treg cell-specific loss of talin1, a β integrin-binding protein, or expression of talin1(L325R), a mutant that selectively abrogates integrin activation, resulted in dysregulation of Treg cell identity and lethal systemic autoimmunity. Moreover, the absence of sustained interactions between the integrin LFA-1 on Treg cells and its ligand ICAM-1 on dendritic cells reduced the expression of Foxp3 and caused Treg cells to adopt an effector CD4+ T cell-like phenotype. Taken together, these results reveal a critical role for tonic, integrin-mediated signals in controlling peripheral tolerance by virtue of maintaining Treg cell identity and stability.

Progenitor cells are mobilized by acute psychological stress but not beta-adrenergic receptor agonist infusion

OBJECTIVES

Stimuli that activate the sympathetic nervous system, such as acute psychological stress, rapidly invoke a robust mobilization of lymphocytes into the circulation. Experimental animal studies suggest that bone marrow-derived progenitor cells (PCs) also mobilize in response to sympathetic stimulation. Here we tested the effects of acute psychological stress and brief pharmacological β-adrenergic (βAR) stimulation on peripheral PC numbers in humans.

METHODS

In two studies, we investigated PC mobilization in response to an acute speech task (n=26) and βAR-agonist (isoproterenol) infusion (n=20). A subset of 8 participants also underwent the infusion protocol with concomitant administration of the βAR-antagonist propranolol. Flow cytometry was used to enumerate lymphocyte subsets, total progenitor cells, total haematopoietic stem cells (HSC), early HSC (multi-lineage potential), late HSC (lineage committed), and endothelial PCs (EPCs).

RESULTS

Both psychological stress and βAR-agonist infusion caused the expected mobilization of total monocytes and lymphocytes and CD8(+) T lymphocytes. Psychological stress also induced a modest, but significant, increase in total PCs, HSCs, and EPC numbers in peripheral blood. However, infusion of a βAR-agonist did not result in a significant change in circulating PCs.

CONCLUSION

PCs are rapidly mobilized by psychological stress via mechanisms independent of βAR-stimulation, although the findings do not exclude βAR-stimulation as a possible cofactor. Considering the clinical and physiological relevance, further research into the mechanisms involved in stress-induced PC mobilization seems warranted.

Effect of cell density and HLA-DR incompatibility on T-cell proliferation and forkhead box P3 expression in human mixed lymphocyte reaction

BACKGROUND

The proliferation rates of human T cells in vitro are affected by some factors such as initial T-cell number, dose of stimulating cells, and duration of culture. The transcription factor forkhead box P3 (FoxP3) has been used to identify regulatory T cells in humans and is thought to correlate with tolerance to allogeneic organ transplant. Thus, it is important to optimize conditions to expand FoxP3 cell proliferation to improve engraftment of allogeneic organ transplants.

METHODS

We studied proliferative responses and FoxP3 expression in divided T cells with the use of flow cytometric analysis of Ki-67 in culture of different concentrations of responding cells (6 × 10(6), 4 × 10(6), 2 × 10(6), 1 × 10(6), and 0.5 × 10(6)cells/mL), different types of stimulating cells (lymphocytes and low density cells), and different numbers of HLA mismatches.

RESULTS

The proportion of CD3(+) cells, CD4(+)CD25(+) cells, and CD4(+)CD25(+)FoxP3(+) cells among mononuclear cells were highest at initial cell concentration of 2 × 10(6) responder cells/mL with lymphocytes as stimulators at day-5 mixed lymphocyte reaction (MLR). They were highest at a concentration of 4 × 10(6) responder cells/mL with low density cells as stimulators. The recovery (%), proportion of CD3(+) cells, CD4(+)CD25(+) cells, and CD4(+)CD25(+)FoxP3(+) cells with 2 HLA-DR incompatibility were significantly higher than those of 1 HLA-DR incompatibility at day-5 MLR.

CONCLUSIONS

Initial cell concentration and HLA-DR incompatibility can affect the generation of FoxP3+ T cells in human MLR. These factors could be considered for efficient generation of Tregs for clinical trials in the future.

Immunodeficiency and autoimmune enterocolopathy linked to NFAT5 haploinsufficiency

The link between autoimmune diseases and primary immunodeficiency syndromes has been increasingly appreciated. Immunologic evaluation of a young man with autoimmune enterocolopathy and unexplained infections revealed evidence of immunodeficiency, including IgG subclass deficiency, impaired Ag-induced lymphocyte proliferation, reduced cytokine production by CD8(+) T lymphocytes, and decreased numbers of NK cells. Genetic evaluation identified haploinsufficiency of NFAT5, a transcription factor regulating immune cell function and cellular adaptation to hyperosmotic stress, as a possible cause of this syndrome. Inhibition or deletion of NFAT5 in normal human and murine cells recapitulated several of the immune deficits identified in the patient. These results provide evidence of a primary immunodeficiency disorder associated with organ-specific autoimmunity linked to NFAT5 deficiency.

Tumor-expressed IL-17D recruits NK cells to reject tumors

Antitumor immunity suppresses tumorigenesis, but we do not understand how transformed cells initiate those immune responses that are essential for effective tumor immunosurveillance. Using the 3-MCA fibrosarcoma model, we identified IL-17D as a tumor-expressed cytokine that recruits natural killer cells, leading to the polarization of M1 macrophages and tumor rejection.

Drak2 is not required for tumor surveillance and suppression

Drak2 is a promising therapeutic target to treat organ-specific autoimmune diseases such as type 1 diabetes and multiple sclerosis without causing generalized immune suppression. Inhibition of Drak2 may also prevent graft rejection following organ transplantation. However, Drak2 may function as a critical tumor suppressor, which would challenge the prospect of targeting Drak2 for therapeutic treatment. Thus, we examined the susceptibility of Drak2 (-/-) mice in several tumor models. We show that Drak2 is not required to prevent tumor formation in a variety of settings. Therefore, Drak2 does not function as an essential tumor suppressor in in vivo tumor models. These data further validate Drak2 as a viable therapeutic target to treat autoimmune disease and graft rejection. Importantly, these data also indicate that while Drak2 may induce apoptosis when overexpressed in cell lines, it is not an essential tumor suppressor.

uPAR induces expression of transforming growth factor β and interleukin-4 in cancer cells to promote tumor-permissive conditioning of macrophages

Cancer cells condition macrophages and other inflammatory cells in the tumor microenvironment so that these cells are more permissive for cancer growth and metastasis. Conditioning of inflammatory cells reflects, at least in part, soluble mediators (such as transforming growth factor β and IL-4) that are released by cancer cells and alter the phenotype of cells of the innate immune system. Signaling pathways in cancer cells that potentiate this activity are incompletely understood. The urokinase receptor (uPAR) is a cell-signaling receptor known to promote cancer cell survival, proliferation, metastasis, and cancer stem cell-like properties. The present findings show that uPAR expression in diverse cancer cells, including breast cancer, pancreatic cancer, and glioblastoma cells, promotes the ability of these cells to condition co-cultured bone marrow-derived macrophages so that the macrophages express significantly increased levels of arginase 1, a biomarker of the alternatively activated M2 macrophage phenotype. Expression of transforming growth factor β was substantially increased in uPAR-expressing cancer cells via a mechanism that requires uPA-initiated cell signaling. uPAR also controlled expression of IL-4 in cancer cells via a mechanism that involves activation of ERK1/2. The ability of uPAR to induce expression of factors that condition macrophages in the tumor microenvironment may constitute an important mechanism by which uPAR promotes cancer progression.

Abstract 1168: Cathelicidin is a novel mediator of cancer immune surveillance

Cathelicidins are evolutionarily conserved anti-microbial peptides that have been identified in several epithelial tissues and a wide variety of immune cells. These peptides display multiple host-defense activities, as well as documented but underexplored antitumor activity. Using the regressor MCA sarcoma system as a model of immune mediated tumor rejection, we observed that deficiency in cathelicidin in cnlp-/- mice impaired the rejection of multiple regressor cell lines. Cnlp-/- mice also developed spontaneous lymphoma with age, thus confirming in a separate model system the requirement for cathelicidin in tumor immune surveillance. To decipher the immune defect that may engender impaired tumor surveillance, macrophages from cnlp-/- versus wild type (wt) mice were examined. Interestingly, cnlp-/- macrophages were defective in polarizing towards an antitumor M1 phenotype and less potent at phagocytosing target tumor cells.

Altogether, these preliminary data suggest a crucial role of cathelicidin in limiting tumor formation and progression. Future experiments will define the role of cathelicidin in tumor surveillance mediated by macrophages and potentially other innate cells that also express cathelicidin, such as neutrophils and natural killer cells.

Citation Format: Emilie T. Gross, Carlos D. Peinado, Isis G. Perez, Samaneh Keshavarz, Jack D. Bui. Cathelicidin is a novel mediator of cancer immune surveillance. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1168. doi:10.1158/1538-7445.AM2014-1168

Interleukin-17D mediates tumor rejection through recruitment of natural killer cells

The process of cancer immunoediting generates a repertoire of cancer cells that can persist in immune-competent hosts. In its most complex form, this process begins with the elimination of highly immunogenic unedited tumor cells followed by the escape of less immunogenic edited cells. Although edited tumors can release immunosuppressive factors, it is unknown whether unedited tumors produce cytokines that enhance antitumor function. Utilizing gene microarray analysis, we found the cytokine interleukin 17D (IL-17D) was highly expressed in certain unedited tumors but not in edited mouse tumor cell lines. Moreover, forced expression of IL-17D in edited tumor cells induced rejection by stimulating MCP-1 production from tumor endothelial cells, leading to the recruitment of natural killer (NK) cells. NK cells promoted M1 macrophage development and adaptive immune responses. IL-17D expression was also decreased in certain high-grade and metastatic human tumors, suggesting that it can be targeted for tumor immune therapy.