Interferon-γ production by Tfh cells is required for CXCR3+ pre-memory B cell differentiation and subsequent lung-resident memory B cell responses

Lung-resident memory B cells (lung-BRMs) differentiate into plasma cells after reinfection, providing enhanced pulmonary protection. Here, we investigated the determinants of lung-BRM differentiation upon influenza infection. Kinetic analyses revealed that influenza nucleoprotein (NP)-specific BRMs preferentially differentiated early after infection and required T follicular helper (Tfh) cell help. BRM differentiation temporally coincided with transient interferon (IFN)-γ production by Tfh cells. Depletion of IFN-γ in Tfh cells prevented lung-BRM differentiation and impaired protection against heterosubtypic infection. IFN-γ was required for expression of the transcription factor T-bet by germinal center (GC) B cells, which promoted differentiation of a CXCR3+ GC B cell subset that were precursors of lung-BRMs and CXCR3+ memory B cells in the mediastinal lymph node. Absence of IFN-γ signaling or T-bet in GC B cells prevented CXCR3+ pre-memory precursor development and hampered CXCR3+ memory B cell differentiation and subsequent lung-BRM responses. Thus, Tfh-cell-derived IFN-γ is critical for lung-BRM development and pulmonary immunity, with implications for vaccination strategies targeting BRMs.

Chitinase-3-like 1 regulates TH2 cells, TFH cells and IgE responses to helminth infection

Introduction

Data from patient cohorts and mouse models of atopic dermatitis, food allergy and asthma strongly support a role for chitinase-3-like-1 protein (CHI3L1) in allergic disease.

Methods

To address whether Chi3l1 also contributes to TH2 responses following nematode infection, we infected Chi3l1 -/- mice with Heligmosomoides polygyrus (Hp) and analyzed T cell responses.

Results

As anticipated, we observed impaired TH2 responses in Hp-infected Chi3l1 -/- mice. However, we also found that T cell intrinsic expression of Chi3l1 was required for ICOS upregulation following activation of naïve CD4 T cells and was necessary for the development of the IL-4+ TFH subset, which supports germinal center B cell reactions and IgE responses. We also observed roles for Chi3l1 in TFH, germinal center B cell, and IgE responses to alum-adjuvanted vaccination. While Chi3l1 was critical for IgE humoral responses it was not required for vaccine or infection-induced IgG1 responses.

Discussion

These results suggest that Chi3l1 modulates IgE responses, which are known to be highly dependent on IL-4-producing TFH cells.

Activation of regulatory dendritic cells by Mertk coincides with a temporal wave of apoptosis in neonatal lungs

Multiple mechanisms restrain inflammation in neonates, most likely to prevent tissue damage caused by overly robust immune responses against newly encountered pathogens. Here, we identify a population of pulmonary dendritic cells (DCs) that express intermediate levels of CD103 (CD103int) and appear in the lungs and lung-draining lymph nodes of mice between birth and 2 weeks of age. CD103int DCs express XCR1 and CD205 and require expression of the transcription factor BATF3 for development, suggesting that they belong to the cDC1 lineage. In addition, CD103int DCs express CCR7 constitutively and spontaneously migrate to the lung-draining lymph node, where they promote stromal cell maturation and lymph node expansion. CD103int DCs mature independently of microbial exposure and TRIF- or MyD88-dependent signaling and are transcriptionally related to efferocytic and tolerogenic DCs as well as mature, regulatory DCs. Correlating with this, CD103int DCs show limited ability to stimulate proliferation and IFN-γ production by CD8+ T cells. Moreover, CD103int DCs acquire apoptotic cells efficiently, in a process that is dependent on the expression of the TAM receptor, Mertk, which drives their homeostatic maturation. The appearance of CD103int DCs coincides with a temporal wave of apoptosis in developing lungs and explains, in part, dampened pulmonary immunity in neonatal mice. Together, these data suggest a mechanism by which DCs sense apoptotic cells at sites of noninflammatory tissue remodeling, such as tumors or the developing lungs, and limit local T cell responses.

A transcriptionally distinct subset of influenza-specific effector memory B cells predicts long-lived antibody responses to vaccination in humans

Seasonal influenza vaccination elicits hemagglutinin (HA)-specific memory B (Bmem) cells, and although multiple Bmem cell populations have been characterized, considerable heterogeneity exists. We found that HA-specific human Bmem cells differed in the expression of surface marker FcRL5 and transcriptional factor T-bet. FcRL5+T-bet+ Bmem cells were transcriptionally similar to effector-like memory cells, while T-betnegFcRL5neg Bmem cells exhibited stem-like central memory properties. FcRL5+ Bmem cells did not express plasma-cell-commitment factors but did express transcriptional, epigenetic, metabolic, and functional programs that poised these cells for antibody production. Accordingly, HA+ T-bet+ Bmem cells at day 7 post-vaccination expressed intracellular immunoglobulin, and tonsil-derived FcRL5+ Bmem cells differentiated more rapidly into antibody-secreting cells (ASCs) in vitro. The T-bet+ Bmem cell response positively correlated with long-lived humoral immunity, and clonotypes from T-bet+ Bmem cells were represented in the secondary ASC response to repeat vaccination, suggesting that this effector-like population predicts influenza vaccine durability and recall potential.

Alloreactivity and autoreactivity converge to support B cell epitope targeting in transplant rejection

Antibody (Ab) responses against human leukocyte antigen (HLA) proteins mismatched between donor and recipient are leading cause of allograft loss in kidney transplantation. However, therapies targeting alloreactive B cell and Ab-secreting cell (ASC) are lacking, motivating the need to understand how to prevent and abrogate these alloresponses. Using molecular, structural, and proteomic techniques, we profiled the B cell response in a kidney transplant recipient with antibody-mediated rejection and graft loss. We found that this response spanned the rejected organ and peripheral blood, stimulated the differentiation of multiple B cell subsets, and produced a high-affinity, donor-specific, anti-HLA response. We found epitopic immunodominance that relied on highly exposed, solvent-accessible mismatched HLA residues as well as structural and biomolecular evidence of autoreactivity against the recipient's self-HLA allele. These alloreactive and autoreactive signatures converged in the recipient's circulating donor-specific Ab repertoire, suggesting that rejection requires both the recognition of non-self and breaches of tolerance to lead to alloinjury and graft loss.

ICOS costimulation is indispensable for the differentiation of T follicular regulatory cells

ICOS is a T-cell costimulatory receptor critical for Tfh cell generation and function. However, the role of ICOS in Tfr cell differentiation remains unclear. Using Foxp3-Cre-mediated ICOS knockout (ICOS FC) mice, we show that ICOS deficiency in Treg-lineage cells drastically reduces the number of Tfr cells during GC reactions but has a minimal impact on conventional Treg cells. Single-cell transcriptome analysis of Foxp3+ cells at an early stage of the GC reaction suggests that ICOS normally inhibits Klf2 expression to promote follicular features including Bcl6 up-regulation. Furthermore, ICOS costimulation promotes nuclear localization of NFAT2, a known driver of CXCR5 expression. Notably, ICOS FC mice had an unaltered overall GC B-cell output but showed signs of expanded autoreactive B cells along with elevated autoantibody titers. Thus, our study demonstrates that ICOS costimulation is critical for Tfr cell differentiation and highlights the importance of Tfr cells in maintaining humoral immune tolerance during GC reactions.

Spiking SARS-CoV-2 antiviral immunity in the respiratory tract

The COVID-19 pandemic enabled the successful launch of mRNA-based vaccines that, when given intramuscularly, elicit spike-specific antibodies and prevent severe disease, but do not promote mucosal immunity. New data suggest how to boost systemic immunity and elicit pulmonary immunity in a way that more effectively controls infection and impairs transmission.

A single intranasal administration of AdCOVID protects against SARS-CoV-2 infection in the upper and lower respiratory tracts

The coronavirus disease 2019 (COVID-19) pandemic has illustrated the critical need for effective prophylactic vaccination to prevent the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Intranasal vaccination is an attractive approach for preventing COVID-19 as the nasal mucosa is the site of initial SARS-CoV-2 entry and viral replication prior to aspiration into the lungs. We previously demonstrated that a single intranasal administration of a candidate adenovirus type 5-vectored vaccine encoding the receptor-binding domain of the SARS-CoV-2 spike protein (AdCOVID) induced robust immunity in both the airway mucosa and periphery, and completely protected K18-hACE2 mice from lethal SARS-CoV-2 challenge. Here we show that a single intranasal administration of AdCOVID limits viral replication in the nasal cavity of K18-hACE2 mice. AdCOVID also induces sterilizing immunity in the lungs of mice as reflected by the absence of infectious virus. Finally, AdCOVID prevents SARS-CoV-2 induced pathological damage in the lungs of mice. These data show that AdCOVID not only limits viral replication in the respiratory tract, but it also prevents virus-induced inflammation and immunopathology following SARS-CoV-2 infection.

Circulating Tregs accumulate in omental tumors and acquire adipose-resident features

Tumors that metastasize in the peritoneal cavity typically end up in the omental adipose tissue, a particularly immune-suppressive environment that includes specialized adipose-resident regulatory T cells (Tregs). Tregs rapidly accumulate in the omentum after tumor implantation and potently suppress anti-tumor immunity. However, it is unclear whether these Tregs are recruited from the circulation or derived from pre-existing adipose-resident Tregs by clonal expansion. Here we show that Tregs in tumor-bearing omenta predominantly have thymus-derived characteristics. Moreover, naïve tumor antigen-specific CD4+ T cells fail to differentiate into Tregs in tumor-bearing omenta. In fact, Tregs derived from the pre-tumor repertoire are sufficient to suppress anti-tumor immunity and promote tumor growth. However, tumor implantation in the omentum does not promote Treg clonal expansion, but instead leads to increased clonal diversity. Parabiosis experiments show that despite tissue-resident (non-circulating) characteristics of omental Tregs in naïve mice, tumor implantation promotes a rapid influx of circulating Tregs, many of which come from the spleen. Finally, we show that newly recruited Tregs rapidly acquire characteristics of adipose-resident Tregs in tumor-bearing omenta. These data demonstrate that most Tregs in omental tumors are recruited from the circulation and adapt to their environment by altering their homing, transcriptional and metabolic properties.

Sequential modulation of the Wnt/β-catenin signaling pathway enhances tumor-intrinsic MHC I expression and tumor clearance

BACKGROUND

Progress in immunotherapy use for gynecologic malignancies is hampered by poor tumor antigenicity and weak T cell infiltration of the tumor microenvironment (TME). Wnt/β-catenin pathway modulation demonstrated patient benefit in clinical trials as well as enhanced immune cell recruitment in preclinical studies. The purpose of this study was to characterize the pathways by which Wnt/β-catenin modulation facilitates a more immunotherapy-favorable TME.

METHODS

Human tumor samples and in vivo patient-derived xenograft and syngeneic murine models were administered Wnt/β-catenin modulating agents DKN-01 and CGX-1321 individually or in sequence. Analytical methods included immunohistochemistry, flow cytometry, multiplex cytokine/chemokine array, and RNA sequencing.

RESULTS

DKK1 blockade via DKN-01 increased HLA/MHC expression in human and murine tissues, correlating with heightened expression of known MHC I regulators: NFkB, IL-1, LPS, and IFNy. PORCN inhibition via CGX-1321 increased production of T cell chemoattractant CXCL10, providing a mechanism for observed increases in intra-tumoral T cells. Diverse leukocyte recruitment was noted with elevations in B cells and macrophages, with increased tumor expression of population-specific chemokines. Sequential DKK1 blockade and PORCN inhibition decreased tumor burden as evidenced by reduced omental weights.

CONCLUSIONS

Wnt/β-catenin pathway modulation increases MHC I expression and promotes tumor leukocytic infiltration, facilitating a pro-immune TME associated with decreased tumor burden. This intervention overcomes common tumor immune-evasion mechanisms and may render ovarian tumors susceptible to immunotherapy.

Single-Dose Intranasal Administration of AdCOVID Elicits Systemic and Mucosal Immunity against SARS-CoV-2 and Fully Protects Mice from Lethal Challenge

The coronavirus disease 2019 (COVID-19) pandemic has highlighted the urgent need for effective prophylactic vaccination to prevent the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Intranasal vaccination is an attractive strategy to prevent COVID-19 as the nasal mucosa represents the first-line barrier to SARS-CoV-2 entry. The current intramuscular vaccines elicit systemic immunity but not necessarily high-level mucosal immunity. Here, we tested a single intranasal dose of our candidate adenovirus type 5-vectored vaccine encoding the receptor-binding domain (RBD) of the SARS-CoV-2 spike protein (AdCOVID) in inbred, outbred, and transgenic mice. A single intranasal vaccination with AdCOVID elicited a strong and focused immune response against RBD through the induction of mucosal IgA in the respiratory tract, serum neutralizing antibodies, and CD4+ and CD8+ T cells with a Th1-like cytokine expression profile. A single AdCOVID dose resulted in immunity that was sustained for over six months. Moreover, a single intranasal dose completely protected K18-hACE2 mice from lethal SARS-CoV-2 challenge, preventing weight loss and mortality. These data show that AdCOVID promotes concomitant systemic and mucosal immunity and represents a promising vaccine candidate.

Scent of a vaccine

Intranasal vaccination should block SARS-CoV-2 transmission at the source

Intestinal cDC1 drive cross-tolerance to epithelial-derived antigen via induction of FoxP3+CD8+ Tregs

Although CD8⁺ T cell tolerance to tissue-specific antigen (TSA) is essential for host homeostasis, the mechanisms underlying peripheral cross-tolerance and whether they may differ between tissue sites remain to be fully elucidated. Here, we demonstrate that peripheral cross-tolerance to intestinal epithelial cell (IEC)-derived antigen involves the generation and suppressive function of FoxP3⁺CD8⁺ T cells. FoxP3⁺CD8⁺ T_reg generation was dependent on intestinal cDC1, whose absence led to a break of tolerance and epithelial destruction. Mechanistically, intestinal cDC1-derived PD-L1, TGFβ, and retinoic acid contributed to the generation of gut-tropic CCR9⁺CD103⁺FoxP3⁺CD8⁺ T_regs Last, CD103-deficient CD8⁺ T cells lacked tolerogenic activity in vivo, indicating a role for CD103 in FoxP3⁺CD8⁺ T_reg function. Our results describe a role for FoxP3⁺CD8⁺ T_regs in cross-tolerance in the intestine for which development requires intestinal cDC1.

ICOS is critical for T follicular regulatory cell differentiation

The Inducible Costimulator (ICOS) is a T cell costimulatory receptor critical for humoral immunity. ICOS-deficient patients suffer from recurrent infections due to lack of protective antibodies. However, some patients also display signs of antibody-mediated autoimmunity. These findings may reflect a dual role of ICOS: facilitating the differentiation and function of T follicular helper (Tfh) and T follicular regulatory (Tfr) cells. While Tfh cells are known to provide help to B cells to produce high affinity antibodies, the main role of Tfr cells seems to be preventing autoantibody generation. Using Foxp3-cre-mediated ICOS knockout (ICOS FC) mice, we show that T regulatory (Treg)-specific ICOS deletion drastically reduces the number of Tfr cells without altering Treg cell numbers. Single cell RNA sequencing further revealed shifts in transitory Tfr precursor populations in immunized ICOS FC mice. Importantly, we observed a lowered ratio of antigen-specific germinal center B (GCB) cells and increased anti-nuclear antibodies in ICOS FC mice, suggesting a rise in autoreactive GCB cells. We also noted variations in isotype composition of total and virus-specific antibodies in infected ICOS FC mice. Mechanistically, our data suggests that ICOS could promote the Treg-to-Tfr transition by regulating CXCR5 expression. Thus, our study demonstrates that ICOS is critical for Tfr cell generation and supports the role of Tfr cells in preventing generation of autoantibodies during germinal center reactions.

Conserved Epigenetic Programming and Enhanced Heme Metabolism Drive Memory B Cell Reactivation

Memory B cells (MBCs) have enhanced capabilities to differentiate to plasma cells and generate a rapid burst of Abs upon secondary stimulation. To determine if MBCs harbor an epigenetic landscape that contributes to increased differentiation potential, we derived the chromatin accessibility and transcriptomes of influenza-specific IgM and IgG MBCs compared with naive cells. MBCs possessed an accessible chromatin architecture surrounding plasma cell-specific genes, as well as altered expression of transcription factors and genes encoding cell cycle, chemotaxis, and signal transduction processes. Intriguingly, this MBC signature was conserved between humans and mice. MBCs of both species possessed a heightened heme signature compared with naive cells. Differentiation in the presence of hemin enhanced oxidative phosphorylation metabolism and MBC differentiation into Ab-secreting plasma cells. Thus, these data define conserved MBC transcriptional and epigenetic signatures that include a central role for heme and multiple other pathways in augmenting MBC reactivation potential.

Class I histone deacetylase inhibition promotes CD8 T cell activation in ovarian cancer

Objective

Patients with epithelial ovarian cancer (EOC) typically present with late‐stage disease, posing a significant challenge to treatment. Although taxane and platinum‐based chemotherapy plus surgical debulking are initially effective, EOC is marked by frequent recurrence with resistant disease. Immunotherapy represents an appealing treatment paradigm given the ability of immune cells to engage metastatic sites and impede recurrence; however, response rates to checkpoint blockade in ovarian cancer have been disappointing. Here, we tested whether class I HDAC inhibition can promote anti‐tumor T cell responses in a spontaneous and nonspontaneous murine model of EOC.

Methods

We used the spontaneous Tg‐MISIIR‐Tag and nonspontaneous ID8 models of murine ovarian cancer to test this hypothesis. Whole tumor transcriptional changes were assessed using the nCounter PanCancer Mouse Immune Profiling Panel. Changes in select protein expression of regulatory and effector T cells were measured by flow cytometry.

Results

We found that treatment with the class I HDAC inhibitor entinostat upregulated pathways and genes associated with CD8 T cell cytotoxic function, while downregulating myeloid derived suppressor cell chemoattractants. Suppressive capacity of regulatory T cells within tumors and associated ascites was significantly reduced, reversing the CD8‐Treg ratio.

Conclusions

Our findings suggest class I HDAC inhibition can promote activation of intratumoral CD8 T cells, potentially by compromising suppressive networks within the EOC tumor microenvironment. In this manner, class I HDAC inhibition might render advanced‐stage EOC susceptible to immunotherapeutic treatment modalities.

Neutralization of TGFβ Improves Tumor Immunity and Reduces Tumor Progression in Ovarian Carcinoma

The immunosuppressive effects of TGFβ promotes tumor progression and diminishes response to therapy. In this study, we used ID8-p53^-/- tumors as a murine model of high-grade serous ovarian cancer. An mAb targeting all three TGFβ ligands was used to neutralize TGFβ. Ascites and omentum were collected and changes in T-cell response were measured using flow. Treatment with anti-TGFβ therapy every other day following injection of tumor cells resulted in decreased ascites volume (4.1 mL vs. 0.7 mL; P < 0.001) and improved the CD8:Treg ratio (0.37 vs. 2.5; P = 0.02) compared with untreated mice. A single dose of therapy prior to tumor challenge resulted in a similar reduction of ascites volume (2.7 vs. 0.67 mL; P = 0.002) and increased CD8:Tregs ratio (0.36 vs. 1.49; P = 0.007), while also significantly reducing omental weight (114.9 mg vs. 93.4 mg; P = 0.017). Beginning treatment before inoculation with tumor cells and continuing for 6 weeks, we observe similar changes and prolonged overall survival (median 70 days vs. 57.5 days). TGFβ neutralization results in favorable changes to the T-cell response within the tumor microenvironment, leading to decreased tumor progression in ovarian cancer. The utilization of anti-TGFβ therapy may be an option for management in patients with ovarian cancer to improve clinical outcomes and warrants further investigation.

Single-dose intranasal administration of AdCOVID elicits systemic and mucosal immunity against SARS-CoV-2 in mice

The coronavirus disease 2019 (COVID-19) pandemic has highlighted the urgent need for effective preventive vaccination to reduce burden and spread of severe acute respiratory syndrome (SARS) coronavirus 2 (SARS-CoV-2) in humans. Intranasal vaccination is an attractive strategy to prevent COVID-19 as the nasal mucosa represents the first-line barrier to SARS-CoV-2 entry before viral spread to the lung. Although SARS-CoV-2 vaccine development is rapidly progressing, the current intramuscular vaccines are designed to elicit systemic immunity without conferring mucosal immunity. Here, we show that AdCOVID, an intranasal adenovirus type 5 (Ad5)-vectored vaccine encoding the receptor binding domain (RBD) of the SARS-CoV-2 spike protein, elicits a strong and focused immune response against RBD through the induction of mucosal IgA, serum neutralizing antibodies and CD4+ and CD8+ T cells with a Th1-like cytokine expression profile. Therefore, AdCOVID, which promotes concomitant systemic and local mucosal immunity, represents a promising COVID-19 vaccine candidate.

Inducible Bronchus-Associated Lymphoid Tissue (iBALT) Attenuates Pulmonary Pathology in a Mouse Model of Allergic Airway Disease

Inducible Bronchus Associated Lymphoid Tissue (iBALT) is an ectopic lymphoid tissue associated with severe forms of chronic lung diseases, including chronic obstructive pulmonary disease, rheumatoid lung disease, hypersensitivity pneumonitis and asthma, suggesting that iBALT may exacerbate these clinical conditions. However, despite the link between pulmonary pathology and iBALT formation, the role of iBALT in pathogenesis remains unknown. Here we tested whether the presence of iBALT in the lung prior to sensitization and challenge with a pulmonary allergen altered the biological outcome of disease. We found that the presence of iBALT did not exacerbate Th2 responses to pulmonary sensitization with ovalbumin. Instead, we found that mice with iBALT exhibited delayed Th2 accumulation in the lung, reduced eosinophil recruitment, reduced goblet cell hyperplasia and reduced mucus production. The presence of iBALT did not alter Th2 priming, but instead delayed the accumulation of Th2 cells in the lung following challenge and altered the spatial distribution of T cells in the lung. These results suggest that the formation of iBALT and sequestration of effector T cells in the context of chronic pulmonary inflammation may be a mechanism by which the immune system attenuates pulmonary inflammation and prevents excessive pathology.

Specialized immune responses in the peritoneal cavity and omentum

The peritoneal cavity is a fluid filled space that holds most of the abdominal organs, including the omentum, a visceral adipose tissue that contains milky spots or clusters of leukocytes that are organized similar to those in conventional lymphoid tissues. A unique assortment of leukocytes patrol the peritoneal cavity and migrate in and out of the milky spots, where they encounter Ags or pathogens from the peritoneal fluid and respond accordingly. The principal role of leukocytes in the peritoneal cavity is to preserve tissue homeostasis and secure tissue repair. However, when peritoneal homeostasis is disturbed by inflammation, infection, obesity, or tumor metastasis, specialized fibroblastic stromal cells and mesothelial cells in the omentum regulate the recruitment of peritoneal leukocytes and steer their activation in unique ways. In this review, the types of cells that reside in the peritoneal cavity, the role of the omentum in their maintenance and activation, and how these processes function in response to pathogens and malignancy will be discussed.

Abstract B77: PORCN inhibition prolongs survival, decreases tumor burden, and alters the immune microenvironment in ovarian cancer

Background: Wnt/β-catenin pathway upregulation has been correlated with immune evasion in multiple cancers, including epithelial ovarian cancer (EOC). Porcupine (PORCN) is an enzyme necessary for cells to produce WNT ligand, which is necessary for the activation of the pathway. Our hypothesis was that the administration of a PORCN inhibitor (CGX1321) would decrease Wnt signaling and thereby lead to a decrease in immune evasion, creating a “hot” tumor microenvironment (TME), which would result in increased survival and a decrease tumor burden.

Methods: RNA sequencing was performed in a cohort of primary ovarian cancer samples. CGX1321 was administered to C57Bl6 mice injected intraperitoneally with ID8 or ID8p53−/− cells. Tumor growth was measured by bioluminescence and omental weight. H&E slides were analyzed for amount of tumor in the omentum. Amount of tumor-infiltrating lymphocytes (TILs), Tregs, dendritic cells (DCs), macrophages, and monocytes in the TME were quantified via flow cytometry. CD11c-cre x β-catenin-flox C57Bl6 mice, a mouse model with no DC-intrinsic β-catenin, and the administration of anti-CD8β antibody were used to evaluate tumor burden with and without CGX1321.

Results: Increased Wnt activity was correlated with a decreased T-cell signature in our human ovarian cancer samples. Treatment with CGX1321 prolonged survival (P=0.0001) and decreased omentum weight (P=0.0056) in mice injected with ID8 cells. H&E slides revealed decreased amount of tumor in the omentum with treatment. There was an increase of DCs (P=0.0159), macrophages (P=0.0079), and monocytes (P value=0.0079) with treatment, which was only significant for mice injected with ID8 cells, not ID8p53−/− mice. Tumor burden was decreased in CD11c-cre x β-catenin-flox mice (P=0.1014) without treatment, and with CGX 1321 treatment (P=0.0450). Tumor burden was not decreased with CGX1321 treatment in the absence of CD8+ T-cells (P=0.3175).

Conclusions: Consistent with EOC TCGA data, we identified a correlation between increased Wnt signaling and decreased T-cell signature (i.e., “cold” tumor). ID8 cells have a higher level of total β-catenin and expression of WNT related genes compared with ID8p53−/−, which may explain the prolonged survival, decreased tumor burden, and more profound increase of DCs, macrophages, and monocytes in the TME. This may suggest a reliance on these cells for tumor recognition with PORCN inhibition. Furthermore, tumor burden was decreased in a DC-intrinsic β-catenin absent model, suggesting the presence of β-catenin in this antigen-presenting cell contributes to immune evasion in the TME. The lack of effect of CGX1321 on tumor burden in the absence of CD8+ T-cells indicates a partial reliance on CD8+ T-cells for tumor recognition. These data warrant further investigation of Wnt inhibition in both preclinical models and clinical trials in EOC.

Citation Format: Whitney N. Goldsberry, Selene Meza-Perez, Ashwini A. Katre, Angelina Londoño, Bryan T. Mott, Jaclyn M. Arquiette, Troy D. Randall, Sara J. Cooper, Lyse A. Norian, Rebecca C. Arend. PORCN inhibition prolongs survival, decreases tumor burden, and alters the immune microenvironment in ovarian cancer [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research; 2019 Sep 13-16, 2019; Atlanta, GA. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(13_Suppl):Abstract nr B77.

Enhancing anticancer activity of checkpoint immunotherapy by targeting RAS

Approximately 30% of human cancers harbor a gain‐in‐function mutation in the RAS gene, resulting in constitutive activation of the RAS protein to stimulate downstream signaling, including the RAS‐mitogen activated protein kinase pathway that drives cancer cells to proliferate and metastasize. RAS‐driven oncogenesis also promotes immune evasion by increasing the expression of programmed cell death ligand‐1, reducing the expression of major histocompatibility complex molecules that present antigens to T‐lymphocytes and altering the expression of cytokines that promote the differentiation and accumulation of immune suppressive cell types such as myeloid‐derived suppressor cells, regulatory T‐cells, and cancer‐associated fibroblasts. Together, these changes lead to an immune suppressive tumor microenvironment that impedes T‐cell activation and infiltration and promotes the outgrowth and metastasis of tumor cells. As a result, despite the growing success of checkpoint immunotherapy, many patients with RAS‐driven tumors experience resistance to therapy and poor clinical outcomes. Therefore, RAS inhibitors in development have the potential to weaken cancer cell immune evasion and enhance the antitumor immune response to improve survival of patients with RAS‐driven cancers. This review highlights the potential of RAS inhibitors to enhance or broaden the anticancer activity of currently available checkpoint immunotherapy.

Resident Memory B Cells

In mammals, adaptive immunity is mediated by a broadly diverse repertoire of naive B and T lymphocytes that recirculate between secondary lymphoid organs. Initial antigen exposure promotes lymphocyte clonal expansion and differentiation, including the formation of memory cells. Antigen-specific memory cells are maintained at higher frequencies than their naive counterparts and have different functional and homing abilities. Importantly, a subset of memory cells, known as tissue-resident memory cells, is maintained without recirculating in nonlymphoid tissues, often at barrier surfaces, where they can be reactivated by antigen and rapidly perform effector functions that help protect the tissue in which they reside. Although antigen-experienced B cells are abundant at many barrier surfaces, their characterization as tissue-resident memory B (BRM) cells is not well developed. In this study, we describe the characteristics of memory B cells in various locations and discuss their possible contributions to immunity and homeostasis as bona fide BRM cells.

Inhibition of the Wnt/β-catenin pathway enhances antitumor immunity in ovarian cancer

Background:

The Wnt/β-catenin pathway is linked to tumorigenesis in a variety of tumors and promotes T cell exclusion and resistance to checkpoint inhibitors. We sought to determine whether a small molecule inhibitor of this pathway, WNT974, would impair tumor growth, affect gene expression patterns, and improve the immune response in human and murine ovarian cancer models.

Methods:

Human ovarian cancer cells were treated with WNT974 in vitro. RNAseq libraries were constructed and differences in gene expression patterns between responders and nonresponders were compared to The Cancer Genome Atlas (TCGA). Mice with subcutaneous or intraperitoneal ID8 ovarian cancer tumors were treated with WNT974, paclitaxel, combination, or control. Tumor growth and survival were measured. Flow cytometry and β-TCR repertoire analysis were used to determine the immune response.

Results:

Gene expression profiling revealed distinct signatures in responders and nonresponders, which strongly correlated with T cell infiltration patterns in the TCGA analysis of ovarian cancer. WNT974 inhibited tumor growth, prevented ascites formation, and prolonged survival in mouse models. WNT974 increased the ratio of CD8⁺ T cells to T regulatory cells (Tregs) in tumors and enhanced the effector functions of infiltrating CD4⁺ and CD8⁺ T cells. Treatment also decreased the expression of inhibitory receptors on CD8⁺ T cells. Combining WNT974 with paclitaxel further reduced tumor growth, prolonged survival, and expanded the T cell repertoire.

Conclusions:

These findings suggest that inhibiting the Wnt/β-catenin pathway may have a potent immunomodulatory effect in the treatment of ovarian cancer, particularly when combined with paclitaxel.

Inhibiting WNT Ligand Production for Improved Immune Recognition in the Ovarian Tumor Microenvironment

In ovarian cancer, upregulation of the Wnt/β–catenin pathway leads to chemoresistance and correlates with T cell exclusion from the tumor microenvironment (TME). Our objectives were to validate these findings in an independent cohort of ovarian cancer subjects and determine whether inhibiting the Wnt pathway in a syngeneic ovarian cancer murine model could create a more T-cell-inflamed TME, which would lead to decreased tumor growth and improved survival. We preformed RNA sequencing in a cohort of human high grade serous ovarian carcinoma subjects. We used CGX1321, an inhibitor to the porcupine (PORCN) enzyme that is necessary for secretion of WNT ligand, in mice with established ID8 tumors, a murine ovarian cancer cell line. In order to investigate the effect of decreased Wnt/β–catenin pathway activity in the dendritic cells (DCs), we injected ID8 cells in mice that lacked β–catenin specifically in DCs. Furthermore, to understand how much the effects of blocking the Wnt/β–catenin pathway are dependent on CD8⁺ T cells, we injected ID8 cells into mice with CD8⁺ T cell depletion. We confirmed a negative correlation between Wnt activity and T cell signature in our cohort. Decreasing WNT ligand production resulted in increases in T cell, macrophage and dendritic cell functions, decreased tumor burden and improved survival. Reduced tumor growth was found in mice that lacked β–catenin specifically in DCs. When CD8⁺ T cells were depleted, CGX1321 treatment did not have the same magnitude of effect on tumor growth. Our investigation confirmed an increase in Wnt activity correlated with a decreased T-cell-inflamed environment; a relationship that was further supported in our pre-clinical model that suggests inhibiting the Wnt/β–catenin pathway was associated with decreased tumor growth and improved survival via a partial dependence on CD8⁺ T cells.

Human Leukocyte Antigen Class I and II Knockout Human Induced Pluripotent Stem Cell-Derived Cells: Universal Donor for Cell Therapy

Background

We aim to generate a line of “universal donor” human induced pluripotent stem cells (hiPSCs) that are nonimmunogenic and, therefore, can be used to derive cell products suitable for allogeneic transplantation.

Methods and Results

hiPSCs carrying knockout mutations for 2 key components (β2 microglobulin and class II major histocompatibility class transactivator) of major histocompatibility complexes I and II (ie, human leukocyte antigen [HLA] I/II knockout hiPSCs) were generated using the Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/CRISPR associated protein 9 (Cas9) gene‐editing system and differentiated into cardiomyocytes. Pluripotency‐gene expression and telomerase activity in wild‐type (WT) and HLAI/II knockout hiPSCs, cardiomyocyte marker expression in WT and HLAI/II knockout hiPSC‐derived cardiomyocytes, and assessments of electrophysiological properties (eg, conduction velocity, action‐potential and calcium transient half‐decay times, and calcium transient increase times) in spheroid‐fusions composed of WT and HLAI/II knockout cardiomyocytes, were similar. However, the rates of T‐cell activation before (≈21%) and after (≈24%) exposure to HLAI/II knockout hiPSC‐derived cardiomyocytes were nearly indistinguishable and dramatically lower than after exposure to WT hiPSC‐derived cardiomyocytes (≈75%), and when WT and HLAI/II knockout hiPSC‐derived cardiomyocyte spheroids were cultured with human peripheral blood mononuclear cells, the WT hiPSC‐derived cardiomyocyte spheroids were smaller and displayed contractile irregularities. Finally, expression of HLA‐E and HLA‐F was inhibited in HLAI/II knockout cardiomyocyte spheroids after coculture with human peripheral blood mononuclear cells, although HLA‐G was not inhibited; these results are consistent with the essential role of class II major histocompatibility class transactivator in transcriptional activation of the HLA‐E and HLA‐F genes, but not the HLA‐G gene. Expression of HLA‐G is known to inhibit natural killer cell recognition and killing of cells that lack other HLAs.

Conclusions

HLAI/II knockout hiPSCs can be differentiated into cardiomyocytes that induce little or no activity in human immune cells and, consequently, are suitable for allogeneic transplantation.

IgM, IgG, and IgA Influenza-Specific Plasma Cells Express Divergent Transcriptomes

Ab-secreting cells (ASC) or plasma cells are essential components of the humoral immune system. Although Abs of different isotypes have distinct functions, it is not known if the ASC that secrete each isotype are also distinct. ASC downregulate their surface BCR upon differentiation, hindering analyses that couple BCR information to other molecular characteristics. In this study, we developed a methodology using fixation, permeabilization, and intracellular staining coupled with cell sorting and reversal of the cross-links to allow RNA sequencing of isolated cell subsets. Using hemagglutinin and nucleoprotein Ag-specific B cell tetramers and intracellular staining for IgM, IgG, and IgA isotypes, we were able to derive and compare the gene expression programs of ASC subsets that were responding to the same Ags following influenza infection in mice. Intriguingly, whereas a shared ASC signature was identified, each ASC isotype-specific population expressed distinct transcriptional programs controlling cellular homing, metabolism, and potential effector functions. Additionally, we extracted and compared BCR clonotypes and found that each ASC isotype contained a unique, clonally related CDR3 repertoire. In summary, these data reveal specific complexities in the transcriptional programming of Ag-specific ASC populations.

Mitochondrial calcium uniporter regulates PGC-1α expression to mediate metabolic reprogramming in pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive disease with an increased mortality. Metabolic reprogramming has a critical role in multiple chronic diseases. Lung macrophages expressing the mitochondrial calcium uniporter (MCU) have a critical role in fibrotic repair, but the contribution of MCU in macrophage metabolism is not known. Here, we show that MCU regulates peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) and metabolic reprogramming to fatty acid oxidation (FAO) in macrophages. MCU regulated PGC-1α expression by increasing the phosphorylation of ATF-2 by the p38 MAPK in a redox-dependent manner. The expression and activation of PGC-1α via the p38 MAPK was regulated by MCU-mediated mitochondrial calcium uptake, which is linked to increased mitochondrial ROS (mtROS) production. Mice harboring a conditional expression of dominant-negative MCU in macrophages had a marked reduction in mtROS and FAO and were protected from pulmonary fibrosis. Moreover, IPF lung macrophages had evidence of increased MCU and mitochondrial calcium, increased phosphorylation of ATF2 and p38, as well as increased expression of PGC-1α. These observations suggest that macrophage MCU-mediated metabolic reprogramming contributes to fibrotic repair after lung injury.

Defining Genetic Variation in Widely Used Congenic and Backcrossed Mouse Models Reveals Varied Regulation of Genes Important for Immune Responses

Genetic variation influences how the genome is interpreted in individuals and in mouse strains used to model immune responses. We developed approaches to utilize next-generation sequencing datasets to identify sequence variation in genes and enhancer elements in congenic and backcross mouse models. We defined genetic variation in the widely used B6-CD45.2 and B6.SJL-CD45.1 congenic model, identifying substantial differences in SJL genetic content retained in B6.SJL-CD45.1 strains on the basis of the vendor source of the mice. Genes encoding PD-1, CD62L, Bcl-2, cathepsin E, and Cxcr4 were within SJL genetic content in at least one vendor source of B6.SJL-CD45.1 mice. SJL genetic content affected enhancer elements, gene regulation, protein expression, and amino acid content in CD4⁺ T helper 1 cells, and mice infected with influenza showed reduced expression of Cxcr4 on B6.SJL-CD45.1 T follicular helper cells. These findings provide information on experimental variables and aid in creating approaches that account for genetic variables.

A Review of the Role of Wnt in Cancer Immunomodulation

Alterations in the Wnt signaling pathway are associated with the advancement of cancers; however, the exact mechanisms responsible remain largely unknown. It has recently been established that heightened intratumoral Wnt signaling correlates with tumor immunomodulation and immune suppression, which likely contribute to the decreased efficacy of multiple cancer therapeutics. Here, we review available literature pertaining to connections between Wnt pathway activation in the tumor microenvironment and local immunomodulation. We focus specifically on preclinical and clinical data supporting the hypothesis that strategies targeting Wnt signaling could act as adjuncts for cancer therapy, either in combination with chemotherapy or immunotherapy, in a variety of tumor types.

T-bet Transcription Factor Promotes Antibody-Secreting Cell Differentiation by Limiting the Inflammatory Effects of IFN-γ on B Cells

Although viral infections elicit robust interferon-γ (IFN-γ) and long-lived antibody-secreting cell (ASC) responses, the roles for IFN-γ and IFN-γ-induced transcription factors (TFs) in ASC development are unclear. We showed that B cell intrinsic expression of IFN-γR and the IFN-γ-induced TF T-bet were required for T-helper 1 cell-induced differentiation of B cells into ASCs. IFN-γR signaling induced Blimp1 expression in B cells but also initiated an inflammatory gene program that, if not restrained, prevented ASC formation. T-bet did not affect Blimp1 upregulation in IFN-γ-activated B cells but instead regulated chromatin accessibility within the Ifng and Ifngr2 loci and repressed the IFN-γ-induced inflammatory gene program. Consistent with this, B cell intrinsic T-bet was required for formation of long-lived ASCs and secondary ASCs following viral, but not nematode, infection. Therefore, T-bet facilitates differentiation of IFN-γ-activated inflammatory effector B cells into ASCs in the setting of IFN-γ-, but not IL-4-, induced inflammatory responses.

Precisely timed histone deacetylase inhibition creates a highly proliferative intratumoral CD8 T cell population and sensitizes tumors to checkpoint blockade

We previously showed that a class I histone deacetylase (HDAC) inhibitor, entinostat (ENT), dramatically improves CD8 T cell-mediated control of TS/A murine mammary tumors, but only when given in a precise window. If given too early ENT halts initial T cell activation and expansion and has no effect if given too late— once T cells start becoming dysfunctional. This led us to hypothesize that HDAC inhibition can maintain CD8 T cells in a less differentiated state that enhances effector and proliferative capacities. To test this, we first treated TS/A tumor-bearing mice with ENT and performed single cell RNA-sequencing on sorted tumor-infiltrating CD8 T cells. Relative to vehicle, ENT treated samples clustered separately and included a distinct, highly proliferative cluster of CD8 T cells, a finding corroborated by bulk RNA-sequencing and flow cytometry. Although TS/A tumors do not respond to anti-PD1 alone, ENT-induced changes in CD8 T cell phenotype sensitized tumors to PD1 blockade, leading to tumor rejection in most mice when both agents were timed appropriately. Patient tumors, however, have often passed this window to intervene; thus, we devised a tripartite strategy to “reset the clock”. Treating first with an oncolytic virus to liberate new antigens and stimulate new tumor-specific CD8 T cells, then with ENT and anti-PD1 at the right times significantly impaired growth of late-stage tumors and even led to rejection. Our findings show that precisely timed HDAC inhibition generates highly proliferative and strongly cytotoxic CD8 T cell populations whose functions can be further elaborated with correctly timed checkpoint blockade. Resetting the clock using a tumor-lytic strategy then renders this a potent immunotherapy platform.

Epigenetic priming underpins enhanced memory B cell differentiation

Immunological memory is a hallmark of the adaptive immune response. Memory B cells (MBC) have increased affinity, expression of costimulatory molecules, and capacity to proliferate and differentiate than their naïve counterparts; however, the epigenetic mechanisms that control enhanced MBC functions are currently unknown. Using a murine model of influenza infection, nucleoprotein (NP)-specific MBC and follicular naïve B cells (nB) were isolated and the chromatin accessibility and transcriptional landscape determined by ATAC and RNA-seq, respectively. MBC displayed distinct gene expression profiles from nB, including an upregulation of plasma cell (PC) signature genes and significant overall increases in total mRNA content. Furthermore, MBC display an open and primed chromatin conformation in gene regulatory regions that map to transcription factors controlling either PC (Prdm1 and Irf4), germinal center (Aicda), or MBC (Zbtb32) fates. These data reveal additional novel MBC-specific transcription factor networks and describe an epigenetic “antigen experience” signature that correlates with enhanced MBC function. To confirm the importance of these molecular changes, naïve and memory mice were challenged with a heterosubtypic influenza infection or isolated and cultured with CD40L, IL-4, and IL-5. In vivo, MBC form germinal centers earlier and to a higher frequency than nB. MBC also form significantly more NP+IgG+ PCs by flow cytometry and ELISPOT, corroborating the open chromatin signature. Ex vivo, MBCs upregulated primed transcription factors earlier than nB, validating the enhanced formation of CD138+ PCs. These data describe an epigenetic basis for enhanced the differentiation capacity and function of MBC.

The antitumor effects of entinostat in ovarian cancer require adaptive immunity

BACKGROUND

Ovarian cancer is poorly immunogenic; however, increased major histocompatibility complex class II (MHCII) expression correlates with improved immune response and prolonged survival in patients with ovarian cancer. The authors previously demonstrated that the histone deacetylase inhibitor entinostat increases MHCII expression on ovarian cancer cells. In the current study, they evaluated whether entinostat treatment and resultant MHCII expression would enhance beneficial immune responses and impair tumor growth in mice with ovarian cancer.

METHODS

C57BL/6 mice bearing intraperitoneal ID8 tumors were randomized to receive entinostat 20 mg/kg daily versus control. Changes in messenger RNA (mRNA) expression of 46 genes important for antitumor immunity were evaluated using NanoString analysis, and multicolor flow cytometry was used to measure changes in protein expression and tumor-infiltrating immune cells.

RESULTS

Entinostat treatment decreased the growth of both subcutaneously and omental ID8 tumors and prolonged survival in immunocompetent C57BL/6 mice. NanoString analysis revealed significant changes in mRNA expression in 21 of 46 genes, including increased expression of the MHCI pathway, the MHCII transactivator (CIITA), interferon γ, and granzyme B. C57BL/6 mice that received entinostat had increased MHCII expression on omental tumor cells and a higher frequency of tumor-infiltrating, CD8-positive T cells by flow cytometry. In immunocompromised mice, treatment with entinostat had no effect on tumor size and did not increase MHCII expression.

CONCLUSIONS

In the current murine ovarian cancer model, entinostat treatment enhances beneficial immune responses. Moreover, these antitumor effects of entinostat are dependent on an intact immune system. Future studies combining entinostat with checkpoint inhibitors or other immunomodulatory agents may achieve more durable antitumor responses in patients with ovarian cancer.

The Histone Demethylase LSD1 Regulates B Cell Proliferation and Plasmablast Differentiation

B cells undergo epigenetic remodeling as they differentiate into Ab-secreting cells (ASC). LSD1 is a histone demethylase known to decommission active enhancers and cooperate with the ASC master regulatory transcription factor Blimp-1. The contribution of LSD1 to ASC formation is poorly understood. In this study, we show that LSD1 is necessary for proliferation and differentiation of mouse naive B cells (nB) into plasmablasts (PB). Following LPS inoculation, LSD1-deficient hosts exhibited a 2-fold reduction of splenic PB and serum IgM. LSD1-deficient PB exhibited derepression and superinduction of genes involved in immune system processes; a subset of these being direct Blimp-1 target-repressed genes. Cell cycle genes were globally downregulated without LSD1, which corresponded to a decrease in the proliferative capacity of LSD1-deficient activated B cells. PB lacking LSD1 displayed increased histone H3 lysine 4 monomethylation and chromatin accessibility at nB active enhancers and the binding sites of transcription factors Blimp-1, PU.1, and IRF4 that mapped to LSD1-repressed genes. Together, these data show that LSD1 is required for normal in vivo PB formation, distinguish LSD1 as a transcriptional rheostat and epigenetic modifier of B cell differentiation, and identify LSD1 as a factor responsible for decommissioning nB active enhancers.

Factors of the bone marrow microniche that support human plasma cell survival and immunoglobulin secretion

Human antibody-secreting cells (ASC) in peripheral blood are found after vaccination or infection but rapidly apoptose unless they migrate to the bone marrow (BM). Yet, elements of the BM microenvironment required to sustain long-lived plasma cells (LLPC) remain elusive. Here, we identify BM factors that maintain human ASC > 50 days in vitro. The critical components of the cell-free in vitro BM mimic consist of products from primary BM mesenchymal stromal cells (MSC), a proliferation-inducing ligand (APRIL), and hypoxic conditions. Comparative analysis of protein-protein interactions between BM-MSC proteomics with differential RNA transcriptomics of blood ASC and BM LLPC identify two major survival factors, fibronectin and YWHAZ. The MSC secretome proteins and hypoxic conditions play a role in LLPC survival utilizing mechanisms that downregulate mTORC1 signaling and upregulate hypoxia signatures. In summary, we identify elements of the BM survival niche critical for maturation of blood ASC to BM LLPC.

Abstract 4710: The effect of Wnt inhibition combined with paclitaxel on tumor burden and CD8+ T cell infiltration in syngeneic murine models of ovarian cancer

Objective: The Wnt/β-catenin pathway is a major signal transduction pathway involved in ovarian cancer (OVCA) metastasis and resistance to chemotherapy. This pathway downregulates protective immunity mediated by intra-tumoral CD8+T cells in other cancer types. WNT974 is a novel drug that inhibits the enzyme Porcupine, which controls Wnt protein secretion. Our objective was to measure the effect of WNT974 alone and in combination with dose dense paclitaxel (ddPac) on tumor growth and on infiltrating CD8+ T cells in two syngeneic OVCA mouse models.

Methods: C57BL/6 mice were injected subcutaneously (SC) (n=20) or intraperitoneally (IP) (n=24) with 7 x 106 ID8 mouse OVCA cells. Mice were treated with vehicle control, ddPac, WNT974, or the combination (combo). C57BL/6 TgMISIIR-Tag-Low transgenic mice were injected with 7 x 106 MOVCAR cells IP (n=8) and treated with vehicle control or combo. WNT974 was given by oral gavage twice a day (5mg/kg for 7 days then decreased to 2.5mg/kg twice a day for up to 4 weeks). Paclitaxel was given IP (5mg/kg) 3 days on and 3 days off for a total of 9 doses. SC tumors were measured with calipers twice per week. In the IP model, mice were sacrificed after 13 days of treatment and tumor weights and ascites volume were determined. Flow cytometry was used to evaluate the presence of CD8+ T cells in IP tumors.

Results: In the ID8 SC model, combo therapy reduced tumor size compared to vehicle control (18 vs. 40mm2, p&lt;0.01) or ddPac alone (18 vs. 39mm2, p&lt;0.01). In the ID8 IP model, tumor weights trended down after treatment (p=NS) and the percentage of intra-tumoral CD8+T cells increased after ddPac or combo treatment (control 4.9%; WNT974 8.3%, p=0.12; ddPac 12.3%, p=0.01; combo 14.9%, p&lt;0.01). In the MOVCAR IP model, combo therapy reduced tumor weight (0.13 vs. 0.19g, p=0.05) and ascites volume (1.0 vs. 8.5 mL, p&lt;0.05), and trended toward increased intra-tumoral CD8+ T cells (33.5 vs. 13.5%, p=0.13).

Conclusions: The combination of WNT974 and ddPac reduced tumor size and increased tumor infiltration of CD8+ T cells in syngeneic OVCA mouse models. This suggests that the improved response observed with the ddPac and WNT974 combination is in part due to upregulation of the intra-tumoral immune response. Further investigation of this pathway is warranted as an immune modulator and a potential therapeutic target in ovarian cancer.

Citation Format: David W. Doo, Angelina I. Londono, Dylana J. Moore, Selene Meza-Perez, Ashwini A. Katre, Tyler R. McCaw, Haller J. Smith, Carol Y. Lin, Sara J. Cooper, J Michael Straughn, Donald J. Buchsbaum, Lyse A. Norian, Troy D. Randall, Rebecca C. Arend. The effect of Wnt inhibition combined with paclitaxel on tumor burden and CD8+ T cell infiltration in syngeneic murine models of ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4710.

Abstract 4700: Manipulating the breast tumor microenvironment with histone deacetylase inhibitors for more robust and durable T cell responses

Malignant cells harbor an imbalance in histone acetyltransferase and histone deacetylase (HDAC) activity, epigenetically contributing to altered cellular programs. HDAC inhibitors disrupt this balance to impact both cellular transcription and protein function, changing the phenotype of tumor cells as well as responding immune cells, including tumor-infiltrating T cells. We hypothesized that HDAC inhibition could be used to boost anti-tumor T cell responses through inducing expression of immunomodulatory proteins on tumor cells as well as directly altering the transcriptional programs of tumor-specific T cells. To test this, we treated two murine breast cancer models, TS/A and 4T1, with HDAC inhibitors representing class I specificity, entinostat, or pan-specificity, panobinostat, in vitro and in vivo. Culture of tumor cells with either inhibitor increased surface expression of molecules involved in T cell recognition and stimulation, including MHCI, MHCII, CD74, 41BB, CD40, and ICOSL as well as the T cell chemoattractant CXCL10. Treating tumor-bearing mice with HDAC inhibitor resulted in a significant reduction in tumor growth that was absolutely dependent on adaptive immunity. Using depleting antibodies, we next showed that IFNγ and CD8 T cells, but not CD4 T cells or B cells, are necessary for the anti-tumor effects of entinostat. Interestingly, tumor infiltration of CD4 T cells was reduced following treatment and their effector functions were largely unchanged. However, CD8 T cell infiltration was dramatically increased, as was their production of IFNγ, TNFα, and granzyme B even at later time points. This upregulation of effector function was paralleled by a significant increase in the transcription factor T-bet, while Eomes actually decreased over time, trends opposite those seen in CD8 T cells from vehicle treated tumors and that would suggest entinostat treatment can imprint T cells with a transcriptional program less susceptible to exhaustion. Strikingly, we also found that simply adjusting the timing of entinostat dosing relative to T cell activation could abolish anti-tumor effects or lead to rejection in nearly 50% of mice. These effects corresponded with a significant shift in the responding T cell repertoire. Collectively, our data suggests that HDAC inhibition has important effects on both tumor cells and T cells; specifically, altering tumor cell gene expression leads to a repolarization of the tumor microenvironment more favorable to anti-tumor immunity and reprogramming transcriptional profiles of activated T cells improves effector functions and reduces susceptibility to exhaustion. Thus, appropriately timed administration of HDAC inhibitors may synergistically potentiate current tumor immunotherapies, especially adoptive cellular transfer and T cell reinvigoration strategies.

Citation Format: Tyler R. McCaw, Mingyong Liu, Mei Li, Dmytro Starenki, Sara J. Cooper, Rebecca C. Arend, Andres Forero, Donald J. Buchsbaum, Troy D. Randall. Manipulating the breast tumor microenvironment with histone deacetylase inhibitors for more robust and durable T cell responses [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4700.

Epigenetic modifiers upregulate MHC II and impede ovarian cancer tumor growth

Expression of MHC class II pathway proteins in ovarian cancer correlates with prolonged survival. Murine and human ovarian cancer cells were treated with epigenetic modulators - histone deacetylase inhibitors and a DNA methyltransferase inhibitor. mRNA and protein expression of the MHC II pathway were evaluated by qPCR and flow cytometry. Treatment with entinostat and azacytidine of ID8 cells in vitro increased mRNA levels of Cd74, Ciita, and H2-Aa, H2-Eb1. MHC II and CD74 protein expression were increased after treatment with either agent. A dose dependent response in mRNA and protein expression was seen with entinostat. Combination treatment showed higher MHC II protein expression than with single agent treatment. In patient derived xenografts, CIITA, CD74, and MHC II mRNA transcripts were significantly increased after combination treatment. Expression of MHC II on ovarian tumors in MISIIR-Tag mice was increased with both agents relative to control. Combination treatment significantly reduced ID8 tumor growth in immune-competent mice. Epigenetic treatment increases expression of MHC II on ovarian cancer cells and impedes tumor growth. This approach warrants further study in ovarian cancer patients.

EZH2 Represses the B Cell Transcriptional Program and Regulates Antibody-Secreting Cell Metabolism and Antibody Production

Epigenetic remodeling is required during B cell differentiation. However, little is known about the direct functions of epigenetic enzymes in Ab-secreting cells (ASC) in vivo. In this study, we examined ASC differentiation independent of T cell help and germinal center reactions using mice with inducible or B cell-specific deletions of Ezh2 Following stimulation with influenza virus or LPS, Ezh2-deficient ASC poorly proliferated and inappropriately maintained expression of inflammatory pathways, B cell-lineage transcription factors, and Blimp-1-repressed genes, leading to fewer and less functional ASC. In the absence of EZH2, genes that normally gained histone H3 lysine 27 trimethylation were dysregulated and exhibited increased chromatin accessibility. Furthermore, EZH2 was also required for maximal Ab secretion by ASC, in part due to reduced mitochondrial respiration, impaired glucose metabolism, and poor expression of the unfolded-protein response pathway. Together, these data demonstrate that EZH2 is essential in facilitating epigenetic changes that regulate ASC fate, function, and metabolism.

Modulation of antitumor immunity with histone deacetylase inhibitors

Histone deacetylase inhibitors possess a broad array of antitumor activities; however, their net impact on the evolving antitumor immune response is highly dependent on the inhibitors used and the histone deacetylases they target. Herein, we sequentially focus on each stage of the antitumor immune response - from dendritic cell activation and migration, antigen uptake and presentation, T-cell activation and differentiation and the enactment of antitumor effector functions within the tumor microenvironment. In particular, we will discuss how various inhibitors have different effects depending on cellular activation, experimental design and specific histone deacetylases being targeted - and how these changes impact the outcome of an antitumor immune response. At last, we consider the impact these inhibitors may have on T-cell exhaustion and implications for combination with other immunomodulating therapies.

sIgM-FcμR Interactions Regulate Early B Cell Activation and Plasma Cell Development after Influenza Virus Infection

Previous studies with mice lacking secreted IgM (sIgM) due to a deletion of the μs splice region (μs^-/- ) had shown sIgM involvement in normal B cell development and in support of maximal Ag-specific IgG responses. Because of the changes to B cell development, it remains unclear to which extent and how sIgM directly affects B cell responses. In this study, we aimed to explore the underlying mechanisms of sIgM-mediated IgG response regulation during influenza virus infection. Generating mice with normally developed μs-deficient B cells, we demonstrate that sIgM supports IgG responses by enhancing early Ag-specific B cell expansion, not by altering B cell development. Lack of FcμR expression on B cells, but not lack of Fcα/μR expression or complement activation, reduced antiviral IgG responses to the same extent as observed in μs^-/- mice. B cell-specific Fcmr^-/- mice lacked robust clonal expansion of influenza hemagglutinin-specific B cells early after infection and developed fewer spleen and bone marrow IgG plasma cells and memory B cells, compared with controls. However, germinal center responses appeared unaffected. Provision of sIgM rescued plasma cell development from μs^-/- but not Fcmr^-/- B cells, as demonstrated with mixed bone marrow chimeric mice. Taken together, the data suggest that sIgM interacts with FcμR on B cells to support early B cell activation and the development of long-lived humoral immunity.

Immunological Functions of the Omentum

The omentum is a visceral adipose tissue with unique immune functions. Although it is primarily an adipose tissue, the omentum also contains lymphoid aggregates, called milky spots (MSs), that contribute to peritoneal immunity by collecting antigens, particulates, and pathogens from the peritoneal cavity and, depending on the stimuli, promoting a variety of immune responses, including inflammation, tolerance, or even fibrosis. Reciprocal interactions between cells in the MS and adipocytes regulate their immune and metabolic functions. Importantly, the omentum collects metastasizing tumor cells and supports tumor growth by immunological and metabolic mechanisms. Here we summarize our current knowledge about the development, organization, and function of the omentum in peritoneal immunity.

Abstract 643: Induced MHCII expression on breast cancer cells broadens the responding T cell repertoire, delays tumor-specific T cell exhaustion, and impairs tumor growth

We recently reported that the aberrant expression of Major Histocompatibility Class II (MHCII) molecules on human triple negative breast cancer (TNBC) cells correlates with prolonged progression-free survival and increased tumor infiltrating lymphocytes. We hypothesized that the expression of MHCII enhances the intratumoral CD4+ T cell response, thereby bolstering the tumor-specific CD8+ T cell response, resulting in more effective tumor control. To test our hypothesis, we created both MHCII-expressing and MHCII-negative tumor cells by transfecting murine breast cancer (TS/A) cells with the human class II transcriptional activator (hCIITA) or empty vector, respectively. Transfected cells were then injected into BALB/c mice and the resulting immune response analyzed by flow cytometry at four time points. We found that hCIITA-expressing tumors grew slower than control tumors in immunocompetent recipients, but that this difference was nullified in immunocompromised and markedly reduced in CD4+ T cell depleted mice. CD4+ T cells isolated from hCIITA-transfected tumors produced more IFNγ, IL-17A, and surprisingly granzyme B for longer times than their counterparts in control tumors. Similarly, CD8+ T cells isolated from hCIITA-transfected tumors displayed a more activated phenotype and produced more IFNγ and granzyme B for longer times. Nevertheless, both CD4+ and CD8+ T cells eventually became exhausted in both groups. In addition to enhanced effector functions, TCR repertoire analysis demonstrated that both the breadth and magnitude of expansion of responding T cell clones were increased in hCIITA-transfected tumors. Interestingly, TS/A-hCIITA tumors harbored more regulatory T cells (Tregs) with a more suppressive phenotype than Tregs from control tumors. Finally, we show that the histone deacetylase inhibitor (HDACi) Entinostat is capable of robust and dose-dependent induction of MHCII on tumor cells in vivo, an effect that correlates with dramatic reduction in tumor size. These results suggest that the clinical benefit associated with MHCII expression on TNBC cells is mediated by a delay in T cell exhaustion and increased intratumoral CD4+ T cell activation, which enhances the cytotoxic capacity of CD8+ T cells. Entinostat, and potentially other epigenetic modifying agents, may enable induction of MHCII expression on TNBC cells clinically and allow more patients to benefit from an augmented T cell response. These effects may be magnified by combinatorial therapy with checkpoint inhibitors to promote durable anti-tumor immune responses.

Citation Format: Tyler R. McCaw, Mei Li, Selene Meza-Perez, Donald J. Buchsbaum, Dmytro Starenki, Sara Cooper, Andres Forero, Troy D. Randall. Induced MHCII expression on breast cancer cells broadens the responding T cell repertoire, delays tumor-specific T cell exhaustion, and impairs tumor growth [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 643. doi:10.1158/1538-7445.AM2017-643

Induced MHCII expression on breast cancer cells broadens the responding T cell repertoire, delays tumor-specific T cell exhaustion, and impairs tumor growth

We recently reported that aberrant expression of Major Histocompatibility Class II (MHCII) on human triple negative breast cancer cells correlates with increased tumor infiltrating lymphocytes and prolonged progression free survival. This observation led us to hypothesize that expression of MHCII enhanced the intratumoral CD4+ T cell response, thereby bolstering the tumor-specific CD8+ T cell response, leading to impaired tumor growth. To test this, we transfected the murine breast cancer line TS/A with human class II transcriptional activator (hCIITA) or empty vector, creating MHCII-expressing and MHCII-negative cell lines, respectively. We found that MHCII-expressing tumors grew slower than controls in immunocompetent recipients, but that this difference was abrogated in CD4-depleted and nullified in SCID mice. CD4+ T cells within hCIITA-transfected tumors produced more IFNγ for longer times than those from control tumors. Similarly, CD8+ T cells in MHCII-expressing tumors displayed a more activated phenotype and produced more IFNγ and granzyme B for longer times. Nevertheless, both CD4+ and CD8+ T cells eventually became exhausted in both groups. In addition to boosted effector function, TCR repertoire analysis demonstrated an increase in both breadth and amplitude of T cell response to MHCII-expressing tumors. We next investigated the possibility of inducing MHCII on non-expressing tumors using the histone deacetylase inhibitor Entinostat. Indeed, Entinostat turned on MHCII expression, which correlated with significantly reduced tumor burden. Thus, epigenetic modifiers capable of inducing MHCII expression on tumor cells could avail this augmented T cell response to all patients for enhanced tumor control.

VAT-associated ST2+Tregs from omentum support tolerance to peripheral tumors

Tumor metastasis to theomentum is associated with poor clinical outcomes. Although the omentum hasimmune function due to the activities of milky spots, the role of this organ inanti-tumor immunity has not been completely described.

By implanting tumor cells in mice we found that peritoneal tumors are not rejected and cause an increasein visceral adipose tissue (VAT)-associated regulatory T cells in the omentumas well as low frequency of tumor specific CD8 T cells. Additionally, peritoneal tumors impaired the immunity to secondary dermal tumors by limiting the expansion of tumor specific CD8 T cells that mediate tumor rejection.

To better understand this phenomenon, we studied the VAT-associated Tregs, which can be divided in ST2+ and ST2- (ST2 a component of the IL-33R). Particularly, VAT-associated ST2+ Tregs are not found in conventional lymphoid organs, nonetheless we find that following peritoneal tumor inoculation ST2+ Tregs are mobilized and home to secondary dermal tumors. To test whether the ST2+ Tregs were responsible for preventing secondary dermal tumors, we inoculate mice lacking ST2 (ST2−/−) with peritoneal tumors and challenged them with dermal tumors; interestingly, we found that secondary dermal tumors where rejected in ST2−/− mice whereas tumors in wild type mice continue to grow. Finally, to corroborate our findings we used a mouse strain that develops spontaneous ovarian tumors that metastasize to the omentum. By treating these mice with anti-ST2 we observed a reduction in tumor weight, decrease in ST2+Tregs and an increase in tumor specific CD8+ cells in omentum and ovaries. Together these data suggest that omental ST2+ Tregs have an important role promoting and maintaining tolerance in tumor metastasis.

Identification of antigen-specific, lung resident memory B cells after influenza infection

B cells display phenotypic and functional heterogeneity in multiple anatomical locations following vaccination or infection. Influenza-specific memory B cells (Flu+BMEM cells) are found in both lymphoid tissues and lung. It is unclear whether these cells represent circulating or resident memory B cell (BRM) populations. We hypothesized that a portion of the Flu+BMEM cell population in the lung would be non-circulating, BRMs. To determine whether Flu+BMEM cells in the lung are circulating or resident, we parabiotically joined previously-infected, congenically-mismatched mice for 2 weeks and marked those cells currently in circulation by infusing anti-B220 and identified those that have trafficked between the partners by their expression of the CD45 congenic marker. The lungs of these mice had large populations of hemagglutinin and nucleoprotein -specific BMEM cells that did not attain equilibrium within 2 weeks of parabiosis, suggesting that they are non-circulating. The Flu+ BRMs in the lungs consisted of 56% IgM+ and 43.9% isotype-switched BRMs. They were established as early as 15 days after infection and maintained for at least 60 days. The formation of Flu+ BRMs required the germinal center (GC), as blocking CD40L with MR1 antibody, during the primary infection abrogated BRM. However, MR1-treatment of mice with established BRM did not affect BRMs in the lung, even though Flu+ GC B cells could be detected in the LN for up to 90 days. These data suggest that GC-dependent lung-BRMs are established early after infection and maintained independently of GCs. These findings are important in the development of vaccines that elicit BRMs and they will provide mechanistic information into the function of Ag+BMEM cells residing in the mucosa.

Dynamic regulation of T Follicular Regulatory (Tfr) cell responses by Interleukin-2 (IL-2) during influenza infection

IL-2 promotes FoxP3+ regulatory T (Treg) cell responses, but inhibits the differentiation of T follicular helper (Tfh) cells. However, it is not clear how IL-2 affects T follicular regulatory (Tfr) cells, a cell type with properties of both Treg and Tfh cells. Here we show that IL-2 prevents, rather than promotes, the development of Tfr cells. Using an influenza infection model, we found that Tfr cells were barely detectable at the peak of the infection, but accumulated as the immune response resolved. High levels of IL-2 at the peak of the infection promoted the expression of Blimp-1 in Treg cells, which suppressed Bcl6 expression and thereby precluded Tfr cell development. However, as IL-2 levels declined some CD25+ Treg cells down-regulated CD25, up-regulated Bcl6 and differentiated into Tfr cells, which prevented the accumulation of self-reactive antibody-secreting cells. Thus, unlike its effects on conventional Treg cells, IL-2 inhibits Tfr cell responses.

The LFA1 ligand, CD54, is not required for the differentiation of TFH cells or germinal center formation

In germinal centers (GC), B cells undergo cellular proliferation and affinity maturation, and ultimately differentiate into either high-affinity antibody-secreting cells (ASCs) or memory B cells. GC B cells present antigen to T follicular helper (TFH) cells in order to elicit survival and proliferation signals. The integrin, Lymphocyte Function-Associated Antigen 1 (LFA1), is required for this process, as mice lacking LFA1 or treated with LFA1 blocking antibodies fail to form GCs or TFH cells. We hypothesized that the counter-receptor for LFA1, ICAM-1 or CD54, would be similarly required for GC formation and TFH differentiation. To test this hypothesis, we infected CD54-deficient (KO) and wild-type (WT) mice with influenza virus (PR8) and enumerated ASCs and GC B cells on days 7, 9, and 14. We found that KO mice had more GC B cells than WT mice on days 9 and 14, but observed no difference in the number of ASCs or TFH cells. To determine if this result was intrinsic to the B cell lineage, we generated 50:50 (KO:WT) bone marrow chimeras. Following reconstitution, we infected the mice with PR8 and assayed donor-specific GC B cells and ASCs on days 9 and 14. On day 9, we found that GC B cells were highly enriched for KO cells, whereas the ASCs were highly enriched for WT cells. In contrast, TFH cells were represented equally in WT and KO populations. On day 14, we found that GC B cells were still highly enriched for KO cells, whereas there was no significant difference between WT and KO ASCs at this time. These results lead us to the surprising conclusion that, although the loss of LFA1 leads to the failure of TFH and GC responses, the loss of CD54 does not affect the TFH compartment and actually improves GC B cell responses.