Ex vivo activation of the GCN2 pathway metabolically reprograms T cells, leading to enhanced adoptive cell therapy

The manipulation of T cell metabolism to enhance anti-tumor activity is an area of active investigation. Here, we report that activating the amino acid starvation response in effector CD8+ T cells ex vivo using the general control non-depressible 2 (GCN2) agonist halofuginone (halo) enhances oxidative metabolism and effector function. Mechanistically, we identified autophagy coupled with the CD98-mTOR axis as key downstream mediators of the phenotype induced by halo treatment. The adoptive transfer of halo-treated CD8+ T cells into tumor-bearing mice led to robust tumor control and curative responses. Halo-treated T cells synergized in vivo with a 4-1BB agonistic antibody to control tumor growth in a mouse model resistant to immunotherapy. Importantly, treatment of human CD8+ T cells with halo resulted in similar metabolic and functional reprogramming. These findings demonstrate that activating the amino acid starvation response with the GCN2 agonist halo can enhance T cell metabolism and anti-tumor activity.

N6-Methyladenosine Reader YTHDF1 Promotes ARHGEF2 Translation and RhoA Signaling in Colorectal Cancer

BACKGROUND & AIMS

N6-methyladenosine (m⁶A) governs the fate of RNAs through m⁶A readers. Colorectal cancer (CRC) exhibits aberrant m⁶A modifications and expression of m⁶A regulators. However, how m⁶A readers interpret oncogenic m⁶A methylome to promote malignant transformation remains to be illustrated.

METHODS

YTH N6-methyladenosine RNA binding protein 1 (Ythdf1) knockout mouse was generated to determine the effect of Ythdf1 in CRC tumorigenesis in vivo. Multiomic analysis of RNA-sequencing, m⁶A methylated RNA immunoprecipitation sequencing, YTHDF1 RNA immunoprecipitation sequencing, and proteomics were performed to unravel targets of YTHDF1 in CRC. The therapeutic potential of targeting YTHDF1-m⁶A-Rho/Rac guanine nucleotide exchange factor 2 (ARHGEF2) was evaluated using small interfering RNA (siRNA) encapsulated by lipid nanoparticles (LNP).

RESULTS

DNA copy number gain of YTHDF1 is a frequent event in CRC and contributes to its overexpression. High expression of YTHDF1 is significantly associated with metastatic gene signature in patient tumors. Ythdf1 knockout in mice dampened tumor growth in an inflammatory CRC model. YTHDF1 promotes cell growth in CRC cell lines and primary organoids and lung and liver metastasis in vivo. Integrative multiomics analysis identified RhoA activator ARHGEF2 as a key downstream target of YTHDF1. YTHDF1 binds to m⁶A sites of ARHGEF2 messenger RNA, resulting in enhanced translation of ARHGEF2. Ectopic expression of ARHGEF2 restored impaired RhoA signaling, cell growth, and metastatic ability both in vitro and in vivo caused by YTHDF1 loss, verifying that ARHGEF2 is a key target of YTHDF1. Finally, ARHGEF2 siRNA delivered by LNP significantly suppressed tumor growth and metastasis in vivo.

CONCLUSIONS

We identify a novel oncogenic epitranscriptome axis of YTHDF1-m⁶A-ARHGEF2, which regulates CRC tumorigenesis and metastasis. siRNA-delivering LNP drug validated the therapeutic potential of targeting this axis in CRC.

Abstract CT124: Sitravatinib and nivolumab in oral cavity cancer window of opportunity study (SNOW)

Background: Squamous cell carcinoma of the oral cavity (SCCOC) often presents at early stages but its prognosis remains guarded, with a 5-year survival rate of 60% despite curative-intent therapies. Preoperative window-of-opportunity (WOO) studies in resectable SCCOC enable pharmacodynamic evaluation of molecular endpoints without compromising curative-intent treatment. Preoperative nivolumab in SCCOC was safe and showed promising tumor responses in CheckMate-358 WOO study (Ferris et al. ESMO 2017, LBA46). Sitravatinib, a receptor tyrosine kinase inhibitor which potently inhibits Tyro, AXL, Mer, and VEGF family of receptors, has shown encouraging results when combined with nivolumab in non-small cell lung cancer patients who have progressed on anti-PD-1 agents (Leal et al. ESMO 2018, 1129O). We hypothesize that sitravatinib and nivolumab have synergistic antitumor and immunogenic effects by increasing tumor immune infiltration and by blocking oncogenic pathways implicated in disease progression and immune-checkpoint resistance.

Methods: Trial design: SNOW is a single-center, non-randomized WOO study of preoperative sitravatinib and nivolumab in patients with resectable SCCOC. Sitravatinib 120 mg is given orally once daily from day 1 until 48h before surgery or for a maximum period of 28 days. Nivolumab 240mg is given intravenously on day 15 for one dose only. Surgery is planned between days 23-30 following study treatment initiation. Fresh tumor biopsies and serial blood samples for extensive immunophenotyping and evaluation of other pharmacodynamic biomarkers, as well as clinical photographs of the tumor, are collected at baseline, on day 15 prior to nivolumab and at the time of surgery. 18FAZA-PET scans are performed at baseline and before surgery.

Key eligibility criteria: previously untreated and resectable SCCOC; T2-4a, N0-2 or T1 (greater than 1 cm)-N2; no history of tumor bleeding or invasion of major vessels; adequate organ function; no autoimmune disorders; no immunosuppressive therapy.

Study objectives: primary objective is to evaluate the immune and pharmacodynamic effects of sitravatinib plus nivolumab. Secondary objectives are: safety and tolerability including toxicity, rate of surgery completion within the planned window and rate of postoperative complications; antitumor activity including rate of complete pathological response; pharmacokinetics of sitravatinib alone and in combination with nivolumab.

Correlative studies: tumor and blood immunophenotyping, tumor genome and transcriptome analysis, changes in intratumoral hypoxia based on 18FAZA-PET testing. Sample size: SNOW is a proof-of-concept study with no specific statistical assumptions at trial onset. We plan to enroll 12-15 patients evaluable for correlative studies.

Study activation: Aug 30th, 2018. Two patients enrolled as of Jan 10th2019.

Clinical trial identification: NCT03575598.

Citation Format: Marc Oliva Bernal, Douglas Chepeha, Amy Prawira, Douglass Vines, Anna Spreafico, Scott Bratman, John De Almeida, Aaron Hansen, David Goldstein, Ralph Gilbert, Patrick Gullane, Dale H. Brown, Ilan Weinreb, Bayardo Perez-Ordoñez, Pamela S. Ohashi, Tracy McGaha, Ben X. Wang, Jonathan Irish, Isan Chen, Lillian L. Siu. Sitravatinib and nivolumab in oral cavity cancer window of opportunity study (SNOW) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr CT124.

Abstract 1500: Mediators of CD8+ cytotoxic T lymphocyte infiltration in pancreatic cancer

Pancreatic cancer continues to have the highest mortality rate of all solid cancers, with a 5-year overall survival of approximately 8%. Despite recent progress in other malignancies, immunotherapy remains ineffective against pancreatic cancer. Previous work from our group and others has shown that tumors with mismatch repair (MMR) and homologous repair (HR) deficiency have increased immune activity, likely attributable to the inherently increased mutational and neoantigen load in these patients. However, there remains a subset of pancreatic cancer patients with increased CD8+ T cell infiltration, despite lacking these specific mutational signatures. Furthermore, an increasing body of evidence has shown that mutational burden and neoantigen load only partially explain the T cell-inflamed phenotype seen in tumors, implicating the presence of additional mechanisms that drive T cell infiltration in cancer. Several recent studies have highlighted the importance of proper CD8+ T cell priming by antigen presenting cells (APCs), particularly Batf3+ dendritic cells (DCs), and subsequent tumor infiltration via chemokines for immunotherapy to be effective. In this study, we investigated the involvement of chemokines in cytotoxic T lymphocyte infiltration in pancreatic cancer. Using a bioinformatics-driven approach, we analyzed 78 treatment-naïve, primary pancreas cancer resections for associations between CD8+ tumour infiltrating lymphocytes (TILs) and chemokine expression by RNAseq. A panel of chemokines, including CCL4, CCL5, CXCL9, CXCL10, and CXCL11, was highly associated with CD8+ TILs (p < 0.001). Segregating 173 tumour-enriched patient RNAseq samples based on expression of CXCL9 and CXCL10, we found those with higher expression of these chemokines had increased immune activation signatures. Importantly, this included increased MHC I presentation, presence of Batf3+ DCs, and T cell/APC co-stimulation (p < 0.001), while we observed no differences in conventional predictors of CD8+ T cell infiltration such as SNV counts or neoantigens between groups. These results were consistent across ICGC and TCGA data sets. Moreover, these results were also recapitulated in 72 tumor-enriched liver metastases, suggesting an underlying immunobiology that may occur in both primary and metastatic sites. The cellular sources of these chemokines, as determined by immunohistochemical analysis, and the role of tumor-sensing innate immune pathways leading to CD8+ T cell priming, by pathway and differential gene expression analysis, are currently being investigated. Taken together, these results demonstrate a potential role for these chemokines in recruiting CD8+ T cells in pancreatic cancer. Understanding mediators driving cytotoxic T cell infiltration will help identify mechanisms leading to proper CD8+ T cell priming and homing into tumors, to stratify patients amenable for known and novel immunotherapies.

Citation Format: Joan Miguel Romero, Barbara Grünwald, Ashton Connor, Gun Ho Jang, Prashant Bavi, Aaditeya Jhaveri, Mehdi Masoomian, Sandra Fischer, Amy Zhang, Robert E. Denroche, Tracy McGaha, Faiyaz Notta, Pamela Ohashi, Grainne O'Kane, Julie Wilson, Jennifer Knox, Steven Gallinger. Mediators of CD8+ cytotoxic T lymphocyte infiltration in pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1500.

An interim report on the investigator-initiated phase 2 study of pembrolizumab immunological response evaluation (INSPIRE)

Background

Immune checkpoint inhibitors (ICIs) demonstrate unprecedented efficacy in multiple malignancies; however, the mechanisms of sensitivity and resistance are poorly understood and predictive biomarkers are scarce. INSPIRE is a phase 2 basket study to evaluate the genomic and immune landscapes of peripheral blood and tumors following pembrolizumab treatment.

Methods

Patients with incurable, locally advanced or metastatic solid tumors that have progressed on standard therapy, or for whom no standard therapy exists or standard therapy was not deemed appropriate, received 200 mg pembrolizumab intravenously every three weeks. Blood and tissue samples were collected at baseline, during treatment, and at progression. One core biopsy was used for immunohistochemistry and the remaining cores were pooled and divided for genomic and immune analyses. Univariable analysis of clinical, genomic, and immunophenotyping parameters was conducted to evaluate associations with treatment response in this exploratory analysis.

Results

Eighty patients were enrolled from March 21, 2016 to June 1, 2017, and 129 tumor and 382 blood samples were collected. Immune biomarkers were significantly different between the blood and tissue. T cell PD-1 was blocked (≥98%) in the blood of all patients by the third week of treatment. In the tumor, 5/11 (45%) and 11/14 (79%) patients had T cell surface PD-1 occupance at weeks six and nine, respectively. The proportion of genome copy number alterations and abundance of intratumoral 4-1BB+ PD-1+ CD8 T cells at baseline (P < 0.05), and fold-expansion of intratumoral CD8 T cells from baseline to cycle 2–3 (P < 0.05) were associated with treatment response.

Conclusion

This study provides technical feasibility data for correlative studies. Tissue biopsies provide distinct data from the blood and may predict response to pembrolizumab.

Electronic supplementary material

The online version of this article (10.1186/s40425-019-0541-0) contains supplementary material, which is available to authorized users.

Apoptotic cell induced, TLR9-dependent AhR activity is a critical driver of tolerance induction and suppression of lupus

The Aryl hydrocarbon receptor (AhR) can potently modulate immunity at multiple levels, but its mechanistic role in immune regulation is still being elucidated. Here we show phagocytes exposed to apoptotic cells exhibit rapid activation of AhR driving IL-10 that antagonizes inflammatory cytokine production. AhR activation was dependent on apoptotic cell DNA-TLR9 interactions and reactive oxygen species (ROS) production in phagocytes that promoted nuclear accumulation and transcriptional activity. In vivo, apoptotic cell-induced AhR signals in myeloid cells were required for prevention of inflammatory innate and adaptive immunity against DNA and histones. Moreover, disease progression in lupus correlated with AhR signal strength, and disease course could be reduced or exacerbated by modulation of AhR activity. Finally, we observed myeloid specific deletion of AhR in mice resulted in systemic autoimmunity, and in SLE patients an increased AhR transcriptional signature correlated with disease. Thus, our findings suggest AhR activity influenced by apoptotic cell death is a key mechanism in maintenance of peripheral tolerance reducing inflammation and thereby retarding systemic autoimmune disease progression.

Apoptotic cell driven ROS burst drives AhR dependent immunologic tolerance and suppression of lupus

Tissue-resident macrophages (MΦ) are crucial in driving tolerance and preventing systemic autoimmunity. We have previously shown that exposure to apoptotic cells triggers a regulatory circuit dependent on IL-10 production in resident MΦ. However, key molecular mechanisms driving the regulatory response to apoptosis are not clear. RNA transcriptome analysis of MΦs after exposure to apoptotic cells identified strong transcript association with the aryl hydrocarbon receptor (AhR) signaling pathway, an association that was confirmed by phenotypic and biochemical analysis. When AhR activity was blocked, apoptotic cells induced an alteration in the mRNA signature enhancing proinflammatory effector expression. Functional analysis revealed that the DNA from apoptotic cells activated AhR in a reactive oxygen species (ROS) dependent mechanism and AhR is required for IL-10 production. Consequently, inhibition or deletion of AhR signals fundamentally altered immune responses to apoptotic cells in vivo resulting in proinflammatory cytokine production, increased effector T cell responses, and failure of long-term tolerance to apoptotic cell-associated antigens. Surprisingly, mice lacking AhR developed progressive systemic autoimmunity characterized by excessive MΦ and lymphocyte activation and renal pathology. Similarly, SLE-prone mice treated with AhR antagonist exhibited poor survival, while agonist treatment ablated disease pathology. Finally, an AhR transcriptional signature was significantly associated with active SLE flare in SLE patients. Thus, the data demonstrates the AhR pathway is a key molecular circuit responsible for apoptotic cell driven tolerance and suppression of inflammatory autoimmunity.

Abstract PR05: IRF8 regulates GM-CSF expression in T cells and tumor cells to mediate myeloid-derived suppressor cell differentiation

Myeloid cells are a heterogenous and abundant population of haematopoietic cells that are virtually present in all mammalian tissues, where they monitor local microenvironment to maintain homeostasis. All myeloid cells originate from the pluripotent hematopoietic stem cells that undergo progressive restriction in their lineage potential to give rise to mature granulocytes and macrophages. Lineage restriction and differentiation are regulated by timely activation of specific set of lineage-specific transcription factors in concert with down-regulation of other set(s) of transcription factors that are important for alternative cell lineage potential. Altered expression of these lineage-specific transcription factors often leads to deregulation of myelopoiesis and resultant hematopoietic disorders. Therefore, lineage-specific transcription factors are essential for myeloid cell lineage differentiation and maturation. Mice with a null mutation of irf8, the gene that encodes IFN regulatory factor 8 (IRF8), exhibit massive accumulation of CD11b+Gr1+ immature myeloid cells (IMCs). Therefore, IRF8 is a myeloid cell lineage-specific transcription factor that plays an essential function in the regulation of myelopoiesis. Particularly, IRF8 may determine differentiation, lineage commitment, and immune function of monocytes versus granulocytes under physiological conditions.

A hallmark of cancer-bearing mice is the accumulation of CD11b+Gr1+ myeloid-derived suppressor cells (MDSCs). Interestingly, IRF8 is silenced in MDSCs from tumor-bearing mice. Therefore, IRF8 is apparently a key transcription factor that mediates MDSC differentiation. However, the molecular mechanism underlying IRF8 regulation of MDSCs is largely unknown. Because MDSCs is induced by inflammation, we therefore hypothesized that IRF8 may repress the expression of proinflammatory factors to mediate differentiation of MDSCs/IMCs under physiological and pathological conditions. To test this hypothesis, we made use of conventional IRF8 KO mice, mice with IRF8 deficiency only in myeloid cells, mice with IRF8 deficiency only in T cells, and tumor-bearing mouse models. Here we report an intriguing finding that although IRF8 conventional mice exhibit deregulated myeloid cell differentiation and resultant accumulation of CD11b+Gr1+ IMCs, surprisingly, mice with IRF8 deficiency only in myeloid cells exhibit normal myeloid cell lineage differentiation. Instead, mice with IRF8 deficiency only in T cells exhibited deregulated myeloid cell differentiation and IMC accumulation. We further demonstrated that IRF8-deficient T cells exhibit elevated GM-CSF expression and secretion. Treatment of mice with GM-CSF increased IMC accumulation, and adoptive transfer of IRF8-deficient T cells, but not GM-CSF-deficient T cells, increased IMC accumulation in the recipient chimera mice. Moreover, overexpression of IRF8 decreased GM-CSF expression in T cells. These data thus determine that IRF8 functions in T cells to repress GM-CSF expression to suppress IMCs. However, in tumor-bearing mice, IRF8 is silenced in MDSCs but not in T cells, suggesting a different mechanism of MDSC regulation by IRF8. We observed that silencing IRF8 using IRF8-specific siRNA dramatically increase GM-CSF expression in tumor cells. Therefore, IRF8 represses GM-CSF expression in tumor cells to mediate MDSC differentiation. In summary, we determine that IRF8 regulates GM-CSF expression in T cells and tumor cells, respectively, to mediate myelopoiesis under physiological and pathological conditions.

This abstract is also presented as Poster A84.

Citation Format: Amy Paschall, Ruihua Zhang, Kankana Bardhan, Chen-Feng Qi, Liang Peng, Geming Lu, Jianjun Yang, Miriam Merad, Mary Zimmerman, Tracy McGaha, Gang Zhou, Andrew Mellor, Scott I. Abrams, Herbert Morse, Keiko Ozato, Huabao Xiong, Kebin Liu. IRF8 regulates GM-CSF expression in T cells and tumor cells to mediate myeloid-derived suppressor cell differentiation. [abstract]. In: Proceedings of the AACR Special Conference: Tumor Immunology and Immunotherapy: A New Chapter; December 1-4, 2014; Orlando, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2015;3(10 Suppl):Abstract nr PR05.

Abstract A84: IRF8 regulates GM-CSF expression in T cells and tumor cells to mediate myeloid-derived suppressor cell differentiation

This abstract is being presented as a short talk in the scientific program. A full abstract is printed in the Proffered Abstracts section (PR05) of the Conference Proceedings.

Citation Format: Amy Paschall, Ruihua Zhang, Kankana Bardhan, Chen-Feng Qi, Liang Peng, Geming Lu, Jianjun Yang, Miriam Merad, Mary Zimmerman, Tracy McGaha, Gang Zhou, Andrew Mellor, Scott I. Abrams, Herbert Morse, Keiko Ozato, Huabao Xiong, Kebin Liu. IRF8 regulates GM-CSF expression in T cells and tumor cells to mediate myeloid-derived suppressor cell differentiation. [abstract]. In: Proceedings of the AACR Special Conference: Tumor Immunology and Immunotherapy: A New Chapter; December 1-4, 2014; Orlando, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2015;3(10 Suppl):Abstract nr A84.

IRF8 expressed in T cells regulates GM-CSF expression to control myeloid derived suppressor cell differentiation (TUM6P.955)

During hematopoiesis, hematopoietic stem cells differentiate into granulocytes and macrophages via a distinct differentiation program that is controlled by myeloid lineage-specific transcription factors. Mice with a null mutation of IFN Regulatory Factor 8 (IRF8) accumulate CD11b+Gr1+ myeloid cells that phenotypically and functionally resemble tumor-induced myeloid-derived suppressor cells (MDSCs), indicating an essential role of IRF8 in myeloid cell lineage differentiation. However, whether IRF8 functions intrinsically or extrinsically in regulation of myeloid cell differentiation is not fully understood. Here we report an intriguing finding that mice with IRF8 deficiency only in myeloid cells exhibit no abnormal myeloid cell lineage differentiation. Instead, mice with IRF8 deficiency only in T cells exhibited MDSC accumulation. We further demonstrated that IRF8-deficient T cells exhibit elevated GM-CSF expression and secretion. Treatment of mice with GM-CSF increased MDSC accumulation, and adoptive transfer of IRF8- deficient T cells, but not GM-CSF-deficient T cells, increased MDSC accumulation in the recipient mice. Overexpression of IRF8 decreased GM-CSF in T cells. Our data determine that in addition to its intrinsic role as an apoptosis regulator in myeloid cells, IRF8 also acts extrinsically to repress GM-CSF expression in T cells to control myeloid cell lineage differentiation, revealing a novel mechanism of adaptive immune cell regulation of myelopoiesis in vivo.

IFN regulatory factor 8 represses GM-CSF expression in T cells to affect myeloid cell lineage differentiation

During hematopoiesis, hematopoietic stem cells constantly differentiate into granulocytes and macrophages via a distinct differentiation program that is tightly controlled by myeloid lineage-specific transcription factors. Mice with a null mutation of IFN regulatory factor 8 (IRF8) accumulate CD11b(+)Gr1(+) myeloid cells that phenotypically and functionally resemble tumor-induced myeloid-derived suppressor cells (MDSCs), indicating an essential role of IRF8 in myeloid cell lineage differentiation. However, IRF8 is expressed in various types of immune cells, and whether IRF8 functions intrinsically or extrinsically in regulation of myeloid cell lineage differentiation is not fully understood. In this study, we report an intriguing finding that, although IRF8-deficient mice exhibit deregulated myeloid cell differentiation and resultant accumulation of CD11b(+)Gr1(+) MDSCs, surprisingly, mice with IRF8 deficiency only in myeloid cells exhibit no abnormal myeloid cell lineage differentiation. Instead, mice with IRF8 deficiency only in T cells exhibited deregulated myeloid cell differentiation and MDSC accumulation. We further demonstrated that IRF8-deficient T cells exhibit elevated GM-CSF expression and secretion. Treatment of mice with GM-CSF increased MDSC accumulation, and adoptive transfer of IRF8-deficient T cells, but not GM-CSF-deficient T cells, increased MDSC accumulation in the recipient chimeric mice. Moreover, overexpression of IRF8 decreased GM-CSF expression in T cells. Our data determine that, in addition to its intrinsic function as an apoptosis regulator in myeloid cells, IRF8 also acts extrinsically to repress GM-CSF expression in T cells to control myeloid cell lineage differentiation, revealing a novel mechanism that the adaptive immune component of the immune system regulates the innate immune cell myelopoiesis in vivo.

STING, nanoparticles, autoimmune disease and cancer: a novel paradigm for immunotherapy?

DNA has potent immunogenic properties that are useful to enhance vaccine efficacy. DNA also incites hyperinflammation and autoimmunity if DNA sensing is not regulated. Paradoxically, DNA regulates immunity and autoimmunity when administered systemically as DNA nanoparticles. DNA nanoparticles regulated immunity via cytosolic DNA sensors that activate the signaling adaptor stimulator of interferon genes. In this review, we describe how DNA sensing to activate stimulator of interferon genes promotes regulatory responses and discuss the biological and clinical implications of these responses for understanding disease progression and designing better therapies for patients with chronic inflammatory diseases, such as autoimmune syndromes or cancer.

The role of GCN2 in type-2 mucosal inflammation within the lung (IRM7P.483)

Infection with the parasitic roundworm Nippostrongylus brasiliensis causes lung damage associated with an inflammatory response dominated by alternative (type-2) inflammation. Macrophages are requisite mediators of lung inflammation and pathology resolution in the N. brasiliensis infection model. Metabolic stress resulting from enzymatic consumption of amino acids engages the GCN2 arm of the integrated stress response, which profoundly alters the inflammatory potential of antigen presenting cells, causing them to suppress type-1 cytokine expression and promote type-2 cytokine expression. Thus, we hypothesized that GCN2 activation, as a result of infection driven nutrient stress, may be a key mechanism promoting M2 macrophage differentiation and type-2 inflammatory processes. When we examined cytokine expression in the lungs of GCN2KO mice infected with N. brasiliensis, we found significantly decreased levels of IL-10 relative to WT controls. This was associated with increased lung infiltration of macrophages that expressed reduced expression of FIZZ1 and YM-1, indicative of a skewing towards an M1 phenotype. Moreover, we observed dramatic increases in lung pathology associated with increased cellular infiltrate and fibrosis in infected GCN2KO mice suggestive of severe helminth-driven lung inflammation. Thus, our findings suggest a novel regulatory role for GCN2 kinase during type-2 inflammatory processes in the lung.

Indoleamine 2,3-dioxygenase inhibits B cell immune response to T independent antigens (IRM8P.710)

T cell independent (TI) antibody responses are crucial for humoral immunity to viruses and encapsulated bacteria. Here we report a novel mechanism where the tryptophan catabolizing enzyme indoleamine 2,3-dioxygenase (IDO) 1 regulates the B cell response to TI antigens. Immunization with NP-Ficoll led to rapid splenic induction of IDO, primarily in the extra-follicular space. When IDO1KO mice were immunized there was a significant increase in humoral responses with increased formation of extra-follicular IgM and IgG3 foci, antibody secreting cells (ASCs), and increased antibody titers. This was not associated with an alteration in affinity maturation suggesting the primary impact of IDO1 deficiency was increased B cell proliferation and plasma cell formation. IDO1 did not affect immune responses to protein antigens as immunization with NP-OVA elicited similar antibody titers regardless of IDO1 function. In addition, adoptive transfer of IDO1 deficient B cells to µMT-/- (B cell deficient) mice was sufficient to replicate increased TI responses observed in IDOKO mice. Moreover, in vitro LPS rapidly induced IDO1 in MACS-purified B cells and IDO deficient B cells display enhanced LPS and CpG-driven proliferation associated with increased production of IgM, IgG3, and IL10. Thus, our results demonstrate a novel role of IDO in suppressing T cell independent antibody response that provides insight into the understanding of B cell immune responses in autoimmunity and vaccine biology.

Early events in immunologic tolerance to apoptotic cells are dependent on marginal zone macrophage CCL22 production. (P4081)

Apoptotic cells (ACs) promote immunologic tolerance but the early innate mechanism(s) involved in the process are not known. Here we report that administration of ACs i/v induced rapid splenic expression of the regulatory T cell chemokine CCL22 by CD169+ marginal zone macrophages (MZMs). Similarly, in-vitro culture with ACs lead to expression of CCL22 in purified MZMs, but not CD11c+ dendritic cells (DCs) and conditioned media from MZM cocultures induced migration of Tregs in a CCL22 dependent manner. Administration of a soluble antagonist for the CCL22 receptor (i.e. CCR4) skewed the early innate immune response to ACs in-vivo shifting the balance from regulatory (IL-10, TGF-β) to inflammatory (TNF-α, IL-6, IL-12) cytokine production in splenic DCs and macrophages. Similarly, CCR4 blockade inhibited splenic accumulation of Tregs after apoptotic cell injection i/v and enhanced effector T cell responses to AC-associated antigens. Short-term CCR4 inhibition at the time of i/v apoptotic cell challenge (i.e. blockade only at the time of apoptotic cell administration) reversed AC-mediated tolerance to skin allografts in both primary recipients and in Treg adoptive transfers to secondary recipients instead promoting more rapid rejection. Suggesting a primary role for CCL22 in AC tolerance. Thus, we show for the first time that selective induction of CCL22 by MZMs is an essential early innate step in the generation of infectious immune tolerance to apoptotic self.

Innate and adaptive tolerance to apoptotic cells is controlled by an IDO- dependent mechanism. (123.49)

Marginal zone macrophages (MZMs) play a crucial role in generation of systemic tolerance to apoptotic cell (AC)-associated antigens. However, the mechanism(s) by which MZMs drive tolerogenic responses is not understood. In this report, we show that systemic administration of ACs induces splenic expression of the immunosuppressive enzyme indoleamine 2-3 dioxygenase (IDO) in Marco+SignR1+ MZMs. Moreover, we found abrogation of IDO activity altered immunity to ACs resulting in decreased TGF-β synthesis and increased pro-inflammatory cytokine production associated with a reduction in Treg function and a loss of T cell tolerance towards AC antigens. When pre-symptomatic, lupus-prone MRLlpr/lpr mice were examined we found significant IDO expression in the splenic MZ analogous to the observations in AC challenged mice. When IDO was inhibited, autoimmunity was rapidly accelerated in MRLlpr/lpr mice with a &gt;10-fold increase in anti-dsDNA IgG titers and increased renal pathology. Finally, IDO-/- mice, which do not show signs of autoimmunity, were challenged chronically with ACs. The mice developed high titer serum IgG autoreactivity, kidney inflammation, and increased mortality compared to B6 mice, which did not develop autoimmunity. Thus, the data demonstrate that a novel IDO-dependent regulatory circuit is induced in MZMs upon apoptotic cell phagocytosis providing clues to future therapeutic targets to re-establish tolerance in systemic autoimmune disease.

IDO modifies TLR-ligand driven macrophage cytokine production by activation of GCN2 kinase arm of the integrated stress response and subsequent CHOP/GADD153 induction (180.3)

Microbial sepsis is characterized by an initial cytokine storm followed by immune suppression, vascular collapse, and multiple organ failure. Indoleamine 2,3 dioxygenase (IDO) is an intracellular tryptophan-catabolizing enzyme that is induced after exposure to LPS in vivo. While generally considered to have immunosuppressive function, IDO blockade was recently demonstrated to protect mice against systemic lipopolysaccharide (LPS)-challenge, however, nothing is known about the underlying molecular mechanisms. In this study, we report that IDO was induced in the spleen of mice 6 hours after exposure to a lethal dose of endotoxin, and IDO deficiency in hematopoietic cells significantly improved survival. Moreover, we found IDO mediated tryptophan depletion in macrophages increased pro-inflammatory cytokine production in response to LPS exposure. This was due to the activation of the GCN2 kinase arm of the integrated stress response and subsequent expression of CHOP (GADD153) resulting in enhanced constitutive NF-κB activity. Lack of either GCN2 or CHOP completely abrogated macrophage production of IL-6 under stress conditions. Further, disruption of GCN2 reduced production of TNF-α and IL-12 in response to LPS stimulation under any condition. Thus, taken together our findings demonstrate that IDO functions to modulate macrophage pro-inflammatory response via a novel amino acid deprivation mechanism dependent on the integrated stress response.

Cellular and molecular studies of B cells exhibiting reverse somatic mutation throughout life

Somatic mutation of immunoglobulin (Ig) genes plays an important role in generating antibody diversity. The frequency of somatic mutation appears to vary throughout life. However, this process has been difficult to study in vivo because the DNA in and around rearranged V genes undergoes random mutation, causing silent or replacement mutations. Therefore, we have developed a transgenic mouse model for studying the frequency of B cells exhibiting mutation in young and old mice. The system is based on a reporter transgene (HuG-X) that encodes a chimeric Ig heavy chain composed of a murine VDJ segment and a human IgG1 constant region. The VDJ has been mutated to contain a TAG stop codon in the D segment. Therefore, the transgene is transcribed but not translated. Point mutation of the stop codon results in expression of the chimeric H chain, which is readily detected as human IgG1 expression. In vivo, we found that the transgene undergoes spontaneous reverse somatic mutation at a low frequency. Treatment of HuG-X mice with anti-IgD greatly increases the frequency of somatic mutation. The observed mutation frequency in anti-IgD-treated mice increases with age until adulthood, then plateaux and finally declines in aged mice. The mutations in the stop codon were associated with increased double-stranded DNA breaks (DSB) within and around the TAG site. Our results demonstrate that the rate of frequency of spontaneous reverse mutation is very low in vivo, yet it is significantly increased after stimulation with anti-IgD antibodies. The frequency of point mutation is age dependent and correlates with increased DSB.

Effect of halofuginone on the development of tight skin (TSK) syndrome

The end point of pathogenic events in scleroderma is fibrosis of the skin and internal organs. Fibrosis in scleroderma results from the over synthesis and deposition of collagen in the connective tissue. The morbidity and mortality of the scleroderm is very high and presently there is no specific treatment. Halofuginone is a drug with great potential for the treatment of scleroderma since it inhibits the synthesis of collagen type I by fibroblasts. We have studied the in vivo effect of halofuginone in tight skin (TSK) mice that spontaneously develop a scleroderma-like disease due to a genetic defect. Our results demonstrate that halofuginone prevented the occurrence of skin sclerosis when administered to newborn mice and reduced cutaneous hyperplasia when administered in adult TSK mice. These effects correlated with a decreased number of cells synthesizing collagen gene transcripts and a reduction in the level of autoantibodies specific for human target antigens. These results indicate that halofuginone may have use as a therapeutic in the treatment of fibrotic disease.

Lack of skin fibrosis in tight skin (TSK) mice with targeted mutation in the interleukin-4R alpha and transforming growth factor-beta genes

Scleroderma is a disorder characterized by fibrosis of the skin and internal organs and autoimmunity. Whereas the cause is unknown, interleukin-4 and transforming growth factor-beta have been postulated to play a major part in the fibrosis. To investigate the part played by these cytokines, we prepared TSK/+ mice with a targeted mutation in the interleukin-4R alpha or transforming growth factor-beta genes. The breeding failed to produce TSK/+ transforming growth factor-beta -/- mice so analysis of the role of transforming growth factor-beta was limited to TSK/+ transforming growth factor-beta +/- mice. We observed that TSK/+ interleukin-4R alpha -/- did not develop dermal thickening, and deletion of one allele of the transforming growth factor-beta gene resulted in diminished dermal thickness compared with TSK/+ mice; however, the deletion of interleukin-4R alpha or transforming growth factor-beta had no effect on lung emphysema, which is another characteristic of TSK syndrome. Electron microscopic analysis of skin showed that the collagen fibrils in TSK/+ interleukin-4R alpha -/- mice exhibit normal periodicity but have a smaller diameter than the fibers found in C57BL/6 mice. Analysis of skin and serum samples showed that the deletion of interleukin-4R alpha or one allele of transforming growth factor-beta prevented the increase of skin thickness paralleled with a decrease in the dermal hydroxyproline content and development of autoantibodies associated with TSK syndrome. These results demonstrate the importance of interleukin-4 and transforming growth factor-beta for the development of cutaneous fibrosis in vivo and suggest an important part for these cytokines in wound healing and connective tissue maintenance in general.

CTLA-4 down-regulates the protective anticryptococcal cell-mediated immune response

Cell-mediated immune (CMI) responses defined by delayed-type hypersensitivity (DTH) reactivity to cryptococcal culture filtrate antigen (CneF) can be either protective or nonprotective against an infection with Cryptococcus neoformans. The protective and nonprotective anticryptococcal DTH responses are induced by different immunogens and have differing activated-T-cell profiles. This study examined the effects of blockade of the interaction between cytotoxic T lymphocyte antigen 4 (CTLA-4) and its ligands B7-1 (CD80) and B7-2 (CD86) on the anticryptococcal DTH responses and protection. We found that CTLA-4 blockade at the time of immunization with the immunogen that induces the protective response, CneF, in complete Freund's adjuvant (CFA) or the immunogen that induces the nonprotective response, heat-killed cryptococcal cells (HKC), enhanced anticryptococcal DTH reactivity. In contrast, blocking CTLA-4 after the immune response was induced failed to enhance responses. Blockade of CTLA-4 in an infection model resulted in earlier development of the anticryptococcal CMI response than in control mice. Concomitant with increases in DTH reactivity in mice treated with anti-CTLA-4 Fab fragments at the time of immunization, there were decreases in cryptococcal CFU in lungs, spleens, and brains compared to controls. Blockade of CTLA-4 resulted in long-term protection, as measured by significantly increased survival times, only in mice given the protective immunogen, CneF-CFA. Anti-CTLA-4 treatment did not shift the response induced by the nonprotective immunogen, HKC, to a long-term protective one. Our data indicate that blockade of CTLA-4 interactions with its ligands may be useful in enhancing host defenses against C. neoformans.