Gamma-interferon-inducible Lysosomal Thiol Reductase Expression Research Articles

Role of GILT and MHC class II in melanoma cells on regulating the anti-tumor immune response

Abstract The MHC class I antigen presentation pathway in melanoma cells has a well-established role in immune-mediated destruction of melanoma. However, the role of the MHC class II pathway in melanoma cells is not fully understood. Gamma-interferon-inducible lysosomal thiol reductase (GILT) is critical for MHC class II-restricted presentation of multiple melanoma antigens by antigen presenting cells. While GILT and MHC class II expression is typically limited to antigen presenting cells, GILT and MHC class II can be expressed constitutively or induced by IFN-γ in melanoma cells. In human melanoma specimens, high GILT expression and an active and intact MHC class II pathway are associated with improved survival. The goal of this project is to investigate a causal role for GILT and MHC class II in melanoma cells, using Yale University Mouse Melanoma (YUMM) lines YUMM2.1, YUMMER1.7, and YUMMERG. These cell lines constitutively expressed GILT, and MHC class II expression was IFN-γ-inducible in a subset of cells under serum-free conditions. We have genetically engineered GILT−/− YUMM2.1 cells and MHC class II (H2Ab1)−/− YUMM2.1 cells via CRISPR/Cas9 and verified the deletion. We have generated lentiviral constructs expressing GILT alone, CIITA alone, and dual expression of H2Ab1 and CIITA, to allow for the generation of melanoma cell lines with and without GILT and MHC class II. Transduction of GILT−/− YUMM2.1 cells with GILT resulted in high transduction efficiency and overexpression. Thus, we have developed models to determine the effect of GILT and MHC class II expression in melanoma cells on regulating in vivo tumor growth and the anti-tumor immune response. This work was supported by a Basic Science Award from the Harry J. Lloyd Charitable Trust and a Merit Review Award I01-BX005336 from the US Department of Veterans Affairs (VA), Biomedical Laboratory Research and Development Service (K.T.H.). The contents do not represent the views of the VA or the US Government.

High GILT Expression Is Associated with Improved Survival in Metastatic Melanoma Patients Treated with Immune Checkpoint Inhibition.

Simple SummarySkin cancer is the most common type of cancer, with melanoma being among the deadliest of skin cancers due to its propensity to metastasize. Immune checkpoint inhibitors (ICI) generate anti-tumor immune responses resulting in improved outcomes in patients with metastatic melanoma. However, only a subset of melanoma patients responds to these therapies, which are costly and come with a risk of adverse effects. Therefore, there is a need for biomarkers to predict which patients will respond to ICI. We found that ICI-treated metastatic melanoma patients with high GILT mRNA expression in bulk tumor samples had improved survival. Additionally, high GILT protein expression within metastatic melanoma cells was associated with improved survival in patients treated with ICI. This study suggests that GILT may serve as a biomarker to predict which patients will respond to ICI, which could improve patient care, reduce healthcare costs, and facilitate appropriate selection of therapies for patients with metastatic melanoma.Gamma-interferon-inducible lysosomal thiol reductase (GILT) is critical for MHC class II restricted presentation of multiple melanoma antigens. There is variable GILT protein expression in malignant melanocytes in melanoma specimens. High GILT mRNA expression in melanoma specimens is associated with improved overall survival, before the advent of immune checkpoint inhibitors (ICI). However, the association of GILT in metastatic melanoma with survival in patients treated with ICI and the cell type expressing GILT associated with survival have not been determined. Using RNA sequencing datasets, high GILT mRNA expression in metastatic melanoma specimens was associated with improved progression-free and overall survival in patients treated with ICI. A clinical dataset of metastatic melanoma specimens was generated and annotated with clinical information. Positive GILT immunohistochemical staining in antigen presenting cells and melanoma cells was observed in 100% and 65% of metastatic melanoma specimens, respectively. In the subset of patients treated with ICI in the clinical dataset, high GILT protein expression within melanoma cells was associated with improved overall survival. The association of GILT mRNA and protein expression with survival was independent of cancer stage. These studies support that high GILT mRNA expression in bulk tumor samples and high GILT protein expression in melanoma cells is associated with improved survival in ICI-treated patients. These findings support further investigation of GILT as a biomarker to predict the response to ICI.

Prognostic value of gamma-interferon-inducible lysosomal thiol reductase expression in female patients diagnosed with breast cancer.

Because of the high heterogeneity of breast cancer outcome, identification of novel prognostic biomarkers is critical to improve patient stratification and guide precise treatment. We examined the prognostic value of gamma-interferon-inducible lysosomal thiol reductase (GILT) expression in a training set of 416 breast cancer patients and a validation set of 210 patients, and performed functional studies to investigate the functions and underlying mechanisms of GILT on breast cancer prognosis. Our results indicated that high GILT expression in breast cancer cells was associated with improved disease-free survival (DFS; hazard ratio [HR]=0.189, 95% confidence interval [CI]: 0.099-0.361) and breast cancer-specific survival (BCSS; HR=0.187, 95% CI: 0.080-0.437) of breast cancer patients both in the training set and the external validation set (HR=0.453, 95% CI: 0.235-0.873 for DFS, HR=0.488, 95% CI: 0.245-0.970 for BCSS). In vitro and in vivo studies showed that GILT overexpression inhibited breast cancer cells proliferation, invasion, migration and tumor formation in nude mice and increased sensitivity of breast cancer cells to standard treatment. Proteomics analysis indicated that GILT inhibited reactive oxygen species (ROS) and autophagy activation in breast cancer cells, and GILT overexpression-mediated tumor growth was further enhanced in the presence of autophagy or ROS inhibitors. Our results demonstrate that GILT expression can be effectively used to predict the prognosis and guide treatment strategies of breast cancer patients.

Gamma-interferon inducible lysosomal thiolreductase (GILT) effect on breast tumor microenvironment through regulating CXCR6/CXCL16 axis.

e15081 Background: Gamma-interferon Inducible Lysosomal Thiolreductase (GILT) is constitutively expressed in most antigens endocytosed by antigen presenting cells (APCs), and its function is to catalyze the reduction of disulfide (S-S) bonds in protein substrates. The cytokine CXCL16 is one of the only two known plasma membrane chemokines which induces chemotaxis of activated T cells and bone marrow plasma cells in tumor microenvironment. It contains a free end folded by two sulfur bonds and therefore could also be a zymolyte of GILT. Previous studies found that specific receptor of CXCL16, CXCR6, was significantly overexpressed in breast cancer tissues and metastatic axillary lymph nodes. We suppose whether CXCR6/CXCL16 axis is regulated by GILT and affect tumor microenvironment, thereby eliciting specific anti-tumor immune responses in breast cancer (BC). Methods: GILT expression in BC was evaluated using publicly available data from The Cancer Genome Atlas (TCGA). GILT gene was analyzed in UALCAN ( http://ualcan.path.uab.edu/analysis-prot.html ) . In vitro, Immunohistochemistry (IHC) was conducted to examine the location and relation of GILT and CXCR6. Gene Set Enrichment Analysis (GSEA) was performed to mine the biological pathways involved in BC related GILT regulatory network. The expression of GILT at protein and RNA levels were detected by Western Blot and RT-PCR assay. Overexpression and knockdown of GILT in BC cell lines was carried out to further analyzed the correlation between GILT and CXCL16/CXCR6. Results: TCGA database showed that GILT expression was increased in the stroma of BC compared with normal, and was correlated to shorter BC overall survival. GSEA suggested that the expression of GILT was associated with chemotactic factors. Pearson analysis and IHC showed GILT had a strong correlation with CXCL16/CXCR6 axis in the aspect of angiogenesis and immunity. qRT-PCR and Western Blot assay also revealed that GILT had high expression in BC. Besides, patients with high expression of GILT in IHC simultaneously showed high immunoreactive to macrophage markers, which was related to neovascularization and anti-tumor immune responses. Compared with the normal breast cell line MCF-10A, GILT protein had high expression in Hs578T and low expression in MDA-MB-231 cell line. GILT was overexpressed in MDA-MB-231 and knockdown in Hs578T. Result showed that high level GILT promoted the production of CXCL16/CXCR6,while GILT siRNA knockdown inhibited the production of CXCL16/CXCR6. Conclusions: GILT could catalyze CXCL16 in BC, function as a key mechanism to affect tumor microenvironment through CXCR6/CXCL16 pathway. GILT-activated CXCL16 levels showed a strong connection with unfavorable outcomes in BC, which could be a potential biomarker of prognosis and a novel therapeutic target.

Variable GILT protein expression in melanoma cells of metastatic tumor specimens

Melanoma is the sixth most common cancer in the US. Immunotherapies, such as anti-CTLA-4 and anti-PD-1, have transformed the treatment of advanced melanoma; however, a subset of patients fail to respond to immunotherapy. Thus, improved predictors of the anti-melanoma immune response and response to immunotherapy are needed. We have previously shown that 1) gamma-interferon-inducible lysosomal thiol reductase (GILT) is critical for MHC class II-restricted presentation of a melanoma antigen, 2) there is variable GILT protein expression in melanoma cells from primary and cutaneous metastatic melanoma specimens, and 3) high GILT mRNA expression in melanoma specimens is associated with improved overall survival. Here, we created a database of n = 43 metastatic melanoma patients (stage III or IV) annotated with clinical outcome. Formalin-fixed, paraffin-embedded sections of pre-treatment metastatic melanoma specimens were tested for GILT protein expression using immunohistochemistry and scored by a dermatopathologist and dermatologist. GILT expression in melanoma cells was detected in 65% of lymph node and distant organ metastases, consistent with our prior finding of GILT expression in 58% of cutaneous metastases. The frequency of GILT-staining melanoma cells was determined by the ratio of the area of tumor cells with positive GILT staining to the total area of tumor cells. The frequency of GILT-staining melanoma cells among specimens with positive GILT staining was 15.2% ± 24.7% (mean ± SD). The median frequency of GILT staining was used to divide the patients into no/low and high GILT expression groups. The median overall survival was 52.8 months in the no/low GILT expression group, while the median overall survival was not reached in the high GILT expression group (log-rank, p = 0.67). For the n = 34 patients who were treated with immunotherapy targeting CTLA-4 and/or PD-1, the median overall survival was 38.2 months in the no/low GILT expression group, while the median overall survival was not reached in the high GILT expression group (log-rank, p = 0.83). These data suggest that high GILT expression in melanoma cells may be associated with improved overall survival, although a statistically significant association of GILT with survival was not observed in the whole group or the subset of patients treated with immunotherapy. A limitation of the current analysis is that 65% of patients have incomplete clinical outcome data. This study demonstrates variable GILT protein expression in tumor cells in metastatic melanoma specimens. Updated clinical outcome data will allow us to better evaluate the association of GILT protein expression in melanoma cells with overall survival and response to immunotherapy in metastatic melanoma patients.

GILT in thymic epithelial cells facilitates central CD4 T cell tolerance to a tissue-restricted, melanoma-associated self antigen

Abstract Central tolerance prevents autoimmunity, but also limits T cell responses to potentially immunodominant tumor epitopes with limited expression in healthy tissues. In peripheral antigen presenting cells (APCs), gamma-interferon-inducible lysosomal thiol reductase (GILT) is critical for MHC class II-restricted presentation of disulfide bond-containing proteins, including the self and melanoma antigen tyrosinase-related protein 1 (TRP1). The role of GILT in thymic antigen processing and generation of central tolerance has not been investigated. We found that GILT enhanced the negative selection of TRP1-specific thymocytes. GILT expression was enriched in thymic APCs capable of mediating deletion, namely medullary thymic epithelial cells (mTECs) and dendritic cells, while TRP1 expression was restricted solely to mTECs. GILT facilitated MHC class II-restricted presentation of endogenous TRP1 by pooled thymic APCs. Using bone marrow chimeras, GILT expression in thymic epithelial cells (TECs), but not hematopoietic cells, was sufficient for complete deletion of TRP1-specific thymocytes. An increased frequency of TRP1-specific regulatory T (Treg) cells was present in chimeras with increased deletion of TRP1-specific thymocytes. Only chimeras that lacked GILT in both TECs and hematopoietic cells had a high conventional T:Treg cell ratio and were protected from melanoma challenge. Thus, GILT expression in thymic APCs, and mTECs in particular, preferentially facilitates MHC class II-restricted presentation, negative selection and increased Treg cells, resulting in a diminished anti-tumor response to a tissue-restricted, melanoma-associated self antigen.

High GILT expression and an active and intact MHC class II antigen presentation pathway are associated with improved survival in melanoma

Abstract The MHC class I antigen presentation pathway in melanoma cells has a well-established role in immune-mediated destruction of tumors. However, the clinical significance of the MHC class II antigen presentation pathway in melanoma cells is less clear. In antigen presenting cells, gamma-interferon-inducible lysosomal thiol reductase (GILT) is critical for MHC class II-restricted presentation of multiple melanoma antigens. While not expressed in benign melanocytes of nevi, GILT and MHC class II expression is induced in malignant melanocytes in a portion of melanoma specimens. Analysis of The Cancer Genome Atlas (TCGA) cutaneous melanoma dataset showed that high GILT mRNA expression was associated with improved overall survival. Expression of IFN-γ, TNF-α, and IL-1β was positively associated with GILT expression in the TCGA melanoma specimens. These cytokines were capable of inducing GILT expression in melanoma cells in vitro. GILT protein expression in melanocytes was induced in halo nevi, which are nevi undergoing immune-mediated regression, and is consistent with the association of GILT expression with improved survival in melanoma. To explore potential mechanisms of GILT’s association with patient outcome, we analyzed the mRNA expression pattern in the MHC class II antigen presentation pathway. In contrast to healthy skin where the MHC class II pathway was nearly uniformly expressed and intact, there was substantial variation in the MHC class II pathway of the TCGA melanoma dataset. Both an active and intact MHC class II pathway were associated with improved overall survival in melanoma. These studies support a role for GILT and the MHC class II antigen presentation pathway in melanoma outcome.

GILT restricts the cellular entry mediated by the envelope glycoproteins of SARS-CoV, Ebola virus and Lassa fever virus

ABSTRACT Interferons (IFNs) control viral infections by inducing expression of IFN-stimulated genes (ISGs) that restrict distinct steps of viral replication. We report herein that gamma-interferon-inducible lysosomal thiol reductase (GILT), a lysosome-associated ISG, restricts the infectious entry of selected enveloped RNA viruses. Specifically, we demonstrated that GILT was constitutively expressed in lung epithelial cells and fibroblasts and its expression could be further induced by type II interferon. While overexpression of GILT inhibited the entry mediated by envelope glycoproteins of SARS coronavirus (SARS-CoV), Ebola virus (EBOV) and Lassa fever virus (LASV), depletion of GILT enhanced the entry mediated by these viral envelope glycoproteins. Furthermore, mutations that impaired the thiol reductase activity or disrupted the N-linked glycosylation, a posttranslational modification essential for its lysosomal localization, largely compromised GILT restriction of viral entry. We also found that the induction of GILT expression reduced the level and activity of cathepsin L, which is required for the entry of these RNA viruses in lysosomes. Our data indicate that GILT is a novel antiviral ISG that specifically inhibits the entry of selected enveloped RNA viruses in lysosomes via disruption of cathepsin L metabolism and function and may play a role in immune control and pathogenesis of these viruses.

Microglia express gamma-interferon-inducible lysosomal thiol reductase in the brains of Alzheimer's disease and Nasu-Hakola disease.

Gamma-interferon-inducible lysosomal thiol reductase (GILT), expressed in antigen-presenting cells (APCs), facilitates the reduction of disulfide bonds of endocytosed proteins in the endocytic pathway and they are further processed for presentation of immunogenic peptides loaded on major histocompatibility complex (MHC) class II. Although the constitutive and IFNγ-inducible expression of GILT was observed in various APCs, such as dendritic cells, monocytes/macrophages, and B cells, GILT-expressing cell types remain unknown in the human central nervous system (CNS). Nasu-Hakola disease (NHD) is a rare autosomal recessive disorder characterized by sclerosing leukoencephalopathy and multifocal bone cysts, caused by a loss-of-function mutation of either TYROBP (DAP12) or TREM2, both of which are expressed on microglia. A rare heterozygous variant of the TREM2 gene encoding p.Arg47His causes a 3-fold increase in the risk for late-onset Alzheimer's disease (LOAD), suggesting that both NHD and AD are induced by dysfunction of the microglial TREM2 signaling pathway in the brains. We studied by immunohistochemistry GILT expression in NHD and AD brains. GILT was expressed on amoeboid microglia with the highest levels of expression in AD brains, compared with those in non-neurological control (NC) brains and in NHD brains. In AD brains, the clusters of amoeboid microglia surrounding amyloid-beta (Aꞵ) deposition strongly expressed GILT. Furthermore, a human microglial cell line expressed GILT in response to IFNγ. These results indicate that microglia, expressing constitutively high levels of GILT, act as a principal cell type of APCs in AD brains, in contrast to baseline levels of GILT expression in NHD brains.

Inflammation induces GILT expression in human melanoma

Abstract T cell-mediated immunity can produce durable anti-melanoma responses resulting in improved survival of metastatic melanoma patients. Gamma-interferon-inducible lysosomal thiol reductase (GILT) is critical for MHC class II-restricted presentation of multiple melanoma antigens to CD4+ T cells and facilitates cross-presentation on MHC class I for activation of CD8+ T cells. Our prior study found that GILT expression is increased in melanocytes of malignant melanoma specimens compared with benign nevi. To determine whether GILT expression is associated with inflammation, expression in halo nevi specimens was compared to nevi without lymphocytic infiltrate by immunohistochemistry. A halo nevus is a benign nevus with a lymphocytic infiltrate which leads to regression of the nevus. GILT, but not MHC class II, expression was increased in melanocytes of halo nevi compared to nevi without lymphocytic infiltrate. Analysis of a publicly available gene expression profiling cohort of 457 cutaneous melanoma specimens revealed that GILT expression was associated with IFN-γ, TNF-α, and IL-1β expression in human melanoma. In vitro exposure of human melanoma cell lines to IFN-γ or inflammatory cytokines, such as TNF-α, induced GILT expression in melanoma cell lines, which lacked GILT expression at baseline. Vemurafenib, a BRAF inhibitor used in the treatment of metastatic melanoma, enhanced IFN-γ-induced GILT and MHC class II expression in a melanoma cell line. Together these data demonstrate that inflammation, alone or in combination with a current therapeutic agent, induces high levels of GILT expression in human melanoma.

GILT in thymic epithelial cells preferentially facilitates MHC class II-restricted presentation in generating central T cell tolerance to a self and melanoma antigen

Abstract Central tolerance prevents autoimmunity, but limits T cell responses to tumor antigens that are self antigens. In peripheral APCs, gamma-interferon-inducible lysosomal thiol reductase (GILT) is critical for MHC class II-restricted presentation of disulfide bond-containing proteins, including the self and melanoma antigen tyrosinase-related protein 1 (TRP1). The role of GILT in thymic antigen processing and generation of central tolerance is unknown. We found that GILT enhanced the clonal deletion of TRP1-specific thymocytes. GILT expression was enriched in thymic APCs capable of mediating deletion, namely medullary thymic epithelial cells (mTECs) and dendritic cells. TRP1 expression was restricted to mTECs. GILT facilitated MHC class II-restricted presentation of endogenous TRP1 by pooled thymic APCs. Using bone marrow chimeras, GILT expression in thymic epithelial cells (TECs), but not hematopoietic cells, was sufficient for deletion of TRP1-specific thymocytes. Chimeras with GILT expression in TECs also had an increased frequency of TRP1-specific regulatory T (Treg) cells. These data demonstrate an advantage of TEC-derived GILT for antigen processing and subsequent T cell tolerance. Only chimeras that lacked GILT in both TECs and hematopoietic cells were protected from melanoma and had a high effector T cell:Treg cell ratio. Thus, GILT diminishes T cell-mediated protection from melanoma through promoting thymic deletion and Treg cells.

Autophagy-dependent crosstalk between GILT and PAX-3 influences radiation sensitivity of human melanoma cells.

Melanoma represents an ever-increasing problem in the western world as incidence rates continue to climb. Though manageable during early stages, late stage metastatic disease is highly resistant to current intervention. We have previously shown that gamma-interferon-inducible lysosomal thiol-reductase (GILT) enhances HLA class II antigen processing and immune detection of human melanoma cells. Here we report that GILT expression inhibits a potential target, paired box-3 (PAX-3) protein, in late stage human metastatic melanoma. We also show that GILT transfection or induction by IFN-γ, decreases PAX-3 protein expression while upregulating the expression of Daxx, which is also a repressor of PAX-3. Confocal microscopic analysis demonstrated that GILT co-localizes with PAX-3 protein, but not with Daxx within melanoma cells. Immunoprecipitation and immunoblotting studies suggest that GILT expression negatively regulates PAX-3 through the autophagy pathway, potentially resulting in increased susceptibility to conventional treatment in the form of chemotherapy or radiotherapy. While high-dose radiation is a common treatment for melanoma patients, our data suggest that GILT expression significantly increased the susceptibility of melanoma cells to low-dose radiation therapy via upregulation of tumor suppressor protein p53. Overall, these data suggest that GILT has multiple roles in inducing human melanoma cells as better targets for radiation and immunotherapy.

Gamma-interferon-inducible lysosomal thiol reductase is upregulated in human melanoma.

T-cell-mediated immunity has the ability to produce durable antimelanoma responses, resulting in improved survival of patients with advanced melanoma. Antigen presentation is a key determinant of T-cell responses. Gamma-interferon-inducible lysosomal thiol reductase (GILT) is critical for MHC class II-restricted presentation of multiple melanoma antigens to CD4+ T cells. However, GILT expression in melanoma has not been defined. We evaluated GILT and MHC class II expression in human primary and metastatic melanomas and nevi using immunohistochemical analysis. GILT staining in melanocytes was observed in 70% of primary and 58% of metastatic melanomas versus 0% of nevi. When present, the GILT staining intensity in melanocytes was typically faint. Both GILT and MHC class II expression were increased in melanocytes of primary and metastatic melanomas compared with nevi. GILT staining in antigen-presenting cells (APCs) was detected in 100% of primary and metastatic melanomas versus 31% of nevi, and it was typically intense. GILT expression was increased in APCs of primary and metastatic melanomas compared with nevi, whereas MHC class II had equivalent high expression in APCs of all melanocytic lesions. GILT staining in keratinocytes was detected in 67% of primary melanomas versus 14% of nevi and 6% of metastatic melanomas. GILT, but not MHC class II, expression was increased in keratinocytes of primary melanomas compared with nevi and metastases. GILT expression is anticipated to result in improved presentation of melanoma antigens and more effective antimelanoma T-cell responses. GILT expression may be a biomarker of immune recognition of melanoma.

Diverse cellular and organismal functions of the lysosomal thiol reductase GILT.

Gamma-interferon-inducible lysosomal thiol reductase (GILT) is the only enzyme known to catalyze disulfide bond reduction in the endocytic pathway. GILT facilitates the presentation of a subset of epitopes from disulfide bond-containing antigens. Enhanced presentation of MHC class II-restricted epitopes alters central tolerance and modulates CD4+ T cell-mediated autoimmunity. Improved cross-presentation of viral epitopes results in improved cross-priming of viral-specific CD8+ T cells. GILT regulates the cellular redox state. In GILT-/- cells, there is a shift from the reduced to the oxidized form of glutathione, resulting in mitochondrial autophagy, decreased superoxide dismutase 2, and elevated superoxide levels. GILT expression diminishes cellular activation, including decreased phosphorylated ERK1/2, and decreases cellular proliferation. GILT enhances the activity of bacterial hemolysins, such as listeriolysin O, and increases bacterial replication and infection. GILT expression in cancer cells is associated with improved patient survival. These diverse roles of GILT are discussed.

Gamma-interferon-inducible lysosomal thiol reductase is upregulated in human melanoma (TUM2P.1038)

Abstract T cell-mediated immunity has the ability to produce durable anti-melanoma responses resulting in improved survival of patients with advanced melanoma. Antigen presentation in the tumor microenvironment directs anti-melanoma T cell responses. Gamma-interferon-inducible lysosomal thiol reductase (GILT) is critical for MHC class II-restricted presentation of multiple melanoma antigens to CD4+ T cells. However, GILT expression in melanoma has not been defined. We evaluated GILT and MHC class II expression in human primary and metastatic melanomas and nevi using immunohistochemistry. Both GILT and MHC class II expression were increased in melanocytes of primary and metastatic melanomas compared with nevi. GILT expression was increased in antigen presenting cells of primary and metastatic melanomas compared to nevi, whereas MHC class II had equivalent high expression in antigen presenting cells of all melanocytic lesions. Keratinocytes in primary melanoma lesions had increased GILT and MHC class II expression compared with nevi. Increased GILT expression in melanocytes, antigen presenting cells and keratinocytes of melanoma demonstrates that changes in the antigen presentation pathway occur in the tumor microenvironment. GILT expression in melanoma is anticipated to result in improved presentation of melanoma antigens and more effective anti-melanoma T cell responses and may be a biomarker of immune recognition of melanoma.

GILT-mediated processing of a self and melanoma antigen in thymic epithelial cells promotes deletion and regulatory T cells (APP3P.113)

Abstract Central tolerance is critical to prevent autoimmunity, but limits T cell responses to tumor Ag that are self Ag. We have identified that gamma-interferon-inducible lysosomal thiol reductase (GILT) is required for thymic deletion of CD4+ T cells specific for the self and melanoma Ag, tyrosinase-related protein 1 (TRP1). To define GILT’s role in central tolerance, we show that GILT expression is enriched in thymic APC capable of mediating deletion, medullary thymic epithelial cells (mTEC) and dendritic cells. TRP1 expression is restricted to mTEC. GILT facilitates MHC class II-restricted presentation of endogenous TRP1 by pooled thymic APC. Bone marrow (BM) chimeras demonstrate that GILT expression in TEC is necessary and sufficient for efficient deletion of TRP1-specific thymocytes. In chimeras that express GILT in TEC, TRP1-specific T cells undergo deletion, and chimeras are not protected from melanoma challenge. Although an intermediate level of TRP1-specific T cells develop in chimeras with GILT expression limited to BM-derived cells, only chimeras lacking GILT in both populations are protected from melanoma challenge. Chimeras that express GILT in TECs or in which GILT is limited to BM-derived cells have a substantially higher percentage of TRP1-specific regulatory T (Treg) cells and lower effector:Treg cell ratio. These findings suggest that GILT operates in mTEC to facilitate the presentation of tissue-specific self Ag and promote deletion and development of Treg cells.

Absence of Gamma-Interferon-Inducible Lysosomal Thiol Reductase (GILT) Is Associated with Poor Disease-Free Survival in Breast Cancer Patients

Tumor immunosurveillance is known to be of critical importance in controlling tumorigenesis and progression in various cancers. The role of gamma-interferon-inducible lysosomal thiol reductase (GILT) in tumor immunosurveillance has recently been studied in several malignant diseases, but its role in breast cancer remains to be elucidated. In the present study, we found GILT as a significant different expressed gene by cDNA microarray analysis. To further determine the role of GILT in breast cancer, we examined GILT expression in breast cancers as well as noncancerous breast tissues by immunohistochemistry and real-time PCR, and assessed its association with clinicopathologic characteristics and patient outcome. The absence of GILT expression increased significantly from 2.02% (2/99) in noncancerous breast tissues to 15.6% (34/218) in breast cancer tissues (P<0.001). In accordance with its proliferation inhibiting function, GILT expression was inversely correlated with Ki67 index (P<0.05). In addition, absence of GILT was positively correlated with adverse characteristics of breast cancers, such as histological type, tumor size, lymph nodes status, and pTNM stage (P<0.05). Consistently, breast cancers with reduced GILT expression had poorer disease-free survival (P<0.005). Moreover, significantly decreased expression of GILT was found in both primary and metastatic breast cancer cells, in contrast to normal epithelial cells. These findings indicate that GILT may act as a tumor suppressor in breast cancer, in line with its previously suggested role in anti-tumor immunity. Thus, GILT has the potential to be a novel independent prognostic factor in breast cancer and further studies are needed to illustrate the underlying mechanism of this relationship.

GILT expression in medullary thymic epithelial cells is required for presentation of tissue-specific self antigens and deletion of autoreactive T cells (P5037)

Abstract Clonal deletion of thymocytes with high avidity for self-peptide:MHC complexes is critical for the maintenance of tolerance and prevention of autoimmunity. We have shown that gamma-interferon-inducible lysosomal thiol reductase (GILT) is required for thymic deletion of T cells specific for a self and melanoma Ag, tyrosinase-related protein 1 (TRP1). To define GILT’s role in central tolerance, we show that GILT expression is enriched in thymic APC capable of mediating deletion, medullary thymic epithelial cells (mTEC) and dendritic cells. TRP1 expression is restricted to mTEC. GILT facilitates the MHC class II-restricted presentation of endogenous TRP1 by pooled thymic APC (TEC and bone marrow (BM)-derived APC). Using BM chimeras, we show that TRP1-specific T cells are deleted in chimeras in which GILT is expressed in both TEC and BM-derived APC or GILT expression is restricted to TEC, indicating that GILT expression in TEC is sufficient for deletion of TRP1-specific thymocytes. In contrast, a large number of TRP1-specific T cells develop in chimeras which lack GILT expression in both TEC and BM-derived APC. Chimeras in which GILT expression is limited to BM-derived APC have intermediate levels of TRP1-specific T cells, demonstrating that GILT expression in TEC is required for efficient deletion of TRP1-specific thymocytes. These findings suggest that GILT operates in mTEC to facilitate the presentation of tissue-specific self Ag and promote deletion of autoreactive T cells.

Low GILT expression is associated with poor survival in diffuse large B cell lymphoma (P5057)

Abstract Diffuse large B-cell lymphoma (DLBCL) is the most common form of aggressive non-Hodgkin lymphoma. Since low MHC class II expression is associated with poor survival in DLBCL, we examined whether expression of other components in the MHC class II antigen processing pathway may be important in DLBCL biology. Gamma-interferon-inducible lysosomal thiol reductase (GILT) reduces protein disulfide bonds in the endocytic compartment exposing additional epitopes for class II binding and facilitating antigen presentation. In four independent gene expression profiling cohorts with a total of 585 DLBCL patients, low GILT expression was significantly associated with poor overall survival. In contrast, low expression of MARCH1, an E3 ligase that regulates class II trafficking, and HLA-DRA, a classical MHC class II gene, were associated with poor survival in one of four cohorts. The association of low GILT expression with poor survival is independent of established clinical and molecular prognostic factors, the International Prognostic Index and cell of origin classification, respectively. GILT protein expression was detected in both tumor cells and tumor-infiltrating antigen presenting cells. These studies demonstrate that GILT expression levels correlate with clinical outcome and underscore that antigen processing is critical to patient survival in DLBCL.

Low GILT Expression is Associated with Poor Patient Survival in Diffuse Large B-Cell Lymphoma

The major histocompatibility complex (MHC) class II-restricted antigen processing pathway presents antigenic peptides acquired in the endocytic route for the activation of CD4+ T cells. Multiple cancers express MHC class II, which may influence the anti-tumor immune response and patient outcome. Low MHC class II expression is associated with poor survival in diffuse large B-cell lymphoma (DLBCL), the most common form of aggressive non-Hodgkin lymphoma. Therefore, we investigated whether gamma-interferon-inducible lysosomal thiol reductase (GILT), an upstream component of the MHC class II-restricted antigen processing pathway that is not regulated by the transcription factor class II transactivator, may be important in DLBCL biology. GILT reduces protein disulfide bonds in the endocytic compartment, exposing additional epitopes for binding to MHC class II and facilitating antigen presentation. In each of four independent gene expression profiling cohorts with a total of 585 DLBCL patients, low GILT expression was significantly associated with poor overall survival. In contrast, low expression of a classical MHC class II gene, HLA-DRA, was associated with poor survival in one of four cohorts. The association of low GILT expression with poor survival was independent of established clinical and molecular prognostic factors, the International Prognostic Index and the cell of origin classification, respectively. Immunohistochemical analysis of GILT expression in 96 DLBCL cases demonstrated variation in GILT protein expression within tumor cells which correlated strongly with GILT mRNA expression. These studies identify a novel association between GILT expression and clinical outcome in lymphoma. Our findings underscore the role of antigen processing in DLBCL and suggest that molecules targeting this pathway warrant investigation as potential therapeutics.