Breast cancer immunopeptidomes contain numerous shared tumor antigens

Hormone receptor-positive breast cancer (HR+) is immunologically cold and has not benefited from advances in immunotherapy. In contrast, subsets of triple-negative breast cancer (TNBC) display high leukocytic infiltration and respond to checkpoint blockade. CD8+ T cells, the main effectors of anticancer responses, recognize MHC I-associated peptides (MAPs). Our work aimed to characterize the repertoire of MAPs presented by HR+ and TNBC tumors. Using mass spectrometry, we identified 57,094 unique MAPs in 26 primary breast cancer samples. MAP source genes highly overlapped between both subtypes. We identified 25 tumor-specific antigens (TSAs) mainly deriving from aberrantly expressed regions. TSAs were most frequently identified in TNBC samples and were more shared among The Cancer Genome Atlas (TCGA) database TNBC than HR+ samples. In the TNBC cohort, the predicted number of TSAs positively correlated with leukocytic infiltration and overall survival, supporting their immunogenicity in vivo. We detected 49 tumor-associated antigens (TAAs), some of which derived from cancer-associated fibroblasts. Functional expansion of specific T cell assays confirmed the in vitro immunogenicity of several TSAs and TAAs. Our study identified attractive targets for cancer immunotherapy in both breast cancer subtypes. The higher prevalence of TSAs in TNBC tumors provides a rationale for their responsiveness to checkpoint blockade.

BamQuery: a proteogenomic tool to explore the immunopeptidome and prioritize actionable tumor antigens

MHC-I-associated peptides deriving from non-coding genomic regions and mutations can generate tumor-specific antigens, including neoantigens. Quantifying tumor-specific antigens' RNA expression in malignant and benign tissues is critical for discriminating actionable targets. We present BamQuery, a tool attributing an exhaustive RNA expression to MHC-I-associated peptides of any origin from bulk and single-cell RNA-sequencing data. We show that many cryptic and mutated tumor-specific antigens can derive from multiple discrete genomic regions, abundantly expressed in normal tissues. BamQuery can also be used to predict MHC-I-associated peptides immunogenicity and identify actionable tumor-specific antigens de novo.

Abstract 2987: BamQuery: a new proteogenomic tool to explore the immunopeptidome and prioritize actionable tumor antigens

MHC class I-associated peptides (MAPs), collectively referred to as the immunopeptidome, have a pivotal role in cancer immunosurveillance. While MAPs were long thought to be solely generated by the degradation of canonical proteins, recent advances in the field of proteogenomics (genomically-informed proteomics) evidenced that ∼10% of them originate from allegedly noncoding genomic sequences. Among these sequences, endogenous retroelements (EREs) are under intense scrutiny as a possible source of actionable tumor antigens (TAs). With the increasing number of cancer-oriented immunopeptidomic and proteogenomic studies comes the need to accurately attribute an RNA expression level to each MAP identified by mass-spectrometry. Here, we introduce BamQuery (BQ), a computational tool to attribute an exhaustive RNA expression to MAPs of any genomic origin (exon, intron, UTR, intergenic) from bulk and single-cell RNA-sequencing data. By using BQ on large datasets of published MAPs identified by mass spectrometry, we show that many of them can arise from more than one genomic region. Indeed, 27% of MAPs reported as deriving from protein-coding exons (canonical MAPs) could also arise from non-canonical genomic regions, sometimes with greater probability, and 61% of non-canonical MAPs could arise from more than a single genomic origin (334 possible regions on average per non-canonical MAP; up to 35,343 for EREs). The consideration of all these origins evidenced an unsuspected high RNA expression in normal human tissues of (i) published neoantigens/TAs (mutated or not); (ii) MAPs derived from proteasomal splicing, supposedly not genomically templated, and (iii) MAPs derived from viruses. In particular, the high expression of candidate immunotherapeutic targets such as TAs highlights the relevance of BamQuery and the necessity of using it to validate such antigens before translating their usage in clinical trials. We also demonstrate that BamQuery can be used to directly identify safe and actionable TAs as well as to predict their immunogenicity through our freely accessible web portal (https://bamquery.iric.ca/search). Therefore, BQ could become an essential tool in any TA prioritization pipeline in the near future.

Citation Format: Maria-Virginia Ruiz Cuevas, Marie-Pierre Hardy, Jean-David Larouche, Anca Apavaloaei, Eralda Kina, Krystel Vincent, Patrick Gendron, Jean-Philippe Laverdure, Chantal Durette, Pierre Thibault, Sebastien Lemieux, Claude Perreault, Gregory Ehx. BamQuery: a new proteogenomic tool to explore the immunopeptidome and prioritize actionable tumor antigens [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2987.

Abstract 2993: Unmutated tumor antigens are abundant and contribute to tumor control in melanoma

Recognition of MHC-I-associated tumor antigens (TAs) by CD8+ T cells is central to antitumor immunity. Owing to the elevated tumor mutational burden (TMB) in melanoma, the marked efficacy of immune checkpoint blockade (ICB) has been attributed to the recognition of mutated TAs. However, recent reports showed that response to ICB in melanomas with low TMB is associated with CD8+ T-cell reactivity against melanocyte lineage-associated antigens (LSAs). Here, we systematically evaluated the contribution of all TA classes, i.e., mutated and unmutated, canonical and non-canonical, to the antigenic landscape of melanoma. We characterized the TAs from melanoma biopsies and patient-derived cell lines using proteogenomics. Out of 79450 MHC-I-associated peptides (MAPs) identified from 19 samples, we found 557 unmutated TAs classified as tumor-specific (TSA), tumor-associated (TAA), or LSAs. These TAs most often derived from annotated open-reading frames, followed by ncRNAs and intergenic regions. By contrast, only 6 MAPs were mutated and tumor-specific, which could be partially explained by a decreased expression of mutations within MAP-generating genomic regions. While the number of unmutated TAs with predicted presentation (TApres) in melanoma patients was similar between responders and non-responders pre-ICB, non-responders showed marks of inefficient antigen presentation. In consequence, only responders lost TApres upon treatment, in tandem with an expansion in tumor-infiltrating lymphocytes. These results reveal a previously underappreciated contribution of unmutated TAs to tumor control in melanoma and suggest that enhancing their recognition could improve the ICB efficacy in non-responders.

Citation Format: Anca Apavaloaei, Qingchuan Zhao, Leslie Hesnard, Krystel Vincent, Marie-Pierre Hardy, Chantal Durette, Joël Lanoix, Jean-Philippe Laverdure, Jean-David Larouche, Maria Virginia Ruiz Cuevas, Grégory Ehx, Sébastien Lemieux, Pierre Thibault, Claude Perreault. Unmutated tumor antigens are abundant and contribute to tumor control in melanoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2993.

OpenCustomDB: Integration of Unannotated Open Reading Frames and Genetic Variants to Generate More Comprehensive Customized Protein Databases

Proteomic diversity in biological samples can be characterized by mass spectrometry (MS)-based proteomics using customized protein databases generated from sets of transcripts previously detected by RNA-seq. This diversity has only been increased by the recent discovery that many translated alternative open reading frames rest unannotated at unsuspected locations of mRNAs and ncRNAs. These novel protein products, termed alternative proteins, have been left out of all previous custom database generation tools. Consequently, genetic variations that impact alternative open reading frames and variant peptides from their translated proteins are not detectable with current computational workflows. To fill this gap, we present OpenCustomDB, a bioinformatics tool that uses sample-specific RNaseq data to identify genomic variants in canonical and alternative open reading frames, allowing for more than one coding region per transcript. In a test reanalysis of a cohort of 16 patients with acute myeloid leukemia, 5666 peptides from alternative proteins were detected, including 201 variant peptides. We also observed that a significant fraction of peptide-spectrum matches previously assigned to peptides from canonical proteins got better scores when reassigned to peptides from alternative proteins. Custom protein libraries that include sample-specific sequence variations of all possible open reading frames are promising contributions to the development of proteomics and precision medicine. The raw and processed proteomics data presented in this study can be found in PRIDE repository with accession number PXD029240.

Induced pluripotent stem cells display a distinct set of MHC I-associated peptides shared by human cancers

Previous reports showed that mouse vaccination with pluripotent stem cells (PSCs) induces durable anti-tumor immune responses via T cell recognition of some elusive oncofetal epitopes. We characterize the MHC I-associated peptide (MAP) repertoire of human induced PSCs (iPSCs) using proteogenomics. Our analyses reveal a set of 46 pluripotency-associated MAPs (paMAPs) absent from the transcriptome of normal tissues and adult stem cells but expressed in PSCs and multiple adult cancers. These paMAPs derive from coding and allegedly non-coding (48%) transcripts involved in pluripotency maintenance, and their expression in The Cancer Genome Atlas samples correlates with source gene hypomethylation and genomic aberrations common across cancer types. We find that several of these paMAPs were immunogenic. However, paMAP expression in tumors coincides with activation of pathways instrumental in immune evasion (WNT, TGF-β, and CDK4/6). We propose that currently available inhibitors of these pathways could synergize with immune targeting of paMAPs for the treatment of poorly differentiated cancers.

Immunopeptidomic analyses of colorectal cancers with and without microsatellite instability

Colorectal cancer is the second leading cause of cancer death worldwide, and the incidence of this disease is expected to increase as global socioeconomic changes occur. Immune checkpoint inhibition therapy is effective in treating a minority of colorectal cancer tumors; however, microsatellite stable tumors do not respond well to this treatment. Emerging cancer immunotherapeutic strategies aim to activate a cytotoxic T cell response against tumor-specific antigens, presented exclusively at the cell surface of cancer cells. These antigens are rare and are most effectively identified with a mass spectrometry-based approach, which allows the direct sampling and sequencing of these peptides. Although the few tumor-specific antigens identified to date are derived from coding regions of the genome, recent findings indicate that a large proportion of tumor-specific antigens originate from allegedly noncoding regions. Here, we employed a novel proteogenomic approach to identify tumor antigens in a collection of colorectal cancer-derived cell lines and biopsy samples consisting of matched tumor and normal adjacent tissue. The generation of personalized cancer databases paired with mass spectrometry analyses permitted the identification of more than 30,000 unique MHC I-associated peptides. We identified 19 tumor-specific antigens in both microsatellite stable and unstable tumors, over two-thirds of which were derived from noncoding regions. Many of these peptides were derived from source genes known to be involved in colorectal cancer progression, suggesting that antigens from these genes could have therapeutic potential in a wide range of tumors. These findings could benefit the development of T cell-based vaccines, in which T cells are primed against these antigens to target and eradicate tumors. Such a vaccine could be used in tandem with existing immune checkpoint inhibition therapies, to bridge the gap in treatment efficacy across subtypes of colorectal cancer with varying prognoses. Data are available via ProteomeXchange with identifier PXD028309.

Atypical acute myeloid leukemia-specific transcripts generate shared and immunogenic MHC class-I-associated epitopes

Acute myeloid leukemia (AML) has not benefited from innovative immunotherapies, mainly because of the lack of actionable immune targets. Using an original proteogenomic approach, we analyzed the major histocompatibility complex class I (MHC class I)-associated immunopeptidome of 19 primary AML samples and identified 58 tumor-specific antigens (TSAs). These TSAs bore no mutations and derived mainly (86%) from supposedly non-coding genomic regions. Two AML-specific aberrations were instrumental in the biogenesis of TSAs, intron retention, and epigenetic changes. Indeed, 48% of TSAs resulted from intron retention and translation, and their RNA expression correlated with mutations of epigenetic modifiers (e.g., DNMT3A). AML TSA-coding transcripts were highly shared among patients and were expressed in both blasts and leukemic stem cells. In AML patients, the predicted number of TSAs correlated with spontaneous expansion of cognate T cell receptor clonotypes, accumulation of activated cytotoxic T cells, immunoediting, and improved survival. These TSAs represent attractive targets for AML immunotherapy.

Most non-canonical proteins uniquely populate the proteome or immunopeptidome

Combining RNA sequencing, ribosome profiling, and mass spectrometry, we elucidate the contribution of non-canonical translation to the proteome and major histocompatibility complex (MHC) class I immunopeptidome. Remarkably, of 14,498 proteins identified in three human B cell lymphomas, 2,503 are non-canonical proteins. Of these, 28% are novel isoforms and 72% are cryptic proteins encoded by ostensibly non-coding regions (60%) or frameshifted canonical genes (12%). Cryptic proteins are translated as efficiently as canonical proteins, have more predicted disordered residues and lower stability, and critically generate MHC-I peptides 5-fold more efficiently per translation event. Translating 5' "untranslated" regions hinders downstream translation of genes involved in transcription, translation, and antiviral responses. Novel protein isoforms show strong enrichment for signaling pathways deregulated in cancer. Only a small fraction of cryptic proteins detected in the proteome contribute to the MHC-I immunopeptidome, demonstrating the high preferential access of cryptic defective ribosomal products to the class I pathway.

The Origin and Immune Recognition of Tumor-Specific Antigens

The dominant paradigm holds that spontaneous and therapeutically induced anti-tumor responses are mediated mainly by CD8 T cells and directed against tumor-specific antigens (TSAs). The presence of specific TSAs on cancer cells can only be proven by mass spectrometry analyses. Bioinformatic predictions and reverse immunology studies cannot provide this type of conclusive evidence. Most TSAs are coded by unmutated non-canonical transcripts that arise from cancer-specific epigenetic and splicing aberrations. When searching for TSAs, it is therefore important to perform mass spectrometry analyses that interrogate not only the canonical reading frame of annotated exome but all reading frames of the entire translatome. The majority of aberrantly expressed TSAs (aeTSAs) derive from unstable short-lived proteins that are good substrates for direct major histocompatibility complex (MHC) I presentation but poor substrates for cross-presentation. This is an important caveat, because cancer cells are poor antigen-presenting cells, and the immune system, therefore, depends on cross-presentation by dendritic cells (DCs) to detect the presence of TSAs. We, therefore, postulate that, in the untreated host, most aeTSAs are undetected by the immune system. We present evidence suggesting that vaccines inducing direct aeTSA presentation by DCs may represent an attractive strategy for cancer treatment.

Abstract B16: Identification of tumor-specific antigens shared by induced pluripotent stem cells

The development of cancer immunotherapeutics is limited by the tumor-specific antigen (TSA) discovery. Cancer cells and pluripotent stem cells, i.e., embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs), show a significant transcriptomic overlap. Indeed, when used as prophylactic vaccines in another study, iPSCs prevented tumor growth in mouse models of lung, breast, and skin cancer, suggesting that we could mine iPSCs for the discovery of TSAs. We use a recently developed proteogenomic approach combining RNA-sequencing and mass spectrometry to characterize the immunopeptidome (MHC class I-associated peptides) of iPSCs. Analyses of hitherto one human iPS cell line allowed us to identify 9 MHC class I-associated antigens that were not expressed by normal somatic tissues and thus are likely immunogenic. 50% of these antigens were highly expressed in different cancer types from The Cancer Genome Atlas, highlighting their potential for cancer immunotherapy. Expression of these TSAs resulted from aberrant expression of noncoding genomic regions and not from mutations, making them ideal candidates for antigen-based cancer vaccines. Our study indicates which stem cell features present in cancer cells might be harnessed for cancer immunotherapy. Moreover, we show for the first time that the immunopeptidome of iPSCs reflects the state of pluripotency. Cancer stem cells are known to drive disease relapse after treatment, while cancer circulating cells possessing pluripotent stem cell features are more efficient at producing metastases. These factors indicate that treatments targeted at stemness could improve clinical outcome, and that iPSC-informed TSAs hold promise for prophylactic and therapeutic cancer vaccines.

Citation Format: Anca Apavaloaei, Marie-Pierre Hardy, Jean-David Larouche, Qingchuan Zhao, Krystel Vincent, Jean-Philippe Laverdure, Chantal Durette, Joel Lanoix, Pierre Thibault, Claude Perreault. Identification of tumor-specific antigens shared by induced pluripotent stem cells [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2019 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(3 Suppl):Abstract nr B16.

The Genomic Landscape of Antigenic Targets for T Cell-Based Leukemia Immunotherapy

Intensive fundamental and clinical research in cancer immunotherapy has led to the emergence and evolution of two parallel universes with surprisingly little interactions: the realm of hematologic malignancies and that of solid tumors. Treatment of hematologic cancers using allogeneic hematopoietic cell transplantation (AHCT) serendipitously led to the discovery that T cells specific for minor histocompatibility antigens (MiHAs) could cure hematopoietic cancers. Besides, studies based on treatment of solid tumor with ex vivo-expanded tumor infiltrating lymphocytes or immune checkpoint therapy demonstrated that anti-tumor responses could be achieved by targeting tumor-specific antigens (TSAs). It is our contention that much insight can be gained by sharing the tremendous amount of data generated in the two-abovementioned universes. Our perspective article has two specific goals. First, to discuss the value of methods currently used for MiHA and TSA discovery and to explain the key role of mass spectrometry analyses in this process. Second, to demonstrate the importance of broadening the scope of TSA discovery efforts beyond classic annotated protein-coding genomic sequences.

Apoptotic endothelial cells release small extracellular vesicles loaded with immunostimulatory viral-like RNAs

Endothelial cells have multifaceted interactions with the immune system, both as initiators and targets of immune responses. In vivo, apoptotic endothelial cells release two types of extracellular vesicles upon caspase-3 activation: apoptotic bodies and exosome-like nanovesicles (ApoExos). Only ApoExos are immunogenic: their injection causes inflammation and autoimmunity in mice. Based on deep sequencing of total RNA, we report that apoptotic bodies and ApoExos are loaded with divergent RNA cargos that are not released by healthy endothelial cells. Apoptotic bodies, like endothelial cells, contain mainly ribosomal RNA whereas ApoExos essentially contain non-ribosomal non-coding RNAs. Endogenous retroelements, bearing viral-like features, represented half of total ApoExos RNA content. ApoExos also contained several copies of unedited Alu repeats and large amounts of non-coding RNAs with a demonstrated role in autoimmunity such as U1 RNA and Y RNA. Moreover, ApoExos RNAs had a unique nucleotide composition and secondary structure characterized by strong enrichment in U-rich motifs and unstably folded RNAs. Globally, ApoExos were therefore loaded with RNAs that can stimulate a variety of RIG-I-like receptors and endosomal TLRs. Hence, apoptotic endothelial cells selectively sort in ApoExos a diversified repertoire of immunostimulatory "self RNAs" that are tailor-made for initiation of innate immune responses and autoimmunity.

PSMB11 Orchestrates the Development of CD4 and CD8 Thymocytes via Regulation of Gene Expression in Cortical Thymic Epithelial Cells

T cell development depends on sequential interactions of thymocytes with cortical thymic epithelial cells (cTECs) and medullary thymic epithelial cells. PSMB11 is a catalytic proteasomal subunit present exclusively in cTECs. Because proteasomes regulate transcriptional activity, we asked whether PSMB11 might affect gene expression in cTECs. We report that PSMB11 regulates the expression of 850 cTEC genes that modulate lymphostromal interactions primarily via the WNT signaling pathway. cTECs from Psmb11 ^-/- mice 1) acquire features of medullary thymic epithelial cells and 2) retain CD8 thymocytes in the thymic cortex, thereby impairing phase 2 of positive selection, 3) perturbing CD8 T cell development, and 4) causing dramatic oxidative stress leading to apoptosis of CD8 thymocytes. Deletion of Psmb11 also causes major oxidative stress in CD4 thymocytes. However, CD4 thymocytes do not undergo apoptosis because, unlike CD8 thymocytes, they upregulate expression of chaperones and inhibitors of apoptosis. We conclude that PSMB11 has pervasive effects on both CD4 and CD8 thymocytes via regulation of gene expression in cTECs.

Noncoding regions are the main source of targetable tumor-specific antigens

Tumor-specific antigens (TSAs) represent ideal targets for cancer immunotherapy, but few have been identified thus far. We therefore developed a proteogenomic approach to enable the high-throughput discovery of TSAs coded by potentially all genomic regions. In two murine cancer cell lines and seven human primary tumors, we identified a total of 40 TSAs, about 90% of which derived from allegedly noncoding regions and would have been missed by standard exome-based approaches. Moreover, most of these TSAs derived from nonmutated yet aberrantly expressed transcripts (such as endogenous retroelements) that could be shared by multiple tumor types. Last, we demonstrated that, in mice, the strength of antitumor responses after TSA vaccination was influenced by two parameters that can be estimated in humans and could serve for TSA prioritization in clinical studies: TSA expression and the frequency of TSA-responsive T cells in the preimmune repertoire. In conclusion, the strategy reported herein could considerably facilitate the identification and prioritization of actionable human TSAs.

Immunoproteasomes Control the Homeostasis of Medullary Thymic Epithelial Cells by Alleviating Proteotoxic Stress

The sole nonredundant role of the thymic medulla is to induce central tolerance, a vital process that depends on promiscuous gene expression (pGE), a unique feature of medullary thymic epithelial cells (mTECs). Although pGE enhances transcription of >3,000 genes in mTECs, its impact on the regulation of protein homeostasis remains unexplored. Here, we report that, because of pGE, mature mTECs synthesize substantially more proteins than other cell types and are exquisitely sensitive to loss of immunoproteasomes (IPs). Indeed, IP deficiency causes proteotoxic stress in mTECs and leads to exhaustion of postnatal mTEC progenitors. Moreover, IP-deficient mice show accelerated thymic involution, which is characterized by a selective loss of mTECs and multiorgan autoimmune manifestations. We conclude that pGE, the quintessential feature of mTECs, is a major burden for the maintenance of proteostasis, which is alleviated by the constitutive expression of IPs in mTECs.

Comparison of the MHC I Immunopeptidome Repertoire of B-Cell Lymphoblasts Using Two Isolation Methods

Significant technological advances in both affinity chromatography and mass spectrometry have facilitated the identification of peptides associated with the major histocompatibility complex class I (MHC I) molecules, and enabled a greater understanding of the dynamic nature of the immunopeptidome of normal and neoplastic cells. While the isolation of MHC I-associated peptides (MIPs) typically used mild acid elution (MAE) or immunoprecipitation (IP), limited information currently exists regarding their respective analytical merits. Here, a comparison of these approaches for the isolation of two different B-cell lymphoblast cell models is presented, and it is reported on the recovery, reproducibility, scalability, and complementarity of identification from each method. Both approaches yielded reproducible datasets for peptide extracts obtained from 2 to 100 million cells, with 2016 to 5093 MIPs, respectively. The IP typically provides up to 6.4-fold increase in MIPs compared to the MAE. The comprehensiveness of these immunopeptidome analyses is extended using personalized genomic database of B-cell lymphoblasts, and it is discovered that 0.4% of their respective MIP repertoire harbored nonsynonymous single nucleotide variations (also known as minor histocompatibility antigens, MiHAs).

Immunoproteasomes shape the transcriptome and regulate the function of dendritic cells (IRM7P.476)

Background: By regulating protein degradation, constitutive proteasomes (CPs) regulate practically all fundamental cellular processes. Vertebrates also express immunoproteasomes (IPs), but the only well-established non-redundant role for IPs is their enhanced ability to generate peptides for MHC-I presentation. Results: Here we show that IPs regulate the expression of 8,104 genes in maturing bone marrow-derived dendritic cells (DCs). IPs regulated transcription of many mRNAs and maturation of a subset of them. These genes were separated into 15 different kinetic patterns, and Gene-Ontology analysis revealed enrichment linked to immune functions and housekeeping cellular processes, highlighting the complexity of the transcriptional cascade regulated by IPs. Notably, IPs’ impact on transcription was mediated through the non-redundant regulation of critical immune-related pathways, such as Nf-kB, STATs and IRFs. Furthermore, even when loaded with optimal amounts of SIINFEKL, IP-deficient DCs were inefficient for in vivo priming of OT-1 T cells. Conclusion: Our study shows that the role of IPs is not limited to antigen processing and highlights a new and critical role for IPs in regulation of gene expression. The dramatic impact of IPs on the transcriptional landscape could explain the various immune and non-immune phenotypes observed in vertebrates with IP-deficiency or -mutation.

Rejection of leukemic cells requires antigen-specific T cells with high functional avidity

In a context where injection of antigen (Ag)-specific T cells probably represents the future of leukemia immunotherapy, identification of optimal target Ags is crucial. We therefore sought to discover a reliable marker for selection of the most potent Ags. To this end, (1) we immunized mice against 8 individual Ags: 4 minor histocompatibility Ags (miHAs) and 4 leukemia-associated Ags (LAAs) that were overexpressed on leukemic relative to normal thymocytes; (2) we assessed their ability to reject EL4 leukemic cells; and (3) we correlated the properties of our Ags (and their cognate T cells) with their ability to induce protective antileukemic responses. Overall, individual miHAs instigated more potent antileukemic responses than LAAs. Three features had no influence on the ability of primed T cells to reject leukemic cells: (1) MHC-peptide affinity; (2) the stability of MHC-peptide complexes; and (3) epitope density at the surface of leukemic cells, as assessed using mass spectrometry. The cardinal feature of successful Ags is that they were recognized by high-avidity CD8 T cells that proliferated extensively in vivo. Our work suggests that in vitro evaluation of functional avidity represents the best criterion for selection of Ags, which should be prioritized in clinical trials of leukemia immunotherapy.

Discovering optimal targets for adoptive T-cell immunotherapy of leukemia (P4346)

The main barrier in allogeneic hematopoietic cell transplantation is the risk of developing graft-versus-host disease. This can be prevented by the injection of CD8 T cells targeted to leukemia associated antigens (LAAs) or minor histocompatibility antigens (MiHAs). Several studies in humans have established the value of LAAs and MiHAs as target for immunotherapy on solid tumors and leukemia, respectively. Importantly, their therapeutic efficacy has never been assessed on a per antigen basis. Thus, our goal is to directly compare the therapeutic efficacy of T-cells targeted to LAAs or MiHAs expressed on EL4 cells. We selected 4 MiHAs and 4 LAAs and confirmed their immunogenicity by in vitro cytotoxicity assays. We evaluated the anti-leukemic activity of antigen-specific CD8 T cells in vivo. Notably, mice immunized against MiHAs showed enhanced survival compared to mice immunized against LAAs. We found that decreased survival of EL4 bearing mice cannot be explained by weaker MHC I/Peptide interactions. Interestingly, we showed that T cells specific for 4 LAAs and 1 MiHA are undetectable by flow cytometry and that the abundance of tetramer positive cells correlates strongly with survival of EL4 bearing mice. We propose that CD8 T cells, mainly targeted to LAAs, bind weakly to their MHC I/Peptide complexes, leading to decreased immunogenicity. We believe that the insights gained from our studies will serve as guide for selecting the best antigens for future clinical trials.

Regulation of gene expression by the immunoproteasome (P5049)

Background: Proteasomes play crucial roles in regulating fundamental cellular processes in eukaryotic cells. Catalytic subunits β1, β2 and β5 of the proteasome are replaced by LMP2, MECL-1 and LMP7 to form the immunoproteasome (IPr). We have shown that the IPr modulates mRNA levels of several clusters of genes in dendritic cells, but the precise mechanism by which it regulates gene expression is unknown. Results: By comparing transcriptome of Lmp7+/+/Mecl1+/+ (WT) and Lmp7-/-/Mecl1-/- (dKO) thymocytes by microarray, we found that the IPr affects the expression of 50 transcripts. The genes source of these transcripts are clustered in the genome, and are enriched in cell cycle-associated functions. Moreover, an overlap of 2% is seen by comparing with transcripts modulated by the IPr in dendritic cells. Chymotrypsin-like activity is higher in dKO than in WT cells, due to β5 overexpression. Furthermore, ubiquitinated proteins levels are similar between WT and dKO cells whereas free ubiquitin is lower in dKO cells. We next investigated levels of ubiquitin on histones, since it represent an important reservoir of ubiquitin and it can regulate transcriptional activity. Our results show that H2B, but not H2A, ubiquitination is increased in dKO cells. Conclusion: The effect of IPr on transcription is tissue-specific and could be due to increased ubiquitinated H2B levels. While proteasomes clearly regulate transcription, the impact of IPr on transcription has never been investigated.

Circadian variation of the response of T cells to antigen

Circadian clocks regulate many important aspects of physiology, and their disturbance leads to various medical conditions. Circadian variations have been found in immune system variables, including daily rhythms in circulating WBC numbers and serum concentration of cytokines. However, control of immune functional responses by the circadian clock has remained relatively unexplored. In this study, we show that mouse lymph nodes exhibit rhythmic clock gene expression. T cells from lymph nodes collected over 24 h show a circadian variation in proliferation after stimulation via the TCR, which is blunted in Clock gene mutant mice. The tyrosine kinase ZAP70, which is just downstream of the TCR in the T cell activation pathway and crucial for T cell function, exhibits rhythmic protein expression. Lastly, mice immunized with OVA peptide-loaded dendritic cells in the day show a stronger specific T cell response than mice immunized at night. These data reveal circadian control of the Ag-specific immune response and a novel regulatory mode of T cell proliferation, and may provide clues for more efficient vaccination strategies.

The MHC I immunopeptidome conveys to the cell surface an integrative view of cellular regulation

Self/non-self discrimination is a fundamental requirement of life. Endogenous peptides presented by major histocompatibility complex class I (MHC I) molecules represent the essence of self for CD8 T lymphocytes. These MHC I peptides (MIPs) are collectively referred to as the immunopeptidome. From a systems-level perspective, very little is known about the origin, composition and plasticity of the immunopeptidome. Here, we show that the immunopeptidome, and therefore the nature of the immune self, is plastic and moulded by cellular metabolic activity. By using a quantitative high-throughput mass spectrometry-based approach, we found that altering cellular metabolism via the inhibition of the mammalian target of rapamycin results in dynamic changes in the cell surface MIPs landscape. Moreover, we provide systems-level evidence that the immunopeptidome projects at the cell surface a representation of biochemical networks and metabolic events regulated at multiple levels inside the cell. Our findings open up new perspectives in systems immunology and predictive biology. Indeed, predicting variations in the immunopeptidome in response to cell-intrinsic and -extrinsic factors could be relevant to the rational design of immunotherapeutic interventions.

Development and function of innate polyclonal TCRalphabeta+ CD8+ thymocytes

Innate CD8 T cells are found in mutant mouse models, but whether they are produced in a normal thymus remains controversial. Using the RAG2p-GFP mouse model, we found that ∼10% of TCRαβ(+) CD4(-)CD8(+) thymocytes were innate polyclonal T cells (GFP(+)CD44(hi)). Relative to conventional T cells, innate CD8 thymocytes displayed increased cell surface amounts of B7-H1, CD2, CD5, CD38, IL-2Rβ, and IL-4Rα and downmodulation of TCRβ. Moreover, they overexpressed several transcripts, including T-bet, Id3, Klf2, and, most of all, Eomes. Innate CD8 thymocytes were positively selected, mainly by nonhematopoietic MHCIa(+) cells. They rapidly produced high levels of IFN-γ upon stimulation and readily proliferated in response to IL-2 and IL-4. Furthermore, low numbers of innate CD8 thymocytes were sufficient to help conventional CD8 T cells expand and secrete cytokine following Ag recognition. This helper effect depended on CD44-mediated interactions between innate and conventional CD8 T cells. We concluded that innate TCRαβ(+) CD8 T cells represent a sizeable proportion of normal thymocytes whose development and function differ in many ways from those of conventional CD8 T cells.

Normoxic expression of hypoxia-inducible factor 1 in rat Leydig cells in vivo and in vitro

Hypoxia-inducible factors (HIF) are transcription factors that serve essential regulatory roles in cellular and molecular responses to oxygen debt. HIFs are composed of hypoxia-dependent α subunits (1α, 2α, 3α) and an oxygen-independent β subunit. Previously we demonstrated that HIF-1, the master regulator of hypoxic responses, is expressed in the adult rat testis. We hypothesized that HIF-1 is involved in regulating responses to oxygen tension in the testis. Goals of this study were to determine if HIF-2α and HIF-3α are expressed in rat testis, identify testis cell types that express HIF-1α, and examine patterns of testicular HIF-1α protein expression under conditions of ischemia and hypoxia in vivo and in vitro. Reverse transcriptase polymerase chain reaction revealed that mRNA for Hif-1α, Hif-2α, and Hif-3α is expressed in the testis. The HIF-1α protein is the predominant subunit in testis. HIF-1α protein was abundant in normoxic testis, and its levels remained unchanged following ischemia created by surgically induced testicular torsion and reperfusion. Immunoblot and immunocytochemical experiments demonstrated that Leydig cells are the major source of HIF-1α in normoxic and hypoxic testes. To examine potential mechanisms of testicular HIF-1 stabilization, nuclear proteins from Leydig cells cultured in 5% or 21% oxygen, or cells cultured with H₂O₂, were analyzed by immunoblotting. Levels of HIF-1α were significantly diminished in 5% or 21% oxygen cultures compared with freshly isolated cells. Treating Leydig cells with H₂O₂ as a source of reactive oxygen species did not affect HIF-1α levels. High levels of constitutively expressed HIF-1α in normoxic Leydig cells suggest potentially unique roles for HIF-1 in Leydig cell responsiveness to oxygen.

Deletion of immunoproteasome subunits imprints on the transcriptome and has a broad impact on peptides presented by major histocompatibility complex I molecules

Proteasome-mediated proteolysis plays a crucial role in many basic cellular processes. In addition to constitutive proteasomes (CPs), which are found in all eukaryotes, jawed vertebrates also express immunoproteasomes (IPs). Evidence suggests that the key role of IPs may hinge on their impact on the repertoire of peptides associated to major histocompatibility complex (MHC) I molecules. Using a label-free quantitative proteomics approach, we identified 417 peptides presented by MHC I molecules on primary mouse dendritic cells (DCs). By comparing MHC I-associated peptides (MIPs) eluted from primary DCs and thymocytes, we found that the MIP repertoire concealed a cell type-specific signature correlating with cell function. Notably, mass spectrometry analyses of DCs expressing or not IP subunits MECL1 and LMP7 showed that IPs substantially increase the abundance and diversity of MIPs. Bioinformatic analyses provided evidence that proteasomes harboring LMP7 and MECL1 have specific cleavage preferences and recognize unstructured protein regions. Moreover, while differences in MIP repertoire cannot be attributed to potential effects of IPs on gene transcription, IP subunits deficiency altered mRNA levels of a set of genes controlling DC function. Regulated genes segregated in clusters that were enriched in chromosomes 4 and 8. Our peptidomic studies performed on untransfected primary cells provide a detailed account of the MHC I-associated immune self. This work uncovers the dramatic impact of IP subunits MECL1 and LMP7 on the MIP repertoire and their non-redundant influence on expression of immune-related genes.

Analysis of blood stem cell activity and cystatin gene expression in a mouse model presenting a chromosomal deletion encompassing Csta and Stfa2l1

The cystatin protein superfamily is characterized by the presence of conserved sequences that display cysteine protease inhibitory activity (e.g., towards cathepsins). Type 1 and 2 cystatins are encoded by 25 genes of which 23 are grouped in 2 clusters localized on mouse chromosomes 16 and 2. The expression and essential roles of most of these genes in mouse development and hematopoiesis remain poorly characterized. In this study, we describe a set of quantitative real-time PCR assays and a global expression profile of cystatin genes in normal mouse tissues. Benefiting from our collection of DelES embryonic stem cell clones harboring large chromosomal deletions (to be reported elsewhere), we selected a clone in which a 95-kb region of chromosome 16 is missing (Del^16qB3Δ/+). In this particular clone, 2 cystatin genes, namely Csta and Stfa2l1 are absent along with 2 other genes (Fam162a, Ccdc58) and associated intergenic regions. From this line, we established a new homozygous mutant mouse model (Del^{16qB3Δ/16qB3Δ}) to assess the in vivo biological functions of the 2 deleted cystatins. Stfa2l1 gene expression is high in wild-type fetal liver, bone marrow, and spleen, while Csta is ubiquitously expressed. Homozygous Del^{16qB3Δ/16qB3Δ} animals are phenotypically normal, fertile, and not overtly susceptible to spontaneous or irradiation-induced tumor formation. The hematopoietic stem and progenitor cell activity in these mutant mice are also normal. Interestingly, quantitative real-time PCR expression profiling reveals a marked increase in the expression levels of Stfa2l1/Csta phylogenetically-related genes (Stfa1, Stfa2, and Stfa3) in Del^{16qB3Δ/16qB3Δ} hematopoietic tissues, suggesting that these candidate genes might be contributing to compensatory mechanisms. Overall, this study presents an optimized approach to globally monitor cystatin gene expression as well as a new mouse model deficient in Stfa2l1/Csta genes, expanding the available tools to dissect cystatin roles under normal and pathological conditions.

ER stress affects processing of MHC class I-associated peptides

Background

Viral infection and neoplastic transformation trigger endoplasmic reticulum (ER) stress. Thus, a large proportion of the cells that must be recognized by the immune system are stressed cells. Cells respond to ER stress by launching the unfolded protein response (UPR). The UPR regulates the two key processes that control major histocompatibility complex class I (MHC I)-peptide presentation: protein synthesis and degradation. We therefore asked whether and how the UPR impinges on MHC I-peptide presentation.

Results

We evaluated the impact of the UPR on global MHC I expression and on presentation of the H2K^b-associated SIINFEKL peptide. EL4 cells stably transfected with vectors coding hen egg lysozyme (HEL)-SIINFEKL protein variants were stressed with palmitate or exposed to glucose deprivation. UPR decreased surface expression of MHC I but did not affect MHC I mRNA level nor the total amount of intracellular MHC I proteins. Impaired MHC I-peptide presentation was due mainly to reduced supply of peptides owing to an inhibition of overall protein synthesis. Consequently, generation of H2K^b-SIINFEKL complexes was curtailed during ER stress, illustrating how generation of MHC I peptide ligands is tightly coupled to ongoing protein synthesis. Notably, the UPR-induced decline of MHC I-peptide presentation was more severe when the protein source of peptides was localized in the cytosol than in the ER. This difference was not due to changes in the translation rates of the precursor proteins but to increased stability of the cytosolic protein during ER stress.

Conclusion

Our results demonstrate that ER stress impairs MHC I-peptide presentation, and that it differentially regulates expression of ER- vs. cytosol-derived peptides. Furthermore, this work illustrates how ER stress, a typical feature of infected and malignant cells, can impinge on cues for adaptive immune recognition.

Modulation of 11beta-hydroxysteroid dehydrogenase expression by bombesin: a possible mechanism for glucocorticoid resistance in androgen independent prostate cancer

Treatment with glucocorticoids is one of a limited number of options for androgen independent prostate cancer. Neuroendocrine differentiation has been shown to contribute to androgen-independent prostate cancer progression. To study the potential link between neuroendocrine differentiation and the glucocorticoid action, we investigated the effects of the product of neuroendocrine differentiation--bombesin on glucocorticoid metabolizing enzymes--11beta-hydroxysteroid dehydrogenases in PC-3 cells. Our Western analysis, RT-PCR, and activity assays demonstrate that while 18-hour exposure to bombesin reduces 11beta-hydroxy-steroid dehydrogenases-1 profiles (activities 25% less, protein level 29% lower, mRNA levels 45% lower), contrarily it increases 11beta-hydroxysteroid dehydrogenases-2 profiles (activities 34%, protein levels 100%, mRNA levels 120%). Blockade bombesin action with bombesin receptor antagonists and the enzyme degrading bombesin prevented these changes, suggesting the observed modulations were bombesin receptor-specific. In addition, bombesin increased the amounts of interleukin-8 and mRNA of vascular endothelial growth factor receptor 2, which were lowered in the presence of cortisol, suggesting that neuropeptide blockade may extend the benefits of glucocorticoids in treating androgen-independent prostate cancer.

The MHC class I peptide repertoire is molded by the transcriptome

Under steady-state conditions, major histocompatibility complex (MHC) I molecules are associated with self-peptides that are collectively referred to as the MHC class I peptide (MIP) repertoire. Very little is known about the genesis and molecular composition of the MIP repertoire. We developed a novel high-throughput mass spectrometry approach that yields an accurate definition of the nature and relative abundance of unlabeled peptides presented by MHC I molecules. We identified 189 and 196 MHC I-associated peptides from normal and neoplastic mouse thymocytes, respectively. By integrating our peptidomic data with global profiling of the transcriptome, we reached two conclusions. The MIP repertoire of primary mouse thymocytes is biased toward peptides derived from highly abundant transcripts and is enriched in peptides derived from cyclins/cyclin-dependent kinases and helicases. Furthermore, we found that approximately 25% of MHC I-associated peptides were differentially expressed on normal versus neoplastic thymocytes. Approximately half of those peptides are derived from molecules directly implicated in neoplastic transformation (e.g., components of the PI3K-AKT-mTOR pathway). In most cases, overexpression of MHC I peptides on cancer cells entailed posttranscriptional mechanisms. Our results show that high-throughput analysis and sequencing of MHC I-associated peptides yields unique insights into the genesis of the MIP repertoire in normal and neoplastic cells.

Endogenous inhibitors (GALFs) of 11beta-hydroxysteroid dehydrogenase isoforms 1 and 2: derivatives of adrenally produced corticosterone and cortisol

Two isoforms of 11beta-HSD exist; 11beta-HSD1 is bi-directional (the reductase usually being predominant) and 11beta-HSD2 functions as a dehydrogenase, conferring kidney mineralocorticoid specificity. We have previously described endogenous substances in human urine, "glycyrrhetinic acid-like factors (GALFs)", which like licorice, inhibit the bi-directional 11beta-HSD1 enzyme as well as the dehydrogenase reaction of 11beta-HSD2. Many of the more potent GALFs are derived from two major families of adrenal steroids, corticosterone and cortisol. For example, 3alpha5alpha-tetrahydro-corticosterone, its derivative, 3alpha5alpha-tetrahydro-11beta-hydroxy-progesterone (produced by 21-deoxygenation of corticosterone in intestinal flora); 3alpha5alpha-tetrahydro-11beta-hydroxy-testosterone (produced by side chain cleavage of cortisol); are potent inhibitors of 11beta-HSD1 and 11beta-HSD2-dehydrogenase, with IC50's in range 0.26-3.0 microM, whereas their 11-keto-3alpha5alpha-tetrahydro-derivatives inhibit 11beta-HSD1 reductase, with IC50's in range 0.7-0.8 microM (their 3alpha5beta-derivatives being completely inactive). Inhibitors of 11beta-HSD2 increase local cortisol levels, permitting it to act as a mineralocorticoid in kidney. Inhibitors of 11beta-HSD1 dehydrogenase/11beta-HSD1 reductase serve to adjust the set point of local deactivation/reactivation of cortisol in vascular and other glucocorticoid target tissues, including adipose, vascular, adrenal tissue, and the eye. These adrenally derived 11-oxygenated C21- and C19 -steroidal substances may serve as 11beta-HSD1- or 11beta-HSD2-GALFs. We conclude that adrenally derived products are likely regulators of local cortisol bioactivity in humans.

IL-7 Receptor Expression Levels Do Not Identify CD8+ Memory T Lymphocyte Precursors following Peptide Immunization

Identification of the mechanisms underlying the survival of effector T cells and their differentiation into memory T lymphocytes are critically important to understanding memory development. Because cytokines regulate proliferation, differentiation, and survival of T lymphocytes, we hypothesized that cytokine signaling dictates the fate of effector T cells. To follow cytokine receptor expression during T cell responses, we transferred murine TCR transgenic T cells into naive recipients followed by immunization with peptide emulsified in adjuvant or pulsed on dendritic cells. Our findings did not correlate IL-7R alpha-chain and IL-2R beta-chain expression on effector CD8+ cells with the generation of memory T lymphocytes. However, we could correlate the extent of IL-7R alpha expression down-regulation on effector T cells with the level of inflammation generated by the immunization. Furthermore, our findings showed that the maintenance of a high level of IL-7R expression by effector T cells at the peak of the response does not preclude their death. This suggests that maintenance of IL-7R expression is not sufficient to prevent T cell contraction. Thus, our results indicate that expression of the IL-7R is not always a good marker for identifying precursors of memory T cells among effectors and that selective expression of the IL-7R by effector T cells should not be used to predict the success of vaccination.

Mucosal deformation from an impinging transonic gas jet and the ballistic impact of microparticles

By means of a transonic gas jet, gene guns ballistically deliver microparticle formulations of drugs and vaccines to the outer layers of the skin or mucosal tissue to induce unique physiological responses for the treatment of a range of conditions. Reported high-speed imaging experiments show that the mucosa deforms significantly while subjected to an impinging gas jet from a biolistic device. In this paper, the effect of this tissue surface deformation on microparticle impact conditions is simulated with computational fluid dynamics (CFD) calculations. The microparticles are idealized as spheres of diameters 26.1, 39 and 99 microm and a density of 1050 kg m-3. Deforming surface calculations of particle impact conditions are compared directly with an immobile surface case. The relative velocity and obliquity of the deforming surface decrease the normal component of particle impact velocity by up to 30% at the outer edge of the impinging gas jet. This is qualitatively consistent with reported particle penetration profiles in the tissue. It is recommended that these effects be considered in biolistic studies requiring quantified particle impact conditions.

Detailed mapping of the ERG-ETS2 interval of human chromosome 21 and comparison with the region of conserved synteny on mouse chromosome 16

We have carried out a detailed annotation of 550 kb of genomic DNA on human chromosome 21 containing the ERG and ETS2 genes. Comparative genomic analysis between this region and the interval of conserved synteny on mouse chromosome 16 indicated that the order and orientation of the ERG and ETS2 genes were conserved and revealed several regions containing potential conserved noncoding sequences. Four pseudogenes including those for small protein G, laminin receptor, human transposase protein and meningioma-expressed antigen were identified. A potentially novel gene (C21orf24) with alternative mRNA transcripts, consensus splice donor and acceptor sites, but no coding potential nor murine orthologue, was identified and found to be expressed in a range of human cell lines. We have identified four novel splice variants that arise from a previously undescribed 5' exon of the human ERG gene. Comparison of the cDNA sequences enabled us to determine the complete exon-intron structure of the ERG gene. We have also identified the presence of noncoding RNAs in the first and second introns of the ETS2 gene. Our studies have important implications for Down syndrome as this region contains multiple mRNA transcripts, both coding and potentially noncoding, that may play as yet undescribed roles in the pathogenesis of this disorder.

Effect of chronic administration of 7alpha-methyl-19-nortestosterone on serum testosterone, number of spermatozoa and fertility in adult male bonnet monkeys (Macaca radiata)

Hormonal approaches to male contraception that are based on the suppression of LH secretion require androgen replacement treatment to maintain sexual behaviour and secondary sexual characteristics. Androgen supplementation not only involves large and frequent doses of testosterone esters but also results in undesirable effects on the prostate gland. In an attempt to avoid such problems, a synthetic androgen, 7alpha-methyl-19-nortestosterone (MENT), which is much more potent than testosterone, has been developed. In the present study, MENT was administered at different doses (25, 50, 100, 300 and 1000 microg day(-1)) either alone or in combination with oestradiol via Silastic implants for a specified period to adult male bonnet monkeys (Macaca radiata). Blood and semen samples were collected at specific intervals and analysed for serum testosterone and seminal parameters, respectively. The results of the present study clearly indicate that administration of MENT at all doses tested results in suppression of the nocturnal surge of testosterone (by day 3), as well as a decrease in the number of spermatozoa (by day 45). Co-administration of oestradiol resulted in a reduction in the dose of MENT required to suppress the nocturnal surge. None of the male bonnet monkeys treated with MENT were able to impregnate females, clearly demonstrating the efficacy of MENT in blocking fertility in male bonnet monkeys.

Prenatal exposure to dexamethasone alters Leydig cell steroidogenic capacity in immature and adult rats

This study examines the effects of prenatal exposure to dexamethasone (DEX) on postnatal testosterone production in male rats. Pregnant female rats were treated on gestation days 14-19 with DEX (100 microg/kg body weight per day; n = 9) or vehicle (n = 9). Results show that 35-day-old male offspring from DEX-treated pregnant females (n = 42) had decreased levels of serum testosterone (45.6% lower, P < .05) compared with control offspring (n = 43), although serum luteinizing hormone (LH) levels were not significantly altered. These findings suggest that a direct programming of developing gonadal cells occurs in response to high levels of maternal glucocorticoid. Indeed, testosterone production was significantly reduced in Leydig cells isolated from immature offspring of DEX-treated pregnant females compared with controls (48.3%, P < .001), and LH stimulation of these cells did not compensate for the lowered steroidogenic capacity. The hypothalamic-pituitary-adrenal axis was also affected, because significant reductions in both serum adrenocorticotropic hormone (ACTH; 26.2%, P < .001) and corticosterone (CORT; 32.3%, P < .001) were measured in DEX-exposed immature male offspring. In contrast, adult male offspring from DEX-treated dams had significantly higher levels of serum ACTH (39.2%, P <. 001) and CORT (37.8%, P < .001). These same animals had higher serum testosterone (31.6%, P < or = .05) and a significant reduction in serum LH (30.8%, P < .001). Moreover, Leydig cells isolated from these adult offspring exhibited an increased capacity for testosterone biosynthesis under basal (38.6%, P < .001) and LH-stimulated conditions (33.5%, P < .001). In summary, sustained changes in steroidogenic capacity were observed in male rats exposed to high levels of glucocorticoid during prenatal development. More specifically, DEX exposure in utero perturbed Leydig cell testosterone production in both pubertal and adult rats.

Modulation of rat Leydig cell steroidogenic function by di(2-ethylhexyl)phthalate

Exposure of rodents to phthalates is associated with developmental and reproductive anomalies, and there is concern that these compounds may be causing adverse effects on human reproductive health. Testosterone (T), secreted almost exclusively by Leydig cells in the testis, is the primary steroid hormone that maintains male fertility. Leydig cell T biosynthesis is regulated by the pituitary gonadotropin LH. Herein, experiments were conducted to investigate the ability of di(2-ethylhexyl)phthalate (DEHP) to affect Leydig cell androgen biosynthesis. Pregnant dams were gavaged with 100 mg(-1) kg(-1) day(-1) DEHP from Gestation Days 12 to 21. Serum T and LH levels were significantly reduced in male offspring, compared to control, at 21 and 35 days of age. However, these inhibitory effects were no longer apparent at 90 days. In a second set of experiments, prepubertal rats, from 21 or 35 days of age, were gavaged with 0, 1, 10, 100, or 200 mg(-1) kg(-1) day(-1) DEHP for 14 days. This exposure paradigm affected Leydig cell steroidogenesis. For example, exposure of rats to 200 mg(-1) kg(-1) day(-1) DEHP caused a 77% decrease in the activity of the steroidogenic enzyme 17beta-hydroxysteroid dehydrogenase, and reduced Leydig cell T production to 50% of control. Paradoxically, extending the period of DEHP exposure to 28 days (Postnatal Days 21-48) resulted in significant increases in Leydig cell T production capacity and in serum LH levels. The no-observed-effect-level and lowest-observed-effect-level were determined to be 1 mg(-1) kg(-1) day(-1) and 10 mg(-1) kg(-1) day(-1), respectively. In contrast to observations in prepubertal rats, exposure of young adult rats by gavage to 0, 1, 10, 100, or 200 mg(-1) kg(-1) day(-1) DEHP for 28 days (Postnatal Days 62-89) induced no detectable changes in androgen biosynthesis. In conclusion, data from this study show that DEHP effects on Leydig cell steroidogenesis are influenced by the stage of development at exposure and may occur through modulation of T-biosynthetic enzyme activity and serum LH levels.

Oestrogenic and antiandrogenic chemicals in the environment: effects on male reproductive health

Exposures of human populations to pesticides and industrial pollutants, and to synthetic chemicals present in foods, beverages, and plastics, have raised concern that these substances can interfere with endogenous sex hormone function. Interference with sex hormone action can, in turn, result in a variety of developmental and reproductive anomalies. Compounds in this class are thus referred to as endocrine disruptors (EDs). EDs that affect reproductive processes in vertebrates act primarily by altering oestrogenic and antiandrogenic activities. The recent cloning of a second oestrogen receptor (ER) subtype (ERbeta) and its widespread tissue distribution pattern indicates that the first ER to be cloned, ERalpha, may not be the only, or even the primary, mediator of oestrogen action. It is anticipated that this discovery will lead to development of antagonist compounds specific to either ER subtype, and help to determine the function of each receptor subtype in reproductive and other tissues. Growing evidence suggests that EDs interfere with reproductive function at low exposure levels and cause distinct effects at different concentrations within the same organ. Developing organisms have increased susceptibility to the actions of EDs because differentiating tissues are more vulnerable to changes in hormonal milieu. Thus, children are at greater risk of toxicant-related illnesses than adults. However, most data are collected from laboratory studies, and it remains to be determined that the levels of chemicals in the environment can impair human reproductive health. There is also significant genetic variability between human and animal species in their reactions to chemicals. The effects of low-dose, chronic, and multiple chemical exposures warrant further investigation in order to characterize the risk of environmental agents to humans. The aims of this review, which will focus on male reproduction, are to: 1) identify synthetic chemicals in the environment that fall into the ED class; 2) describe their mechanisms of toxicity in reproductive tissues; and, 3) outline the direction of future research efforts with respect to EDs.

Müllerian inhibiting substance inhibits testosterone synthesis in adult rats

Müllerian inhibiting substance (MIS) is a gonadal hormone that causes regression of the Müllerian ducts during male sexual differentiation. Postnatally, MIS inhibits the proliferation and differentiation of immature Leydig cells, and transgenic mice that overexpress MIS have decreased serum testosterone concentrations. To elucidate the effects of MIS on androgen regulation in the postnatal testis, we examined testosterone synthesis in adult Sprague-Dawley rats following intratesticular and intraperitoneal injections of MIS. Intratesticular MIS injection achieved high local concentrations of MIS (574.0 +/- 60.0 ng/mL) at 4 hours, with a corresponding decline in serum testosterone concentrations to 0.7 +/- 0.1 ng/mL, compared to 1.1 +/- 0.2 ng/mL with intraperitoneal MIS and 1.6 +/- 0.1 ng/mL with intratesticular vehicle (IT-Veh) (P < .001). Intratesticular administration of MIS (IT-MIS) resulted in much higher serum and testicular interstitial fluid MIS concentrations than the intraperitoneal route. To directly examine the testosterone production rate in MIS-treated animals, we isolated Leydig cells from MIS and vehicle-injected testes. Primary Leydig cells exposed to MIS had a lower testosterone production rate and decreased expression of p450c17 (hydroxylase/lyase) and luteinizing hormone (LH) receptor mRNAs than that of vehicle-injected controls or the noninjected contralateral testis. In conclusion, intratesticular administration of MIS caused a decline in serum testosterone concentrations by decreasing the rate of testosterone biosynthesis, confirming that MIS can regulate adult Leydig cell androgen production. The ability of MIS to down-regulate mRNA expression of the p450c17 and LH receptor genes suggests that this effect is mediated transcriptionally. These data indicate that, in addition to its role in embryonic differentiation of the male reproductive tract, MIS has a regulatory function in the postnatal testis. We conclude that one such function is for MIS to directly inhibit adult Leydig cell steroidogenesis.

Purification of rat leydig cells: increased yields after unit-gravity sedimentation of collagenase-dispersed interstitial cells

Procedures for purification of Leydig cells have facilitated studies of their regulatory biology. A multistep procedure that includes a filtration with nylon mesh (100-micron pore size) to separate interstitial cells from the seminiferous tubules, combining centrifugal elutriation and Percoll density gradient sedimentation, has been used to obtain a 95% enrichment of rat Leydig cells. However, the number of recovered Leydig cells by this procedure represents only a small fraction of the 25 million, on average, that exist in the adult rat testis. The objective of this study was to test whether the yield of purified Leydig cells might be enhanced by substitution of unit-gravity sedimentation (S method) for the filter step (F method). We also asked whether a greater number of Leydig cell clusters, macrophages, or both would be recovered by this new method, and if the presence of Leydig cell clusters is associated with increased capacity for testosterone production in vitro. The number of purified Leydig cells was 1.9-fold higher for the S method than for the F method, with no differences in purity assessed by 3beta-hydroxysteroid dehydrogenase histochemical staining. Leydig cell clusters were also found in greater numbers with the S method both after collagenase dispersion and at the end of the purification. No differences were seen in testosterone production or in the number of macrophages present in the Leydig cells that were prepared by the 2 methods. These results indicate that the new method recovers greater numbers of Leydig cells by collecting clustered Leydig cells that are systematically eliminated when a filtration step is used.

The soluble murine type I interferon receptor Ifnar-2 is present in serum, is independently regulated, and has both agonistic and antagonistic properties

The ability to modify responses to type I interferons (IFNs) could alter processes such as hematopoiesis and immunity, which involve endogenous IFNs and responses to exogenous IFNs. The data presented here support a significant role for a recently identified soluble isoform of the murine type I IFN receptor, muIfnar-2a, as an efficient regulator of IFN responses. The messenger RNA (mRNA) transcript encoding muIfnar-2a is generally more abundant than that encoding the transmembrane isoform, muIfnar-2c. Furthermore, the ratio of muIfnar-2a:2c transcripts varied from more than 10:1 in the liver and other organs to less than 1:1 in bone-marrow macrophages, indicating independent regulation of the 2 transcripts encoding receptor isoforms and suggesting that the soluble muIfnar-2a levels are biologically relevant in some organs. Western blot analysis showed that soluble muIfnar-2 was present at high levels in murine serum and other biologic fluids and bound type I IFN. Recombinant muIfnar-2a competitively inhibited the activity of both IFNalpha and beta in reporter assays using the L929 cell line and in antiproliferative and antiviral assays using primary cells. Surprisingly, using primary thymocytes from Ifnar-2(-/-) mice, recombinant muIfnar-2a formed a complex with IFN alpha or beta and muIfnar-1 at the cell surface and transmitted an antiproliferative signal. These data indicate potential dual actions of soluble muIfnar-2 and imply that a signal can be transduced through the Ifnar-1 chain of the receptor complex in the absence of the cytoplasmic domain of Ifnar-2. Therefore, our results suggest that soluble Ifnar-2 is an important regulator of endogenous and systemically administered type I IFN.

Effects of androgen on androgen receptor expression in rat testicular and epididymal cells: a quantitative immunohistochemical study

Androgen is essential for maintenance of spermatogenesis in the testis and for maturation of spermatozoa in the epididymis. The effects of androgen are mediated through its receptor (AR), the levels of which are, in turn, regulated by androgen. Previous studies have shown that AR concentrations in Leydig and Sertoli cells are differentially regulated during development. The aim of the present study was to determine if cell-type-specific regulation of AR by androgen occurs in testicular and epididymal cells during adulthood. Adult male rats were treated with the LHRH-antagonist Azaline B (100 g/day) by osmotic pump for 1, 2, 3, 4, or 8 wk to suppress endogenous androgen, with identical numbers of intact control animals at each time period. An androgen replacement group was simultaneously treated with the antagonist and a synthetic androgen, 7 alpha-methyl-19-nortestosterone (MENT), during the final 4 wk of the experiment. Levels of nuclear AR protein in specific cell types were quantified by immunohistochemistry in conjunction with computer-assisted image analysis. Levels of AR in testicular cells declined sharply after treatment with the LHRH antagonist. In Sertoli cells, nuclear AR levels decreased to 8% of control (P < 0. 01) after 4 wk treatment; and to 12% and 17% of control (P < 0.01) in Leydig and myoid cells, respectively. Androgen replacement resulted in complete recovery of nuclear AR levels in Sertoli cells (93%, P > 0.05) but in only partial recovery in myoid (69%, P < 0. 01) and Leydig cells (56%, P < 0.01). In the epididymis, tubular epithelial cells and stromal cells differed in their responses to the LHRH antagonist. After 1 wk, nuclear AR levels in caput stromal cells decreased dramatically to 34% of control (P < 0.01) and in cauda stromal cells to 43% (P < 0.01). In contrast, the decline of AR levels in epididymal epithelial cells was not as dramatic as that in stromal cells. After 1 wk, the decline in the caput and cauda was to 87% and 76% of control, respectively. After 8 wk, nuclear AR levels in stromal cells further declined to 1.1% in caput and 1.4% in cauda, whereas in the epithelial cells, a smaller decline in nuclear AR was noted (to 30% in the caput and 45% in the cauda). After androgen replacement with MENT, nuclear AR levels recovered to more than 90% of control in both epididymal cell types. These results indicate that AR levels in the nuclei of adult Sertoli cells depend mainly on the level of androgen, whereas in the adult Leydig and myoid cells, the androgen dependency is more limited. The results also indicate that in the epididymis, stromal cells are more sensitive than epithelial cells to the regulation of AR levels by androgen.

Identification of the oxidative 3alpha-hydroxysteroid dehydrogenase activity of rat Leydig cells as type II retinol dehydrogenase

Dihydrotestosterone (DHT) is the most potent naturally occurring androgen, and its production in the testis may have important consequences in developmental and reproductive processes. In the rat testis, three factors can contribute to intracellular DHT levels: 1) synthesis of DHT from T by 5alpha-reductase, 2) conversion of DHT to 5alpha-androstane-3alpha, 17beta-diol (3alpha-DIOL) by the reductive activity of 3alpha-hydroxysteroid dehydrogenase (3alpha-HSD), and 3) conversion of 3alpha-DIOL by an oxidative 3alpha-HSD activity. While the type I 3alpha-HSD enzyme (3alpha-HSD1 or AKR1C9) is an oxidoreductase in vitro and could theoretically be responsible for factors 2 and 3, we have shown previously that rat Leydig cells have two 3alpha-HSD activities: a cytosolic NADP(H)- dependent activity, characteristic of 3alpha-HSD1, and a microsomal NAD(H)-dependent activity. The two activities were separable by both developmental and biochemical criteria, but the identity of the second enzyme was unknown. To identify the microsomal NAD(H)-dependent 3alpha-HSD in rat Leydig cells, degenerate primers were used to amplify a number of short-chain alcohol dehydrogenases. Sequence analysis of cloned PCR products identified retinol dehydrogenase type II (RoDH2) as the prevalent species in purified Leydig cells. RoDH2 cDNA was subcloned into expression vectors and transiently transfected into CHOP and COS-1 cells. Its properties were compared with transiently transfected 3alpha-HSD1. When measured in intact CHOP and COS-1 cells, RoDH2 cDNA produced a protein that catalyzed the conversions of 3alpha-DIOL to DHT and androsterone to androstanedione, but not the reverse reactions. Therefore, the 3alpha-HSD activity of RoDH2 was exclusively oxidative. In contrast, type I 3alpha-HSD cDNA produced a protein that was exclusively a 3alpha-HSD reductase. In cell homogenates and subcellular fractions, RoDH2 catalyzed both 3alpha-HSD oxidation and reduction reactions that were NAD(H) dependent, and the enzyme activities were located in the microsomes. Type I 3alpha-HSD also catalyzed both oxidation and reduction, but was located in the cytosol and was NADP(H) dependent. We conclude that type I 3alpha-HSD and RoDH2 have distinct 3alpha-HSD activities with opposing catalytic directions, thereby controlling the rates of DHT production by Leydig cells.

Point mutation in kit receptor tyrosine kinase reveals essential roles for kit signaling in spermatogenesis and oogenesis without affecting other kit responses

The Kit receptor tyrosine kinase functions in hemato- poiesis, melanogenesis and gametogenesis. Kit receptor-mediated cellular responses include proliferation, survival, adhesion, secretion and differentiation. In mast cells, Kit-mediated recruitment and activation of phosphatidylinositol 3'-kinase (PI 3-kinase) produces phosphatidylinositol 3'-phosphates, plays a critical role in mediating cell adhesion and secretion and has contributory roles in mediating cell survival and proliferation. To investigate the consequences in vivo of blocking Kit-mediated PI 3-kinase activation we have mutated the binding site for the p85 subunit of PI 3-kinase in the Kit gene, using a knock-in strategy. Mutant mice have no pigment deficiency or impairment of steady-state hematopoiesis. However, gametogenesis is affected in several ways and tissue mast cell numbers are affected differentially. While primordial germ cells during embryonic development are not affected, Kit(Y719F)/Kit(Y719F) males are sterile due to a block at the premeiotic stages in spermatogenesis. Furthermore, adult males develop Leydig cell hyperplasia. The Leydig cell hyperplasia implies a role for Kit in Leydig cell differentiation and/or steroidogenesis. In mutant females follicle development is impaired at the cuboidal stages resulting in reduced fertility. Also, adult mutant females develop ovarian cysts and ovarian tubular hyperplasia. Therefore, a block in Kit receptor-mediated PI 3-kinase signaling may be compensated for in hematopoiesis, melanogenesis and primordial germ cell development, but is critical in spermatogenesis and oogenesis.

A metabolite of methoxychlor, 2,2-bis(p-hydroxyphenyl)-1,1, 1-trichloroethane, reduces testosterone biosynthesis in rat leydig cells through suppression of steady-state messenger ribonucleic acid levels of the cholesterol side-chain cleavage enzyme

Postnatal development of Leydig cells involves transformation through three stages: progenitor, immature, and adult Leydig cells. The process of differentiation is accompanied by a progressive increase in the capacity of Leydig cells to produce testosterone (T). T promotes the male phenotype in the prepubertal period and maintains sexual function in adulthood; therefore, disruption of T biosynthesis in Leydig cells can adversely affect male fertility. The present study was designed to evaluate the ability of a xenoestrogen, methoxychlor (the methoxylated isomer of DDT [1,1, 1-trichloro-2,2-bis(p-chlorophenyl)ethane]), to alter Leydig cell steroidogenic function. Purified progenitor, immature, and adult Leydig cells were obtained from, respectively, 21-, 35-, and 90-day-old Sprague-Dawley rats treated with graded concentrations of the biologically active metabolite of methoxychlor, 2, 2-bis(p-hydroxyphenyl)-1,1,1-trichloroethane (HPTE), and assessed for T production. HPTE caused a dose-dependent inhibition of basal and LH-stimulated T production by Leydig cells. Compared to the control value, reduced T production by progenitor and immature Leydig cells was apparent after 10 h of HPTE treatment in culture; the equivalent time for adult Leydig cells was 18 h. The reversibility of HPTE-induced inhibition was evaluated by incubating Leydig cells for 3, 6, 10, 14, or 18 h and measuring T production after allowing time for recovery. After treatment with HPTE for 3 h, T production by immature and adult Leydig cells for the 18-h posttreatment period was similar to the control value, but that of progenitor Leydig cells was significantly lower. The onset of HPTE action and the reversibility of its effect showed that Leydig cells are more sensitive to this compound during pubertal differentiation than in adulthood. T production was comparable when control and HPTE-treated immature Leydig cells were incubated with pregnenolone, progesterone, and androstenedione, but HPTE-treated Leydig cells produced significantly reduced amounts of T when incubations were conducted with 22R-hydroxycholesterol (P < 0.01). This finding suggested that HPTE-induced inhibition of T production is related to a decrease in the activity of cytochrome P450 cholesterol side-chain cleavage enzyme (P450(scc)) and cholesterol utilization. The reduced steady-state mRNA level for P450(scc) in HPTE-treated Leydig cells was demonstrated by reverse transcription-polymerase chain reaction and densitometry. In conclusion, this study showed that HPTE causes a direct inhibition of T biosynthesis by Leydig cells at all stages of development. This effect suggests that reduced T production could be a contributory factor in male infertility associated with methoxychlor and, possibly, other DDT-related compounds.

Initial predominance of the oxidative activity of type I 11beta-hydroxysteroid dehydrogenase in primary rat Leydig cells and transfected cell lines

Glucocorticoids suppress testosterone production in Leydig cells. The level of glucocorticoid action is set within the Leydig cell by the number of glucocorticoid receptors and by the activity of 11beta-hydroxysteroid dehydrogenase (11betaHSD). This enzyme acts either as an oxidase inactivating glucocorticoid or as a reductase amplifying its action. It is currently unknown whether extracellular conditions might cause 11betaHSD oxidative and reductive activities in Leydig cells to change inversely or independently. The aim of the present study was to determine whether extracellular conditions set in vitro by various culture time and media components, such as glucose and pyruvate, affect the relative rates of 11betaHSD oxidation and reduction. Primary rat Leydig cells and cell lines (COS1 and CHOP cells) transfected with 11betaHSD-I complementary DNA (cDNA), were incubated with 25 nmol/L (physiologic range) or 500 nmol/L (stress range) concentrations of radiolabeled substrates, corticosterone or 11-hydrocorticosterone, for 0 to 24 hours. Oxidative activity predominated over reductive activity under initial conditions when product formation increased linearly with time. For example, in Dulbecco's modified Eagle medium/F12 medium (containing 5.5 mmol/L glucose), the peak ratio of oxidation to reduction (with 1 denoting equivalence of oxidative and reductive activities) was 5.5 in rat Leydig cells, 19.7 in COS1 cells, and 20.8 in CHOP cells. Glucose stimulated reductive activity but did not change the predominant direction of 11betaHSD catalysis at earlier times. In COS1 cells transfected with 11betaHSD-I cDNA, oxidative activity rapidly increased during the first 2 hours of the incubation, then gradually decreased while reductive activity increased steadily. The relative ratio of oxidation to reduction rapidly declined to less than 0.5 at 6 hours, and thus the favored direction of catalysis changed from oxidation to reduction. However, in transfected CHOP cells, 11betaHSD oxidative activity rapidly increased during the first 2 hours and continued to increase for 24 hours. The ratio of oxidative to reductive activity rapidly declined but kept above 1 in CHOP cells for 24 hours, and the favored direction of catalysis remained predominantly oxidative. These results revealed that 11betaHSD-I is a predominant oxidase initially in Leydig cells and 2 cell lines, and that the oxidative activity is gradually lost over time. The data suggest that type I 11betaHSD is a predominant oxidase in Leydig cells in vivo.