A differential molecular biology search for genes preferentially expressed in functional T lymphocytes: the CTLA genes

Analysis of the heterogeneity and complexity of murine extraorbital lacrimal gland via single-cell RNA sequencing

PURPOSE

The lacrimal gland is essential for maintaining ocular surface health and avoiding external damage by secreting an aqueous layer of the tear film. However, a healthy lacrimal gland's inventory of cell types and heterogeneity remains understudied.

METHODS

Here, 10X Genome-based single-cell RNA sequencing was used to generate an unbiased classification of cellular diversity in the extraorbital lacrimal gland (ELG) of C57BL/6J mice. From 43,850 high-quality cells, we produced an atlas of cell heterogeneity and defined cell types using classic marker genes. The possible functions of these cells were analyzed through bioinformatics analysis. Additionally, the CellChat was employed for a preliminary analysis of the cell-cell communication network in the ELG.

RESULTS

Over 37 subclasses of cells were identified, including seven types of glandular epithelial cells, three types of fibroblasts, ten types of myeloid-derived immune cells, at least eleven types of lymphoid-derived immune cells, and five types of vascular-associated cell subsets. The cell-cell communication network analysis revealed that fibroblasts and immune cells play a pivotal role in the dense intercellular communication network within the mouse ELG.

CONCLUSIONS

This study provides a comprehensive transcriptome atlas and related database of the mouse ELG.

Exploring Immune Cell Diversity in the Lacrimal Glands of Healthy Mice: A Single-Cell RNA-Sequencing Atlas

The lacrimal gland is responsible for maintaining the health of the ocular surface through the production of tears. However, our understanding of the immune system within the lacrimal gland is currently limited. Therefore, in this study, we utilized single-cell RNA sequencing and bioinformatic analysis to identify and analyze immune cells and molecules present in the lacrimal glands of normal mice. A total of 34,891 cells were obtained from the lacrimal glands of mice and classified into 18 distinct cell clusters using Seurat clustering. Within these cell populations, 26 different immune cell subpopulations were identified, including T cells, innate lymphocytes, macrophages, mast cells, dendritic cells, and B cells. Network analysis revealed complex cell-cell interactions between these immune cells, with particularly significant interactions observed among T cells, macrophages, plasma cells, and dendritic cells. Interestingly, T cells were found to be the main source of ligands for the Thy1 signaling pathway, while M2 macrophages were identified as the primary target of this pathway. Moreover, some of these immune cells were validated using immunohistological techniques. Collectively, these findings highlight the abundance and interactions of immune cells and provide valuable insights into the complexity of the lacrimal gland immune system and its relevance to associated diseases.

Endocrine Toxicity of Cancer Immunotherapy Targeting Immune Checkpoints

Immune checkpoints are small molecules expressed by immune cells that play critical roles in maintaining immune homeostasis. Targeting the immune checkpoints cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) and programmed death 1 (PD-1) with inhibitory antibodies has demonstrated effective and durable antitumor activity in subgroups of patients with cancer. The US Food and Drug Administration has approved several immune checkpoint inhibitors (ICPis) for the treatment of a broad spectrum of malignancies. Endocrinopathies have emerged as one of the most common immune-related adverse events (irAEs) of ICPi therapy. Hypophysitis, thyroid dysfunction, insulin-deficient diabetes mellitus, and primary adrenal insufficiency have been reported as irAEs due to ICPi therapy. Hypophysitis is particularly associated with anti-CTLA-4 therapy, whereas thyroid dysfunction is particularly associated with anti-PD-1 therapy. Diabetes mellitus and primary adrenal insufficiency are rare endocrine toxicities associated with ICPi therapy but can be life-threatening if not promptly recognized and treated. Notably, combination anti-CTLA-4 and anti-PD-1 therapy is associated with the highest incidence of ICPi-related endocrinopathies. The precise mechanisms underlying these endocrine irAEs remain to be elucidated. Most ICPi-related endocrinopathies occur within 12 weeks after the initiation of ICPi therapy, but several have been reported to develop several months to years after ICPi initiation. Some ICPi-related endocrinopathies may resolve spontaneously, but others, such as central adrenal insufficiency and primary hypothyroidism, appear to be persistent in most cases. The mainstay of management of ICPi-related endocrinopathies is hormone replacement and symptom control. Further studies are needed to determine (i) whether high-dose corticosteroids in the treatment of ICPi-related endocrinopathies preserves endocrine function (especially in hypophysitis), and (ii) whether the development of ICPi-related endocrinopathies correlates with tumor response to ICPi therapy.

Low doses of cholera toxin and its mediator cAMP induce CTLA-2 secretion by dendritic cells to enhance regulatory T cell conversion

Immature or semi-mature dendritic cells (DCs) represent tolerogenic maturation stages that can convert naive T cells into Foxp3⁺ induced regulatory T cells (iTreg). Here we found that murine bone marrow-derived DCs (BM-DCs) treated with cholera toxin (CT) matured by up-regulating MHC-II and costimulatory molecules using either high or low doses of CT (CT^hi, CT^lo) or with cAMP, a known mediator CT signals. However, all three conditions also induced mRNA of both isoforms of the tolerogenic molecule cytotoxic T lymphocyte antigen 2 (CTLA-2α and CTLA-2β). Only DCs matured under CT^hi conditions secreted IL-1β, IL-6 and IL-23 leading to the instruction of Th17 cell polarization. In contrast, CT^lo- or cAMP-DCs resembled semi-mature DCs and enhanced TGF-β-dependent Foxp3⁺ iTreg conversion. iTreg conversion could be reduced using siRNA blocking of CTLA-2 and reversely, addition of recombinant CTLA-2α increased iTreg conversion in vitro. Injection of CT^lo- or cAMP-DCs exerted MOG peptide-specific protective effects in experimental autoimmune encephalomyelitis (EAE) by inducing Foxp3⁺ Tregs and reducing Th17 responses. Together, we identified CTLA-2 production by DCs as a novel tolerogenic mediator of TGF-β-mediated iTreg induction in vitro and in vivo. The CT-induced and cAMP-mediated up-regulation of CTLA-2 also may point to a novel immune evasion mechanism of Vibrio cholerae.

Ipilimumab (Anti-Ctla-4 Mab) in the treatment of metastatic melanoma: Effectiveness and toxicity management

In the last years the onset of new therapies changed the management of malignant melanoma. Anti CTLA-4 antibody ipilimumab was the first drug to achieve a significant improvement in survival of advanced stage melanoma. This new therapeutic agent is characterized by a number of side effects that are totally different from those of traditional chemotherapy, mainly caused by the immune system activation. The purpose of this paper is to underline the central role of ipilimumab in the treatment of metastatic melanoma and to characterize related adverse events in terms of incidence, duration and severity of presentation. The early recognition of these side effects is crucial in order to ensure an appropriate management of the toxicities, thus reducing the long term clinical sequelae and the inappropriate treatment discontinuation.

Identification of CTLA2A, DEFB29, WFDC15B, SERPINA1F and MUP19 as Novel Tissue-Specific Secretory Factors in Mouse

Secretory factors in animals play an important role in communication between different cells, tissues and organs. Especially, the secretory factors with specific expression in one tissue may reflect important functions and unique status of that tissue in an organism. In this study, we identified potential tissue-specific secretory factors in the fat, muscle, heart, lung, kidney and liver in the mouse by analyzing microarray data from NCBI’s Gene Expression Omnibus (GEO) public repository and searching and predicting their subcellular location in GeneCards and WoLF PSORT, and then confirmed tissue-specific expression of the genes using semi-quantitative PCR reactions. With this approach, we confirmed 11 lung, 7 liver, 2 heart, 1 heart and muscle, 7 kidney and 2 adipose and liver-specific secretory factors. Among these genes, 1 lung-specific gene - CTLA2A (cytotoxic T lymphocyte-associated protein 2 alpha), 3 kidney-specific genes - SERPINA1F (serpin peptidase inhibitor, Clade A, member 1F), WFDC15B (WAP four-disulfide core domain 15B) and DEFB29 (defensin beta 29) and 1 liver-specific gene - MUP19 (major urinary protein 19) have not been reported as secretory factors. These genes were tagged with hemagglutinin at the 3’end and then transiently transfected to HEK293 cells. Through protein detection in cell lysate and media using Western blotting, we verified secretion of the 5 genes and predicted the potential pathways in which they may participate in the specific tissue through data analysis of GEO profiles. In addition, alternative splicing was detected in transcripts of CTLA2A and SERPINA1F and the corresponding proteins were found not to be secreted in cell culture media. Identification of novel secretory factors through the current study provides a new platform to explore novel secretory factors and a general direction for further study of these genes in the future.

CTLA-4 blockade with ipilimumab: biology, safety, efficacy, and future considerations

Melanoma remains a critical public health problem worldwide. Patients with stage IV disease have very poor prognosis and their 1-year survival rate is only 25%. Until recently, systemic treatments with a positive impact on overall survival (OS) had remained elusive. In recent years, the United States Food and Drug Administration (FDA) – approved several novel agents targeting the RAS/RAF/MEK/ERK pathway (vemurafenib, dabrafenib, and trametinib) – critical in cell division and proliferation of melanoma, and an immune checkpoint inhibitor (ipilimumab) directed against the cytotoxic T lymphocyte Antigen - (CTLA-4). Moreover, recent reports of clinical trials studying other immune checkpoint modulating agents will most likely result in their FDA approval within the next months. This review focuses on ipilimumab, its safety and efficacy, and future considerations. Ipilimumab has demonstrated a positive OS impact after a several-year follow-up. It is also recognized that due to its mechanism of action, the response patterns to ipilimumab can differ from those observed in patients following treatment with conventional cytotoxic agents and even the most recently approved BRAF inhibitors. Most patients (84.8%) experience drug-related adverse events (AEs) of any grade; most of these are mild to moderate and immune mediated. However, a minority of patients may also experience severe and life-threatening AEs. In clinical studies, AEs were managed according to guidelines that emphasized close clinical monitoring and early use of corticosteroids when appropriate. Preliminary results have taught us the potential greater toxicity when in combination with vemurafenib, and the greater antitumor efficacy when combined with nivolumab, a monoclonal antibody directed against programmed death receptor-1 (PD-1), another immune checkpoint inhibitor. Future challenges include the optimization of dosing and toxicities when used as a single agent, and studying the safety and efficacy of combinations with targeted small molecules and other monoclonal antibodies to treat patients with melanoma and other malignancies.

A history of microarrays in biomedicine

The fundamental strategy of the current postgenomic era or the era of functional genomics is to expand the scale of biologic research from studying single genes or proteins to studying all genes or proteins simultaneously using a systematic approach. As recently developed methods for obtaining genome-wide mRNA expression data, oligonucleotide and DNA microarrays are particularly powerful in the context of knowing the entire genome sequence and can provide a global view of changes in gene expression patterns in response to physiologic alterations or manipulation of transcriptional regulators. In biomedical research, such an approach will ultimately determine biologic behavior of both normal and diseased tissues, which may provide insights into disease mechanisms and identify novel markers and candidates for diagnostic, prognostic and therapeutic intervention. However, microarray technology is still in a continuous state of evolution and development, and it may take time to implement microarrays as a routine medical device. Many limitations exist and many challenges remain to be achieved to help inclusion of microarrays in clinical medicine. In this review, a brief history of microarrays in biomedical research is provided, including experimental overview, limitations, challenges and future developments.

Cytotoxic T lymphocyte antigen-2 alpha induces apoptosis of murine T-lymphoma cells and cardiac fibroblasts and is regulated by cAMP/PKA

The mechanism of cAMP-promoted apoptosis is not well defined. In wild-type (WT) murine S49 lymphoma cells, cAMP promotes apoptosis in a protein kinase A (PKA)-dependent manner. We find that treatment of WT S49 cells with 8-CPT-cAMP prominently increases the expression (as determined by DNA microarray analysis, real-time PCR and immunblotting) of cytotoxic T lymphocyte antigen-2α (CTLA-2α), a cathepsin L-like cysteine protease inhibitor. By contrast, CTLA-2α expression is only slightly increased by 8-CPT-cAMP treatment of D-S49 cells, which lack cAMP/PKA-promoted apoptosis. Raising endogenous cAMP (by use of forskolin or inhibition of phosphodiesterase [PDE] 4) or a PKA-selective, but not an Epac-selective, cAMP analogue, increases CTLA-2α mRNA expression; PKA, and not Epac, thus mediates the increase in CTLA-2α expression. An adenoviral CLTA-2α (Ad-CTLA-2α) construct induces apoptosis and enhances cAMP-promoted apoptosis in WT S49 cells but such cells do not have an increase in cathepsin L activity nor does a cathepsin L inhibitor alter cAMP-promoted apoptosis. 8-CPT-cAMP also increases CTLA-2α expression and induces apoptosis in murine cardiac fibroblasts; knockdown of CTLA-2α expression by siRNA blocks 8-CPT-cAMP-promoted apoptosis. Thus, cAMP increases CTLA-2α expression in murine lymphoma and cardiac fibroblasts and this increase in CTLA-2α contributes to cAMP/PKA-promoted apoptosis by mechanisms that are independent of the ability of CTLA-2α to inhibit cathepsin L.

Costimulation of Th17 cells: Adding fuel or putting out the fire in the inflamed gut?

Inflammatory bowel disease, typified by Crohn's disease and ulcerative colitis, is a common disorder characterized by recurrent and serious inflammation of the gastrointestinal tract. It is well documented that T cells play a pivotal role in the development of inflammatory bowel disease. Th17 cells are a unique T cell subpopulation implicated in inflammatory bowel disease and many other autoimmune/inflammatory diseases. However, the regulatory mechanism of Th17 activation and proliferation has not been defined completely. Recent studies have shown that the ligation of several costimulatory receptor-ligand pairs contributes to the activation, differentiation, and proliferation of T lymphocytes including the Th17 subset. In this review, we will discuss the emerging evidence on the role of Th17 cells in inflammatory bowel disease pathogenesis as well as the effect of costimulatory molecules on Th17 development and consider if the need for such costimulation of T lymphocytes provides a target for the development of novel therapeutic strategy.

The clinical utility of inhibiting CD28-mediated costimulation

SUMMARY

This volume covers many topics in the field of T-cell costimulation. The need for such a volume is testament to the growth of the field. From its beginning as a concept in the 1980s, we have now progressed to the point where many molecules now have functionally defined roles in T-cell costimulation. In addition, the field has progressed 'from bench to bedside'. Abatacept [cytotoxic T-lymphocyte antigen-4 (CTLA-4)-immunoglobulin (Ig) (CTLA-4-Ig)], an inhibitor of CD28-mediated T-cell costimulation, was approved for the treatment of moderate-to-severe rheumatoid arthritis in 2006 by the Food and Drug Administration and in 2007 by the European Medicines Agency. This chapter first presents a personal historical perspective on the early basic studies on the elucidation of the CD28/B7 T-cell costimulatory pathway and the discovery of CTLA-4-Ig. We next present an overview of studies of CTLA-4-Ig in preclinical animal studies. The material discussed in these first two sections is selective rather than exhaustive; their purpose is to provide context for the final section, a summary of human clinical studies performed with abatacept.

Chipping into the human genome: novel insights for transplantation

High throughput, high density platforms for transcriptional, proteomic, and metabonomic analyses are opening new doors for improving our understanding of the complexity and redundancy of the immune system in the interplay of the innate and allo-immune responses in organ transplantation. New insights are being obtained into the possible discrepancies between the gold standard of tissue pathological diagnosis and clinical graft outcomes, as new transcriptional categories of transplant rejection evolve. The bystander effects of chronic immunosuppression underlying the complexities of graft dysfunction are beginning to be understood. Non-invasive mechanisms to monitor transplants, by following 'footprints' of biomarker sets that reflect the disease phenotype, are being pursued for their clinical application for direct patient care. Utilization of these same biomarker sets may also offer a unique means to titrate immunosuppression and predict specific graft dysfunction events prior to clinical decline, thus bringing in the potential to reduce patient morbidity from infection and malignancy, preserve graft integrity, and limit the progression of chronic graft injury. Bioinformatics support is integral to the unraveling of the mysteries of the human genome, proteome, and metabolome in disease and in health.

T lymphocyte activation gene identification by coregulated expression on DNA microarrays

High-capacity methods for assessing gene function have become increasingly important because of the increasing number of newly identified genes emerging from large-scale genome sequencing and cDNA cloning efforts. We investigated the use of DNA microarrays to identify uncharacterized genes specifically involved in human T cell activation. Activation of human peripheral blood T lymphocytes induced significant changes in hundreds of transcripts, but most of these were not unique to T cell activation. Variation of experimental parameters and analysis techniques allowed better enrichment for gene expression changes unique to T cell activation. Best results were achieved by identification of genes that were most highly coregulated with the T-cell-specific transcript interleukin 2 (IL2) in a "compendium" of experiments involving both T cells and other cell types. Among the genes most highly coregulated with IL2 were many genes known to function during T cell activation, together with ESTs of unknown function. Four of these ESTs were extended to novel full-length clones encoding T-cell-regulated proteins with predicted functions in GTP metabolism, cell organization, and signal transduction.

Arraying the orchestration of allograft pathology

Microarrays, or gene chips, are exciting investigative tools for analyzing expression changes across thousands of genes in concert in tissues and cells of interest. Despite the relatively recent application of microarrays to transplant research, they hold great promise for unraveling the staging of rejection, stratifying patients towards more individualized treatment regimes, and discovering noninvasive biomarkers for monitoring of intragraft events. Bioinformatics tools are being developed to sift through the large data sets generated as "genomic fingerprints" of the underlying biologic pathways. Gene clustering and class prediction tools allow discovery of diagnostic and prognostic molecular signatures of health and disease. Oligonucleotide-based microarrays also have utility in genotyping polymorphic markers. This report reviews the current literature of microarray use in transplantation research, compares currently available array platforms, and discusses future application of this technology to clinical organ transplantation.

Induction of Cytotoxic T-lymphocyte Antigen-2β, A Cysteine Protease Inhibitor in Decidua

During early pregnancy, the steroid hormone progesterone induces differentiation of uterine stroma to decidual cells, which regulate embryo-uterine interactions. The progesterone-induced signaling molecules that participate in the formation and function of decidua remain poorly understood. We recently utilized high-density oligonucleotide microarrays to identify several genes whose expression is markedly altered in pregnant uterus in response to RU486, a well characterized antagonist of the progesterone receptor (PR). Our study revealed that the gene encoding cytotoxic T-lymphocyte antigen-2beta (CTLA-2beta), a cysteine protease inhibitor, is expressed during PR-induced decidualization. The spatio-temporal expression of CTLA-2beta mRNA precisely overlapped with the decidual phase of pregnancy. Interestingly, administration of progesterone to estrogen-primed ovariectomized mice failed to induce CTLA-2beta expression. A concomitant artificial decidual stimulation was necessary to trigger this expression. Uteri of PR knockout mice failed to express this mRNA, even after a combined administration of steroid hormones and artificial stimulation. The uterine expression of CTLA-2beta was, therefore, dependent on PR as well as other unknown factor(s) associated with decidual response. To identify the molecular target(s) of CTLA-2beta,we analyzed its interaction with proteins present in soluble extracts prepared from day 7 pregnant uteri containing implanted embryos. A protein affinity strategy employing recombinant CTLA-2beta helped us to determine that cathepsin L, a cysteine protease, is one of its targets in the pregnant uterus. Consistent with this finding, expression of cathepsin L was detected in the giant trophoblast cells of the ectoplacental cone on day 7 of pregnancy. Collectively, our results support the hypothesis that expression of CTLA-2beta in the decidua may regulate implantation of the embryo by neutralizing the activities of one or more proteases generated by the proliferating trophoblast.

Historical background and anticipated developments

Expression profiling using DNA arrays is often believed to have appeared during the second half of the 1990s, and to be based exclusively on nonisotopic methods. In fact, the first article describing the application of cDNA arrays to expression analysis was published in 1992, relied on radioactive labeling, and was a new development of "high-density" membranes used until then essentially for efficient screening of libraries. Several papers described the use of this technology for simultaneous expression measurement of thousands of genes at the time when the first glass microarrays were published. Simultaneously, oligonucleotide chips, originally developed for resequencing and mutation detection applications, were shown to be capable of expression measurement as well. The three approaches have developed over the years and still coexist, as each of them has specific advantages (and drawbacks); the major issues have become those of data quality, data analysis and storage (ideally in a common public database). Meanwhile, the technology continues to evolve. The most obvious trend is a shift towards using arrays of relatively long oligonucleotides that combine most of the advantages of very long (cDNA) and very short (25-mer) DNA segments. The search for better detection methods, ideally without labeling of the sample, is continuing, although it seems difficult to reach the required sensitivity. New materials for microarray manufacture and new implementations of existing methods have appeared. In addition, the field is progressively becoming segmented into high gene number, low volume (research) applications on the one hand, and low gene number, high throughput (diagnostic) uses on the other.

A native soluble form of CTLA-4

CTLA-4 is an immunoregulatory receptor expressed on the surface of activated T and B lymphocytes. The counterreceptors for CTLA-4 are the B7 family molecules. We describe alternatively spliced mRNAs expressed in hematolymphoid tissues of humans, mice, and rats that lack the transmembrane domain coded by exon 3 of the CTLA-4 gene. These alternate transcripts were detected by RT-PCR in B cells and resting T cells of both the CD4 and the CD8 phenotype. Activation of human blood mononuclear cells with PHA or anti-CD3 + anti-CD28 monoclonal antibodies appears to effect a decrease in the amount of the alternative transcript relative to the full-length transcript. Recombinant sCTLA-4 is a B7-binding protein and has immunomodulatory effects as measured by inhibition of the mixed leukocyte response. Human serum contains immunoreactive material consistent with a native soluble form of CTLA-4.

Granulysin: a novel antimicrobial peptide of cytolytic T lymphocytes and natural killer cells

Granulysin is a novel antimicrobial protein produced by human cytolytic T lymphocytes and natural killer cells. It is active against a broad range of microbes, including Gram-positive and Gram-negative bacteria, fungi, and parasites. The fact that it kills Mycobacterium tuberculosis is particularly important, since the current vaccine (Bacille Calmette-Guerin, BCG) is of limited efficacy and antibiotic resistance is increasing. Although functionally related to other antibacterial peptides, defensins and magainins, granulysin is structurally distinct. Like porcine NK lysin and amoebapores made by Entamoeba histolytica, granulysin is related to saposins, small lipid-associated proteins present in the central nervous system. The identification of this novel molecule indicates a broader and perhaps more significant role for T lymphocytes in both innate and acquired antimicrobial defenses.

Genetic, physical, and transcript map of the fld region on mouse chromosome 12

The fatty liver dystrophy (fld) mutation is manifested in abnormalities of lipid and glucose metabolism and peripheral neuropathy. To identify the gene affected by this mutation, we generated a genetic map of the fld region on chromosome 12 by the analysis of F2 offspring from an intersubspecific cross between strains BALB/cByJ-fld and CAST/EiJ. The results localize fld to the 0.42-cM interval between the microsatellite markers D12Mit170 and D12Mit184. A contig of YACs and BACs covering the nonrecombinant genomic region has been constructed and used for the identification of genes. Expressed sequence tag mapping and exon trapping identified three transcripts within the critical interval: Ctla2b, which encodes a cysteine protease inhibitor, and mouse homologs of KIAA0188 and KIAA0575, two long human transcripts of unknown function. Expression analysis revealed that Kiaa0188 is expressed in wildtype but not in fld liver, implicating this gene as a candidate for harboring the fld mutation.

Sphingomyelin-ceramide turnover in CD28 costimulatory signaling

When the CD28 membrane glycoprotein of T cells binds to its ligand, a signal is transmitted that is required for T cell receptor-induced proliferation and cytokine secretion: T cells are not stimulated by the CD28 signal alone. Ligation of CD28 initiated sphingomyelin hydrolysis and generated ceramide. Treatment of T cells with either exogenous sphingomyelinase or a cell-permeable ceramide analogue. C6-ceramide, mimicked the CD28 signal by inducing T cell proliferation and interleukin-2 gene transcription. Stabilization of interleukin-2 mRNA was also observed in C6-ceramide-treated cells. Thus, the sphingomyelin-ceramide pathway is a candidate for mediating the costimulatory signal.

T cells of staphylococcal enterotoxin B-tolerized autoimmune MRL-lpr/lpr mice require co-stimulation through the B7-CD28/CTLA-4 pathway for activation and can be reanergized in vivo by stimulation of the T cell receptor in the absence of this co-stimulatory signal

The CD28/CTLA-4 receptors on T cells interact with the B7 molecule on antigen-presenting cells (APC) to produce a co-stimulatory signal that determines the outcome of activation. The role of this co-stimulatory signal in T cell activation and loss of tolerance in autoimmune MRL-lpr/lpr mice has not been investigated previously. The present study examines the contribution of the CD28/CTLA-4 co-stimulatory pathway to the loss of T cell tolerance in V beta 8 transgenic MRL-lpr/lpr and (-)+/+ mice in which neonatal tolerance has been induced by the superantigen staphylococcal enterotoxin B (SEB). An artificial APC transfected with the murine B7 gene, and a CTLA-4-Ig fusion protein were used to analyze the significance of the CD28/CTLA-4 pathway in vitro. The CTLA-4-Ig fusion protein was also used to inhibit the pathway in vivo. Our results demonstrate that CD28 and CTLA-4 mRNA was overexpressed in the lymph nodes of lpr/lpr mice (MRL, C57BL/6, C3H and AKR), but not in +/+ mice of the same background strain. Lymph node T cells and thymocytes from SEB neonatally tolerized MRL-lpr/lpr mice that had undergone tolerance loss, proliferated when cultured with SEB and B7+ fibroblasts in vitro, but did not proliferate when the SEB was presented in the context of B7- fibroblasts. This in vitro tolerance loss could be prevented by blocking of B7 signaling by CTLA-4-Ig. This loss of tolerance did not occur in lymph node T cells from thymectomized MRL-lpr/lpr mice. SEB challenge of tolerized MRL-lpr/lpr mice in vivo led to weight loss, increased serum cytokine levels and depletion of V beta 8+ T cells. These effects were blocked by blocking of the co-stimulatory pathway by treatment with the CTLA-4-Ig fusion protein prior to and during challenge with SEB. T cells from thymus and lymph nodes of these mice did not proliferate later in response to stimulation in vitro with SEB even in the presence of B7+ APC. Nonresponsiveness was not due to deletion of V beta 8+ CD28+ T cells, as the number of these cells was increased after treatment with SEB and the CTLA-4-Ig fusion protein.(ABSTRACT TRUNCATED AT 250 WORDS)

The B7 adhesion molecule is expressed on activated human T cells: functional involvement in T-T cell interactions

The B cell antigen B7 delivers a strong co-stimulatory signal for the activation of T cells by binding to its ligands CD28 and CTLA4. Here we demonstrate the surface expression of the B7 molecule on activated human T cells in vitro and under certain conditions in vivo and its functional importance in T-T cell interactions. B7 was detected by flow cytometry on antigen-specific CD4+ and allospecific CD8+ cloned T cells from different donors with anti-B7 monoclonal antibody (mAb) or a soluble CTLA4-C gamma 1 chimera molecule and by reverse transcription-polymerase chain reactions. The expression of B7 was up-regulated following restimulation of the T cell clones and peaked after 7-9 days. Moreover, we show that the B7 molecule on T cells is functionally involved in T-T cell interactions: mAb to CD28 and the CTLA4-Ig fusion protein could inhibit the proliferation of specific T cell clones in response to T cells as antigen-presenting cells (APC) or the proliferation of peripheral blood mononuclear cells in a primary allostimulation with activated T cells as stimulator cells. Finally, we found that B7 can be expressed on freshly isolated circulating T cells since in a preliminary study with a limited number of patients, B7 was present on a subset of CD3+ cells. B7 was expressed on activated T cells (CD4+ and CD8+) of certain human immunodeficiency virus (HIV)-infected individuals (0.5-20% B7+CD8+ cells) or some patients with autoimmune diseases whereas CD3+ cells of healthy individuals did not express B7. The coexpression of major histocompatibility complex class II molecules and B7 may be relevant for the capacity of activated T cells to function as APC. The expression of B7 on T cells in vivo in autoimmune diseases and in HIV infection may be important for a better understanding of these diseases.

Effects of taxol and taxol/hyperthermia treatments on the functional polarization of cytotoxic T lymphocytes

Immunofluorescence staining, electron microscopy, and (51Cr) cytolytic release assays are used to investigate the effects of taxol and taxol/hyperthermia treatments on the microtubule organization and cytolytic activity of cytotoxic T lymphocytes (CTLs). A 4 h treatment of CTLs with 1 microM taxol results in an extensive reorganization of the microtubule system to form one to a few large microtubule bundles that extend from the centrosome. The Golgi apparatus is not disrupted by this treatment and remains associated with the microtubule organizing centre (MTOC). This microtubule reorganization has no effect on the ability of CTLs to orient their MTOC towards a bound target cell, nor on their cytolytic activity. In control CTLs, not treated with taxol, a mild hyperthermia treatment (42 degrees C, 30 min) results in an aggregation of the pericentriolar material, a loss of MTOC orientation, an inhibition of cytolytic activity, and a disorganization of the microtubule system [Knox et al.: Exp. Cell Res. 194:275-283, 1991]. In contrast, in taxol-treated CTLs the stabilized microtubule bundles are unaffected by such hyperthermia treatment; however, the other effects of hyperthermia appear identical in control and taxol-treated CTLs. These results indicate that a dynamic, radially arranged microtubule array is not required for the functional polarization of CTLs and suggest that a component of the pericentriolar material may play a key role in effecting MTOC orientation.

Cytotoxicity with target DNA breakdown by rat basophilic leukemia cells expressing both cytolysin and granzyme A

The noncytotoxic rat mast cell tumor line RBL was transfected with genes for the cytotoxic lymphocyte granule proteins cytolysin (perforin) and granzyme A, giving transfectants with mRNA and protein expression levels comparable with cloned cytotoxic T lymphocytes. Both RBL-cytolysin and RBL-cytolysin-granzyme A transfectants showed extremely potent killing of red cell targets and lysed 20%-60% of EL4 lymphoma targets at an effector-to-target ratio of 30. RBL transfectants expressing only granzyme A were not cytotoxic. Significant EL4 DNA breakdown accompanying lysis was observed only with RBL that was transfected with both cytolysin and granzyme A. These results support the granule-exocytosis model for lymphocyte cytotoxicity and show that effector granzyme A plays a role in target cell DNA breakdown.

Murine B7 antigen provides an efficient costimulatory signal for activation of murine T lymphocytes via the T-cell receptor/CD3 complex

We demonstrate that the murine B7 (mB7) protein is a potent costimulatory molecule for the activation of resting murine CD4+ T cells through the T-cell receptor (TCR)/CD3 complex. Stable mB7-transfected Chinese hamster ovary cells, but not vector-transfected controls, synergize with anti-CD3 monoclonal antibody and Con A-induced T-cell activation, resulting ultimately in proliferation. mB7 exerted its effect by inducing production of interleukin 2 and expression of the interleukin 2 receptor. Thus, mB7 costimulates T-cell activation through the TCR/CD3 complex by positively modulating the normal pathway of T-cell expansion. In contrast to the pronounced effect of mB7 on the activation of T cells through the TCR/CD3 complex, the mB7-transfected CHO cell line costimulated T-cell activation via the glycosylphosphatidylinositol-anchored proteins Thy-1 and Ly-6A.2 only inefficiently. Finally, the combination of a calcium ionophore and mB7 is not sufficient to cause T-cell proliferation, while the combination of a calcium ionophore and phorbol 12-myristate 13-acetate (PMA) stimulates T cells efficiently. The signals that mB7 and PMA provide for murine T lymphocyte activation are therefore not interchangeable, although both costimulate activation through the TCR/CD3 complex.

CTLA-4 is a second receptor for the B cell activation antigen B7

Functional interactions between T and B lymphocytes are necessary for optimal activation of an immune response. Recently, the T lymphocyte receptor CD28 was shown to bind the B7 counter-receptor on activated B lymphocytes, and subsequently to costimulate interleukin 2 production and T cell proliferation. CTLA-4 is a predicted membrane receptor from cytotoxic T cells that is homologous to CD28 and whose gene maps to the same chromosomal band as the gene for CD28. It is not known, however, if CD28 and CTLA-4 also share functional properties. To investigate functional properties of CTLA-4, we have produced a soluble genetic fusion between the extracellular domain of CTLA-4 and an immunoglobulin C gamma chain. Here, we show that the fusion protein encoded by this construct, CTLA4Ig, bound specifically to B7-transfected Chinese hamster ovary cells and to lymphoblastoid cells. CTLA4Ig also immunoprecipitated B7 from cell surface 125I-labeled extracts of these cells. The avidity of 125I-labeled B7Ig fusion protein for immobilized CTLA4Ig was estimated (Kd approximately 12 nM). Finally, we show that CTLA4Ig was a potent inhibitor of in vitro immune responses dependent upon cellular interactions between T and B lymphocytes. These findings provide direct evidence that, like its structural homologue CD28, CTLA-4 is able to bind the B7 counter-receptor on activated B cells. Lymphocyte interactions involving the B7 counter-receptor are functionally important for alloantigen responses in vitro.

Effects of hyperthermia on microtubule organization and cytolytic activity of murine cytotoxic T lymphocytes

When murine cytotoxic T lymphocytes (CTL) are heated at 42 degrees C for 30 min their ability to lyse their target cells (TC) is severely impaired. When the CTL are allowed to recover at 37 degrees C, a partial recovery of cytolytic activity that peaks within 6 h is observed. A dye exclusion assay demonstrated that such a heat shock does not affect the viability of the CTL and direct microscopic observations established that their ability to bind to TC is not impaired. Therefore, the step or steps inhibited by hyperthermia are subsequent to TC recognition and binding. Kupfer et al. ((1983) Proc. Natl. Acad. Sci. USA 80, 7224-7228) demonstrated that upon binding to an appropriate TC, a rapid orientation of the Golgi apparatus and the microtubule organizing center (MTOC) occurred within the CTL so that the two organelles face the TC. This orientation is a prerequisite for efficient TC lysis. We have shown by immunofluorescence and confocal microscopy, using a monoclonal antibody to tubulin and a rabbit autoimmune serum that binds a centriole-associated protein, that the organization of the MTOC-microtubule array is disrupted by hyperthermia. EM suggests that this disorganization of the microtubules may result from an aggregation of the pericentriolar material. The recovery of cytolytic activity is coincident with the reorganization of the microtubules about the MTOC. These findings suggest that the initial inhibitory effect of hyperthermia on CTL function results from the disruption of microtubule organization.

Novel structures CTLA-2 alpha and CTLA-2 beta expressed in mouse activated T cells and mast cells and homologous to cysteine proteinase proregions

Differential screening of a subtracted cDNA library led to the detection of two distinct but homologous mouse cDNA, called CTLA-2 alpha and CTLA-2 beta. The corresponding transcripts have a tissue distribution restricted to T lymphocytes, where they are inducible upon activation, and to mast cells. The open-frame regions of both cDNA encode proteins homologous to cysteine proteinase precursors, remarkably, however, only to the proregion of these. The ctla-2 alpha and ctla-2 beta genes both map to the C1 band of mouse chromosome 13. Sequence comparisons suggest that the proregion of an ancestor proteinase gene evolved to the ctla-2 genes by successive duplications, first to autonomy, then to amplification. These results raise the question of the possible role of cysteine proteinase proregions, of cysteine proteinases themselves and of inhibitors thereof in activated T lymphocytes; from a different point of view, they also show that some protease proregions may have evolved as autonomous modules.