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T cell exhaustion is a state of T cell dysfunction associated with expression of programmed death 1 (PD-1). Exhausted [CD8.sup.+] T cells are maintained by self-renewing stem-like T cells that provide differentiated [TIM3.sup.+] cells, a part of which possesses effector-like properties. PD-1-targeted therapies enhance T cell response by promoting differentiation of stem- like T cells toward [TIM3.sup.+] cells, but the role of mTOR during T cell exhaustion remains elusive. Here, we showed that mTOR inhibition has distinct outcomes during the beginning of and after the establishment of chronic viral infection. Blocking mTOR during the T cell expansion phase enhanced the T cell response by causing accumulation of stem-like T cells, leading to improved efficacy of PD-1 immunotherapy; whereas, after exhaustion progressed, mTOR inhibition caused immunosuppression, characterized by decreased [TIM3.sup.+] cells and increased viral load with minimal changes in stem-like T cells. Mechanistically, a cell- intrinsic mTOR signal was vital for differentiation of stem-like T cells into the [TIM3.sup.+] state in the early and late phases of chronic infection as well as during PD-1 immunotherapy. Thus, PD-1 blockade worked after cessation of mTOR inhibition, but simultaneous treatment failed to induce functional [TIM3.sup.+] cells, reducing efficacy of PD-1 immunotherapy. Our data demonstrate that mTOR regulates T cell exhaustion and have important implications for combination cancer therapies with PD-1 blockade., Introduction T cell exhaustion is a state of T cell dysfunction; it is characterized by poor effector function, impaired proliferative capacity, and expression of multiple inhibitory receptors, most notably programmed [...]

Author(s): Jinfang Zhang [1]; Xia Bu [2]; Haizhen Wang [3]; Yasheng Zhu [4]; Yan Geng [3]; Naoe Taira Nihira [1]; Yuyong Tan [1, 5]; Yanpeng Ci [1, 6]; Fei Wu [...]

Author(s): Se Jin Im [1]; Masao Hashimoto [1]; Michael Y. Gerner [2, 3]; Junghwa Lee [1]; Haydn T. Kissick [1, 4]; Matheus C. Burger [5]; Qiang Shan [6]; J. Scott [...]

The immune system influences the fate of developing cancers by not only functioning as a tumour promoter that facilitates cellular transformation, promotes tumour growth and sculpts tumour cell immunogenicity (1-6), but also as an extrinsic tumour suppressor that either destroys developing tumours or restrains their expansion (1,2,7). Yet, clinically apparent cancers still arise in immunocompetent individuals in part as a consequence of cancer-induced immunosuppression. In many individuals, immunosuppression is mediated by cytotoxic T-lymphocyte associated antigen-4 (CTLA-4) and programmed death-1 (PD-1), two immunomodulatory receptors expressed on T cell (s8,9). Monoclonal-antibody-based therapies targeting CTLA-4 and/or PD-1 (checkpoint blockade) have yielded significant clinical benefits--including durable responses--to patients with different malignancies (10-13). However, little is known about the identity of the tumour antigens that function as the targets of T cells activated by checkpoint blockade immunotherapy and whether these antigens can be used to generate vaccines that are highly tumour-specific. Here we use genomics and bioinformatics approaches to identify tumour-specific mutant proteins as a major class of T-cell rejection antigens following anti-PD-1 and/or anti-CTLA-4 therapy of mice bearing progressively growing sarcomas, and we show that therapeutic synthetic long-peptide vaccines incorporating these mutant epitopes induce tumour rejection comparably to checkpoint blockade immunotherapy. Although mutant tumour-antigen-specific T cells are present in progressively growing tumours, they are reactivated following treatment with anti-PD-1 and/or anti-CTLA-4 and display some overlapping but mostly treatment-specific transcriptional profiles, rendering them capable of mediating tumour rejection. These results reveal that tumour-specific mutant antigens are not only important targets of checkpoint blockade therapy, but they can also be used to develop personalized cancer-specific vaccines and to probe the mechanistic underpinnings of different checkpoint blockade treatments., In this study, we used two distinct progresser 3-methylcholanthrene-induced (MCA) sarcoma cell lines (d42m1-T3 and F244) and asked whether they expressed sufficient immunogenicity to be controlled by checkpoint blockade immunotherapy. [...]

The inhibitory receptor programmed cell death 1 (PD-1) plays a major role in functional exhaustion of T cells during chronic infections and cancer, and recent clinical data suggest that blockade [...]

The majority of HIV-infected individuals fail to produce protective antibodies and have diminished responses to new immunizations (1-3). We report here that even though there is an expansion of follicular helper T ([T.sub.FH]) cells in HIV-infected individuals, the cells are unable to provide adequate B cell help. We found a higher frequency of programmed cell death ligand 1 ([PD-L1).sup.+] germinal center B cells from lymph nodes of HIV-infected individuals suggesting a potential role for PD-1-PD-L1 interaction in regulating [T.sub.FH] cell function. In fact, we show that engagement of PD-1 on [T.sub.FH] cells leads to a reduction in cell proliferation, activation, inducible T-cell co-stimulator (ICOS) expression and interleukin-21 (IL-21) cytokine secretion. Blocking PD-1 signaling enhances HIV-specific immunoglobulin production in vitro. We further show that at least part of this defect involves IL-21, as addition of this cytokine rescues antibody responses and plasma cell generation in vitro. Our results suggest that deregulation of [T.sub.FH] cell-mediated B cell help diminishes B cell responses during HIV infection and may be related to PD-1 triggering on [T.sub.FH] cells. These results demonstrate a role for [T.sub.FH] cell impairment in HIV pathogenesis and suggest that enhancing their function could have a major impact on the outcome and control of HIV infection, preventing future infections and improving immune responses to vaccinations., During HIV infection there is a profound deregulation in B cell function (4-6). However, little is known about the underlying mechanisms that alter B cell responses and antibody production at [...]

Hyperimmune activation is a strong predictor of disease progression during pathogenic immunodeficiency virus infections and is mediated in part by sustained type I IFN signaling in response to adventitious microbial infection. The immune inhibitory receptor programmed death-1 (PD-1) regulates functional exhaustion of virus-specific [CD8.sup.+] T cells during chronic infections, and in vivo PD-1 blockade has been shown to improve viral control of SIV. Here, we show that PD-1 blockade during chronic SIV infection markedly reduced the expression of transcripts associated with type I IFN signaling in the blood and colorectal tissue of rhesus macaques (RMs). The effect of PD-1 blockade on type I IFN signaling was durable and persisted even under conditions of high viremia. Reduced type I IFN signaling was associated with enhanced expression of some of the junction-associated genes in colorectal tissue and with a profound decrease in plasma LPS levels, suggesting a possible repair of gut-associated junctions and decreased microbial translocation into the blood. PD-1 blockade enhanced immunity to gut-resident pathogenic bacteria, control of gut-associated opportunistic infections, and survival of SIV-infected RMs. Our results suggest PD-1 blockade as a potential novel therapeutic approach to enhance combination antiretroviral therapy by suppressing hyperimmune activation in HIV-infected individuals., Introduction The immune inhibitory receptor programmed death-1 (PD-1) plays an important role in regulating functional exhaustion of virus-specific CD8+ T cells during chronic infections (1). Studies in mice demonstrated that [...]

During infection with the hepatitis A virus (HAV), most patients develop mild or asymptomatic disease. However, a small number of patients develop serious, life-threatening hepatitis. We investigated this variability in disease severity by examining 30 Argentinean patients with HAV-induced acute liver failure in a case-control, cross-sectional, observational study. We found that HAV-induced severe liver disease was associated with a 6-amino-acid insertion in TIM1/HAVCR1 (157insMTTTVP), the gene encoding the HAV receptor. This polymorphism was previously shown to be associated with protection against asthma and allergic diseases and with HIV progression. In binding assays, the TIM-1 protein containing the 157insMTTTVP insertion polymorphism bound HAV more efficiently. When expressed by human natural killer T (NKT) cells, this long form resulted in greater NKT cell cytolytic activity against HAV-infected liver cells, compared with the shorter TIM-1 protein without the polymorphism. To our knowledge, the 157insMTTTVP polymorphism in TIM1 is the first genetic susceptibility factor shown to predispose to HAV-induced acute liver failure. Furthermore, these results suggest that HAV infection has driven the natural selection of shorter forms of the TIM-1 protein, which binds HAV less efficiently, thereby protecting against severe HAV-induced disease, but which may predispose toward inflammation associated with asthma and allergy., Introduction Hepatitis A virus (HAV) infection, one of the most common viral infections in humans, affects approximately 10 million people annually worldwide. HAV, a single-stranded RNA picornavirus, is transmitted by [...]

Rapid progression to AIDS is a significant problem, especially in developing countries, where the majority of HIV-infected individuals reside. As rapid disease progression is also frequently observed in SIV-infected macaques, they represent a valuable tool to investigate the pathogenesis of this condition in humans. Here, we have shown that pathogenic SIV infection in rhesus macaques resulted in a rapid depletion (as early as week 2) of activated memory B ([CD21.sup.-][CD27.sup.+]; [mB.sub.Act]) cells that was strongly associated with rapid disease progression. This depletion was progressive and sustained in rapid progressors, but less severe and transient in typical progressors. Because of the rapid and sustained depletion of [mB.sub.Act] cells, rapid progressors failed to develop SIV-specific Ab responses, showed a decline in non-SIV-specific Ab titers, and succumbed faster to intestinal bacterial infections. Depletion of [mB.sub.Act] cells was strongly associated with preferential depletion of [mB.sub.Act] cells expressing programmed death-1 (PD-1), and in vitro blockade of PD-1 improved their survival. Furthermore, in vivo PD-1 blockade in SIV-infected macaques enhanced Ab responses to non-SIV as well as SIV Ags. Our results identify depletion of [mB.sub.Act] cells as a very early predictor of rapid disease progression in pathogenic SIV infection and suggest an important role for the PD-1 pathway in depletion of [mB.sub.Act] cells and impaired humoral immune responses in SIV-infected macaques., Introduction The pathogenesis of rapid progression to AIDS following HIV-1 infection remains poorly understood, despite more than 2 decades of intensive study. Rapid disease progression has been substantially curbed by [...]

Allogeneic blood or BM transplantation (BMT) is the most commonly applied form of adoptive cellular therapy for cancer. In this context, the ability of donor T cells to respond to recipient antigens is coopted to generate graft-versus-tumor (GVT) responses. The major reason for treatment failure is tumor recurrence, which is linked to the eventual loss of functional, host-specific CTLs. In this study, we have explored the role of recipient antigen expression by nonhematopoietic cells in the failure to sustain effective CTL immunity. Using clinically relevant models, we found that nonhematopoietic antigen severely disrupts the formation of donor [CD8.sup.+] T cell memory at 2 distinct levels that operate in the early and late phases of the response. First, initial and direct encounters between donor [CD8.sup.+] T cells and nonhematopoietic cells blocked the programming of memory precursors essential for establishing recall immunity. Second, surviving [CD8.sup.+] T cells became functionally exhausted with heightened expression of the coinhibitory receptor programmed death-1 (PD-1). These 2 factors acted together to induce even more profound failure in long-term immunosurveillance. Crucially, the functions of exhausted [CD8.sup.+] T cells could be partially restored by late in vivo blockade of the interaction between PD-1 and its ligand, PD-L1, without induction of graft-versus-host disease, suggestive of a potential clinical strategy to prevent or treat relapse following allogeneic BMT., Introduction Allogeneic blood or BM transplantation (BMT) represents the most commonly applied form of adoptive cellular therapy for cancer. This treatment exploits donor T cell alloreactivity to generate a graft-versus-tumor [...]

[CD8.sup.+] T cells in chronic viral infections such as HIV develop functional defects including loss of interleukin-2 (IL-2) secretion and decreased proliferative potential that are collectively termed 'exhaustion' (1). Exhausted T cells express increased amounts of multiple inhibitory receptors, such as programmed death-1 (PD-1) (2,3), that contribute to impaired virus-specific T cell function. Although reversing PD-1 inhibition is therefore an attractive therapeutic strategy, the cellular mechanisms by which PD-1 ligation results in T cell inhibition are not fully understood. PD-1 is thought to limit T cell activation by attenuating T cell receptor (TCR) signaling (4,5). It is not known whether PD-1 also acts by upregulating genes in exhausted T cells that impair their function. Here we analyzed gene expression profiles from HIV-specific [CD8.sup.+] T cells in individuals with HIV and show that PD-1 coordinately upregulates a program of genes in exhausted [CD8.sub.+] T cells from humans and mice. This program includes upregulation of basic leucine transcription factor, ATF-like (BATF), a transcription factor in the AP-1 family. Enforced expression of BATF was sufficient to impair T cell proliferation and cytokine secretion, whereas BATF knockdown reduced PD-1 inhibition. Silencing BATF in T cells from individuals with chronic viremia rescued HIV-specific T cell function. Thus, inhibitory receptors can cause T cell exhaustion by upregulating genes--such as BATF--that inhibit T cell function. Such genes may provide new therapeutic opportunities to improve T cell immunity to HIV., We hypothesized that inhibitory receptors such as PD-1 function to inhibit T cells not only by reducing TCR signaling but also by inducing the expression of genes that impair T [...]

Inhibitory receptors play a crucial role in regulating CD8 T-cell function during chronic viral infection. T-cell Ig- and mucin-domain--containing molecule-3 (Tim-3) is well known to negatively regulate T-cell responses, but its role in CD8 T-cell exhaustion during chronic infection in vivo remains unclear. In this study, we document coregulation of CD8 T cell exhaustion by Tim-3 and PD-1 during chronic lymphocytic choriomeningitis virus infection. Whereas Tim-3 was only transiently expressed by CD8 T cells after acute infection, virus-specific CD8 T cells retained high Tim-3 expression throughout chronic infection. The majority (approximately 65% to 80%) of lymphocytic choriomeningitis virus--specific CD8 T cells in lymphoid and nonlymphoid organs coexpressed Tim-3 and PD-1. This coexpression of Tim-3 and PD-1 was associated with more severe CD8 T-cell exhaustion in terms of proliferation and secretion of effector cytokines such as IFN-[gamma], TNF-[alpha], and IL-2. Interestingly, CD8 T cells expressing both inhibitory receptors also produced the suppressive cytokine IL-10. Most importantly, combined blockade of Tim-3 and PD-1 pathways in vivo synergistically improved CD8 T cell responses and viral control in chronically infected mice. Taken together, our study defines a parameter for determining the severity of CD8 T cell dysfunction and for identifying virus-specific CD8 T cells that produce IL-10, and shows that targeting both PD-1 and Tim-3 is an effective immune strategy for treating chronic viral infections. doi/ 10.1073/pnas.1009731107

The ability to induce durable transplantation tolerance predictably and consistently in the clinic is a highly desired but elusive goal. Progress is hampered by lack of appropriate experimental models in which to study resistance to transplantation tolerance. Here, we demonstrate that T helper 1-associated T box 21 transcription factor (Tbet) KO recipients exhibit allograft tolerance resistance specifically mediated by IL-17-producing CD8 T (T17) cells. Neutralization of IL-17 facilitates long-term cardiac allograft survival with combined T cell co-stimulation (CD28-CD80/86 and CD154-CD40) blockade in Tbet KO recipients. We have used this T17-biased Tbet KO model of allograft tolerance resistance to study the impact of targeting a T cell-costimulatory pathway, and demonstrate that targeting T cell Ig and mucin domain-1 (Tim-1) with anti-Tim-1 overcomes this resistance by specifically inhibiting the pathogenic IL-17-producing CD8 T17 cells. These data indicate that in the absence of Th1 immunity, CD8 T17 alloreactivity constitutes a barrier to transplantation tolerance. Targeting TIM-1 provides an approach to overcome resistance to tolerance in clinical transplantation. costimulation | IL-17 | rejection | immunosuppression

Chronic immunodeficiency virus infections are characterized by dysfunctional cellular and humoral antiviral immune responses (1-3). As such, immune modulatory therapies that enhance and/or restore the function of virus-specific immunity may protect from disease progression. Here we investigate the safety and immune restoration potential of blockade of the co-inhibitory receptor programmed death 1 (PD-1) (4,5) during chronic simian immunodeficiency virus (SIV) infection in macaques. We demonstrate that PD-1 blockade using an antibody to PD-1 is well tolerated and results in rapid expansion of virus-specific CD8 T cells with improved functional quality. This enhanced T-cell immunity was seen in the blood and also in the gut, a major reservoir of SIV infection. PD-1 blockade also resulted in proliferation of memory B cells and increases in SIV envelope-specific antibody. These improved immune responses were associated with significant reductions in plasma viral load and also prolonged the survival of SIV-infected macaques. Blockade was effective during the early (week 10) as well as late (~week 90) phases of chronic infection even under conditions of severe lymphopenia. These results demonstrate enhancement of both cellular and humoral immune responses during a pathogenic immunodeficiency virus infection by blocking a single inhibitory pathway and identify a novel therapeutic approach for control of human immunodeficiency virus infections., Virus-specific T cells show varying degrees of functional impairment during chronic infections (6,7). Although these T cells retain some antiviral functions, they are less polyfunctional compared with antiviral T cells [...]

Suppression of T-cell responses by host-derived regulatory factors is a key event leading to viral persistence. Antibody blockade of either IL-10 or programmed death-ligand 1 (PD-L1) during viral persistence enhances T-cell function and reduces viral titers. Because blockade of these immunoregulatory networks represents a powerful approach to establish immune control during persistent infection, it is important to determine whether these immunoinhibitory factors act independently or jointly and if combined blockade of these factors further enhances T-cell immunity and viral clearance. Herein, we demonstrate that the IL-10 and PD-L1 immunosuppressive pathways are mechanistically distinct. As a result, simultaneous blockade of IL-10 and PD-L1 was significantly more effective in restoring antiviral T-cell responses than blockade of either alone, and led to substantially enhanced control of an established persistent viral infection. Thus, combinatorial blockade of multiple immune-regulatory molecules may ultimately restore the T-cell responses required to tip the balance from viral persistence to immune-mediated control or elimination of persistent infection. T-cell exhaustion | virus persistence | functional restoration | immune regulation | immunosuppression

Programmed death-1 (PD-1) regulates T cell exhaustion during chronic infections. Blocking the PD-1:PD-ligand (PD-L) pathway reinvigorates exhausted CD8 T cells. Exactly how blocking PD-1:PD-L interactions improves T cell immunity, however, remains unclear. PD-1:PD-L blockade could reprogram all exhausted T cells to become antiviral effectors. Alternatively, this blockade might selectively expand a subset of exhausted T cells. We have identified two subpopulations of exhausted CD8 T cells during chronic viral infection in mice. One subset of exhausted CD8 T cells is rescued by [alpha]PD-L1 blockade, whereas the other subset appears more terminally differentiated and responds poorly to PD-1:PD-L blockade. Blocking PD-1:PD-L interactions reduces spontaneous apoptosis and enhances expansion and protective immunity of the rescuable subset, but not the more terminally differentiated subset of exhausted CD8 T cells. These results have implications for predicting clinical responses to PD-1-based therapeutic interventions and for understanding T cell dynamics during persisting infections. chronic infection | lymphocytic choriomeningitis virus | T cell exhaustion | PD-1 | T cell memory

The PD-1 costimulatory receptor inhibits T cell receptor signaling upon interacting with its ligands PD-L1 and PD-L2. The PD-1/PD-L pathway is critical in maintaining self-tolerance, in this study, we examined the role of PD-1 in a mouse model of acute infection with Histoplasma capsulatum, a major human pathogenic fungus. In a lethal model of histoplasmosis, all PD-1-deficient mice survived infection, whereas the wild-type mice died with disseminated disease. PD-L expression on macrophages and splenocytes was up-regulated during infection, and macrophages from infected mice inhibited in vitro T cell activation. Of interest, antibody blocking of PD-1 significantly increased survival of lethally infected wild-type mice. Thus, our studies extend the role of the PD-1/PD-L pathway in regulating antimicrobial immunity to fungal pathogens. The results show that the PD-1/PD-L pathway has a key role in the regulation of antifungal immunity, and suggest that manipulation of this pathway represents a strategy of immunotherapy for histoplasmosis. costimulation | fungal infection | programmed death-1

Many chronic viral infections are marked by pathogen persistence and a generalized immunosuppression. The exact mechanisms by which this occurs are still unknown. Using a mouse model of persistent lymphocytic choriomeningitis virus (LCMV) infection, we demonstrate viral targeting of fibroblastic reticular cells (FRC) in the lymphoid organs. The FRC stromal networks are critical for proper lymphoid architecture and function. High numbers of FRC were infected by LCMV clone 13, which causes a chronic infection, whereas few were infected by the acute strain, LCMV Armstrong. The function of the FRC conduit network was altered after clone 13 infection by the action of [CD8.sup.+] T cells. Importantly, expression of the inhibitory programmed death ligand 1, which was up-regulated on FRC after infection, reduced early [CD8.sup.+] T cell-mediated immunopathology and prevented destruction of the FRC architecture in the spleen. Together, this reveals an important tropism during a persistent viral infection. These data also suggest that the inhibitory PD-1 pathway, which likely evolved to prevent excessive immunopathology, may contribute to viral persistence in FRC during chronic infection. immunopathology | stromal cells | viral infection

Both positive and negative regulatory roles have been suggested for the B7 family member PD-L1(BT-H1). PD-L1 is expressed on antigen-presenting cells (APCs), activated T cells, and a variety of tissues, but the functional significance of PD-L1 on each cell type is not yet clear. To dissect the functions of PD-L1 in vivo, we generated PD-Ll-deficient (PD-L[1.sup.-/-]) mice. CD[4.sup.+] and CD[8.sup.+] T cell responses were markedly enhanced in pD-L[1.sup.-/-] mice compared with wild-type mice in vitro and in vivo. PD-L[1.sup.-/-] dendritic cells stimulated greater wild-type CD[4.sup.+] T cell responses than wild-type dendritic cells, and PD-L[1.sup.-/-] CD[4.sup.+] T cells produced more cytokines than wild-type CD[4.sup.+] T cells in vitro, demonstrating an inhibitory role for PD-L1 on APCs and T cells. In vivo CD[8.sup.+] T cell responses also were significantly enhanced, indicating that PD-L1 has a role in limiting the expansion or survival of CD[8.sup.+] T cells. Studies using the myelin oligodendrocyte model of experimental autoimmune encephalomyelitis showed that PD-L1 on T cells and in host tissues limits responses of self-reactive CD[4.sup.+] T cells in vivo. PD-L1 deficiency converted the 129S4/SvJae strain from a resistant to experimental autoimmune encephalomyelitis-susceptible strain. Transfer of encephalitogenic T cells from wild-type mice into PD-L[1.sup.-/-] recipients led to exacerbated disease. Disease was even more severe in PD-L[1.sup.-/-] recipients of PD-L[1.sup.-/-] T cells. These results demonstrate that PD-L1 on T cells, APCs, and host tissue inhibits naive and effector T cell responses and plays a critical role in T cell tolerance.

Author(s): Laurent Monney [1]; Catherine A. Sabatos [1]; Jason L. Gaglia [1]; Akemi Ryu [1]; Hanspeter Waldner [1]; Tatyana Chernova [2]; Stephen Manning [3]; Edward A. Greenfield [1, 2]; Anthony [...]

Author(s): Alexander J. McAdam [1]; Rebecca J. Greenwald [1]; Michele A. Levin [1]; Tatyana Chernova [2]; Nelly Malenkovich [2]; Vincent Ling [3]; Gordon J. Freeman [2, 4]; Arlene H. Sharpe [...]

Although recent in vitro studies have begun to decipher the molecular events that characterize the anergic state, their in vivo biologic relevance and potential clinical importance remain unclear. Here, using anergic human T-cell clones and tolerant alloreactive mouse T cells that do not induce graft-versus-host disease, we show that p27[sup.kip1] cyclin-dependent kinase inhibitor is an essential regulator responsible for the blockade of clonal expansion of anergic T cells in vitro and in vivo. Moreover, in anergic cells, p27[sup.kip1] associates with the c-Jun co-activator JAB1, resulting in defective transactivation of AP-1 and interleukin 2 transcription. Therefore, pharmacological agents that upregulate the expression of or prevent the degradation of p27[sup.kip1] during antigen recognition should be part of new therapeutic strategies to induce antigen-specific T-cell unresponsiveness., Author(s): Vassiliki A. Boussiotis (corresponding author) [1]; Gordon J. Freeman [1]; Patricia A. Taylor [2]; Alla Berezovskaya [1]; Isabelle Grass [1]; Bruce R. Blazar [2, 3]; Lee M. Nadler [1, [...]

The function of CD48 is determined by generating mice deficient in CD48 expression. The results of the experiment show that CD48 plays a crucial role in T cell activation through the T receptor cell/CD3 complex. Reduced proliferation in response to stimulation with lectins, alloantigen and anti-CD3 mAb were observed from the T cells of CD48-deficient mice. The use of phorbol ester phorbol 12-Myristate 13-Acetate as a costimulatory signal instead of antigen-presenting cells resulted in impairments. T cell responses were reconstituted with the addition of irradiated APCs.

Herein we describe the molecular characterization of the human leukocyte activation antigen CD100 and identify it as the first semaphorin, to our knowledge, in the immune system. Semaphorins have recently been described as neuronal chemorepellants that direct pioneering neurons during nervous system development. In this study we demonstrate that CD100 induces B cells to aggregate and improves their viability in vitro. We show that CD100 modifies CD40-CD40L B-cell signaling by augmenting B-cell aggregation and survival and down-regulating CD23 expression. Thus, these results suggest that semaphorins as exemplified by CD100 also play a functional role in the immune system.

The strong expression of major histocompatibility complex and the minor expression of some adhesion and B7 costimulatory molecules do not present alloantigen efficiently in humans follicular lymphoma cells. However, in vitro, the activation of follicular lymphoma cells via CD40 pathway provides signals to T cells to become efficient alloantigen-presenting cells. This evidence implies that expression of major histocompatibility complex and expression of multiple adhesion and costimulatory molecules are required for the correction of defective tumor immunity.

Cross-linking of the T-cell surface molecule CTLA4 enables clonal deletion of human T lymphocytes, that have been activated previously. This apoptosis is regulated by antigen, as revealed by the necessity for a concomitant signal T-cell receptor signal. These T-cells can be deleted by regulating the signal pathway. The ligand that causes cell death is expressed on LBL-DR7 cells.

When stimulated through their antigen receptor without requisite costimulation, T cells enter a state of antigen-specific unresponsiveness, termed anergy. in this study, signaling through the common γ chain of the interleukin-2 (IL-2), IL-4, and IL-7 receptors in the presence of antigen was found to be sufficient to prevent the induction of anergy. After culture with IL-2, IL-4, or IL-7, Jak3 kinase was tyrosine-phosphorylated, which correlated with the prevention of anergy. Therefore, a signal through the common y chain may regulate the decision of T cells to either clonally expand or enter a state of anergy., Although little is known about the molecular mechanisms responsible for the induction and maintenance of anergy (1), the critical costimulatory signal necessary to prevent the induction of anergy is probably [...]

Human leukotriene (LT) C4 synthase, an integral membrane protein, connects LTA4 and reduced glutathione to form a proinflammatory mediator, LTC4. Fluorescence-linked immunoassay helps expression cloning of cDNA for human LTC4 synthase from a KG-1 cDNA expression library in COS-7 cells. Step-wise resolution identifies individual clones having high LTC4 synthase activity. Amino acid sequence of LTC4 synthase exhibits homology to the 5-lipoxygenase activating protein (FLAP). The peptide structure reveals three transmembrane domains that are superimposable on those of FLAP. The difference between LTC4 synthase and known GSH S-transferases suggest that it belongs to a distinct gene family.

Activation of self-reactive T cells may depend on aberrant B7 expression on peripheral tissues in mice. Several T-cell mediated autoimmune disease may involve extraordinary expression of costimulatory receptors. Transgenic mice expressing the costimulatory mouse molecule B7-1, a ligand for the CD28 receptor, have been analyzed.

An analysis of CTLA-4 counterreceptors reveals that a pair of this type of counterreceptors are expressed on stimulated human B lymphocytes BB-1, B7-3 and B7-2. The pair can costimulate the T-cell, and their costimulatory signals may be necessary for the production of an immune response.

Tetanus toxoid peptide antigen in a human antigen-specific construct, when presented by cells cotransfected with HLA-DR7 and B7, yields interleukin 2 generation and optimal T-cell proliferation. Antigen presentation without B7 coactivation causes T-cell clonal energy. Antigen-specific clonal tolerance can be stimulated in human T cells already sensitized to antigen.

A study shows that mouse sarcoma cells that were genetically designed to offer antigent specific and costimulatory T-cell activation signals activate potent tumor-specific CD4+T cells that result in the rejection of engineered and wild-type neoplastic cells. Results portray the influence of the B7 activation molecule in this activation and rejection, and offer a theoretical foundation for immunotherapy of established tumors.

The identification of a murine lymphocyte protein, termed sgp-60, as the homologue of CD48 was reported. The murine glycoprotein is expressed on all lymphocytes of both T- and B-cell origin. Protein sequencing of the sgp-60 antigen and gene transfection experiments demonstrate that sgp-60 is identical to the CD48 antigen, which is also called Blast-1 in humans, BCM1 in mice and OX-45 in rats.

A hamster-anti-murine B7 (mB7) monoclonal antibody (mAb) was generated. The mAb recognizes a protein with an apparent molecular mass of 60 kDa. With this mAb the expression and function of mB7 by normal and transformed cells were characterized. The results indicate that mB7 is the major costimulatory molecule expressed by peritoneal exudate cells and that there may be other molecules besides mB7 that can costimulate the activation of CD4+ T cells.

The costimulatory role of murine B7 (mB7) antigen for the activation of murine CD4 T lymphocytes through the T-cell receptor/CD3 complex was reported. Murine B7 antigen modulated the normal pathway of T-cell expansion by enhancing the production of interleukin 2 and expression of its receptor. Experiments showed Chinese ovary hamster cells transfected with mB7 combined with anti-CD3 monoclonal antibody and Con A-induced T cell activation that led to the production of T cells. This finding indicated the specificity of the effects of mB7.

Expression of new leukocyte cell surface antigens (Ags) HB-6, CDw75 and CD76 through beta-galactoside alpha-2,6-sialytransferase (alpha2,6-ST) expression is functionally exclusive to the Golgi apparatus. These Ags, though equally important for lymphocyte activity, exhibit differences in hematopoietic expression. Erthrocytes and young B lymphocytes preferentially express HB-6 antigens while older B cells favor CDw75 and CD76 expression. These observations indicate the indispensable regulatory role in lymphocyte activity of alpha2,6-ST.

One of the factors limiting the dosage of chemotherapeutic agents is bone marrow toxicity. To permit the use of greater and more effective doses of chemotherapy, it is possible to remove some of the patient's own bone marrow and replace it following the chemotherapeutic treatment, thereby providing new cells to recolonize the marrow destroyed by the drug treatment. However, for some conditions, such as lymphoma, there is concern that the bone marrow itself may contain tumor cells, and thus the autologous replacement of the patient's own marrow may lead to a relapse. Techniques have been developed to permit the purging of tumor cells from the bone marrow prior to replacement. However, the evaluation of this technique is hampered by the difficulty of determining whether a few tumor cells are indeed present among the myriad of bone marrow cells. Researchers have now applied the sensitive polymerase chain reaction (PCR) to this problem. PCR was used before and after bone marrow purging to identify residual lymphoma cells in 114 patients. These patients all had a B-cell non-Hodgkin's lymphoma with a chromosomal abnormality; it is this abnormality that permitted the PCR technique to detect the small numbers of lymphoma cells scattered among the normal bone marrow cells. The purging procedure reduced the number of lymphoma cells in the bone marrow from one thousand to one million times. In 57 cases, no lymphoma cells were detected following the purging procedure. Only four cases relapsed among these 57 cases. Among the remaining 57 patients who experienced a reduction but not an elimination of lymphoma cells, there were 26 relapses. Two important conclusions follow from these results. Successful purging results in a significant increase in the freedom from relapse. Furthermore, tumor cells in the transplanted bone marrow significantly contribute to the likelihood of relapse. (Consumer Summary produced by Reliance Medical Information, Inc.)

Evasion of the immune system is an all too common feature of cancer. A new study suggests one evasion mechanism: induction of T-cell apoptosis through B7-H1, a molecule expressed on [...]

Although presentation of antigen to the T cell receptor is necessary for the initiation of an immune response, additional molecules expressed on antigen-presenting cells deliver essential costimulatory signals. T cell [...]

B7 delivers a costimulatory signal through CD28, resulting in interleukin-2 secretion and T cell proliferation. Blockade of this pathway results in T cell anergy. The in vivo role of B7 [...]

Author(s): Cheryl L. Day [1, 2, 3, 8]; Daniel E. Kaufmann [2, 8]; Photini Kiepiela [1]; Julia A. Brown [4]; Eshia S. Moodley [1]; Sharon Reddy [1]; Elizabeth W. Mackey [...]

Author(s): Daniel L. Barber [1]; E. John Wherry [2]; David Masopust [1]; Baogong Zhu [3]; James P. Allison [4]; Arlene H. Sharpe [5]; Gordon J. Freeman [3]; Rafi Ahmed (corresponding [...]

Anti-Porimin (Pro-oncosis receptor inducing membrane injury mAb mediates oncosis-like cell death in Jurkat cells. Porimin cDNA was isolated from a Jurkat cell cDNA library by COS cell-expression cloning. The 3,337-bp cDNA has an ORF of 567 bp, encoding a type I transmembrane protein of 189 amino acids. The extracellular domain of Porimin contains many 0-linked and seven N-linked glycosylation sites that define it as a new member of the mucin family. COS7 and 293 cells transiently transfected with Porimin cDNA were specifically recognized by anti-Porimin Ab in cell staining and immunoblotting experiments. When expressed in Jurkat cells, a His-tagged Porimin cDNA construct resulted in the generation of a specific 110-kDa-size protein that matched the molecular mass of the endogenous Porimin protein. Crosslinking of the Porimin receptor expressed on COS7 transfectants resulted in the loss of cell membrane integrity and cell death as measured by the leakage of intracellular lactate dehydrogenase. Both COS7 and 293 cells expressing transfected Porimin at a relatively high level lost their ability to adhere to culture dishes, suggesting a role for Porimin in cell adhesion. The Porimin gene was mapped to human chromosome 11q22.1 and is composed of four exons spanning 133 kb of genomic DNA.

Author(s): Jennifer J. McIntire [1]; Sarah E. Umetsu [1]; Claudia Macaubas [1]; Elizabeth G. Hoyte [1]; Cengiz Cinnioglu [2]; Luigi L. Cavalli-Sforza [2]; Gregory S. Barsh [2]; Joachim F. Hallmayer [...]