Co-stimulatory members of the TNFR family: keys to effective T-cell immunity?

A chimeric T cell antigen receptor that augments cytokine release and supports clonal expansion of primary human T cells

The transduction of primary T cells to express chimeric T cell receptors (cTCR) for redirected targeting of tumor cells is an attractive strategy for generating tumor-specific T cells for adoptive therapy. However, tumor cells rarely provide costimulatory signals and hence cTCRs that transmit just a CD3zeta signal can only initiate target cell killing and interferon-gamma release and fail to induce full activation. Although incorporation of a CD28 component results in IL-2 release and limited proliferation, T cell activation remains incomplete. OX40 transmits a potent and prolonged T cell activation signal and is crucial for maintaining an immunological response. We hypothesize that the CD28-OX40-CD3zeta tripartite cytoplasmic domain will provide a full complement of activation, proliferation, and survival signals for enhanced anti-tumor activity.

Glucocorticoid-Induced TNF Receptor Functions as a Costimulatory Receptor That Promotes Survival in Early Phases of T Cell Activation

Glucocorticoid-induced TNFR (GITR) is a member of the TNFR family that can inhibit the suppressive function of regulatory T cells and promote the survival and activation of T cells. However, little is known about the molecular mechanisms regulating T cell survival and activation downstream of GITR. To gain further insight into the cellular events and signaling pathways triggered by GITR, survival, proliferation, and cytokine production as well as activation of MAPKs and NF-kappaB were monitored after cross-linking of the receptor on naive and activated T cells. GITR cross-linking provided costimulation of naive and activated T cells and resulted in activation of MAPKs and NF-kappaB. Although GITR-induced signaling pathways augmented the survival of naive T cells, they were not sufficient to inhibit activation-induced cell death triggered by CD3 cross-linking of activated T cells. Differences in the contributions of GITR to cell survival between naive and activated T cells suggest that the receptor triggers specific pathways depending on the activation state of the T cell.

Recombinant Tumor-Associated MUC1 Glycoprotein Impairs the Differentiation and Function of Dendritic Cells

Tumors exploit several strategies to evade immune recognition, including the production of a large number of immunosuppressive factors, which leads to reduced numbers and impaired functions of dendritic cells (DCs) in the vicinity of tumors. We have investigated whether a mucin released by tumor cells could be involved in causing these immunomodulating effects on DCs. We used a recombinant purified form of the MUC1 glycoprotein, an epithelial associated mucin that is overexpressed, aberrantly glycosylated, and shed during cancer transformation. The O-glycosylation profile of the recombinant MUC1 glycoprotein (ST-MUC1) resembled that expressed by epithelial tumors in vivo, consisting of large numbers of sialylated core 1 (sialyl-T, ST) oligosaccharides. When cultured in the presence of ST-MUC1, human monocyte-derived DCs displayed a modified phenotype with decreased expression of costimulatory molecules (CD86, CD40), Ag-presenting molecules (DR and CD1d), and differentiation markers (CD83). In contrast, markers associated with an immature phenotype, CD1a and CD206 (mannose receptor), were increased. This effect was already evident at day 4 of DC culture and was dose dependent. The modified phenotype of DCs corresponded to an altered balance in IL-12/IL-10 cytokine production, with DC expressing an IL-10(high)IL-12(low) phenotype after exposure to ST-MUC1. These DCs were defective in their ability to induce immune responses in both allogeneic and autologous settings, as detected in proliferation and ELISPOT assays. The altered DC differentiation and Ag presentation function induced by the soluble sialylated tumor-associated mucin may represent a mechanism by which epithelial tumors can escape immunosurveillance.

Glucocorticoid-Induced TNF Receptor, a Costimulatory Receptor on Naive and Activated T Cells, Uses TNF Receptor-Associated Factor 2 in a Novel Fashion as an Inhibitor of NF-κB Activation

Glucocorticoid-induced TNFR (GITR) has been implicated as an essential regulator of immune responses to self tissues and pathogens. We have recently shown that GITR-induced cellular events promote survival of naive T cells, but are insufficient to protect against activation-induced cell death. However, the molecular mechanisms of GITR-induced signal transduction that influence physiologic and pathologic immune responses are not well understood. TNFR-associated factors (TRAFs) are pivotal adapter proteins involved in signal transduction pathways of TNFR-related proteins. Yeast two-hybrid assays and studies in HEK293 cells and primary lymphocytes indicated interactions between TRAF2 and GITR mediated by acidic residues in the cytoplasmic domain of the receptor. GITR-induced activation of NF-kappaB is blocked by A20, an NF-kappaB-inducible protein that interacts with TRAFs and functions in a negative feedback mechanism downstream of other TNFRs. Interestingly, in contrast with its effects on signaling triggered by other TNFRs, our functional studies revealed that TRAF2 plays a novel inhibitory role in GITR-triggered NF-kappaB activation.

Mice deficient in OX40 and CD30 signals lack memory antibody responses because of deficient CD4 T cell memory

Recently, we reported that a CD4(+)CD3(-)CD11c(-) accessory cell provided OX40-dependent survival signals to follicular T cells. These accessory cells express both OX40 ligand and CD30 ligand, and the receptors, OX40 and CD30, are both expressed on Th2-primed CD4 T cells. OX40 and CD30 signals share common signaling pathways, suggesting that CD30 signals might substantially compensate in OX40-deficient mice. In this report we have dissected the signaling roles of CD30 alone and in combination with OX40. CD30-deficient mice showed an impaired capacity to sustain follicular germinal center responses, and recall memory Ab responses were substantially reduced. Deficiencies in OX40 and CD30 signals were additive; secondary Ab responses were ablated in double-deficient mice. Although the initial proliferation of OX40/CD30 double-knockout OTII transgenic T cells was comparable to that of their normal counterparts, they failed to survive in vivo, and this was associated with reduced T cell numbers associated with CD4(+)CD3(-) cells in B follicles. Finally, we show that OX40/CD30 double-knockout OTII transgenic T cells fail to survive compared with normal T cells when cocultured with CD4(+)CD3(-) cells in vitro.

Constitutive expression and costimulatory function of LIGHT/TNFSF14 on human melanoma cells and melanoma-derived microvesicles

Neoplastic cells are thought to have defective expression of costimulatory molecules. However, in this study, we show that human melanoma cells express LIGHT/TNFSF14, a ligand of herpesvirus entry mediator on T cells and of lymphotoxin beta receptor on stromal cells. In vitro, melanoma cells stained for LIGHT in the intracellular compartment, with weak or negative cell surface expression. However, LIGHT was expressed on tumor-derived microvesicles released from melanoma cells. In vivo, LIGHT was found in metastatic lesions, and the extent of lymphotoxin beta receptor expression on the stromal cells was significantly associated with a "brisk" T-cell infiltrate in the neoplastic tissue. In the lesions with a brisk T-cell infiltrate, stromal cells surrounding the tumor also stained for the T-cell attractant chemokine CCL21. The intratumoral T lymphocytes frequently expressed herpesvirus entry mediator and were characterized by a differentiated phenotype. Coculture of lymphocytes with LIGHT(+) melanoma-derived microvesicles or even with LIGHT(+) melanoma cells in the presence of interleukin-2 costimulated LIGHT-dependent CD3(+)CD8(+) T-cell proliferation. However, lymphocyte coculture with LIGHT(+) microvesicles in the presence of interleukin-2 was also associated with an apoptotic response as documented by increased binding of Annexin V by CD3(+)CD8(+) T cells. These data suggest that LIGHT constitutively expressed in human melanoma cells and microvesicles may contribute to regulate T-cell responses to tumor cells.

Costimulation: critical pathways in the immunologic regulation of asthma

T cells play an important role in the pathogenesis of allergy and asthma. T-cell receptor engagement by antigenic peptides presented to major histocompatibility complex (MHC) class II molecules and activation of costimulatory molecules are crucial in the regulation of T-cell immune responses. Costimulatory molecules are responsible for second signals that induce T-cell activation and proliferation. The best characterized costimulatory pathways include CD80/CD86 interacting with CD28, and a number of additional costimulatory molecules have recently been identified, including members of the tumor necrosis family. The positive signals induced by these molecules are counterbalanced by other members of the costimulatory family, including cytotoxic T lymphocyte-associated antigen (CTLA)-4, programmed death (PD)-1, and B and T lymphocyte attenuator (BTLA), which dampen immune responses. In this review, we describe the fundamental properties of costimulatory molecules and address the influence of costimulatory signals on allergic responses.

CD27 and CD70 in T cell and B cell activation

In vitro work has defined the TNF receptor family member CD27 as a T and B cell co-stimulatory molecule. Its activity is governed by the transient availability of its TNF-like ligand CD70 on lymphocytes and dendritic cells. Recent studies, enforcing or abrogating CD27 function by genetic or protein intervention in mouse models have revealed key contributions of the CD27-CD70 system to effector and memory T cell formation, which is probably based on improved cell survival. The stimulatory effects of CD27 on B cell function appear to oppose those of CD70, which also has a signaling role. Targeting CD27-CD70 for therapy is attractive but should take into account the fact that constitutive CD27 stimulation culminates in lethal immunodeficiency.

The evolving crosstalk between co-stimulatory and co-inhibitory receptors: HVEM–BTLA

Receptors and their ligands on T cells and antigen-presenting cells are crucial for delivering inhibitory or stimulatory signals that enable immune cells to remain dormant or to respond effectively to various stimuli. The CD28-B7 and tumor necrosis factor receptor (TNFR)-TNF superfamilies contain many of these molecules and were thought to be distinct functioning modules. However, two studies have now provided a new perspective in this already complex area, showing not only a crosstalk between these superfamilies but potentially between co-stimulatory and co-inhibitory receptors.

Endothelial cell co-stimulation through OX40 augments and prolongs T cell cytokine synthesis by stabilization of cytokine mRNA

Human endothelial cells (ECs) constitutively express OX40L and co-stimulate memory CD4(+) T cell proliferation that is dependent upon OX40-OX40L interaction. In vivo, OX40 prolongs T cell survival; however, an unanswered question is whether it can also prolong synthesis of proliferation-sustaining cytokines such as IL-2. Here we show that EC co-stimulation results in the secretion of T cell IL-2, IL-3 and IFN-gamma and that in the absence of OX40 signals synthesis largely ceases by 12-18 h, but is prolonged up to 60 h in the presence of OX40 signaling. Blocking OX40-mediated cytokine expression at later times suppresses T cell proliferation and this can be overcome by addition of exogenous IL-2. We find that OX40 signaling has discrete effects on T cell activation as it does not affect expression of IL-10, CD25, CD69 or soluble IL-2R. Also, OX40 does not appear to alter IL-2 transcription, but rather acts to stabilize a subset of cytokine mRNAs, increasing their half-lives by 3-6-fold. We further show that OX40L induces activation of p38 mitogen-activated protein kinase (MAPK) and phosphotidyl-inositol-3-kinase (PI3K) in T cells, and using specific inhibitors, we find that increased mRNA half-life is dependent upon both these pathways but is independent of c-jun-N-terminal kinase (JNK). Thus, EC co-stimulation through OX40 leads to prolonged T cell cytokine synthesis and enhanced proliferation.

Enhanced CD4 T Cell Responsiveness in the Absence of 4-1BB

The 4-1BB (CD137) is a member of the TNFR superfamily, and is expressed on several cell types, including activated T cells. Although 4-1BB ligation by agonistic Ab or 4-1BB ligand-expressing APCs can costimulate T cells, the physiological significance of 4-1BB expression in vivo during T cell responses is still being elucidated. In this study, we have addressed the impact on CD4 T cell priming when 4-1BB is absent after gene targeting. Surprisingly, 4-1BB(-/-) mice generated more enhanced effector CD4 T cell responses to OVA protein in adjuvant, even though Ab responses in 4-1BB(-/-) mice were normal. Using an adoptive transfer system with OT-II TCR transgenic CD4 T cells, we found that 4-1BB(-/-) CD4 cells responding in a 4-1BB-sufficient environment had enhanced cell division compared with wild-type cells and displayed augmented clonal expansion during the primary response. This was not due to a developmental defect as 4-1BB-deficient CD4 cells could respond normally to Ag in vitro. These results demonstrate that the absence of 4-1BB can make CD4 T cells hyperresponsive to protein Ag in vivo, suggesting a new unappreciated negative regulatory role of 4-1BB when expressed on a T cell.

The role of herpesvirus entry mediator as a negative regulator of T cell-mediated responses

Herpesvirus entry mediator (HVEM), a TNF receptor superfamily member, has been previously described as a T cell costimulatory receptor. Surprisingly, HVEM-/- T cells showed enhanced responses to in vitro concanavalin A (ConA) stimulation when compared with WT T cells. Consistent with these findings, HVEM-/- mice exhibited increased morbidity and mortality as compared with WT mice in a model of ConA-mediated T cell-dependent autoimmune hepatitis. HVEM-/- mice produced higher levels of multiple cytokines, which were dependent on the presence of CD4+ T cells. Furthermore, HVEM-/- mice were more susceptible to MOG peptide-induced experimental autoimmune encephalopathy, and they showed increased T cell proliferation and cytokine production in response to antigen-specific challenge. Taken together, our data revealed an unexpected regulatory role of HVEM in T cell-mediated immune responses and autoimmune diseases.

The role of herpesvirus entry mediator as a negative regulator of T cell-mediated responses

Herpesvirus entry mediator (HVEM), a TNF receptor superfamily member, has been previously described as a T cell costimulatory receptor. Surprisingly, HVEM-/- T cells showed enhanced responses to in vitro concanavalin A (ConA) stimulation when compared with WT T cells. Consistent with these findings, HVEM-/- mice exhibited increased morbidity and mortality as compared with WT mice in a model of ConA-mediated T cell-dependent autoimmune hepatitis. HVEM-/- mice produced higher levels of multiple cytokines, which were dependent on the presence of CD4+ T cells. Furthermore, HVEM-/- mice were more susceptible to MOG peptide-induced experimental autoimmune encephalopathy, and they showed increased T cell proliferation and cytokine production in response to antigen-specific challenge. Taken together, our data revealed an unexpected regulatory role of HVEM in T cell-mediated immune responses and autoimmune diseases.

Cutting Edge: CD95 Maintains Effector T Cell Homeostasis in Chronic Immune Activation

The elimination of activated T cells is important to maintain homeostasis and avoid immunopathology. CD95 (Fas/APO-1) has been identified as a death mediator for activated T cells in vitro but the function of CD95 in death of mature T cells in vivo is still controversial. Here we show that triggering of the costimulatory TNF receptor family member CD27 sensitized T cells for CD95-induced apoptosis. CD95-deficient (lpr/lpr) T cells massively expanded and differentiated into IFN-gamma-secreting effector cells in transgenic mice that constitutively express the CD27 ligand, CD70. Concomitantly, CD95-deficient CD70 transgenic mice became moribund by 4 wk of age with severe liver pathology and bone marrow failure. These findings establish that CD95 is a critical regulator of effector T cell homeostasis in chronic immune activation.

Enhancement of CD4 and CD8 immunity by anti-CD137 (4-1BB) monoclonal antibodies during hepatitis C vaccination with recombinant adenovirus

The induction of protective or therapeutic cellular immunity against hepatitis C virus (HCV) is a difficult goal. In a previous work we showed that immunization with a recombinant adenovirus encoding HCV-NS3 (RAdNS3) could partially protect mice from challenge with a vaccinia virus encoding HCV antigens. We sought to investigate whether systemic administration of an immunostimulatory monoclonal antibody directed against the lymphocyte surface molecule CD137 could enhance the immunity elicited by RAdNS3. It was found that treatment with anti-CD137 mAb after the administration of a suboptimal dose of RAdNS3 enhanced cytotoxic and T helper cell responses against HCV NS3. Importantly, the ability of RAdNS3 to induce protective immunity against challenge with a recombinant vaccinia virus expressing HCV proteins was markedly augmented. Thus, combination of immunostimulatory anti-CD137 mAb with recombinant adenoviruses expressing HCV proteins might be useful in strategies of immunization against HCV.

Impaired IL-4 and c-Maf expression and enhanced Th1-cell development in Vav1-deficient mice

Although c-Maf is crucial for Th2 differentiation and production of interleukin 4 (IL-4), its regulation is poorly understood. We report that Vav1-/- CD4+ T cells display deficient T-cell receptor (TCR)/CD28-induced IL-4 and c-Maf expression and, conversely, enhanced interferon gamma (IFN-gamma) production and T-bet expression (even when cultured under Th2-polarizing conditions), but intact expression of other Th2 cytokines and GATA-3. Up-regulation of c-Maf was dependent on Ca2+/nuclear factor of activated T cell (NFAT) and, together with IL-4 production, could be rescued in Vav1-/- T cells by Ca2+ ionophore. Deficient IL-4 production was restored by retrovirus-mediated Vav1 expression, but only partially by retroviral c-Maf expression. Similar IL-4 --> IFN-gamma skewing was observed in intact, antigen-primed Vav1-/- mice. Thus, Vav1 is selectively required for IL-4 and c-Maf expression, a requirement reflecting, at least in part, the dependence of c-Maf expression on Ca2+/NFAT signaling.

Proteomic analysis of human natural killer cells: insights on new potential NK immune functions

Applying high-throughput proteomic analysis of mammalian cells can facilitate the identification of a large number of proteins expressed in the examined samples. Moreover, extensive research efforts are being made to perform large-scale characterization of membrane proteins. Here we use mass spectrometry-based proteomic strategy to characterize protein expression in membrane-enriched fractions derived from human NK lymphoma cell line YTS. This query yielded a list of over 1000 identified proteins, and provided us with new insights on NK cell biology. We highlight the expression of CD86 on YTS and its ability to co-stimulate TCR responses of human CD4+ T-cells, providing an unexpected link between innate and adaptive immune systems.

TIM-1 induces T cell activation and inhibits the development of peripheral tolerance

We have examined the function of TIM-1, encoded by a gene identified as an 'atopy susceptibility gene' (Havcr1*), and demonstrate here that TIM-1 is a molecule that costimulates T cell activation. TIM-1 was expressed on CD4(+) T cells after activation and its expression was sustained preferentially in T helper type 2 (T(H)2) but not T(H)1 cells. In vitro stimulation of CD4(+) T cells with a TIM-1-specific monoclonal antibody and T cell receptor ligation enhanced T cell proliferation; in T(H)2 cells, such costimulation greatly enhanced synthesis of interleukin 4 but not interferon-gamma. In vivo, the use of antibody to TIM-1 plus antigen substantially increased production of both interleukin 4 and interferon-gamma in unpolarized T cells, prevented the development of respiratory tolerance, and increased pulmonary inflammation. Our studies suggest that immunotherapies that regulate TIM-1 function may downmodulate allergic inflammatory diseases.

An innately interesting decade of research in immunology

"Nature has provided, in the white corpuscles as you call them-in the phagocytes as we call them-a natural means of devouring and destroying all disease germs. There is at bottom only one genuinely scientific treatment for all diseases, and that is to stimulate the phagocytes." So opined B.B. in G.B. Shaw's The Doctor's Dilemma in a dramatic restatement of a key portion of Ilya Metchnikoff's Nobel Prize address: "Whenever the organism enjoys immunity, the introduction of infectious microbes is followed by the accumulation of mobile cells, of white corpuscles of the blood in particular which absorb the microbes and destroy them. The white corpuscles and the other cells capable of doing this have been designated 'phagocytes,' (i.e., devouring cells) and the whole function that ensures immunity has been given the name of 'phagocytosis'". Based on these insights into the foundation of resistance to infectious disease, Metchnikoff was awarded the 1908 Nobel Prize in Physiology or Medicine together with Paul Ehrlich (Fig. 1). Although both were cited for discoveries in immunity, the contributions of the two men seem worlds apart. Ehrlich's studies did not deal with generic responses to infection, but rather with the highly specific nature of antibodies and their relationship to the cells producing them: "As the cell receptor is obviously preformed, and the artificially produced antitoxin only the consequence, i.e. secondary, one can hardly fail to assume that the antitoxin is nothing else but discharged components of the cell, namely receptors discharged in excess". But biological systems are just that-systems-and the parts need to work together. And so we arrive, a century later, at an appreciation for just how intimately related these two seemingly disparate aspects of host defense really are.

Critical contribution of CD80 and CD86 to induction of anterior chamber-associated immune deviation

Intraocular inoculation of antigens induces anterior chamber-associated immune deviation (ACAID), which is mediated by development of regulatory T cells in response to antigen-presenting cells (APC) pre-conditioned by intraocular transforming growth factor-beta (TGF-beta). In this study, we examined the involvement of T-cell co-stimulatory molecules in this process. To mimic the intraocular APC, thioglycollate-elicited peritoneal exudate cells (PEC) were pre-treated with TGF-beta in vitro. Expression of CD80, CD86, OX40 ligand (OX40L) and CD70 was analyzed by flow cytometry. Contribution of these molecules to co-stimulatory activity of TGF-beta-treated PEC on antigen-stimulated T-cell proliferation and cytokine production was determined by inhibition with blocking antibodies in vitro. Contribution of CD80 and CD86 to induction of ACAID was determined by the administration of blocking antibodies at intraocular antigen inoculation in vivo. TGF-beta-treated PEC expressed CD80 and CD86 but not OX40L or CD70. Antigen-stimulated T cells proliferated and produced IL-10, but not IFN-gamma, in response to co-stimulation by TGF-beta-treated PEC, which was abrogated by blocking antibodies against CD80 and CD86. Induction of regulatory cells mediating ACAID was abolished by in vivo blockade of CD80 and CD86. The present results indicated that CD80 and CD86 play a critical role in induction of ACAID, possibly by co-stimulating expansion and IL-10 production of regulatory T cells in response to TGF-beta-conditioned APC.

Costimulation by CD137/4-1BB inhibits T cell apoptosis and induces Bcl-xLand c-FLIPshortvia phosphatidylinositol 3-kinase and AKT/protein kinase B

Costimulation is essential for induction of T lymphocyte proliferation and inhibition of activation-induced cell death. While signaling pathways activated following the ligation of the costimulatory molecule CD28 are well defined, less is known about the molecular events induced by alternative costimulators. CD137/4-1BB, a costimulatory member of the tumor necrosis factor receptor family, plays an important role during late primary T cell stimulation. Here, we demonstrate for the first time that inhibition of activation-induced cell death by exposure to the CD137/4-1BB ligand involves up-regulation of the anti-apoptotic protein c-FLIP(short). Inhibition of T cell death by 4-1BB ligation and up-regulation of c-FLIP(short) and Bcl-x(L) were abolished by blocking the phosphatidylinositol 3-kinase or the AKT/protein kinase B, which also mediate CD28-induced inhibition of activation-induced cell death. Our findings, therefore, demonstrate that costimulatory molecules, although belonging to different protein families and participating in distinct upstream signaling pathways, employ common downstream signaling pathways.

[Regulation of immune response by T cell co-signaling. ]

The activation of naive T cells requires two signals from the antigen presenting cells (APC). Firstly, an antigen specific signal which is triggered by the binding of the T cell receptor (TCR) to the peptide-MHC complex, and secondly, antigen nonspecific signals initiated through a set of co-signalling receptors. Co-signalling molecules are cell-surface glycoproteins that play essential roles for the communication of a T cell with virtually all other host cells by modulating and fine-tuning TCR signals. On the basis of their functional outcome, co-signalling molecules can be divided into co-stimulators and co-inhibitors, which promote or suppress T-cell activation, respectively. By expression at the appropriate time and location, co-signalling molecules positively and negatively control the priming, growth, differentiation and functional maturation of a T-cell response. In this article, I overview property of co-signaling molecules in the CD28- and TNFR family and discuss their potential functional relationships with each other. In addition, role of these co-signalling molecules in various diseases, such as autoimmune diseases, graft rejection, allergy, inflammatory bowel disease, and cancer, and the therapeutic potential of targeting these molecules to enhance or curtail an ongoing immune response in these diseases are discussed.

Peripheral Tolerance of CD8 T Lymphocytes

Whereas high-avidity recognition of peptide-MHC complexes by developing T cells in the thymus results in deletion and promotes self-tolerance, such recognition by mature T cells in the periphery results in activation and clonal expansion. This dichotomy represents the basis of a dilemma that has stumped immunologists for many years, how are self-specific T cells tolerized in the periphery? There appear to be two important criteria used to achieve this goal. The first is that in the absence of inflammatory pathogens, tolerance is promoted when T cells recognize antigen presented by quiescent dendritic cells (DCs) expressing low levels of costimulatory molecules. A second critical factor that defines "self" and drives tolerance through deletion, anergy, or suppression is the persistence of antigen.

Co-stimulation: novel methods for preventing viral-induced lung inflammation

Respiratory infections cause significant morbidity and mortality worldwide. Although an immune response is required to eliminate respiratory pathogens, if unchecked, it can damage surrounding tissues and block primary lung function. Based on our knowledge of immune T-cell activation, there are several pathways to which immune intervention could be applied. However, relatively few interventions target only those immune cells that are responding to antigens. OX40 and 4-1BB are members of the tumour necrosis factor receptor family and are expressed on the surface of T cells in several inflammatory conditions. Recently, the inhibition of OX40 has proved beneficial during influenza virus infection. This review highlights the recent advances in the manipulation of such molecules and how they have been applied to inflammatory conditions that are caused by viruses in the lung.

NK cell regulation of T cell-mediated responses

NK cells promote adaptive immune responses through their production of type 1 and type 2 cytokines or chemokines. Secretion of these factors by activated NK cells influences the differentiation of B and T lymphocytes. Increasing evidence indicates that NK cells are also directly involved in dendritic cell (DC) maturation. By contrast, a potential role for direct cell-cell interactions between NK and T lymphocytes, in particular CD4(+) T cells, has not been explored. We provide evidence that activated human NK cells are able of promoting TcR-dependent proliferation of resting autologous peripheral blood CD4(+) T cells by a process that involves costimulatory molecules of the immunoglobulin (Ig) and tumor necrosis factor (TNF) superfamilies. These findings suggest a novel link between natural and adaptative immune responses.

Liposome-encapsulated CpG oligodeoxynucleotides as a potent adjuvant for inducing type 1 innate immunity

Unmethylated cytosine-phosphorothioate-guanine oligodeoxynucleotides (CpG-ODNs) exhibit potent immunostimulating activity by binding with Toll-like receptor 9 (TLR9) expressed on antigen-presenting cells. Here, we show that CpG-ODN encapsulated in cationic liposomes (CpG-liposomes) improves its incorporation into CD11c(+) dendritic cells (DCs) and induces enhanced serum interleukin (IL)-12 levels compared with unmodified CpG-ODN. CpG-liposome potently activated natural killer (NK) cells (84.3%) and NKT cells (48.3%) to produce interferon-gamma (IFN-gamma), whereas the same dose of unmodified CpG-ODN induced only low numbers of IFN-gamma-producing NK cells (12.7%) and NKT cells (1.6%) to produce IFN-gamma. In contrast with the NKT cell agonist alpha-galactosylceramide, which induces both IFN-gamma and IL-4 production by NKT cells, CpG-liposome only induced IFN-gamma production by NKT cells. Such potent adjuvant activities of CpG-liposome were absent in TLR9-deficient mice, indicating that CpG-liposome was as effective as CpG-ODN in stimulating type 1 innate immunity through TLR9. In addition to TLR9, at least two other factors, IL-12 production by DCs and direct contact between DCs and NK or NKT cells, were essential for inducing type 1 innate immunity by CpG-liposome. Furthermore, ligation of TLR9 by CpG-liposome coencapsulated with ovalbumin (OVA) caused the induction of OVA-specific CTLs, which exhibited potent cytotoxicity against OVA-expressing tumor cells. These results indicate that CpG-liposome alone or combined with tumor antigen protein provides a promising approach for the prevention or therapy of tumors.

Immunological ignorance of solid tumors

Many peripheral solid tumors such as sarcomas and carcinomas express tumor-specific antigens that can serve as targets for immune effector T cells. Nevertheless, the immune surveillance against clinically manifest carcinomas and sarcomas seems relatively inefficient. Naïve cytotoxic T cells are activated exclusively in secondary lymphoid organs including the spleen and lymph nodes. Tumor antigen might be either cross-presented to naïve cytotoxic T cells by professional antigen-presenting cells (pAPC), or presented directly by tumor cells that migrated to secondary lymphoid organs. Direct priming is quite inefficient during early tumor development because metastasis to lymphoid organs is usually limited to advanced stage diseases. Similarly, the process of cross-priming by pAPC seems to depend on relatively large antigen amounts and on maturation stimuli for dendritic cells, and both requirements may be limiting during initial tumorigenesis. Therefore, the immunosurveillance of solid tumors may fail because they are ignored for too long by the immune system. However, these situations may prove promising for the induction of tumor-specific T cell immunity by vaccination, as the T cell repertoire against these antigens has a naïve phenotype and is not yet affected by tolerance mechanisms.

OX40 Signals during Priming on Dendritic Cells Inhibit CD4 T Cell Proliferation: IL-4 Switches off OX40 Signals Enabling Rapid Proliferation of Th2 Effectors

In this study we examined the role and regulation of OX40 signals during CD4 T cell priming on dendritic cells (DCs). Contrary to expectation, OX40-deficient cells proliferated more rapidly than their normal counterparts, particularly when stimulated with peptide in the absence of added cytokines. This proliferative advantage was not apparent for Th2-differentiated cells. When the reasons for this were investigated, we found that the cytokine IL-4 specifically down-regulated expression of OX40 ligand on T, B, and DCs, but not on the CD4(+)CD3(-) cells linked with selection of Th2 cells into the memory compartment. OX40 ligand expression was also down-regulated on rapidly proliferating Th1 effectors. These data are compatible with OX40 signals acting during priming as a check on naive T cell proliferation while T cells integrate additional DC signals. This would serve to limit inappropriate T cell responses. In contrast, OX40 signals from CD4(+)CD3(-) cells located in the outer T zone select proliferating Th2 effectors into the memory T cell pool.

A coreceptor interaction between the CD28 and TNF receptor family members B and T lymphocyte attenuator and herpesvirus entry mediator

Immune cell cosignaling receptors are important modulators of immune cell function. For T cells, cosignaling receptors supply necessary secondary signals supporting activation or attenuation after engagement of antigen-presenting cells. The primary cosignaling receptors belong to either the Ig (CD28-like) or TNF receptor (TNFR) superfamilies. The CD28 family is comprised of coinhibitory and costimulatory receptors. The three coinhibitory receptors are cytotoxic T lymphocyte antigen 4, programmed death-1, and B and T lymphocyte attenuator (BTLA). Although cytotoxic T lymphocyte antigen 4 and programmed death-1 interact with B7-Ig family counter receptors, the ligand for BTLA is less clear. From a protein-protein interaction screen, we identified the TNFR family member herpesvirus entry mediator (HVEM) as a counter receptor for BTLA. Here we show that HVEM binds BTLA with high affinity and can form a ternary complex with its known ligands homologous to lymphotoxin, showing inducible expression, and competing with herpes simplex virus glycoprotein D for HVEM, a receptor expressed by T lymphocytes (LIGHT) or lymphotoxin alpha and BTLA. In addition, binding of HVEM to BTLA attenuates T cell activation, identifying HVEM/BTLA as a coinhibitory receptor pair. This study is a demonstration of a direct interaction between the primary T cell cosignaling receptors of the CD28 and TNFR families.

The integration of conventional and unconventional T cells that characterizes cell-mediated responses

This review builds on evidence that cell-mediated immune responses to bacteria, viruses, parasites, and tumors are an integration of conventional and unconventional T-cell activities. Whereas conventional T cells provide clonal antigen-specific responses, unconventional T cells profoundly regulate conventional T cells, often suppressing their activities such that immunopathology is limited. By extrapolation, immunopathologies and inflammatory diseases may reflect defects in regulation by unconventional T cells. To explore the function of unconventional T cells, several extensive gene expression analyses have been undertaken. These studies are reviewed in some detail, with emphasis on the mechanisms by which unconventional T cells may exert their regulatory functions. Highlighting the fundamental nature of T-cell integration, we also review emerging data that the development of conventional and unconventional T cells is also highly integrated.

Modulation of cord blood CD8+ T-cell effector differentiation by TGF-β1 and 4-1BB costimulation

Transforming growth factor-β1 (TGF-β1), an immunosuppressive cytokine, inhibits cytotoxic T cell (CTL) immune responses. In contrast, 4-1BB (CD137), a costimulatory molecule in the tumor necrosis factor (TNF) receptor family, amplifies CTL-mediated antitumor immune responses. We investigated whether TGF-β1 responses could be reversed by 4-1BB costimulation during in vitro differentiation of naive CD8+ T cells into effector CTL cells. TGF-β1 potently suppressed CTL differentiation of human cord blood naive CD8+ T cells as determined by reduced induction of characteristic phenotypes of effector cells and cytotoxic activity. TGF-β1-mediated suppression of CTL differentiation was abrogated by 4-1BB costimulation but not by CD28 or another member in the TNF receptor family, CD30. 4-1BB costimulation suppressed Smad2 phosphorylation induced by TGF-β1, suggesting that 4-1BB effects were at the level of TGF-β1 signaling. 4-1BB effects on the TGF-β1-mediated suppression were enhanced by interleukin 12 (IL-12) but counteracted by IL-4; 4-1BB expression was up- or down-regulated, respectively, by IL-12 and IL-4. IL-4 was more dominant than IL-12 when both cytokines were present during 4-1BB costimulation in the presence of TGF-β1. This indicates critical roles for IL-4 and IL-12 in regulating 4-1BB effects on TGF-β1-mediated suppression. (Blood. 2005;105:274-281)

Role of T cell costimulation in anti-viral immunity

Members of both the CD28 and TNFR families can have costimulatory roles in T cell activation. Gene targeted mice as well as in vivo blocking experiments have established distinct roles for CD28/B7; ICOS/ICOSL; CD27/CD70; 4-1BB/4-1BBL and OX40/OX40L during viral infection. Many issues remain to be addressed, including the timing and location of the interactions, the possibility of partial redundancy between related family members and the molecular basis for the specific phenotypes observed in the different gene targeted mice.

Biological activities of reverse signal transduction through CD137 ligand

CD137 is a member of the tumor necrosis factor receptor family and a potent regulator of T cell activities. Agonists of CD137 have been used widely and successfully to treat cancer in animal models, and recently, it has become evident that CD137 agonists can also be used to treat autoimmune disease. An aspect of the CD137 receptor/ligand system, which has been comparatively little-explored, is its ability of reverse signaling. Just as is CD137, the CD137 ligand is also expressed as a cell membrane protein, and it too can transduce signals into the cells on which it is expressed. This bidirectional signaling capacity allows the CD137 receptor/ligand system to mediate extensive cross-talk between immune cells and between immune and nonimmune cells. This review summarizes the known activities of the CD137 ligand on the different leukocyte subsets and on cancer cells and discusses their influence on the course of immune responses.

Prevention of diabetes in NOD mice at a late stage by targeting OX40/OX40 ligand interactions

Autoreactive T cells play a major role in the development of insulin-dependent diabetes mellitus, suggesting that costimulatory molecules that regulate T cell responses might be essential for disease progression. In NOD mice, CD28/B7 and CD40/CD40 ligand (L) interactions control the onset of diabetes from 2 to 4 weeks of age, but blocking these molecules has little effect after this time. Hence, it is possible that other ligand/receptor pairs control a later phase of disease. We now show that OX40 is expressed on CD4 and CD8 T cells several weeks prior to islet destruction, which is initiated around weeks 12-14, and that OX40L is present on dendritic cells in both secondary lymphoid organs and the pancreas from 11 to 13 weeks of age. Blocking OX40L at 6, 9, or 15 weeks after birth had little effect on disease; however, inhibiting OX40/OX40L interactions at week 12, or continuous treatment from week 12 onwards, significantly reduced the incidence of diabetes. Histological examination showed that islet destruction was prevented and insulitis reduced by targeting OX40L. These studies show that OX40/OX40L interactions form a late checkpoint in diabetes development and suggest that these molecules are realistic targets for therapeutic intervention.

Cancer immunotherapy with mRNA-transfected dendritic cells

Bone marrow-derived dendritic cells (DCs) are the most potent antigen-presenting cells capable of activating naïve T cells. Loading DCs ex vivo with tumor antigens can stimulate potent antitumor immunity in tumor-bearing mice. This review describes the use of mRNA-encoded tumor antigens as a form of antigen loaded onto DCs, including our early experience from clinical trials in urological cancers. Transfection of DCs with mRNA is simple and effective. Comparative studies suggest that mRNA transfection is superior to other antigen-loading techniques in generating immunopotent DCs. The ability to amplify RNA from microscopic amounts of tumor tissue extends the use of DC vaccination to virtually every cancer patient. The striking observation from two phase I clinical trials, in patients with prostate cancer immunized with prostate-specific antigen mRNA-transfected DCs and patients with renal cancer immunized with autologous tumor RNA-transfected DCs, was that the majority of patients exhibited a vaccine-induced T-cell response. Suggestive evidence of clinically related responses was seen in both the trials. Immunization with mRNA-transfected DCs is a promising strategy to stimulate potent antitumor immunity and could serve as a foundation for developing effective treatments for cancer.

Novel APC-like properties of human NK cells directly regulate T cell activation

Initiation of the adaptive immune response is dependent on the priming of naive T cells by APCs. Proteomic analysis of unactivated and activated human NK cell membrane-enriched fractions demonstrated that activated NK cells can efficiently stimulate T cells, since they upregulate MHC class II molecules and multiple ligands for TCR costimulatory molecules. Furthermore, by manipulating antigen administration, we show that NK cells possess multiple independent unique pathways for antigen uptake. These results highlight NK cell-mediated cytotoxicity and specific ligand recognition by cell surface-activating receptors on NK cells as unique mechanisms for antigen capturing and presentation. In addition, we analyzed the T cell-activating potential of human NK cells derived from different clinical conditions, such as inflamed tonsils and noninfected and CMV-infected uterine decidual samples, and from transporter-associated processing antigen 2-deficient patients. This in vivo analysis revealed that proinflammatory, but not immune-suppressive, microenvironmental requirements can selectively dictate upregulation of T cell-activating molecules on NK cells. Taken together, these observations offer new and unexpected insights into the direct interactions between NK and T cells and suggest novel APC-like activating functions for human NK cells.

B and T lymphocyte attenuator regulates T cell activation through interaction with herpesvirus entry mediator

B and T lymphocyte attenuator (BTLA) provides an inhibitory signal to B and T cells. Previously, indirect observations suggested that B7x was a ligand for BTLA. Here we show that BTLA does not bind B7x; instead, we identify herpesvirus entry mediator (HVEM) as the unique BTLA ligand. BTLA bound the most membrane-distal cysteine-rich domain of HVEM, distinct from regions where the ligands LIGHT and lymphotoxin-alpha bound HVEM. HVEM induced BTLA tyrosine phosphorylation and association of the tyrosine phosphatase SHP-2 and repressed antigen-driven T cell proliferation, providing an example of reverse signaling to a non-tumor necrosis factor family ligand. The conservation of the BTLA-HVEM interaction between mouse and human suggests that this system is an important pathway regulating lymphocyte activation and/or homeostasis in the immune response.

Molecular transfer of CD40 and OX40 ligands to leukemic human B cells induces expansion of autologous tumor-reactive cytotoxic T lymphocytes

Clinical benefits from monoclonal antibody therapy for B-chronic lymphocytic leukemia (B-CLL) have increased interest in developing additional immunotherapies for the disease. CD40 ligand is an accessory signal for T-cell activation and can overcome T-cell anergy. The OX40-OX40 ligand pathway is involved in the subsequent expansion of memory antigen-specific T cells. We expressed both CD40L and OX40L on B-CLL cells by exploiting the phenomenon of molecular transfer from fibroblasts overexpressing these ligands. We analyzed the effects of the modified B-CLL cells on the number, phenotype, and cytotoxic function of autologous T cells in 7 B-CLL patients. Transfer of CD40L and OX40L was observed in all and was followed by the up-regulation of B7-1 and B7-2. The culture of CD40L/OX40L-expressing B-CLL cells with autologous T cells generated CD4+/CD8+ cytotoxic T-cell lines, which secreted interferon-gamma (IFN-gamma) and granzyme-B/perforin in response to autologous, but not to allogeneic, B-CLL cells or to autologous T-cell blasts. CD40L or OX40L alone was insufficient to expand tumor-reactive T cells. The combination of CD40L and OX40L on B-CLL cells may allow the generation of therapeutic immune responses to B-CLL, either by active immunization with modified tumor cells or by adoptive immunotherapy with tumor-reactive autologous T cells.

Selective depletion of activated T cells: the CD40L-specific antibody experience

Blocking the signal that provides co-stimulation to T cells during their encounter with antigen is thought to make T cells anergic or tolerant. Recently, treatments using CD40L-specific antibody, a co-stimulation blocking reagent, in primate transplant models indicated that this elegant concept could finally be turning into reality. In this context, the finding that CD40L-specific antibody acts through depletion of activated T cells rather than through co-stimulation blockade might seem undesirable. However, the selective removal of cells that are key effectors of immunopathology could provide a powerful tool for containing unwanted immune responses such as those that mediate autoimmune diseases and transplant rejection.

Cross-talk between activated human NK cells and CD4+ T cells via OX40-OX40 ligand interactions

It is important to understand which molecules are relevant for linking innate and adaptive immune cells. In this study, we show that OX40 ligand is selectively induced on IL-2, IL-12, or IL-15-activated human NK cells following stimulation through NKG2D, the low affinity receptor for IgG (CD16) or killer cell Ig-like receptor 2DS2. CD16-activated NK cells costimulate TCR-induced proliferation, and IFN-gamma produced by autologous CD4+ T cells and this process is dependent upon expression of OX40 ligand and B7 by the activated NK cells. These findings suggest a novel and unexpected link between the natural and specific immune responses, providing direct evidence for cross-talk between human CD4+ T cells and NK receptor-activated NK cells.

Dendritic cell-mediated T cell polarization

Effective defense against diverse types of micro-organisms that invade our body requires specialized classes of antigen-specific immune responses initiated and maintained by distinct subsets of effector CD4(+) T helper (Th) cells. Excessive or detrimental (e.g., autoimmune) responses by effector T cells are controlled by regulatory T cells. The optimal balance in the development of the different types of effector and regulatory Th cells is orchestrated by dendritic cells (DC). This review discusses the way DC adapt the T cell response to the type of pathogen, focusing on the tools that DC use in this management of the T cell response.

Engagement of Glucocorticoid-Induced TNFR Family-Related Receptor on Effector T Cells by its Ligand Mediates Resistance to Suppression by CD4+CD25+ T Cells

Nonactivated CD4+CD25+ regulatory T cells constitutively express glucocorticoid-induced TNFR family-related receptor (GITR), a TNFR family member whose engagement was presumed to abrogate regulatory T cell-mediated suppression. Using GITR-/- mice, we report that GITR engagement on CD25-, not CD25+ T cells abrogates T cell-mediated suppression. Mouse APCs constitutively express GITR ligand (GITR-L), which is down-regulated following TLR signaling in vivo. Although GITR-/-CD25- T cells were capable of mounting proliferative responses, they were incapable of proliferation in the presence of physiological numbers of CD25+ T cells. Thus, GITR-L provides an important signal for CD25- T cells, rendering them resistant to CD25+ -mediated regulation at the initiation of the immune response. The down-regulation of GITR-L by inflammatory stimuli may enhance the susceptibility of effector T cells to suppressor activity during the course of an infectious insult.

Critical Role of TNF Receptor Type-2 (p75) as a Costimulator for IL-2 Induction and T Cell Survival: A Functional Link to CD28

CD28 provides important signals that lower the threshold of T cell activation, augment the production of IL-2, and promote T cell survival. The recent identification of a second family of costimulatory molecules within the TNFR family has reshaped the "two-signal" model of T cell activation. In this study the role of p75 as a T cell costimulatory molecule in controlling cell fate during TCR/CD28-mediated stimulation was examined. We found that p75-deficient T cells possess a profound defect in IL-2 production in response to TCR/CD28-mediated stimulation. Examination of key signaling intermediates revealed that TCR proximal events such as global tyrosine phosphorylation and ZAP70 phosphorylation, as well as downstream MAPK cascades are unperturbed in p75-deficient T cells. In contrast, p75 is nonredundantly coupled to sustained AKT activity and NF-kappaB activation in response to TCR/CD28-mediated stimulation. Moreover, p75-deficient T cells possess a defect in survival during the early phase of T cell activation that is correlated with a striking defect in Bcl-x(L) expression. These data indicate discrete effects of p75 on the intracellular signaling milieu during T cell activation, and reveal the synergistic requirement of TCR, CD28, and p75 toward optimal IL-2 induction and T cell survival. We propose that p75 acts as one of the earliest of the identified costimulatory members of the TNFR family, and is functionally linked to CD28 for initiating and determining T cell fate during activation.

CD137-Deficient Mice Have Reduced NK/NKT Cell Numbers and Function, Are Resistant to Lipopolysaccharide-Induced Shock Syndromes, and Have Lower IL-4 Responses

CD137, a member of the TNF superfamily, is involved in T cell and NK cell activation and cytokine production. To establish its in vivo role in systems dependent on NK and NKT cells, we studied the response of CD137-/- mice to LPS-induced shock, tumor killing, and their IL-4-controlled Th2 responses. In both high and low dose shock models, all the CD137-deficient mice, but none of the wild-type BALB/c mice, survived. After injection of LPS/2-amino-2-deoxy-D-galactose (D-gal), CD137-/- mice had reduced serum cytokine levels and substantially impaired liver IFN-gamma and TNF-alpha mRNA levels. Phenotypic analysis of mononuclear cells revealed fewer NK and NKT cells in the CD137-/- mice. The knockout mice did not generate a rapid IL-4 response after systemic T cell activation, or effective Ag-specific Th2 responses. In addition, both in vitro and in vivo NK-specific cytolytic activities were reduced. These findings suggest that CD137-directed NK/NKT cells play an important role in the inflammatory response leading to the production of proinflammatory cytokines, LPS-induced septic shock, and tumor killing, as well as IL-4-dependent Th2 responses.

Tumor rejection induced by CD70-mediated quantitative and qualitative effects on effector CD8+ T cell formation

In vivo priming of antigen-specific CD8+ T cells results in their expansion and differentiation into effector T cells followed by contraction into a memory T cell population that can be maintained for life. Recent evidence suggests that after initial antigenic stimulation, the magnitude and kinetics of the CD8+ T cell response are programmed. However, it is unclear to what extent CD8+ T cell instruction in vivo is modulated by costimulatory signals. Here, we demonstrate that constitutive ligation of the tumor necrosis factor receptor family member CD27 by its ligand CD70 quantitatively augments CD8+ T cell responses to influenza virus infection and EL-4 tumor challenge in vivo by incrementing initial expansion and maintaining higher numbers of antigen-specific T cells in the memory phase. Concomitantly, the quality of antigen-specific T cells improved as evidenced by increased interferon (IFN)-gamma production and a greater cytotoxic potential on a per cell basis. As an apparent consequence, the superior effector T cell formation induced by CD70 protected against a lethal dose of poorly immunogenic EL4 tumor cells in a CD8+ T cell- and IFN-gamma-dependent manner. Thus, CD70 costimulation enhances both the expansion and per cell activity of antigen-specific CD8+ T cells.

4-1BB and OX40 Dual Costimulation Synergistically Stimulate Primary Specific CD8 T Cells for Robust Effector Function

CD40, 4-1BB, and OX40 are costimulatory molecules belonging to the TNF/nerve growth factor superfamily of receptors. We examined whether simultaneous costimulation affected the responses of T cells using several different in vivo tracking models in mice. We show that enforced dual costimulation through 4-1BB and OX40, but not through CD40, induced profound specific CD8 T cell clonal expansion. In contrast, the response of specific CD4 T cells to dual costimulation was additive rather than synergistic. The synergistic response of the specific CD8 T cells persevered for several weeks, and the expanded effector cells resided throughout lymphoid and nonlymphoid tissue. Dual costimulation through 4-1BB and OX40 did not increase BrdU incorporation nor an increase in the number of rounds of T cell division in comparison to single costimulators, but rather enhanced accumulation in a cell-intrinsic manner. Mechanistically speaking, we show that CD8 T cell clonal expansion and effector function did not require T help, but accumulation in (non)lymphoid tissue was predominantly CD4 T cell dependent. To determine whether this approach would be useful in a physiological setting, we demonstrated that dual costimulation mediated rejection of an established murine sarcoma. Importantly, effector function directed toward established tumors was CD8 T cell dependent while being entirely CD4 T cell independent, and the timing of enforced dual costimulation was exquisitely regulated. Collectively, these data suggest that simultaneous dual costimulation through 4-1BB and OX40 induces a massive burst of CD8 T cell effector function sufficient to therapeutically treat established tumors even under immunocompromising conditions.

Contribution of CD30/CD153 but not of CD27/CD70, CD134/OX40L, or CD137/4-1BBL to the optimal induction of protective immunity toMycobacterium avium

A panel of monoclonal antibodies specific for CD27 ligand (CD70), CD30 ligand (CD153), CD134 ligand (OX40L), and CD137 ligand (4-1BBL) were screened in vivo for their ability to affect the control of Mycobacterium avium infection in C57Bl/6 mice. Only the blocking of CD153 led to increased mycobacterial burdens. We then used CD30-deficient mice and found an increase in the proliferation of two strains of M. avium in these mice as compared with control animals. The increased mycobacterial growth was associated with decreased T cell expansion and reduced interferon-gamma (IFN-gamma) responses as a result of reduced polarization of the antigen-specific, IFN-gamma-producing T cells. At late times but not early in infection, the lymphoid cuff surrounding granulomas was depleted in the CD30-deficient animals. This report expands our knowledge about tumor necrosis factor superfamily members involved in the immune responses to mycobacterial infection by identifying CD30-CD153 interactions as required for optimal immune control of M. avium infection.

In situ tumor ablation creates an antigen source for the generation of antitumor immunity

Tumor-destructing techniques, like radiofrequency ablation (RFA), allow eradication of large tumors. Potentially, in situ tumor destruction also can provide the immune system with an antigen source for the induction of antitumor immunity. Antigen-presenting cells could take up antigens in the periphery after which they induce specific immune responses. Recent data show that especially antigen-presenting dendritic cells are crucial for the induction of potent immune responses. However, virtually nothing is known regarding the induction of immune responses after in situ tumor destruction in mice or humans. We used the well-defined murine B16-OVA melanoma cell line to develop a novel tumor model to explore: (a). the immunologic consequences of in situ tumor destruction; and (b). the efficacy of a combination approach of tumor destruction and immunostimulation. Applying this model system we demonstrate that following RFA, a weak but detectable immune response develops, directed against OVA, but also against a broader range of B16 antigens. Adoptive transfer experiments further indicate that antitumor reactivity can be transferred to naïve mice by splenocytes. To augment the response observed, we administered a blocking monoclonal antibody against cytotoxic T-lymphocyte-associated antigen 4 at the time of tumor destruction. Interestingly, this strongly enhanced antitumor immunity, resulting in long-lasting tumor protection. These results illustrate that in situ tumor destruction can provide a useful antigen source for the induction of antitumor immunity, provided that additional immunostimulatory signals are coadministered.

Herpes simplex virus: receptors and ligands for cell entry

Entry of herpes simplex virus (HSV) into cells depends upon multiple cell surface receptors and multiple proteins on the surface of the virion. The cell surface receptors include heparan sulphate chains on cell surface proteoglycans, a member of the tumor necrosis factor (TNF) receptor family and two members of the immunoglobulin superfamily related to the poliovirus receptor. The HSV ligands for these receptors are the envelope glycoproteins gB and gC for heparan sulphate and gD for the protein receptors and specific sites in heparan sulphate generated by certain 3-O-sulfotransferases. HSV gC also binds to the C3b component of complement and can block complement-mediated neutralization of virus. The purposes of this review are to summarize available information about these cell surface receptors and the viral ligands, gC and gD, and to discuss roles of these viral glycoproteins in immune evasion and cellular responses as well as in viral entry.