ICOS costimulation requires IL-2 and can be prevented by CTLA-4 engagement

Addressing the Elephant in the Immunotherapy Room: Effector T-Cell Priming versus Depletion of Regulatory T-Cells by Anti-CTLA-4 Therapy

Cytotoxic T-lymphocyte Associated Protein 4 (CTLA-4) is an immune checkpoint molecule highly expressed on regulatory T-cells (Tregs) that can inhibit the activation of effector T-cells. Anti-CTLA-4 therapy can confer long-lasting clinical benefits in cancer patients as a single agent or in combination with other immunotherapy agents. However, patient response rates to anti-CTLA-4 are relatively low, and a high percentage of patients experience severe immune-related adverse events. Clinical use of anti-CTLA-4 has regained interest in recent years; however, the mechanism(s) of anti-CTLA-4 is not well understood. Although activating T-cells is regarded as the primary anti-tumor mechanism of anti-CTLA-4 therapies, mounting evidence in the literature suggests targeting intra-tumoral Tregs as the primary mechanism of action of these agents. Tregs in the tumor microenvironment can suppress the host anti-tumor immune responses through several cell contact-dependent and -independent mechanisms. Anti-CTLA-4 therapy can enhance the priming of T-cells by blockading CD80/86-CTLA-4 interactions or depleting Tregs through antibody-dependent cellular cytotoxicity and phagocytosis. This review will discuss proposed fundamental mechanisms of anti-CTLA-4 therapy, novel uses of anti-CTLA-4 in cancer treatment and approaches to improve the therapeutic efficacy of anti-CTLA-4.

Acazicolcept (ALPN-101), a dual ICOS/CD28 antagonist, demonstrates efficacy in systemic sclerosis preclinical mouse models

Background

Uncontrolled immune response with T cell activation has a key role in the pathogenesis of systemic sclerosis (SSc), a disorder that is characterized by generalized fibrosis affecting particularly the lungs and skin. Costimulatory molecules are key players during immune activation, and recent evidence supports a role of CD28 and ICOS in the development of fibrosis. We herein investigated the efficacy of acazicolcept (ALPN-101), a dual ICOS/CD28 antagonist, in two complementary SSc-related mouse models recapitulating skin fibrosis, interstitial lung disease, and pulmonary hypertension.

Methods

Expression of circulating soluble ICOS and skin-expressed ICOS was investigated in SSc patients. Thereafter, acazicolcept was evaluated in the hypochlorous acid (HOCL)-induced dermal fibrosis mouse model and in the Fra-2 transgenic (Tg) mouse model. In each model, mice received 400 μg of acazicolcept or a molar-matched dose of an Fc control protein twice a week for 6 weeks. After 6 weeks, skin and lung were evaluated.

Results

ICOS was significantly increased in the sera from SSc patients and in SSc skin biopsies as compared to samples from healthy controls. Similar body weight changes were observed between Fc control and acazicolcept groups in both HOCL and Fra-2 Tg mice suggesting a good tolerance of acazicolcept treatment. In mice challenged with HOCL, acazicolcept induced a significant decrease in dermal thickness, collagen content, myofibroblast number, and inflammatory infiltrates characterized by B cells, T cells, neutrophils, and macrophages. In the Fra-2 Tg mouse model, acazicolcept treatment reduced lung collagen content, fibrillar collagen, histological fibrosis score, and right ventricular systolic pressure (RVSP). A reduction in frequency of CD4+ and T effector memory cells and an increase in the percentage of CD4+ T naïve cells in spleen and lung of acazicolcept-treated Fra-2 Tg mice was observed as compared to Fc control-treated Fra-2 Tg mice. Moreover, acazicolcept reduced CD69 and PD-1 expression on CD4+ T cells from the spleen and the lung. Target engagement by acazicolcept was demonstrated by blockade of CD28 and ICOS detection by flow cytometry in treated mice.

Conclusions

Our results confirm the importance of costimulatory molecules in inflammatory-driven fibrosis. Our data highlight a key role of ICOS and CD28 in SSc. Using complementary models, we demonstrated that dual ICOS/CD28 blockade by acazicolcept decreased dermal and pulmonary fibrosis and alleviated pulmonary hypertension. These results pave the way for subsequent research on ICOS/CD28-targeted therapies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13075-021-02709-2.

Inducible T-Cell Costimulator Ligand Plays a Dual Role in Melanoma Metastasis upon Binding to Osteopontin or Inducible T-Cell Costimulator

Recently, we demonstrated that inducible T-cell costimulator (ICOS) shares its unique ligand (ICOSL) with osteopontin (OPN), and OPN/ICOSL binding promotes tumor metastasis and angiogenesis in the 4T1 breast cancer model. Literature showed that OPN promotes melanoma metastasis by suppressing T-cell activation and recruiting myeloid suppressor cells (MDSC). On the opposite, ICOS/ICOSL interaction usually sustains an antitumor response. Here, we engineered murine B16F10 melanoma cells, by transfecting or silencing ICOSL. In vitro data showed that loss of ICOSL favors anchorage-independent growth and induces more metastases in vivo, compared to ICOSL expressing cells. To dissect individual roles of the three molecules, we compared data from C57BL/6 with those from OPN-KO, ICOS-KO, and ICOSL-KO mice, missing one partner at a time. We found that OPN produced by the tumor microenvironment (TME) favors the metastasis by interacting with stromal ICOSL. This activity is dominantly inhibited by ICOS expressed on TME by promoting Treg expansion. Importantly, we also show that OPN and ICOSL highly interact in human melanoma metastases compared to primary tumors. Interfering with this binding may be explored in immunotherapy either for nonresponding or patients resistant to conventional therapies.

Tackling Immune Targets for Breast Cancer: Beyond PD-1/PD-L1 Axis

The burden of breast cancer is imposing a huge global problem. Drug discovery research and novel approaches to treat breast cancer have been carried out extensively over the last decades. Although immune checkpoint inhibitors are showing promising preclinical and clinical results in treating breast cancer, they are facing multiple limitations. From an immunological perspective, a recent report highlighted breast cancer as an "inflamed tumor" with an immunosuppressive microenvironment. Consequently, researchers have been focusing on identifying novel immunological targets that can tune up the tumor immune microenvironment. In this context, several novel non-classical immune targets have been targeted to determine their ability to uncouple immunoregulatory pathways at play in the tumor microenvironment. This article will highlight strategies designed to increase the immunogenicity of the breast tumor microenvironment. It also addresses the latest studies on targets which can enhance immune responses to breast cancer and discusses examples of preclinical and clinical trial landscapes that utilize these targets.

T cell costimulation, checkpoint inhibitors and anti-tumor therapy

The hallmarks of the adaptive immune response are specificity and memory. The cellular response is mediated by T cells which express cell surface T cell receptors (TCRs) that recognize peptide antigens in complex with major histocompatibility complex (MHC) molecules on antigen presenting cells (APCs). However, binding of cognate TCRs with MHC-peptide complexes alone (signal 1) does not trigger optimal T cell activation. In addition to signal 1, the binding of positive and negative costimulatory receptors to their ligands modulates T cell activation. This complex signaling network prevents aberrant activation of T cells. CD28 is the main positive costimulatory receptor on naı¨ve T cells; upon activation, CTLA4 is induced but reduces T cell activation. Further studies led to the identification of additional negative costimulatory receptors known as checkpoints, e.g. PD1. This review chronicles the basic studies in T cell costimulation that led to the discovery of checkpoint inhibitors, i.e. antibodies to negative costimulatory receptors (e.g. CTLA4 and PD1) which reduce tumor growth. This discovery has been recognized with the award of the 2018 Nobel prize in Physiology/Medicine. This review highlights the structural and functional roles of costimulatory receptors, the mechanisms by which checkpoint inhibitors work, the challenges encountered and future prospects.

Anti-CD40 mAb enhanced efficacy of anti-PD1 against osteosarcoma

The overall survival rate of patients with osteosarcoma has remained stagnant at 15-30% for several decades. Although immunotherapy has revolutionized the oncology field, largely attributed to the success of immune-checkpoint blockade, the durability and efficacy of anti-PD1 (programmed cell death protein 1) mAb vary across different malignancies. Among the major reasons for tumor resistance to this immune checkpoint therapy is the absence of tumor-infiltrating cytotoxic T lymphocytes. However, the presence of intratumor exhausted PD1^hi T cells also contributes to insensitivity to anti-PD1 treatment. In this study, we established the osteosarcoma mouse tumor model resistant to anti-PD1 mAb that harbored PD1^hi T cells. Furthermore, flow cytometry analysis of tumor infiltrating leukocytes after treatment was used as a screening platform to identify agents that could re-sensitize T cells to anti-PD1 mAb. Results showed that anti-CD40 mAb treatment converted PD1^hi T cells to PD1^lo T cells, reversing phenotypic T cell exhaustion and sensitizing anti-PD1 refractory tumors to respond to anti-PD1 mAb. Results also showed that intratumor Treg presented with a less activated and attenuated suppressive phenotype after anti-CD40 mAb treatment. Our study provides proof of concept to systematically identify immune conditioning agents, which are able to convert PD1^hi T cells to PD1^lo T cells, with clinical implications in the treatment against refractory osteosarcoma to anti-PD1 mAb.

Pilot Study of Delayed ICOS/ICOS-L Blockade With αCD40 to Modulate Pathogenic Alloimmunity in a Primate Cardiac Allograft Model

Supplemental digital content is available in the text.

Background

Inducible costimulator (ICOS) is rapidly upregulated with T-cell stimulation and may represent an escape pathway for T-cell costimulation in the setting of CD40/CD154 costimulation blockade. Induction treatment exhibited no efficacy in a primate renal allograft model, but rodent transplant models suggest that the addition of delayed ICOS/ICOS-L blockade may prolong allograft survival and prevent chronic rejection. Here, we ask whether ICOS-Ig treatment, timed to anticipate ICOS upregulation, prolongs NHP cardiac allograft survival or attenuates pathogenic alloimmunity.

Methods

Cynomolgus monkey heterotopic cardiac allograft recipients were treated with αCD40 (2C10R4, d0-90) either alone or with the addition of delayed ICOS-Ig (d63-110).

Results

Median allograft survival was similar between ICOS-Ig + αCD40 (120 days, 120-125 days) and αCD40 (124 days, 89-178 days) treated animals, and delayed ICOS-Ig treatment did not prevent allograft rejection in animals with complete CD40 receptor coverage. Although CD4⁺ T_EM cells were decreased in peripheral blood (115 ± 24) and mLNs (49 ± 1.9%) during ICOS-Ig treatment compared with monotherapy (214 ± 27%, P = 0.01; 72 ± 9.9%, P = 0.01, respectively), acute and chronic rejection scores and kinetics of alloAb elaboration were similar between groups.

Conclusions

Delayed ICOS-Ig treatment with the reagent tested is probably ineffective in modulating pathogenic primate alloimmunity in this model.

Baseline gut microbiota predicts clinical response and colitis in metastatic melanoma patients treated with ipilimumab

Background

Ipilimumab, an immune checkpoint inhibitor targeting CTLA-4, prolongs survival in a subset of patients with metastatic melanoma (MM) but can induce immune-related adverse events, including enterocolitis. We hypothesized that baseline gut microbiota could predict ipilimumab anti-tumor response and/or intestinal toxicity.

Patients and methods

Twenty-six patients with MM treated with ipilimumab were prospectively enrolled. Fecal microbiota composition was assessed using 16S rRNA gene sequencing at baseline and before each ipilimumab infusion. Patients were further clustered based on microbiota patterns. Peripheral blood lymphocytes immunophenotypes were studied in parallel.

Results

A distinct baseline gut microbiota composition was associated with both clinical response and colitis. Compared with patients whose baseline microbiota was driven by Bacteroides (cluster B, n = 10), patients whose baseline microbiota was enriched with Faecalibacterium genus and other Firmicutes (cluster A, n = 12) had longer progression-free survival (P = 0.0039) and overall survival (P = 0.051). Most of the baseline colitis-associated phylotypes were related to Firmicutes (e.g. relatives of Faecalibacterium prausnitzii and Gemmiger formicilis), whereas no colitis-related phylotypes were assigned to Bacteroidetes. A low proportion of peripheral blood regulatory T cells was associated with cluster A, long-term clinical benefit and colitis. Ipilimumab led to a higher inducible T-cell COStimulator induction on CD4+ T cells and to a higher increase in serum CD25 in patients who belonged to Faecalibacterium-driven cluster A.

Conclusion

Baseline gut microbiota enriched with Faecalibacterium and other Firmicutes is associated with beneficial clinical response to ipilimumab and more frequent occurrence of ipilimumab-induced colitis.

Signals that drive T follicular helper cell formation

T follicular helper (Tfh) cells are a distinct type of CD4⁺ T cell specialized in providing help to B cells during the germinal centre (GC) reaction. As such, they are critical determinants of the quality of an antibody response following antigen challenge. Excessive production of Tfh cells can result in autoimmunity whereas too few can result in inadequate protection from infection. Hence, their differentiation and maintenance must be tightly regulated to ensure appropriate but limited help to B cells. Unlike the majority of other CD4⁺ T-cell subsets, Tfh cell differentiation occurs in three phases defined by their anatomical location. During each phase of differentiation the emerging Tfh cells express distinct patterns of co-receptors, which work together with the T-cell receptor (TCR) to drive Tfh differentiation. These signals provided by both TCR and co-receptors during Tfh differentiation alter proliferation, survival, metabolism, cytokine production and transcription factor expression. This review will discuss how engagement of TCR and co-receptors work together to shape the formation and function of Tfh cells.

Inhibition of Donor-Reactive CD8+ T Cell Responses by Selective CD28 Blockade Is Independent of Reduced ICOS Expression

Programmed T cell differentiation is critically influenced by the complement of costimulatory and coinhibitory signals transmitted during initial antigen encounter. We previously showed that selective CD28 blockade with novel domain antibodies that leave CTLA-4-mediated coinhibitory signaling intact resulted in more profound attenuation of donor-reactive T cell responses and improved graft survival in a murine transplant model. Selective CD28 blockade was also associated with decreased ICOS expression on donor-reactive CD8⁺ T cell responses as compared to CTLA-4 Ig, but the functional importance of this reduced ICOS expression was not known. In this study, we created retrogenic donor-reactive CD8⁺ T cells that overexpress ICOS in order to determine whether reduced ICOS expression mechanistically underlies the increased efficacy of selective CD28 blockade in controlling graft-specific T cell responses as compared to conventional costimulation blockade with CTLA-4 Ig. Results indicated that the ability of selective CD28 blockade to blunt donor-reactive CD8⁺ T cell expansion following transplantation was independent of its ability to inhibit ICOS expression. Furthermore, we have previously published that 2B4 coinhibitory signals are functionally important for controlling graft-specific CD8⁺ T cell responses in mice treated with CD28 blockade. Here we used a co-adoptive transfer approach to determine that 2B4 coinhibitory signals on antigen-specific CD8⁺ T cells function in a cell-intrinsic manner to limit ICOS expression in the setting of selective CD28 blockade.

Lack of association between cytotoxic T-lymphocyte antigen-4 -318C/T polymorphism and cancer risk: a meta-analysis of case-control studies

Cytotoxic T-lymphocyte antigen-4 (CTLA-4) is important for the down regulation of T-cell activation. Number of studies assessed the association between CTLA-4 -318C/T polymorphisms and cancer in different populations. However, the studies have provided conflicting results. We performed a meta-analysis to examine the association between CTLA-4 -318C/T polymorphisms and cancer susceptibility. Eligible studies were identified by searching several databases for relevant reports published up to September 30, 2012. Sixteen eligible studies with a total of 6190 patients and 6560 controls were included to summarize the association between CTLA-4 -318C/T polymorphisms and the risk of cancer. Odds ratios (ORs) with 95% confidence intervals (CIs) were used to assess the strength of associations. Overall, no significant associations were found in all genetic models when all studies were pooled into the meta-analysis (for -318C/T polymorphisms as estimated using a fixed effect model: TT vs. (CC + CT), OR = 1.02, 95% CI = 0.83-1.24; (TT + CT) vs. CC, OR = 1.20, 95% CI = 1.00-1.44; TT vs. CC, OR = 1.09, 95% CI = 0.74-1.59; CT vs. CC, OR = 1.21, 95% CI = 1.00-1.46). In further subgroup analyses for the -318C/T polymorphisms, stratified by design of ethnicity, cancer types, solid tumors to non-solid tumors, epithelial tumors to non-epithelial tumors, no significant associations were found in any subgroup of the population. This meta-analysis strongly suggests that -318C/T polymorphisms in CTLA-4 are not associated with an increased risk of cancer.

Phosphatidylinositol 3-kinase-independent signaling pathways contribute to ICOS-mediated T cell costimulation in acute graft-versus-host disease in mice

We and others have previously shown that ICOS plays an important role in inducing acute graft-versus-host disease (GVHD) in murine models of allogeneic bone marrow transplantation. ICOS potentiates TCR-mediated PI3K activation and intracellular calcium mobilization. However, ICOS signal transduction pathways involved in GVHD remain unknown. In this study, we examined the contribution of ICOS-PI3K signaling in the pathogenic potential of T cells using a knock-in mouse strain, ICOS-YF, which selectively lost the ability to activate PI3K. We found that when total T cells were used as alloreactive T cells, ICOS-YF T cells caused less severe GVHD compared with ICOS wild-type T cells, but they induced much more aggressive disease than ICOS knockout T cells. This intermediate level of pathogenic capacity of ICOS-YF T cells was correlated with similar levels of IFN-γ-producing CD8 T cells that developed in the recipients of ICOS-WT or ICOS-YF T cells. We further evaluated the role of ICOS-PI3K signaling in CD4 versus CD8 T cell compartment using GVHD models that are exclusively driven by CD4 or CD8 T cells. Remarkably, ICOS-YF CD8 T cells caused disease similar to ICOS wild-type CD8 T cells, whereas ICOS-YF CD4 T cells behaved very similarly to their ICOS knockout counterparts. Consistent with their in vivo pathogenic potential, CD8 T cells responded to ICOS ligation in vitro by PI3K-independent calcium flux, T cell activation, and proliferation. Thus, in acute GVHD in mice, CD4 T cells heavily rely on ICOS-PI3K signaling pathways; in contrast, CD8 T cells can use PI3K-independent ICOS signaling pathways, possibly through calcium.

Expression of NTRK1/TrkA affects immunogenicity of neuroblastoma cells

High levels of the NTRK1/TrkA receptor are expressed in low-stage neuroblastomas, which are characterized by a good patient prognosis and often undergo spontaneous regression. In addition to apoptosis, tumor-immune responses might contribute to this regression. We hypothesized that TrkA expression might enhance the immune response to neuroblastomas. Immunohistochemistry on neuroblastoma tissue microarrays confirmed significantly higher lymphocyte infiltration in low-stage compared with high-stage tumors. Flow cytometry of human SH-SY5Y cells stably transfected with NTRK1/TrkA cDNA revealed significant upregulation of major histocompatibility complex (MHC) class I complexes on TrkA-expressing cells. Corresponding to this upregulation, T cell activity and cytoxicity was enhanced in the presence of SY5Y-TrkA cells or by medium conditioned by them, suggesting the existence of additional soluble factors stimulating the T cell response. Activation of natural killer (NK) cells was only increased in the presence of SY5Y-TrkA conditioned medium (CM) and not in co-culture assays, suggesting a dominant inhibitory effect of upregulated MHC class I as the primary NK cell escape mechanism of TrkA-expressing neuroblastomas. We reanalyzed gene expression data obtained from the cell culture model to identify additional genes involved in the TrkA-mediated modulation of immune responses. Upregulation of selected target genes in SY5Y-TrkA cells was confirmed on transcript and protein levels. However, none of the proteins were detected in medium conditioned by SY5Y-TrkA cells, arguing against these factors as soluble mediators of the TrkA-induced immune response. We here provide evidence that TrkA expression in neuroblastoma leads to an increased immunogenicity that may contribute to a less malignant phenotype and/or spontaneous regression of neuroblastoma cells.

ICOS-ligand expression on plasmacytoid dendritic cells supports breast cancer progression by promoting the accumulation of immunosuppressive CD4+ T cells

Human breast tumors are infiltrated by memory CD4(+) T cells along with increased numbers of regulatory T cells (Treg) and plasmacytoid dendritic cells (pDC) that facilitate immune escape and correlate with poor prognosis. Here, we report that inducible costimulatory molecule (ICOS), a T cell costimulatory molecule of the CTLA4/PD1/CD28 family, is expressed mostly by tumor-associated Treg in primary breast tumors. A large proportion of these ICOS(+) Treg were Ki67(+) and this evident proliferative expansion was found to rely on interactions with tumor-associated pDC. Indeed, tumor-associated Treg highly expanded in presence of pDC but failed to proliferate under CD3/CD28 signal. In vitro experiments revealed that the addition of a neutralizing anti-ICOS antibody blocked pDC-induced Treg expansion and interleukin-10 secretion by memory CD4(+) T cells, establishing a pivotal role for ICOS in this process. Supporting these findings, the presence of ICOS(+) cells in clinical specimens of breast cancer correlated with a poor prognosis. Together, our results highlight an important relationship between Treg and pDC in breast tumors, and show that ICOS/ICOS-L interaction is a central event in immunosuppression of tumor-associated memory CD4(+) T cells. These findings strongly rationalize antibody-mediated ICOS blockade as a powerful clinical strategy to correct immune escape and promote therapeutic responses in breast cancer.

CD28 family and chronic rejection: "to belatacept...And beyond!"

Kidneys are one of the most frequently transplanted human organs. Immunosuppressive agents may prevent or reverse most acute rejection episodes; however, the graft may still succumb to chronic rejection. The immunological response involved in the chronic rejection process depends on both innate and adaptive immune response. T lymphocytes have a pivotal role in chronic rejection in adaptive immune response. Meanwhile, we aim to present a general overview on the state-of-the-art knowledge of the strategies used for manipulating the lymphocyte activation mechanisms involved in allografts, with emphasis on T-lymphocyte costimulatory and coinhibitory molecules of the B7-CD28 superfamily. A deeper understanding of the structure and function of these molecules improves both the knowledge of the immune system itself and their potential action as rejection inducers or tolerance promoters. In this context, the central role played by CD28 family, especially the relationship between CD28 and CTLA-4, becomes an interesting target for the development of immune-based therapies aiming to increase the survival rate of allografts and to decrease autoimmune phenomena. Good results obtained by the recent development of abatacept and belatacept with potential clinical use aroused better expectations concerning the outcome of transplanted patients.

Tumour cell generation of inducible regulatory T-cells in multiple myeloma is contact-dependent and antigen-presenting cell-independent

Regulatory T-cells (T_Reg cells) are increased in patients with multiple myeloma (MM). We investigated whether MM cells could generate and/or expand T_Reg cells as a method of immuno-surveillance avoidance. In an in vitro model, CD4⁺CD25^-FoxP3^- T-cells co-cultured with malignant plasma cells (primary MM cells and cell lines) induced a significant generation of CD4⁺CD25⁺FoxP3⁺ inducible T_Reg cells (tT_Reg cells; p<0.0001), in a contact-dependent manner. tT_Reg cells were polyclonal, demonstrated a suppressive phenotype and phenotypically, demonstrated increased FoxP3 (p = 0.0001), increased GITR (p<0.0001), increased PD1 (p = 0.003) and decreased CD62L (p = 0.007) expression compared with naturally occurring T_Reg cells. FACS-sorted tT_Reg cells differentiated into FoxP⁺IL-17⁺ and FoxP3^-IL-17⁺ CD4⁺ cells upon TCR-mediated stimulation. Blocking experiments with anti-ICOS-L MoAb resulted in a significant inhibition of tT_Reg cell generation whereas both IL-10 & TGFβ blockade did not. MM tumour cells can directly generate functional T_Reg cells in a contact-dependent manner, mediated by ICOS/ICOS-L. These features suggest that tumour generation of T_Reg cells may contribute to evasion of immune surveillance by the host.

Critical co-stimulatory pathways in the stability of Foxp3+ Treg cell homeostasis in Type I diabetes

Mechanisms of peripheral tolerance maintain a controlled balance between self-tolerance, protective immunity against a spectrum of non-self antigens, and suppressing pathology in various disorders. CD4(+) regulatory T cells (T(reg)) expressing the Foxp3 transcription factor dominantly control the activity and pathological consequences of a variety of effector T cell lineages in various inflammatory settings. This review will focus on recent advances on the roles of B7 family members in regulating Treg cell development, function and homeostasis during tolerance induction and organ-specific autoimmunity.

The ICOS/ICOSL pathway is required for optimal antitumor responses mediated by anti-CTLA-4 therapy

The anti-CTL-associated antigen 4 (anti-CTLA-4) antibody ipilimumab is the first agent to show improved survival in a randomized phase III trial that enrolled patients with metastatic melanoma. Studies are ongoing to identify mechanisms that elicit clinical benefit in the setting of anti-CTLA-4 therapy. We previously reported that treated patients had an increase in the frequency of T cells expressing the inducible costimulator (ICOS) molecule, a T-cell-specific molecule that belongs to the CD28/CTLA-4/B7 immunoglobulin superfamily. ICOS and its ligand (ICOSL) have been shown to play diverse roles in T-cell responses such as mediating autoimmunity as well as enhancing the development/activity of regulatory T cells. These seemingly opposing roles have made it difficult to determine whether the ICOS/ICOSL pathway is necessary for antitumor responses. To determine whether the ICOS/ICOSL pathway might play a causal role in the antitumor effects mediated by anti-CTLA-4, we conducted studies in ICOS-sufficient and ICOS-deficient mice bearing B16/BL6 melanoma. We show that ICOS(+) T cells comprised a population of Th1 cytokine producing and tumor antigen-specific effector cells. Furthermore, in the absence of ICOS, antitumor T-cell responses elicited by anti-CTLA-4 are significantly diminished, thereby impairing tumor rejection. Our findings establish that the ICOS/ICOSL pathway is necessary for the optimal therapeutic effect of anti-CTLA-4, thus implicating this pathway as a target for future combinatorial strategies to improve the efficacy of anti-CTLA-4 therapy.

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

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

Th1 cytokine responses fail to effectively control Chlamydia lung infection in ICOS ligand knockout mice

ICOS ligand (ICOSL) plays an important role in controlling specific aspects of T cell activation, differentiation, and function. Th1-type immune responses have been shown to be critical in host defense against chlamydial infections. To assess the role of ICOSL-ICOS interaction in host defense against chlamydial infection, we compared the immune responses and pathological reactions in ICOSL gene knockout (KO) and wild-type (WT) mice following Chlamydia muridarum lung infection. The results showed that ICOSL KO mice exhibited greater body weight loss, higher pathogen burden, and more severe histopathology in their lung than did WT mice. Cytokine analysis revealed that ICOSL KO mice produced lower levels of Th2 (IL-4 and IL-5) and anti-inflammatory (TGF-beta1 and IL-10) cytokines, but higher Th1-related (IFN-gamma and IL-12p40/IL-23) and proinflammatory (IL-6 and TNF-alpha) cytokines. ICOSL KO mice also showed reduced Chlamydia-specific Ab levels in their sera and lung homogenates. In addition, ICOSL KO mice demonstrated significantly lower ICOS expression in T cells and lower Th17 responses than did WT mice. Finally, we showed that ICOS-ICOSL interaction and cell-cell contact are essential for CD4(+) T cells to inhibit chlamydial growth in the cultured lung fibroblasts. The data suggest that ICOSL plays a significant role in immunoregulation and protective immunity against Chlamydia infections and that the Th1 skew in cytokine responses per se is not sufficient for effective control of Chlamydia infections.

CTLA4 gene variations and haplotypes in patients with lung cancer

The CTLA4 protein downmodulates and terminates immune responses by sending inhibitory signals to activated T cells. In this study, six main single-nucleotide polymorphisms of the CTLA4 gene were investigated in 127 lung cancer patients and 124 healthy control subjects: -1722T/C, -1661 A/G, -318 C/T, +49A/G, +1822 C/T, and +6230 A/G (CT60). Statistical analyses revealed no significant differences in the frequencies of genotypes, alleles, and haplotypes between patients and control subjects. We also could not find significant association between CTLA4 variants and any defined lung tumor type. These six single-nucleotide polymorphisms in CTLA4 were not associated with susceptibility to lung cancer in Iranian population.

Roquin differentiates the specialized functions of duplicated T cell costimulatory receptor genes CD28 and ICOS

During evolutionary adaptation in the immune system, host defense is traded off against autoreactivity. Signals through the costimulatory receptor CD28 enable T cells to respond specifically to pathogens, whereas those through the related costimulatory receptor, ICOS, which arose by gene duplication, are critical for affinity maturation and memory antibody responses. ICOS ligand, unlike the pathogen-inducible CD28 ligands, is widely and constitutively expressed in the immune system. Here, we show that crosstalk between these two pathways provides a mechanism for obviating the normal T cell dependence on CD28. Several CD28-mediated responses-generation of follicular helper T cells, germinal center formation, T helper 1 cell-dependent extrafollicular antibody responses to Salmonella and bacterial clearance, and regulatory T cell homeostasis-became independent of CD28 and dependent on ICOS when the E3 ubiquitin ligase Roquin was mutated. Mechanisms to functionally compartmentalize ICOS and CD28 signals are thus critical for two-signal control of normal immune reactions.

JTA-009, a fully human antibody against human AILIM/ICOS, ameliorates graft-vs-host reaction in SCID mice grafted with human PBMCs

OBJECTIVE

Activation-inducible lymphocyte immunomediatory molecule (AILIM; also referred to as inducible costimulator [ICOS]) is the third molecule identified in the CD28 family participating in T-cell activation. AILIM/ICOS has been implicated in both effector and pathogenic T-cell functions, as evidenced by the beneficial effects of AILIM/ICOS blockade in several murine disease models. In the present study, the role of human AILIM/ICOS in T-cell function was investigated using a fully human monoclonal antibody specific to human AILIM/ICOS (JTA-009).

MATERIALS AND METHODS

The effect of JTA-009 on allogenic T-cell proliferation was examined using human mixed lymphocyte reaction (MLR). To investigate the efficacy of AILIM/ICOS blockade in vivo, a graft-vs-host disease (GVHD) model, in which severe combined immunodeficient (SCID) mice were grafted with human peripheral blood mononuclear cells (PBMCs), was used.

RESULTS

In MLR, suppressive effect of JTA-009 on allogenic T-cell proliferation was detected with comparable potency to CD28 blockade by cytotoxic T-lymphocyte antigen 4 (CTLA4)-Ig at an intermediate culture phase. JTA-009 acts as a blocking antibody in vivo and inhibited binding of human AILIM/ICOS to mouse AILIM/ICOS ligand (B7h). Treatment with JTA-009 significantly prolonged survival of mice, with reductions of human interferon-gamma levels in blood and number of human cells in spleens.

CONCLUSION

These results demonstrate that human AILIM/ICOS plays a role in the GVHD pathogenesis mediated by human T cells, and its blockade is attractive for abrogating undesired T-cell responses as is well-documented in mice.

Expression of ICOS on human melanoma-infiltrating CD4+CD25highFoxp3+ T regulatory cells: implications and impact on tumor-mediated immune suppression

OBJECTIVE

Interaction of ICOS with its ligand (ICOSL, B7-H2) promotes T cell responses. As CD4+CD25highFoxp3+ naturally occurring T regulatory cells in melanoma patients express ICOS, we investigated the impact of ICOS on naturally occurring T regulatory cell function.

METHODS

Expression of ICOS and T regulatory (Treg) cell markers was determined on CD4+CD25high T cells in PBMC and tumor-infiltrating lymphocytes from melanoma patients (n=10) and PBMC of normal controls (n=10) by multicolor flow cytometry. Suppression mediated by sorted ICOShigh and ICOSlow Treg was assessed in CFSE-based suppression assays with autologous CD4+CD25- responder cells (RC). Transwell inserts separating Treg from RC were used to evaluate suppression mechanisms used by Treg. ICOShigh or ICOSlow Treg were coincubated with RC+/-TCR and IL-2 stimulation. ICOShigh and ICOS- Treg were also expanded under conditions previously shown to induce Tr1 from RC.

RESULTS

Treg in tumor-infiltrating lymphocytes expressed ICOS (mean fluorescence intensity=70+/-10), while Treg in PBMC had low ICOS expression (mean fluorescence intensity=3.5+/-2.5, p<or=0.001). ICOShigh Treg up-regulated Treg markers (p<or=0.0016) and mediated stronger suppression (p<or=0.001) relative to ICOSlow Treg. ICOShigh Treg induced Tr1 cells in nonactivated RC and Th2 cells in preactivated RC. ICOShigh Treg exposed to Tr1 cytokines expressed IL-10 and suppressed RC (92+/-12%) in contrast to ICOSlow Treg, which mediated low suppression (21+/-15%; p<or=0.0028).

CONCLUSION

ICOShigh Treg can induce diverse immune responses in RC, depending on activation signals and cytokines present. ICOShigh Treg induce Tr1 or Th2 cells depending on the activation state of RC. In a "Tr1" cytokine milieu, ICOShigh Treg transit to Tr1.

Critical role of activation-inducible lymphocyte immunomediatory molecule/inducible costimulator in the effector function of human T cells: a comparative in vitro study of effects of its blockade and CD28 blockade in human beings and monkeys

Activation-inducible lymphocyte immunomediatory molecule (AILIM; also referred to as inducible costimulator, ICOS) is the third homolog of the "professional" costimulatory molecule, CD28. To date, the characteristics and role of AILIM/ICOS, especially in effector function of T cells, have been determined through numerous studies in vitro and in vivo using mice. Considering potential differences among species, whether the AILIM/ICOS blockade acts as an efficacious immunomodulator for human diseases remains to be elucidated. In the present study, ability of AILIM/ICOS blockade to modulate immune responses of human and monkey cells was investigated using a fully human antibody (JTA-009), comparing the effect of CD28 blockade. JTA-009 blocked the response of human and monkey T cells co-stimulated with anti-CD3 and AILIM/ICOS ligand, B7h. AILIM/ICOS and CD28 blockade both inhibited human mixed lymphocyte reaction in different fashions, as well as cytokine production in T helper (Th) 1-/Th2-type recall responses. In monkeys however, CD28 blockade by CTLA4-Ig effectively prevented mixed lymphocyte reaction to a greater extent than AILIM/ICOS blockade. These results suggest that AILIM/ICOS blockade is valuable for suppressing both primary allogenic response and recall responses of T cell in human beings, and that there are differences between human and monkey use preferences for costimulatory molecules.

Cutting edge: Foxp3-mediated induction of pim 2 allows human T regulatory cells to preferentially expand in rapamycin

Addition of rapamycin to cultures of expanding natural CD4+CD25+Foxp3+ T regulatory cells (Tregs) helps maintain their suppressive activity, but the underlying mechanism is unclear. Pim 2 is a serine/threonine kinase that can confer rapamycin resistance. Unexpectedly, pim 2 was found to be constitutively expressed in freshly isolated, resting Tregs, but not in CD4+CD25- T effector cells. Introduction of Foxp3, but not Foxp3Delta2, into effector T cells induced pim 2 expression and conferred preferential expansion in the presence of rapamycin, indicating that Foxp3 can regulate pim 2 expression. Finally, we determined there is a positive correlation between Treg expansion and Foxp3 expression in the presence of rapamycin. Together, these results indicate that Tregs are programmed to be resistant to rapamycin, providing further rationale for why this immunosuppressive drug should be used in conjunction with expanded Tregs.

Follicular associated T cells and their B-cell helper qualities

The immune system utilizes sophisticated cellular surveillance mechanisms to maintain the integrity of the multicellular host. Adaptive immunosurveillance in particular constitutes a powerful branch of the immune system that houses the capacity to mount exquisitely specific responses against a diverse array of foreign antigens. Central to the development of adaptive immunity is the activation of T and B cells. Upon antigen engagement, T and B cells have been observed to undergo striking changes in their migratory status and distribution within secondary lymphoid organs, a phenomenon that is to a large extent controlled through their altered responsiveness to homeostatic T- and B-zone chemokines. Changes in their chemokine receptor expression and/or sensitivity to their respective ligands assist in bringing rare antigen-specific T and B lymphocytes, dendritic cells and CD4+CD3(-) accessory cells together. Cognate interaction between these cells at the T-B junction can support the generation of extrafollicular foci of antibody producing plasma cells and the formation of germinal centers. Such T-dependent antibody responses are highly dependent on the functional properties and activity of a specialized subset of CXCR5+ICOS+ CD4 T cells referred to as T follicular helper cells (T FH). This review presents an overview of some of the defining characteristics of this subset of T-helper cells and the chemokine receptors and their ligands that help dictate the migratory activity of T(FH) cells within secondary lymphoid organs.

CD4+ICOS+ T lymphocytes inhibit T cell activation 'in vitro' and attenuate autoimmune encephalitis 'in vivo'

The inducible co-stimulator (ICOS, CD278) is essential to the efficient development of normal and pathological immune reactions. Since ICOS-deficient mice have enhanced susceptibility to experimental allergic encephalomyelitis (EAE), we have functionally analyzed a CD4+ICOS+ population comprising 6-15% of all CD4+ T cells in secondary lymphoid organs of unmanipulated wild-type mice and checked for their ability to suppress EAE. In C57BL/6 mice, CD4+ICOS+ cells were a major source of cytokines including IFN-gamma, IL-2, IL-4, IL-10 or IL-17A. Upon activation, these cells showed preferentially enhanced production of IL-4 or IL-10 but inhibited IFN-gamma production. In contrast, CD4+ICOS- cells mainly produced IFN-gamma. Interestingly, CD4+ICOS+ cells partially suppressed the proliferation of CD4+ICOS- or CD4+CD25- lymphocytes 'in vitro' by an IL-10-dependent mechanism. Furthermore, CD4+ICOS+ activated and expanded under appropriate conditions yielded a population enriched in cells producing IL-10 and T(h)2 cytokines that also suppressed the proliferation of CD4+CD25- lymphocytes. CD4+ICOS+ cells, before or after expansion in vitro, reduced the severity of EAE when transferred to ICOS-deficient mice. In the same EAE model, lymph node cells from ICOS-deficient mice receiving ICOS+ cells showed reduced IL-17A production and enhanced IL-10 secretion upon antigen activation in vitro. Thus, naturally occurring CD4+ICOS+ cells, expanded or not in vitro, are functionally relevant cells able of protecting ICOS-deficient mice from severe EAE.

Germinal-center organization and cellular dynamics

Germinal centers (GCs) are important sites of antibody affinity maturation. In the classical model, the GC dark zone contains large centroblasts that are rapidly proliferating and undergoing somatic hypermutation of their antibody variable-region genes. Centroblasts give rise to smaller nonproliferating centrocytes in the light zone that compete for binding antigen on follicular dendritic cells. Recently, the approach of real-time imaging of GCs by two-photon microscopy of intact lymph nodes has provided new insights into GC dynamics that both support and challenge fundamental aspects of this model. Here we review recent and older findings on cell migration, proliferation, and interaction dynamics in the GC and discuss a model in which dark- and light-zone cells are morphologically similar, proliferation occurs in both zones, and GC B cells compete for T cell help as well as antigen.

ICOS and B7 costimulatory molecule expression identifies activated cellular subsets in rheumatoid arthritis

To better define important cell subsets expressing activation markers in rheumatoid arthritis (RA), we compared selective lymphocyte and monocyte B7H1, B7H2, B7RP.1, B7RP.2, and inducible costimulatory molecule (ICOS) expression from normal peripheral blood (NL PB), RA PB, and RA synovial fluid (SF) by multicolor flow cytometry and immunohistochemistry. RA SF memory lymphocytes expressed B7RP.1 and B7RP.2, suggesting that T-cells may function as antigen presenting cells (APCs) in RA joints. We found similar results for ICOS expression. RA SF CD14+ monocytes also expressed B7RP.1 (an ICOS ligand) and the homologous ligand B7RP.2, identifying monocytes as potential mediators of antigen processing and lymphocyte activation in RA. Furthermore, we found an increased population of RA SF CD14+ monocytes expressing B7H1 and B7H2. [The FACS analysis was supported by immunohistochemistry, showing intense lymphocyte and APC (macrophages with dendritic morphology) ICOS staining in RA synovial tissue (ST). Overall, these results define elevated populations of memoryT-lymphocytes expressing proinflammatory B7 molecules in RA SF that either stimulate T cells through ICOS (via ICOS ligands B7RP.1 and B7RP.2), or down-regulate RA ST T-lymphocytes through B7H1 and B7H2.] Therefore, in the same joint, there may exist positive and negative influences on the inflammatory response, and perhaps, the negative signals dominate as joint inflammation resolves.

IL-10 inhibits CD28 and ICOS costimulations of T cells via src homology 2 domain-containing protein tyrosine phosphatase 1

BACKGROUND

Specific T-cell activation requires T-cell receptor stimulation and the generation of costimulatory signals. Major costimulatory signals are delivered to T cells by the interaction of CD28 and inducible costimulator (ICOS).

OBJECTIVE

To investigate the molecular pathways involved in direct T-cell suppression by IL-10.

METHODS

T-cell proliferation analysis, immunoprecipitations, and Western blots were performed after T-cell receptor and CD28 and ICOS stimulations in the absence or presence of IL-10. Dominant-negative src homology 2 domain-containing protein tyrosine phosphatase 1 (SHP-1) overexpression, small inhibitory RNA, and SHP-1-deficient and IL-10-deficient mice were used.

RESULTS

IL-10 receptor-associated tyrosine kinase Tyk-2 acts as a constitutive reservoir for SHP-1 in resting T cells, and then tyrosine phosphorylates SHP-1 on IL-10 binding. SHP-1 rapidly binds to CD28 and ICOS costimulatory receptors and dephosphorylates them within minutes. In consequence, the binding of phosphatidylinositol 3-kinase to either costimulatory receptor no longer occurs, and downstream signaling is inhibited. Accordingly, spleen cells from SHP-1-deficient mice showed increased proliferation with CD28 and ICOS stimulation in comparison with wild-type mice, which was not suppressed by IL-10. Generation of dominant-negative SHP-1-overexpressing T cells or silencing of the SHP-1 gene by small inhibitory RNA both altered SHP-1 functions and abolished the T-cell suppressive effect of IL-10.

CONCLUSION

The rapid inhibition of the CD28 or ICOS costimulatory pathways by SHP-1 represents a novel mechanism for direct T-cell suppression by IL-10.

CLINICAL IMPLICATIONS

Molecular mechanisms of direct T-cell suppression by IL-10 may provide a novel target for therapy of allergy/asthma and autoimmune disease.

CTLA-4 gene exon-1 +49 A/G polymorphism: lack of association with autoimmune disease in patients with common variable immune deficiency

The presence of the G allele of exon-1 +49 A/G polymorphisms of the cytotoxic T lymphocyte antigen 4 (CTLA-4) gene has been described as a risk factor associated with the development of autoimmune diseases. Since Common Variable Immune Deficiency (CVID) is associated with autoimmune manifestations in approximately 25% of patients, we sought to examine the association of the CTLA-4 single nucleotide polymorphism with autoimmunity and other inflammatory complications. Sixteen of 47 CVID (34%) patients had a history of autoimmunity, and 15 (32%) had known granulomatous disease with or without lymphoid hyperplasia. CTLA-4 genotype frequencies were AA 40% (19), AG 45% (21), and GG 15% (7). Allele frequencies were A 63% and G 37%, similar to control populations. There were no significant associations between CTLA-4 exon-1 +49 A/G polymorphism and autoimmune or lymphoid hyperplasia and granulomatous disease in this mostly Caucasian CVID patient population.

Approaches to studying costimulation of human antiviral T cell responses: prospects for immunotherapeutic vaccines

The generation of strong and specific CD8 T cell responses is important in the control of viral infections. Costimulatory molecules provide signals necessary for the development or maintenance of these responses. A major focus of our laboratory is to investigate the role of costimulatory molecules of the TNFR and CD28 families in antiviral responses. Our aim is to translate information obtained using murine models to the study of these molecules using human cells. We have devised an in vitro system using recombinant replication- deficient adenovirus to deliver costimulatory molecules to antigen-presenting cells that are then used to stimulate autologous T cells from both healthy and HIV-infected individuals. Here we describe our findings and discuss the implications of incorporating costimulatory molecules into viral vector vaccine strategies.

Update on the treatment of lupus nephritis

Lupus nephritis (LN) is a major cause of morbidity and mortality in patients with systemic lupus erythematosus. Although the use of aggressive immunosuppression has improved both patient and renal survival over the past several decades, the optimal treatment of LN remains challenging. Improved outcomes have come at the expense of significant adverse effects owing to therapy. Moreover with long-term survival, the chronic adverse effects of effective therapies including risk of malignancy, atherosclerosis, infertility, and bone disease all become more important. Finally, some patients fail to achieve remission with standard cytotoxic therapy and others relapse when therapy is reduced. For these reasons, recent clinical trials have attempted to define alternate treatment protocols that appear to be efficacious in achieving and maintaining remission, but with less toxicity than standard regimens. This paper discusses established and newer treatment options for patients with proliferative and membranous LN, with an emphasis on the results of these recent clinical trials. We also review the experimental and human data regarding some of the novel targeted forms of therapy that are under investigation and in different phases of clinical trials.

Follicular B helper T cell activity is confined to CXCR5(hi)ICOS(hi) CD4 T cells and is independent of CD57 expression

The generation of high-affinity antibody-secreting plasma cells critically depends on the presence of CD4 T cells during the germinal center (GC) reaction. GC T cells are so far incompletely characterized in terms of phenotype and function. Here, we show that human follicular B helper T (T(FH)) cells are characterized by high expression of the homeostatic chemokine receptor CXCR5 and the costimulatory molecule ICOS, but not CD57 expression. CXCR5(hi)ICOS(hi) CD4 T cells are the most potent inducers of IgG production that also secrete large amounts of the B cell-attracting chemokine CXCL13. CXCR5(hi)ICOS(hi) CD4 T cells differ from other tonsillar CD4 T cell subsets in their stimulatory activity, proliferative capacity and susceptibility to apoptosis. Large-scale gene expression analysis revealed that T(FH) cells are only distantly related to CXCR5(-) and CXCR5(+) central memory T (T(CM)) as well as effector memory T (T(EM)) cells present in the periphery. CXCR5(hi)ICOS(hi) CD4 T cells appear to be terminally differentiated T helper cells that express a unique set of transcription factors related to the Notch signaling pathway and thus differentiate independent of other T helper cell populations.

Inducible costimulator: a modulator of IFN-gamma production in human tuberculosis

Effective host defense against Mycobacterium tuberculosis requires the induction of Th1 cytokine responses. We investigated the regulated expression and functional role of the inducible costimulator (ICOS), a receptor known to regulate Th cytokine production, in the context of human tuberculosis. Patients with active disease, classified as high responder (HR) or low responder (LR) patients according to their in vitro T cell responses against the Ag, were evaluated for T cell expression of ICOS after M. tuberculosis-stimulation. We found that ICOS expression significantly correlated with IFN-gamma production by tuberculosis patients. ICOS expression levels were regulated in HR patients by Th cytokines: Th1 cytokines increased ICOS levels, whereas Th2-polarizing conditions down-regulated ICOS in these individuals. Besides, in human polarized Th cells, engagement of ICOS increased M. tuberculosis IFN-gamma production with a magnitude proportional to ICOS levels on those cells. Moreover, ICOS ligation augmented Ag-specific secretion of the Th1 cytokine IFN-gamma from responsive individuals. In contrast, neither Th1 nor Th2 cytokines dramatically affected ICOS levels on Ag-stimulated T cells from LR patients, and ICOS activation did not enhance IFN-gamma production. However, simultaneous activation of ICOS and CD3 slightly augmented IFN-gamma secretion by LR patients. Together, our data suggest that the regulation of ICOS expression depends primarily on the response of T cells from tuberculosis patients to the specific Ag. IFN-gamma released by M. tuberculosis-specific T cells modulates ICOS levels, and accordingly, ICOS ligation induces IFN-gamma secretion. Thus, ICOS activation may promote the induction of protective Th1 cytokine responses to intracellular bacterial pathogens.

CD28 and ICOS: Similar or separate costimulators of T cells?

Numerous studies have revealed that the B7.1/B7.2-CD28 and B7RP-1-ICOS (Inducible COStimulator) pathways provide crucial costimulatory signals to T cells. We have compared the contribution of these pathways during primary and effector responses, in vitro and in vivo, molecularly as well as functionally. This comparison between CD28 an ICOS after initiation of T cell activation demonstrates that both CD28 and ICOS function similarly during expansion, survival and differentiation of T cells and that both CD28 and ICOS are necessary for proper IgG responses. The major differences between CD28 and ICOS are differences in expression of both receptors and ligands, and the fact that CD28 induces IL-2 production, whereas ICOS does not. In addition, ICOS is more potent in the induction of IL-10 production, a cytokine important for suppressive function of T regulatory cells. All data available at present indicate that both molecules are very suitable candidates for immunotherapy, each in their own unique way.

B and T Lymphocyte Attenuator-Mediated Signal Transduction Provides a Potent Inhibitory Signal to Primary Human CD4 T Cells That Can Be Initiated by Multiple Phosphotyrosine Motifs

The B and T lymphocyte attenuator (BTLA) is a recently identified member of the CD28 family of cell receptors. Initial reports demonstrated that mice deficient in BTLA expression were more susceptible to experimental autoimmune encephalomyelitis, indicating that BTLA was likely to function as a negative regulator of T cell activation. However, cross-linking of BTLA only resulted in a 2-fold reduction of IL-2 production, questioning the potency with which BTLA engagement blocks T cell activation. We established a model in which BTLA signaling could be studied in primary human CD4 T cells. We observed that cross-linking of a chimeric receptor consisting of the murine CD28 extracellular domain and human BTLA cytoplasmic tail potently inhibits IL-2 production and completely suppresses T cell expansion. Mutation of any BTLA tyrosine motifs had no effect on the ability of BTLA to block T cell activation. Only mutation of all four tyrosines rendered the BTLA cytoplasmic tail nonfunctional. We performed structure-function studies to determine which factors recruited to the BTLA cytoplasmic tail correlated with BTLA function. Using pervanadate as a means to phosphorylate the BTLA cytoplasmic tail, we observed both Src homology protein (SHP)-1 and SHP-2 recruitment. However, upon receptor engagement, we observed only SHP-1 recruitment, and mutations that abrogated SHP-1 recruitment did not impair BTLA function. These studies question whether SHP-1 or SHP-2 have any role in BTLA function and caution against the use of pervanadate as means to initiate signal transduction cascades in primary cells.

Cytotoxic T lymphocyte antigen-4 promoter variants in breast cancer

CTLA4 is a coinhibitory molecule expressed mainly on activated T lymphocytes. To test the putative involvement of CTLA-4 in inhibitory state of immunity to breast cancer, we genotyped 283 patients and 245 healthy control subjects for -1722 T/C, -1661 A/G, and -318 C/T single nucleotide polymorphisms in the promoter region of the CTLA4 gene. There were no significant differences in genotype, allele, or haplotype frequencies in all three loci between patients and healthy controls. Moreover, the incidence of the most frequent haplotype combination (TAC/TAC, T -1722, A -1661, C -318) was only slightly higher among healthy controls than patients (68.4 vs. 64.8%, P = 0.2). This haplotype combination was associated with lower stages of the disease (P = 0.0007), however, and higher estrogen receptor (ER) expression in patients (P = 0.006). Association with tumor prognostic or predictive factors was also observed with certain genotypes: the -1661 AA genotype was associated with lesser lymph node (LN) involvement (P = 0.017) and higher ER expression (P = 0.004), and the -318 CC genotype with lesser LN involvement (P = 0.007). These results suggest that CTLA4 promoter variants participate in the progression of breast cancer rather than in its initial development.

Expression and function of inducible co-stimulator in patients with systemic lupus erythematosus: possible involvement in excessive interferon-gamma and anti-double-stranded DNA antibody production

Inducible co-stimulator (ICOS) is the third member of the CD28/cytotoxic T-lymphocyte associated antigen-4 family and is involved in the proliferation and activation of T cells. A detailed functional analysis of ICOS on peripheral blood T cells from patients with systemic lupus erythematosus (SLE) has not yet been reported. In the present study we developed a fully human anti-human ICOS mAb (JTA009) with high avidity and investigated the immunopathological roles of ICOS in SLE. JTA009 exhibited higher avidity for ICOS than a previously reported mAb, namely SA12. Using JTA009, ICOS was detected in a substantial proportion of unstimulated peripheral blood T cells from both normal control individuals and patients with SLE. In CD4⁺CD45RO⁺ T cells from peripheral blood, the percentage of ICOS⁺ cells and mean fluorescence intensity with JTA009 were significantly higher in active SLE than in inactive SLE or in normal control individuals. JTA009 co-stimulated peripheral blood T cells in the presence of suboptimal concentrations of anti-CD3 mAb. Median values of [³H]thymidine incorporation were higher in SLE T cells with ICOS co-stimulation than in normal T cells, and the difference between inactive SLE patients and normal control individuals achieved statistical significance. ICOS co-stimulation significantly increased the production of IFN-γ, IL-4 and IL-10 in both SLE and normal T cells. IFN-γ in the culture supernatants of both active and inactive SLE T cells with ICOS co-stimulation was significantly higher than in normal control T cells. Finally, SLE T cells with ICOS co-stimulation selectively and significantly enhanced the production of IgG anti-double-stranded DNA antibodies by autologous B cells. These findings suggest that ICOS is involved in abnormal T cell activation in SLE, and that blockade of the interaction between ICOS and its receptor may have therapeutic value in the treatment of this intractable disease.

Cooperation between 4-1BB and ICOS in the immune response to influenza virus revealed by studies of CD28/ICOS-deficient mice

CD28, ICOS, and 4-1BB each play distinct roles in the CD8 T cell response to influenza virus. CD28-/- mice are severely impaired in primary CD8 T cell expansion and fail to mount a secondary response to influenza. Influenza-specific CD8 T cells expand normally in ICOS-/- mice, with only a small and transient defect late in the primary response and an unimpaired secondary response. Conversely, 4-1BB/4-1BBL interaction is dispensable for the primary CD8 T cell response to influenza, but maintains CD8 T cell survival and controls the size of the secondary response. Previous results showed that a single dose of agonistic anti-4-1BB Ab at priming allowed partial restoration of primary CD8 T cell expansion and full recovery of the secondary CD8 T cell responses to influenza in CD28-/- mice. In this study we show that anti-4-1BB fails to correct the CD8 T cell defect in CD28-/-ICOS-/- mice, suggesting that ICOS partially compensates for CD28 in this model. In support of this hypothesis, we found that anti-4-1BB enhances ICOS expression on both T cell subsets and that anti-4-1BB and anti-ICOS can synergistically activate CD4 and CD8 T cells. Furthermore, ICOS and 4-1BB can cooperate to directly stimulate isolated CD28-/- CD8 T cells. These results reveal a novel interaction between the ICOS and 4-1BB costimulatory pathways as well as unexpected redundancy between CD28 and ICOS in primary CD8 T cell expansion. These findings have implications for costimulation of human T cell responses in diseases such as AIDS or rheumatoid arthritis, in which CD28- T cells accumulate.

The ICOS Molecule Plays a Crucial Role in the Development of Mucosal Tolerance

The ICOS molecule stimulates production of the immunoregulatory cytokine IL-10, suggesting an important role for ICOS in controlling IL-10-producing regulatory T cells and peripheral T cell tolerance. In this study we investigate whether ICOS is required for development of oral, nasal, and high dose i.v. tolerance. Oral administration of encephalitogenic myelin oligodendrocyte glycoprotein (MOG) 35-55 peptide to ICOS-deficient (ICOS-/-) mice did not inhibit experimental autoimmune encephalomyelitis (EAE), T cell proliferation, or IFN-gamma production, in striking contrast to wild-type mice. Similarly, intranasal administration of MOG(35-55) before EAE induction suppressed EAE and T cell responses in wild-type, but not in ICOS-/-, mice. In contrast, ICOS-/- mice were as susceptible as wild-type mice to high dose tolerance. These results indicate that ICOS plays an essential and specific role in mucosal tolerance and that distinct costimulatory pathways differentially regulate different forms of peripheral tolerance. Surprisingly, CD4+ cells from MOG-fed wild-type and ICOS-/- mice could transfer suppression to wild-type recipients, indicating that functional regulatory CD4+ cells can develop in the absence of ICOS. However, CD4+ T cells from MOG-fed wild-type mice could not transfer suppression to ICOS-/- recipients, suggesting that ICOS may have a key role in controlling the effector functions of regulatory T cells. These results suggest that stimulating ICOS may provide an effective therapeutic approach for promoting mucosal tolerance.

ICOS contributes to T cell expansion in CTLA-4 deficient mice

Both CD28 and ICOS are important costimulatory molecules that promote Ag-specific cellular and humoral immune reactions. Whereas CD28 is generally thought to be the most important molecule in the initiation of a T cell response, ICOS is considered to act during the effector phase. We have investigated the contribution of ICOS to T cell responses in the absence of CTLA-4-mediated inhibition. Mice lacking CTLA-4, which show spontaneous CD28-mediated CD4(+) T cell activation, expansion and differentiation, were treated with antagonistic alphaICOS antibodies. Blocking the interaction between ICOS and its ligand B7RP-1 significantly reduced this aberrant T cell activation and caused a reduction in T cell numbers. In vitro analysis of CD4(+) T cells from treated mice revealed that ICOS blockade significantly reduced Th1 differentiation, while Th2 differentiation was only moderately inhibited. Further in vitro stimulation experiments demonstrated that ICOS is able to induce proliferation of murine CD4(+) and CD8(+) T cells but only in the presence of IL-2. These results indicate that ICOS is not only important for T cell effector function but also contributes to the expansion phase of a T cell response in the presence of CD28 signaling.

Costimulation through NKG2D Enhances Murine CD8+ CTL Function: Similarities and Differences between NKG2D and CD28 Costimulation

Multiple studies have demonstrated that the NK cell activating receptor NKG2D can function as a costimulatory receptor for both mouse and human CD8+ T cells. However, it has recently been suggested that stimulation through NKG2D is insufficient for costimulation of CD8+ T cells. To aid in the delineation of NKG2D function in CTL responses, we investigated whether stimulation of NKG2D by the natural ligand RAE1epsilon was able to costimulate effector functions of a murine CTL line generated from DUC18 TCR transgenic mice. We found that NKG2D was able to costimulate DUC CTL responses and did so in a manner similar to CD28 costimulation. The T cells exhibited increased proliferation, IFN-gamma release, and cytotoxicity when presented antigenic peptide by P815 cells expressing RAE1epsilon or B7-1 compared with untransfected P815. In addition, both RAE1epsilon and B7-1 enhanced Ag-independent IFN-gamma secretion in response to IL-12 and IL-18 by DUC CTL. However, only costimulation through CD28 allowed for DUC CTL survival upon secondary stimulation, whereas ligation of NKG2D, but not CD28, induced DUC CTL to form an immune synapse with target cells in the absence of TCR stimulation. Understanding the outcomes of these differences may allow for a better understanding of T cell costimulation in general.