Costimulatory regulation of T cell function

Cohort- and time-specific associations of CTLA4 genotypes with HIV-1 disease progression

BACKGROUND

CTLA4 in the chromosome 2q33 region encodes cytotoxic T-lymphocyte (CTL) associated antigen 4, which downregulates CTL responses. We examined the relationships between common CTLA4 variants and several outcomes of HIV-1 infection in adults and adolescents.

METHODS

We studied 765 HIV-1-infected persons: 558 Caucasian seroconverters from three cohorts (MACS, ACS, and DCG) and 207 infected adolescents (mostly female) from another cohort (REACH) of mixed ethnicity. Single nucleotide polymorphisms in CTLA4 promoter (-1147C/T, -658C/T, -318C/T), coding sequence (49A/G) and the 3' untranslated region (CT60A/G) were resolved by PCR-based techniques. Repeated measures and survival analyses were used to test allelic and haplotypic associations with HIV-1 viral load (VL) and time to AIDS, respectively.

RESULTS

Individuals carrying -318T or the (-1147) T-(-318) T haplotype had elevated HIV-1 VL in MACS and REACH but reduced VL in DCG and ACS participants. Time-dependent associations of CTLA4-318T with VL were observed in MACS and REACH (P = 0.03-0.09). In Cox regression models adjusted for age and established contributory markers in CCR5 and HLA class I genes, CTLA4-318T was associated with rapid progression to AIDS in MACS (relative hazard 1.69; 95% confidence interval, 1.15-2.49; P < 0.01) as opposed to a non-significant slower disease progression in ACS and no appreciable association in DCG.

CONCLUSIONS

Association of CTLA4 genotypes with clinical and virological outcomes following HIV-1 infection appeared to vary with time and among the cohorts. Further analyses in conjunction with other biologically and positionally related genes, such as CD28 and ICOS, may help explain the disparate findings.

Induction of regulatory T cells from mature T cells by allogeneic thymic epithelial cells in vitro

The ability of thymic epithelial cells (TEC) to re-educate mature T cells to be regulatory T cells has not been addressed. In the present study, this issue was directly investigated by co-culturing of mature T cells and allo-TECs. B6 macrophage cell line 1C21-cultured BALB/c splenocytes responded to B6 antigens in vitro. However, BALB/c splenocytes precultured with B6-derived TECs 1-4C18 or 1C6 did not proliferate to B6 antigens, but responded to rat antigens. Exogenous interleukin-2 (IL-2) failed to revise the unresponsiveness of these T cells. Allo-TEC-cultured T cells predominantly expressed Th2 cytokines (IL-4 and IL-10). B6 TEC-cultured BALB/c splenocytes markedly inhibited the immune responses of naïve BALB/c splenocytes to B6 antigens, but not to rat or the third-party mouse antigens. BALB/c nude mice that received naïve syngeneic splenocytes rejected B6 or rat skin grafts by 17 days postskin grafting; however, co-injection of B6 TEC-cultured BALB/c splenocytes significantly delayed B6 skin graft rejection (P < 0.01), with the unchanged rejection of rat skin grafts. These studies demonstrate that allo-TECs are able to 'educate' mature T cells to be regulatory cells, and suggest that regulatory cells derived from mature T cells by TECs may play an important role in T cell tolerance to allo- and auto-antigens.

BTNL2, a butyrophilin-like molecule that functions to inhibit T cell activation

B7 family members regulate T cell activation and tolerance. Although butyrophilin proteins share sequence homology with the B7 molecules, it is unclear whether they have any function in immune responses. In the present study, we characterize an MHC class II gene-linked butyrophilin family member, butyrophilin-like 2 (BTNL2), the mutation of which has been recently associated with the inflammatory autoimmune diseases sarcoidosis and myositis. Mouse BTNL2 is a type I transmembrane protein with two pairs of Ig-like domains separated by a heptad peptide sequence. BTNL2 mRNA is highly expressed in lymphoid tissues as well as in intestine. To characterize the function of BTNL2, we produced a BTNL2-Ig fusion protein. It recognized a putative receptor whose expression on B and T cells was significantly enhanced after activation. BTNL2-Ig inhibited T cell proliferation and TCR activation of NFAT, NF-kappaB, and AP-1 signaling pathways. BTNL2 is thus the first member of the butyrophilin family that regulates T cell activation, which has implications in immune diseases and immunotherapy.

Analysis of CD28 and bcl-2 Expression on Peripheral Blood and Liver-Infiltrating Mononuclear Cells in Patients with Autoimmune Hepatitis

Because the underlying mechanism of hepatocellular damages in autoimmune hepatitis (AIH) still remains unclear, analysis of CD28 and bcl-2 molecules, which are critical for T cell activation and survival, was performed in patients with AIH. The number of CD28(+)CD4(+) peripheral blood mononuclear cells (PBMC) in corticosteroid (CS)-treated patients was comparable to normal control individuals but decreased in untreated AIH patients. In contrast, the number of CD28(+)CD8(+) PBMC was decreased in both CS-treated and untreated AIH patients. Analysis of liver-infiltrating mononuclear cells (LIMC) showed that the number of CD28(+)CD4(+) and CD28(-)CD8(+) LIMC were positively correlated with the histology activity index score. Bcl-2(+)CD4(+) LIMC were observed in the portal area of the liver and the numbers fluctuated with disease activity during the time course after CS administration. By contrast, CD8(+) LIMC were shown not to express bcl-2. Taken collectively, these results suggest that bcl-2(+)CD28(+)CD4(+) and bcl-2(-)CD28(-)CD8(+) cells may play critical and distinct roles in hepatocellular damage in AIH.

T-cell tolerance or function is determined by combinatorial costimulatory signals

Activated in immune responses, T lymphocytes differentiate into effector cells with potent immune function. CD28 is the most prominent costimulatory receptor for T-cell activation. However, absence of CD28 costimulation did not completely impair effector function of CD4 or CD8 T cells. Moreover, increasing number of costimulatory molecules are recently found on antigen-presenting cells to regulate T-cell activation. To understand the molecular mechanisms that determine T-cell function or tolerance, we have collectively examined the roles of positive and negative costimulatory molecules. Antigen-specific naïve CD4 and CD8 T cells, only when activated in the absence of both CD28 and ICOS pathways, were completely impaired in effector function. These tolerant T cells not only were anergic with profound defects in TcR signal transduction but also completely lacked expression of effector-specific transcription factors. T-cell tolerance induction in this system requires the action by negative costimulatory molecules; T-cell proliferation and function was partially restored by inhibiting PD-1, B7-H3 or B7S1. This work demonstrates that T-cell function or tolerance is controlled by costimulatory signals.

Immunohistochemical localization of programmed death-1 ligand-1 (PD-L1) in gastric carcinoma and its clinical significance

The present study examined programmed death-1 ligand-1 (PD-L1) detected by immunohistochemical labeling in 102 cases of human gastric carcinoma, 10 adenoma and 10 normal tissues. The relationship between PD-L1 immunolocalization and clinical pathological features, as well as the prognosis of gastric carcinoma, was explored. There was no PD-L1 detectable in normal gastric tissues and very weak immunolabeling in gastric adenomas, but it could be detected in 42.2% of gastric carcinoma tissues. There was no correlation between PD-L1 immunolocalization and patient age, sex, tumor location or the degree of tumor differentiation in the gastric carcinomas. However, PD-L1 immunodetection was significantly correlated to tumor size, invasion, lymph node metastasis and survival time of patients. PD-L1 immunolabeling was significantly enhanced (P<0.01) when the tumor infiltrated into the deep muscular layers, with lymph node metastasis or survival time of less than 2 years, Moreover, multivariate analysis demonstrated that PD-L1 immunodetection could be used as an independent factor to evaluate the prognosis of gastric carcinoma.

Cutting Edge: CD28 controls dominant regulatory T cell activity during active immunization

Ligation of CD28 during Ag recognition plays an important role in the generation of effective T cell responses. However, its peripheral control of regulatory T cell function remains obscure. In this study, we show that naive wild-type or CD28(-/-) CD4(+)CD25(-) T cells exposed to peptide in vivo develop regulatory activity that suppresses the response of adoptively transferred naive T cells to a subsequent immunogenic challenge. We find that although CD28 is engaged during the initial peptide-priming event and is essential to sustain T cell survival, it is not sufficient to prevent the dominance of regulatory T cell function. Immunization with adjuvant abrogates regulatory dominance, reducing overall Foxp3 expression in a CD28-dependent manner. We conclude that CD28 licenses active immunization by regulating Ag-induced immunoregulation.

Expression, purification, and in vitro refolding of a humanized single-chain Fv antibody against human CTLA4 (CD152)

A human-derived single-chain Fv (scFv) antibody fragment specific against human CTLA4 (CD152) was produced at high level in Escherichia coli. The scFv gene was cloned from a phagemid to the expression vector pQE30 with a N-terminal 6His tag fused in-frame, and expressed as a 29 kDa protein in E. coli as inclusion bodies. The inclusion body of scFv was isolated from E. coli lysate, solubilized in 8M urea with 10mM dithiothreitol, and purified by ion-exchange chromatography. Method for in vitro refolding of the scFv was established. The effects of refolding buffer composition, protein concentration and temperature on the refolding yield were investigated. The protein was renatured finally by dialyzing against 3mM GSH, 1mM GSSG, 150 mM NaCl, 1M urea, and 50 mM Tris-Cl (pH 8.0) for 48 h at 4 degrees C, and then dialyzed against phosphate-buffered saline (pH 7.4) to remove remaining denaturant. This refolding protocol generated up to a 70% yield of soluble protein. Soluble scFv was characterized for its specific antigen-binding activity by indirect cellular ELISA. The refolded scFv was functionally active and was able to bind specifically to CTLA4 (CD152). The epitopes recognized by refolded anti-CTLA4 scFv do not coincide with those epitopes recognized by CD80/CD86.

RasGRP1 and RasGRP3 regulate B cell proliferation by facilitating B cell receptor-Ras signaling

The RasGRPs are a family of Ras activators that possess diacylglycerol-binding C1 domains. In T cells, RasGRP1 links TCR signaling to Ras. B cells coexpress RasGRP1 and RasGRP3. Using Rasgrp1 and Rasgrp3 single and double null mutant mice, we analyzed the role of these proteins in signaling to Ras and Erk in B cells. RasGRP1 and RasGRP3 both contribute to BCR-induced Ras activation, although RasGRP3 alone is responsible for maintaining basal Ras-GTP levels in unstimulated cells. Surprisingly, RasGRP-mediated Ras activation is not essential for B cell development because this process occurs normally in double-mutant mice. However, RasGRP-deficient mice do exhibit humoral defects. Loss of RasGRP3 led to isotype-specific deficiencies in Ab induction in immunized young mice. As reported previously, older Rasgrp1-/- mice develop splenomegaly and antinuclear Abs as a result of a T cell defect. We find that such mice have elevated serum Ig levels of several isotypes. In contrast, Rasgrp3-/- mice exhibit hypogammaglobulinemia and show no signs of splenomegaly or autoimmunity. Double-mutant mice exhibit intermediate serum Ab titers, albeit higher than wild-type mice. Remarkably, double-mutant mice exhibit no signs of autoimmunity or splenomegaly. B cell proliferation induced by BCR ligation with or without IL-4 was found to be RasGRP1- and RasGRP3-dependent. However, the RasGRPs are not required for B cell proliferation per se, because LPS-induced proliferation is unaffected in double-mutant mice.

Costimulation of T-cell proliferation by anti-L-selectin antibody is associated with the reduction of a cdk inhibitor p27

In this study, we investigated the costimulatory activity of l-selectin in primary mouse T cells. Proliferation induced by immobilized anti-CD3 antibody was enhanced by immobilized anti-l-selectin antibody. In contrast to the anti-CD28 antibody, anti-l-selectin antibody did not enhance interleukin-2 (IL-2) expression. One of the cyclin-dependent kinase (cdk) inhibitors, p27, was reduced by costimulation with anti-l-selectin antibody, as with anti-CD28 antibody, suggesting that the enhancement of T-cell proliferation is the result of a reduced p27 level. Since anti-l-selectin antibody enhanced the activation of extracellular signal-regulated protein kinase (ERK) induced by anti-CD3 antibody, ERK plays an important role in signal integration during costimulation. These results suggest that the mechanism of T-cell costimulation is at least partially different between CD28 and l-selectin, although the two mechanisms share a common downstream event, a reduction of p27 level, as a critical biochemical event in the cell cycle progression of T cells.

CD28 is required for induction and maintenance of immunological memory in toxin-reactive CD4+ T cells in vivo

We previously reported that Vbeta3+ CD4+ T cells maintained a protracted expansion, with the phenotypes of memory Th2 cells, for 30 days in C57BL/6 (B6) mice implanted with SEA-containing mini-osmotic pumps. In the present study, we followed the fate of Vbeta3+ CD4+ T cells in CD28-/- mice. Vbeta3+ CD4+ T cells increased to a degree similar to that of B6 Vbeta3+ CD4+ T cells until day 10 after implantation, then declined rapidly reaching the control level by 28 days. Remaining Vbeta3+ CD4+ T cells at that time did not exhibit memory phenotypes nor Th2-deviated responses. The rapid drop in Vbeta3+ CD4+ T cells in CD28-/- mice was attributable to upregulated induction of apoptosis owing to marginal inductions of Bcl-2 and Bcl-xL. Collectively, these data indicate CD28 to play critical roles in the generation and maintenance of SEA-reactive CD4+ T cells in vivo.

Genes to vaccines for immunotherapy: how the molecular biology revolution has influenced cancer immunology

Recent advances in our understanding of the complex signaling pathways involved in immune system regulation, along with analyses of genetic differences between tumors and their normal cellular counterparts, have accelerated development of immune-based strategies for cancer treatment and prevention. More clinically relevant animal models have shown that successful immune-based strategies will require the integration of interventions that target specific tumor antigens with regulators of the antitumor immune response. Immunotherapy for cancer is at a critical crossroad, as therapeutics designed to target cancer-associated antigens and regulatory signaling molecules enter clinical trials. We outline here a paradigm for early-stage clinical development of immunotherapy combinations that use vaccines to drive tumor antigen-specific responses while simultaneously targeting immune regulatory pathways.

Alteration of phosphatidylinositol 3-kinase cascade in the multilobulated nuclear formation of adult T cell leukemia/lymphoma (ATLL)

Adult T cell leukemia/lymphoma (ATLL) has been characterized as one of the most aggressive human neoplasias and its incidence is thought to be caused by both genetic and epigenetic alterations to the host cellular genes of T cells infected with human T cell leukemia virus type I (HTLV-I). A multilobulated nuclear appearance is an important diagnostic marker of ATLL, and we have now identified that the molecular mechanisms underlying these formations occur through microtubule rearrangement via phosphatidylinositol 3-kinase (PI3-kinase) activation by AILIM/ICOS signaling. We also show that PTEN and/or SHIP-1, which are PIP3 inositol phosphatases that inhibit the activation of downstream effectors of the PI3-kinase cascade, are disrupted in both ATLL neoplasias and in multilobulated nuclei-forming Jurkat cells. This down-regulation of PTEN was found to be essential for the formation of ATLL-type nuclear lobules. Furthermore, PI3-kinase and PTEN activities were observed to be closely associated with cellular proliferation. Thus, our results suggest that alteration of PI3-kinase signaling cascades, as a result of the down-regulation of inositol phosphatases, induces ATLL-type multilobulated nuclear formation and is also associated with the cellular proliferation of malignant T cell leukemias/lymphomas.

In vivo costimulatory role of B7-DC in tuning T helper cell 1 and cytotoxic T lymphocyte responses

B7-DC, one of the recently described B7 family members, has the capacity to inhibit T cell responses via engagement of the immunoreceptor tyrosine-based inhibitory motif–containing inhibitory PD-1 receptor as well as enhance responses via an as yet unidentified costimulatory receptor. B7-DC is highly homologous to a coinhibitory B7 family member, B7-H1, which also binds PD-1. It is currently unclear which B7-DC function—costimulation or inhibition—predominates in vivo. To study in vivo functions of B7-DC, we evaluated immune responses in B7-DC knockout (KO) mice. Although not eliminated, interferon-γ (IFN-γ) production by CD4 T cells and IFN-γ–dependent humoral responses were reduced in B7-DC KO mice relative to wild type mice. Antigen-specific CD8 T cell responses and cytotoxic T lymphocyte (CTL) activity were also diminished in B7-DC KO mice. Hepatic tumors grew more quickly in B7-DC KO mice, associated with a decrease in intrahepatic tumor-specific CD8 T cells. These results highlight the contrasting in vivo roles of B7-DC and B7-H1 and indicate that B7-DC functions as a tuning molecule, selectively augmenting T helper 1 and CTL responses.

Phase I/II Study of Galiximab, an Anti-CD80 Antibody, for Relapsed or Refractory Follicular Lymphoma

Purpose

This multicenter, dose-escalation study evaluates the safety, pharmacokinetics, and efficacy of galiximab (anti-CD80 monoclonal antibody) in patients with relapsed or refractory follicular lymphoma.

Patients and Methods

Patients had follicular lymphoma that had relapsed or failed to respond to primary therapy; the majority (90%) presented with stage III or IV disease. Four weekly intravenous infusions of galiximab were administered at doses of 125, 250, 375, or 500 mg/m2.

Results

Thirty-seven patients received galiximab treatment and were evaluated for safety; 35 were assessable for response. Antibody infusions were safe and well tolerated with no dose-limiting toxicities. A total of 22 (60%) of 37 patients experienced adverse events related to galiximab. All but one of the events were grade 1 or 2; the most common were fatigue, nausea, and headache. Cytopenias were rare; only one patient experienced anemia and febrile neutropenia, which were unrelated to galiximab and resolved after treatment. No patient developed antigaliximab antibody formation. The mean serum half-life ranged from 13 to 24 days. The overall response rate was 11% (two complete responses and two partial responses). Time to best response was delayed (months 3, 6, 9, and 12). Twelve patients (34%) maintained stable disease. Nearly half of all patients (49%) had a decrease in indicator lesions. Two responders remain on study without progression (22 and 24.4 months).

Conclusion

The favorable safety profile of galiximab and evidence of single-agent biologic activity and dose-dependent pharmacokinetics support further evaluation of galiximab as a treatment for follicular lymphoma, possibly in combination with other lymphoma therapies.

Therapeutic peptidomimetic strategies for autoimmune diseases: costimulation blockade*

Cognate interactions between immune effector cells and antigen-presenting cells (APCs) govern immune responses. Specific signals occur between the T-cell receptor peptide and APCs and nonspecific signals between pairs of costimulatory molecules. Costimulation signals are required for full T-cell activation and are assumed to regulate T-cell responses as well as other aspects of the immune system. As new discoveries are made, it is becoming clear how important these costimulation interactions are for immune responses. Costimulation requirements for T-cell regulation have been extensively studied as a way to control many autoimmune diseases and downregulate inflammatory reactions. The CD28:B7 and the CD40:CD40L families of molecules are considered to be critical costimulatory molecules and have been studied extensively. Blocking the interaction between these molecules results in a state of immune unresponsiveness termed 'anergy'. Several different strategies for blockade of these interactions are explored including monoclonal antibodies (mAbs), Fab fragments, chimeric, and/or fusion proteins. We developed novel, immune-specific approaches that interfere with these interactions. Using experimental autoimmune encephalomyelitis (EAE), an animal model for multiple sclerosis mediated by central nervous system (CNS)-specific T-cells, we developed a multi-targeted approach that utilizes peptides for blockade of costimulatory molecules. We designed blocking peptide mimics that retain the functional binding area of the parent protein while reducing the overall size and are thus capable of blocking signal transduction. In this paper, we review the role of costimulatory molecules in autoimmune diseases, two of the most well-studied costimulatory pathways (CD28/CTLA-4:B7 and CD40:CD40L), and the advantages of peptidomimetic approaches. We present data showing the ability of peptide mimics of costimulatory molecules to suppress autoimmune disease and propose a mechanism for disease suppression.

Anti-CD154 mAb treatment but not recipient CD154 deficiency leads to long-term survival of xenogeneic islet grafts

The aim of the study was to evaluate the role of recipient CD40 and CD154 in the rejection process of concordant and discordant islets xenotransplantation (Tx). Diabetic C57BL/6 mice, CD40- or CD154-knockout (KO) and complement C3-deficient (C3-/-) mice were transplanted with either rat or human islets. Group 1, C57BL/6 Tx without therapy; Group 2, C57BL/6 Tx with anti-CD154 monoclonal antibody (mAb) (MR1) therapy; Group 3, CD40-KO; and Group 4, CD154-KO Tx without therapy; Group 5, C3-/- Tx without therapy and Group 6, C3-/-Tx with MR1 therapy. Mixed lymphocyte reactions (MLR) were performed. Compared to Group 1, MR1 induced long-term survival of xenografts in Group 2, but not in Group 6, survival of islets was not prolonged significantly in Groups 3 and 4. MLR responses in Group 2 were reduced approximately 50% compared to Group 1. In Groups 3, 4 and 6, MLR responses were not modified by the absence of CD40 or CD154 molecules, or MR1 and were similar to Group 1. Improved graft survival and reduced MLR responses in Group 2, but not in Group 6, could be explained by specific targeting of activated T cells with inactivation by complement- or cellular-mediated mechanisms. Rejection of xenografts and strong MLR responses in Groups 3 and 4 are possible through efficient activation of alternate pathways of costimulation.

HIV Type 1 Can Act as an APC upon Acquisition from the Host Cell of Peptide-Loaded HLA-DR and CD86 Molecules

It is well documented that a wide range of host-derived cell surface constituents is inserted within HIV type 1 (HIV-1) and located on the exterior of the virion. Although no virus-associated protein of host origin has been shown to be absolutely required for virus replication, studies have revealed that many of these proteins are functional and can affect several steps of the virus life cycle. In this study, we found that HIV-1 acquires peptide-loaded class II MHC (MHC-II) and the costimulatory CD86 molecules from the host cell. Moreover, we present evidence that virions bearing such peptide-loaded MHC-II and CD86 proteins can lead to activation of the transcription factors NF-kappa B and NF-AT in an Ag-specific human T cell line. A linear correlation was found between activation of NF-kappa B and the amount of peptide-loaded MHC-II molecules inserted within HIV-1. Finally, transcription of unintegrated and integrated HIV-1 DNA was promoted upon exposure of peptide-specific human T cells to viruses bearing both peptide-loaded MHC-II and CD86 proteins. These data suggest that HIV-1 can operate as an APC depending on the nature of virus-anchored host cell membrane components. It can be proposed that HIV-1 can manipulate one of its primary targets through the process of incorporation of host-derived proteins.

Molecular cloning and characterization of canine ICOS

Inducible costimulatory receptor (ICOS) is one recently identified member of the CD28 family of costimulatory molecules. Evidence suggests ICOS functions as a critical immune regulator and, to evaluate these effects, we employed the canine model system that has been used to develop strategies currently in clinical use for hematopoietic stem cell transplantation. To investigate the effects of blocking the ICOS pathway in the canine hematopoietic cell transplantation model, we tested existing murine and human reagents and cloned the full length of the open reading frame of canine ICOS cDNA to allow the development of reagents specific for the canine ICOS. Canine ICOS contains a major open reading frame of 624 nucleotides, encoding a protein of 208 amino acids, and localizes to chromosome 37. Canine ICOS shares 79% sequence identity with human ICOS, 70% with mouse, and 69% with rat. Canine ICOS expression is limited to stimulated PBMC.

Immunological aspects of head and neck cancer: biology, pathophysiology and therapeutic mechanisms

Advanced cancer and head and neck cancer, in particular, remains a major clinical challenge with its associated morbidity and inevitable mortality. Local control of early disease is achievable in many solid tumours with current surgical and radiotherapeutic techniques but metastatic disease is associated with poor outcome and prognosis. It is known that, by the time of presentation, many patients will already have occult microscopic metastatic disease, and surgery and radiotherapy will not result in long-term survival. What little effect modern chemotherapeutic agents have on microscopic disease is, however, limited by systemic toxicity and multi-drug resistance. Immune surveillance is postulated to be operative in man. There is evidence, however, that patients with progressive tumour growth have failure of host defences both locally and systemically. Various possible defects and tumour escape mechanisms are discussed in the review. Immunotherapy and, in particular adoptive T cell therapy and DC therapy, show promise as putative tumour-specific therapy with clinical benefits. These techniques are undergoing development and evaluation in phase 1 clinical trials. Preliminary data suggest that the treatments are well tolerated. Unfortunately, there is limited evidence of significant and prolonged improvements in clinical outcome. Further developments of beneficial protocols (adjuvants, mode and frequency of vaccination etc) and multicentre studies of the use of immunotherapy in cancer are now required.

Augmentation of T cell levels and responses induced by androgen deprivation

Androgen has been implicated as a negative regulator of host immune function and a factor contributing to the gender dimorphism of autoimmunity. Conversely, androgen deprivation has been suggested to potentiate male host immunity. Studies have shown that removal of androgen in postpubertal male mice produces an increase in size and cellularity of primary and peripheral lymphoid organs, and enhances a variety of immune responses. Yet, few details are known about the effect of androgen removal on T cell-mediated immunity. In this study, we demonstrate two pronounced and independent alterations in T cell immunity that occur in response to androgen deprivation, provided by castration, in postpubertal male mice. First, we show that levels of T cells in peripheral lymphoid tissues of mice are increased by androgen deprivation. Second, T cells from these mice transiently proliferate more vigorously to TCR- and CD28-mediated costimulation as well as to Ag-specific activation. In addition, androgen deprivation accelerates normalization of host T and B cell levels following chemotherapy-induced lymphocyte depletion. Such alterations induced by androgen deprivation may have implications for enhancing immune responses to immunotherapy and for accelerating the recovery of the immune system following chemotherapy.

Impact of LL-37 on anti-infective immunity

Host defense peptides (often called cationic antimicrobial peptides) have pleiotropic immunomodulatory functions. The human host defense peptide LL-37 is up-regulated at sites of infection and has little or no antimicrobial activity in tissue-culture media but under the same conditions, demonstrates immunomodulatory effects on epithelial cells, monocytes, and dendritic cells (DC). These effects include the induction of chemokine production in a mitogen-activated protein kinase-dependent manner in epithelial cell lines and monocytes and profound alterations of DC differentiation, resulting in the capacity to enhance a T helper cell type 1 response. Although the exact mechanisms of interaction between LL-37 and these cell types have not been elucidated, there is evidence for specific (i.e., receptor-mediated) and nonspecific interactions. The relative significance of the direct antimicrobial activities and immunomodulatory properties of LL-37 and other cationic host defense peptides in host defense remains unresolved. To demonstrate that antimicrobial activity was not necessarily required for protection in vivo, model peptides were synthesized and tested for antimicrobial and immunomodulatory activities. A peptide with no antimicrobial activity was found to be protective in animal models of Staphylococcus aureus and Salmonella infection, implying that a host defense peptide can protect by exerting immunomodulatory properties.

Role of 4-1BB:4-1BB ligand in cancer immunotherapy

The activation of T cells plays a central role in antitumor immunity. In order to activate naïve T cells, two key signals are required. Signal one is provided through the T-cell receptor (TCR) while signal two is that of costimulation. The CD28:B7 molecules are one of the best-studied costimulatory pathways, thought to be the main mechanism through which primary T-cell stimulation occurs. However, a number of molecules have been identified which serve to amplify and diversify the T-cell response, following initial T-cell activation. These include the more recently described 4-1BB:4-1BB ligand (4-1BBL) molecules. 4-1BB:4-1BBL are a member of the TNFR:TNF ligand family, which are expressed on T cells and antigen-presenting cells (APCs), respectively. Therapies utilizing the 4-1BB:4-1BBL signaling pathway have been shown to have antitumor effects in a number of model systems. In this paper, we focus on the 4-1BB:4-1BBL costimulatory molecules. In particular, we will describe the structure and function of the 4-1BB molecule, its receptor and how 4-1BB:4-1BBL costimulation has and may be used for the immunotherapy of cancer.

Murine B7-H3 is a negative regulator of T cells

T cell activation is regulated by the innate immune system through positive and negative costimulatory molecules. B7-H3 is a novel B7-like molecule with a putative receptor on activated T cells. Human B7-H3 was first described as a positive costimulator, most potently inducing IFN-gamma production and cellular immunity. In this study we examined the expression and function of mouse B7-H3. B7-H3 is mostly expressed on professional APCs; its expression on dendritic cells appears to be up-regulated by LPS. In contrast to human B7-H3, we found that mouse B7-H3 protein inhibited T cell activation and effector cytokine production. An antagonistic mAb to B7-H3 enhanced T cell proliferation in vitro and led to exacerbated experimental autoimmune encephalomyelitis in vivo. Therefore, mouse B7-H3 serves as a negative regulator of T cell activation and function.

Vaccine and antibody-directed T cell tumour immunotherapy

Clearer evidence for immune surveillance in malignancy and the identification of many new tumour-associated antigens (TAAs) have driven novel vaccine and antibody-targeted responses for therapy in cancer. The exploitation of active immunisation may be particularly favourable for TAA where tolerance is incomplete but passive immunisation may offer an additional strategy where the immune repertoire is affected by either tolerance or immune suppression. This review will consider how to utilise both active and passive types of therapy delivered by T cells in the context of the failure of tumour-specific immunity by presenting cancer patients. This article will outline the progress, problems and prospects of several different vaccine and antibody-targeted approaches for immunotherapy of cancer where proof of principle pre-clinical studies have been or will soon be translated into the clinic. Two examples of vaccination-based therapies where both T cell- and antibody-mediated anti-tumour responses are likely to be relevant and two examples of oncofoetal antigen-specific antibody-directed T cell therapies are described in the following sections: (1) therapeutic vaccination against human papillomavirus (HPV) antigens in cervical neoplasia; (2) B cell lymphoma vaccines including against immunoglobulin idiotype; (3) oncofoetal antigens as tumour targets for redirecting T cells with antibody strategies.

Ubiquitin ligases and the immune response

Ubiquitin (Ub)-protein conjugation represents a novel means of posttranscriptional modification in a proteolysis-dependent or -independent manner. E3 Ub ligases play a key role in governing the cascade of Ub transfer reactions by recognizing and catalyzing Ub conjugation to specific protein substrates. The E3s, which can be generally classified into HECT-type and RING-type families, are involved in the regulation of many aspects of the immune system, including the development, activation, and differentiation of lymphocytes, T cell-tolerance induction, antigen presentation, immune evasion, and virus budding. E3-promoted ubiquitination affects a wide array of biological processes, such as receptor downmodulation, signal transduction, protein processing or translocation, protein-protein interaction, and gene transcription, in addition to proteasome-mediated degradation. Deficiency or mutation of some of the E3s like Cbl, Cbl-b, or Itch, causes abnormal immune responses such as autoimmunity, malignancy, and inflammation. This review discusses our current understanding of E3 Ub ligases in both innate and adaptive immunity. Such knowledge may facilitate the development of novel therapeutic approaches for immunological diseases.

Anti-Class II Antibodies, but not Cytotoxic T-Lymphocyte Antigen 4-Immunoglobulin Hybrid Molecules, Prevent Rejection of Major Histocompatibility Complex Class II-Negative Myeloma in T-Cell Receptor-Transgenic Mice

We have previously shown that tumour-specific CD4+ T cells protect against subcutaneous injections of major histocompatibility complex (MHC) class II-negative MOPC315 myeloma cells. Here, we have interfered with the immunologic events that lead to successful rejection of MOPC315 challenges in T-cell receptor (TCR)-transgenic mice. The CD4+ T cells have a transgene-encoded TCR specific for a MOPC315 V-region idiotypic (Id) peptide presented on the MHC class II molecule E(d). A side-by-side comparison indicated that DNA-recombination-deficient TCR-transgenic mice were better protected against MOPC315 tumour development than recombination-sufficient counterparts, suggesting that B cells or endogenous TCR chains might facilitate tumour progression in this model. Intraperitoneal injections of E(d)-specific antibodies over a period of initial 24 days, abrogated protection against tumours in both strains of mice. By contrast, injections of anticostimulatory molecules (cytotoxic T-lymphocyte antigen 4-immunoglobulin hybrid molecules) had no effect. The findings demonstrate that tumour rejection depends on the presence of MHC class II molecules, despite the fact that MOPC315 tumour cells themselves do not express them. The results are consistent with the idea that secreted myeloma protein is processed and presented by class II+ antigen-presenting cells to Id-specific naïve CD4+ T cells that become activated and kill the myeloma cells by a bystander mechanism. While Id presentation on class II molecules is absolutely required for tumour rejection, costimulatory CD80/CD86 molecules might be dispensible in this process.

Translocation of CD28 to lipid rafts and costimulation of IL-2

Stimulation of the CD28 costimulatory receptor can lead to an increased surface lipid raft expression in T lymphocytes. Here, we demonstrate that CD28 itself is recruited to lipid rafts in both Jurkat and peripheral blood T lymphocytes. This recruitment of CD28 is triggered by engagement with either anti-CD28 mAbs or a natural ligand of CD28, B7.2 (CD86). All detectable tyrosine-phosphorylated CD28 is in the lipid raft fractions, as is all of the CD28 associated with phosphatidylinositol 3-kinase, which is recruited to CD28 by tyrosine phosphorylation. Targeting the CD28 cytoplasmic domain to lipid rafts results in its tyrosine phosphorylation, indicating that tyrosine phosphorylation of CD28 may occur after translocation to lipid rafts. Studies with Jurkat cells deficient in Lck and CD45 demonstrate that movement of CD28 into lipid rafts does not require Lck and CD45 and can occur despite reduction of CD28 tyrosine phosphorylation to below the levels of detection. Analysis of murine CD28 mutants reveals a correlation between translocation to lipid rafts and costimulation of IL-2 production. Taken together with the known importance of lipid rafts in T cell activation, these observations suggest that translocation to lipid rafts may play an important role in CD28 signaling.

Tumor Necrosis Factor-α and CD80 Modulate CD28 Expression through a Similar Mechanism of T-cell Receptor-independent Inhibition of Transcription

Replicative senescence of human T cells is characterized by the loss of CD28 expression, exemplified by the clonal expansion of CD28(null) T cells during repeated stimulation in vitro as well as in chronic inflammatory and infectious diseases and in the normal course of aging. Because CD28 is the major costimulatory receptor for the induction of T cell-mediated immunity, the mechanism(s) underlying CD28 loss is of paramount interest. Current models of replicative senescence involve protracted procedures to generate CD28(null) cells from CD28(+) precursors; hence, a T-cell line model was used to examine the dynamics of CD28 expression. Here, we show the versatility of the JT and Jtag cell lines in tracking CD28(null) <--> CD28(hi) phenotypic transitions. JT and Jtag cells were CD28(null) and CD28(lo), respectively, but expressed high levels of CD28 when exposed to phorbol 12-myristate 13-acetate. This was a result of the reconstitution of the CD28 gene transcriptional initiator (INR). Tumor necrosis factor-alpha reduced CD28 expression because of the inhibition of INR-driven transcription. Ligation of CD28 by an antibody or by CD80 also down-regulated CD28 transcription through the same mechanism, providing evidence that CD28 can generate a T cell receptor-independent signal with a unique biological outcome. Collectively, these data unequivocally demonstrate the critical role of the INR in the regulation of CD28 expression. T cell lines with transient expression of CD28 are invaluable in the dissection of the biochemical processes involved in the transactivation of the CD28 INR, the silencing of which is a key event in the ontogenesis of senescent T cells.

Induction of B7-1 in podocytes is associated with nephrotic syndrome

Kidney podocytes and their slit diaphragms form the final barrier to urinary protein loss. This explains why podocyte injury is typically associated with nephrotic syndrome. The present study uncovered an unanticipated novel role for costimulatory molecule B7-1 in podocytes as an inducible modifier of glomerular permselectivity. B7-1 in podocytes was found in genetic, drug-induced, immune-mediated, and bacterial toxin-induced experimental kidney diseases with nephrotic syndrome. The clinical significance of our results is underscored by the observation that podocyte expression of B7-1 correlated with the severity of human lupus nephritis. In vivo, exposure to low-dose LPS rapidly upregulates B7-1 in podocytes of WT and SCID mice, leading to nephrotic-range proteinuria. Mice lacking B7-1 are protected from LPS-induced nephrotic syndrome, suggesting a link between podocyte B7-1 expression and proteinuria. LPS signaling through toll-like receptor-4 reorganized the podocyte actin cytoskeleton in vitro, and activation of B7-1 in cultured podocytes led to reorganization of vital slit diaphragm proteins. In summary, upregulation of B7-1 in podocytes may contribute to the pathogenesis of proteinuria by disrupting the glomerular filter and provides a novel molecular target to tackle proteinuric kidney diseases. Our findings suggest a novel function for B7-1 in danger signaling by nonimmune cells.

Effect of tetravalent bispecific CD19×CD3 recombinant antibody construct and CD28 costimulation on lysis of malignant B cells from patients with chronic lymphocytic leukemia by autologous T cells

To develop an effective antitumor immunotherapy for B-lineage non-Hodgkin's lymphoma, we constructed a tetravalent tandem diabody (tanDb) specific for both human CD19 (B-cell marker) and CD3 (T-cell antigen). Here, we report the effective killing of malignant primary B cells from patients with B-cell chronic lymphocytic leukemia (B-CLL) by autologous T cells induced by tanDb at very low E:T ratios. Mononuclear cells from patients with B-CLL were cultured with bispecific antibody fragments in either the presence or absence of monospecific anti-CD28 antibody. Use of tetravalent tanDbs caused almost quantitative elimination of malignant B cells from the blood samples of 19 patients and some cytotoxic activity in 3 of 23 analyzed cases. In contrast, the structurally similar but bivalent diabody and single-chain diabody demonstrated nearly no antitumor activity in an autologous system. tanDb-induced activation and proliferation of T cells occurred only in the presence of CD19+ target cells. Expression of the B7-1 (CD80) and B7-2 (CD86) molecules on the surface of leukemia cells made unnecessary the additional CD28-costimulation of T cells. When only a few tanDb molecules were present, the effect of CD28 costimulation on T-cell activation was more pronounced. Depending on the patient sample, we observed a 10- to 1,000-fold decrease of the half-maximal concentrations of tanDb for cell lysis. Upon CD28 crosslinking by agonistic MAb, specific tumor cell lysis was found at tanDb concentrations as low as 0.5 pM. These data demonstrate that the tetravalent CD19xCD3 tanDb might be a promising tool for the immunotherapy of human B-cell leukemias and lymphomas.

DNA vaccines suppress tumor growth and metastases by the induction of anti-angiogenesis

Four novel oral DNA vaccines provide long-lived protection against melanoma, colon, breast, and non-small cell lung carcinoma in mouse model systems. The vaccines are delivered by attenuated Salmonella typhimurium to secondary lymphoid organs and are directed against targets such as carcinoembryonic antigen, tyrosine-related protein, vascular endothelial growth factor receptor-2 [also called fetal liver kinase-1 (FLK-1)], and transcription factor Fos-related antigen-1 (Fra-1). The FLK-1 and Fra-1 vaccines are effective in suppressing angiogenesis in the tumor vasculature. All four vaccines are capable of inducing potent cell-mediated protective immunity, breaking peripheral T-cell tolerance against these self-antigens resulting in effective suppression of tumor growth and metastasis. It is anticipated that such research efforts will contribute toward the rational design of future DNA vaccines that will be effective for prevention and treatment of human cancer.

Evaluation of safety and clinical activity of multiple doses of the anti-CD80 monoclonal antibody, galiximab, in patients with moderate to severe plaque psoriasis

BACKGROUND

Reduction in lesional, activated T cells induces improvement in psoriatic plaques. Galiximab (IDEC-114), an IgG(1) anti-CD80 antibody, binds to CD80, a costimulatory molecule involved in T-cell activation.

OBJECTIVE

A Phase I/II, multidose, multischedule, dose-finding study of galiximab to evaluate safety, pharmacokinetics, and clinical activity was conducted in 35 patients with moderate to severe plaque psoriasis.

METHODS

Seven cohorts of five patients received galiximab intravenously on three different schedules at different dose levels.

RESULTS

Adverse events (AEs) commonly occurred as mild and self-limiting. Improvements were observed in most cohorts without evidence of a dose response in Psoriasis Area and Severity Index (50% or greater reduction in PASI score in 40% of patients), Physician's Global Psoriasis Assessment (PGA rating of Good or above in 57% of patients), and Psoriasis Severity Scale (PSS, baseline mean of 7.6 decreased by Study Day 127 to 5.0). An association was observed between reduction in CD3(+) cell count in histologic studies and reduction in PASI score. No antibodies to galiximab were detected.

CONCLUSION

Galiximab appears to be safe and well tolerated with preliminary evidence of clinical and histologic response.

Induction of B7-1 in podocytes is associated with nephrotic syndrome

Kidney podocytes and their slit diaphragms form the final barrier to urinary protein loss. This explains why podocyte injury is typically associated with nephrotic syndrome. The present study uncovered an unanticipated novel role for costimulatory molecule B7-1 in podocytes as an inducible modifier of glomerular permselectivity. B7-1 in podocytes was found in genetic, drug-induced, immune-mediated, and bacterial toxin-induced experimental kidney diseases with nephrotic syndrome. The clinical significance of our results is underscored by the observation that podocyte expression of B7-1 correlated with the severity of human lupus nephritis. In vivo, exposure to low-dose LPS rapidly upregulates B7-1 in podocytes of WT and SCID mice, leading to nephrotic-range proteinuria. Mice lacking B7-1 are protected from LPS-induced nephrotic syndrome, suggesting a link between podocyte B7-1 expression and proteinuria. LPS signaling through toll-like receptor-4 reorganized the podocyte actin cytoskeleton in vitro, and activation of B7-1 in cultured podocytes led to reorganization of vital slit diaphragm proteins. In summary, upregulation of B7-1 in podocytes may contribute to the pathogenesis of proteinuria by disrupting the glomerular filter and provides a novel molecular target to tackle proteinuric kidney diseases. Our findings suggest a novel function for B7-1 in danger signaling by nonimmune cells.

Revival of the regulatory T cell: new targets for drug development

Compelling new evidence supports the idea that regulatory T cells play a major role in our immune system. Several subsets of these regulators have been identified recently. Differences in the phenotypical and functional characteristics of these subsets have immunological implications. From our growing knowledge of the field of immunology, we could potentially generate a new class of therapeutic agents that target immune-related diseases.

Immune regulation by novel costimulatory molecules

CD4 helper T (Th)-cells and the cytokines that they produce play essential regulatory roles in immune and autoimmune responses. Th activation and differentiation is regulated by costimulatory receptors. CD28 and CTLA-4 are important in maintaining the threshold of T-cell activation. ICOS and PD-1 are novel costimulatory receptors expressed on activated T-cells. B7-H3 recognizes a putative costimulatory receptor on activated T-cells. Here we summarize the latest developments in the novel costimulatory molecules and their roles in regulating Th activation, differentiation, and function.

Microparticulate β-glucan upregulates the expression of B7.1, B7.2, B7-H1, but not B7-DC on cultured murine peritoneal macrophages

Beta-1,3-(D)-glucan from a variety of biological sources has been shown to enhance both humoral and cellular immune responses to a variety of antigens, infectious agents, and tumors. Nevertheless, its mode of action has not been fully defined. We sought to determine whether a 1-2 microm diameter microparticulate form of beta-glucan (MG) from the yeast Saccharomyces cerevisiae could regulate expression of B7 family glycoproteins on resident peritoneal macrophages from BALB/c mice. We discovered that MG uregulated B7.2 mRNA expression and enhanced the surface membrane expression of B7.2 glycoprotein. Although B7.1 mRNA was not upregulated above constitutive levels, MG treatment enhanced B7.1 glycoprotein expression on the macrophages, albeit to a lesser extent than B7.2. At the same time, the gene and cell surface expression of B7-H1, a putative negative regulator of T cell activity, was also upregulated by MG. The expression of B7-DC, another B7 family molecule with negative regulatory activity, was not affected by incubation with MG. This study has demonstrated that a microparticulate form of beta-glucan can enhance B7 co-stimulatory molecule expression on macrophages, thereby enabling these antigen-presenting cells to deliver the second signal to T-lymphocytes that express CD28. In addition, because MG also induces the expression of B7-H1, it may enable macrophages to provide a concomitant downregulatory signal to T-lymphocytes expressing PD-1 or related receptors.

Importance of IL-10 for CTLA-4-Mediated Inhibition of Tumor-Eradicating Immunity

In this study, we show that engagement of CTLA-4 on tumor-infiltrating lymphocytes from low-dose melphalan (L-phenylalanine mustard (L-PAM))-treated MOPC-315 tumor bearers led to IL-10 secretion. In addition, the inhibitory activity of CTLA-4 ligation for IFN-gamma secretion following stimulation with anti-CD3 plus anti-CD28 mAb depended on IL-10 production. Consistent with the importance of IL-10 for CTLA-4-mediated inhibition, administration of neutralizing anti-IL-10 mAb to low-dose L-PAM-treated MOPC-315 tumor bearers (administration of blocking anti-CTLA-4 mAb) resulted in enhanced tumor-infiltrating lymphocyte-mediated anti-MOPC-315 cytotoxicity and led to complete tumor eradication in a higher percentage of mice than that observed with low-dose L-PAM alone. The percentage of MOPC-315 tumor-bearing mice cured following administration of neutralizing anti-IL-10 mAb to low-dose L-PAM-treated MOPC-315 tumor bearers was comparable to that observed following administration of blocking anti-CTLA-4 mAb. Moreover, IL-10 neutralization together with CTLA-4 blockade did not provide added therapeutic benefits to low-dose L-PAM-treated MOPC-315 tumor bearers. Taken together, these results indicate that CTLA-4 blockade improves the therapeutic outcome of low-dose L-PAM for MOPC-315 tumor bearers by inhibiting IL-10 secretion as a consequence of blocking CTLA-4 ligation.

PI3-kinase and MAP-kinase signaling cascades in AILIM/ICOS- and CD28-costimulated T-cells have distinct functions between cell proliferation and IL-10 production

Both AILIM/ICOS and CD28 provide positive costimulatory signals for T-cell activation, resulting in proliferation and cytokine production. In this study, we attempted to clarify the key signaling molecules in T-cell proliferation, and also IL-2 and IL-10 production, during T-cell activation by CD3 induced by costimulation with either AILIM/ICOS or CD28. We examined the role of both the PI3-kinase/Akt pathway and MAP kinase family members such as ERK1/2, JNK, and p38 kinase in this process. PI3-kinase and Erk1/2 were shown to potentially regulate primary T-cell activation and subsequent proliferation via both AILIM/ICOS- or CD28-mediated costimulation and the Erk signaling cascade was essential for this proliferation induction and also for IL-2 production. The JAK inhibitor, AG490, inhibited this induction. Our studies indicate that IL-2 is necessary for induction of T-cell proliferation and that the quantities of IL-2 produced by AILIM/ICOS ligation are also sufficient for T-cells to proliferate. In contrast, inhibition of Akt and p38, that are phosphorylated by both AILIM/ICOS and CD28-ligation, could downregulate IL-10 production but not T-cell proliferation. These data raise the interesting possibility that the signaling cascades between T-cell proliferation and IL-10 production are regulated by different molecules in AILIM/ICOS- and CD28-costimulated T-cells.

Transplant Immunology

Since the early days of transplantation, it has been known that the immune system is the major barrier to long-term graft survival. Due to the unique “fingerprint” of different individuals’ cells, donor organs are detected as foreign, invasivematerial by the recipient’s immunesystem and, subsequently, attacked and rejected. The difficulty that has continuously faced the transplant community is the multifaceted nature of the immune response and halting the numerous pathways of immune stimulation. The ultimate goal of all transplant research is graft acceptance, also known as tolerance, without the use of long-term immunosuppressant medication. Various reviews of the different facets of transplant rejection exist. The following summary will attempt to outline the major known pathways involved in organ recognition and acute rejection.

B7h is required for T cell activation, differentiation, and effector function

T helper (Th) cell activation, differentiation, and immune function are regulated by costimulatory molecules. Inducible costimulator (ICOS) is a recently identified costimulatory receptor expressed on activated T cells. A ligand for ICOS, B7h, is expressed on B cells and other types of antigen-presenting cells (APC). Although ICOS has been shown to be essential in T cell activation and differentiation, the regulatory roles of B7h at different stages of T cell immune responses have not been examined genetically. In this study, we generated and analyzed B7h-deficient mice. We present evidence that B7h is the only ligand for ICOS, and ICOS, its only corresponding receptor. Th cells, when activated with B7h-deficient APC, exhibited reduced proliferation and IL-2 production. In addition, Th cells produced significantly reduced amounts of IL-4 and -13 after differentiation at the presence of B7h-/- APC. This cytokine defect was associated with a deficiency in c-Maf expression and could be rescued completely by c-Maf overexpression in T cells. Furthermore, we showed that effector T cells, when restimulated in the presence of B7h-deficient APC, exhibited reduced Th2 cytokine production. Therefore, B7h is required for proper Th cell activation, differentiation, and effector cytokine expression.

Regulation of immune and autoimmune responses by ICOS

Proper T cell activation and function are regulated by the innate immune system, importantly through positive and negative costimulatory molecules in the B7 superfamily. Inducible costimulator (ICOS), the receptor for B7h (also known as B7RP-1), is expressed on T cells after T cell activation. Recently, using ICOS-deficient mice, we have examined the roles of ICOS in immune responses. ICOS is required for humoral immunity. In organ-specific autoimmune responses, however, ICOS has contrast roles in different disease models. On the one hand, ICOS-/- mice exhibited extreme sensitivity to experimental autoimmune encephalomyelitis (EAE); on the other, ICOS gene deletion led to complete resistance to collagen-induced arthritis (CIA) in mice. Our work not only illustrates the complexity of immune regulation by costimulatory molecules, but also suggests novel therapeutic strategies for various autoimmune diseases.

CD4+ T, but not CD8+ or B, lymphocytes mediate facial motoneuron survival after facial nerve transection

The capacity of facial motor neurons (FMN) to survive injury and successfully regenerate is substantially compromised in immunodeficient mice, which lack T and B lymphocytes (). The goal of the present study was to determine which T cell subset (CD4+ and/or CD8+), and whether the B lymphocyte, is involved in FMN survival after nerve injury. All mice were subjected to a right facial nerve axotomy, with the left (uncut) side serving as an internal control. FMN survival, of the right (cut) side, was measured 4 weeks post-operative, and expressed as a percentage of the left (uncut) control side. FMN survival in wild-type mice was 86%+/-1.5. In contrast, FMN survival in CD4 KO mice was 60%+/-2.0. Reconstitution of either CD4 KO mice, or recombinase activating gene-2 knockout (RAG-2 KO) mice (which lack functional T and B cells) with CD4+ T cells alone restored FMN survival to wild-type levels (85%+/-1.2 and 84%+/-2.5, respectively). There was no difference in FMN survival between wild-type, CD8 KO and MmuMT (B cell deficient) mice. Reconstitution of RAG-2 KO mice with CD8+ T cells alone, or B cells alone, failed to restore FMN survival levels (65%+/-1.5 and 63%+/-1.0, respectively). It is concluded that, of the population of FMN that do not survive injury, CD4+ T lymphocytes, but not CD8+ T lymphocytes or B cells, mediate FMN survival after peripheral nerve injury.

Mouse B7-H3 induces antitumor immunity

Members of the B7 family costimulate the proliferation of lymphocytes during the initiation and maintenance of antigen-specific humoral and cell-mediated immune responses. While B7-1 and -2 are restricted to lymphoid tissues, and activate naïve T cells, recently identified members including B7-H2 and -H3 are widely expressed on nonlymphoid tissues, and regulate effector lymphocytes in the periphery. B7-H3 has properties that suggested it may display antitumor activity, including the ability to stimulate Th1 and cytotoxic T-cell responses. Here, we test this notion by determining whether intratumoral injection of an expression plasmid encoding a newly described mouse homologue of B7-H3 is able to eradicate EL-4 lymphomas. Intratumoral injection of a mouse B7-H3 pcDNA3 expression plasmid led to complete regression of 50% tumors, or otherwise significantly slowed tumor growth. Mice whose tumors completely regressed resisted a challenge with parental tumor cells, indicating systemic immunity had been generated. B7-H3-mediated antitumor immunity was mediated by CD8(+) T and NK cells, with no apparent contribution from CD4(+) T cells. In summary, the results indicate that B7-H3 interactions may play a role in regulating cell-mediated immune responses against cancer, and that B7-H3 is a potential therapeutic tool.

Inhibitory signal override increases susceptibility to mercury-induced autoimmunity

After exposure to subtoxic doses of heavy metals such as mercury, H-2(s) mice develop an autoimmune syndrome consisting of the rapid production of IgG autoantibodies that are highly specific for nucleolar autoantigens and a polyclonal increase in serum IgG1 and IgE. In this study, we explore the role of two inhibitory immunoreceptors, CTLA-4 and FcgammaRIIB, in the regulation of mercury-induced autoimmunity. In susceptible mice treated with mercuric chloride (HgCl(2)), administration of a blocking anti-CTLA-4 Ab resulted in a further increase in anti-nucleolar autoantibodies and in total serum IgG1 levels. Furthermore, in some DBA/2 mice, which are normally resistant to heavy metal-induced autoimmunity, anti-CTLA-4 treatment leads to the production of anti-nucleolar Abs, thereby overcoming the genetic restriction of the disease. In mice deficient for the FcgammaRIIB, HgCl(2) administration did not trigger autoantibody production, but resulted in an increase in IgE serum levels. Taken together, these results indicate that different inhibitory mechanisms regulate various manifestations of this autoimmune syndrome.

Paired activating and inhibitory immunoglobulin-like receptors, MAIR-I and MAIR-II, regulate mast cell and macrophage activation

Immune responses are regulated by opposing positive and negative signals triggered by the interaction of activating and inhibitory cell surface receptors with their ligands. Here, we describe novel paired activating and inhibitory immunoglobulin-like receptors, designated myeloid-associated immunoglobulin-like receptor (MAIR) I and MAIR-II, whose extracellular domains are highly conserved by each other. MAIR-I, expressed on the majority of myeloid cells, including macrophages, granulocytes, mast cells, and dendritic cells, contains the tyrosine-based sorting motif and the immunoreceptor tyrosine-based inhibitory motif-like sequences in the cytoplasmic domain and mediates endocytosis of the receptor and inhibition of IgE-mediated degranulation from mast cells. On the other hand, MAIR-II, expressed on subsets of peritoneal macrophages and B cells, associates with the immunoreceptor tyrosine-based activation motif-bearing adaptor DAP12 and stimulates proinflammatory cytokines and chemokine secretions from macrophages. Thus, MAIR-I and MAIR-II play important regulatory roles in cell signaling and immune responses.

Influence of CCR7 ligand DNA preexposure on the magnitude and duration of immunity

The CC chemokine receptor (CCR) 7 ligands CCL21 and CCL19 were recently described as essential elements for establishing the microenvironment needed to initiate optimal immune responses in secondary lymphoid tissues. In the present study we have kinetically investigated the primary responses of naive DO11.10 TCR-transgenic CD4+ T cells (OVA323-339 peptide specific) adoptively transferred into normal BALB/c mice given plasmid DNA encoding CCR7 ligands. The primary responses of CD4+ Tg-T cells in CCR7 ligand DNA recipients occurred more promptly, reaching levels higher than those observed in vector controls. In line with enhanced specific immunity, the T-cell population in CCR7 ligand recipients underwent more in vivo cell division following Ag stimulation, and a higher percentage of Ag-specific T cells expressed an activation phenotype. Moreover, the enhanced primary responses of naive CD4+ T cells appeared to act via affects on migration and maturation of CD11c+ dendritic cells in the draining lymph nodes. In addition following mucosal challenge of herpes simplex virus-immune mice with virus, those that had received CCL21 or CCL19 during priming contained a higher frequency of responding CD4 T cells in lymph nodes and the site of infection. Moreover, CCL21- and CCL19-treated mice showed less severe disease and better survival following challenge. Our results are discussed in terms of the relevance of CCR7 ligand preimmunization to improve vaccine.