Signaling lymphocytic activation molecule is expressed on CD40 ligand-activated dendritic cells and directly augments production of inflammatory cytokines

SLAM-family receptors come of age as a potential molecular target in cancer immunotherapy

The signaling lymphocytic activation molecule (SLAM) family receptors were discovered in immune cells for the first time. The SLAM-family receptors are a significant player in cytotoxicity, humoral immune responses, autoimmune diseases, lymphocyte development, cell survival, and cell adhesion. There is growing evidence that SLAM-family receptors have been involved in cancer progression and heralded as a novel immune checkpoint on T cells. Previous studies have reported the role of SLAMs in tumor immunity in various cancers, including chronic lymphocytic leukemia, lymphoma, multiple myeloma, acute myeloid leukemia, hepatocellular carcinoma, head and neck squamous cell carcinoma, pancreas, lung, and melanoma. Evidence has deciphered that the SLAM-family receptors may be targeted for cancer immunotherapy. However, our understanding in this regard is not complete. This review will discuss the role of SLAM-family receptors in cancer immunotherapy. It will also provide an update on recent advances in SLAM-based targeted immunotherapies.

Identification of tumor microenvironment-associated immunological genes as potent prognostic markers in the cancer genome analysis project HOPE

Project High-tech Omics-based Patient Evaluation (HOPE), which used whole-exome sequencing and gene expression profiling, was launched in 2014. A total of ~2,000 patients were enrolled until March 2016, and the survival time was observed up to July 2019. In our previous study, a tumor microenvironment immune type classification based on the expression levels of the programmed death-ligand 1 (PD-L1) and CD8B genes was performed based on four types: A, adaptive immune resistance; B, intrinsic induction; C, immunological ignorance; and D, tolerance. Type A (PD-L1⁺ and CD8B⁺) exhibited upregulated features of T helper 1 antitumor responses. In the present study, survival time analysis at 5 years revealed that patients in type A had a better prognosis than those in other categories [5 year survival rate (%); A (80.5) vs. B (73.9), C (73.4) and D (72.6), P=0.0005]. Based on the expression data of 293 immune response-associated genes, 62 specific genes were upregulated in the type A group. Among these genes, 18 specific genes, such as activated effector T-cell markers (CD8/CD40LG/GZMB), effector memory T-cell markers (PD-1/CD27/ICOS), chemokine markers (CXCL9/CXCL10) and activated dendritic cell markers (CD80/CD274/SLAMF1), were significantly associated with a good prognosis using overall survival time analysis. Finally, multivariate Cox proportional hazard regression analyses of overall survival demonstrated that four genes (GZMB, HAVCR2, CXCL9 and CD40LG) were independent prognostic markers, and GZMB, CXCL9 and CD40LG may contribute to the survival benefit of patients in the immune type A group.

SLAMF1 signaling induces Mycobacterium tuberculosis uptake leading to endolysosomal maturation in human macrophages

Tuberculosis dates back to ancient times but it is not a problem of the past. Each year, millions of people die from tuberculosis. After inhalation of infectious droplet nuclei, Mycobacterium tuberculosis reaches the lungs where it can manipulate the immune system and survive within host macrophages, establishing a persistent infection. The signaling lymphocytic activation molecule family member 1 (SLAMF1) is a self-ligand receptor that can internalize gram-negative bacteria and regulate macrophages' phagosomal functions. In tuberculosis, SLAMF1 promotes Th1-protective responses. In this work, we studied the role of SLAMF1 on macrophages' functions during M. tuberculosis infection. Our results showed that both M. tuberculosis and IFN-γ stimulation induce SLAMF1 expression in macrophages from healthy donor and Tohoku Hospital Pediatrcs-1 cells. Costimulation through SLAMF1 with an agonistic antibody resulted in an enhanced internalization of M. tuberculosis by macrophages. Interestingly, we found that SLAMF1 interacts with M. tuberculosis and colocalizes with the bacteria and with early and late endosomes/lysosomes markers (EEA1 and LAMP2), suggesting that SLAMF1 recognize M. tuberculosis and participate in the endolysosomal maturation process. Notably, increased levels of SLAMF1 were detected in CD14 cells from pleural effusions of tuberculosis patients, indicating that SLAMF1 might have an active function at the site of infection. Taken together, our results provide evidence that SLAMF1 improves the uptake of M. tuberculosis by human monocyte-derived macrophages.

Identification of amino acid residues involved in the interaction between peste-des-petits-ruminants virus haemagglutinin protein and cellular receptors

Peste-des-petits-ruminants virus (PPRV) haemagglutinin (H) protein mediates binding to cellular receptors and then initiates virus entry. To identify the key residues of PPRV H (Hv) protein of the Nigeria 75/1 strain involved in binding to receptors, interaction of the Hv and mutated Hv (mHv) proteins with receptors (SLAM and Nectin 4) and their mutants (mSLAM1, mSLAM2, mSLAM3 and mNectin 4) was investigated using surface plasmon resonance imaging (SPRi) and coimmunoprecipitation (co-IP) assays. The results showed that the Hv protein failed to interact with mSLAM3, but interacted at a strong or medium intensity with SLAM, mSLAM2, Nectin 4 and mNectin 4, and at a low level with mSLAM1. The mHv protein was unable to interact with SLAM and its mutants, but bound to Nectin 4 and mNectin 4 with medium and weak intensity, respectively. Further analysis showed that the Hv protein could precipitate mSLAM1, mSLAM2 and mNectin 4, but not mSLAM3. The mHv protein failed to coprecipitate with SLAM and its mutants. The binding activities of mNectin 4 and Nectin 4 to mHv were less than 30.36 and 51.94 % of the wild-type levels, respectively. Based on the results obtained, amino acids at positions R389, L464, I498, R503, R533, Y541, Y543, F552 and Y553 of H protein and I61, H62, L64, K76, K78, E123, H130, I210, A211, S226 and R227 in SLAM were identified to be essential for the specificity of H-SLAM interaction, while the critical residues of H-Nectin 4 interaction require further study. These findings would improve our understanding of the invasive mechanisms of PPRV.

SLAM Family Receptor Signaling in Viral Infections: HIV and Beyond

The signaling lymphocytic activation molecule (SLAM) family of receptors are expressed on the majority of immune cells. These receptors often serve as self-ligands, and play important roles in cellular communication and adhesion, thus modulating immune responses. SLAM family receptor signaling is differentially regulated in various immune cell types, with responses generally being determined by the presence or absence of two SLAM family adaptor proteins-Ewing's sarcoma-associated transcript 2 (EAT-2) and SLAM-associated adaptor protein (SAP). In addition to serving as direct regulators of the immune system, certain SLAM family members have also been identified as direct targets for specific microbes and viruses. Here, we will discuss the known roles for these receptors in the setting of viral infection, with special emphasis placed on HIV infection. Because HIV causes such complex dysregulation of the immune system, studies of the roles for SLAM family receptors in this context are particularly exciting.

Vedolizumab is associated with changes in innate rather than adaptive immunity in patients with inflammatory bowel disease

OBJECTIVE

Vedolizumab, a monoclonal antibody directed against the integrin heterodimer α4β7, is approved for the treatment of Crohn's disease and ulcerative colitis. The efficacy of vedolizumab has been suggested to result from inhibition of intestinal T cell trafficking although human data to support this conclusion are scarce. We therefore performed a comprehensive analysis of vedolizumab-induced alterations in mucosal and systemic immunity in patients with inflammatory bowel disease (IBD), using anti-inflammatory therapy with the TNFα antibody infliximab as control.

DESIGN

Immunophenotyping, immunohistochemistry, T cell receptor profiling and RNA sequencing were performed using blood and colonic biopsies from patients with IBD before and during treatment with vedolizumab (n=18) or, as control, the anti-TNFα antibody infliximab (n=20). Leucocyte trafficking in vivo was assessed using single photon emission computed tomography and endomicroscopy.

RESULTS

Vedolizumab was not associated with alterations in the abundance or phenotype of lamina propria T cells and did not affect the mucosal T cell repertoire or leucocyte trafficking in vivo. Surprisingly, however, α4β7 antibody treatment was associated with substantial effects on innate immunity including changes in macrophage populations and pronounced alterations in the expression of molecules involved in microbial sensing, chemoattraction and regulation of the innate effector response. These effects were specific to vedolizumab, not observed in response to the TNFα antibody infliximab, and associated with inhibition of intestinal inflammation.

CONCLUSION

Our findings suggest that modulation of innate immunity contributes to the therapeutic efficacy of vedolizumab in IBD.

TRIAL REGISTRATION NUMBER

NCT02694588.

SLAMF1/CD150 in hematologic malignancies: Silent marker or active player?

SLAMF1/CD150 receptor is a founder of signaling lymphocyte activation molecule (SLAM) family of cell-surface receptors. It is widely expressed on cells within hematopoietic system. In hematologic malignancies CD150 cell surface expression is restricted to cutaneous T-cell lymphomas, few types of B-cell non-Hodgkin's lymphoma, near half of cases of chronic lymphocytic leukemia, Hodgkin's lymphoma, and multiple myeloma. Differential expression among various types of hematological malignancies allows considering CD150 as diagnostical and potential prognostic marker. Moreover, CD150 may be a target for antibody-based or measles virus oncolytic therapy. Due to CD150 signaling properties it is involved in regulation of malignant cell fate decision and tumor microenvironment in Hodgkin's lymphoma and chronic lymphocytic leukemia. This review summarizes evidence for the important role of CD150 in pathogenesis of hematologic malignancies.

Early B-cell factor 1 (EBF1) is critical for transcriptional control of SLAMF1 gene in human B cells

Signaling lymphocytic activation molecule family member 1 (SLAMF1)/CD150 is a co-stimulatory receptor expressed on a variety of hematopoietic cells, in particular on mature lymphocytes activated by specific antigen, costimulation and cytokines. Changes in CD150 expression level have been reported in association with autoimmunity and with B-cell chronic lymphocytic leukemia. We characterized the core promoter for SLAMF1 gene in human B-cell lines and explored binding sites for a number of transcription factors involved in B cell differentiation and activation. Mutations of SP1, STAT6, IRF4, NF-kB, ELF1, TCF3, and SPI1/PU.1 sites resulted in significantly decreased promoter activity of varying magnitude, depending on the cell line tested. The most profound effect on the promoter strength was observed upon mutation of the binding site for Early B-cell factor 1 (EBF1). This mutation produced a 10-20 fold drop in promoter activity and pinpointed EBF1 as the master regulator of human SLAMF1 gene in B cells. We also identified three potent transcriptional enhancers in human SLAMF1 locus, each containing functional EBF1 binding sites. Thus, EBF1 interacts with specific binding sites located both in the promoter and in the enhancer regions of the SLAMF1 gene and is critical for its expression in human B cells.

Jagged1 Instructs Macrophage Differentiation in Leprosy

As circulating monocytes enter the site of disease, the local microenvironment instructs their differentiation into tissue macrophages (MΦ). To identify mechanisms that regulate MΦ differentiation, we studied human leprosy as a model, since M1-type antimicrobial MΦ predominate in lesions in the self-limited form, whereas M2-type phagocytic MΦ are characteristic of the lesions in the progressive form. Using a heterotypic co-culture model, we found that unstimulated endothelial cells (EC) trigger monocytes to become M2 MΦ. However, biochemical screens identified that IFN-γ and two families of small molecules activated EC to induce monocytes to differentiate into M1 MΦ. The gene expression profiles induced in these activated EC, when overlapped with the transcriptomes of human leprosy lesions, identified Jagged1 (JAG1) as a potential regulator of MΦ differentiation. JAG1 protein was preferentially expressed in the lesions from the self-limited form of leprosy, and localized to the vascular endothelium. The ability of activated EC to induce M1 MΦ was JAG1-dependent and the addition of JAG1 to quiescent EC facilitated monocyte differentiation into M1 MΦ with antimicrobial activity against M. leprae. Our findings indicate a potential role for the IFN-γ-JAG1 axis in instructing MΦ differentiation as part of the host defense response at the site of disease in human leprosy.

Mycobacterial diseases, such as leprosy, continue to be serious causes of mortality and morbidity worldwide. They pose a unique treatment challenge due to their ability to modify the immune response in infected individuals. For example, in leprosy there are two distinct manifestations of the disease, each characterized by the immune response of the individual. One results in a more disseminated and severe form of the disease, lepromatous leprosy, and the other is a more limited form with marked antimicrobial activity, tuberculoid leprosy. These differences in the immune response can be characterized by the phenotype and activation state of the macrophage. We illustrate how the local endothelial microenvironment can “educate” macrophages, identifying Jagged1 and select small molecules that can regulate this pathway. Therefore, these studies identify a potential strategy to intervene in infection and inflammation, by targeting macrophage instruction at the site of disease. Through the integration of in vitro modeling and gene expression profiles at the site of disease, we found that Jagged 1 harnesses the endothelial microenvironment to instruct antimicrobial macrophage responses in leprosy.

Lentiviral Protein Transfer Vectors Are an Efficient Vaccine Platform and Induce a Strong Antigen-Specific Cytotoxic T Cell Response

To induce and trigger innate and adaptive immune responses, antigen-presenting cells (APCs) take up and process antigens. Retroviral particles are capable of transferring not only genetic information but also foreign cargo proteins when they are genetically fused to viral structural proteins. Here, we demonstrate the capacity of lentiviral protein transfer vectors (PTVs) for targeted antigen transfer directly into APCs and thereby induction of cytotoxic T cell responses. Targeting of lentiviral PTVs to APCs can be achieved analogously to gene transfer vectors by pseudotyping the particles with truncated wild-type measles virus (MV) glycoproteins (GPs), which use human SLAM (signaling lymphocyte activation molecule) as a main entry receptor. SLAM is expressed on stimulated lymphocytes and APCs, including dendritic cells. SLAM-targeted PTVs transferred the reporter protein green fluorescent protein (GFP) or Cre recombinase with strict receptor specificity into SLAM-expressing CHO and B cell lines, in contrast to broadly transducing vesicular stomatitis virus G protein (VSV-G) pseudotyped PTVs. Primary myeloid dendritic cells (mDCs) incubated with targeted or nontargeted ovalbumin (Ova)-transferring PTVs stimulated Ova-specific T lymphocytes, especially CD8(+) T cells. Administration of Ova-PTVs into SLAM-transgenic and control mice confirmed the observed predominant induction of antigen-specific CD8(+) T cells and demonstrated the capacity of protein transfer vectors as suitable vaccines for the induction of antigen-specific immune responses.

IMPORTANCE

This study demonstrates the specificity and efficacy of antigen transfer by SLAM-targeted and nontargeted lentiviral protein transfer vectors into antigen-presenting cells to trigger antigen-specific immune responses in vitro and in vivo. The observed predominant activation of antigen-specific CD8(+) T cells indicates the suitability of SLAM-targeted and also nontargeted PTVs as a vaccine for the induction of cytotoxic immune responses. Since cytotoxic CD8(+) T lymphocytes are a mainstay of antitumoral immune responses, PTVs could be engineered for the transfer of specific tumor antigens provoking tailored antitumoral immunity. Therefore, PTVs can be used as safe and efficient alternatives to gene transfer vectors or live attenuated replicating vector platforms, avoiding genotoxicity or general toxicity in highly immunocompromised patients, respectively. Thereby, the potential for easy envelope exchange allows the circumventing of neutralizing antibodies, e.g., during repeated boost immunizations.

Expression of CD150 in tumors of the central nervous system: identification of a novel isoform

CD150 (IPO3/SLAM) belongs to the SLAM family of receptors and serves as a major entry receptor for measles virus. CD150 is expressed on normal and malignant cells of the immune system. However, little is known about its expression outside the hematopoietic system, especially tumors of the central nervous system (CNS). Although CD150 was not found in different regions of normal brain tissues, our immunohistochemical study revealed its expression in 77.6% of human CNS tumors, including glioblastoma, anaplastic astrocytoma, diffuse astrocytoma, ependymoma, and others. CD150 was detected in the cytoplasm, but not on the cell surface of glioma cell lines, and it was colocalized with the endoplasmic reticulum and Golgi complex markers. In addition to the full length mRNA of the mCD150 splice isoform, in glioma cells we found a highly expressed novel CD150 transcript (nCD150), containing an 83 bp insert. The insert is derived from a previously unrecognized exon designated Cyt-new, which is located 510 bp downstream of the transmembrane region exon, and is a specific feature of primate SLAMF1. Both mCD150 and nCD150 cDNA variants did not contain any mutations and had the leader sequence. The nCD150 transcript was also detected in normal and malignant B lymphocytes, primary T cells, dendritic cells and macrophages; however, in glioma cells nCD150 was found to be the predominant CD150 isoform. Similarly to mCD150, cell surface expression of nCD150 allows wild type measles virus entry to the cell. Our data indicate that CD150 expression in CNS tumors can be considered a new diagnostic marker and potential target for novel therapeutic approaches.

G-CSF regulates hematopoietic stem cell activity, in part, through activation of Toll-like receptor signaling

Recent studies demonstrate that inflammatory signals regulate hematopoietic stem cells (HSCs). Granulocyte-colony stimulating factor (G-CSF) is often induced with infection and plays a key role in the stress granulopoiesis response. However, its effects on HSCs are less clear. Herein, we show that treatment with G-CSF induces expansion and increased quiescence of phenotypic HSCs, but causes a marked, cell-autonomous HSC repopulating defect associated with induction of toll-like receptor (TLR) expression and signaling. The G-CSF-mediated expansion of HSCs is reduced in mice lacking TLR2, TLR4 or the TLR signaling adaptor MyD88. Induction of HSC quiescence is abrogated in mice lacking MyD88 or in mice treated with antibiotics to suppress intestinal flora. Finally, loss of TLR4 or germ free conditions mitigates the G-CSF-mediated HSC repopulating defect. These data suggest that low level TLR agonist production by commensal flora contributes to the regulation of HSC function and that G-CSF negatively regulates HSCs, in part, by enhancing TLR signaling.

Regulation of hematopoietic stem cell activity by inflammation

Hematopoietic stem cells (HSCs) are quiescent cells with self-renewal capacity and the ability to generate all mature blood cells. HSCs normally reside in specialized niches in the bone marrow that help maintain their quiescence and long-term repopulating activity. There is emerging evidence that certain cytokines induced during inflammation have significant effects on HSCs in the bone marrow. Type I and II interferons, tumor necrosis factor, and lipopolysaccharide (LPS) directly stimulate HSC proliferation and differentiation, thereby increasing the short-term output of mature effector leukocytes. However, chronic inflammatory cytokine signaling can lead to HSC exhaustion and may contribute the development of hematopoietic malignancies. Pro-inflammatory cytokines such as G-CSF can also indirectly affect HSCs by altering the bone marrow microenvironment, disrupting the stem cell niche, and leading to HSC mobilization into the blood. Herein, we review our current understanding of the effects of inflammatory mediators on HSCs, and we discuss the potential clinical implications of these findings with respect to bone marrow failure and leukemogenesis.

Function of feline signaling lymphocyte activation molecule as a receptor of canine distemper virus

Morbilliviruses use signaling lymphocyte activation molecule (SLAM) as a receptor for their entry to cells. In this study, a complete gene encoding SLAM of a domestic cat was identified. The identity of feline SLAM with canine one was 73%, and feline SLAM formed the same cluster with those of carnivores. Furthermore, feline cell expressing feline SLAM supported growth of canine distemper virus (CDV) as well as that expressing canine one. These results indicated that feline SLAM can function as a receptor for morbilliviruses, and our established feline cells that express feline SLAM might be useful for analysis of morbilliviruses originated from felids.

Vaccines expressing the innate immune modulator EAT-2 elicit potent effector memory T lymphocyte responses despite pre-existing vaccine immunity

The mixed results from recent vaccine clinical trials targeting HIV-1 justify the need to enhance the potency of HIV-1 vaccine platforms in general. Use of first-generation recombinant adenovirus serotype 5 (rAd5) platforms failed to protect vaccinees from HIV-1 infection. One hypothesis is that the rAd5-based vaccine failed due to the presence of pre-existing Ad5 immunity in many vaccines. We recently confirmed that EAT-2-expressing rAd5 vectors uniquely activate the innate immune system and improve cellular immune responses against rAd5-expressed Ags, inclusive of HIV/Gag. In this study, we report that use of the rAd5-EAT-2 vaccine can also induce potent cellular immune responses to HIV-1 Ags despite the presence of Ad5-specific immunity. Compared to controls expressing a mutant SH2 domain form of EAT-2, Ad5 immune mice vaccinated with an rAd5-wild-type EAT-2 HIV/Gag-specific vaccine formulation significantly facilitated the induction of several arms of the innate immune system. These responses positively correlated with an improved ability of the vaccine to induce stronger effector memory T cell-biased, cellular immune responses to a coexpressed Ag despite pre-existing anti-Ad5 immunity. Moreover, inclusion of EAT-2 in the vaccine mixture improves the generation of polyfunctional cytolytic CD8(+) T cell responses as characterized by enhanced production of IFN-γ, TNF-α, cytotoxic degranulation, and increased in vivo cytolytic activity. These data suggest a new approach whereby inclusion of EAT-2 expression in stringent human vaccination applications can provide a more effective vaccine against HIV-1 specifically in Ad5 immune subjects.

Protection of porcine islet xenografts in mice using sertoli cells and monoclonal antibodies

BACKGROUND

To remedy the shortage of human donor islets, xenotransplantation of neonatal porcine islets (NPI) provides an attractive alternative source of donor tissue so long as graft rejection can be circumvented. Thus, in this study, we sought to determine whether cotransplantation of NPI with Sertoli cells (SC) combined with a short-course treatment of monoclonal antibody (mAb) could provide long-term islet xenograft survival.

METHODS

NPI alone or NPI cotransplanted with neonatal porcine SC were transplanted into diabetic C57BL/6 mice. These mice were left untreated or were treated with a short course of antileukocyte function associated antigen-1 (LFA-1), anti-CD154, or anti-CD45RB mAb. Blood glucose levels were monitored twice a week to assess graft function. At more than 100 days posttransplantation or on the day of rejection, graft-bearing kidneys were collected for characterization using immunohistochemistry.

RESULTS

None of the untreated control mice transplanted with NPI alone (0/5) or NPI cotransplanted with SC (0/8) achieved normoglycemia. However, of the mice receiving NPI alone, 3 of 7 treated with anti-LFA-1 mAb, 2 of 7 treated with anti-CD154 mAb, and 1 of 7 treated with anti-CD45RB mAb achieved long-term graft survival (>100 days). These proportions improved considerably when NPI were cotransplanted with SC, as 15 of 15 mice treated with anti-LFA-1 mAb, 7 of 8 mice treated with anti-CD154 mAb, and 4 of 9 mice treated with anti-CD45RB mAb achieved long-term graft survival.

CONCLUSIONS

These results show that transient administration of anti-LFA-1 mAb or anti-CD154 mAb is efficacious in prolonging NPI xenograft survival when islets are cotransplanted with SC. Interleukin-4 and Serpina3n may be important mediators of protection observed in this model.

A new synthetic TLR4 agonist, GLA, allows dendritic cells targeted with antigen to elicit Th1 T-cell immunity in vivo

Protein-based vaccines offer safety and cost advantages but require adjuvants to induce immunity. Here we examined the adjuvant capacity of glucopyranosyl lipid A (GLA), a new synthetic non-toxic analogue of lipopolysaccharide. In mice, in comparison with non-formulated LPS and monophosphoryl lipid A, formulated GLA induced higher antibody titers and generated Type 1 T-cell responses to HIV gag-p24 protein in spleen and lymph nodes, which was dependent on TLR4 expression. Immunization was greatly improved by targeting HIV gag p24 to DCs with an antibody to DEC-205, a DC receptor for antigen uptake and processing. Subcutaneous immunization induced antigen-specific T-cell responses in the intestinal lamina propria. Immunity did not develop in mice transiently depleted of DCs. To understand how GLA works, we studied DCs directly from vaccinated mice. Within 4 h, GLA caused DCs to upregulate CD86 and CD40 and produce cytokines including IL-12p70 in vivo. Importantly, DCs removed from mice 4 h after vaccination became immunogenic, capable of inducing T-cell immunity upon injection into naïve mice. These data indicate that a synthetic and clinically feasible TLR4 agonist rapidly stimulates full maturation of DCs in vivo, allowing for adaptive immunity to develop many weeks to months later.

Vaccine platforms combining circumsporozoite protein and potent immune modulators, rEA or EAT-2, paradoxically result in opposing immune responses

Background

Malaria greatly impacts the health and wellbeing of over half of the world's population. Promising malaria vaccine candidates have attempted to induce adaptive immune responses to Circumsporozoite (CS) protein. Despite the inclusion of potent adjuvants, these vaccines have limited protective efficacy. Conventional recombinant adenovirus (rAd) based vaccines expressing CS protein can induce CS protein specific immune responses, but these are essentially equivalent to those generated after use of the CS protein subunit based vaccines. In this study we combined the use of rAds expressing CS protein along with rAds expressing novel innate immune response modulating proteins in an attempt to significantly improve the induction of CS protein specific cell mediated immune (CMI) responses.

Methods and Findings

BALB/cJ mice were co-vaccinated with a rAd vectors expressing CS protein simultaneous with a rAd expressing either TLR agonist (rEA) or SLAM receptors adaptor protein (EAT-2). Paradoxically, expression of the TLR agonist uncovered a potent immunosuppressive activity inherent to the combined expression of the CS protein and rEA. Fortunately, use of the rAd vaccine expressing EAT-2 circumvented CS protein's suppressive activity, and generated a fivefold increase in the number of CS protein responsive, IFNγ secreting splenocytes, as well as increased the breadth of T cells responsive to peptides present in the CS protein. These improvements were positively correlated with the induction of a fourfold improvement in CS protein specific CTL functional activity in vivo.

Conclusion

Our results emphasize the need for caution when incorporating CS protein into malaria vaccine platforms expressing or containing other immunostimulatory compounds, as the immunological outcomes may be unanticipated and/or counter-productive. However, expressing the SLAM receptors derived signaling adaptor EAT-2 at the same time of vaccination with CS protein can overcome these concerns, as well as significantly improve the induction of malaria antigen specific adaptive immune responses in vivo.

Tissue distribution and expression of signaling lymphocyte activation molecule receptor to peste des petits ruminant virus in goats detected by real-time PCR

In the present study, we investigated the tissue distribution and expression of signaling lymphocyte activation molecule (SLAM) in 40 tissues and organs of goats by real-time RT-PCR, in order to determine the role of these receptors in tissue tropism. SLAM mRNA was detected in all the samples investigated. The expression of SLAM mRNA was detected at high levels in spleen, mesenteric lymph node, hilar lymph node, mandibular lymph node, superficial cervical lymph node, nasal mucosa, duodenum, heart, gallbladder, thymus and blood; this is similar to the tissue tropism of peste des petits ruminant virus. However, it was surprising that expression of SLAM was low in lungs, colon and rectum which are the major sites of replication of PPRV. In addition, very low levels were detected in larynx, tongue and esophagus, which suggest the possible presence of an alternative receptor for PPRV. This study provided the first data on caprine SLAM for use in further studies of the pathogenesis of PPRV in goats.

CD40-targeted recombinant adenovirus significantly enhances the efficacy of antitumor vaccines based on dendritic cells and B cells

Despite the advantages of using adenoviral vectors for specific antigenic gene delivery in the development of antigen-presenting cell (APC)-based vaccines, the lack of the coxsackievirus-adenovirus receptor (CAR) on APCs limits the use of adenoviral vectors for in vitro gene delivery. In this study, we used a recombinant adapter protein, CFm40L, which consists of the ectodomain of CAR genetically fused to the ectodomain of CD40 ligand (CD40L) via a trimerization motif, to target Her-2/neu- or human papillomavirus 16 (HPV16) E6/E7-encoding adenoviruses to CD40 on dendritic cells (DCs) and B cells. Targeting CD40 enabled the enhancement of tumor antigen delivery and simultaneous activation of APCs via the CD40-CD40L interaction. We found that these transduced DCs and B cells substantially enhanced the CTL response against human Her-2/neu- and HPV16 E6/E7-expressing tumors, resulting in significant inhibition of tumor growth in a murine tumor model. In addition, the use of the CFm40L adapter protein in combination with gemcitabine treatment allowed for a successful immune response against a self-tumor antigen, murine Her-2/neu. Our results suggest that targeting adenovirus to APCs via CD40, using CFm40L, represents a great improvement in anticancer cellular vaccines.

SLAM family receptors and SAP adaptors in immunity

The signaling lymphocyte activation molecule (SLAM)-associated protein, SAP, was first identified as the protein affected in most cases of X-linked lymphoproliferative (XLP) syndrome, a rare genetic disorder characterized by abnormal responses to Epstein-Barr virus infection, lymphoproliferative syndromes, and dysgammaglobulinemia. SAP consists almost entirely of a single SH2 protein domain that interacts with the cytoplasmic tail of SLAM and related receptors, including 2B4, Ly108, CD84, Ly9, and potentially CRACC. SLAM family members are now recognized as important immunomodulatory receptors with roles in cytotoxicity, humoral immunity, autoimmunity, cell survival, lymphocyte development, and cell adhesion. In this review, we cover recent findings on the roles of SLAM family receptors and the SAP family of adaptors, with a focus on their regulation of the pathways involved in the pathogenesis of XLP and other immune disorders.

Monocyte-derived DC maturation strategies and related pathways: a transcriptional view

Ex vivo production of highly stimulator mature dendritic cells (DCs) for cellular therapy has been used to treat different pathological conditions with the aim of inducing a specific immune response. In the last decade, several protocols have been developed to mature monocyte-derived DCs: each one has led to the generation of DCs showing different phenotypes and stimulatory abilities, but it is not yet known which one is the best for inducing effective immune responses. We grouped several different maturation protocols according to the downstream pathways they activated and reviewed the shared features at a transcriptomic level to reveal the potential of DCs matured by each protocol to develop Th-polarized immune responses.

Expression of the SLAM family of receptors adapter EAT-2 as a novel strategy for enhancing beneficial immune responses to vaccine antigens

Recent studies have shown that activation of the signaling lymphocytic activation molecule (SLAM) family of receptors plays an important role in several aspects of immune regulation. However, translation of this knowledge into a useful clinical application has not been undertaken. One important area where SLAM-mediated immune regulation may have keen importance is in the field of vaccinology. Because SLAM signaling plays such a critical role in the innate and adaptive immunity, we endeavored to develop a strategy to improve the efficacy of vaccines by incorporation of proteins known to be important in SLAM-mediated signaling. In this study, we hypothesized that coexpression of the SLAM adapter EWS-FLI1-activated transcript 2 (EAT-2) along with a pathogen-derived Ag would facilitate induction of beneficial innate immune responses, resulting in improved induction of Ag-specific adaptive immune responses. To test this hypothesis, we used rAd5 vector-based vaccines expressing murine EAT-2, or the HIV-1-derived Ag Gag. Compared with appropriate controls, rAd5 vectors expressing EAT-2 facilitated bystander activation of NK, NKT, B, and T cells early after their administration into animals. EAT-2 overexpression also augments the expression of APC (macrophages and dendritic cells) surface markers. Indeed, this multitiered activation of the innate immune system by vaccine-mediated EAT-2 expression enhanced the induction of Ag-specific cellular immune responses. Because both mice and humans express highly conserved EAT-2 adapters, our results suggest that human vaccination strategies that specifically facilitate SLAM signaling may improve vaccine potency when targeting HIV Ags specifically, as well as numerous other vaccine targets in general.

Macrophages in renal development, injury, and repair

Macrophages have long been regarded as classic mediators of innate immunity because of their production of proinflammatory cytokines and their ability to induce apoptotic cell death. As a result of such activities and the detrimental long-term effect of kidney inflammation, macrophages principally have been regarded as mediators of glomerular damage, tubular cell death, and the downstream fibrotic events leading to chronic kidney disease. Although this has been the accepted consequence of macrophage infiltration in kidney disease, macrophages also play a critical role in normal organ development, cell turnover, and recovery from injury in many organs, including the kidney. There is also a growing awareness that there is considerable heterogeneity of phenotype and function within the macrophage population and that a greater understanding of these different states of activation may result in the development of therapies specifically designed to capitalize on this variation in phenotype and cellular responses. In this review, we discuss the current understanding of induction and consequences of classic versus alternative macrophage activation and highlight what additional therapeutic options this may provide for the management of both acute and chronic kidney disease as well as renal cancer.

SLAM-family receptors: immune regulators with or without SAP-family adaptors

The signaling lymphocytic activation molecule (SLAM) family of receptors and the SLAM-associated protein (SAP) family of intracellular adaptors are expressed in immune cells. By way of their cytoplasmic domain, SLAM-related receptors physically associate with SAP-related adaptors. Evidence is accumulating that the SLAM and SAP families play crucial roles in multiple immune cell types. Moreover, the prototype of the SAP family, that is SAP, is mutated in a human immunodeficiency, X-linked lymphoproliferative (XLP) disease. In the presence of SAP-family adaptors, the SLAM family usually mediates stimulatory signals that promote immune cell activation or differentiation. In the absence of SAP-family adaptors, though, the SLAM family undergoes a "switch-of-function," thereby mediating inhibitory signals that suppress immune cell functions. The molecular basis and significance of this mechanism are discussed herein.

Development of murine lupus involves the combined genetic contribution of the SLAM and FcgammaR intervals within the Nba2 autoimmune susceptibility locus

Autoantibodies are of central importance in the pathogenesis of Ab-mediated autoimmune disorders. The murine lupus susceptibility locus Nba2 on chromosome 1 and the syntenic human locus are associated with a loss of immune tolerance that leads to antinuclear Ab production. To identify gene intervals within Nba2 that control the development of autoantibody-producing B cells and to determine the cellular components through which Nba2 genes accomplish this, we generated congenic mice expressing various Nba2 intervals where genes for the FcgammaR, SLAM, and IFN-inducible families are encoded. Analysis of congenic strains demonstrated that the FcgammaR and SLAM intervals independently controlled the severity of autoantibody production and renal disease, yet are both required for lupus susceptibility. Deregulated homeostasis of terminally differentiated B cells was found to be controlled by the FcgammaR interval where FcgammaRIIb-mediated apoptosis of germinal center B cells and plasma cells was impaired. Increased numbers of activated plasmacytoid dendritic cells that were distinctly CD19+ and promoted plasma cell differentiation via the proinflammatory cytokines IL-10 and IFNalpha were linked to the SLAM interval. These findings suggest that SLAM and FcgammaR intervals act cooperatively to influence the clinical course of disease through supporting the differentiation and survival of autoantibody-producing cells.

Therapeutic interventions targeting CD40L (CD154) and CD40: the opportunities and challenges

CD40 was originally identified as a receptor on B-cells that delivers contact-dependent T helper signals to B-cells through interaction with CD40 ligand (CD40L, CD154). The pivotal role played by CD40-CD40L interaction is illustrated by the defects in B-lineage cell development and the altered structures of secondary lymphoid tissues in patients and engineered mice deficient in CD40 or CD40L. CD40 signaling also provides critical functions in stimulating antigen presentation, priming of helper and cytotoxic T-cells and a variety of inflammatory reactions. As such, dysregulations in the CD40-CD40L costimulation pathway are prominently featured in human diseases ranging from inflammatory conditions to systemic autoimmunity and tissue-specific autoimmune diseases. Moreover, studies in CD40-expressing cancers have provided convincing evidence that the CD40-CD40L pathway regulates survival of neoplastic cells as well as presentation of tumor-associated antigens to the immune system. Extensive research has been devoted to explore CD40 and CD40L as drug targets. A number of anti-CD40L and anti-CD40 antibodies with diverse biological effects are in clinical development for treatment of cancer and autoimmune diseases. This chapter reviews the role of CD40-CD40L costimulation in disease pathogenesis, the characteristics of therapeutic agents targeting this pathway and status of their clinical development.

Host-virus specificity of morbilliviruses predicted by structural modeling of the marine mammal SLAM, a receptor

Signaling lymphocyte activation molecule (SLAM) is thought to be a major cellular receptor for high-host specificity morbilliviruses, which cause devastating and highly infectious diseases in mammals. We determined the sequences of SLAM cDNA from five species of marine mammal, including two cetaceans, two pinnipeds and one sirenian, and generated three-dimensional models to understand the receptor-virus interaction. Twenty-one amino acid residues in the immunoglobulin-like V domains of the SLAMs were shown to bind the viral protein. Notably, the sequences from pinnipeds and dogs were highly homologous, which is consistent with the fact that canine distemper virus was previously shown to cause a mass die-off of seals. Among these twenty-one residues, eight (63, 66, 68, 72, 84, 119, 121 and 130) were shared by animal groups susceptible to a particular morbillivirus species. This set of residues appears to determine host-virus specificity and may be useful for risk estimation for morbilliviruses.

The SLAM and SAP gene families control innate and adaptive immune responses

The nine SLAM-family genes, SLAMF1-9, a subfamily of the immunoglobulin superfamily, encode differentially expressed cell-surface receptors of hematopoietic cells. Engagement with their ligands, which are predominantly homotypic, leads to distinct signal transduction events, for instance those that occur in the T or NK cell immune synapse. Upon phosphorylation of one or more copies of a unique tyrosine-based signaling motif in their cytoplasmic tails, six of the SLAM receptors recruit the highly specific single SH2-domain adapters SLAM-associated protein (SAP), EAT-2A, and/or EAT-2B. These adapters in turn bind to the tyrosine kinase Fyn and/or other protein tyrosine kinases connecting the receptors to signal transduction networks. Individuals deficient in the SAP gene, SH2D1A, develop an immunodeficiency syndrome: X-linked lympho-proliferative disease. In addition to operating in the immune synapse, SLAM receptors initiate or partake in multiple effector functions of hematopoietic cells, for example, neutrophil and macrophage killing and platelet aggregation. Here we discuss the current understanding of the structure and function of these recently discovered receptors and adapter molecules in the regulation of adaptive and innate immune responses.

DC-SIGN and CD150 have distinct roles in transmission of measles virus from dendritic cells to T-lymphocytes

Measles virus (MV) is among the most infectious viruses that affect humans and is transmitted via the respiratory route. In macaques, MV primarily infects lymphocytes and dendritic cells (DCs). Little is known about the initial target cell for MV infection. Since DCs bridge the peripheral mucosal tissues with lymphoid tissues, we hypothesize that DCs are the initial target cells that capture MV in the respiratory tract and transport the virus to the lymphoid tissues where MV is transmitted to lymphocytes. Recently, we have demonstrated that the C-type lectin DC-SIGN interacts with MV and enhances infection of DCs in cis. Using immunofluorescence microscopy, we demonstrate that DC-SIGN⁺ DCs are abundantly present just below the epithelia of the respiratory tract. DC-SIGN⁺ DCs efficiently present MV-derived antigens to CD4⁺ T-lymphocytes after antigen uptake via either CD150 or DC-SIGN in vitro. However, DC-SIGN⁺ DCs also mediate transmission of MV to CD4⁺ and CD8⁺ T-lymphocytes. We distinguished two different transmission routes that were either dependent or independent on direct DC infection. DC-SIGN and CD150 are both involved in direct DC infection and subsequent transmission of de novo synthesized virus. However, DC-SIGN, but not CD150, mediates trans-infection of MV to T-lymphocytes independent of DC infection. Together these data suggest a prominent role for DCs during the initiation, dissemination, and clearance of MV infection.

Despite the availability of an effective vaccine, measles virus (MV) is still a major cause of childhood morbidity and mortality in developing countries. Almost all non-vaccinated children catch the highly contagious virus during an MV outbreak. This suggests an efficient route for primary infection. However, the main target cells for MV replication, CD150⁺ lymphocytes, are barely present in the respiratory tract where MV enters the body. Here we demonstrate an alternative route of MV transmission: dendritic cells that are abundantly present in the sub-epithelial tissues of the respiratory tract may capture MV through binding to either CD150 or DC-SIGN. Although some virus particles are processed for antigen presentation, others escape from degradation. After virus capture, DCs migrate to the lymphoid tissues where they encounter CD150⁺ lymphocytes and transmit the virus, after which viral replication is started. Our data provide new insights into the transmission of measles virus, and suggest a dual role for DCs in the pathogenesis of measles.

Enhancement of anti-tumor activity in vitro and in vivo by CD150 and SAP

Signaling lymphocyte activation molecule (SLAM, CD150) is a co-stimulatory receptor involved in T cell activation. The activity of CD150 is dependent on the intracellular signaling molecule SAP. Here, we investigated anti-CD3 activated human lymphocytes, transfected either with CD150-plasmid or with CD150- or SAP-siRNA in cytotoxicity assays against human colon cancer cells in vitro and in a xenograft model (CB/Scid/CrL mice) in vivo. Up-regulation or silencing of CD150 was accompanied by increased or decreased cytotoxic activity, respectively. Similar effects could also be shown in an IFN-gamma ELISpot assay. Furthermore, CD150 co-localized after activation with lipid rafts in specific membrane compartments on CD8 T cells. Treatment of xenografted mice with CD150 over-expressing lymphocytes decelerated tumor growth significantly. Lymphocytes were detectable in spleen 18 days after injection and expressed mainly CD8, CD45RO and CD150 above average. In conclusion, over-expression of CD150 in lymphocytes is accompanied with enhanced cytotoxic activity and IFN-gamma secretion in vitro and anti-tumor activity in vivo, whereas silencing of CD150 down-regulates effector functions. Adoptive cell transfer of CD150 over-expressing lymphocytes results in an accumulation of CD8, CD45RO and CD150 cells in tumor and spleen indicating together with the observed CD150 co-localization with lipid rafts that CD150 mediates a Th1 response.

Molecular architecture of signal complexes regulating immune cell function

Signals transmitted via multichain immunoreceptors control the development, differentiation and activation of hematopoetic cells. The cytoplasmic parts of these receptors contain immunoreceptor tyrosine-based activation motifs (ITAMs) that upon phosphorylation by members of the Src tyrosine kinase family orchestrate a complex set of signaling events involving tyrosine phosphorylation, generation of second messengers like DAG, IP3 and Ca2+, activation of effector molecules like Ras and MAPKs and the translocation and activation of transcription factors like NFAT, API and NF-kB. Spatial and temporal organization of these signaling events is essential both to connect the receptors to downstream cascades as well as to control the functional outcome of the immune activation. Throughout this process control and fine-tuning of the different signals are necessary both for effective immune function and in order to avoid inappropriate or exaggerated immune activation and autoimmunity. This control includes modulating mechanisms that set the threshold for activation and reset the activation status after an immune response has been launched. One immunomodulating pathway is the cAMP-protein kinase A-Csk pathway scaffolded by a supramolecular complex residing in lipid rafts with the A kinase-anchoring protein (AKAP) ezrin, the Csk-binding protein PAG and a linker between the two, EBP50. Failure of correct scaffolding and loss of spatiotemporal control can potentially have severe consequences, leading to immune failure or autoimmunity. The clinical relevance of supramolecular complexes specifically organized by scaffolding proteins in regulating immune activity and the specter of genetic diseases linked to different signaling components suggest that protein-protein contact surfaces can be potential targets for drug intervention. It is also of interest to note that different pathogens have evolved strategies to specifically modulate signal integration, thereby rewiring the signal in a way beneficial for their survival. In addition to demonstrating the importance of different signal processes, these adaptations are elegant illustrations of the potential for drug targeting of protein assembly. This chapter reviews some of the important scaffolding events downstream of immunoreceptors with focus on signaling transduction through the T-cell receptor (TCR).

Gene transfer of noncleavable cell surface mutants of human CD154 induces the immune response and diminishes systemic inflammatory reactions

CD154 (CD40-ligand) is a critical transmembrane molecule with potent immune-stimulatory properties that is used in clinical applications of gene therapy for leukemia and lymphoma. However, CD154 is cleaved into a soluble form, and high levels of sCD154 contribute to systemic inflammatory and cardiovascular diseases, suggesting a deleterious side effect of CD154 gene therapy. In this study, we engineered noncleavable mutants of human CD154 with point mutations to develop a potentially less toxic molecule in vivo. In contrast to wild-type CD154 (CD154-WT) subsequently released as sCD154, both mutants CD154-M3 and CD154-M4 were resistant to cleavage in tumor cells. Also, CD40-expressing leukemia B cells transfected with CD154-M3 mutant were highly effective stimulators in a mixed lymphocyte-leukemia reaction, indicating that CD154-M3 mutant did not lose biologic activity. In mice transplanted with tumors expressing CD154-WT, we found increased plasma levels of human sCD154 followed by various systemic inflammatory reactions such as glomerulonephritis and an increased number of infiltrating mononuclear cells in the liver. However, CD154-M3 mutant did not induce any systemic inflammatory effects in vivo. As such, the noncleavable mutant of CD154 is fully capable of inducing the immune response with less toxic properties and is a useful tool for CD154 immune gene therapy.

The role of SLAM family receptors in immune cell signaling

The signaling lymphocyte-activating molecule (SLAM) family immunoreceptors are expressed in a wide array of immune cells, including both T and B lymphocytes. By virtue of their ability to transduce tyrosine phosphorylation signals through the so-called ITSM (immunoreceptor tyrosine-based switch motif) sequences, they play an important part in regulating both innate and adaptive immune responses. The critical role of the SLAM immunoreceptors in mediating normal immune reactions was highlighted in recent findings that SAP, a SLAM-associated protein, modulates the activities of various immune cells through interactions with different members of the SLAM family expressed in these cells. Importantly, mutations or deletions of the sap gene in humans result in the X-linked lymphoproliferative syndrome. In this review, we summarize current knowledge and survey the latest developments in signal transduction events triggered by the activation of SLAM family receptors in different cell types.

SLAM and CD31: Signaling molecules involved in cytokine secretion during the development of innate and adaptive immune responses

Immune cells are modulated through the crosslinking of receptors named "immunoreceptors". Ligation of immunoreceptors by their ligands induces a tyrosine-phosphorylation signal that is essential for cell activation or inhibition. Physiologically, immunoreceptor triggering is not enough for cell activation, and stimulation of co-receptors is necessary for antigen-evoked cytokine production. Thus, signal transduction pathways mediated by proteins that regulate cytokine secretion are critical to achieve an effective immune response of the host, where the balance between positive and negative signaling allows effective immune responses, preventing tolerance and autoimmunity. This review deals with recent studies based on the role of the receptor signaling lymphocytic activation molecule (SLAM), a signaling protein that modulates cytokine secretion by immune cells, and the transmembrane glycoprotein CD31, which plays multiple roles in cellular signaling events by modulating the balance between inhibitory and stimulatory signals to immune cells. Recent studies have shed light on the ability of these molecules to transmit different signals that regulate the ability of innate and adaptive immune cells to synthesize stimulatory and inhibitory cytokines.

Measles virus infection of SLAM (CD150) knockin mice reproduces tropism and immunosuppression in human infection

The human signaling lymphocyte activation molecule (SLAM, also called CD150), a regulator of antigen-driven T-cell responses and macrophage functions, acts as a cellular receptor for measles virus (MV), and its V domain is necessary and sufficient for receptor function. We report here the generation of SLAM knockin mice in which the V domain of mouse SLAM was replaced by that of human SLAM. The chimeric SLAM had an expected distribution and normal function in the knockin mice. Splenocytes from the SLAM knockin mice permitted the in vitro growth of a virulent MV strain but not that of the Edmonston vaccine strain. Unlike in vitro infection, MV could grow only in SLAM knockin mice that also lacked the type I interferon receptor (IFNAR). After intraperitoneal or intranasal inoculation, MV was detected in the spleen and lymph nodes throughout the body but not in the thymus. Notably, the virus appeared first in the mediastinal lymph node after intranasal inoculation. Splenocytes from MV-infected IFNAR(-/-) SLAM knockin mice showed suppression of proliferative responses to concanavalin A. Thus, MV infection of SLAM knockin mice reproduces lymphotropism and immunosuppression in human infection, serving as a useful small animal model for measles.

Histone deacetylase activities are required for innate immune cell control of Th1 but not Th2 effector cell function

Histone deacetylases (HDACs) play a critical role in regulating gene expression and key biological processes. However, how HDACs are involved in innate immunity is little understood. Here, in this first systematic investigation of the role of HDACs in immunity, we show that HDAC inhibition by a small-molecule HDAC inhibitor (HDACi), LAQ824, alters Toll-like receptor 4 (TLR4)-dependent activation and function of macrophages and dendritic cells (DCs). Surprisingly, pan-HDAC inhibition modulates only a limited set of genes involved in distinct arms of immune responses. Specifically, it inhibited DC-controlled T helper 1 (Th1) effector but not Th2 effector cell activation and migration. It also inhibited macrophage- and DC-mediated monocyte but not neutrophil chemotaxis. These unexpected findings demonstrate the high specificity of HDAC inhibition in modulating innate and adaptive immune responses, and highlight the potential for HDACi to alter the Th1 and Th2 balance in therapeutic settings.

Identification of gene expression changes induced by chemical allergens in dendritic cells: opportunities for skin sensitization testing

Cellular changes within resident skin dendritic cells (DCs) after allergen uptake and processing are critical events in the acquisition of skin sensitization. Here we describe the development of a set of selection criteria to derive a list of potential target genes from previous microarray analyses of human peripheral blood-derived (peripheral blood mononuclear cells (PBMCs)-DCs) treated with dinitrobenzene sulfonic acid for predicting skin-sensitizing chemicals. Based on those criteria, a probing evaluation of the target genes has been conducted using an extended chemical data set, comprising five skin irritants and 11 contact allergens. PBMCs-DCs were treated for 24 hours with various concentrations of chemicals and in each instance the expression of up to 60 genes was examined by real-time PCR analysis. Consistent allergen-induced changes in the expression of many genes were observed and further prioritization of the targets was conducted by analysis of the same genes in DCs treated with non-sensitizing chemicals to determine their specificity for skin sensitization. Real-time PCR analyses of multiple chemical allergens, irritants, and non-sensitizers have identified 10 genes that demonstrate reproducibly high levels of selectivity, specificity, and dynamic range consistent with providing the basis for robust and sensitive alternative approaches for the identification of skin-sensitizing chemicals.

Immune regulation by SLAM family receptors and SAP-related adaptors

The signalling lymphocytic activation molecule (SLAM) family of receptors is expressed by a wide range of immune cells. Through their cytoplasmic domain, SLAM family receptors associate with SLAM-associated protein (SAP)-related molecules, a group of cytoplasmic adaptors composed almost exclusively of an SRC homology 2 domain. SAP, the prototype of the SAP family, is mutated in a human immunodeficiency named X-linked lymphoproliferative (XLP) disease. Recent observations indicate that SLAM family receptors, in association with SAP family adaptors, have crucial roles during normal immune reactions in innate and adaptive immune cells. The latest progress in this field is reviewed here.

Immunosuppression caused by measles virus: role of viral proteins

Measles virus (MV) causes transient but profound immunosuppression resulting in increased susceptibility to secondary bacterial and viral infections. Due to the development of these opportunistic infections, measles remains the leading vaccine-preventable cause of child death worldwide. Different immune abnormalities have been associated with measles, including disappearance of delayed-type hypersensitivity reactions, impaired lymphocyte and antigen-presenting cell functions, down-regulation of pro-inflammatory interleukin 12 production and altered interferon alpha/beta signalling pathways. Several MV proteins have been suggested to hinder immune functions: hemagglutinin, fusion protein, nucleoprotein and the non-structural V and C proteins. This review will focus on the novel functions attributed to MV proteins in the immunosuppression associated with measles. Here, we highlight new advances in the field, emphasising the interaction between MV proteins and their cellular targets, in particular the cell membrane receptors, CD46, CD150, TLR2 and FcgammaRII in the induction of immunological abnormalities associated with measles.

Impaired maturation and altered regulatory function of plasmacytoid dendritic cells in multiple sclerosis

Plasmacytoid dendritic cells (pDCs) represent a DC subtype that exerts divergent functions in innate and adoptive immunity including the immediate reaction to microbial factors and the induction of immunoregulatory responses. It is thought that different DC subtypes may be critically involved in the pathogenesis of multiple sclerosis (MS). In our study we assessed the phenotype, maturation and functional properties of peripheral blood pDCs from 35 clinically stable, untreated multiple sclerosis patients, 30 healthy controls and 9 patients with pneumonia, which was used as a non-specific inflammatory condition (NIC). Ex vivo expression of CD86 and 4-1BBL was significantly lower on pDCs from multiple sclerosis patients than from controls and patients with NIC (22 versus 47 versus 41% and 12 versus 35 versus 32%, respectively). When stimulated with IL-3 and CD40L, pDCs of multiple sclerosis patients showed inefficient maturation as demonstrated by significantly lower or delayed upregulation of CD86, 4-1BBL, CD40 and CD83. Additionally, in multiple sclerosis, stimulation of pDCs by unmethylated cytosine-phosphate-guanosine oligodeoxynucleotides (CpG ODN) resulted in a significantly lower interferon (IFN) alpha secretion than in controls. In multiple sclerosis, but not in controls, pDCs failed to upregulate proliferative responses and IFN-gamma secretion of autologous peripheral blood mononuclear cells (PBMC) in a co-culture system. Moreover, depletion of pDCs in multiple sclerosis patients, but not in controls, had no effect on generation of CD4+Foxp3+ regulatory T cells. We also provide data showing that glatiramer acetate (GA) treatment partially restores phenotype and function of pDCs in multiple sclerosis patients. These findings suggest functional abnormalities of pDCs in these patients, which might be of importance in the understanding of the development of immune dysregulation in this disease.

Fine-tuning of immune responses by SLAM-related receptors

The modulation of antigen receptor signals is important for a productive immune response. The main function of the recently identified members of the signaling lymphocyte activating molecule (SLAM)-related receptors (SRR) is the fine-tuning of immune cell activation. Disruption of SRR function is the cause for severe immune disorders such as X-linked lymphoproliferative syndrome (XLP), where XLP patients carry a mutation in SLAM-associated protein (SAP) (SH2D1A), an important adaptor molecule for the signal transduction of SRR. Recent data also suggest that SRR may play a role in autoimmune diseases and the function of hematopoietic stem and progenitor cells. Here, we review the current understanding of SRR function in different immune cells.

SLAM/SLAM interactions inhibit CD40-induced production of inflammatory cytokines in monocyte-derived dendritic cells

Signaling lymphocyte activation molecule (SLAM, CD150, or SLAMF1) is a self-ligand receptor on the surface of activated T- and B-lymphocytes, macrophages, and dendritic cells (DCs). Here we examine the effect of SLAM/SLAM interactions on CD40L-induced CD40 signaling pathways in human DCs. CD40L-expressing L929 cells induced DCs to produce interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-alpha), and IL-12, which was strongly inhibited by coexpression of SLAM on the surface of the L929 cells. Similarly, transfection of DCs with SLAM strongly reduced CD40L-induced IL-12 production. Furthermore, the negative effect of SLAM/SLAM interactions on CD40L-induced DC activation was also detected in the presence of lipopolysaccharide (LPS). LPS-induced IL-12 secretion, however, was not inhibited by SLAM engagement. CD40L-activated DCs affected by exposure to SLAM/SLAM engagement were impaired in their ability to induce differentiation of naive T lymphocytes into interferon-gamma (IFN-gamma)-producing T-helper 1 (Th1) effector cells. These inhibitory effects were not the result of a general unresponsiveness of DCs to CD40L, as SLAM/SLAM interactions did not prevent CD40L-induced up-regulation of CD83, CD86, or human leukocyte antigen (HLA)-DQ on the surface of DCs. Taken together, the results indicate that SLAM/SLAM interactions inhibit CD40-induced signal transduction in monocyte-derived dendritic cells, an effect that was not detectable in earlier studies using anti-SLAM monoclonal antibodies.

Simultaneous targeting of CD3 on T cells and CD40 on B or dendritic cells augments the antitumor reactivity of tumor-primed lymph node cells

To date, molecular targets chosen for Ab activation to generate antitumor effector cells have been confined on T cells, such as TCR/CD3, CD28, CD137 (4-1BB), CD134 (OX40), and inducible costimulator. In this report we investigated the immune function of murine tumor-draining lymph node (TDLN) cells after simultaneous Ab targeting of CD3 on T cells and CD40 on APCs. Anti-CD3 plus anti-CD40-activated TDLN cells secreted significantly higher amounts of IFN-gamma, but less IL-10, compared with anti-CD3-activated cells. In adoptive immunotherapy, ligation of CD3 and CD40 resulted in the generation of more potent effector cells in mediating tumor regression. Freshly harvested TDLN cells were composed of approximately 60% CD3+ T cells, 30-35% CD19+ B cells, 5% CD11c+ dendritic cells (DC), and few CD14+ or NK cells (each <3%). CD40 was distributed predominantly on B cells and DCs. Cell depletion indicated that simultaneous targeting was toward CD3 on T cells and CD40 on APCs, respectively. Elimination of APCs completely abrogated the augmented antitumor responses induced by anti-CD40. Either B cell or DC removal partially, but significantly, reduced the therapeutic efficacy conferred by CD40 engagement. Furthermore, the immunomodulation function of anti-CD40 was associated with its capability to increase IL-12 secretion while inhibiting IL-4 production. Our study establishes a role for CD40 expressed on B cells or DCs in the costimulation of TDLN cells. Eliciting antitumor activity via simultaneous targeting of CD3 on T cells and CD40 on APCs is relevant for the design of effective T cell-based cancer immunotherapy.

SAP and SLAM expression in anti-CD3 activated lymphocytes correlates with cytotoxic activity

Signalling lymphocyte activation molecule (SLAM)-associated protein (SAP) is a small protein that is mutant in humans with X-linked lymphoproliferative (XLP) disease. Patients with XLP disease are affected by fatal EBV infection and malignant B-cell lymphomas. The increased risk for B-cell lymphomas is suggested to result from impaired immunosurveillance of B-cell proliferation by T cells. In this study, we investigated the role of SLAM and SAP in activation of effector cells with cytotoxic activity, cytokine-induced killer (CIK) cells, which are generated by non-specific stimulation of the TCR and addition of exogenous IL-2. Agonistic TCR activation 1 day after preparation (day +1) resulted in cell activation, with a peak of SLAM on day +6 visible at both the protein and mRNA level as well as membrane detectable SLAM. This increase in SLAM expression correlated significantly with SAP expression at the mRNA level as well as at the protein level. Cytotoxic activity peaked 1 day after the observed SAP and SLAM peaks. At that point in time, IL-10 secretion, which was high during the early days of culture, decreased. In conclusion, activation of peripheral blood cells with agonistic anti-CD3 antibody and exogenous IL-2, as used for generation of CIK cells, results in significant SLAM and SAP activation 5 days after TCR stimulation. This peak correlates with cytotoxic activity against tumour cells. Expression of SLAM and SAP seems to be important in the activation of cytotoxic effector cells.

Profiling dendritic cell maturation with dedicated microarrays

Dendritic cell (DC) maturation is the process by which immature DC in the periphery differentiate into fully competent antigen-presenting cells that initiate the T cell response. However, DC respond to many distinct maturation stimuli, and different types of mature DC induce qualitatively different T cell responses. As DC maturation involves the coordinated regulation of hundreds of genes, comprehensive assessment of DC maturation status would ideally involve monitoring the expression of all of these transcripts. However, whole-genome microarrays are not well-suited for routine phenotyping of DC, as the vast majority of genes represented on such chips are not relevant to DC biology, and their cost limits their use for most laboratories. We therefore developed a DC-dedicated microarray, or "DC Chip", incorporating probes for 121 genes up-regulated during DC maturation, 93 genes down-regulated during maturation, 14 DC-specific genes, and 90 other genes with known or probable immune functions. These microarrays were used to study the kinetics of DC maturation and the differences in maturation profiles among five healthy donors after stimulation with tumor necrosis factor-alpha + polyI:C. Results obtained with the DC Chip were consistent with flow cytometry, enzyme-linked immunosorbent assay, and real-time polymerase chain reaction, as well as previously published data. Furthermore, the coordinated regulation of a cluster of genes (indoleamine dioxygenase, kynureninase, kynurenine monoxygenase, tryptophanyl tRNA synthetase, and 3-hydroxyanthranilate 3,4-dioxygenase) involved in tryptophan metabolism was observed. These data demonstrate the use of the DC Chip for monitoring the molecular processes involved in the orientation of the immune response by DC.