Upregulation Of Costimulatory Molecules Research Articles

Tight control – decision-making during T cell–vascular endothelial cell interaction

Vascular endothelial cells (ECs) form the inner layer of blood vessels and exert crucial functions during immune reactions including coagulation, inflammation, and regulation of innate immunity. Importantly, ECs can interact with T cells in an antigen-specific, i.e., T cell receptor-dependent manner. In this review, we will discuss EC actions and reactions during acute inflammation and focus on the interaction of T cells with ECs at two vascular sites: the high endothelial venule (HEV) of lymph nodes, and the vascular lesion during transplant vasculopathy (TV). HEVs are characterized by a highly active endothelium that produces chemoattracting factors and expresses adhesion molecules to facilitate transit of lymphocytes into the lymph node (LN) parenchyma. Yet, T cell–EC interaction at this anatomical location results neither in T cell activation nor tolerization. In contrast, the endothelium at sites of chronic inflammation, such as solid organ transplants, can promote T cell activation by upregulation of major histocompatibility complex (MHC) and costimulatory molecules. Importantly, a major function of ECs in inflamed tissues must be the maintenance of vascular integrity including the efficient attenuation of effector T cells that may damage the vascular bed. Thus, antigen-specific T cell–EC interaction is characterized by a tightly controlled balance between immunological ignorance, immune activation, and tolerization.

Effects of 4-1BB signaling on the biological function of murine dendritic cells

4-1BB signaling has profound effects on the T cell-induced cell immune response, but its biological function in dendritic cells (DCs) has remained largely uncharacterized. In this study, we investigated the function of 4-1BB in murine DCs with an agonistic mAb to 4-1BB. Interleukin (IL)-6 and IL-12 production was assessed by an enzyme-linked immunosorbent assay (ELISA). Co-stimulatory molecules (CD80 and CD86) in DCs were analyzed by flow cytometry. The results showed that 4-1BB was strongly expressed in DCs during the maturation process. Triggering 4-1BB increased the secretion of IL-6 and IL-12 and the upregulation of co-stimulatory molecules (CD80 and CD86) from DCs, indicating that agonistic mAb to 4-1BB directly improves the activation of DCs. Moreover, triggering 4-1BB induced a higher survival rate of DCs compared to that of hamster IgG isotype control, due to the upregulated expression of Bcl-2 and Bcl-xL. To further assess the role of 4-1BB on DCs stimulating T-cell proliferation, allogeneic mixed lymphocyte reactions were analyzed. The agonistic anti-4-1BB mAb induced a higher T-cell proliferation. These results suggest that 4-1BB affects the duration, DC-T interaction and immunogenicity of DCs.

Generation of immunogenic and tolerogenic clinical-grade dendritic cells

Immunotherapy with dendritic cells (DCs), which have been manipulated ex vivo to become immunogenic or tolerogenic, has been tested in clinical trials for disease therapy. DCs are sentinels of the immune system, which after exposure to antigenic or inflammatory signals and crosstalk with effector CD4(+) T cells express high levels of costimulatory molecules and cytokines. Upregulation of either costimulatory molecules or cytokines promotes immunologic DCs, whereas their downregulation generates tolerogenic DCs (TDCs), which induce T regulatory cells (Tregs) and a state of tolerance. Immunogenic DCs are used for the therapy of infectious diseases such as HIV-1 and cancer, whereas tolerogenic DCs are used in treating various autoimmune diseases and in transplantation. DC vaccination is still at an early stage, and improvements are mainly needed in quality control of monitoring assays to generate clinical-grade DC products and to assess the effect of DC vaccination in future clinical trials. Here, we review the recent work in DC generation and monitoring approaches for DC-based trials with immunogenic or tolerogenic DCs.

Ad-ISF35-Transduced Autologous Cells In Combination with Fludarabine, Cyclophosphamide, Rituximab (FCR) Induces Complete and Partial Responses In a Phase 1b Study for Patients with Fludarabine-Refractory and/or Del(17p)/p53-Defective Chronic Lymphocytic Leukemia (CLL)

Abstract 168▪FN2▪This icon denotes a clinically relevant abstractCLL cells with del(17p) typically have loss of functional p53, rendering them refractory to chemotherapeutic agents. However, del(17p) CLL cells activated by CD40 ligand (CD154) are induced to express pro-apoptotic factors to overcome resistance to the cytotoxic activity of p53-dependent drugs, such as fludarabine. To examine whether a CD154-based therapeutic strategy can be developed in vivo for del(17p) and/or fludarabine-refractory CLL, a phase 1b clinical study evaluating an autologous cellular gene immunotherapy is being conducted. Autologous CLL cells transduced ex vivo with a replication-defective adenovirus vector encoding a membrane-stable, re-engineered form of CD154 (Ad-ISF35) are administered, followed by standard courses of FCR.Subjects with fludarabine-refractory and/or del(17p) CLL received three IV doses (one dose every two weeks) of 3×108autologous Ad-ISF35-transduced CLL cells. Two weeks following the third dose of Ad-ISF35-transduced cells, subjects receive up to six monthly cycles of FCR. Study endpoints include analysis of safety and efficacy.Nine (9) subjects have been enrolled and treated on study. Median age was 63 (range 48–70). All subjects were del(17p) (range 14–96%), and included treatment naïve (n=4) and previously treated (n=5) subjects. The number of prior treatments range from 0–5, including three subjects that previously received fludarabine-containing regimens. The overall response rate was 67% with 56% of subjects achieving a complete response (CR), including 3 CRu pending bone marrow assessment. Two subjects with a marked percentage del(17p) (range 63–66%) continue to have an ongoing complete response (CR) after a median follow up of >2 years, and no detectable minimal residual disease (MRD) in one subject. Three subjects that showed disease progression were treated with either alemtuzumab (1 subject) or ofatumumab plus high dose methylprednisolone therapy followed by allogeneic stem cell transplant (2 subjects). We observed clinical responses not only after FCR but also after infusion of Ad-ISF35-transduced cell. These ISF35-specific responses included reductions in absolute lymphocyte counts in all subjects (decrease from baseline 4–89%), and decreased lymphadenopathy (>50% reduction) in 78% of the subjects (decrease from baseline 19–100%). Infusion of Ad-ISF35-transduced cells plus FCR has been well-tolerated. The primary non-hematologic adverse events have been flu-like symptoms following infusion of Ad-ISF35 transduced cells. This includes transient grade I/II fever (89%), fatigue (56%) and chills (56%). The primary hematologic adverse events have been cytopenias following FCR treatment, including grade III/IV neutropenia (33%) and anemia (22%). Grade I/II hypophosphatemia (56%) following ISF35 has been observed and this might be related to increased serum cytokine levels following Ad-ISF35-transduced cell administration. Correlative studies on CLL cells obtained before and after infusions of Ad-ISF35-transduced CLL cells demonstrated that CLL cells prior to treatment were refractory to the cytoxic effects of P53-dependent drugs (e.g. F-ara-A). However, the CLL cells obtained after treatment with Ad-ISF35-transduced CLL had increases of p73, p21 and Bid and became sensitive in vitro to the cytotoxic activity of F-ara-A. We also observed up-regulation of costimulatory molecules (CD80, CD86, CD54) and death receptors (CD95). The majority of subjects developed antibodies against adenovirus with neutralizing activity. However, they did not developed antibodies against human CD154. Subjects also showed increases in TNFα, IL-6 and IL12 after infusion of Ad-ISF35 transduced cells.In conclusion, the combination of Ad-ISF35 transduced CLL cells plus FCR appears to be well-tolerated and highly effective in CLL patients with fludarabine-refractory disease and/or del(17p). The CR rate that we have observed in this high-risk CLL population is higher than those reported in the literature and makes our results very encouraging. Correlative data suggest that Ad-ISF35 promotes upregulation of costimulatory and death receptor molecules as well as pro-apoptotic proteins that may overcome resistance to FCR in vivo. These encouraging data suggest the combination of Ad-ISF35 plus chemoimmunotherapy could offer an effective treatment option for patients who otherwise would be resistant to standard forms of therapy. Disclosures:Cantwell:Memgen, LLC: Employment, Patents & Royalties.

Inhibition of Autoimmune Diabetes by TLR2 Tolerance

We have reported that apoptotic β cells undergoing secondary necrosis, called "late apoptotic (LA) β cells," stimulated APCs and induced diabetogenic T cell priming through TLR2, which might be one of the initial events in autoimmune diabetes. Indeed, diabetogenic T cell priming and the development of autoimmune diabetes were significantly inhibited in TLR2-null NOD mice, suggesting the possibility that TLR2 blockade could be used to inhibit autoimmune diabetes. Because prolonged TLR stimulation can induce TLR tolerance, we investigated whether repeated TLR2 administration affects responses to LA β cells and inhibits autoimmune diabetes in NOD mice by inducing TLR2 tolerance. Treatment of primary peritoneal macrophages with a TLR2 agonist, Pam3CSK(4), suppressed cytokine release in response to LA insulinoma cells or further TLR2 stimulation. The expression of signal transducer IRAK-1 and -4 proteins was decreased by repeated TLR2 stimulation, whereas expression of IRAK-M, an inhibitory signal transducer, was enhanced. Chronic Pam3CSK(4) administration inhibited the development of diabetes in NOD mice. Diabetogenic T cell priming by dendritic cells and upregulation of costimulatory molecules on dendritic cells by in vitro stimulation were attenuated by Pam3CSK(4) administration in vivo. Pam3CSK(4) inhibited diabetes after adoptive transfer of diabetogenic T cells or recurrence of diabetes after islet transplantation by pre-existing sensitized T cells. These results showed that TLR2 tolerance can be achieved by prolonged treatment with TLR2 agonists, which could inhibit priming of naive T cells, as well as the activity of sensitized T cells. TLR2 modulation could be used as a novel therapeutic modality against autoimmune diabetes.

Eosinophils elicit proliferation of naive and fungal-specific cells in vivo so enhancing a T helper type 1 cytokine profile in favour of a protective immune response against Cryptococcus neoformans infection.

Experimental Cryptococcus neoformans infection in rats has been shown to have similarities with human cryptococcosis, because as in healthy humans, rats can effectively contain cryptococcal infection. Moreover, it has been shown that eosinophils are components of the immune response to C.neoformans infections. In a previous in vitro study, we demonstrated that rat peritoneal eosinophils phagocytose opsonized live yeasts of C.neoformans, thereby triggering their activation, as indicated by the up-regulation of MHC and co-stimulatory molecules and the increase in interleukin-12, tumour necrosis factor-α and interferon-γ production. Furthermore, this work demonstrated that C.neoformans-specific CD4(+) and CD8(+) T lymphocytes cultured with these activated C.neoformans-pulsed eosinophils proliferated, and produced important amounts of T helper type 1 (Th1) cytokines in the absence of Th2 cytokine synthesis. In the present in vivo study, we have shown that C.neoformans-pulsed eosinophils are also able to migrate into lymphoid organs to present C.neoformans antigens, thereby priming naive and re-stimulating infected rats to induce T-cell and B-cell responses against infection with the fungus. Furthermore, the antigen-specific immune response induced by C.neoformans-pulsed eosinophils, which is characterized by the development of a Th1 microenvironment with increased levels of NO synthesis and C.neoformans-specific immunoglobulin production, was demonstrated to be able to protect rats against subsequent infection with fungus. In summary, the present work demonstrates that eosinophils act as antigen-presenting cells for the fungal antigen, hence initiating and modulating a C.neoformans-specific immune response. Finally, we suggest that C.neoformans-loaded eosinophils might participate in the protective immune response against these fungi.

Heat-shock protein 70-dependent dendritic cell activation by 5-aminolevulinic acid-mediated photodynamic treatment of human glioblastoma spheroids in vitro

Background:T-cell responses contribute to the anti-tumoural effect of photodynamic therapy (PDT). For such responses to occur, dendritic cells (DCs) have to migrate to the tumour, take up tumour antigens and respond to danger signals with maturation, before they engage in T-cell activation. Here, we have studied the effect of 5-aminolevulinic acid (ALA)-mediated PDT on DCs in vitro in a human spheroid model of glioblastoma (GB).Methods:Spheroids of the GB cell lines U87 and U251 were treated with ALA/PDT, and effects on attraction, uptake of tumour antigens and maturation of DCs were studied. To block heat-shock protein-70 (HSP-70) on the spheroids, neutralising antibodies were used.Results:5-Aminolevulinic acid /PDT-treated GB spheroids attracted DCs that acquired tumour antigens from the spheroids effectively. Moreover, co-culture with ALA/PDT-treated spheroids induced DC maturation as indicated by the upregulation of CD83 and co-stimulatory molecules as well as increased T-cell stimulatory activity of the DCs. Heat-shock protein-70 was upregulated on the spheroids after ALA/PDT treatment. Uptake of tumour antigens and DC maturation induced by the ALA/PDT-treated spheroids were inhibited when HSP-70 was blocked.Conclusion:ALA/PDT treatment of glioma spheroids promotes the three initial steps of the afferent phase of adaptive immunity, which is at least partially mediated by HSP-70.

Impact of Toll-Like Receptor 2 Deficiency on Immune Responses to Mycobacterial Antigens

In the present study, we addressed the question of whether Toll-like receptor 2 (TLR2)-mediated innate immunity can contribute to the development of acquired immune responses. We immunized TLR2(-/-) and wild-type (WT) mice three times subcutaneously with the mycobacterial antigen (Ag19kDa) (a TLR2 ligand) or Ag85A (not a TLR2 ligand). One week after the last immunization, sera and spleens were collected. To evaluate cellular responses, we measured gamma interferon (IFN-γ) after in vitro restimulation of spleen cells with antigen alone or antigen-pulsed bone marrow-derived macrophages (BMM(Ag)) or pulmonary macrophages (PuM(Ag)). Antibody responses were comparable in the two mouse strains, but we observed differences in the cellular responses. Recall responses to Ag85A were similar in the two strains, but responses to Ag19kDa given alone or presented by BMM or PuM were lower in TLR2(-/-) than in WT mice. The largest differences in cellular responses were observed when Ag19kDa was presented by PuM. To understand this, we analyzed phenotypic and functional differences between BMM and PuM upon stimulation with various ligands. Generally, PuM had a lower response to the TLR2 ligand Pam(3)Cys-Ser-(Lys)(4) trihydrochloride and to anti-CD40 than BMM, as measured by cytokine secretion and upregulation of costimulatory molecules. This might provide a partial explanation for the lower capacity of PuM when pulsed with Ag19kDa, also a TLR2 ligand. Altogether, our results revealed weaknesses in the T cell and antigen-presenting cell (APC) compartments of the Ag19kDa-immunized TLR2(-/-) mice but indicated that specific immune responses could be generated in the absence of TLR2 regardless of the characteristics of the antigen used.

Intracellular TLR4/MD-2 in macrophages senses Gram-negative bacteria and induces a unique set of LPS-dependent genes

Toll-like receptor (TLR)4/MD-2, a sensor for LPS, delivers the MyD88-dependent signal from the cell surface, then traffics to endolysosomes and delivers the TRIF/TICAM-1-dependent signal. Both signals are thought to be dependent on cell surface TLR4/MD-2. Although TLR4/MD-2 is located also in recycling endosomes, the Golgi apparatus or the endoplasmic reticulum, little is known about a role for intracellular TLR4/MD-2 in LPS responses. We here studied intracellular LPS sensing in macrophages. PRAT4A (protein associated with TLR4 A) is a cochaperone for a general chaperone gp96 and required for cell surface expression of TLR4/MD-2. Cell surface TLR4/MD-2 was undetectable on PRAT4A(-/-) thioglycollate-elicited peritoneal macrophages (P-Macs) and bone marrow-derived macrophages (BM-Macs). LPS responses were all abolished in PRAT4A(-/-) P-Macs, whereas a part of LPS responses remained detectable in PRAT4A(-/-) BM-Macs. Of note, LPS responses in PRAT4A(-/-) BM-Macs were not necessarily dependent on TRIF/TICAM-1 signaling. PRAT4A(-/-) BM-Macs showed unimpaired production of both TRIF/TICAM-1-dependent chemokine RANTES (CCL5) and MyD88-dependent chemokine MCP-1 (CCL2). Moreover, up-regulation of co-stimulatory molecules, CD40 and CD86 was not altered. In contrast, TRIF/TICAM-1-dependent production of type I IFN was profoundly impaired. In response to heat-killed bacteria Escherichia coli, BM-Macs also required PRAT4A-independent TLR4/MD-2 for production of MCP-1 (CCL2) and RANTES (CCL5) and for up-regulation of CD40 and CD86, indicating that intracellular TLR4/MD-2 is able to sense phagocytosed bacteria and activate immune responses. These results demonstrate that intracellular TLR4/MD-2 is responsible for unique set of LPS responses.

Tumor-Infiltrating Programmed Death Receptor-1+ Dendritic Cells Mediate Immune Suppression in Ovarian Cancer

Within the ovarian cancer microenvironment, there are several mechanisms that suppress the actions of antitumor immune effectors. Delineating the complex immune microenvironment is an important goal toward developing effective immune-based therapies. A dominant pathway of immune suppression in ovarian cancer involves tumor-associated and dendritic cell (DC)-associated B7-H1. The interaction of B7-H1 with PD-1 on tumor-infiltrating T cells is a widely cited theory of immune suppression involving B7-H1 in ovarian cancer. Recent studies suggest that the B7-H1 ligand, programmed death receptor-1 (PD-1), is also expressed on myeloid cells, complicating interpretations of how B7-H1 regulates DC function in the tumor. In this study, we found that ovarian cancer-infiltrating DCs progressively expressed increased levels of PD-1 over time in addition to B7-H1. These dual-positive PD-1(+) B7-H1(+) DCs have a classical DC phenotype (i.e., CD11c(+)CD11b(+)CD8(-)), but are immature, suppressive, and respond poorly to danger signals. Accumulation of PD-1(+)B7-H1(+) DCs in the tumor was associated with suppression of T cell activity and decreased infiltrating T cells in advancing tumors. T cell suppressor function of these DCs appeared to be mediated by T cell-associated PD-1. In contrast, ligation of PD-1 expressed on the tumor-associated DCs suppressed NF-κB activation, release of immune regulatory cytokines, and upregulation of costimulatory molecules. PD-1 blockade in mice bearing ovarian cancer substantially reduced tumor burden and increased effector Ag-specific T cell responses. Our results reveal a novel role of tumor infiltrating PD-1(+)B7-H1(+) DCs in mediating immune suppression in ovarian cancer.

Coupling presentation of MHC class I peptides to constitutive activation of antigen-presenting cells through the product of a single gene

Priming of naive CD8 T cells by dendritic cells (DCs) entails both effective antigen presentation on MHC class I products and co-stimulatory signaling. Their optimal coupling is a major goal in the development of CTL-inducing vaccines. We recently reported that a membranal derivative of the invariant MHC-I light chain, β(2)-microglobulin (β(2)m), markedly stabilizes MHC-I molecules and can serve as a universal platform for exceptional presentation of genetically linked peptides. To test whether it is possible to equip the resulting MHC-I complexes with an inherent ability to activate antigen-presenting cells, we engrafted the intracellular Toll/IL-1 receptor domain of mouse Toll-like receptor (TLR) 4 or TLR2 onto the peptide-β(2)m scaffold. We evaluated the level of peptide presentation and status of cell activation conferred by such constructs in stably transfected mouse RAW264.7 macrophages and mRNA-transfected mouse DC2.4 DCs. We show that the encoded peptide-β(2)m-TLR polypeptides are expressed at the cell surface, pair with endogenous heavy chains, stabilize MHC-I products, prompt efficient peptide-specific T-cell recognition and confer a constitutively activated phenotype on the transfected cells, as judged by the up-regulation of pro-inflammatory genes and surface co-stimulatory molecules. Our results provide evidence that the product of a single recombinant gene can couple MHC peptide presentation to TLR-mediated signaling and offer a safe, economical and highly versatile modality for a novel category of genetic CTL-inducing vaccines.

TLR9 agonists: Immune mechanisms and therapeutic potential in domestic animals

Toll like receptors (TLRs) are transmembrane glycoproteins that recognize conserved microbial molecules. Engagement of TLRs activates innate and adaptive immunity. TLR-mediated activation of immune cells results in upregulation of cytokines, chemokines and costimulatory molecules. These early innate responses control pathogen spread and initiates adaptive immune responses. Synthetic CpG oligodeoxynucleotides (ODN), agonists for TLR9, had shown great promise as immunotherapeutic agents and vaccine adjuvants in laboratory animal models of infectious disease, allergy and cancer. However, it has become apparent that CpG ODN are less potent immune activators in domestic animals and humans. The disparity in immune responses between rodents and mammals has been mainly attributed to differences in cellular expression of TLR9 in the various species. In this article, our current understanding of the immune mechanisms, as well as the potential applications of CpG ODN will be reviewed, with particular emphasis on domestic animals.

Subversion of innate and adaptive immune activation induced by structurally modified lipopolysaccharide from Salmonella typhimurium

Salmonella are successful pathogens that infect millions of people every year. During infection, Salmonella typhimurium changes the structure of its lipopolysaccharide (LPS) in response to the host environment, rendering bacteria resistant to cationic peptide lysis in vitro. However, the role of these structural changes in LPS as in vivo virulence factors and their effects on immune responses and the generation of immunity are largely unknown. We report that modified LPS are less efficient than wild-type LPS at inducing pro-inflammatory responses. The impact of this LPS-mediated subversion of innate immune responses was demonstrated by increased mortality in mice infected with a non-lethal dose of an attenuated S.typhimurium strain mixed with the modified LPS moieties. Up-regulation of co-stimulatory molecules on antigen-presenting cells and CD4(+) T-cell activation were affected by these modified LPS. Strains of S.typhimurium carrying structurally modified LPS are markedly less efficient at inducing specific antibody responses. Immunization with modified LPS moiety preparations combined with experimental antigens, induced an impaired Toll-like receptor 4-mediated adjuvant effect. Strains of S.typhimurium carrying structurally modified LPS are markedly less efficient at inducing immunity against challenge with virulent S.typhimurium. Hence, changes in S.typhimurium LPS structure impact not only on innate immune responses but also on both humoral and cellular adaptive immune responses.

Abstract 4741: Therapeutic efficacy of a human-derived antibody against cancer-testis antigen NY-ESO-1

Abstract Rationale: It is accepted that the immune system can control cancer and a favorable clinical course correlates with high infiltration by CD8+ T cells in different cancer entities. Thus, boosting cancer-specific immunity is an interesting therapeutic modality. Cancer-testis antigens (CTA) are promising target antigens due to their tumor-restricted expression pattern and high immunogenicity. NY-ESO-1 is one of the best characterized CTA, and spontaneous anti-NY-ESO-1 humoral and cellular responses were described in patients with various cancers. We propose that antibodies (Abs) against intracellular CTA have therapeutic potential because they may facilitate the uptake and presentation of antigens by dendritic cells (DC), which supports cancer-specific T cell responses. This effect may be more pronounced when Abs are used in combination with therapies that result in death, and thus antigen release, of cancer cells. We report here the characterization of the first human anti-NY-ESO-1 monoclonal Ab. Methods: Human-derived monoclonal Ab 12D7 was obtained by molecular cloning from memory B cells of a melanoma patient, ZH-311. To characterize the binding of 12D7 we performed ELISA, Biacore analysis and tissue staining. In addition, we used 12D7 to immunoprecipitate native NY-ESO-1 from human melanoma cell line SK-MEL-37. As a proof of concept, we compared the activation of NY-ESO-1-specific CD8+ T cell clones by DC fed with NY-ESO-1 vs. NY-ESO-1/12D7 immune complexes (IC) in vitro. To determine the therapeutic effect in vivo, we treated BALB/c mice bearing syngeneic CT26/NY-ESO-1 colorectal tumors with 5-FU +/- 12D7. To investigate Ab accumulation in established tumors 12D7 was labeled with FITC and injected into mice 2 days after 5-FU treatment. Results: Human monoclonal 12D7 specifically bound to NY-ESO-1 with high affinity (pM range) and precipitated endogenous NY-ESO-1 from SK-MEL-37. The uptake and cross-presentation of NY-ESO-1 by DC was greatly enhanced when NY-ESO-1 was complexed with 12D7 before feeding. Importantly, uptake of NY-ESO-1/12D7 IC, but not NY-ESO-1, resulted in maturation of DCs as determined by upregulation of co-stimulatory molecules. Finally, 12D7 significantly improved the therapeutic efficacy of 5-FU treatment in established CT26/NY-ESO-1 tumors. Ab accumulation in CT26/NY-ESO-1 tumors was enhanced when mice were treated with 5-FU as compared with untreated mice. Conclusion: We propose that the release of intracellular tumor antigens by chemotherapy and the accumulation of Ab to such antigens results in the local formation of IC. These IC are efficiently cross-presented to tumor-specific CD8+ T cells by DCs and may induce in situ maturation of the latter, both of which support tumor-specific effector function and thus contributes to tumor control. Our results suggest that targeting intracellular antigens, more specifically CTA, with Abs is a useful strategy for cancer treatment. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4741. doi:10.1158/1538-7445.AM2011-4741

Impact of pre-existing immunity on the selection of rare adenovirus vector candidates: implications for HIV vaccine development (53.27)

Abstract Adenovirus serotype 5 (Ad5) phase IIb vaccine trial (STEP) was prematurely stopped due to a lack of efficacy and two-fold higher incidence of HIV infection among Ad5 seropositive vaccine recipients. We have recently demonstrated that Ad5 immune complexes (Ad5 ICs)-mediated activation of the dendritic cell (DC)-T cell axis was associated with the enhancement of HIV infection in vitro. Although the direct role of Ad5 neutralizing antibodies (NAbs) in the increase of HIV susceptibility during the STEP trial is still under debate, vector-specific NAbs remain a major hurdle for vector-based gene therapies or vaccine strategies. To surmount this obstacle, vectors based on “rare” Ad serotypes including Ad6, Ad26, Ad36 and Ad41 were engineered. The present study aimed to determine whether Ad IC-mediated DC maturation could be circumvented using these Ad-vector candidates. We found that all Ad vectors tested forming ICs with plasma containing serotype-specific NAbs had the capacity to 1) mature human DCs as monitored by the up-regulation of co-stimulatory molecules and the release of pro-inflammatory cytokines (TNF-α), via the stabilization of Ad capsid at endosomal but not lysosomal pH rendering Ad DNA/TLR9 interactions possible and 2) potentiate Ad-specific CD4 and CD8 T cell responses. In conclusion, despite a conserved DC maturation potential, the low prevalence of serotype-specific NAbs renders rare Ad vectors attractive for vaccine strategies.

ESAT-6 inhibits IL-12, but promotes IL-23 production of human dendritic cells (56.9)

Abstract Early secreted antigenic target of 6 kD (ESAT-6) is a M. tuberculosis protein that induces protective immunity against tuberculosis in animal models and is a putative vaccine candidate. However, this protein also contributes to virulence and inhibits immune cells activation. In this study, we evaluated the effects of ESAT-6 on the function of human dendritic cells. Immature dendritic cells (DC) were induced from monocytes cultured with GM-CSF plus IL-4. ESAT-6 inhibited IL-12, but promotes IL-23 production of DC during maturation stimulated by LPS plus CD40L. This is correlated with downregulated IL-12p35 and upregulated IL-23p19 transcripts, respectively. ESAT-6 did not affect the induction of TNF-α, IL-6 and IL-8 from DC during maturation. ESAT-6 also inhibited upregulation of co-stimulatory molecules, CD80, CD86, HLA-DR, in both monocyte derived DC and myeloid DC freshly purified from human blood, in response to stimulation of LPS plus CD40L. DC pretreated with ESAT-6 induced less IL-2 and IFN-γ production in mixed lymphocyte reactions, and stimulated less IFN-γ, but more IL-17 production from M.tuberculosis responsive T cells compared to nontreated DC. Blocking TLR1/2 on DC or removing 20 amino acids in C-terminus did not ablate the inhibition of ESAT-6 on IL-12 production. We conclude that ESAT-6 enhances IL-23 production at the expense of IL-12 in a TLR2 independent mechanism, which favors Th17 over Th1 activation. (Supported by the NIH grants AI082335 and AI063514)

B7-CTLA4 reverse signaling is responsible for regulatory T cell-induced suppression of dendritic cells (168.23)

Abstract CD4+CD25+Foxp3+ regulatory T cells (Treg) are essential for maintaining immune tolerance and homeostasis. It has been shown that natural Treg can inhibit up-regulation of costimulatory molecules on dendritic cells (DC). However, the mechanism leading to this phenomenon has not been elucidated. Whether inducible Treg (iTreg) also possess this function has not been previously investigated. Here, we demonstrate that iTreg could inhibit LPS-induced DC maturation and mediate down-regulation of CD80 and CD86 on mature DC. This process is CTLA4-dependent as Treg isolated from CTLA4-/- mice did not down-modulate B7 molecules on DC. Furthermore, CTLA4Ig, but not CD28Ig, mimicked iTreg action. Down-regulation of CD80/CD86 was not due to endocytosis or protease-dependent shedding, but rather to a reverse signaling through B7. CTLA4Ig treatment decreased CD80 and CD86 transcription, as well as NFκB activity upon LPS stimulation. Interestingly, both CTLA4Ig and co-incubation with iTreg induced a profound STAT3 phosphorylation in DC, whereas no significant effect on the proximal NFκB pathway was observed. Inhibition of STAT3 activation partially abolished CTLA4Ig-induced CD80/CD86 down-modulation suggesting involvement of this molecule in the observed process. Our data reveal a novel signaling pathway by which Treg can suppress DC via reverse signaling, and may provide new opportunities for therapies targeting costimulatory pathways.

The Pathogenesis of Sepsis

Sepsis is a serious clinical condition that represents a patient's response to a severe infection and has a very high mortality rate. Normal immune and physiologic responses eradicate pathogens, and the pathophysiology of sepsis is due to the inappropriate regulation of these normal reactions. In an ideal scenario, the first pathogen contact with the inflammatory system should eliminate the microbe and quickly return the host to homeostasis. The septic response may accelerate due to continued activation of neutrophils and macrophages/monocytes. Upregulation of lymphocyte costimulatory molecules and rapid lymphocyte apoptosis, delayed apoptosis of neutrophils, and enhanced necrosis of cells/tissues also contribute to the pathogenesis of sepsis. The coagulation system is closely tied to the inflammatory response, with cross talk between the two systems driving the dysregulated response. Biomarkers may be used to help diagnose patients with sepsis, and they may also help to identify patients who would benefit from immunomodulatory therapies.

Uptake of antigens from modified vaccinia Ankara virus-infected leukocytes enhances the immunostimulatory capacity of dendritic cells

Modified vaccinia Ankara (MVA) is a promising vaccine vector for infectious diseases and malignancies. It is fundamental to ascertain its tropism in human leukocyte populations and immunostimulatory mechanisms for application in immunotherapy. Human peripheral blood mononuclear cells (PBMC) and leukocyte subpopulations [monocyte-derived dendritic cells (DC), monocytes and B cells] were infected with MVA in order to evaluate their infection rate, changes in surface markers, cytokine expression and apoptosis. Monocytes, DC and B cells were most susceptible to MVA infection, followed by natural killer (NK) cells. Monocytes were activated strongly, with upregulation of co-stimulatory molecules, major histocompatibility complex (MHC) molecules and chemokine (C-C motif) receptor (CCR7), while immature DC showed partial activation and B cells were inhibited. Furthermore, expression of chemokine (C-X-C motif) ligand (CXCL10), tumor necrosis factor (TNF)-α, interleukin (IL)-6 and IL-12p70 was enhanced but IL-1β and IL-10 were stable or even downregulated. MVA induced a high apoptosis rate of antigen-presenting cells (APC). Nevertheless, incubation of MVA-infected leukocytes with uninfected immature DC (iDC) led to complete maturation of the DC. Subsequently, the matured DC were able to stimulate cytomegalovirus (CMV)-immediate early protein (IE1)-specific T cells. MVA induces a T-helper (Th)-1-polarizing cytokine expression in APC. Furthermore, incubation of MVA-infected leukocytes with uninfected iDC leads to complete maturation of the DC and may be the basis for cross-presentation of MVA-encoded antigens. Thus this approach seems to be an ideal model for further studies with MVA-encoded viral antigens regarding immunotherapy and vaccination strategies.

LiEIF and its recombinant polypeptides enhance the maturation of mouse dendritic cells and the production of the protective IL-12 cytokine

Dendritic cells (DCs) maturation is associated with upregulation of costimulatory molecules (CD80, CD86, CD40) and secretion of cytokines including IL-12 which is important for generation of effective T cells. Proteins of Leishmania parasite that stimulate the production of IL-12 could be of significant interest either as immunotherapeutic components for leishmaniasis or as adjuvants. LeIF (Leishmania eukaryotic initiation factor) belongs to this group of proteins since it induces the production of IL-12, IL-10 and TNF-α by human monocytes of healthy volunteers. In particular, the induction of cytokines appears to be located in the N-terminal part (1-226) of the protein. In the present study we evaluated the ability of the recombinant protein L. infantum eIF (LieIF) and its constructs to induce in vitro the maturation of myeloid DCs (mDCs) and the production of cytokines supporting the polarization of Th1 type immune response. For this purpose, we used five synthetic peptides (16-18 aa) belonging in the N-terminal region, eight overlapped recombinant polypeptides covering the full protein sequence and the full-length protein. Enriched mDCs were obtained by ex vivo expansion of bone marrow cells, from BALB/c mice, cultured with the hematopoietic factor GM-CSF. The incubation of mDCs with the recombinant polypeptides, led to their maturation since it was observed a significant augmentation of the percentage of mDCs that express the molecules CD40, CD80 and CD86. On the contrary, the synthetic peptides did not enhance CD40 and CD86 expression and drove only to significant augmentation of CD80. In addition, we evaluated the ability of LieIF and its polypeptides to induce the production of IL-12, IL-10 and the expression of iNOS by mouse mDCs. We determined an augmentation of the percentage of mDCs that produce IL-12 upon their incubation with LieIF as well as with all the recombinant polypeptides and with three synthetic peptides whereas negligible amount of IL-10 was obtained. Augmentation of iNOS was found after incubation with the entire molecule of LieIF and with the recombinant polypeptides. In conclusion, LieIF and some of its recombinant polypeptides seem to have immunomodulatory properties demonstrating their potential use as therapeutic and prophylactic vaccine antigens.