Neonatal Fc receptor is involved in the protection of fibrinogen after its intake in peripheral blood mononuclear cells.

BACKGROUND: Fibrinogen is a central player in the blood coagulation cascade and one of the most abundant plasma proteins. This glycoprotein also triggers important events (e.g., cell spreading, the respiratory burst and degranulation) in neutrophil cells via a αMß2 integrin-mediated binding to the cell surface. Yet, little is known about the interaction of fibrinogen with leukocytes other than neutrophils or stimulated monocytes, although high amounts of fibrinogen protein can also be found in lymphocytes, particularly in T-cells. The aim of the present work is to unveil the dynamics and the function of fibrinogen intake in T-cells. METHODS: Using the Jurkat cell line as a T-cells model we performed fibrinogen intake/competition experiments. Moreover, by means of a targeted gene knock-down by RNA-interference, we investigated the dynamics of the intake mechanism. RESULTS: Here we show that (i) fibrinogen, although not expressed in human peripheral blood mononuclear cells, can be internalized by these cells; (ii) fibrinogen internalization curves show a hyperbolic behavior, which is affected by the presence of serum in the medium, (iii) FITC-conjugated fibrinogen is released and re-internalized by adjacent cells, (iv) the presence of human serum albumin (HSA) or immunoglobulin G (IgG), which are both protected from intracellular degradation by the interaction with the neonatal Fc receptor (FcRn), results in a decreased amount of internalized fibrinogen, and (v) FcRn-knockdown affects the dynamics of fibrinogen internalization. CONCLUSIONS: We demonstrated here for the first time that fibrinogen can be internalized and released by T-lymphocyte cells. Moreover, we showed that the presence of serum, HSA or IgG in the culture medium results in a reduction of the amount of internalized fibrinogen in these cells. Thus, we obtained experimental evidence for the expression of FcRn in T-lymphocyte cells and we propose this receptor as involved in the protection of fibrinogen from intracellular lysosomal degradation.

The Major Histocompatibility Complex Class II Transactivator CIITA Inhibits the Persistent Activation of NF-κB by the Human T Cell Lymphotropic Virus Type 1 Tax-1 Oncoprotein.

UNLABELLED: Human T cell lymphotropic virus type 1 (HTLV-1) Tax-1, a key protein in HTLV-1-induced T cell transformation, deregulates diverse cell signaling pathways. Among them, the NF-κB pathway is constitutively activated by Tax-1, which binds to NF-κB proteins and activates the IκB kinase (IKK). Upon phosphorylation-dependent IκB degradation, NF-κB migrates into the nucleus, mediating Tax-1-stimulated gene expression. We show that the transcriptional regulator of major histocompatibility complex class II genes CIITA (class II transactivator), endogenously or ectopically expressed in different cells, inhibits the activation of the canonical NF-κB pathway by Tax-1 and map the region that mediates this effect. CIITA affects the subcellular localization of Tax-1, which is mostly retained in the cytoplasm, and this correlates with impaired migration of RelA into the nucleus. Cytoplasmic and nuclear mutant forms of CIITA reveal that CIITA exploits different strategies to suppress Tax-1-mediated NF-κB activation in both subcellular compartments. CIITA interacts with Tax-1 without preventing Tax-1 binding to both IKKγ and RelA. Nevertheless, CIITA affects Tax-1-induced IKK activity, causing retention of the inactive p50/RelA/IκB complex in the cytoplasm. Nuclear CIITA associates with Tax-1/RelA in nuclear bodies, blocking Tax-1-dependent activation of NF-κB-responsive genes. Thus, CIITA inhibits cytoplasmic and nuclear steps of Tax-1-mediated NF-κB activation. These results, together with our previous finding that CIITA acts as a restriction factor inhibiting Tax-1-promoted HTLV-1 gene expression and replication, indicate that CIITA is a versatile molecule that might also counteract Tax-1 transforming activity. Unveiling the molecular basis of CIITA-mediated inhibition of Tax-1 functions may be important in defining new strategies to control HTLV-1 spreading and oncogenic potential. IMPORTANCE: HTLV-1 is the causative agent of human adult T cell leukemia-lymphoma (ATLL). The viral transactivator Tax-1 plays a central role in the onset of ATLL, mostly by deregulating the NF-κB pathway. We demonstrate that CIITA, a key regulator of adaptive immunity, suppresses Tax-1-dependent activation of NF-κB by acting at several levels: it retains most of Tax-1 and RelA in the cytoplasm and inhibits their residual functional activity in the nucleus. Importantly, this inhibition occurs in cells that are targets of HTLV-1 infection. These findings are of interest in the field of virology because they expand the current knowledge of the functional relationship between viral products and cellular interactors and provide the basis for a better understanding of the molecular countermeasures adopted by the host cell to antagonize HTLV-1 spreading and transforming properties. Within this framework, our results may contribute to the establishment of novel strategies against HTLV-1 infection and virus-dependent oncogenic transformation.

The MHC-II transactivator CIITA inhibits Tat function and HIV-1 replication in human myeloid cells.

BACKGROUND: We previously demonstrated that the HLA class II transactivator CIITA inhibits HIV-1 replication in T cells by competing with the viral transactivator Tat for the binding to Cyclin T1 subunit of the P-TEFb complex. Here, we analyzed the anti-viral function of CIITA in myeloid cells, another relevant HIV-1 target cell type. We sinvestigated clones of the U937 promonocytic cell line, either permissive (Plus) or non-permissive (Minus) to HIV-1 replication. This different phenotype has been associated with the expression of TRIM22 in U937 Minus but not in Plus cells. METHODS: U937 Plus cells stably expressing CIITA were generated and HLA-II positive clones were selected by cell sorting and cloning. HLA and CIITA proteins were analyzed by cytofluorometry and western blotting, respectively. HLA-II DR and CIITA mRNAs were quantified by qRT-PCR. Tat-dependent transactivation was assessed by performing the HIV-1 LTR luciferase gene reporter assay. Cells were infected with HIV-1 and viral replication was evaluated by measuring the RT activity in culture supernatants. RESULTS: CIITA was expressed only in HLA-II-positive U937 Minus cells, and this was strictly correlated with inhibition of Tat-dependent HIV-1 LTR transactivation in Minus but not in Plus cells. Overexpression of CIITA in Plus cells restored the suppression of Tat transactivation, confirming the inhibitory role of CIITA. Importantly, HIV-1 replication was significantly reduced in Plus-CIITA cells with respect to Plus parental cells. This effect was independent of TRIM22 as CIITA did not induce TRIM22 expression in Plus-CIITA cells. CONCLUSIONS: U937 Plus and Minus cells represent an interesting model to study the role of CIITA in HIV-1 restriction in the monocytic/macrophage cell lineage. The differential expression of CIITA in CIITA-negative Plus and CIITA-positive Minus cells correlated with their capacity to support or not HIV-1 replication, respectively. In Minus cells CIITA targeted the viral transactivator Tat to inhibit HIV-1 replication. The generation of Plus-CIITA cells was instrumental to demonstrate the specific contribution of CIITA in terms of inhibition of Tat activity and HIV-1 restriction, independently from other cellular factors, including TRIM22. Thus, CIITA acts as a general restriction factor against HIV-1 not only in T cells but also in myeloid cells.

Localization, quantification and interaction with host factors of endogenous HTLV-1 HBZ protein in infected cells and ATL.

BACKGROUND: Human T cell lymphotropic virus type 1 (HTLV-1) is the etiological agent of a severe form of neoplasia designated Adult T cell Leukaemia (ATL). It is widely accepted that the viral transactivator Tax-1 is the major viral product involved in the onset, but not in the maintenance, of neoplastic phenotype, as only 30-40% of ATL cells express Tax-1. It has been recently demonstrated that HBZ (HTLV-1 bZIP factor), a protein encoded by the minus strand of HTLV-1 genome, constantly expressed in infected cells and in ATL tumor cells, is also involved in the pathogenesis of leukaemia. The full role played by HBZ in oncogenesis is not clarified in detail also because of the limited availability of tools to assess quantitative expression, subcellular location and interaction of HBZ with host factors in ATL. RESULTS: By the use of the first reported monoclonal antibody against HBZ, 4D4-F3, generated in our laboratory it has been possible to carefully assess for the first time the above parameters in HTLV-1 chronically infected cells and, most importantly, in fresh leukemic cells from patients. Endogenous HBZ is expressed in speckle-like structures localized in the nucleus. The calculated number of endogenous HBZ molecules varies between 17.461 and 39.615 molecules per cell, 20- to 50-fold less than the amount expressed in HBZ transfected cells used by most investigators to assess the expression, function and subcellular localization of the viral protein. HBZ interacts in vivo with p300 and JunD and co-localizes only partially, and depending on the amount of expressed HBZ, not only with p300 and JunD but also with CBP and CREB2. CONCLUSIONS: The possibility to study endogenous HBZ in detail may significantly contribute to a better delineation of the role of HBZ during HTLV-1 infection and cellular transformation.

Major histocompatibility complex class II transactivator CIITA is a viral restriction factor that targets human T-cell lymphotropic virus type 1 Tax-1 function and inhibits viral replication.

Human T-cell lymphotropic virus type 1 (HTLV-1) is the causative agent of an aggressive malignancy of CD4+ T lymphocytes. Since the viral transactivator Tax-1 is a major player in T-cell transformation, targeting Tax-1 protein is regarded as a possible strategy to arrest viral replication and to counteract neoplastic transformation. We demonstrate that CIITA, the master regulator of major histocompatibility complex class II gene transcription, inhibits HTLV-1 replication by blocking the transactivating function of Tax-1 both when exogenously transfected in 293T cells and when endogenously expressed by a subset of U937 promonocytic cells. Tax-1 and CIITA physically interact in vivo via the first 108 amino acids of Tax-1 and two CIITA adjacent regions (amino acids 1 to 252 and 253 to 410). Interestingly, only CIITA 1-252 mediated Tax-1 inhibition, in agreement with the fact that CIITA residues from positions 64 to 124 were required to block Tax-1 transactivation. CIITA inhibitory action on Tax-1 correlated with the nuclear localization of CIITA and was independent of the transcription factor NF-YB, previously involved in CIITA-mediated inhibition of Tax-2 of HTLV-2. Instead, CIITA severely impaired the physical and functional interaction of Tax-1 with the cellular coactivators p300/CBP-associated factor (PCAF), cyclic AMP-responsive element binding protein (CREB), and activating transcription factor 1 (ATF1), which are required for the optimal activation of HTLV-1 promoter. Accordingly, the overexpression of PCAF, CREB, and ATF1 restored Tax-1-dependent transactivation of the viral long-terminal-repeat promoter inhibited by CIITA. These findings strongly support our original observation that CIITA, beside increasing the antigen-presenting function for pathogen antigens, acts as an endogenous restriction factor against human retroviruses by blocking virus replication and spreading.

Optimal MHC-II-restricted tumor antigen presentation to CD4+ T helper cells: the key issue for development of anti-tumor vaccines.

Present immunoprevention and immunotherapeutic approaches against cancer suffer from the limitation of being not "sterilizing" procedures, as very poor protection against the tumor is obtained. Thus newly conceived anti-tumor vaccination strategies are urgently needed. In this review we will focus on ways to provide optimal MHC class II-restricted tumor antigen presentation to CD4+ T helper cells as a crucial parameter to get optimal and protective adaptive immune response against tumor. Through the description of successful preventive or therapeutic experimental approaches to vaccinate the host against the tumor we will show that optimal activation of MHC class II-restricted tumor specific CD4+ T helper cells can be achieved in various ways. Interestingly, the success in tumor eradication and/or growth arrest generated by classical therapies such as radiotherapy and chemotherapy in some instances can be re-interpreted on the basis of an adaptive immune response induced by providing suitable access of tumor-associated antigens to MHC class II molecules. Therefore, focussing on strategies to generate better and suitable MHC class II-restricted activation of tumor specific CD4+ T helper cells may have an important impact on fighting and defeating cancer.

Molecular and cellular correlates of the CIITA-mediated inhibition of HTLV-2 Tax-2 transactivator function resulting in loss of viral replication.

BACKGROUND: MHC class II transactivator CIITA inhibits the function of HTLV-2 Tax-2 viral transactivator and, consequently, the replication of the virus in infected cells. Moreover overexpression of the nuclear factor NF-YB, that cooperates with CIITA for the expression of MHC class II genes, results also in inhibition of Tax-2 transactivation. The purpose of this investigation was to assess the cellular and molecular basis of the CIITA-mediated inhibition on Tax-2, and the relative role of NF-YB in this phenomenon. METHODS: By co-immunoprecipitation of lysates from 293T cells cotransfected with CIITA or fragments of it, and Tax-2 it was assessed whether the two factors interact in vivo. A similar approach was used to assess Tax-2-NF-YB interaction. In parallel, deletion fragments of CIITA were tested for the inhibition of Tax-2-dependent HTLV-2 LTR-luciferase transactivation. Subcellular localization of CIITA and Tax-2 was investigated by immunofluorescence and confocal microscopy. RESULTS: CIITA and Tax-2 interact in vivo through at least two independent regions, at the 1-252 N-term and at the 410-1130 C-term, respectively. Interestingly only the 1-252 N-term region mediates Tax-2 functional inhibition. CIITA and Tax-2 are localized both in the cytoplasm and in the nucleus, when separately expressed. Instead, when coexpressed, most of Tax-2 colocalize with CIITA in cytoplasm and around the nuclear membrane. The Tax-2 minor remaining nuclear portion also co-localizes with CIITA. Interestingly, when CIITA nucleus-cytoplasm shuttling is blocked by leptomycin B treatment, most of the Tax-2 molecules are also blocked and co-localize with CIITA in the nucleus, suggesting that CIITA-Tax-2 binding does not preclude Tax-2 entry into the nucleus.Finally, the nuclear factor NF-YB, also strongly binds to Tax-2. Notably, although endogenous NF-YB does not inhibit Tax-2-dependent HTLV-2 LTR transactivation, it still binds to Tax-2, and in presence of CIITA, this binding seems to increase. CONCLUSIONS: These results strongly suggest that CIITA inhibit Tax-2 by binding the viral transactivator both directly or through a tripartite interaction with NF-YB in. CIITA is therefore a viral restriction factor for HTLV-2 and this open the possibility to control HTLV-2 viral replication and spreading by the controlled induction of CIITA in infected cells.

Crystallization and preliminary X-ray diffraction data analysis of stenodactylin, a highly toxic type 2 ribosome-inactivating protein from Adenia stenodactyla.

Ribosome-inactivating proteins (RIPs) inhibit protein synthesis and induce cell death by removing a single adenine from a specific rRNA loop. They can be divided into two main groups: type 1 and type 2 RIPs. Type 1 RIPs are single-chain enzymes with N-glycosidase activity. Type 2 RIPs contain two chains (A and B) linked by a disulfide bond. The A chain has RIP enzymatic activity, whereas the B chain shows lectin activity and is able to bind to glycosylated receptors on the cell surface. Stenodactylin is a type 2 RIP from the caudex of Adenia stenodactyla from the Passifloraceae family that has been recently purified and characterized. It shows a strong enzymatic activity towards several substrates and is more cytotoxic than other toxins of the same type. Here, the crystallization and preliminary X-ray diffraction data analysis of stenodactylin are reported. This RIP forms crystals that diffract to high resolution (up to 2.15 A). The best data set was obtained by merging data collected from two crystals. Stenodactylin crystals belonged to the centred monoclinic space group C2 and contained two molecules in the asymmetric unit.

Structure/function studies on two type 1 ribosome inactivating proteins: Bouganin and lychnin.

The three-dimensional structures of two type 1 RIPs, bouganin and lychnin, has been solved. Their adenine polynucleotide glycosylase activity was also determined together with other known RIPs: dianthin 30, PAP-R, momordin I, ricin A chain and saporin-S6. Saporin-S6 releases the highest number of adenine molecules from rat ribosomes, and poly(A), while its efficiency is similar to dianthin 30, bouganin and PAP-R on herring sperm DNA. Measures of the protein synthesis inhibitory activity confirmed that saporin-S6 is the most active. The overall structure of bouganin and lychnin is similar to the other considered RIPs and the typical RIP fold is conserved. The superimpositioning of their C(alpha) atoms highlights some differences in the N-terminal and C-terminal domains. A detailed structural analysis indicates that the efficiency of saporin-S6 on various polynucleotides can be ascribed to a negative electrostatic surface potential at the active site and several exposed positively charged residues in the region around that site. These two conditions, not present at the same time in other examined RIPs, could guarantee an efficient interaction with the substrate and an efficient catalysis.

Crystallization of proteins on functionalized surfaces.

Functionalized mica sheets and polystyrene films exposing ionisable groups have been used as heterogeneous nucleating surfaces for model proteins. Surfaces with different densities of amino or sulfonated groups have been prepared. Crystallization trials were carried out using the hanging-drop vapour-diffusion method. The results show that using these surfaces the starting protein concentration necessary to form crystals is reduced. The effect of these surfaces on the crystallization process may be the consequence of electrostatic interactions between charged residues of proteins and ionisable groups on surfaces. These interactions can be attractive or repulsive, depending on the relative charge of the protein and the surface at the crystallization pH. Both phenomena can induce an increase of the local protein concentration on the surface or in its proximity, favouring nucleation. Moreover, a reduction of the waiting time (an estimation of the nucleation time) was also observed for some proteins, suggesting a surface-stabilization effect on crystal nuclei.

Structural probing of Zn(II), Cd(II) and Hg(II) binding to human ubiquitin.

A structural investigation performed on adducts of human ubiquitin with group-12 metal ions reveals common preferential anchoring sites, the most populated one being His68; at higher metal ion concentration a second and a third site, close to the N-terminus of the protein, become populated and promote a polymorphic transition from orthorhombic to cubic form; Glu16 and Glu18, involved in the latter metal binding, undergo a remarkable displacement from their position in native ubiquitin; the aggregate stereochemistry appears to be driven by the clustering of deshielded backbone hydrogen-bond patches, and metal ions foster this process.

Fowlpoxvirus recombinants coding for the CIITA gene increase the expression of endogenous MHC-II and Fowlpox Gag/Pro and Env SIV transgenes.

A complete eradication of an HIV infection has never been achieved by vaccination and the search for new immunogens that can induce long-lasting protective responses is ongoing. Avipoxvirus recombinants are host-restricted for replication to avian species and they do not have the undesired side effects induced by vaccinia recombinants. In particular, Fowlpox (FP) recombinants can express transgenes over long periods and can induce protective immunity in mammals, mainly due to CD4-dependent CD8+ T cells. In this context, the class II transactivator (CIITA) has a pivotal role in triggering the adaptive immune response through induction of the expression of class-II major histocompatibility complex molecule (MHC-II), that can present antigens to CD4+ T helper cells. Here, we report on construction of novel FPgp and FPenv recombinants that express the highly immunogenic SIV Gag-pro and Env structural antigens. Several FP-based recombinants, with single or dual genes, were also developed that express CIITA, driven from H6 or SP promoters. These recombinants were used to infect CEF and Vero cells in vitro and determine transgene expression, which was evaluated by real-time PCR and Western blotting. Subcellular localisation of the different proteins was evaluated by confocal microscopy, whereas HLA-DR or MHC-II expression was measured by flow cytometry. Fowlpox recombinants were also used to infect syngeneic T/SA tumour cells, then injected into Balb/c mice to elicit MHC-II immune response and define the presentation of the SIV transgene products in the presence or absence of FPCIITA. Antibodies to Env were measured by ELISA. Our data show that the H6 promoter was more efficient than SP to drive CIITA expression and that CIITA can enhance the levels of the gag/pro and env gene products only when infection is performed by FP single recombinants. Also, CIITA expression is higher when carried by FP single recombinants than when combined with FPgp or FPenv constructs and can induce HLA-DR cell surface expression. However, in-vivo experiments did not show any significant increase in the humoral response. As CIITA already proved to elicit immunogenicity by improving antigen presentation, further in-vivo experiments should be performed to increase the immune responses. The use of prime/boost immunisation protocols and the oral administration route of the recombinants may enhance the immunogenicity of Env peptides presented by MHC-II and provide CD4+ T-cell stimulation.

Major histocompatibility complex class II transcriptional platform: assembly of nuclear factor Y and regulatory factor X (RFX) on DNA requires RFX5 dimers.

Major histocompatibility complex class II (MHC-II) genes are regulated in a B-cell-specific and gamma interferon-inducible manner. Conserved upstream sequences (CUS) in their compact promoters bind nuclear factor Y (NFY) and regulatory factor X (RFX) complexes. These DNA-bound proteins form a platform that attracts the class II transactivator, which initiates and elongates MHC-II transcription. In this report, we analyzed the complex assembly of these DNA-bound proteins. First, we found that NFY can interact with RFX in cells. In particular, NFYA and NFYC bound RFXANK/B in vitro. Next, RFX5 formed dimers in vivo and in vitro. Within a leucine-rich stretch N-terminal to the DNA-binding domain in RFX5, the leucine at position 66 was found to be critical for this self-association. Mutant RFX5 proteins that could not form dimers also did not support the formation of higher-order DNA-protein complexes on CUS in vitro or MHC-II transcription in vivo. We conclude that the MHC-II transcriptional platform begins to assemble off CUS and then binds DNA via multiple, spatially constrained interactions. These findings offer one explanation of why in the Bare Lymphocyte Syndrome, which is a congenital severe combined immunodeficiency, MHC-II promoters are bare when any subunit of RFX is mutated or missing.

CIITA-induced MHC class II expression in mammary adenocarcinoma leads to a Th1 polarization of the tumor microenvironment, tumor rejection, and specific antitumor memory.

PURPOSE: We have shown previously that the MHC class II-negative murine TS/A adenocarcinoma is rejected in vivo if induced to express MHC class II molecules by transfection of the MHC class II transactivator CIITA. In this study, we explored the immunologic basis of tumor rejection and the correlation between histopathology of tumor tissue and immune rejection. EXPERIMENTAL DESIGN: Stable TS/A-CIITA transfectants were generated and injected into mice. In vivo cell depletion, immunohistochemistry of tumor tissues, and immune functional assays were done to assess the cellular and immunologic basis of rejection. RESULTS: Ninety-two percent of mice injected with TS/A-CIITA rejected the tumor and were completely resistant to challenge with parental TS/A. Only CD4+ and CD8+ cells were required for rejection. The tumor microenvironment in TS/A-CIITA-injected mice changed dramatically when compared with the TS/A parental-injected mice. Rapid infiltration with CD4+ T cells followed by dendritic cells, CD8+ T cells, and granulocytes was observed. Importantly, TS/A-CIITA cells could act as antigen-presenting cells because they process and present nominal antigens to CD4+ T cells. Tumor-specific CD4+ T cells of TS/A-CIITA-injected mice had the functional characteristics of Th1 cells and produced IFN-gamma and this was relevant for generation and maintenance of protective antitumor response, because IFN-gamma knockout mice were no longer rejecting TS/A-CIITA tumor cells. CONCLUSION: CIITA-dependent MHC class II expression confers to TS/A tumor cells the capacity to act as a protective vaccine against the tumor by triggering tumor antigen presentation to T helper cells, antitumor polarization of cellular and soluble components of the tumor microenvironment, and establishment of antitumor immune memory.

CIITA-driven MHC class II expressing tumor cells can efficiently prime naive CD4+ TH cells in vivo and vaccinate the host against parental MHC-II-negative tumor cells.

Our previous studies showed that non-immunogenic H-2d tumor cells of distinct epithelial histotypes can become highly immunogenic, induce a protective CD4+ T cell response and vaccinate the animals against parental MHC-II-negative cells if they are rendered MHC class II-positive by stable transfection with the Air-1-encoded MHC-II transcriptional activator CIITA. These studies did not establish, however, whether tumor immunity was the consequence of a direct priming of naive CD4+ T lymphocytes by CIITA-driven MHC-II-expressing tumor cells or by MHC-II-tumor antigen complexes engulfed by dendritic cells (DC) and exposed on the surface of these professional antigen presenting cells (APC). In the present investigation, we provide definitive evidence that CIITA-tumor cells are the crucial APC in vivo for CD4+ T cell priming. By using a transgenic H-2b mouse model, the CD11c.DTR C57BL/6 mice, in which DC can be functionally deleted by administration of diphteria toxin, we show that CIITA-tumor cells of two distinct histotypes can be rejected or strongly retarded in their growth in DC-deleted mice. To rule out that in absence of DC, other professional APC could prime naive CD4+ T cells, we deleted the macrophages in CD11c.DTR C57BL/6 mice by administration of liposome Clodronate and still obtained rejection or strong retardation in tumor growth of CIITA-tumor cells. Our results challenge the diffuse belief that non-professional APC cannot efficiently prime naive T cells in vivo. Moreover, the demonstration of the general validity of our approach in different genetic backgrounds may open a way for new strategies of antitumor treatment in clinical settings.

Tumor Immunology meets Immunology: Modified cancer cells as professional APC for priming naïve tumor-specific CD4+ T cells.

Although recent therapeutic approaches have revitalized the enthusiasm of the immunological way to combat cancer, still the comprehension of immunity against tumors is largely incomplete. Due to their specific function, CD8+ T cells with cytolytic activity (CTL) have attracted the attention of most investigators because CTL are considered the main effectors against tumor cells. Nevertheless, CTL activity and persistence is largely dependent on the action of CD4+ T helper cells (TH). Thus establishment of tumor-specific TH cell response is key to the optimal response against cancer. Here we describe emerging new strategies to increase the TH cell recognition of tumor antigens. In particular, we review recent data indicating that tumor cells themselves can act as surrogate antigen presenting cells for triggering TH response and how these findings can help in constructing immunotherapeutic protocols for anti-cancer vaccine development.

Tripartite Motif-Containing Protein 22 Interacts with Class II Transactivator and Orchestrates Its Recruitment in Nuclear Bodies Containing TRIM19/PML and Cyclin T1.

Among interferon (IFN) inducible antiviral factors both tripartite motif-containing protein 22 (TRIM22) and class II transactivator (CIITA) share the capacity of repressing human immunodeficiency virus type 1 (HIV-1) proviral transcription. TRIM22 is constitutively expressed in a subset of U937 cell clones poorly permissive to HIV-1 replication, whereas CIITA has been shown to inhibit virus multiplication in both T lymphocytic and myeloid cells, including poorly HIV-1 permissive U937 cells, by suppressing Tat-mediated transactivation of HIV-1 transcription. Therefore, we tested whether TRIM22 and CIITA could form a nuclear complex potentially endowed with HIV-1 repressive functions. Indeed, we observed that TRIM22, independent of its E3 ubiquitin ligase domain, interacts with CIITA and promotes its recruitment into nuclear bodies. Importantly, TRIM19/promyelocytic leukemia (PML) protein, another repressor of HIV-1 transcription also acting before proviral integration, colocalize in these nuclear bodies upon TRIM22 expression induced by IFN-γ. Finally, tTRIM22 nuclear bodies also contained CyclinT1, a crucial elongation factor of HIV-1 primary transcripts. These findings show that TRIM22 nuclear bodies are a site of recruitment of factors crucial for the regulation of HIV-1 transcription and highlight the potential existence of a concerted action between TRIM22, CIITA, and TRIM19/PML to maintain a state of proviral latency, at least in myeloid cells.

Cytoplasmic Localization of HTLV-1 HBZ Protein: A Biomarker of HTLV-1-Associated Myelopathy/Tropical Spastic Paraparesis (HAM/TSP).

HTLV-1 is the causative agent of a severe form of adult T cell leukemia/Lymphoma (ATL), and of a chronic progressive neuromyelopathy designated HTLV-1 associated myelopathy/tropical spastic paraparesis (HAM/TSP). Two important HTLV-1-encoded proteins, Tax-1 and HBZ, play crucial roles in the generation and maintenance of the oncogenic process. Less information is instead available on the molecular and cellular mechanisms leading to HAM/TSP. More importantly, no single specific biomarker has been described that unambiguously define the status of HAM/TSP. Here we report for the first time the finding that HBZ, described until now as an exclusive nuclear protein both in chronically infected and in ATL cells, is instead exclusively localized in the cytoplasm of peripheral blood mononuclear cells (PBMC) from patients suffering of HAM/TSP. Interestingly, at the single cell level, HBZ and Tax-1 proteins are never found co-expressed in the same cell, suggesting the existence of mechanisms of expression uncoupling of these two important HTLV-1 viral products in HAM/TSP patients. Cells expressing cytoplasmic HBZ were almost exclusively found in the CD4+ T cell compartment that was not, at least in a representative HAM/TSP patient, expressing the CD25 marker. Less than 1 percent CD8+ T cells were fond positive for HBZ, while B cells and NK cells were found negative for HBZ in HAM/TSP patients. Our results identify the cytoplasmic localization of HBZ in HAM/TSP patient as a possible biomarker of this rather neglected tropical disease, and raise important hypotheses on the role of HBZ in the pathogenesis of the neuromyelopathy associated to HTLV-1 infection.

Investigating human T cell lymphotropic retrovirus (HTLV) Tax function with molecular and immunophenotypic techniques.

Human T cell Lymphotropic Viruses 1 and 2 (HTLV-1 and HTLV-2) are the first described human retroviruses. HTLV-1 is the causative agent of an aggressive malignancy of CD4+ T lymphocytes named adult T-cell leukemia/lymphoma (ATLL) and of a chronic neurological disease known as HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). HTLV-2 shares many similarities with HTLV-1, but displays lower or absent association to diseases. Among the proteins encoded by HTLVs, the viral transactivator Tax exerts an essential role in viral transcription as well as in cell transformation. Different experimental methods to study Tax activity on HTLV-LTR promoter and Tax subcellular distribution are described. Emphasis is given to the functional and physical interaction between Tax-1/Tax-2 and cellular cofactors which may have an impact on the infectivity process of the HTLVs and on the capacity of cell transformation.

Boosting the MHC Class II-Restricted Tumor Antigen Presentation to CD4+ T Helper Cells: A Critical Issue for Triggering Protective Immunity and Re-Orienting the Tumor Microenvironment Toward an Anti-Tumor State.

Although the existence of an immune response against tumor cells is well documented, the fact that tumors take off in cancer patients indicates that neoplastic cells can circumvent this response. Over the years many investigators have described strategies to rescue the anti-tumor immune response with the aim of creating specific and long-lasting protection against the disease. When exported to human clinical settings, these strategies have revealed in most cases a very limited, if any, positive outcome. We believe that the failure is mostly due to the inadequate triggering of the CD4+ T helper (TH) cell arm of the adaptive immunity, as TH cells are necessary to trigger all the immune effector mechanisms required to eliminate tumor cells. In this review, we focus on novel strategies that by stimulating MHC class II-restricted activation of TH cells generate a specific and persistent adaptive immunity against the tumor. This point is of critical importance for both preventive and therapeutic anti-tumor vaccination protocols, because adaptive immunity with its capacity to produce specific, long-lasting protection and memory responses is indeed the final goal of vaccination. We will discuss data from our as well as other laboratories which strongly suggest that triggering a specific and persistent anti-tumor CD4+ TH cell response stably modify not only the tumor microenvironment but also tumor-dependent extratumor microenvironments by eliminating and/or reducing the blood-derived tumor infiltrating cells that may have a pro-tumor growth function such as regulatory CD4+/CD25+ T cells and myeloid-derived-suppressor cells. Within this frame, therefore, we believe that the establishment of a pro-tumor environment is not the cause but simply the consequence of the tumor strategy to primarily counteract components of the adaptive cellular immunity, particularly TH lymphocytes.