Exploiting a new strategy to induce immunogenic cell death to improve dendritic cell-based vaccines for lymphoma immunotherapy

Although promising, the clinical benefit provided by dendritic cell (DC)-based vaccines is still limited and the choice of the optimal antigen formulation is still an unresolved issue. We have developed a new DC-based vaccination protocol for aggressive and/or refractory lymphomas which combines the unique features of interferon-conditioned DC (IFN-DC) with highly immunogenic tumor cell lysates (TCL) obtained from lymphoma cells undergoing immunogenic cell death. We show that treatment of mantle cell lymphoma (MCL) and diffuse large B-cell lymphoma (DLBCL) cell lines with 9-cis-retinoic acid and IFNα (RA/IFNα) induces early membrane exposure of Calreticulin, HSP70 and 90 together with CD47 down-regulation and enhanced HMGB1 secretion. Consistently, RA/IFNα-treated apoptotic cells and -TCLs were more efficiently phagocytosed by DCs compared to controls. Notably, cytotoxic T cells (CTLs) generated with autologous DCs pulsed with RA/IFNα-TCLs more efficiently recognized and specifically lysed MCL or DLBCL cells or targets loaded with several HLA-A*0201 cyclin D1 or HLA-B*0801 survivin epitopes. These cultures also showed an expansion of Th1 and Th17 cells and an increased Th17/Treg ratio. Moreover, DCs loaded with RA/IFNα-TCLs showed enhanced functional maturation and activation. NOD/SCID mice reconstituted with human peripheral blood lymphocytes and vaccinated with autologous RA/IFNα-TCL loaded-IFN-DCs showed lymphoma-specific T-cell responses and a significant decrease in tumor growth with respect to mice treated with IFN-DC unpulsed or loaded with untreated TCLs. This study demonstrates the feasibility and efficacy of the use of RA/IFNα to generate a highly immunogenic TCL as a suitable tumor antigen formulation for the development of effective anticancer DC-based vaccines.

Immune-based mechanisms of cytotoxic chemotherapy: implications for the design of novel and rationale-based combined treatments against cancer

Conventional anticancer chemotherapy has been historically thought to act through direct killing of tumor cells. This concept stems from the fact that cytotoxic drugs interfere with DNA synthesis and replication. Accumulating evidence, however, indicates that the antitumor activities of chemotherapy also rely on several off-target effects, especially directed to the host immune system, that cooperate for successful tumor eradication. Chemotherapeutic agents stimulate both the innate and adaptive arms of the immune system through several modalities: (i) by promoting specific rearrangements on dying tumor cells, which render them visible to the immune system; (ii) by influencing the homeostasis of the hematopoietic compartment through transient lymphodepletion followed by rebound replenishment of immune cell pools; (iii) by subverting tumor-induced immunosuppressive mechanisms and (iv) by exerting direct or indirect stimulatory effects on immune effectors. Among the indirect ways of immune cell stimulation, some cytotoxic drugs have been shown to induce an immunogenic type of cell death in tumor cells, resulting in the emission of specific signals that trigger phagocytosis of cell debris and promote the maturation of dendritic cells, ultimately resulting in the induction of potent antitumor responses. Here, we provide an extensive overview of the multiple immune-based mechanisms exploited by the most commonly employed cytotoxic drugs, with the final aim of identifying prerequisites for optimal combination with immunotherapy strategies for the development of more effective treatments against cancer.

Inhibition of human immunodeficiency virus (HIV-1) infection in human peripheral blood leucocytes-SCID reconstituted mice by rapamycin

The capacity of the immunomodulatory drug rapamycin (RAPA) to inhibit replication of the CCR5 strain of human immunodeficiency virus (HIV) in vitro prompted us to test its effects in a murine preclinical model of HIV infection. RAPA (0.6 or 6 mg/kg body weight) or its vehicle were administered daily, per os, to SCID mice reconstituted with human peripheral blood leucocytes (hu-PBL) starting 2 days before the intraperitoneal challenge with the R5 tropic SF162 strain of HIV-1 (1000 50% tissue culture infective dose/ml). Relative to hu-PBL-SCID mice that received no treatment, HIV-infected hu-PBL-SCID mice treated with the vehicle control for 3 weeks exhibited a severe depletion of CD4(+) cells (90%), an increase in CD8(+) cells and an inversion of the CD4(+)/CD8(+) cell ratio. In contrast, treatment of HIV-infected mice with RAPA prevented a decrease in CD4(+) cells and the increase of CD8(+) cells, thereby preserving the original CD4(+):CD8(+) cell ratio. Viral infection also resulted in the detection of HIV-DNA within peritoneal cells and spleen, and lymph node tissues of the vehicle-treated mice within 3 weeks of the viral challenge. In contrast, treatment with RAPA decreased cellular provirus integration and reduced HIV-RNA levels in the blood. Furthermore, in co-cultivation assays, spleens from RAPA-treated mice exhibited a reduced capacity for infecting allogeneic T cells which was dose-dependent. These data show that RAPA possesses powerful anti-viral activity against R5 strains of HIV in vivo and support the use of additional studies to evaluate the potential application of this drug in the management of HIV patients.

IRF-1 deficiency skews the differentiation of dendritic cells toward plasmacytoid and tolerogenic features

Members of the IFN regulatory factors (IRFs) family are transcriptional regulators that play essential roles in the homeostasis and function of the immune system. Recent studies indicate a direct involvement of some members of the family in the development of different subsets of dendritic cells (DC). Here, we report that IRF-1 is a potent modulator of the development and functional maturation of DC. IRF-1-deficient mice (IRF-1(-/-)) exhibited a predominance of plasmacytoid DC and a selective reduction of conventional DC, especially the CD8alpha(+) subset. IRF-1(-/-) splenic DC were markedly impaired in their ability to produce proinflammatory cytokines such as IL-12. By contrast, they expressed high levels of IL-10, TGF-beta, and the tolerogenic enzyme indoleamine 2,3 dioxygenase. As a consequence, IRF-1(-/-) DC were unable to undergo full maturation and retained plasmacytoid and tolerogenic characteristics following virus infection ex vivo and in vivo. Accordingly, DC from IRF-1(-/-) mice were less efficient in stimulating the proliferation of allogeneic T cells and instead, induced an IL-10-mediated, suppressive activity in allogeneic CD4(+)CD25(+) regulatory T cells. Together, these results indicate that IRF-1 is a key regulator of DC differentiation and maturation, exerting a variety of effects on the functional activation and tolerogenic potential of these cells.

Immunological relevance of the tumor associated antigen (TAA) COA-1 in colorectal cancer (CRC)

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Background: Immunotherapy (IT) in CRC has often produced discouraging results. COA-1 is a new TAA recognized by CD4+ T cells from peripheral blood (PB) of a CRC pt; its immunogenic epitope is presented on the surface of tumor cells in association with DRβ1*1301 or *0402 HLA class II molecules. Our aim is verifying whether an immune response directed against COA-1 mediated by CD4+ T cells can be isolated from PB of CRC pts. To achieve a more efficient anti-tumor response a recognition of a specific antigen by both the CD4+ and CD8+ lymphocytes should be performed; so different epitopes deriving from the processing of the same antigen should be presented to the immune system in association with both class I and class II MHC molecules. We identified a list of COA-1 derived peptides with the calculated score for the binding to HLA-A2, the more common HLA class I molecule within the Caucasian population. A failure in generating COA-1 specific T cells was observed in stage I-II CRC pts. Methods: From Jan 04 to day PB samples from 36 CRC pts (14 stage III/ 22 stage IV) have been collected and the HLA typing has been performed. Pts. expressing HLA DRbβ*0402, HLA DRβ1*1301 or HLA-A2 have been selected to collect other blood drawns and verifying whether an immune response directed against COA-1 could be isolated from their PB. Results: 4 pts were positive for the expression of DRβ1*1301 and 2 for the expression of DRβ1*0402. PB lymphocytes have been in vitro stimulated with the COA-1 derived epitopes and tumor reactivity has been verified. An immune response directed to COA-1 was detected in the PB of these 6 pts; anti-COA-1 CD4+ T cells were in vitro isolated and their cytotoxicity measured by granzyme B release. 9 pts were positive for the expression of HLA-A2 and we are stimulating the lymphocytes isolated from these pts with 6 selected COA-1 derived peptides binding the HLA-A2. We observed specific CD8+ T cells for 2 peptides in 1 pt. Conclusions: Our data identify COA-1 like an immunogenic antigen that can evoke an anti-tumor immune response CD4+ mediated in CRC; the response correlates with disease progression. Experiments are ongoing to evaluate an immune response mediated by both CD4+ and CD8+ T cells. These results will determine whether COA-1 could be used for future protocols of IT in CRC.

No significant financial relationships to disclose.

Impaired myelopoiesis in mice devoid of interferon regulatory factor 1

Interferon regulatory factor (IRF)-1 is a transcription factor controlling the expression of several genes, which are differentially induced depending on the cell type and signal. IRF-1 modulates multiple functions, including regulation of immune responses and host defence, cell growth, cytokine signalling and hematopoietic development. Here, we investigated the role of IRF-1 in granulocytic differentiation in mice with a null mutation in the IRF-1 gene. We show that IRF-1(-/-) bone marrow cells exhibit an increased number of immature granulocytic precursors, associated with a decreased number of mature granulocytic elements as compared to normal mice, suggestive of a defective maturation process. Clonogenetic analyses revealed a reduced number of CFU-G, CFU-M and CFU-GM colonies in IRF-1(-/-) mice, while the number of BFU-E/CFU-E colonies was unchanged. At the molecular level, the expression of CAAT-enhancer-binding protein (C/EBP)-epsilon, -alpha and PU.1 was substantially lower in the CD11b(+) cells from the bone marrow of IRF-1(-/-) mice as compared to cells from wild-type mice. These results, together with the fact that IRF-1 is markedly induced early during granulo-monocytic differentiation of CD34+ cells, highlight the pivotal role of IRF-1 in the early phases of myelopoiesis.

A new type I IFN-mediated pathway for the rapid differentiation of monocytes into highly active dendritic cells

Dendritic cells (DCs) are a unique leukocyte type consisting of different subsets of professional antigen-presenting cells. Since DCs initiate and govern the immune response, they represent an ideal target for intervention aimed at modulating and potentiating immune responses against cancer and infectious diseases. We recently described and characterized, at a functional level, a novel DC subset, interferon (IFN)-DCs, derived from blood monocytes after a short exposure to type I IFN and GM-CSF. Here, we review our recent studies on IFN-DCs and discuss their possible use in clinical immunotherapeutic strategies.

Vaginal transmission of HIV-1 in hu-SCID mice: a new model for the evaluation of vaginal microbicides

OBJECTIVE

To develop an animal model of vaginal transmission of HIV-1 for the evaluation of vaginal microbicides.

DESIGN

Vaginal infection was performed in SCID mice reconstituted with 4 x 107 human peripheral blood lymphocytes (hu-PBL) by non-invasive vaginal administration. The hu-PBL were previously infected in vitro with a non-syncytium (NSI) strain of HIV-1 (SF162) (hu-PBL-SCID). Lymphocyte migration in vivo was examined using fluorescently labelled human lymphocytes.

METHODS

The percentage of CD4 T cells, plasma viral load and p24 antigen were evaluated using fluorescent activated cell sorting (FACS), the Amplicor HIV-1 monitor kit and enzyme-linked immunosorbent assay, respectively. Polymerase chain reaction (PCR) analysis was performed on DNA extracted from spleen and lymph nodes. For in vivo migration of labelled lymphocytes, the mice were sacrificed after 4, 24 and 48 h; vaginae and local lymph nodes were removed, snap frozen with OCT, sectioned and examined by fluorescent microscopy and FACS.

RESULTS

HIV transmission was established using virus-infected cells inoculated vaginally, as shown by FACS, HIV viral load, p24 and PCR results. Labelled cells were easily located within the vaginal tissues after 4 h. However, few or no cells could be identified after 24 or 48 h at the vaginal level, whereas labelled cells could be detected at the level of regional lymph nodes.

CONCLUSIONS

Because of its simplicity and practical features compared with other animal models, the vaginal HIV-infected hu-SCID mouse model may prove useful to test the activity of compounds against cell-associated HIV and, possibly, other sexually transmitted diseases.

Expression of CCR-7, MIP-3beta, and Th-1 chemokines in type I IFN-induced monocyte-derived dendritic cells: importance for the rapid acquisition of potent migratory and functional activities

The migration capability of dendritic cells (DCs) is regulated by their response to factors, namely chemokines, that characterize maturation stage and shape their functional activities. This study examines the morphology, expression of chemokines/chemokine receptors, and migration properties of DCs generated after treatment of monocytes with type I interferon (IFN) and granulocyte-macrophage colony-stimulating factor (GM-CSF) (IFN-DCs). IFN-DCs showed phenotypical and morphologic features undetectable in DCs generated in the presence of interleukin 4 (IL-4) and GM-CSF, such as expression of CD83 and CD25 and the presence of CD44+, highly polarized, thin, and long dendrites. IFN-DCs markedly migrated in response to beta-chemokines (especially MIP-1beta) and expressed the Th-1 chemokine IP-10. Notably, IFN-DCs showed an up-regulation of CCR7 as well as of its natural ligand MIP-3beta, characteristics typical of mature DCs. Of interest, IFN-DCs exhibited a marked chemotactic response to MIP-3beta in vitro and strong migratory behavior in severe combined immunodeficient (SCID) mice. In SCID mice reconstituted with human peripheral blood leukocytes, IFN-DCs induced a potent primary human antibody response and IFN-gamma production, indicative of a Th-1 immune response. These results define the highly specialized maturation state of IFN-DCs and point out the existence of a "natural alliance" between type I IFN and monocyte/DC development, instrumental for ensuring an efficient connection between innate and adaptive immunity.

IFN-beta stimulates the production of beta-chemokines in human peripheral blood monocytes. Importance of macrophage differentiation

We investigated the effect of IFN-beta on beta-chemokine expression in differentiating human peripheral blood monocytes. MCP-1, MIP-1alpha and MIP-1beta were constitutively expressed in 1 day-cultured monocytes, and their secretion increased with time in culture despite any change in mRNA accumulation. IFN-beta treatment of differentiating monocytes resulted in a marked and dose-dependent increase of beta-chemokine secretion, which was regulated differently with respect to the differentiation stage. In particular, IFN-beta upregulated MCP-1 secretion in monocytes at all stages of differentiation although its effect was significantly higher in 1-day cultured monocytes as compared to monocyte-derived macrophages (MDM). In contrast, MIP-1alpha and MIP-1beta secretion was up-regulated by IFN-beta only in MDM. Although MCP-1, MIP-1alpha and MIP-1beta mRNA expression was up-regulated by IFN-beta in both 1 day-cultured monocytes and MDM, no correlation was found between mRNA level and protein secretion. These results suggest that the regulation of beta-chemokine secretion in monocytes/macrophages by IFN-beta occurred through different mechanisms, involving both a direct effect of this cytokine on chemokine gene expression and translational/post-translational steps of regulation more likely linked to the differentiation process. This finding reveals a novel role for this cytokine in the recruitment of specific cell types during the immune response, which may be relevant in the control of viral infections in vivo.

Chimeric plant virus particles as immunogens for inducing murine and human immune responses against human immunodeficiency virus type 1

The high-yield expression of a neutralizing epitope from human immunodeficiency virus type 1 (HIV-1) on the surface of a plant virus and its immunogenicity are presented. The highly conserved ELDKWA epitope from glycoprotein (gp) 41 was expressed as an N-terminal translational fusion with the potato virus X (PVX) coat protein. The resulting chimeric virus particles (CVPs), purified and used to immunize mice intraperitoneally or intranasally, were able to elicit high levels of HIV-1-specific immunoglobulin G (IgG) and IgA antibodies. Furthermore, the human immune response to CVPs was studied with severe combined immunodeficient mice reconstituted with human peripheral blood lymphocytes (hu-PBL-SCID). hu-PBL-SCID mice immunized with CVP-pulsed autologous dendritic cells were able to mount a specific human primary antibody response against the gp41-derived epitope. Notably, sera from both normal and hu-PBL-SCID mice showed an anti-HIV-1-neutralizing activity. Thus, PVX-based CVPs carrying neutralizing epitopes can offer novel perspectives for the development of effective vaccines against HIV and, more generally, for the design of new vaccination strategies in humans.

Chimeric plant virus particles as immunogens for inducing murine and human immune responses against human immunodeficiency virus type 1

The high-yield expression of a neutralizing epitope from human immunodeficiency virus type 1 (HIV-1) on the surface of a plant virus and its immunogenicity are presented. The highly conserved ELDKWA epitope from glycoprotein (gp) 41 was expressed as an N-terminal translational fusion with the potato virus X (PVX) coat protein. The resulting chimeric virus particles (CVPs), purified and used to immunize mice intraperitoneally or intranasally, were able to elicit high levels of HIV-1-specific immunoglobulin G (IgG) and IgA antibodies. Furthermore, the human immune response to CVPs was studied with severe combined immunodeficient mice reconstituted with human peripheral blood lymphocytes (hu-PBL-SCID). hu-PBL-SCID mice immunized with CVP-pulsed autologous dendritic cells were able to mount a specific human primary antibody response against the gp41-derived epitope. Notably, sera from both normal and hu-PBL-SCID mice showed an anti-HIV-1-neutralizing activity. Thus, PVX-based CVPs carrying neutralizing epitopes can offer novel perspectives for the development of effective vaccines against HIV and, more generally, for the design of new vaccination strategies in humans.

IL-15 is expressed by dendritic cells in response to type I IFN, double-stranded RNA, or lipopolysaccharide and promotes dendritic cell activation

Cytokines that are induced by infection may contribute to the initiation of immune responses through their ability to stimulate dendritic cells (DCs). In this paper, we have addressed the role of IL-15 in DC activation, investigating its expression by DCs in response to three different signals of infection and examining its ability to stimulate DCs. We report that the expression of both IL-15 and the IL-15 receptor alpha-chain are increased in splenic DCs from mice inoculated with dsRNA (poly(I:C)), LPS, or IFN-alphabeta, and in purified murine splenic DCs treated with IFN-alphabeta in vitro. Furthermore, IL-15 itself was able to activate DCs, as in vivo or in vitro exposure of splenic DCs to IL-15 resulted in an up-regulation of costimulatory molecules, markedly increased production of IFN-gamma by DC and an enhanced ability of DCs to stimulate Ag-specific CD8(+) T cell proliferation. The magnitude of all of the IL-15-induced changes in DCs was reduced in mice deficient for the IFN-alphabeta receptor, suggesting a role for IFN-alphabeta in the stimulation of DCs by IL-15. These results identify IL-15 as a stimulatory cytokine for DCs with the potential for autocrine activity and link its effects to expression of IFN-alphabeta.

HIV-1 gp120 stimulates the production of beta-chemokines in human peripheral blood monocytes through a CD4-independent mechanism

The present study was designed to evaluate the effect of the HIV-1 envelope glycoprotein gp120 on the expression of beta-chemokines in cultured monocytes/macrophages. Treatment of either freshly isolated 1-day-cultured monocytes or 7-day-cultured monocyte-derived macrophages (MDM) with recombinant gp120-IIIB resulted in a specific and dose-dependent enhancement of secretion of monocyte chemoattractant protein-1, macrophage inflammatory protein-1beta, and RANTES as well as a clear-cut increase in transcript accumulation. The expression of these mRNA was increased, but not superinduced, in the presence of cycloheximide. beta-Chemokine secretion was also induced after exposure of monocyte cultures to gp120-JRFL and aldrithiol-2-inactivated R5 and X4 HIV-1 strains, retaining conformational and functional integrity of envelope proteins. In contrast, no beta-chemokine secretion was triggered by X4 and R5 gp120 or aldrithiol-2-inactivated virus treatment of monocytoid cell lines that were fully responsive to LPS. The gp120-mediated effect was independent of its interaction with CD4, as preincubation with soluble CD4 did not abrogate beta-chemokine induction. Moreover, triggering of CD4 receptor by a specific Ab did not result in any beta-chemokine secretion. Interestingly, engagement of CCR5 and CXCR4 receptors by specific Abs as well as treatment with CCR5 and CXCR4 ligands induced beta-chemokine secretion. On the whole, these results indicate that HIV-1 stimulates monocytes/macrophages to produce beta-chemokines by a specific interaction of gp120 with HIV-1 coreceptors on the cell membrane. The expression of these related polypeptides may represent an important cellular response for regulating both the extent of viral infection and the recruitment of immune cells.

Type i interferons potently enhance humoral immunity and can promote isotype switching by stimulating dendritic cells in vivo

Type I interferons (IFN-I) are rapidly induced following infection and play a key role in nonspecific inhibition of virus replication. Here we have investigated the effects of IFN-I on the generation of antigen-specific antibody responses. The data show that IFN-I potently enhance the primary antibody response to a soluble protein, stimulating the production of all subclasses of IgG, and induce long-lived antibody production and immunological memory. In addition, endogenous production of IFN-I was shown to be essential for the adjuvant activity of CFA. Finally, IFN-I enhanced the antibody response and induced isotype switching when dendritic cells were the only cell type responding to IFN-I. The data reveal the potent adjuvant activity of IFN-I and their important role in linking innate and adaptive immunity.

Antitumor activity of recombinant adenoviral vectors expressing murine IFN-alpha in mice injected with metastatic IFN-resistant tumor cells

Recent studies have shown that gene therapy with type I interferon (IFN) in an adenovirus vector is a powerful tool to suppress the growth of human tumors transplanted in immune-deficient mice. However, in these studies the host immune-mediated effects, which may be important in mediating the long-term control of tumor growth by these cytokines, was not studied. In this paper, we evaluate the antitumor efficacy of different adenoviral vectors containing mouse IFN-alpha genes (i.e., a first-generation replication-defective vector containing IFN-alpha1 and two different second-generation vectors containing IFN-alpha2) in immunocompetent DBA/2 mice transplanted with highly metastatic Friend leukemic cells resistant in vitro to type I IFN. We found that injection of all the different adenovirus vectors containing mouse IFN-alpha( genes resulted in a marked antitumor response in mice transplanted either subcutaneously or intravenously with IFN-resistant Friend leukemic cells compared to tumor-bearing animals inoculated with a control vector. Tumor growth inhibition after injection of IFN-adenovirus vectors was associated with a prolonged presence of high IFN levels in the sera of the injected mice. Suppression of metastatic tumor growth was also observed after a single injection of the IFN--adenovirus recombinant vectors, whereas a comparable antitumor response generally required several injections of high doses of IFN. Altogether, these results demonstrate that IFN--adenoviral vectors can efficiently inhibit metastatic tumor growth by host-mediated mechanisms and suggest that adenovirus-mediated IFN-alpha gene therapy may represent an attractive alternative to the conventional clinical use of this cytokine, which generally requires multiple injections of high IFN doses for a prolonged period of time.

Inhibition of the constitutive and induced IFN-beta production by IL-4 and IL-10 in murine peritoneal macrophages

We had previously reported that freshly harvested peritoneal macrophages (PM) are in a type I IFN-mediated antiviral state, which is lost during in vitro culture of PM, concomitantly with a progressive decline in the expression of IFN-beta. We report herein that in vitro culture of PM in the presence of IL-4 or IL-10 results in an enhanced decay of the IFN-beta-mediated antiviral state to vesicular stomatitis virus (VSV). Moreover, IL-4 and IL-10 inhibited the production of type I IFN induced by LPS or NDV infection, as assessed by IFN production and induction of IFN-mediated antiviral state. The accumulation and physiological turnover of IFN-beta mRNA was not affected by IL-4 or IL-10. Finally, neither IL-10 nor IL-4 exerted any inhibitory effect on the antiviral activity induced by exogenous type-I IFN. These results suggest that Th2 cytokines, such as IL-4 and IL-10, act as negative regulators of the type I IFN-mediated antiviral response in PM and may represent stop signals for the constitutive or induced type I IFN expression in PM.

Impairment of human immunodeficiency virus type 1 (HIV-1) entry into Jurkat T cells by constitutive expression of the HIV-1 vpr protein: role of CD4 down-modulation

Jurkat T-cell clones, stably expressing the human immunodeficiency virus type 1 (HIV-1) Vpr protein, exhibited an impaired susceptibility to HIV-1 infection. A marked down-modulation of surface CD4 receptors was detected in Vpr-expressing clones with respect to control cells. Likewise, a reduced CD4 expression was also observed in parental Jurkat cells infected with wild-type but not with Vpr-mutant HIV-1. Notably, Vpr-expressing clones were fully susceptible to infection with a vesicular stomatitis virus G protein-pseudotyped HIV-1 virus, indicating that a block at the level of viral entry was responsible for the inhibition of viral replication. The effect exerted by Vpr on HIV replication and CD4 expression suggests that this protein can regulate both the establishment of a productive HIV-1 infection and CD4-mediated T-cell functions.

IFN-alpha and IL-18 exert opposite regulatory effects on the IL-12 receptor expression and IL-12-induced IFN-gamma production in mouse macrophages: novel pathways in the regulation of the inflammatory response of macrophages

We characterized the IL-12 response of mouse macrophages in terms of modulation of IFN-gamma production by cytokines (IFN-alpha and IL-18) and regulation of IL-12 receptor expression. Beta1 and beta2 IL-12R chain mRNA expression increased with time in culture in the absence of exogenous stimulation, with concomitant acquisition of responsiveness to IL-12 for IFN-gamma production. Expression of the IL-12R beta1 chain mRNA was increased further following IL-12 treatment as a consequence of IFN-gamma expression. IL-12 response was regulated differentially by IFN-alpha and IL-18. Neutralization of endogenous type I IFN increased IFN-gamma secretion, whereas exogenous IFN-alpha reduced it. In contrast, IL-18 enhanced IFN-gamma mRNA accumulation and IFN-gamma secretion in IL-12-stimulated, but not -untreated, cultures. The opposite effects exerted by IFN-alpha and IL-18 mirror their mutual capacity of regulating-in a negative or positive manner, respectively-the expression of the IL-12R beta1 chain. We suggest that differential regulation of IL-12 response by IFN-alpha and IL-18 can represent previously unrecognized regulatory mechanisms for maintaining suitable levels of differentiation/activation in macrophages.

Dual role of the HIV-1 vpr protein in the modulation of the apoptotic response of T cells

We investigated the effect of vpr, physiologically expressed during the course of an acute HIV-1 infection, on the response of infected cells to apoptotic stimuli as well as on the HIV-induced apoptosis. At 48 h after infection, Jurkat cells exhibited a lower susceptibility to undergo apoptosis with respect to uninfected cells. This effect was not observed following infection with either a vpr-mutated virus or a wild-type strain in the presence of antisense oligodeoxynucleotides targeted at vpr mRNA. Single-cell analysis, aimed at simultaneously identifying apoptotic and infected cells, revealed that resistance to apoptosis correlated with productive infection. Notably, vpr-dependent protection from induced apoptosis was also observed in HIV-1-infected PBMC. In contrast, at later stages of infection, a marked increase in the number of cells spontaneously undergoing apoptosis was detected in infected cultures. This virus-induced apoptosis involved vpr expression and predominantly occurred in productively infected cells. These results indicate that HIV-1 vpr can exert opposite roles in the regulation of apoptosis, which may depend on the level of its intracellular expression at different stages of HIV-1 infection. The dual function of vpr represents a novel mechanism in the complex strategy evolved by HIV to influence the turnover of T lymphocytes leading to either viral persistence or virus release and spreading.