Combined effect of antiretroviral therapy and blockade of IDO in SIV-infected rhesus macaques.

Increased activity of IDO, which catalyzes the degradation of Trp into kynurenine (Kyn), is observed during HIV/SIV infection, and it may contribute to the persistence of HIV/SIV by suppressing antiviral T cell responses. We administered the IDO inhibitor 1-methyl-d-tryptophan (d-1mT) for 13 days to SIV-infected rhesus macaques receiving antiretroviral therapy (ART). d-1mT treatment increased the plasma levels of Trp, without reducing the levels of Kyn, suggesting only a partial effect on IDO enzymatic activity.

Reduced protection from simian immunodeficiency virus SIVmac251 infection afforded by memory CD8+ T cells induced by vaccination during CD4+ T-cell deficiency.

Adaptive CD4(+) and CD8(+) T-cell responses have been associated with control of human immunodeficiency virus/simian immunodeficiency virus (HIV/SIV) replication. Here, we have designed a study with Indian rhesus macaques to more directly assess the role of CD8 SIV-specific responses in control of viral replication. Macaques were immunized with a DNA prime-modified vaccinia virus Ankara (MVA)-SIV boost regimen under normal conditions or under conditions of antibody-induced CD4(+) T-cell deficiency.

Immune activation driven by CTLA-4 blockade augments viral replication at mucosal sites in simian immunodeficiency virus infection.

The importance of chronic immune activation in progression to AIDS has been inferred by correlative studies in HIV-infected individuals and in nonhuman primate models of SIV infection. Using the SIV(mac251) macaque model, we directly address the impact of immune activation by inhibiting CTLA-4, an immunoregulatory molecule expressed on activated T cells and a subset of regulatory T cells. We found that CTLA-4 blockade significantly increased T cell activation and viral replication in primary SIV(mac251) infection, particularly at mucosal sites, and increased IDO expression and activity.

Interleukin-15 but not interleukin-7 abrogates vaccine-induced decrease in virus level in simian immunodeficiency virus mac251-infected macaques.

The loss of CD4(+) T cells and the impairment of CD8(+) T cell function in HIV infection suggest that pharmacological treatment with IL-7 and IL-15, cytokines that increase the homeostatic proliferation of T cells and improve effector function, may be beneficial. However, these cytokines could also have a detrimental effect in HIV-1-infected individuals, because both cytokines increase HIV replication in vitro. We assessed the impact of IL-7 and IL-15 treatment on viral replication and the immunogenicity of live poxvirus vaccines in SIV(mac251)-infected macaques (Macaca mulatta).

Decreased number of CD4+ and CD8+ T cells that express the interleukin-7 receptor in blood and tissues of SIV-infected macaques.

Acute HIV/SIV (human/simian immunodeficiency virus) infection results in severe CD4(+) T cell depletion in lymphoid compartments. During the chronic phase of infection, CD4(+) T cell numbers rebound in blood but remain low in the gut-associated lymphoid tissue (GALT), even when viral replication is suppressed by antiretroviral therapy (ART). Thus, strategies to repopulate lymphoid compartments may ameliorate the clinical outcome of HIV/SIV infection.

CTLA-4 blockade decreases TGF-beta, IDO, and viral RNA expression in tissues of SIVmac251-infected macaques.

Regulatory T (T(reg)) cells are a subset of CD25(+)CD4(+) T cells that constitutively express high levels of cytotoxic T lymphocyte antigen-4 (CTLA-4) and suppress T-cell activation and effector functions. T(reg) cells are increased in tissues of individuals infected with HIV-1 and macaques infected with simian immunodeficiency virus (SIV(mac251)). In HIV-1 infection, T(reg) cells could exert contrasting effects: they may limit viral replication by decreasing immune activation, or they may increase viral replication by suppressing virusspecific immune response.

Subunit recombinant vaccine protects against monkeypox.

The smallpox vaccine Dryvax, a live vaccinia virus (VACV), protects against smallpox and monkeypox, but is contraindicated in immunocompromised individuals. Because Abs to VACV mediate protection, a live virus vaccine could be substituted by a safe subunit protein-based vaccine able to induce a protective Ab response. We immunized rhesus macaques with plasmid DNA encoding the monkeypox orthologs of the VACV L1R, A27L, A33R, and B5R proteins by the intradermal and i.

Improved vaccine protection from simian AIDS by the addition of nonstructural simian immunodeficiency virus genes.

An HIV-1 vaccine able to induce broad CD4+ and CD8+ T cell responses may provide long-term control of viral replication. In this study we directly assess the relative benefit of immunization with vaccines expressing three structural Ags (Gag, Pol, and Env), three early regulatory proteins (Rev, Tat, and Nef), or a complex vaccine expressing all six Ags. The simultaneous administration of all six Ags during vaccination resulted in Ag competition manifested by a relative reduction of CD8+ T cell and lymphoproliferative responses to individual Ags.

Contrasting effects of low-dose IL-2 on vaccine-boosted simian immunodeficiency virus (SIV)-specific CD4+ and CD8+ T cells in macaques chronically infected with SIVmac251.

IL-2, the first cytokine discovered with T cell growth factor activity, is now known to have pleiotropic effects on T cells. For example, it can promote growth, survival, and differentiation of Ag-selected cells, or facilitate Ag-induced cell death of T cells when Ag persists, and in vivo, it is thought to contribute to the regulation of the size of adaptive T cell response. IL-2 is deficient in HIV-1 infection and has been used in the management of HIV-1-infected individuals undergoing antiretroviral therapy.

Recombinant interleukin-7 induces proliferation of naive macaque CD4+ and CD8+ T cells in vivo.

Interleukin-7 (IL-7) regulates T-cell homeostasis, and its availability is augmented in lymphopenic hosts. Naive CD8+ T cells transferred to lymphopenic mice acquire a memory-like phenotype, raising the possibility that IL-7 is the biological mediator of this effect. Here, we provide direct evidence that IL-7 induces the acquisition of memory-cell markers not only in CD8+ T cells but also in CD4+ T-cell subsets in immune-competent Indian rhesus macaques.

Avipox-based simian immunodeficiency virus (SIV) vaccines elicit a high frequency of SIV-specific CD4+ and CD8+ T-cell responses in vaccinia-experienced SIVmac251-infected macaques.

The ability of ALVAC- or fowlpox-based simian immunodeficiency virus (SIV) vaccines to boost SIV-specific CD4+ and CD8+ T-cell responses was tested in 10 vaccinia-experienced macaques infected with SIVmac251. The CD8+ T-cell response to the dominant Gag(181-189) CM9 was quantitated in seven Mamu-A*01-positive macaques by tetramer staining, by ex vivo cytotoxic T-lymphocyte (CTL) activity, and by intracellular cytokine staining (ICS) with the specific Gag(181-189) CM9 peptide. The overall CD8+ T-cell response to Gag was assessed using a peptide pool encompassing the entire Gag protein followed by measurement of TNF-alpha production in ICS assay.

High frequency of virus-specific CD8+ T cells in the central nervous system of macaques chronically infected with simian immunodeficiency virus SIVmac251.

Infection with human immunodeficiency virus or simian immunodeficiency virus (SIV) induces virus-specific CD8(+) T cells that traffic to lymphoid and nonlymphoid tissues. In this study, we used Gag-specific tetramer staining to investigate the frequency of CD8(+) T cells in peripheral blood and the central nervous system of Mamu-A*01-positive SIV-infected rhesus macaques. Most of these infected macaques were vaccinated prior to SIVmac251 exposure.

Modeling a safer smallpox vaccination regimen, for human immunodeficiency virus type 1-infected patients, in immunocompromised macaques.

We have modeled smallpox vaccination with Dryvax (Wyeth) in rhesus macaques that had depletion of CD4(+) T cells induced by infection with simian immunodeficiency virus or simian/human immunodeficiency virus. Smallpox vaccination induced significantly larger skin lesions in immunocompromised macaques than in healthy macaques. Unexpectedly, "progressive vaccinia" was infrequent.

Prior DNA immunization enhances immune response to dominant and subdominant viral epitopes induced by a fowlpox-based SIVmac vaccine in long-term slow-progressor macaques infected with SIVmac251.

A therapeutic vaccine for individuals infected with HIV-1 and treated with antiretroviral therapy (ART) should be able to replenish virus-specific CD4+ T-cells and broaden the virus-specific CD8+ T-cell response in order to maintain CD8+ T-cell function and minimize viral immune escape after ART cessation. Because a combination of DNA and recombinant poxvirus vaccine modalities induces high levels of virus-specific CD4+ T-cell response and broadens the cytolytic activity in naive macaques, we investigated whether the same results could be obtained in SIVmac251-infected macaques. The macaques studied here were long-term nonprogressors that naturally contained viremia but were nevertheless treated with a combination of antiviral drugs to assess more carefully the effect of vaccination in the context of ART.

Emergence of cytotoxic T lymphocyte escape mutants following antiretroviral treatment suspension in rhesus macaques infected with SIVmac251.

Structured treatment interruption (STI) of antiretroviral drugs has been proposed as an alternative approach for managing patients infected with HIV-1. While STI is thought to spare drug-related side effects and enhance the HIV-1-specific immune response, the long-lasting clinical benefit of this approach remains uncertain, particularly in patients with long-standing HIV-1 infection. Here, we investigated the basis of unabated virological replication following different STI regimens in rhesus macaques that expressed the MHC class I Mamu-A*01 molecule treated during acute and long-standing infection with SIVmac251.

Equivalent immunogenicity of the highly attenuated poxvirus-based ALVAC-SIV and NYVAC-SIV vaccine candidates in SIVmac251-infected macaques.

Therapeutic immunization of HIV-1-infected individuals may induce and/or enhance HIV-1-specific immune responses and decrease the dependency on antiretroviral drug treatment. However, repeated immunizations with live-recombinant vectors may induce vector-specific immune responses that interfere with the elicitation of vigorous immune responses to the desired antigen. Therefore, the use of mixed-modality vaccinations may be necessary to induce sustained virus-specific immune responses in HIV-1-infected individuals treated with antiretroviral therapy (ART).

Containment of simian immunodeficiency virus infection in vaccinated macaques: correlation with the magnitude of virus-specific pre- and postchallenge CD4+ and CD8+ T cell responses.

Macaques infected with the SIV strain SIVmac251 develop a disease closely resembling human AIDS characterized by high viremia, progressive loss of CD4(+) T cells, occurrence of opportunistic infection, cachexia, and lymphomas. We report in this study that vaccination with the genetically attenuated poxvirus vector expressing the structural Ags of SIVmac (NYVAC-SIV-gag, pol, env) in combination with priming with DNA-SIV-gag, env resulted in significant suppression of viremia within 2 mo after mucosal exposure to the highly pathogenic SIVmac251 in the majority of vaccinated macaques. The control of viremia in these macaques was long lasting and inversely correlated to the level of both pre- and postchallenge Gag-specific lymphoproliferative responses, as well as to the level of total SIV-specific CD4(+) T lymphocyte responses at the peak of acute viremia as detected by intracellular cytokine-staining assay.

A novel chimeric Rev, Tat, and Nef (Retanef) antigen as a component of an SIV/HIV vaccine.

The human immunodeficiency virus type 1 (HIV-1) regulatory proteins Rev, Tat, and Nef are expressed at early time post-infection and represent attractive targets to be included in a vaccine candidate for AIDS. However, the putative immunosuppressive activities of some of these proteins may limit their immunogenicity. To circumvent these issues, a novel chimeric polyprotein vaccine candidate (Retanef), comprising genetically modified and re-assorted rev, tat, and nef open reading frames of simian immunodeficiency virus (SIV), was constructed and optimized for its expression in mammalian cells.