(1/681) HIV-1-specific CTL responses primed in vitro by blood-derived dendritic cells and Th1-biasing cytokines.

Vaccine strategies designed to elicit strong cell-mediated immune responses to HIV Ags are likely to lead to protective immunity against HIV infection. Dendritic cells (DC) are the most potent APCs capable of priming both MHC class I- and II-restricted, Ag-specific T cell responses. Utilizing a system in which cultured DC from HIV-seronegative donors were used as APC to present HIV-1 Ags to autologous T cells in vitro, the strength and specificity of primary HIV-specific CTL responses generated to exogenous HIV-1 Nef protein as well as intracellularly expressed nef transgene product were investigated. DC expressing the nef gene were able to stimulate Nef-specific CTL, with T cells from several donors recognizing more than one epitope restricted by a single HLA molecule. Primary Nef-specific CTL responses were also generated in vitro using DC pulsed with Nef protein. T cells primed with Nef-expressing DC (via protein or transgene) were able to lyse MHC class I-matched target cells pulsed with defined Nef epitope peptides as well as newly identified peptide epitopes. The addition of Th1-biasing cytokines IL-12 or IFN-alpha, during priming with Nef-expressing DC, enhanced the Nef-specific CTL responses generated using either Ag-loading approach. These results suggest that this in vitro vaccine model may be useful in identifying immunogenic epitopes as vaccine targets and in evaluating the effects of cytokines and other adjuvants on Ag-specific T cell induction. Successful approaches may provide information important to the development of prophylactic HIV vaccines and are envisioned to be readily translated into clinical DC-based therapeutic vaccines for HIV-1.  (+info)

(2/681) Long-lasting protection by live attenuated simian immunodeficiency virus in cynomolgus monkeys: no detection of reactivation after stimulation with a recall antigen.

The infection of cynomolgus monkeys with an attenuated simian immunodeficiency virus (SIV) (C8) carrying a deletion in the nef gene results in a persistent infection associated with an extremely low viral burden in peripheral blood mononuclear cells. The aim of this study was to determine (1) the breadth of the protection after repeated challenges of monkeys with SIV homologous strains of different pathogenicity, (2) the genotypic stability of the live virus vaccine, (3) whether the protection might depend on cellular resistance to superinfection, and (4) whether immunogenic stimuli such as recall antigens could reactivate the replication of the C8 virus. To address these goals, the monkeys were challenged at 40 weeks after C8 infection with 50 MID50 of cloned SIVmac251, BK28 grown on macaque cells. They were protected as indicated by several criteria, including virus isolation, anamnestic serological responses, and viral diagnostic PCR. At 92 weeks after the first challenge, unfractionated peripheral blood mononuclear cells from protected monkeys were susceptible to the in vitro infection with SIVmac32H, spl. At 143 weeks after C8 infection, the four protected monkeys were rechallenged with 50 MID50 of the pathogenic SIVmac32H, spl grown on macaque cells. Once again, they were protected. The C8 virus remained genotypically stable, and depletion of CD4(+) cells was not observed during approximately 3 years of follow-up. In contrast, it was found that the infection with SIVmac32H, spl induced CD4(+) cell depletion in three of three control monkeys. Of importance, stimulation with tetanus toxoid, although capable of inducing specific humoral and T cell proliferative responses, failed to induce a detectable reactivation of C8 virus.  (+info)

(3/681) Nef enhances human immunodeficiency virus replication and responsiveness to interleukin-2 in human lymphoid tissue ex vivo.

The nef gene is important for the pathogenicity associated with simian immunodeficiency virus infection in rhesus monkeys and with human immunodeficiency virus type 1 (HIV-1) infection in humans. The mechanisms by which nef contributes to pathogenesis in vivo remain unclear. We investigated the contribution of nef to HIV-1 replication in human lymphoid tissue ex vivo by studying infection with parental HIV-1 strain NL4-3 and with a nef mutant (DeltanefNL4-3). In human tonsillar histocultures, NL4-3 replicated to higher levels than DeltanefNL4-3 did. Increased virus production with NL4-3 infection was associated with increased numbers of productively infected cells and greater loss of CD4(+) T cells over time. While the numbers of productively infected T cells were increased in the presence of nef, the levels of viral expression and production per infected T cell were similar whether the nef gene was present or not. Exogenous interleukin-2 (IL-2) increased HIV-1 production in NL4-3-infected tissue in a dose-dependent manner. In contrast, DeltanefNL4-3 production was enhanced only marginally by IL-2. Thus, Nef can facilitate HIV-1 replication in human lymphoid tissue ex vivo by increasing the numbers of productively infected cells and by increasing the responsiveness to IL-2 stimulation.  (+info)

(4/681) Immunization with a live, attenuated simian immunodeficiency virus vaccine leads to restriction of viral diversity in Rhesus macaques not protected from pathogenic challenge.

Rhesus macaques immunized with simian immunodeficiency virus SIVmac239Deltanef but not protected from SIVmac251 challenge were studied to determine the genetic and biological characteristics of the breakthrough viruses. Assessment of SIV genetic diversity (env V1-V2) revealed a reduction in the number of viral species in the immunized, unprotected macaques, compared to the number in nonimmunized controls. However, no evidence for selection of a specific V1-V2 genotype was observed, and biologically cloned isolates from the animals with breakthrough virus were similar with respect to replication kinetics and coreceptor use in vitro.  (+info)

(5/681) Type 1 CD4(+) T-cell help is required for induction of antipeptide multispecific cytotoxic T lymphocytes by a lipopeptidic vaccine in rhesus macaques.

We have optimized the induction of antiviral cytotoxic T lymphocytes (CTL) in rhesus macaques by a lipopeptide vaccine containing seven peptides from simian immunodeficiency virus (SIV) Nef and Gag proteins and a strong T-helper peptide from tetanus toxoid (TT) that is promiscuous in humans (peptide TT 830-846). Two of the eight immunized macaques showed T-helper (Th) cell proliferation and a specific synthesis of gamma interferon in response to TT 830-846 peptide. They also showed multispecific cytotoxic activity against three to five of the immunizing SIV peptides. These results show the importance of a strong specific type 1 Th response for inducing a multispecific CTL response in vivo, which is essential for the development of an anti-human immunodeficiency virus vaccine.  (+info)

(6/681) Nef-induced CD4 degradation: a diacidic-based motif in Nef functions as a lysosomal targeting signal through the binding of beta-COP in endosomes.

The Nef protein of primate lentiviruses downregulates the cell surface expression of CD4 through a two-step process. First, Nef connects the cytoplasmic tail of CD4 with adaptor protein complexes (AP), thereby inducing the formation of CD4-specific clathrin-coated pits that rapidly endocytose the viral receptor. Second, Nef targets internalized CD4 molecules for degradation. Here we show that Nef accomplishes this second task by acting as a connector between CD4 and the beta subunit of COPI coatomers in endosomes. A sequence encompassing a critical acidic dipeptide, located nearby but distinct from the AP-binding determinant of HIV-1 Nef, is responsible for beta-COP recruitment and for routing to lysosomes. A novel class of endosomal sorting motif, based on acidic residues, is thus revealed, and beta-COP is identified as its downstream partner.  (+info)

(7/681) The acidic region and conserved putative protein kinase C phosphorylation site in Nef are important for SIV replication in rhesus macaques.

Variants of the pathogenic SIVmac239 clone with changes in Nef were analyzed to assess the functional relevance of two highly conserved regions in Nef in vitro and in vivo. Changes in a region with an acidic charge (Aci-Nef), or a potential protein kinase C phosphorylation site (PKC-Nef), impaired the ability of Nef to down-regulate CD4 and MHC class I surface expression and to alter CD3-initiated signal transduction in Jurkat T cells. The Aci-Nef, but not the PKC-Nef, associated with the previously described p65 phosphoprotein. SIV containing Aci-Nef, but not SIV containing PKC-Nef, showed reduced infectivity and replication in cell culture systems. One of two rhesus macaques infected with the PKC-Nef mutant virus showed rapid reversion and progressed to disease. In the second animal no reversions and nonprogressive infection was observed. In one of two macaques infected with the Aci-Nef variant, the mutations were stable during the first 40 weeks after infection. Thereafter, variants evolved in which up to six of the eight mutated positions in Nef were reverted and functional activity in vitro was partially restored. These changes occurred concomitantly with increasing viral load and disease progression. The second animal infected with the Aci-Nef variant showed no reversions and remained asymptomatic. Our study suggests that the acidic region and conserved PKC phosphorylation site in Nef are important for SIV replication in rhesus macaques and for several in vitro Nef functions. An almost wild-type activity in in vitro infectivity and replication assays seems insufficient to confer a full nef-positive phenotype in vivo.  (+info)

(8/681) HIV-1 Nef plays an essential role in two independent processes in CD4 down-regulation: dissociation of the CD4-p56(lck) complex and targeting of CD4 to lysosomes.

Human immunodeficiency virus type 1 (HIV-1) Nef down-regulates CD4 by triggering rapid endocytosis of cell surface CD4. To better understand how Nef induces CD4 down-regulation, we generated a series of Nef mutants with small in-frame deletions in the coding region. Three classes of mutants were obtained. The first class produces neither CD4 down-regulation nor dissociation of the CD4-p56(lck) complex. The second class induces CD4 down-regulation in cells lacking p56(lck) expression, but not in cells with p56(lck);these mutants fail to dissociate CD4 from p56lck. These results show that Nef-mediated CD4 dissociation from p56(lck) is important for CD4 down-regulation. The third class of mutants is able to dissociate the CD4-p56(lck) complex but fails to down-regulate surface CD4; internalized CD4 molecules are recycled back to the cell surface. This result suggests that Nef diverts the CD4 recycling pathway to a degradative pathway. We also demonstrate that Nef associates with phosphatidylinositol-3-kinase (PI3K) activity, which is known to be involved in several aspects of membrane trafficking. However, Nef mutants that cause internalized CD4 to be recycled do not associate with PI3K activity; thus Nef-associated PI3K activity might be involved in the latter process of targeting CD4 to a degradative pathway. We conclude that HIV-1 Nef plays a critical role in multiple processes in CD4 down-regulation: (i) disrupting the CD4-p56(lck) complex on the cell surface to allow CD4 internalization and (ii) diverting the internalized CD4 to a lysosomal pathway for its degradation, likely through a PI3K activity.  (+info)