Pathogenic conversion of live attenuated simian immunodeficiency virus vaccines is associated with expression of truncated Nef

Host factors determine differential disease progression after infection with nef-deleted simian immunodeficiency virus

Infection of macaques with live attenuated simian immunodeficiency virus (SIV) usually results in long-lasting efficient protection against infection with pathogenic immunodeficiency viruses. However, attenuation by deletion of regulatory genes such as nef is not complete, leading to a high viral load and fatal disease in some animals. To characterize immunological parameters and polymorphic host factors, we studied 17 rhesus macaques infected with attenuated SIVmac239ΔNU. Eight animals were able to control viral replication, whereas the remaining animals (non-controllers) displayed variable set-point viral loads. Peak viral load at 2 weeks post-infection (p.i.) correlated significantly with set-point viral load (P<0.0001). CD4(+) T-cell frequencies differed significantly soon after infection between controllers and non-controllers. Abnormal B-cell activation previously ascribed to Nef function could already be observed in non-controllers 8 weeks after infection despite the absence of Nef. Two non-controllers developed an AIDS-like disease within 102 weeks p.i. Virus from these animals transmitted to naïve animals replicated at low levels and the recipients did not develop immunodeficiency. This suggested that host factors determined differential viral load and subsequent disease course. Known Mhc class I alleles associated with disease progression in SIV WT infection only marginally influenced the viral load in Δnef-infected animals. Protection from SIVmac251 was associated with homozygosity for MHC class II in conjunction with a TLR7 polymorphism and showed a trend with initial viral replication. We speculated that host factors whose effects were usually masked by Nef were responsible for the different disease courses in individual animals upon infection with nef-deleted viruses.

HIV's Nef interacts with β-catenin of the Wnt signaling pathway in HEK293 cells

The Wnt signaling pathway is implicated in major physiologic cellular functions, such as proliferation, migration, cell fate specification, maintenance of pluripotency and induction of tumorigenicity. Proliferation and migration are important responses of T-cells, which are major cellular targets of HIV infection. Using an informatics screen, we identified a previously unsuspected interaction between HIV’s Nef protein and β-catenin, a key component of the Wnt pathway. A segment in Nef contains identical amino acids at key positions and structurally mimics the β-catenin binding sites on endogenous β-catenin ligands. The interaction between Nef and β-catenin was confirmed in vitro and in a co-immunoprecipitation from HEK293 cells. Moreover, the introduction of Nef into HEK293 cells specifically inhibited a Wnt pathway reporter.

The design and evaluation of HIV-1 vaccines

There is renewed optimism that the goal of developing a highly effective AIDS vaccine is attainable. The HIV-1 vaccine field has seen its first trial of a vaccine candidate that prevents infection. Although modest in efficacy, this finding, along with the recent discovery that the human immune system can produce broadly neutralizing antibodies capable of inhibiting greater than 90% of circulating viruses, provides a guide for the rational design of vaccines and protection by passive immunization. Together, these findings will help shape the next generation of HIV vaccines.

Identification of a highly conserved valine-glycine-phenylalanine amino acid triplet required for HIV-1 Nef function

Background

The Nef protein of HIV facilitates virus replication and disease progression in infected patients. This role as pathogenesis factor depends on several genetically separable Nef functions that are mediated by interactions of highly conserved protein-protein interaction motifs with different host cell proteins. By studying the functionality of a series of nef alleles from clinical isolates, we identified a dysfunctional HIV group O Nef in which a highly conserved valine-glycine-phenylalanine (VGF) region, which links a preceding acidic cluster with the following proline-rich motif into an amphipathic surface was deleted. In this study, we aimed to study the functional importance of this VGF region.

Results

The dysfunctional HIV group O8 nef allele was restored to the consensus sequence, and mutants of canonical (NL4.3, NA-7, SF2) and non-canonical (B2 and C1422) HIV-1 group M nef alleles were generated in which the amino acids of the VGF region were changed into alanines (VGF→AAA) and tested for their capacity to interfere with surface receptor trafficking, signal transduction and enhancement of viral replication and infectivity. We found the VGF motif, and each individual amino acid of this motif, to be critical for downregulation of MHC-I and CXCR4. Moreover, Nef’s association with the cellular p21-activated kinase 2 (PAK2), the resulting deregulation of cofilin and inhibition of host cell actin remodeling, and targeting of Lck kinase to the trans-golgi-network (TGN) were affected as well. Of particular interest, VGF integrity was essential for Nef-mediated enhancement of HIV virion infectivity and HIV replication in peripheral blood lymphocytes. For targeting of Lck kinase to the TGN and viral infectivity, especially the phenylalanine of the triplet was essential. At the molecular level, the VGF motif was required for the physical interaction of the adjacent proline-rich motif with Hck.

Conclusion

Based on these findings, we propose that this highly conserved three amino acid VGF motif together with the acidic cluster and the proline-rich motif form a previously unrecognized amphipathic surface on Nef. This surface appears to be essential for the majority of Nef functions and thus represents a prime target for the pharmacological inhibition of Nef.

CD40L-containing virus-like particle as a candidate HIV-1 vaccine targeting dendritic cells

The central role of dendritic cell (DC) in mounting an immune response to a novel antigen is now well established. We sought to demonstrate the use of a particular vaccine strategy based on directing HIV-1 Gag proteins to DCs in conjunction with an activation signal. CD40L was expressed on the surface of virus-like particles (VLPs) to target HIV-1 Gag antigens to the CD40 receptor on DCs, whereas CD40L-CD40 interaction would also result in cellular activation. Multiple CD40L VLP constructs were made and evaluated in vitro and in vivo. Indeed, one VLP that expressed CD40L to the highest level showed greatest capacity to activate DCs in vitro. Correspondingly, this CD40L-VLP also proved to be most immunogenic in mice in raising both humoral and cellular responses to HIV-1 Gag. Confirmatory studies were performed to demonstrate the increased immunogenicity of CD40L-VLP is no longer observed when tested in CD40-/- mice. Our findings lend support to the belief that vaccine strategies that both target and activate DCs could yield a superior immune response.

The cytokine network of acute HIV infection: a promising target for vaccines and therapy to reduce viral set-point?

Cytokines play a central role in the pathogenesis of many diseases, including HIV infection. However, the role of the cytokine network in early HIV infection is only now starting to be elucidated. A number of studies conducted in recent years have indicated that cytokines of the acute/early stages of HIV and SIV infection can impact viral set-point months later, and this is of critical importance since viral set-point during chronic HIV infection affects virus transmission and disease progression. This raises the question whether modulating the cytokine environment during acute/early HIV infection can be a target for novel approaches to develop a vaccine and therapeutics. In this review we focus on the kinetics and function of cytokines during acute HIV and SIV infection and how these may impact viral set-point. We also discuss unresolved questions that are essential for our understanding of the role of acute infection cytokines in HIV infection and that, if answered, may suggest novel therapeutic and vaccine strategies to control the worldwide HIV pandemic.

Vaccination with live attenuated simian immunodeficiency virus causes dynamic changes in intestinal CD4+CCR5+ T cells

Background

Vaccination with live attenuated SIV can protect against detectable infection with wild-type virus. We have investigated whether target cell depletion contributes to the protection observed. Following vaccination with live attenuated SIV the frequency of intestinal CD4+CCR5+ T cells, an early target of wild-type SIV infection and destruction, was determined at days 3, 7, 10, 21 and 125 post inoculation.

Results

In naive controls, modest frequencies of intestinal CD4+CCR5+ T cells were predominantly found within the LPL T_TrM-1 and IEL T_TrM-2 subsets. At day 3, LPL and IEL CD4+CCR5+ T_EM cells were dramatically increased whilst less differentiated subsets were greatly reduced, consistent with activation-induced maturation. CCR5 expression remained high at day 7, although there was a shift in subset balance from CD4+CCR5+ T_EM to less differentiated T_TrM-2 cells. This increase in intestinal CD4+CCR5+ T cells preceded the peak of SIV RNA plasma loads measured at day 10. Greater than 65.9% depletion of intestinal CD4+CCR5+ T cells followed at day 10, but overall CD4+ T cell homeostasis was maintained by increased CD4+CCR5- T cells. At days 21 and 125, high numbers of intestinal CD4+CCR5- naive T_N cells were detected concurrent with greatly increased CD4+CCR5+ LPL T_TrM-2 and IEL T_EM cells at day 125, yet SIV RNA plasma loads remained low.

Conclusions

This increase in intestinal CD4+CCR5+ T cells, following vaccination with live attenuated SIV, does not correlate with target cell depletion as a mechanism of protection. Instead, increased intestinal CD4+CCR5+ T cells may correlate with or contribute to the protection conferred by vaccination with live attenuated SIV.

Multi-low-dose mucosal simian immunodeficiency virus SIVmac239 challenge of cynomolgus macaques immunized with "hyperattenuated" SIV constructs

Hyperattenuated simian immunodeficiency virus SIVmac239-derived constructs Delta5-CMV and Delta6-CCI are an effort to render SIV incapable of, in practical terms, both reversion and recombination while maintaining the immune features of SIV as a retrovirus. Primary inoculation of cynomolgus macaques with 10(8) 50% tissue culture infective doses (TCID(50)) of Delta5-CMV or Delta6-CCI induced low-level humoral and cellular responses detectable in the absence of measureable in vivo replication. The first of three DNA boosts resulted in elevated gamma interferon (IFN-gamma) enzyme-linked immunospot (ELISPOT) responses to Gag, Pol, and Env in the Delta5-CMV vaccine group compared to the Delta6-CCI vaccine group (P = 0.001). Weekly intrarectal challenge with a low dose of SIVmac239 followed by a dose escalation was conducted until all animals became infected. The mean peak viral load of the Delta5-CMV-vaccinated animals (3.7 x 10(5) copies/ml) was approximately 1 log unit lower than that of the control animals. More dramatically, the viral load set point of these animals was decreased by 3 log units compared to that of the controls (<50 versus 1.64 x 10(4) copies/ml; P < 0.0001). Seventy-five percent (6/8) of vaccine recipients controlled virus below 1,000 copies/ml for at least 6 months, with a subset controlling virus and maintaining substantial CD4 T-cell counts for close to 2 years of follow-up. The correlates of protection from SIV disease progression may lie in the rapidity and protective value of immune responses that occur early in primary SIV infection. Prior immunization with hyperattenuated SIVmac239, even if sterilizing immunity is not achieved, may allow a more advantageous host response.

Gammadelta T cell immune manipulation during chronic phase of simian-human immunodeficiency virus infection [corrected] confers immunological benefits

Vgamma2Vdelta2 T cells, a major human gammadelta T cell subset, recognize the phosphoantigen (E)-4-hydroxy-3-methyl-but-2-enyl pyrophosphate (HMBPP) produced by mycobacteria and some opportunistic pathogens, and they contribute to innate/adaptive/homeostatic and anticancer immunity. As initial efforts to explore Vgamma2Vdelta2 T cell-based therapeutics against HIV/AIDS-associated bacterial/protozoal infections and neoplasms, we investigated whether a well-defined HMBPP/IL-2 therapeutic regimen could overcome HIV-mediated immune suppression to massively expand polyfunctional Vgamma2Vdelta2 T cells, and whether such activation/expansion could impact AIDS pathogenesis in simian HIV (SHIV)-infected Chinese rhesus macaques. While HMBPP/IL-2 coadministration during acute or chronic phase of SHIV infection induced massive activation/expansion of Vgamma2Vdelta2 T cells, the consequences of such activation/expansions were different between these two treatment settings. HMBPP/IL-2 cotreatment during acute SHIV infection did not prevent the increases in peak and set-point viral loads or the accelerated disease progression seen with IL-2 treatment alone. In contrast, HMBPP/IL-2 cotreatment during chronic infection did not exacerbate disease, and more importantly it could confer immunological benefits. Surprisingly, although viral antigenic loads were not increased upon HMBPP/IL-2 cotreatment during chronic SHIV infection, HMBPP activation of Vgamma2Vdelta2 T cells boosted HIV Env-specific Ab titers. Such increases in Abs were sustained for >170 days and were immediately preceded by increased production of IFN-gamma, TNF-alpha, IL-4, and IL-10 during peak expansion of Vgamma2Vdelta2 T cells displaying memory phenotypes, as well as the short-term increased effector function of Vgamma2Vdelta2 T cells and CD4(+) and CD8(+) alphabeta T cells producing antimicrobial cytokines. Thus, HMBPP/Vgamma2Vdelta2 T cell-based intervention may potentially be useful for combating neoplasms and HMBPP-producing opportunistic pathogens in chronically HIV-infected individuals.

Interactions between SIVNef, SIVGagPol and Alix correlate with viral replication and progression to AIDS in rhesus macaques

Infection with Simian Immunodeficiency Virus (SIV) leads to high viral loads and progression to Simian AIDS (SAIDS) in rhesus macaques. The viral accessory protein Nef is required for this phenotype in monkeys as well as in HIV-infected humans. Previously, we determined that HIVNef binds HIVGagPol and Alix for optimal viral replication in cells. In this study, we demonstrated that these interactions could correlate with high viral loads leading to SAIDS in the infected host. By infecting rhesus macaques with a mutant SIV(mac239), where sequences in the nef gene that are required for these interactions were mutated, we observed robust viral replication and disease in two out of four monkeys, where they reverted to the wild type genotype and phenotype. These two rhesus macaques also died of SAIDS. Two other monkeys did not progress to disease and continued to harbor mutant nef sequences. We conclude that interactions between Nef, GagPol and Alix contribute to optimal viral replication and progression to disease in the infected host.

Human immunodeficiency virus type 1 Nef incorporation into virions does not increase infectivity

The viral protein Nef contributes to the optimal infectivity of human and simian immunodeficiency viruses. The requirement for Nef during viral biogenesis particles suggests that Nef might play a role in this process. Alternatively, because Nef is incorporated into viruses, it might play a role when progeny virions reach target cells. We challenged these hypotheses by manipulating the amounts of Nef incorporated in viruses while keeping its expression level constant in producer cells. This was achieved by forcing the incorporation of Nef into viral particles by fusing a Vpr sequence to the C-terminal end of Nef. A cleavage site for the viral protease was introduced between Nef and Vpr to allow the release of Nef fragments from the fusion protein during virus maturation. We show that the resulting Nef-CS-Vpr fusion partially retains the ability of Nef to downregulate cell surface CD4 and that high amounts of Nef-CS-Vpr are incorporated into viral particles compared with what is seen for wild-type Nef. The fusion protein is processed during virion maturation and releases Nef fragments similar to those found in viruses produced in the presence of wild-type Nef. Unlike viruses produced in the presence of wild-type Nef, viruses produced in the presence of Nef-CS-Vpr do not have an increase in infectivity and are as poorly infectious as viruses produced in the absence of Nef. These findings demonstrate that the presence of Nef in viral particles is not sufficient to increase human immunodeficiency virus type 1 infectivity and suggest that Nef plays a role during the biogenesis of viral particles.

Human immunodeficiency virus type 1 Nef induces programmed death 1 expression through a p38 mitogen-activated protein kinase-dependent mechanism

Chronic viral infection is characterized by the functional impairment of virus-specific T-cell responses. Recent evidence has suggested that the inhibitory receptor programmed death 1 (PD-1) is specifically upregulated on antigen-specific T cells during various chronic viral infections. Indeed, it has been reported that human immunodeficiency virus (HIV)-specific T cells express elevated levels of PD-1 and that this expression correlates with the viral load and inversely with CD4(+) T-cell counts. More importantly, antibody blockade of the PD-1/PD-L1 pathway was sufficient to both increase and stimulate virus-specific T-cell proliferation and cytokine production. However, the mechanisms that mediate HIV-induced PD-1 upregulation are not known. Here, we provide evidence that the HIV type 1 (HIV-1) accessory protein Nef can transcriptionally induce the expression of PD-1 during infection in vitro. Nef-induced PD-1 upregulation requires its proline-rich motif and the activation of the downstream kinase p38. Further, inhibition of Nef activity by p38 MAPK inhibitor effectively blocked PD-1 upregulation, suggesting that p38 MAPK activation is an important initiating event in Nef-mediated PD-1 expression in HIV-1-infected cells. These data demonstrate an important signaling event of Nef in HIV-1 pathogenesis.

Pathogenicity and immunogenicity of attenuated, nef-deleted HIV-1 strains in vivo

In efforts to develop an effective vaccine, sterilizing immunity to primate lentiviruses has only been achieved by the use of live attenuated viruses carrying major deletions in nef and other accessory genes. Although live attenuated HIV vaccines are unlikely to be developed due to a myriad of safety concerns, opportunities exist to better understand the correlates of immune protection against HIV infection by studying rare cohorts of long-term survivors infected with attenuated, nef-deleted HIV strains such as the Sydney blood bank cohort (SBBC). Here, we review studies of viral evolution, pathogenicity, and immune responses to HIV infection in SBBC members. The studies show that potent, broadly neutralizing anti-HIV antibodies and robust CD8+ T-cell responses to HIV infection were not necessary for long-term control of HIV infection in a subset of SBBC members, and were not sufficient to prevent HIV sequence evolution, augmentation of pathogenicity and eventual progression of HIV infection in another subset. However, a persistent T-helper proliferative response to HIV p24 antigen was associated with long-term control of infection. Together, these results underscore the importance of the host in the eventual outcome of infection. Thus, whilst generating an effective antibody and CD8+ T-cell response are an essential component of vaccines aimed at preventing primary HIV infection, T-helper responses may be important in the generation of an effective therapeutic vaccine aimed at blunting chronic HIV infection.

The central nervous system in mucosal vaccination of rhesus macaques with simian immunodeficiency virus Deltanef

We studied the central nervous system (CNS) of rhesus macaques during series of vaccination experiments in which attenuated simian immunodeficiency virus (SIV), SIVmac239Deltanef, was applied to the tonsils and the animals were later challenged with pathogenic SIVmac251 or SHIV/89.6P via tonsils or rectum. The pathologic lesions were graded on a scale of 0-5. The lesions were in general very mild, with a score of 0.5, except for one case, in which the animal had progressed to simian AIDS (SAIDS) and had severe lesions of grade 4. Except for the SAIDS case, the most common lesions were meningitis, ependymitis, inflammation of choroid plexus, and astrocytosis. Invasion of the challenge virus, SIVmac251, and pathologic lesions were detected 4 days post infection. The main features of the pathological lesions were similar during short-term follow-up (4 days to 2 weeks) and long-term follow-up (23 to 56 weeks) after challenge. No significant difference was found between unvaccinated controls infected with the challenge viruses and vaccinated and challenged animals. The pathological lesions in the one SAIDS case consisted of extensive lesions of the white matter in connection with confluent ependymitis, indicating an invasion through the choroid plexus. The lesions were characterized by a myriad of multinucleated giant cells of macrophage origin, which showed, together with individual macrophages, strong labelling for viral RNA and proteins. Productive infection of astrocytes was a very rare finding. In three cases infected via tonsils with SIVmac239Deltanef without challenge, we detected expression of Nef-derived peptides, indicating a selective pressure for Nef functions in the CNS.

Vaccination of cats with attenuated feline immunodeficiency virus proviral DNA vaccine expressing gamma interferon

A feline immunodeficiency virus (FIV) provirus with a vif gene deletion (FIVDelta vifATGgamma) that coexpresses feline gamma interferon (IFN-gamma) was tested as a proviral DNA vaccine to extend previous studies showing efficacy with an FIV-pPPRDelta vif DNA vaccine. Cats were vaccinated with either FIVDelta vifATGgamma or FIV-pPPRDelta vif proviral plasmid DNA or with both FIV-pPPRDelta vif DNA and a feline IFN-gamma expression plasmid (pCDNA-IFNgamma). A higher frequency of FIV-specific T-cell proliferation responses was observed in cats immunized with either FIVDelta vifATGgamma or FIV-pPPRDelta vif plus pCDNA-IFNgamma, while virus-specific cytotoxic-T-lymphocyte responses were comparable between vaccine groups. Antiviral antibodies were not observed postvaccination. Virus-specific cellular and humoral responses were similar between vaccine groups after challenge with a biological FIV isolate (FIV-PPR) at 13 weeks postimmunization. All vaccinated and unvaccinated cats were infected after FIV-PPR challenge and exhibited similar plasma virus loads. Accordingly, inclusion of plasmids containing IFN-gamma did not enhance the efficacy of FIV-pPPRDelta vif DNA immunization. Interestingly, the lack of protection associated with FIV-pPPRDelta vif DNA immunization contrasted with findings from a previous study and suggested that multiple factors, including timing of FIV-pPPRDelta vif inoculations and challenge, as well as route of challenge virus delivery, may significantly impact vaccine efficacy.

HIV-1 Nef selectively activates Src family kinases Hck, Lyn, and c-Src through direct SH3 domain interaction

Nef is an HIV-1 virulence factor that promotes viral pathogenicity by altering host cell signaling pathways. Nef binds several members of the Src kinase family, and these interactions have been implicated in the pathogenesis of HIV/AIDS. However, the direct effect of Nef interaction on Src family kinase (SFK) regulation and activity has not been systematically addressed. We explored this issue using Saccharomyces cerevisiae, a well defined model system for the study of SFK regulation. Previous studies have shown that ectopic expression of c-Src arrests yeast cell growth in a kinase-dependent manner. We expressed Fgr, Fyn, Hck, Lck, Lyn, and Yes as well as c-Src in yeast and found that each kinase was active and induced growth suppression. Co-expression of the negative regulatory kinase Csk suppressed SFK activity and reversed the growth-inhibitory effect. We then co-expressed each SFK with HIV-1 Nef in the presence of Csk. Nef strongly activated Hck, Lyn, and c-Src but did not detectably affect Fgr, Fyn, Lck, or Yes. Mutagenesis of the Nef PXXP motif essential for SH3 domain binding greatly reduced the effect of Nef on Hck, Lyn, and c-Src, suggesting that Nef activates these Src family members through allosteric displacement of intramolecular SH3-linker interactions. These data show that Nef selectively activates Hck, Lyn, and c-Src among SFKs, identifying these kinases as proximal effectors of Nef signaling and potential targets for anti-HIV drug discovery.

Interactions between Nef and AIP1 proliferate multivesicular bodies and facilitate egress of HIV-1

Background

Nef is an accessory protein of primate lentiviruses, HIV-1, HIV-2 and SIV. Besides removing CD4 and MHC class I from the surface and activating cellular signaling cascades, Nef also binds GagPol during late stages of the viral replicative cycle. In this report, we investigated further the ability of Nef to facilitate the replication of HIV-1.

Results

To this end, first the release of new viral particles was much lower in the absence of Nef in a T cell line. Since the same results were obtained in the absence of the viral envelope using pseudo-typed viruses, this phenomenon was independent of CD4 and enhanced infectivity. Next, we found that Nef not only possesses a consensus motif for but also binds AIP1 in vitro and in vivo. AIP1 is the critical intermediate in the formation of multivesicular bodies (MVBs), which play an important role in the budding and release of viruses from infected cells. Indeed, Nef proliferated MVBs in cells, but only when its AIP1-binding site was intact. Finally, these functions of Nef were reproduced in primary macrophages, where the wild type but not mutant Nef proteins led to increased release of new viral particles from infected cells.

Conclusion

We conclude that by binding GagPol and AIP1, Nef not only proliferates MVBs but also contributes to the egress of viral particles from infected cells.

Vaccination of mice with replication-defective human immunodeficiency virus induces cellular and humoral immunity and protects against vaccinia virus-gag challenge

Here we describe as a potential vaccine candidate a replication-defective HIV that encodes multiple viral genes in addition to a cassette that includes both truncated cyclin T1 and an autofluorescent protein. After confirming functionality of the cyclin T1, we immunized mice intramuscularly once or twice with the replication-defective HIV vector pseudotyped with vesicular stomatitis virus (VSV) G protein (RD HIV), a plasmid encoding CMV-driven gag (gag DNA), or adenovirus gag (Ad5-gag). Capsid-specific antibody titers following RD HIV immunization were >10(6)/ml and approximately equivalent to those induced by gag DNA and Ad5-gag. Antibodies against the autofluorescent protein and VSV G were also detected. After RD HIV immunization ELISpot assays demonstrated Gag-specific interferon-gamma (IFN-gamma) SFU equivalent to that of Ad5-gag and fourfold greater than that of gag DNA. HIV polymerase-specific IFN-gamma SFU values were similar, and boosting increased both antibody titers and the IFN-gamma response. Challenge using vaccinia virus (VV)-gag demonstrated significantly lower recoverable VV for RD HIV-immunized mice compared to controls. No significant differences were observed in vaccinated mice challenged with wild-type VV. This study demonstrates the efficacy of RD HIV in conferring HIV-specific immunity and protection in mice and suggests its potential use in humans as either a prophylactic or a therapeutic vaccine.

Construction and characterization of feline immunodeficiency virus proviral mutants that coexpress interferon gamma and green fluorescent protein

Vif deletion mutants of the feline immunodeficiency virus (FIV) were designed to express either enhanced green fluorescent protein (EGFP) (FIVdeltavifATGgfp) or feline interferon-gamma (IFN-gamma) (FIVdeltavifATGgamma) by insertion of the nonviral gene into the deletion site of the viral vif gene. Two in-frame start codons within vif were mutated without altering the overlapping pol translation frame to enhance expression of inserted genes. Expression of EGFP and IFN-gamma from FIVdeltavifATGgfp and FIVdeltavifATGgamma proviruses, respectively, was confirmed by fluorescent microscopy and immunocytochemical assays, respectively. Replication of viruses generated from these proviruses was detectable but severely restricted when compared to that of wild-type (WT) FIV-pPPR. A previous study demonstrated induction of protection against homologous FIV challenge by vaccination of cats with an attenuated FIV-pPPRdeltavif proviral DNA vaccine (Lockridge K et al.: Virology 2000;273:67-79). Coexpression of IFN-gamma or other cytokines from this attenuated provirus provides the opportunity to evaluate the ability of an immunomodulator to enhance the safety and efficacy of an infectious attenuated DNA vaccine. Moreover, a vif-deleted FIV provirus that coexpresses a reporter gene such as EGFP may be used to examine the localization of vif mutant viruses in vivo.

Protein kinase CK2 phosphorylates the Nef protein from a neurovirulent simian immunodeficiency virus

The Nef protein of Human Immunodeficiency Virus (HIV) and Simian Immunodeficiency Virus (SIV) is a pluripotent accessory protein that plays a critical role in disease progression. One analogous characteristic of Nef proteins from SIV and HIV is the ability to associate with cellular kinases. We have previously reported that the Nef protein from a macrophage-tropic neurovirulent SIV clone, SIV/17E-Fr, is associated with an unknown kinase activity that is distinct from the p21-associated kinase that interacts with SIVmac239 Nef. Using site-directed mutagenesis and kinase-specific inhibitors, we have identified this kinase as the ubiquitous serine/threonine kinase, protein kinase CK2.

Longitudinal analysis of human immunodeficiency virus type 1 nef/long terminal repeat sequences in a cohort of long-term survivors infected from a single source

We studied the evolution of human immunodeficiency virus type 1 (HIV-1) in a cohort of long-term survivors infected with an attenuated strain of HIV-1 acquired from a single source. Although the cohort members experienced differing clinical courses, we demonstrate similar evolution of HIV-1 nef/long-terminal repeat (LTR) sequences, characterized by progressive sequence deletions tending toward a minimal nef/LTR structure that retains only sequence elements required for viral replication. The in vivo pathogenicity of attenuated HIV-1 is therefore dictated by viral and/or host factors other than those that impose a unidirectional selection pressure on the nef/LTR region of the HIV-1 genome.

Activation of p21-activated kinase 2 and its association with Nef are conserved in murine cells but are not sufficient to induce an AIDS-like disease in CD4C/HIV transgenic mice

A well conserved feature of human immunodeficiency virus, type 1 (HIV-1) and simian immunodeficiency virus (SIV) Nef is the interaction with and activation of the human p21-activated kinase 2 (PAK2). The conservation of this interaction in other species and its significance for Nef pathogenesis in vivo are poorly documented. In the present study, we measured these parameters in Nef-expressing thymocytes, macrophages, and dendritic cells of a transgenic (Tg) mouse model of AIDS (CD4C/HIV). We found that Nef binds to and activates PAK2, but not PAK1 and -3, in these three cell subsets. Nef associates with only a small fraction of PAK2. The Nef-PAK2 complex also comprises beta-PIX-COOL. The impact of the Nef-PAK2 association on disease development was also analyzed in Tg mice expressing 10 different Nef mutant alleles. CD4C/HIV Tg mice expressing Nef alleles defective in Nef-PAK2 association (P69A, P72A/P75A, R105A/R106A, Delta56-66, or G2A (myristoylation site)) failed to develop disease of the non-lymphoid organs (kidneys and lungs). Among these, only Tg mice expressing Nef(P69A) and Nef(G2A) showed some depletion of CD4(+) T cells, although a down-regulation of the CD4 surface protein was documented in all these Tg lines, except those expressing Nef(Delta56-66). Among other Tg mice expressing Nef mutants having conserved the Nef-PAK2 association (RD35AA, D174K, P147A/P150A, Delta8-17, and Delta25-65), only Tg mice expressing Nef(Delta8-17) develop kidney and lung diseases, but all showed partial CD4(+) T cell depletion despite some being defective for CD4 down-regulation (RD35AA and D174K). Therefore, Nef can activate murine PAK2 and associate with a small fraction of it, as in human cells. Such activation and binding of PAK2 is clearly not sufficient but may be required to induce a multiorgan AIDS-like disease in Tg mice.

CD8+ lymphocytes do not mediate protection against acute superinfection 20 days after vaccination with a live attenuated simian immunodeficiency virus

In order to test the hypothesis that CD8+ cytotoxic T lymphocytes mediate protection against acute superinfection, we depleted >99% of CD8+ lymphocytes in live attenuated simian immunodeficiency virus macC8 (SIVmacC8) vaccinees from the onset of vaccination, maintained that depletion for 20 days, and then challenged with pathogenic, wild-type SIVmacJ5. Vaccinees received 5 mg per kg of humanized anti-CD8 monoclonal antibody (MAb) 1 h before inoculation, followed by the same dose again on days 3, 7, 10, 13, and 17. On day 13, peripheral CD8+ T lymphocytes were >99% depleted in three out of four anti-CD8 MAb-treated vaccinees. At this time attenuated SIVmacC8 viral RNA loads in anti-CD8 MAb-treated vaccinees were significantly higher than control vaccinees treated contemporaneously with nonspecific human immunoglobulin. Lymphoid tissue CD8+ T lymphocyte depletion was >99% in three out of four anti-CD8 MAb-treated vaccinees on the day of wild-type SIVmacJ5 challenge. All four control vaccinees and three out of four anti-CD8 MAb-treated vaccinees were protected against detectable superinfection with wild-type SIVmacJ5. Although superinfection with wild-type SIVmacJ5 was detected at postmortem in a single anti-CD8 MAb-treated vaccinee, this did not correlate with the degree of preceding CD8+ T lymphocyte depletion. Clearance of attenuated SIVmacC8 viremia coincided with recovery of normal CD8+ T lymphocyte counts between days 48 and 76. These results support the view that cytotoxic T lymphocytes are important for host-mediated control of SIV primary viremia but do not indicate a central role in protection against acute superinfection conferred by inoculation with live attenuated SIV.

Evolution of nef variants in gut associated lymphoid tissue of rhesus macaques during primary simian immunodeficiency virus infection

We utilized the simian immunodeficiency virus model of AIDS to examine evolution of nef gene in gut-associated lymphoid tissue (GALT) during primary and early asymptomatic stages of infection. Macaques were infected with a cloned virus, SIVmac239/nef-stop harboring a premature stop codon in the nef gene. Restoration of the nef open reading frame occurred in GALT early at 3 days post-infection. Analysis of nef sequences by phylogenetic tools showed that evolution of nef was neutral thereafter, as evidenced by the ratio of synonymous to nonsynonymous substitutions, a star pattern in unrooted trees and distribution of amino acid replacements fitting a simple Poisson process. Two regions encoding for a nuclear localization signal and a CTL epitope were conserved. Thus, GALT was a site for strong positive selection of functional nef during initial stages of infection. However, evolution of the nef gene thereafter was neutral during early asymptomatic stage of infection.

Evaluation of live feline immunodeficiency virus vaccines with modified antigenic properties

Live-attenuated viruses have typically been generated from pathogenic viruses by genetic modifications that modified their replicative capacity. The present study investigated whether modification of the antigenic properties of live-attenuated viruses might improve upon the protection that such vaccines afford against lentivirus infection. In a previous study, random amino acid substitutions were introduced into the transmembrane envelope glycoprotein of the feline immunodeficiency virus (FIV), within a highly conserved domain (principal immunodominant domain) bearing immunodominant B-cell epitopes. Amongst a wide set of mutants, mutations that modified antibody specificity without abolishing infectivity ex vivo were selected. In the present study, two such mutants, TN14 and TN92, were evaluated for their replicative capacities and pathogenic properties in vivo in comparison with the parental virus, FIV 34TF10. No significant differences in viral load were observed between mutant and parental viruses. After 1 year of infection, all animals were subjected to a heterologous intraclade superinfection with a primary strain of FIV. Whilst both parental and modified viruses protected cats from high viral loads after superinfection, the TN92 virus afforded a higher degree of protection (P=0·0079). Such improvement in protection might correlate with a decrease in the immunogenicity of a B-cell epitope potentially involved in antibody enhancement of infection.

Non-human primate models for AIDS vaccine research

Since the discovery of simian immunodeficiency viruses (SIV) causing AIDS-like diseases in Asian macaques, non-human primates (NHP) have played an important role in AIDS vaccine research. A multitude of vaccines and immunization approaches have been evaluated, including live attenuated viruses, DNA vaccines, viral and bacterial vectors, subunit proteins, and combinations thereof. Depending on the particular vaccine and model used, varying degrees of protection have been achieved, including prevention of infection, reduction of viral load, and amelioration of disease. In a few instances, potential safety concerns and vaccine-enhanced pathogenicity have also been noted. In the past decade, sophisticated methodologies have been developed to define the mechanisms of protective immunity. However, a clear road map for HIV vaccine development has yet to emerge. This is in part because of the intrinsic nature of the surrogate model and in part because of the improbability of any single model to fully capture the complex interactions of natural HIV infection in humans. The lack of standardization, the limited models available, and the incomplete understanding of the immunobiology of NHP contribute to the difficulty to extrapolate findings from such models to HIV vaccine development. Until efficacy data become available from studies of parallel vaccine concepts in humans and macaques, the predictive value of any NHP model remains unknown. Towards this end, greater appreciation of the utility and limitations of the NHP model and further developments to better mimic HIV infection in humans will likely help inform future AIDS vaccine efforts.

Current situation in the development of a preventive HIV vaccine

The uncontrolled progression of the aids epidemic has made the development of an efficacious human immunodeficiency virus (HIV) vaccine a major objective of scientific research. No effective preventive vaccine against HIV is currently available and sterilizing immunity has not yet been achieved in animal models. This review analyses the major challenges in developing an aids vaccine, in particular the mechanisms involved in viral escape from the immune response, and summarizes the results obtained with the different prototypes of therapeutic and preventive vaccines. Finally, social, economic and healthcare aspects of research into HIV vaccines and current controversies regarding the development of clinical trials are discussed.

Situación actual en el desarrollo de una vacuna preventiva frente al VIH

El avance de la epidemia de sida ha convertido la obtención de una vacuna eficaz frente al virus de la inmunodeficiencia humana (VIH) como un objetivo científico prioritario. En el momento actual no disponemos de una vacuna preventiva frente a la infección por el VIH y en ningún modelo animal se ha conseguido la protección frente a la infección. En esta revisión se analizan las dificultades existentes en el desarrollo de una vacuna contra el sida, en especial los mecanismos de escape viral a la respuesta inmunitaria y se describen los prototipos de vacunas preventivas y terapéuticas en desarrollo y los resultados obtenidos. Por otra parte se sitúa esta investigación en el contexto sanitario, económico y social de la pandemia de sida y se analizan las polémicas actualmente planteadas en el desarrollo de ensayos clínicos con los diferentes tipos de vacunas.

Disease progression in macaques with low SIV replication levels: on the relevance of TREC counts

BACKGROUND

An attenuated immunodeficiency virus has been long considered innocuous. Nevertheless, converging data suggest that low levels of viral replication can still provoke AIDS. Pathogenesis of these attenuated infections is not understood.

OBJECTIVES

To determine the pathogenicity of a long-term attenuated infection and to delineate T-cell dynamics during such an infection.

METHODS

This is a cross-sectional study of 12 rhesus macaques infected with SIV Delta nef for 8 years. We evaluated apoptosis (annexin V), activation (HLA-DR, Ki67), and newly generated T cells (TCR excision circle: TREC).

RESULTS

Infection with SIV Delta nef induced pathological CD4 T-cell depletion after 8 years of infection. Virus replication and CD8 T-cell activation positively correlated with the rate of disease progression. The frequency of TREC within CD8+CD45RA+ cells increased in SIV Delta nef-infected animals compared to age-matched non-infected controls. Moreover, in the cohort of infected animals, TREC+CD45RA+CD4+ T-cell counts correlated strongly with non-progression to AIDS. The animal with the lowest rate of disease progression exhibited a 115-fold increase in TREC+CD45RA+CD4+ T-cell counts compared to age-matched non-infected controls. In contrast, the animal showing the fastest rate of progression to AIDS displayed 600-fold lower TREC+CD45RA+CD4+ T-cell counts compared to age-matched non-infected controls.

CONCLUSIONS

Our results suggest that the thymus plays a major role in the pathogenesis of an attenuated SIV infection and that a sustained thymic output could maintain CD4 T-cell homeostasis in the context of low viral loads.

Evaluation of feline immunodeficiency virus ORF-A mutants as candidate attenuated vaccine

Feline immunodeficiency virus (FIV) made defective in the accessory gene ORF-A were previously shown to be greatly attenuated in its ability to replicate in lymphocytes but to grow normally or near normally in other cell types. Here, we examined whether FIV thus mutated could protect specific pathogen-free cats against challenge with ex vivo fully virulent homologous virus. No reversion of the vaccinating infections to wild type ORF-A was noted over 22 months of in vivo infection. Following challenge, 6/6 unvaccinated control cats became readily and heavily infected. In contrast, 3/9 vaccinees showed no evidence of the challenge virus over a 15-month observation period. In the other vaccinees, the challenge virus was predominant for various periods of time, but pre-existing viral loads and CD4 lymphocyte counts were either unaffected or altered only marginally and transiently. These findings show that ORF-A-defective FIV should be further examined as a candidate live attenuated vaccine.

Comprehensive analysis of nef functions selected in simian immunodeficiency virus-infected macaques

A variety of simian immunodeficiency virus (SIVmac) nef mutants have been investigated to clarify which in vitro Nef functions contribute to efficient viral replication and pathogenicity in rhesus macaques. Most of these nef alleles, however, were only functionally characterized for their ability to down-modulate CD4 and class I major histocompatibility complex (MHC-I) cell surface expression and to enhance SIV replication and infectivity. To obtain information on the in vivo relevance of more recently established Nef functions, we examined the ability of a large panel of constructed SIVmac Nef mutants and of variants that emerged in infected macaques to down-regulate CD3, CD28, and MHC-II and to up-regulate the MHC-II-associated invariant chain (Ii). We found that all these four Nef functions were restored in SIV-infected macaques. In most cases, however, the initial mutations and the changes selected in vivo affected several in vitro Nef functions. For example, truncated Nef proteins that emerged in animals infected with SIVmac239 containing a 152-bp deletion in nef efficiently modulated both CD3 and Ii surface expression. Overall, our results suggest that the effect of Nef on each of the six cellular receptors investigated contributes to viral fitness in the infected host but also indicate that modulation of CD3, MHC-I, MHC-II, or Ii surface expression alone is insufficient for SIV virulence.

Macaques infected long-term with attenuated simian immunodeficiency virus (SIVmac) remain resistant to wild-type challenge, despite declining cytotoxic T lymphocyte responses to an immunodominant epitope

To further investigate mechanisms of protective immunity that are induced by live, attenuated simian immunodeficiency virus (SIV), three macaques were infected with SIVmacGX2, a nef-disrupted molecular clone. In two of these animals, which expressed the MamuA*01 major histocompatibility complex class I allele, loss of functional activity against an SIV-Gag-encoded immunodominant cytotoxic T lymphocyte (CTL) epitope was observed following prolonged infection. Nonetheless, all three animals were resistant to challenge with an uncloned pool of wild-type SIVmac, whereas four naïve controls became infected. Tetramer staining revealed the rapid generation of CD8+ T-cell responses against gag- and tat-encoded immunodominant epitopes in MamuA*01+ challenge controls. The dynamics of these T-cell responses to the wild-type virus were similar to those observed following primary infection of the vaccine group with attenuated virus. In contrast, neither tetramer staining nor gamma interferon ELISpot assay revealed an immediate, systemic, anamnestic response in the wild-type-challenged, attenuated SIV-infected animals. Functional CTL capacity had not been lost in this group, as lytic activity was still evident 17 weeks after challenge. Both attenuated and wild-type viruses induced a disseminated CD8+ T-cell response, which was of a higher magnitude in lymphoid tissues than in the periphery. These results suggest that, at least as measured in the periphery, protection against wild-type infection that is induced by live, attenuated SIV is not dependent on a rechallenge-driven expansion of immunodominant epitope-specific CD8+ T cells and, therefore, pre-existing activity may be sufficient to prevent superinfection.

A human immunodeficiency virus type 1-infected individual with low viral load harbors a virus variant that exhibits an in vitro RNA dimerization defect

We investigated the in vitro RNA dimerization properties of the untranslated leader RNA derived from human immunodeficiency virus type 1 variants circulating in an individual with a low viral load and slow disease progression. The leader sequences of these viruses contain highly unusual polymorphisms within the dimerization initiation site (DIS): an insert that abolishes dimerization and a compensatory substitution. The dimerization of leader RNA from late stages of infection is further improved by additional mutations outside the DIS motif that facilitate a secondary structure switch from a dimerization-incompetent to a dimerization-competent RNA conformation.

Nef binds p6* in GagPol during replication of human immunodeficiency virus type 1

The atypical Nef protein (NefF12) from human immunodeficiency virus type 1 strain F12 (HIV-1(F12)) interferes with virion production and infectivity via a mysterious mechanism. The correlation of these effects with the unusual perinuclear subcellular localization of NefF12 suggested that the wild-type Nef protein could bind to assembly intermediates in late stages of viral replication. To test this hypothesis, Nef from HIV-1(NL4-3) was fused to an endoplasmic reticulum (ER) retention signal (NefKKXX). This mutant NefKKXX protein recapitulated fully the effects of NefF12 on on Gag processing and virion production, either alone or as a CD8 fusion protein. Importantly, the mutant NefKKXX protein also localized to the intermediate compartment, between the ER and the trans-Golgi network. Furthermore, Nef bound the GagPol polyprotein in vitro and in vivo. This binding mapped to the C-terminal flexible loop in Nef and the transframe p6* protein in GagPol. The significance of this interaction was demonstrated by a genetic assay in which the release of a mutant HIV-1 provirus lacking the PTAP motif in the late domain that no longer binds Tsg101 was rescued by a Nef.Tsg101 chimera. Importantly, this rescue as well as incorporation of Nef into HIV-1 virions correlated with the ability of Nef to interact with GagPol. Our data demonstrate that the retention of Nef in the intermediate compartment interferes with viral replication and suggest a new role for Nef in the production of HIV-1.

Live attenuated HIV vaccines: pitfalls and prospects

PURPOSE OF REVIEW

When simian immunodeficiency virus (SIV) deleted in the nef gene caused no disease in macaques and provided protection against wild-type SIV challenge, hopes were high that the removal of nef would convert a pathogenic immunodeficiency virus into a live attenuated vaccine. We seek to highlight recent studies focused on several major issues regarding live attenuated AIDS viruses as vaccine candidates: (1). safety, (2). efficacy, (3). the correlates of immune protection, and (4) the molecular determinants for lentiviral virulence or attenuation.

RECENT FINDINGS

Nef-deletion mutants have retained virulence; compared with wild-type SIV, disease progression was slowed but not abrogated. After long-term observation, all adult macaques given SIVmac239delta3 exhibited immune dysfunction; over 50% had T-cell depletion, and 18% developed AIDS. Vaccine efficacy has been disappointing, with limited or no cross-protection and no protection against homologous virus challenge years after initial vaccination. To date, the correlates of protective immunity have defied precise definition; no dominant mechanism has yet emerged. Data from passive serum transfer and CD8+ T-cell depletion studies have raised the possibility that alternate mechanism of protection may be operative. Due to relentless viral replication and continuous selective pressure, initially benign viruses can generate virulent progeny with unpredictable genotypes.

SUMMARY

Neither safety nor efficacy of the current live attenuated primate immunodeficiency virus vaccines has withstood the test of time. However, such viruses are invaluable tools to address two key questions: (1). what are the correlates of protection, and (2). what are the molecular determinants of viral immunopathogenesis?

Simian immunodeficiency virus promoter exchange results in a highly attenuated strain that protects against uncloned challenge virus

Among the many simian immunodeficiency virus (SIV) immunogens, only live attenuated viral vaccines have afforded strong protection to a natural pathogenic isolate. Since the promoter is crucial to the tempo of viral replication in general, it was reasoned that promoter exchange might confer a novel means of attenuating SIV. The core enhancer and promoter sequences of the SIV macaque 239nefstop strain (NF-kappaB/Sp1 region from -114 bp to mRNA start) have been exchanged for those of the human cytomegalovirus immediate-early promoter (CMV-IE; from -525 bp to mRNA start). During culture of the resulting virus, referred to as SIVmegalo, on CEMx174 or rhesus macaque peripheral blood mononuclear cells, deletions arose in distal regions of the CMV-IE sequences that stabilized after 1 or 2 months of culture. However, when the undeleted form of SIVmegalo was inoculated into rhesus macaques, animals showed highly controlled viremia during primary and persistent infection. Compared to parental virus infection in macaques, primary viremia was reduced by >1,000-fold to undetectable levels, with little sign of an increase of cycling cells in lymph nodes, CD4(+) depletion, or altered T-cell activation markers in peripheral blood. Moreover, in contrast to wild-type infection in most infected animals, the nef stop mutation did not revert to the wild-type codon, indicating yet again that replication was dramatically curtailed. Despite such drastic attenuation, antibody titers and enzyme-linked immunospot reactivity to SIV peptides, although slower to appear, were comparable to those seen in a parental virus infection. When animals were challenged intravenously at 4 or 6 months with the uncloned pathogenic SIVmac251 strain, viremia was curtailed by approximately 1,000-fold at peak height without any sign of hyperactivation in CD4(+)- or CD8(+)-T-cell compartment or increase in lymph node cell cycling. To date, there has been a general inverse correlation between attenuation and protection; however, these findings show that promoter exchange constitutes a novel means to highly attenuate SIV while retaining the capacity to protect against challenge virus.

HIV-1 Nef protein in the nucleus influences adipogenesis as well as viral transcription through the peroxisome proliferator-activated receptors

BACKGROUND

Although the HIV-1 Nef protein (27 kDa) localizes primarily in cytoplasm, there is considerable evidence suggesting its occasional localization in the nucleus. Nef is known to play an important role in transcriptional events and viral replication, but the actual target of Nef in the nucleus remains to be identified.

OBJECTIVE

To examine the functional roles of Nef in the nucleus and its possible interactions with other unknown factors in the nucleus.

METHODS

High-density microarray analysis was used to screen directly the unique functions of Nef on host gene transcription. The nuclear localization of Nef and its effects on the expression of peroxisome proliferator-activated receptors (PPAR) was examined using PPAR promoter/reporter assay and immunoblotting. A long terminal repeat/reporter assay was used to investigated the effects of Nef and PPAR on viral transcription.

RESULTS

Nef in the nucleus suppressed PPAR gamma expression and reduced fatty acid levels in human T and macrophage cell lines. Expression of Nef or PPAR suppressed viral replication; the effect of PPAR gamma or retinoid X receptor-alpha on viral replication were reduced by coexpression of Nef in MT(-)4 T cells.

CONCLUSION

Nef may be involved in both viral replication and the wasting syndrome associated with AIDS.

High Attenuation and Immunogenicity of a Simian Immunodeficiency Virus Expressing a Proteolysis-resistant Inhibitor of NF-κB

NF-kappaB/IkappaB proteins play a major role in the transcriptional regulation of human immunodeficiency virus, type-1 (HIV-1). In the case of simian immunodeficiency virus (SIV) the cellular factors required for the viral transcriptional activation and replication in vivo remain undefined. Here, we demonstrate that the p50/p65 NF-kappaB transcription factors enhanced the Tat-mediated transcriptional activation of SIVmac239. In addition, IkappaB-alpha S32/36A, a proteolysis-resistant inhibitor of NF-kappaB, strongly inhibited the Tat-mediated transactivation of SIVmac239. Based on this evidence, we have generated a self-regulatory virus by endowing the genome of SIV-mac239 with IkappaB-alpha S32/36A; the resulting virus, SIVIkappaB-alpha S32/36A, was nef-deleted and expressed the NF-kappaB inhibitor. We show that SIVIkappaB-alpha S32/36A was highly and stably attenuated both in cell cultures and in vivo in rhesus macaque as compared with a nef-deleted control virus. Moreover, the high attenuation was associated with a robust immune response as measured by SIV-specific antibody production, tetramer, and intracellular IFN-gamma staining of SIV gag-specific T cells. These results underscore the crucial role of NF-kappaB/IkappaB proteins in the regulation of SIV replication both in cell cultures and in monkeys. Thus, inhibitors of NF-kappaB could efficiently counteract the SIV/HIV replication in vivo and may assist in developing novel approaches for AIDS vaccine and therapy.

CD4 and major histocompatibility complex class I downregulation by the human immunodeficiency virus type 1 nef protein in pediatric AIDS progression

The human immunodeficiency virus type 1 (HIV-1) nef gene is a crucial determinant in AIDS disease progression. Although several in vitro activities have been attributed to the Nef protein, identifying the one critical for in vivo pathogenicity remains elusive. In this study, we examined a large number of nef alleles derived at various time points from 13 perinatally infected children showing different progression rates: six nonprogressors (NPs), three slow progressors (SPs), and four rapid progressors (RPs). The patient-derived nef alleles were analyzed for their steady-state expression of a Nef protein, for their relative ability to downregulate cell surface expression of CD4 and major histocompatibility complex class I (MHC-I) and for their capacity to bind the clathrin adaptor AP-1 complex. We found that NP-derived nef alleles, compared to nef alleles isolated from SPs and RPs, had reduced CD4 and MHC-I downregulation activities. In contrast, SP- and RP-derived nef alleles did not differ and efficiently downregulated both CD4 and MHC-I. AP-1 binding was a conserved function of primary nef alleles not correlated with clinical progression. Defective Nef proteins from NPs, rather than sharing common specific changes in their sequences, accumulated various amino acid substitutions, mainly located outside the conserved domains previously associated with Nef biological properties. Our data indicate that Nef-mediated downregulation of cell surface CD4 and MHC-I significantly contributes to the expression of the pathogenic potential of HIV-1.

The effects of HHV-8 vMIP-II on SIVmac251 infection and replication competent and incompetent SIVmac239Delta3 vectors

Human herpesvirus type 8 vMIP-II has one of the broadest ranges of chemokine receptor binding and therefore a multiplicity of biologic effects, both immunologic and antiviral. These properties make vMIP-II an attractive effector gene to be expressed from gene therapy vectors. The present studies were concerned with both therapeutic approaches: (1) an anti-simian immunodeficiency virus (SIV) biologic, and (2) an effector gene in SIV-based vectors. Regarding its antiviral properties, vMIP-II expressed from bacteria and SIV-based vectors bound the surface of CEMx174 cells and specifically suppressed SIVmac251 infection. A CCR3 monoclonal antibody partially inhibited vMIP-II binding, suggesting that both SIVmac251 and vMIP-II utilize a similar CCR3-like receptor for CEMx174 cell binding. Replication competent SIV-based vectors containing forward and reverse vMIP-II produced neither identifiable vMIP-II nor virions for the first 21 days. Virus replication occurred after this period. Significant sequence alterations in the forward vMIP-II containing replication competent vector transcripts were responsible for the failure of vMIP-II expression. The genetic basis for the initial failure to replicate virus and its later restoration was not determined but appeared in the II-PIMv containing vectors to coincide with deletions and compensatory rearrangements in nef 3' of the polypurine tract. Cells transfected with SIVmac239Delta3DeltaLTR-vMIP-II vectors expressed biologically active vMIP-II that bound CEMx174 cells and suppressed SIVmac251 infection. These data suggest that replication defective SIV vectors expressing immunobiolgic genes such as vMIP-II may prove useful in gene therapies, particularly in augmenting immune responses in chronically infected individuals.

Potent, persistent induction and modulation of cellular immune responses in rhesus macaques primed with Ad5hr-simian immunodeficiency virus (SIV) env/rev, gag, and/or nef vaccines and boosted with SIV gp120

Immunity elicited by multicomponent vaccines delivered by replication-competent Ad5hr-simian immunodeficiency virus (SIV) recombinants was systematically investigated. Rhesus macaques were immunized mucosally at weeks 0 and 12 with Ad5hr-SIV(smH4) env/rev, with or without Ad5hr-SIV(mac239) gag or Ad5hr-SIV(mac239) nef, or with all three recombinants. The total Ad5hr dosage was comparably adjusted among all animals with empty Ad5hr-DeltaE3 vector. The macaques were boosted with SIV gp120 in monophosphoryl A-stable emulsion adjuvant at 24 and 36 weeks. Controls received Ad5hr-DeltaE3 vector or adjuvant only. By ELISPOT analysis, all four SIV gene products elicited potent cellular immune responses that persisted 42 weeks post-initial immunization. Unexpectedly, modulation of this cellular immune response was observed among macaques receiving one, two, or three Ad5hr-SIV recombinants. Env responses were significantly enhanced throughout the immunization period in macaques immunized with Ad5hr-SIV env/rev plus Ad5hr-SIV gag and tended to be higher in macaques that also received Ad5hr-SIV nef. Macaques primed with all three recombinants displayed significant down-modulation in numbers of gamma interferon (IFN-gamma)-secreting cells specific for SIV Nef, and the Env- and Gag-specific responses were also diminished. Modulation of antibody responses was not observed. Down-modulation was seen only during the period of Ad5hr-recombinant priming, not during subunit boosting, although SIV-specific IFN-gamma-secreting cells persisted. The effect was not attributable to Ad5hr replication differences among immunization groups. Vaccine delivery via replication-competent live vectors, which can persistently infect new cells and continuously present low-level antigen, may be advantageous in overcoming competition among complex immunogens for immune recognition. Effects of current multicomponent vaccines on individual immune responses should be evaluated with regard to future vaccine design.

Determinants of increased replicative capacity of serially passaged simian immunodeficiency virus with nef deleted in rhesus monkeys

Most rhesus macaques infected with simian immunodeficiency virus SIVmac239 with nef deleted (either Delta nef or Delta nef Delta vpr Delta US [Delta 3]) control viral replication and do not progress to AIDS. Some monkeys, however, develop moderate viral load set points and progress to AIDS. When simian immunodeficiency viruses (SIVs) recovered from two such animals (one Delta nef and the other Delta 3) were serially passaged in rhesus monkeys, the SIVs derived from both lineages were found to consistently induce moderate viral loads and disease progression. Analysis of viral sequences in the serially passaged derivatives revealed interesting changes in three regions: (i) an unusually high number of predicted amino acid changes (12 to 14) in the cytoplasmic domain of gp41, most of which were in regions that are usually conserved; these changes were observed in both lineages; (ii) an extreme shortening of nef sequences in the region of overlap with U3; these changes were observed in both lineages; and (iii) duplication of the NF-kappa B binding site in one lineage only. Neither the polymorphic gp41 changes alone nor the U3 deletion alone appeared to be responsible for increased replicative capacity because recombinant SIVmac239 Delta nef, engineered to contain either of these changes, induced moderate viral loads in only one of six monkeys. However, five of six monkeys infected with recombinant SIVmac239 Delta nef containing both TM and U3 changes did develop persisting moderate viral loads. These genetic changes did not increase lymphoid cell-activating properties in the monkey interleukin-2-dependent T-cell line 221, but the gp41 changes did increase the fusogenic activity of the SIV envelope two- to threefold. These results delineate sequence changes in SIV that can compensate for the loss of the nef gene to partially restore replicative and pathogenic potential in rhesus monkeys.

Live attenuated, nef-deleted SIV is pathogenic in most adult macaques after prolonged observation

OBJECTIVE

A live attenuated SIV vaccine strain, termed SIVmac239Delta3 and containing large deletions in, and the negative regulatory element, was previously shown to cause AIDS mostly in monkeys vaccinated as infants. In the present study, we demonstrate that SIVmac239Delta3 is pathogenic in most vaccinated adult monkeys, given enough time.

METHODS

Eleven rhesus macaques vaccinated as adults with SIVmac239Delta3 were followed for extended periods (up to 6.8 years).

RESULTS

We found signs of immune dysregulation in all 11 adult vaccinees. All animals developed persistently inverted CD4 : CD8 T-cell ratios, seven (64%) had persistent recurrent viremia, and six (55%) had decreased CD4 T-cell counts (< 500 x 10 cells/l). Further signs included low CD4CD29 lymphocyte subsets, loss of anti-Gag antibodies, anemia, thrombocytopenia, wasting, and opportunistic infections. Two adult vaccinees (18%) subsequently developed AIDS. Development of chronic, recurrent viremia with plasma viral RNA loads > or = 10 copies/ml and cytoviremia was a poor prognostic sign.

CONCLUSION

Our data demonstrate that with time, a live attenuated, multiply deleted SIV vaccine can cause immune dysregulation in most vaccine recipients, even in initially immune competent, healthy adults. Immune dysfunction can progress to full AIDS. However, pathogenic effects became evident only several years after vaccination. Thus, mass vaccination of humans with similarly constructed live attenuated HIV vaccines, recently suggested for countries with high HIV-1 transmission rates, seems contraindicated.

Suppression of breast cancer growth and angiogenesis by an antisense oligodeoxynucleotide to p21(Waf1/Cip1)

Under some conditions, p21(Waf1/Cip1) plays an assembly factor role for the cyclins and cyclin-dependent kinases, and recent reports demonstrate that p21 can act as an anti-apoptotic protein. Thus, it is logical to exploit this function of p21 as an anti-cancer target. We have performed a pilot study showing that daily subcutaneous injection of a phosphorothioate antisense p21 oligodeoxynucleotide, which we have previously shown to attenuate p21 levels in vitro, into nude mice who have been implanted with highly metastatic breast cancer cells results in inhibition of tumor growth and angiogenesis. Inhibition of in vitro endothelial capillary formation confirms that these oligodeoxynucleotides have a direct effect upon tumor angiogenesis. The attractiveness of our novel approach to breast cancer therapy, which capitalizes on the anti-apoptotic function of p21, derives from the ease of transfection of antisense oligodeoxynucleotides as well as the observations that p21(-/-) mice do not develop spontaneous tumors, making techniques exploiting the assembly factor and anti-apoptotic role of p21 worthy of further study against breast cancer.

A truncated form of Nef selected during pathogenic reversion of simian immunodeficiency virus SIVmac239Deltanef increases viral replication

The live, attenuated vaccine simian immunodeficiency virus SIVmac239Deltanef efficiently protects rhesus macaques against infection with wild-type SIVmac but occasionally causes CD4(+) T-cell depletion and progression to simian AIDS (SAIDS). Virus recovered from a vaccinated macaque (Rh1490) that progressed to SAIDS had acquired an additional deletion in the nef gene, resulting in a frameshift that restored the original nef open reading frame (R. I. Connor, D. C. Montefiori, J. M. Binley, J. P. Moore, S. Bonhoeffer, A. Gettie, E. A. Fenamore, K. E. Sheridan, D. D. Ho, P. J. Dailey, and P. A. Marx, J. Virol. 72:7501-7509, 1998). Intravenous inoculation of the Rh1490 viral isolate into four naive rhesus macaques induced CD4(+) T-cell depletion and disease in three out of four animals within 2 years, indicating a restoration of virulence. A DNA fragment encompassing the truncated nef gene amplified from the Rh1490 isolate was inserted into the genetic backbone of SIVmac239. The resulting clone, SIVmac239-Delta2nef, expressed a Nef protein of approximately 23 kDa, while the original SIVmac239Deltanef clone expressed a shorter protein of 8 kDa. The revertant form of Nef did not cause downregulation of CD4, CD3, or major histocompatibility complex class I. The infectivity of SIVmac239-Delta2nef was similar to that of SIVmac239Deltanef in single-cycle assays using indicator cell lines. In contrast, SIVmac239-Delta2nef replicated more efficiently than SIVmac239Deltanef in peripheral blood mononuclear cell (PBMC) cultures infected under unstimulated conditions. The p27 Gag antigen levels in SIVmac239-Delta2nef-infected cultures were still lower than those obtained with wild-type SIVmac239, consistent with a partial recovery of Nef function. The transcriptional activity of long terminal repeat (LTR)-luciferase constructs containing the nef deletions did not differ markedly from that of wild-type LTR. Introduction of a premature stop codon within Nef-Delta2 abolished the replicative advantage in PBMCs, demonstrating that the Nef-Delta2 protein, rather than the structure of the U3 region of the LTR, was responsible for the increase in viral replication. Taken together, these results show that SIV with a deletion in the nef gene can revert to virulence and that expression of a form of nef with multiple deletions may contribute to this process by increasing viral replication.

T-cell receptor:CD3 down-regulation is a selected in vivo function of simian immunodeficiency virus Nef but is not sufficient for effective viral replication in rhesus macaques

We investigated the function of severely truncated simian immunodeficiency virus (SIV) Nef proteins (tNef) in vitro and in vivo. These variants emerged in rhesus monkeys infected with SIVmac239 containing a 152-bp deletion in the nef-unique region and have been suggested to enhance SIV virulence (E. T. Sawai, M. S. Hamza, M. Ye, K. E. Shaw, and P. A. Luciw, J. Virol. 74:2038-2045, 2000). We found that the tNef proteins were unable to down-regulate the cell surface expression of major histocompatibility complex class I proteins, CD4, and CD28 and neither stimulated SIV replication nor enhanced virion infectivity. The tNef proteins did efficiently down-regulate T-cell receptor (TCR):CD3 cell surface expression. Nevertheless, the SIVmac239 tnef variants were strongly attenuated in six infected juvenile rhesus macaques. Thus, while the ability of SIV Nef to down-modulate TCR:CD3 cell surface expression apparently confers a selective advantage in vivo, it is insufficient for efficient viral replication in infected macaques. Additional mutations elsewhere in SIVmac239 tnef genomes are required for a virulent phenotype.

[Present situation regarding development of an HIV vaccine]

The AIDS epidemic continues to advance, and the development of a preventive HIV vaccine has become a major objective for scientific research. An effective vaccine against this virus is not available and complete protection still has not been achieved in animal models. In this review the major challenges related to the development of a vaccine against HIV are analyzed, particularly the mechanisms involved in viral escape from the immune response, and the results obtained with the various therapeutic and preventive vaccine prototypes are summarized. Finally, the social, economic and health aspects related to research on HIV vaccines and the current controversy around the performance of clinical trials with these agents is discussed.