Human Immunodeficiency Virus-Type 1 Specific Cellular Immunity in Chronic Infected Patients on Prolonged Highly Active Antiretroviral Treatment and on Structured Treatment Interruption

We have followed 15 HIV-1 chronically infected patients during prolonged highly active antiretroviral treatment (HAART) and subsequent long term structured treatment interruption (STI). We analyzed Nef, Tat, and p24 specific cellular immunity using IFN-gamma enzyme-linked immunospot assays and T cell proliferation assays. Eight HAART patients showed IFN-gamma responses to at least one antigen, but no positive responses were seen during STI. We observed retained or increased p24 specific IFN-gamma responses in most patients during HAART with viral suppression. These results showed persisting HIV-1 specific cellular immunity during HAART; however, in prolonged STI with viral rebound this immunity declined.

The new small-molecule mixed-lineage kinase 3 inhibitor URMC-099 is neuroprotective and anti-inflammatory in models of human immunodeficiency virus-associated neurocognitive disorders

Human immunodeficiency virus (HIV)-associated neurocognitive disorders (HAND) is a significant source of disability in the HIV-infected population. Even with stringent adherence to anti-retroviral therapy, >50% of patients living with HIV-1 will develop HAND (Heaton et al., 2010). Because suppression of viral replication alone is not enough to stop HAND progression, there is a need for an adjunctive neuroprotective therapy in this population. To this end, we have developed a small-molecule brain-penetrant inhibitor with activity against mixed-lineage kinase 3 (MLK3), named URMC-099. MLK3 activation is associated with many of the pathologic hallmarks of HAND (Bodner et al., 2002, 2004; Sui et al., 2006) and therefore represents a prime target for adjunctive therapy based on small-molecule kinase inhibition. Here we demonstrate the anti-inflammatory and neuroprotective effects of URMC-099 in multiple murine and rodent models of HAND. In vitro, URMC-099 treatment reduced inflammatory cytokine production by HIV-1 Tat-exposed microglia and prevented destruction and phagocytosis of cultured neuronal axons by these cells. In vivo, URMC-099 treatment reduced inflammatory cytokine production, protected neuronal architecture, and altered the morphologic and ultrastructural response of microglia to HIV-1 Tat exposure. In conclusion, these data provide compelling in vitro and in vivo evidence to investigate the utility of URMC-099 in other models of HAND with the goal of advancement to an adjunctive therapeutic agent.

Impact of antibody quality and anamnestic response on viremia control post-challenge in a combined Tat/Env vaccine regimen in rhesus macaques

Previously, priming rhesus macaques with Adenovirus type 5 host range mutant-recombinants encoding Tat and Env and boosting with Tat and Env protein in MPL-SE controlled chronic viremia by 4 logs following homologous intravenous SHIV89.6P challenge. Here we evaluated Tat, Env, and Tat/Env regimens for immunogenicity and protective efficacy using clade C Env, alum adjuvant, and a heterologous intrarectal SHIV1157ipd3N4 challenge. Despite induction of strong cellular and humoral immunity, Tat/Env group T and B-cell memory responses were not significantly enhanced over Tat- or Env-only groups. Lack of viremia control post-challenge was attributed to lower avidity Env antibodies and no anamnestic ADCC response or SHIV1157ipd3N4 neutralizing antibody development post-challenge. Poor biologic activity of the Tat immunogen may have impaired Tat immunity. In the absence of sterilizing immunity, strong anamnestic responses to heterologous virus can help control viremia. Both antibody breadth and optimal adjuvanticity are needed to elicit high-quality antibody for protective efficacy.

Characterization of Tat antibody responses in Chinese individuals infected with HIV-1

HIV-1 Tat is an important regulatory protein involved in AIDS pathogenesis. However, the immunoprofiles of anti-Tat responses remain unclear. We analysed the immunoprofiles of the anti-Tat antibody responses and the neutralizing activities. Out of 326 HIV-1-seropositive individuals, 12.9% were positive for anti-Tat antibodies. We found six different immunological profiles of anti-Tat antibody responses: full-potential response, combined response, N-specific response, C-specific response, full-length Tat-specific response and Tat-related response. These responses represent two types of anti-Tat responses: the major complete response and the alternative C-prone response. A Tat-neutralizing activity is significantly higher in anti-Tat-seropositive samples than anti-Tat-negative or healthy blood-donor samples, and significantly correlates with the anti-Tat reactivities. The data here could contribute to a better understanding of the significance of anti-Tat responses in preventing HIV pathogenesis and could be useful for designing more effective vaccines in the future.

[Construction, expression and immunogenicity analysis of a Tat N-terminus-deleted mutant fusion protein of human immunodeficiency virus type 1]

In the study, a gene encoding Tat protein N terminal 1- 21 amino acid residues-deleted mutant (Tat22-101) was amplified by PCR from a full length Tat gene of human immunodeficiency virus type 1, and the prokaryotic expression plasmid pET32a-Tat22-101 was constructed. After identification by digestion with endonucleases and sequencing, the recombinant plasmid pET32a-Tat22-101 was transformed into E. coli BL21(DE3) and expressed with IPTG induction. The mutant fusion protein with deleted Tat N terminal was purified by an affinity chromatography column Ni(2+)-NTA and subsequently identified by SDS-PAGE and Western blotting. The results showed that the molecular weight of the mutant protein was approximately 26.9kD. Furthermore, BALB/c mice were immunized with the mutant protein and the anti-sera were collected. ELISA results showed that the mutant protein preserved its immunogenicity, particularly it could improve the production of antibodies to other epitopes in addition to the N terminal epitope of Tat protein, which might provide some valuable information for the study of Tat functions as well as for development of potential novel HIV Tat vaccine.

AVOIDING DECEPTIVE IMPRINTING OF THE IMMUNE RESPONSE TO HIV-1 INFECTION IN VACCINE DEVELOPMENT

Lymphocyte clonal restriction is caused by priming the immune system with an antigen and has been referred to infectious disease study as "original antigenic sin" (OAS), described first for influenza by Francis. OAS is a dominant feature of a normal immune response. Benefits of OAS come from the initial contact with the pathogen, which induces immunological memory. Memory is achieved by priming B and T cells of an immunologically naïve host, and confers protection against infection with the antigen-related pathogen. Thus, a restricted antibody response to viral or parasite antigens is not per se pathogenic. However, the interplay between a "locked-in" immune response and the high genetic variation of the pathogenic agent can result in a deception of the immune system. In the following, clonal restriction of the immune response to HIV is described by giving examples of restricted anti-HIV antibody formation in maternally infected children. Clonal restriction results in host resistance of infected individuals to emerging HIV variants and quasispecies. The problems of classical approaches of vaccine design in AIDS and the lack of protection in vaccinated patients is reviewed.

The heat shock protein 27 (Hsp27) operates predominantly by blocking the mitochondrial-independent/extrinsic pathway of cellular apoptosis

Heat shock protein 27 (Hsp27) is a molecular chaperone protein which regulates cell apoptosis by interacting directly with the caspase activation components in the apoptotic pathways. With the assistance of the Tat protein transduction domain we directly delivered the Hsp27 into the myocardial cell line, H9c2 and demonstrate that this protein can reverse hypoxia-induced apoptosis of cells. In order to characterize the contribution of Hsp27 in blocking the two major apoptotic pathways operational within cells, we exposed H9c2 cells to staurosporine and cobalt chloride, agents that induce mitochondria-dependent (intrinsic) and -independent (extrinsic) pathways of apoptosis in cells respectively. The Tat-Hsp27 fusion protein showed a greater propensity to inhibit the effect induced by the cobalt chloride treatment. These data suggest that the Hsp27 predominantly exerts its protective effect by interfering with the components of the extrinsic pathway of apoptosis.

Differential patterns of immune escape at Tat-specific cytotoxic T cell epitopes in pigtail macaques

Cytotoxic T lymphocyte responses to conserved proteins such as Gag within HIV- or SIV-infected hosts can facilitate partial control of viremia. However, the utility of targeting variable viral proteins by CTL responses is unclear. We studied CTL responses to regulatory and accessory proteins of SIV in pigtail macaques. The regulatory and accessory proteins were the most commonly targeted proteins by CTL responses from pigtail macaques. We identified 2 novel Tat-specific CTL responses that were both restricted by the Mane-A10 allele. Viral escape at one of the Tat epitopes, KSA10, was slower in comparison to another Tat epitope KVA10. The kinetics of escape of the KSA10 Tat epitope were more similar to an immunodominant KP9 Gag epitope also restricted by Mane-A10. Our results suggest that some regulatory or accessory CTL epitopes may be useful targets for vaccination against HIV.

Enhancement of cytotoxic T lymphocyte activity by dendritic cells loaded with Tat-protein transduction domain-fused hepatitis B virus core antigen

The protein transduction domain (PTD) of human immunodeficiency virus-1-Tat protein has a unique potency to penetrate the cellular membranes. To synthesize the sequence of Tat-PTD47-57 and hepatitis B virus core antigen (HBcAg), we spliced these sequences and linked a fusion gene into the pMAL-c2x vector. The fusion proteins were purified by affinity chromatography and pulsed with bone marrow-derived dendritic cells (DCs), and the transduction of recombinant protein was detected by immunofluorescence antibody assay. Results showed that recombinant PTD-HBcAg could penetrate into DC cytoplasm while recombinant HBcAg was detected on the surface of cells. The percentage of DC surface molecules, such as CD80, CD86 and major histocompatibility complex II, and production of cytokine (IL-12p70) induced by recombinant PTD-HBcAg were significantly higher than those induced by recombinant HBcAg or tumor necrosis factor-alpha. DCs treated with PTD-HBcAg induced T cells to differentiate into specific cytotoxic T lymphocytes (CTLs) and enhanced the CTL killing response. In conclusion, the expressed and purified PTD-HBcAg fusion protein could penetrate into cells through the plasma membrane, promote DC maturation, and enhance T cells response to generate HBcAg-specific CTLs efficiently.

Modification of CEA with both CRT and TAT PTD induces potent anti-tumor immune responses in RNA-pulsed DC vaccination

Carcinoembryonic antigen (CEA) is expressed on human colon carcinomas, is well characterized, and continues to be a promising target for cancer immunotherapy in humans. To enhance the immunogenecity of CEA, we developed a fusion gene (CRT-TAT-DeltaCEA) of the TAT protein transduction domain (PTD) and calreticulin (CRT) with human CEA devoid of its signal sequences (DeltaCEA) and evaluated anti-tumor immunity using RNA-pulsed dendritic cell (DC) vaccination. Mice vaccinated with DC by electroporation with mRNA encoding TAT-DeltaCEA (DC/TAT-DeltaCEA) and CRT-DeltaCEA (DC/CRT-DeltaCEA) had enhanced induction of tumor-specific cytotoxic T lymphocyte (CTL) and increased numbers of IFN-gamma-secreting T cells by ELISPOT, as compared to mice vaccinated with DC/DeltaCEA. DC/CRT-DeltaCEA and DC/TAT-DeltaCEA vaccines preferentially stimulated CD4+ and CD8+ T cells, respectively. The DC vaccine by electroporation with mRNA encoding CRT-TAT-DeltaCEA (DC/CRT-TAT-DeltaCEA) enhanced both CD4+ and CD8+ T cells. DC/CRT-TAT-DeltaCEA had the additional effects of CRT and TAT PTD and enhanced the anti-tumor effect against CEA-expressing tumors compared to DC/CRT-DeltaCEA or DC/TAT-DeltaCEA. These findings suggest that modification of CEA with both CRT and TAT PTD induces potent anti-tumor immune responses in RNA-pulsed DC vaccination and may be a useful approach for DC-based immunotherapy.

CTL responses to regulatory proteins Tat and Rev in HIV-1 B'/C virus-infected individuals

OBJECTIVE

To characterize HIV-1 specific CTL responses to regulatory proteins Tat and Rev in HIV-B'/C virus-infected ART-naive individuals.

METHODS

HIV-1-specific CTL responses were analyzed by IFN-gamma ELISPOT assay using overlapping peptides spanning the consensus sequences of HIV-1 clade C Tat and Rev proteins. Statistical analysis and graphical presentation were performed using SIGMAPLOT 10.0 and SIGMASTAT 3.5. For samples with a positive response, the magnitude of CTL responses was compared between HIV-1 C proteins by Wilcoxon rank sum test, and the significance threshold was P<0.05.

RESULTS

Tat and Rev were frequently recognized, with 23% and 52% of the tested individuals having detectable responses to these proteins, respectively. Several immunodominant regions were detected in Rev. No significant correlation was observed between the magnitude and breadth of CTL responses to regulatory proteins and the control of virus replication in this study.

CONCLUSION

Tat and Rev can serve as targets for HIV-1-specific CTL, and several immunodominant regions are detectable in Rev. Further characterization of epitopes and their role in virus control may shed light on pathogenesis of HIV-1 natural infection and also be useful for the design and testing of candidate vaccines.

Immune-response profiles induced by human immunodeficiency virus type 1 vaccine DNA, protein or mixed-modality immunization: increased protection from pathogenic simian–human immunodeficiency virus viraemia with protein/DNA combination

Current data suggest that prophylactic human immunodeficiency virus type 1 (HIV) vaccines will be most efficacious if they elicit a combination of adaptive humoral and T-cell responses. Here, we explored the use of different vaccine strategies in heterologous prime–boost regimes and evaluated the breadth and nature of immune responses in rhesus monkeys induced by epidermally delivered plasmid DNA or recombinant HIV proteins formulated in the AS02A adjuvant system. These immunogens were administered alone or as either prime or boost in mixed-modality regimes. DNA immunization alone induced cell-mediated immune (CMI) responses, with a strong bias towards Th1-type cytokines, and no detectable antibodies to the vaccine antigens. Whenever adjuvanted protein was used as a vaccine, either alone or in a regime combined with DNA, high-titre antibody responses to all vaccine antigens were detected in addition to strong Th1- and Th2-type CMI responses. As the vaccine antigens included HIV-1 Env, Nef and Tat, as well as simian immunodeficiency virus (SIV)mac239 Nef, the animals were subsequently exposed to a heterologous, pathogenic simian–human immunodeficiency virus (SHIV)89.6p challenge. Protection against sustained high virus load was observed to some degree in all vaccinated groups. Suppression of virus replication to levels below detection was observed most frequently in the group immunized with protein followed by DNA immunization, and similarly in the group immunized with DNA alone. Interestingly, control of virus replication was associated with increased SIV Nef- and Gag-specific gamma interferon responses observed immediately following challenge.

Formulation of HIV-1 Tat and p24 antigens by PLA nanoparticles or MF59 impacts the breadth, but not the magnitude, of serum and faecal antibody responses in rabbits

Biodegradable nanoparticles coated with proteins represent a promising method for in vivo delivery of vaccines. Here we used a rabbit model to compare quantitatively and qualitatively the antibody responses induced by poly(D,L-lactide) nanoparticles (PLA) and by emulsion adjuvant MF59 using three HIV-1 antigens: p24gag, WT Tat and a mutated, detoxified form of Tat. We could show that all antigens and adjuvants lead to the induction of similar level of IgG titres in serum when injected subcutaneously. p24, but not Tat, could also induce faecal IgG in rabbits when formulated with PLA or MF59. The nature of the adjuvant had consequences on the spectrum of specificity induced, depending on the antigen: PLA adjuvant focussed the anti-p24 response to an immunodominant domain when compared to MF59. With wild-type Tat, no difference between adjuvants was observed in the spectrum of specificity induced. On the opposite, detoxified Tat coated on PLA increased the number of epitopes recognized by serum IgG compared to MF59 adjuvantation. The impact of these qualitative differences depending on the antigen/adjuvant associations will be important to take into account for further designs of vaccinal formulation using particulate adjuvants.

Efficacy of a multigenic protein vaccine containing multimeric HIV gp160 against heterologous SHIV clade C challenges

OBJECTIVE

To determine whether multigenic protein immunogens including native, trimeric HIV clade C (HIV-C) gp160 could cross-protect macaques against mucosal challenge with clade C (SHIV-C) mismatched for env.

DESIGN

Because AIDS vaccine recipients are unlikely to encounter exactly matched HIV strains and to represent the diversity of locally circulating HIV-C strains, we selected env genes to generate the gp160 immunogen and SHIV-C from different, recently infected infants of the same clinical cohort in Zambia. In a model of postnatal HIV-C transmission, infant macaques were immunized with soluble viral proteins, including trimeric HIV1084i Env, and challenged with SHIV-1157ip; protein-only vaccination was compared with a DNA prime/protein boost strategy.

METHODS

All vaccinated and control monkeys were exposed orally to low-dose, R5-tropic SHIV-1157ip encoding heterologous env. Animals with no or only transient infection were rechallenged intrarectally with a high dose of R5 SHIV-1157ipd3N4, a 'late', animal-evolved SHIV-1157ip variant. Animals were followed prospectively for immune parameters and viral RNA loads.

RESULTS

Vaccination induced cross-neutralizing antibodies. Compared to controls, vaccinees had significantly lower peak viral RNA loads, and one vaccine recipient remained completely virus-free, even in lymphoid tissues. There was a trend for the protein-only vaccine to yield better protection than the combined modality approach.

CONCLUSION

Protein-only immunogens induced significant protection against heterologous viruses encoding env from locally circulating viruses.

Design and characterization of an HIV-1 Tat mutant: Inactivation of viral and cellular functions but not antigenicity

Among HIV-1 proteins, Tat is a promising antigen for consideration as a component of anti-HIV-1 vaccine formulations. Nevertheless, this viral protein is able to affect the expression of several cellular genes that are implicated in immune response. In this study, we designed and characterized a mutant form of Tat ("STLA Tat"), which is unable to transactivate viral transcription, and which has lost the deleterious effects on the expression of MHC I, IL-2, and CD25 genes compared with wild-type Tat, as observed in lymphoid Jurkat cells that stably express the tat genes. In vivo experiments in mice revealed that STLA Tat induces anti-Tat antibodies at the same titers as wild-type Tat, which recognize both autologous and heterologous Tat antigens. Finally, STLA Tat did not induce the immunosuppression observed after injection of wild-type Tat. Therefore, this STLA Tat mutant appears to be a safe and promising antigen for further evaluation in anti-HIV-1 vaccine strategies.

Candidate HIV-1 gp140DeltaV2, Gag and Tat vaccines protect against experimental HIV-1/MuLV challenge

Pre-clinical HIV-1 vaccine protocols, using multiple vaccine modalities and a potent adjuvant were assessed for vaccine efficacy in an experimental HIV-1 challenge model. C57Bl/6 mice were immunized with DNA plasmids encoding HIV-1 gp140, Gag and Tat alone or in combination with the corresponding recombinant proteins formulated in the adjuvant MF59. HIV-1 DNA alone or a DNA prime protein boost schedule resulted in complete protection against challenge with HIV-1/MuLV-infected murine cells. Although HIV-1 protein immunization in combination with MF59 resulted in partial protection, the DNA priming seemed to be crucial for obtaining full protection against the challenge. It is likely that the partial protection seen after immunization with protein alone is, to a certain extent, due to effects of the adjuvant since some animals that received the adjuvant MF59 alone were protected from the challenge. For the most part, antigen-specific cell-mediated immune responses as detected in the spleen (in contrast to responses detected in peripheral blood) of immunized animals appeared to be associated with protection in this study.

Addition of TAT protein transduction domain and GrpE to human p53 provides soluble fusion proteins that can be transduced into dendritic cells and elicit p53-specific T-cell responses in HLA-A*0201 transgenic mice

The protein p53 has been shown to be an efficient tumour antigen in both murine and human cancer vaccine studies and cancer vaccines targeting p53 based on major histocompatibility complex (MHC) class I binding p53-derived peptides that induce cytotoxic T lymphocytes (CTLs) without p53-specific CD4(+) T-cell help have been tested by several research groups including ours. To obtain such CD4(+) T-cell help and cover a broader repertoire of MHC haplotypes we have previously attempted to produce recombinant human p53 for vaccination purposes. However, attempts to refold a hexahis-tagged p53 protein in our laboratory were unsuccessful. Here, we show that fusion of an 11-amino-acid region of the human immunodeficiency virus TAT protein transduction domain (PTD) to human p53 increases the solubility of the otherwise insoluble p53 protein and this rTAT-p53 protein can be transduced into human monocyte-derived dendritic cells (DCs). The induction of a p53-specific HLA-A*0201 immune response was tested in HLA-A*0201/K(b) transgenic mice after immunization with rTAT-p53-transduced bone-marrow-derived DCs. In these mice, p53-specific CD4(+) and CD8(+) T-cell proliferation was observed and immunization resulted in the induction of HLA-A*0201-restricted CTLs specific for two human p53-derived HLA-A*0201-binding peptides, p53(65-73) and p53(149-157). Addition of GrpE to generate rTAT-GrpE-p53 led to a further increase in protein solubility and to a small increase in DC maturation but did not increase the observed p53-specific T-cell responses. The use of rTAT-p53 in ongoing clinical protocols should be applicable and offers advantages to current strategies omitting the use of HLA-typed patients.

Reconstruction and function of ancestral center-of-tree human immunodeficiency virus type 1 proteins

The extensive diversity of human immunodeficiency virus type 1 (HIV-1) and its capacity to mutate and escape host immune responses are major challenges for AIDS vaccine development. Ancestral sequences, which minimize the genetic distance to circulating strains, provide an opportunity to design immunogens with the potential to elicit broad recognition of HIV epitopes. We developed a phylogenetics-informed algorithm to reconstruct ancestral HIV sequences, called Center of Tree (COT). COT sequences have potentially significant benefits over isolate-based strategies, as they minimize the evolutionary distances to circulating strains. COT sequences are designed to surmount the potential pitfalls stemming from sampling bias with the consensus method and outlier bias with the most-recent-common-ancestor approach. We computationally derived COT sequences from circulating HIV-1 subtype B sequences for the genes encoding the major viral structural protein (Gag) and two regulatory proteins, Tat and Nef. COT genes were synthesized de novo and expressed in mammalian cells, and the proteins were characterized. COT Gag was shown to generate virus-like particles, while COT Tat transactivated gene expression from the HIV-1 long terminal repeat and COT Nef mediated downregulation of cell surface major histocompatibility complex class I. Thus, retrodicted ancestral COT proteins can retain the biological functions of extant HIV-1 proteins. Additionally, COT proteins were immunogenic, as they elicited antigen-specific cytotoxic T-lymphocyte responses in mice. These data support the utility of the COT approach to create novel and biologically active ancestral proteins as a starting point for studies of the structure, function, and biological fitness of highly variable genes, as well as for the rational design of globally relevant vaccine candidates.

A role for mitogen-activated protein kinase and Ets-1 in the induction of interleukin-10 transcription by human immunodeficiency virus-1 Tat

The human immunodeficiency virus (HIV) Tat protein has multiple regulatory roles, including trans-activation of the HIV genome and regulation of immune signalling processes, including kinase activation and cytokine expression. We recently demonstrated that HIV-1 Tat induces the expression of interleukin (IL)-10 via p38 mitogen-activated protein kinase (MAPK) activation. We further delineated that the Tat-responsive element of the IL-10 promoter was located within 625 to 595 bp upstream from the transcription start site. Using electrophoretic mobility shift assays, the transcription factors Ets-1 and Sp-1 were shown to bind to the IL-10 promoter to activate transcription of the gene. Furthermore, sequential deletional mutations of the Ets-1- and Sp-1-binding sites in the -625/-595 region reduced the DNA binding and transcription activity of the IL-10 promoter. Our results also showed that both the Tat-induced and Ets-1-regulated IL-10 promoter-driven luciferase activity can be abrogated by inhibitors of the p38 MAPK activity. In conclusion, the coordinated activities of p38 MAPK and the transcription factors, Ets-1 and Sp-1, may play an important role in the HIV-1 Tat-induced IL-10 transcription.

Cyclooxygenase-2 is involved in HIV-1 Tat-induced inflammatory responses in the brain

Cyclooxygenase (COX)-2, a rate-limiting enzyme for prostanoid synthesis, can be involved in inflammatory-mediated cytotoxicity. Although the contribution of COX-2 to peripheral inflammation is well understood, its role in brain inflammation is not fully recognized. In particular, COX-2 involvement in inflammatory responses induced by HIV proteins in the central nervous system is not known. Therefore, the present study focused on COX-2 expression and its role in modulating the expression of brain inflammatory-related genes following exposure to the HIV-1 transactivating protein Tat. Intrahippocampal injections of Tat induced dose-dependent upregulation of COX-2 mRNA and protein levels in C57BL/6 mice. COX-2 immunoreactivity was primarily localized in microglial cells and astrocytes. Tat-induced COX-2 expression was partially prevented by pyrrolidine dithiocarbamate, a potent antioxidant and an inhibitor of the transcription factor, nuclear factor kappaB. Most importantly, administration of the COX-2 inhibitor NS-398 attenuated Tat-mediated upregulation of mRNA and protein expression of inflammatory mediators, such as monocyte chemoattractant protein-1, interleukin-1beta, tumor necrosis factor-alpha, and inducible nitric oxide synthase. Moreover, treatment with NS-398 significantly attenuated Tat-induced activation of microglial cells. These results provide evidence that COX-2 overexpression can modulate induction of brain inflammatory mediators in response to HIV-1 Tat protein. Such alterations may play an important role in the development of brain inflammatory reactions in HIV-infected patients and contribute to the development of neurological complications in the course of HIV-1 infection.

Human immunodeficiency virus type-1 protein Tat induces tumor necrosis factor-alpha-mediated neurotoxicity

HIV-1 infection causes, with increasing prevalence, neurological disorders characterized in part by neuronal cell death. The HIV-1 protein Tat has been shown to be directly and indirectly neurotoxic. Here, we tested the hypothesis that a non-neurotoxic epitope of Tat can, through actions on immune cells, increase neuronal cell death. Tat(1-72) and a mutant Tat(1-72) lacking the neurotoxic epitope (Tat(Delta31-61)) concentration-dependently and markedly increased TNF-alpha production in macrophage-like differentiated human U937 and THP-1 cells, in mouse peritoneal macrophages and in mouse brain microglia. Tat(1-72) was but Tat(Delta31-61) was not neurotoxic when applied directly to neurons. Supernatants from U937 cells treated with either Tat(1-72) or Tat(Delta31-61) were neurotoxic and their immunoneutralization with an anti-TNF-alpha antibody decreased Tat(1-72)- and Tat(Delta31-61)-induced neurotoxicity. Together, these results demonstrate that the neurotoxic epitope of Tat(1-72) is different from the epitope that is indirectly neurotoxic following production of TNF-alpha from immune cells, and suggest that therapeutic interventions against TNF-alpha might be beneficial against HIV-1 associated neurological disorders.

Antibodies against a multiple-peptide conjugate comprising chemically modified human immunodeficiency virus type-1 functional Tat peptides inhibit infection

We demonstrated recently that selective side-chain modification of functional cysteine-rich (Tat(21-40)) and arginine-rich (Tat(53-68)) domains of the HIV-1 Tat protein blocks pathogenic activities of these peptides while retaining their immunological characteristics. In the present study, we have synthesized a multiple-peptide conjugate system comprising modified Tat(21-40) and Tat(53-68) peptides (HIV-1-Tat-MPC). Immunization of mice with this highly homogeneous 10.7 kDa HIV-1-Tat-MPC synthetic construct induced an effective immune response in mice. The antibodies generated against HIV-1-Tat-MPC efficiently suppressed Tat-induced viral replication and significantly reduced HIV-associated cytopathic effects in human monocytes. These results indicate that epitope-specific antibodies directed against functional sites of Tat protein using non-pathogenic peptides inhibit HIV pathogenesis. The HIV-1-Tat-MPC, therefore, has potential for the development of a safe, effective, and economical therapeutic vaccine to reduce the progression of HIV infection.

Functional Synergy between CD40 Ligand and HIV-1 Tat Contributes to Inflammation: Implications in HIV Type 1 Dementia

HIV type 1 (HIV-1)-associated dementia (HAD) is believed to occur due to aberrant activation of monocyte-derived macrophages and brain-resident microglial cells by viral proteins as well as by the proinflammatory mediators released by infected cells. To investigate the inflammatory aspects of the disease, we examined the levels of soluble CD40L (sCD40L) in paired samples of plasma and cerebrospinal fluid obtained from 25 HIV-infected individuals. A significantly higher level of sCD40L was detected in both cerebrospinal fluid and plasma from HIV-infected patients with cognitive impairment, compared with their nonimpaired counterparts. The contribution of sCD40L to the pathogenesis of HAD was then examined by in vitro experiments. rCD40L synergized with HIV-1 Tat to increase TNF-alpha release from primary human monocytes and microglia, in an NF-kappaB-dependent manner. The mechanistic basis for this synergism was attributed to a Tat-mediated up-regulation of CD40 in monocytes and microglia. Finally, the CD40L-mediated increase in TNF-alpha production by monocytes was shown to be biologically important; immunodepletion experiments revealed that TNF-alpha was essential for the neurotoxic effects of conditioned medium recovered from Tat/CD40L-treated monocytes. Taken together, our results show that CD40 signaling in microglia and monocytes can synergize with the effects of Tat, further amplifying inflammatory processes within the CNS and influencing neuronal survival.

Design, engineering and in vitro evaluation of MHC class-II targeting allergy vaccines

BACKGROUND

The worldwide increasing incidence of allergic diseases requires the development of new, efficient vaccination strategies, the only curative treatment with a long-lasting effect. Current allergen-specific immunotherapy protocols suffer from limited efficacy and a long treatment time.

METHODS

We engineered modular antigen translocating (MAT) molecules for intracellular targeting of allergens to the major histocompatibility class-II (MHC-II) presentation pathway to enhance antigen presentation. MAT-fusions were evaluated for their ability to localize intracellularly, to induce proliferation, and for their influence on cytokine patterns in peripheral blood mononuclear cells (PBMCs) cultures.

RESULTS

We show that MAT-allergen fusions are able to rapidly translocate into the cytoplasm of PBMCs, whereas naked recombinant allergens are only marginally taken up. MAT vaccines accumulate intracellularly and induce strong proliferation of PBMC cultures at concentrations 10-100 times lower than the corresponding naked allergens, indicating an enhanced presentation through the MHC-II presentation pathway. In PBMC cultures of allergic donors, MAT vaccines induce a cytokine shift from a T(H)2 to a T(H)1 profile, resulting in a stronger and earlier secretion of INF-gamma and Interleukin (IL)-10, and a decreased secretion of IL-4, IL-5 and IL-2, compared with those induced by the corresponding recombinant allergens.

CONCLUSION

Modular antigen translocation vaccines induce strong proliferation responses in PBMC cultures at low concentration and induce a T(H)1/T(H)2 shift in the cytokine profile, reflecting those reported to occur in successfully desensitized allergic patients. Therefore, MAT molecules represent promising lead compounds for the development of potent allergy vaccines.

A replication-competent adenovirus-human immunodeficiency virus (Ad-HIV) tat and Ad-HIV env priming/Tat and envelope protein boosting regimen elicits enhanced protective efficacy against simian/human immunodeficiency virus SHIV89.6P challenge in rhesus macaques

We previously demonstrated that replication-competent adenovirus (Ad)-simian immunodeficiency virus (SIV) recombinant prime/protein boost regimens elicit potent immunogenicity and strong, durable protection of rhesus macaques against SIV(mac251). Additionally, native Tat vaccines have conferred strong protection against simian/human immunodeficiency virus SHIV(89.6P) challenge of cynomolgus monkeys, while native, inactivated, or vectored Tat vaccines have failed to elicit similar protective efficacy in rhesus macaques. Here we asked if priming rhesus macaques with replicating Ad-human immunodeficiency virus (HIV) tat and boosting with the Tat protein would elicit protection against SHIV(89.6P). We also evaluated a Tat/Env regimen, adding an Ad-HIV env recombinant and envelope protein boost to test whether envelope antibodies would augment acute-phase protection. Further, expecting cellular immunity to enhance chronic viremia control, we tested a multigenic group: Ad-HIV tat, -HIV env, -SIV gag, and -SIV nef recombinants and Tat, Env, and Nef proteins. All regimens were immunogenic. A hierarchy was observed in enzyme-linked immunospot responses (with the strongest response for Env, followed by Gag, followed by Nef, followed by Tat) and antibody titers (with the highest titer for Env, followed by Tat, followed by Nef, followed by Gag). Following intravenous SHIV(89.6P) challenge, all macaques became infected. Compared to controls, no protection was seen in the Tat-only group, confirming previous reports for rhesus macaques. However, the multigenic group blunted acute viremia by approximately 1 log (P = 0.017), and both the multigenic and Tat/Env groups reduced chronic viremia by 3 and 4 logs, respectively, compared to controls (multigenic, P = 0.0003; Tat/Env, P < 0.0001). The strikingly greater reduction in the Tat/Env group than in the multigenic group (P = 0.014) was correlated with Tat and Env binding antibodies. Since prechallenge anti-Env antibodies lacked SHIV(89.6P)-neutralizing activity, other functional anti-Env and anti-Tat activities are under investigation, as is a possible synergy between the Tat and Env immunogens.

Changes in HIV-specific antibody responses and neutralization titers in patients under ART

In this study, we tested for antibody reactivities against gp120 and gp41-derived peptides, recombinant gp160, gp41 and tat in HIV-positive sera under antiretroviral therapy (ART) and determined their neutralization capacity. As a baseline, sera from patients in stage A, B and C of the disease, long term non-progressors (LNPs) and HIV-negative individuals were included. Compared to LNPs or sera from patients in group A, the reactivity of sera in stage B or C against gp120-derived peptides was reduced parallel to disease progression. Reactivity of these samples was compared with sera of patients under ART. Parallel to the decrease of viral load, the reactivity against gp120 and gp41-derived epitopes, recombinant gp160 and gp41 or the native gp120/41 complex was significantly reduced. Antibody-mediated neutralization of HIV-1 was detectable prior to ART but revealed substantial decreases coupled with progression of therapy. Responses to recombinant tat dropped after three months of therapy, increased however at later time points to initial levels. These data indicate that in parallel to the decrease in viral load and antibodies against gp120, the neutralization capacity of sera under ART is reduced, and can not be compensated by an increase in tat-specific antibodies.

Evaluation of cellular immune responses in subjects chronically infected with HIV type 1

The importance of host cellular immune responses, particularly CD8(+) cytotoxic T-lymphocyte (CTL) responses, in control of human immunodeficiency virus type 1 (HIV-1) infection has been demonstrated in many clinical studies. These studies, along with vaccination challenge studies in rhesus macaques, indicate the importance of cellular immune responses against HIV-1. Toward this end, we evaluated anti-HIV-1 cellular immune responses in a cohort of 54 subjects who were chronically infected with HIV-1. By validation of IFN-gamma ELISpot assay, we established a dual cut-off criterion for scoring a positive response. The magnitude and frequency of cellular immune responses were measured against HIV-1 antigens (Gag, Pol, Nef, Rev, and Tat), using synthetic peptides as antigens in ELISpot assay. Here we showed that HIV-1 Gag, Pol, and Nef were frequent targets of T cell responses in these subjects, whereas Tat and Rev were less frequently recognized. We further evaluated the possible association between host cellular immune responses and corresponding plasma viral loads in this cohort. By performing ranking correlation analysis, we demonstrated a positive correlation between host viral loads and ELISpot responses of HIV Gag and Pol in untreated subjects. For the subjects under antiviral regimens, however, we did not find any significant association. Our findings suggest that the high levels of ELISpot responses in chronically infected subjects were reflective of their persistent viral infection.

Polyvalent vaccines for optimal coverage of potential T-cell epitopes in global HIV-1 variants

HIV-1/AIDS vaccines must address the extreme diversity of HIV-1. We have designed new polyvalent vaccine antigens comprised of sets of 'mosaic' proteins, assembled from fragments of natural sequences via a computational optimization method. Mosaic proteins resemble natural proteins, and a mosaic set maximizes the coverage of potential T-cell epitopes (peptides of nine amino acids) for a viral population. We found that coverage of viral diversity using mosaics was greatly increased compared to coverage by natural-sequence vaccine candidates, for both variable and conserved proteins; for conserved HIV-1 proteins, global coverage may be feasible. For example, four mosaic proteins perfectly matched 74% of 9-amino-acid potential epitopes in global Gag sequences; 87% of potential epitopes matched at least 8 of 9 positions. In contrast, a single natural Gag protein covered only 37% (9 of 9) and 67% (8 of 9). Mosaics provide diversity coverage comparable to that afforded by thousands of separate peptides, but, because the fragments of natural proteins are compressed into a small number of native-like proteins, they are tractable for vaccines.

Immune response and protection by DNA vaccines expressing antigen 85B of Mycobacterium tuberculosis

A plasmid DNA containing two different expression cassettes was prepared to independently drive antigen 85B (85B) of Mycobacterium tuberculosis and HIV-Tat in C57BL/6 mice. In vivo expression of the plasmid was demonstrated by efficient transcription of 85B and Tat mRNAs in mouse fibroblasts. DNA-85B or DNA-(85B-Tat) were immunogenic and protected mice to the same extent against M. tuberculosis infection, with a decrease in the numbers of CFU lung-1 in comparison with nonimmunized animals down to levels (0.64 log10 CFU) not significantly different from protection conferred by bacillus Calmette-Guérin vaccine (0.97 log10 CFU decrease). Multipromoter plasmids, which permit the reduction of the total amount of DNA injected, can be useful for DNA vaccination against tuberculosis.

Evidence for CTL-mediated selection of Tat and Rev mutants after the onset of the asymptomatic period during HIV type 1 infection

The evolution of HIV-1 sequences over time is the result of the selection of mutant variants that have escaped from host immune responses or the outgrowth of mutants with increased viral replication, or both. We investigated the contribution of both selection processes to the overall evolution of the Tat and Rev regulatory gene sequences from four individuals, ranging in time from just prior to seroconversion to stable asymptomatic infection. After sequencing at least 15 clones per sample per gene, we analyzed the sequence evolution of the MHC-I motifs that were predicted from the MHC-I haplotypes of these patients. For each identified Tat sequence, we tested the activity of the corresponding encoded protein in a transactivation assay in vitro. Our results suggest that the evolution of the Tat and Rev sequences from these individuals can be explained by mutational escape of the MHC-I epitopes and that no mutations that replaced the original sequences in the viral population are associated with either an increase or decrease in Tat activity. CTL-mediated selection appears to be an important determinant of HIV-1 regulatory gene sequence evolution during the early stages of infection.

Expression of human immunodeficiency virus type 1 tat from a replication-deficient herpes simplex type 1 vector induces antigen-specific T cell responses

Herpes simplex type-1 virus (HSV-1) based vectors have been widely used in different gene therapy approaches and also as experimental vaccines against HSV-1 infection. Recent advances in the HSV-1 technology do support the use of replication defective HSV-1 as vaccine vectors for delivery of foreign antigens. We have examined the ability of a recombinant replication-defective HSV-1 vector expressing the HIV-1 Tat protein to induce long-term Tat-specific immune responses in the Balb/c murine model. The results showed that vector administration by the subcutaneous route elicits anti-Tat specific T-cell mediated immune responses in mice characterized by the presence of the Tat-specific cytotoxic activity and production of high levels of IFN-gamma.

EGCG mitigates neurotoxicity mediated by HIV-1 proteins gp120 and Tat in the presence of IFN-gamma: role of JAK/STAT1 signaling and implications for HIV-associated dementia

Human immunodeficiency virus (HIV)-1 infection of the central nervous system occurs in the vast majority of HIV-infected patients. HIV-associated dementia (HAD) represents the most severe form of HIV-related neuropsychiatric impairment and is associated with neuropathology involving HIV proteins and activation of proinflammatory cytokine circuits. Interferon-gamma (IFN-gamma) activates the JAK/STAT1 pathway, a key regulator of inflammatory and apoptotic signaling, and is elevated in HIV-1-infected brains progressing to HAD. Recent reports suggest green tea-derived (-)-epigallocatechin-3-gallate (EGCG) can attenuate neuronal damage mediated by this pathway in conditions such as brain ischemia. In order to investigate the therapeutic potential of EGCG to mitigate the neuronal damage characteristic of HAD, IFN-gamma was evaluated for its ability to enhance well-known neurotoxic properties of HIV-1 proteins gp120 and Tat in primary neurons and mice. Indeed, IFN-gamma enhanced the neurotoxicity of gp120 and Tat via increased JAK/STAT signaling. Additionally, primary neurons pretreated with a JAK1 inhibitor, or those derived from STAT1-deficient mice, were largely resistant to the IFN-gamma-enhanced neurotoxicity of gp120 and Tat. Moreover, EGCG treatment of primary neurons from normal mice reduced IFN-gamma-enhanced neurotoxicity of gp120 and Tat by inhibiting JAK/STAT1 pathway activation. EGCG was also found to mitigate the neurotoxic properties of HIV-1 proteins in the presence of IFN-gamma in vivo. Taken together, these data suggest EGCG attenuates the neurotoxicity of IFN-gamma augmented neuronal damage from HIV-1 proteins gp120 and Tat both in vitro and in vivo. Thus EGCG may represent a novel natural copound for the prevention and treatment of HAD.

Complexes of DNA vaccines with cationic, antigenic peptides are potent, polyvalent CD8(+) T-cell-stimulating immunogens

A priority in current vaccine research is the development of multivalent vaccines that support the efficient priming of long-lasting CD8(+) T-cell immunity. We developed a novel vaccination strategy that used synthetic, cationic (positively charged), and antigenic peptides complexed to negatively charged nucleic acids: antigenic, major histocompatibility complex-class I-binding epitopes fused with a cationic sequence derived from the HIV tat protein (tat50-57: KKRRQRRR) were mixed with nucleic acids (e.g., CpG-containing oligonucleotides) to quantitatively form peptide/nucleic acid complexes. The injection of these complexes efficiently primed long-lasting, specific CD8(+) T-cell immunity of high magnitude. This chapter describes a novel strategy to codeliver complexes of cationic/antigenic peptides bound to antigen-encoding plasmid DNA vaccines in a way that enhances the immunogenicity of both components for T cells.

Inhibition of tumor necrosis factor-alpha signaling prevents human immunodeficiency virus-1 protein Tat and methamphetamine interaction

Our previous studies demonstrated that the psychostimulant methamphetamine (MA) and the human immunodeficiency virus-1 (HIV-1) protein Tat interacted to cause enhanced dopaminergic neurotoxicity. The present study examined whether tumor necrosis factor-alpha (TNF-alpha) mediates the interaction between Tat and MA. In Sprague-Dawley rats, injections of Tat caused a small but significant increase in striatal TNF-alpha level, whereas MA resulted in no change. The increase in TNF-alpha induced by Tat + MA was not significantly different from that induced by Tat alone. Temporal analysis of TNF-alpha levels revealed a 50-fold increase 4 h after Tat administration. In C57BL/6 mice, Tat + MA induced a 50% decline in striatal dopamine levels, which was significantly attenuated in mice lacking both receptors for TNF-alpha. TNF-alpha synthesis inhibitors significantly attenuated Tat + MA neurotoxicity in hippocampal neuronal culture. The results suggest that Tat-induced elevation of TNF-alpha may predispose the dopaminergic terminals to subsequent damage by MA.

Transactivation and signaling functions of Tat are not correlated: biological and immunological characterization of HIV-1 subtype-C Tat protein

Background

Of the diverse subtypes of Human Immunodeficiency Virus Type-1 (HIV-1), subtype-C strains cause a large majority of infections worldwide. The reasons for the global dominance of HIV-1 subtype-C infections are not completely understood. Tat, being critical for viral infectivity and pathogenesis, may differentially modulate pathogenic properties of the viral subtypes. Biochemical studies on Tat are hampered by the limitations of the current purification protocols. Tat purified using standard protocols often is competent for transactivation activity but defective for a variety of other biological functions. Keeping this limitation in view, we developed an efficient protein purification strategy for Tat.

Results

Tat proteins obtained using the novel strategy described here were free of contaminants and retained biological functions as evaluated in a range of assays including the induction of cytokines, upregulation of chemokine coreceptor, transactivation of the viral promoter and rescue of a Tat-defective virus. Given the highly unstable nature of Tat, we evaluated the effect of the storage conditions on the biological function of Tat following purification. Tat stored in a lyophilized form retained complete biological activity regardless of the storage temperature. To understand if variations in the primary structure of Tat could influence the secondary structure of the protein and consequently its biological functions, we determined the CD spectra of subtype-C and -B Tat proteins. We demonstrate that subtype-C Tat may have a relatively higher ordered structure and be less flexible than subtype-B Tat. We show that subtype-C Tat as a protein, but not as a DNA expression vector, was consistently inferior to subtype-B Tat in a variety of biological assays. Furthermore, using ELISA, we evaluated the anti-Tat antibody titers in a large number of primary clinical samples (n = 200) collected from all four southern Indian states. Our analysis of the Indian populations demonstrated that Tat is non-immunodominant and that a large variation exists in the antigen-specific antibody titers.

Conclusion

Our report not only describes a simple protein purification strategy for Tat but also demonstrates important structural and functional differences between subtype-B and -C Tat proteins. Furthermore, this is the first report of protein purification and characterization of subtype-C Tat.

The absence of anti-Tat antibodies is associated with risk of disease progression in HIV-2 infection

The Tat protein of human immunodeficiency virus (HIV) is essential for viral replication and has extracellular pathogenic activity. We sought to determine whether the anti-Tat antibody response was predictive of disease progression in 144 HIV type 2 (HIV-2)-infected subjects observed longitudinally between 1985 and 2003. Sixty-eight percent of the subjects tested positive for anti-Tat antibodies, with reactivity notably established early after seroconversion and stably maintained over the course of infection. The risk and rate of progression to advanced HIV-2 AIDS was significantly higher in anti-Tat-negative subjects than in anti-Tat-positive subjects, extending the importance of this prognostic marker for HIV-2 AIDS.

Induction of human immunodeficiency virus type-1-specific immunity with a novel gene transport unit (GTU)-MultiHIV DNA vaccine

A multiHIV fusion gene expressing an antigenic fusion protein composed of regulatory HIV-1 proteins Rev, Nef, and Tat, as well as Gag p17/p24 and a stretch of 11 cytotoxic T lymphocyte (CTL) epitope clusters from Pol and Env, was cloned into a novel DNA vector named the Gene Transport Unit (GTU). A mouse H-2(d)-restricted HIV-1 gp120 epitope (RGPGRAFVTI) was cloned into the fusion gene as well. In addition to the HIV- 1 genes the GTU codes for a nuclear anchoring protein (bovine papilloma virus E2), ensuring the long maintenance of the vector and a high expression level of the selected immunogens. BALB/c mice were immunized with the GTU-MultiHIV DNA construct by different routes and regimens of immunization to assess the immunogenicity of the DNA vaccine in vivo. Mice developed strong CD8(+) CTL responses to HIV-1 Env and Gag measured by an ELISPOT-IFN-gamma assay and chromium release assay. In addition, T cell responses to regulatory proteins Rev, Nef, and Tat were induced. Antibody responses were detected to each of the HIV antigens encoded by the DNA construct. Minimal doses of the GTU-MultiHIV DNA delivered by gene gun were potent in inducing significant HIV-specific CTL responses. The equivalent doses of the conventional plasmid expressing MultiHIV DNA delivered by gene gun failed to do so. An ideal DNA vaccine should yield high expression of the viral antigens for a prolonged period of time, and expression of the multiple viral antigens is probably required for the induction of a broad and protective immune response. The GTU-MultiHIV DNA vaccine described is a good vaccine candidate that meets the above criteria.

DNA prime and protein boost immunization with innovative polymeric cationic core-shell nanoparticles elicits broad immune responses and strongly enhance cellular responses of HIV-1 tat DNA vaccination

Novel biocompatible core-shell cationic nanoparticles, composed of an inner hard core of poly(methylmethacrylate) (PMMA) and a hydrophilic tentacular shell bearing positively charged groups and poly(ethyleneglycol) chains covalently bound to the core, were prepared by emulsion polymerization and characterized in vitro and in vivo for DNA vaccine applications. The nanoparticles reversibly adsorbed large amounts of DNA, mainly through electrostatic interactions, preserved its functional structure, efficiently delivered it intracellularly, and were not toxic in vitro or in mice. Furthermore, two intramuscular (i.m.) immunizations (4 weeks apart) with a very low dose (1 microg) of the plasmid pCV-tat delivered by these nanoparticles followed by one or two protein boosts induced significant antigen-specific humoral and cellular responses and greatly increased Th1-type T cell responses and CTLs against HIV-1 Tat.

Cross-clade protection induced by human immunodeficiency virus-1 DNA immunogens expressing consensus sequences of multiple genes and epitopes from subtypes A, B, C, and FGH

The correlate of protection in human immunodeficiency virus (HIV) infection is not known, but preclinical and clinical studies support the involvement of both antibodies and cellular immunity. In addition, the existence of multiple HIV clades makes HIV vaccine design especially challenging. We have constructed a vaccine platform with an HIV-1 subtype B DNA immunogen expressing full length consensus sequences from HIV-1 rev, nef, tat, and gag with additional cellular epitope clusters from the env and pol regions. Furthermore, this platform has been extended to three additional plasmids expressing the same immunogens but originating from subtypes A or C consensus or FGH ancestral sequences. Immunogenicity in BALB/c mice, by gene gun or intramuscular delivery, revealed strong IFN-gamma production in response to in vitro re-stimulation with a H-2d restricted gag peptide (AMQMLKETI) or even stronger toward an env epitope (RGPGRAFVTI). Weak humoral immunity was detected. Gene gun immunization with a cocktail of all four plasmids induced pre-challenge cellular immunity in C57Bl6/A2.01 mice and subsequently a robust frequency of protection (11/12 animals) after experimental challenge with subtype A or B HIV-1/Murine Leukemia Virus (HIV-1/MuLV). The cross-clade protection observed in this challenge experiment demonstrates that these multigene/multiepitope HIV DNA immunogens are likely to be potent immunogens also against the HIV-infection of human beings.

HIV-1 Tat-coated nanoparticles result in enhanced humoral immune responses and neutralizing antibodies compared to alum adjuvant

HIV-1 Tat has been identified as an attractive target for vaccine development and is currently under investigation in clinical trials as both a therapeutic and preventative vaccine for HIV-1. It is well known that protein based vaccines produce poor immune responses by themselves and therefore require adjuvants to enhance immune responses. We have previously reported on the use of anionic nanoparticles (NPs) for enhancing cellular and humoral immune responses to Tat (1-72). The purpose of this study was to further evaluate the immune response of HIV-1 Tat (1-72) coated on anionic nanoparticles compared to alum using various doses of Tat (1-72). Nanoparticles were effective at generating comparable antibody titers at both 1 and 5 microg doses of Tat (1-72), whereas the antibody titers significantly decreased at the lower dose of Tat (1-72) using alum. Anti-sera from Tat (1-72) immunized mice reacted greatest to the N-terminal and basic regions of Tat, with the NP groups showing stronger reactivity to these regions compared to alum. Moreover, the anti-sera from all Tat (1-72) immunized groups contained Tat-neutralizing antibodies and were able to significantly inhibit Tat-mediated long terminal repeat (LTR) transactivation.

Delivery of the HIV-1 Tat protein to dendritic cells by the CyaA vector induces specific Th1 responses and high affinity neutralizing antibodies in non human primates

The human immunodeficiency virus type 1 (HIV-1) Tat is a key protein playing a major role in the infectivity of the virus. Thus, HIV-Tat based vaccines have been proposed as an attractive option to treat AIDS. Recently, we have shown that the recombinant detoxified adenylate cyclase (CyaA) from Bordetella pertussis carrying HIV-Tat (CyaA-E5-Tat), targets dendritic cells (DCs) and induces specific Th1 polarized and neutralizing antibody responses in mice. To further explore the potentialities of this prototype vaccine for human use, we analyzed the CyaA-E5-Tat induced antibody responses in non-human primates and established the biological characteristics of these antibodies. African Green Monkeys (AGM) were immunized with CyaA-E5-Tat in the presence or in the absence of alum adjuvant. First, we showed that the anti-CyaA antibodies induced by such immunization does not interfere with the binding of CyaA-E5-Tat to its receptor at the DC surface, the alphaMbeta2 integrin. Monkeys immunized with CyaA-E5-Tat, with or without alum, produced anti-Tat antibodies that mainly recognized the N-terminal domain of the Tat protein. Importantly, all sera obtained after three immunizations displayed the capacity to bind to Tat and neutralize its transactivating function in vitro. Finally, in the absence of alum, CyaA-E5-Tat, induced Th1 Tat specific T cell responses. These findings reveal that CyaA-E5-Tat is efficiently delivered in non-human primates and had a significant impact on the generation of neutralizing anti-Tat antibodies. These observations are, thus, encouraging for the use of the CyaA vector in human and also suggest that CyaA-E5-Tat might be a useful tool to decipher the biological characteristic of such antibodies.

Targeting of HIV-1 Tat traffic and function by transduction-competent single chain antibodies

Human immunodeficiency virus type 1-encoded Tat protein is a transactivating factor essentially required for viral replication. Tat binds specifically to the transactivation response RNA stem loop, which is formed at the 5' end of all viral transcripts. The TAR binding motif of Tat also contains a protein transduction domain, PTD that mediates not only nuclear localization of Tat but is also capable of transducing cargo across cellular membranes. In order to target a Tat antagonist directly to the TAR binding site in the nucleus, we engineered a chimeric protein consisting of the Tat-derived PTD fused to the anti-Tat single chain antibody scFvtat1 that binds intracellularly to Tat. Recombinant scFvtat1-PTD(TAT) fusion antibody retained both, anti-Tat specificity and PTD(TAT)-mediated transduction-competence leading to its nuclear accumulation within living cells. Incubation of Jurkat T cells with scFvtat1-PTD(TAT) suppressed Tat-dependent transcription of a HIV-1 reporter gene by >80%. Transfection of a scFvtat1-PTD(TAT) expression plasmid in HEK293 cells resulted in diffuse cytoplasmic and nuclear expression. ScFvtat1-PTD(TAT) did not inhibit HIV-1 Tat translocation to the nucleus, yet showed increased inhibition of 78%, indicating a nuclear site of scFvtat1-PTD(TAT) action. Strikingly, the PTD(TAT) alone showed 55% inhibition in the HIV-1 luciferase reporter assay, indicating competition with HIV-1 Tat binding to the TAR element. The results of this study suggest that Tat traffic can only marginally be affected by anti-Tat antibodies and that effective inhibition of Tat function requires both competition with HIV Tat for TAR binding mediated by PTD(TAT) and steric hindrance mediated by the scFvtat1 moiety.

DNA immunization in combination with effective antiretroviral drug therapy controls viral rebound and prevents simian AIDS after treatment is discontinued

DNA immunization in conjunction with antiretroviral therapy was evaluated in SIV-infected rhesus macaques treated with [R]-9-[2-phosphonylmethoxypropyl]adenine (PMPA). Macaques were immunized monthly with DNA vaccines expressing either SIV gag/tat or SIV gag/tat and 19 CD8+ T cell epitopes during 7 months of therapy. Half the animals from each group were additionally immunized before infection. Only 60% of the animals (4 controls, 20 vaccinated) responded to PMPA (ART responders). All 4 ART responder controls demonstrated viral rebound or CD4 decline after PMPA was withdrawn. In contrast, 17 of 20 vaccinated ART responders contained viral rebound for over 7 months after PMPA was withdrawn. Viral control correlated with stable CD4 counts, higher lymphoproliferation and an increase in the magnitude and breadth of the CD8+ T cell response. Immunizing before infection or with multi-epitopes enhanced these effects. These results demonstrate that DNA immunization during antiretroviral therapy may be an effective strategy to treat HIV infection.

Selective side-chain modification of cysteine and arginine residues blocks pathogenic activity of HIV-1-Tat functional peptides

Extracellular Tat protein of HIV-1 activates virus replication in HIV-infected cells and induces a variety of host factors in the uninfected cells, some of which play a critical role in the progression of HIV infection. The cysteine-rich and arginine-rich basic domains represent key components of the HIV-Tat protein for pathogenic effects of the full-length Tat protein and, therefore, could be ideal candidates for the development of a therapeutic AIDS vaccine. The present study describes selective modifications of the side-chain functional groups of cysteine and arginine amino acids of these HIV-Tat peptides to minimize the pathogenic effects of these peptides while maintaining natural peptide linkages. Modification of cysteine by introducing either a methyl or t-butyl group in the free sulfhydryl group and replacing the guanidine group with a urea linkage in the side chain of arginine in the cysteine-rich and arginine-rich Tat peptide sequences completely blocked the ability of these peptides to induce HIV replication, chemokine receptor CCR-5 expression, and NF-kappaB activity in monocytes. Such modifications also inhibited angiogenesis and migration of Kaposi's sarcoma cells normally induced by Tat peptides. Such chemical modifications of the cysteine-rich and arginine-rich peptides did not affect their reactivity with antibodies against the full-length Tat protein. With an estimated 40 million HIV-positive individuals worldwide and approximately 4 million new infections emerging every year, a synthetic subunit HIV-Tat vaccine comprised of functionally inactive Tat domains could provide a safe, effective, and economical therapeutic vaccine to reduce the progression of HIV disease.

Antibody mediated transduction of therapeutic proteins into living cells

Protein therapy refers to the direct delivery of therapeutic proteins to cells and tissues with the goal of ameliorating or modifying a disease process. Current techniques for delivering proteins across cell membranes include taking advantage of receptor-mediated endocytosis or using protein transduction domains that penetrate directly into cells. The most commonly used protein transduction domains are small cell-penetrating peptides derived from such proteins as the HIV-1 Tat protein. A novel protein transduction domain developed as the single chain fragment (Fv) of a murine anti-DNA autoantibody, mAb 3E10, has recently been developed and used to deliver biologically active proteins to living cells in vitro. This review will provide a brief overview of the development of the Fv fragment and provide a summary of recent studies using Fv to deliver therapeutic peptides and proteins (such as a C-terminal p53 peptide, C-terminal p53 antibody fragment, full-length p53, and micro-dystrophin) to cells.

Efficient systemic and mucosal responses against the HIV-1 Tat protein by prime/boost vaccination using the lipopeptide MALP-2 as adjuvant

A major goal of HIV-1 vaccine development is the induction of mucosal immune responses able to stop or reduce viral infection directly at the portal of entry. We established a heterologous prime/boost vaccination protocol based on intradermal priming with the HIV-1 Tat protein and intranasal boosting with the Tat protein co-administered with the mucosal adjuvant MALP-2. Strong Tat-specific humoral responses were elicited in vaccinated mice at both systemic and mucosal levels. The cellular responses were characterized by a Th1 dominant helper pattern. The heterologous prime/boost regimen was also able to induce Tat-specific CTL, which were absent in animals receiving the homologous prime boost scheme. Thus, the heterologous prime/boost protocol was the only regimen able to evoke both CTL and sIgA responses. This suggests that a similar approach can be exploited to develop multi-component vaccines against HIV-1 infections able to induce both systemic and mucosal immune responses.

Genetic fusion of proteins to the SIV Tat protein enhances their immunogenicity

The potential of genetically fusing recombinant proteins to the simian immunodeficiency virus (SIV) Tat protein has been investigated. The recombinant SIV Tat protein was initially expressed in very low amounts in E. coli, but optimization of the coding sequence for translation in the bacterial host significantly improved protein expression. Whilst fusion of SIV Tat to an experimental antigen (GST) facilitated the binding of the antigen to cell surfaces it did not appear to facilitate the transport of the protein into the cytosol. The immunogenicity of GST was significantly enhanced, in the absence of adjuvants, when fused to SIV Tat, with the induction of IgG1 and IgG2a antibodies indicative of a Th1 response being induced. However, no evidence was obtained that such an immunization scheme efficiently induced a CTL response.