Recognition of prominent viral epitopes induced by immunization with human immunodeficiency virus type 1 regulatory genes

In vitro Anti-HIV-1 Activity of the Recombinant HIV-1 TAT Protein Along With Tenofovir Drug

BACKGROUND

HIV-1 TAT protein is essential for the regulation of viral genome transcription. The first exon of TAT protein has a fundamental role in the stimulation of the extrinsic and intrinsic apoptosis pathways, but its anti-HIV activity is not clear yet.

METHODS

In the current study, we firstly cloned the first exon of the TAT coding sequence in the pET-24a expression vector and then protein expression was done in the Rosetta expression host. Next, the expressed TAT protein was purified by Ni-NTA column under native conditions. After that, the protein yield was determined by Bradford kit and NanoDrop spectrophotometry. Finally, the cytotoxicity effect and anti-Scr-HIV-1 activity of the recombinant TAT protein alone and along with Tenofovir drug were assessed by MTT and ELISA, respectively.

RESULTS

The recombinant TAT protein was successfully generated in E. coli, as confirmed by 13.5% SDS-PAGE and western blotting. The protein yield was ~150-200 μg/ml. In addition, the recombinant TAT protein at a certain dose with low toxicity could suppress Scr-HIV replication in the infected HeLa cells (~30%) that was comparable with a low toxic dose of Tenofovir drug (~40%). It was interesting that the recombinant TAT protein could enhance anti-HIV potency of Tenofovir drug up to 66%.

CONCLUSION

Generally, a combination of TAT protein and Tenofovir drug could significantly inhibit HIV-1 replication. It will be required to determine their mechanism of action in the next studies.

Molecular and genetic characterization of natural HIV-1 Tat Exon-1 variants from North India and their functional implications

BACKGROUND

Designing an ideal vaccine against HIV-1 has been difficult due to enormous genetic variability as a result of high replication rate and lack of proofreading activity of reverse transcriptase leading to emergence of genetic variants and recombinants. Tat transactivates HIV-1 LTR, resulting in a remarkable increase in viral gene expression, and plays a vital role in pathogenesis. The aim of this study was to characterize the genetic variations of Tat exon-1 from HIV-1 infected patients from North India.

METHODS

Genomic DNA was isolated from PBMCs and Tat exon-1 was PCR amplified with specific primers followed by cloning, sequencing and sequence analyses using bioinformatic tools for predicting HIV-1 subtypes, recombination events, conservation of domains and phosphorylation sites, and LTR transactivation by luciferase assay.

RESULTS

Phylogenetic analysis of Tat exon-1 variants (n = 120) revealed sequence similarity with South African Tat C sequences and distinct geographical relationships were observed for B/C recombinants. Bootscan analysis of our variants showed 90% homology to Tat C and 10% to B/C recombinants with a precise breakpoint. Natural substitutions were observed with high allelic frequencies which may be beneficial for virus. High amino acid conservation was observed in Tat among Anti Retroviral Therapy (ART) recipients. Barring few changes, most of the functional domains, predicted motifs and phosphorylation sites were well conserved in most of Tat variants. dN/dS analysis revealed purifying selection, implying the importance of functional conservation of Tat exon-1. Our Indian Tat C variants and B/C recombinants showed differential LTR transactivation.

CONCLUSIONS

The possible role of Tat exon-1 variants in shaping the current HIV-1 epidemic in North India was highlighted. Natural substitutions across conserved functional domains were observed and provided evidence for the emergence of B/C recombinants within the ORF of Tat exon-1. These events are likely to have implications for viral pathogenesis and vaccine formulations.

HIV-1 Tat protein induces viral internalization through Env-mediated interactions in dose-dependent manner

OBJECTIVE

To study the dose-dependent manner of HIV-1 Tat-induced effects on viral replication, internalization and spread, and to directly observe these effects on soluble Env immunogens and virus-like particles.

DESIGN

In order to determine the manner through which Tat affects viral replication, we incubated cells, virions and soluble Env spikes with Tat at different concentrations, and directly visualized the effects of such incubation.

METHODS

Cell-based infectivity assays were carried out to assay Tat dose-dependency of viral infectivity. Transmission electron microscopy of virus-like particles and soluble gp140 immunogens incubated with Tat at various concentrations was performed to directly observe Tat-induced effects.

RESULTS

Treating virus with exogenous Tat increased infectivity in a dose-dependent manner. In the presence of anti-Tat antibodies, virus replication and spread were repressed, postulating Tat contributions to disease progression. When CXCR4 coreceptors were blocked, Tat treatment overcame the inhibition relative to absence of Tat treatment. Similarly, syncytium formation between chronically infected and uninfected target cells was also increased by exogenous Tat treatment. Inhibiting the CD4 receptor for virus entry abolished syncytium formation and Tat treatment was unable to overcome CD4 dependency. We show that Tat reduces virus infectivity at higher Tat concentrations through Env interactions resulting in viral aggregation.

CONCLUSION

Treating virions or chronically infected cells with exogenous Tat could enhance virus infectivity and spread through coreceptor tropism switch or through another undetermined mechanism. The aggregation potential of Tat suggests a mechanism of negative-feedback regulation of viral replication, providing another regulative function to control viral replication.

IL-12 and GM-CSF in DNA/MVA immunizations against HIV-1 CRF12_BF Nef induced T-cell responses with an enhanced magnitude, breadth and quality

In Argentina, the HIV epidemic is characterized by the co-circulation of subtype B and BF recombinant viral variants. Nef is an HIV protein highly variable among subtypes, making it a good tool to study the impact of HIV variability in the vaccine design setting. We have previously reported a specific cellular response against NefBF with low cross-reactivity to NefB in mice. The aim of this work was to analyze whether the co-administration of IL-12 and GM-CSF, using DNA and MVA vaccine vectors, could improve the final cellular response induced. Mice received three DNA priming doses of a plasmid that express NefBF plus DNAs expressing IL-12 and/or GM-CSF. Afterwards, all the groups were boosted with a MVAnefBF dose. The highest increase in the magnitude of the NefBF response, compared to that induced in the control was found in the IL-12 group. Importantly, a response with higher breadth was detected in groups which received IL-12 or GM-CSF, evidenced as an increased frequency of recognition of homologous (BF) and heterologous (B) Nef peptides, as well as a higher number of other Nef peptide pools representing different viral subtypes. However, these improvements were lost when both DNA cytokines were simultaneously administered, as the response was focused against the immunodominant peptide with a detrimental response towards subdominant epitopes. The pattern of cytokines secreted and the specific-T-cell proliferative capacity were improved in IL-12 and IL-12+GM-CSF groups. Importantly IL-12 generated a significant higher T-cell avidity against a B heterologous peptide.

This study indicates that the incorporation of DNA expressing IL-12 in DNA/MVA schemes produced the best results in terms of improvements of T-cell-response key properties such as breadth, cross-reactivity and quality (avidity and pattern of cytokines secreted). These relevant results contribute to the design of strategies aimed to induce T-cell responses against HIV antigens with higher quality.

Induction of anti-Tat neutralizing antibodies by the CyaA vector targeting dendritic cells: influence of the insertion site and of the delivery of multicopies of the dominant Tat B-cell epitope

HIV-Tat based vaccines have been proposed as an attractive option to prevent or treat AIDS. A vaccine to induce optimal anti-Tat neutralizing antibody responses was designed by inserting this protein, or its dominant B-cell epitope, into the CyaA vector, which targets dendritic cells (DC). Tat was inserted into various sites of CyaA, including regions that do not translocate into the cytosol of the targeted DC. The presentation of the Tat CD4(+) T-cell epitope delivered by the CyaA-Tat proteins was observed with a recombinant CyaA in which the entire AC domain was replaced by the entire Tat protein (Tat-Δ373 CyaA) but was abolished with large deletions of the N-terminal region. Moreover, CyaA carrying multiple copies of the dominant Tat: 1-21 B-cell epitope were shown to induce high titers of anti-Tat antibodies, even after a single immunization, that persisted up to 10 weeks post-immunization.

HIV-1 Tat-based vaccines: an overview and perspectives in the field of HIV/AIDS vaccine development

The HIV epidemic continues to represent one of the major problems worldwide, particularly in the Asia and Sub-Saharan regions of the world, with social and economical devastating effects. Although antiretroviral drugs have had a dramatically beneficial impact on HIV-infected individuals that have access to treatment, it has had a negligible impact on the global epidemic. Hence, the inexorable spreading of the HIV pandemic and the increasing deaths from AIDS, especially in developing countries, underscore the urgency for an effective vaccine against HIV/AIDS. However, the generation of such a vaccine has turned out to be extremely challenging. Here we provide an overview on the rationale for the use of non-structural HIV proteins, such as the Tat protein, alone or in combination with other HIV early and late structural HIV antigens, as novel, promising preventative and therapeutic HIV/AIDS vaccine strategies.

DNA vaccine therapy for chronic hepatitis C virus (HCV) infection: immune control of a moving target

The use of DNA plasmids for DNA vaccination was first described in the early 1990 s. DNA vaccinations were successful in small animal models but in larger animals and humans problems appeared. One major obstacle, effective delivery, has been partly overcome by new delivery techniques, such as transdermal delivery with the gene gun, and in vivo electroporation. We are entering a new era of DNA vaccination, where such techniques can be tested in humans. DNA vaccination may be a useful therapy for chronic hepatitis C virus (HCV) infections. Patients with these infections have a reduced T cell response to the invading virus. The genetic variability of HCV, its immunomodulatory properties and high replication rate contribute to chronicity. By providing the correct stimulus T cells may be activated to clear the infection. The vaccination is intended to induce a coordinated immune-based attack on the continuously moving HCV target. If effective, this should help in clearing the infection.

Priming with a very low dose of DNA complexed with cationic block copolymers followed by protein boost elicits broad and long-lasting antigen-specific humoral and cellular responses in mice

Cationic block copolymers spontaneously assemble via electrostatic interactions with DNA molecules in aqueous solution giving rise to micellar structures that protect the DNA from enzymatic degradation both in vitro and in vivo. In addition, we have previously shown that they are safe, not immunogenic and greatly increased antigen-specific CTL responses following six intramuscular inoculations of a very low dose (1microg) of the vaccine DNA as compared to naked DNA. Nevertheless, they failed to elicit detectable humoral responses against the antigen. To gain further insight in the potential application of this technology, here we show that a shorter immunization protocol based on two DNA intramuscular inoculations of 1microg of DNA delivered by these copolymers and a protein boost elicits in mice broad (both humoral and cellular) and long-lasting responses and increases the antigen-specific Th1-type T cell responses and CTLs as compared to priming with naked DNA. These results indicate that cationic block copolymers represent a promising adjuvant and delivery technology for DNA vaccination strategies aimed at combating intracellular pathogens.

The therapeutic phase I trial of the recombinant native HIV-1 Tat protein

The native HIV-1 Tat protein was chosen as a vaccine candidate based on its key role in the virus life cycle and on the correlation of Tat-specific immune responses with the asymptomatic stage and lower disease progression rates, but also due to its sequence conservation amongst the various HIV clades as well as the adjuvant effects on dendritic cells. Safety, immunogenicity and efficacy data in monkeys support the development of this vaccine concept.

Safety and immunogenicity, after nasal application of HIV-1 DNA gagp37 plasmid vaccine in young mice

BACKGROUND

There is a need for safe and potent adjuvants capable of delivering vaccine candidates over the mucosal barrier, with good capacity to stimulate both mucosal and systemic cell-mediated and humoral immunity. An adjuvant aimed for intranasal delivery should preferably deliver the antigen and minimize the transfer into the close proximity of the central nervous system, thus avoiding damage on the olfactory tissues. Advantages with a mucosal delivery route would be to provide mucosal and systemic immunity, requiring lower vaccine doses then when given parentally. The aim of this study was to study if the N3 adjuvant intranasally administered with HIV DNA plasmids would be transferred into the olfactory tissues and cause local inflammation and tissue damage.

RESULTS

The N3 adjuvant alone and when combined with HIV-1 DNA gag plasmid and delivered intranasally did not cause detectable damage to the nasal epithelium or the olfactory epithelium or bulb over a period of 3 days after delivery. The intranasal administration of HIV-1 gagp37 DNA induced both a humoral and a cell-mediated immunity against the gag antigen. Significantly higher HIV-1-specific humoral, but not cell-mediated immune responses were seen in DNA/N3-immunized mice in comparison with HIV-1 DNA/saline-immunized animals.

CONCLUSIONS

A safe and convenient intranasal mode of HIV-1 DNA plasmid and adjuvant delivery was shown not to interfere with the tissues in close proximity to the central nervous system. The N3 adjuvant combined with HIV-1 plasmids enhances the HIV-1-specific immunogenicity and merits to be clinically tested.

Presence of HIV-1 Nef specific CD4 T cell response is associated with non-progression in HIV-1 infection

The ex vivo response to three HLA-DR-restricted Nef peptides (Nef 66-97, Nef 133-159, Nef 180-202) and one HLA-DQ-restricted Nef peptide (Nef 56-68) was evaluated in 28 HIV-seropositive patients and 6 Long-term Non-Progressors (LTNPs). Analyzing specific proliferative response and IFN-gamma secretion, patients were identified as high responders, medium responders and non-responders to peptides. As high responder patients, LTNP patients showed strong proliferative response to all the Nef-peptides as strong IFN-gamma secretion. Twenty-four months later, all high responder patients were always without antiretroviral treatment whereas 50% of medium responders and at least 66% of low responder patients followed bi-therapy. CDC classification confirmed also unfavourable evolution for these two last groups. All high responder patients conserved stable CD4 counts, proliferative response to Nef peptides as strong IFN-gamma secretion during this 24-month period. So, early good T CD4 response to peptides of the Nef protein could thus be regarded as a factor of good prognosis in HIV infection and a tool of importance in the decision to put or not a patient under treatment.

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.

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.

Current developments in viral DNA vaccines: shall they solve the unsolved?

This review describes the mechanisms of immune response following DNA vaccination. The efficacy of DNA vaccines in animal models is highlighted, especially in viral diseases against which no widely accepted vaccination is currently available. Emphasis is given to possible therapeutic vaccination in chronic infections due to persisting virus genomes, such as recurrent herpes (HSV-1 and HSV-2), pre-AIDS (HIV-1) and/or chronic hepatitis B (HBV). In these, the problem of introducing foreign viral DNA may not be of crucial importance, since the immunised subject is already a viral DNA (or provirus) carrier. The DNA-based immunisation strategies may overcome several problems of classical viral vaccines. Novel DNA vaccines could induce immunity against multiple viral epitopes including the conservative type common ones, which do not undergo antigenic drifts. Within the immunised host, they mimic the effect of live attenuated viral vaccines when continuously expressing the polypeptide in question. For this reason they directly stimulate the antigen-presenting cells, especially dendritic cells. The antigen encoded by plasmid elicits T helper cell activity (Th1 and Th2 type responses), primes the cytotoxic T cell memory and may induce a satisfactory humoral response. The efficacy of DNA vaccines can be improved by adding plasmids encoding immunomodulatory cytokines and/or their co-receptors.

Induction of neutralizing antibodies and Th1-polarized and CD4-independent CD8+ T-cell responses following delivery of human immunodeficiency virus type 1 Tat protein by recombinant adenylate cyclase of Bordetella pertussis

HIV-Tat, a conserved protein playing a key role in the early life cycle of the human immunodeficiency virus (HIV) has been proposed as a potential AIDS vaccine. An HIV-Tat-based vaccine should elicit a broad, long-lasting, and neutralizing immune response. We have previously demonstrated that the adenylate cyclase (CyaA) from Bordetella pertussis targets dendritic cells and delivers CD8(+) and CD4(+) T-cell epitopes into the major histocompatibility complex class I and class II presentation pathways. We have also showed that CyaA induced specific and protective cytotoxic T cell responses in vivo. Here, we designed a prototype vaccine based on the HIV type 1 Tat delivered by CyaA (CyaA-E5-Tat) and tested its capacity to induce HIV-Tat-specific cellular as well as antibody responses. We showed that immunization of mice by CyaA-E5-Tat in the absence of adjuvant elicited strong and long-lasting neutralizing anti-Tat antibody responses more efficient than those obtained after immunization with Tat toxoid in aluminum hydroxide adjuvant. Analyses of the anti-Tat immunoglobulin G isotypes and the cytokine pattern showed that CyaA-E5-Tat induced a Th1-polarized immune response in contrast to the Th2-polarized immune responses obtained with the Tat toxoid. In addition, our data demonstrated that HIV-Tat-specific gamma interferon-producing CD8(+) T cells were generated after vaccination with CyaA-E5-Tat in a CD4(+) T-cell-independent manner. Based on these findings, CyaA-E5-Tat represents an attractive vaccine candidate for both preventive and therapeutic vaccination involving CyaA as an efficient nonreplicative vector for protein delivery.

Protection against influenza virus infection in BALB/c mice immunized with a single dose of neuraminidase-expressing DNAs by electroporation

The ability of a single dose of plasmid DNA encoding neuraminidase (NA) or hemagglutinin (HA) from influenza virus A/PR/8/34 (PR8) (H1N1) to protect against homologous virus infection was examined in BALB/c mice. In the present study, mice were immunized once with 30 microg of NA or HA DNA by electroporation. Four weeks or 28 weeks after immunization, mice were challenged with a lethal dose of homologous virus and the ability of NA or HA DNA to protect the mice from influenza was evaluated. We found that a single inoculation of NA DNA could provide protection against influenza virus challenge as well as long-term protection against viral infection. Whereas, the mice immunized with a single dose of HA DNA could not be protected. In addition, neonatal mice immunized with a single dose of 30 microg of NA DNA could be provided with significant protection against viral infection.

Sequence variation within the dominant amino terminus epitope affects antibody binding and neutralization of human immunodeficiency virus type 1 Tat protein

Tat is among the required regulatory genes of human immunodeficiency virus type 1 (HIV-1). Tat functions both within infected cells as a transcription factor and as an extracellular factor that binds and alters bystander cells. Some functions of extracellular Tat can be neutralized by immune serum or monoclonal antibodies. In order to understand the antibody response to Tat, we are defining antibody epitopes and the effects of natural Tat sequence variation on antibody recognition. The dominant Tat epitope in macaque sera is within the first 15 amino acids of the protein amino terminus. Together with a subdominant response to amino acids 57 to 60, these two regions account for most of the macaque response to linear Tat epitopes and both regions are also sites for the binding of neutralizing antibodies. However, the dominant and subdominant epitope sequences differ among virus strains, and this natural variation can preclude antibody binding and Tat neutralization. We also examined serum samples from 31 HIV-positive individuals that contained Tat binding antibodies; 23 of the 31 sera recognized the amino terminus peptide. Similar to binding in macaques, human antibody binding to the amino terminus was affected by variations at positions 7 and 12, sequences that are distinct for clade B compared to other viral clades. Tat-neutralizing antibodies to the dominant amino terminus epitope are affected by HIV clade variation.

Nonstructural HIV proteins as targets for prophylactic or therapeutic vaccines

By the end of 2004, more than 20 HIV-1 vaccine candidates will have entered clinical testing in at least 30 trials worldwide. Almost half of these vaccines include nonstructural HIV-1 gene products. This represents an important innovation in the HIV vaccine field, because until 9 years ago not even preclinical testing in small animal models had been carried out with such immunogens. This review briefly discusses the experimental evidence that provides the rationale for the use of nonstructural HIV-1 gene products as vaccine antigens, and summarizes the current status and the future development of these novel vaccines.

Codon optimization of the tat antigen of human immunodeficiency virus type 1 generates strong immune responses in mice following genetic immunization

DNA vaccines have been successful in eliciting potent immune responses in mice. Their efficiency, however, is restricted in larger animals. One reason for the limited performance of the DNA vaccines is the lack of molecular strategies to enhance immune responses. Additionally, genes directly cloned from pathogenic organisms may not be efficiently translated in a heterologous host expression system as a consequence of codon bias. To evaluate the influence of codon optimization on the immune response, we elected to use the Tat antigens of human immunodeficiency virus type 1 (HIV-1) (subtype C) and HIV-2, as these viral antigens are poorly immunogenic in natural infection and in experimental immunization and they are functionally important in viral infectivity and pathogenesis. Substituting codons that are optimally used in the mammalian system, we synthetically assembled Tat genes and compared them with the wild-type counterparts in two different mouse strains. Codon-optimized Tat genes induced qualitatively and quantitatively superior immune responses as measured in a T-cell proliferation assay, enzyme-linked immunospot assay, and chromium release assay. Importantly, while the wild-type genes promoted a mixed Th1-Th2-type cytokine profile, the codon-optimized genes induced a predominantly Th1 profile. Using a pepscan strategy, we mapped an immunodominant T-helper epitope to the core and basic domains of HIV-1 Tat. We also identified cross-clade immune responses between HIV-1 subtype B and C Tat proteins mapped to this T-helper epitope. Developing molecular strategies to optimize the immunogenicity of DNA vaccines is critical for inducing strong immune responses, especially to antigens like Tat. Our identification of a highly conserved T-helper epitope in the first exon of HIV-1 Tat of subtype C and the demonstration of a cross-clade immune response between subtypes B and C are important for a more rational design of an HIV vaccine.

Topical delivery of imiquimod to a mouse model as a novel adjuvant for human immunodeficiency virus (HIV) DNA

We evaluated the compound imiquimod as a possible adjuvant for DNA immunization against human immunodeficiency virus (HIV). We found that gene-gun epidermal delivery of the DNA in combination with imiquimod resulted in the strongest HIV specific immune responses. The effect of imiquimod was further compared to that of recombinant granulocyte macrophage-colony stimulating factor (GM-CSF), a known DNA vaccine adjuvant. Both adjuvants were able to enhance the immune responses induced by the HIV-1 genes alone. The delivery of an adjuvant as a topical cream rather than through injections has a clear clinical benefit. We show for the first time that imiquimod can act as an adjuvant for DNA vaccination.

Gene immunization may induce secondary antibodies reacting with DNA

The fear of autoimmunity in DNA-vaccine recipients initiated screening for anti-DNA antibodies in rabbits immunized with genes of viral nucleic acid-binding and adapter proteins. Of 11 DNA/protein-immunized rabbits, seven had developed secondary antibodies against DNA detected at weeks 11-50 from the on-start of immunization. Two rabbits immunized with HIV-1 reverse transcriptase gene developed transient anti-double-stranded DNA antibodies of high avidity that recognized DNA in the kinetoplasts of Crithidia luciliae. Others developed antibodies reacting with DNA in ELISA and targeting nuclear-associated antigens in the immunofluoresence test. No anti-DNA antibodies were detected at these time-points in any of the controls (P=0.036). Induction of anti-DNA antibodies by epitope spreading from protein domains involved in nucleic acid-binding versus maturation of anti-protein antibodies to dual protein-DNA specificity is discussed. (126 words).

Codon optimization and ubiquitin conjugation of human immunodeficiency virus-1 Tat lead to enhanced cell-mediated immune responses

The transactivator protein, Tat, is a potential candidate for developing a vaccine against human immunodeficiency virus (HIV-1). Since Tat is not immunodominant, especially when delivered as a genetic vaccine, we expressed codon-optimized subtype-C Tat as a molecular conjugate of ubiquitin, to elicit antigen-specific cell-mediated immune responses. Immunization of mice with different ubiquitin-Tat constructs elicited a strong cellular, but not a humoral, immune response. The combination of codon-optimization and ubiquitin-mediated processing of Tat induced a Th-1 type cellular immune response that was detectable without in vitro stimulation, suggesting its potential utility for destruction of virus-infected cells via CTL-mediated lysis. Preliminary attempts at characterizing the immunodominant regions identified a novel T-helper epitope within the core domain of Tat.

Primary murine cells as a model for HIV-1 infection

Immortalized and transduced cell lines are traditionally used in model of the HIV-1 life cycle. Primary cells may better represent the tissue of origin and events in vivo. We utilized an HIV-1/murine leukemia A4070 pseudotype virus and human Cyclin T1 to replicate HIV-1 in primary murine cells, and demonstrate that primary murine cells support HIV-1 infection better than immortalized cells.

Identification of antigenic regions of duck hepatitis B virus core protein with antibodies elicited by DNA immunization and chronic infection

The induction of humoral response in ducks by DNA-based immunization against duck hepatitis B virus (DHBV) core protein (DHBc) was investigated. In addition, the amino acid specificity of the induced response was compared by using peptide scanning to that elicited either by protein immunization or during chronic DHBV infection. Immunization of ducks with a plasmid expressing DHBc protein led to the induction of a long-lasting antibody response able to specifically recognize viral protein in chronically infected duck livers. Peptide scanning analysis of anti-DHBc response induced during chronic DHBV infection allowed us to identify six major antigenic regions (AR1 to AR6). The reactivity spectrum of duck sera elicited by protein immunization appeared narrower and was restricted to only four of these antigenic regions in spite of higher anti-DHBc antibody titers. Interestingly, anti-DHBc antibodies induced by DNA-based immunization recognized five of six antigenic regions, and the epitope pattern was broader and more closely related to that observed in chronic viral infections. To gain more insight into the location of antigenic regions, we built a three-dimensional (3-D) model of DHBc protein based on human and duck core sequence alignment data and the HBc 3-D crystal structure. The results suggest that two identified antigenic regions (AR2, amino acids [aa] (64)T-P(84), and AR5, aa (183)A-R(210)) are located at positions on the protein surface equivalent to those of the two HBc major epitopes. Moreover, we identified another antigenic region (AR3, aa (99)I-I(112)) that was recognized by all sera from chronically infected, DNA- or protein-immunized ducks within the large 45-aa insertion in DHBc protein, suggesting that this region, which lacks HBc, is externally exposed.

Microarray profiling of antibody responses against simian-human immunodeficiency virus: postchallenge convergence of reactivities independent of host histocompatibility type and vaccine regimen

We developed antigen microarrays to profile the breadth, strength, and kinetics of epitope-specific antiviral antibody responses in vaccine trials with a simian-human immunodeficiency virus (SHIV) model for human immunodeficiency virus (HIV) infection. These arrays contained 430 distinct proteins and overlapping peptides spanning the SHIV proteome. In macaques vaccinated with three different DNA and/or recombinant modified vaccinia virus Ankara (rMVA) vaccines encoding Gag-Pol or Gag-Pol-Env, these arrays distinguished vaccinated from challenged macaques, identified three novel viral epitopes, and predicted survival. Following viral challenge, anti-SHIV antibody responses ultimately converged to target eight immunodominant B-cell regions in Env regardless of vaccine regimen, host histocompatibility type, and divergent T-cell specificities. After challenge, responses to nonimmunodominant epitopes were transient, while responses to dominant epitopes were gained. These data suggest that the functional diversity of anti-SHIV B-cell responses is highly limited in the presence of persisting antigen.

DNA immunization efficiently targets conserved functional domains of protease and ATPase/helicase of nonstructural 3 protein (NS3) of human hepatitis C virus

Nonstructural protein 3 (NS3) of human hepatitis C virus (HCV) is a conserved multi-functional protein essential for replication and translation of viral RNA and polyprotein processing. Early T-cell response against NS3 is capable of restricting viremia. We aimed at characterizing the immunogenicity in gene immunization of the conserved regions of NS3 critical for protein folding and activity. C57BL/6 mice were injected with NS3 gene of Russian HCV 1b isolate 274933RU. Immunization did not exert any overt histological changes and had no long-term effects on the immune status of NS3 gene-recipients. The immune response in NS3 gene-recipients was screened by antibody ELISA, T-cell proliferation test and immune assays for specific cytokine production. T-lymphocytes of NS3 gene-recipients proliferated in response to peptides representing conserved regions of protease and ATPase/helicase. Stimulated T-lymphocytes produced IL-2, and in response to protease-derived peptides, also IFN-gamma. Potent and long-lasting antibody response was raised against conserved NS3 regions including "Greek-key" motif of protease, motifs II, V and polynucleotide-binding domains of ATPase/helicase. Thus, gene immunization effectively targeted conserved regions critical for NS3 protease and helicase function. In type and specificity, immune response of NS3 gene-immunized mice mimicked immunity achieved in the acute self-limiting HCV infection of human and primates and in virus-exposed healthy individuals, indicating promiscuity of NS3 as immunogen.

Immunization with low doses of HIV-1 tat DNA delivered by novel cationic block copolymers induces CTL responses against Tat

Cytotoxic T cell responses are key to the control of intracellular pathogens including HIV-1. In particular, HIV-1 vaccines based on regulatory proteins, such as Tat, are aimed at controlling HIV-1 replication and at blocking disease development by inducing cytotoxic T cell responses. Naked DNA is capable of inducing such responses but it requires several inoculations of high amounts of DNA, and/or prime-boost regimens. Here, we show that a novel class of cationic block copolymers protect the DNA from DNAse I digestion, and improve DNA delivery to antigen-presenting cells (APCs) after intramuscular (i.m.) vaccination. In particular, three cationic block copolymers (K1, K2 and K5) were used to deliver the HIV-1 pCV-tat DNA vaccine in BALB/c mice. The results indicate that vaccination with a very low dose (1 microg) of pCV-tat delivered by the cationic block copolymer K2 is safe and, as compared to naked DNA (up to 30 microg), greatly increases the CTL response against Tat, which was detected in all animals in the absence or in the presence of re-stimulation.

Toxoplasma gondii: analysis of the active site insertion of its ferredoxin-NADP(+)-reductase by peptide-specific antibodies and homology-based modeling

Apicomplexan parasites possess an apicoplast-localized redox system consisting of a plant-type ferredoxin-NADP(+)-reductase (FNR) and its redox partner ferredoxin, a small [2Fe-2S] protein. We show here that several apicomplexan FNRs contain unique amino acid insertions of various lengths which are located in close proximity to the enzymatically important FAD and ferredoxin-binding sites of these proteins. Using the insertion of the Toxoplasma gondii reductase as an example we raised epitope-specific antibodies against an 11 amino acids long peptide predicted to be surface-exposed within this insertion. This peptide was found to be immunogenic when presented to the immune system as part of a carrier protein, but also in its natural structural context in the whole recombinant protein, implying that the epitope is surface-exposed. Three-dimensional modeling of T. gondii FNR based on the known 3D-structure of maize root FNR predicts that the overall structure of plant and apicomplexan FNRs are very similar and that the 11 amino acids are part of an alpha-helix, looping out of the molecule. Collectively, these data suggest that the insertion in T. gondii FNR does not affect the overall structure of the protein but may have an effect on the binding dynamics of FAD, NADP(+), and/or ferredoxin to FNR.

HIV-1 Tat-based vaccines: from basic science to clinical trials

Vaccination against human immunodeficiency virus (HIV)-1 infection requires candidate antigen(s) (Ag) capable of inducing an effective, broad, and long-lasting immune response against HIV-1 despite mutation events leading to differences in virus clades. The HIV-1 Tat protein is more conserved than envelope proteins, is essential in the virus life cycle and is expressed very early upon virus entry. In addition, both humoral and cellular responses to Tat have been reported to correlate with a delayed progression to disease in both humans and monkeys. This suggested that Tat is an optimal target for vaccine development aimed at controlling virus replication and blocking disease onset. Here are reviewed the results of our studies including the effects of the Tat protein on monocyte-derived dendritic cells (MDDCs) that are key antigen-presenting cells (APCs), and the results from vaccination trials with both the Tat protein or tat DNA in monkeys. We provide evidence that the HIV-1 Tat protein is very efficiently taken up by MDDCs and promotes T helper (Th)-1 type immune responses against itself as well as other Ag. In addition, a Tat-based vaccine elicits an immune response capable of controlling primary infection of monkeys with the pathogenic SHIV89.6P at its early stages allowing the containment of virus spread. Based on these results and on data of Tat conservation and immune cross-recognition in field isolates from different clades, phase I clinical trials are being initiated in Italy for both preventive and therapeutic vaccination.

Potent, persistent cellular immune responses elicited by sequential immunization of rhesus macaques with Ad5 host range mutant recombinants encoding SIV Rev and SIV Nef

Vaccines incorporating multiple HIV components should elicit broad immunity and protection against a spectrum of HIV strains. Early regulatory and accessory gene products are attractive candidates for such vaccines. Here, immunogenicity studies on SIV Rev and Nef expressed in replication competent Adenovirus type 5 host range mutant vectors (Ad5hr) are summarized. Interferon-gamma (IFN-gamma)-secreting cells in response to Env and Rev peptides were enumerated by ELISPOT after two sequential immunizations of 55 macaques with Ad5hr-SIVenv/rev. Responses to SIV Nef were assessed in 16 macaques also immunized with Ad5hr-SIVnef. Potent cellular immunity to both Rev and Nef was induced following the second Ad-recombinant immunization and persisted for at least 30 weeks. Persistent cellular immunity to SIV Env was also seen, with a mean of 700 IFN-gamma-secreting cells per million PBMC. Rev and Env responses were positively correlated. While greater responses to early gene products occur in natural infection, as immunogens Rev and Nef elicited the same number of IFN-gamma secreting cells as Env, after adjusting for differences in protein size. The same percentage of macaques also responded to Rev, Nef, and Env: 59, 63, and 64%, respectively. Overall, Ad5hrSIVenv/rev and -SIVnef were highly effective immunogens. Their contribution to protective efficacy will be addressed in future studies.

Production of antibodies by single DNA immunization: comparison of various immunization routes

DNA immunization is a recent vaccination method that induces humoral and cellular immune responses in a range of hosts. Different immunization routes induce a different degree of the immune response. In the present report, we demonstrate that multiple intramuscular immunizations of plasmid DNA encoding various leukocyte surface molecules induced a specific antibody response. In contrast, a single intramuscular immunization could not induce antibody production. To study the induction of antibody response after a single immunization of plasmid DNA, mice were single-dose intramuscularly, intraperitoneally, intravenously and intrasplenically immunized, simultaneously, with the same preparation of plasmid DNA encoding CD147 membrane protein. We observed that only the intrasplenic route induced specific antibody production. The induction of antibody by intrasplenic immunization was confirmed by using plasmid DNA encoding CD54 molecule. By this single-dose DNA intrasplenic immunization, the generated antibodies could be detected in mice up to 6 months. These results suggest that the injected DNA is expressing the relevant protein antigen in the spleen for several months after injection. Our results demonstrate that direct immunization of antigen-encoding DNA into the spleen is a more effective method for induction of antibody production. This finding may support future investigations of DNA vaccination strategies that specifically promote the uptake of plasmid by splenocytes. Intrasplenic immunization may also be helpful in the understanding of the early events of the immune response to DNA vaccine and be useful as an effective route for the induction of immune responses.

Characterization of humoral and cellular immune responses in mice induced by immunization with HIV-1 Nef regulatory protein encapsulated in poly(DL-lactide-co-glycolide) microparticles

We have characterized the humoral and cellular immune responses of BALB/c mice immunized with HIV-1 Nef regulatory protein encapsulated in poly(DL-lactide-co-glycolide) PLG particles. Three groups of mice were immunized with Nef PLG, Nef in the presence of complete Freund's adjuvant (CFA) or Nef alone in PBS. When titers were compared 7 months after the last injection, anti-Nef titers in mice immunized with Nef PLG were still close to the maximum, whereas a significant decrease was observed in mice immunized with Nef alone (five times lower) or with Nef in CFA (three times lower). These results indicate that Nef PLG is at least a similar or better vector/adjuvant than Nef in CFA concerning the duration of the humoral immune response. The analysis of cytokine profiles (IL-5 and IL-10) and the isotypic patterns of anti-Nef antibodies (predominantly IgG1), in the three groups of mice, indicated a predominant Th2 immune response. Using synthetic peptides covering the entire sequence of Nef, we identified at least three linear epitopes within sequences 32-64, 118-167 and 185-205 in the sera of mice immunized with Nef PLG or Nef CFA. In contrast, anti-Nef antibodies against Nef alone failed to recognize synthetic peptides, indicating that the majority of anti-Nef antibodies were primarily directed against conformational epitopes. We then examined the ability of Nef PLG to prime for the antigen-specific proliferative responses in vitro. The data obtained indicate the presence of both B-cell and T-cell epitopes in the C-terminal fragment of the protein after immunization of mice with Nef encapsulated in PLG particles.

Enhanced immunogenicity of a human immunodeficiency virus type 1 env DNA vaccine by manipulating N-glycosylation signals. Effects of elimination of the V3 N306 glycan

DNA encoding HIV-1 env is a poorly efficient B-cell immunogen and one probable explanation is that the numerous gp120 N-linked glycans gp120 may interfere with B-cell epitope presentation. The N306 glycan in gp120 shields HIV-1 from neutralizing antibodies. A DNA immunogen lacking the N306 glycosylation signal (T308A) was constructed to determine whether this glycan affected the immune response. Mice were immunized intranasally twice with DNA containing either the wild type or the mutant env. Two additional groups were primed with wild type or mutant env and boosted with rgp160 protein, containing the complete set of N-linked glycans. Immunization with DNA alone resulted in priming of B-cell clones but was not sufficient to induce a complete antibody response. Animals primed with the N306 mutant and subsequently boosted with rgp160 protein displayed higher serum IgG-binding titers to gp120 than animals primed with wild type env DNA. The manipulation of the glycosylation sites of the env DNA strongly primes antibody responses (but non-neutralizing) as well as T-cell responses to the wild type strain gp160. However, priming with mutant plasmid did not result in higher neutralization titers to wild type or T308A-mutated virus than did the wild type plasmid. With the N306 mutant DNA we thus immunized a non-neutralization epitope, but obtained strong env-binding IgG after rgp160 boosting.

Gene combination raises broad human immunodeficiency virus-specific cytotoxicity

DNA plasmid immunization has the important advantage over traditional vaccines of making it possible to combine selected genes into one vaccine. The efficacy of a combination of DNA plasmids encoding the nef, rev, and tat HIV-1 regulatory genes in inducing cellular immune responses was analyzed in asymptomatic HIV-1-infected patients. Patients initially selected for having low or no detectable immune responses to Nef, Rev, or Tat antigens developed MHC class I-restricted cytolytic activities as well as enhanced bystander effects. The induction of memory cells against target cells infected with the whole HIV-1 genome was analyzed by using a pseudovirus HIV-1/murine leukemia virus (MuLV), and target cells infected with vaccinia virus carrying the respective gene. The most remarkable change observed after immunization with the gene combination was an increase in cytotoxic T lymphocyte (CTL) precursors to target cells infected with the whole HIV-1 genome. Infection by the pseudotype HIV-1/MuLV virus should result in a multitude of HIV-1 peptides presented on the target cell surface, representative of the in vivo situation. An in vitro assessment of the expression of the single and combined gene products showed that this was consistent with the induction of CTL responses in vivo. No clinical advantage or adverse effects were noted. Therapeutic effects of such immunization may become measurable by structured therapy interruption.

Interactions of single and combined human immunodeficiency virus type 1 (HIV-1) DNA vaccines

DNA immunization permits evaluation of possible antagonistic or synergistic effects between the encoded components. The protein expression capacity in vitro was related to the immunogenicity in vivo of plasmids encoding the HIV-1 regulatory genes tat rev, and nef. Neither Tat nor Rev expression was influenced by co-expression in vitro of all three proteins, while Nef expression was slightly inhibited. With the combination of genes, the T-cellular responses of mice against Rev and Nef were inhibited compared with those when single gene immunization was used. No interference was detected for the Tat T-cell response. Thus, co-immunization with certain genes may result in inhibition of specific immune responses.

Characterization of HIV-1 Tat proteins mutated in the transactivation domain for prophylactic and therapeutic application

Previous work from our group showed that genetic immunization of mice with HIV-1 tat genes (tat22 and tat22/37), encoding Tat proteins mutated in the transactivation domain and lacking Tat-transactivating activity, evoke an immune response to wild-type Tat, both humoral and cellular. In the present work we report that the mutated Tat proteins localize within the cells, are released and taken up by the cells in a fashion similar to wild-type Tat. Moreover, the exogenous mutated Tat proteins interfere with the transactivating function of extracellular wild-type Tat. These results support the notion that tat22 and tat22/37 genes may represent good candidates for the development of an anti-HIV-1 vaccine, especially for HIV-1 infected patients.

DNA vaccination in mice using HIV-1 nef, rev and tat genes in self-replicating pBN-vector

The immunogenicity of a self-replicating DNA-vector containing HIV-1 nef gene (pBN-Nef) was characterized using various DNA delivery methods. In addition, gene gun immunisation was used for assessing immunogenicity of two other HIV-1 genes (rev and tat) given in the same vector. The pBN-Nef was the most immunogenic raising both humoral and cell-mediated immune responses in mice; these responses lasted for up to six months. The pBN-Nef vector was immunogenic also when given intramuscularly or intradermally. The pBN-Rev construct did not elicit humoral responses but did elicit proliferative as well as CTL-response against the corresponding protein. The pBN-Tat was a poor immunogen in all respects. The antibodies elicited with various DNA delivery methods belonged to different antibody subclasses; however, two main epitopes in Nef were frequently recognized by all of them.

Production of polyclonal and monoclonal antibodies against CD54 molecules by intrasplenic immunization of plasmid DNA encoding CD54 protein

DNA immunization, in theory, is of great interest as a source of specific antibodies against different antigens. In an attempt to produce polyclonal and monoclonal antibodies against cell surface molecules by using the DNA immunization strategy, intramuscular and intrasplenic routes of DNA injection were compared. Two to five, but not a single, intramuscular DNA immunizations induced anti-CD54 and anti-CD147 antibody production. In contrast, a single intrasplenic immunization of CD54-encoding DNA could induce anti-CD54 antibody production. To produce monoclonal antibody (mAb), spleen cells obtained from an intrasplenic CD54-encoding DNA immunized mouse were fused with myeloma cells using the standard hybridoma technique. A hybridoma secreting specific mAb to CD54 was established. The generated mAb reacted to CD54 protein expressed on transfected COS cells and various cell types, the same as using standard CD54 mAb MEM-111. Our results demonstrated that direct immunization of antigen-encoding DNA into spleen is an effective route for production of both polyclonal and monoclonal antibodies to cell surface molecules. This finding is very useful for the production of antibodies to cell surface molecules where the protein antigen is not available or difficult to prepare, but cDNA encoding the corresponding protein is available.

Induction of immune responses and break of tolerance by DNA against the HIV-1 coreceptor CCR5 but no protection from SIVsm challenge

An inactivating mutation in the human CCR5 gene reduces the risk of HIV-1 infection in individuals with homozygous alleles. We explored whether genetic immunization would induce an immune response directed to CCR5 structures and if immunological tolerance toward endogenous CCR5 could be broken. We also studied whether this immunization approach could protect cynomolgus monkeys from an infection, with SIVsm, which primarily uses CCR5 as a coreceptor. Epidermal but not intramuscular delivery of the CCR5 gene to mice elicited strong IgG antibody binding responses to CCR5. Intramucosal immunization of cynomolgus macaques with CCR5 DNA followed by boosts with CCR5 peptides induced prominent IgG and IgA antibody responses in serum and vaginal washings. The CCR5-specific antibodies neutralized the infectivity of primary human R5 HIV-1 strains, and the macaque SIVsm but not that of a tissue culture-adapted X4 HIV-1 strain. The consecutive CCR5 gene and CCR5 peptide immunizations induced B- and T-cell responses to peptides representing both human and macaque amino acid sequences of the respective CCR5 proteins. This indicates that tolerance was broken against endogenous macaque CCR5, which has a 98% homology to the human CCR5 gene. After the final boost, the vaccinated monkeys together with two control monkeys were challenged with SIVsm. Neither protection against nor enhancement of SIVsm infection was achieved.

Immunogenic properties of reverse transcriptase of HIV type 1 assessed by DNA and protein immunization of rabbits

Genetic immunization may be one way to prime individuals for a subsequent broad anti-HIV-1 immune response. Reverse transcriptase of HIV-1 (RT) presents a selective target for attempts to arrest replication of HIV-1. Rabbits immunized with a plasmid carrying the gene for reverse transcriptase HIV-1 (RT DNA) developed potent antibody and cellular responses to the gene product. The immunogenic properties of RT DNA and recombinant reverse transcriptase were compared in rabbits. The specific immune responses were similar to those reported previously for HIV-1 infected humans. The array of B and T cell epitopes recognized in RT DNA-immunized rabbits was broader than in rabbits immunized with the recombinant RT. We localized seven novel B and T cell epitopes and concordance between B cell and helper T cell epitopes was observed. B cell epitopes of RT induced proliferation of peripheral blood mononuclear cells and were active as helper T cell epitopes. T cell-proliferative responses to the epitopes of RT preceded or paralleled the production of antibodies of the same specificity. Subdomains of reverse transcriptase involved in the enzymatic activity of RT were highly immunogenic. Anti-RT IgG partially inhibited reverse transcription in vitro.