Multi-subtype gp160 DNA immunization induces broadly neutralizing anti-HIV antibodies

Immunization with HIV-1 envelope T20-encoding DNA vaccines elicits cross-clade neutralizing antibody responses

Background: Genetic immunization is expected to induce the expression of antigens in a native form. The encoded peptide epitopes are presented on endogenous MHC molecules, mimicking antigen presentation during a viral infection. We have explored the potential of enfuvirtide (T20), a short HIV peptide with antiviral properties, to enhance immune response to HIV antigens. To generate an expression vector, the T20 sequence was cloned into a conventional plasmid, the novel minicircle construct, and a replicon plasmid. In addition, 3 conventional plasmids that express the envelope of HIV-1 subtypes A, B and C and contain T20 in their gp41 sequences were also tested. Results: All combinations induced HIV-specific antibodies and cellular responses. The addition of T20 as a peptide and as an expression cassette in the 3 DNA vectors enhanced antibody responses. The highest anti-HIV-1 Env titers were obtained by the replicon T20 construct. This demonstrates that besides its known antiviral activity, T20 promotes immune responses. We also confirm that the combination of slightly divergent antigens improves immune responses. Conclusions: The antiretroviral T20 HIV-1 sequence can be used as an immunogen to elicit binding and neutralizing antibodies against HIV-1. These, or similarly modified gp41 genes/peptides, can be used as priming or boosting components for induction of broadly neutralizing anti-HIV antibodies. Future comparative studies will reveal the optimal mode of T20 administration.

HIVIS-DNA or HIVISopt-DNA priming followed by CMDR vaccinia-based boosts induce both humoral and cellular murine immune responses to HIV

Background

In order to develop a more effective prophylactic HIV-1 vaccine it is important optimize the components, improve Envelope glycoprotein immunogenicity as well as to explore prime-boost immunization schedules. It is also valuable to include several HIV-1 subtype antigens representing the world-wide epidemic.

Methods

HIVIS-DNA plasmids which include Env genes of subtypes A, B and C together with Gag subtypes A and B and RTmut/Rev of subtype B were modified as follows: the Envelope sequences were shortened, codon optimized, provided with an FT4 sequence and an immunodominant region mutated. The reverse transcriptase (RT) gene was shortened to contain the most immunogenic N-terminal fragment and fused with an inactivated viral protease vPR gene. HIVISopt-DNA thus contains fewer plasmids but additional PR epitopes compared to the native HIVIS-DNA. DNA components were delivered intradermally to young Balb/c mice once, using a needle-free Biojector® immediately followed by dermal electroporation. Vaccinia-based MVA-CMDR boosts including Env gene E and Gag-RT genes A were delivered intramuscularly by needle, once or twice.

Results

Both HIVIS-DNA and HIVISopt-DNA primed humoral and cell mediated responses well. When boosted with heterologous MVA-CMDR (subtypes A and E) virus inhibitory neutralizing antibodies were obtained to HIV-1 subtypes A, B, C and AE. Both plasmid compositions boosted with MVA-CMDR generated HIV-1 specific cellular responses directed against HIV-1 Env, Gag and Pol, as measured by IFNγ ELISpot. It was shown that DNA priming augmented the vector MVA immunological boosting effects, the HIVISopt-DNA with a trend to improved (Env) neutralization, the HIVIS-DNA with a trend to better (Gag) cell mediated immune reponses.

Conclusions

HIVIS-DNA was modified to obtain HIVISopt-DNA that had fewer plasmids, and additional epitopes. Even with one DNA prime followed by two MVA-CMDR boosts, humoral and cell-mediated immune responses were readily induced by priming with either DNA construct composition. Priming by HIV-DNA augmented neutralizing antibody responses revealed by boosting with the vaccinia-based heterologous sequences. Cellular and antibody responses covered selected strains representing HIV-1 subtypes A, B, C and CRF01_AE. We assume this is related to the inclusion of heterologous full genes in the vaccine schedule.

Intranasal Vaccination against HIV-1 with Adenoviral Vector-Based Nanocomplex Using Synthetic TLR-4 Agonist Peptide as Adjuvant

Recombinant type 5 adenovirus (rAd5) vaccines hold the promise to prevent HIV-1 infections. Intranasal vaccination not only stimulates systemic immunity but also elicits mucosal immunity that provides first defense for mucosally transmitted diseases like HIV-1. Adjuvants such as TLR agonists are usually codelivered with antigens to enhance the immunogenicity of vaccines. Here, we present a rAd5 vaccine delivery system using DEG-PEI as the carrier. Adenovirus encoding HIV gag was used as antigen, and was complexed with DEG-PEI polymer via electrostatic interaction. A novel synthetic TLR-4 agonist, RS09, was either chemically linked with DEG-PEI (DP-RS09) or physically mixed with it(DP/RS09) to enhance the immunogenticity of rAd5 vaccine. After intranasal immunization, the systemic antigen-specific immune responses and cytotoxicity T lymphocytes responses induced by DP-RS09-rAd5 and DP/RS09-rAd5 were analyzed. The mucosal secretory IgA level was detected in both nasal and vaginal washes to determine the mucosal immunity. Furthermore, cytokine productions on RAW264.7 cells were tested after preincubation with TLR-4 pathway inhibitors. The results indicated that DEG-PEI could facilitate the intranasal delivery of rAd5 vaccine. Both chemically linked (DP-RS09) and physically mixed RS09 (DP/RS09) could further enhance the mucosal immunity of rAd5 vaccine via TLR-4 pathway. This RS09 adjuvanted DEG-PEI polymer represents a potential intranasal vaccine delivery system and may have a wider application for other viral vectors.

Neutralizing antibodies to HIV-1 induced by immunization

Most neutralizing antibodies act at the earliest steps of viral infection and block interaction of the virus with cellular receptors to prevent entry into host cells. The inability to induce neutralizing antibodies to HIV has been a major obstacle to HIV vaccine research since the early days of the epidemic. However, in the past three years, the definition of a neutralizing antibody against HIV has been revolutionized by the isolation of extremely broad and potent neutralizing antibodies from HIV-infected individuals. Considerable hurdles remain for inducing neutralizing antibodies to a protective level after immunization. Meanwhile, novel technologies to bypass the induction of antibodies are being explored to provide prophylactic antibody-based interventions. This review addresses the challenge of inducing HIV neutralizing antibodies upon immunization and considers notable recent advances in the field. A greater understanding of the successes and failures for inducing a neutralizing response upon immunization is required to accelerate the development of an effective HIV vaccine.

Evaluation of heterologous vaginal SHIV SF162p4 infection following vaccination with a polyvalent Clade B virus-like particle vaccine

The vast diversity of HIV-1 infections has greatly impeded the development of a successful HIV-1/AIDS vaccine. Previous vaccine work has demonstrated limited levels of protection against SHIV/SIV infection, but protection was observed only when the challenge virus was directly matched to the vaccine strain. As it is likely impossible to directly match the vaccine strain to all infecting strains in nature, it is necessary to develop an HIV-1 vaccine that can protect against a heterologous viral challenge. In this study we investigated the ability of polyvalent and consensus vaccines to protect against a heterologous clade B challenge. Rhesus macaques were vaccinated with ConB or PolyB virus-like particle vaccines. All vaccines were highly immunogenic with high titers of antibody found in all vaccinated groups against SIV Gag. Antibody responses were also observed against a diverse panel of clade B envelopes. Following vaccination nonhuman primates (NHPs) were challenged via the vaginal route with SHIV(SF162p4). The PolyB vaccine induced a 66.7% reduction in the rate of infection as well as causing a two log reduction in viral burden if infection was not blocked. ConB vaccination had no effect on either the infection rate or viral burden. These results indicate that a polyvalent clade-matched vaccine is better able to protect against a heterologous challenge as compared to a consensus vaccine.

Polyvalent AIDS vaccines

A major hurdle in the development of a global HIV-1 vaccine is viral diversity. For close to three decades, HIV vaccine development has focused on either the induction of T cell immune responses or antibody responses, and only rarely on both components. After the failure of the STEP trial, the scientific community concluded that a T cell-based vaccine would likely not be protective if the T cell immune responses were elicited against only a few dominant epitopes. Similarly, for vaccines focusing on antibody responses, one of the main criticisms after VaxGen's failed Phase III trials was on the limited antigen breadth included in the two formulations used. The successes of polyvalent vaccine approaches against other antigenically variable pathogens encourage implementation of the same approach for the design of HIV-1 vaccines. A review of the existing HIV-1 vaccination approaches based on the polyvalent principle is included here to provide a historical perspective for the current effort of developing a polyvalent HIV-1 vaccine. Results summarized in this review provide a clear indication that the polyvalent approach is a viable one for the future development of an effective HIV vaccine.

Heterologous Prime-Boost HIV-1 Vaccination Regimens in Pre-Clinical and Clinical Trials

Currently, there are more than 30 million people infected with HIV-1 and thousands more are infected each day. Vaccination is the single most effective mechanism for prevention of viral disease, and after more than 25 years of research, one vaccine has shown somewhat encouraging results in an advanced clinical efficacy trial. A modified intent-to-treat analysis of trial results showed that infection was approximately 30% lower in the vaccine group compared to the placebo group. The vaccine was administered using a heterologous prime-boost regimen in which both target antigens and delivery vehicles were changed during the course of inoculations. Here we examine the complexity of heterologous prime-boost immunizations. We show that the use of different delivery vehicles in prime and boost inoculations can help to avert the inhibitory effects caused by vector-specific immune responses. We also show that the introduction of new antigens into boost inoculations can be advantageous, demonstrating that the effect of `original antigenic sin' is not absolute. Pre-clinical and clinical studies are reviewed, including our own work with a three-vector vaccination regimen using recombinant DNA, virus (Sendai virus or vaccinia virus) and protein. Promising preliminary results suggest that the heterologous prime-boost strategy may possibly provide a foundation for the future prevention of HIV-1 infections in humans.

Enhancement of the expression of HCV core gene does not enhance core-specific immune response in DNA immunization: advantages of the heterologous DNA prime, protein boost immunization regimen

BACKGROUND

Hepatitis C core protein is an attractive target for HCV vaccine aimed to exterminate HCV infected cells. However, although highly immunogenic in natural infection, core appears to have low immunogenicity in experimental settings. We aimed to design an HCV vaccine prototype based on core, and devise immunization regimens that would lead to potent anti-core immune responses which circumvent the immunogenicity limitations earlier observed.

METHODS

Plasmids encoding core with no translation initiation signal (pCMVcore); with Kozak sequence (pCMVcoreKozak); and with HCV IRES (pCMVcoreIRES) were designed and expressed in a variety of eukaryotic cells. Polyproteins corresponding to HCV 1b amino acids (aa) 1-98 and 1-173 were expressed in E. coli. C57BL/6 mice were immunized with four 25-microg doses of pCMVcoreKozak, or pCMV (I). BALB/c mice were immunized with 100 microg of either pCMVcore, or pCMVcoreKozak, or pCMVcoreIRES, or empty pCMV (II). Lastly, BALB/c mice were immunized with 20 microg of core aa 1-98 in prime and boost, or with 100 microg of pCMVcoreKozak in prime and 20 microg of core aa 1-98 in boost (III). Antibody response, [3H]-T-incorporation, and cytokine secretion by core/core peptide-stimulated splenocytes were assessed after each immunization.

RESULTS

Plasmids differed in core-expression capacity: mouse fibroblasts transfected with pCMVcore, pCMVcoreIRES and pCMVcoreKozak expressed 0.22 +/- 0.18, 0.83 +/- 0.5, and 13 +/- 5 ng core per cell, respectively. Single immunization with highly expressing pCMVcoreKozak induced specific IFN-gamma and IL-2, and weak antibody response. Single immunization with plasmids directing low levels of core expression induced similar levels of cytokines, strong T-cell proliferation (pCMVcoreIRES), and antibodies in titer 103(pCMVcore). Boosting with pCMVcoreKozak induced low antibody response, core-specific T-cell proliferation and IFN-gamma secretion that subsided after the 3rd plasmid injection. The latter also led to a decrease in specific IL-2 secretion. The best was the heterologous pCMVcoreKozak prime/protein boost regiment that generated mixed Th1/Th2-cellular response with core-specific antibodies in titer >or= 3 x 10(3).

CONCLUSION

Thus, administration of highly expressed HCV core gene, as one large dose or repeated injections of smaller doses, may suppress core-specific immune response. Instead, the latter is induced by a heterologous DNA prime/protein boost regiment that circumvents the negative effects of intracellular core expression.

Human immunodeficiency virus-like particles with consensus envelopes elicited broader cell-mediated peripheral and mucosal immune responses than polyvalent and monovalent Env vaccines

Envelope (Env) sequences from human immunodeficiency virus (HIV) strains can vary by 15-20% within a single clade and as much as 35% between clades. Previous AIDS vaccines based upon a single isolate often could not elicit protective immune responses against heterologous viral challenges. In order to address the vast sequence diversity in Env sequences, consensus sequences were constructed for clade B and clade C envelopes and delivered to the mouse lung mucosa on the surface of virus-like particles (VLP). Consensus sequences decrease the genetic difference between the vaccine strain and any given viral isolate. The elicited immune responses were compared to a mixture of VLPs with Envs from primary viral isolates. This polyvalent vaccine approach contains multiple, diverse Envs to increase the breadth of epitopes recognized by the immune response and thereby increase the potential number of primary isolates recognized. Both consensus and polyvalent clade B Env VLP vaccines elicited cell-mediated immune responses that recognized a broader number of clade B Env peptides than a control monovalent Env VLP vaccine in both the systemic and the mucosal immune compartments. All three clade C Env vaccine strategies elicited similar responses to clade C peptides. However, both the consensus B and C Env VLP vaccines were more effective at eliciting cross-reactive cellular immune responses to epitopes in other clades. This is the first study to directly compare the breadth of cell-mediated immune responses elicited by consensus and polyvalent Env vaccines.

Neutralizing antibody responses to subtype B and C adjuvanted HIV envelope protein vaccination in rabbits

Improving the potency, breadth, and durability of neutralizing antibody responses to HIV are major challenges for HIV vaccine development. To address these challenges, the studies described evaluate in rabbits the titers, breadth, and epitope specificities of antibody responses elicited by HIV envelope subunit vaccines adjuvanted with MF59 with or without CpG oligodeoxynucleotide (ODN). Animals were immunized with trimeric o-gp140DeltaV2 derived from subtype B HIV-1(SF162) or subtype C HIV-1(TV1), or proteins from both strains. Immunization with SF162 or TV1 with MF59/CpG elicited higher titers of binding and neutralizing antibodies to SF162 than monovalent immunization with MF59 alone (P<0.01). Bivalent immunization increased binding and neutralizing antibody titers over single envelope immunization in MF59 (P<0.01). Bivalent immunization also improved neutralization breadth. Epitope mapping indicated neutralizing activity in rabbits was directed to V3 and V4. Overall, our data suggests that a multivalent vaccination approach with MF59 and CpG can enhance humoral responses to HIV-1.

Broad immunogenicity of a multigene, multiclade HIV-1 DNA vaccine boosted with heterologous HIV-1 recombinant modified vaccinia virus Ankara

BACKGROUND

A human immunodeficiency virus (HIV) vaccine that limits disease and transmission is urgently needed. This clinical trial evaluated the safety and immunogenicity of an HIV vaccine that combines a plasmid-DNA priming vaccine and a modified vaccinia virus Ankara (MVA) boosting vaccine.

METHODS

Forty healthy volunteers were injected with DNA plasmids containing gp160 of HIV-1 subtypes A, B, and C; rev B; p17/p24 gag A and B, and RTmut B by use of a needle-free injection system. The vaccine was administered intradermally or intramuscularly, with or without recombinant granulocyte macrophage colony-stimulating factor, and boosted with a heterologous MVA containing env, gag, and pol of CRF01A_E. Immune responses were monitored with HIV-specific interferon (IFN)-gamma and interleukin (IL)-2 ELISpot and lymphoproliferative assays (LPAs).

RESULTS

Vaccine-related adverse events were mild and tolerable. After receipt of the DNA priming vaccine, 11 (30%) of 37 vaccinees had HIV-specific IFN-gamma responses. After receipt of the MVA boosting vaccine, ELISpot assays showed that 34 (92%) of 37 vaccinees had HIV-specific IFN-gamma responses, 32 (86%) to Gag and 24 (65%) to Env. IFN-gamma production was detected in both the CD8(+) T cell compartment (5 of 9 selected vaccinees) and the CD4(+) T cell compartment (9 of 9). ELISpot results showed that 25 (68%) of 37 vaccinees had a positive IL-2 response and 35 (92%) of 38 had a positive LPA response. Of 38 subjects, a total of 37 (97%) were responders. One milligram of HIV-1 DNA administered intradermally was as effective as 4 mg administered intramuscularly in priming for the MVA boosting vaccine.

CONCLUSION

This HIV-DNA priming-MVA boosting approach is safe and highly immunogenic.

TRIALS REGISTRATION

International Standard Randomised Controlled Trial number: ISRCTN32604572 .

Viral sequence diversity: challenges for AIDS vaccine designs

Among the greatest challenges facing AIDS vaccine development is the intrinsic diversity among circulating populations of HIV-1 in various geographical locations and the need to develop vaccines that can elicit enduring protective immunity to variant HIV-1 strains. While variation is observed in all of the viral proteins, the greatest diversity is localized to the viral envelope glycoproteins, evidently reflecting the predominant role of these proteins in eliciting host immune recognition and responses that result in progressive evolution of the envelope proteins during persistent infection. Interestingly, while envelope glycoprotein variation is widely assumed to be a major obstacle to AIDS vaccine development, there is very little experimental data in animal or human lentivirus systems addressing this critical issue. In this review, the state of vaccine development to address envelope diversity will be presented, focusing on the use of centralized and polyvalent sequence design as mechanisms to elicit broadly reactive immune responses.

Combining DNA technologies and different modes of immunization for induction of humoral and cellular anti-HIV-1 immune responses

We show here that it is possible to combine two different genetic immunogens, one designed to induce HIV-1 specific humoral immune responses (pKCMVgp160B) and one designed to induce cellular anti-HIV-1 immune responses (Auxo-GTU-MultiHIV), and still retain the major properties of both vaccine constructs. The two different constructs were delivered using two different methods; the gene-gun and the Biojector, which both are needle-free devices. In BALB/c mice we were able to induce high levels of HIV-1-specific T cell responses as well as high levels of anti-gp160 antibodies by co-administrating the vaccine constructs. The cellular immune responses, but not antibody responses, were moderately compromised from the combination. This study shows that it is a feasible strategy to combine different vaccines and modes of delivery, but that interference as to magnitude may occur to certain gene products.

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.

Increased immunogenicity of a DNA-launched Venezuelan equine encephalitis virus-based replicon DNA vaccine

A novel genetic vaccine that is based on a Venezuelan equine encephalitis virus (VEE) replicon launched from plasmid DNA is described. The plasmid encodes a VEE replicon under the transcriptional control of the cytomegalovirus immediate-early promoter (VEE DNA). The VEE DNA consistently expressed 3- to 15-fold more green fluorescent protein in vitro than did a conventional DNA vaccine. Furthermore, transfection with the DNA-launched VEE replicon induced apoptosis and type I interferon production. Inoculation of mice with VEE DNA encoding human immunodeficiency virus type 1 gp160 significantly increased humoral responses by several orders of magnitude compared to an equal dose of a conventional DNA vaccine. These increases were also observed at 10- and 100-fold-lower doses of the VEE DNA. Cellular immune responses measured by gamma interferon and interleukin 2 enzyme-linked immunospot assay were significantly higher in mice immunized with the VEE DNA at decreased doses. The immune responses induced by the VEE DNA-encoded antigen, however, were independent of an intact type I interferon signaling pathway. Moreover, the DNA-launched VEE replicon induced an efficient prime to a VEE replicon particle (VRP) boost, increasing humoral and cellular immunity by at least 1 order of magnitude compared to VEE DNA only. Importantly, immunization with VEE DNA, as opposed to VRP, did not induce any anti-VRP neutralizing antibodies. Increased potency of DNA vaccines and reduced vector immunity may ultimately have an impact on the design of vaccination strategies in humans.

A New Multi-clade DNA Prime/Recombinant MVA Boost Vaccine Induces Broad and High Levels of HIV-1-specific CD8+ T-cell and Humoral Responses in Mice

The results presented here are from the preclinical evaluation in BALB/c mice of a DNA prime/modified vaccinia virus Ankara (MVA) boost multi-gene multi-subtype human immunodeficiency virus-1 (HIV-1) vaccine intended for use in humans. The plasmid DNA vaccine was delivered intradermally using a Biojector, and the MVA was delivered intramuscularly by needle. This combination of recombinant DNA and MVA proved to induce extraordinarily strong cellular responses, with more than 80% of the CD8(+) T cells specific for HIV-1 antigens. Furthermore, we show that the DNA priming increases the number of T-cell epitopes recognized after the MVA boost. In the prime/boost-immunized animals, a significant proportion of CD8(+) T cells were stained positive for both interferon-gamma (IFN-gamma) and interleukin-2 (IL-2), a feature that has been associated with control of HIV-1 infection in long-term non-progressors. The HIV-1-specific antibody levels were moderate after the plasmid DNA immunizations but increased dramatically after the MVA boost. Although the initial injection of MVA induced significant levels of vaccinia-neutralizing antibodies, the HIV-specific responses were still significantly boosted by the second MVA immunization. The results from this study demonstrate the potency of this combination of DNA plasmids and MVA construct to induce broad and high levels of immune responses against several HIV-1 proteins of different subtypes.

DNA-VLP prime-boost intra-nasal immunization induces cellular and humoral anti-HIV-1 systemic and mucosal immunity with cross-clade neutralizing activity

The immune response to HIV-1 virus-like particles (VLPs), presenting a clade A Ugandan gp120, has been evaluated in a mouse model by intra-nasal (i.n.) administration by a VLP+VLP homologous or a DNA+VLP heterologous prime-boost immunization protocol, including a HIV-1 DNA gp160/rev plasmid. Furthermore, the effect of the Eurocine lipid-based mucosal L3 adjuvant on the VLP immunogenicity has been assessed as well. The designed heterologous protocol is able to increase the env-specific humoral and cellular immune response, compared to the homologous protocol, which is to some extent increased by the administration of L3-adjuvanted VLP boosting dose. The anti-gag response is statistically increased in both homologous and heterologous protocols, particularly when the VLP boosting dose is adjuvanted. Immune sera from immunized animals exhibit >50% ex vivo neutralizing activity against heterologous A and B-clade viral isolates. An envelope B-cell epitope mapping shows an enhanced response against V3 epitopes all across the C2-V5 region in the heterologous prime-boost immunization strategy. The induction of humoral immunity at mucosal sites, which represents the main port of entry for the HIV-1 infection, is extremely relevant. In this framework, the DNA-VLP heterologous prime-boost protocol appears a promising preventive vaccine approach which can significantly benefit from specific mucosal adjuvants, as the Eurocine L3.

Safety and immunogenicity of a Gag-Pol candidate HIV-1 DNA vaccine administered by a needle-free device in HIV-1-seronegative subjects

OBJECTIVE

To evaluate the safety and immunogenicity of a candidate HIV DNA vaccine administered using a needle-free device.

DESIGN

In this phase 1, dose escalation, double-blind, placebo-controlled clinical trial, 21 healthy adults were randomized to receive placebo or 0.5, 1.5, or 4 mg of a single plasmid expressing a Gag/Pol fusion protein. Each participant received repeat immunizations at days 28 and 56 after the first inoculation. Safety and immunogenicity data were collected.

RESULTS

The vaccine was well tolerated, with most adverse events being mild injection site reactions, including pain, tenderness, and erythema. No dose-limiting toxicities occurred. HIV-specific antibody response was not detected in any vaccinee by enzyme-linked immunosorbent assay. HIV-specific T-cell responses to Gag or Pol as measured by enzyme-linked immunospot assay and intracellular cytokine staining were of low frequency and magnitude.

CONCLUSIONS

This candidate HIV DNA vaccine was safe and well tolerated. No HIV-specific antibody responses were detected, and only low-magnitude HIV-specific T-cell responses were detected in 8 (53%) of 15 vaccinees. This initial product led to the development of a 4-plasmid multiclade HIV DNA Vaccine Research Center vaccine candidate in which envelope genes expressing Env from clades A, B, and C and a Nef gene from clade B have been added.

Clarification of how HIV-1 DNA and protein immunizations may be better used to obtain HIV-1-specific mucosal and systemic immunity

More focused research on a mucosal HIV-1 vaccine is needed urgently. An increasing amount of collected data, using heterologous multimodality prime-booster strategies, suggest that an efficient and protective HIV-1 vaccine must generate broad, long-lasting HIV-specific CD8(+) cytotoxic T-lymphocyte and neutralizing antibody responses. In the mucosa, these responses would be most effective if a preferential stimulus of HIV-1 neutralizing secretory immunoglobulin A and G were obtained. The attractive property of mucosal immunization is the obtained mucosal and systemic immunity, whereas systemic immunization induces a more limited immunity, predominantly in systemic sites. These objectives will require new vaccine regimens, such as multiclade HIV DNA and protein vaccines (nef, tat, gag and env expressed in DNA plasmids) delivered onto mucosal surfaces with needle-free delivery methods, such as nasal drop, as well as oral and rectal/vaginal delivery, and should merit clinical trials.

Evaluation of immunogenicity and efficacy of combined DNA and adjuvanted protein vaccination in a human immunodeficiency virus type 1/murine leukemia virus pseudotype challenge model

A DNA plasmid encoding human immunodeficiency virus type 1 (HIV-1) env, nef and tat genes was used in mice in a prime-boost immunization regimen with the corresponding recombinant proteins. The genetic immunogen was delivered with a gene gun and the proteins were injected intramuscularly together with the adjuvant AS02A. Immunizations were followed by experimental challenge with pseudotyped HIV-1 subtype A or B virus. In an initial experiment in which animals were challenged four weeks after the final immunization, all single modality and prime-boost vaccinations resulted in a significant level of protection as compared to control animals. There was a trend for DNA-alone immunization yielding the highest protection. In a subsequent study, a late challenge was performed 19 weeks after the final immunization. All groups having received the DNA vaccine, either alone or in combination with adjuvanted protein, exhibited strong protection against HIV replication. The subtype-specific protection against the experimental HIV challenge was significantly stronger than the cross-protection. Cellular and humoral immune responses were assessed during immunization and after challenge, but without clear correlation to protection against HIV replication. The data suggest that either DNA or protein antigens alone provide partial protection against an HIV-1/MuLV challenge and that DNA immunization is essential for achieving very high levels of efficacy in this murine HIV-1 challenge model. While prime-boost combinations were more immunogenic than DNA alone, they did not appear to provide any further enhancement over DNA vaccine mediated efficacy. The DNA immunogen might prime low levels of CD8+ T cells responsible for virus clearance or possibly a yet unidentified mechanism of protection.

Phase 1 safety and immunogenicity evaluation of a multiclade HIV-1 DNA candidate vaccine

BACKGROUND

Gene-based vaccine delivery is an important strategy in the development of a preventive vaccine for acquired immunodeficiency syndrome (AIDS). Vaccine Research Center (VRC) 004 is the first phase 1 dose-escalation study of a multiclade HIV-1 DNA vaccine.

METHODS

VRC-HIVDNA009-00-VP is a 4-plasmid mixture encoding subtype B Gag-Pol-Nef fusion protein and modified envelope (Env) constructs from subtypes A, B, and C. Fifty healthy, uninfected adults were randomized to receive either placebo (n=10) or study vaccine at 2 mg (n=5), 4 mg (n=20), or 8 mg (n=15) by needle-free intramuscular injection. Humoral responses (measured by enzyme-linked immunosorbant assay, Western blotting, and neutralization assay) and T cell responses (measured by enzyme-linked immunospot assay and intracellular cytokine staining after stimulation with antigen-specific peptide pools) were measured.

RESULTS

The vaccine was well tolerated and induced cellular and humoral responses. The maximal CD4(+) and CD8(+) T cell responses occurred after 3 injections and were in response to Env peptide pools. The pattern of cytokine expression by vaccine-induced HIV-specific T cells evolved over time, with a diminished frequency of interferon- gamma -producing T cells and an increased frequency of interleukin-2-producing T cells at 1 year.

CONCLUSIONS

DNA vaccination induced antibody to and T cell responses against 3 major HIV-1 subtypes and will be further evaluated as a potential component of a preventive AIDS vaccine regimen.

Therapeutic immunization for HIV

Vaccines have entered into human clinical trials against infectious diseases and as therapies against cancer. The HIV virus establishes a latent infection at a very early stage and the T cell memory of the infected patient is rapidly destroyed. However, results of immunotherapy after DNA and protein immunization show that vaccine-induced immune responses might be present for a long period of time. Patients subjected to therapeutic immunization appear to do well, and to have a small immunological advantage, which, however, will have to be improved. The vaccine therapy should start early, while adequate reservoirs of appropriate T helper cells are available and still inducible. The DNA vaccines induce a relatively long-lived immunological memory, and gene-based immunization is effective in inducing cytotoxic CD8(+) T cells and CD4+ helper cells. Protein vaccines, on the other hand, primarily give T cell help. It thus appears that DNA and protein approaches to HIV immunization complement each other. A surprisingly broad reactivity to peptides from different subtypes of HIV was identified in individuals infected with several subtypes of HIV.

A group M consensus envelope glycoprotein induces antibodies that neutralize subsets of subtype B and C HIV-1 primary viruses

HIV-1 subtype C is the most common HIV-1 group M subtype in Africa and many parts of Asia. However, to date HIV-1 vaccine candidate immunogens have not induced potent and broadly neutralizing antibodies against subtype C primary isolates. We have used a centralized gene strategy to address HIV-1 diversity and generated a group M consensus envelope gene with shortened consensus variable loops (CON-S) for comparative studies with wild-type (WT) Env immunogens. Our results indicate that the consensus HIV-1 group M CON-S Env elicited cross-subtype neutralizing antibodies of similar or greater breadth and titer than the WT Envs tested, indicating the utility of a centralized gene strategy. Our study also shows the feasibility of iterative improvements in Env immunogenicity by rational design of centralized genes.

Building collaborative networks for HIV/AIDS vaccine development: the AVIP experience

The need for an effective HIV/AIDS vaccine is imperative to halt a pandemic that involves more than 40 million individuals worldwide as of 2005 and is causing enormous socio-economic losses, especially in developing countries (DC). The overall failure of more than two decades of HIV vaccine research justifies the demands for a concerted effort for the rapid development of new and efficacious vaccines against HIV/AIDS. In this context, building international collaborative networks is a must for speeding up scientific research and optimizing the use of funding in a synergistic fashion, as resources for HIV/AIDS are limited and do not involve most of the biggest Pharmas that are more interested in drug discovery. The AIDS Vaccine Integrated Project (AVIP) consortium is an example of synergistic partnership of international European Union and DC experts with a common research goal. AVIP is a European Commission-funded (FP-6), consortium-based, 5-year program directed to the fast development of new HIV/AIDS vaccine candidates to be tested in phase I clinical trials in Europe for future advancement to phase II/III testing in DC. To ensure their rapid development, AVIP novel combined vaccines include both regulatory and structural HIV antigens, which have already been tested, as single components, in phase I clinical trials. In particular, such combination vaccines may be superior to earlier vaccine candidates, the vast majority of which are based only on either structural or regulatory HIV products. In fact, the generation of immune responses to both types of viral antigens expressed either early (regulatory products) or late (structural products) during the viral life cycle can maximize immune targeting of both primary or chronic viral infection. Further, the rational design of combined vaccines allows exploitation of immunomodulatory functions of HIV regulatory proteins, which can improve immunity against structural vaccine components. The building of the AVIP consortium and its scientific strategy will be reviewed in this paper as an example of the establishment of a consortium regulated by a specific intellectual property agreement.

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.

Aiming to induce broadly reactive neutralizing antibody responses with HIV-1 vaccine candidates

Neutralizing antibody induction is a key feature of many effective vaccines and is the only immune response that has proven to be capable of completely blocking AIDS virus infection in animal models. Unfortunately, the extensive genetic variability and complex immune-evasion strategies of HIV-1 have thwarted all attempts to date at eliciting an effective neutralizing antibody response with candidate HIV-1 vaccine immunogens. Recent advances in our understanding of how these evasion strategies operate, coupled with growing progress in unravelling the structure and immunobiology of the viral envelope glycoproteins, are contributing to novel immunogen designs to overcome the many barriers to inducing protective antibodies against HIV-1.

Responses of mice immunized with a DNA vaccine encoding carcinoembryonic antigen (CEA)

C57BL/6 and BALB/c mice were immunized with two different plasmids (p91023B and pKCEA66) encoding different forms of the tumor-associated antigen carcinoembryonic antigen (CEA). The wild type form of CEA (p91023B), which is expressed at the cell surface, induces stronger anti-CEA IgG response after DNA-plasmid immunizations than the modified intracellular form of CEA (pKCEA66), which was designed to mount strong cellular responses. Boosting with recombinant CEA (rCEA) increased the anti-CEA IgG response significantly. In the tumor protection model used, where SCID mice are challenged with human tumor cells mixed with splenocytes from immunized mice, both innate and specific immune responses are responsible for the protective effect.

A novel DNA adjuvant, N3, enhances mucosal and systemic immune responses induced by HIV-1 DNA and peptide immunizations

AIMS

The study was designed to evaluate a novel cationic lipid DNA adjuvant (N3) and its function for HIV-1gp160/rev DNA plasmid delivered intranasally. The primary N3/HIV-DNA plasmid immunizations were boosted intranasally with a gp41 peptide in a anionic L3 adjuvant. This novel prime-boost strategy of mucosal immunization provided a broad HIV-1 envelope specific immunity, and recognition of viruses of subtypes A, B and C.

CONCLUSIONS

Intranasal N3-adjuvanted gp160/rev DNA prime followed by one L3-peptide boosting immunization, induced broadly neutralizing antibodies against HIV-1 in the mucosa and systemically. The needle-free intranasal prime-boost strategy using two different adjuvant formulations reduced significantly the dose of DNA needed.

Multigene/Multisubtype HIV-1 Vaccine Induces Potent Cellular and Humoral Immune Responses by Needle-Free Intradermal Delivery

Gene vaccination encounters problems different from those of gene therapy since both a short half-life of the gene and a strong immune response to the gene product are desirable. We have evaluated a DNA vaccine consisting of seven plasmids encoding nine HIV-1 proteins. Using a needle-free delivery device, the Biojector, together with recombinant mouse GM-CSF, this vaccine induced strong gp160 Env- and p24 Gag-specific cellular and humoral immune responses in mice. The rGM-CSF was crucial for inducing both antibodies and antigen-specific CD8(+) T cell responses against both gp160 and p24. A GMP-produced lot of this vaccine, intended for human use, was delivered intradermally or intramuscularly into BALB/c mice at a GLP-accredited animal facility. This vaccine induced strong cellular responses independent of the route of immunization; moreover, no signs of toxicity were detected after histopathological examination of various tissues. Overall, the results indicate that the intradermal delivery of multigene/multisubtype HIV DNA in combination with recombinant GM-CSF is a safe and efficacious strategy for inducing high levels of specific CD8(+) T cells and unusually high titers of antibodies. This vaccine has been approved by the Swedish Medicinal Products Agency and is currently in a Phase I clinical trial.

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.

DNA vaccines: progress and challenges

In the years following the publication of the initial in vivo demonstration of the ability of plasmid DNA to generate protective immune responses, DNA vaccines have entered into a variety of human clinical trials for vaccines against various infectious diseases and for therapies against cancer, and are in development for therapies against autoimmune diseases and allergy. They also have become a widely used laboratory tool for a variety of applications ranging from proteomics to understanding Ag presentation and cross-priming. Despite their rapid and widespread development and the commonplace usage of the term "DNA vaccines," however, the disappointing potency of the DNA vaccines in humans underscores the challenges encountered in the efforts to translate efficacy in preclinical models into clinical realities. This review will provide a brief background of DNA vaccines including the insights gained about the varied immunological mechanisms that play a role in their ability to generate immune responses.

Human dendritic cells transduced with herpes simplex virus amplicons encoding human immunodeficiency virus type 1 (HIV-1) gp120 elicit adaptive immune responses from human cells engrafted into NOD/SCID mice and confer partial protection against HIV-1 challenge

Small-animal models are needed to test human immunodeficiency virus (HIV) vaccine efficacy following viral challenge. To this end, we examined HIV-1-specific immune responses following immunization of nonobese diabetic-severe combined immunodeficient mice that were repopulated with human peripheral blood lymphocytes (hu-PBL-NOD/SCID mice). Autologous dendritic cells (DC) were transduced ex vivo with replication-defective, helper virus-free, herpes simplex virus type 1 (HSV-1) amplicons that expressed HIV-1 gp120 and were then injected into the hu-PBL-NOD/SCID mice. This resulted in primary HIV-1-specific humoral and cellular immune responses. Serum samples from vaccinated animals contained human immunoglobulin G that reacted with HIV-1 Env proteins by enzyme-linked immunosorbent assay and neutralized the infectivity of HIV-1 LAI and ADA strains. T cells isolated from the mice responded to viral antigens by producing gamma interferon when analyzed by enzyme-linked immunospot assay. Importantly, exposure of the vaccinated animals to infectious HIV-1 demonstrated partial protection against infectious HIV-1 challenge. This was reflected by a reduction in HIV-1(ADA) and by protection of the engrafted human CD4(+) T lymphocytes against HIV-1(LAI)-induced cytotoxicity. These data demonstrate that transduction of DC by HSV amplicon vectors expressing HIV-1 gp120 induce virus-specific immune responses in hu-PBL-NOD/SCID mice. This mouse model may be a useful tool to evaluate human immune responses and protection against viral infection following vaccination.