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

Vaccination against drug resistance in HIV infection

HIV-1 resistance to currently employed antiretroviral drugs and drug-associated adverse reactions and toxicity point to a need for additional measures to control HIV-1 replication in HIV-infected patients. The immune system of HIV-infected individuals mount an immune response against the regions harboring drug-resistance mutations, sometimes stronger than that against the parental wild-type sequences. A potent cross-reactive immune response against drug-resistant pol proteins can suppress the replication of drug-escaping HIV. This suggests the possibility for a vaccination against existing and anticipated drug-resistant HIV variants. If successful, therapeutic vaccines against drug resistance would ease the therapeutic modalities and limit the spread of drug-resistant HIV. A better understanding of the complex interactions between patterns of drug-resistance mutations, immune responses against these mutations and their antigen presentation by particular human lymphocyte antigen alleles could help to tailor these vaccines after new drugs/new mutations. In this review, we describe the developments in the field of immunization against mutations conferring drug resistance and evaluate their prospects for human vaccination.

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.

Intranasal immunization of young mice with a multigene HIV-1 vaccine in combination with the N3 adjuvant induces mucosal and systemic immune responses

One of the major challenges for the development of an HIV vaccine is to induce potent virus-specific immune responses at the mucosal surfaces where transmission of virus occurs. Intranasal delivery of classical vaccines has been shown to induce good mucosal antibody responses, but so far for genetic vaccines the success has been limited. This study shows that young individuals are sensitive to nasal immunization with a genetic vaccine delivered in a formulation of a lipid adjuvant, the Eurocine N3. Intranasal delivery of a multiclade/multigene HIV-1 genetic vaccine gave rise to vaginal and rectal IgA responses as well as systemic humoral and cellular responses. As electroporation might become the preferred means of delivering genetic vaccines for systemic HIV immunity, nasal delivery by droplet formulation in a lipid adjuvant might become a means of priming or boosting the mucosal immunity.

Intradermal/subcutaneous immunization by electroporation improves plasmid vaccine delivery and potency in pigs and rhesus macaques

In an effort to improve DNA vaccine immune potency electroporation has emerged as a method of delivery of plasmids to target tissues. However, few studies have examined the use of this technology to deliver plasmid vaccines to the skin. Here we studied the effect of electroporation on DNA vaccine potency and gene delivery using skin as a target tissue in larger animal species. Using a pig model, we determined that high plasmid concentrations resulted in improved gene expression for plasmid GFP delivered by the intradermal/subcutaneous (ID/SQ) route. In a macaque model, we observed higher cellular and humoral responses to an HIV DNA vaccine, which included plasmid-encoded IL-12, with electroporation compared to ID/SQ injection alone. The induced responses were TH1 mediated. These results support that skin electroporation may have importance as an immunization approach in larger animal models.

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.

Pre-clinical evaluation of a CEA DNA prime/protein boost vaccination strategy against colorectal cancer

In preparation for a clinical trial in patients diagnosed with colorectal cancer, a vaccination strategy targeting the carcinoembryonic antigen (CEA) was evaluated in mice using a GMP-produced plasmid DNA vaccine, CEA66, encoding a truncated form of the tumour-associated antigen, CEA. The GMP-produced CEA DNA vaccine was also evaluated for toxicity. Repeated intradermal administration of the GMP-produced vaccine using a novel needle-free jet injection device (Biojector) induced robust CD4 and CD8 T-cell responses in mice, and did not result in any vaccine-related toxicity. In a heterologous DNA prime/protein boost setting, cellular immune responses were of higher magnitude in animals primed with CEA66 DNA than in animals receiving repeated doses of recombinant CEA protein. These responses were further enhanced if recombinant murine granulocyte-macrophage colony-stimulating factor was given as an adjuvant prior to vaccination. In contrast to repeated administration of recombinant CEA protein as a single modality vaccine, the heterologous CEA66 DNA prime/rCEA boost vaccination strategy resulted in a qualitatively broader immune response, and supports clinical testing of this vaccination regimen 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.

Immunization of mice with the nef gene from Human Immunodeficiency Virus type 1: study of immunological memory and long-term toxicology

Background

The human immunodeficiency virus type 1 (HIV-1) regulatory protein, Nef, is an attractive vaccine target because it is involved in viral pathogenesis, is expressed early in the viral life cycle and harbors many T and B cell epitopes. Several clinical trials include gene-based vaccines encoding this protein. However, Nef has been shown to transform certain cell types in vitro. Based on these findings we performed a long-term toxicity and immunogenicity study of Nef, encoded either by Modified Vaccinia virus Ankara or by plasmid DNA. BALB/c mice were primed twice with either DNA or MVA encoding Nef and received a homologous or heterologous boost ten months later. In the meantime, the Nef-specific immune responses were monitored and at the time of sacrifice an extensive toxicological evaluation was performed, where presence of tumors and other pathological changes were assessed.

Results

The toxicological evaluation showed that immunization with MVAnef is safe and does not cause cellular transformation or other toxicity in somatic organs.

Both DNAnef and MVAnef immunized animals developed potent Nef-specific cellular responses that declined to undetectable levels over time, and could readily be boosted after almost one year. This is of particular interest since it shows that plasmid DNA vaccine can also be used as a potent late booster of primed immune responses. We observed qualitative differences between the T cell responses induced by the two different vectors: DNA-encoded nef induced long-lasting CD8⁺ T cell memory responses, whereas MVA-encoded nef induced CD4⁺ T cell memory responses. In terms of the humoral immune responses, we show that two injections of MVAnef induce significant anti-Nef titers, while repeated injections of DNAnef do not. A single boost with MVAnef could enhance the antibody response following DNAnef prime to the same level as that observed in animals immunized repeatedly with MVAnef. We also demonstrate the possibility to boost HIV-1 Nef-specific immune responses using the MVAnef construct despite the presence of potent anti-vector immunity.

Conclusion

This study shows that the nef gene vectored by MVA does not induce malignancies or other adverse effects in mice. Further, we show that when the nef gene is delivered by plasmid or by a viral vector, it elicits potent and long-lasting immune responses and that these responses can be directed towards a CD4⁺ or a CD8⁺ T cell response depending on the choice of vector.

Combined use of cytokines, hormones and therapeutic vaccines during effective antiretroviral therapy

Immune-based therapies using vaccines, cytokines and hormones are being considered in the context of effective antiretroviral therapy to induce immunologically defined long-term nonprogressor status in chronically infected HIV-1 patients. Such immunotherapy must allow induction or regeneration of anti-HIV-1 immune responses with the potential to control viremia, activate and eradicate viral reservoirs, and alleviate the immunosuppression caused by HIV-1, eventually possibly reaching the status of a virologically defined ‘elite controller’ with an absence of detectable viremia and no progression to disease over a long period of time. This article summarizes pilot studies utilizing therapeutic vaccines, cytokines and/or hormones in treated HIV-1 infection, and focuses on novel agents and immunotherapeutic options that may have the potential to augment or replace existing antiretroviral therapy with the aim of inducing nonprogressor status in the infected host.

Structure and immunogenicity of alternative forms of the simian immunodeficiency virus gag protein expressed using Venezuelan equine encephalitis virus replicon particles

Venezuelan equine encephalitis virus replicon particles (VRP) were engineered to express different forms of SIV Gag to compare expression in vitro, formation of intra- and extracellular structures and induction of humoral and cellular immunity in mice. The three forms examined were full-length myristylated SIV Gag (Gagmyr+), full-length Gag lacking the myristylation signal (Gagmyr-) or a truncated form of Gagmyr- comprising only the matrix and capsid domains (MA/CA). Comparison of VRP-infected primary mouse embryo fibroblasts, mouse L929 cells and primate Vero cells showed comparable expression levels for each protein, as well as extracellular virus-like particles (VRP-Gagmyr+) and distinctive cytoplasmic aggregates (VRP-Gagmyr-) with each cell type. VRP were used to immunize BALB/c mice, and immune responses were compared using an interferon (IFN)-gamma ELISPOT assay and a serum antibody ELISA. Although all three VRP generated similar levels of IFN-gamma-producing cells at 1 week post-boost, at 10 weeks post-boost the MA/CA-VRP-induced response was maintained at a significantly higher level relative to that induced by Gagmyr+-VRP. Antibody responses to MA/CA-VRP and Gagmyr+-VRP were not significantly different.

Chemical adjuvants for plasmid DNA vaccines

Plasmid DNA vaccines are a promising modality for immunization against a variety of human pathogens. Immunization via multiple routes with plasmid DNA can elicit potent cellular immune responses, and these immunogens can be administered repeatedly without inducing anti-vector immunity. Nonetheless, the immunogenicity of plasmid DNA vaccines has been limited by problems associated with delivery. A number of adjuvants have been designed to improve plasmid DNA immunogenicity, either by directly stimulating the immune system or by enhancing plasmid DNA expression. Chemical adjuvants for enhancing plasmid DNA expression include liposomes, polymers, and microparticles, all of which have shown promise for enhancing the expression and immunogenicity of plasmid DNA vaccines in animal models. Micro- and nanoparticles have not been shown to enhance immune responses to plasmid DNA vaccines. However, formulation of plasmid DNA with some non-particulate polymeric adjuvants has led to a statistically significant enhancement of immune responses. Further development of these technologies will significantly improve the utility of plasmid DNA vaccination.

Virus-like particles: designing an effective AIDS vaccine

Viruses that infect eukaryotic organisms have the unique characteristic of self-assembling into particles. The mammalian immune system is highly attuned to recognizing and attacking these viral particles following infection. The use of particle-based immunogens, often delivered as live-attenuated viruses, has been an effective vaccination strategy for a variety of viruses. The development of an effective vaccine against the human immunodeficiency virus (HIV) has proven to be a challenge, since HIV infects cells of the immune system causing severe immunodeficiency resulting in the syndrome known as AIDS. In addition, the ability of the virus to adapt to immune pressure and reside in an integrated form in host cells presents hurdles for vaccinologists to overcome. A particle-based vaccine strategy has promise for eliciting high titer, long-lived, immune responses to a diverse number of viral epitopes against different HIV antigens. Live-attenuated viruses are effective at generating both cellular and humoral immune responses. However, while these vaccines stimulate immunity, challenged animals rarely clear the viral infection and the degree of attenuation directly correlates with protection from disease. Further, a live-attenuated vaccine has the potential to revert to a pathogenic form. Alternatively, virus-like particles (VLPs) mimic the viral particle without causing an immunodeficiency disease. VLPs are self-assembling, non-replicating, non-pathogenic particles that are similar in size and conformation to intact virions. A variety of VLPs for lentiviruses are currently in preclinical and clinical trials. This review focuses on our current status of VLP-based AIDS vaccines, regarding issues of purification and immune design for animal and clinical trials.

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.

Gene-based vaccines: recent technical and clinical advances

DNA vaccines have been widely used in efforts to develop vaccines against various pathogens as well as for cancer, autoimmune diseases and allergy. DNA vaccines offer broad efficacy (particularly for their ability to generate both cellular and humoral immunity), ease of construction and manufacture and the potential for world-wide usage even in low-resource settings. However, despite their successful application in many preclinical disease models, their potency in human clinical trials has been insufficient to provide protective immunity. Nevertheless, two DNA vaccines were recently licensed for use in animals (horse and fish), underscoring the potential of this technology. Here, we describe recent advances in increasing the potency of these vaccines, in understanding their immunological mechanisms, and in their applications and efficacy in clinical trials so far.