An HIV type 2 DNA vaccine induces cross-reactive immune responses against HIV type 2 and SIV

Recent advances on HIV DNA vaccines development: Stepwise improvements to clinical trials

According to WHO (World Health Organization) reports, more than 770,000 people died from HIV and almost 1.7 million people becoming newly infected in the worldwide in 2018. Therefore, many attempts should be done to produce a forceful vaccine to control the AIDS. DNA-based vaccines have been investigated for HIV vaccination by researches during the recent 20 years. The DNA vaccines are novel approach for induction of both type of immune responses (cellular and humoral) in the host cells and have many advantages including high stability, fast and easy of fabrication and absence of severe side effects when compared with other vaccination methods. Recent studies have been focused on vaccine design, immune responses and on the use of adjuvants as a promising strategy for increased level of responses, delivery approaches by viral and non-viral methods and vector design for different antigens of HIV virus. In this review, we outlined the aforementioned advances on HIV DNA vaccines. Then we described the future trends in clinical trials as a strong strategy even in healthy volunteers and the potential developments in control and prevention of HIV.

Immunostimulant patches containing Escherichia coli LT enhance immune responses to DNA- and recombinant protein-based Alzheimer's disease vaccines

Immunotherapeutic approaches to treating Alzheimer's disease (AD) using vaccination strategies must overcome the obstacle of achieving adequate responses to vaccination in the elderly. Here we demonstrate for the first time that application of the Escherichia coli heat-labile enterotoxin adjuvant-laden immunostimulatory patches (LT-IS) dramatically enhances the onset and magnitude of immune responses to DNA- and protein-based vaccines for Alzheimer's disease following intradermal immunization via gene gun and conventional needles, respectively. Our studies suggest that the immune activation mediated by LT-IS offers improved potency for generating AD-specific vaccination responses that should be investigated as an adjuvant in the clinical arena.

Vaccination of mice using the West Nile virus E-protein in a DNA prime-protein boost strategy stimulates cell-mediated immunity and protects mice against a lethal challenge

West Nile virus (WNV) is a mosquito-borne flavivirus that is endemic in Africa, the Middle East, Europe and the United States. There is currently no antiviral treatment or human vaccine available to treat or prevent WNV infection. DNA plasmid-based vaccines represent a new approach for controlling infectious diseases. In rodents, DNA vaccines have been shown to induce B cell and cytotoxic T cell responses and protect against a wide range of infections. In this study, we formulated a plasmid DNA vector expressing the ectodomain of the E-protein of WNV into nanoparticles by using linear polyethyleneimine (lPEI) covalently bound to mannose and examined the potential of this vaccine to protect against lethal WNV infection in mice. Mice were immunized twice (prime – boost regime) with the WNV DNA vaccine formulated with lPEI-mannose using different administration routes (intramuscular, intradermal and topical). In parallel a heterologous boost with purified recombinant WNV envelope (E) protein was evaluated. While no significant E-protein specific humoral response was generated after DNA immunization, protein boosting of DNA-primed mice resulted in a marked increase in total neutralizing antibody titer. In addition, E-specific IL-4 T-cell immune responses were detected by ELISPOT after protein boost and CD8⁺ specific IFN-γ expression was observed by flow cytometry. Challenge experiments using the heterologous immunization regime revealed protective immunity to homologous and virulent WNV infection.

DNA prime-protein boost increased the titer, avidity and persistence of anti-Abeta antibodies in wild-type mice

Recently, we reported that a DNA vaccine, composed of three copies of a self B cell epitope of amyloid-beta (Abeta(42)) and the foreign T-cell epitope, Pan DR epitope (PADRE), generated strong anti-Abeta immune responses in wild-type and amyloid precursor protein transgenic animals. Although DNA vaccines have several advantages over peptide-protein vaccines, they induce lower immune responses in large animals and humans compared with those in mice. The focus of this study was to further enhance anti-Abeta(11) immune responses by developing an improved DNA vaccination protocol of the prime-boost regimen, in which the priming step would use DNA and the boosting step would use recombinant protein. Accordingly, we generated DNA and recombinant protein-based epitope vaccines and showed that priming with DNA followed by boosting with a homologous recombinant protein vaccine significantly increases the anti-Abeta antibody responses and do not change the immunoglobulin G1 (IgG1) profile of humoral immune responses. Furthermore, the antibodies generated by this prime-boost regimen were long-lasting and possessed a higher avidity for binding with an Abeta(42) peptide. Thus, we showed that a heterologous prime-boost regimen could be an effective protocol for developing a potent Alzheimer's disease (AD) vaccine.

Prototype Alzheimer's disease vaccine using the immunodominant B cell epitope from beta-amyloid and promiscuous T cell epitope pan HLA DR-binding peptide

Immunization of amyloid precursor protein transgenic mice with fibrillar beta-amyloid (Abeta) prevents Alzheimer's disease (AD)-like neuropathology. The first immunotherapy clinical trial used fibrillar Abeta, containing the B and T cell self epitopes of Abeta, as the immunogen formulated with QS21 as the adjuvant in the vaccine. Unfortunately, the clinical trial was halted during the phase II stage when 6% of the participants developed meningoencephalitis. The cause of the meningoencephalitis in the patients that received the vaccine has not been definitively determined; however, analysis of two case reports from the AN-1792 vaccine trial suggest that the meningoencephalitis may have been caused by a T cell-mediated autoimmune response, whereas production of anti-Abeta Abs may have been therapeutic to the AD patients. Therefore, to reduce the risk of an adverse T cell-mediated immune response to Abeta immunotherapy we have designed a prototype epitope vaccine that contains the immunodominant B cell epitope of Abeta in tandem with the synthetic universal Th cell pan HLA DR epitope, pan HLA DR-binding peptide (PADRE). Importantly, the PADRE-Abeta(1-15) sequence lacks the T cell epitope of Abeta. Immunization of BALB/c mice with the PADRE-Abeta(1-15) epitope vaccine produced high titers of anti-Abeta Abs. Splenocytes from immunized mice showed robust T cell stimulation in response to peptides containing PADRE. However, splenocytes from immunized mice were not reactivated by the Abeta peptide. New preclinical trials in amyloid precursor protein transgenic mouse models may help to develop novel immunogen-adjuvant configurations with the potential to avoid the adverse events that occurred in the first clinical trial.

Costimulatory molecule immune enhancement in a plasmid vaccine model is regulated in part through the Ig constant-like domain of CD80/86

There is great interest in understanding the role of costimulatory molecules in immune activation. In both the influenza and HIV DNA immunization models, several groups have reported that coimmunization of mice with plasmids encoding immunogen and CD86, but not CD80, effectively boosts Ag-specific T cell activation. This difference in immune priming provided an opportunity to examine the functional importance of different regions of the B.7 molecules in immune activation. To examine this issue, we developed a series of chimeric CD80 and CD86 constructs as well as deletion mutants, and examined their immune activating potential in the DNA vaccine model. We demonstrate that the lack of an Ig constant-like region in the CD80 molecule is critically important to the enhanced immune activation observed. CD80 C-domain deletion mutants induce a highly inflammatory Ag-specific cellular response when administered as part of a plasmid vaccine. The data suggest that the constant-like domains, likely through intermolecular interactions, are critically important for immune regulation during costimulation and that engineered CD80/86 molecules represent more potent costimulatory molecules and may improve vaccine adjuvant efficacy.

Generation and characterization of the humoral immune response to DNA immunization with a chimeric beta-amyloid-interleukin-4 minigene

Active immunization with fibrillar beta-amyloid peptide (Abeta(42)) as well as passive transfer of anti-Abeta antibodies significantly reduces Abeta plaque deposition, neuritic dystrophy, and astrogliosis in the brain of mutant amyloid precursor protein (APP)-transgenic mice. Although the mechanism(s) of clearance of Abeta from the brain following active or passive immunization remains to be determined, it is clear that anti-Abeta antibodies are critical for clearance. DNA immunization provides an attractive alternative to direct peptide and adjuvant approaches for inducing a humoral response to Abeta. We constructed a DNA minigene with Abeta fused to mouse interleukin-4 (pAbeta(42)-IL-4) as a molecular adjuvant to generate anti-Abeta antibodies and enhance the Th2-type of immune responses. Gene gun immunizations induced primarily IgG1 and IgG2b anti-Abeta antibodies. Fine epitope analysis with overlapping peptides of the Abeta(42) sequence identified the 1-15 region as a dominant B cell epitope. The DNA minigene-induced anti-Abeta antibodies bound to Abeta plaques in brain tissue from an Alzheimer's disease patient demonstrating functional activity of the antibodies and the potential for therapeutic efficacy.

Adjuvant-dependent modulation of Th1 and Th2 responses to immunization with beta-amyloid

The role of adjuvant on the T(h)1 and T(h)2 immune responses to Abeta-immunotherapy (Abeta(42 )peptide) was examined in wild-type mice. Fine epitope analysis with overlapping oligomers of the Abeta(42) sequence identified the 1-15 region as a dominant B cell epitope. The 6-20 peptide was recognized only weakly by antisera from mice administrated with Abeta(42) peptide formulated in complete Freund's adjuvant (CFA), alum or TiterMax Gold (TMG). However, mice immunized with Abeta(42) mixed with QS21 induced a significant antibody response to the 6-20 peptide. The only T cell epitope found was within the 6-28 sequence of Abeta(42). QS21 and CFA induced the strongest humoral response to Abeta, alum was intermediate, and TMG the weakest adjuvant. Analysis of antibody isotypes specific for Abeta indicates that alum induces primarily T(h)2-type immune response, whereas TMG, CFA and QS21 shift the immune responses toward a T(h)1 phenotype. Stimulation of splenocytes from Abeta-immunized mice with Abeta(40) peptide induced strikingly different cytokine expression profiles. QS21 and CFA induced significant IFN-gamma, IL-4 and tumor necrosis factor-alpha expression, whereas alum induced primarily IL-4 production. As T(h)1-type immune responses have been implicated in many autoimmune disorders, whereas T(h)2-type responses have been shown to inhibit autoimmune disease, the choice of adjuvant may be critical for the design of a safe and effective immunotherapy for Alzheimer's disease.

A retroviral DNA vaccine vector

A versatile DNA vaccine (pdIV3) was constructed by replacing the integrase, vif, vpx, and vpr genes of a pathogenic simian immunodeficiency virus (SIV) molecular clone with a linker containing unique cloning sites. The 5' long terminal repeat (LTR) is truncated and transcription is controlled by a cytomegalovirus (CMV) promoter. The construct expresses Gag and Env in vitro and noninfectious virus particles are produced from transfected cells. The ability of pdIV3 to promote cellular and humoral immune responses, along with the flexibility of the linker design to allow insertion of immunostimulatory genes in future constructs, makes this a useful base vector for immunization against primate lentiviruses. We present the construction of a retroviral plasmid designed to serve as a template for the development of safe and effective vaccines against primate immunodeficiency retroviruses. This vaccine component should facilitate the simultaneous induction of cellular and humoral immune responses that protect primates against infection with SIV and human immunodeficiency virus (HIV) and the development of acquired immune deficiency syndrome (AIDS). This plasmid could induce the appropriate immune response required to attack both cell-free and cell-associated viruses. The lack of infectivity, the inability to integrate, and the SIV origin make this construct a safe alternative to attenuated vaccines based on HIV. In addition, we intend to develop this construct as an immunotherapeutic approach to lower the viremia in AIDS patients.

DNA-immunization with a V2 deleted HIV-1 envelope elicits protective antibodies in macaques

Rhesus macaques immunized with the HIV-1 SF162DeltaV2 gp140 envelope using the DNA-prime plus protein-boost vaccination methodology, developed HIV envelope-specific T-cell lymphoproliferative responses and potent neutralizing antibodies. To evaluate the protective potential of these antibodies during acute infection, the animals were depleted of their CD8+ T lymphocytes using specific monoclonal antibodies and subsequently challenged intravenously with the pathogenic SHIV(SF162P4) isolate. As compared to non-vaccinated animals (one of which died from AIDS 16 weeks post-exposure) the vaccinated macaques had lower levels of peak viremia, rapidly cleared virus from the periphery and developed delayed seroconversion to SIV core antigens.

Modulation of cellular and humoral immune responses to a multiepitopic HIV-1 DNA vaccine by interleukin-18 DNA immunization/viral protein boost

In this study, the impact of Th1-inducing cytokine gene co-delivery and antigen boosting on humoral and cellular responses induced by multiepitopic DNA immunization in mice have been investigated. Intramuscular injection of mixed DNA constructs encoding for HIV-1 Gag, Tat and Nef proteins, co-administered with the DNA encoding for interleukin-18 (IL-18) have been used. The effect of boosting with the recombinant proteins was also evaluated on the outcome of the responses in DNA-primed mice. It was demonstrated that at least two DNA immunizations were necessary to generate virus specific Th-1 responses detected by the presence of cytotoxic T lymphocyte (CTL) and by the secretion of IL-2 and IFN-gamma, but not IL-4 and IL-10, in antigen-stimulated splenocyte cultures. Interestingly, co-delivery of Th-1-inducing IL-18 gene was able to shorten by 2 weeks, the CTL induction time, and to increase the antigen-induced secretion of IL-2 and IFN-gamma. Furthermore, IL-18 co-delivery enhanced antigen-specific lymphoproliferative responses, and this was most evident in mice that were primed and boosted with plasmid DNA. However, the induction of detectable antibodies in mice required two DNA vaccinations and a protein boost. In contrast to the effects on cell-mediated immunity, co-administration of IL-18-plasmid resulted in decreased antibody titers against viral proteins.

Modulation of antigen-specific cellular immune responses to DNA vaccination in rhesus macaques through the use of IL-2, IFN-gamma, or IL-4 gene adjuvants

Extensive experiments have shown DNA vaccines' ability to elicit immune responses in vivo in a safe and well-tolerated manner in several model systems, including rodents and non-human primates. As the DNA-based vaccine and immunotherapy approaches are being explored in humans, significant efforts have also been focused on further improving the immune potency of this technology. One strategy to enhance immune responses for DNA vaccines is the use of molecular or genetic adjuvants. These molecular adjuvant constructs (which encodes for immunologically important molecules such as cytokines) can be co-administered along with DNA vaccine constructs. Once delivered, these adjuvants have shown to modulate the magnitude and direction (humoral or cellular) of the vaccine-induced immune responses in rodent models. To date, however, there has been very little data reported from studies in primates. In this study, we examined the effects of cytokine gene adjuvants to enhance the level of cell-mediated immune responses in rhesus macaques. We co-immunized rhesus macaques with expression plasmids encoding for IL-2, IFN-gamma or IL-4 cytokines along with the DNA vaccine constructs encoding for HIV env/rev (pCEnv) and SIV gag/pol (pCSGag/pol) proteins. We observed that coadministration of IL-2 and IFN-gamma cDNA resulted in enhancement of antigen-specific T cell-mediated immune responses.

DNA vaccination with the human immunodeficiency virus type 1 SF162DeltaV2 envelope elicits immune responses that offer partial protection from simian/human immunodeficiency virus infection to CD8(+) T-cell-depleted rhesus macaques

DNA immunization of macaques with the SF162DeltaV2 envelope elicited lymphoproliferative responses and potent neutralizing antibodies. The animals were depleted of their CD8(+) T lymphocytes and then challenged intravenously with SHIV162P4. Compared to unvaccinated animals, the vaccinated macaques had lower peak viremia levels, rapidly cleared plasma virus, and showed delayed seroconversion.

Vaccination of chimpanzees with plasmid DNA encoding the hepatitis C virus (HCV) envelope E2 protein modified the infection after challenge with homologous monoclonal HCV

Hepatitis C virus (HCV) is an important cause of chronic liver disease worldwide. Development of vaccines to prevent HCV infection, or at least prevent progression to chronicity, is a major goal. In mice and rhesus macaques, a DNA vaccine encoding cell-surface HCV-envelope 2 (E2) glycoprotein stimulated stronger immune responses than a vaccine encoding intracellular E2. Therefore, we used DNA encoding surface-expressed E2 to immunize chimpanzees 2768 and 3001. Chimpanzee 3001 developed anti-E2 after the second immunization and antibodies to hypervariable region 1 (HVR1) after the third immunization. Although chimpanzee 2768 had only low levels of anti-E2 after the third immunization, an anamnestic response occurred after HCV challenge. CTL responses to E2 were not detected before challenge, but a strong response was detected after HCV challenge in chimpanzee 2768. An E2-specific CD4+ response was detected in chimpanzee 2768 before challenge and in both chimpanzees postchallenge. Three weeks after the last immunization, animals were challenged with 100 50% chimpanzee-infectious doses (CID(50)) of homologous monoclonal HCV. As a control, a naive chimpanzee was inoculated with 3 CID(50) of the challenge virus. The vaccine did not generate sterilizing immunity because both vaccinated chimpanzees were infected. However, both vaccinated chimpanzees resolved the infection early whereas the control animal became chronically infected. Compared with the control animal, hepatitis appeared earlier in the course of the infection in both vaccinated chimpanzees. Therefore, DNA vaccine encoding cell surface-expressed E2 did not elicit sterilizing immunity in chimpanzees against challenge with a monoclonal homologous virus, but did appear to modify the infection and might have prevented progression to chronicity.

Interleukin-18 modulates immune responses induced by HIV-1 Nef DNA prime/protein boost vaccine

Many different HIV-1 vaccine strategies have been developed, but as yet none has been completely successful. Promising results from combined DNA prime/protein boost vaccines have been reported. Specific immune responses generated by DNA vaccines can be modulated by the co-delivery of genes coding for cytokines. In this study, we have used the intradermal route by needle injection of a plasmid coding for the HIV-1 Nef accessory protein. We show that DNA prime/protein boost vaccine combinations increase the humoral and cellular immune responses against HIV-1 Nef and that the co-injection of DNA encoding Interleukin-18 (IL-18) modulates the specific immune response towards a Th1 type.

Macrophage colony-stimulating factor can modulate immune responses and attract dendritic cells in vivo

Studies have indicated that professional APCs in the periphery, such as dendritic cells and macrophages, play an important role in initiating DNA vaccine-specific immune responses. To engineer the immune response induced by DNA vaccines in vivo we investigated the modulatory effects of codelivering growth factor genes for the hematopoietic APCs along with DNA vaccines. Specifically, we examined the effects on the antigen-specific immune responses following the codelivery of the gene expression cassettes for M-CSF, G-CSF, and GM-CSF along with HIV-1 DNA immunogen constructs. We observed that coimmunization with GM-CSF increased the antibody response and resulted in a significant enhancement of lymphoproliferative response. Furthermore, among all coinjection combinations, we found that M-CSF coinjections resulted in a high level of CTL enhancement. This enhancement of CTL responses observed from the coinjection with M-CSF was CD8+ T cell dependent and was associated with the presence of CD11c+ cells at the site of injection and with the antigen-specific induction of the beta-chemokine MIP-1beta, suggesting a role for this chemokine in CTL induction. These results suggest that hematopoietic growth factors should be further studied as potential adjuvants for in vivo modulators of immune responses.

Antigen-specific humoral and cellular immune responses can be modulated in rhesus macaques through the use of IFN-gamma, IL-12, or IL-18 gene adjuvants

DNA or nucleic acid immunization has been shown to induce both antigen-specific cellular and humoral immune responses in vivo. Moreover, immune responses induced by DNA immunization can be enhanced and modulated by the use of molecular adjuvants. To engineer the immune response in vivo towards more T-helper (Th)1-type cellular responses, we investigated the co-delivery of inteferon (IFN)-gamma, interleukin (IL)-12, and IL-18 genes along with DNA vaccine constructs. We observed that both antigen-specific humoral and cellular immune responses can be modulated through the use of cytokine adjuvants in mice. Most of this work has been performed in rodent models. There has been little confirmation of this technology in primates. We also evaluated the immunomodulatory effects of this approach in rhesus macaques, since non-human primates represent the most relevant animal models for human immunodeficiency virus (HIV) vaccine studies. As in the murine studies, we also observed that each Th1 cytokine adjuvant distinctively regulated the level of immune responses generated. Co-immunization of IFN-gamma and IL-18 in macaques enhanced the level of antigen-specific antibody responses. Similarly, co-delivery of IL-12 and IL-18 also enhanced the level of antigen-specific Th proliferative responses. These results extend this adjuvant strategy in a more relevant primate model and support the potential utility of these molecular adjuvants in DNA vaccine regimens.

CD86 (B7-2) Can Function to Drive MHC-Restricted Antigen-Specific CTL Responses In Vivo

Activation of T cells requires both TCR-specific ligation by direct contact with peptide Ag-MHC complexes and coligation of the B7 family of ligands through CD28/CTLA-4 on the T cell surface. We recently reported that coadministration of CD86 cDNA along with DNA encoding HIV-1 Ags i.m. dramatically increased Ag-specific CTL responses. We investigated whether the bone marrow-derived professional APCs or muscle cells were responsible for the enhancement of CTL responses following CD86 coadministration. Accordingly, we analyzed CTL induction in bone marrow chimeras. These chimeras are capable of generating functional viral-specific CTLs against vaccinia virus and therefore represent a useful model system to study APC/T cell function in vivo. In vaccinated chimeras, we observed that only CD86 + Ag + MHC class I results in 1) detectable CTLs following in vitro restimulation, 2) detectable direct CTLs, 3) enhanced IFN-γ production in an Ag-specific manner, and 4) dramatic tissue invasion of T cells. These results support that CD86 plays a central role in CTL induction in vivo, enabling non-bone marrow-derived cells to prime CTLs, a property previously associated solely with bone marrow-derived APCs.

Cytokine molecular adjuvants modulate immune responses induced by DNA vaccine constructs for HIV-1 and SIV

DNA or nucleic acid immunization has been shown to induce both antigen-specific cellular and humoral immune responses in vivo. Moreover, immune responses induced by DNA immunization can be enhanced and modulated by the use of molecular adjuvants. To further engineer the immune response in vivo, we investigated the induction and regulation of immune responses from the codelivery of Thl cytokines (interleukin-2 [IL-2] and IL-12), Th2 cytokines (IL-4 and IL-10), and granulocyte-macrophage colony-stimulating factor (GM-CSF) genes along with a DNA vaccine construct encoding for simian immunodeficiency virus (SIV) gag/pol proteins. We observed that coinjection with IL-2, IL-4, IL-10, and GM-CSF resulted in increased levels of antigen-specific antibodies. In addition, we found that coinjection with cytokine genes drove the immune responses toward a more Thl or Th2 phenotype. We also observed that coadministration of IL-2, IL-12, and GM-CSF genes resulted in a dramatic enhancement of Th proliferation responses. Moreover, coimmunization with IL-12 genes resulted in a dramatic enhancement of antigen-specific cytotoxic T lymphocyte (CTL) responses. These results support the potential utility of molecular adjuvants in DNA vaccine regimens.

Engineering DNA vaccines via co-delivery of co-stimulatory molecule genes

DNA immunization has been investigated as a potential immunization strategy against infectious diseases and cancer. To enhance a DNA vaccine's ability to induce CTL response in vivo, we co-administered CD80 and CD86 expression cassettes along with HIV-1 immunogens. This manipulation resulted in a dramatic increase in MHC class I-restricted and CD8+ T-cell-dependent CTL responses in both mice and chimpanzees. This strategy of engineering vaccine producing cells to be more efficient T-cell activators could be an important tool for optimizing antigen-specific T-cell-mediated immune responses in the pursuit of more rationally designed vaccines and immune therapies.