Use of DNAs expressing HIV-1 Env and noninfectious HIV-1 particles to raise antibody responses in mice

Effect of different promoters on immune responses elicited by HIV-1 gag/env multigenic DNA vaccine in Macaca mulatta and Macaca nemestrina

pCMV-NL(Deltapol) and pAKV-NL(Deltapol) expressed human immunodeficiency virus type 1 (HIV-1) gag and env under the regulation of the human cytomegalovirus (CMV) immediate-early (IE) promoter/enhancer and the endogenous AKV murine leukemia viral long terminal repeat (LTR), respectively. Analysis of the immune responses elicited by direct DNA injection of pCMV-NL(Deltapol) and pAKV-NL(Deltapol) in macaques indicated that generation of the humoral and T-cell proliferative responses correlated directly with the promoter strength of the vaccine DNAs. In Macaca mulatta, pCMV-NL(Deltapol) generated stronger humoral responses and T-cell proliferative responses to Gag and Env using less DNA and fewer number of injections than pAKV-NL(Deltapol). Similarly, in Macaca nemestrina pCMV-NL(Deltapol) elicited high humoral responses, which persisted long-term and were boostable. Injection of large amounts of pAKV-NL(Deltapol), in general, failed to produce antibody levels comparable to pCMV-NL(Deltapol). However, injection of a control animal with large amounts of vector DNA produced a generalized enzyme-linked immunosorbent assay (ELISA) reactivity to HIV-1. The results indicated that generation of high immune responses to HIV-1 cannot be achieved by increasing the vaccine DNA dose and may require high protein expression from the DNA by including a strong promoter or by the use of other boosting agents. Furthermore, safety concerns may arise with increasing the DNA dose that could need additional investigation.

DNA-based vaccination induces humoral and cellular immune responses against hepatitis B virus surface antigen in mice without activation of C-myc

AIM: To develop a safe and effective DNA vaccine for inducing humoral and cellular immunological responses against hepatitis B virus surface antigen (HBsAg).

METHODS: BALB/c mice were inoculated with NV-HB/s, a recombinant plasmid that had been inserted S gene of hepatitis B virus genome and could express HBsAg in eukaryotes. HBsAg expression was measured by ABC immunohistochemical assay, generation of anti-HBs by ELISA and cytotoxic T lymphocyte (CTL), by MTT method, existence of vaccine DNA by Southern blot hybridization and activation of oncogene C-myc by in situ hybridization.

RESULTS: With NV-HB/s vaccination by intramuscular injection, anti-HBs was initially positive 2 wk after inoculation while all mice tested were HBsAg positive in the muscles. The titers and seroconversion rate of anti-HBs were steadily increasing as time went on and were dose-dependent. All the mice inoculated with 100 μg NV-HB/s were anti-Bs positive one month after inoculation, the titer was 1∶1024 or more. The humoral immune response was similar induced by either intramuscular or intradermal injection. CTL activities were much stronger (45.26%) in NV-HB/s DNA immunized mice as compared with those (only 6%) in plasma-derived HBsAg vaccine immunized mice. Two months after inoculation, all muscle samples were positive by Southern-blot hybridization for NV-HB/s DNA detection, but decreased to 25% and all were undetectable by in situ hybridization after 6 mo. No oncogene C-myc activation was found in the muscle of inoculation site.

CONCLUSION: NV-HB/s could generate humoral and cellular immunological responses against HBsAg that had been safely expressed in situ by NV-HB/s vaccination.

Augmentation of immune responses to HIV-1 and simian immunodeficiency virus DNA vaccines by IL-2/Ig plasmid administration in rhesus monkeys

The potential utility of plasmid DNA as an HIV-1 vaccination modality currently is an area of active investigation. However, recent studies have raised doubts as to whether plasmid DNA alone will elicit immune responses of sufficient magnitude to protect against pathogenic AIDS virus challenges. We therefore investigated whether DNA vaccine-elicited immune responses in rhesus monkeys could be augmented by using either an IL-2/Ig fusion protein or a plasmid expressing IL-2/Ig. Sixteen monkeys, divided into four experimental groups, were immunized with (i) sham plasmid, (ii) HIV-1 Env 89.6P and simian immunodeficiency virus mac239 Gag DNA vaccines alone, (iii) these DNA vaccines and IL-2/Ig protein, or (iv) these DNA vaccines and IL-2/Ig plasmid. The administration of both IL-2/Ig protein and IL-2/Ig plasmid induced a significant and sustained in vivo activation of peripheral T cells in the vaccinated monkeys. The monkeys that received IL-2/Ig plasmid generated 30-fold higher Env-specific antibody titers and 5-fold higher Gag-specific, tetramer-positive CD8+ T cell levels than the monkeys receiving the DNA vaccines alone. IL-2/Ig protein also augmented the vaccine-elicited immune responses, but less effectively than IL-2/Ig plasmid. Augmentation of the immune responses by IL-2/Ig was evident after the primary immunization and increased with subsequent boost immunizations. These results demonstrate that the administration of IL-2/Ig plasmid can substantially augment vaccine-elicited humoral and cellular immune responses in higher primates.

DNA and RNA-based vaccines: principles, progress and prospects

DNA vaccines were introduced less than a decade ago but have already been applied to a wide range of infectious and malignant diseases. Here we review the current understanding of the mechanisms underlying the activities of these new vaccines. We focus on recent strategies designed to enhance their function including the use of immunostimulatory (CpG) sequences, dendritic cells (DC), co-stimulatory molecules and cytokine- and chemokine-adjuvants. Although genetic vaccines have been significantly improved, they may not be sufficiently immunogenic for the therapeutic vaccination of patients with infectious diseases or cancer in clinical trials. One promising approach aimed at dramatically increasing the immunogenicity of genetic vaccines involves making them 'self-replicating'. This can be accomplished by using a gene encoding RNA replicase, a polyprotein derived from alphaviruses, such as Sindbis virus. Replicase-containing RNA vectors are significantly more immunogenic than conventional plasmids, immunizing mice at doses as low as 0.1 microg of nucleic acid injected once intramuscularly. Cells transfected with 'self-replicating' vectors briefly produce large amounts of antigen before undergoing apoptotic death. This death is a likely result of requisite double-stranded (ds) RNA intermediates, which also have been shown to super-activate DC. Thus, the enhanced immunogenicity of 'self-replicating' genetic vaccines may be a result of the production of pro-inflammatory dsRNA, which mimics an RNA-virus infection of host cells.

Gene gun mediated vaccination is superior to manual delivery for immunisation with DNA vaccines expressing protective antigens from Yersinia pestis or Venezuelan Equine Encephalitis virus

Plasmids expressing the V antigen of Yersinia pestis or the E2 glycoprotein of Venezuelan Equine Encephalitis (VEE) virus were used to vaccinate mice by intra-dermal or intra-muscular injection, or by particle-mediated bombardment using the Helios gene gun. After two immunizations, groups of mice which had received 4 microg doses of plasmid DNA using the gene gun had IgG levels which were higher than in other groups manually immunised with 12-fold more plasmid DNA. The immunoglobulin isotype profile was predominantly IgG1 following inoculation with either plasmid. Our results indicate that gene gun mediated vaccination can be used to increase the magnitude of the immune response to both bacterial and viral antigens expressed by plasmid DNA.

Evaluation of novel human immunodeficiency virus type 1 Gag DNA vaccines for protein expression in mammalian cells and induction of immune responses

Human immunodeficiency virus (HIV)-specific cytotoxic T lymphocytes (CTL) are an important parameter of host defenses that limit viral replication after infection. Induction of effective CTL against conserved viral proteins such as Gag may be essential to the development of a safe and effective HIV type 1 (HIV-1) vaccine. DNA vaccination represents a novel strategy for inducing potent CD8(+) CTL responses in vivo. However, expression of HIV-1 structural proteins by DNA vectors has been hampered by a stringent requirement for coexpression with other viral components, such as Rev and RRE. Furthermore, even with Rev and RRE present, the level of expression of HIV-1 Gag, Pol, or Env is very low in murine cells. These problems have limited our ability to address the key issue of how to generate effective CTL responses to Gag in a mouse model. To overcome this problem, we compared several novel DNA expression vectors for HIV-1 Gag protein expression in primate and mouse cells and for generating immune responses in mice after DNA vaccination. A DNA vector containing wild type HIV-1 gag coding sequences did not induce detectable Gag expression in any of the cells tested. Attempts to increase nuclear export of Gag expression RNA by adding the constitutive transport element yielded only a moderate increase in Gag expression in monkey-derived COS cells and an even lower increase in Gag expression in HeLa cells or several mouse cell lines. In contrast, silent-site mutations in the HIV-1 gag coding sequences significantly increased Gag expression levels in all cells tested. Furthermore, this construct induced both Gag-specific antibody and CTL responses in mice after DNA vaccination. Using this construct, we achieved stable expression of HIV-1 Gag in the mouse cell line p815, which can now be used as a target cell for measuring HIV-1 Gag-specific CTL responses in immunized mice. The DNA vectors described in this study should make it possible to systematically evaluate the approaches for maximizing the induction of CTL responses against HIV-1 Gag in mouse and other animal systems.

DNA vaccines: technology and application as anti-parasite and anti-microbial agents

DNA vaccines have been termed The Third Generation of Vaccines. The recent successful immunization of experimental animals against a range of infectious agents and several tumour models of disease with plasmid DNA testifies to the powerful nature of this revolutionary approach in vaccinology. Among numerous advantages, a major attraction of DNA vaccines over conventional vaccines is that they are able to induce protective cytotoxic T-cell responses as well as helper T-cell and humoral immunity. Here we review the current state of nucleic acid vaccines and cover a wide range of topics including delivery mechanisms, uptake and expression of plasmid DNA, and the types of immune responses generated. Further, we discuss safety issues, and document the use of nucleic acid vaccines against viral, bacterial and parasitic diseases, and cancer. The early potential promise of DNA vaccination has been fully substantiated with recent, exciting developments including the movement from testing DNA vaccines in laboratory models to non-human primates and initial human clinical trials. These advances and the emerging voluminous literature on DNA vaccines highlight the rapid progress that has been made in the DNA immunization field. It will be of considerable interest to see whether the progress and optimism currently prevailing can be maintained, and whether the approach can indeed fulfil the medical and commerical promise anticipated.

Effective induction of HIV-specific CTL by multi-epitope using gene gun in a combined vaccination regime

Reliable and effective induction of cytotoxic T-lymphocytes (CTL) is one of the prime objectives of vaccine research. Previously, novel HIV vaccine candidates were constructed as a string of CTL epitopes (20 human, 3 macaque and 1 mouse) delivered using a DNA vector [Hanke T, Schneider J, Gilbert SG, Hill AVS, McMichael A. DNA multi-CTL epitope vaccines for HIV and Plasmodium falciparum: immunogenicity in mice. Vaccine 1998;16:426-435.] or modified vaccinia Ankara (MVA [Hanke T, Blanchard TJ, Schneider J, Ogg GS, Tan R, Becker MSC, Gilbert SG, Hill AVS, Smith GL, McMichael A. Immunogenicities of intravenous and intramuscular administrations of MVA-based multi-CTL epitope vaccine for HIV in mice. J Gen Virol 1998;79:83-90.]), i.e. vaccine vehicles acceptable for use in humans. In mice, a single intramuscular (i.m.) needle injection of either vaccine alone elicited good CTL responses. Here, it is demonstrated that the multi-epitope DNA also induced CTL when delivered intradermally using the Accell gene gun. The CTL responses increased after re-immunization and after three deliveries were comparable to those induced by a single i.m. injection. Recent evidence indicates that combining routes and vaccine vehicles enhances the immunogenicity of vaccine-delivered or -encoded antigens. Here, it is shown that administration of DNA by an i.m. priming/gene gun boosting more efficiently induced CTL than gene gun priming/i.m. boosting. A similar increment was obtained by sequential vaccinations using a gene gun-delivered DNA followed by recombinant MVA. Thus particular sequences of routes or vaccine vehicles rather than simple prime-boost delivery of a single vaccine is critical for an effective elicitation of CTL.

Attempt to modify the immune response developed against FIV gp120 protein by preliminary FIV DNA injection

Following inactivated virus vaccination trials, the surface glycoprotein gp120 (SU) of the feline immunodeficiency virus (FIV) was considered as one of the determinants for protection. However, several vaccination trials using recombinant Env protein or some Env-derived peptides failed to induce protection. To study the influence of the environment in which the surface protein (SU) is injected. we analyzed the impact of a nucleocapsid (NC) DNA immunization on the presentation of the recSU protein to the immune system. Cats were vaccinated either with the recSU protein alone or with NC DNA followed by the recSU protein. Two routes of nucleocapsid DNA vaccination were tested: intramuscular and mucosal injections. Cats immunized with the recSU protein showed a facilitation of infection, since they presented the earliest and the highest humoral response correlating with the highest proviral load. They also showed an acceleration of the appearance of IL4 mRNA signal. Preliminary injection of the DNA coding for NC protein, regardless the route of inoculation, seemed to inhibit the facilitation induced by vaccination with the recSU protein alone. The previously nucleocapsid DNA immunized cats had infectious status similar to those of the control cats, but with lower proviral load and less developed anti-FIV humoral response. Cat No. 2, belonging to the group vaccinated with NC protein by the mucosal route, had a protected-like status which did not correlate with the humoral response. This cat was the only one to have a persisting IFN mRNA signal after challenge specific for the p10 nucleocapsid and recSU proteins. However, no NC specific cytotoxic cells were observed throughout the experiment in this cat. The role of nucleocapsid DNA vaccination is still unknown nevertheless we did demonstrate that the facilitation observed in vaccination trial with recombinant proteins could be modified and that recombinant proteins could be a component of an effective vaccine.

DNA inoculations with HIV-1 recombinant genomes that express cytokine genes enhance HIV-1 specific immune responses

Vaccination with HIV-1 DNA sequences induce both humoral and cellular immune responses in experimental animals. However, these responses are relatively weak and are often only transient in their nature. In order to enhance the level of HIV-1 specific immunity, we have engineered HIV-1 DNA constructs which contained various cytokine genes such as interleukin-2 (IL-2), granulocyte-macrophage colony stimulating factor (GM-CSF) and interferon-gamma (IFN-gamma) gene. These constructs have deleted the tat and nmf genes of HIV-1 to eliminate their immunosuppressive effects. Immunizations with these recombinant constructs elicited moderate proliferative T cell responses but poor antibody responses in rats. However, inoculations of HIV-1 DNA that contained the GM-CSF or the IL-2 gene significantly enhanced humoral and proliferative T cell responses, respectively. Thus, recombinant HIV-1 genomes such as those described here may increase the efficacy of DNA vaccination.

Intranasal Immunization with Plasmid DNA-Lipid Complexes Elicits Mucosal Immunity in the Female Genital and Rectal Tracts

The development of vaccines against pathogens transmitted across the genito-rectal mucosa that effectively stimulate both secretory IgA Abs and cytotoxic T lymphocytes in the genital tract and CTL in the draining lymph nodes (LN) has proven a major challenge. Here we report a novel, noninvasive approach of genetic vaccination via the intranasal route. Such vaccination elicits immune responses in the genital and rectal mucosa, draining LNs, and central lymphoid system. Intranasal immunization with plasmid DNA-lipid complexes encoding the model Ag firefly luciferase resulted in dissemination of the DNA and the encoded transcript throughout the respiratory and gastrointestinal tracts, draining LNs, and spleen. Complexing the plasmid DNA with the lipid DMRIE/DOPE enhanced expression of the encoded protein in the respiratory tract, increased specific secretory IgA Ab in the vaginal and rectal tracts, and increased the circulating levels of specific IgA and IgG. In addition, intranasal DNA immunization resulted in generation of Ag-specific CTL that were localized in the genital and cervical LNs and spleen. These results suggest that intranasal immunization with plasmid DNA-lipid complexes may represent a generic immunization strategy against pathogens transmitted across the genito-rectal and other mucosal surfaces.

Induction of human cytomegalovirus (HCMV)-glycoprotein B (gB)-specific neutralizing antibody and phosphoprotein 65 (pp65)-specific cytotoxic T lymphocyte responses by naked DNA immunization

Plasmids expressing the human cytomegalovirus (HCMV) glycoprotein B (gB) (UL55) or phosphoprotein 65 (pp65) (UL83) were constructed and evaluated for their ability to induce immune responses in mice. The full-length gB as well as a truncated form expressing amino acids 1-680 of gB, and lacking the fragment encoding amino acids 681 907 including the transmembrane domain of gB (gB680) were evaluated. Immunization of mice with plasmids coding for gB or gB680 induced ELISA and neutralizing antibodies, with the highest titres in mice immunized with the gB680 plasmid. Mice immunized with the gB plasmid predominantly produced IgG2a gB-specific antibody, while the gB680 plasmid raised mostly IgG1 anti-gB antibody. Mice immunized with the pp65 plasmid developed pp65-specific cytotoxic T lymphocytes (CTL) and ELISA antibodies. Immunization with a mixture of both gB and pp65 plasmids raised antibodies to both proteins and pp65-specific CTL, indicating a lack of interference between these two plasmids. These results suggest that DNA immunization is a useful approach for vaccination against HCMV disease.

DNA vaccines for viral diseases

DNA vaccines, with which the antigen is synthesized in vivo after direct introduction of its encoding sequences, offer a unique method of immunization that may overcome many of the deficits of traditional antigen-based vaccines. By virtue of the sustained in vivo antigen synthesis and the comprised stimulatory CpG motifs, plasmid DNA vaccines appear to induce strong and long-lasting humoral (antibodies) and cell-mediated (T-help, other cytokine functions and cytotoxic T cells) immune responses without the risk of infection and without boost. Other advantages over traditional antigen-containing vaccines are their low cost, the relative ease with which they are manufactured, their heat stability, the possibility of obtaining multivalent vaccines and the rapid development of new vaccines in response to new strains of pathogens. The antigen-encoding DNA may be in different forms and formulations, and may be introduced into cells of the body by numerous methods. To date, animal models have shown the possibility of producing effective prophylactic DNA vaccines against numerous viruses as well as other infectious pathogens. The strong cellular responses also open up the possibility of effective therapeutic DNA vaccines to treat chronic viral infections.

Enhanced T-cell immunogenicity and protective efficacy of a human immunodeficiency virus type 1 vaccine regimen consisting of consecutive priming with DNA and boosting with recombinant fowlpox virus

The induction of human immunodeficiency virus (HIV)-specific T-cell responses is widely seen as critical to the development of effective immunity to HIV type 1 (HIV-1). Plasmid DNA and recombinant fowlpox virus (rFPV) vaccines are among the most promising safe HIV-1 vaccine candidates. However, the immunity induced by either vaccine alone may be insufficient to provide durable protection against HIV-1 infection. We evaluated a consecutive immunization strategy involving priming with DNA and boosting with rFPV vaccines encoding common HIV-1 antigens. In mice, this approach induced greater HIV-1-specific immunity than either vector alone and protected mice from challenge with a recombinant vaccinia virus expressing HIV-1 antigens. In macaques, a dramatic boosting effect on DNA vaccine-primed HIV-1-specific helper and cytotoxic T-lymphocyte responses, but a decline in HIV-1 antibody titers, was observed following rFPV immunization. The vaccine regimen protected macaques from an intravenous HIV-1 challenge, with the resistance most likely mediated by T-cell responses. These studies suggest a safe strategy for the enhanced generation of T-cell-mediated protective immunity to HIV-1.

Studies of the neutralizing activity and avidity of anti-human immunodeficiency virus type 1 Env antibody elicited by DNA priming and protein boosting

DNA vaccination is an effective means of eliciting strong antibody responses to a number of viral antigens. However, DNA immunization alone has not generated persistent, high-titer antibody and neutralizing antibody responses to human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein (Env). We have previously reported that DNA-primed anti-Env antibody responses can be augmented by boosting with Env-expressing recombinant vaccinia viruses. We report here that recombinant Env protein provides a more effective boost of DNA-initiated antibody responses. In rabbits primed with Env-expressing plasmids, protein boosting increased titer, persistence, neutralizing activity, and avidity of anti-Env responses. While titers increased rapidly after boosting, avidity and neutralizing activity matured more slowly over a 6-month period following protein boosting. DNA priming and protein immunization with HIV-1 HXB-2 Env elicited neutralizing antibody for T cell line-adapted, but not primary isolate, viruses. The most effective neutralizing antibody responses were observed after priming with plasmids which expressed noninfectious virus-like particles. In contrast to immunizations with HIV-1 Env, DNA immunizations with the influenza virus hemagglutinin glycoprotein did not require a protein boost to achieve high-titer antibody with good avidity and persistence.

Safety and immunogenicity of HIV-1 DNA constructs in chimpanzees

A global effort to control the HIV epidemic is likely to rely heavily on immunization strategies. As our closest genetic relative, the chimpanzee provides the most important model for preclinical safety and immunogenicity studies. We have immunized adult, pregnant and infant chimpanzees with our plasmid vaccines. We have found these vaccines to be safe and well tolerated in all of these groups. The same vaccines have induced both humoral and cellular immunity in each instance.

Construction of attenuated HIV-1 accessory gene immunization cassettes

Delivery of genetic expression cassettes into animals can effectively induce both humoral and cellular immunity to the expressed gene product. Previously, we used this strategy to immunize against HIV-1 structural and enzymatic proteins in mice, non-human primates and in humans. In contrast, the use of the accessory genes including vif, vpr, vpu and nef as immunotherapeutic vaccine targets has not been well characterized. Our goal is to design an effective genetic HIV vaccine, which includes the accessory genes as part of a multi-component immunogen. In order to develop accessory genes as genetic vaccines, we have molecularly cloned and analysed the sequence variation and immunogenic potential present in these genes derived from viral isolates obtained from HIV-1 infected patients and laboratory isolates. Prototype genetic variants were selected and their ability to induce humoral and cellular immune responses was studied in animal models. We observed that attenuated accessory genes can effectively induce both humoral and cellular responses in mice and the resulting immune response is directly correlated with DNA concentrations delivered and the number of boosts. This strategy can be used generally to develop an effective, safe DNA vaccine for any pathogen.

Comparison of Humoral Immune Responses Elicited by DNA and Protein Vaccines Based on Merozoite Surface Protein-1 from Plasmodium yoelii, a Rodent Malaria Parasite

Immunization with DNA vaccines encoding relevant Ags can induce not only cell-mediated immune response but also humoral immune responses against pathogenic microorganisms in several animal models. Our previous results demonstrated that, when the C terminus (PyC2) of Plasmodium yoelii merozoite surface protein-1 (MSP-1), a leading vaccine candidate against erythrocytic stages of malaria, was expressed as a fusion protein (GST-PyC2) with glutathione S-transferase (GST), it elicited Ab-mediated protective immune responses in BALB/c mice. In our present study, we wished to examine the humoral responses to a DNA vaccine (V3) encoding GST-PyC2. The GST-PyC2 expressed in V3-transfected Cos 7 cells was recognized by a protective monoclonal Ab to PyC2 (mAb302), although the secreted product had undergone N-linked glycosylation. When BALB/c mice were immunized with V3 plasmid, anti-PyC2 Abs were successfully induced. These Abs immunoprecipitated native PyMSP-1 protein and competed with mAb302 for binding to its epitope at a level similar to those elicited by GST-PyC2 protein immunization. However, these Abs had significantly lower titers and avidities, and different isotype profiles and protective capacities against a lethal erythrocytic stage challenge, than those resulting from immunization with GST-PyC2 protein. Most surprising was the finding that, in contrast to protein immunization, there was no significant increase in the avidity of either GST-specific or PyC2-specific IgG Abs during the course of DNA immunization. This suggests that there may be little or no affinity maturation of specific Abs during DNA immunization in this system.

DNA/genetic vaccination (minireview)

An important new approach to vaccination is plasmid DNA injection in vivo that can elicit an immune response against protein(s) encoded. Antigen that is expressed from the in vivo transfected cells induces both humoral and cellular immune response. DNA immunization is generally applicable for a wide range of proteins. It can provide an organism with immunity against viruses, bacteria, parasites, and tumors. DNA vaccines can overcome the disadvantages of vaccines presently used as well as provide various new vaccines that are currently not available. This minireview provides an overview of evaluated DNA vaccine candidates against infectious agents and certain cancers.

DNA vaccination affords significant protection against feline immunodeficiency virus infection without inducing detectable antiviral antibodies

To test the potential of a multigene DNA vaccine against lentivirus infection, we generated a defective mutant provirus of feline immunodeficiency virus (FIV) with an in-frame deletion in pol (FIVDeltaRT). In a first experiment, FIVDeltaRT DNA was administered intramuscularly to 10 animals, half of which also received feline gamma interferon (IFN-gamma) DNA. The DNA was administered in four 100-microg doses at 0, 10, and 23 weeks. Immunization with FIVDeltaRT elicited cytotoxic T-cell (CTL) responses to FIV Gag and Env in the absence of a serological response. After challenge with homologous virus at week 26, all 10 of the control animals became seropositive and viremic but 4 of the 10 vaccinates remained seronegative and virus free. Furthermore, quantitative virus isolation and quantitative PCR analysis of viral DNA in peripheral blood mononuclear cells revealed significantly lower virus loads in the FIVDeltaRT vaccinates than in the controls. Immunization with FIVDeltaRT in conjunction with IFN-gamma gave the highest proportion of protected cats, with only two of five vaccinates showing evidence of infection following challenge. In a second experiment involving two groups (FIVDeltaRT plus IFN-gamma and IFN-gamma alone), the immunization schedule was reduced to 0, 4, and 8 weeks. Once again, CTL responses were seen prior to challenge in the absence of detectable antibodies. Two of five cats receiving the proviral DNA vaccine were protected against infection, with an overall reduction in virus load compared to the five infected controls. These findings demonstrate that DNA vaccination can elicit protection against lentivirus infection in the absence of a serological response and suggest the need to reconsider efficacy criteria for lentivirus vaccines.

Comparisons of DNA-mediated immunization procedures directed against surface glycoproteins of human immunodeficiency virus type-1 and hepatitis B virus

DNA vaccination methods were compared to examine the in vivo expression of HIV-1 gp160 and beta-galactosidase, and the resulting immune response. Beta-galactosidase plasmid showed expression rates of 2-5% of muscle fibers with or without pretreatments using bupivacaine or cardiotoxin facilitators 1 or 5 days earlier, respectively. In contrast, HIV gp160 expression was lower in untreated or bupivacaine-treated muscles, but was improved by pretreatment with cardiotoxin. Equal expression of beta-galactosidase and HIV gp160 was obtained using gene gun delivery to the epidermis. Unlike the i.m. in situ expression of gp160, the anti-HIV antibody response did not improve after muscle pretreatments but depended on the vaccination intervals. Gene gun delivery of pMN160 also resulted in a slow and low titered antibody response. In contrast, a single i.m. injection of plasmid encoding another viral envelope, HBsAg, resulted in earlier seroconversion to high titers without the need for pretreatments or boostings. Intradermal inoculation by gene gun using 100-fold less DNA resulted in the same anti-HBsAg antibody profile only after boostings. In contrast to the differences in antibody responses, a specific CTL response was obtained in all cases. Bupivacaine-treated muscles showed an extreme degree of edema with disruption of connective tissue (endo- and mesomysium) and was not well tolerated (4 of 19 mice died). Cardiotoxin created muscle necrosis and occasional (2 of 20 mice) development of fibrotic muscles. It is concluded that in vivo expression cannot be properly predicted using reporter gene experiments and that the resulting immune response does not follow directly with the expression rate. It is suggested that the antibody response may depend primarily on the nature of the antigen expressed rather than the DNA vaccination method. It is proposed that gene gun or i.m. injection be used without pretreatment in the case of DNA vaccination with plasmid encoding HIV MN gp160.

Induction of systemic and mucosal immune responses to human immunodeficiency virus type 1 by a DNA vaccine formulated with QS-21 saponin adjuvant via intramuscular and intranasal routes

Induction of mucosal and cell-mediated immunity is critical for development of an effective vaccine against human immunodeficiency virus (HIV). We compared intramuscular and intranasal immunizations with a DNA vaccine encoding env of HIV-1 and evaluated the QS-21 saponin adjuvant for augmentation of the systemic and mucosal immune responses to HIV-1 in a murine model. Vaccination via the two routes elicited comparable systemic immune responses, and QS-21 consistently enhanced antigen-specific serum immunoglobulin G2a (IgG2a) production, delayed-type hypersensitivity reaction, and cytolytic activity of splenocytes. Intestinal secretory IgA production and cytolytic activity of the mesenteric lymph node cells are preferentially elicited by intranasal immunization, and QS-21 augmented these activities as well. This adjuvant augmented production of interleukin-2 (IL-2) and gamma interferon (IFN-gamma) associated with decrease in IL-4 synthesis by antigen-restimulated splenocytes. The serum immunoglobulin subtype profile showed a dominant IgG2a response and less strong IgG1 and IgE production in a QS-21 dose-dependent manner. As expected, enhancements of humoral and cell-mediated immune responses by QS-21 were abrogated by treatment with anti-IL-2 and anti-IFN-gamma monoclonal antibodies. These results suggest that the intranasal route of DNA immunization is more efficient than the intramuscular route in inducing mucosal immunity mediated by sIgA and mesenteric lymphocytes. Furthermore, QS-21 is able to act as a mucosal adjuvant in DNA vaccination and demonstrates its immunomodulatory property via stimulation of the Th1 subset. This study emphasizes the importance of the route of immunization and the use of an adjuvant for effective DNA vaccination against HIV-1.

Increased immune response elicited by DNA vaccination with a synthetic gp120 sequence with optimized codon usage

DNA vaccination elicits humoral and cellular immune responses and has been shown to confer protection against several viral, bacterial, and parasitic pathogens. Here we report that optimized codon usage of an injected DNA sequence considerably increases both humoral and cellular immune responses. We recently generated a synthetic human immunodeficiency virus type 1 gp120 sequence in which most wild-type codons were replaced with codons from highly expressed human genes (syngp120). In vitro expression of syngp120 is considerably increased in comparison to that of the respective wild-type sequence. In BALB/c mice, DNA immunization with syngp120 resulted in significantly increased antibody titers and cytotoxic T-lymphocyte reactivity, suggesting a direct correlation between expression levels and the immune response. Moreover, syngp120 is characterized by rev-independent expression and a low risk of recombination with viral sequences. Thus, synthetic genes with optimized codon usage represent a novel strategy to increase the efficacy and safety of DNA vaccination.

Immunogenicity of DNA vaccines expressing human immunodeficiency virus type 1 envelope glycoprotein with and without deletions in the V1/2 and V3 regions

DNA vaccines that express the human immunodeficiency virus type 1 HXB-2 envelope glycoprotein (Env) with or without deletions of the major variable regions V1/V2 and V3 were tested for the ability to raise enzyme-linked immunosorbent assay (ELISA) and neutralizing antibody in New Zealand White (NZW) rabbits. Three forms of the Envs were examined: gp120, the surface (SU) receptor-binding domain; gp140, the entire extracellular domain of Env; and gp160, the complete form of Env. For the forms of Env containing the variable regions, the gp120-expressing DNA plasmid was more immunogenic than the gp140- or gp160-expressing DNA plasmids. Removing the V1/2 and V3 variable regions increased the immunogenicity of the gp140- and gp160-expressing DNAs. Deletion of the variable regions also resulted in antibody responses against determinants that were not presented by the forms of Env containing the variable regions. Despite the improved immunogenicity, removing the V1/V2 and V3 domains did not improve the ability of Env to raise neutralizing antibodies. These results suggest that increasing the exposure of internal structures of Env that include the CD4-binding site does not necessarily result in the generation of better neutralizing antibody.

Adjuvant effect of Ubenimex on a DNA vaccine for HIV-1

Enhancement of DNA vaccine immunogenicity is a current topic of high priority in the field of applied immunology, especially as a means of controlling HIV infection. The adjuvant effect of Ubenimex (UBX), an anti-cancer immunomodulator, on a DNA AIDS vaccine which we developed was examined in a murine model. UBX was formulated into a preparation containing DNA plasmids encoding env and rev genes of HIV-1 strain III(B), and was inoculated intramuscularly into BALB/c mice. The sera obtained with this mixture had 2(3)-2(5) times higher specific IgG titres than those obtained without the use of the adjuvant. UBX also elicited both a stronger HIV-1-specific DTH reaction, as measured by the footpad swelling test, and stronger cytotoxic T lymphocyte activity, as assayed by the 51Cr-release method, compared with responses using DNA alone. The cytokine secretion profile of restimulated immune lymphoid cells showed that UBX raised IL-2 and interferon-gamma levels and decreased IL-4 production. HIV-1-specific immunoglobulin subtype analysis demonstrated that UBX stimulated IgG2a production but suppressed synthesis of IgG1 and IgE. These results indicate that activation of the T-helper type 1 subset was induced by UBX, suggesting a mechanism of immunomodulation mediated by this agent. We conclude that UBX acts as an immunologic adjuvant for DNA vaccination against HIV-1. UBX may be a suitable adjuvant for clinical use because of its lack of antigenicity and low toxicity.

Gene therapy for infectious diseases

Gene therapy is being investigated as an alternative treatment for a wide range of infectious diseases that are not amenable to standard clinical management. Approaches to gene therapy for infectious diseases can be divided into three broad categories: (i) gene therapies based on nucleic acid moieties, including antisense DNA or RNA, RNA decoys, and catalytic RNA moieties (ribozymes); (ii) protein approaches such as transdominant negative proteins and single-chain antibodies; and (iii) immunotherapeutic approaches involving genetic vaccines or pathogen-specific lymphocytes. It is further possible that combinations of the aforementioned approaches will be used simultaneously to inhibit multiple stages of the life cycle of the infectious agent.

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

We have previously reported on the generation of specific functional immune responses after inoculation of animals with expression vectors encoding HIV-1 genes. This article provides the details of the first application of this new technology to induce immune responses against HIV-2. This virus is molecularly and serologically distinct from HIV-1 and is in fact more closely related to the simian immunodeficiency virus (SIV). Anti-HIV-2 and SIV antibodies were induced in mice of three different haplotypes following a single intramuscular inoculation with an HIV-2/ROD envelope glycoprotein expression vector (pcEnv-2). Boosting of animals with pcEnv-2 induced both anti-HIV-2 neutralizing antibodies and T cell-proliferative responses against HIV-2 and SIVmac proteins. We compared the humoral and cellular immune responses of mice injected with pcEnv-2 and then boosted with either the homologous DNA construct or a recombinant Env protein. Animals boosted with pcEnv-2 generated B and T cell immune responses as strong as those of mice boosted with recombinant gp140 protein in adjuvant. Finally, cellular immune responses were significantly increased with the coadministration of pcEnv-2 and a plasmid expressing interleukin 12. We therefore conclude that DNA plasmid inoculation induces cross-reactive anti-HIV-2 and anti-SIVmac immune responses in mice. This technology should be further investigated as a potential vaccine component for this human pathogen.

Enhancement of feline immunodeficiency virus (FIV) infection after DNA vaccination with the FIV envelope

Despite intensive experimentation to develop effective and safe vaccines against the human immunodeficiency viruses and other pathogenic lentiviruses, it remains unclear whether an immune response that does not afford protection may, on the contrary, produce adverse effects. In the present study, the effect of genetic immunization with the env gene was examined in a natural animal model of lentivirus pathogenesis, infection of cats by the feline immunodeficiency virus (FIV). Three groups of seven cats were immunized by intramuscular transfer of plasmid DNAs expressing either the wild-type envelope or two envelopes bearing mutations in the principal immunodominant domain of the transmembrane glycoprotein. Upon homologous challenge, determination of plasma virus load showed that the acute phase of viral infection occurred earlier in the three groups of cats immunized with FIV envelopes than in the control cats. Genetic immunization, however, elicited low or undetectable levels of antibodies directed against envelope glycoproteins. These results suggest that immunization with the FIV env gene may result in enhancement of infection and that mechanisms unrelated to enhancing antibodies underlay the observed acceleration.

Cationic liposomes are a strong adjuvant for a DNA vaccine of human immunodeficiency virus type 1

Liposomes have been widely used to enhance the immune response. In the present investigation, we studied their in vivo immunomodulation of an HIV-1-specific DNA vaccine candidate (pCMV160/REV) constructed with the cytomegalovirus (CMV) promoter-conjugated HIV-1 env and rev DNA plasmids. By immunizing with pCMV160/REV and cationic liposomes through various routes (intramuscular, intraperitoneal, subcutaneous, intradermal, and intranasal), we induced higher levels of both antibody production and delayed-type hypersensitivity (DTH) than by using DNA vaccine alone. The HIV-1-specific cytotoxic T lymphocyte (CTL) activity was observed to be stronger on immunization with the DNA vaccine and cationic liposome combination. The intramuscular, intraperitoneal, and intranasal inoculation routes were more effective in inducing strong DTH and antibody responses than the subcutaneous and intradermal routes. Taken together, these results suggest that cationic liposomes can be highly effective when used with DNA vaccines and administered by various routes.

Development of genetic vaccines for pathogenic genes: construction of attenuated vif DNA immunization cassettes

OBJECTIVE

To develop a putative immunization cassette using HIV-1 vif accessory gene derived from HIV-1 clinical specimens as a component of a DNA vaccine for HIV-1.

METHODS

vif genes were cloned from HIV-1-infected patients and the sequence variation present within the patients was analyzed. Prototypic genetic variants were selected and the ability of these clones to induce humoral and cellular immune responses was studied in animals. The selected protective genetic variants were biologically characterized through transcomplementation assays using primary cells infected with a vif-defective HIV-1 proviral clone.

RESULTS

Analysis of vif variants from different patients revealed that vif is highly conserved with the open reading frame remaining intact in vivo. It was shown that attenuated vif clones from HIV-1-infected subjects can effectively induce both humoral and cellular responses against Vif protein in mice. Evaluation of the cellular responses in vitro using human cellular targets infected with a clinical HIV-1 isolate showed that vif clones could induce cellular responses capable of destroying the virus.

CONCLUSIONS

The vif variants developed in this study exhibited non-productive phenotypes, yet were capable of inducing specific immune responses against HIV-1. These constructs could be used as part of a DNA vaccine strategy for HIV-1. This vaccine adaptation strategy could be used for the development of immunogens for any pathogen resulting in cross-reactive immunity and attenuated gene pathogenesis.

Monophosphoryl lipid A enhances both humoral and cell-mediated immune responses to DNA vaccination against human immunodeficiency virus type 1

To enhance immunity induced by DNA vaccination against human immunodeficiency virus type 1 (HIV-1), we evaluated the efficacy of monophosphoryl lipid A (MPL), an adjuvant of bacterial origin. BALB/c mice were intramuscularly injected with immunogenic DNA, encoding the env and rev genes of the HIV-1(IIIB) strain, formulated with MPL dissolved in different vehicles (MPL in stable emulsion and MPL in aqueous formulation). The sera from mice immunized with the two preparations of MPL revealed 2(6) to 2(9) times higher HIV-1-specific immunoglobulin G (IgG) titers than the sera from mice immunized without MPL. In virus neutralization tests for HIV-1(IIIB), by p24 assay and antifusion assay of infected MOLT-4 cells, MPL tends to elicit antibody more protective than antibody elicited without adjuvant. MPL also elicited stronger delayed-type hypersensitivity and cytotoxic-T-lymphocyte activity against HIV-1(IIIB) compared to DNA alone. HIV-1-specific IgG subclass analysis showed that MPL tends to facilitate IgG2a production, suggesting enhancement of a predominant T-helper-type-1 response, and this enhancement may help to facilitate protective-antibody induction. Furthermore, a chloramphenicol acetyltransferase (CAT) assay was employed to determine whether MPL affected the gene expression process. Interestingly, both MPL preparations reduced CAT activity in the muscle injected with CAT expression vector but increased anti-CAT antibody production. These results indicate that MPL acts as an effective adjuvant for immunogenic DNA injection despite reduced expression of encoding protein in muscle. We conclude that MPL has a strong adjuvant effect on DNA vaccination against HIV-1.

Immunization with plasmid DNA encoding hepatitis C virus envelope E2 antigenic domains induces antibodies whose immune reactivity is linked to the injection mode

Plasmids expressing different domains of the hepatis C virus (HCV) envelope E2 glycoprotein from a genotype 1a isolate were constructed to compare the immunogenic potential of E2 in nucleic acid-based immunizations. One plasmid, pCIE2t, expressed a C-terminally truncated form of E2, while others, pS2.SE2A to pS2.SE2E, encoded the adjacent 60-amino-acid (aa) sequences of E2 (inserts A to E) expressed as a fusion with the hepatitis B virus surface antigen. BALB/c mice were given injections of the plasmids intramuscularly (i.m.) or intraepidermally (i.e.) via a gene gun (biolistic introduction), and induced humoral immune responses were evaluated. The i.e. injections resulted in higher seroconversion rates and antibody titers, up to 100-fold, than did the i.m. injections (P = 0.01 to 0.04). Three restricted immunogenic domains, E2A (aa 384 to 443), E2C (aa 504 to 555), and E2E (aa 609 to 674), that yielded antibody titers ranging from 1:59 to > 1:43,700 could be identified. Subtype 1a- and 1b-derived E2 antigens and synthetic peptides were used in Western blot and enzyme-linked immunosorbent assay analyses, which revealed that the cross-reactivity of the plasmid-induced antibodies was linked both to the type of antigen expressed and to the injection mode. Induced anti-E2 antibodies could immunoprecipitate noncovalent E1E2 complexes believed to exist on the surface of HCV virions. This study allowed us to identify restricted immunogenic domains within E2 and demonstrated that different routes of injection of HCV E2 plasmids can result in quantitatively and qualitatively different humoral immune responses.

Recombinant human immunodeficiency Pr55gag virus-like particles presenting chimeric envelope glycoproteins induce cytotoxic T-cells and neutralizing antibodies

Very recently, we demonstrated that the replacement of the human immunodeficiency virus type-1 (HIV-1) gp41 transmembrane protein by an Epstein-Barr virus gp220/350-derived membrane anchor resulted in the incorporation of chimeric envelope (Env) oligomers into Pr55gag virus-like particles (VLPs), exceeding that of wild-type gp160 by a factor of 10. In this study, we examined the immunostimulatory properties of Pr55gag VLPs to both (i) chimeric HIV-1 gp120 external envelope proteins and (ii) full-length gp160 presented on the outer surface of the particles. Immunization studies carried out with VLPs presenting different derivatives of the chimeric and wild-type Env proteins elicited a consistent anti-Pr55gag as well as anti-Env antibody response in complete absence of additional adjuvants. In both cases, the immune sera exhibited an in vitro neutralizing activity against homologous HIV-1 infection in MT4 cells. Noteworthy, these VLPs were also capable of inducing a strong CD8+ cytotoxic T-cell (CTL) response in immunized BALB/c mice that was directed toward a known CTL epitope in the third variable domain V3 of the gp120 external glycoprotein. However, the induction of V3-loop-specific CTLs critically depended on the amounts of Env proteins that were presented by the Pr55gag VLPs. Moreover, the CD8+ CTL response was not significantly altered by adsorbing the VLPs to alum or by repeated booster immunizations. These results illustrate that Pr55gag VLPs provide a safe and effective means of enhancing neutralizing humoral responses to particle-entrapped gp120 proteins and are also capable of delivering these proteins to the MHC class I antigen processing and presentation pathway. Therefore, antigenically expanded Pr55gag VLPs represent an attractive approach in the design of vaccines for which specific stimulation of neutralizing antibodies and cytotoxic effector functions to complex glycoproteins is desired.

DNA vaccination against virus infection and enhancement of antiviral immunity following consecutive immunization with DNA and viral vectors

Recent demonstrations of the immunogenicity of antigens encoded in DNA plasmids following delivery by various routes have heralded a new era in vaccine development. In this article, we review progress in DNA-based antiviral immunoprophylaxis. Preclinical studies have already established the immunogenicity of DNA plasmids encoding protective antigens from a wide variety of viral pathogens and work published in recent months has raised real prospects of broadly protective DNA vaccination against infections with influenza virus and HIV. We also describe a consecutive immunization protocol consisting of a priming dose of vaccine antigen encoded in DNA plasmids followed by a booster with the same antigen encoded in recombinant fowlpox virus vectors. We have used this strategy to generate protective antiviral cell-mediated immunity and sustained, high-level antibody responses both systemically and at mucosae, and to elucidate immunological mechanisms underlying the development of immunity to antigens delivered in DNA vectors.

Gene gun-based nucleic acid immunization alone or in combination with recombinant vaccinia vectors suppresses virus burden in rhesus macaques challenged with a heterologous SIV

Gene gun-based DNA immunization alone or in combination with recombinant vaccinia vectors was evaluated for the ability to elicit protective immune responses in rhesus macaques challenged with a pathogenic, heterologous simian immunodeficiency virus (SIV). Six monkeys primed with seven consecutive doses of DNA encoding SIVmac239 gp120 and gp160 (DNA + DNA) were divided into two groups. Three of these animals received another DNA booster immunization and the remaining three received a booster immunization containing a homologous, live recombinant vaccinia virus expressing SIVmac251 gp160 (DNA + VAC). In addition, a group of 15 animals primed with recombinant vaccinia vectors were divided into two groups. One group of six monkeys received another immunization of vaccinia (VAC + VAC) and the other nine animals received a DNA (mac239) booster immunization (VAC + DNA). Geometric mean end-point IgG titres in the DNA + VAC and VAC + DNA groups were substantially higher than the responses seen in the VAC + VAC and DNA + DNA groups, demonstrating a synergistic relationship between DNA-based vaccines and recombinant vaccinia virus-based vaccines. All vaccinates and five naive controls were challenged 19 weeks after the final booster immunization with 10 animal infectious doses of SIVDelta/B670. The vaccines did not prevent infection. However, all vaccine groups showed significant virus load reductions from seven to 56 days post challenge when compared to controls. Although the DNA + DNA group developed the lowest prechallenge antibody responses, the most significant reduction (200-fold) in virus load was associated with this group. In addition, a significant delay in CD4+ T cell loss relative to controls was observed in the DNA + DNA group. These results demonstrate that a gene gun-based DNA vaccine provided some attenuation of infection and CD4+ T cell loss after a heterologous challenge.

DNA vaccination using expression vectors carrying FIV structural genes induces immune response against feline immunodeficiency virus

Following inactivated virus vaccination trials, the surface glycoprotein gp120 of the feline immunodeficiency virus (FIV) was considered as one of the determinants for protection. However, several vaccination trials using recombinant Env protein or some peptides failed to induce protection. To understand the role of the gp120 protein in vivo, we vaccinated cats with naked DNA coding for FIV structural proteins gp120 and p10. We analyzed the ability of these vaccinations to induce immune protection and to influence the onset of infection. Injection in cat muscles of expression vectors coding for the FIV gp120 protein induced a humoral response. Cats immunized twice with the gp120 gene showed different patterns after challenge. Two cats were, like the control cats, infected from the second week after infection onwards. The two others maintained a low proviral load with no modification of their antibody pattern. The immune response induced by gp120 DNA injection could control the level of viral replication. This protective-like immune response was not correlated to the humoral response. All the cats immunized with the gp120 gene followed by the p10 gene were infected, like the control cats, from the second week but they developed a complete humoral response against viral proteins after challenge. Furthermore, they showed a sudden but transient drop of the proviral load at 4 weeks after infection. Under these conditions, one injection of the p10 gene after one injection of the gp120 gene was not sufficient to stimulate protection. On the contrary, after a period, it seems to facilitate virus replication.

Protection of chimpanzees from high-dose heterologous HIV-1 challenge by DNA vaccination

Novel approaches for the generation of more effective vaccines for HIV-1 are of significant importance. In this report we analyze the immunogenicity and efficacy of an HIV-1 DNA vaccine encoding env, rev and gag/pol in a chimpanzee model system. The immunized animals developed specific cellular and humoral immune responses. Animals were challenged with a heterologous chimpanzee titered stock of HIV-1 SF2 virus and followed for 48 weeks after challenge. Polymerase chain reaction coupled with reverse transcription (RT-PCR) results indicated infection in the control animal, whereas those animals vaccinated with the DNA constructs were protected from the establishment of infection. These studies serve as an important benchmark for the use of DNA vaccine technology for the production of protective immune responses.

Screening of HIV-1 Env glycoproteins for the ability to raise neutralizing antibody using DNA immunization and recombinant vaccinia virus boosting

HIV-1 envelopes from two series of primary isolates (from Swedish patients 5 and 6), from JR-FL and BaL (prototypic monocyte/macrophage tropic viruses) and from HXB-2 (a prototypic T-cell-line-adapted virus), have been screened for their ability to elicit neutralizing antibody to HIV-1. Rabbits were primed by gene gun inoculation with plasmids expressing secreted monomeric (gp120) and oligomeric (gp140) forms of each Env. After four to six DNA immunizations administered over a 1-year period, rabbits were boosted with 10(8) plaque-forming units of a mixture of seven recombinant vaccinia viruses which express chimeric gp140 Envs (primary clade B sequences in a IIIb-related BH10 backbone). Neutralizing antibodies were assayed against two T-cell-line-adapted viruses (MN and IIIb), two non-syncytium-inducing (NSI) and two syncytium-inducing (SI) primary isolates, and two HIV-1-NL4-3-recombinants with patients 5 or 6 Envs (NL4-3/5A, NL4-3/6C). The DNA priming and recombinant vaccinia virus boosting raised low titers of neutralizing antibody in 10 of 19 rabbits. The highest titers of neutralizing activity (approximately 1:150 for MN) were raised in rabbits DNA primed with Envs from Swedish patients 5. These sera cross neutralized IIIb and MN but did not neutralize the primary isolates or the NL4-3 recombinant with the homologous 5A Env. Sera from rabbits primed with the HXB-2 Env DNA were, for the most part, type-specific for neutralization of IIIb. In one of three assays, sera from rabbits primed with plasmids expressing the JR-FL and BaL had possible low titer neutralizing activity for two NSI, but not two SI, primary isolates. Our results highlight the low immunogenic potential of the HIV-1 Env and demonstrate that different Envs have different potentials to raise low titer neutralizing antibody.

DNA-based immunization induces anti-CD4 antibodies directed primarily to native epitopes

DNA-based immunization is one of the most promising strategies to induce protective immunity against a variety of pathogens, presenting clear advantages as compared to the use of recombinant antigens. One of these advantages might be the ability to induce antibodies directed primarily against conformational determinants, as compared to immunization with recombinant proteins. To test this possibility, we have analyzed the antibody responses induced in mice by immunization with either recombinant soluble CD4 (rCD4) or by immunization with plasmid DNA-encoding CD4 (CD4-DNA). Mice immunized with CD4-DNA had lower titers of antibodies able to recognize rCD4 than mice immunized with rCD4. However, immunization with CD4-DNA induced antibodies reactive with the native cell surface CD4 molecule in all mice, whereas only two out of five mice immunized with rCD4 produced antibodies reactive with cell surface CD4, thus demonstrating that the genetic immunization approach may lead to an antibody response more consistent and superior at a qualitative level as compared to immunization with the corresponding recombinant protein. In addition, differences in the kinetics of appearance of antibodies directed against the native CD4 molecule were observed between mice immunized with CD4-DNA or rCD4. In the first case, antibodies reacting with cell surface CD4 were present 28 days after the first immunization, whereas mice immunized with rCD4 produced antibodies directed against the native molecule only following a booster injection. Finally, the two groups of mice produced antibodies with a different isotype distribution. No clear predominance of a specific IgG subclass was detected in the antibody population produced in response to DNA immunization. Conversely, mice immunized with rCD4 produced predominantly antibodies of the IgG1 isotype, indicating generation of a TH2 response. Together, results from this study indicate that the CD4 molecule endogenously produced following DNA immunization is expressed, at least partially, in a native conformation. This feature confers a major advantage to the DNA immunization approach as compared to immunization with the corresponding recombinant protein, which seems to elicit antibodies predominantly directed to epitopes uniquely expressed on the recombinant molecule.

The enhanced immune response to the HIV gp160/LAMP chimeric gene product targeted to the lysosome membrane protein trafficking pathway

The lysosome-associated membrane proteins (LAMP), found in the outer membrane of lysosomes and also in a multilaminar compartment that contains major histocompatibility complex class II (MHC II) proteins, are directed to their localization by a cytoplasmic carboxyl-terminal sequence. Our studies of the immune response to LAMP-targeted proteins has led to the application of a HIV-1 gp160/LAMP chimeric gene as a novel means to enhance the MHC II presentation of gp160. Immunofluorescence microscopy confirmed that the gp160/LAMP protein had a cellular localization corresponding to that of lysosomes. Pulse-chase analysis confirmed that the rates of synthesis of gp160/LAMP and wild type gp160 were comparable and that both proteins were processed to gp120 at similar rates. However, the gp160/LAMP was degraded more rapidly than the wild type gp160. MHC II-mediated T cell proliferation assays performed with cloned human cell lines showed that gp160/LAMP stimulated greater responses than did the wild type gp160. Moreover, mice vaccinated with recombinant vaccinia expressing gp160/LAMP had greater gp160-specific lymphoproliferation responses and higher titers of anti-V3 loop antibodies than mice vaccinated with recombinant vaccinia expressing wild type gp160.

Comparative efficiency of feline immunodeficiency virus infection by DNA inoculation

Direct inoculation of genetic material in DNA form is a novel approach to vaccination that has proved efficacious for a number of viral agents. We are interested in the potential of this approach for the delivery of vaccines based on attenuated or replication-defective retroviruses. Toward this goal, we tested the effect of intramuscular inoculation of a plasmid containing the entire genome of feline immunodeficiency virus (FIV-Petaluma, F14 clone). DNA delivery was compared with intramuscular or intraperitoneal inoculation of virus reconstituted from the same molecular clone. The outcome was monitored by serological analysis and quantitative virus load determination over a 31-week period. DNA inoculation was found to be a reliable means of infection, although seroconversion and the rise in PBMC virus load were delayed relative to intramuscular or intraperitoneal inoculation of virus. At 31 weeks, similar levels of proviral DNA were detected in central lymphoid tissue of all infected animals. In conclusion, DNA inoculation of proviral DNA will be of use as a novel method of cell-free virus challenge and may have further potential for the delivery of lentiviral vaccines.

HIV-1 Env glycoproteins from two series of primary isolates: replication phenotype and immunogenicity

Seven envelope regions from two series of patient isolates have been molecularly cloned and analyzed for replication phenotypes and immunogenicity. Growth potential was analyzed for env sequences substituted into an HIV-1-NL4-3 backbone (NL4-3/env recombinants). Immunogenicity studies were conducted on secreted monomeric (gp120) and oligomeric (gp140) forms of the Envs using Env-expressing plasmid DNAs for immunizations. The env regions of the patient isolates conferred a spectrum of replication kinetics and cytotropisms on the NL4-3/env recombinants. Both patient series included non-syncytium-inducing viruses with no ability to grow on T-cell lines, and highly syncytium inducing viruses which grew well on T-cell lines. These differences in growth potential did not correlate with the ability of the DNA-expressed Envs to raise antibody in rabbits. Rather, the relative immunogenicity of the Envs was patient and form specific. The Envs from patient 5 raised higher titers of antibody than the Envs from patient 6. For each primary Env, the gp120 form of the Env raised higher titers of antibody than the gp140 form. Thus, structural features of Env that affect replication do not necessarily affect the ability to raise antibody.

Safety and immunogenicity of intramuscular and intravaginal delivery of HIV-1 DNA constructs to infant chimpanzees

Any global strategy for controlling the human immunodeficiency virus (HIV) epidemic is likely to rely heavily on immunization of infants and children. Given the well-documented differences in children's responses to traditional vaccines, we initiated this study to extend our findings on DNA vaccination of adult chimpanzees to immunologically immature infant chimpanzees. Our findings were consistent with our previous work in adults as we observed that the DNA vaccines used here were both well tolerated and immunogenic within weeks of the initial vaccination.

DNA vaccines

Observations in the early 1990s that plasmid DNA could directly transfect animal cells in vivo sparked exploration of the use of DNA plasmids to induce immune responses by direct injection into animals of DNA encoding antigenic proteins. This method, termed DNA immunization, now has been used to elicit protective antibody and cell-mediated immune responses in a wide variety of preclinical animal models for viral, bacterial, and parasitic diseases. DNA vaccination is particularly useful for the induction of cytotoxic T cells. This review summarizes current knowledge on the vectors, immune responses, immunological mechanisms, safety considerations, and potential for further application of this novel method of immunization.