Induction of humoral and cellular immune responses to the human immunodeficiency type 1 virus in nonhuman primates by in vivo DNA inoculation

Characterization of Monoclonal Antibodies against HA Protein of H1N1 Swine Influenza Virus and Protective Efficacy against H1 Viruses in Mice

H1N1 swine influenza viruses (SIV) are prevalent in pigs globally, and occasionally emerge in humans, which raises concern about their pandemic threats. To stimulate hemagglutination (HA) of A/Swine/Guangdong/LM/2004 (H1N1) (SW/GD/04) antibody response, eukaryotic expression plasmid pCI-neo-HA was constructed and used as an immunogen to prepare monoclonal antibodies (mAbs). Five mAbs (designed 8C4, 8C6, 9D6, 8A4, and 8B1) against HA protein were obtained and characterized. Western blot showed that the 70 kDa HA protein could be detected by all mAbs in MDCK cells infected with SW/GD/04. Three mAbs—8C4, 8C6, and 9D6—have hemagglutination inhibition (HI) and neutralization test (NT) activities, and 8C6 induces the highest HI and NT titers. The protection efficacy of 8C6 was investigated in BALB/c mice challenged with homologous or heterologous strains of the H1 subtype SIV. The results indicate that mAb 8C6 protected the mice from viral infections, especially the homologous strain, which was clearly demonstrated by the body weight changes and reduction of viral load. Thus, our findings document for the first time that mAb 8C6 might be of potential therapeutic value for H1 subtype SIV infection.

Vaginal gene therapy

In the last years, vaginal gene therapy has gained increasing attention mainly for the treatment and control of sexually transmitted infections. DNA delivery has been also suggested to improve reproductive outcomes for women with deficiencies in the female reproductive tract. Although no product has reached clinical phase, preclinical investigations reveal the potential of the vaginal tract as an effective administration route for gene delivery. This review focuses on the main advantages and challenges of vaginal gene therapy, and on the most used nucleic acid delivery systems, including viral and non-viral vectors. Additionally, the advances in the application of vaginal gene therapy for the treatment and/or prevention of infectious diseases such as the human immunodeficiency virus (HIV), the human papillomavirus (HPV) or the herpes simplex virus (HSV) are presented.

DNA/MVA Vaccines for HIV/AIDS

Since the initial proof-of-concept studies examining the ability of antigen-encoded plasmid DNA to serve as an immunogen, DNA vaccines have evolved as a clinically safe and effective platform for priming HIV-specific cellular and humoral responses in heterologous "prime-boost" vaccination regimens. Direct injection of plasmid DNA into the muscle induces T- and B-cell responses against foreign antigens. However, the insufficient magnitude of this response has led to the development of approaches for enhancing the immunogenicity of DNA vaccines. The last two decades have seen significant progress in the DNA-based vaccine platform with optimized plasmid constructs, improved delivery methods, such as electroporation, the use of molecular adjuvants and novel strategies combining DNA with viral vectors and subunit proteins. These innovations are paving the way for the clinical application of DNA-based HIV vaccines. Here, we review preclinical studies on the DNA-prime/modified vaccinia Ankara (MVA)-boost vaccine modality for HIV. There is a great deal of interest in enhancing the immunogenicity of DNA by engineering DNA vaccines to co-express immune modulatory adjuvants. Some of these adjuvants have demonstrated encouraging results in preclinical and clinical studies, and these data will be examined, as well.

A brief history of the global effort to develop a preventive HIV vaccine

Soon after HIV was discovered as the cause of AIDS in 1983-1984, there was an expectation that a preventive vaccine would be rapidly developed. In trying to achieve that goal, three successive scientific paradigms have been explored: induction of neutralizing antibodies, induction of cell mediated immunity, and exploration of combination approaches and novel concepts. Although major progress has been made in understanding the scientific basis for HIV vaccine development, efficacy trials have been critical in moving the field forward. In 2009, the field was reinvigorated with the modest results obtained from the RV144 trial conducted in Thailand. Here, we review those vaccine development efforts, with an emphasis on events that occurred during the earlier years. The goal is to provide younger generations of scientists with information and inspiration to continue the search for an HIV vaccine.

Human immunodeficiency virus (HIV) immunopathogenesis and vaccine development: a review

The development of a safe, effective and globally affordable HIV vaccine offers the best hope for the future control of the HIV-1 pandemic. Since 1987, scores of candidate HIV-1 vaccines have been developed which elicited varying degrees of protective responses in nonhuman primate models, including DNA vaccines, subunit vaccines, live vectored recombinant vaccines and various prime-boost combinations. Four of these candidate vaccines have been tested for efficacy in human volunteers, but, to the exception of the recent RV144 Phase III trial in Thailand, which elicited a modest but statistically significant level of protection against infection, none has shown efficacy in preventing HIV-1 infection or in controlling virus replication and delaying progression of disease in humans. Protection against infection was observed in the RV144 trial, but intensive research is needed to try to understand the protective immune mechanisms at stake. Building-up on the results of the RV144 trial and deciphering what possibly are the immune correlates of protection are the top research priorities of the moment, which will certainly accelerate the development of an highly effective vaccine that could be used in conjunction with other HIV prevention and treatment strategies. This article reviews the state of the art of HIV vaccine development and discusses the formidable scientific challenges met in this endeavor, in the context of a better understanding of the immunopathogenesis of the disease.

Protection against Mucosal SHIV Challenge by Peptide and Helper-Dependent Adenovirus Vaccines

Groups of rhesus macaques that had previously been immunized with HIV-1 envelope (env) peptides and first generation adenovirus serotype 5 (FG-Ad5) vaccines expressing the same peptides were immunized intramuscularly three times with helper-dependent adenovirus (HD-Ad) vaccines expressing only the HIV-1 envelope from JRFL. No gag, pol, or other SHIV genes were used for vaccination. One group of the FG-Ad5-immune animals was immunized three times with HD-Ad5 expressing env. One group was immunized by serotype-switching with HD-Ad6, HD-Ad1, and HD-Ad2 expressing env. Previous work demonstrated that serum antibody levels against env were significantly higher in the serotype-switched group than in the HD-Ad5 group. In this study, neutralizing antibody and T cell responses were compared between the groups before and after rectal challenge with CCR5-tropic SHIV-SF162P3. When serum samples were assayed for neutralizing antibodies, only weak activity was observed. T cell responses against env epitopes were higher in the serotype-switched group. When these animals were challenged rectally with SHIV-SF162P3, both the Ad5 and serotype-switch groups significantly reduced peak viral loads 2 to 10-fold 2 weeks after infection. Peak viral loads were significantly lower for the serotype-switched group as compared to the HD-Ad5-immunized group. Viral loads declined over 18 weeks after infection with some animals viremia reducing nearly 4 logs from the peak. These data demonstrate significant mucosal vaccine effects after immunization with only env antigens. These data also demonstrate HD-Ad vectors are a robust platform for vaccination.

DNA vaccines: developing new strategies to enhance immune responses

We have focused our research on understanding the basic biology of and developing novel therapeutic and prophylactic DNA vaccines. We have among others three distinct primary areas of interest which include: 1. Enhancing in vivo delivery and transfection of DNA vaccine vectors 2. Improving DNA vaccine construct immunogenicity 3. Using molecular adjuvants to modulate and skew immune responses. Key to the immunogenicity of DNA vaccines is the presentation of expressed antigen to antigen-presenting cells. To improve expression and presentation of antigen, we have investigated various immunization methods with current focus on a combination of intramuscular injection and electroporation. To improve our vaccine constructs, we also employed methods such as RNA/codon optimization and antigen consensus to enhance expression and cellular/humoral cross-reactivity, respectively. Our lab also researches the potential of various molecular adjuvants to skew Th1/Th2 responses, enhance cellular/humoral responses, and improve protection in various animal models. Through improving our understanding of basic immunology as it is related to DNA vaccine technology, our goal is to develop the technology to the point of utility for human and animal health.

Production of monoclonal antibody by DNA immunization with electroporation

DNA immunization with in vivo electroporation is an efficient alternative protocol for the production of monoclonal antibodies (mAb). Generation of mAb by DNA immunization is a novel approach to circumvent the following technical hurdles associated with problematic antigens: low abundance and protein instability and use of recombinant proteins that lack posttranslational modifications. This chapter describes the use of a DNA-based immunization protocol for the production of mAb against a house dust mite allergen, designated as Blo t 11, which is a paramyosin homologue found in Blomia tropicalis mites. The Blo t 11 cDNA fused at the N terminus to the sequence of a signal peptide was cloned into the pCI mammalian expression vector. The DNA construct was injected intramuscularly with in vivo electroporation into mice, and the specific antibody production in mice was analyzed by enzyme-linked immunosorbent assay (ELISA). Hybridomas were generated by fusing mouse splenocytes with myeloma cells using the ClonaCell-HY Hybridoma Cloning Kit. Six hybridoma clones secreting Blo t 11 mAb were successfully generated, and these mAb are useful reagents for immunoaffinity purification and immunoassays.

Study on the antifertility effects of the plasmid DNA vaccine expressing partial brLDH-C4′

Partial cDNA sequence coding forMicrotus brandti radde(Brandt’s vole) testes-specific lactate dehydrogenase (brLDH-C4) was amplified by reverse transcription-polymerase chain reaction (RT-PCR). By inserting the product into the eukaryotic expression vector pCR3.1, pCR3.1-brLDH-C4′ was obtained as the prototype of contraceptive DNA vaccine. Immunization with pCR3.1-brLDH-C4′ in BALB/c mice generated antibodies specific to purified brLDH-C4′ and native mouse LDH-C4 protein. The birth rate of the pCR3.1-brLDH-C4′ immunized mice was found to be decreased significantly (80% lower than that of those immunized with pCR3.1). Functions of the elicited antibodies in sera from pCR3.1-brLDH-C4′ inoculated mice were further explored. The results indicated that the antibodies from the mice injected with pCR3.1-brLDH-C4′ could cause the agglutination of normal sperm suspension, while the ovarian structure and the development of ovarian follicles of these mice were not impaired, which gives a possible explanation for the immunocontraceptive effects of the pCR3.1-brLDH-C4′ DNA vaccine.

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

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

DNA vaccines expressing different forms of simian immunodeficiency virus antigens decrease viremia upon SIVmac251 challenge

We have tested the efficacy of DNA immunization as a single vaccination modality for rhesus macaques followed by highly pathogenic SIVmac251 challenge. To further improve immunogenicity of the native proteins, we generated expression vectors producing fusion of the proteins Gag and Env to the secreted chemokine MCP3, targeting the viral proteins to the secretory pathway and to a beta-catenin (CATE) peptide, targeting the viral proteins to the intracellular degradation pathway. Macaques immunized with vectors expressing the MCP3-tagged fusion proteins developed stronger antibody responses. Following mucosal challenge with pathogenic SIVmac251, the vaccinated animals showed a statistically significant decrease in viral load (P = 0.010). Interestingly, macaques immunized with a combination of vectors expressing three forms of antigens (native protein and MCP3 and CATE fusion proteins) showed the strongest decrease in viral load (P = 0.0059). Postchallenge enzyme-linked immunospot values for Gag and Env as well as gag-specific T-helper responses correlated with control of viremia. Our data show that the combinations of DNA vaccines producing native and modified forms of antigens elicit more balanced immune responses able to significantly reduce viremia for a long period (8 months) following pathogenic challenge with SIVmac251.

DNA prime Listeria boost induces a cellular immune response to SIV antigens in the rhesus macaque model that is capable of limited suppression of SIV239 viral replication

DNA vaccines and recombinant Listeria monocytogenes that express and secrete SIV Gag and Env antigens were combined in a nonhuman primate prime-boost immunogenicity study followed by a challenge with SIV239. We report that recombinant DNA vaccine delivered intramuscularly, and recombinant L. monocytogenes delivered orally each individually have the ability to induce CD8+ and CD4+ T cell immune responses in a nonhuman primate. Four rhesus monkeys were immunized at weeks 0, 4, 8, and 12 with the pCSIVgag and pCSIVenv DNA plasmids and boosted with SIV expressing L. monocytogenes vaccines at weeks 16, 20, and 28. Four rhesus monkeys received only the L. monocytogenes vaccines at weeks 16, 20, and 28. A final group of monkeys served as a control group. Blood samples were taken before vaccination and 2 weeks post each injection and analyzed by ELISPOT for CD4+ and CD8+ T cell responses. Moderate vaccine induced SIV-specific cellular immune responses were observed following immunization with either DNA or L. monocytogenes vectors. However, the SIV antigen-specific immune responses were significantly increased when Rhesus macaques were primed with SIV DNA vaccines and boosted with the SIV expressing L. monocytogenes vectors. In addition, the combined vaccine was able to impact SIV239 viral replication following an intrarectal challenge. This study demonstrates for the first time that oral L. monocytogenes can induce a cellular immune response in a nonhuman primate and is able to enhance the efficacy of a DNA vaccine as well as provide modest protection against SIV239 challenge.

DNA vaccines against human immunodeficiency virus type 1 in the past decade

This article reviews advances in the field of human immunodeficiency virus type 1 (HIV-1) and AIDS vaccine development over the last decade, with an emphasis on the DNA vaccination approach. Despite the discovery of HIV-1 and AIDS in humans nearly 20 years ago, there is no vaccine yet that can prevent HIV-1 infection. The focus has shifted toward developing vaccines that can control virus replication and disease progression by eliciting broadly cross-reactive T-cell responses. Among several approaches evaluated, the DNA-based modality has shown considerable promise in terms of its ability to elicit cellular immune responses in primate studies. Of great importance are efforts aimed at improvement of the potency of this modality in the clinic. The review discusses principles of DNA vaccine design and the various mechanisms of plasmid-encoded antigen presentation. The review also outlines current DNA-based vaccine strategies and vectors that have successfully been shown to control virus replication and slow disease progression in animal models. Finally, it lists recent strategies that have been developed as well as novel approaches under consideration to enhance the immunogenicity of plasmid-encoded HIV-1 antigen in various animal models.

The use of gene-specific IgY antibodies for drug target discovery

Genomics and gene expression data require interpretation at the protein level to validate the biological or pathological findings. To match with the efficiency and capacity of DNA microarray application, methods and approaches of protein analysis in multiplex and high-throughput manner are required for effectively discovering disease-related proteins. Two-dimensional gel and MS-based technologies provide researchers with such approaches, but neither of them can directly and selectively detect target proteins in situ. Antibodies are one of the most crucial tools for meeting this need. Efficient generation of antibodies based on genomics and gene-expression information is an important strategy for producing gene-specific antibodies to link genome to proteome. Avian immunoglobulins isolated from egg yolk (so-called IgY) have several attractive advantages over conventional IgG antibodies.

DNA vaccination against hepatitis E virus infection in cynomolgus macaques

BACKGROUND

: The feasibility of DNA vaccination against hepatitis E in non-human primates has not been evaluated. In the present study a full-length hepatitis E virus (HEV) open reading frame (ORF)2 (Burmese strain) was assembled, cloned, and used for genetic immunization of cynomolgus macaques (cynos), which were subsequently challenged with a heterologous HEV strain (Mexico).

METHODS

: Four cynos were vaccinated intramuscularly with the HEV ORF2 DNA cassette and one animal was vaccinated with a mock DNA construct.

RESULTS

: Following vaccination anti-HEV antibodies were detected in the four HEV-DNA-vaccinated cynos, but not in the control animal. When challenged, two of the four HEV-DNA-vaccinated cynos were protected against HEV infection and had no elevated alanine aminotransferase activity, viremia, or fecal shedding. The two other DNA-vaccinated animals developed HEV infection and disease.

CONCLUSION

: These findings demonstrate the feasibility of DNA vaccination for the protection of HEV infection and warrant further studies to explore routes other than intramuscular for induction of a stronger and efficacious immune response.

Transport of nanoparticles across the rat nasal mucosa

The transport of 125I-radiolabelled latex nanoparticles across the nasal mucosa of rats was studied using a range of particle sizes and surface coatings. Translocation of the particles into the blood stream was examined by means of monitoring the radiolabel associated with the particles. Particles were detected in the blood after 5 minutes. The number of particles in the blood peaked at 60 minutes, and then remained constant for a further 2 hours. The smallest particles (20 nm) showed greater uptake than the largest particles investigated (1000 nm). The total maximum uptake seen for the smallest particles was in the order of 3.25% of administered dose. 100 nm particles coated with chitosan showed an increase in both the extent and rate of uptake, with the concentration in the blood peaking at 15 minutes rather than at 60 minutes. It is suggested that transport of the particles across the nasal membrane is due mainly to a transcellular transport mechanisms by the nasal associated lymphoid tissue (NALT), especially the M-cell like cells. However, some paracellular transport cannot totally be ruled out for the smallest particles, especially if coated with chitosan.

A prime-boost immunisation regimen using DNA followed by recombinant modified vaccinia virus Ankara induces strong cellular immune responses against the Plasmodium falciparum TRAP antigen in chimpanzees

Two chimpanzees were vaccinated intramuscularly against malaria using plasmid DNA expressing the pre-erythrocytic antigens thrombospondin related adhesion protein (PfTRAP) and liver stage specific antigen-1 (PfLSA-1) of Plasmodium falciparum together with GM-CSF protein. A recombinant modified vaccinia virus Ankara (MVA) expressing PfTRAP was injected intramuscularly 6 weeks later to boost the immune response. This sequence of antigen delivery induced a specific and long-lasting T cell and antibody response to PfTRAP as detected by ELISPOT assay and ELISA. Antibody responses were detected after four DNA injections, and were boosted by injection of recombinant MVA expressing PfTRAP. Interferon-gamma secreting antigen-specific T cells were detected in both animals, but only after boosting with recombinant MVA. By screening a panel of PfTRAP-derived peptides, an epitope was identified that was recognized by cytotoxic T lymphocytes in one of the chimpanzees studied. T cells specific for this epitope were present in PBMCs and liver-infiltrating lymphocytes at a frequency of between 1 in 200 and 1 in 500. The high immunogenicity of this prime-boost regimen in chimpanzees supports further assessment of this delivery strategy for the induction of protection against P. falciparum malaria in humans.

Mice genetic immunization with plasmid DNA encoding a secreted form of HSV-1 gB induces a protective immune response against herpes simplex virus type 1 infection

Intramuscularly (i.m.) delivered plasmid DNA encoding a secreted form of glycoprotein B of herpes simplex virus type 1 (HSV-1 gB1s) was evaluated for the ability to elicit a protective immune response in Balb/c mice. Animals received three i.m. injections of a gB1s expression plasmid (pRP-RSV-gB1s) or of a wild-type transmembrane gB1 coding plasmid (pRP-RSV-gB1), while control mice were injected with the vector alone (pRP-RSV). A specific antibody response was observed in almost all immunized animals, and in most cases antibodies were also detected after 1 month in the absence of further vaccine boosts. Serum antibodies mostly displayed neutralizing activity against HSV-1. Glycoprotein B1s DNA immunization was also effective in protecting animals against the primary infection induced by a subsequent HSV-1 challenge and limited HSV-1 infection of sensitive ganglia.

A DNA-based immunization protocol to produce monoclonal antibodies to blood group antigens

A major challenge facing transfusion medicine is the establishment of immunological methods to produce specific and avid blood group typing reagents to the many polymorphic blood group antigens. This is especially true when sources of human antibody are limited. Based on the knowledge that inoculation with plasmid DNA can induce a humoral response in the host animal, we inoculated mice with plasmid DNA followed by a single boost injection with plasmid-transfected cells that have a high level of expression of the same target protein. Using this method, several hybridoma clones that produced strongly reactive antibodies specific for the Kell polymorphic antigens (anti-K, anti-k, anti-Kp(a)) were isolated. The monoclonal antibodies that were produced with this method have potential clinical utility for identifying a patient's blood type and for screening for antigen-negative donor blood.

Interleukin 7 can enhance antigen-specific cytotoxic-T-lymphocyte and/or Th2-type immune responses in vivo

Interleukin 7 (IL-7) protein has been reported to be important in the development of cytotoxic-T-lymphocyte (CTL) responses. However, other studies also support a partial Th2 phenotype for this cytokine. In an effort to clarify this unusual conflict, we compared IL-7 along with IL-12 (Th1 control) and IL-10 (Th2 control) for its ability to induce antigen (Ag)-specific CTL and Th1- versus Th2-type immune responses using a well established DNA vaccine model. In particular, IL-7 codelivery showed a significant increase in immunoglobulin G1 (IgG1) levels compared to IgG2a levels. IL-7 coinjection also decreased production of Th1-type cytokine IL-2, gamma interferon, and the chemokine RANTES but increased production of the Th2-type cytokine IL-10 and the similarly biased chemokine MCP-1. In herpes simplex virus (HSV) challenge studies, IL-7 coinjection decreased the survival rate after lethal HSV type 2 (HSV-2) challenge compared with gD plasmid vaccine alone in a manner similar to IL-10 coinjection, whereas IL-12 coinjection enhanced the protection, further supporting that IL-7 drives immune responses to the Th2 type, resulting in reduced protection against HSV-2 challenge. Moreover, coinjection with human immunodeficiency virus type 1 env and gag/pol genes plus IL-12 or IL-7 cDNA enhanced Ag-specific CTLs, while coinjection with IL-10 cDNA failed to influence CTL induction. Thus, IL-7 could drive Ag-specific Th2-type cellular responses and/or CTL responses. These results support that CTLs could be induced by IL-7 in a Th2-type cytokine and chemokine environment in vivo. This property of IL-7 allows for an alternative pathway for CTL development which has important implications for host-pathogen responses.

Simian immunodeficiency virus (SIV) gag DNA-vaccinated rhesus monkeys develop secondary cytotoxic T-lymphocyte responses and control viral replication after pathogenic SIV infection

The potential contribution of a plasmid DNA construct to vaccine-elicited protective immunity was explored in the simian immunodeficiency virus (SIV)/macaque model of AIDS. Making use of soluble major histocompatibility class I/peptide tetramers and peptide-specific killing assays to monitor CD8(+) T-lymphocyte responses to a dominant SIV Gag epitope in genetically selected rhesus monkeys, a codon-optimized SIV gag DNA vaccine construct was shown to elicit a high-frequency SIV-specific cytotoxic T-lymphocyte (CTL) response. This CTL response was demonstrable in both peripheral blood and lymph node lymphocytes. Following an intravenous challenge with the highly pathogenic viral isolate SIVsm E660, these vaccinated monkeys developed a secondary CTL response that arose with more rapid kinetics and reached a higher frequency than did the postchallenge CTL response in control plasmid-vaccinated monkeys. While peak plasma SIV RNA levels were comparable in the experimentally and control-vaccinated monkeys during the period of primary infection, the gag plasmid DNA-vaccinated monkeys demonstrated better containment of viral replication by 50 days following SIV challenge. These findings indicate that a plasmid DNA vaccine can elicit SIV-specific CTL responses in rhesus monkeys, and this vaccine-elicited immunity can facilitate the generation of secondary CTL responses and control of viral replication following a pathogenic SIV challenge. These observations suggest that plasmid DNA may prove a useful component of a human immunodeficiency virus type 1 vaccine.

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.

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.

Murine monoclonal antibodies biologically active against the amino region of HIV-1 gp120: isolation and characterization

The human immunodeficiency virus (HIV)-1 envelope glycoprotein is synthesized as a precursor (gp160) and subsequently cleaved to generate the external gp120 and transmembrane gp41 glycoproteins. Both gp120 and gp41 have been demonstrated to mediate critical functions of HIV, including viral attachment and fusion with the cell membrane. The antigenic variability of the HIV-1 envelope glycoprotein has presented a significant problem in the design of appropriate and successful vaccines and offers one explanation for the ability of HIV to evade immune surveillance. Therefore, the development and characterization of functional antibodies against conserved regions of the envelope glycoprotein is needed. Because of this need, we generated a panel of murine monoclonal antibodies (MuMabs) against the HIV-1 envelope glycoprotein. To accomplish this, we immunized Balb/C mice with a recombinant glycoprotein 160 (gp160) that was synthesized in a baculovirus expression system. From the growth-positive hybridomas, three MuMabs were generated that demonstrated significant reactivity with recombinant gp120 but failed to show reactivity against HIV-1 gp41, as determined by enzyme-linked immunosorbent assay (ELISA). Using vaccinia constructs that synthesize variant truncated subunits of gp160, we were able to map reactivity of all three of the Mabs (ID6, AC4, and AD3) to the first 204 residues of gp120 (i.e., the N terminus of gp120) via Western blot analysis. Elucidation of the epitopes for these Mabs may have important implications for inhibition of infection by HIV-1. Our initial attempts to map these Mabs with linear epitopes have not elucidated a specific antigenic determinant; however, several physical characteristics have been determined that suggest a continuous surface epitope. Although these antibodies failed to neutralize cell-free or cell-associated infection by HIV-1, they did mediate significant antibody-dependent cellular cytotoxicity (ADCC) activity, indicating potential therapeutic utility. In summary, these data suggest the identification of a potentially novel site in the first 200 aa of gp120 that mediates ADCC.

Immunogenicity and protective efficacy of DNA vaccines encoding secreted and non-secreted forms of Mycobacterium tuberculosis Ag85A

OBJECTIVE

To determine the efficacy of Ag85A-DNA against challenge with a highly virulent human clinical isolate of Mycobacterium tuberculosis (CSU37) and to compare the potencies of two types of Ag85A-DNA vaccines; those expressing secreted and non-secreted forms of the protein.

DESIGN

Ag85A-DNA vaccinated mice were challenged with a highly virulent clinical isolate of M. tuberculosis (CSU37) in order to compare the efficacy of these vaccines. In vitro studies were also performed.

RESULTS

Enhanced humoral and cellular responses were induced in mice vaccinated with the secreted Ag85A-DNA compared to the non-secreted Ag85A-DNA. In addition, secreted Ag85A-DNA conferred protective immunity against infection with M. tuberculosis (CSU37).

CONCLUSIONS

DNA vaccines encoding M. tuberculosis Ag85A have been shown to induce potent humoral and cellular immune responses leading to protection from M. tuberculosis (Erdman) challenge in mouse models. In this study we demonstrate that Ag85A can confer protection in a rigorous challenge model using a highly virulent human clinical isolate of M. tuberculosis (CSU37). This challenge model appears able to discriminate between DNA vaccines of differing potencies, as the more immunogenic DNA construct encoding a secreted form of Ag85A was protective, whereas the less immunogenic DNA construct encoding a non-secreted form of Ag85A was not.

Semiliki forest virus vector carrying the bovine viral diarrhea virus NS3 (p80) cDNA induced immune responses in mice and expressed BVDV protein in mammalian cells

Bovine viral diarrhea virus (BVDV) is a primary pathogen responsible for bovine enteric, respiratory and reproductive failure. A genetic region is encoding the p80 (NS3) of BVDV as the most conserved protein among Pestiviruses. BVDV infection in cattle induces NS3 specific lymphocyte proliferation and humoral responses. To generate a DNA vaccine against BVDV, the gene for BVDV-NADL NS3 was cloned into an eukaryotic expression vector of Semiliki Forest virus (pSFV-1). Quadriceps muscles of BALB/c mice were injected with recombinant DNA generated statistically significant cytotoxic T-lymphocyte activity (CTL) and cell mediated immune (CMI) responses against cytopathic and noncytopathic BVDV. Whereas, the BVDV-NS3 did not generate neutralizing antibodies against BVDVin mice. pSFV-1-NS3 DNA was subjected to in vitro transcription into mRNA. The mRNA was transfected into baby hamster kidney cells (BHK-21) and Madin-Darby bovine kidney cells (MDBK). The recombinant cells were used in the detection of DNA antigen responses by immunological assays. This report establishes the ability of BVDV-NS3 DNA inoculation to induce a strong cellular immune responses in mice.

HIV-1 DNA vaccines and chemokines

DNA vaccines have a demonstrated ability to induce humoral and cellular immune responses in animal models and humans. The technology, although it dates back to the 1950's, has had an insurgence of interest within the past few years following concurrent research papers. The basic technology is being applied broadly to viral, bacterial and parasitic infections. It has also been demonstrated that genes delivered via plasmid expression vectors result in expression of functional proteins in the inoculated host. Further, injection of plasmids encoding cytokine, chemokine or co-stimulatory molecules, also referred to as immunomodulatory plasmids can lead to the further expansion of this technology to include directed immunology. We have been developing DNA technology specifically with a focus as a vaccine against HIV-1 infection. We report that such vaccines can stimulate immune responses in a variety of relevant animal systems including humoral and cellular responses as well as the production of beta-chemokines. We describe that the beta-chemokines can both modulate the immune response induced by DNA vaccines and be modulated by the DNA vaccines in the murine and chimpanzee models as well as in humans.

DNA vaccination strategies against infectious diseases

DNA immunisation represents a novel approach to vaccine and immunotherapeutic development. Injection of plasmid DNA encoding a foreign gene of interest can result in the subsequent expression of the foreign gene products and the induction of an immune response within a host. This is relevant to prophylactic and therapeutic vaccination strategies when the foreign gene represents a protective epitope from a pathogen. The recent demonstration by a number of laboratories that these immune responses evoke protective immunity against some infectious diseases and cancers provides support for the use of this approach. In this article, we attempt to present an informative and unbiased representation of the field of DNA immunisation. The focus is on studies that impart information on the development of vaccination strategies against a number of human and animal pathogens. Investigations that describe the mechanism(s) of protective immunity induced by DNA immunisation highlight the advantages and disadvantages of this approach to developing vaccines within a given system. A variety of systems in which DNA vaccination has resulted in the induction of protective immunity, as well as the correlates associated with these protective immune responses, will be described. Particular attention will focus on systems involving parasitic diseases. Finally, the potential of DNA immunisation is discussed as it relates to veterinary medicine and its role as a possible vaccine strategy against animal coccidioses.

Genetic live vaccines mimic the antigenicity but not pathogenicity of live viruses

The development of an effective HIV vaccine is both a pressing and a formidable problem. The most encouraging results to date have been achieved using live-attenuated immunodeficiency viruses. However, the frequency of pathogenic breakthroughs has been a deterrent to their development. We suggest that expression libraries generated from viral DNA can produce the immunologic advantages of live vaccines without risk of reversion to pathogenic viruses. The plasmid libraries could be deconvoluted into useful components or administered as complex mixtures. To explore this approach, we designed and tested several of these genetic live vaccines (GLVs) for HIV. We constructed libraries by cloning overlapping fragments of the proviral genome into mammalian expression plasmids, then used them to immunize mice. We found that inserting library fragments into a vector downstream of a secretory gene sequence led to augmented antibody responses, and insertion downstream of a ubiquitin sequence enhanced cytotoxic lymphocyte responses. Also, fragmentation of gag into subgenes broadened T-cell epitope recognition. We have fragmented the genome by sequence-directed and random methods to create libraries with different features. We propose that the characteristics of GLVs support their further investigation as an approach to protection against HIV and other viral pathogens.

Inhibition of PHA-induced cell proliferation by polyclonal CD4 antibodies generated by DNA immunization

Although the role of CD4 molecule as associative binding element to MHC class II is well documented, their role in T cell activation is unclear. In the present report we used DNA immunization, which is currently shown to induce potent immune responses, to produce the polyclonal antibodies specific for the CD4 molecule and used the generated antibodies to characterize the CD4 function. A rabbit was pre-treated with bupivacaine hydrochloride for 24 h which was followed by intramuscular injection of DNA encoding CD4 protein (CD4-DNA) at weekly interval. By this procedure, CD4 antibodies were detected in the immunized serum after two DNA inoculations. The CD4 antibodies titer was up to 1:800 after five DNA inoculations. The rabbit polyclonal CD4 antibodies recognized both recombinant CD4 protein expressed on CD4-DNA transfected COS cells and native CD4 protein presented on peripheral lymphocytes and CD4+ cell lines. These generated CD4 antibodies could block the binding of standard CD4 mAb, Leu3a and 13B8.2, to the CD4 molecule. To characterize the function of CD4 molecule, PBMC were cultured in the presence of sub-optimal dose of PHA and the produced polyclonal CD4 antibodies. We found that the polyclonal CD4 antibodies strongly suppressed PHA induced cell proliferation. The inhibitory effect of CD4 antibodies may be due to their steric inhibition of the CD4-TCR/CD3 association or may interfere with the binding of CD4 to its ligand IL-16, resulting in the reduction of signal transduction and subsequent cellular responses. Our results indicate the possibility of utilizing DNA immunization to produce polyclonal antibodies against cell surface molecule.

Comparison of immunity generated by nucleic acid-, MF59-, and ISCOM-formulated human immunodeficiency virus type 1 vaccines in Rhesus macaques: evidence for viral clearance

The kinetics of T-helper immune responses generated in 16 mature outbred rhesus monkeys (Macaca mulatta) within a 10-month period by three different human immunodeficiency virus type 1 (HIV-1) vaccine strategies were compared. Immune responses to monomeric recombinant gp120SF2 (rgp120) when the protein was expressed in vivo by DNA immunization or when it was delivered as a subunit protein vaccine formulated either with the MF59 adjuvant or by incorporation into immune-stimulating complexes (ISCOMs) were compared. Virus-neutralizing antibodies (NA) against HIV-1SF2 reached similar titers in the two rgp120SF2 protein-immunized groups, but the responses showed different kinetics, while NA were delayed and their levels were low in the DNA-immunized animals. Antigen-specific gamma interferon (IFN-gamma) T-helper (type 1-like) responses were detected in the DNA-immunized group, but only after the fourth immunization, and the rgp120/MF59 group generated both IFN-gamma and interleukin-4 (IL-4) (type 2-like) responses that appeared after the third immunization. In contrast, rgp120/ISCOM-immunized animals rapidly developed marked IL-2, IFN-gamma (type 1-like), and IL-4 responses that peaked after the second immunization. To determine which type of immune responses correlated with protection from infection, all animals were challenged intravenously with 50 50% infective doses of a rhesus cell-propagated, in vivo-titrated stock of a chimeric simian immunodeficiency virus-HIVSF13 construct. Protection was observed in the two groups receiving the rgp120 subunit vaccines. Half of the animals in the ISCOM group were completely protected from infection. In other subunit vaccinees there was evidence by multiple assays that virus detected at 2 weeks postchallenge was effectively cleared. Early induction of potent type 1- as well as type 2-like T-helper responses induced the most-effective immunity.

Immunological properties of gene vaccines delivered by different routes

Gene vaccines represent a new and promising approach to control infectious diseases, inducing a protective immune response in the appropriate host. Several routes and methods of genetic immunization have been shown to induce antibody production as well as T helper (Th) cell and cytotoxic T lymphocyte activation. However, few studies have compared the nature of the immune responses generated by different gene vaccination delivery systems. In the present study we reviewed some aspects of immunity induced by gene immunization and compared the immune responses produced by intramuscular (i.m.) DNA injection to gene gun-mediated DNA transfer into the skin of BALB/c mice. Using a reporter gene coding for beta-galactosidase, we have demonstrated that i.m. injection raised a predominantly Th1 response with mostly IgG2a anti-beta gal produced, while gene gun immunization induced a mixed Th1/Th2 profile with a balanced production of IgG2a and IgG1 subclasses. Distinct types of immune responses were generated by different methods of gene delivery. These findings have important implications for genetic vaccine design. Firstly, a combination between these two systems may create optimal conditions for the induction of a broad-based immune response. Alternatively, a particular gene vaccine delivery method might be used according to the immune response required for host protection. Here, we describe the characteristics of the immune response induced by gene vaccination and the properties of DNA involved in this process.

Glutathione S-transferases of 28kDa as major vaccine candidates against schistosomiasis

For the development of vaccine strategies to generate efficient protection against chronic infections such as parasitic diseases, and more precisely schistosomiasis, controlling pathology could be more relevant than controlling the infection itself. Such strategies, motivated by the need for a cost-effective complement to existing control measures, should focus on parasite molecules involved in fecundity, because in metazoan parasite infections pathology is usually linked to the output of viable eggs. In numerous animal models, vaccination with glutathione S-transferases of 28kDa has been shown to generate an immune response strongly limiting the worm fecundity, in addition to the reduction of the parasite burden. Recent data on acquired immunity directed to 28GST in infected human populations, and new development to draw adapted vaccine formulations, are presented.

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.

HIV-1 DNA vaccines

HIV-1 was among the original DNA vaccine targets and HIV DNA vaccines are now in human trials. Lack of strong correlates of protective immunity makes vaccine design difficult; however, DNA vaccines have the potential to be an ideal vaccine and therapeutic approach against HIV-1. DNA vaccines induce conformational-dependent antibodies, mimic live vaccines but without the pathogenic potential, and can easily be made polyvalent. Genes which encode important CTL and antibody epitopes can be included while those that confer pathogenicity, virulence, antibody enhancement or represent non-conserved epitopes can be excluded. In our hands pre-treatment of muscles with bupivacaine or cardiotoxin did not offer any advantage over no muscle pre-treatment or gene gun inoculation of skin although gene gun immunization seem to favour a Th2 type response. As DNA vaccine candidates we have compared vaccines encoding native HIV MN gp160 with Rev-independent synthetic genes encoding MNgp160 and MNgp120 using mammalian high expression codons. In these experiments the gene encoding secreted gp120 gave highest antibody neutralizing titers. High and fast antibody responses could also be obtained by transferring the HIV-1 MN V3 loop to the secreted HBsAg as a fusion gene vaccine. Thus, in the case of HIV-1 MN genes encoding secreted surface glycoproteins may be preferred instead of membrane bound envelopes. CTL responses were induced in all cases. However, in order to meet the high diversity of HIV and HLA types our approach is to include many CTL epitopes in a multivalent minigene vaccine. We found that gene gun DNA vaccination with minimal epitopes could induce specific CTL. Flanking sequences influenced the CTL response but was not needed. DNA vaccines encoding known and computer predicted CTL epitopes are now being developed.

Enhancement of cellular immune response in HIV-1 seropositive individuals: A DNA-based trial

A DNA-based vaccine containing HIV-1 Env and Rev genes was tested for safety and host immune response in 15 HIV-infected asymptomatic patients with CD4-positive lymphocyte counts >/=500/microl of blood and receiving no antiviral therapy. Successive groups of patients received three doses of vaccine at 30, 100, or 300 microg at 10-week intervals in a dose-escalation trial. Some changes were noted in cytotoxic T-lymphocyte activity against gp160-bearing targets. Importantly, enhanced specific lymphocyte proliferative activity against HIV-1 envelope was observed in multiple patients. Three of three patients in the 300-microg dose group also developed increased MIP-1alpha levels which were detectable in their serum. Interestingly patients in the lowest dose group showed no overall changes in the immune parameters measured. The majority of patients who exhibited increases in any immune parameters were contained within the 300 microg, which was the highest dose group. These studies support further investigation of this technology for the production of antigen-specific immune responses in humans.

DNA vaccination with HIV-1 expressing constructs elicits immune responses in humans

Humoral and cellular immune responses have been produced by intramuscular vaccination with DNA plasmids expressing HIV-1 genes, suggesting possible immunotherapeutic and prophylactic value for these constructs. Vaccination with these constructs has decreased HIV-1 viral load in HIV-1-infected chimpanzees. In addition, naive (i.e. non-HIV-1-infected) chimpanzees were protected against a heterologous challenge with HIV-1. Ongoing phase I clinical trials show that therapeutic vaccinations indeed boost anti-HIV-1 immune responses in humans. A therapeutic phase I trial on humans with these constructs induced a good safety profile and also demonstrated an immunological potentiation. These findings indicate that further studies with these constructs in humans are warranted.

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.

Immune responses but no protection against SHIV by gene-gun delivery of HIV-1 DNA followed by recombinant subunit protein boosts

The efficacy of combining immunization with human immunodeficiency vitus type 1 (HIV-1) DNA and HIV-1 recombinant proteins to obtain protection from chimeric simian/human immunodeficiency virus (SHIV) was determined. Four cynomolgus monkeys received four gene-gun immunizations intraepidermally of plasmid DNA encoding HIV-1lai env (gp160), gag, tat, nef, and rev proteins. Ten micrograms of DNA was used per immunization. The animals were boosted twice intramuscularly with 50 microgram of HIV-1lai Env (MicroGeneSys), Gag, Tat, Nef, and Rev recombinant proteins mixed in Ribi adjuvant. The antibody responses were amplified following the administration of the recombinant subunit boosts. One month after the final subunit immunization, the vaccinated animals together with four control animals were challenged intravenously with 10 monkey infectious doses of SHIV that expresses the env, tat and rev genes of HIV-1 and gag and nef from SIV. However, only low titers of neutralizing antibodies were present at the day of challenge. The consecutive HIV-1 DNA and recombinant protein immunizations induced B- and T-cell responses but not protection against SHIV replication nor reduction of the viral load.

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.

Characterization of humoral immune responses induced by immunization with plasmid DNA expressing HIV-1 Nef accessory protein

Mice immunized with plasmid DNA encoding Nef accessory protein of human immunodeficiency virus type 1 developed high levels of anti-Nef antibodies which were maintained for at least 16 months. These antibodies produced in response to Nef-expressing plasmid DNA did not recognize the linear peptides except the long C-terminal peptide for three of the ten sera. With anti-Nef antibodies produced in mice immunized with the protein Nef without any adjuvant, the same restraint epitope binding was found. On the contrary, anti-Nef antibodies from mice immunized with the protein in Freund's adjuvant showed a broader epitope reactivity pattern. Interestingly, the analysis of immunoglobulin isotype profiles of antibodies generated by the different protocols of immunization showed that plasmid DNA immunization induced predominantly IgG2a, whereas immunization with Nef protein, with or without adjuvant, yielded a preponderance of IgG1 antibodies.

Augmentation and Suppression of Immune Responses to an HIV-1 DNA Vaccine by Plasmid Cytokine/Ig Administration

The use of cytokines has shown promise as an approach for amplifying vaccine-elicited immune responses, but the application of these immunomodulatory molecules in this setting has not been systematically explored. In this report we investigate the use of protein- and plasmid-based cytokines to augment immune responses elicited by an HIV-1 gp120 plasmid DNA vaccine (pV1J-gp120) in mice. We demonstrate that immune responses elicited by pV1J-gp120 can be either augmented or suppressed by administration of plasmid cytokines. A dicistronic plasmid expressing both gp120 and IL-2 induced a surprisingly weaker gp120-specific immune response than did the monocistronic pV1J-gp120 plasmid. In contrast, systemic delivery of soluble IL-2/Ig fusion protein following pV1J-gp120 vaccination significantly amplified the gp120-specific immune response as measured by Ab, proliferative, and CTL levels. Administration of plasmid IL-2/Ig had different effects on the DNA vaccine-elicited immune response that depended on the temporal relationship between Ag and cytokine delivery. Injection of plasmid IL-2/Ig either before or coincident with pV1J-gp120 suppressed the gp120-specific immune response, whereas injection of plasmid IL-2/Ig after pV1J-gp120 amplified this immune response. To maximize immune responses elicited by a DNA vaccine, therefore, it appears that the immune system should first be primed with a specific Ag and then amplified with cytokines. The data also show that IL-2/Ig is more effective than native IL-2 as a DNA vaccine adjuvant.

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.