Issues for improving multiplasmid DNA vaccines for HIV-1

Since the first reports of plasmid vaccines, there have been substantial changes made to the design of plasmid backbones, as well as to the antibiotic resistance markers chosen for clinical vectors compared with first generation vectors. These changes aid manufacturing, production and scale up and at the same time aid conceptual safety by limiting the ability of the vaccines to transfer useful genetic selection genes to other bacterial infectious agents. In contrast, there has been little change to the original promoters or polyadenlyation tracts in the last decade. We have learned that these first generation plasmid vaccines for HIV-1 appear very well tolerated in humans. However, while safe and immunogenic, improving the immune potency of DNA vaccines is a critical goal for this technology. The combination of antigens used should be carefully examined for possible immune interference. Such interference may only become apparent when each component of the vaccine is tested individually. This interference also suggests one mechanism of immune pathogenesis possibly by HIV-1. Optimization of the immune response can come through manipulation of the transfection efficiency, expression or through the use of various T cell and B cell plasmid adjuvants. It is likely that the combination of such advancements will significantly improve the clinical phenotype of this important vaccine modality.

Therapeutic immunization of HIV-infected chimpanzees using HIV-1 plasmid antigens and interleukin-12 expressing plasmids

OBJECTIVE

To assess HIV-1 DNA vaccination and co-immunization with interleukin (IL)-12 and IL-10 as immunotherapy in the HIV-1 infected chimpanzee model system.

METHODS

Four chimpanzees that were infected with HIV-1-IIIB for longer than 4 years and remained symptom free were immunized with HIV-1 plasmid vaccines. Two chimpanzees were immunized with DNA plasmids that encoded env/rev, gag/pol along with a plasmid that encoded both chains of human IL-12. A third animal was immunized with HIV-1 DNA vaccine constructs and co-immunized with an IL-10 expressing plasmid. Finally a control animal received the HIV-1 DNA vaccine constructs alone.

RESULTS

There was no evidence of systemic toxicity associated with the administration of the DNA vaccines or the cytokine-expressing plasmids. We observed that the IL-12/HIV-1 DNA vaccinated animals had enhanced proliferative responses to multiple HIV-1 antigens at multiple time points. The animal that was co-immunized with HIV-1 and IL-10 did not have any changes in the proliferative responses. Finally, the control chimpanzee demonstrated moderate increases in the proliferative responses to HIV-1 antigens. The animal that received HIV-1 vaccines alone and the animals co-immunized with IL-12 all had declines in viral load over the course of the study, however, the decrease in viral loads were transient in all animals.

CONCLUSION

Immunization of HIV-1 infected chimpanzees with DNA based vaccines containing the env, gag and pol genes can transiently boost the env specific proliferative responses. Co-administration of IL-12 expressing plasmids further leads to transient boosting of the proliferative response to the core protein, p24 as well. However, at these doses the impact on viral load is minimal.

Vaccination of seronegative volunteers with a human immunodeficiency virus type 1 env/rev DNA vaccine induces antigen-specific proliferation and lymphocyte production of beta-chemokines

There is a pressing need to test novel vaccine concepts in an effort to develop an effective vaccine for human immunodeficiency virus (HIV) type 1. A phase I clinical study was done to test the immunogenicity of an HIV env/rev DNA vaccine, which was administered intramuscularly to HIV-1-seronegative persons. Subjects received 3 doses of vaccine at a single concentration (100 or 300 microgram) at 0, 4, 8, and 24 weeks. In at least 1 of multiple assays, the 6 subjects who received the 300-microgram dose had DNA vaccine-induced antigen-specific lymphocyte proliferative responses and antigen-specific production of both interferon-gamma and beta-chemokine. Furthermore, 4 of 5 subjects in the 300 microgram-dose group responded to both the rev and env components of the vaccine. The responses did not persist within inoculated individuals and scored in different individuals at different times in the trial. This study supports that HIV-1 DNA vaccine antigens can stimulate multiple immune responses in vaccine-naive individuals, and it warrants additional studies designed to enhance DNA vaccine immunogenicity.

Systemic and mucosal immunity is elicited after both intramuscular and intravaginal delivery of human immunodeficiency virus type 1 DNA plasmid vaccines to pregnant chimpanzees

DNA vaccines encoding human immunodeficiency virus type 1 (HIV-1) env/rev and gag/pol were delivered intravaginally (IVAG) and intramuscularly (IM) to 2 pregnant chimpanzees. Vaccination was well tolerated and each chimpanzee developed antibodies (up to 1 year later) to both vaccines. Placental transfer of anti-Env and anti-Gag IgG was demonstrated in both maternal/infant pairs. Specific IgG was also demonstrated in saliva, vaginal, and rectal washes after IVAG immunization. Predominantly anti-HIV-1 IgA was detected in the milk of both mothers after both IM and IVAG immunization. Cellular responses included Gag-specific proliferation of lymphocytes and cytotoxic T lymphocytes against both antigens. These data suggest a strategy for induction of mucosal and systemic responses after both IM and IVAG delivery of DNA vaccines in a primate model and could ultimately be useful in lowering maternal-to-fetal transmission of HIV-1, perinatally and through breastfeeding.

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.

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.

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

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

First human trial of a DNA-based vaccine for treatment of human immunodeficiency virus type 1 infection: safety and host response

A DNA-based vaccine containing human immunodeficiency virus type 1 (HIV-1) env and rev genes was tested for safety and host immune response in 15 asymptomatic HIV-infected patients who were not using antiviral drugs and who had CD4+ lymphocyte counts of > or = 500 per microliter of blood. Successive groups received three doses of vaccine (30, 100, or 300 microg) at 10-week intervals in a dose-escalation trial. Vaccine administration induced no local or systemic reactions, and no laboratory abnormalities were detected. Specifically, no patient developed anti-DNA antibody or muscle enzyme elevations. No consistent change occurred in CD4 or CD8 lymphocyte counts or in plasma HIV concentration. Antibody against gp120 increased in individual patients in the 100- and 300-/microg groups. Some increases were noted in cytotoxic T lymphocyte activity against gp160-bearing targets and in lymphocyte proliferative activity. The safety and potential immunogenicity of an HIV-directed DNA-based vaccine was demonstrated, a finding that should encourage further studies.

DNA vaccination as anti-human immunodeficiency virus immunotherapy in infected chimpanzees

The role of the immune response in controlling human immunodeficiency virus type 1 (HIV-1) replication is controversial. Immunotherapeutic strategies that have the ability to broaden immune responses might play a role in slowing disease progression. DNA immunization was studied as immunotherapy in infected chimpanzees. Two HIV-1-infected chimpanzees were vaccinated with DNA plasmid vaccines, one with plasmid pCMN160, which expresses the envelope glycoprotein of HIV-1MN and rev, and the other with a control plasmid. The chimpanzee immunized with pCMN160 demonstrated enhanced humoral responses. Virus load was monitored. Virus load in the chimpanzee receiving pCMN160 decreased at week 20 and has remained at background levels. The control chimpanzee was subsequently vaccinated with pCMN160. After immunization, the antibody responses increased and, as in the first animal, the virus load decreased. These results indicate the potential of the immune response to have a direct impact on HIV-1 replication in chimpanzees.

Engineering of in vivo immune responses to DNA immunization via codelivery of costimulatory molecule genes

Nucleic acid immunization is a novel vaccination technique to induce antigen-specific immune responses. We have developed expression cassettes for cell surface markers CD80 and CD86, two functionally related costimulatory molecules that play an important role in the induction of T cell-mediated immune responses. Coimmunization of these expression plasmids, along with plasmid DNA encoding for HIV-1 antigens, did not result in any significant change in the humoral response; however, we observed a dramatic increase in cytotoxic T-lymphocyte (CTL) induction as well as T-helper cell proliferation after the coadministration of CD86 genes. In contrast, coimmunization with a CD80 expression cassette resulted in a minor, but positive increase in T-helper cell or CTL responses. This strategy may be of value for the generation of rationally designed vaccines and immune therapeutics.

Development of a multicomponent candidate vaccine for HIV-1

Nucleic acid or DNA immunization represents a novel approach to both vaccine and immune therapeutic development. DNA vaccination induces antigen-specific cellular and humoral immune responses through the delivery of non-replicating transcription units which drive the synthesis of specific foreign proteins within the inoculated host. We have previously reported on the potential use of DNA immunization as a novel vaccine strategy for HIV-1. We found that both antigen-specific cellular and humoral immune responses could be induced in vivo with various DNA vaccine constructs against different antigenic targets within HIV-1. In order to enhance the DNA vaccine's ability to elicit cell-mediated immune responses, we co-delivered plasmids encoding costimulatory molecule B7 and interleukin-12 genes with DNA vaccine for HIV-1. We observed a dramatic increase in both antigen-specific T helper cell proliferation and CTL response. Eventual development of successful vaccines for HIV-1 would likely involve targeting multiple antigenic components of the virus to direct and empower the immune system to protect the host from viral infection. We present here the utility of multicomponent DNA immunization to elicit specific humoral and cell-mediated immune responses against different antigenic targets of HIV-1 as well as the ability of this immunization strategy to achieve significant enhancements of antigen-specific cellular immune responses.

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.

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.

In vivo engineering of a cellular immune response by coadministration of IL-12 expression vector with a DNA immunogen

Recent studies support the importance of investigating a DNA vaccination approach for the immunologic control of HIV-1. In this regard, it may be important to specifically engineer immune responses in order to improve on first generation vaccine attempts. Especially for HIV, induction of cell-mediated immunity may be an important feature for any candidate vaccine. In an attempt to engineer in vivo the enhancement of cellular immune response and to direct Ag-dependent immune response from Th2 to Th1 type, we investigated the role of codelivery of genes for IL-12 and granulocyte-macrophage-CSF along with DNA vaccine formulations for HIV-1 Ag. We found that codelivery of IL-12 expression cassettes with DNA vaccines for HIV-1 in mice resulted in splenomegaly as well as a shift in the specific immune responses induced. The codelivery of IL-12 genes resulted in the reduction of specific Ab response, while the coinjection of granulocyte-macrophage-CSF genes resulted in the enhancement of specific Ab response. In addition, we observed a significant Ag-specific stimulation of T cells with codelivery of both cytokines. Most importantly, we observed a dramatic increase in specific CTL response from the group coimmunized with the HIV-1 DNA vaccine and IL-12 genes. This work demonstrates the power of DNA delivery in vivo for both the production of a new generation of more effective and targeted vaccines or immunotherapies as well as an analytic tool for the molecular dissection of the mechanisms of immune function.

In vivo engineering of a cellular immune response by coadministration of IL-12 expression vector with a DNA immunogen

Recent studies support the importance of investigating a DNA vaccination approach for the immunologic control of HIV-1. In this regard, it may be important to specifically engineer immune responses in order to improve on first generation vaccine attempts. Especially for HIV, induction of cell-mediated immunity may be an important feature for any candidate vaccine. In an attempt to engineer in vivo the enhancement of cellular immune response and to direct Ag-dependent immune response from Th2 to Th1 type, we investigated the role of codelivery of genes for IL-12 and granulocyte-macrophage-CSF along with DNA vaccine formulations for HIV-1 Ag. We found that codelivery of IL-12 expression cassettes with DNA vaccines for HIV-1 in mice resulted in splenomegaly as well as a shift in the specific immune responses induced. The codelivery of IL-12 genes resulted in the reduction of specific Ab response, while the coinjection of granulocyte-macrophage-CSF genes resulted in the enhancement of specific Ab response. In addition, we observed a significant Ag-specific stimulation of T cells with codelivery of both cytokines. Most importantly, we observed a dramatic increase in specific CTL response from the group coimmunized with the HIV-1 DNA vaccine and IL-12 genes. This work demonstrates the power of DNA delivery in vivo for both the production of a new generation of more effective and targeted vaccines or immunotherapies as well as an analytic tool for the molecular dissection of the mechanisms of immune function.