Evaluation of immunogenicity and efficacy of combined DNA and adjuvanted protein vaccination in a human immunodeficiency virus type 1/murine leukemia virus pseudotype challenge model

Role of adjuvants in modeling the immune response

PURPOSE OF REVIEW

Recent clinical trial results have indicated that it may be possible for vaccines to induce protection against HIV. To build on this result, strategies should be designed to enhance duration, breadth, and magnitude of antibody production. Strategic formulation of agonists of the innate immune system and carriers that selectively present the target antigen yields a class of pharmaceuticals, named 'adjuvants', that greatly influence immunity resulting from vaccination. As researchers begin to focus not only on creating an immune response to an antigen, but also on the quality of that response, the role of adjuvants is becoming increasingly significant. This review is intended to give an overview of recent findings on how adjuvants model the immune response to antigens with a focus on the field of vaccines for HIV.

RECENT FINDINGS

It is clear that innate and adaptive immunity are linked by communication channels that allow innate signals to influence the quality of adaptive responses as well as adaptive signals that temper innate responses. Adjuvants take advantage of this bridge to shape the immune response to antigens. In this review, we will discuss the different classes of adjuvants currently available; recent findings on the relationship between adjuvants and the type of immune profile generated; and the breadth of neutralizing antibodies as influenced by adjuvants.

SUMMARY

Because adjuvants influence the breadth of antibodies generated and the type of cells that proliferate in response to a vaccine this review is relevant for scientists clinicians involved in creating a new HIV vaccine.

HIV-1 Tat-based vaccines: an overview and perspectives in the field of HIV/AIDS vaccine development

The HIV epidemic continues to represent one of the major problems worldwide, particularly in the Asia and Sub-Saharan regions of the world, with social and economical devastating effects. Although antiretroviral drugs have had a dramatically beneficial impact on HIV-infected individuals that have access to treatment, it has had a negligible impact on the global epidemic. Hence, the inexorable spreading of the HIV pandemic and the increasing deaths from AIDS, especially in developing countries, underscore the urgency for an effective vaccine against HIV/AIDS. However, the generation of such a vaccine has turned out to be extremely challenging. Here we provide an overview on the rationale for the use of non-structural HIV proteins, such as the Tat protein, alone or in combination with other HIV early and late structural HIV antigens, as novel, promising preventative and therapeutic HIV/AIDS vaccine strategies.

Characterization of DNA and MVA vectors expressing Nef from HIV-1 CRF12_BF revealed high immune specificity with low cross-reactivity against subtype B

The HIV epidemic in Argentina is characterized by the high prevalence of infections caused by subtype B and BF variants. In this study, the Nef protein was used as a tool to study the impact of HIV-1 BF variants in the design of future vaccines. DNA and MVA vectors expressing Nef of the CRF12_BF recombinant form of HIV-1 were generated and characterized. After the administration of single DNAprime/MVAboost immunization schedules in Balb/c mice we found that NefBF delivered from these vectors generated a response of high specificity with low cross-reactivity against subtype B. But, when a more potent response was induced after 3 priming DNA doses and a booster with MVA virus, cross-reactivity against NefB was detected, although of lower magnitude than the NefBF specific. These results will be pivotal for vaccines designs in our region, indicating that antigens from these viral variants must be considered for a future vaccine.

Characterization of Chikungunya pseudotyped viruses: Identification of refractory cell lines and demonstration of cellular tropism differences mediated by mutations in E1 glycoprotein

Chikungunya virus (CHIKV) is an alphavirus responsible for a number of large outbreaks. Here we describe the efficient incorporation of CHIKV envelope glycoproteins into lentiviral and rhabdoviral particles. Vectors pseudotyped with CHIKV envelope proteins efficiently transduced many cell types from different species. However, hematopoietic cell types were either partially or completely refractory. A mutation in E1 (A226V) has been linked with expansion of tropism for mosquito species, although differences in in vitro infection of mosquito cell lines have not been noted. However, pseudovirion infectivity assays detected subtle differences in infection of mosquito cells, suggesting an explanation for the changes in mosquito tropism. The presence of C-type lectins increased CHIKV pseudotyped vector infectivity, but not infection of refractory cells, suggesting that they act as attachment factors rather than primary receptors. CHIKV pseudotypes will serve as an important tool for the study of neutralizing antibodies and the analysis of envelope glycoprotein functions.

Murine models for HIV vaccination and challenge

HIV-1 only infects humans and chimpanzees. SIV or SHIV are, therefore, used as models for HIV in rhesus, cynomologus and pigtail macaques. Since conducting experiments in primate models does not fully mimic infection or vaccination against HIV-1 and is expensive, there is a great need for small-animal models in which it is possible to study HIV-1 infection, immunity and vaccine efficacy. This review summarizes the available murine models for studying HIV-1 infection with an emphasis on our experience of the HIV-1-infected-cell challenge as a model for evaluating candidate HIV-1 vaccines. In the cell-based challenge model, several important factors that, hopefully, can be related to vaccine efficacy in humans were discovered: the efficiency of combining plasmid DNA representing several of the viral genes originating from multiple clades of HIV-1, the importance of adjuvants activating innate and induced immunity and the enhanced HIV eradication by drug-conjugated antibody.

Improved HIV-1 specific T-cell responses by short-interval DNA tattooing as compared to intramuscular immunization in non-human primates

The new intradermal DNA delivery technique, termed DNA tattooing might overcome the discrepancy between the encouraging immunogenicity results obtained with DNA vaccines in murine studies and the poor results obtained in non-human primates and humans, the so called "simian barrier". Here, we demonstrate a 10- to 100-fold increase in the magnitude of vaccine specific T-cell responses in peripheral blood from DNA tattooed rhesus macaques, as compared to T-cell responses in animals immunized via intramuscular (IM) route. A marked increase in the magnitude of the antigen specific T-cell responses as well as an increase in the number of animals responding to the immunogens was observed. These findings in non-human primates suggest that similar results may be observed in humans. Clinical trials are planned to validate tattooing as an optimal method of DNA vaccine delivery in humans.

Immune-response profiles induced by human immunodeficiency virus type 1 vaccine DNA, protein or mixed-modality immunization: increased protection from pathogenic simian–human immunodeficiency virus viraemia with protein/DNA combination

Current data suggest that prophylactic human immunodeficiency virus type 1 (HIV) vaccines will be most efficacious if they elicit a combination of adaptive humoral and T-cell responses. Here, we explored the use of different vaccine strategies in heterologous prime–boost regimes and evaluated the breadth and nature of immune responses in rhesus monkeys induced by epidermally delivered plasmid DNA or recombinant HIV proteins formulated in the AS02A adjuvant system. These immunogens were administered alone or as either prime or boost in mixed-modality regimes. DNA immunization alone induced cell-mediated immune (CMI) responses, with a strong bias towards Th1-type cytokines, and no detectable antibodies to the vaccine antigens. Whenever adjuvanted protein was used as a vaccine, either alone or in a regime combined with DNA, high-titre antibody responses to all vaccine antigens were detected in addition to strong Th1- and Th2-type CMI responses. As the vaccine antigens included HIV-1 Env, Nef and Tat, as well as simian immunodeficiency virus (SIV)mac239 Nef, the animals were subsequently exposed to a heterologous, pathogenic simian–human immunodeficiency virus (SHIV)89.6p challenge. Protection against sustained high virus load was observed to some degree in all vaccinated groups. Suppression of virus replication to levels below detection was observed most frequently in the group immunized with protein followed by DNA immunization, and similarly in the group immunized with DNA alone. Interestingly, control of virus replication was associated with increased SIV Nef- and Gag-specific gamma interferon responses observed immediately following challenge.

Characterization of immune responses elicited in mice by intranasal co-immunization with HIV-1 Tat, gp140 DeltaV2Env and/or SIV Gag proteins and the nontoxicogenic heat-labile Escherichia coli enterotoxin

The development of a vaccine against HIV/AIDS capable of inducing broad humoral and cellular responses at both systemic and mucosal sites, able to stop or reduce viral infection at the portal of entry, represents the only realistic way to control the infection caused by HIV world-wide. The promising results obtained with the HIV-1 Tat-based vaccines in preclinical and clinical settings, the evidence that a broad immunity against HIV correlates with reduced viral load or virus control, as well as the availability of novel gp140 V2-loop deleted HIV-1 Env (DeltaV2Env) immunogens capable of inducing cross-reactive neutralizing antibodies, have led to the design of new vaccine strategies based on the combination of non-structural and structural proteins. In this study, we demonstrate that immunization with a biologically active HIV-1 Tat protein in combination with the oligomeric HIV-1 gp140 DeltaV2Env and/or SIV Gag proteins, delivered intranasally with the detoxified LTK63 mucosal adjuvant, whose safety has been recently shown in humans, elicits long-lasting local and systemic antibody and cellular immune responses against the co-administered antigens in a fashion similar to immune responses induced by vaccination with Tat, DeltaV2Env and Gag proteins alone. The results indicate lack of antigen interference implying that HIV-1 Tat is an optimal co-antigen for combined vaccine strategies employing DeltaV2Env and/or Gag proteins.

Vaccine-induced protection from infection of mice by chimeric human immunodeficiency virus type 1, EcoHIV/NL4-3

EcoHIV/NL4-3 is a chimeric human immunodeficiency virus type 1 (HIV-1) that can productively infect mice. This study tests the utility of EcoHIV/NL4-3 infection to reveal protective immune responses to an HIV-1 vaccine. Immunocompetent mice were first immunized with VRC 4306 which encodes subtype B consensus sequences of gag, pol, and nef and then were infected by EcoHIV/NL4-3. Anti-Gag antibodies were sampled during immunization and infection. The extent of EcoHIV/NL4-3 infection in spleen cells and peritoneal macrophages was determined by quantitative real-time PCR (QPCR). Although antibody titres were not significantly different in control and vaccinated groups, VRC 4306 immunization induced protective responses that significantly reduced virus burden in both lymphocyte and macrophage compartments. These results indicate that EcoHIV/NL4-3 infection can be controlled by HIV-1 vaccine-induced responses, introducing a small animal model to test vaccine efficacy against HIV-1 infection.