DNA immunization in combination with effective antiretroviral drug therapy controls viral rebound and prevents simian AIDS after treatment is discontinued

Effects of therapeutic vaccination on the control of SIV in rhesus macaques with variable responsiveness to antiretroviral drugs

A therapeutic vaccine that induces lasting control of HIV infection could eliminate the need for lifelong adherence to antiretroviral therapy. This study investigated a therapeutic DNA vaccine delivered with a single adjuvant or a novel combination of adjuvants to augment T cell immunity in the blood and gut-associated lymphoid tissue in SIV-infected rhesus macaques. Animals that received DNA vaccines expressing SIV proteins, combined with plasmids expressing adjuvants designed to increase peripheral and mucosal T cell responses, including the catalytic subunit of the E. coli heat-labile enterotoxin, IL-12, IL-33, retinaldehyde dehydrogenase 2, soluble PD-1 and soluble CD80, were compared to mock-vaccinated controls. Following treatment interruption, macaques exhibited variable levels of viral rebound, with four animals from the vaccinated groups and one animal from the control group controlling virus at median levels of 10³ RNA copies/ml or lower (controllers) and nine animals, among all groups, exhibiting immediate viral rebound and median viral loads greater than 10³ RNA copies/ml (non-controllers). Although there was no significant difference between the vaccinated and control groups in protection from viral rebound, the variable virological outcomes during treatment interruption enabled an examination of immune correlates of viral replication in controllers versus non-controllers regardless of vaccination status. Lower viral burden in controllers correlated with increased polyfunctional SIV-specific CD8⁺ T cells in mesenteric lymph nodes and blood prior to and during treatment interruption. Notably, higher frequencies of colonic CD4⁺ T cells and lower Th17/Treg ratios prior to infection in controllers correlated with improved responses to ART and control of viral rebound. These results indicate that mucosal immune responses, present prior to infection, can influence efficacy of antiretroviral therapy and the outcome of immunotherapeutic vaccination, suggesting that therapies capable of modulating host mucosal responses may be needed to achieve HIV cure.

Impact of analytical treatment interruption on the central nervous system in a simian-HIV model

OBJECTIVE(S)

Analytical treatment interruption (ATI) studies are often used to evaluate potential HIV cure strategies. This study was conducted to determine the impact of ATI on simian-HIV (SHIV) infection in the central nervous system.

DESIGN

Animal study.

METHODS

Nine rhesus macaques were inoculated with SHIV-1157ipd3N4. Antiretroviral therapy (ART) was administered from week 2 to 18. At week 18, four animals were euthanized (no-ATI-group) and five underwent ATI (ATI-group) and were euthanized at 12 weeks post viral rebound. Plasma and cerebrospinal fluid (CSF) SHIV-RNA, markers of inflammation and brain CD3+, CD68+/CD163+ and RNA+ cells were measured.

RESULTS

All nine animals were SHIV-infected, with median pre-ART plasma and CSF SHIV-RNA of 6.2 and 3.6 log10copies/ml. Plasma and CSF IL-15, monocyte chemoattractant protein-1, IFN-γ-induced protein-10 and neopterin increased postinfection. ART initiation was associated with rapid and complete suppression of plasma viremia and reductions in plasma and CSF IL-15, IFN-γ-induced protein-10, neopterin and CSF monocyte chemoattractant protein-1. Median time to plasma viral rebound was 21 days post-ATI. At 12 weeks postrebound, CSF SHIV-RNA was undetectable and no increases in plasma and CSF markers of inflammation were found. Higher numbers of CD3+ and CD68+/CD163+ cells were seen in the brains of 3/5 and 1/5 animals, respectively, in the ATI-group when compared with no-ATI-group. SHIV-RNA+ cells were not identified in the brain in either group post-ATI.

CONCLUSION

ATI in macaques that initiated ART during early SHIV-1157ipd3N4 infection was associated with mild, localized T-cell infiltrate in the brain without detectable SHIV-RNA in the brain or CSF, or elevation in CSF soluble markers of inflammation.

Comparative analysis and generation of a robust HIV-1 DNA quantification assay

HIV-1 infection cannot be cured due to the presence of the latent reservoir (LR). Novel cure or treatment strategies, such as "shock and kill" or therapeutic vaccination, aim to reduce or eradicate the LR. Cure strategies utilise robust DNA quantification assays to measure the change in the LR in low copy scenarios. No standard assay exists, which impedes the reliable comparison of results from different therapy and vaccine trials and HIV-1 total DNA quantification methods have not been previously compared. The HIV-1 long terminal repeat (LTR) has been shown to be the best target for DNA quantification. We have analysed two HIV-1 quantification assays, both able to differentiate between the variant HIV-1 DNA forms via the use of pre-amplification and primers targeting LTR. We identify a strong correlation (r=0.9759, P<0.0001) between assays which is conserved in low copy samples (r=0.8220, P<0.0001) indicating that these assays may be used interchangeably. The RvS assay performed significantly (P=0.0021) better than the CV assay when quantifying HIV-1 total DNA in patient CD4+ T lymphocytes. Sequence analysis demonstrated that viral diversity can limit DNA quantification, however in silico analysis of the primers indicated that within the target region nucleotide miss-matches appear infrequently. Further in silico analysis using up to-date sequence information led to the improvement of primers and enabled us to establish a more broadly specific assay with significantly higher HIV-1 DNA quantification capacity in patient samples (p=0.0057, n=17).

Kinetics of Myeloid-Derived Suppressor Cell Frequency and Function during Simian Immunodeficiency Virus Infection, Combination Antiretroviral Therapy, and Treatment Interruption

During chronic lentiviral infection, poor clinical outcomes correlate both with systemic inflammation and poor proliferative ability of HIV-specific T cells; however, the connection between the two is not clear. Myeloid-derived suppressor cells (MDSC), which expand during states of elevated circulating inflammatory cytokines, may link the systemic inflammation and poor T cell function characteristic of lentiviral infections. Although MDSC are partially characterized in HIV and SIV infection, questions remain regarding their persistence, activity, and clinical significance. We monitored MDSC frequency and function in SIV-infected rhesus macaques. Low MDSC frequency was observed prior to SIV infection. Post-SIV infection, MDSC were elevated in acute infection and persisted during 7 mo of combination antiretroviral drug therapy (cART). After cART interruption, we observed MDSC expansion of surprising magnitude, the majority being granulocytic MDSC. At all stages of infection, granulocytic MDSC suppressed CD4+ and CD8+ T cell proliferation in response to polyclonal or SIV-specific stimulation. In addition, MDSC frequency correlated significantly with circulating inflammatory cytokines. Acute and post-cART levels of viremia were similar, however, the levels of inflammatory cytokines and MDSC were more pronounced post-cART. Expanded MDSC during SIV infection, especially during the post-cART inflammatory cytokine surge, likely limit cellular responses to infection. As many HIV curative strategies require cART interruption to determine efficacy, our work suggests treatment interruption-induced MDSC may especially undermine the effectiveness of such strategies. MDSC depletion may enhance T cell responses to lentiviral infection and the effectiveness of curative approaches.

HIV therapeutic vaccines: moving towards a functional cure

Anti-viral T-cell and B-cell responses play a crucial role in suppressing HIV and SIV replication during chronic infection. However, these infections are rarely controlled by the host immune response, and most infected individuals need lifelong antiretroviral therapy (ART). Recent advances in our understanding of how anti-HIV immune responses are elicited and regulated prompted a surge of interest in harnessing these responses to reduce the HIV 'residual disease' that is present in ART-treated HIV-infected individuals. Novel approaches that are currently explored include both conventional therapeutic vaccines (i.e., active immunization strategies using HIV-derived immunogens) as well as the use of checkpoint blockers such as anti-PD-1 antibodies. These approaches appear promising as key components of complex therapeutic strategies aimed at curing HIV infection.

Therapeutic vaccination using cationic liposome-adjuvanted HIV type 1 peptides representing HLA-supertype-restricted subdominant T cell epitopes: safety, immunogenicity, and feasibility in Guinea-Bissau

We have designed a therapeutic HIV-1 vaccine concept based on peptides together with the adjuvant CAF01. Peptides represented 15 HLA-supertype-restricted subdominant and conserved CD8 T cell epitopes and three CD4 T-helper cell epitopes. In this phase I clinical trial, safety and immunogenicity were assessed in untreated HIV-1-infected individuals in Guinea-Bissau, West Africa. Twenty-three HIV-1-infected individuals were randomized to receive placebo (n=5) or vaccine (n=18). Safety was appraised by clinical follow-up combined with monitoring of biochemistry, hematology, CD4 T cell counts, and HIV-1 viral loads. T cell immunogenicity was monitored longitudinally by interferon (IFN)-γ ELISpot. New vaccine-specific T cell responses were induced in 6/14 vaccinees for whom ELISpot data were valid. CD4 T cell counts and viral loads were stable. The study shows that therapeutic immunization is feasible and safe in Guinea-Bissau and that it is possible to redirect T cell immunity with CAF01-adjuvanted HIV-1 peptide vaccine during untreated HIV-1 infection in some patients. However, relatively few preexisting and vaccine-induced HIV-1 T cell responses to CD8 T cell epitopes were detected against HIV-1 using IFN-γ ELISpot in this chronically infected African population.

Optimizing particle-mediated epidermal delivery of an influenza DNA vaccine in ferrets

Particle-mediated DNA delivery technologies ("gene guns") have been shown in both animal and clinical studies to be an effective means of increasing the immunogenicity and protective efficacy of DNA vaccines. The primary goal in optimizing particle-mediated epidermal delivery (PMED) vaccination in different animal models is to achieve delivery of DNA-coated gold beads into the viable epidermis. Two key para-meters that influence this outcome include the delivery pressure, which controls the penetrative force of the beads into the skin, and the anatomical site of DNA delivery. Although the ferret has been extensively used as an experimental model for influenza infection in humans, very few studies have investigated the capacity for PMED DNA vaccination to induce protective immune responses in ferrets. Here we describe methods to optimize DNA vaccine delivery using the PowderJect XR1 gene delivery in ferrets. We first assess the effects of firing pressure on both the delivery of DNA-coated gold beads into the desired epidermal layer and the degree of DNA vaccine reporter gene expression at the target site. Second, we evaluate the impact of vaccination site (skin or tongue) on DNA vaccine immunogenicity by measuring serum antibody responses to the model antigens influenza virus hemagglutinin and hepatitis B core antigen. Results from these studies support the use of the PowderJect XR1 device in ferrets for the study of prophylactic and therapeutic DNA vaccines against clinically important diseases such as influenza virus infection.

Response of simian immunodeficiency virus to the novel nucleoside reverse transcriptase inhibitor 4'-ethynyl-2-fluoro-2'-deoxyadenosine in vitro and in vivo

Nucleoside/nucleotide reverse transcriptase inhibitors (NRTIs) are essential components in first-line therapy for human immunodeficiency virus (HIV) infection. However, long-term treatment with existing NRTIs can be associated with significant toxic side effects and the emergence of drug-resistant strains. The identification of new NRTIs for the continued management of HIV-infected people therefore is paramount. In this report, we describe the response of a primary isolate of simian immunodeficiency virus (SIV) to 4'-ethynyl-2-fluoro-2'-deoxyadenosine (EFdA) both in vitro and in vivo. EFdA was 3 orders of magnitude better than tenofovir (TFV), zidovudine (AZT), and emtricitabine (FTC) in blocking replication of SIV in monkey peripheral blood mononuclear cells (PBMCs) in vitro, and in a preliminary study using two SIV-infected macaques with advanced AIDS, it was highly effective at treating SIV infection and AIDS symptoms in vivo. Both animals had 3- to 4-log decreases in plasma virus burden within 1 week of EFdA therapy (0.4 mg/kg of body weight, delivered subcutaneously twice a day) that eventually became undetectable. Clinical signs of disease (diarrhea, weight loss, and poor activity) also resolved within the first month of treatment. No detectable clinical or pathological signs of drug toxicity were observed within 6 months of continuous therapy. Virus suppression was sustained until drug treatment was discontinued, at which time virus levels rebounded. Although the rebound virus contained the M184V/I mutation in the viral reverse transcriptase, EFdA was fully effective in maintaining suppression of mutant virus throughout the drug treatment period. These results suggest that expanded studies with EFdA are warranted.

Prolonged tenofovir treatment of macaques infected with K65R reverse transcriptase mutants of SIV results in the development of antiviral immune responses that control virus replication after drug withdrawal

BACKGROUND

We reported previously that while prolonged tenofovir monotherapy of macaques infected with virulent simian immunodeficiency virus (SIV) resulted invariably in the emergence of viral mutants with reduced in vitro drug susceptibility and a K65R mutation in reverse transcriptase, some animals controlled virus replication for years. Transient CD8+ cell depletion or short-term tenofovir interruption within 1 to 5 years of treatment demonstrated that a combination of CD8+ cell-mediated immune responses and continued tenofovir therapy was required for sustained suppression of viremia. We report here follow-up data on 5 such animals that received tenofovir for 8 to 14 years.

RESULTS

Although one animal had a gradual increase in viremia from 3 years onwards, the other 4 tenofovir-treated animals maintained undetectable viremia with occasional viral blips (≤ 300 RNA copies/ml plasma). When tenofovir was withdrawn after 8 to 10 years from three animals with undetectable viremia, the pattern of occasional episodes of low viremia (≤ 3600 RNA/ml plasma) continued throughout the 10-month follow-up period. These animals had low virus levels in lymphoid tissues, and evidence of multiple SIV-specific immune responses.

CONCLUSION

Under certain conditions (i.e., prolonged antiviral therapy initiated early after infection; viral mutants with reduced drug susceptibility) a virus-host balance characterized by strong immunologic control of virus replication can be achieved. Although further research is needed to translate these findings into clinical applications, these observations provide hope for a functional cure of HIV infection via immunotherapeutic strategies that boost antiviral immunity and reduce the need for continuous antiretroviral therapy.

Induction of mucosal HIV-specific B and T cell responses after oral immunization with live coxsackievirus B4 recombinants

Given the limited success of clinical HIV vaccine trials, new vaccine strategies are needed for the HIV pipeline. The present study explored the novel concept that a live enteric virus, with limited disease potential, is a suitable vaccine vector to elicit HIV-specific immune responses in the gut mucosa of immunized mice. Two coxsackievirus B4 (CVB4) vaccine vectors were designed to induce HIV-specific B or T cell responses. A B cell immunogen, CVB4/gp41(2F5), was constructed by expressing an epitope from the membrane proximal external region (MPER) of gp41 as a structural peptide within a surface loop of a capsid protein of CVB4. The T cell immunogen, CVB4/p24(73(3)), was constructed previously by expressing a gag p24 sequence as a non-structural peptide at the amino-terminus of the CVB4 polyprotein. The CVB4/gp41(2F5) recombinant was antigenic in mice and elicited anti-gp41 antibodies in both the mucosal and systemic compartments. The route of immunization affected the antibody response since oral delivery of CVB4/gp41(2F5) induced anti-gp41 antibodies in the mucosal but not in the systemic compartment while parenteral delivery induced anti-gp41 antibodies in both compartments. In contrast, oral immunization with CVB4/p24(73(3)) elicited both mucosal and systemic gag p24-specific T cell responses. Since coxsackieviruses are ubiquitous in the human population, a key question is whether pre-existing vector immunity will inhibit the ability of a CVB4-based vaccine to induce HIV-specific immune responses. We show that pre-existing vector immunity did not preclude the development of mucosal anti-gp41 antibodies or gag p24-specific T cell responses after oral immunization with the CVB4/HIV recombinants. We suggest that the CVB4/HIV recombinants have the potential to be a viable vaccine product because of ease of delivery, safety, immunogenicity, ease of large-scale production, and storage conditions requiring cold-chain temperatures provided by refrigeration.

Therapeutic DNA vaccine induces broad T cell responses in the gut and sustained protection from viral rebound and AIDS in SIV-infected rhesus macaques

Immunotherapies that induce durable immune control of chronic HIV infection may eliminate the need for life-long dependence on drugs. We investigated a DNA vaccine formulated with a novel genetic adjuvant that stimulates immune responses in the blood and gut for the ability to improve therapy in rhesus macaques chronically infected with SIV. Using the SIV-macaque model for AIDS, we show that epidermal co-delivery of plasmids expressing SIV Gag, RT, Nef and Env, and the mucosal adjuvant, heat-labile E. coli enterotoxin (LT), during antiretroviral therapy (ART) induced a substantial 2-4-log fold reduction in mean virus burden in both the gut and blood when compared to unvaccinated controls and provided durable protection from viral rebound and disease progression after the drug was discontinued. This effect was associated with significant increases in IFN-γ T cell responses in both the blood and gut and SIV-specific CD8+ T cells with dual TNF-α and cytolytic effector functions in the blood. Importantly, a broader specificity in the T cell response seen in the gut, but not the blood, significantly correlated with a reduction in virus production in mucosal tissues and a lower virus burden in plasma. We conclude that immunizing with vaccines that induce immune responses in mucosal gut tissue could reduce residual viral reservoirs during drug therapy and improve long-term treatment of HIV infection in humans.

The use of nonhuman primate models of HIV infection for the evaluation of antiviral strategies

Several nonhuman primate models are used in HIV/AIDS research. In contrast to natural host models, infection of macaques with virulent simian immunodeficiency virus (SIV) isolates results in a disease (simian AIDS) that closely resembles HIV infection and AIDS. Although there is no perfect animal model, and each of the available models has its limitations, a carefully designed study allows experimental approaches that are not feasible in humans, but that can provide better insights in disease pathogenesis and proof-of-concept of novel intervention strategies. In the early years of the HIV pandemic, nonhuman primate models played a minor role in the development of antiviral strategies. Since then, a better understanding of the disease and the development of better compounds and assays to monitor antiviral effects have increased the usefulness and relevance of these animal models in the preclinical development of HIV vaccines, microbicides, and antiretroviral drugs. Several strategies that were first discovered to have efficacy in nonhuman primate models are now increasingly used in humans. Recent trends include the use of nonhuman primate models to explore strategies that could reduce viral reservoirs and, ultimately, attempt to cure infection. Ongoing comparison of results obtained in nonhuman primate models with those observed in human studies will lead to further validation and improvement of these animal models so they can continue to advance our scientific knowledge and guide clinical trials.

SIV antigen immunization induces transient antigen-specific T cell responses and selectively activates viral replication in draining lymph nodes in retroviral suppressed rhesus macaques

Background

HIV infection causes a qualitative and quantitative loss of CD4⁺ T cell immunity. The institution of anti-retroviral therapy (ART) restores CD4⁺ T cell responses to many pathogens, but HIV-specific responses remain deficient. Similarly, therapeutic immunization with HIV antigens of chronically infected, ART treated subjects results in poor induction of HIV-specific CD4 responses. In this study, we used a macaque model of ART treatment during chronic infection to study the virologic consequences of SIV antigen stimulation in lymph nodes early after immunization. Rhesus CMV (RhCMV) seropositive, Mamu A*01 positive rhesus macaques were chronically infected with SIVmac251 and treated with ART. The immune and viral responses to SIV gag and RhCMV pp65 antigen immunization in draining lymph nodes and peripheral blood were analyzed. Animals were immunized on contralateral sides with SIV gag and RhCMV pp65 encoding plasmids, which allowed lymph nodes draining each antigen to be obtained at the same time from the same animal for direct comparison.

Results

We observed that both SIV and RhCMV immunizations stimulated transient antigen-specific T cell responses in draining lymph nodes. The RhCMV-specific responses were potent and sustained (50 days post-immunization) in the periphery, while the SIV-specific responses were transient and extinguished quickly. The SIV antigen stimulation selectively induced transient SIV replication in draining lymph nodes.

Conclusions

The data are consistent with a model whereby viral replication in response to SIV antigen stimulation limits the generation of SIV antigen-specific responses and suggests a potential mechanism for the early loss and poor HIV-specific CD4⁺ T cell response observed in HIV-infected individuals.

GM-CSF increases mucosal and systemic immunogenicity of an H1N1 influenza DNA vaccine administered into the epidermis of non-human primates

Background

The recent H5N1 avian and H1N1 swine-origin influenza virus outbreaks reaffirm that the threat of a world-wide influenza pandemic is both real and ever-present. Vaccination is still considered the best strategy for protection against influenza virus infection but a significant challenge is to identify new vaccine approaches that offer accelerated production, broader protection against drifted and shifted strains, and the capacity to elicit anti-viral immune responses in the respiratory tract at the site of viral entry. As a safe alternative to live attenuated vaccines, the mucosal and systemic immunogenicity of an H1N1 influenza (A/New Caledonia/20/99) HA DNA vaccine administered by particle-mediated epidermal delivery (PMED or gene gun) was analyzed in rhesus macaques.

Methodology/Principal Findings

Macaques were immunized at weeks 0, 8, and 16 using a disposable single-shot particle-mediated delivery device designed for clinical use that delivers plasmid DNA directly into cells of the epidermis. Significant levels of hemagglutination inhibiting (HI) antibodies and cytokine-secreting HA-specific T cells were observed in the periphery of macaques following 1–3 doses of the PMED HA DNA vaccine. In addition, HA DNA vaccination induced detectable levels of HA-specific mucosal antibodies and T cells in the lung and gut-associated lymphoid tissues of vaccinated macaques. Importantly, co-delivery of a DNA encoding the rhesus macaque GM-CSF gene was found to significantly enhance both the systemic and mucosal immunogenicity of the HA DNA vaccine.

Conclusions/Significance

These results provide strong support for the development of a particle-mediated epidermal DNA vaccine for protection against respiratory pathogens such as influenza and demonstrate, for the first time, the ability of skin-delivered GM-CSF to serve as an effective mucosal adjuvant for vaccine induction of immune responses in the gut and respiratory tract.

Repeated DNA therapeutic vaccination of chronically SIV-infected macaques provides additional virological benefit

We have previously reported that therapeutic immunization by intramuscular injection of optimized plasmid DNAs encoding SIV antigens effectively induces immune responses able to reduce viremia in antiretroviral therapy (ART)-treated SIVmac251-infected Indian rhesus macaques. We subjected such therapeutically immunized macaques to a second round of therapeutic vaccination using a combination of plasmids expressing SIV genes and the IL-15/IL-15 receptor alpha as molecular adjuvant, which were delivered by the more efficacious in vivo constant-current electroporation. A very strong induction of antigen-specific responses to Gag, Env, Nef, and Pol, during ART (1.2-1.6% of SIV-specific T cells in the circulating T lymphocytes) was obtained with the improved vaccination method. Immunological responses were characterized by the production of IFN-gamma, IL-2, and TNF-alpha either alone, or in combination as double or triple cytokine positive multifunctional T cells. A significant induction of CD4(+) T cell responses, mainly targeting Gag, Nef, and Pol, as well as of CD8(+) T cells, mainly targeting Env, was found in both T cells with central memory and effector memory markers. After release from ART, the animals showed a virological benefit with a further approximately 1 log reduction in viremia. Vaccination with plasmid DNAs has several advantages over other vaccine modalities, including the possibility for repeated administration, and was shown to induce potent, efficacious, and long-lasting recall immune responses. Therefore, these data support the concept of adding DNA vaccination to the HAART regimen to boost the HIV-specific immune responses.

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.

Prospects for developing an effective particle-mediated DNA vaccine against influenza

Vaccine strategies capable of conferring broad protection against both seasonal and pandemic strains of influenza are urgently needed. DNA vaccines are an attractive choice owing to their capacity to induce robust humoral and cellular immune responses at low doses and because they can be developed and manufactured rapidly to more effectively meet the threat of an influenza epidemic or pandemic. Particle-mediated epidermal delivery (PMED), or the gene gun, is a DNA vaccine delivery technology shown to induce protective levels of antibody and T-cell responses in animals and humans against a wide variety of diseases, including influenza. This review focuses on current advances toward the development of an effective PMED DNA vaccine against influenza, including strategies to enhance vaccine immunogenicity, the potential for PMED-based DNA vaccines to improve protection in the vulnerable elderly population, and the prospects for a vaccine capable of providing cross-protection against both seasonal and pandemic strains of influenza.

Evaluation of antiretrovirals in animal models of HIV infection

Animal models of HIV infection have played an important role in the development of antiretroviral drugs. Although each animal model has its limitations and never completely mimics HIV infection of humans, a carefully designed study allows experimental approaches that are not feasible in humans, but that can help to better understand disease pathogenesis and to provide proof-of-concept of novel intervention strategies. While rodent and feline models are useful for initial screening, further testing is best done in non-human primate models, such as simian immunodeficiency virus (SIV) infection of macaques, because they share more similarities with HIV infection of humans. In the early years of the HIV pandemic, non-human primate models played a relatively minor role in the antiretroviral drug development process. Since then, a better understanding of the disease and the development of better drugs and assays to monitor antiviral efficacy have increased the usefulness of the animal models. In particular, non-human primate models have provided proof-of-concept for (i) the benefits of chemoprophylaxis and early treatment, (ii) the preclinical efficacy of novel drugs such as tenofovir, (iii) the virulence and clinical significance of drug-resistant viral mutants, and (iv) the role of antiviral immune responses during drug therapy. Ongoing comparison of results obtained in animal models with those observed in human studies will further validate and improve these animal models so they can continue to help advance our scientific knowledge and to guide clinical trials. This article forms part of a special issue of Antiviral Research marking the 25th anniversary of antiretroviral drug discovery and development, Vol 85, issue 1, 2010.

Enhanced antibody responses elicited by a CpG adjuvant do not improve the protective effect of an aldrithiol-2-inactivated simian immunodeficiency virus therapeutic AIDS vaccine

The potential benefit of using unmethylated CpG oligoribodeoxynucleotides (ODN) as an adjuvant in a therapeutic simian immunodeficiency virus (SIV) vaccine consisting of AT2-inactivated SIVmac239 was evaluated in SIV-infected rhesus macaques receiving antiretroviral therapy (ART). We hypothesized that using CpG ODN as an adjuvant in therapeutic vaccination would enhance SIV-specific immune responses and suppress SIV replication after ART was stopped. To test our hypothesis, we immunized chronically SIV-infected rhesus macaques receiving ART with one of the following therapeutic vaccines: (i) AT2-inactivated SIVmac239, (ii) CpG10103 plus AT2-inactivated SIVmac239, (iii) CpG10103, and (iv) saline. While immunization with CpG plus AT2-SIVmac239 significantly increased SIV-specific immunoglobulin G (IgG) antibody titers, the mean plasma viral RNA (vRNA) level in these animals after ART did not differ from those of saline-treated animals. The AT2-inactivated SIVmac239-immunized animal group had a significantly higher mean SIV-specific gamma interferon T-cell response after three immunizations and lower plasma vRNA levels for 6 weeks after ART was withdrawn compared to the saline-treated animal group. Compared to the saline control group, the animal group treated with CpG alone had a significantly higher mean SIV-specific lymphocyte proliferation index and a higher rate of plasma vRNA rebound after ART. These results demonstrate that while the use of CpG as an adjuvant enhances SIV-specific antibody responses, this does not improve the control of SIV replication after ART is stopped. The lack of benefit may be related to the high levels of SIV-specific lymphocyte proliferation in the CpG adjuvant group.

Effect of therapeutic immunization using Ad5/35 and MVA vectors on SIV infection of rhesus monkeys undergoing antiretroviral therapy

Antiretroviral therapy (ART) effectively slows the progression of AIDS. However, drug resistance and/or toxicity can limit the utility of ART in many patients. In this study, we assessed whether a viral vector-based vaccine can be used as a therapeutic vaccine in simian immunodeficiency virus (SIV)-infected monkeys. The effect of vaccinating SIVmac239-infected rhesus monkeys with an SIV gag and gp120-expressing adenovirus (Ad) vector vaccine and a modified vaccinia Ankara (MVA) vaccine was explored while being treated with ART. Rhesus monkeys were intravenously infected with 10 and 1000 TCID(50) (50% tissue culture infectious dose) of SIVmac239. Two months after SIV infection, the monkeys received a 4-month treatment with ART. Some of the monkeys were immunized with adenovirus-based vaccine and MVA-based vaccine with 2 months interval during ART. Viral load, CD4 count and SIV-specific immune responses were observed for 7 months after interruption of ART. The vaccinated animals had higher (i) CD4 counts, (ii) SIV-specific cell-mediated immune responses and (iii) anti-SIV-neutralizing antibody (Ab) titers than monkeys treated with ART alone. More importantly, the vaccination significantly reduced the SIV RNA load from animals infected with a low dose of SIV (10 TCID(50)). The anti-SIV cell-mediated and humoral responses induced by the vaccination was inversely correlated with a reduction in SIV viral load and positively correlated with an increase in CD4(+) T cell counts. These results suggest that vaccination can improve antiviral cell-mediated and humoral immunity, which may contribute to controlling viral replication.

A therapeutic SIV DNA vaccine elicits T-cell immune responses, but no sustained control of viremia in SIVmac239-infected rhesus macaques

The immunologic and virologic outcome of therapeutic DNA-vaccines administered during antiretroviral therapy (ART) using electroporation with or without (interleukin) IL-2 treatment was evaluated in the SIVmac239/macaque model. Rhesus macaques inoculated with pathogenic SIVmac239 were treated with ART [(R(-9-(2-phosphonomethoxypropyl) adenine) (PMPA), FTC, Zerit] from weeks 13 to 41 postinfection (wpi). Group 1 (n = 7) received ART only, groups 2 and 3 (each n = 6) additionally received SIVmac239-derived gp140Env, GagPol, and TatRevNef plasmids by in vivo electroporation at 22, 26, 30, and 34 wpi, and group 3 also IL-2 for 14 days after each vaccination. Endpoints evaluated were viral load, Gag(181189)-specific CD8+ T-cell responses in MamuA01+ animals, lymphoproliferative responses, and CD4 T-cell counts. Viremia in all animals dropped below 200 RNA copies/ml during ART. Frequencies of Gag(181189)-specific CD8+ T cells prior to ART were detectable in all three groups (1.27-3.01%) and increased significantly (p < 0.01) postvaccination with maximum responses after the fourth immunization (0.2% versus 3.49-7.15%). Gag(181189)-specific CD8+ T-cell frequencies increased post-ART cessation in all groups and remained at significantly higher levels (p < 0.001) until the end of the study (75 wpi) in both groups of vaccinated animals. Lymphoproliferative responses were detected against Gag in a limited number of animals after vaccination and post-ART. However, plasma RNA viral loads rebounded after ART termination to similar levels in all three groups, but remained below 10(5) copies/ml until the end of the study, which could be a late effect of the triple drug therapy.

Control of viremia and prevention of AIDS following immunotherapy of SIV-infected macaques with peptide-pulsed blood

Effective immunotherapies for HIV are needed. Drug therapies are life-long with significant toxicities. Dendritic-cell based immunotherapy approaches are promising but impractical for widespread use. A simple immunotherapy, reinfusing fresh autologous blood cells exposed to overlapping SIV peptides for 1 hour ex vivo, was assessed for the control of SIV_mac251 replication in 36 pigtail macaques. An initial set of four immunizations was administered under antiretroviral cover and a booster set of three immunizations administered 6 months later. Vaccinated animals were randomized to receive Gag peptides alone or peptides spanning all nine SIV proteins. High-level, SIV-specific CD4 and CD8 T-cell immunity was induced following immunization, both during antiretroviral cover and without. Virus levels were durably ∼10-fold lower for 1 year in immunized animals compared to controls, and a significant delay in AIDS-related mortality resulted. Broader immunity resulted following immunizations with peptides spanning all nine SIV proteins, but the responses to Gag were weaker in comparison to animals only immunized with Gag. No difference in viral outcome occurred in animals immunized with all SIV proteins compared to animals immunized against Gag alone. Peptide-pulsed blood cells are an immunogenic and effective immunotherapy in SIV-infected macaques. Our results suggest Gag alone is an effective antigen for T-cell immunotherapy. Fresh blood cells pulsed with overlapping Gag peptides is proceeding into trials in HIV-infected humans.

Effective immunotherapies for HIV are needed. We assessed a simple technique, reinfusion of fresh blood cells incubating with overlapping SIV peptides (Overlapping Peptide-pulsed Autologous ceLls, OPAL), in 36 randomly allocated SIV-infected monkeys. We analyzed this therapy for the stimulation of immunity, control of virus levels, and prevention of AIDS. The OPAL immunotherapy was safe and stimulated remarkable levels of T-cell immunity. Levels of virus in vaccinated monkeys were 10-fold lower than in controls, and this was durable for over 1 year after the initial vaccinations. The immunotherapy resulted in fewer deaths from AIDS. We conclude this is a promising immunotherapy technique. Trials in HIV-infected humans of OPAL therapy are planned.

Immunogenicity of hybrid DNA vaccines expressing hepatitis B core particles carrying human and simian immunodeficiency virus epitopes in mice and rhesus macaques

An effective HIV vaccine will likely need to induce broad and potent CTL responses. Epitope-based vaccines offer significant potential for inducing multi-specific CTL, but often require conjugation to T helper epitopes or carrier moieties to induce significant responses. We tested hybrid DNA vaccines encoding one or more HIV or SIV CTL epitopes fused to a hepatitis B core antigen (HBcAg) carrier gene as a means to improve the immunogenicity of epitope-based DNA vaccines. Immunization of mice with a HBcAg-HIV epitope DNA vaccine induced CD8(+) T cell responses that significantly exceeded levels induced with DNA encoding either the whole HIV antigen or the epitope alone. In rhesus macaques, a multi-epitope hybrid HBcAg-SIV DNA vaccine induced CTL responses to 13 different epitopes, including 3 epitopes that were previously not detected in SIV-infected macaques. These data demonstrate that immunization with hybrid HBcAg-epitope DNA vaccines is an effective strategy to increase the magnitude and breadth of HIV-specific CTL responses.

Phenotypic and Functional Analysis of Immune CD8+ T Cell Responses Induced by a Single Injection of a HIV DNA Vaccine in Mice

HIV DNA vaccines are potent inducers of cell-mediated immune (CMI) response in mice but elicit poor HIV-specific IFN-gamma-producing T cells in monkeys and humans. In this study, we performed kinetic analyses on splenocytes of BALB/c mice that were immunized by a single injection with a unique DNA vaccine. Using IFN-gamma-ELISPOT and multiparametric FACS analysis, we characterized the induced CMI response. We found that the response was detectable for at least 63 wk. ELISPOT detection of IFN-gamma-producing T cells showed a profile with two waves separated by a long period of minimal response. Multiparametric FACS analysis showed two populations of CD3(+)CD8(+) T cells that were specific for all HIV Ags. These cells had similar robust proliferation abilities and contained granzyme B. However, only a few produced IFN-gamma. Both IFN-gamma-producing and non-IFN-gamma-producing HIV-specific CD8(+) T cells were detected in the early stage (week (W)1 and W2 postimmunization (PI)), in the prolonged intermediate period of minimal response (W4-W26 PI), and in the final late phase of increased response (W30-W63 PI). Our longitudinal characterization showed that both subsets of cells underwent expansion, contraction, and memory generation/maintenance phases throughout the lifespan of the animal. Altogether, these findings bring insight to the heterogeneity of the immune T cell response induced by a single immunization with this DNA and strengthen the concept that used of the IFN-gamma-ELISPOT assay alone may be insufficient to detect critical T cell responses to candidate HIV vaccines.

Preclinical and clinical progress of particle-mediated DNA vaccines for infectious diseases

This review provides an overview of studies employing particle-mediated epidermal delivery (PMED) or the gene gun to administer DNA vaccines for infectious diseases in preclinical studies employing large animal models and in human clinical trials. It reviews the immunogenicity and protective efficacy of PMED DNA vaccines in nonhuman primates and swine and studies that have directly compared the effectiveness of PMED in these large animal models to existing licensed vaccines and intramuscular or intradermal delivery of DNA vaccines with a needle. Various clinical trials employing PMED have been completed and an overview of the immunogenicity, safety, and tolerability of this approach in humans is described. Finally, efforts currently in progress for commercial development of particle-mediated DNA vaccines are discussed.

Effects of monotherapy with (R)-9-(2-phosphonylmethoxypropyl)adenine (PMPA) on the evolution of a primary Simian immunodeficiency virus (SIV) isolate

Determining the impact of antiretroviral therapy on virus evolution could advance the development of improved therapeutics/vaccines against HIV. Toward this goal, we analyzed virus burden, quasispecies complexity, and T cell responses in SIV/DeltaB670-infected rhesus macaques+/-treatment for 7 months with PMPA (2-30 weeks postinfection). Treatment divided the animals into two groups: poor responders (a reduction of < or =1 log) and responders (> or =2 log reduction) in virus burden. Virus evolution in poor responders and untreated controls was characterized by expression of a complex quasispecies that evolved as the disease progressed. This included the universal loss of a viral genotype selected against by in vitro passage in monkey cells and selected for by propagation in human cells. In contrast, a good response to PMPA was characterized by infection with a less complex quasispecies that evolved more slowly. Interestingly, in 2 of the best responders, the human-preferred genotype persisted until the study was discontinued (89 weeks p.i.). Neither virus burden nor the magnitude of the T cell response at 2 weeks postinfection predicted PMPA responsiveness. However, responders expressed a less complex quasispecies than nonresponders prior to treatment. These data suggest a role for intrinsic host factors in treatment responsiveness, and lend support for therapeutic vaccination as an adjunct to effective therapy.