Sustained peptide-specific gamma interferon T-cell response in rhesus macaques immunized with human immunodeficiency virus gag DNA vaccines

Functional profiling of Covid 19 vaccine candidate by flow virometry

Vaccine development is a complex process, starting with selection of a promising immunogen in the discovery phase, followed by process development in the preclinical phase, and later by clinical trials in tandem with process improvements and scale up. A large suite of analytical techniques is required to gain understanding of the vaccine candidate so that a relevant immunogen is selected and subsequently manufactured consistently throughout the lifespan of the product. For viral vaccines, successful immunogen production is contingent on its maintained antigenicity and/or infectivity, as well as the ability to characterize these qualities within the context of the process, formulation, and clinical performance. In this report we show the utility of flow virometry during preclinical development of a Covid 19 vaccine candidate based on SARS-CoV-2 spike (S) protein expressed on vesicular stomatitis virus (VSV). Using a panel of monoclonal antibodies, we were able to detect the S protein on the surface of the recombinant VSV virus, monitor the expression levels, detect differences in the antigen based on S protein sequence and after virus inactivation, and monitor S protein stability. Collectively, flow virometry provided important data that helped to guide preclinical development of this vaccine candidate.

Validation of an IFN-gamma ELISpot assay to measure cellular immune responses against viral antigens in non-human primates

Adeno-Associated Virus (AAV)-based gene therapy vectors are in development for many inherited human disorders. In nonclinical studies, cellular immune responses mediated by cytotoxic T cells may target vector-transduced cells, which could impact safety and efficacy. Here, we describe the bioanalytical validation of an interferon-gamma (IFN-γ)-based Enzyme-Linked Immunospot (ELISpot) assay for measuring T cell responses against viral antigens in cynomolgus monkeys. Since ELISpots performed with antigen-derived peptides offer a universal assay format, method performance characteristics were validated using widely available peripheral blood mononuclear cells (PBMCs) responsive to cytomegalovirus peptides. The limit of detection and confirmatory cut point were established using statistical methods; precision, specificity, and linearity were confirmed. Monkey PBMCs from an AAV5 gene therapy study were then analyzed, using peptide pools spanning the vector capsid and transgene product. AAV5-specific T cell responses were detected only in 2 of 18 monkeys at Day 28, but not at Day 13 and 56 after vector administration, with no correlation to liver enzyme elevations or transgene expression levels. No transgene product-specific T cell responses occurred. In conclusion, while viral peptide-specific IFN-γ ELISpots can be successfully validated for monkey PBMCs, monitoring peripheral T cell responses in non-clinical AAV5 gene therapy studies was of limited value to interpret safety or efficacy.

Evaluation of candidate vaccine approaches for MERS-CoV

The emergence of Middle East respiratory syndrome coronavirus (MERS-CoV) as a cause of severe respiratory disease highlights the need for effective approaches to CoV vaccine development. Efforts focused solely on the receptor-binding domain (RBD) of the viral Spike (S) glycoprotein may not optimize neutralizing antibody (NAb) responses. Here we show that immunogens based on full-length S DNA and S1 subunit protein elicit robust serum-neutralizing activity against several MERS-CoV strains in mice and non-human primates. Serological analysis and isolation of murine monoclonal antibodies revealed that immunization elicits NAbs to RBD and, non-RBD portions of S1 and S2 subunit. Multiple neutralization mechanisms were demonstrated by solving the atomic structure of a NAb-RBD complex, through sequencing of neutralization escape viruses and by constructing MERS-CoV S variants for serological assays. Immunization of rhesus macaques confers protection against MERS-CoV-induced radiographic pneumonia, as assessed using computerized tomography, supporting this strategy as a promising approach for MERS-CoV vaccine development.

Unmet need exists for a vaccine against Middle East respiratory syndrome coronavirus (MERS-CoV). Here the authors report the establishment and evaluation, in mice and primates, of a series of MERS-CoV immunogens and show that they can serve as promising leads for vaccine development.

Block copolymers have differing adjuvant effects on the primary immune response elicited by genetic immunization and on further induced allergy

Block copolymers were recently used to promote gene delivery in various tissues. Using a plasmid encoding a food allergen, bovine beta-lactoglobulin (BLG), we studied the effects of block copolymers on gene expression levels and primary immune response and on further induced allergy. Block copolymers (i.e., Tetronic 304, 908, and 1107) and various quantities of DNA were injected into the tibialis muscles of BALB/c mice. The BLG levels in injected muscle and the BLG-specific induced immune response were analyzed after injection. DNA-immunized mice were further experimentally sensitized with BLG, and the effects of block copolymer and DNA doses on allergic sensitization and elicitation were compared. Tetronic 304 induced a 12-fold increase in BLG production, while Tetronic 1107 increased the duration of BLG expression. Different Th1 primary specific immune responses were observed, either strong humoral and cellular (304), only cellular (1107), or weak cellular and humoral (908) responses. After BLG sensitization, increased BLG-specific IgG2a production was observed in all groups of mice independently of the presence and nature of the block copolymer. Increased BLG-specific IgG1 production was also detected after sensitization, except with Tetronic 1107. Compared with naked DNA, Tetronic 304 was the only block polymer that decreased BLG-specific IgE concentrations. However, after allergen challenge, Tetronic 1107 was the only block copolymer to reduce eosinophils and Th2 cytokines in bronchoalveolar lavage (BAL) fluid. Tetronic 304 amplified local inflammation. Each block copolymer elicited a different immune response, although always Th1 specific, in BALB/c mice.

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.

Comparison of replication-competent, first generation, and helper-dependent adenoviral vaccines

All studies using human serotype 5 Adenovirus (Ad) vectors must address two major obstacles: safety and the presence of pre-existing neutralizing antibodies. Helper-Dependent (HD) Ads have been proposed as alternative vectors for gene therapy and vaccine development because they have an improved safety profile. To evaluate the potential of HD-Ad vaccines, we compared replication-competent (RC), first-generation (FG) and HD vectors for their ability to induce immune responses in mice. We show that RC-Ad5 and HD-Ad5 vectors generate stronger immune responses than FG-Ad5 vectors. HD-Ad5 vectors gave lower side effects than RC or FG-Ad, producing lower levels of tissue damage and anti-Ad T cell responses. Also, HD vectors have the benefit of being packaged by all subgroup C serotype helper viruses. We found that HD serotypes 1, 2, 5, and 6 induce anti-HIV responses equivalently. By using these HD serotypes in heterologous succession we showed that HD vectors can be used to significantly boost anti-HIV immune responses in mice and in FG-Ad5-immune macaques. Since HD vectors have been show to have an increased safety profile, do not possess any Ad genes, can be packaged by multiple serotype helper viruses, and elicit strong anti-HIV immune responses, they warrant further investigation as alternatives to FG vectors as gene-based vaccines.

Vesicular stomatitis virus-based vaccines protect nonhuman primates against aerosol challenge with Ebola and Marburg viruses

Considerable progress has been made over the last decade in developing candidate preventive vaccines that can protect nonhuman primates against Ebola and Marburg viruses. A vaccine based on recombinant vesicular stomatitis virus (VSV) seems to be particularly robust as it can also confer protection when administered as a postexposure treatment. While filoviruses are not thought to be transmitted by aerosol in nature the inhalation route is among the most likely portals of entry in the setting of a bioterrorist event. At present, all candidate filoviral vaccines have been evaluated against parenteral challenges but none have been tested against an aerosol exposure. Here, we evaluated our recombinant VSV-based Zaire ebolavirus (ZEBOV) and Marburg virus (MARV) vaccines against aerosol challenge in cynomolgus macaques. All monkeys vaccinated with a VSV vector expressing the glycoprotein of ZEBOV were completely protected against an aerosol exposure of ZEBOV. Likewise, all monkeys vaccinated with a VSV vector expressing the glycoprotein of MARV were completely protected against an aerosol exposure of MARV. All control animals challenged by the aerosol route with either ZEBOV or MARV succumbed. Interestingly, disease in control animals appeared to progress slower than previously seen in macaques exposed to comparable doses by intramuscular injection.

Physical characterization and in vivo evaluation of poloxamer-based DNA vaccine formulations

BACKGROUND

Plasmid DNA (pDNA) vaccines have generated significant interest for the prevention or treatment of infectious diseases. Broader applications may benefit from the identification of safe and potent vaccine adjuvants. This report describes the development of a novel polymer-based formulation to enhance the immunogenicity of pDNA-based vaccines.

METHODS

Plasmid DNA was formulated with a nonionic block copolymer, poloxamer CRL1005, and the cationic surfactant benzalkonium chloride (BAK) to produce a thermodynamically stable, self-assembling system. The influence of parameters such as polymer concentration and BAK composition on the immune responses was evaluated in mice vaccinated with pDNA encoding influenza nucleoprotein.

RESULTS

At concentrations of 7.5 mg/ml CRL1005, 0.3 mM BAK and 5 mg/ml pDNA, CRL1005/BAK/pDNA particles had a mean diameter of 261 +/- 0.2 nm and a surface charge of - 11.6 +/- 0.9 mV. The negative surface charge and atomic force microscopy images suggested that pDNA binds to BAK adsorbed to the surface of poloxamer particles. The CRL1005/BAK/pDNA formulation significantly enhanced antigen-specific cellular and humoral immune responses, and increased transgene levels in muscle and serum. The complexity of the formulation was reduced by replacing the commercial BAK, which is a mixture of four alkyl chains, with a C14 BAK homolog. The substitution yielded an analytically preferable formulation with equivalent physical characteristics and immunogenicity.

CONCLUSIONS

The results suggest that the CRL1005/BAK/pDNA formulation may enhance immunogenicity by improving the delivery of pDNA-based vaccines. This formulation is currently being evaluated for the prevention of CMV-associated disease in a phase 2 clinical trial.

Identification and characterization of IS1 transposition in plasmid amplification mutants of E. coli clones producing DNA vaccines

Merck Research Laboratories has developed a highly productive Escherichia coli fermentation process to produce plasmid DNA for use as vaccines. The process consists of a fed-batch fermentation in a chemically defined medium. Initiation of the feed stream precedes a growth-limited phase in which plasmid DNA is amplified. The fermentation is only maximally productive for a small fraction of E. coli transformants designated as high-producers, while the predominant low-producer population does not amplify plasmid DNA. In experiments undertaken to probe this phenomenon, transposition of the 768-bp E. coli insertion sequence IS1 into an HIV DNA vaccine vector was observed in several low-producer clones. IS1 was found to insert in or near the neomycin resistance gene in nearly a dozen unique sites from within a single population of plasmid molecules. The fraction of IS1-containing plasmids within several clones was determined by quantitative polymerase chain reaction and was found to increase with increasing cultivation time in the chemically defined medium. Because transposition into an antibiotic-resistance gene is unlikely to affect plasmid amplification, the genomes of high- and low-producers of three different HIV DNA vaccine vectors were subsequently profiled by restriction fragment length polymorphism analysis. In all three cases, IS1 insertional mutations were found in the genomes of the predominant low-producers, while the genomes of the high-producers were indistinguishable from untransformed cells. The insertions reside on similarly sized fragments for two of the low-producer clones, and the fragment size is smaller for the third clone. The third clone also produces much less plasmid DNA than a typical low-producer. The results suggest the presence of an IS1 insertional mutation that affects plasmid replication and amplification, possibly in a position-dependent manner.

Group M-based HIV-1 Gag peptides are frequently targeted by T cells in chronically infected US and Zambian patients

BACKGROUND

The enormous sequence diversity of HIV-1 has been a major obstacle in the development of a globally useful vaccine for AIDS. The consensus and ancestral sequence-based immunogens minimize the genetic distance between contemporary isolates and vaccine strains. Hence these sequences may be promising candidates for HIV vaccines or serve as a universal reagent set for evaluating Gag-specific responses.

METHODS

In this study, we measured the T-cell reactivity to consensus (subtype A, B, C and group M), ancestral (group M and subtype B) and HXB2 Gag peptides (15-mers overlapping by 11) in HIV-1-infected subjects from two reference populations. We evaluated the Gag-specific T-cell responses in 43 chronically infected US (subtype B) and 13 Zambian (subtype C) subjects using an interferon-gamma enzyme-linked immunosorbent spot assay.

RESULTS

Our findings demonstrate a broad cross-reactivity of nearly 70% among all the seven Gag immunogens evaluated. Consensus M sequences elicited similar levels of responses as did the consensus B, ancestral subtype B and HXB2 peptides in subtype B-infected US patients. In subtype C-infected Zambian subjects, responses of similar breadth and magnitude were elicited by consensus C, consensus M and ancestral M peptides.

CONCLUSION

Our data demonstrate that peptide pools based on consensus or ancestral M-based sequences can be used to evaluate Gag-specific responses elicited by subtype B or subtype C-based immunogens.

A T-cell HCV vaccine eliciting effective immunity against heterologous virus challenge in chimpanzees

Three percent of the world's population is chronically infected with the hepatitis C virus (HCV) and at risk of developing liver cancer. Effective cellular immune responses are deemed essential for spontaneous resolution of acute hepatitis C and long-term protection. Here we describe a new T-cell HCV genetic vaccine capable of protecting chimpanzees from acute hepatitis induced by challenge with heterologous virus. Suppression of acute viremia in vaccinated chimpanzees occurred as a result of massive expansion of peripheral and intrahepatic HCV-specific CD8(+) T lymphocytes that cross-reacted with vaccine and virus epitopes. These findings show that it is possible to elicit effective immunity against heterologous HCV strains by stimulating only the cellular arm of the immune system, and suggest a path for new immunotherapy against highly variable human pathogens like HCV, HIV or malaria, which can evade humoral responses.

Preclinical evaluation of cellular immune responses elicited by a polyvalent DNA prime/protein boost HIV-1 vaccine

While DNA vaccines have been shown to prime cellular immune responses, levels are often low in nonhuman primates or humans. Hence, efforts have been directed toward boosting responses by combining DNA with different vaccination modalities. To this end, a polyvalent DNA prime/protein boost vaccine, consisting of codon optimized HIV-1 env (A, B, C, E) and gag (C) and homologous gp120 proteins in QS-21, was evaluated in rhesus macaques and BALB/c mice. Humoral and cellular responses, detected following DNA immunization, were increased following protein boost in macaques and mice. In dissecting cellular immune responses in mice, protein-enhanced responses were found to be mediated by CD4+ and CD8+ T cells with a Th1 cytokine bias. Our study reveals that, in addition to augmenting humoral responses, protein boosting of DNA-primed animals augments cellular immune responses mediated by CD8+ CTL, CD4+ T-helper cells and Th1 cytokines; thus, offering much promise in controlling HIV-1 in vaccinees.

Characterization and biological evaluation of a microparticle adjuvant formulation for plasmid DNA vaccines

We describe the physiochemical characterization and immunological evaluation of plasmid DNA vaccine formulations containing a nonionic triblock copolymer adjuvant (CRL1005) in the presence and absence of a cationic surfactant, benzalkonium chloride (BAK). CRL1005 forms particles of 1-10 microns upon warming above its phase-transition temperature (approximately 6-8 degrees C) and the physical properties of the particles are altered by BAK. DNA/CRL1005 vaccines formulated with and without BAK were evaluated in rhesus macaques to determine the effect of CRL1005 and BAK on the ability of plasmid DNA to induce a cellular immune response. Immunogenicity results indicate that the addition of CRL1005 to human immunodeficiency virus-1 gag plasmid DNA formulated in phosphate-buffered saline leads to an enhancement in the gag-specific cellular immune response. Moreover, the addition of BAK to human immunodeficiency virus-1 gag plasmid DNA/CRL1005 formulations produces an additional enhancement in gag-specific cellular immunity. In vitro characterization studies of DNA/CRL1005 formulations indicate no detectable binding of DNA to CRL1005 particles in the absence of BAK, suggesting that the enhancement of cellular immunity induced by DNA/CRL1005 formulations is not due to enhanced DNA delivery. In the presence of BAK, however, results indicate that BAK binds to CRL1005 particles, producing cationic microparticles that bind DNA through electrostatic interactions. If BAK is present at the phase-transition temperature, it reduces the particle size from approximately 2 microns to approximately 300 nm, presumably by binding to hydrophobic surfaces during particle formation. Zeta potential measurements indicate that the surface charge of CRL1005-BAK particles changes from positive to negative upon DNA binding, and DNA bound to the surface of CRL1005-BAK particles was visualized by fluorescence microscopy. These results indicate that the addition of BAK to DNA/CRL1005 formulations leads to the formation of approximately 300 nm CRL1005-BAK-DNA particles that enhance the cellular immune response in rhesus monkeys.

Plasmid vaccines and therapeutics: from design to applications

In the late 1980s, Vical and collaborators discovered that the injection into tissues of unformulated plasmid encoding various proteins resulted in the uptake of the plasmid by cells and expression of the encoded proteins. After this discovery, a period of technological improvements in plasmid delivery and expression and in pharmaceutical and manufacturing development was quickly followed by a plethora of human clinical trials testing the ability of injected plasmid to provide therapeutic benefits. In this chapter, we summarize in detail the technologies used in the most recent company-sponsored clinical trials and discuss the potential for future improvements in plasmid design, manufacturing, delivery, formulation and administration. A generic path for the clinical development of plasmid-based products is outlined and then exemplified using a case study on the development of a plasmid vaccine from concept to clinical trial.

Efficient priming of simian/human immunodeficiency virus (SHIV)-specific T-cell responses with DNA encoding hybrid SHIV/hepatitis B surface antigen particles

Recent efforts to design an human immunodeficiency virus type 1 (HIV-1) vaccine candidate have focused on means of eliciting anti-viral T-cell responses. We tried to improve the immunogenicity of DNA vaccines by designing hybrid DNA constructs encoding hepatitis B surface antigen (HBsAg) fused to antigenic domains of simian/human immunodeficiency virus (SHIV 89.6P). Immunisation with hybrid DNA induced both effector and long-lasting precursor T-cells. Following boosting with a recombinant modified vaccinia Ankara (rMVA) producing full-length SIV and HIV antigens, it appeared that priming with hybrid DNA had increased virus-specific T-cell responses in terms of both the number of virus-specific IFN-gamma-secreting T-cells and virus-specific lymphoproliferation. After intrarectal challenge with SHIV 89.6P, immunised animals demonstrated early control of SHIV 89.6P replication and stable CD4+ T-cell counts.

Flow cytometric analysis of vaccine responses: how many colors are enough?

The past 5 years have seen an explosion in technological advances related to measuring immunogenicity. Specifically, two distinct areas of development have led to considerably more detailed analysis of T cell responses: first, the ability to measure over a dozen distinct antigens expressed by individual cells simultaneously (12-color flow cytometry); and second, a host of assays that rapidly and viably identify antigen-specific T cells. Together, these technologies reveal the complex heterogeneity of an immune response generated during infection or after vaccine challenge. The next 5 years will see the determination of which underlying variables will be most important to quantifying vaccine efficacy. In this manuscript, we discuss these technologies, with a focus on assisting in the design and implementation of immunogenicity trials for future vaccine efforts.

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.

Enhanced immunogenicity of DNA fusion vaccine encoding secreted hepatitis B surface antigen and chemokine RANTES

To increase the potency of DNA vaccines, we constructed genetic fusion vaccines encoding antigen, secretion signal, and/or chemokine RANTES. The DNA vaccines encoding secreted hepatitis B surface antigen (HBsAg) were constructed by inserting HBsAg gene into an expression vector with an endoplasmic reticulum (ER)-targeting secretory signal sequence. The plasmid encoding secretory HBsAg (pER/HBs) was fused to cDNA of RANTES, generating pER/HBs/R. For comparison, HBsAg genes were cloned into pVAX1 vector with no signal sequence (pHBs), and further linked to the N-terminus of RANTES (pHBs/R). Immunofluorescence study showed the cytoplasmic localization of HBsAg protein expressed from pHBs and pHBs/R, but not from pER/HBs and pER/HBs/R at 48 h after transfection. In mice, RANTES-fused DNA vaccines more effectively elicited the levels of HBsAg-specific IgG antibodies than pHBs. All the DNA vaccines induced higher levels of IgG(2a) rather than IgG(1) antibodies. Of RANTES-fused vaccines, pER/HBs/R encoding the secreted fusion protein revealed much higher humoral and CD8(+) T cell-stimulating responses compared to pHBs/R. These results suggest that the immunogenicity of DNA vaccines could be enhanced by genetic fusion to a secretory signal peptide sequence and RANTES.

Detection of antigen-specific T cell interferon γ expression by ELISPOT and cytokine flow cytometry assays in rhesus macaques

Both enzyme-linked immunospot (ELISPOT) and cytokine flow cytometry (CFC) methods have been developed for the detection of low-frequency, antigen-specific, cytokine-producing T cells following short-term in vitro stimulation. Peptide-based ELISPOT and CFC assays were compared for the quantitative detection of interferon gamma-positive (IFN-gamma+) antigen-specific T cells in rhesus macaques. Ten normal and nine simian immunodeficiency virus (SIV)-infected monkeys were tested for the detection of IFN-gamma+ memory T cells specific for p27(gag) peptides of SIV with both assays. The CFC assay detected more IFN-gamma+ cells than the ELISPOT assay and this assay was more informative in identifying the phenotype of responding cells. Cryopreserved cells were as functional as fresh cells in heparinized blood samples and compared to EDTA, heparin was the better anticoagulant for yielding IFN-gamma+ cells. Using overlapping peptide pools, 20-mer peptides were more efficient in stimulating CD4+ T cells than 15-mer peptides in the ELISPOT assay, but there was no significant difference between 20- and 15-mer peptides in detecting CD4 or CD8+, IFN-gamma+ T cells in the CFC assay.

Use of interleukin 15 to enhance interferon-gamma production by antigen-specific stimulated lymphocytes from rhesus macaques

The enzyme-linked immune spot (ELISPOT) assay is receiving increased attention as a means for quantifying antigen-specific CD8 T-cell responses in rhesus macaques. Further improving the sensitivity of this assay could aid in the evaluation of vaccine candidates and/or immune therapeutic candidates. Interleukin (IL)-15 has been demonstrated to stimulate expansion of human immunodeficiency virus (HIV)-specific cytotoxic T lymphocytes (CTL) and to regulate homeostatic proliferation of CD8+ memory cells. We evaluated the in vitro effect of IL-15 to increase the detection of interferon-gamma (IFN-gamma) production by antigen-specific stimulated lymphocytes from a group of rhesus macaques exposed to simian-human immunodeficiency virus (SHIV) and a second group infected with SIVmac251, before and after antiretroviral treatment (ART). Results from these studies demonstrate that the presence of IL-15 during stimulation in a peptide-based ELISPOT assay greatly enhanced IFN-gamma production in both SHIV and simian immunodeficiency virus (SIV)-infected macaques. IFN-gamma production was mainly mediated by CD8 lymphocytes. The optimal concentrations of IL-15 that give enhancement of IFN-gamma production to specific antigen, without a significant increase in the spontaneous IFN-gamma release, ranged from 0.5 to 2.5 ng/ml. The mean number of IFN-gamma spots was increased 3.1- to 3.6-fold in response to SIV gag or HIV env peptide pools, respectively, in peripheral blood mononuclear cells (PBMC) from SHIV-infected macaques. Similarly, in SIV-infected macaques, IL-15 increased the mean number of IFN-gamma spots 2.7-fold in response to both SIV gag and env peptide pools. In samples obtained after ART in the same macaques, the increase factor was 2.5 for SIV gag and 1.8 for the env peptide pools. Thus, the sensitivity of the ELISPOT assay can be enhanced by addition of IL-15. This modified assay will be useful for detection of low frequencies of IFN-gamma producing cells in rhesus macaques.

Vaccine-induced immunity in baboons by using DNA and replication-incompetent adenovirus type 5 vectors expressing a human immunodeficiency virus type 1 gag gene

The cellular immunogenicity of formulated plasmid DNA and replication-defective human adenovirus serotype 5 (Ad5) vaccine vectors expressing a codon-optimized human immunodeficiency virus type 1 gag gene was examined in baboons. The Ad5 vaccine was capable of inducing consistently strong, long-lived CD8(+)-biased T-cell responses and in vitro cytotoxic activities. The DNA vaccine-elicited immune responses were weaker than those elicited by the Ad5 vaccine and highly variable; formulation with chemical adjuvants led to moderate increases in the levels of Gag-specific T cells. Increasing the DNA-primed responses with booster doses of either Ad5 or modified vaccinia virus Ankara vaccines suggests a difference in the relative levels of cytotoxic and helper responses. The implications of these results are discussed.

Twenty years of therapy for HIV-1 infection

Antiretroviral therapy, where available, has transformed HIV-1 disease into a treatable and somewhat chronic infection. This article summarizes the accomplishments thus far and what lies ahead in our struggle to improve the treatment of, and possibly eliminate, HIV-1 infection.

Comparative immunogenicity in rhesus monkeys of DNA plasmid, recombinant vaccinia virus, and replication-defective adenovirus vectors expressing a human immunodeficiency virus type 1 gag gene

Cellular immune responses, particularly those associated with CD3(+) CD8(+) cytotoxic T lymphocytes (CTL), play a primary role in controlling viral infection, including persistent infection with human immunodeficiency virus type 1 (HIV-1). Accordingly, recent HIV-1 vaccine research efforts have focused on establishing the optimal means of eliciting such antiviral CTL immune responses. We evaluated several DNA vaccine formulations, a modified vaccinia virus Ankara vector, and a replication-defective adenovirus serotype 5 (Ad5) vector, each expressing the same codon-optimized HIV-1 gag gene for immunogenicity in rhesus monkeys. The DNA vaccines were formulated with and without one of two chemical adjuvants (aluminum phosphate and CRL1005). The Ad5-gag vector was the most effective in eliciting anti-Gag CTL. The vaccine produced both CD4(+) and CD8(+) T-cell responses, with the latter consistently being the dominant component. To determine the effect of existing antiadenovirus immunity on Ad5-gag-induced immune responses, monkeys were exposed to adenovirus subtype 5 that did not encode antigen prior to immunization with Ad5-gag. The resulting anti-Gag T-cell responses were attenuated but not abolished. Regimens that involved priming with different DNA vaccine formulations followed by boosting with the adenovirus vector were also compared. Of the formulations tested, the DNA-CRL1005 vaccine primed T-cell responses most effectively and provided the best overall immune responses after boosting with Ad5-gag. These results are suggestive of an immunization strategy for humans that are centered on use of the adenovirus vector and in which existing adenovirus immunity may be overcome by combined immunization with adjuvanted DNA and adenovirus vector boosting.