DNA vaccines against human immunodeficiency virus type 1

Anti-regulatory T cell vaccines in immunotherapy: focusing on FoxP3 as target

Anti- tumor vaccination elicits imperfect immune responses against tumor cells; that is related to the presence of suppressive obstacles in the tumor microenvironment. The main members of suppressive milieu of tumor are heteroogenous groups of immune cells in which regulatory T cell is a substantial component. Tregs express different immunomodulatory molecules such as FoxP3. Transcription factor, FoxP3, is a specific intracellular marker of Treg and crucial for Treg development. Therefore it is an attractive target for cancer treatment. This article reviews some recent anti-Treg vaccine focusing on FoxP3 to ameliorate anti-tumor immune responses. Among them, fusion vaccine of FoxP3-Fc(IgG) recombinant DNA vaccine and its accordant protein vaccine represents effective results.

Inducing Humoral Immune Responses Against Regulatory T Cells by Foxp3-Fc(IgG) Fusion Protein

The existence of a developed network of suppressory factors and cells against an immune response in different cancers has been proven; regulatory T cells are a typical issue. Therefore their depletion, elimination, or suppression has been assessed in different research studies that were not entirely successful. By applying an improved vaccine against regulatory T cells, we have evaluated the B cell response elicited by the vaccine in an experimental design. A previously described DNA vaccine and recombinant protein of Foxp3-Fc fusion were produced and used in the vaccination regimen. DNA construct and respective protein were injected into C57BL/6 mice. After 2 weeks, serum levels of IgG antibody and its subtypes against Foxp3 were investigated by ELISA. To produce recombinant Foxp3 for ELISA antigen coating, pET24a-Foxp3 vector was transformed into Escherichia coli strain BL21 as host cells. Afterward, protein was expressed and then purified using Ni-NTA agarose. SDS-PAGE and Western blot analysis were carried out to confirm protein expression. The expression analysis of Foxp3 was confirmed by SDS-PAGE followed by Western blot analysis. FOXP3-Fc DNA vaccine/fusion protein vaccination regimen could induce T helper-dependent humoral responses. Due to the effectiveness of Foxp3-Fc(IgG) in inducing humoral responses, it would be expected to be useful in developing vaccines in tumor therapies for the removal of regulatory T cells as a strategy for increasing the efficiency of other means of immunotherapy.

HIV/AIDS vaccines for Africa: scientific opportunities, challenges and strategies

More than decades have already elapsed since human immunodeficiency virus (HIV) was identified as the causative agent of acquired immunodeficiency syndrome (AIDS). The HIV has since spread to all parts of the world with devastating effects. In sub-saharan Africa, the HIV/AIDS epidemic has reached unprecedented proportions. Safe, effective and affordable HIV/AIDS vaccines for Africans are therefore urgently needed to contain this public health problem. Although, there are challenges, there are also scientific opportunities and strategies that can be exploited in the development of HIV/AIDS vaccines for Africa. The recent RV144 Phase III trial in Thailand has demonstrated that it is possible to develop a vaccine that can potentially elicit modest protective immunity against HIV infection. The main objective of this review is to outline the key scientific opportunities, challenges and strategies in HIV/AIDS vaccine development in Africa.

Safety and tolerability of conserved region vaccines vectored by plasmid DNA, simian adenovirus and modified vaccinia virus ankara administered to human immunodeficiency virus type 1-uninfected adults in a randomized, single-blind phase I trial

Trial Design

HIV-1 vaccine development has advanced slowly due to viral antigenic diversity, poor immunogenicity and recently, safety concerns associated with human adenovirus serotype-5 vectors. To tackle HIV-1 variation, we designed a unique T-cell immunogen HIVconsv from functionally conserved regions of the HIV-1 proteome, which were presented to the immune system using a heterologous prime-boost combination of plasmid DNA, a non-replicating simian (chimpanzee) adenovirus ChAdV-63 and a non-replicating poxvirus, modified vaccinia virus Ankara. A block-randomized, single-blind, placebo-controlled phase I trial HIV-CORE 002 administered for the first time candidate HIV-1- vaccines or placebo to 32 healthy HIV-1/2-uninfected adults in Oxford, UK and elicited high frequencies of HIV-1-specific T cells capable of inhibiting HIV-1 replication in vitro. Here, detail safety and tolerability of these vaccines are reported.

Methods

Local and systemic reactogenicity data were collected using structured interviews and study-specific diary cards. Data on all other adverse events were collected using open questions. Serum neutralizing antibody titres to ChAdV-63 were determined before and after vaccination.

Results

Two volunteers withdrew for vaccine-unrelated reasons. No vaccine-related serious adverse events or reactions occurred during 190 person-months of follow-up. Local and systemic events after vaccination occurred in 27/32 individuals and most were mild (severity grade 1) and predominantly transient (<48 hours). Myalgia and flu-like symptoms were more strongly associated with MVA than ChAdV63 or DNA vectors and more common in vaccine recipients than in placebo. There were no intercurrent HIV-1 infections during follow-up. 2/24 volunteers had low ChAdV-63-neutralizing titres at baseline and 7 increased their titres to over 200 with a median (range) of 633 (231-1533) post-vaccination, which is of no safety concern.

Conclusions

These data demonstrate safety and good tolerability of the pSG2.HIVconsv DNA, ChAdV63.HIVconsv and MVA.HIVconsv vaccines and together with their high immunogenicity support their further development towards efficacy studies.

Trial Registration

ClinicalTrials.gov NCT01151319

Clustered epitopes within a new poly-epitopic HIV-1 DNA vaccine shows immunogenicity in BALB/c mice

Despite a huge number of studies towards vaccine development against human immunodeficiency virus-1, no effective vaccine has been approved yet. Thus, new vaccines should be provided with new formulations. Herein, a new DNA vaccine candidate encoding conserved and immunogenic epitopes from HIV-1 antigens of tat, pol, gag and env is designed and constructed. After bioinformatics analyses to find the best epitopes and their tandem, nucleotide sequence corresponding to the designed multiepitope was synthesized and cloned into pcDNA3.1+ vector. Expression of pcDNA3.1-tat/pol/gag/env plasmid was evaluated in HEK293T cells by RT-PCR and western-blotting. Seven groups of BALB/c mice were intramuscularly immunized three times either with 50, 100, 200 µg of plasmid in 2-week intervals or with similar doses of insert-free plasmid. Two weeks after the last injection, proliferation of T cells and secretion of IL4 and IFN-γ cytokines were evaluated using Brdu and ELISA methods, respectively. Results showed the proper expression of the plasmid in protein and mRNA levels. Moreover, the designed multiepitope plasmid was capable of induction of both proliferation responses as well as IFN-γ and IL-4 cytokine production in a considerable level compared to the control groups. Overall, our primary data warranted further detailed studies on the potency of this vaccine.

Conserved immunogens in prime-boost strategies for the next-generation HIV-1 vaccines

INTRODUCTION

Effective vaccines are the best solution for stopping the spread of HIV/AIDS and other infectious diseases. Their development and in-depth understanding of pathogen-host interactions rely on technological advances.

AREAS COVERED

Rational vaccine development can be effectively approached by conceptual separation of, on one hand, design of immunogens from improving their presentation to the immune system and, on the other, induction of antibodies from induction of killer CD8(+) T cells. The biggest roadblock for many vaccines is the pathogens' variability. This is best tackled by focusing both antibodies and T cells on the functionally most conserved regions of proteins common to many variants, including escape mutants. For vectored vaccines, these 'universal' subunit immunogens are most efficiently delivered using heterologous prime-boost regimens, which can be further optimised by adjuvantation and route of delivery.

EXPERT OPINION

Development of vaccines against human diseases has many features in common. Acceleration of vaccine discovery depends on basic research and new technologies. Novel strategies should be safely, but rapidly tested in humans. While out-of-the-box thinking is important, vaccine success largely depends on incremental advances best achieved through small, systematic, iterative clinical studies. Failures are inevitable, but the end rewards are huge. The future will be exciting.

Immunization with a poly (lactide co-glycolide) encapsulated plasmid DNA expressing antigenic regions of HPV 16 and 18 results in an increase in the precursor frequency of T cells that respond to epitopes from HPV 16, 18, 6 and 11

A phase II trial was conducted in subjects with human papillomavirus (HPV) associated high-grade cervical dysplasia testing the safety and efficacy of a microparticle encapsulated pDNA vaccine. Amolimogene expresses T cell epitopes from E6 and E7 proteins of HPV types 16 and 18. An analysis was performed on a subset of HLA-A2+ subjects to test whether CD8+ T cells specific to HPV 16, 18, 6 and 11 were increased in response to amolimogene immunization. Of the 21 subjects receiving amolimogene, 11 had elevated CD8+ T cell responses to HPV 16 and/or 18 peptides and seven of these also had increases to corresponding HPV 6 and/or 11 peptides. In addition, T cells primed and expanded in vitro with an HPV 18 peptide demonstrated cross-reactivity to the corresponding HPV 11 peptide. These data demonstrate that treatment with amolimogene elicits T cell responses to HPV 16, 18, 6 and 11.

HIV-1 matrix protein p17: a candidate antigen for therapeutic vaccines against AIDS

The success in the development of anti-retroviral therapies (HAART) that contain human immunodeficiency virus type 1 (HIV-1) infection is challenged by the cost of this lifelong therapy and by its toxicity. Immune-based therapeutic strategies that boost the immune response against HIV-1 proteins or protein subunits have been recently proposed to control virus replication in order to provide protection from disease development, reduce virus transmission, and help limit the use of anti-retroviral treatments. HIV-1 matrix protein p17 is a structural protein that is critically involved in most stages of the life cycle of the retrovirus. Besides its well established role in the virus life cycle, increasing evidence suggests that p17 may also be active extracellularly in deregulating biological activities of many different immune cells that are directly or indirectly involved in AIDS pathogenesis. Thus, p17 might represent a promising target for developing a therapeutic vaccine as a contribution to combating AIDS. In this article we review the biological characteristics of HIV-1 matrix protein p17 and we describe why a synthetic peptide representative of the p17 functional epitope may work as a vaccine molecule capable of inducing anti-p17 neutralizing response against p17 derived from divergent HIV-1 strains.

Immune hierarchy among HIV-1 CD8+ T cell epitopes delivered by dendritic cells depends on MHC-I binding irrespective of mode of loading and immunization in HLA-A*0201 mice

Recent human immunodeficiency virus type 1 (HIV-1) vaccination strategies aim at targeting a broad range of cytotoxic T lymphocyte (CTL) epitopes from different HIV-1 proteins by immunization with multiple CTL epitopes simultaneously. However, this may establish an immune hierarchical response, where the immune system responds to only a small number of the epitopes administered. To evaluate the feasibility of such vaccine strategies, we used the human leukocyte antigen (HLA)-A*0201 transgenic (tg) HHD murine in vivo model and immunized with dendritic cells pulsed with seven HIV-1-derived HLA-A*0201 binding CTL epitopes. The seven peptides were simultaneously presented on the same dendritic cell (DC) or on separate DCs before immunization to one or different lymphoid compartments. Data from this study showed that the T-cell response, as measured by cytolytic activity and γ-interferon (IFN-γ)-producing CD8⁺ T cells, mainly focused on two of seven administered epitopes. The magnitude of individual T-cell responses induced by immunization with multiple peptides correlated with their individual immunogenicity that depended on major histocompatibility class I binding and was not influenced by mode of loading or mode of immunization. These findings may have implications for the design of vaccines based on DCs when using multiple epitopes simultaneously.

A prime-boost immunisation regimen using recombinant BCG and Pr55(gag) virus-like particle vaccines based on HIV type 1 subtype C successfully elicits Gag-specific responses in baboons

Mycobacterium bovis BCG is considered an attractive live bacterial vaccine vector. In this study, we investigated the immune response of baboons to a primary vaccination with recombinant BCG (rBCG) constructs expressing the gag gene from a South African HIV-1 subtype C isolate, and a boost with HIV-1 subtype C Pr55(gag) virus-like particles (Gag VLPs). Using an interferon enzyme-linked immunospot assay, we show that although these rBCG induced only a weak or an undetectable HIV-1 Gag-specific response on their own, they efficiently primed for a Gag VLP boost, which strengthened and broadened the immune responses. These responses were predominantly CD8+ T cell-mediated and recognised similar epitopes as those targeted by humans with early HIV-1 subtype C infection. In addition, a Gag-specific humoral response was elicited. These data support the development of HIV-1 vaccines based on rBCG and Pr55(gag) VLPs.

Multimeric soluble CD40 ligand (sCD40L) efficiently enhances HIV specific cellular immune responses during DNA prime and boost with attenuated poxvirus vectors MVA and NYVAC expressing HIV antigens

The attenuated poxvirus vectors MVA and NYVAC are now in clinical trials against HIV/AIDS. Due to the vectors restricted replication capacity in human cells, approaches to enhance their immunogenicity are highly desirable. Here, we have analyzed the ability of a soluble form of hexameric CD40L (sCD40L) to stimulate specific immune responses to HIV antigens when inoculated in mice during priming with DNA and in the booster with MVA or NYVAC, expressing the vectors HIV-1 Env, Gag, Pol and Nef antigens from clade B. Our findings revealed that sCD40L in DNA/poxvirus combination enhanced the magnitude about 2-fold (DNA-B/MVA-B) and 4-fold (DNA-B/NYVAC-B), as well as the breath of the HIV antigen specific cellular immune responses. sCD40L was necessary in both prime and boost inoculations triggering a potent polarization of the Th response towards a Th1 type. In DNA-B/NYVAC-B regime the addition of sCD40L significantly enhanced the humoral immune response against HIV gp160, but not in DNA-B/MVA-B combination. These findings provided evidence for the immunostimulatory benefit of sCD40L when DNA and the poxvirus vectors MVA and NYVAC are used as immunogens.

HIV-1 subtype C Pr55gag virus-like particle vaccine efficiently boosts baboons primed with a matched DNA vaccine

A DNA vaccine expressing human immunodeficiency virus type 1 (HIV-1) southern African subtype C Gag (pTHGag) and a recombinant baculovirus Pr55gag virus-like particle prepared using a subtype C Pr55gag protein (Gag VLP) was tested in a prime-boost inoculation regimen in Chacma baboons. The response of five baboons to Gag peptides in a gamma interferon (IFN-gamma) enzyme-linked immunospot (ELISPOT) assay after three pTHGag immunizations ranged from 100 to 515 spot-forming units (s.f.u.) per 10(6) peripheral blood mononuclear cells (PBMCs), whilst the response of two baboons to the Gag VLP vaccine ranged from 415 to 465 s.f.u. per 10(6) PBMCs. An increase in the Gag-specific response to a range of 775-3583 s.f.u. per 10(6) PBMCs was achieved by boosting with Gag VLPs the five baboons that were primed with pTHGag. No improvement in Gag responses was achieved in this prime-boost inoculation regimen by increasing the number of pTHGag inoculations to six. IFN-gamma responses were mapped to several peptides, some of which have been reported to be targeted by PBMCs from HIV-1 subtype C-infected individuals. Gag VLPs, given as a single-modality regimen, induced a predominantly CD8+ T-cell IFN-gamma response and interleukin-2 was a major cytokine within a mix of predominantly Th1 cytokines produced by a DNA-VLP prime-boost modality. The prime-boost inoculation regimen induced high serum p24 antibody titres in all baboons, which were several fold above that induced by the individual vaccines. Overall, this study demonstrated that these DNA prime/VLP boost vaccine regimens are highly immunogenic in baboons, inducing high-magnitude and broad multifunctional responses, providing support for the development of these products for clinical trials.

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.

Long-term storage of DNA-free RNA for use in vaccine studies

RNA replicons represent potential vaccine delivery vehicles, but are considered too unstable for such use. This study examined the recovery, integrity and function of in vitro transcribed replicon RNA encoding hepatitis C virus (HCV) proteins. To remove residual template DNA, the RNA was digested with TURBO DNase followed by RNeasy DNase set and purified through an RNeasy column. The RNA was freeze-dried in distilled water or trehalose, stored under nitrogen gas for up to 10 months and analyzed at different time points. The recovery of RNA stored at < or = 4 degrees C that was freeze-dried in distilled water varied between 66% to zero of that recovered from RNA freeze-dried in 10% trehalose, a figure that depended on the duration of storage. In contrast, the recovery of the RNA stored in trehalose was consistently high for all time points. After recovery, both RNAs were translationally competent and expressed high levels of proteins after transfection, although the level of expression from the trehalose-stored RNA was consistently higher. Thus the addition of trehalose permitted stable storage of functional RNA at 4 degrees C for up to 10 months and this permits the development of RNA vaccines, even in developing countries where only minimum storage conditions (e.g., 4 degrees C) can be achieved.

Safety and immunogenicity of cytotoxic T-lymphocyte poly-epitope, DNA plasmid (EP HIV-1090) vaccine in healthy, human immunodeficiency virus type 1 (HIV-1)-uninfected adults

We evaluated EP HIV-1090 vaccine, a DNA plasmid encoding 21 cytotoxic T-lymphocyte (CTL) epitopes of human immunodeficiency virus type 1 (HIV-1) and the pan-DR helper T-lymphocyte epitope (PADRE), in a dose escalation, randomized, double-blinded, placebo-controlled Phase 1 trial. Vaccine, at 0.5, 2.0, or 4.0mg doses, or placebo was injected four times over 6 months. Forty-two healthy, HIV-1-uninfected adults were enrolled. Using an interferon-gamma ELISPOT assay, a response to PADRE was detected in one vaccine recipient. Three vaccine recipients raised anti-HIV-1 CD8+ CTL measured by chromium-release assay. The vaccine was safe and well-tolerated, but only weakly immunogenic.

HIV-1 prophylactic vaccine comprised of topical DermaVir prime and protein boost elicits cellular immune responses and controls pathogenic R5 SHIV162P3

Topical DNA vaccination (DermaVir) facilitates antigen presentation to naive T cells. DermaVir immunization in mice, using HIV-1 Env and Gag, elicited cellular immune responses. Boosting with HIV-1 gp120 Env and p41 Gag augmented Th1 cytokine levels. Intramuscular DNA administration was less efficient in priming antigen-specific cytokine production and memory T cells. In rhesus macaques, DermaVir immunization induced Gag- and Env-specific Th1 and Th2 cytokines and generation of memory T cells. Boosting of DermaVir-primed serum antibody levels was noted following gp140(SHIV89.6P)/p27(SIV) immunization. Rectal challenge with pathogenic R5-tropic SHIV162P3 resulted in control of plasma viremia (4/5 animals) that was reflected in jejunum, colon and mesenteric lymph nodes. An inverse correlation was found between Gag- and Env-specific central memory T cell responses on the day of challenge and plasma viremia at set point. Overall, the topical DermaVir/protein vaccination yields central memory T cell responses and facilitates control of pathogenic SHIV infection.

Fusion of antigen to Fas-ligand in a DNA vaccine enhances immunogenicity

DNA vaccines have considerable potential for the prophylaxis and therapy of a range of diseases, but their potential has not been realised largely due to poor immunogenicity. Fas ligand is a pro-apoptotic molecule, able to induce death of Fas expressing cells. We describe the construction of a DNA vaccine encoding a chimeric fusion between Fas ligand and a truncated version of HIV gp120 as a model antigen. The fusion DNA was used as a priming vaccine, along with boosting with recombinant gp120 protein. Priming with fusion protein DNA resulted in a powerful enhancement of immune responses to the protein boost, and, in the presence of aluminum phosphate, to a strong enhancement in T helper 2 type responses. Fas ligand delivered in a separate plasmid also had an adjuvant effect, although it was weaker than that delivered by the fusion protein.

Clinical experience with plasmid DNA- and modified vaccinia virus Ankara-vectored human immunodeficiency virus type 1 clade A vaccine focusing on T-cell induction

Candidate human immunodeficiency virus type 1 (HIV-1) vaccines focusing on T-cell induction, constructed as pTHr.HIVA DNA and modified vaccinia virus Ankara (MVA).HIVA, were delivered in a heterologous prime-boost regimen. The vaccines were tested in several hundred healthy or HIV-1-infected volunteers in Europe and Africa. Whilst larger trials of hundreds of volunteers suggested induction of HIV-1-specific T-cell responses in <15 % of healthy vaccinees, a series of small, rapid trials in 12-24 volunteers at a time with a more in-depth analysis of vaccine-elicited T-cell responses proved to be highly informative and provided more encouraging results. These trials demonstrated that the pTHr.HIVA vaccine alone primed consistently weak and mainly CD4(+), but also CD8(+) T-cell responses, and the MVA.HIVA vaccine delivered a consistent boost to both CD4(+) and CD8(+) T cells, which was particularly strong in HIV-1-infected patients. Thus, whilst the search is on for ways to enhance T-cell priming, MVA is a useful boosting vector for human subunit genetic vaccines.

Immunization of rhesus macaques with a polyvalent DNA prime/protein boost human immunodeficiency virus type 1 vaccine elicits protective antibody response against simian human immunodeficiency virus of R5 phenotype

The immunogenicity of a poylvalent HIV-1 vaccine comprised of Env antigens from primary R5 isolates was evaluated in rhesus macaques. DNA vaccines encoding four Env antigens from multiple HIV-1 subtypes and HIV-1 Gag antigen from a single subtype elicited a persistent level of binding antibodies to gp120 from multiple HIV-1 isolates that were markedly enhanced following boosting with homologous gp120 proteins in QS-21 adjuvant irrespective of the route of DNA immunization. These sera neutralized homologous and, to a lesser degree, heterologous HIV-1 isolates. Four of the six immunized animals were completely protected following rectal challenge with a SHIV encoding Env from HIV-1(Ba-L), whereas the virus load was reduced in the remaining animals compared to naïve controls. Hence priming with DNA encoding Env antigens from multiple HIV-1 clades followed by boosting with homologous Env proteins elicits anti-HIV-1 immune responses capable of protecting macaques against mucosal transmission of R5 tropic SHIV isolate.

Long-term persistence of hepatitis B surface antigen and antibody induced by DNA-mediated immunization results in liver and kidney lesions in mice

DNA-mediated immunization has been recognized as a new approach for prevention and treatment of hepatitis B virus (HBV) infection. However, the side effects of this approach have not been well described. Here we report that DNA-mediated immunization by intramuscular injection of plasmid DNA encoding HBV surface antigen (HBsAg) induced long-term persistence of HBsAg and HBsAg-specific antibody (anti-HBs) in the sera of the immunized BALB/c mice and resulted in liver and kidney lesions. The lesions persisted for 6 months after injection. Lesions were also found in normal mice injected with the sera from immunized mice, and in HBV-transgenic mice injected with anti-HBs antibody, or sera from immunized mice. Furthermore, lesions were accompanied by deposition of circulating immune complex (CIC) of HBsAg and anti-HBs antibody in the damaged organs. These results indicate that long-term persistence of HBsAg and anti-HBs in the immunized mice can result in deposited CIC in liver and kidney, and in development of lesions. The use of DNA containing mammalian replication origins, such as the plasmids used in this study, is not appropriate for human vaccines due to safety concerns relating to persistence of DNA; nevertheless, the safety of DNA-mediated immunization protocols still needs to be carefully evaluated before practical application.

Immunization with SARS-CoV S DNA vaccine generates memory CD4+ and CD8+ T cell immune responses

An effective vaccine for severe acute respiratory syndrome (SARS) will probably require the generation and maintenance of both humoral and cellular immune responses. It has been reported that after natural infection in humans and immunization in animals with SARS-CoV vaccine, antibody is produced and persistent for a long period of time. In the present study, mice were immunized i.m. with SARS-CoV S DNA vaccine, and three different methods (ELISA, ELISPOT and FACS) were used to evaluate the immune responses when the cells were stimulated in vitro with a pool of peptides overlapping entire SARS spike protein. The results show that prime-immunization with SARS-CoV S DNA vaccine can induce both CD4⁺ and CD8⁺ T cell responses. Boosting with the same vaccine enhances CD4⁺ and CD8⁺ T cell responses in both lymphoid and nonlymphoid organs and were persistent over two months. The SARS-CoV S-specific CD4⁺ and CD8⁺ T cells were CD62L⁻, a marker for memory cells, and −30 to 50% of the cells expressed IL-7Rα (CD127), a marker for the capacity of effector cells to develop into memory cells. In addition, immunization with the DNA vaccine elicited high levels of antibody production. Taken together, these data demonstrate that immunization with SARS-CoV S DNA vaccine can generate antigen-specific humoral and cellular immune responses that may contribute to long-term protection.

Antigen-specific therapies in multiple sclerosis: going beyond proteins and peptides

Multiple sclerosis (MS) is a complex immune-mediated disease resulting largely from an autoimmune attack against components of central nervous system myelin, including several proteins and lipids. Knowledge about the details of this anomalous immune response has come mostly from studies in the animal model experimental autoimmune encephalomyelitis (EAE). In this model, it has been possible to prevent and effectively treat established disease through several antigen-specific therapeutic strategies, which have included administration of whole myelin or myelin proteins by various routes, random copolymers consisting of the main major histocompatability complex (MHC) and T-cell receptor (TCR) contact amino acid residues, altered peptide ligands of dominant myelin epitopes in which one or more residues are selectively substituted, and lately DNA vaccination encoding self-myelin antigens. However, there have been difficulties in making successful transitions from animal models to human clinical trials, due either to lack of efficacy or unforeseen complications. Despite these problems, antigen-specific therapies have retained their attraction for clinicians and scientists alike, and hopefully the upcoming generation of agents--including altered peptide ligands and DNA vaccines--will benefit from the increasing knowledge about this disease and surmount existing difficulties to make an impact in the treatment of multiple sclerosis.

Multimeric soluble CD40 ligand and GITR ligand as adjuvants for human immunodeficiency virus DNA vaccines

For use in humans, human immunodeficiency virus (HIV) DNA vaccines may need to include immunostimulatory adjuvant molecules. CD40 ligand (CD40L), a member of the tumor necrosis factor (TNF) superfamily (TNFSF), is one candidate adjuvant, but it has been difficult to use because it is normally expressed as a trimeric membrane molecule. Soluble trimeric forms of CD40L have been produced, but in vitro data indicate that multimeric, many-trimer forms of soluble CD40L are more active. This multimerization requirement was evaluated in mice using plasmids that encoded either 1-trimer, 2-trimer, or 4-trimer soluble forms of CD40L. Fusion with the body of Acrp30 was used to produce the 2-trimer form, and fusion with the body of surfactant protein D was used to produce the 4-trimer form. Using plasmids for secreted HIV-1 antigens Gag and Env, soluble CD40L was active as an adjuvant in direct proportion to the valence of the trimers (1 < 2 < 4). These CD40L-augmented DNA vaccines elicited strong CD8(+) T-cell responses but did not elicit significant CD4(+) T-cell or antibody responses. To test the applicability of the multimeric fusion protein approach to other TNFSFs, a 4-trimer construct for the ligand of glucocorticoid-induced TNF family-related receptor (GITR) was also prepared. Multimeric soluble GITR ligand (GITRL) augmented the CD8(+) T-cell, CD4(+) T-cell, and antibody responses to DNA vaccination. In summary, multimeric CD40L and GITRL are new adjuvants for DNA vaccines. Plasmids for expressing multimeric TNFSF fusion proteins permit the rapid testing of TNFSF molecules in vivo.

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.

Vaccine route, dose and type of delivery vector determine patterns of primary CD8+ T cell responses

The dynamics of primary CD8+ T cell responses following administration of modified virus Ankara (MVA)- and DNA-vectored vaccines was investigated in a mouse model. To overcome the low frequency of naive antigen-specific precursors and follow the early expansion events, naive CFSE-labelled T cell receptor-transgenic F5 lymphocytes were transferred into syngeneic non-transgenic recipients prior to vaccination. Using the i.d., i.v. and i.m. routes and increasing recombinant MVA (rMVA) vaccine doses, the primary response was analysed on a divisional basis at local and distant lymphoid organs at various times after vaccination. The results indicated that F5 cell divisions were initiated in the local draining lymph nodes and cells only after five to six divisions appeared at more distant sites. The rMVA dose affected frequencies of cells entering division and at the peak response. When priming induced by rMVA and plasmid DNA was compared, dramatic differences in the cycling patterns were observed with plasmid DNA inducing a response slower and more sustained over the first 2 wk than rMVA. Both rMVA and DNA induced comparable IFN-gamma production, which increased with cell divisions. Taken together, the vaccine type, dose and route have a strong influence on the spatial and temporal patterns of initial T cell responses.

Anti-HIV-1 activity of anti-TAR polyamide nucleic acid conjugated with various membrane transducing peptides

The transactivator responsive region (TAR) present in the 5′-NTR of the HIV-1 genome represents a potential target for antiretroviral intervention and a model system for the development of specific inhibitors of RNA–protein interaction. Earlier, we have shown that an anti-TAR polyamide nucleotide analog (PNA_TAR) conjugated to a membrane transducing (MTD) peptide, transportan, is efficiently taken up by the cells and displays potent antiviral and virucidal activity [B. Chaubey, S. Tripathi, S. Ganguly, D. Harris, R. A. Casale and V. N. Pandey (2005) Virology, 331, 418–428]. In the present communication, we have conjugated five different MTD peptides, penetratin, tat peptide, transportan-27, and two of its truncated derivatives, transportan-21 and transportan-22, to a 16mer PNA targeted to the TAR region of the HIV-1 genome. The individual conjugates were examined for their uptake efficiency as judged by FACScan analysis, uptake kinetics using radiolabeled conjugate, virucidal activity and antiviral efficacy assessed by inhibition of HIV-1 infection/replication. While FACScan analysis revealed concentration-dependent cellular uptake of all the PNA_TAR–peptide conjugates where uptake of the PNA_TAR–penetratin conjugate was most efficient as >90% MTD was observed within 1 min at a concentration of 200 nM. The conjugates with penetratin, transportan-21 and tat-peptides were most effective as an anti-HIV virucidal agents with IC₅₀ values in the range of 28–37 nM while IC₅₀ for inhibition of HIV-1 replication was lowest with PNA_TAR–transportan-27 (0.4 μM) followed by PNA_TAR–tat (0.72 μM) and PNA_TAR–penetratin (0.8 μM). These results indicate that anti-HIV-1 PNA conjugated with MTD peptides are not only inhibitory to HIV-1 replication in vitro but are also potent virucidal agents which render HIV-1 virions non-infectious upon brief exposure.

Evaluating the immunogenicity of a disulfide-stabilized, cleaved, trimeric form of the envelope glycoprotein complex of human immunodeficiency virus type 1

The human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein (Env) complex comprises three gp120 exterior glycoproteins each noncovalently linked to a gp41 transmembrane glycoprotein. Monomeric gp120 proteins can elicit antibodies capable of neutralizing atypically sensitive test viruses in vitro, but these antibodies are ineffective against representative primary isolates and the gp120 vaccines failed to provide protection against HIV-1 transmission in vivo. Alternative approaches to raising neutralizing antibodies are therefore being pursued. Here we report on the antibody responses generated in rabbits against a soluble, cleaved, trimeric form of HIV-1(JR-FL) Env. In this construct, the gp120 and gp41 moieties are covalently linked by an intermolecular disulfide bond (SOS gp140), and an I559P substitution has been added to stabilize gp41-gp41 interactions (SOSIP gp140). We investigated the value of DNA priming and compared the use of membrane-bound and soluble priming antigens and of repeat boosting with soluble and particulate protein antigen. Compared to monomeric gp120, SOSIP gp140 trimers elicited approximately threefold lower titers of anti-gp120 antibodies. Priming with DNA encoding a membrane-bound form of the SOS gp140 protein, followed by several immunizations with soluble SOSIP gp140 trimers, resulted in antibodies capable of neutralizing sensitive strains at high titers. A subset of these sera also neutralized, at lower titers, HIV-1(JR-FL) and some other primary isolates in pseudovirus and/or whole-virus assays. Neutralization of these viruses was immunoglobulin mediated and was predominantly caused by antibodies to gp120 epitopes, but not the V3 region.

Evaluating therapeutic vaccines in patients infected with HIV

Long-term survival of HIV infection can mean decades of treatment for a patient, with major side effects and costs that limit their efficacy and accessibility. Although antiretroviral therapy remains the only standard of care, alternative therapeutic strategies must be found to ensure efficient and safe clinical management of the disease in the long term. Therapeutic immunization against HIV might be a significant approach to enhancing immune control of the virus and limiting disease progression and thus the requirement for medication. Several anti-HIV vaccines are currently being evaluated in attempts to prolong periods of treatment interruption in HIV patients. The design and end-points of clinical trials, and the clinical settings in which these new strategies should be evaluated and will be of benefit, have yet to be defined and are the focus of this review.