Immunogenicity and toxicity testing of an experimental HIV-1 vaccine in nonhuman primates

Nanotechnology-empowered vaccine delivery for enhancing CD8+ T cells-mediated cellular immunity

After centuries of development, using vaccination to stimulate immunity has become an effective method for prevention and treatment of a variety of diseases including infective diseases and cancers. However, the tailor-made efficient delivery system for specific antigens is still urgently needed due to the low immunogenicity and stability of antigens, especially for vaccines to induce CD8⁺ T cells-mediated cellular immunity. Unlike B cells-mediated humoral immunity, CD8⁺ T cells-mediated cellular immunity mainly aims at the intracellular antigens from microorganism in virus-infected cells or genetic mutations in tumor cells. Therefore, the vaccines for stimulating CD8⁺ T cells-mediated cellular immunity should deliver the antigens efficiently into the cytoplasm of antigen presenting cells (APCs) to form major histocompatibility complex I (MHCI)-antigen complex through cross-presentation, followed by activating CD8⁺ T cells for immune protection and clearance. Importantly, nanotechnology has been emerged as a powerful tool to facilitate these multiple processes specifically, allowing not only enhanced antigen immunogenicity and stability but also APCs-targeted delivery and elevated cross-presentation. This review summarizes the process of CD8⁺ T cells-mediated cellular immunity induced by vaccines and the technical advantages of nanotechnology implementation in general, then provides an overview of the whole spectrum of nanocarriers studied so far and the recent development of delivery nanotechnology in vaccines against infectious diseases and cancer. Finally, we look forward to the future development of nanotechnology for the next generation of vaccines to induce CD8⁺ T cells-mediated cellular immunity.

Vaccine Potentiation by Combination Adjuvants

Adjuvants are crucial components of vaccines. They significantly improve vaccine efficacy by modulating, enhancing, or extending the immune response and at the same time reducing the amount of antigen needed. In contrast to previously licensed adjuvants, current successful adjuvant formulations often consist of several molecules, that when combined, act synergistically by activating a variety of immune mechanisms. These "combination adjuvants" are already registered with several vaccines, both in humans and animals, and novel combination adjuvants are in the pipeline. With improved knowledge of the type of immune responses needed to successfully induce disease protection by vaccination, combination adjuvants are particularly suited to not only enhance, but also direct the immune responses desired to be either Th1-, Th2- or Th17-biased. Indeed, in view of the variety of disease and population targets for vaccine development, a panel of adjuvants will be needed to address different disease targets and populations. Here, we will review well-known and new combination adjuvants already licensed or currently in development-including ISCOMs, liposomes, Adjuvant Systems Montanides, and triple adjuvant combinations-and summarize their performance in preclinical and clinical trials. Several of these combination adjuvants are promising having promoted improved and balanced immune responses.

GlaxoSmithKline Adjuvant Systems in vaccines: concepts, achievements and perspectives

The need for potentiating immune responses to recombinant or subunit antigens has prompted GlaxoSmithKline (GSK) Biologicals to develop various Adjuvant Systems for the design of prophylactic and therapeutic vaccines. Adjuvant Systems are formulations of classical adjuvants mixed with immunomodulators, specifically adapted to the antigen and the target population. They can activate the appropriate innate immune system and subsequently impact on adaptive immune responses. AS04 is an Adjuvant System that has demonstrated significant achievements in several vaccines against viral diseases. AS02, another Adjuvant System, is being evaluated in various contexts, where a strong T-cell response is needed to afford protection. Likewise, AS01 has been developed for vaccines where the induction of a yet stronger T-cell-mediated immune response is required. Altogether, the promising clinical results strongly support the concept of Adjuvant Systems and allow for further development of new vaccines, best adapted to the target population and the immune mechanisms of protection.

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.

Mucosal AIDS vaccines

Debates are still being waged over what is the best strategy for developing a potent AIDS vaccine. All the obvious approaches to making AIDS vaccines have been tried in the past two decades without much success. It is clear that new thinking and a revision of prevailing dogmas needs to be in place if we really want a vaccine. Conventional envelope-based antibody-inducing vaccines do not appear to hold promise, and broadly-neutralizing antibodies are now being searched as an alternative to the failed approach with subunit vaccines. The current consensus is that cellular immune responses, especially those mediated by CD8 cytotoxic/suppressor (CTL) and CD4 helper T lymphocytes, are needed to control HIV. Vaccines capable of inducing cell-mediated responses are, therefore, considered critical for controlling the spread of HIV. DNA-based vaccines triggering CTL reaction are currently thought to be an answer, but will they fulfill the promise? In the following paragraphs, a critical assessment of the state of the art will be provided in an attempt to analyze what we know and still don't know. The focus of this review is primarily on mucosal vaccines-a relatively new area in AIDS research. The update on V-1 Immunitor, the first mucosal AIDS vaccine available commercially, is provided within this context. Some of the reviewed concepts may be disputable, but without departure from the uninspiring consensus no substantial progress in the AIDS vaccine field can be envisioned.

QS-21 promotes an adjuvant effect allowing for reduced antigen dose during HIV-1 envelope subunit immunization in humans

Three separate studies were undertaken in HIV-1 uninfected persons to determine if the adjuvant QS-21 improves the magnitude or kinetics of immune responses induced by recombinant soluble gp120 HIV-1(MN) protein (rsgp120) immunization. The QS-21 was administered at two doses (50 and 100 microg), either alone or in combination with aluminum hydroxide (600 microg). At the highest doses of rsgp120 (100, 300, and 600 microg), QS-21 exerted no significant effect on either binding or neutralizing antibody titers. Antibody binding and neutralizing responses fell dramatically when rsgp120, formulated with alum alone, was given at low doses (3 and 30 microg). In contrast, antibody responses similar in titer to those in the high dose antigen groups were induced with the low dose rsgp120 formulated with QS-21. In addition, the lymphocyte proliferation and delayed type hypersensitivity skin testing were superior in the QS-21 recipients compared with the alum recipients at the low antigen doses. Moderate to severe pain was observed in majority of the volunteers receiving QS-21 formulations, and vasovagal episodes and hypertension were not infrequent. Thus, the use of QS-21 may provide a means to reduce the dose of a soluble protein immunogen.

The adjuvant combination monophosphoryl lipid A and QS21 switches T cell responses induced with a soluble recombinant HIV protein from Th2 to Th1

The induction of protective immunity with recombinant vaccines is dependent on the identification of adjuvant or delivery systems that can augment immune responses, especially cellular immune responses, to soluble protein antigen. In this study we demonstrate that an adjuvant formulation comprising QS21, a purified form of saponin and 3D-monophosphoryl lipid A (MPL), a nontoxic derivative of lipopolysaccharide (LPS), enhances cellular and humoral immune responses to a recombinant HIV protein. Analysis of cytokine secretion by antigen-specific T-cells from the spleen demonstrated that QS21 augmented Th1 and Th2 responses, whereas addition of 3D-MPL resulted in preferential induction of type 1 T-cells. Furthermore, analysis of the subclass of the IgG antibody in the serum in mice immunized with gp120 with the combined adjuvant formulation confirmed the selective activation of Th1 cells in vivo. 3D-MPL was found to enhance B7-1 expression and IL-12 production by macrophages, which are known to be involved in the LPS-induced enhancement of Th1 responses. Thus 3D-MPL appears to act as an adjuvant, without the toxicity associated with LPS, by controlled and selective potentiating effects on antigen presentation and T-cell activation.

The V3 loop based multi-epitope polypeptide TAB9 adjuvated with montanide ISA720 is highly immunogenic in nonhuman primates and induces neutralizing antibodies against five HIV-1 isolates

In a previous work we selected montanide ISA720 (M-ISA720) among different adjuvants for the vaccination with a V3 loop based multi-epitope polypeptide TAB9. In this paper we present the evaluation of the toxicity and immunogenicity of this formulation in non-human primates. TAB9 in M-ISA720 was highly immunogenic in macaques (Macaca fascicularis) inducing antibodies against TAB9 in all animals after one inoculation and a strong anamnestic response after booster injections. Furthermore 97% of the V3 peptides included were recognized by TAB9 sera. No differences between doses of 200 microg and 1 mg of TAB9 in M-ISA720 were observed after four immunizations. Neutralizing antibodies against five HIV-1 isolates were detected in most animals. Animals remain healthy throughout the study and did not show lesions at the inoculation site.

Approaches to new vaccines

The explosive technological advances in the fields of immunology and molecular biology in the last 5 years had an enormous impact on the identification of candidate vaccines against diseases, which until a few years ago seemed uncontrollable. Increased knowledge of the immune system has helped to define the mechanisms that underlie successful immunization and is now being exploited to develop improved versions of existing vaccines and new vaccines against emerging pathogens, tumors, or autoimmune diseases. An understanding of the mechanisms of action of novel adjuvants and the development of new vector and delivery systems will have a major impact on vaccine strategies. The use of DNA encoding antigens from pathogenic viruses, bacteria, and parasites as vaccines is a new approach that is receiving considerable attention. This and other innovative approaches, including vaccine production in plants, are appraised in this review. The successful eradication of smallpox and the imminent eradication of poliomyelitis by worldwide immunization campaigns provide positive examples of how the vaccine-mediated approach can lead to disease elimination; with the advent of new vaccines and improved delivery systems, there is no scientific reason why these successes cannot be repeated.

Immunological requirements for a subunit vaccine against tuberculosis

Tuberculosis remains one of the most important threats to world health. Current vaccination and prevention strategies are inadequate and there is an urgent need for a new vaccine. The current vaccine bacille Calmette-Guérin (BCG), is unable to protect against re-activation of disease in later life and its efficacy varies tremendously in different human populations. An ideal replacement would be a non-living subunit vaccine that could impart protective efficacy greater than BCG but without its drawbacks. Before such a goal is achieved, however, there are many parameters that need to be examined in experimental systems. Such studies have revealed that apart from the selection of immunologically relevant antigens, dosage of antigen and type of adjuvant need to be chosen carefully. These parameters need to be examined in the context of the complex biology of the disease and, despite recent progress in defining host/pathogen interactions, experimental vaccines tested so far have fallen short of the protective efficacy of BCG. A coordinated approach, stimulating the various facets of cell-mediated immunity will probably be essential for development of protective immunity through subunit vaccination.

Study of the adjuvant activity of new MDP derivatives and purified saponins and their influence on HIV-1 replication in vitro

Muramyl dipeptide (MDP), eight new lipophilic MDP derivatives (MDPs) and three purified saponins were evaluated for their ability to induce immune responses in mice immunized with HIV-1 envelope protein rgp160 and for their ability to influence the HIV-1 replication in vitro. Three of nine new synthetic MDP derivatives (beta-butyl-MDP, MTPO-26 and beta-cholesteryl-MDP) and one saponin (Taurosid I) have been shown to induce strong humoral immune responses to HIV-1 envelope glycoproteins rgp160 and rgp120. Three substances (beta-butyl-MDP, MDP-cholyl and beta-G27-MDP) induced high levels of T-cell stimulation to HIV-1 rgp160. beta-butyl-MDP induced the strongest B- and T-cell responses to HIV-1 glycoproteins. Two substances (beta-butyl-MDP and Taurosid I) did not induce an enhancement of HIV-1 replication in vitro and can be considered as promising adjuvants.

Safety, efficacy, and immunogenicity of a recombinant Osp subunit canine Lyme disease vaccine

A subunit canine Lyme disease vaccine formulated with recombinant lipidated Osp A and OspB and saponin QS21 was assessed for safety, protective efficacy, and immunogenicity. Ten normal beagles were subcutaneously vaccinated twice at age 12 and 16 weeks, respectively. Three months after the second vaccination, the vaccinates and another 10 nonvaccinated control beagles were challenged by feeding ticks on each dog for 5 days using eight field-collected adult female and six adult male Ixodes scapularis infected with Lyme disease spirochetes per dog. Adverse reactions associated with the vaccinations were limited to injection site swellings which occurred within the first 48 h and resolved within a week. The local reaction was independent of vaccination times and tick challenge. On the basis of typical clinical signs, xenodiagnosis, and diagnostic immunoblotting, all 10 controls were infected; five developed lameness and three of them experienced at least two to three episodes of limping during a 10-month monitoring period. In contrast, eight of ten vaccinates were protected and two infected vaccinates, as judged by xenodiagnosis, were asymptomatic. None of the protected vaccinates developed antibodies to diagnostic spirochetal antigens other than OspA and OspB. In contrast, most controls produced antibodies to borrelial antigens, but not to OspA and OspB. Antibody production in vaccinates receiving a third vaccination 10 months postchallenge was greatly boosted; the geometric mean antibody titer was significantly higher (P < 0.0001) than that tested prechallenge. Thus, the subunit canine Lyme disease vaccine was safe and protective and elicited immunological memory. Vaccinated dogs were serologically distinguishable from those naturally exposed.

Structure of the saponin adjuvant QS-21 and its base-catalyzed isomerization product by 1H and natural abundance 13C NMR spectroscopy

The saponin QS-21, derived from the bark of the Quillaja saponaria Molina tree, has shown great potential as an adjuvant with a number of vaccines. Kinetic studies carried out to establish the stability of vaccine formulations show that commercially supplied QS-21 (primarily QS-21A) is converted slowly at pH 5.5, and rapidly at higher pH, to an equilibrium mixture of two regioisomers, QS-21A and QS-21B, in a ratio of 20:1. NMR studies show that QS-21A and QS-21B differ only in the point of attachment of the fatty acyl moiety to the fucose sugar ring. The major isomer, QS-21A, has the fatty acyl portion attached at the 4-hydroxyl group whereas the minor isomer, QS-21B, has the fatty acyl portion attached at the 3-hydroxyl group. The isomerization most likely involves ionization of the 3-hydroxy group and intramolecular acyl transfer from the 4-hydroxy group. The relative stereochemistry of the triterpene and the sugar anomeric centers is also established by NMR methods.

Isomerization and formulation stability of the vaccine adjuvant QS-21

The stability of the immunologic adjuvant QS-21 (Cambridge Biotech Corp.) was optimized for use in the MN rgp120 HIV-1 subunit vaccine. QS-21, a saponin purified by reversed phase HPLC from an extract of the bark of the Quillaja saponaria Molina tree, consisted initially of one species (QS-21A), but converted to two species, QS-21A and QS-21B, in aqueous solution. NMR studies indicated that the two species are structural isomers and that isomerization occurs by intramolecular trans-esterification of the fatty acid moiety between the 3- and 4-hydroxyl groups of the fucose ring (Jacobsen et al. Carbohydr. Res., in press). Both isomers were adjuvant active. Storage of QS-21 in aqueous solution resulted in the interconversion between these isomer forms, as well as the slow formation of degradation products due to ester hydrolysis. The critical micellar concentration of QS-21 in succinate buffer was measured by a fluorescent probe method to be 51 +/- 9 micrograms/mL. Studies were performed at different concentrations of QS-21 to assess the influence of micelle formation on stability. These experiments indicated that QS-21 is more stable in the micellar form, presumably because the most labile ester bond linking the fatty acid moiety to fucose is constrained or buried in the hydrophobic micellar environment. The pH of maximum stability was pH 5.5, the pH for minimum degradation of most esters. The final formulation, 500 micrograms/mL QS-21 in 20 mM sodium succinate, 150 mM NaCl, pH 5.5, provided a shelf-life of greater than 2 years.

Liposomes as carriers of peptide antigens: induction of antibodies and cytotoxic T lymphocytes to conjugated and unconjugated peptides

In the quest for effective immunization against complex diseases such as cancer, parasitic diseases, AIDS, and other viral infections, numerous peptides and recombinant proteins have been synthesized, examined for the ability to induce antibodies and CTLs, and tested for binding capability and therapeutic or prophylactic efficacy against the original target cell or organism. A liposome formulation, consisting of alum-adsorbed liposomes containing both a potent adjuvant, lipid A, and encapsulated or surface bound antigen, has had a record of safety and strong effectiveness for induction of antibodies in human vaccine trials. These same liposomes can also serve as effective vehicles for delivering conjugated or unconjugated peptides and proteins to antigen presenting cells for presentation via MHC class I and class II pathways for induction of CTLs and antibodies in experimental animal models. Liposomal lipid A appears to be extremely important, and is often a requirement, as an adjuvant for induction of CTLs against liposomal peptide antigens. Computer-generated molecular modelling analysis of small unconjugated or lipid-conjugated peptides strongly suggests that the expression of peptide antigen on the surface of the liposomes can be an important factor both in the induction of antibodies and in determining antibody specificities to small peptides. However, antigenic surface expression of liposomal peptide is not required for induction of CTLs. The data suggest that small synthetic peptides, synthesized with or without a lipid tail, or chemically conjugated to the surface of liposomes, might serve as effective antigenic epitopes, in combination with liposomal lipid A for induction of antibodies and CTLs.

Adjuvant activity of QS-21 for experimental E. coli 018 polysaccharide vaccines

Three types of experimental vaccines containing O-side-chain polysaccharide from the enterotoxigenic strain Escherichia coli 018 were evaluated. The immunogenicity of free O-polysaccharide (PS), a polysaccharide-diphtheria toxoid conjugate (PS-conj), and detoxified lipopolysaccharide (dLPS) was tested in female ICR mice, either alone or in combination with QS-21, a purified saponin adjuvant derived from the bark of the tree Quillaja saponaria Molina. Both the number of individual mice responding and the titres of O-polysaccharide specific antibodies in pools of sera were increased by the addition of QS-21. The immune response to both O-specific polysaccharide and carrier was primarily IgM and IgG1. The addition of QS-21 not only increased the level of IgG1, but also had a significant adjuvant effect on antigen-specific IgG2a, IgG2b and IgG3.

Impact of the saponin adjuvant QS-21 and aluminium hydroxide on the immunogenicity of recombinant OspA and OspB of Borrelia burgdorferi

The impact of the adjuvants QS-21 and aluminium hydroxide (alum) on the immunogenicity of recombinant outer surface proteins A (OspA) and B (OspB) of Borrelia burgdorferi was investigated. Both non-acylated OspA and OspB derived from strain B31 were expressed in Escherichia coli and purified by reversible citraconylation and anion-exchange chromatography. Antisera to OspA or OspB were prepared in mice with antigens formulated with QS-21 or alum, and evaluated for specific immunoglobulin G isotypes, agglutination and borreliacidal activity. QS-21 significantly enhanced IgG2a and IgG2b antibody responses to OspA and OspB, and IgG1 response to OspA when compared with the formulation containing antigen alone. In contrast, alum significantly inhibited the induction of IgG2a and IgG2b responses to OspA. Alum had no significant effect on IgG1 response to OspA, or IgG2a and IgG2b responses to OspB, but significantly enhanced IgG1 antibody response to OspB. Antisera to OspA or OspB formulated by QS-21 possessed higher titres of agglutinating antibody than antisera to OspA or OspB alone. Borreliacidal activity was eight- to 64-fold higher in antisera to OspA formulated with QS-21 than in antisera to OspA formulated with or without alum. These antisera were highly borreliacidal to New York strain B31, a California isolate CA-2-87, German isolate Fr, and Swedish isolate G25. Antisera to OspB formulated with QS-21 were highly borreliacidal to strains B31 and Fr, but not to CA-2-87 and G25. Antisera to OspB formulated with alum were borreliacidal only to B31. Thus, OspA was superior to OspB and QS-21 superior to alum at eliciting functional antibody responses.(ABSTRACT TRUNCATED AT 250 WORDS)

Induction of antigen-specific killer T lymphocyte responses using subunit SIVmac251 gag and env vaccines containing QS-21 saponin adjuvant

Subunit vaccines based on recombinant proteins have proved useful for inducing antibody responses and they are safe for widespread use because they do not contain any live components. Unfortunately, they do not typically induce the types of cell-mediated immune responses required to control viral pathogens; specifically, they do not induce CD8+ cytotoxic T lymphocyte (CTL) responses. To increase the immunogenicity of recombinant proteins, we have used the QS-21 saponin adjuvant in subunit vaccine formulations. In the current study, experimental subunit vaccine formulations containing recombinant p55gag or gp120env proteins from the mac251 strain of the simian immunodeficiency virus (SIVmac251) and the QS-21 adjuvant were used to immunize rhesus macaques. These formulations induced SIV gag- or env-specific cellular immunity that was detectable in vitro and included killer cell activity. The induction of killer cells required prior vaccination and the responses were antigen specific for the immunogens contained in the vaccine formulations. Autologous target cells were required to detect these responses, suggesting genetic restriction, and effector cells appeared to be present in both the CD4+ and CD8+ T lymphocyte subpopulations. These data suggest that the vaccine-induced killer cell activity that was detected was mediated by both CD4+ and CD8+ lymphocytes. Despite the presence of these killer cells, all of the animals became infected with the SIVmac251 on experimental challenge. These findings demonstrated that antigen-specific killer cell responses could be induced by a subunit vaccine formulated with the QS-21 saponin adjuvant. The characteristics of the responses suggested that the effector cells were T lymphocytes, expressing either CD4 or CD8.(ABSTRACT TRUNCATED AT 250 WORDS)

Vaccinology, immunology, and comparative pathogenesis of measles in the quest for a preventative against AIDS

Current approaches to the prevention and control of AIDS by vaccines and by chemotherapy have failed to provide satisfactory solutions to this important medical problem and have failed, in addition, to provide definitive guidelines for future research endeavor. Vaccine research must and will continue but it is possible that a safe and effective vaccine may never be developed and it may be timely to explore, in addition, alternative means for immunological intervention in AIDS. Both immunoprophylactic and immunotherapeutic efforts might be assisted by manipulating the T helper 1 (Th1) and T helper 2 (Th2) subsets of CD4+ T helper cells, which is therefore worthy of exploration. Selective control of immune response by the two T helper subsets is by release of different cytokines that promote either cellular or humoral immunity, the latter of which may be associated with inappropriate immune responses and with immune dysfunction. Discovery of the Th1 and Th2 subsets and definition of the cytokines they release provide a new avenue toward possible development of a safe and effective vaccine and an approach, in addition, to correction of immune dysfunction by selective cytokine administration or by cytokine ablation by antagonists or antibodies. AIDS pathogenesis and immune dysfunction are complex and understanding them may be overwhelmed by an excess of possibilities. Simplification of the endeavor might benefit from comparative studies of the pathogenesis of measles, in which there also is immune deficiency but usually with spontaneous viral clearance, reversal of immune dysfunction, and total recovery. In addition, measles presents as a single disease and is caused by antigenically stable virus. Identification of the process whereby measles immunodeficiency is spontaneously reversed might be of importance in attempting to devise means for similar reversal in AIDS.

Use of particulate forms of protein antigens to increase the sensitivity of antigen-specific proliferation assays

Different forms of recombinant HIV-1 gp160 and tetanus toxoid were adsorbed onto latex microspheres and this particulate form of the proteins was used to measure antigen-specific proliferation in vaccinated rhesus macaques. Proliferative responses to proteins bound to microspheres were significantly greater and allowed for the detection of antigen-specific responses that were not detected using soluble proteins. The responses were antigen-specific and required prior immunization of the animals. Additionally, the presence and magnitude of the proliferative responses was associated with antibody responses to the same proteins suggesting the results were representative of in vivo responses and that the assay format did not induce in vitro artifacts.