Abstract
A 5-day workshop on adjuvant for vaccines was held in Trinidad, Cuba, on the 16–21 May 2010. Organized by the Latin American Association for Immunology and the Cuban Society for Immunology, the workshop attracted more than 60 scientists from different parts of the world. The meeting summarizes current knowledge regarding vaccine adjuvants, including delivery systems and parasitic vaccines. Main discussion topics were the discovery of new adjuvant formulations, action mechanisms for adjuvants, adjuvants for a different route of immunization, focused on mucosal vaccines, and nano- and micro-particles as a delivery system. This article highlights the most important issues presented.
Adjuvant2010 was the follow-up to the successful 2002, 2004, 2006 and 2008 meetings held in Varadero, Matanzas, Cuba. This meeting series offered a unique setting to an open discussion from basic research, development, production and regulation of vaccine adjuvants in an exceptional environment that permitted project collaboration and funding opportunities between colleagues. In the last two meetings, antiparasite vaccines were also included because parasites include most neglected diseases that require potent adjuvants, not only for prophylaxis, but also for immunotherapy or therapeutic vaccines. Finally, taking into consideration that only structural changes can increased adjuvanticity, Adjuvant2010 was also focused on nano- and micro-particles as adjuvants. This article will only discuss the adjuvant section of the meeting.
Novel vaccine & adjuvant formulations
The first keynote address of the meeting was given by Andrew Heath (University of Sheffield and Adjuvantix Ltd., Sheffield, UK) who focused his presentation on the adjuvant effect of conjugated anti-CD40 (ADX40). ADX40 and Ag85A, a secreted protein from Mycobacterium tuberculosis, were chemically conjugated and tested in mice. It was demonstrated that the ADX40-adjuvanted vaccine was immunogenic in immunocompromised mice and after an intratracheal challenge with 105 cfu H37Rv; the ADX40 enhanced antibody responses against Ag85A. It also enhanced both Th1- and Th2-associated cytokines and prolonged survival. In conclusion, Heath suggested that conjugate vaccines could provide a new way to increase vaccine efficacy in immunocompromised patients. Anselmo J Otero (Centre for Protein Studies, Havana University, Cuba) discussed the possibility of using antimicrobial peptides from marine invertebrates as adjuvants. There are many marine invertebrates in the Cuban sea that have peptides with antimicrobial properties already tested against Escherichia coli and Staphylococcus aureus and its adjuvant activity is ongoing. Isabela Thommen (Faculty of Agronomy and Veterinary Medicine, Federal University of Mato Grosso, Cuiabá, Mato Grosso, Brazil) presented the adjuvant activity of rice oil using ovalbumin which induce higher response than ovalbumin alone but less than Freund’s adjuvant.
Adjuvants: mechanisms of action
Ali M Harandi (Institute of Biomedicine, University of Gothenburg, Gothenburg, Sweden) documented the potential of the TLR-9 targeting molecule CpG oligodeoxynucelotide and the invariant natural killer T-cell agonist α-galactosylceramide to function as potent mucosal adjuvants for the generation of immunity in the murine female genital tract. He identified a group of common genes, including proinflammatory and regulatory cytokines, as well as CC and CXC chemokines whose expression in the murine vagina correlate with mucosal adjuvanticity. Martin Rumbo (National University of Plata, La Plata, Argentina) obtained and cloned three different chemokine promoters; constructs were obtained upon selection for inducibility and reporter luciferase. The CCL20 promoter was characterized at the molecular level, and stably transfected reporter cell lines were obtained for CCL20/luciferase constructs. Reporter transgenic mice were then obtained for CCL20/luciferase and this phenotype is now under characterization.
Malou Henriksen-Lacey (Aston University, Birmingham, UK) talked about the dual-radiolabeling method developed by her group, through which the biodistribution and pharmacokinetics of liposomes and antigen, labeled with 3H and 125I can be followed. Neutral liposomes composed of the lipid distearoyl-glycero-phosphatidylcholine are well retained at the injection site; however, antigen administered with the liposome drains rapidly. By contrast, rigid cationic liposomes such as dimethyldioctadecyl-ammonium are well retained at the injection site with their adsorbing antigen. Her results suggest that while liposome retention at the site of injection is affected by liposome bilayer fluidity, the retention of antigen at the injection site is affected by the surface charge of the liposome and therefore its ability to adsorb antigen.
Mucosal vaccination & adjuvants
Per Brandtzaeg (Centre for Immune Regulation, University of Oslo, Oslo University Hospital, Oslo, Norway) discussed how numerous genes are involved in innate and adaptive immunity, with modifications introduced over millions of years. During this evolution, the mucosal immune system developed two anti-inflammatory mechanisms: immune exclusion by secretory antibodies (SIgA and SIgM) to control epithelial colonization of microorganisms and inhibit penetration of harmful substances; and immunosuppression to counteract local and peripheral hypersensitivity against innocuous antigens such as food proteins. The latter mechanism is referred to as oral tolerance when induced via the gut. Homeostatic mechanisms also control immune responses to commensal bacteria.
Study of the efficacy of mucosal adjuvants in enhancing T-cell priming is essential for the rational design of novel adjuvants. Donata Medaglini (Università di Siena, Siena, Italy) using a TCR-transgenic CD4+ and CD8+ T-cell adoptive transfer model had assessed the ability of different mucosal adjuvants and delivery systems of priming CD4+ and CD8+ T cells and shown results allowed to conclude that the adoptive transfer model is a powerful tool to study in vivo priming of T lymphocytes following mucosal vaccination. Julio Balboa (Finlay Institute, Havana, Cuba) talked about the development of single time vaccination strategy (SinTimVaS) in mice where mucosal and parenteral priming were given simultaneously. Their results demonstrated that SinTimVaS, using the Finlay Adjuvants (AFCo1 and AFPL1) and combining the intranasal with the intramuscular route, induced both systemic and mucosal immune responses against Neisseria meningitidis B and against the others antigens tested (bovine serum albumin and tetanus toxoid). This strategy is not limited to the combination of the intranasal/intramuscular route. Belkis Romeu (Finlay Institute, Cuba) presented results that suggest that polysaccharide of N. meningitidis serogroup C (PsC) and PL from N. meningitidis serogroup B as component of VA-MENGOC-BC®, is immunogenic against PsC. She also showed that AFCo1 coadministered with CsP was capable to induce mucosal and systemic immune response.
Nano- & micro-particles & delivery systems
Delivery systems in vaccinology improve the immune response against an antigen and protect by different administration routes. Peter L Andersen (Statens Serum Institut, Copenhagen, Denmark) imparted a keynote address focusing his presentation on cationic liposomes as adjuvants for various vaccines, specifically focusing on the use of CAF01 adjuvant. This consists of dimethyldioctadecylammonium as a delivery vehicle and a synthetic mycobacterial cordfactor synthetic glycolipid trehalose 6,6’-dibehenate that promotes a non-TLR immune activation. It was demonstrated that the CAF01 promotes high levels of Th1/Th17 responses and it is stably expressed as a long-lived memory response and, furthermore, it induces strong humoral responses to various vaccine antigens. Karin Riedl (Intercell AG, Vienna, Austria) documented the potential of the IC31® adjuvant, which is a mixture of two synthetic components: antimicrobial peptide KLK (MW1323) and oligodeoxynucleotide ODN1a (MW7782). IC31 has been shown in several preclinical studies to offer a significant impact on the immunogenicity of different antigenic vaccine candidates. The first clinical results have further confirmed the potential of IC31 as a safe adjuvant for an injectable subunit TB vaccine.
Leonardo Sáenz (Veterinary Biotechnological Center, Faculty of Veterinary and Animal Sciences, University of Chile, Chile) discussed the evaluation of microparticles of chitosan polymer as a delivery system and adjuvant. He demonstrated that chitosan polymer ≤5 µm in size increased the immune response against a low immunogenic peptide triggering to a Th1 pattern similar to incomplete Freund’s adjuvant.
Steven P Schwendeman (University of Michigan, MI, USA) described his group’s recent advances in the formulation of poly(lactic-co-glycolic acid) microspheres as antigen delivery systems. Three types of excipients were combined to stabilize tetanus toxoid encapsulated in PLGA 85/15 microspheres (depot size >20 µm) during extended release, namely: an antacid (e.g., MgCO3); a strongly formaldehyde-interacting amino acid (e.g., free lysine) and a polyol (e.g., sorbitol) or sugar (trehalose). A strong and persistent antibody response was observed when co-encapsulating an antacid with a human chorionic gonadotropin-based peptide antigen and administered to rabbits by a single intramuscular injection. María C Luzardo (Havana Univerity, Havana, Cuba) showed results on the evaluation of the ability of liposomes, comprised of dipalmitoylphosphatidylcholine and cholesterol and co-encapsulating ovalbumin and StII, to reverse the ovalbumin-specific asthma-like response in mice. Mice immunized with liposome preparation showed lower eosinophil numbers and IL-5 levels in the bronchoalveolar fluid than the control group (allergic mice). Reinier Borrero (Finlay Institute, Havana, Cuba) presented results concerning obtaining and characterizing liposomes containing lipid extracted from Mycobacterium smegmatis. The liposomes were tested in mice and the results showed the presence of immunogenic glycolipids in M. smegmatis, which could be included to enhance the protective effects of subunit vaccine formulations against TB.
Conclusion
Adjuvant2010 was organized to improve understanding between the scientific communities and to summarize the current state of knowledge in the vaccine adjuvants field. After 5 days of constructive discussions, conferences and posters. Oliver Pérez (Finlay Institute, Cuba) highlighted that: Adjuvant2010 clearly showed the golden era of adjuvants; nine adjuvants were already licensed for human use, namely the AFPL1, constituent of the meningococcal B vaccine, from the Finlay Institute, the more extensively used TLR-agonists with more than 60 million doses applied; and the three components of Alum. Two new adjuvants have reached the clinical trials: CAF01 and IC31. Furthermore, other adjuvants that are concluding the preclinical assay and are ready, or nearly ready, to enter clinical trials, these are: ADX40, chitosan microparticles, CpG, flagellin, PLGA and AFCo1.
Financial & competing interests disclosure
The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.
No writing assistance was utilized in the production of this manuscript.