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Introductory Chapter: Immunization - Vaccine Adjuvant Delivery System and Strategies

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Ning Wang and Ting Wang

Submitted: 09 October 2018 Published: 05 November 2018

DOI: 10.5772/intechopen.81981

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1. Introduction

Immunization plays a key role in maintaining human health as it saves millions of lives in the most economical way from lethal pathogens and other fatal diseases each year, thanks to the advanced development of model vaccines, which are biological preparations containing an antigenic agent that resembles a disease-causing microorganism to stimulate the host’s immune system, thus providing active acquired immunity to a particular disease and destroying it [1, 2]. Since Jenner’s pioneering inoculations in the late eighteenth century, vaccines have been successfully developed to combat various diseases and each year saved numerous lives from, mostly, lethal infections and now also certain cancers [3, 4]. Especially, taking advantage of the tools discovered in microbiology and immunology, vaccines have recently obtained great achievements as demonstrated by their successful performances in conquering some formidable pathogens, such as smallpox and rabies, which are used to claim many lives. However, the list of pathogens for which there exist no vaccines is still long, and, in particular, many pathogens, such as human immunodeficiency virus (HIV), herpes simplex virus (HSV), and Ebola virus (EBV), are still posing a big threat to human life, therefore needing urgently the effective products to cope with their infections [5].

Vaccines can stimulate the host immune system to develop an armament of immunity capable of clearing the abnormalities after administration, because they are developed with the antigenic components that are featured by pathogens or neoplasms and usually include three types: the live attenuated microbes, killed microbes, and just purified antigens (Ags) of microbes or neoplasms [6]. The former two consisting of live attenuated or killed microbes are the conventional vaccines with high immunogenicity but, unfortunately, are also linked to a relatively poor safety profile as they possess the potential to revert the virulence and induce the drifted immune responses leading to incontrollable immunity as well as unacceptable inflammations. In contrast, the third one with purified Ags, called a subunit vaccine, has defined components to induce immune responses aiming just at the matched targets causing few safety concerns and thus can be employed to fight the infectious pathogens as well as malignant neoplasms that are carrying the identical Ags [7]. Presently, subunit vaccines are attracting more and more research interests owing to also their diverse applications, adaptive functions, and numerous advantages over the whole microbe-based conventional ones, and these aspects may well be comprehensively summarized as follows [8]:

  1. Their defined noninfectious components effectively confine capricious reversion to virulence while reducing significantly the risk of allergic or autoimmune response [9].

  2. Their production may avoid the use of dangerous microorganisms but may be carried out with solid-phase peptide synthesis in a reproducible, scalable, and economical manner, providing an alternative tool to obtain products to conquer certain pathogens that are problematic to culture (e.g., sporozoites for malaria vaccines) for attenuation of virulence [10].

  3. Ags in subunit vaccines are generally water-soluble allowing them to form a solution together with cryoprotectants such as disaccharide, followed by freeze-drying into the stable anhydrous fitting storage and transportation in a controlled temperature chain (CTC) or completely at room temperature [11].

  4. Also, subunit vaccines can be tailored with certain pathogen-/damage-associated molecular patterns (PAMP/DAMP) to be recognized by APCs for efficient activation, even including several peptide epitopes targeting different stages in the life cycle of a pathogen [8, 12, 13]; obviously, this is particularly useful for developing anticancer vaccines, wherein whole protein can hardly be used due to its similarity to the endogenous human proteins and carcinogenic properties [14].

However, unfortunately, subunit vaccines often have a rather weak immunogenicity, due to lack of the immunostimulatory components broadly shared by pathogens while being distinguishable from host molecules, which are collectively referred to as pathogen-associated molecular patterns (PAMPs) [15] able to bind to and trigger mammalian pattern recognition receptors (PRRs), such as the TLRs (toll-like receptors), NOD-like receptors (the nucleotide-binding oligomerization domain-like receptors), RIG-I-like receptors (retinoic acid-inducible gene-I-like receptor), and C-type lectin receptors, thus playing an adjuvant role to activate the innate immunity, followed by sponsoring a series of adaptive reactions involved in establishing the Ag-specific immunity [16].

Thus, while subunit vaccines are regarded as a safer product than the whole microbe-based conventional ones, they are also poorly immunogenic and often require an adjuvant or a vaccine adjuvant-delivery system (VADS) able to target the professional Ag-presenting cells (APCs), such as dendritic cells (DCs) and macrophages (MPs), to make full use of Ags and boost their immunostimulatory activity [17, 18, 19, 20, 21]. A vaccine adjuvant is defined as a non-specific immunopotentiating substance but capable of enhancing the body’s immune response to the Ag or changing the type of immune responses, when administered either alone in advance or simultaneously together with the vaccine Ag. Although its immune-boosting mechanisms remain elusive, an adjuvant is argued to fulfill the functions involving, roughly, two aspects: (1) generating damages on host cells/tissues, thus sending dangerous signals out to activate the immune system and (2) binding to PRRs and exciting the innate immune cells, such as DCs, MPs, histiocytes, and mast cells, which subsequently initiate the innate immune responses to sponsor the subsequent adaptive immune responses [22, 23]. Accordingly, vaccine adjuvants may well be classified into two types: type I, the natural or synthetic substances with intrinsic adjuvanticity, squalene/squalane, saponin, chitosan, hyaluronic acid (HA), and various pattern recognition receptor agonists (PRRas) and type II, the micron-/nanometer-sized particles, such as alum (insoluble aluminum salt) and vaccine adjuvant-delivery systems (VADSs) that are carriers engineered with at least two fundamental functions, i.e., adjuvanticity and Ag delivery. VADSs are usually constructed with a variety of biocompatible nanoparticles (NPs) made of various organic or inorganic materials, such as liposomes, ISCOMs (immune-stimulating complexes), polymeric NPs, VLPs (virus-like particles), emulsions, and the inorganic NPs, which are often incorporated with type I substances to further enhance their immunopotentiating functions [6, 24].


2. Immune responses for establishing the Ag-specific immunity

Always confronting and fighting with dangerous pathogens, mammals have gradually evolved to form a complexed defensive immune system, which can be classified into subsystems of the innate immune system versus the adaptive immune system [25]. The innate immune system consists of surface barriers, complement system, and various leukocytes including the phagocytes (macrophages, neutrophils, and dendritic cells), innate lymphoid cells, mast cells, eosinophils, basophils, and natural killer cells, which fulfill the role of non-specific immune defenses responding to pathogens in a generic way conferring short-lasting immunity against a pathogen [26]. For this, mammalian leukocytes are evolutionarily equipped with receptors able to recognize certain pathogen components bearing specific structural characteristics, such as free bacterial and viral DNA, lipoproteins, lipopolysaccharides, and flagellins, which are pathogen-/danger-associated molecular patterns (PAMPs/DAMPs) [27]. These functional receptors are expressed by host immune cells, such as TLR1 to TLR13, NOD-like receptors, RIG-I-like receptors, and C-type lectin of mannose receptors, which are collectively called pattern recognition receptors (PRRs), with each capable of selectively binding to specific PAMPs/DAMPs of pathogens, leading to the activation of the innate immune cells, which subsequently sponsor the immunoresponses of the whole immune system, thus providing the bases for defending against pathogens [28].

However, establishing the Ag-specific immunity for defending against pathogens involves several complex immune pathways going with the orchestration of numerous immunocytes, cytokines, and chemokines and starts, usually, upon the activation of APCs for innate immune reactions triggered by their internalized antigenic substances (Ags) that they distinguished as dangerous signals through, in most cases, the process of PRR-PAMP/DAMP recognition [23]. Briefly, positioned at the frontier of pathogen/vaccine recognition, APCs first take up, in a size-dependent manner (e.g., NPs with a size of <150 nm are taken up by APCs by clathrin-mediated endocytosis, while microparticles by phagocytosis); the Ags appeared in peripheral tissues or in the draining lymph nodes (dLNs), wherein APCs will mature and process the internalized Ags into pieces with epitopes, which are finally bound to MHC-II (major histocompatibility complex II) and/or MHC-I and displayed on cell surfaces for presentation to T cells [29]. MHC-I molecules are assembled in the endoplasmic reticulum (ER) with stabilization by chaperone proteins (including calreticulin, Erp57, protein disulfide isomerase (PDI), and tapasin) and are loaded, under tapasin mediation, with exogenous (viral or self-originated) Ags, which are translocated from the cytoplasm into the ER by TAP (transporter associated with antigen presentation) for presentation via T-cell receptors (TCRs) to CD8+ T cells for their activation [30]. MHC-II molecules are assembled in the ER, stabilized by an invariant chain (Ii) and transported through the Golgi to fuse with a late endosome forming the MHC-II endosome compartment (MIIC) with an acidic interior containing proteases cathepsin S and cathepsin L, which when activated will digest Ii, leaving in the peptide-binding groove of the MHC-II a residual class II-associated Ii peptide (CLiP), which later is exchanged for an antigenic peptide (usually exogenous Ags) derived from a protein degraded in the endosomal pathway for presentation via T-cell receptors (TCRs) to CD4+ T cells for their activation [30].

During Ag presentation, a substantial number of various signaling cytokines such as interleukins and interferons, as well as chemokines, are secreted by matured APCs and other immunocytes to promote the MHC-II-Ag epitope-triggered CD4+ T-cell differentiation into either T-helper type-1 (Th1) cells that will secrete IFN-γ, IL-12, and IL-2 or Th2 cells that will secrete IL-4. Then, Th1 cells will further secrete IL-12 and IFN-γ facilitating the MHC-I-Ag epitope-triggered CD8+ T cells to proliferate and differentiate into the Ag-specific cytotoxic T lymphocytes (CTLs), thus establishing the cellular immunity while forming memory T cells [31, 32]. Meanwhile, the Th2 cells mature to favor Ag presentation to B cells via B cell receptors (BCRs) and to secrete IL-4, IL-6, and IL-10, which are also beneficial for promoting the Ag-activated B cells to proliferate and differentiate into plasma cells to produce the anti-Ag antibodies, establishing finally the humoral immunity while forming memory B cells [33]. With memory T and B cells, upon encountering pathogens, both humoral and cellular immunity can be rapidly established; while humoral immunity neutralizes the extracellular pathogens during or before the infection and thus is fitting for the prophylaxis of pathogen invasion, cellular immunity is mainly responsible for destroying already infected or abnormal human cells and therefore may be employed for the clearance of the cell-hidden pathogens or malignant tumors, through specialized TCR recognition of the precisely matched Ags nestled in the groove of MHC-I on cells [12].


3. Immunization: vaccine adjuvant-delivery system and strategies

In designing the NP-based VADSs, what should be emphasized is that the differently sourced Ags are processed and trigger immune signal transduction in different ways [34]. Usually, the internalized exogenous Ags delivered by NPs are processed intracellularly by APCs into small antigens just inside the endolysosomal vesicles and then loaded favorably on MHC-II molecules, leading to activation of CD4+ T cells to differentiate into Th2 cells, which will further stimulate production of antibodies by B cells [8]. In contrast, the endogenous Ags, such as viral Ags, cancer components, and intracellular-degraded proteins, are usually presented in the cytosol and often loaded on MHC-I molecules, allowing for further activation of CD8+ T cells to differentiate into CTLs and to engender cellular immunity [35]. However, it is generally believed that, though not well understood, provided the exogenous Ags are transported via membrane fusion or other ways engendering Ag lysosome escape into the cytosol, they can also be processed via MHC-I presentation in just the same manner as that for endogenous Ags, and this process is known as Ag cross presentation [36]. This provides the basis for designing the NP-based VADS which are exogenous particles favoring of inducing humoral immunity but may be adorned with materials that can facilitate APC internalization in the membrane fusion manner or promote endolysosome escape and cross presentation of Ags to induce cellular immunity, thus expanding VADS into various applications, including mainly prophylaxis of infections, treatment of autoimmunity diseases, and immunotherapy of cancer [12]. In particular, as a multifunctional VADS, NPs modified with different materials with intrinsic and specific adjuvanticity, such as TLRas (e.g., MPL and CpG ODN), squalene, and saponin (e.g., water-soluble QS-21), though showing individually distinctive features, share some key characteristics in immune-boosting functions [37]. Summarily, these multifunctional Nps as a VADS trigger immunoresponses with features including, mainly, early activation, though at different levels, of innate immunity, which will subsequently translate into strong antibody and cellular responses to the delivered antigens [5]; a wide breadth of adaptive immunity is able to confer protections against heterovariants of pathogens; for example, vaccines delivered by liposomes containing MPL can defend against influenza viruses or human papillomavirus (HPV) strains that are not contained in the vaccines [38]; significant enhancement of the immunoresponses and the efficacy of vaccines in the elderly who show a waning immune responsiveness to infection and vaccination, as shown for vaccines formulated with MPL-liposomes against herpes zoster virus [39]. These results, together with the feasibility of large-scale manufacture and the track records of acceptable safety profiles of many liposome-based medications, pave the way for developing novel multifunctional liposomes to be used as a VADS for producing the vaccine products fitting humans of different age against infections with a high toll of morbidity and mortality.


Conflict of interest

All the authors declared no conflict of interest.


  1. 1. De Gregorio E, Rappuoli R. From empiricism to rational design: A personal perspective of the evolution of vaccine development. Nature Reviews Immunology. 2014;14(7):505-514
  2. 2. Delany I, Rappuoli R, De Gregorio E. Vaccines for the 21st century. EMBO Molecular Medicine. 2014;6(6):708-720
  3. 3. Plotkin SA. Vaccines: The fourth century. Clinical and Vaccine Immunology. 2009;16(12):1709-1719
  4. 4. Melief CJ, van Hall T, Arens R, Ossendorp F, van der Burg SH. Therapeutic cancer vaccines. The Journal of Clinical Investigation. 2015;125(9):3401-3412
  5. 5. Germain RN. Vaccines and the future of human immunology. Immunity. 2010;33(4):441-450
  6. 6. Gregory AE, Titball R, Williamson D. Vaccine delivery using nanoparticles. Frontiers in Cellular and Infection Microbiology. 2013;3:13-25
  7. 7. Moyle PM, Toth I. Modern subunit vaccines: Development, components, and research opportunities. ChemMedChem. 2013;8(3):360-376
  8. 8. Skwarczynski M, Toth I. Recent advances in peptide-based subunit nanovaccines. Nanomedicine (London, England). 2014;9(17):2657-2669
  9. 9. Karch CP, Burkhard P. Vaccine technologies: From whole organisms to rationally designed protein assemblies. Biochemical Pharmacology. 2016;120:1-14
  10. 10. Draper SJ, Sack BK, King CR, Nielsen CM, Rayner JC, Higgins MK, et al. Malaria vaccines: Recent advances and new horizons. Cell Host & Microbe. 2018;24(1):43-56
  11. 11. Wang N, Wang T, Zhang M, Chen R, Niu R, Deng Y. Mannose derivative and lipid A dually decorated cationic liposomes as an effective cold chain free oral mucosal vaccine adjuvant-delivery system. European Journal of Pharmaceutics and Biopharmaceutics. 2014;88(1):194-206
  12. 12. Moyer TJ, Zmolek AC, Irvine DJ. Beyond antigens and adjuvants: Formulating future vaccines. The Journal of Clinical Investigation. 2016;126(3):799-808
  13. 13. Rey FA, Lok SM. Common features of enveloped viruses and implications for immunogen design for next-generation vaccines. Cell. 2018;172(6):1319-1334
  14. 14. Terbuch A, Lopez J. Next generation cancer vaccines-make it personal! Vaccines (Basel). 2018;6(3)
  15. 15. Miyaji EN, Carvalho E, Oliveira MLS, Raw I, Ho PL. Trends in adjuvant development for vaccines: DAMPs and PAMPs as potential new adjuvants. Brazilian Journal of Medical and Biological Research. 2011;44(6):500-513
  16. 16. Coffman RL, Sher A, Seder RA. Vaccine adjuvants: Putting innate immunity to work. Immunity. 2010;33(4):492-503
  17. 17. Wang X, Wang N, Li N, Zhen Y, Wang T. Multifunctional particle-constituted microneedle arrays as cutaneous or mucosal vaccine adjuvant-delivery systems. Human Vaccines & Immunotherapeutics. 2016;12(8):2075-2089
  18. 18. Wang T, Zhen YY, Ma XY, Wei B, Wang N. Phospholipid bilayer-coated aluminum nanoparticles as an effective vaccine adjuvant-delivery system. ACS Applied Materials & Interfaces. 2015;7(12):6391-6396
  19. 19. Wang T, Wang N. Preparation of the multifunctional liposome-containing microneedle arrays as an oral cavity mucosal vaccine adjuvant-delivery system. Methods in Molecular Biology. 2016;1404:651-667
  20. 20. Wang T, Wang N. Biocompatible mater constructed microneedle arrays as a novel vaccine adjuvant-delivery system for cutaneous and mucosal vaccination. Current Pharmaceutical Design. 2015;21(36):5245-5255
  21. 21. Wang N, Wang T. Preparation of multifunctional liposomes as a stable vaccine delivery-adjuvant system by procedure of emulsification-lyophilization. Methods in Molecular Biology. 2016;1404:635-649
  22. 22. Di Pasquale A, Preiss S, Tavares Da Silva F, Garcon N. Vaccine adjuvants: From 1920 to 2015 and beyond. Vaccines (Basel). 2015;3(2):320-343
  23. 23. Akira S. Innate immunity and adjuvants. Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences. 2011;366(1579):2748-2755
  24. 24. Sahdev P, Ochyl LJ, Moon JJ. Biomaterials for nanoparticle vaccine delivery systems. Pharmaceutical Research. 2014;31(10):2563-2582
  25. 25. Iwasaki A, Medzhitov R. Control of adaptive immunity by the innate immune system. Nature Immunology. 2015;16(4):343-353
  26. 26. Kumar H, Kawai T, Akira S. Pathogen recognition by the innate immune system. International Reviews of Immunology. 2011;30(1):16-34
  27. 27. Bachmann MF, Jennings GT. Vaccine delivery: A matter of size, geometry, kinetics and molecular patterns. Nature Reviews Immunology. 2010;10(11):787-796
  28. 28. Vajjhala PR, Ve T, Bentham A, Stacey KJ, Kobe B. The molecular mechanisms of signaling by cooperative assembly formation in innate immunity pathways. Molecular Immunology. 2017;86:23-37
  29. 29. Du J, Zhang YS, Hobson D, Hydbring P. Nanoparticles for immune system targeting. Drug Discovery Today. 2017;22(9):1295-1301
  30. 30. Neefjes J, Jongsma ML, Paul P, Bakke O. Towards a systems understanding of MHC class I and MHC class II antigen presentation. Nature Reviews Immunology. 2011;11(12):823-836
  31. 31. Ariotti S, Beltman JB, Chodaczek G, Hoekstra ME, van Beek AE, Gomez-Eerland R, et al. Tissue-resident memory CD8+ T cells continuously patrol skin epithelia to quickly recognize local antigen. Proceedings of the National Academy of Sciences of the United States of America. 2012;109(48):19739-19744
  32. 32. Akondy RS, Fitch M, Edupuganti S, Yang S, Kissick HT, Li KW, et al. Origin and differentiation of human memory CD8 T cells after vaccination. Nature. 2017;552(7685):362-367
  33. 33. Weisel FJ, Zuccarino-Catania GV, Chikina M, Shlomchik MJ. A temporal switch in the germinal center determines differential output of memory B and plasma cells. Immunity. 2016;44(1):116-130
  34. 34. Brutkiewicz RR. Cell signaling pathways that regulate antigen presentation. Journal of Immunology. 2016;197(8):2971-2979
  35. 35. De Temmerman ML, Rejman J, Demeester J, Irvine DJ, Gander B, De Smedt SC. Particulate vaccines: On the quest for optimal delivery and immune response. Drug Discovery Today. 2011;16(13-14):569-582
  36. 36. Arens R. Rational design of vaccines: Learning from immune evasion mechanisms of persistent viruses and tumors. Advances in Immunology. 2012;114:217-243
  37. 37. Del Giudice G, Rappuoli R, Didierlaurent AM. Correlates of adjuvanticity: A review on adjuvants in licensed vaccines. Seminars in Immunology. 2018
  38. 38. Perez S, Zimet GD, Tatar O, Stupiansky NW, Fisher WA, Rosberger Z. Human papillomavirus vaccines: Successes and future challenges. Drugs. 2018;78(14):1385-1396
  39. 39. Van Den Ende C, Marano C, Van Ahee A, Bunge EM, De Moerlooze L. The immunogenicity and safety of GSK's recombinant hepatitis B vaccine in adults: A systematic review of 30 years of experience. Expert Review of Vaccines. 2017;16(8):811-832

Written By

Ning Wang and Ting Wang

Submitted: 09 October 2018 Published: 05 November 2018