General Characteristics of Adjuvants and Their Mechanism of Action (Part 1)

One of priority issues of the present-day healthcare system is development of new vaccines and improvement of existing ones due to decreasing immunocompetence of the population, emergence of new infections and reemergence of old ones which were previously thought to be under control. Adjuvants have proven to be integral and important components of modern vaccines, as they enhance immune response to the vaccine antigen. However, despite a lot of effort put into their development, only a small number of adjuvants are currently used in clinical practice. The aim of the study was to systematise literature data on the adjuvants’ mechanisms of action, their specific structure, composition, and stimulation effects that mediate their immunoadjuvant properties. The paper summarises data on adjuvants used as components in licensed vaccines, describes their characteristics, analyses molecular mechanisms of their action in order to establish correlation between their structure and activity, which is important for the development of more efficacious and safe adjuvants. The paper cites advanced developments aimed at enhancing stimulation effects of existing adjuvants. It concludes by stating that the key research area aimed at improving vaccination efficacy is the study of mechanisms that contribute to the development of effective protection against infectious agents, as well as analysis of how to use adjuvants to stimulate the body’s defensive mechanisms, primarily by impacting the innate immunity.

1. Shi S, Zhu H, Xia X, Liang Z, Ma X, Sun B. Vaccine adjuvants: understanding the structure and mechanism of adjuvanticity. Vaccine. 2019;37(24):3167–78. https://doi.org/10.1016/j.vaccine.2019.04.055

2. Medunitsyn NV, Mironov AN, Movsesyants AA. Theory and practice of vaccinology. Moscow: REMEDIUM; 2015 (In Russ.)

3. Chan EH, Brewer TF, Madoff LC, Pollack MP, Sonricker AL, Keller M, et al. Global capacity for emerging infectious disease detection. Proc Natl Acad Sci USA. 2010;107(50):21701–6. https://doi.org/10.1073/pnas.1006219107

4. WHO Ebola Response Team, Aylward B, Barboza P, Bawo L, Bertherat E, Bilivogui P, et al. Ebola virus disease in West Africa – the first 9 months of the epidemic and forward projections. N Engl J Med. 2014;371(16):1481–95. https://doi.org/10.1056/NEJMoa1411100

5. Gupta T, Gupta SK. Potential adjuvants for the development of a SARS-CoV-2 vaccine based on experimental results from similar coronaviruses. Int Immunopharmacol. 2020;86:106717. https://doi.org/10.1016/j.intimp.2020.106717

6. Falsey AR, Treanor JJ, Tornieporth N, Capellan J, Gorse GJ. Randomized, double-blind controlled phase 3 trial comparing the immunogenicity of high-dose and standard-dose influenza vaccine in adults 65 years of age and older. J Infect Dis. 2009;200(2):172–80. https://doi.org/10.1086/599790

7. Leroux-Roels G. Unmet needs in modern vaccinology: adjuvants to improve the immune response. Vaccine. 2010;28(Suppl 3):25–36. https://doi.org/10.1016/j.vaccine.2010.07.021

8. Banzhoff A, Gasparini R, Laghi-Pasini F, Staniscia T, Durando P, Montomoli E, et al. MF59-adjuvanted H5N1 vaccine induces immunologic memory and heterotypic antibody responses in non-elderly and elderly adults. PLoS ONE. 2009;4(2):e4384. https://doi.org/10.1371/journal.pone.0004384

9. Jackson LA, Campbell JD, Frey SE, Edwards KM, Keitel WA, Kotloff KL, et al. Effect of varying doses of a monovalent H7N9 influenza vaccine with and without AS03 and MF59 adjuvants on immune response: a randomized clinical trial. JAMA. 2015;314(3):237–46. https://doi.org/10.1001/jama.2015.7916

10. Reed SG, Orr MT, Fox CB. Key roles of adjuvants in modern vaccines. Nat Med. 2013;19(12):1597–608. https://doi.org/10.1038/nm.3409

11. Powell BS, Andrianov AK, Fusco PC. Polyionic vaccine adjuvants: another look at aluminum salts and polyelectrolytes. Clin Exp Vaccine Res. 2015;4(1):23–45. https://doi.org/10.7774/cevr.2015.4.1.23

12. Coffman RL, Sher A, Seder RA. Vaccine adjuvants: putting innate immunity to work. Immunity. 2010;33(4):492–503. https://doi.org/10.1016/j.immuni.2010.10.002

13. Harandi AM. Systems analysis of human vaccine adjuvants. Semin Immunol. 2018;39:30–4. https://doi.org/10.1016/j.smim.2018.08.001

14. Sarkar I, Garg R, van Drunen Littel-van den Hurk S. Selection of adjuvants for vaccines targeting specific pathogens. Expert Rev Vaccines. 2019;18(5):505–21. https://doi.org/10.1080/14760584.2019.1604231

15. Alving CR, Matyas GR, Torres O, Jalah R, Beck Z. Adjuvants for vaccines to drugs of abuse and addiction. Vaccine. 2014;32(42):5382–9. https://doi.org/10.1016/j.vaccine.2014.07.085

16. HogenEsch H, O'Hagan DT, Fox CB. Optimizing the utilization of aluminum adjuvants in vaccines: you might just get what you want. NPJ Vaccines. 2018;3:51. https://doi.org/10.1038/s41541-018-0089-x

17. He P, Zou Y, Hu Z. Advances in aluminum hydroxide-based adjuvant research and its mechanism. Hum Vaccin Immunother. 2015;11(2):477–88. https://doi.org/10.1080/21645515.2014.1004026

18. Trier NH, Güven E, Skogstrand K, Ciplys E, Slibinskas R, Houen G. Comparison of immunological adjuvants. APMIS. 2019;127(9):635–41. https://doi.org/10.1111/apm.12976

19. Glenny AT, Pope CG, Waddington H, Wallace U. Immunology notes. XXIII. The antigenic value of toxoid precipitated by potassium alum. J Pathol Bacteriol. 1926;29:31–40. http://dx.doi.org/10.1002/path.1700290106

20. Awate S, Babiuk LA, Mutwiri G. Mechanisms of action of adjuvants. Front Immunol. 2013;4:114. https://doi.org/10.3389/fimmu.2013.00114

21. Aimanianda V, Haensler J, Lacroix-Desmazes S, Kaveri SV, Bayry J. Novel cellular and molecular mechanisms of induction of immune responses by aluminum adjuvants. Trends Pharmacol Sci. 2009;30(6):287–95. https://doi.org/10.1016/j.tips.2009.03.005

22. Ghimire TR, Benson RA, Garside P, Brewer JM. Alum increases antigen uptake, reduces antigen degradation and sustains antigen presentation by DCs in vitro. Immunol Lett. 2012;147(1-2):55–62. https://doi.org/10.1016/j.imlet.2012.06.002

23. Calabro S, Tortoli M, Baudner BC, Pacitto A, Cortese M, O'Hagan DT, et al. Vaccine adjuvants alum and MF59 induce rapid recruitment of neutrophils and monocytes that participate in antigen transport to draining lymph nodes. Vaccine. 2011;29(9):1812–23. https://doi.org/10.1016/j.vaccine.2010.12.090

24. Lu F, Hogenеsch H. Kinetics of the inflammatory response following intramuscular injection of aluminum adjuvant. Vaccine. 2013;31(37):3979–86. https://doi.org/10.1016/j.vaccine.2013.05.107

25. Apostólico JS, Lunardelli VA, Coirada FC, Boscardin SB, Rosa DS. Adjuvants: classification, modus operandi, and licensing. J Immunol Res. 2016;2016:1459394. https://doi.org/10.1155/2016/1459394

26. Hutchison S, Benson RA, Gibson VB, Pollock AH, Garside P, Brewer JM. Antigen depot is not required for alum adjuvanticity. FASEB J. 2012;26(3):1272–9. https://doi.org/10.1096/fj.11-184556

27. Hornung V, Bauernfeind F, Halle A, Samstad EO, Kono H, Rock KL, et al. Silica crystals and aluminum salts activate the NALP3 inflammasome through phagosomal destabilization. Nat Immunol. 2008;9(8):847–56. https://doi.org/10.1038/ni.1631

28. Eisenbarth SC, Colegio OR, O'Connor W, Sutterwala FS, Flavell RA. Crucial role for the Nalp3 inflammasome in the immunostimulatory properties of aluminium adjuvants. Nature. 2008;453(7198):1122–6. https://doi.org/10.1038/nature06939

29. Li H, Willingham SB, Ting JP, Re F. Cutting edge: inflammasome activation by alum and alum's adjuvant effect are mediated by NLRP3. J Immunol. 2008;181(1):17–21. https://doi.org/10.4049/jimmunol.181.1.17

30. Marrack P, McKee AS, Munks MW. Towards an understanding of the adjuvant action of aluminium. Nat Rev Immunol. 2009;9(4):287–93. https://doi.org/10.1038/nri2510

31. Del Giudice G, Rappuoli R, Didierlaurent AM. Correlates of adjuvanticity: a review on adjuvants in licensed vaccines. Semin Immunol. 2018;39:14–21. https://doi.org/10.1016/j.smim.2018.05.001

32. Franchi L, Núñez G. The Nlrp3 inflammasome is critical for aluminium hydroxide-mediated IL-1beta secretion but dispensable for adjuvant activity. Eur J Immunol. 2008;38(8):2085–9. https://doi.org/10.1002/eji.200838549

33. McKee AS, Munks MW, MacLeod MKL, Fleenor CJ, Van Rooijen N, Kappler JW, Marrack P. Alum induces innate immune responses through macrophage and mast cell sensors, but these sensors are not required for alum to act as an adjuvant for specific immunity. J Immunol. 2009;183(7):4403–14. https://doi.org/10.4049/jimmunol.0900164

34. Flach TL, Ng G, Hari A, Desrosiers MD, Zhang P, Ward SM, et al. Alum interaction with dendritic cell membrane lipids is essential for its adjuvanticity. Nat Med. 2011;17(4):479–87. https://doi.org/10.1038/nm.2306

35. Kool M, Soullié T, van Nimwegen M, Willart MAM, Muskens F, Jung S, et al. Alum adjuvant boosts adaptive immunity by inducing uric acid and activating inflammatory dendritic cells. J Exp Med. 2008;205(4):869–82. https://doi.org/10.1084/jem.20071087

36. Liang F, Lindgren G, Sandgren KJ, Thompson EA, Francica JR, Seubert A, et al. Vaccine priming is restricted to draining lymph nodes and controlled by adjuvant-mediated antigen uptake. Sci Transl Med. 2017;9(393):eaal2094. https://doi.org/10.1126/scitranslmed.aal2094

37. Kooijman S, Brummelman J, van Els CACM, Marino F, Heck AJR, Mommen GPM, et al. Novel identified aluminum hydroxide-induced pathways prove monocyte activation and pro-inflammatory preparedness. J Proteomics. 2018;175:144–55. https://doi.org/10.1016/j.jprot.2017.12.021

38. Kooijman S, Brummelman J, van Els CACM, Marino F, Heck AJR, van Riet E, et al. Vaccine antigens modulate the innate response of monocytes to Al(OH)3. PLoS One. 2018;13(5):e0197885. https://doi.org/10.1371/journal.pone.0197885

39. HogenEsch H. Mechanisms of stimulation of the immune response by aluminium adjuvants. Vaccine. 2002;20(Suppl 3):S34–9. https://doi.org/10.1016/S0264-410X(02)00169-X

40. Marichal T, Ohata K, Bedoret D, Mesnil C, Sabatel C, Kobiyama K, et al. DNA released from dying host cells mediates aluminum adjuvant activity. Nat Med. 2011;17(8):996–1002. https://doi.org/10.1038/nm.2403

41. Mckee AS, Burchill MA, Munks MW, Jin L, Kappler JW, Friedman RS, et al. Host DNA released in response to aluminum adjuvant enhances MHC class II-mediated antigen presentation and prolongs CD4 T-cell interactions with dendritic cells. Proc Natl Acad Sci USA. 2013;110(12):Е1122–31. https://doi.org/10.1073/pnas.1300392110

42. Stephen J, Scales HE, Benson RA, Erben D, Garside P, Brewer JM. Neutrophil swarming and extracellular trap formation play a significant role in Alum adjuvant activity. NPJ Vaccines. 2017;2:1. https://doi.org/10.1038/s41541-016-0001-5

43. Mori A, Oleszycka E, Sharp FA, Coleman M, Ozasa Y, Singh M, et al. The vaccine adjuvant alum inhibits IL-12 by promoting PI3 kinase signaling while chitosan does not inhibit IL-12 and enhances Th1 and Th17 responses. Eur J Immunol. 2012;42(10):2709–19. https://doi.org/10.1002/eji.201242372

44. Oleszycka E, McCluskey S, Sharp FA, Muñoz-Wolf N, Hams E, Gorman AL, et al. The vaccine adjuvant alum promotes IL-10 production that suppresses Th1 responses. Eur J Immunol. 2018;48(4):705–15. https://doi.org/10.1002/eji.201747150

45. Didierlaurent AM, Morel S, Lockman L, Giannini SL, Bisteau M, Carlsen H, et al. AS04, an aluminum salt- and TLR4 agonist-based adjuvant system, induces a transient localized innate immune response leading to enhanced adaptive immunity. J Immunol. 2009;183(10):6186–97. https://doi.org/10.4049/jimmunol.0901474

46. Ebensen T, Delandre S, Prochnow B, Guzmán CA, Schulze K. The combination vaccine adjuvant system alum/c-di-AMP results in quantitative and qualitative enhanced immune responses post immunization. Front Cell Infect Microbiol. 2019;9:31. https://doi.org/10.3389/fcimb.2019.00031

47. Orr MT, Khandhar AP, Seydoux E, Liang H, Gage E, Mikasa T, et al. Reprogramming the adjuvant properties of aluminum oxyhydroxide with nanoparticle technology. NPJ Vaccines. 2019;4:1. https://doi.org/10.1038/s41541-018-0094-0

48. Ko EJ, Kang SM. Immunology and efficacy of MF59-adjuvanted vaccines. Hum Vaccin Immunother. 2018;14(12):3041–5. https://doi.org/10.1080/21645515.2018.1495301

49. Zedda L, Forleo-Neto E, Vertruyen A, Raes M, Marchant A, Jansen W, et al. Dissecting the immune response to MF59-adjuvanted and nonadjuvanted seasonal influenza vaccines in children less than three years of age. Pediatr Infect Dis J. 2015;34(1):73–8. http://dx.doi.org/10.1097/INF.0000000000000465

50. O'Hagan DT, Ott GS, Nest GV, Rappuoli R, Giudice GD. The history of MF59® adjuvant: a phoenix that arose from the ashes. Expert Rev Vaccines. 2013;12(1):13–30. https://doi.org/10.1586/erv.12.140

51. Seubert A, Calabro S, Santini L, Galli B, Genovese A, Valentini S, et al. Adjuvanticity of the oil-in-water emulsion MF59 is independent of Nlrp3 inflammasome but requires the adaptor protein MyD88. Proc Natl Acad Sci USA. 2011;108(27):11169–74. https://doi.org/10.1073/pnas.1107941108

52. Vono M, Taccone M, Caccin P, Gallotta M, Donvito G, Falzoni S, et al. The adjuvant MF59 induces ATP release from muscle that potentiates response to vaccination. Proc Natl Acad Sci USA. 2013;110(52):21095–100. https://doi.org/10.1073/pnas.1319784110

53. Mosca F, Tritto E, Muzzi A, Monaci E, Bagnoli F, Iavarone C, et al. Molecular and cellular signatures of human vaccine adjuvants. Proc Natl Acad Sci USA. 2008;105(30):10501–6. https://doi.org/10.1073/pnas.0804699105

54. Seubert A, Monaci E, Pizza M, O'Hagan DT, Wack A. The adjuvants aluminum hydroxide and MF59 induce monocyte and granulocyte chemoattractants and enhance monocyte differentiation toward dendritic cells. J Immunol. 2008;180(8):5402–12. https://doi.org/10.4049/jimmunol.180.8.5402

55. De Gregorio E, Caproni E, Ulmer JB. Vaccine adjuvants: mode of action. Front Immunol. 2013;4:214. https://doi.org/10.3389/fimmu.2013.00214

56. Cioncada R, Maddaluno M, Vo HTM, Woodruff M, Tavarini S, Sammicheli C, et al. Vaccine adjuvant MF59 promotes the intranodal differentiation of antigen-loaded and activated monocyte-derived dendritic cells. PLoS One. 2017;12(10):e0185843. https://doi.org/10.1371/journal.pone.0185843

57. Ko EJ, Lee YT, Kim KH, Jung YJ, Lee Y, Denning TL, Kang SM. Effects of MF59 adjuvant on induction of isotype-switched IgG antibodies and protection after immunization with T-dependent influenza virus vaccine in the absence of CD4+ T cells. J Virol. 2016;90(15):6976–88. https://doi.org/10.1128/JVI.00339-16

58. Ko EJ, Lee YT, Kim KH, Lee Y, Jung YJ, Kim MC, et al. Roles of aluminum hydroxide and monophosphoryl lipid A adjuvants in overcoming CD4+ T cell deficiency to induce isotype-switched IgG antibody responses and protection by T-dependent influenza vaccine. J Immunol. 2017;198(1):279–91. https://doi.org/10.4049/jimmunol.1600173

59. Pittman PR. Aluminum-containing vaccine associated adverse events. Role of route of administration and gender. Vaccine. 2002;20(Suppl 3):S48–50. https://doi.org/10.1016/s0264-410x(02)00172-x

60. Reisinger KS, Holmes SJ, Pedotti P, Arora AK, Lattanzi M. A dose-ranging study of MF59®-adjuvanted and non-adjuvanted A/H1N1 pandemic influenza vaccine in young to middle-aged and older adult populations to assess safety, immunogenicity, and antibody persistence one year after vaccination. Hum Vaccin Immunother. 2014;10(8):2395–407. https://doi.org/10.4161/hv.29393

61. Garçon N, Vaughn DW, Didierlaurent AM. Development and evaluation of AS03, an Adjuvant System containing α-tocopherol and squalene in an oil-in-water emulsion. Expert Rev Vaccines. 2012;11(3):349–66. https://doi.org/10.1586/erv.11.192

62. Morel S, Didierlaurent A, Bourguignon P, Delhaye S, Baras B, Jacob V, et al. Adjuvant system AS03 containing α-tocopherol modulates innate immune response and leads to improved adaptive immunity. Vaccine. 2011;29(13):2461–73. https://doi.org/10.1016/j.vaccine.2011.01.011

63. Givord C, Welsby I, Detienne S, Thomas S, Assabban A, Lima Silva V, et al. Activation of the endoplasmic reticulum stress sensor IRE1α by the vaccine adjuvant AS03 contributes to its immunostimulatory properties. NPJ Vaccines. 2018;3:20. https://doi.org/10.1038/s41541-018-0058-4

64. Moris P, van der Most R, Leroux-Roels I, Clement F, Dramé M, Hanon E, et al. H5N1 influenza vaccine formulated with AS03A induces strong cross-reactive and polyfunctional CD4 T-cell responses. J Clin Immunol. 2011;31(3):443–54. https://doi.org/10.1007/s10875-010-9490-6

65. Petrovsky N, Aguilar JC. Vaccine adjuvants: current state and future trends. Immunol Cell Biol. 2004;82(5):488–96. https://doi.org/10.1111/j.0818-9641.2004.01272.x

66. Didierlaurent AM, Morel S, Lockman L, Giannini SL, Bisteau M, Carlsen H, et al. AS04, an aluminum salt- and TLR4 agonist-based adjuvant system, induces a transient localized innate immune response leading to enhanced adaptive immunity. J Immunol. 2009;183(10):6186–97. https://doi.org/10.4049/jimmunol.0901474

67. Cekic C, Casella CR, Eaves CA, Matsuzawa A, Ichijo H, Mitchell TC. Selective activation of the p38 MAPK pathway by synthetic monophosphoryl lipid A. J Biol Chem. 2009;284(46):31982–91. https://doi.org/10.1074/jbc.M109.046383

68. Coccia M, Collignon C, Hervé C, Chalon A, Welsby I, Detienne S, et al. Cellular and molecular synergy in AS01-adjuvanted vaccines results in an early IFNγ response promoting vaccine immunogenicity. NPJ Vaccines. 2017;2:25. https://doi.org/10.1038/s41541-017-0027-3

69. Mastelic B, Ahmed S, Egan WM, Del Giudice G, Golding H, Gust I, et al. Mode of action of adjuvants: implications for vaccine safety and design. Biologicals. 2010;38(5):594–601. https://doi.org/10.1016/j.biologicals.2010.06.002

70. Marciani DJ. Elucidating the mechanisms of action of saponin-derived adjuvants. Trends Pharm Sci. 2018;39(6):573–85. https://doi.org/10.1016/j.tips.2018.03.005

71. Marty-Roix R, Vladimer GI, Pouliot K, Weng D, Buglione-Corbett R, West K, et al. Identification of QS-21 as an inflammasome-activating molecular component of saponin adjuvants. J Biol Chem. 2016;291(3):1123–36. https://doi.org/10.1074/jbc.M115.683011

72. Lacaille-Dubois MA. Updated insights into the mechanism of action and clinical profile of the immunoadjuvant QS-21: A review. Phytomedicine. 2019;60:152905. https://doi.org/10.1016/j.phymed.2019.152905

73. Didierlaurent AM, Laupèze B, Di Pasquale A, Hergli N, Collignon C, Garçon N. Adjuvant system AS01: helping to overcome the challenges of modern vaccines. Expert Rev Vaccines. 2017;16(1):55–63. https://doi.org/10.1080/14760584.2016.1213632

74. Garçon N, Chomez P, Van Mechelen M. GlaxoSmithKline adjuvant systems in vaccines: concepts, achievements and perspectives. Expert Rev Vaccines. 2007;6(5):723–39. https://doi.org/10.1586/14760584.6.5.723

75. Laurens MB. RTS,S/AS01 vaccine (Mosquirix™): an overview. Hum Vaccin Immunother. 2020;16(3):480–9. https://doi.org/10.1080/21645515.2019.1669415

76. Leroux-Roels I, Leroux-Roels G, Clement F, Vandepapelière P, Vassilev V, Ledent E, Heineman TC. A phase 1/2 clinical trial evaluating safety and immunogenicity of a varicella zoster glycoprotein E subunit vaccine candidate in young and older adults. J Infect Dis. 2012;206(8):1280–90. https://doi.org/10.1093/infdis/jis497

77. Van der Meeren O, Hatherill M, Nduba V, Wilkinson RJ, Muyoyeta M, Van Brakel E, et al. Phase 2b controlled trial of M72/AS01E vaccine to prevent tuberculosis. N Engl J Med. 2018;379(13):1621–34. https://doi.org/10.1056/NEJMoa1803484

78. Burny W, Callegaro A, Bechtold V, Clement F, Delhaye S, Fissette L, et al. Different adjuvants induce common innate pathways that are associated with enhanced adaptive responses against a model antigen in humans. Front Immunol. 2017;8:943. https://doi.org/10.3389/fimmu.2017.00943

79. Giannini SL, Hanon E, Moris P, Van Mechelen M, Morel S, Dessy F, et al. Enhanced humoral and memory B cellular immunity using HPV16/18 L1 VLP vaccine formulated with the MPL/aluminium salt combination (AS04) compared to aluminium salt only. Vaccine. 2006;24(33-34):5937–49. https://doi.org/10.1016/j.vaccine.2006.06.005

80. Keam SJ, Harper DM. Human papillomavirus types 16 and 18 vaccine (recombinant, AS04 adjuvanted adsorbed) [Cervarix™]. Drugs. 2008;68(3):359–72. https://doi.org/10.2165/00003495-200868030-00007

81. Toussi DN, Massari P. Immune adjuvant effect of molecularly-defined toll-like receptor ligands. Vaccines (Basel). 2014;2(2):323–53. https://doi.org/10.3390/vaccines2020323

82. Garçon N, Morel S, Didierlaurent A, Descamps D, Wettendorff M, Van Mechelen M. Development of an AS04-adjuvanted HPV vaccine with the adjuvant system approach. BioDrugs. 2011;25(4):217–26. https://doi.org/10.2165/11591760-000000000-00000

83. Fabrizi F, Tarantino A, Castelnovo C, Martín P, Messa P. Recombinant Hepatitis B vaccine adjuvanted with as04 in dialysis patients: a prospective cohort study. Kidney Blood Press Res. 2015;40(6):584–92. https://doi.org/10.1159/000368534