General characteristics of adjuvants and their mechanisms of action (part 2)

One of the major public health challenges today is development of new vaccines and technologies to optimize the vaccination process. There is a growing scientific interest in vaccine adjuvants that enhance vaccine immunogenicity. At present, numerous studies are underway to develop COVID-19 vaccines, including inactivated and subunit vaccines which contain adjuvants for efficient induction of immune response and solid immunity. The aim of the study was to systematise literature related to the analysis of the structure, mechanisms of action and stimulating properties of vaccine adjuvants (synthetic oligodeoxynucleotides, virosomes, polyoxidonium, sovidone), as well as to summarise data on the effects of adjuvants used in SARS-CoV, MERS-CoV, and SARS-CoV-2 vaccine development studies. The paper analyses the prospects for enhancing the stimulating effect of the adjuvants when used in combination with compounds having a different mechanism of action. It also analyses the results of studies of adjuvanted vaccines against SARS-CoV and MERS-CoV, which may be useful when selecting adjuvants with optimal efficacy and safety profiles to be used in SARS-CoV-2 vaccines under development. It was concluded that understanding of the mechanisms of action of adjuvants that mediate their stimulating effect on the body’s immune system will contribute to safe and effective use of adjuvants to enhance the immunogenicity of both authorised and new vaccines.

1. Liang Z, Zhu H, Wang X, Jing B, Li Z, Xia X, et al. Adjuvants for coronavirus vaccines. Front Immunol. 2020;11:589833. https://doi.org/10.3389/fimmu.2020.589833

2. Onishchenko GG, Sizikova TE, Lebedev VN, Borisevich SV. Analysis of promising approaches to COVID-19 vaccine development. BIOpreparaty. Profilaktika, diagnostika, lechenie = BIOpreparations. Prevention, Diagnosis, Treatment. 2020;20(4):216–27 (In Russ.) https://doi.org/10.30895/2221-996X-2020-20-4-216-227

3. Lau EH, Hsiung CA, Cowling BJ, Chen CH, Ho LM, Tsang T, et al. A comparative epidemiologic analysis of SARS in Hong Kong, Beijing and Taiwan. BMC Infect Dis. 2010;10:50. https://doi.org/10.1186/1471-2334-10-50

4. Polovinkina VS, Markov EYu. Structure and immune adjuvant properties of CPG-D. Meditsinskaya immunologiya = Medical Immunology (Russia). 2010;12(6):469–76 (In Russ.) https://doi.org/10.15789/1563-0625-2010-6-469-476

5. Vollmer J, Krieg AM. Immunotherapeutic applications of CpG oligodeoxynucleotide TLR9 agonists. Adv Drug Deliv Rev. 2009;61(3):195–204. https://doi.org/10.1016/j.addr.2008.12.008

6. Scheiermann J, Klinman DM. Clinical evaluation of CpG oligonucleotides as adjuvants for vaccines targeting infectious diseases and cancer. Vaccine. 2014;32(48):6377–89. https://doi.org/10.1016/j.vaccine.2014.06.065

7. Campbell JD. Development of the CpG adjuvant 1018: a case study. In: Fox C, ed. Vaccine Adjuvants. Methods in Molecular Biology. V. 1494. New York: Humana Press; 2017. P. 15–27. https://doi.org/10.1007/978-1-4939-6445-1_2

8. Svitich OA, Lavrov VF, Kukina PI, Iskandaryan AA, Gankovskaya LV, Zverev VV. Agonists of receptors of the innate immunity and defective viral particles as new generation of adjuvants. Epidemiologiya i vaktsinoprofilaktika = Epidemiology and Vaccinal Prevention. 2018;17(1):76–86 (In Russ.). https://doi.org/10.31631/2073-3046-2018-17-1-76-86

9. Barton GM, Kagan JC. A cell biological view of Toll-like receptor function: regulation through compartmentalization. Nat Rev Immunol. 2009;9(8):535–42. https://doi.org/10.1038/nri2587

10. Klinman DM. Immunotherapeutic uses of CpG oligodeoxynucleotides. Nat Rev Immunol. 2004;4(4):249–59. https://doi.org/10.1038/nri132

11. Bode C, Zhao G, Steinhagen F, Kinjo T, Klinman DM. CpG DNA as a vaccine adjuvant. Expert Rev Vacсines. 2011;10(4):499–511. https://doi.org/10.1586/erv.10.174

12. Krieg AM. CpG motifs in bacterial DNA and their immune effects. Annu Rev Immunol. 2002;20:709–60. https://doi.org/10.1146/annurev.immunol.20.100301.064842

13. Sparwasser T, Vabulas RM, Villmow B, Lipford GB, Wagner H. Bacterial CpG-DNA activates dendritic cells in vivo: T helper cell-independent cytotoxic T cell responses to soluble proteins. Eur J Immunol. 2000;30(12):3591–7. https://doi.org/10.1002/1521-4141(200012)30:12%3C3591::aidimmu3591%3E3.0.co;2-j

14. Lipford GB, Sparwasser T, Zimmermann S, Heeg K, Wagner H. CpG-DNA-mediated transient lymphadenopathy is associated with a state of Th1 predisposition to antigen-driven responses. J Immunol. 2000;165(3):1228–35. https://doi.org/10.4049/jimmunol.165.3.1228

15. Hyer R, McGuire DK, Xing B, Jackson S, Janssen R. Safety of a two-dose investigational hepatitis B vaccine, HBsAg-1018, using a toll-like receptor 9 agonist adjuvant in adults. Vaccine. 2018;36(19):2604–11. https://doi.org/10.1016/j.vaccine.2018.03.067

16. Ko EJ, Lee Y, Lee YT, Kim YJ, Kim KH, Kang SM. MPL and CpG combination adjuvants promote homologous and heterosubtypic cross protection of inactivated split influenza virus vaccine. Antiviral Res. 2018;156:107–15. https://doi.org/10.1016/j.antiviral.2018.06.004

17. Huckriede A, Bungener L, Stegmann T, Daemen T, Medema J, Palache AM, Wilschut J. The virosome concept for influenza vaccines. Vaccine. 2005;23(Suppl 1):S26–38. https://doi.org/10.1016/j.vaccine.2005.04.026

18. Bron R, Ortiz A, Dijkstra J, Stegmann T, Wilschut J. Preparation, properties, and applications of reconstituted influenza virus envelopes (virosomes). Methods Enzymol. 1993;220:313–31. https://doi.org/10.1016/0076-6879(93)20091-g

19. Wilschut J. Influenza vaccines: the virosome concept. Immunol Lett. 2009;122(2):118–21. https://doi.org/10.1016/j.imlet.2008.11.006

20. Moser C, Müller M, Kaeser MD, Weydemann U, Amacker M. Influenza virosomes as vaccine adjuvant and carrier system. Expert Rev Vaccines. 2013;12(7):779–91. https://doi.org/10.1586/14760584.2013.811195

21. Bovier PA. Epaxal®: a virosomal vaccine to prevent hepatitis A infection. Expert Rev Vaccines. 2008;7(8):1141–50. https://doi.org/10.1586/14760584.7.8.1141

22. Liu H, de Vries-Idema J, Ter Veer W, Wilschut J, Huckriede A. Influenza virosomes supplemented with GPI-0100 adjuvant: a potent vaccine formulation for antigen dose sparing. Med Microbiol Immunol. 2014;203(1):47–55. https://doi.org/10.1007/s00430-013-0313-2

23. Dong W, Bhide Y, Marsman S, Holtrop M, Meijerhof T, de Vries-Idema J, et al. Monophosphoryl lipid A-adjuvanted virosomes with Ni-chelating lipids for attachment of conserved viral proteins as cross-protective influenza vaccine. Biotechnol J. 2018;13(4):e1700645. https://doi.org/10.1002/biot.201700645

24. Kabanov VA. From synthetic polyelectrolytes to polymersubunit vaccines. Pure Appl Chem. 2004;76(9):1659–77. https://doi.org/10.1351/pac200476091659

25. Pinegin BV, Nekrasov AV, Khaitov RM. Immunomodulator Polyoxidonium: mechanisms of action and aspects of clinical application. Tsitokiny i vospalenie = Cytokines and Inflammation. 2004;3(3):41–7 (In Russ.)

26. Alexia C, Cren M, Louis-Plence P, Vo DN, El Ahmadi Y, Dufourcq-Lopez E, et al. Polyoxidonium® activates cytotoxic lymphocyte responses through dendritic cell maturation: clinical effects in breast cancer. Front Immunol. 2019;10:2693. https://doi.org/10.3389/fimmu.2019.02693

27. 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

28. Luss LV. The role of Polyoxidonium as immunomodulating and immunoadjuvant agent in flu prevention. Meditsinskiy sovet = Medical Council. 2013;(8):50–5 (In Russ.)

29. Talayev V, Zaichenko I, Svetlova M, Matveichev A, Babaykina O, Voronina E, Mironov A. Low-dose influenza vaccine Grippol Quadrivalent with adjuvant Polyoxidonium induces a T helper-2 mediated humoral immune response and increases NK cell activity. Vaccine. 2020;38(42):6645–55. https://doi.org/10.1016/j.vaccine.2020.07.053

30. Nikiforova AN, Mironov AN. Vaccinal prevention and search of new adjuvants. Sibirskiy meditsinskiy zhurnal (Irkutsk) = Siberian Medical Journal (Irkutsk). 2011;104(5):15–9 (In Russ.)

31. 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

32. Wu A, Peng Y, Huang B, Ding X, Wang X, Niu P, et al. Genome composition and divergence of the novel coronavirus (2019-nCoV) originating in China. Cell Host Microbe. 2020;27(3):325–8. https://doi.org/10.1016/j.chom.2020.02.001

33. Zhou P, Yang XL, Wang XG, Hu B, Zhang L, Zhang W, et al. A pneumonia outbreak associated with a new coronavirus of probable bat origin. Nature. 2020;579(7798):270–3. https://doi.org/10.1038/s41586-020-2012-7

34. Lu R, Zhao X, Li J, Niu P, Yang B, Wu H, et al. Genomic characterisation and epidemiology of 2019 novel coronavirus: implications for virus origins and receptor binding. Lancet. 2020;395(10224):565–74. https://doi.org/10.1016/S0140-6736(20)30251-8

35. Du L, Tai W, Zhou Y, Jiang S. Vaccines for the prevention against the threat of MERS-CoV. Expert Rev Vaccines. 2016;15(9):1123–34. https://doi.org/10.1586/14760584.2016.1167603

36. Jiang S, He Y, Liu S. SARS vaccine development. Emerg Infect Dis. 2005;11(7):1016–20. https://doi.org/10.3201/1107.050219

37. Tang L, Zhu Q, Qin E, Yu M, Ding Z, Shi H, et al. Inactivated SARS-CoV vaccine prepared from whole virus induces a high level of neutralizing antibodies in BALB/c mice. DNA Cell Biol. 2004;23(6):391–4. https://doi.org/10.1089/104454904323145272

38. Coleman CM, Liu YV, Mu H, Taylor JK, Massare M, Flyer DC, et al. Purified coronavirus spike protein nanoparticles induce coronavirus neutralizing antibodies in mice. Vaccine. 2014;32(26):3169– 74. https://doi.org/10.1016/j.vaccine.2014.04.016

39. Zakhartchouk AN, Sharon C, Satkunarajah M, Auperin T, Viswanathan S, Mutwiri G, et al. Immunogenicity of a receptorbinding domain of SARS coronavirus spike protein in mice: implications for a subunit vaccine. Vaccine. 2007;25(1):136– 43. https://doi.org/10.1016/j.vaccine.2006.06.084

40. Takasuka N, Fujii H, Takahashi Y, Kasai M, Morikawa S, Itamura S, et al. A subcutaneously injected UV-inactivated SARS coronavirus vaccine elicits systemic humoral immunity in mice. Int Immunol. 2004;16(10):1423–30. https://doi.org/10.1093/intimm/dxh143

41. Bolles M, Deming D, Long K, Agnihothram S, Whitmore A, Ferris M, et al. A double-inactivated severe acute respiratory syndrome coronavirus vaccine provides incomplete protection in mice and induces increased eosinophilic proinflammatory pulmonary response upon challenge. J Virol. 2011;85(23):12201–15. https://doi.org/10.1128/jvi.06048-11

42. Zhou Z, Post P, Chubet R, Holtz K, McPherson C, Petric M, Cox M. A recombinant baculovirus-expressed S glycoprotein vaccine elicits high titers of SARS-associated coronavirus (SARS-CoV) neutralizing antibodies in mice. Vaccine. 2006;24(17):3624–31. https://doi.org/10.1016/j.vaccine.2006.01.059

43. Agrawal AS, Tao X, Algaissi A, Garron T, Narayanan K, Peng BH, et al. Immunization with inactivated Middle East Respiratory Syndrome coronavirus vaccine leads to lung immunopathology on challenge with live virus. Hum Vaccin Immunother. 2016;12(9):2351–6. https://doi.org/10.1080/21 645515.2016.1177688

44. Yasui F, Kai C, Kitabatake M, Inoue S, Yoneda M, Yokochi S, et al. Prior immunization with severe acute respiratory syndrome (SARS)-associated coronavirus (SARS-CoV) nucleocapsid protein causes severe pneumonia in mice infected with SARS-CoV. J Immunol. 2008;181(9):6337–48. https://doi.org/10.4049/jimmunol.181.9.6337

45. Gao Q, Bao L, Mao H, Wang L, Xu K, Yang M, et al. Development of an inactivated vaccine for SARSCoV-2. Science. 2020;369(6499):77–81. https://doi.org/10.1101/2020.04.17.046375

46. Chen WH, Tao X, Agrawal AS, Algaissi A, Peng BH, Pollet J, et al. Yeast-expressed SARS-CoV recombinant receptorbinding domain (RBD219-N1) formulated with aluminum hydroxide induces protective immunity and reduces immune enhancement. Vaccine. 2020;38(47):7533–41. https://doi.org/10.1016/j.vaccine.2020.09.061

47. Graham BS. Rapid COVID-19 vaccine development. Science. 2020;368(6494):945–6. https://doi.org/10.1126/science.abb8923

48. Rydyznski Moderbacher C, Ramirez SI, Dan JM, Grifoni A, Hastie KM, Weiskopf D, et al. Antigen-specific adaptive immunity to SARS-CoV-2 in acute COVID-19 and associations with age and disease severity. Cell. 2020;183(4):996–1012. e19. https://doi.org/10.1016/j.cell.2020.09.038

49. Tseng CT, Sbrana E, Iwata-Yoshikawa N, Newman PC, Garron T, Atmar RL, et al. Immunization with SARS coronavirus vaccines leads to pulmonary immunopathology on challenge with the SARS virus. PLoS One. 2012;7(4):e35421. https://doi.org/10.1371/journal.pone.0035421

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

51. 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

52. O’Hagan DT, Ott GS, De Gregorio E, Seubert A. The mechanism of action of MF59 — an innately attractive adjuvant formulation. Vaccine. 2012;30(29):4341–8. https://doi.org/10.1016/j.vaccine.2011.09.061

53. Zhang N, Channappanavar R, Ma C, Wang L, Tang J, Garron T, et al. Identification of an ideal adjuvant for receptorbinding domain-based subunit vaccines against Middle East respiratory syndrome coronavirus. Cell Mol Immunol. 2016;13(2):180–90. https://doi.org/10.1038/cmi.2015.03

54. Kong WP, Xu L, Stadler K, Ulmer JB, Abrignani S, Rappuoli R, Nabel GJ. Modulation of the immune response to the severe acute respiratory syndrome spike glycoprotein by gene-based and inactivated virus immunization. J Virol. 2005;79(22):13915–23. https://doi.org/10.1128/jvi.79.22.13915-13923.2005

55. Tang J, Zhang N, Tao X, Zhao G, Guo Y, Tseng CT, et al. Optimization of antigen dose for a receptor-binding domain-based subunit vaccine against MERS coronavirus. Hum Vaccin Immunother. 2015;11(5):1244–50. https://doi.org/10.1080/21645515.2015.1021527

56. Stadler K, Roberts A, Becker S, Vogel L, Eickmann M, Kolesnikova L, et al. SARS vaccine protective in mice. Emerg Infect Dis. 2005;11(8):1312–4. https://doi.org/10.3201/eid1108.041003

57. Kim YS, Son A, Kim J, Kwon SB, Kim MH, Kim P, et al. Chaperna-Mediated Assembly of ferritin-based Middle East respiratory syndrome-coronavirus nanoparticles. Front Immunol. 2018;9:1093. https://doi.org/10.3389/fimmu.2018.01093

58. Bisht H, Roberts A, Vogel L, Subbarao K, Moss B. Neutralizing antibody and protective immunity to SARS coronavirus infection of mice induced by a soluble recombinant polypeptide containing an N-terminal segment of the spike glycoprotein. Virology. 2005;334(2):160–5. https://doi.org/10.1016/j.virol.2005.01.042

59. Roberts A, Lamirande EW, Vogel L, Baras B, Goossens G, Knott I, et al. Immunogenicity and protective efficacy in mice and hamsters of a β-propiolactone inactivated whole virus SARS-CoV vaccine. Viral Immunol. 2010;23(5):509–19. https://doi.org/10.1089/vim.2010.0028

60. Iwata-Yoshikawa N, Uda A, Suzuki T, Tsunetsugu-Yokota Y, Sato Y, Morikawa S, et al. Effects of Toll-like receptor stimulation on eosinophilic infiltration in lungs of BALB/c mice immunized with UV-inactivated severe acute respiratory syndrome-related coronavirus vaccine. J Virol. 2014;88(15):8597–614. https://doi.org/10.1128/jvi.00983-14

61. Zhao J, Wohlford-Lenane C, Zhao J, Fleming E, Lane TE, McCray PB Jr, Perlman S. Intranasal treatment with poly(I•C) protects aged mice from lethal respiratory virus infections. J Virol. 2012;86(21):11416–24. https://doi.org/10.1128/ jvi.01410-12

62. Steinhagen F, Kinjo T, Bode C, Klinman DM. TLR-based immune adjuvants. Vaccine. 2011;29(17):3341–55. https://doi.org/10.1016/j.vaccine.2010.08.002

63. Channappanavar R, Fett C, Zhao J, Meyerholz DK, Perlman S. Virus-specific memory CD8 T cells provide substantial protection from lethal severe acute respiratory syndrome coronavirus infection. J Virol. 2014;88(19):11034–44. https://doi.org/10.1128/jvi.01505-14

64. Zhao K, Wang H, Wu C. The immune responses of HLAA*0201 restricted SARS-CoV S peptide-specific CD8+ T cells are augmented in varying degrees by CpG ODN, PolyI:C and R848. Vaccine. 2011;29(38):6670–8. https://doi.org/10.1016/j.vaccine.2011.06.100

65. Duthie MS, Windish HP, Fox CB, Reed SG. Use of defined TLR ligands as adjuvants within human vaccines. Immunol Rev. 2011;239(1):178–96. https://doi.org/10.1111/j.1600-065x.2010.00978.x

66. Gai W, Zou W, Lei L, Luo J, Tu H, Zhang Y, et al. Effects of different immunization protocols and adjuvant on antibody responses to inactivated SARS-CoV vaccine. Viral Immunol. 2008;21(1):27–37. https://doi.org/10.1089/vim.2007.0079

67. Weeratna RD, Brazolot Millan CL, McCluskie MJ, Davis HL. CpG ODN can re-direct the Th bias of established Th2 immune responses in adult and young mice. FEMS Immunol Med Microbiol. 2001;32(1):65–71. https://doi.org/10.1111/j.1574-695X.2001.tb00535.x

68. Jiaming L, Yanfeng Y, Yao D, Yawei H, Linlin B, Baoying H, et al. The recombinant N-terminal domain of spike proteins is a potential vaccine against Middle East respiratory syndrome coronavirus (MERS-CoV) infection. Vaccine. 2017;35(1):10– 8. https://doi.org/10.1016/j.vaccine.2016.11.064

69. Lan J, Deng Y, Chen H, Lu G, Wang W, Guo X, et al. Tailoring subunit vaccine immunity with adjuvant combinations and delivery routes using the Middle East respiratory coronavirus (MERS-CoV) receptor-binding domain as an antigen. PLoS One. 2014;9(11):e112602. https://doi.org/10.1371/journal.pone.0112602

70. Honda-Okubo Y, Barnard D, Ong CH, Peng BH, Tseng CT, Petrovsky N. severe acute respiratory syndrome-associated coronavirus vaccines formulated with delta inulin adjuvants provide enhanced protection while ameliorating lung eosinophilic immunopathology. J Virol. 2015;89(6):2995–3007. https://doi.org/10.1128/jvi.02980-14

71. Thanh Le T, Andreadakis Z, Kumar A, Gómez Román R, Tollefsen S, Saville M, Mayhew S. The COVID-19 vaccine development landscape. Nat Rev Drug Discov. 2020;19(5):305–6. https://doi.org/10.1038/d41573-020-00073-5

72. Iwasaki A, Yang Y. The potential danger of suboptimal antibody responses in COVID-19. Nat Rev Immunol. 2020;20(6):339– 41. https://doi.org/10.1038/s41577-020-0321-6

73. Wang Q, Zhang L, Kuwahara K, Li L, Liu Z, Li T, et al. Immunodominant SARS coronavirus epitopes in humans elicited both enhancing and neutralizing effects on infection in non-human primates. ACS Infect Dis. 2016;2(5):361–76. https://doi.org/10.1021/acsinfecdis.6b00006

74. Wan Y, Shang J, Sun S, Tai W, Chen J, Geng Q, et al. Molecular mechanism for antibody-dependent enhancement of coronavirus entry. J Virol. 2020;94(5):e02015–19. https://doi.org/10.1128/JVI.02015-19

75. Heaton PM. The Covid-19 vaccine-development multiverse. N Engl J Med. 2020;383(20):1986–8. https://doi.org/10.1056/nejme2025111

76. Kuo TY, Lin MY, Coffman RL, Campbell JD, Traquina P, Lin YJ, et al. Development of CpG-adjuvanted stable prefusion SARS-CoV-2 spike antigen as a subunit vaccine against COVID-19. Sci Rep. 2020;10(1):20085. https://doi.org/10.1038/s41598-020-77077-z

77. V’kovski P, Gultom M, Kelly J, Steiner S, Russeil J, Mangeat B, et al. Disparate temperature-dependent virus — host dynamics for SARS-CoV-2 and SARS-CoV in the human respiratory epithelium. BioRxiv. 2020.04.27.062315. https://doi.org/10.1101/2020.04.27.062315

78. Uematsu S, Fujimoto K, Jang MH, Yang BG, Jung YJ, Nishiyama M, et al. Regulation of humoral and cellular gut immunity by lamina propria dendritic cells expressing Tolllike receptor 5. Nat Immunol. 2008;9(7):769–76. https://doi.org/10.1038/ni.1622