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. Author manuscript; available in PMC: 2010 Mar 28.
Published in final edited form as: Adv Drug Deliv Rev. 2009 Jan 7;61(3):193–194. doi: 10.1016/j.addr.2008.12.003

CpG oligonucleotides as immunotherapeutic adjuvants: Innovative applications and delivery strategies

Editors: Aliasger K Salem1,*, George J Weiner2
PMCID: PMC2667912  NIHMSID: NIHMS106271  PMID: 19166888

Cytosine-phosphorothioate-guanine oligodeoxynucleotides (CpG ODN) have shown significant potential for treatment of a wide variety of diseases including cancer. CpG ODN can be used either as a standalone molecule or as an adjuvant to alternative therapies. CpG ODN with sequence patterns like those found in bacterial DNA activate potent cell-mediated immune responses [1, 2]. The specific sequence motif present in bacterial DNA that is responsible for triggering these immune responses is the unmethylated CpG dinucleotide flanked by two 5' purines and two 3' pyrimidines [1-4]. CpG ODN are taken up by cells via adsorptive endocytosis and bind to the toll-like receptor 9 (TLR9) present within the endosomes in the intracellular compartment of B cells and plasmacytoid dendritic cells [5-7]. The binding triggers an immunostimulatory cascade inducing the maturation, differentiation and proliferation of multiple immune cells including B and T lymphocytes, macrophages, natural killer cells and monocytes/macrophages that produce interleukin 1, 6, 12 and 18, interferon γ and tumor necrosis factor- α [8-10].

In contrast to anti-sense therapeutics which require continuous and prolonged exposure to the therapeutic nucleotide, the effects of CpG ODN can last for long periods of time even after a brief exposure. On the other hand, the duration, location, and formulation of CpG ODN therapy can have a profound effect on the immune response, and on the resulting therapeutic effects. This variability in immunologic and therapeutic response is not surprising given that CpG ODN can enhance antigen presentation, improve cellular killing mediated by T cells or NK cells, increase phagocytosis, increase production of cytokines that have anti tumor effects or initiate proapoptotic effects on malignant cells that express TLR9. Which of these mechanisms is most important therapeutically depends on many factors including the underlying condition being treated, the state of the immune system, the selection of other agents used in combination with CpG ODN, the route of administration and the formulation of the therapy.

It is therefore to be expected that the efficacy of CpG ODN as an adjuvant can be substantially improved using a range of drug delivery systems. This theme issue of Advanced Drug Delivery Reviews is to provide a comprehensive summary of the therapeutic potential of CpG ODN in a range of diseases and cancer models and the drug delivery systems that are being developed to further enhance CpG ODN adjuvant efficacy. Vollmer and Krieg provide a strong current overview of CpG ODN as a TLR9 agonist and its therapeutic potential [1, 11-13]. Krishnamachari and Salem discuss several drug delivery strategies for ensuring that both CpG ODN and antigen are co-delivered to the same antigen-presenting cells. These approaches include the use of biodegradable microparticles [14], CpG-antigen conjugates [15], liposomes [16], metallic nanorods [17], pulsatile releasing chips [18], and cell-microparticle hybrids [19]. Malyala, O'Hagan and Singh provide a more in depth review of the use of biodegradable microparticles for delivering CpG ODN whilst Tam offers an analysis of the use of liposomes for enhancing CpG ODN adjuvant efficacy in a variety of infectious diseases [20-22]. Mutwiri and colleagues discuss the use of polyphosphazenes, depot-forming formulations and simultaneous activation with other TLR agonists as methods through which CpG ODNs efficacy as an adjuvant can be improved [23]. Wagner's review provides an in depth analysis of CpG ODN-antigen conjugates and their comparison to biodegradable microparticles [24]. The theme issue then covers some of the recent developments on the therapeutic application of CpG ODN. Klinman and colleagues discuss the use of CpG ODN as an adjuvant for treatment of infectious diseases [21, 25]. Fonseca and Kline provide an overview of the use of CpG ODN in treating asthma, including its use in preventing development of airway remodelling and inhibition of atopic responses [26, 27]. Weiner provides an overview of the use of CpG ODN based therapy of lymphoid malignancies [28]. Lubaroff and Karan discuss the development of CpG ODN as an adjuvant to a vaccine for treating prostate cancer that is based on an adenovirus transduced to express a prostate specific antigen [29]. Finally Miles and Sandler discuss the use of CpG ODN for treating neuroblastoma either as a standalone molecule or as an adjuvant to alternative vaccine strategies [30].

This theme issue on the applications and delivery strategies of CpG ODN brings together a diverse and highly inter-disciplinary set of investigators that range from clinicians to basic scientists. The clinical application of CpG ODN as therapeutic agents is just beginning. This issue provides an up to date comprehensive reference guide of the therapeutic potential and complexities of CpG ODN as an immunotherapeutic adjuvant and the advanced drug delivery methods that can be used to enhance its efficacy.

Footnotes

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References

  • [1].Krieg AM, Yi AK, Matson S, Waldschmidt TJ, Bishop GA, Teasdale R, Koretzky GA, Klinman DM. Cpg Motifs in Bacterial-DNA Trigger Direct B-Cell Activation. Nature. 1995;374(6522):546–549. doi: 10.1038/374546a0. [DOI] [PubMed] [Google Scholar]
  • [2].Hemmi H, Takeuchi O, Kawai T, Kaisho T, Sato S, Sanjo H, Matsumoto M, Hoshino K, Wagner H, Takeda K, Akira S. A Toll-like receptor recognizes bacterial DNA. Nature. 2000;408(6813):740–745. doi: 10.1038/35047123. [DOI] [PubMed] [Google Scholar]
  • [3].Akira S, Takeda K, Kaisho T. Toll-like receptors: critical proteins linking innate and acquired immunity. Nature Immunology. 2001;2(8):675–680. doi: 10.1038/90609. [DOI] [PubMed] [Google Scholar]
  • [4].Millan CLB, Weeratna R, Krieg AM, Siegrist CA, Davis HL. CpG DNA can induce strong Th1 humoral and cell-mediated immune responses against hepatitis B surface antigen in young mice. Proc. Natl. Acad. Sci. U. S. A. 1998;95(26):15553–15558. doi: 10.1073/pnas.95.26.15553. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [5].Roman M, MartinOrozco E, Goodman S, Nguyen MD, Sato Y, Ronaghy A, Kornbluth RS, Richman DD, Carson DA, Raz E. Immunostimulatory DNA sequences function as T helper-1-promoting adjuvants. Nature Medicine. 1997;3(8):849–854. doi: 10.1038/nm0897-849. [DOI] [PubMed] [Google Scholar]
  • [6].Stacey KJ, Sweet MJ, Hume DA. Macrophages ingest and are activated by bacterial DNA. Journal of Immunology. 1996;157(5):2116–2122. [PubMed] [Google Scholar]
  • [7].Sun SQ, Zhang XH, Tough DF, Sprent J. Type I interferon-mediated stimulation of T cells by CgG DNA. Journal of Experimental Medicine. 1998;188(12):2335–2342. doi: 10.1084/jem.188.12.2335. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [8].Cowdery JS, Krieg AM, Hooker NA, Mildenstein KL, Chace JH. Bacterial DNA induced NK cell IFN-gamma production is dependent on macrophage secretion of IL-12. Journal of Allergy and Clinical Immunology. 1997;99(1):1970–1970. doi: 10.1006/clin.1997.4380. [DOI] [PubMed] [Google Scholar]
  • [9].Halpern MD, Kurlander RJ, Pisetsky DS. Bacterial DNA induces murine interferon-gamma production by stimulation of interleukin-12 and tumor necrosis factor alpha. Cellular Immunology. 1996;167(1):72–78. doi: 10.1006/cimm.1996.0009. [DOI] [PubMed] [Google Scholar]
  • [10].Yi AK, Chace JH, Cowdery JS, Krieg AM. IFN-gamma promotes IL-6 and IgM secretion in response to CpG motifs in bacterial DNA and oligodeoxynucleotides. Journal of Immunology. 1996;156(2):558–564. [PubMed] [Google Scholar]
  • [11].Hartmann G, Weiner GJ, Krieg AM. CpG DNA: A potent signal for growth, activation, and maturation of human dendritic cells. Proceedings of the National Academy of Sciences of the United States of America; 1999. pp. 9305–9310. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [12].Krieg AM. CpG motifs: the active ingredient in bacterial extracts? Nature Medicine. 2003;9(7):831–835. doi: 10.1038/nm0703-831. [DOI] [PubMed] [Google Scholar]
  • [13].Vollmer J, Weeratna R, Payette P, Jurk M, Schetter C, Laucht M, Wader T, Tluk S, Liu M, Davis HL, Krieg AM. Characterization of three CpG oligodeoxynucleotide classes with distinct immunostimulatory activities. European Journal of Immunology. 2004;34(1):251–262. doi: 10.1002/eji.200324032. [DOI] [PubMed] [Google Scholar]
  • [14].Zhang XQ, Dahle CE, Baman NK, Rich N, Weiner GJ, Salem AK. Potent antigen-specific immune responses stimulated by codelivery of CpG ODN and antigens in degradable microparticles. Journal of Immunotherapy. 2007;30(5):469–478. doi: 10.1097/CJI.0b013e31802fd8c6. [DOI] [PubMed] [Google Scholar]
  • [15].Zhang XQ, Dahle CE, Weiner GJ, Salem AK. A comparative study of the antigen-specific immune response induced by co delivery of CpG ODN and antigen using fusion molecules or biodegradable microparticles. Journal of Pharmaceutical Sciences. 2007;96:3283–3292. doi: 10.1002/jps.20978. [DOI] [PubMed] [Google Scholar]
  • [16].Zaks K, Jordan M, Guth A, Sellins K, Kedl R, Izzo A, Bosio C, Dow S. Efficient immunization and cross priming by vaccine adjuvants containing TLR3 or TLR9 agonists complexed to cationic liposomes. Journal of Immunology. 2006;176(12):7335–7345. doi: 10.4049/jimmunol.176.12.7335. [DOI] [PubMed] [Google Scholar]
  • [17].Salem AK, Hung CF, Kim TW, Wu TC, Searson PC, Leong KW. Multi-component nanorods for vaccination applications. Nanotechnology. 2005;16(4):484–487. [Google Scholar]
  • [18].Intra J, Glasgow JM, Mai HQ, Salem AK. Pulsatile release of biomolecules from polydimethylsiloxane (PDMS) chips with hydrolytically degradable seals. Journal of Controlled Release. 2008;127:280–287. doi: 10.1016/j.jconrel.2008.02.001. [DOI] [PubMed] [Google Scholar]
  • [19].Krishnamachari Y, Pearce ME, Salem AK. Self-assembly of cell-microparticle hybrids. Advanced Materials. 2008;20(5):989–993. [Google Scholar]
  • [20].Singh M, Briones M, Ott G, O'Hagan D. Cationic microparticles: A potent delivery system for DNA vaccines. Proceedings of the National Academy of Sciences of the United States of America; 2000. pp. 811–816. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [21].Xie H, Gursel I, Ivins BE, Singh M, O'Hagan DT, Ulmer JB, Klinman DM. CpG oligodeoxynucleotides adsorbed onto polylactide-co-glycolide microparticles improve the immunogenicity and protective activity of the licensed anthrax vaccine. Infection and Immunity. 2005;73(2):828–833. doi: 10.1128/IAI.73.2.828-833.2005. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [22].de Jong S, Chikh G, Sekirov L, Raney S, Semple S, Klimuk S, Yuan N, Hope M, Cullis P, Tam Y. Encapsulation in liposomal nanoparticles enhances the immunostimulatory, adjuvant and anti-tumor activity of subcutaneously administered CpG ODN. Cancer Immunology Immunotherapy. 2007;56(8):1251–1264. doi: 10.1007/s00262-006-0276-x. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [23].Mutwiri G, Benjamin P, Soita H, Babiuk LA. Co-administration of polyphosphazenes with CpG oligodeoxynucleotides strongly enhances immune responses in mice immunized with Hepatitis B virus surface antigen. Vaccine. 2008;26(22):2680–2688. doi: 10.1016/j.vaccine.2008.03.031. [DOI] [PubMed] [Google Scholar]
  • [24].Heit A, Schmitz F, O'Keeffe M, Staib C, Busch DH, Wagner H, Huster KM. Protective CD8 T cell immunity triggered by CpG-protein conjugates competes with the efficacy of live vaccines. Journal of Immunology. 2005;174(7):4373–4380. doi: 10.4049/jimmunol.174.7.4373. [DOI] [PubMed] [Google Scholar]
  • [25].Klinman DM, Yi AK, Beaucage SL, Conover J, Krieg AM. CpG motifs present in bacterial DNA rapidly induce lymphocytes to secrete interleukin 6, interleukin 12, and interferon gamma. Proceedings of the National Academy of Sciences of the United States of America; 1996. pp. 2879–2883. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [26].Kitagaki K, Businga TR, Kline JN. Oral administration of CpG-ODNs suppresses antigen induced asthma in mice. Clinical and Experimental Immunology. 2006;143(2):249–259. doi: 10.1111/j.1365-2249.2005.03003.x. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [27].Kline JN, Waldschmidt TJ, Businga TR, Lemish JE, Weinstock JV, Thorne PS, Krieg AM. Cutting edge: Modulation of airway inflammation by CpG oligodeoxynucleotides in a murine model of asthma. Journal of Immunology. 1998;160(6):2555–2559. [PubMed] [Google Scholar]
  • [28].Weiner GJ, Liu HM, Wooldridge JE, Dahle CE, Krieg AM. Immunostimulatory oligodeoxynucleotides containing the CpG motif are effective as immune adjuvants in tumor antigen immunization. Proceedings of the National Academy of Sciences of the United States of America; 1997. pp. 10833–10837. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [29].Lubaroff DM, Karan D, Andrews MP, Acosta A, Abouassaly C, Sharma M, Krieg AM. Decreased cytotoxic T cell activity generated by co administration of PSA vaccine and CpG ODN is associated with increased tumor protection in a mouse model of prostate cancer. Vaccine. 2006;24(3536):6155–6162. doi: 10.1016/j.vaccine.2006.04.022. [DOI] [PubMed] [Google Scholar]
  • [30].Sandler AD, Chihara H, Kobayashi G, Zhu XY, Miller MA, Scott DL, Krieg AM. CpG oligonucleotides enhance the tumor antigen-specific immune response of a granulocyte macrophage colony-stimulating factor-based vaccine strategy in neuroblastoma. Cancer Research. 2003;63(2):394–399. [PubMed] [Google Scholar]

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