Immunostimulatory oligodeoxynucleotides containing the CpG motif are effective as immune adjuvants in tumor antigen immunization

Abstract

Recent advances in our understanding of the immune response are allowing for the logical design of new approaches to cancer immunization. Bacterial DNA is capable of inducing activation of B cells, NK cells, and monocytes (1-5). In addition, bacterial DNA can induce production in vitro and in vivo of a variety of proinflammatory cytokines (6-8). In contrast, vertebrate DNA does not induce lymphocyte activation. Bacterial DNA contains a much higher frequency of unmethylated CpG dinucleotides than does vertebrate DNA due to (i) CpG suppression (the under representation of CpG in vertebrate genomes) and (ii) methylation of 80% of the CpG in vertebrates. It is possible that lymphocyte activation by the CpG motif in bacterial DNA represents an immune defense mechanism that can distinguish bacterial from host DNA (1). Select synthetic oligodeoxynucleotides containing unmethylated CpG motifs (CpG ODN) have immunologic effects similar to those seen with bacterial DNA. CpG ODN can stimulate monocytes, macrophages, and dendritic cells that then produce several cytokines, including the TH1 cytokine interleukin 12. This effect synergizes with CpG ODN to induce NK cell production of interferon ␥ (6). Both human and murine leukocytes respond to this novel pathway of immune activation, although individual CpG ODN differ somewhat in their ability to activate various immune cell populations and induce cytokine production in human and murine systems.The molecular mechanisms responsible for CpG ODNinduced immune cell activation are still under investigation. We have recently reported that CpG ODN trigger the production of reactive oxygen species that activate NF-B (9). This activation, in turn, leads to cellular activation. Irrespective of the mechanism involved, it is clear that select CpG ODN can have powerful immunologic effects and might be useful therapeutic agents in a number of circumstances, including cancer immunotherapy. For example, we have demonstrated that CpG ODN can enhance antibody-dependent cellular cytotoxicity and improve the in vivo efficacy of monoclonal antibody therapy in a syngeneic murine lymphoma model (10).CpG ODN can induce activation of antigen-presenting cells and enhance production of cytokines known to participate in the development of an active immune response. They also enhance B cell activation, particularly when the B cell receptor is cross-linked (1). These effects are likely to promote antigenspecific responses. Indeed, Branda et al. (11) demonstrated that an anti-sense ODN, which in retrospect is noted to contain the CpG motif, enhances antibody response to antigen. We therefore used a well-established animal model to assess whether CpG ODN can function as an immune adjuvant in antitumor immunization.

Polarisation of a T-helper cell immune response by activation of dendritic cells with CpG-containing oligonucleotides: a potential therapeutic regime for bladder cancer immunotherapy

“…It has been reported that nonmethylated palindromic DNA containing CpG-ODN can activate an innate immune response by activation of NK cells, DC and B cells in an antigen-independent manner (Weiner et al, 1997). Recognition of these microbial sequences is mediated by a member of the TLR family, namely TLR9.…”

Oligodeoxynucleotides containing CpG motifs can induce T cell–dependent arthritis in rats

“…It is well known that bacterial DNA and synthetic oligodeoxynucleotides (ODNs) containing specific motifs centered on a CpG dinucleotide (CpG ODNs) are potent immunostimulatory agents (1)(2)(3)(4)(5). Unmethylated CpG sequences are present at a frequency of 1 in every 16 dinucleotides in bacteria, while mammals have a CG dinucleotide suppression with only one-fourth of the expected frequency, and the majority of the CpG sequences are methylated in mammals (6).…”

“…Unmethylated CpG sequences are present at a frequency of 1 in every 16 dinucleotides in bacteria, while mammals have a CG dinucleotide suppression with only one-fourth of the expected frequency, and the majority of the CpG sequences are methylated in mammals (6). CpG ODNs act rapidly on a variety of cell types such as B cells, natural killer (NK) cells, and antigen-presenting cells including monocytes, macrophages, and dendritic cells (5,7). CpG mediates its effect through Toll-like receptor 9 (TLR-9) (8), initiating a rapid inflammatory response and production of cytokines such as interleukin-6 (IL-6), IL-12, IL-1, interferon-␥ (IFN␥), and tumor necrosis factor ␣ (TNF␣) (7)(8)(9)(10).…”

Drug delivery systems based on nucleic acid nanostructures

“…CpG motifs are short oligonucleotides where a 2′-deoxycytidine is connected by a phosphodiester bond to 2′-deoxyguanosine. When these nucleotides are unmethylated as in natural viral and bacterial DNA they have immunostimulatory activity [54]. This CpG motif occurs very rarely in vertebrate genomes and is therefore considered a pathogen-associated molecular pattern indicating invasion of pathogens [55].…”