Deoxycytidyl-Deoxyguanosine Oligonucleotide Classes A, B, and C Induce Distinct Cytokine Gene Expression Patterns in Rhesus Monkey Peripheral Blood Mononuclear Cells and Distinct Alpha Interferon Responses in TLR9-Expressing Rhesus Monkey Plasmacytoid Dendritic Cells |
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| Authors: | Kristina Abel Yichuan Wang Linda Fritts Eleonora Sanchez Eugene Chung Patricia Fitzgerald-Bocarsly Arthur M. Krieg Christopher J. Miller |
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| Affiliation: | Center for Comparative Medicine,1. California National Primate Research Center,2. Department of Pathology, Microbiology and Immunology, School of Veterinary Medicine, University of California—Davis, Davis, California,3. Department of Pathology and Laboratory Medicine, UMDNJ-New Jersey Medical School and Graduate School of Biomedical Sciences, Newark, New Jersey,4. Coley Pharmaceutical Group, Inc., Wellesley, Massachusetts5. |
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| Abstract: | To determine if deoxycytidyl-deoxyguanosine oligonucleotides (CpG ODN) can be used effectively as nonspecific inducers of innate immune defenses for preventative or therapeutic interventions in infectious disease models for nonhuman primates, the present study evaluated the response of rhesus monkey peripheral blood mononuclear cells to three different synthetic CpG ODN classes by defining the cytokine gene expression patterns and by characterizing IFN-α/β responses. Depending on the type and dose of CpG ODN used for stimulation, distinct gene expression patterns were induced. CpG ODN class A (CpG-A ODN) and CpG-C ODN, but not CpG-B ODN, were potent inducers of alpha interferon (IFN-α), and this response was due to IFN-α production by TLR9-positive plasmacytoid dendritic cells. Importantly, there was a dose-dependent increase in IFN-α responses to CpG-A ODN but a dose-dependent decrease in IFN-α responses by CpG-B ODN. The most sustained IFN-α response was induced by CpG-A ODN and was associated with a stronger induction of interferon regulatory factor 7 and the induction of several interferon-stimulated genes. In contrast, and independent of the dose, CpG-B ODN were the weakest inducers of IFN-α but the most potent inducers of proinflammatory cytokines. CpG-C ODN induced cytokine gene expression patterns that were intermediate between those of CpG-A and CpG-B ODN. Thus, the different types of CpG ODN induce different post-TLR9 signaling pathways that result in distinct cytokine gene expression patterns. Based on these findings, A and C class CpG ODN, but not B class CpG ODN, may be particularly suited for use as therapeutic or prophylactic antiviral interventions.In recent years, many nonhuman primate models of viral infections have been developed to study virus-host interactions and to test the efficacy of possible vaccine candidates (9, 42, 45, 53, 54). Importantly, monkey models of simian immunodeficiency virus (SIV) infection are the best animal models available to study human immunodeficiency virus (HIV) infection and AIDS pathogenesis (48, 49). As the AIDS pandemic continues at an uncontrolled rate, and as new infectious diseases emerge (20, 47), there is an urgent need to design strategies aimed at the prevention of viral transmission and control of early virus replication. Part of this effort is the development of immunomodulatory drugs that have the ability to stimulate innate antiviral immune responses that can block transmission or reduce early virus replication and thereby limit virus dissemination.IFN-α/β are critical cytokines in the initial phase of antiviral immune responses, as they serve two important functions: they exert direct innate antiviral effects via interferon-stimulated genes (ISG), and they promote adaptive cellular antiviral immune responses (6, 11, 12, 14, 18, 29, 32, 39, 40, 43, 51, 52, 57, 58). Thus, the manipulation of the interferon system by immunomodulatory compounds, such as deoxycytidyl-deoxyguanosine oligonucleotides (CpG ODN), has potential utility as a therapeutic intervention aimed at the prevention and control of viral infections (36).There are three main classes of synthetic CpG ODN that differ in the type and magnitude of immune responses induced. CpG ODN of the A class (CpG-A ODN) are very strong inducers of alpha interferon (IFN-α) by plasmacytoid dendritic cells (PDC) and are especially potent NK cell activators (35, 55, 56). CpG-B ODN are weaker inducers of IFN-α, but are potent activators of B cells (25, 35). CpG-C ODN have the combined features of CpG-A and CpG-B ODN: they are strong inducers of PDC IFN-α/β production and strong B-cell activators (24, 44, 67). All classes of CpG ODN promote T helper 1 (Th1) responses to coadministered antigens through the induction of cytokines in activated dendritic cells.Thus, due to the robust induction of IFN-α, CpG-A ODN are potential candidates for prophylactic inducers of innate immune defenses in the prevention of viral infections and other infectious diseases. However, CpG-A ODN are not currently being developed for clinical use, because their poly(G) motifs render them more difficult to produce than the other CpG ODN classes (24, 35). Few studies have yet investigated the immune properties of CpG-C ODN, but based on their known ability to induce strong IFN-α/β production in human cells (24, 44, 67), they could be used for therapeutic interventions in infectious disease settings.Nonhuman primates can respond to the same CpG-A and CpG-B ODN that have strong immune activity in humans, and CpG-B ODN have been used successfully as vaccine adjuvants in several monkey studies (31, 62, 65, 66). However, there are no published reports that CpG ODN can be used effectively for preventative or therapeutic interventions in viral diseases in nonhuman primates or humans.The goal of the present study was to compare the relative suitability of the three CpG ODN classes for in vivo virus studies by defining the gene expression pattern in rhesus monkey peripheral blood mononuclear cells (PBMC) to stimulation with the three CpG ODN classes. Further, we sought to characterize the basis for the very different IFN-α/β responses they induce and to determine the nature of the IFN-α-producing cell types in CpG ODN-stimulated rhesus monkey PBMC. We found that the gene expression pattern induced in rhesus monkey PBMC is dependent on the type and dose of CpG ODN used for stimulation. Thus, CpG-A and CpG-C ODN, but not CpG-B ODN, were potent inducers of IFN-α responses, and this response was mediated predominantly by TLR9-expressing PDC. CpG-A ODN induced the most sustained IFN-α response, and this was associated with a stronger induction of the interferon regulatory factor 7 (IRF-7) and resulted in the strong and prolonged induction of several interferon-stimulated genes. The distinct cytokine expression patterns induced by the different CpG ODN classes suggest that each may have a unique clinical application. |
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