Stimulation of thymocyte proliferation by phosphorothioate DNA oligonucleotides

DNA is a complex macromolecule the immunological properties of which depend on short sequence motifs called CpG motifs or immunostimulatory sequences (ISS). These sequences are mitogenic for B cells and can stimulate macrophage cytokine production. While these sequences do not directly activate T cells, they can augment effects of stimulation via the TCR. Furthermore, ISS can affect T cells because of macrophage production of IL-12 and IFN-alpha/beta. In these studies, we further evaluated the immune effects of DNA on T cells, testing the possibility that certain T cell populations can respond directly to this stimulus. We therefore tested the in vitro responses of thymocytes to a series of phosphodiester (Po) and phosphorothioate (Ps) oligonucleotides (ODNs) varying in sequence. In in vitro cultures, phosphorothioate ODNs (sODNs) containing CpG motifs induced significant proliferation of murine thymocytes, although phosphodiester compounds lacked activity. The magnitude of stimulation varied with sequences flanking the CpG motifs, as both dA and dT sequences enhanced the stimulatory capacity of the CpG motif. Furthermore, CpG sODNs were strong costimulators of anti-CD3-mediated thymocyte activation, increasing proliferation compared to anti-CD3 in the absence of DNA. This activation was only partially inhibited by cyclosporine A and was not dependent on a calcium influx. Together, these results indicate that phosphorothioate oligonucleotides containing CpG motifs can directly induce thymocyte proliferation as well as augment TCR activation. These observations thus extend the range of actions of CpG DNA and suggest additional mechanisms for its function as an immunomodulatory agent or adjuvant.     

Oligodeoxynucleotides without CpG motifs work as adjuvant for the induction of Th2 differentiation in a sequence-independent manner

The outcomes of immune responses are regulated by various parameters including how Ags are handled by APCs. In this study, we describe the intrinsic immunomodulatory characteristics of oligodeoxynucleotides (ODNs) that improve the Ag presentation by APCs. ODNs (20-mer) containing CpG motifs induced strong Th1-skewed responses. In contrast, those without CpG motifs enhanced cytokine production by effector Th cells without particular skewing toward Th1 responses or induced the differentiation of unprimed CD4(+) T cells toward Th2 cells. These functional features were prominently envisaged when ODNs were conjugated to the Ag, and were underlain by the facilitated binding of ODN-conjugated Ag to Ia(+) cells. Despite the functional differences between ODNs with CpG motifs and those without CpG motifs, both ODNs bound to Ia(+) cells with similar affinity and kinetics. Immunoenhancing activities of the ODNs were not sequence-dependent; the characteristics, including the facilitation of Ag capture, enhancement of effector Th cell responses, and induction of Th2 cells, were shared by randomly synthesized ODNs conjugated to Ag. This is the first study suggesting that ODNs, independent of the sequences, enhance immune responses through the promoted capture of ODN-conjugated Ag by APCs.     

G3139 and other CpG-containing immunostimulatory phosphorothioate oligodeoxynucleotides are potent suppressors of the growth of human tumor xenografts in nude mice

Several phosphorothioate antisense oligodeoxynucleotides (ODN) are developed to target factors potentially involved in tumor growth and apoptosis suppression. Among them, the 18-mer G3139 (Oblimersen), which targets Bcl-2, is currently being tested in phase II and phase III clinical trials for various tumors in combination with chemotherapy. On the other hand, ODNs containing CpG dinucleotides (CpG-ODN) within specific-sequence contexts (CpG motifs) have been shown to activate rodent or primate immune cells via toll-like receptor 9 (TLR9) and have demonstrated remarkable T cell-dependent antitumor efficacy in a series of murine tumor models. However, immune cell activation by CpG-ODN is largely diminished upon C-5 methylation at CpG cytosine. As G3139 contains CpG motifs, we questioned whether the antitumor effects seen in human tumor xenografts might be abrogated by cytosine C-5 methylation of G3139, which retained the ability of G3139 to suppress Bcl-2 expression in tissue culture, or by similar derivatization of other phosphorothioate ODNs developed for the immune activation of rodent or human cells. The in vivo antitumor efficacy of the immunostimulatory H1826 and H2006 ODNs was compared with that of G3139. Bcl-2 suppression achieved by G3139 purportedly sensitizes tumor cells toward cytotoxic agents, and some of the experiments employed combinations of ODN with such drugs as cisplatin or etoposide. H1826, H2006, and G3139 all produced similar, striking, growth inhibitory effects on either H69 SCLC, A2780 ovarian carcinoma, or A549 lung adenocarcinoma human tumor xenografts at doses of 0.3 mg/kg and 1 mg/kg (H1826, H2006) or 12 mg/kg (G3139) per day. In contrast, the H2006-mC (1 mg/kg) or G3139-mC (12 mg/kg) derivatives demonstrated no significant antitumor effects. The combination of G3139 (12 mg/kg) with cisplatin produced some additive antitumor efficacy, which was not seen in combinations of G3139-mC (12 mg/kg) or H1826 (1 mg/kg) with cisplatin. G3139, at a dose of 12 mg/kg, alone induced extensive enlargement of the spleen. Immunostimulation was evaluated in vitro by flow cytometric measurements of the CD80 and CD86 activation markers found on CD19+ murine splenocytes. The CpG-ODN producing strong antitumor effects in vivo also induced these activation markers in vitro, in contrast to the in vivo inactive G3139-mC. Our data indicate a significant contribution of the immunostimulatory properties of CpG-ODN (including G3139) to the antitumor effects observed in nude mouse xenograft models. This is in contrast to previous data presented by other authors indicating that the activity of G3139 in human tumor xenografts was Bcl-2 specific. Furthermore, as nude mice are devoid of T cells, a T cell-mediated immune response apparently is not required for the potent antitumor responses observed here; innate immune responses are sufficient.     

PyNTTTTGT and CpG Immunostimulatory Oligonucleotides: Effect on Granulocyte/Monocyte Colony-Stimulating Factor (GM-CSF) Secretion by Human CD56+ (NK and NKT) Cells

CD56⁺ cells have been recognized as being involved in bridging the innate and acquired immune systems. Herein, we assessed the effect of two major classes of immunostimulatory oligonucleotides (ODNs), PyNTTTTGT and CpG, on CD56⁺ cells. Incubation of human peripheral blood mononuclear cells (hPBMC) with some of these ODNs led to secretion of significant amounts of interferon gamma (IFN-γ), tumor necrosis factor alpha (TNF-α) and granulocyte/monocyte colony-stimulating factor (GM-CSF), but only if interleukin 2 (IL2) was present. IMT504, the prototype of the PyNTTTTGT ODN class, was the most active. GM-CSF secretion was very efficient when non-CpG ODNs with high T content and PyNTTTTGT motifs lacking CpGs were used. On the other hand, CpG ODNs and IFNα inhibited this GM-CSF secretion. Selective cell type removal from hPBMC indicated that CD56⁺ cells were responsible for GM-CSF secretion and that plasmacytoid dendritic cells (PDCs) regulate this process. In addition, PyNTTTTGT ODNs inhibited the IFNα secretion induced by CpG ODNs in PDCs by interference with the TLR9 signaling pathway. Since IFNα is essential for CD56⁺ stimulation by CpG ODNs, there is a reciprocal interference of CpG and PyNTTTTGT ODNs when acting on this cell population. This suggests that these synthetic ODNs mimic different natural alarm signals for activation of the immune system.     

Cytosine-phosphate-guanine oligodeoxynucleotides containing GACGTT motifs enhance the immune responses elicited by keyhole limpet hemocyanin antigen in dairy cattle

Adjuvants are important components of vaccine formulations. Effective adjuvants line innate and adaptive immunity by signaling through pathogen recognition receptors. Synthetic cytosine-phosphate-guanine (CpG) oligodeoxynucleotides (ODNs) have been shown to have potentials as adjuvants for vaccines. However, the immunostimulatory effect of CpG is species-specific and depends on the sequence of CpG motifs. A CpG ODN (2135), containing 3 identical copies of GTCGTT motif, was previously reported to have the strongest effects on bovine peripheral blood mononuclear cells (PBMC). Based on the sequence of 2135, we replaced the GTCGTT motif with 11 other sequences containing CG and investigated their effects on bovine lymphocyte proliferation. Results showed that the CpG ODNs containing 3 copies of GACGTT motif had the highest lymphocyte stimulation index (7.91±1.18), which was significantly (P<0.05) higher than that of 2135 (4.25±0.56). The CpG ODNs containing 3 copies of GACGTT motif also significantly increased the mRNA expression of interferon (IFN)-α, interleukin (IL)-12, and IL-21 in bovine PBMC. When dairy cows were immunized with the keyhole limpet hemocyanin (KLH) antigen formulated with CpG ODNs containing 3 copies of GACGTT, production of KLH-specific antibodies in serum and in milk whey was significantly (P<0.05) enhanced. IFN-γ in whole blood stimulated by KLH was also significantly (P<0.05) increased in cows immunized with KLH plus CpG ODNs. Our results indicate that CpG ODNs containing 3 copies of the GACGTT motifs is a potential adjuvant for bovine vaccines.     

Divergent therapeutic and immunologic effects of oligodeoxynucleotides with distinct CpG motifs.

Immune stimulatory oligodeoxynucleotides (ODN) with unmethylated CpG motifs are potent inducers of both innate and adaptive immunity. It initially appeared that a single type of optimal CpG motif would work in all applications. We now report that specific motifs of CpG ODN can vary dramatically in their ability to induce individual immune effects and that these differences impact on their antitumor activity in different tumor models. In particular, a distinct type of CpG motif, which has a chimeric backbone in combination with poly(G) tails, is a potent inducer of NK lytic activity but has little effect on cytokine secretion or B cell proliferation. One such NK-optimized CpG ODN (1585) can induce regression of established melanomas in mice. Surprisingly, no such therapeutic effects were seen with CpG ODN optimized for activation of B cells and Th1-like cytokine expression (ODN 1826). The therapeutic effects of CpG 1585 in melanoma required the presence of NK but not T or B cells and were not associated with the induction of a tumor-specific memory response. In contrast, CpG 1826, but not CpG 1585, was effective at inducing regression of the EL4 murine lymphoma; this rejection was associated with the induction of a memory response and although NK cells were necessary, they were not sufficient. These results demonstrate that selection of optimal CpG ODN for cancer immunotherapy depends upon a careful analysis of the cellular specificities of various CpG motifs and an understanding of the cellular mechanisms responsible for the antitumor activity in a particular tumor.     

Construction of a recombinant plasmid containing multi-copy CpG motifs and its effects on the innate immune responses of aquatic animals

Bacterial DNA and synthetic oligodeoxynucleotides (ODNs) containing unmethylated CpG dinucleotides (CpG motifs) have been shown to induce potential immune responses. In this study, we designed a recombinant plasmid containing multi-copy CpG motifs, and observed its effects on innate immune responses of fish and prawn. The results showed that such plasmid DNA, compared to the vacant vector, can highly induce the activation of head kidney macrophages and the proliferation of peripheral blood leukocytes in Carassius auratus and Lateolabrax japonicus in vitro, as well as the activity of humoral defense proteins and the antibacterial activity of haemolymph in Litopenaeus vannamei in vivo. It implies that the multi-copy CpG motifs harboured in plasmid could contribute to these innate immunostimulatory effects. Therefore, the study suggested that the plasmid containing multi-copy CpG motifs might have its potential application in improving host resistance to pathogen insults in aquaculture, and have its notable advantages of high efficacy, economical cost and application to a broad range of aquatic species.     

Highly immunostimulatory CpG-free oligodeoxynucleotides for activation of human leukocytes

Synthetic oligodeoxynucleotides (ODNs) bearing CpG dinucleotides can mimic the immunostimulatory effects of bacterial DNA in vertebrates. Besides the known CpG motifs, no other sequence motif has been shown to have independent immunostimulatory effects. Several past investigators have demonstrated that the nucleotide content or the phosphorothioate (PS) backbone may have effects independently of the sequence. However, the effect of both nucleotide content and PS backbone to stimulate human leukocytes is not well understood. We investigated the immunostimulatory activity of 34 PS-ODNs with different nucleotide contents, lengths, and methylation status on human leukocytes. The thymidine content showed strong CpG-independent contribution to immunostimulation. In contrast, ODNs rich in other nucleotides (guanosine, cytosine, or adenosine) induced no or much lower levels of immunostimulation. The observed effects were highly dependent on the PS backbone chemistry. In addition to the base content and the backbone chemistry, the length of the PS-ODN was directly related to the magnitude of its stimulatory effects, especially on B cells. In addition, methylation of CpG dinucleotides did not always cause an abrogation of the immunostimulation. Immunostimulatory effects could be observed with methylated CpG ODNs, specifically as the ODN length was increased from 18 to 24 or more nucleotides (nt). In contrast, PS-ODNs with inverted CpG dinucleotides showed some but only weak immunostimulation. Our results demonstrate that non-CpG ODNs rich in thymidine or ODNs with methylated CpG motifs have length-dependent immunostimulatory effects. Such ODNs can induce effects similar to those seen with CpG ODNs but are much less efficient in stimulating human immune cells.     

CpG DNA: recognition by and activation of monocytes

Unmethylated CpG motifs present in bacterial DNA rapidly trigger an innate immune response characterized by the activation of Ig- and cytokine-secreting cells. Synthetic oligonucleotides (ODNs) containing CpG motifs mimic this activity, triggering monocytes to proliferate, secrete and/or differentiate. Analysis of hundreds of novel ODNs led to the identification of two structurally distinct classes of CpG motif that differentially activate human monocytes. ODNs of the "K"-type interact with Toll-like receptor 9 and induce monocytes to proliferate and secrete IL-6. In contrast, "D"-type ODNs trigger monocytes to differentiate into mature dendritic cells.     

Oligodeoxynucleotides differentially modulate activation of TLR7 and TLR8 by imidazoquinolines

Among the 11 human TLRs, a subfamily TLR7, TLR8, and TLR9 display similarities in structure and endosomal localization. Natural agonists consisting of nucleic acids, such as ssRNA or DNA with CpG motifs, activate the innate immune cells through these TLRs. Immune response modifiers (IRMs) of imidazoquinoline class compounds 3M-001, 3M-002, and 3M-003 have been shown to activate the innate immune system via TLR7, TLR8, and TLR7/8, respectively. In looking at the effect of the agonists of the TLR7, TLR8, and TLR9 on the activation of NF-kappaB of transfected HEK cells, we discovered that some oligodeoxynucleotides (ODNs) could modulate imidazoquinoline effects in a negative or positive manner. In this study we demonstrate that poly(T) ODNs can inhibit TLR7 and enhance TLR8 signaling events involving NF-kappaB activation in HEK cells and cytokine production (IFN-alpha, TNF, and IL-12) by human primary PBMC. In contrast, TLR3 agonist poly(I:C) does not affect imidazoquinoline-induced responses. The modulation of TLR7 and TLR8 responses is independent of CpG motifs or the nature of the ODN backbone structure. Furthermore, we show that to be an effective modulator, the ODNs need to be in the cell at the same time with either of the TLR7 or TLR8 agonist. We have also demonstrated that there is a physical interaction between IRMs and ODNs. The cross-talk between ODNs, IRMs, and TLR7 and TLR8 uncovered by this study may have practical implications in the field of microbial infections, vaccination, and tumor therapy.     

Newly identified CpG ODNs,M5-30 and M6-395, stimulate mouse immune cells to secrete TNF-α and enhance Th1-mediated immunity

Bacterial CpG motifs are known to induce both innate and adaptive immunity in infected hosts via toll-like receptor 9 (TLR9). Because small oligonucleotides (ODNs) mimicking bacterial CpG motifs are easily synthesized, they have found use as immunomodulatory agents in a number of disease models. We have developed a novel bioinformatics approach to identify effective CpG ODN sequences and evaluate their function as TLR9 ligands in a murine system. Among the CpG ODNs we identified, M5-30 and M6-395 showed significant ability to stimulate TNF-α and IFN-γ production in a mouse macrophage cell line and mouse splenocytes, respectively. We also found that these CpG ODNs activated cells through the canonical NF-κ B signaling pathway. Moreover, both CpG ODNs were able to induce Th1-mediated immunity in Mycobacterium tuberculosis (Mtb)-infected mice. Our results demonstrate that M5-30 and M6-395 function as TLR9-specific ligands, making them useful in the study of TLR9 functionality and signaling in mice.     

CpG oligodeoxynucleotides protect normal and SIV-infected macaques from Leishmania infection

Oligodeoxynucleotides containing CpG motifs (CpG ODNs) mimic microbial DNA and activate effectors of the innate immune response, which limits the spread of pathogens and promotes an adaptive immune response. CpG ODNs have been shown to protect mice from infection with intracellular pathogens. Unfortunately, CpG motifs that optimally stimulate humans are only weakly active in mice, mandating the use of nonhuman primates to monitor the activity and safety of "human" CpG ODNs in vivo. This study demonstrates that CpG ODN treatment of rhesus macaques significantly reduces the severity of the lesions caused by a challenge with Leishmania: Leishmania superinfection is common in immunocompromised hosts, particularly those infected with HIV. This study shows that PBMCs from HIV-infected subjects respond to stimulation with CpG ODNs. To determine whether CpG ODNs can protect retrovirus-infected primates, SIV-infected macaques were treated with CpG ODNs and then challenged with Leishmania: Both lesion size and parasite load were significantly reduced in the CpG-treated animals. These findings support the clinical development of CpG ODNs as immunoprotective agents in normal and HIV-infected patients.     

Immunostimulatory CpG oligodeoxynucleotides stimulate expression of IL-1beta and interferon-like cytokines in rainbow trout macrophages via a chloroquine-sensitive mechanism.

Synthetic oligodeoxynucleotides (ODNs) containing unmethylated CpG motifs are known to stimulate immune responses and are potent adjuvants in higher vertebrates, but so far the effects in fish are poorly described. We here report that CpG ODNs induce IL-1beta expression and production of interferon-like cytokines in rainbow trout head-kidney macrophages, whereas ODNs with an inverted motif (GpC) have a much less stimulatory effect. We further demonstrate that endosomal maturation is essential for CpG signalling, as chloroquine, a compound known to block endosomal acidification, inhibits cytokine expression in the macrophages.     

Peritumoral CpG DNA elicits a coordinated response of CD8 T cells and innate effectors to cure established tumors in a murine colon carcinoma model

The immune system of vertebrates is able to detect bacterial DNA based on the presence of unmethylated CpG motifs. We examined the therapeutic potential of oligodeoxynucleotides with CpG motifs (CpG ODN) in a colon carcinoma model in BALB/c mice. Tumors were induced by s.c. injection of syngeneic C26 cells or Renca kidney cancer cells as a control. Injection of CpG ODN alone or in combination with irradiated tumor cells did not protect mice against subsequent tumor challenge. In contrast, weekly injections of CpG ODN into the margin of already established tumors resulted in regression of tumors and complete cure of mice. The injection site was critical, since injection of CpG ODN at distant sites was not effective. Mice with two bilateral C26 tumors rejected both tumors upon peritumoral injection of one tumor, indicating the development of a systemic immune response. The tumor specificity of the immune response was demonstrated in mice bearing a C26 tumor and a Renca tumor at the same time. Mice that rejected a tumor upon peritumoral CpG treatment remained tumor free and were protected against rechallenge with the same tumor cells, but not with the other tumor, demonstrating long term memory. Tumor-specific CD8 T cells as well as innate effector cells contributed to the antitumor activity of treatment. In conclusion, peritumoral CpG ODN monotherapy elicits a strong CD8 T cell response and innate effector mechanisms that seem to act in concert to overcome unresponsiveness of the immune system toward a growing tumor.     

Direct immunologic activities of CpG DNA and implications for gene therapy

Vertebrate immune systems have evolved the ability to detect and be activated by most microbial and viral DNAs by virtue of their content of unmethylated 'CpG motifs', which are selectively suppressed in vertebrate DNA. Because their CpGs are also unmethylated, the DNA in gene therapy vectors routinely induces direct immune stimulation through activating this host defense mechanism. Administration of such 'CpG DNA' by injection or inhalation triggers rapid activation of B cells, monocytes, macrophages, dendritic cells, and natural killer cells, along with the release of pro-inflammatory cytokines. These immune stimulatory effects can be prevented by chloroquine and other drugs that interfere with endosomal maturation or by the presence of certain neutralizing DNA sequences, which block the immune stimulatory CpG motifs. Aside from serving as the genetic code, DNA can have direct immune activities. Vertebrate immune systems have evolved a defense mechanism that is able to broadly detect most microbial and viral DNAs because of differences in the frequency and methylation of CpG dinucleotides in particular base contexts. B cells, monocytes, macrophages, and dendritic cells spontaneously take up DNA of any type. If the DNA contains these immune stimulatory 'CpG-S motifs', the cells become activated within minutes and begin producing pro-inflammatory cytokines such as IL-6 and IL-12 and upregulate expression of co-stimulatory molecules. This results in the activation of both innate and acquired immune responses. The pro-inflammatory effects of CpG-S motifs are opposed by CpG dinucleotides in certain distinct base contexts, termed neutralizing or CpG-N motifs. Increasing the ratio of CpG-S to CpG-N motifs enhances the immune stimulatory effects of DNA, even if the total level of CpGs in the DNA is not altered. While this is useful in generating enhanced genetic vaccines, the opposite strategy is likely to become useful for the generation of gene therapy vectors with reduced inflammatory effects.     

CpG ODNs对肿瘤细胞端粒酶活性及细胞周期和凋亡的影响

应用TRAP PCR ELISA法检测CpGODNs及E .coliDNA对肿瘤细胞端粒酶活性的影响变化 ,同时用流式细胞仪检测细胞周期的变化及凋亡的产生 ,从基因水平探讨其抗肿瘤机制。实验发现活性形式的CpGODNs可显著降低肿瘤细胞端粒酶活性 ,E .coliDNA的下调作用出现在 48h之后 ,二者均可使G0 /G1期细胞含量增加 ,但均未引起凋亡。结果表明 ,CpGODNs及E .coliDNA在基因水平可通过抑制端粒酶活性达到抗肿瘤目的 ,但不能诱导肿瘤细胞凋亡。     

Strong cytosine-guanosine-independent immunostimulation in humans and other primates by synthetic oligodeoxynucleotides with PyNTTTTGT motifs

Synthetic oligodeoxynucleotides (ODNs) containing cytosine-guanosine (CpG) motifs stimulate B and plasmacytoid dendritic cells of the vertebrate immune system. We found that in primates strong stimulation of these cells could also be achieved using certain non-CpG ODNs. The immunostimulatory motif in this case is a sequence with the general formula PyNTTTTGT in which Py is C or T, and N is A, T, C, or G. Assays performed on purified cells indicated that the immunostimulatory activity is direct. The use of a nuclease-resistant phosphorothioate backbone is not a necessary condition, since phosphodiester PyNTTTTGT ODNs are active. It was also demonstrated that ODN 2006, a widely used immunostimulant of human B cells, possess two kinds of immunostimulatory motifs: one of them mainly composed of two successive TCG trinucleotides located at the 5' end and another one (duplicated) of the PyNTTTTGT kind here described. Even though PyNTTTTGT ODNs are mainly active on primate cells, some of them, bearing the CATTTTGT motif, have a small effect on cells from other mammals. This suggests that the immunostimulatory mechanism activated by these ODNs was present before, but optimized during, evolution of primates. Significant differences in the frequency of PyNTTTTGT sequences between bacterial and human DNA were not found. Thus, the possibility that PyNTTTTGT ODNs represent a class of pathogen-associated molecular pattern is unlikely. They could, more reasonably, be included within the category of danger signals of cell injury.     

Immunostimulatory CpG oligodeoxynucleotides stimulate expression of IL-1β and interferon-like cytokines in rainbow trout macrophages via a chloroquine-sensitive mechanism

Synthetic oligodeoxynucleotides (ODNs) containing unmethylated CpG motifs are known to stimulate immune responses and are potent adjuvants in higher vertebrates, but so far the effects in fish are poorly described. We here report that CpG ODNs induce IL-1β expression and production of interferon-like cytokines in rainbow trout head-kidney macrophages, whereas ODNs with an inverted motif (GpC) have a much less stimulatory effect. We further demonstrate that endosomal maturation is essential for CpG signalling, as chloroquine, a compound known to block endosomal acidification, inhibits cytokine expression in the macrophages.