Activation of human B cells by phosphorothioate oligodeoxynucleotides

CpG DNA Is a Potent Enhancer of Specific Immunity in Mice Immunized with Recombinant Hepatitis B Surface Antigen

Unmethylated CpG dinucleotides in bacterial DNA or synthetic oligodeoxynucleotides (ODN) cause B cell proliferation and Ig secretion, monocyte cytokine secretion, and activation of NK cell lytic activity and IFN-γ secretion in vivo and in vitro. The potent immune activation by CpG ODN suggests possible utility for enhancing immune responses to vaccines. Mice immunized with recombinant hepatitis B virus surface Ag and a CpG ODN as an immune enhancer have titers of Abs against HBsAg (anti-HBs) that are five times higher than those of mice immunized with HBsAg and the standard adjuvant, aluminum hydroxide (alum). Ab titers in mice immunized with HBsAg and both CpG ODN plus alum were 35 times higher than the titers in mice immunized with alum alone, indicating a strong synergistic interaction between the CpG ODN and alum. ODN without CpG motifs had little or no immune-enhancing activity at the doses used herein. Alum induces a Th2 humoral response (mostly IgG1) and no CTL. In contrast, CpG ODN gives a strong Th1 response with predominantly IgG2a Abs and CTL, even when mixed with alum. In vitro studies to determine possible mechanisms of CpG immune-enhancing effects show that CpG ODN induce expression of costimulatory molecules on Ag-presenting cells and drive B cell isotype switching in the appropriate cytokine milieu. These studies demonstrate that CpG ODN are promising new immune enhancers for vaccination applications.

The role of CpG dinucleotides in DNA vaccines

DNA vaccines can induce potent humoral and cellular immune responses without any additional adjuvant. Recent studies indicate that unmethylated CpG dinucleotides within DNA vaccines are immune stimulatory and exert an essential endogenous adjuvant activity. These CpG motifs can be added deliberately to DNA or conventional protein vaccines to enhance the Th1 immune response.

Evaluation of the toxicity of ISIS 2302, a phosphorothioate oligonucleotide, in a 4-week study in CD-1 mice

The subchronic toxicity of ISIS 2302 and ISIS 3082, phosphorothioate oligonucleotides with antisense activity against human and murine ICAM-1 mRNA, respectively, was investigated in CD-1 mice. ISIS 2302 is currently in clinical trials as an anti-inflammatory agent. Because of the differences in mRNA sequence targets between humans and mice, ISIS 2302 has no pharmacologic activity in mice. ISIS 3082 was specifically designed to inhibit murine ICAM-1 and was included in this study to evaluate the effects of prolonged ICAM-1 inhibition. The oligonucleotides were administered by bolus i.v. injection (via tail vein) every other day for 27 days (14 doses) at dose levels of 0, 0.8, 4, 20, and 100 mg/kg per injection ISIS 2302 or 20 mg/kg per injection ISIS 3082. The basic group size consisted of 10 male and 10 female mice, which were sacrificed 2 days after the last dose and an additional 5 mice per sex in vehicle control and 100 mg/kg ISIS 2302 dose groups, which remained on study for a 28-day treatment-free period. No treatment-related deaths occurred during this study, and there were no effects of either oligonucleotide on body weight gain or food consumption. The most common changes observed in this study included a mixed mononuclear cell infiltrate seen in a number of organs or tissues, splenomegaly, and lymphoid hyperplasia at dose levels of > or = 20 mg/kg ISIS 2302. In the group that received the highest dose level of ISIS 2302 (100 mg/kg), there were alterations in serum chemistry parameters that appeared to be related to perturbations in the liver, including 3- to 4-fold increases in aspartate and alanine aminotransferase and smaller changes in bilirubin, alkaline phosphatase, cholesterol, triglycerides, and albumin levels. Treatment-related effects on hematologic parameters were limited to the 100 mg/kg ISIS 2302 dose group and included slight monocytosis and thrombocytopenia. None of the effects observed appeared to be life threatening. Complete or partial reversal of all effects was evident in the remaining high-dose ISIS 2302 animals at the end of the 4-week recovery period. Comparison of the effects produced by the same dose level (20 mg/kg) of ISIS 2302 and ISIS 3082 did not reveal any differences that could be attributed to exaggerated pharmacology. In conclusion, treatment-related alterations were observed primarily at the 100 mg/kg dose level, including immune stimulation and hepatic alterations, which were partially reversed following a 4-week treatment-free period.

Characterization and modulation of immune stimulation by modified oligonucleotides

Single-stranded oligodeoxynucleotides (ODNs) were tested for their ability to stimulate NK cells isolated from murine spleens to lyse target cells. Various sequences were evaluated, some of which have been shown previously to exhibit pharmacologic activity in murine model systems. It was confirmed that the CpG motif was stimulatory only in specific sequence contexts, and we found that phosphorothioate backbones were, in general, less stimulatory than phosphodiester backbones. In addition, this stimulation could be reduced by methylating the cytosine of the CpG and eliminated by modifying all of the cytosines contained in an ODN with methyl, bromo, or iodo modifications to the 5 position of the cytosine ring. These results were compared with the ability of a subset of these ODN sequences to stimulate B cell proliferation in vitro. In this comparison, phosphorothioate backbones were found to be required, and the context of the CpG motif was found to be less critical for activation. Finally, one of the most potent ODNs was shown to activate NK and B lymphocytes when administered in vivo.

Specific inhibition of nitric oxide production in macrophages by phosphorothioate antisense oligonucleotides

The effects of antisense oligonucleotides (ODNs) on nitric oxide (NO) production induced by lipopolysaccharide (LPS) were investigated using thioglycollate-induced mouse peritoneal macrophages. Antisense phosphorothioate ODNs (S-oligo) corresponding to a sequence in the neighborhood of the AUG initiation codon of a mouse inducible nitric oxide synthase (iNOS) mRNA, which has a G-quartet motif in its antisense sequence, inhibited NO induction in a dose-dependent manner. Antisense phosphodiester ODNs (D-oligo), 5'- and 3'-terminal phosphorothioate-modified antisense ODNs and control scramble and missense S-oligos had no such effect. In addition, control nonsense and two mismatched S-oligos, which include G-quartet motif in their sequences, inhibited NO induction to approximately 50% of those in the control. Antisense S-oligo showed the inhibitory effect on NO production by exposure of macrophages to various concentrations of LPS. Western blot analysis using anti-mouse inducible nitric oxide synthase (iNOS) antibody revealed that antisense S-oligo specifically removed an immunoreactive band at 130 kDa. In addition, the results of reverse transcription-polymerase chain reaction (RT-PCR) revealed that the antisense effect originated from a specific reduction of the targeted iNOS mRNA by hybridization with the antisense S-oligo. Furthermore, no ODNs affected beta-actin mRNA and tumor necrosis factor alpha (TNF-alpha) expression in macrophages stimulated by LPS. These findings demonstrated that antisense S-oligo inhibited NO production derived from iNOS expression in macrophages by an antisense mechanism, including the aptameric effect partially mediated by the G-quartet motif.

Inhibition of coagulation by a phosphorothioate oligonucleotide

In the development of antisense therapeutics, there have been a number of hybridization-independent effects characterized for phosphorothioate oligodeoxynucleotides. One such effect is the transient prolongation of clotting times following intravenous infusion of high doses. In this study, inhibition of clotting times was characterized by determining the time course of both APTT and plasma oligonucleotide following intravenous infusion of ISIS 2302 in cynomolgus monkeys. Prolongation of APTT was also achieved by addition of ISIS 2302 to citrated blood from untreated monkeys, allowing the investigation of the mechanism of inhibition in vitro. Results from this study clearly indicate that the intrinsic pathway (APTT) was more sensitive to inhibition than the extrinsic pathway (PT). The prolongation of APTT was also shown to be transient and closely correlated with plasma oligonucleotide concentrations. The extent of APTT prolongation can be controlled by minimizing peak plasma oligonucleotide concentrations through lowering the dose or prolonging infusion duration. Direct addition of ISIS 2302 to blood produced quantitatively similar inhibition of clotting times. This effect was similar for a number of different phosphorothioate oligodeoxynucleotides, but oligonucleotides containing phosphodiester linkages and 2'-propoxy linkages were much less inhibitory. Additional in vitro studies indicated that the mechanism of inhibition was independent of that of heparin and possibly involved selective inhibition of the intrinsic pathway as well as the common clotting pathway. Investigation of selective clotting factors indicated that there was no direct inhibition of the enzymatic activity of factor Xa, XIa, or thrombin using chromogenic substrates. However, ISIS 2302 did produce a concentration-dependent increase in clotting time when fibrinogen was used as the substrate for thrombin.

Macrophages sense pathogens via DNA motifs: induction of tumor necrosis factor-alpha-mediated shock

Cell surface components of pathogens, such as lipopolysaccharide (LPS), are an important signal for receptor-mediated activation of immune cells. Here we demonstrate that DNA of gram-positive and gram-negative bacteria or certain synthetic oligonucleotides displaying unmethylated CpG-motifs can trigger macrophages in vitro to induce nuclear translocation of nuclear factor-kappa B, accumulate tumor necrosis factor (TNF)-alpha mRNA and release large amounts of TNF-alpha. In vivo these events culminate in acute cytokine-release syndrome which includes systemic but transient accumulation of TNF-alpha. D-Galactosamine (DGalN)-sensitized mice succumb to lethal toxic shock due to macrophage-derived TNF-alpha resulting in fulminant apoptosis of liver cells. LPS and a specific oligonucleotide synergized in vivo as measured by TNF-alpha-release, suggesting that macrophages integrate the respective signals. The ability of macrophages to discriminate and to respond to bacterial DNA with acute release of pro-inflammatory cytokines may point out an important and as yet unappreciated sensing mechanism for foreign DNA.