Effective postexposure treatment of retrovirus-induced disease with immunostimulatory DNA containing CpG motifs

Pharmacological modulation of nucleic acid sensors - therapeutic potential and persisting obstacles

Nucleic acid sensors, primarily TLR and RLR family members, as well as cGAS-STING signalling, play a critical role in the preservation of cellular and organismal homeostasis. Accordingly, deregulated nucleic acid sensing contributes to the origin of a diverse range of disorders, including infectious diseases, as well as cardiovascular, autoimmune and neoplastic conditions. Accumulating evidence indicates that normalizing aberrant nucleic acid sensing can mediate robust therapeutic effects. However, targeting nucleic acid sensors with pharmacological agents, such as STING agonists, presents multiple obstacles, including drug-, target-, disease- and host-related issues. Here, we discuss preclinical and clinical data supporting the potential of this therapeutic paradigm and highlight key limitations and possible strategies to overcome them.

Friend retrovirus studies reveal complex interactions between intrinsic, innate and adaptive immunity

Approximately 4.4% of the human genome is comprised of endogenous retroviral sequences, a record of an evolutionary battle between man and retroviruses. Much of what we know about viral immunity comes from studies using mouse models. Experiments using the Friend virus (FV) model have been particularly informative in defining highly complex anti-retroviral mechanisms of the intrinsic, innate and adaptive arms of immunity. FV studies have unraveled fundamental principles about how the immune system controls both acute and chronic viral infections. They led to a more complete understanding of retroviral immunity that begins with cellular sensing, production of type I interferons, and the induction of intrinsic restriction factors. Novel mechanisms have been revealed, which demonstrate that these earliest responses affect not only virus replication, but also subsequent innate and adaptive immunity. This review on FV immunity not only surveys the complex host responses to a retroviral infection from acute infection to chronicity, but also highlights the many feedback mechanisms that regulate and counter-regulate the various arms of the immune system. In addition, the discovery of molecular mechanisms of immunity in this model have led to therapeutic interventions with implications for HIV cure and vaccine development.

Recent advances in the discovery and development of TLR ligands as novel therapeutics for chronic HBV and HIV infections

INTRODUCTION

Toll-like receptor (TLR) ligands remain as promising antiviral drug candidates for the treatment of chronic viral infections. Basic research on the mechanisms of antiviral activity of TLR ligands in preclinical animal models and clinical testing of drug candidates have been carried out in recent years. Areas covered: This review provides an overview of the preclinical and clinical testing of TLR ligands in two major viral infections: hepatitis B virus (HBV) and human immunodeficiency virus (HIV). Recent results have further demonstrated the potent antiviral activity of various TLR ligands . A TLR7 agonist is in clinical trials for the treatment of chronic HBV infection while a HBV vaccine using a TLR9 ligand as an adjuvant has proven to be superior to conventional HBV vaccines and has been approved for clinical use. Generally, TLR activation may achieve viral control mainly by promoting adaptive immunity to viral proteins. Expert opinion: Recent research in this field indicates that TLR ligands could be developed as clinically effective drugs if the obstacles concerning toxicity and application routes are overcome. TLR-mediated promotion of adaptive immunity is a major issue for future studies and will determine the future development of TLR ligands as drugs for immunomodulation.

Toll-like receptor (TLR)21 signalling-mediated antiviral response against avian influenza virus infection correlates with macrophage recruitment and nitric oxide production

Cytosine-guanosinedeoxynucleotide (CpG) DNA can be used for the stimulation of the toll-like receptor (TLR)21 signalling pathway in avian species which ultimately leads to up-regulation of gene transcription for pro-inflammatory molecules including nitric oxide and recruitment of innate immune cells. The objective of this study was to determine the antiviral effect of NO, produced in response to in ovo delivery of CpG DNA, against avian influenza virus (AIV) infection. We found that when CpG DNA is delivered at embryo day (ED)18 in ovo and subsequently challenged with H4N6 AIV at ED19 pre-hatch and day 1 post-hatching, CpG DNA reduces H4N6 AIV replication associated with enhanced NO production and macrophage recruitment in lungs. In vitro, we showed that NO originating from macrophages is capable of eliciting an antiviral response against H4N6 AIV infection. This study provides insights into the mechanisms of CpG DNA-mediated antiviral response, particularly against AIV infection in avian species.

TLR ligand induced IL-6 counter-regulates the anti-viral CD8(+) T cell response during an acute retrovirus infection

We have previously shown that Toll-like receptor (TLR) agonists contribute to the control of viral infection by augmenting virus-specific CD8⁺ T-cell responses. It is also well established that signaling by TLRs results in the production of pro-inflammatory cytokines such as interleukin 6 (IL-6). However, how these pro-inflammatory cytokines influence the virus-specific CD8⁺ T-cell response during the TLR agonist stimulation remained largely unknown. Here, we investigated the role of TLR-induced IL-6 in shaping virus-specific CD8⁺ T-cell responses in the Friend retrovirus (FV) mouse model. We show that the TLR agonist induced IL-6 counter-regulates effector CD8⁺ T-cell responses. IL-6 potently inhibited activation and cytokine production of CD8⁺ T cells in vitro. This effect was mediated by a direct stimulation of CD8⁺ T cells by IL-6, which induced upregulation of STAT3 phosphorylation and SOCS3 and downregulated STAT4 phosphorylation and T-bet. Moreover, combining TLR stimulation and IL-6 blockade during an acute FV infection resulted in enhanced virus-specific CD8⁺ T-cell immunity and better control of viral replication. These results have implications for our understanding of the role of TLR induced pro-inflammatory cytokines in regulating effector T cell responses and for the development of therapeutic strategies to overcome T cell dysfunction in chronic viral infections.

Immunotherapeutic potential of CpG oligodeoxynucleotides in veterinary species

Innate immunity plays a critical role in host defense against infectious diseases by discriminating between self and infectious non-self. The recognition of infectious non-self involves germ-line encoded pattern recognition receptors (PRRs) that recognize pathogen-associated molecular patterns (PAMPs). The PAMPs are the components of pathogenic microbes which include not only the cell wall constituents but also the unmethylated 2'-deoxy-ribo-cytosine-phosphate-guanosine (CpG) motifs. These CpG motifs present within bacterial and viral DNA are recognized by toll-like receptor 9 (TLR9), and signaling by this receptor triggers a proinflammatory cytokine response which, in turn, influences both innate and adaptive immune responses. The activation of TLR9 with synthetic CpG oligodeoxynucleotides (ODNs) induces powerful Th1-like immune responses. It has been shown to provide protection against infectious diseases, allergy and cancer in laboratory animal models and some domestic animal species. With better understanding of the basic biology and immune mechanisms, it would be possible to exploit the potential of CpG motifs for animal welfare. The research developments in the area of CpG and TLR9 and the potential applications in animal health have been reviewed in this article.

Preclinical development of TLR ligands as drugs for the treatment of chronic viral infections

INTRODUCTION

Toll-like receptors (TLRs) have been identified as key regulators of innate and adaptive immune responses in viral infection. Recent progress in this field revealed that there are significant interactions between the TLR system and pathogens in chronic viral infections. Therefore, TLR ligands have great potential for the treatment of chronic viral infections.

AREAS COVERED

This review provides an overview of the methodology for preclinical testing of TLR ligands for three major viral infections: hepatitis B virus (HBV), hepatitis C virus (HCV) and human immunodeficiency virus (HIV). TLR ligands have shown potent antiviral activity in different cell culture systems as well as animal models for these infections and induce the production of antiviral cytokines, modulated cellular immunological functions and antiviral effects in vivo.

EXPERT OPINION

The recent progress in this field demonstrated that activation of a large number of TLR ligands is effective against viral infections in cell culture systems and animal models. Exploring these models, further in-depth elucidation of the molecular and immunological mechanisms of the antiviral activity of TLR ligands will be necessary to develop them into clinical useful drugs.

Innate defense regulator peptide synergizes with CpG ODN for enhanced innate intestinal immune responses in neonate piglets

The in vivo immunoadjuvant effects of the combination of CpG oligodeoxynucleotide (CpG ODN) and innate defense-regulator peptides (IDRs) have been studied in mice. However, little is known about the efficacy of these molecules in stimulating the innate intestinal immune system in neonatal piglets. In this study, we observed that intranasal (IN) administration of CpG-IDR (peptide HH2 (VQLRIRVAVIRA)) complex significantly increased intestinal mRNA expression of Th1 cytokines, CC chemokines and CXC chemokines when compared to HH2 and CpG ODN alone. Also an obvious cellular infiltration was observed in the intestine of CpG-HH2-treated neonatal piglets, which was associated with increased protection against Enterotoxigenic Escherichia coli (ETEC). Moreover, we showed that pro-inflammatory cytokine TNF-α was inhibited when CpG ODN combined with HH2. This was the first report that deciphered the role played by CpG-HH2 complex in the intestine of neonatal piglets. This work clearly demonstrated that efficiency of the IN route inducing intestinal responses in neonatal piglets might be taken into consideration for further vaccine development against neonatal intestinal diseases.

Targeting of Toll-like receptors: a decade of progress in combating infectious diseases

Toll-like receptors (TLRs) recognise highly conserved molecular structures, collectively known as pathogen-associated molecular patterns. In the past two decades, development and clinical implementation of TLR ligands-ie, chemically modified synthetic derivatives of naturally occurring ligands and fully synthetic small molecules-have been topics of intense research. Targeted manipulation of TLR signalling has been applied clinically to boost vaccine effectiveness, promote a robust T helper 1-predominant immune response against viral infection, or dampen the exaggerated inflammatory response to bacterial infection. Use of these new therapeutic molecules as adjuncts to conventional pharmacotherapy or stand-alone treatments might offer solutions to unmet clinical needs or could replace existing partly effective therapeutic strategies.

CpG oligodeoxynucleotide promotes protective immunity in the enteric mucosa and suppresses enterotoxigenic E. coli in the weaning piglets

CpG oligodeoxynucleotide (CpG ODN) has been described as an effective activator of the innate immune system, with potential to protect against infection caused by a range of pathogens in a non-specific manner. We therefore investigated if intranasal (IN), oral (OR)-mucosal, and intramuscular (IM)-systemic administrations of CpG ODN without antigen codelivery could all enhance innate immunity in the enteric mucosa and control the extent of enterotoxigenic Escherichia coli (ETEC) infection in weaning piglets. Here our data showed that CpG ODN dosed by IN, OR or IM routes protected weaning piglets against a subsequent challenge with ETEC. The level of protection was greater when CpG ODN was administered IN and OR than IM, demonstrating a clear relationship between the route of CpG dosing and protection. IN and OR treatments with CpG ODN reduced bacterial load in the phases at days 3-5 post challenge. The CXC chemokine (CXCL10 and CXCL11) and CC chemokine (CCL4 and CCL5) mRNA expressions were elevated in the intestinal tissues from animals treated IN or OR with CpG ODN compared to untreated controls. Significantly enhanced mRNA expressions for cathelicidins (PR-39 and protegrin-1), but moderately for β-defensin (pBD1 and pBD2), were observed in IN or OR CpG-treatments. Also, significant production of cytokines (IL-12, IFN-γ, and MCP-1) and F4-specific antibodies (IgG/IgA) was detected in intestinal washings following IN and OR CpG-treatments. In contrast, IM delivery induced marked production of sera F4-specific antibodies. It was possible that these chemokines, cytokines, cathelicidins and antibodies played a role in the clearance of ETEC. These findings suggested that IN or OR administration of CpG ODN without antigen codelivery might represent a valuable strategy for induction of innate immunity against ETEC infection.

Synthetic innate defence regulator peptide enhances in vivo immunostimulatory effects of CpG-ODN in newborn piglets

The in vivo immunoadjuvant effects of CpG oligodeoxynucleotides (CpG-ODN) have been studied extensively in mice and relatively fewer studies have been done in piglets. But so far, the innate immunostimulatory effects of CpG-ODN combination with innate defense-regulator peptides (IDRs) have not been demonstrated. The purpose of this study is to determine the potential effects of CpG-ODN with IDR in newborn piglets. The immunostimulatory abilities of four selected IDRs were compared, among them HH2 showed best immunostimulatory effects in newborn piglets. Hereafter, the abilities of CpG-ODN combined with HH2 to enhance innate immune responses were examined in newborn piglets. The complex of HH2 and CpG-ODN could induce much stronger Th1 cytokine and chemokine responses than HH2 or CpG-ODN alone. HH2-CpG-ODN immunized piglets showed higher B cell percentage in PBMCs than CpG-ODN alone. These in vivo data demonstrated for the first time that subcutaneously (SC) administration of CpG-ODN combined with HH2 is efficient to stimulate innate immune system in newborn piglets.

Amphipathic DNA polymers exhibit antiviral activity against systemic murine Cytomegalovirus infection

Background

Phosphorothioated oligonucleotides (PS-ONs) have a sequence-independent, broad spectrum antiviral activity as amphipathic polymers (APs) and exhibit potent in vitro antiviral activity against a broad spectrum of herpesviruses: HSV-1, HSV-2, HCMV, VZV, EBV, and HHV-6A/B, and in vivo activity in a murine microbiocide model of genital HSV-2 infection. The activity of these agents against animal cytomegalovirus (CMV) infections in vitro and in vivo was therefore investigated.

Results

In vitro, a 40 mer degenerate AP (REP 9) inhibited both murine CMV (MCMV) and guinea pig CMV (GPCMV) with an IC₅₀ of 0.045 μM and 0.16 μM, respectively, and a 40 mer poly C AP (REP 9C) inhibited MCMV with an IC₅₀ of 0.05 μM. Addition of REP 9 to plaque assays during the first two hours of infection inhibited 78% of plaque formation whereas addition of REP 9 after 10 hours of infection did not significantly reduce the number of plaques, indicating that REP 9 antiviral activity against MCMV occurs at early times after infection. In a murine model of CMV infection, systemic treatment for 5 days significantly reduced virus replication in the spleens and livers of infected mice compared to saline-treated control mice. REP 9 and REP 9C were administered intraperitoneally for 5 consecutive days at 10 mg/kg, starting 2 days prior to MCMV infection. Splenomegaly was observed in infected mice treated with REP 9 but not in control mice or in REP 9 treated, uninfected mice, consistent with mild CpG-like activity. When REP 9C (which lacks CpG motifs) was compared to REP 9, it exhibited comparable antiviral activity as REP 9 but was not associated with splenomegaly. This suggests that the direct antiviral activity of APs is the predominant therapeutic mechanism in vivo. Moreover, REP 9C, which is acid stable, was effective when administered orally in combination with known permeation enhancers.

Conclusion

These studies indicate that APs exhibit potent, well tolerated antiviral activity against CMV infection in vivo and represent a new class of broad spectrum anti-herpetic agents.

All three classes of CpG ODNs up-regulate IP-10 gene in pigs

The analysis of CpG ODN induced innate immune responses in different animal species has shown substantial similarities and differences in levels and types of induced cytokines profile. The objectives of these studies were to identify innate immune biomarkers activated by three classes of CpG ODNs in pigs. For this purpose, we investigated the kinetics of innate immune responses in immune cells from pigs following in vitro and in vivo stimulation with CpG ODNs. The mRNA expression of cytokine and chemokine genes were assayed by SYBR green based quantitative real time PCR. A-class CpG ODN induced significant but transient levels of IFN-gamma, IL-12 (P40), IL-6, IL-4 and TNF-alpha mRNA, C-class CpG ODN induced significant level of IFN-gamma, IFN-alpha and IL-12 mRNA and the lowest level of IL-4 (Th-2 type) mRNA. A very low level of some cytokines stimulation was observed by GC ODNs. It is noteworthy, that IL-12 (P35) mRNA was significantly stimulated by B-class GpC ODN 7909. Interestingly, all classes of CpG ODNs induced significant level of IP-10 at 12h post stimulation. These in vitro and in vivo observations suggest that interferon-gamma inducible protein 10 (IP-10) may be a reliable biomarker for immune activity induced by CpG ODNs in pigs.

CpG DNA: Trigger of Sepsis, Mediator of Protection, or Both?

Unmethylated CpG motifs are prevalent in bacterial but not vertebrate genomic DNAs and activate immune cells that express the TLR9 receptor. This triggers the production of reactive oxygen species and the secretion of proinflammatory cytokines and chemokines. Under some conditions these effects can result in the systemic inflammatory response syndrome. Under other conditions, the immune stimulatory effects of CpG motifs can protect against pathogen challenge and initiate prophylactic and therapeutic innate and adaptive immune responses.

A proviral role for CpG in cytomegalovirus infection

TLR9-dependent signaling in plasmacytoid dendritic cells is a key contributor to innate immune defense to mouse CMV infection. We aimed to study the expression and potential contribution of TLR9 signaling in human CMV (HCMV) infection of primary fibroblasts. HCMV infection strongly induced TLR9 expression in two of three fibroblast types tested. Furthermore, the TLR9 ligand CpG-B induced a strong proviral effect when added shortly after HCMV infection, enhancing virus production and cell viability. However, not all CpG classes displayed proviral activity, and this correlated with their IFN-beta-inducing ability. The proviral effect of CpG-B correlated completely with concurrent viral up-regulation of TLR9 in fibroblasts. Importantly, the timing of CpG addition was a critical parameter; in striking contrast to the proviral effect, CpG addition at the time of infection blocked viral uptake and nearly abolished HCMV production. The contrasting and time-dependent effects of CpG on HCMV infectivity reveal a complex interplay between CpG, TLR9, and HCMV infection. Additionally, the data suggest a potentially harmful role for CpG in the promotion of HCMV infection.

Immunotherapeutic applications of CpG oligodeoxynucleotide TLR9 agonists

Toll-like receptor 9 (TLR9) agonists have demonstrated substantial potential as vaccine adjuvants, and as mono- or combination therapies for the treatment of cancer and infectious and allergic diseases. Commonly referred to as CpG oligodeoxynucleotides (ODN), TLR9 agonists directly induce the activation and maturation of plasmacytoid dendritic cells and enhance differentiation of B cells into antibody-secreting plasma cells. Preclinical and early clinical data support the use of TLR9 agonists as vaccine adjuvants, where they can enhance both the humoral and cellular responses to diverse antigens. In mouse tumor models TLR9 agonists have shown activity not only as monotherapy, but also in combination with multiple other therapies including vaccines, antibodies, cellular therapies, other immunotherapies, antiangiogenic agents, radiotherapy, cryotherapy, and some chemotherapies. Phase I and II clinical trials have indicated that these agents have antitumor activity as single agents and enhance the development of antitumor T-cell responses when used as therapeutic vaccine adjuvants. CpG ODN have shown benefit in multiple rodent and primate models of asthma and other allergic diseases, with encouraging results in some early human clinical trials. Although their potential clinical contributions are enormous, the safety and efficacy of these TLR9 agonists in humans remain to be determined.

Anti-retroviral effects of type I IFN subtypes in vivo

Type I IFN play a very important role in immunity against viral infections. Murine type I IFN belongs to a multigene family including 14 IFN-alpha subtypes but the biological functions of IFN-alpha subtypes in retroviral infections are unknown. We have used the Friend retrovirus model to determine the anti-viral effects of IFN-alpha subtypes in vitro and in vivo. IFN-alpha subtypes alpha1, alpha4, alpha6 or alpha9 suppressed Friend virus (FV) replication in vitro, but differed greatly in their anti-viral efficacy in vivo. Treatment of FV-infected mice with the IFN-alpha subtypes alpha1, alpha4 or alpha9, but not alpha6 led to a significant reduction in viral loads. Decreased splenic viral load after IFN-alpha1 treatment correlated with an expansion of activated FV-specific CD8(+) T cells and NK cells into the spleen, whereas in IFN-alpha4- and -alpha9-treated mice it exclusively correlated with the activation of NK cells. The results demonstrate the distinct anti-retroviral effects of different IFN-alpha subtypes, which may be relevant for new therapeutic approaches.

Broad-spectrum drugs against viral agents

Development of antivirals has focused primarily on vaccines and on treatments for specific viral agents. Although effective, these approaches may be limited in situations where the etiologic agent is unknown or when the target virus has undergone mutation, recombination or reassortment. Augmentation of the innate immune response may be an effective alternative for disease amelioration. Nonspecific, broad-spectrum immune responses can be induced by double-stranded (ds)RNAs such as poly (ICLC), or oligonucleotides (ODNs) containing unmethylated deocycytidyl-deoxyguanosinyl (CpG) motifs. These may offer protection against various bacterial and viral pathogens regardless of their genetic makeup, zoonotic origin or drug resistance.

Therapeutic applications of synthetic CpG oligodeoxynucleotides as TLR9 agonists for immune modulation

Vertebrate toll-like receptors (TLRs) sense invading pathogens by recognizing bacterial and viral structures and, as a result, activate innate and adaptive immune responses. Ten human functional TLRs have been reported so far; three of these (TLR7, 8, and 9) are expressed in intracellular compartments and respond to single-stranded nucleic acids as natural ligands. The pathogen structure selectively recognized by TLR9 in bacterial or viral DNA was identified to be CpG dinucleotides in specific sequence contexts (CpG motifs). Short phosphorothioate-stabilized oligodeoxynucleotides (ODNs) containing such motifs are used as synthetic TLR9 agonists, and different classes of ODN TLR9 agonists have been identified with distinct immune modulatory profiles. The TLR9-mediated activation of the vertebrate immune system suggests using such TLR9 agonists as effective vaccine adjuvants for infectious disease, and for the treatment of cancer and asthma/allergy. Immune activation by CpG ODNs has been demonstrated to be beneficial in animal models as a vaccine adjuvant and for the treatment of a variety of viral, bacterial, and parasitic diseases. Antitumor activity of CpG ODNs has also been established in numerous mouse models. In clinical vaccine trials in healthy human volunteers or in immunocompromised HIV-infected patients, CpG ODNs strongly enhanced vaccination efficiency. Most encouraging results in the treatment of cancers have come from human phase I and II clinical trials using CpG ODNs as a tumor vaccine adjuvant, monotherapy, or in combination with chemotherapy. Therefore, CpG ODNs represent targeted immune modulatory drugs with a broad range of potential applications.

A CpG oligodeoxynucleotide inducing anti-coxsackie B3 virus activity in human peripheral blood mononuclear cells

Coxsackie B3 virus (CVB3) is the most significant pathogen causing myocarditis in humans, and antiviral therapy would be most effective in the early stages of the disease. Here we provide evidence that BW001, a C-type CpG oligodeoxynucleotide, induces anti-CVB3 activity in human peripheral blood mononuclear cells (PBMCs). In parallel, we have demonstrated that BW001 induces human PBMCs to express mRNAs of multiple types of interferon (IFN), including IFN-alpha, IFN-beta, IFN-omega and IFN-gamma, and to express mRNAs of at least 11 subtypes of IFN-alpha. The induced IFNs may contribute to the anti-CVB3 activity. The results suggest that BW001 could be developed into a medication with the potential to treat CVB3 infectious diseases by inducing natural mixed IFNs.

Antiinfective applications of toll-like receptor 9 agonists

The innate immune system detects pathogens by the presence of highly conserved pathogen-expressed molecules, which trigger host immune defenses. Toll-like receptor (TLR) 9 detects unmethylated CpG dinucleotides in bacterial or viral DNA, and can be stimulated for therapeutic applications with synthetic oligodeoxynucleotides containing immune stimulatory "CpG motifs." TLR9 activation induces both innate and adaptive immunity. The TLR9-induced innate immune activation can be applied in the prevention or treatment of infectious diseases, and the adaptive immune-enhancing effects can be harnessed for improving vaccines. This article highlights the current understanding of the mechanism of action of CpG oligodeoxynucleotides, and provides an overview of the preclinical data and early human clinical trial results, applying these TLR9 agonists in the field of infectious diseases.

The level of friend retrovirus replication determines the cytolytic pathway of CD8+ T-cell-mediated pathogen control

Cytotoxic T cells (CTL) play a central role in the control of viral infections. Their antiviral activity can be mediated by at least two cytotoxic pathways, namely, the granule exocytosis pathway, involving perforin and granzymes, and the Fas-FasL pathway. However, the viral factor(s) that influences the selection of one or the other pathway for pathogen control is elusive. Here we investigate the role of viral replication levels in the induction and activation of CTL, including their effector potential, during acute Friend murine leukemia virus (F-MuLV) infection. F-MuLV inoculation results in a low-level infection of adult C57BL/6 mice that is enhanced about 500-fold upon coinfection with the spleen focus-forming virus (SFFV). Both the low- and high-level F-MuLV infections generated CD8+ effector T cells that were essential for the control of viral replication. However, the low-level infection induced CD8+ T cells expressing solely FasL but not the cytotoxic molecules granzymes A and B, whereas the high-level infection resulted in induction of CD8+ effector T cells secreting molecules of the granule exocytosis pathway. By using knockout mouse strains deficient in one or the other cytotoxic pathway, we found that low-level viral replication was controlled by CTL that expressed FasL but control of high-level viral replication required perforin and granzymes. Additional studies, in which F-MuLV replication was enhanced experimentally in the absence of SFFV coinfection, supported the notion that only the replication level of F-MuLV was the critical factor that determined the differential expression of cytotoxic molecules by CD8+ T cells and the pathway of CTL cytotoxicity.

CpG oligodeoxynucleotides allow for effective adoptive T-cell therapy in chronic retroviral infection

Adoptive T-cell therapy in cancer or chronic viral infections is often impeded by the development of functional impairment of the transferred cells. To overcome this therapeutic limitation we combined adoptive transfer of naive, virus-specific CD8+ T cells with immunostimulative CpG oligodeoxynucleotides (ODNs) in mice chronically infected with the Friend retrovirus. The CpG-ODN co-injection prevented the T cells from developing functional defects in IFNgamma and granzyme production and degranulation of cytotoxic molecules. Thus, the transferred T cells were able to reduce chronic viral loads when combined with CpG-ODNs. This strategy provides a new approach for developing successful adoptive T-cell therapy against chronic infections.

HIV-1 infection of mononuclear phagocytic cells: the case for bacterial innate immune deficiency in AIDS

HIV-1 infection of mononuclear phagocytic cells, comprising monocytes, macrophages, and dendritic cells, has been the subject of extensive research over the past 20 years. The roles of mononuclear phagocytic cells in transmission of HIV-1 infection and as reservoirs of actively replicating virus have received particular attention. Experimental data have also accumulated about the effects of HIV-1 on the physiological function of mononuclear phagocytic cells, particularly their role in innate immunity to bacteria. The effects of HIV-1 on bacterial innate immune responses by mononuclear phagocytic cells are discussed here together with reports of direct interactions between HIV-encoded products and bacterial innate immune signalling pathways. These reports demonstrate mechanisms for HIV-mediated disruption of innate immune responses by mononuclear phagocytic cells that could provide novel therapeutic targets in HIV-infected patients. The clinical urgency is highlighted by greatly increased risk of invasive bacterial disease in this population, even in the era of highly active antiretroviral therapy. HIV-mediated injury to bacterial innate immunity provides an experimental paradigm that could broaden our overall understanding of innate immunity and be used to study responses to pathogens other than bacteria.

In vivo immunostimulatory effects of CpG ODN in newborn piglets

The in vivo immunoadjuvant effects of CpG oligodeoxynucleotides (CpG ODN) have been studied extensively in mice and relatively fewer studies have been done in other species. But so far, the innate immunostimulatory effects of CpG ODN have been demonstrated just in mouse, monkey, sheep and chicken in some reports. The purpose of this study is to determine the potential effects of CpG ODN in newborn piglets. The proportion of CD4(+), CD8(+) T lymphocytes subpopulations and the major histocompability complex (MHC-II) antigen expression of peripheral blood mononuclear cells (PBMCs) and IFN-gamma in serum were tested at various time-points. The results suggested that, the CD4(+)/CD8(+) ratio decreased over time in piglets inoculated with phosphate buffer saline (PBS) alone, however, it was stable in CpG ODN-inoculated piglets; the use of CpG ODN can prevent effectively the reduction of the proportion of CD4(+) T lymphocytes. The MHC-II antigen expression and IFN-gamma level of CpG ODN-injected piglets were significantly higher than those of PBS-injected piglets. The ODN-induced responses were stronger in animals injected with CpG ODN formulated in 30% emulsigen than in PBS. The innate immunostimulatory activity of CpG ODN appeared to be in dose-dependent manner. These in vivo data demonstrate for the first time that CpG ODN can stimulate innate immune system in newborn piglets.

Therapeutic potential of Toll-like receptor 9 activation

In the decade since the discovery that mouse B cells respond to certain unmethylated CpG dinucleotides in bacterial DNA, a specific receptor for these 'CpG motifs' has been identified, Toll-like receptor 9 (TLR9), and a new approach to immunotherapy has moved into the clinic based on the use of synthetic oligodeoxynucleotides (ODN) as TLR9 agonists. This review highlights the current understanding of the mechanism of action of these CpG ODN, and provides an overview of the preclinical data and early human clinical trial results using these drugs to improve vaccines and treat cancer, infectious disease and allergy/asthma.

In vivo effects of oligodeoxynucleotides containing synthetic immunostimulatory motifs in weaned piglets

The innate immunostimulatory effects of CpG ODN have been demonstrated in mouse, monkey, sheep and chicken in some reports. Unfortunately, little work has been carried out with regard to their effects on the innate immune system of weaned piglets. In this study, the proportion of CD4(+), CD8(+) T lymphocytes subpopulations and interferon-gamma (IFN-gamma) and IL-4 in serum, proliferation of peripheral blood mononuclear cells (PBMCs) were tested at different time-points. The results suggested that, the CD4(+)/CD8(+) ratio decreased significantly in weaned piglets inoculated with phosphate buffer saline (PBS) alone, however, it was stable in CpG ODN-inoculated piglets. Proliferation of PBMCs and IFN-gamma levels of CpG ODN-injected piglets were significantly higher than those of PBS-injected piglets. The ODN-induced responses were stronger in animals injected with CpG ODN formulated in 30% emulsigen than in PBS and alum. The innate immunostimulatory activity of CpG ODN appeared to be in dose-dependent manner. These in vivo data demonstrate for the first time that CpG ODN can stimulate innate immune system in weaned piglets.

CpG oligodeoxynucleotides protect newborn mice from a lethal challenge with the neurotropic Tacaribe arenavirus

The innate immune system is key to limiting the early spread of most pathogens and directing the development of Ag-specific immunity. Recently, a number of synthetic molecules that activate the innate immune system by stimulating TLRs have been identified. Among them, synthetic oligodeoxynucleotides (ODNs) containing unmethylated CpG motifs (CpG ODNs) were shown to activate TLR9-bearing B cells, macrophages, and dendritic cells to induce a strong proinflammatory milieu and a type 1-biased immune response that protects mice from a variety of parasitic, bacterial, and viral infections. Although the protective effect of CpG ODN in adult mice was well established, its effectiveness in neonates, which have lower numbers of dendritic, B, and T cells and tend to favor Th2 responses, was unclear. This study uses the New World arenavirus Tacaribe, a neurotropic pathogen that is lethal in newborn mice, to explore the effectiveness of TLR-mediated innate immune responses. Neonatal BALB/c mice treated with CpG ODN at the time of infection had reduced viral load (p < 0.01) and increased survival (52%, p < 0.001 i.p.; 36%, p < 0.05 intranasally). Protection was achieved in mice treated no later than 3 days postchallenge and appears to be mediated by an increase in Ag-specific Abs (IgG and IgM) and to require inducible NO synthase expression and NO production. To our knowledge, this is the first study assessing the mechanisms by which CpG ODN can protect mice from a neurotropic viral infection.

The Toll-like receptor 7 (TLR7) agonist, imiquimod, and the TLR9 agonist, CpG ODN, induce antiviral cytokines and chemokines but do not prevent vaginal transmission of simian immunodeficiency virus when applied intravaginally to rhesus macaques

The initial host response to viral infection occurs after Toll-like receptors (TLRs) on dendritic cells (DC) are stimulated by viral nucleic acids (double-stranded RNA, single-stranded RNA) and alpha interferon (IFN-alpha) and IFN-beta are produced. We hypothesized that pharmacologic induction of innate antiviral responses in the cervicovaginal mucosa by topical application of TLR agonists prior to viral exposure could prevent or blunt vaginal transmission of simian immunodeficiency virus (SIV). To test this hypothesis, we treated rhesus monkeys intravaginally with either the TLR9 agonist, CpG oligodeoxynucleotides (ODN), or the TLR7 agonist, imiquimod. Both immune modifiers rapidly induced IFN-alpha and other antiviral effector molecules in the cervicovaginal mucosa of treated animals. However, both CpG ODN and imiquimod also induced proinflammatory cytokine expression in the cervicovaginal mucosa. In the vaginal mucosa of imiquimod-treated monkeys, we documented a massive mononuclear cell infiltrate consisting of activated CD4(+) T cells, DC, and beta-chemokine-secreting cells. After vaginal SIV inoculation, all TLR agonist-treated animals became infected and had plasma vRNA levels that were higher than those of control monkeys. We conclude that induction of mucosal innate immunity including an IFN-alpha response is not sufficient to prevent sexual transmission of human immunodeficiency virus.

Effective treatment of retrovirus-induced suppression of antibody responses with CpG oligodeoxynucleotides

Most retroviruses induce severe immunosuppression during acute infection. We have used the Friend retrovirus mouse model to demonstrate that immunostimulatory B-type CpG oligodeoxynucleotides (ODN) have a protective effect against retrovirus-induced suppression of antibody responses to potent B-cell antigens. CD8+ T cells were critical for effective treatment with CpG-ODN, since in vivo depletion of these cells from treated mice impaired protection from retrovirus-induced immunosuppression. Protection also required IFN-gamma, as neutralization of this cytokine abolished the therapeutic effect of CpG-ODN. These findings may have implications for the treatment of immunosuppressive virus infections.

Anti-SARS-CoV immunity induced by a novel CpG oligodeoxynucleotide

To develop CpG oligodeoxynucleotides (CpG ODNs) based therapy for prevention and treatment of severe acute respiratory syndrome (SARS), we selected a novel CpG ODN (BW001), which displays B-type CpG ODN structure feature at the 5′ and A-type CpG ODN structure feature at the 3′, and tested for its anti-SARS-CoV activity. We found that the supernatants of human PBMCs stimulated by BW001 significantly protected Vero cells from SARS-CoV infection. BW001 could stimulate human PBMCs and pDCs to secrete high level of IFN-α and promote human PBMCs and B cells to proliferate. Furthermore, we demonstrated that BW001 could activate CD19⁺ B cells and CD56⁺ NK cells in human PBMCs. In addition, BW001 could enhance NK cytotoxicity and IFN-γ secretion in human PBMCs. Together, BW001 represents a novel type of CpG ODN and may have potential for the development of treatment and prevention for SARS as well as other viral associated diseases.

Immunostimulatory DNA activates production of type I interferons and interleukin-6 in equine peripheral blood mononuclear cells in vitro

This study aimed to evaluate different nucleic acid preparations as cytokine inducers in equine cells. To induce cytokine production, bacterial plasmid DNA or short synthetic oligodeoxyribonucleotides (ODN), with or without the transfection reagent lipofectin, were added to cultures of purified equine peripheral blood mononuclear cells (PBMC). Cytokine activity was detected with bioassays in cell culture supernatants after 24h of induction and cytokine mRNA expression was detected using RT-PCR at 6h post induction. For IFN-alpha/beta it was found that both plasmid DNA and phosphodiester ODN, containing an unmethylated CpG-motif, were able to induce IFN production in the presence of lipofectin but not without. The levels of IFN varied with individuals and were often quite low. Moreover, methylation or removal of the CpG sequence completely abolished IFN induction. CpG-containing ODN with poly-guanine (G) sequences in the 5' and 3' ends induced considerably higher levels of IFN, especially when the poly-G sequences had a phosphorothioate backbone. ODN with poly-G sequences also had the ability to induce IFN in the absence of lipofectin but the levels of IFN induced were radically reduced compared to those induced with lipofectin. In contrast to IFN, which was only detected upon induction, low spontaneous IL-6 production was observed in unstimulated control cultures. Nevertheless, plasmid DNA and CpG-containing ODN were able to increase the IL-6 production threefold. All the IFN inducing ODN also induced IL-6 production and the levels of IL-6 induced seemed influenced by addition of lipofectin and presence of poly-G sequences in the same way as was observed for the IFN-production. However, a complete phosphorothioate ODN with a central CpG-motif and poly-C sequences, that did not induce IFN, readily induced IL-6 both in the presence and absence of lipofectin. In addition, there was also evidence that some ODN induced increased expression of IL-12p40 mRNA. To conclude, equine PBMC were able to recognize CpG-DNA and respond with both IFN-alpha/beta and/or IL-6 production. The levels of cytokine induced, and sometimes which cytokine induced, varied with, e.g., CpG-motifs used, the presence of poly-G sequences, ODN backbone chemistry and presence of lipofectin.

A point of view: HIV-1/AIDS is an allergy but CpG ODN treatments may inhibit virus replication and reactivate the adaptive immunity--hypothesis and implications

Reevaluation of the increase in the levels of IgE and IL-4 in sera of HIV-1 infected and AIDS patients led to the suggestion that AIDS resembles allergy. Studies on the properties of the viral shed gp120 revealed that it resemble environmental allergens in their ability to induce hematopoietic cells to release large amounts of Th2 cytokines, inhibitors of the patients adaptive immune response. Yet, induction of TLR9+ plasmacytoid DCs by CpG ODNs cause the release of type I interferons, inhibitors of HIV-1 replication and IL-4 release from hematopoietic cells. CpG ODN binding to TLR+ B cells inhibits IgE synthesis and reactivates the failing adaptive immunity. The possible use of CpG ODNs as treatment to patients is discussed.

CpG ODNs treatments of HIV-1 infected patients may cause the decline of transmission in high risk populations - a review, hypothesis and implications

The Joint United Nations Program on HIV-1/AIDS (UNAIDS) announced its goal to stop HIV-1 transmission by antiviral (HAART) treatment of patients since at the end of 2003 the number of people living with HIV-1 was 38 million, 25 million in the sub-Saharan region of Africa. The present review deals with a new approach to simultaneously treat HIV-1/AIDS patients in HIV-1 endemic regions with CpG oligodeoxynucleotides (ODNs) and people at high risk of infection with a vaccine containing CpG ODNs combined with synthetic HIV-1 peptides by intranasal and intradermal applications. During HIV-1 infection a gradual increase in the levels of IL-4 and IgE in the patients' serum, was reported. It was suggested that such an increase of the cytokine IL-4 and the IgE immunoglobulin are interconnected and may serve as indicators for the coming stage of AIDS. It was also suggested that the IL-4 and IgE increase in the serum of HIV-1 infected people resemble the increase of IL-4 and IgE levels in allergic patients that were exposed to endogenous or environmental allergens [Becker, Virus Genes 28, 5--18, 2004]. Indeed, it was reported that the HIV-1 virions' shed gp120 molecules, which contain a superantigen (superallergen) domain that enables the viral glycoprotein to bind the V(H)3 domain of IgE molecules that are bound to FcepsilonRI+ hematopoietic cells [basophils, mast cells, dendritic cells (DCs) and plasmacytoid DCs (pDCs)]. Such interaction was reported to induce the hematopoietic cells to release large amounts of Th2 cytokines IL-4, IL-5, IL-10 and IL-13. These findings led to the hypothesis [Op. cit.] that the cure of HIV-1/AIDS patients requires the induction of endogenous synthesis of type I interferons (INF alpha and beta) with a bacterial CpG rich DNA that will induce the patients' pDCs to release large amounts of type I IFNs. Under these conditions HIV-1 replication in polarized to Th2 cells is inhibited. Type I IFNs reactivate the patients' inhibited Th1 cells to synthesize IL-2 and IL-12 cytokines that activate the maturation of CTL precursors. The unmethylated bacterial DNA activates B synthesis to switch to IgG and IgA synthesis. The novel drug CpG ODNs is being tested for the prevention and the treatment of allergic humans and in the experimental system of allergic mice. It was also reported that treatment of mice with CpG ODN prior to or after retrovirus infections protected and cured, respectively, the retrovirus infection. It was also reported that CpG ODNs treatments of mice exposed to allergen protected them against the development of the allergic response. Phase I treatment of healthy people with CpG ODNs provided information on the safety of these compounds. The CpG ODNs A and B bind to Toll like receptors that are present in pDCs and B cells, respectively, CpG ODN - A is the ligand for TLR9+ pDCs and induce the release of large amounts of IFN-alpha, beta. CpG ODN-B is the ligand for TLR9+ in B cells and induce the synthesis of IgG and IgA. CpG ODN-C contains motifs from CpG ODNs A and B and is more active. The present review is based on findings from studies that reported that CpG ODNs treatment of retrovirus infected mice, monkeys and allergic mice prevented the virus and allergens caused diseases, respectively. Based on these studies, a hypothesis is presented that treatment of HIV-1 infected and AIDS patients with CpG ODN-A and B or CpG ODN-C have the potential to inhibit IL-4 synthesis and release from FcrepsilonRI+ hematopoietic cells by inducing TLR9+ pDCs to release large amounts of type I IFNs. TLR9+ B cells are induced by CpG ODN-B to switch from IgE to IgG, IgA synthesis. In addition, type I IFNs (alpha, beta) have the capacity to inhibit HIV-1 replication in polarized Th2 cells. Type I IFNs reactivate the patients' Th1 cells to synthesize IL-2 and IL-12 cytokines, activators of the precursor cytotoxic T cells (CTLs), leading to the reactivation of the inhibited adaptive immune response. Antiviral CTLs have the ability to clear the virus infection. The present novel approach to the treatment and of HIV-1/AIDS patients with CpG ODNs may prevent HIV-1 transmission and the AIDS pandemic if controlled studies on the treatments with CpG ODNs of HIV-1 infected people will be done by international and private agencies and companies to define the effective treatment regime and the efficacy of the treatments to HIV-1 infected people at different times post-infection. It is also hypothesized that in order to stop HIV-1 transmission in HIV-1 endemic regions the people at high risk of HIV-1 infection should be treated at the same time as HIV-1 infected people with a vaccine containing synthetic CpG-ODNs combined with synthetic HIV-1 peptides, compatible with the major HLA haplotypes of the regional population. The vaccine may be self-applied by people at high risk of infection by the intra-nasal route and by intra-dermal application as a "peplotion vaccine". The stimulation of the antiviral CTL response by HIV-1 infected people and the active antiviral immune response in the vaccinated population may lead to a decline in HIV-1 transmission and may be a model for control of the HIV-1/AIDS pandemic.

Enhanced HIV-1 specific immune response by CpG ODN and HIV-1 immunogen-pulsed dendritic cells confers protection in the Trimera murine model of HIV-1 infection

We have recently developed a novel small animal model for HIV-1 infection (Ayash-Rashkovsky et al., http://www.fasebj.org/cgi/doi/10.1096/fj.04-3184fje; doi:10.1096/fj.04-3184fje). The mice were successfully infected with HIV-1 for 4-6 wk with different clades of either T- or M-tropic isolates. HIV-1 infection was accompanied by rapid loss of human CD4+ T cells, decrease in CD4/CD8 ratio, and increased T cell activation. HIV specific human humoral and cellular immune responses were observed in all HIV-1 infected animals. In the present study, HIV specific human immune responses, both humoral and cellular, were generated in noninfected Trimera mice, after their immunization with gp120-depleted HIV-1 antigen, presented by autologous human dendritic cells. Addition of CpG ODN to the antigen-pulsed DCs significantly enhanced (by 2- to 30-fold) the humoral and cellular HIV-1 specific immune responses. Only mice immunized with the HIV-1 immunogen and CpG were completely protected from infection with HIV-1 after challenge with high infection titers of the virus. This novel small animal model for HIV-1 infection may thus serve as an attractive platform for rapid testing of candidate HIV-1 vaccines and of adjuvants and may shorten the time needed for the development and final assessment of protective HIV-1 vaccines in human trials.

CpG oligodeoxynucleotides enhance neonatal resistance to Listeria infection

Infection by Listeria monocytogenes causes serious morbidity and mortality during the neonatal period. Previous studies established that immunostimulatory CpG oligodeoxynucleotides (ODN) can increased the resistance of adult mice to many infectious pathogens, including Listeria. This work examines the capacity of CpG ODN to stimulate a protective immune response in newborns. Results indicate that dendritic cells, macrophages, and B cells from 3-day-old mice respond to CpG stimulation by secreting IFN-gamma, IL-12, and/or TNF-alpha. Spleen cells from CpG-treated neonates produce large amounts of cytokine and NO when exposed to bacteria in vitro. Newborns treated with CpG ODN are protected from lethal Listeria challenge and generate Ag-specific CD4 and CD8 T cells that afford long-term protection against subsequent infection. These results demonstrate that cellular elements of the neonatal immune system respond to stimulation by CpG ODN, thereby reducing host susceptibility to infectious pathogens.

Strategies for enhancing the immunostimulatory effects of CpG oligodeoxynucleotides

Synthetic oligodeoxynucleotides (ODN) containing CpG sequences are recognized as a "danger" signal by the immune system of mammals. As a consequence, CpG ODN stimulate innate and adaptive immune responses in humans and a variety of animal species. Indeed, the potential of CpG ODN as therapeutic agents and vaccine adjuvants has been demonstrated in animal models of infectious diseases, allergy and cancer and are currently undergoing clinical trials in humans. While CpG ODN are potent activators of the immune system, their biologic activity is often transient, subsequently limiting their therapeutic application. Modifications in the CpG ODN backbone chemistry, various delivery methods including mixing or cross-linking of ODN to other carrier compounds have been shown to significantly enhance the biologic activity of ODN. However, the exact mechanisms that mediate this enhancement of activity are not well understood and may include local cell recruitment and activation, cytokine production, upregulation of receptor expression and increasing the half-life of ODN through creation of a depot. We will review the various approaches that have been used in enhancing the immunostimulatory effects of CpG ODN in vivo and also discuss the possible mechanisms that may be involved in this enhancement.

CpG oligodeoxynucleotides block human immunodeficiency virus type 1 replication in human lymphoid tissue infected ex vivo

Oligodeoxynucleotides (ODNs) with immunomodulatory motifs control a number of microbial infections in animal models, presumably by acting through toll-like receptor 9 (TLR9) to induce a number of cytokines (e.g., alpha interferon and tumor necrosis factor alpha). The immunomodulatory motif consists of unmethylated sequences of cytosine and guanosine (CpG motif). ODNs without CpG motifs do not trigger TLR9. We hypothesized that triggering of TLR9 generates a cellular environment unfavorable for human immunodeficiency virus (HIV) replication. We tested this hypothesis in human lymphocyte cultures and found that phosphorothioate-modified ODN CpG2006 (type B ODNs) inhibited HIV replication nearly completely and prevented the loss of CD4(+) T cells. ODNs CpG2216 and CpG10 (type A ODNs) were less effective. CpG2006 blocked HIV replication in purified CD4(+) T cells and T-cell lines; CpG10 was ineffective in this setting, indicating that type A ODNs may inhibit HIV replication in CD4(+) T-cell lines indirectly through a separate cell subset. However, control ODNs without CpG motifs also showed anti-HIV effects, indicating that these effects are nonspecific and not due to TLR9 triggering. The mechanism of action is not clear. CpG2006 and its control ODN blocked syncytium formation in a cell fusion-based assay, but CpG10, CpG2216, and their control ODNs did not. The latter types interfered with the HIV replication cycle during disassembly or reverse transcription. In contrast, CpG2006 and CpG2216 specifically induced cytokines critical to initiation of the innate immune response. In summary, the nonspecific anti-HIV activity of CpG ODNs, their ability to stimulate HIV replication in latently infected cells, potentially resulting in their elimination, and their documented ability to link the innate and adaptive immune responses make them attractive candidates for further study as anti-HIV drugs.

Use of CpG oligodeoxynucleotides as immunoprotective agents

Single-stranded oligodeoxynucleotides (ODNs) synthesised to express unmethylated 'CpG motifs' mimic the ability of bacterial DNA to trigger the innate immune system. CpG ODNs stimulate cells that express Toll-like receptor 9, initiating an immunomodulatory cascade resulting in the activation of B and T lymphocytes, natural killer cells, monocytes, macrophages and dendritic cells. CpG ODNs improve the host's ability to resist infection by accelerating and improving the induction of an innate and then adaptive immune response, characterised by the production of Th1 and pro-inflammatory cytokines, chemokines and polyreactive antibodies. Studies in rodents and non-human primates demonstrate that CpG ODNs can protect the host against bacterial, viral, fungal and parasitic infections. CpG-induced protection develops rapidly but persists for only a few weeks. Preclinical and clinical trials suggest that CpG ODNs can be used safely to activate the human immune system.

Protection of mice against Friend retrovirus infection by vaccination with antigen-loaded, spleen-derived dendritic cells

Antigen-loaded dendritic cells (DC) have been shown to induce specific immune responses in vivo. In the current study we used Friend virus (FV) as a model to analyze whether a DC vaccine is capable of inducing protective immunity against retroviral infections. Mice were vaccinated twice with spleen-derived DC loaded with FV antigen. All control mice that received DC without antigen developed progressive leukemia after FV challenge. In contrast, five of the 14 vaccines were protected against infection, three recovered from FV-induced disease, and only six progressed to lethal leukemia. Animals that progressed to disease had high viral loads in blood and spleen similar to the control mice. Virus-specific antibody responses were not induced by DC vaccination. In contrast, protection correlated with a vaccine-induced CD8+ T-cell response directed against an immunodominant epitope of FV. CD8+ T-cells were critical for the protective effect of the DC vaccine, since in vivo depletion of these cells from immunized mice prevented their protection. Our results demonstrate that antigen-loaded DC can induce specific cellular immune responses and prevent retrovirus-induced disease.

CEL-1000—a peptide with adjuvant activity for Th1 immune responses

CEL-1000 (derG, DGQEEKAGVVSTGLIGGG) is a small immunomodulatory peptide which delivers demonstrated protective activity in two infectious disease challenge models (HSV and malaria) and an allogenic tumor vaccine model. CEL-1000 and other activators (defensin-beta, CpG ODN, and imiquimod) of the innate immune system promote IFN-gamma-associated protective responses. CEL-1000 is an improved form of peptide G (a peptide from human MHC II beta chain second domain, aa 135-149) known to enhance immune responses of other immunogenic peptides. Since defensin-beta, CpG ODN, and imiquimod have been shown to possess adjuvant activity, we investigated the adjuvant effect of peptide G and CEL-1000 as conjugates with HIV and malaria peptides. Antibody titers and isotypes were evaluated on serum taken from select days following immunization. Results for CEL-1000 and G peptide conjugates were compared with results for KLH conjugates of the same HIV peptide from the p17 molecule (87-116) referred to as HGP-30. Studies demonstrated that comparable titers were seen on day 28, 42, 63, and 77 with either G or KLH-HGP-30 peptide conjugates. In another study, CEL-1000 conjugates (CEL-1000-HGP-30) demonstrated a 4-10-fold higher titer antibody response than seen with several other peptide conjugates of the same HGP-30 peptide. Improved adjuvant activity of CEL-1000 in peptide conjugates was also demonstrated by a shift in the antibody isotypes toward a Th1 response (IgG2a). The IgG2a/IgG1, ratio for G-HGP-30 HIV or KLH-HGP-30 HIV conjugates were lower than for the CEL-1000-HGP-30 HIV conjugate. A similar favoring of the IgG2a/IgG1 ratio was seen for a malaria peptide conjugate (CEL-1000-SF/GF) compared to the un-conjugated peptide (SF-GF). CEL-1000 also showed adjuvant activity in an allogenic tumor vaccine model. As expected for an adjuvant, CEL-1000 or G does not induce detectable self-directed or cross reactive antibodies. CEL-1000 is currently being investigated for use as an adjuvant with conventional vaccines. It is expected that IgG2a antibodies would be preferably generated by CEL-1000 adjuvancy and could enhance in vivo clearance of antigens or pathogens.

CpG oligodeoxynucleotides activate HIV replication in latently infected human T cells

CpG oligodeoxynucleotides (CpG ODNs) stimulate immune cells via the Toll-like receptor 9 (TLR9). In this study, we have investigated the effects of CpG ODNs on latent human immunodeficiency virus (HIV) infection in human T cells. Treatment of the latently infected T cell line ACH-2 with CpG ODNs 2006 or 2040 stimulated HIV replication, whereas no effects were evident when ODNs without the CpG motif were used. CpG-induced virus reactivation was blocked by chloroquine, indicating the involvement of TLR9. In contrast to the responsiveness of ACH-2 cells, CpG ODNs failed to activate HIV provirus in the latently infected Jurkat clone J1.1. We also studied the effects of CpG ODNs on productive HIV infection and found enhancement of viral replication in A3.01 T cells, whereas again no stimulating effects were observed in Jurkat T cells. CpG ODN treatment activated NF-kappaB in ACH-2 cells, which was similarly triggered in uninfected A3.01 T cells following exposure to CpG ODNs, indicating that TLR9-induced signal transduction was not dependent on proviral infection. Our study demonstrates that CpG ODNs directly trigger the activation of NF-kappaB and reactivation of latent HIV in human T cells. Our results point to a novel role for CpG ODNs as stimulators of HIV replication and open new avenues to eradicate the latent viral reservoirs in HIV-infected patients treated with antiretroviral therapy.

CpG oligodeoxynucleotide induction of antiviral effector molecules in sheep

Immunostimulatory CpG oligodeoxynucleotide (ODN) can protect mice against infection by many pathogens but the mechanisms mediating disease protection are not well defined. Furthermore, the mechanisms of CpG ODN induced disease protection in vivo have not been investigated in other species. We investigated the induction of antiviral effector molecules in sheep treated with a class B CpG ODN (2007). Subcutaneous injection of ODN 2007 induced a dose-dependent increase in serum levels of the antiviral effector molecule, 2'5'-A synthetase. Peak levels of enzyme were observed 4 days following ODN injection and enzyme levels remained elevated for the following 3-5 days. Repeated ODN injections induced a more sustained elevation of serum 2'5'-A synthetase activity. Finally, formulation of ODN 2007 in emulsigen increased the level of serum 2'5'-A synthetase activity and this response was CpG-specific. Elevated serum 2'5'-A synthetase activity suggested that CpG ODN acted through the induction of either interferon (IFN)-alpha or IFN-gamma. ODN 2007 did not induce detectable levels of IFN-alpha or IFN-gamma when incubated with peripheral blood mononuclear cells, but both IFN-alpha and IFN-gamma were detected following stimulation of lymph node cells with ODN 2007. CpG ODN induction of 2'5'-A synthetase in vitro correlated with the secretion of both IFN-alpha and IFN-gamma. Furthermore, immunohistochemical staining of skin revealed a marked cellular infiltration at the site of ODN 2007 injection. This cellular infiltration was CpG-specific and consisted of primarily CD172(+) myeloid cells. Many of the cells recruited to the site of ODN 2007 injection expressed IFN-alpha and some IFN-gamma. These observations support the conclusion that localized cell recruitment and activation contribute to CpG ODN induction of antiviral effector molecules, such as interferon and 2'5'-A synthetase.

Immunization with Th-CTL fusion peptide and cytosine-phosphate-guanine DNA in transgenic HLA-A2 mice induces recognition of HIV-infected T cells and clears vaccinia virus challenge

We evaluated immunogenicity of a novel Th-CTL fusion peptide composed of the pan DR Th epitope and a CTL epitope derived from HIV-pol in two transgenic HLA-A*0201/K(b) mouse models. The immunogenicity of peptides of this structure is highly dependent on coadministered cytosine-phosphate-guanine DNA. Initial evaluations of peptide-specific immunity are based on results of chromium release assay, intracellular cytokine, and tetramer staining. Significant cytotoxic T cell responses are found upon a single immunization with as low as 0.1 nmol both peptide and cytosine-phosphate-guanine DNA. Splenocytes from immunized mice recognize naturally processed HIV-pol expressed from vaccinia virus (pol-VV). Translation of immunologic criteria into more relevant assays was pursued using systemic challenge of immunized mice with pol-VV. Only mice receiving both peptide and DNA together successfully cleared upward of 6 logs of virus from ovaries, compared with controls. Challenge with pol-VV by intranasal route of intranasal immunized mice showed a significant reduction in the levels of VV in lung compared with naive mice. A convincing demonstration of the relevance of these vaccines is the robust lysis of HIV-infected Jurkat T cells (JA2/R7/Hyg) by immune splenocytes from peptide- and DNA-immunized mice. This surprisingly effective immunization merits consideration for clinical evaluation, because it succeeded in causing immune recognition and lysis of cells infected with its target virus and reduction in titer of highly pathogenic VV.

Treatment of infectious diseases with immunostimulatory oligodeoxynucleotides containing CpG motifs

Bacterial DNA with CpG motifs can efficiently stimulate the vertebrate immune system. Thus, synthetic oligodeoxynucleotides that contain such CpG motifs (CpG-ODN) are currently used in preclinical and clinical studies to develop new allergy or cancer therapies and vaccine adjuvants. Recent animal studies indicate that CpG-ODN therapies can also be used for successful treatment of infections caused by bacteria, parasites or viruses. In these experiments, innate and adaptive immune responses against pathogens were augmented by CpG-ODN and subsequently induced resistance against infectious diseases. The stimulation of dendritic cells played a central role for the therapeutic effect of CpG-ODN. However, CpG-ODN can also have negative side effects, which accelerate disease progression in some viral infections. Clinical studies with CpG-ODN will determine their potential for the therapy of infectious diseases in humans.

Preinfection treatment of resistant mice with CpG oligodeoxynucleotides renders them susceptible to friend retrovirus-induced leukemia

We recently reported that immunostimulatory oligodeoxynucleotides (CpG oligodeoxynucleotides [CpG-ODN]) were effective in postexposure treatment of retrovirus-induced disease (A. R. M. Olbrich et al., J. Virol. 76:11397-11404, 2002). We now show that the timing of treatment is a critical factor in treatment efficacy. In stark contrast to the success of postexposure treatments, we found that CpG treatment of susceptible mice prior to Friend retrovirus infection accelerated the development of virus-induced erythroleukemia. Furthermore, 70.8% of mice that were resistant to Friend virus-induced leukemia developed disease after inoculation of CpG-ODN before infection. The CpG pretreatment of these mice enhanced viral loads in their spleens and blood compared to controls that received ODN without CpG motifs. The main target cells of Friend virus, erythroid precursor cells and B cells, proliferated after CpG-ODN inoculation and provided an enlarged target cell population for viral infection. Our present findings together with our previous report demonstrate that CpG-ODN treatment of viral infections may be a double-edged sword that can result in an effective therapy but also in an acceleration of disease progression depending on the time point of treatment.

Immunoregulatory activity of CpG oligonucleotides in humans and nonhuman primates

Oligodeoxynucleotides (ODN) containing CpG motifs mimic the ability of microbial DNA to activate the innate immune system. The resultant response limits the early spread of infectious organisms while promoting the development of adaptive immunity. CpG ODN show promise as vaccine adjuvants and in the treatment of asthma, allergy, infection, and cancer. Due to evolutionary divergence in CpG recognition between species, CpG ODN that are most active in rodents are poorly immunostimulatory in primates. Thus, evidence that CpG ODN have therapeutic activity in mice must be confirmed in primates. Two distinct types of CpG ODN were identified that stimulate primate PBMC. D-type ODN trigger plasmacytoid DC to secrete IFNalpha, monocytes to mature into functionally active DC, and NK cells to secrete IFNgamma. K-type ODN stimulate B cells and monocytes to proliferate and secrete IgM, IL-10, and/or IL-6. In vivo studies in nonhuman primates indicate that proinflammatory or humoral immune responses can be selectively facilitated by judicious use of these distinct types of ODN.