Induction of humoral and cellular immune response to hepatitis B virus (HBV) vaccine can be upregulated by CpG oligonucleotides complexed with Dectin-1 ligand

A persistent hepatitis B virus (HBV) infection is characterized by a lack of or a weak immune response to HBV, which may be reflective of tolerance to HBV. Efficient induction of HBV-specific immune response leads to the clearance of HBV in patients with a chronic HBV infection. CpG oligodeoxynucleotides (ODN) has a powerful adjuvant effect in HBV vaccination. A recent report demonstrated that the immunization by B/K CpG ODN (K3) wrapped by the nonagonistic Dectin-1 ligand, schizophyllan (SPG), namely K3-SPG, was more effective in the induction of antigen-specific immune response than that by K3. In this study, we examined the efficacy of K3-SPG as a HBV vaccine adjuvant. Wild-type (WT) mice and HBV transgenic (HBV-Tg) mice were subcutaneously immunized with hepatitis B surface antigen (HBsAg) alone, HBsAg and K3, or HBsAg and K3-SPG. The vaccination with HBsAg and K3-SPG significantly enhanced humoral and cellular immune response to HBV antigen compared to the other vaccinations in WT and HBV-Tg mice. K3-SPG induced the accumulation of dendritic cells (DCs) into draining lymph node and the activation of DCs. The expression of cytokines and chemokines related to Th1 and Th2 responses was upregulated after the vaccination including with K3-SPG. In conclusion, these results indicated that the vaccination using K3-SPG may overcome tolerance even in patients with chronic HBV infection.

Mycobacterial hypersensitivity pneumonitis requires TLR9-MyD88 in lung CD11b+ CD11c+ cells

Mycobacteria are among the most common causes of hypersensitivity pneumonitis (HP), but controversy persists with regard to the involvement of the infectious potency of the organism in mycobacterial HP (hot tub lung). This study aimed to establish a mouse model of hot tub lung to clarify its pathophysiology. Mice were exposed intranasally to formalin-killed Mycobacterium avium from a patient with hot tub lung (HP strain) or chronic pulmonary infection (non-HP strain), and bronchoalveolar lavage fluids and lung tissues were evaluated for allergic inflammation. Dead M. avium HP strain, but not non-HP strain, elicited marked HP-like pulmonary inflammation in wild-type mice. Although the inflammation was induced in mice lacking CD4 or CD8, the induction of HP-like responses was prevented in mice lacking myeloid differentiation factor (MyD)88 or Toll-like receptor (TLR)9. Cultured lung CD11c+ cells responded to M. avium in a TLR9-dependent manner, and reconstitution of TLR9-/- mice with lung CD11c+ cells from wild-type mice restored the inflammatory responses. Further investigation revealed that pulmonary exposure to M. avium HP strain increased the number of lung CD11b+ CD11c+ cells (dendritic cells) through TLR9 signalling. Our results provide evidence that hot tub lung develops via the mycobacterial engagement of TLR9-MyD88 signalling in lung CD11b+ dendritic cells independent of the mycobacterial infectious capacity.

Response of peripheral blood mononuclear cells from lupus patients to stimulation by CpG oligodeoxynucleotides

OBJECTIVES

Increased levels of hypomethylated CpG-containing DNA in sera from patients with systemic lupus erythematosus (SLE) may contribute to the initiation and/or perpetuation of the disease. This study characterizes the in vitro response of peripheral blood mononuclear cells (PBMC) from SLE patients to CpG DNA.

METHODS

Secretion of cytokines and IgM, cell proliferation and up-regulation of co-stimulatory molecules were evaluated in PBMC from SLE patients (n=24) and normal controls (n=24) after stimulation with synthetic oligodeoxynucleotides (ODN) containing CpG motifs.

RESULTS

Up-regulation of co-stimulatory molecules and the secretion of interferon-alpha and interleukin-6 (IL-6) in response to CpG ODN was significantly reduced in monocytes and dendritic cells from SLE patients. Secretion of interferon-gamma by natural killer (NK) cells was also reduced. In contrast, the IgM and IL-10 response of B cells to CpG ODN was normal.

CONCLUSION

Monocytes, dendritic cells and NK cells from SLE patients respond abnormally to CpG ODN stimulation, which may contribute to the cytokine imbalance observed in SLE.

Transfection of single-stranded hepatitis A virus RNA activates MHC class I pathway

Although infection of single-stranded RNA viruses can enhance expression of major histocompatibility complex (MHC) class I genes, the mechanism underlying this process remains unclear. Recent studies have indicated that exposure of non-immune cells to double-stranded deoxyribonucleic acid (DNA) or ribonucleic acid (RNA) of viral origin can directly increase the expression of MHC class I and related molecules without immune cell interaction. In this report, we show that transfection of single-stranded hepatitis A virus RNA into cultured hepatocytes results in the induction of genes for MHC class I, LMP2 and transporter for antigen processing (TAP1), in addition to the generation of viral proteins. We suggest that this stimulatory effect is due to the double-stranded RNA formed during replication of single-stranded viral RNA, and involves both double-stranded, RNA-dependent protein kinase PKR and the secretion of IFNbeta.

Cutting edge: Role of Toll-like receptor 9 in CpG DNA-induced activation of human cells

Unmethylated CpG motifs present in bacterial DNA stimulate a rapid and robust innate immune response. Human cell lines and PBMC that recognize CpG DNA express membrane-bound human Toll-like receptor 9 (hTLR9). Cells that are not responsive to CpG DNA become responsive when transfected with hTLR9. Expression of hTLR9 dramatically increases uptake of CpG (but not control) DNA into endocytic vesicles. Upon cell stimulation, hTLR9 and CpG DNA are found in the same endocytic vesicles. Cells expressing hTLR9 are stimulated by CpG motifs that are active in primates but not rodents, suggesting that evolutionary divergence between TLR9 molecules underlies species-specific differences in the recognition of bacterial DNA. These findings indicate that hTLR9 plays a critical role in the CpG DNA-mediated activation of human cells.

Sterically stabilized cationic liposomes improve the uptake and immunostimulatory activity of CpG oligonucleotides

Immunostimulatory CpG oligonucleotides (ODN) show promise as immune adjuvants, anti-allergens, and immunoprotective agents. Increasing the bioavailability and duration of action of CpG ODN should improve their therapeutic utility. Encapsulating ODN in sterically stabilized cationic liposomes provides protection from serum nucleases while facilitating uptake by B cells, dendritic cells, and macrophages. In a pathogen challenge model, sterically stabilized cationic liposomes encapsulation doubled the duration of CpG ODN-induced immune protection. In an immunization model, coencapsulation of CpG ODN with protein Ag (OVA) magnified the resultant Ag-specific IFN-gamma and IgG responses by 15- to 40-fold compared with Ag plus CpG ODN alone. These findings support the use of sterically stabilized cationic liposomes to significantly enhance the therapeutic efficacy of CpG ODN.

Genomic DNA released by dying cells induces the maturation of APCs

Mature APCs play a key role in the induction of Ag-specific immunity. This work examines whether genomic DNA released by dying cells provides a stimulus for APC maturation. Double-stranded but not single-stranded genomic DNA triggered APC to up-regulate expression of MHC class I/II and various costimulatory molecules. Functionally, dsDNA enhanced APC function in vitro and improved primary cellular and humoral immune responses in vivo. These effects were dependent on the length and concentration of the dsDNA but were independent of nucleotide sequence. The maturation of APC induced by dsDNA may promote host survival by improving immune surveillance at sites of tissue injury/infection.

Human peripheral blood cells differentially recognize and respond to two distinct CPG motifs

Oligodeoxynucleotides (ODN) that contain unmethylated CpG dinucleotides trigger a strong innate immune response in vertebrates. CpG ODN show promise as vaccine adjuvants, anti-allergens, and immunoprotective agents in animal models. Their transition to clinical use requires the identification of motifs that are optimally stimulatory in humans. Analysis of hundreds of novel ODN resulted in the identification and characterization of two structurally distinct "clusters" of immunostimulatory CpG ODN. One cluster ("D") preferentially stimulates IFN-gamma production by NK cells, whereas the other ("K") stimulates cell proliferation and the production of IL-6 and IgM by monocytes and B cells. The distinct immunostimulatory properties of K and D ODN can improve the design of CpG-based products to achieve specific therapeutic goals.

CpG oligodeoxynucleotides induce murine macrophages to up-regulate chemokine mRNA expression

Intramuscular injection of synthetic oligodeoxynucleotides (ODN) expressing unmethylated CpG motifs trigger the rapid development of a local inflammatory response. In vitro studies demonstrate that macrophages exposed to CpG ODN up-regulate expression of mRNA encoding the chemokines MIP-1alpha, MIP-1beta, MIP-2, RANTES, JE/MCP-1, and IP-10. Within 6 h of in vivo administration, CpG ODN induce a significant increase in chemokine mRNA levels at the site of injection and draining lymph nodes. These chemokines may contribute to the migration and stimulation of inflammatory cells that contribute to the development of CpG ODN-induced immune responses.

Immunotherapeutic applications of CpG-containing oligodeoxynucleotides

Bacterial DNA and synthetic oligodeoxynucleotides (ODN) expressing unmethylated CpG motifs stimulate the mammalian immune system to mount a rapid innate immune response. This response is characterized by the production of polyreactive IgM, immunomodulatory cytokines and chemokines. CpG ODN directly stimulate lymphocytes, natural killer cells and professional antigen-presenting cells (such as macrophages and dendritic cells). Owing to the strength and nature of this stimulation, CpG ODN are being harnessed for a variety of therapeutic uses. They are being tested for their ability to act as immune adjuvants, boosting the immune response elicited by conventional and DNA vaccines. As a result of their ability to activate a strong interferon gamma-dominated Th1 response while blocking the development of Th2-dependent allergies, CpG ODN are being examined for their antiallergic properties. Finally, CpG ODN are being used as "immunoprotective agents", since the innate immune response they elicit can protect the host from a variety of pathogenic bacteria, viruses and parasites.

Positive and negative regulatory elements contribute to CpG oligonucleotide-mediated regulation of human IL-6 gene expression

Oligonucleotides (ODN) expressing immunostimulatory "CpG motifs" activate human RPMI 8226 myeloma cells to secrete IL-6. Using deletion and site-directed mutagenesis of the human (h)IL-6 promoter region, two positive regulatory elements (the binding sites for the 5'-CCAAT / enhancer binding protein-beta and NF-kappaB) were identified. Two negative regulatory elements, the 3'-retinoblastoma control element (RCE) and the binding site for Epstein-Barr virus C-promoter binding factor 1 (CBF1), also contributed to CpG ODN induction of hIL-6 gene expression. Of interest, CpG ODN treatment induced the dissociation of a repressor protein from its 3'-RCE binding site. Thus, CpG ODN regulation of hIL-6 gene expression involves both enhancer and derepression mechanisms.

Prevention of neonatal tolerance by a plasmid encoding granulocyte-macrophage colony stimulating factor

A plasmid DNA vaccine encoding the circumsporozoite protein of malaria (pCSP) induces protective immunity in adult mice but persistent tolerance when administered to neonates. In an effort to improve antigen presenting cell (APC) function in newborns, we co-administered pCSP with a plasmid encoding granulocyte-macrophage colony stimulating factor (pGMCSF). This combination of plasmids prevented the development of neonatal tolerance, instead eliciting a primary IgG anti-CSP immune response. Mice primed as neonates and boosted as adults mounted anamnestic responses characterized by high serum antibody titers, cytotoxic T-cell activity and antigen-specific interferon gamma (IFNgamma) production. Neonatal administration of pGMCSF accelerated the maturation of local dendritic cells, suggesting that APC function plays a key role in determining whether tolerance or immunity results from neonatal exposure to antigen.

Factors associated with the development of neonatal tolerance after the administration of a plasmid DNA vaccine

A plasmid DNA vaccine encoding the circumsporozoite protein of malaria (pCSP) induces tolerance rather than immunity when administered to newborn mice. We find that this tolerance persists for >1 yr after neonatal pCSP administration and interferes with the induction of protective immunity in animals challenged with live sporozoites. Susceptibility to tolerance induction wanes rapidly with age, disappearing within 1 wk of birth. Higher doses of plasmid are more tolerogenic, and susceptibility to tolerance is not MHC-restricted. CD8+ T cells from tolerant mice suppress the in vitro Ag-specific immune response of cells from adult mice immunized with pCSP. Similarly, CD8+ T cells from tolerant mice transfer nonresponsiveness to naive syngeneic recipients. These findings clarify the cellular basis and factors contributing to the development of DNA vaccine-induced neonatal tolerance.

Activation of target-tissue immune-recognition molecules by double-stranded polynucleotides

Abnormal expression of major histocompatibility complex (MHC) class I and class II in various tissues is associated with autoimmune disease. Autoimmune responses can be triggered by viral infections or tissue injuries. We show that the ability of a virus or a tissue injury to increase MHC gene expression is duplicated by any fragment of double-stranded (ds) DNA or dsRNA introduced into the cytoplasm of nonimmune cells. Activation is sequence-independent, is induced by ds polynucleotides as small as 25 bp in length, and is not duplicated by single-stranded polynucleotides. In addition to causing abnormal MHC expression, the ds nucleic acids increase the expression of genes necessary for antigen processing and presentation: proteasome proteins (e.g., LMP2), transporters of antigen peptides; invariant chain, HLA-DM, and the costimulatory molecule B7.1. The mechanism is different from and additive to that of gamma-interferon (gammaIFN), i.e., ds polynucleotides increase class I much more than class II, whereas gammaIFN increases class II more than class I. The ds nucleic acids also induce or activate Stat1, Stat3, mitogen-activated protein kinase, NF-kappaB, the class II transactivator, RFX5, and the IFN regulatory factor 1 differently from gammaIFN. CpG residues are not responsible for this effect, and the action of the ds polynucleotides could be shown in a variety of cell types in addition to thyrocytes. We suggest that this phenomenon is a plausible mechanism that might explain how viral infection of tissues or tissue injury triggers autoimmune disease; it is potentially relevant to host immune responses induced during gene therapy.

Activity and safety of DNA plasmids encoding IL-4 and IFN gamma

Cytokine-encoding DNA plasmids can act as 'genetic adjuvants', improving the immune response stimulated by co-administered DNA vaccines. We examined whether plasmids encoding the Th1 cytokine IFN gamma (pIFN gamma) or the Th2 cytokine IL-4 (pIL-4) have long-term effects on immune homeostasis when administered to adult mice, or alter immune maturation in neonates. Both plasmids boosted immunity against a co-administered vaccine, with pIFN gamma promoting the development of a Th1 response (characterized by the production of IgG2a antibodies), and pIL-4 preferentially stimulating a Th2 response (characterized by increased IgG1 antibody production). Both pIFN gamma and pIL-4 influenced the ratio of cells actively secreting Th1 versus Th2 cytokines, consistent with an effect on Th cell maturation. Interestingly, this effect persisted for only a few weeks and was not magnified by repeated plasmid administration. Cytokine-encoding plasmids had no long-term effect on the immune response of newborn or adult mice to subsequent antigenic stimulation, nor did they selectively induce the production of pathogenic anti-DNA autoantibodies. These results suggest cytokine-encoding plasmids may be safe as immune adjuvants.

A plasmid encoding murine granulocyte-macrophage colony-stimulating factor increases protection conferred by a malaria DNA vaccine

Using the murine parasite Plasmodium yoelii (Py) as a model for malaria vaccine development, we have previously shown that a DNA plasmid encoding the Py circumsporozoite protein (PyCSP) can protect mice against sporozoite infection. We now report that mixing a new plasmid PyCSP1012 with a plasmid encoding murine granulocyte-macrophage colony-stimulating factor (GM-CSF) increases protection against malaria, and we have characterized in detail the increased immune responses due to GM-CSF. PyCSP1012 plasmid alone protected 28% of mice, and protection increased to 58% when GM-CSF was added (p < 0.0001). GM-CSF plasmid alone did not protect, and control plasmid expressing inactive GM-CSF did not enhance protection. GM-CSF plasmid increased Abs to PyCSP of IgG1, IgG2a, and IgG2b isotypes, but not IgG3 or IgM. IFN-gamma responses of CD8+ T cells to the PyCSP 280-288 amino acid epitope increased but CTL activity did not change. The most dramatic changes after adding GM-CSF plasmid were increases in Ag-specific IL-2 production and CD4+ T cell proliferation. We hypothesize that GM-CSF may act on dendritic cells to enhance presentation of the PyCSP Ag, with enhanced IL-2 production and CD4+ T cell activation driving the increases in Abs and CD8+ T cell function. Recombinant GM-CSF is already used in humans for medical purposes, and GM-CSF protein or plasmids may be useful as enhancers of DNA vaccines.