Therapeutic vaccination with papillomavirus E6 and E7 long peptides results in the control of both established virus-induced lesions and latently infected sites in a pre-clinical cottontail rabbit papillomavirus model.

This study was performed to test the therapeutic efficacy of overlapping long E6 and E7 peptides, containing both CD4+ T-helper and CD8+ CTL epitopes, on CRPV-induced lesions, which is an appropriate pre-clinical model for HPV diseases, including recurrent respiratory papillomatosis (RRP). Therapeutic peptide vaccination was able to significantly control wart growth (p < 0.01) and abrogate latent CRPV infection (p = 0.0006) compared to controls. Vaccination was associated with a T(H)1 T cell response, as suggested by a strong DTH skin test, antigen-specific proliferation of PBMC and a minimal IgG antibody response. Thus, this study shows promise for treatment of RRP by vaccination with long peptides.

Human TLR9 confers responsiveness to bacterial DNA via species-specific CpG motif recognition.

The Toll-like receptor (TLR) family consists of phylogenetically conserved transmembrane proteins, which function as mediators of innate immunity for recognition of pathogen-derived ligands and subsequent cell activation via the Toll/IL-1R signal pathway. Here, we show that human TLR9 (hTLR9) expression in human immune cells correlates with responsiveness to bacterial deoxycytidylate-phosphate-deoxyguanylate (CpG)-DNA. Notably "gain of function" to immunostimulatory CpG-DNA is achieved by expressing TLR9 in human nonresponder cells. Transfection of either human or murine TLR9 conferred responsiveness in a CD14- and MD2-independent manner, yet required species-specific CpG-DNA motifs for initiation of the Toll/IL-1R signal pathway via MyD88. The optimal CpG motif for hTLR9 was GTCGTT, whereas the optimal murine sequence was GACGTT. Overall, these data suggest that hTLR9 conveys CpG-DNA responsiveness to human cells by directly engaging immunostimulating CpG-DNA.

Bacterial CpG-DNA triggers activation and maturation of human CD11c-, CD123+ dendritic cells.

Human plasmacytoid precursor dendritic cells (ppDC) are a major source of type I IFN upon exposure to virus and bacteria, yet the stimulus causing their maturation into DCs is unknown. After PBMC activation with immunostimulatory bacterial DNA sequences (CpG-DNA) we found that ppDC are the primary source of IFN-alpha. In fact, either CpG-DNA or dsRNA (poly(I:C)) induced IFN-alpha from purified ppDC. Surprisingly, only CpG-DNA triggered purified ppDC survival, maturation, and production of TNF, GM-CSF, IL-6, and IL-8, but not IL-10 or IL-12. Known DC activators such as CD40 ligation triggered ppDC maturation, but only IL-8 production, while bacterial LPS was negative for all activation criteria. An additional finding was that only CpG-DNA could counteract IL-4-induced apoptosis in ppDC. Therefore, CpG-DNA represents a pathogen-associated molecular pattern for ppDC. In contrast to these finding, CpG-DNA, like LPS, caused TNF, IL-6, and IL-12 release from PBMC and purified monocytes; however, differentiation of monocytes into DCs with GM-CSF and IL-4 unexpectedly resulted in refractoriness to CpG-DNA, but not LPS. Taken together, these results suggest that within a DC subset a multiplicity of responses can be generated by distinct environmental stimuli and that responses to a given stimulus may be dissimilar between DC subsets.

Poly-guanosine motifs costimulate antigen-reactive CD8 T cells while bacterial CpG-DNA affect T-cell activation via antigen-presenting cell-derived cytokines.

Pathogen-derived pattern recognition ligands like lipopolysaccharide (LPS) and bacterial cytidine-guanosine (CpG)-DNA not only activate dendritic cells and macrophages but are also mitogenic for B cells. Less clear are the claimed effects of CpG-DNA on T cells, which range from direct activation, costimulation, or indirect transient activation via antigen-presenting cell (APC)-derived interferon type I (IFN type I). Here we demonstrate that CpG-DNA sequence specifically triggers macrophages to produce IFN type I, interleukin (IL)-12, IL-6 and tumour necrosis factor (TNF), but lacks the ability to directly costimulate T cells. Strikingly, poly-guanosine (poly-G) extensions to CpG-containing oligonucleotides (ODN) abolished the macrophage stimulatory potential yet generated T-cell costimulatory activities. In fact, independently of CpG-motifs, poly-G-ODN displayed the ability to costimulate T cells. Costimulation was operative on CD8 T cells but not CD4 T cells. Poly-G-mediated costimulation resulted in IL-2-driven T-cell proliferation and induced cytolytic T cells. Overall the data imply that poly-G motifs costimulate antigen reactive CD8 T cells, while CpG-DNA motifs fail to do so but may affect T-cell activation via APC derived cytokines such as IFN type I.

CpG-DNA-mediated transient lymphadenopathy is associated with a state of Th1 predisposition to antigen-driven responses.

Infections can influence concurrent and subsequent Th1 vs Th2 immune responses to Ags. Through pattern recognition of foreign unmethylated CpG dinucleotides, the vertebrate innate immune system can sense infectious danger and typically replies with a Th1-polarized adaptive immune response. We examined whether CpG-DNA exposure would influence subsequent responses to infection and soluble Ags. CpG-DNA injection led to local lymphadenopathy characterized by maintenance of cellular composition with some biasing toward elevated dendritic cell composition. Sustained local production of IL-12 and IFN-gamma from dendritic cells and T cells was shown. Prior injection by up to 2 wk with CpG-DNA protected BALB/c mice from Th2 driven lethal leishmaniasis. CpG-DNA injection by up to 5 wk before soluble Ag challenge resulted in the generation of Ag-specific CTL, Th1 recall responses to Ag, and Th1-polarized Ag-specific Abs. Thus, CpG-DNA instigated a local predisposition for intense CTL responses and Th1-polarized immune responses to subsequent infections or Ag challenge. The induction by the innate immune system of a locally contained hypersensitivity could represent a capacitating immune reaction yielding rapid conditioned responses to secondary infections.

Role of interleukin-18 (IL-18) during lethal shock: decreased lipopolysaccharide sensitivity but normal superantigen reaction in IL-18-deficient mice.

Lethal shock can be associated with excessive secretion of cytokines such as tumor necrosis factor (TNF) and gamma interferon (IFN-gamma). IFN-gamma mediates macrophage activation and appears to be controlled by interleukin (IL)-12 and IL-18. To investigate the role of IL-18 in vivo, we generated IL-18-deficient mice by gene targeting. IL-18(-/-) mice showed decreased sensitivity towards lipopolysaccharide (LPS)-induced shock. LPS-induced IFN-gamma production was abrogated, yet induction of IL-12 and TNF was not affected. Both wild-type and IL-18-deficient mice succumbed to LPS-induced lethal shock after sensitization with D-galactosamine. However, in marked contrast to LPS, the bacterial superantigen Staphylococcus aureus enterotoxin B (SEB) induced comparable serum levels of IFN-gamma in IL-18(+/+) and IL-18(-/-) mice, accompanied by an upregulation of cell surface markers CD14, CD122 (IL-2Rbeta), and CD132 (IL-2Rgamma) on peritoneal macrophages. Moreover, SEB injection rendered IL-18-deficient mice sensitive for subsequent challenge with LPS. The degree of sensitization was comparable to that in wild-type controls with respect to lethality. However, LPS-induced TNF levels in serum were significantly reduced in SEB-sensitized IL-18-deficient mice. These results imply that IL-18 plays an important role in induction of IFN-gamma and lethality in response to LPS.

Immunostimulatory CpG-oligonucleotides induce functional high affinity IL-2 receptors on B-CLL cells: costimulation with IL-2 results in a highly immunogenic phenotype.

OBJECTIVE: CpG-oligodeoxynucleotides (CpG-ODN) have been shown to induce proliferation, cytokine production, and surface molecule regulation in normal and malignant human B cells. In the present study, we investigated the potential of CpG-ODN to induce functional high-affinity receptors in leukemic and normal B cells and the effects of costimulation with IL-2 on proliferation, cytokine secretion, and surface molecule regulation. METHODS: Highly purified B cells from B-CLL patients and normal controls were stimulated with CpG-ODN with or without IL-2. Expression of CD25 was determined using FACS, and the presence of high-affinity IL-2 receptors was determined by scatchard analysis. Costimulatory effects of IL-2 and CpG-ODN were investigated using proliferation assays, ELISA (IL-6, TNF-alpha), and FACS analysis (CD80, CD86 expression). Reactivity of autologous and allogeneic T cells toward activated B-CLL cells was determined in mixed lymphocyte reactions and Interferon-gamma Elispot assays. RESULTS: The CpG-ODN DSP30 caused a significantly stronger induction of the IL-2 receptor alpha chain in malignant as compared with normal B cells (p = 0.03). This resulted in the expression of functional high-affinity IL-2 receptors in B-CLL cells, but fewer numbers of receptors with less affinity were expressed in normal B cells. Although addition of IL-2 to CpG-ODN-stimulated cells augmented proliferation in both normal B cells and B-CLL cells, no costimulatory effect on cytokine production or surface molecule expression could be observed in normal B cells. In contrast, TNF-alpha and IL-6 production was increased in B-CLL cells, and the expression of CD80 and CD86 was further enhanced when IL-2 was used as a costimulus. Autologous and allogeneic immune recognition of B-CLL cells stimulated with CpG-ODN and IL-2 was increased compared with B-CLL cells stimulated with CpG-ODN alone. CONCLUSION: Stimulation of B-CLL cells with CpG-ODN and IL-2 might be an attractive strategy for potential immunotherapies for B-CLL patients.

HPV type 16 protein E7 HLA-A2 binding peptides are immunogenic but not processed and presented.

Human papillomaviruses (HPV) have been implicated in the etiology of cervical malignancies and a high percentage of cervical carcinoma cells express HPV-16 E6 and E7 oncoproteins. These proteins are attractive targets for cytolytic T lymphocyte (CTL) mediated immunotherapy. We screened peptides derived from the HPV-16 E7 protein for binding to HLA-A2 and tested their potential to induce specific CTL responses in chimeric HLA-A2/H2-Kb transgenic mice. From eight potential binding peptides four displayed binding and were tested for immunogenicity. CTL activity was tested using target cells pulsed with peptide or expressing E7 protein. While there was no CTL induction observed with the peptides 7-15, 66-74 and 82-90, CTL from mice immunized with 86-93 lysed targets presenting the peptide in the context of the HLA-A2/H2-Kb molecule or wild-type HLA-A2. In contrast, 86-93 induced CTL showed no cytolytic activity against cells expressing the protein E7 and vaccination with the E7 protein did not lead to cytotoxicity against targets pulsed with the 86-93 peptide. Therefore the peptide 86-93, which binds to HLA-A2, is able to induce CTL responses in context of HLA-A2, but the peptide appears not to be processed or presented by HPV type 16 infected cells.

CpG-DNA activates in vivo T cell epitope presenting dendritic cells to trigger protective antiviral cytotoxic T cell responses.

MHC class I-restricted T cell epitopes lack immunogenicity unless aided by IFA or CFA. In an attempt to circumvent the known inflammatory side effects of IFA and CFA, we analyzed the ability of immunostimulatory CpG-DNA to act as an adjuvant for MHC class I-restricted peptide epitopes. Using the immunodominant CD8 T cell epitopes, SIINFEKL from OVA or KAVYNFATM (gp33) from lymphocytic choriomeningitis virus glycoprotein, we observed that CpG-DNA conveyed immunogenicity to these epitopes leading to primary induction of peptide-specific CTL. Furthermore, vaccination with the lymphocytic choriomeningitis virus gp33 peptide triggered not only CTL but also protective antiviral defense. We also showed that MHC class I-restricted peptides are constitutively presented by immature dendritic cells (DC) within the draining lymph nodes but failed to induce CTL responses. The use of CpG-DNA as an adjuvant, however, initiated peptide presenting immature DC progression to professional licensed APC. Activated DC induced cytolytic CD8 T cells in wild-type mice and also mice deficient of Th cells or CD40 ligand. CpG-DNA thus incites CTL responses toward MHC class I-restricted T cell epitopes in a Th cell-independent manner. Overall, these results provide new insights into CpG-DNA-mediated adjuvanticity and may influence future vaccination strategies for infectious and perhaps tumor diseases.

CpG-oligodeoxynucleotides enhance T-cell receptor-triggered interferon-gamma production and up-regulation of CD69 via induction of antigen-presenting cell-derived interferon type I and interleukin-12.

Bacterial cytidine-phosphate-guanosine (CpG-DNA) activates antigen-presenting cells (APC) and drives T helper 1 (Th1)-polarized immune responses in the mouse. Claims have been made that CpG-DNA costimulates murine T cells. We examined the direct and indirect effects of CpG-oligodeoxynucleotides (CpG-ODN) on human T-cell activation. CpG-ODN failed to costimulate purified human T cells activated with alpha-CD3 or alpha-T-cell receptor (TCR)alphabeta antibodies. In contrast, CpG-ODN sequence-specifically caused increased expression of CD69 on CD4 and CD8 T cells when peripheral blood mononuclear cells (PBMC) were stimulated via alpha-CD3. CpG-ODN and alpha-CD3 stimulation synergized to induce interferon-gamma (IFN-gamma) in T cells and natural killer (NK) cells, as shown by intracellular fluorescence-activated cell sorter (FACS) staining. These effects of CpG-ODN on human T cells were caused by the release of IFN type I (IFN-I) and interleukin-12 (IL-12) from PBMC. Enhancement of CD69 expression on alpha-CD3-triggered T cells could be reproduced in a coculture transwell system of purified T cells and PBMC, was inhibited by neutralizing antibodies to IFN-I and could be mimicked by adding exogenous IFN-I. Furthermore, neutralization of either IFN-I or IL-12 diminished, and in combination abolished, IFN-gamma production. These findings show that CpG-ODN potentiate TCR-triggered activation of human T cells in an APC-dependent manner.

Immunostimulatory CpG-oligonucleotides cause proliferation, cytokine production, and an immunogenic phenotype in chronic lymphocytic leukemia B cells.

Bacterial DNA and synthetic CpG-oligodeoxynucleotides (ODNs) derived thereof have attracted attention because they activate cells of the immune system in a sequence-dependent manner. Here we investigated the potential of CpG-ODNs to cause proliferation, cytokine production, and regulation of surface molecules in human B-chronic lymphocytic leukemia (CLL) cells. CpG-ODN induced proliferation in both B-CLL cells and normal B cells; however, only B-CLL cells increased proliferative responses when CpG-ODN was added to co-cultures of CD40-ligand transfected mouse fibroblasts (CD40LF) and B cells. Production of interleukin-6 and tumor necrosis factor alpha was detectable at borderline levels, using CpG-ODN as the only stimulus. In contrast, when CpG-ODN was added to co-cultures of B cells and CD40LF, a strong increase in cytokine production occurred in B-CLL cells as well as in normal B cells. The surface molecules CD40, CD58, CD80, CD86, CD54, and MHC class I molecules were up-regulated in B-CLL cells, whereas CD95 expression was not influenced by CpG-ODN stimulation. The same pattern of surface molecule regulation was observed in normal B cells, but up-regulation of CD40 was significantly stronger in B-CLL cells. Costimulation with CpG-ODN and CD40LF resulted in further up-regulation of CD58, CD80, CD86, and MHC class I molecules. In contrast, CD95 expression induced by CD40-ligation was inhibited by CpG-ODN. CpG-ODN activated B-CLL cells acquired a strong stimulatory capacity toward T cells in allogeneic mixed lymphocyte reaction. This effect was completely inhibited by a combination of anti-CD80 and anti-CD86 monoclonal antibody. Taken together, these findings suggest the possible use of CpG-ODN for immunotherapeutic strategies in patients with B-CLL.

Bacterial CpG-DNA activates dendritic cells in vivo: T helper cell-independent cytotoxic T cell responses to soluble proteins.

Receptors for conserved molecular patterns associated with microbial pathogens induce synthesis of co-stimulatory molecules and cytokines in immature dendritic cells (DC), as do antigen-reactive CD4 T helper cells via CD40 signaling. Once activated, antigen-presenting DC may activate CD8 T cell responses in a T helper cell-independent fashion. Using immunostimulatory CpG-oligonucleotides (ODN) mimicking bacterial CpG-DNA, we tested whether CpG-DNA bypasses the need for T helper cells in CTL responses towards proteins by directly activating antigen-presenting DC to transit into professional APC. We describe that immature DC in situ constitutively process soluble proteins and generate CD8 T cell determinants yet CD8 T cell responses remain abortive. Induction of primary antigen-specific CD8 cytotoxic T lymphocyte (CTL)-mediated responses becomes initiated in wild-type as well as T helper cell-deficient mice, provided soluble protein and CpG-ODN are draining into the same lymph node. Specifically we show that CpG-ODN trigger antigen-presenting immature DC within the draining lymph node to acutely up-regulate co-stimulatory molecules and produce IL-12. These results provide new insights for generating in vivo efficient CTL responses to soluble proteins which may influence vaccination strategies.

Guanosine-rich oligodeoxynucleotides induce proliferation of macrophage progenitors in cultures of murine bone marrow cells.

Widely used to specifically inhibit gene expression, synthetic oligodeoxynucleotides (ODN) can exert a plethora of non-antisense effects. Immunostimulation by CpG-ODN has attracted particular attention. ODN rich in the nucleotide guanosine (G-rich ODN) constitute another type of sequences displaying non-antisense-mediated effects. We have examined the effects of CpG- and G-rich ODN on primary mouse bone marrow cells (BMC) in vitro. CpG-ODN induced rapid proliferation of B cells and production of IL-6 and IL-12p40. However, when tested in agar colony assays, CpG-ODN failed to promote the formation of colonies. In marked contrast, G-rich non-CpG-ODN led to sustained proliferation of macrophage-like cells without inducing cytokines or hemopoietic growth factors. Unlike CpG-ODN, G-rich ODN effectively induced the formation of macrophage colonies in agar assays, indicating a direct action on progenitor cells. Electrophoretic mobility shift assays revealed specific binding of G-rich ODN to a non-nuclear protein. The ability of a panel of ODN to compete for binding correlated with their potential to induce proliferation of macrophage-like cells from primary mouse BMC. As such, these data reveal a so far unrecognized potential of G-rich ODN to signal directly outgrowth of macrophage progenitors from BMC.

DNA activates human immune cells through a CpG sequence-dependent manner.

While bacterial DNA and cytosine-guanosine-dinucleotide-containing oligonucleotides (CpG ODN) are well described activators of murine immune cells, their effect on human cells is inconclusive. We investigated their properties on human peripheral blood mononuclear cells (PBMC) and subsets thereof, such as purified monocytes, T and B cells. Here we demonstrate that bacterial DNA and CpG ODN induce proliferation of B cells, while other subpopulations, such as monocytes and T cells, did not proliferate. PBMC mixed cell cultures, as well as purified monocytes, produced interleukin-6 (IL-6), IL-12 and tumour necrosis factor-alpha upon stimulation with bacterial DNA; however, only IL-6 and IL-12 secretion became induced upon CpG ODN stimulation. We conclude that monocytes, but not B or T cells, represent the prime source of cytokines. Monocytes up-regulated expression of antigen-presenting, major histocompatibility complex class I and class II molecules in response to CpG DNA. In addition, both monocytes and B cells up-regulate costimulatory CD86 and CD40 molecules. The activation by CpG ODN depended on sequence motifs containing the core dinucleotide CG since destruction of the motif strongly reduced immunostimulatory potential.

CpG-oligodeoxynucleotides co-stimulate primary T cells in the absence of antigen-presenting cells.

CpG-containing oligodeoxynucleotides (CpG-ODN) act as powerful adjuvant during in vivo induction of T cell responses. While CpG-ODN directly activate antigen-presenting cells (APC) and thus exert an extrinsic activity on T cells, it is unclear whether they directly affect T cells (intrinsic activity). Here we analyze the effects of CpG-ODN on T cells in an APC-free cell culture. We report that CpG-ODN co-stimulate T cells provided they were triggered via their TCR. CpG-ODN induced IL-2 production, IL-2 receptor expression and thus proliferation. Proliferation was blocked by cyclosporin A or anti-IL-2 monoclonal antibodies (mAb) but not by anti-IL-4 mAb. Moreover, CpG-co-stimulated T cells differentiated into cytolytic T lymphocytes in vitro. Of note, IL-2-driven growth of primed T cells was not affected by CpG-ODN. Co-stimulation was also operative in T cells from CD28-/- mice and in TCR-transgenic T cells stimulated with peptide. CpG-ODN-mediated co-stimulation of T cells in vitro may thus explain part of the potent adjuvant effects of CpG-ODN in vivo.

Immunostimulatory CpG-oligodeoxynucleotides cause extramedullary murine hemopoiesis.

Bacterial DNA and the synthetic CpG-oligodeoxynucleotides (ODNs) derived thereof have attracted attention because they activate cells of the adaptive immune system (lymphocytes) and the innate immune system (APCs) in a sequence-dependent manner. Here, we addressed whether CpG-ODNs affect hemopoiesis. Challenging mice with immunostimulatory CpG-ODN sequences led to transient splenomegaly, with a maximum increase of spleen weight at day 6. The induction of splenomegaly by CpG-ODNs was sequence-specific, dose-dependent, and associated with an increase in splenic cell count, in numbers of granulocyte-macrophage CFUs (GM-CFUs), and early erythroid progenitors (burst-forming units-erythroid). The transfer of spleen cells from CpG-ODN-pretreated animals into lethally irradiated syngeneic mice yielded an increase of spleen CFUs. Furthermore, the challenge of sublethally irradiated mice with CpG-ODNs caused radioprotective effects, in that recovery of GM-CFUs and cytotoxic T cell function was enhanced. The increase in GM-CFU and CTL function correlated with an enhanced resistance to Listeria infection in irradiated mice. We conclude from these data that CpG-ODNs trigger extramedullary hemopoiesis, and that this finding could be of therapeutic relevance in myelosuppression.