CpG-A and CpG-B oligonucleotides differentially enhance human peptide-specific primary and memory CD8+ T-cell responses in vitro

Quantitative expression of Toll-like receptor-2, -4, and -9 in dendritic cells generated from blasts of patients with acute myeloid leukemia

BACKGROUND

Dendritic cells (DCs) generated from leukemic blasts constitute a promising tool in immunotherapy for acute myeloid leukemia patients (AML-DCs), because AML-DCs express human leukocyte antigens and costimulatory molecules such as CD40, CD80, and CD86 at a higher level than leukemic blasts. Potentiation of AML-DC vaccine might become feasible by the addition of adjuvants such as lipopolysaccharides (LPS) or CPG-rich oligodeoxyribonucleotides binding to Toll-like receptors (TLR) and inducing a stronger Type 1 T-cell response.

STUDY DESIGN AND METHODS

mRNA and protein expression of TLR-2, -4, and -9 were analyzed with quantitative real-time polymerase chain reaction, Western blot, and flow cytometry for mature monocyte-derived DCs generated from 14 AML patients versus 14 healthy volunteers (HV-DCs), and the response of the AML- and HV-DCs to different microbial TLR ligands was determined by enzyme-linked immunosorbent assay for the proinflammatory cytokines tumor necrosis factor (TNF)-alpha, inducible protein (Ip)-10, and interleukin (IL)-6.

RESULTS

AML-DCs and HV-DCs strongly expressed TLR-2 and TLR-4, while TLR-9 was expressed at a lower level in both groups. There was no significant difference in TLR expression between the two groups of AML-DCs and HV-DCs. In accordance with the TLR expression levels, DCs generated from both AML patients and HVs responded to the known microbial ligands peptidoglycan (PGN) and lipoteichoic acid for TLR-2 and LPS as ligand for TLR-4, by producing TNF-alpha and IL-6. A response to the ODNs 2006 and 2216 binding to TLR-9 was only detected in AML-DCs.

CONCLUSION

Microbial ligands like ODNs and LPS constitute promising adjuvants for enhancing (AML-) DC vaccines.

Plasmacytoid dendritic cells and type I IFN: 50 years of convergent history

It has been 50 years since the initial descriptions of what are now known as plasmacytoid dendritic cells (pDC) and type I IFN. pDC, which are infrequent cells found in the peripheral blood and lymphoid organs, are the most potent producers of type I and type III IFNs in the body. pDC produce IFN-alpha in response to both DNA and RNA enveloped viruses by virtue of their ribonucleic acids signaling in the endosome through TLR9 and TLR7, respectively. This stimulation, which also occurs with DNA or RNA-containing immune complexes and synthetic TLR7 and -9 agonists, is dependent upon the transcription factor IRF-7, which is expressed at high constitutive levels in pDC. In addition to releasing as much as 3-10pg of IFN-alpha/cell, pDC are also potent modulators of the immune response. In this review, we discuss the signaling pathways in pDC, their roles in linking innate and adaptive immunity, and their roles in infectious disease and autoimmunity.

Vaccination with NY-ESO-1 protein and CpG in Montanide induces integrated antibody/Th1 responses and CD8 T cells through cross-priming

The use of recombinant tumor antigen proteins is a realistic approach for the development of generic cancer vaccines, but the potential of this type of vaccines to induce specific CD8(+) T cell responses, through in vivo cross-priming, has remained unclear. In this article, we report that repeated vaccination of cancer patients with recombinant NY-ESO-1 protein, Montanide ISA-51, and CpG ODN 7909, a potent stimulator of B cells and T helper type 1 (Th1)-type immunity, resulted in the early induction of specific integrated CD4(+) Th cells and antibody responses in most vaccinated patients, followed by the development of later CD8(+) T cell responses in a fraction of them. The correlation between antibody and T cell responses, together with the ability of vaccine-induced antibodies to promote in vitro cross-presentation of NY-ESO-1 by dendritic cells to vaccine-induced CD8(+) T cells, indicated that elicitation of NY-ESO-1-specific CD8(+) T cell responses by cross-priming in vivo was associated with the induction of adequate levels of specific antibodies. Together, our data provide clear evidence of in vivo cross-priming of specific cytotoxic T lymphocytes by a recombinant tumor antigen vaccine, underline the importance of specific antibody induction for the cross-priming to occur, and support the use of this type of formulation for the further development of efficient cancer vaccines.

The role of type I interferon production by dendritic cells in host defense

Type I interferons (IFN) and dendritic cells (DC) share an overlapping history, with rapidly accumulating evidence for vital roles for both production of type 1 IFN by DC and the interaction of this IFN both with DC and components of the innate and adaptive immune responses. Within the innate immune response, the plasmacytoid DC (pDC) are the "professional" IFN producing cells, expressing specialized toll-like receptors (TLR7 and -9) and high constitutive expression of IRF-7 that allow them to respond to viruses with rapid and extremely robust IFN production; following activation and production of IFN, the pDC subsequently mature into antigen presenting cells that help to shape the adaptive immune response. However, like most cells in the body, the myeloid or conventional DC (mDC or cDC) also produce type I IFNs, albeit typically at a lower level than that observed with pDC, and this IFN is also important in innate and adaptive immunity induced by these classic antigen presenting cells. These two major DC subsets and their IFN products interact both with each other as well as with NK cells, monocytes, T helper cells, T cytotoxic cells, T regulatory cells and B cells to orchestrate the early immune response. This review discusses some of the converging history of DC and IFN as well as mechanisms for IFN induction in DC and the effects of this IFN on the developing immune response.

Development of TLR9 agonists for cancer therapy

In vertebrates, the TLRs are a family of specialized immune receptors that induce protective immune responses when they detect highly conserved pathogen-expressed molecules. Synthetic agonists for several TLRs, including TLR3, TLR4, TLR7, TLR8, and TLR9, have been or are being developed for the treatment of cancer. TLR9 detects the unmethylated CpG dinucleotides prevalent in bacterial and viral DNA but not in vertebrate genomes. As discussed in this Review, short synthetic oligodeoxynucleotides containing these immune stimulatory CpG motifs activate TLR9 in vitro and in vivo, inducing innate and adaptive immunity, and are currently being tested in multiple phase II and phase III human clinical trials as adjuvants to cancer vaccines and in combination with conventional chemotherapy and other therapies.

IMP321 (sLAG-3), an immunopotentiator for T cell responses against a HBsAg antigen in healthy adults: a single blind randomised controlled phase I study

Background

LAG-3 (CD223) is a natural high affinity ligand for MHC class II. The soluble form (sLAG-3) induces maturation of monocyte-derived dendritic cells in vitro and is used as a potent Th1-like immune enhancer with many antigens in animal models. To extend this observation to human, a proof of concept study was conducted with a clinical-grade sLAG-3, termed IMP321, coinjected with alum-non-absorbed recombinant hepatitis B surface antigen.

Methods

In a randomised, single blind controlled phase I dose escalation study, 48 seronegative healthy volunteers aged 18–55 years were vaccinated at 0, 4 and 8 weeks by subcutaneous injection with 10 μg HBsAg mixed with saline (control) or with IMP321 at one of four doses (3, 10, 30 and 100 μg). To evaluate the efficacy of this three injections over 2 months immunization protocol, an additional control group was injected with the commercial vaccine Engerix-B^®.

Results

IMP321 was very well tolerated. Indeed, a lower incidence of adverse events was reported from the HBsAg plus IMP321 groups than from the Engerix-B^® group. HBsAg-specific antibody responses (anti-HBs) appeared sooner and were higher at 8 and 12 weeks in IMP321 recipients compared to HBsAg control subjects. More importantly, increased numbers of responders to HBsAg were found in IMP321 recipients compared HBsAg group, as revealed by higher post-vaccination frequencies of CD4 Th1 or CD8 Tc1 antigen specific T cells. IMP321 induced CD4 Th1 antigen-specific T cells in some of these naïve individuals after only one injection, especially in the 10 and 30 μg dose groups.

Conclusion

IMP321 as an adjuvant to HBsAg was well-tolerated and enhanced T cell response vaccine immunogenicity (i.e. induced both CD4 Th1 and CD8 Tc1 antigen-specific T cells). This latter property has allowed the development of IMP321 as an immunopotentiator for therapeutic vaccines.

Early activation markers of human peripheral dendritic cells

Two major populations of dendritic cells (DCs), myeloid and plasmacytoid, can be isolated from human peripheral blood, and are distinguished by differential expression of the cell surface markers CD11c and CD123. These two populations of DCs also are different in their expression of Toll-like receptor (TLRs), which are involved in their activation. To investigate the early events during activation of peripheral DCs, the cells were stimulated in vitro with ligands for TLR-4 (as in lipopolysaccharides [LPS]) or TLR-9 (CpG-containing oligonucleotide [CpG]). The earliest change in protein expression detected after stimulating peripheral DCs with lipopolysaccharide (LPS) or CpG was increased production of the chemokine interleukin (IL)-8. Enhanced production of IL-8 occurred already within 2 hours of stimulation in both myeloid dendritic cells (M-DCs) and plasmacytoid dendritic cells (P-DCs), and preceded expression of the well established activation marker CD40. Although both populations of DCs secreted IL-8 upon activation, the levels of IL-8 produced was several times higher within the M-DCs compared with the P-DCs population. Before activation, both subsets of DCs expressed the IL-8 receptor type B (CD128b); but after stimulation the IL-8 receptor was down-regulated in both populations of DCs. Increased expression of MHC class II molecules is generally regarded as an early activation marker of DCs. However, only the P-DCs showed a significant up-regulation of MHC class II after stimulation. The M-DC population up-regulated MHC class II without any prior activation; thus care should be taken using increased expression of MHC class II molecules as an early activation marker of peripheral M-DCs after activation in vitro. In conclusion, we propose that during activation of human DCs the production of IL-8 and loss of CD128b are the earliest signs of activation preceding both MHC class II, CD40, CD80, and CD86 expression.

Immunostimulatory properties of CpG-oligonucleotides are enhanced by the use of protamine nanoparticles

The aim of this paper was to investigate if the immunostimulatory effects of CpG-oligonucleotides (CpG-ODN) can be enhanced by the use of biodegradable protamine nanoparticles (proticles). We analyzed size, surface charge, and morphology of protamine nanoparticles containing CpG-ODN with photon correlation spectroscopy and transmission electron microscopy. Immunostimulatory effects of these nanoparticles on B cells, plasmacytoid dendritic cells (PDC), peripheral blood mononuclear cells, and whole blood were studied. Cytokine production, activation of the cells in terms of upregulation of surface molecules and uptake of nanoparticles were examined. We found that the use of protamine nanoparticles significantly increased (20-fold) CpG-ODN mediated interferon (IFN)-alpha production of PDC. ODN uptake in PDC was only marginally enhanced. CpG-ODN mediated IP-10 production in whole blood was strongly enhanced by the use of nanoparticles. Apart from a slight increase in CpG-ODN-induced interleukin (IL)-6 production in B cells, other parameters like the CpG-mediated activation of B cells and PDC as well as tumor necrosis factor (TNF)-alpha production of PDC remained largely unchanged. The use of control ODN indicated that the protamine nanoparticles themselves have no immunostimulatory properties. These results strongly support the use of particulate delivery systems like biodegradable protamine nanoparticles for the development of CpG-ODN-based therapeutics.

Phase II trial of a toll-like receptor 9-activating oligonucleotide in patients with metastatic melanoma

PURPOSE

The recent identification of toll-like receptors (TLRs) and respective ligands allows the evaluation of novel dendritic cell (DC) -activating strategies. Stimulation of TLR9 directly activates human plasmacytoid DCs (PDCs) and indirectly induces potent innate immune responses in preclinical tumor models. We performed an open-label, multicenter, single-arm, phase II pilot trial with a TLR9-stimulating oligodeoxynucleotide in melanoma patients.

PATIENTS AND METHODS

Patients with unresectable stage IIIb/c or stage IV melanoma received 6 mg PF-3512676 weekly by subcutaneous injection for 24 weeks or until disease progression to evaluate safety as well as clinical and immunologic activity. Clinical and laboratory safety assessments were performed weekly; blood samples for immunological measurements were taken every 8 weeks. Tumor measurements were performed according to Response Evaluation Criteria in Solid Tumors.

RESULTS

Twenty patients received PF-3512676 for a mean of 10.9 weeks with a mean of 10.7 injections. Laboratory and nonlaboratory adverse events were limited, transient, and did not result in any withdrawals. Two patients experienced a confirmed partial response; one response is ongoing for 140+ weeks. Three patients experienced stable disease. Immunologic measurements revealed induction of an activated phenotype of PDC, elevation of serum levels of 2',5'-oligoadenylate, a surrogate marker of type I interferon production, and significant stimulation of natural killer cell cytotoxicity (the latter was associated with clinical benefit).

CONCLUSION

These results indicate that TLR9-targeted therapy can stimulate innate immune responses in cancer patients, identify biomarkers that may be associated with TLR9-induced tumor regression, and encourage the design of follow-up studies to evaluate the ability of this therapeutic approach to target human cancer.

Plasmacytoid dendritic cells from human lung cancer draining lymph nodes induce Tc1 responses

Dendritic cells (DC) resident in draining lymph nodes (LN) of patients with lung cancer are proposed to have a critical role in stimulating anti-tumor immunity. CpG oligodeoxynucleotides are undergoing clinical trials in patients with lung cancer and are likely to target plasmacytoid-DC. The present study, therefore, investigated the capacity of plasmacytoid-DC from human lung cancer draining LN to respond to CpG for activation of T cell responses relevant to anti-tumor immunity. The phenotype of DC was examined by flow cytometry, and cytokine production by cytometric bead array (CBA) and ELISA. Plasmacytoid-DC, purified by cell sorting, were immature but expressed the toll-like receptor, TLR9. Plasmacytoid-DC responded to the CpG oligodeoxynucleotide, CpG 2216, by production of the proinflammatory cytokines, IFN-alpha and IL-6. DC were cocultured with normal, allogeneic T cells, and cytokine production determined by CBA and immunophenotyping. CpG 2216 enhanced IFN-gamma production and induced intracellular production of IFN-gamma by CD8(+) and CD4(+), granzyme B by CD8(+), and IL-2 by CD4(+) T cells, respectively. Ligation of CD40 on plasmacytoid-DC combined with exposure to CpG 2216 also strongly enhanced IFN-gamma production. There was no significant difference between the responses of plasmacytoid-DC from patients with lung cancer and patients with benign carcinoid tumors with no pathologic LN involvement. These results indicate that plasmacytoid DC from the draining LN of patients with lung cancer effectively induce Tc1 immunity and could, therefore, represent a novel and attractive target for immunotherapeutic intervention.

Enhancement of infectious disease vaccines through TLR9-dependent recognition of CpG DNA

The adaptive immune system-with its remarkable ability to generate antigen-specific antibodies and T lymphocytes against pathogens never before "seen" by an organism-is one of the marvels of evolution. However, to generate these responses, the adaptive immune system requires activation by the innate immune system. Toll-like receptors (TLRs) are perhaps the best-understood family of innate immune receptors for detecting infections and stimulating adaptive immune responses. TLR9 appears to have evolved to recognize infections by a subtle structural difference between eukaryotic and prokaryotic/viral DNA; only the former frequently methylates CpG dinucleotides. Used as vaccine adjuvants, synthetic oligodeoxynucleotide (ODN) ligands for TLR9--CpG ODN--greatly enhance the speed and strength of the immune responses to vaccination.

Innate immune responses induced by classes of CpG oligodeoxynucleotides in ovine lymph node and blood mononuclear cells

CpG ODN signal through Toll-like receptor 9 (TLR9) and trigger a cascade of events that lead to activation of innate and adaptive immune responses. Our current understanding of the immunobiology of host responses to CpG is based largely on studies on peripheral blood mononuclear cells (PBMC) and splenocytes. Little is known regarding CpG-induced responses in other lymphoid tissues. In the present study, we investigated responses induced by CpG in both PBMC and lymph nodes. Cells were isolated from the superficial cervical lymph node (LNC) and blood and then stimulated with CpG ODN (either A-, or B- or C-class ODN). Cytokine production was assayed by ELISA, and lymphocyte proliferation was determined by (3)H-thymidine incorporation. NK-like cytotoxicity was analyzed by lysis of (51)Cr-labelled target cells. All three classes of CpG induced IFNalpha and IFNgamma in LNC. In contrast, only A and C-class ODN induced IFNalpha and IFNgamma in PBMC. Moreover, the IFN levels in LNC were 20-40-fold higher than in PBMC. Furthermore, all classes of ODN induced higher IL-12 levels in LNC (five- to six-fold) than in PBMC. Both B and C-class ODN induced good proliferative responses in PBMC and LNC, but the A-class ODN did not induce proliferation of PBMC and only induced moderate proliferation of LNC. A-class ODN induced significant NK-like activity in LNC. Thus, all three classes of CpG ODN induced similar responses in LNC, and these responses were consistently higher than in PBMC. These observations indicate that CpG ODN-induced responses differ between blood and lymph nodes, and suggest that the functional classification of CpG ODN based on PBMC responses may not be directly applicable to cells from other immune tissues.

CpG oligodeoxynucleotides as DNA adjuvants in vertebrates and their applications in immunotherapy

The genomes of bacterial and viral DNA contain a much higher frequency of unmethylated CpG dinucleotides than those of vertebrates. This difference in genome structure allows the innate immune system of vertebrates to distinguish bacterial or viral DNA from self-DNA, and consequently to perceive a 'danger signal' when bacterial or viral DNA is encountered. Multiple sources of evidence suggest that CpG motifs, including bacterial DNA and CpG ODNs (synthetic oligodeoxynucleotides containing unmethylated CpG), are capable of evoking a range of immunostimulatory effects in vertebrates and have a tremendous potential to be used as therapeutic agents and adjuvants. CpG motifs with different sequences have been shown to induce various types or levels of immunostimulatory responses whereas the immunostimulatory effects of CpG motifs are species-specific. A better understanding of CpG recognition at the molecular level is fundamental to the identification of those motifs that have desired immunostimulatory responses. It is hoped that this would allow the optimization and application of CpG motifs as therapeutic agents and adjuvants, for numerous diseases in various species.

Soluble human LAG-3 molecule amplifies the in vitro generation of type 1 tumor-specific immunity

The adjuvant activities of the human lymphocyte activation gene-3 (LAG-3) molecule have been evaluated in a human setting by investigating the ability of a soluble recombinant human LAG-3 protein (hLAG-3Ig) to enhance the in vitro induction of viral- and tumor-specific CTLs. We found that soluble human LAG-3 significantly sustained the generation and expansion of influenza matrix protein Melan-A/MART-1 and survivin-specific CD8+ T lymphocytes in peripheral blood mononuclear cells (PBMC) of both cancer patients and healthy donors, showing its ability to boost CD8+ T-cell memory response or to prime naive T cells in vitro. The peptide-specific T cells generated in the presence of hLAG-3Ig were endowed with cytotoxic activity and enhanced release of type 1 cytotoxic T (Tc1) cytokines and were able to recognize tumor cells expressing their nominal antigen. Phenotype and cytokine/chemokines produced by antigen-presenting cells (APC) of PBMCs exposed in vitro for 2 days to peptide and hLAG-3Ig indicate that the LAG-3-mediated adjuvant effect may depend on a direct activation of circulating APCs. Our data revealed the activity of hLAG-3Ig in inducing tumor-associated, antigen-specific CD8+ T-cell responses in a human setting and strongly support the conclusion that this recombinant protein is a potential candidate adjuvant for cancer vaccines.

Prostaglandin E2 is a negative regulator on human plasmacytoid dendritic cells

Prostaglandin E2 (PGE2), a major lipid derived from the metabolism of arachidonic acid, is an environmentally bioactive substance produced by inflammatory processes and acts as a cAMP up-regulator that plays an important role in immune responses. It has been reported that PGE2 has the ability to inhibit the production of interleukin-12 by myeloid dendritic cells (MDCs) and macrophages, and then induce preferential T helper type 2 (Th2) cell responses. However, little is known of the function of PGE2 for plasmacytoid dendritic cells (PDCs), which may contribute to the innate and adaptive immune response to viral infection, allergy and autoimmune diseases. In the present study, we compared the biological effect of PGE2 on human PDCs and MDCs. PGE2 caused the death of PDCs but MDCs survived. Furthermore, we found that, whereas PGE2 inhibited interferon-alpha production by PDCs in response to virus or cytosine-phosphate-guanosine, it inhibited interleukin-12 production by MDCs in response to lipopolysaccharide (LPS) or poly(I:C). Although both virus-stimulated PDCs and LPS-stimulated MDCs preferentially induced the development of interferon-gamma-producing Th1 cells, pretreatment with PGE2 led both DC subsets to attenuate their Th1-inducing capacity. These findings suggest that PGE2 represents a negative regulator on not only MDCs but also PDCs.

In vitro expansion of polyclonal T-cell subsets for adoptive immunotherapy by recombinant modified vaccinia Ankara

OBJECTIVE

Adoptive cellular therapy of cytomegalovirus (CMV)-specific T cells in allogeneic hematopoietic stem cell transplantation (HSCT) patients is a promising approach for controlling CMV viremia and its morbidity. We sought to develop a clinically suitable strategy to dually expand infusible CD8(+) and CD4(+) T-cell subsets specific for CMV.

METHODS

Polyclonal CMV T-cell lines were generated using peripheral blood mononuclear cell (PBMCs) treated with synthetic single-stranded CpG motif-containing oligodeoxynucleotides (ODNs) and infected with recombinant (r) modified vaccinia Ankara (MVA) expressing CMV antigens. Cultures derived from 12 healthy CMV-positive donors were analyzed using chromium release and lymphoproliferation assays, intracellular staining for interferon-gamma (IFN-gamma), and HLA tetramers.

RESULTS

A 3-day incubation with a combination of ODN 2006 and 2216 was found to reproducibly generate a highly rMVA infectable population of PBMCs with concomitant high expression of CMV antigens. CpG ODN-treated autologous PBMCs infected with rMVA elicited a 30-fold average expansion of both CMV-specific CD4(+) and CD8(+) T cells in 10 days. The enriched T-cell populations showed minimal alloreactivity, high levels of CMV-specific HLA class I tetramer binding, cytotoxic activity, and IFN-gamma production from both CD8(+) and CD4(+) T cells.

CONCLUSIONS

The ability to quickly produce autologous professional antigen-presenting cells, capable of stimulating clinically useful amounts of CMV-specific CD4(+) and CD8(+) T-cell lines, enhances the attractiveness of using rMVA for immunotherapeutic interventions to manage HSCT-related CMV disease.

A soluble LAG-3 protein as an immunopotentiator for therapeutic vaccines: Preclinical evaluation of IMP321

A soluble LAG-3 (CD223) molecule (sLAG-3) is a natural high affinity ligand for MHC class II. It is known to induce maturation of monocyte-derived dendritic cells in vitro and is used as a vaccine adjuvant to induce CD4 Th1 and CD8 T cell responses in vivo. The work presented herein was performed to study the biological activity of a preclinical grade human sLAG-3 protein, called IMP321: (i) binding on murine APC, (ii) induction of dendritic cell maturation, (iii) safety of repeated injections in mice. The results show that IMP321 binds MHC class II(+) murine APC, induces the maturation of dendritic cells and is well tolerated either injected alone or as an adjuvant with strongly immunogenic antigens.

Induction of interferon-gamma from natural killer cells by immunostimulatory CpG DNA is mediated through plasmacytoid-dendritic-cell-produced interferon-alpha and tumour necrosis factor-alpha

Immunostimulatory sequences (ISS) that contain CpG motifs have been demonstrated to exert antipathogen and antitumour immunity in animal models through several mechanisms, including the activation of natural killer (NK) cells to secrete interferon-gamma (IFN-gamma) and to exert lytic activity. Since NK cells lack the ISS receptor TLR9, the exact pathway by which NK cells are activated by ISS is unclear. We determined that ISS-induced IFN-gamma from NK cells is primarily dependent upon IFN-alpha release from plasmacytoid dendritic cells (PDCs), which directly activates the NK cell. However, further analysis indicated that other PDC-released soluble factor(s) may contribute to IFN-gamma induction. Indeed, tumour necrosis factor-alpha (TNF-alpha) was identified as a significant contributor to ISS-mediated activation of NK cells and was observed to act in an additive fashion with IFN-alpha in the induction of IFN-gamma from NK cells and to up-regulate CD69 expression on NK cells. This activity of TNF-alpha, however, was dependent upon the presence of PDC-derived factors such as type I interferon. These results illustrate an important function for type I interferon in innate immunity, which is not only to activate effectors like NK cells directly, but also to prime them for enhanced activation by other factors such as TNF-alpha.

Scarring skin lesions of discoid lupus erythematosus are characterized by high numbers of skin-homing cytotoxic lymphocytes associated with strong expression of the type I interferon-induced protein MxA

BACKGROUND

Infiltrating T lymphocytes are considered to play a major pathological role in skin lesions of cutaneous lupus erythematosus (CLE), a cutaneous autoimmune disease of unknown aetiology. Earlier histological studies revealed that the inflammatory infiltrate in CLE skin lesions is predominantly composed of T lymphocytes, with a slight predominance of CD4+ over CD8+ T cells, but failed to explain the development of scarring skin lesions, characteristic for chronic discoid lupus erythematosus (CDLE). Because recent investigations have highlighted the relevance of cytotoxic lymphocytes in autoimmune tissue destruction, we hypothesized that the scarring CDLE lesions might be caused by cytotoxic T lymphocytes.

OBJECTIVES

To analyse skin biopsies of 15 patients with CLE [10 female, five male; localized CDLE (lCDLE), n = 5; disseminated CDLE (dCDLE), n = 5, subacute CLE (SCLE), n = 5] and five control biopsies taken from healthy controls and to characterize the inflammatory infiltrate. Methods We used immunohistochemistry, including staining for the cytotoxic molecule granzyme B, the skin-homing molecule cutaneous lymphocyte antigen (CLA) and the protein MxA, which is specifically induced by type I interferons (IFNs).

RESULTS

We found a strong coexpression of granzyme B and CLA on lesional lymphocytes of patients with scarring lCDLE and dCDLE, which was significantly enhanced when compared with nonscarring SCLE and healthy controls. The increased expression of granzyme B was closely associated with the lesional expression of the type I IFN-induced protein MxA.

CONCLUSIONS

Our results provide evidence that type I IFNs and potentially autoreactive cytotoxic lymphocytes targeting adnexal structures are highly associated with scarring lupus erythematosus lesions and might be responsible for their scarring character.

HIV-infected cells are major inducers of plasmacytoid dendritic cell interferon production, maturation, and migration

Plasmacytoid dendritic cells (PDC), natural type-1 interferon (IFN) producing cells, could play a role in the innate anti-HIV immune response. Previous reports indicated that PDC IFN production is induced by HIV. Our results show a more robust IFN induction when purified PDC (>95%) were exposed to HIV-infected cells. This effect was not observed with non-viable cells, DNA, and RNA extracted from infected cells, and viral proteins. The response was blocked by anti-CD4 and neutralizing anti-gp120 antibodies as well as soluble CD4. IFN induction by HIV-infected cells was also prevented by low-dose chloroquine, which inhibits endosomal acidification. PDC IFN release resulted in reduced HIV production by infected CD4+ cells, supporting an anti-HIV activity of PDC. Stimulated CD4+ cells induced PDC activation and maturation; markers for PDC migration (CCR7) were enhanced by HIV-infected CD4+ cells only. This latter finding could explain the decline in circulating PDC in HIV-infected individuals.

CpG ODN enhance antigen-specific NKT cell activation via plasmacytoid dendritic cells

Human Valpha24+ Vbeta11+ natural killer T cells (NKT cells) are "natural memory" T cells that detect glycolipid antigens such as alpha-galactosylceramide (alpha-GalCer) presented on CD1d. In the present study we found that highly purified Valpha24+ NKT cells lack TLR9 mRNA, and thus are not sensitive towards stimulation with CpG oligodeoxynucleotides (ODN). Within PBMC, however, CpG ODN synergistically activated NKT cells stimulated with their cognate antigen alpha-GalCer. Depletion of plasmacytoid dendritic cells (PDC) or myeloid dendritic cells (MDC) revealed that both DC subsets were necessary for the synergistic activation of NKT cells by alpha-GalCer and CpG ODN. While PDC were responsible for the stimulation of NKT cells with CpG ODN, MDC but not PDC presented alpha-GalCer via CD1d. Partial activation of NKT cells was mediated by PDC-derived IFN-alpha, whereas full activation of NKT cells as indicated by IFN-gamma production required cell-to-cell contact of PDC and NKT cells in addition to IFN-alpha; OX40 was involved in this interaction. We conclude that CpG-activated PDC enhance alpha-GalCer-specific NKT cell activation, and bias activated NKT cells towards a Th1 phenotype. Our results lead to a novel concept of PDC function: to regulate effector activity of antigen-stimulated T cells in a cell contact-dependent manner without the need of simultaneous presentation of the cognate T cell antigen.

B-cell lymphomas differ in their responsiveness to CpG oligodeoxynucleotides

Human B cells detect CpG motifs within microbial DNA via TLR9. Synthetic CpG oligodeoxynucleotides are currently being tested in clinical trials for the therapy of different types of B cell non-Hodgkin's lymphoma. However, there is only limited information on the CpG oligodeoxynucleotide sensitivity of primary malignant B cells of different non-Hodgkin's lymphoma entities. Here we found that most B-cell malignancies except plasmacytoma respond to CpG oligodeoxynucleotides by up-regulating expression of costimulatory and antigen-presenting molecules, by increasing expression of CD20, and by proliferation. In an in vitro analysis of 41 individual patient-derived primary tumor samples, B-cell chronic lymphocytic leukemia (B-CLL) and marginal zone lymphoma showed the strongest activation upon stimulation with CpG oligodeoxynucleotides. Small lymphocytic lymphoma, follicular lymphoma, mantle cell lymphoma, and large cell lymphoma showed an intermediate response. Consistent with CpG oligodeoxynucleotides sensitivity, TLR9 mRNA was present in B-CLL but absent in plasmacytoma. Although CpG oligodeoxynucleotides induced proliferation in all CpG oligodeoxynucleotide-sensitive types of B-cell malignancies, proliferation was weaker than in normal B cells and at least for B-CLL was followed by increased apoptosis. In conclusion, B-cell malignancies show significant differences in their responsiveness to CpG oligodeoxynucleotides. Focusing clinical studies on patients with highly CpG oligodeoxynucleotide-sensitive B-cell malignancies may improve the clinical outcome of such trials.

No Indication for a Defect in Toll-Like Receptor Signaling in Patients with Hyper-IgE Syndrome

Hyper-IgE syndrome is a rare primary immunodeficiency of unknown etiology characterized by recurrent infections of the skin and respiratory system, chronic eczema, elevated total serum IgE, and a variety of associated skeletal symptoms. Recent reports about susceptibility to pyogenic bacterial infections and high IgE levels in patients and animals with defects in toll-like receptor (TLR) signaling pathways prompted us to search for TLR signaling defects as an underlying cause of hyper-IgE syndrome. Blood samples from six patients with hyper-IgE syndrome were analyzed for serum cytokine levels, intracellular cytokine production in T cells after stimulation with PMA/ionomycin, and cytokine production from peripheral blood mononuclear cells stimulated by TLR ligands and bacterial products including LPS (TLR4), peptidoglycan (TLR2), PolyIC (TLR3), R848 (TLR7/8), CpG-A, and CpG-B (TLR9), zymosan and heat killed Listeria monocytogenes. All results were compared to data from healthy controls. A reduction in IFN-gamma, IL-2, and TNF-alpha producing T cells after PMA stimulation suggested a reduced inflammatory T cell response in patients with hyper-IgE syndrome. Increased serum levels of IL-5 indicated a concomitant Th2 shift. However, normal production of cytokines (TNF-alpha, IL-6, IL-10, IFN-alpha, IP-10) and upregulation of CD86 on B cells and monocytes after TLR stimulation made a defect in TLR signaling pathways highly unlikely. In summary, our data confirmed an imbalance in T cell responses of patients with hyper-IgE syndrome as previously described but showed no indication for an underlying defect in toll-like receptor signaling.

Functional Diversity and Plasticity of Human Dendritic Cell Subsets

The induction of different types of innate and adaptive immune responses, depending on the nature of the antigens and the environmental context, is crucial to cope with a variety of pathogens and concurrently to avoid pathologic reaction to self antigens. Recent studies have elucidated that the diversity of immune responses is critically controlled by dendritic cells (DCs). Two DC subsets, myeloid DCs and plasmacytoid DCs, have been identified in humans. The DC subsets recognize different microbial pathogens by expressing distinct repertoires of Toll-like receptors and induce different types of innate and adaptive immune responses, depending on the environmental factors. In particular, plasmacytoid DC precursors produce vast amounts of type I interferons in response to viruses and thus play an important role in antiviral immunity. Elucidating the cellular and molecular mechanisms that modulate the functions of the 2 DC subsets will lead to an understanding of the pathogenesis of various immune-related diseases and to the development of novel immunologic therapies.

Sequence-specific potent induction of IFN-alpha by short interfering RNA in plasmacytoid dendritic cells through TLR7

Short interfering RNA (siRNA) is used in RNA interference technology to avoid non-target-related induction of type I interferon (IFN) typical for long double-stranded RNA. Here we show that in plasmacytoid dendritic cells (PDC), an immune cell subset specialized in the detection of viral nucleic acids and production of type I IFN, some siRNA sequences, independent of their GU content, are potent stimuli of IFN-alpha production. Localization of the immunostimulatory motif on the sense strand of a potent IFN-alpha-inducing siRNA allowed dissection of immunostimulation and target silencing. Injection into mice of immunostimulatory siRNA, when complexed with cationic liposomes, induced systemic immune responses in the same range as the TLR9 ligand CpG, including IFN-alpha in serum and activation of T cells and dendritic cells in spleen. Immunostimulation by siRNA was absent in TLR7-deficient mice. Thus sequence-specific TLR7-dependent immune recognition in PDC needs to be considered as an additional biological activity of siRNA, which then should be termed immunostimulatory RNA (isRNA).

Spontaneous formation of nucleic acid-based nanoparticles is responsible for high interferon-alpha induction by CpG-A in plasmacytoid dendritic cells

Plasmacytoid dendritic cells (PDC) represent a highly specialized immune cell subset that produces large quantities of the anti-viral cytokines type I interferons (IFN-alpha and IFN-beta) upon viral infection. PDC employ a member of the family of toll-like receptors, TLR9, to detect CpG motifs (unmethylated CG dinucleotides in certain base context) present in viral DNA. A certain group of CpG motif-containing oligodeoxynucleotides (CpG ODN), CpG-A, was the first synthetic stimulus available that induced large amounts of interferon-alpha (IFN-alpha) in PDC. However, the mechanism responsible for this activity remained elusive. CpG-A is characterized by a central palindrome and poly(G) at the 5' and 3' end. Here we demonstrate that CpG-A self-assembles to higher order tertiary structures via G-tetrad formation of their poly(G) motifs. Spontaneous G-tetrad formation of CpG-A required the palindrome sequence allowing structure formation in a physiological environment. Once formed, G-tetrad-linked structures were stable even under denaturing conditions. Atomic force microscopy revealed that the tertiary structures formed by CpG-A represent nucleic acid-based nanoparticles in the size range of viruses. Similarly sized preformed polystyrene nanoparticles loaded with a CpG ODN that is otherwise weak at inducing IFN-alpha (CpG-B) gained the potency of CpG-A to induce IFN-alpha. Higher ODN uptake in PDC was not responsible for the higher IFN-alpha-inducing activity of CpG-A or of CpG-B-coated nanoparticles as compared with CpG-B. Based on these results we propose a model in which the spatial configuration of CpG motifs as particle is responsible for the virus-like potency of CpG-A to induce IFN-alpha in PDC.

Novel APC-like properties of human NK cells directly regulate T cell activation

Initiation of the adaptive immune response is dependent on the priming of naive T cells by APCs. Proteomic analysis of unactivated and activated human NK cell membrane-enriched fractions demonstrated that activated NK cells can efficiently stimulate T cells, since they upregulate MHC class II molecules and multiple ligands for TCR costimulatory molecules. Furthermore, by manipulating antigen administration, we show that NK cells possess multiple independent unique pathways for antigen uptake. These results highlight NK cell-mediated cytotoxicity and specific ligand recognition by cell surface-activating receptors on NK cells as unique mechanisms for antigen capturing and presentation. In addition, we analyzed the T cell-activating potential of human NK cells derived from different clinical conditions, such as inflamed tonsils and noninfected and CMV-infected uterine decidual samples, and from transporter-associated processing antigen 2-deficient patients. This in vivo analysis revealed that proinflammatory, but not immune-suppressive, microenvironmental requirements can selectively dictate upregulation of T cell-activating molecules on NK cells. Taken together, these observations offer new and unexpected insights into the direct interactions between NK and T cells and suggest novel APC-like activating functions for human NK cells.

Anti-hepatitis B virus effects of human peripheral blood mononuclear cells activated by CpG-ODN

AIM: To investigate the inhibitory effect of peripheral blood mononuclear cells (PBMCs) activated by synthetic oligodeoxynucleotides (ODN) containing unmethylated CpG dinucleotides (CpG-ODN) on hepatitis B virus (HBV) in vitro.

METHODS: CpG-ODN was co-cultured with PBMCs. The IFN-α and IFN-γ in the supernatant were measured by ELISA. PBMCs activated by CpG-ODN were added to HBV transfected HepG2.2.15 cells After 1, 2 and 3 days, HBsAg and HBeAg in the supernatant were measured by ELISA; HBV DNA and HBV mRNA in HepG2.2.15 cells were detected by fluorogenic quantitative PCR method. MTT method and enzyme assays were used to detect PBMC-mediated lytic activity against HepG2.2.15 cells.

RESULTS: CpG-ODN induced high amounts of IFN-α as well as IFN-γ production (382.69±136.62, 37.42±6.55). Though CpG-ODN was unable to inhibit HBV replication directly, PMBC activated by CpG-ODN significantly reduced HBsAg and HBeAg secretion of HepG2.2.15 cells with rates of 82.6% and 52.4% at 72 h respectively (P < 0.05). The remarkable inhibitory effects of PMBC activated by CpG-ODN on HBV DNA (21.5%) and HBV mRNA (81.3%) in HepG2.2.15 cells were also observed (P < 0.05, P < 0.01).

CONCLUSION: PMBC activated by CpG-ODN can indirectly inhibit HBV replication and expression in vitro.

Induction of Systemic TH1-Like Innate Immunity in Normal Volunteers Following Subcutaneous but Not Intravenous Administration of CPG 7909, a Synthetic B-Class CpG Oligodeoxynucleotide TLR9 Agonist

Subcutaneous injection of normal human volunteers with a B-class CpG oligodeoxynucleotide (ODN) TLR9 agonist, CPG 7909, induced a TH1-like pattern of systemic innate immune activation manifested by expression of IL-6, IL-12p40, IFN-alpha, and IFN-inducible chemokines. Serum IP-10 was found to be the most sensitive assay for subcutaneous CPG 7909 stimulation; its level was significantly increased in all subjects at all dose levels, including the lowest tested dose of just 0.0025 mg/kg. This pattern of chemokine and cytokine induction was markedly different from that previously reported to be induced by TLR9 stimulation in rodents, most likely reflecting species-specific differences in the cell types expressing TLR9. Subcutaneous CPG 7909 injection induced transient shifts in blood neutrophils, lymphocytes, and monocytes, consistent with the increased chemokine expression. Levels of acute phase reactants such as C-reactive protein were also increased. A second subcutaneous CPG 7909 injection administered 2 weeks after the first elicited similar immune responses, showing little or no tolerance to the effects of repeated in vivo TLR9 stimulation. Subjects developed dose-dependent transient injection site reactions and flu-like symptoms but otherwise tolerated injection well, with no evidence of organ toxicity or systemic autoimmunity. The activation of innate immunity was dependent on the route of ODN administration, since intravenous injection caused no such effects. These studies indicate that in vivo activation of TLR9 by subcutaneous administration of CPG 7909 could be a well-tolerated immunotherapeutic approach for induction of TH1 innate immune activation.

Modulation of immune responses - strategies for optimising vaccines

Over decades, vaccination has considerably reduced the morbidity and mortality caused by infectious pathogens. Efficient vaccines conferring long-term protection have been developed despite a minimal understanding of the specific immunological mechanisms involved in this protection. Recent technological advances have provided valuable insights into host-pathogen interactions and considerably improved our knowledge of the effector and regulatory mechanisms behind the innate and adaptive immune responses. With the ability to initiate and manipulate immune responses, it is now possible to develop and optimise safe and effective vaccination strategies using a more rational approach.