Immunostimulatory CpG Oligodeoxynucleotides Enhance the Immune Response to Vaccine Strategies Involving Granulocyte-Macrophage Colony-Stimulating Factor

Cooperation of Oligodeoxynucleotides and Synthetic Molecules as Enhanced Immune Modulators

Unmethylated cytosine–guanine dinucleotide (CpG) motifs are potent stimulators of the host immune response. Cellular recognition of CpG motifs occurs via Toll-like receptor 9 (TLR9), which normally activates immune responses to pathogen-associated molecular patterns (PAMPs) indicative of infection. Oligodeoxynucleotides (ODNs) containing unmethylated CpGs mimic the immunostimulatory activity of viral/microbial DNA. Synthetic ODNs harboring CpG motifs resembling those identified in viral/microbial DNA trigger an identical response, such that these immunomodulatory ODNs have therapeutic potential. CpG DNA has been investigated as an agent for the management of malignancy, asthma, allergy, and contagious diseases, and as an adjuvant in immunotherapy. In this review, we discuss the potential synergy between synthetic ODNs and other synthetic molecules and their immunomodulatory effects. We also summarize the different synthetic molecules that function as immune modulators and outline the phenomenon of TLR-mediated immune responses. We previously reported a novel synthetic ODN that acts synergistically with other synthetic molecules (including CpG ODNs, the synthetic triacylated lipopeptide Pam₃CSK₄, lipopolysaccharide, and zymosan) that could serve as an immune therapy. Additionally, several clinical trials have evaluated the use of CpG ODNs with other immune factors such as granulocyte-macrophage colony-stimulating factor, cytokines, and both endosomal and cell-surface TLR ligands as adjuvants for the augmentation of vaccine activity. Furthermore, we discuss the structural recognition of ODNs by TLRs and the mechanism of functional modulation of TLRs in the context of the potential application of ODNs as wide-spectrum therapeutic agents.

Synthetic CpG-ODN rapidly enriches immune compartments in neonatal chicks to induce protective immunity against bacterial infections

Oligodeoxynucleotides containing CpG motifs (CpG-ODN) induce innate immunity against bacterial infections. Despite recent advances, how CpG-ODN alone protects against bacterial infections remained elusive. Here, we report for the first time, to our knowledge, that CpG-ODN orchestrates anti-microbial protective immunity by inducing a rapid enrichment of various immune compartments in chickens. In this study, eighteen-day-old embryonated eggs were injected with either 50 µg of CpG-ODN or saline (~n = 90 per group). In the first experiment, four days after CpG-ODN treatment, chicks were challenged subcutaneously with a virulent strain of Escherichia coli (E. coli) and mortality was monitored for 8 days. We found significant protection, and reduced clinical scores in CpG-ODN treated chicks. To gain insights into mechanisms of protection induced by CpG-ODN, first we investigated cytokine expression kinetics elicited by CpG-ODN. The spleen and lung were collected from embryos or chicks (n = 3-4 per group) at 10 time points post-CpG-ODN inoculation. Multiplex gene analysis (interleukin (IL)-1, IL-4, IL-6, IL-10, IL-18, interferon (IFN)-γ, IFN-α, and lipopolysaccharide induced tumor necrosis factor (LITAF), revealed a significantly higher expression of pro-inflammatory cytokines following CpG-ODN treatment compared to the saline controls. In our study, LITAF stands out in the cytokine profiles of spleen and lungs, underscoring its role in CpG-ODN-induced protection. The third experiment was designed to examine the effects of CpG-ODN on immune cell populations in spleen, lungs, and thymus. Flow cytometry analysis was conducted at 24, 48 and 72 hrs (thymus only collected at 72 hr) after CpG-ODN administration to examine the changes in CD4⁺ and CD8⁺ T-cell subsets, monocyte/macrophage cell populations and their expression of maturation markers (CD40 and CD86). Flow cytometry data indicated a significant enrichment of macrophages, CD4⁺ and CD8⁺ T-cell subsets in both spleen and lungs of CpG-ODN treated embryos and chicks. Macrophages in spleen and lungs showed an upregulation of CD40 but not CD86, whereas thymocytes revealed significantly high CD4 and CD8 expression. Overall, the present study has demonstrated that CpG-ODN provides protection in neonatal chicks against E. coli infection not only by eliciting cytokine responses and stimulating immune cells but also through enriching immunological niches in spleen and lungs.

In vivo cancer vaccination: Which dendritic cells to target and how?

The field of cancer immunotherapy has been revolutionized with the use of immune checkpoint blockade antibodies such as anti-programmed cell death 1 protein (PD-1) and chimeric antigen receptor T cells. Significant clinical benefits are observed in different cancer types with these treatments. While considerable efforts are made in augmenting tumor-specific T cell responses with these therapies, other immunotherapies that actively stimulate endogenous anti-tumor T cells and generating long-term memory have received less attention. Given the high cost of cancer immunotherapies especially with chimeric antigen receptor T cells, not many patients will have access to such treatments. The next-generation of cancer immunotherapy could entail in vivo cancer vaccination to activate both the innate and adaptive anti-tumor responses. This could potentially be achieved via in vivo targeting of dendritic cells which are an indispensable link between the innate and adaptive immunities. Dendritic cells highly expressed toll-like receptors for recognizing and eliminating pathogens. Synthetic toll-like receptors agonists could be synthesized at a low cost and have shown promise in preclinical and clinical trials. As different subsets of human dendritic cells exist in the immune system, activation with different toll-like receptor agonists could exert profound effects on the quality and magnitude of anti-tumor T cell responses. Here, we reviewed the different subsets of human dendritic cells. Using published preclinical and clinical cancers studies available on PubMed, we discussed the use of clinically approved and emerging toll-like receptor agonists to activate dendritic cells in vivo for cancer immunotherapy. Finally, we searched www.clinicaltrials.gov and summarized the active cancer trials evaluating toll-like receptor agonists as an adjuvant.

Intranasal administration of a two-dose adjuvanted multi-antigen TMV-subunit conjugate vaccine fully protects mice against Francisella tularensis LVS challenge

Tularemia is a fatal human disease caused by Francisella tularensis, a Gram-negative encapsulated coccobacillus bacterium. Due to its low infectious dose, ease of aerosolized transmission, and lethal effects, the CDC lists F. tularensis as a Category A pathogen, the highest level for a potential biothreat agent. Previous vaccine studies have been conducted with live attenuated, inactivated, and subunit vaccines, which have achieved partial or full protection from F. tularensis live vaccine strain (LVS) challenge, but no vaccine has been approved for human use. We demonstrate the improved efficacy of a multi-antigen subunit vaccine by using Tobacco Mosaic virus (TMV) as an antigen carrier for the F. tularensis SchuS4 proteins DnaK, OmpA, SucB and Tul4 (DOST). The magnitude and quality of immune responses were compared after mice were immunized by subcutaneous or intranasal routes of administration with a TMV-DOST mixture, with or without four different adjuvants. Immune responses varied in magnitude and isotype profile, by antigen, by route of administration, and by protection in an F. tularensis LVS challenge model of disease. Interestingly, our analysis demonstrates an overwhelming IgG2 response to SucB after intranasal dosing, as well as a robust cellular response, which may account for the improved two-dose survival imparted by the tetravalent vaccine, compared to a previous study that tested efficacy of TMV-DOT. Our study provides evidence that potent humoral, cellular and mucosal immunity can be achieved by optimal antigen combination, delivery, adjuvant and appropriate route of administration, to improve vaccine potency and provide protection from pathogen challenge.

Preparation and characterization of the antibody recognizing AMACR inside its catalytic center

Alpha-methylacyl-CoA racemase (AMACR) catalyzes the β-oxidation of fatty acids and is overexpressed in carcinomas in various organs, while its inactivation results in the inhibition of cancer growth. In the present study, we prepared and characterized 20 different mouse monoclonal antibodies against human AMACR. In the course of biopanning of a phage peptide commercial library against in-house prepared 6H9 and 2A5, and commercial 13H4 antibodies, 10 phage mimotopes recognized by each type of the antibody were selected. Using the program Pepitope and the crystal structure of AMACR from Mycobacterium tuberculosis, we reveal for the first time, at least to the best of our knowledge, that the epitopes recognizing the antibody against AMACR are composed of conformation sequences localized inside the AMACR catalytic center. When delivered into live HeLa cells using cationic lipid-based PULSin reagent, the specific antibodies against AMACR were co-localized with peroxisomes. The in-house made 6H9 antibody exhibited a low level of this co-localization compared to the commercially available 63340 antibody, and did not inhibit the growth rate of HeLa and T98G cells. The results obtained suggest that antibody against AMACR may possess anti-AMACR catalytic activity and needs to be further investigated as a potential drug for use in anticancer therapy. On the whole, in this study, we generated several clones of AMACR antibodies and demonstrated that these antibodies can be colonized into live cells. Currently, we are testing the growth inhibitory properties of these antibodies against AMACR.

Applying biodegradable particles to enhance cancer vaccine efficacy

One of the primary goals of our group and our collaborators here at the University of Iowa is to develop therapeutic cancer vaccines using biodegradable and biocompatible polymer-based vectors. A major advantage of using discretely packaged immunogenic cargo over non-encapsulated vaccines is that they promote enhanced cellular immunity, a key requirement in achieving antitumor activity. We discuss the importance of co-encapsulation of tumor antigen and adjuvant, with specific focus on the synthetic oligonucleotide adjuvant, cytosine-phosphate-guanine oligodeoxynucleotides. We also discuss our research using a variety of polymers including poly(α-hydroxy acids) and polyanhydrides, with the aim of determining the effect that parameters, such as size and polymer type, can have on prophylactic and therapeutic tumor vaccine formulation efficacy. Aside from their role as vaccine vectors per se, we also address the research currently underway in our group that utilizes more novel applications of biodegradable polymer-based particles in facilitating other types of immune-based therapies.

Radiation as immunomodulator: implications for dendritic cell-based immunotherapy

The last decade has witnessed significant progress in the field of cancer immunotherapy. This has, in part, been driven by a growing recognition that elements of the innate immune response can be harnessed to induce robust immunity against tumor-associated targets. Nonetheless, as clinically effective immunotherapy for the majority of cancers remains a distant goal, attention has shifted toward multimodality approaches to cancer therapy, sometimes combining novel immunotherapeutics and conventional therapeutics. The traditional view of radiation therapy as immunosuppressive has been challenged, prompting a re-evaluation of its potential as an adjunct to, or even a component of immunotherapy. Radiation therapy may enhance expression of tumor-associated antigens, induce targeting of tumor stroma, diminish regulatory T-cell activity and activate effectors of innate immunity such as dendritic cells through Toll-like receptor (TLR)-dependent mechanisms. Here, we review recent progress in the field of dendritic cell-based immunotherapy, evidence for radiation-induced antitumor immunity and TLR signaling and the results of efforts to rationally integrate radiation into dendritic cell-based immunotherapy strategies.

Early development of the Toll-like receptor 9 agonist, PF-3512676, for the treatment of patients with advanced cancers

BACKGROUND

Unmethylated oligodeoxynucleotides (ODNs) with cytosine-phosphate-guanine (CpG) motifs can potently activate the immune system through Toll-like receptor (TLR) 9. PF-3512676 is a synthetic CpG ODN that induces strong Th1-type immune responses through TLR9 and is now in clinical development.

OBJECTIVE

To review discovery and development of synthetic CpG ODNs and their effects on immune cells and to relate preclinical and early clinical development of PF-3512676.

METHODS

A literature search was performed on databases available through the National Library of Medicine (PubMed), the European Society of Medical Oncology and the American Society of Clinical Oncology.

RESULTS/CONCLUSIONS

Unmethylated CpG motifs were identified as the element of bacillus Calmette-Guérin responsible for immunostimulatory activity. Preclinical studies identified the mechanism of action (i.e., TLR9) and an optimal human sequence for antitumor activity. On the basis of preclinical studies, PF-3512676, a B-class CpG ODN, was selected for further clinical development. Phase I/II clinical trials have shown PF-3512676 to be well tolerated and to have antitumor activity as a single agent in patients with several types of advanced cancer, and to show promise as a vaccine adjuvant.

The meningococcal adhesin NhhA provokes proinflammatory responses in macrophages via toll-like receptor 4-dependent and -independent pathways

Activation of macrophages by Toll-like receptors (TLRs) and functionally related proteins is essential for host defense and innate immunity. TLRs recognize a wide variety of pathogen-associated molecules. Here, we demonstrate that the meningococcal outer membrane protein NhhA has immunostimulatory functions and triggers release of proinflammatory cytokines from macrophages. NhhA-induced cytokine release was found to proceed via two distinct pathways in RAW 264.7 macrophages. Interleukin-6 (IL-6) secretion was dependent on activation of TLR4 and required the TLR signaling adaptor protein MyD88. In contrast, release of tumor necrosis factor (TNF) was TLR4 and MyD88 independent. Both pathways involved NF-κB-dependent gene regulation. Using a PCR-based screen, we could identify additional targets of NhhA-dependent gene activation such as the cytokines and growth factors IL-1α, IL-1β, granulocyte colony-stimulating factor (G-CSF), and granulocyte-macrophage colony-stimulating factor (GM-CSF). In human monocyte-derived macrophages, G-CSF, GM-CSF, and IL-6 were found to be major targets of NhhA-dependent gene regulation. NhhA induced transcription of IL-6 and G-CSF mRNA via TLR4-dependent pathways, whereas GM-CSF transcription was induced via TLR4-independent pathways. These data provide new insights into the role of NhhA in host-pathogen interaction.

Clinicobiologic importance of cytogenetic lesions in chronic lymphocytic leukemia

Molecular cytogenetic lesions play a major role in the pathogenesis of chronic lymphocytic leukemia (CLL) and represent important prognostic markers. Besides FISH, conventional banding analysis using effective mitogens is important for an accurate assessment of the cytogenetic profile of CLL. The most frequent aberrations are represented by 13q-, 11q-, +12, 6q- and 14q32/IGH translocations and 17p-. Chromosome translocations and complex karyotype may occur in up to 30 and 16% of the cases, respectively. The frequency of 17p- and 11q- is higher in patients requiring treatment and in relapsed/refractory patients, reflecting the association of these rearrangements with unfavorable prognosis. Mutations of the TP53 gene may also confer an inferior outcome, as is the case with 14q32 translocations and unbalanced translocations. Evidence was provided that distinct treatment approaches may be effective in specific cytogenetic entities of CLL, making molecular cytogenetic investigations a necessary tool for a modern diagnostic work-up in CLL.

Induction of homologous rather than heterologous antigen-specific CD4 T cell responses is critical for functional CD8 T cell responses in mice transgenic for a foreign antigen

The development of a successful cancer vaccine requires the ability to break immunological tolerance to self-Ags expressed on tumor cells. The transgenic rat insulin promoter (RIP) OVA(LOW) mouse model has been reported to be hyporesponsive for both OVA-specific CD4 and CD8 T cell responses. The experiments described in the current study show that this hyporesponsiveness can be overcome by inclusion of GM-CSF and the TLR7 agonist imiquimod as adjuvants in a DNA immunization regimen with OVA-encoding plasmids. High frequencies of OVA-specific CD8 and CD4 T cells, including a response to a CD4 T cell epitope seen only in the RIP OVA(LOW) mice, were generated by this regimen. These responses were associated with the development of autoimmunity and increased protection to tumor challenge in the RIP OVA(LOW) mice. Heterologous CD4 T cell help has been shown to improve functional CD8 T cell responses, and we confirmed that inclusion of the CD4 T cell epitope pan HLA-DR-binding epitope improved CD8 T cell responses compared with self-Ag alone. Addition of GM-CSF and imiquimod, however, resulted in dominance of the pan HLA-DR-binding epitope-specific response over the OVA-specific CD4 T cell responses, decreased OVA-specific CD8 T cell numbers and function in tolerant RIP OVA(LOW) mice, and failure to induce diabetes. The results of this study suggest that the use of heterologous help needs to be evaluated carefully in the context of specific immunization regimes and that a preferable approach may be adjuvantization of DNA vaccines.

CpG oligodeoxynucleotide-based therapy of lymphoid malignancies

Preclinical and early clinical trials indicate synthetic oligodeoxynucleotides containing unmethylated CG dinucleotides (CpG ODN) have potent immunostimulatory effects. CpG ODN are being explored as immune adjuvants in vaccination strategies and as potential treatments for a wide variety of disorders including cancer and asthma. Therapeutic approaches designed to take advantage of this potent class of agents are based largely on the ability of CpG ODN to activate professional antigen presenting cells (APCs) that express the target receptor - Toll-Like Receptor 9 (TLR9). B-cell malignancies are unique in that the malignant cells themselves express TLR9. CpG ODN can have a direct effect on the malignant B cells and lead to activation induced cell death. CpG ODN also alter the phenotype of target malignant B cells as indicated by upregulation of MHC, immunostimulatory molecules, and antigens that serve as targets for other approaches to lymphoma immunotherapy such as CD20. B cell malignancies are also relatively sensitive to the cytokines that are produced by dendritic cells in response to CpG ODN. Thus, B cell malignancies appear to be uniquely sensitive to CpG ODN because of both the direct and indirect effects the CpG ODN on target cells and the sensitivity of B cell malignancies to an immune response. Preclinical studies support further exploration of the potential of CpG ODN as a component of therapy for lymphoid malignancies. Ongoing clinical trials are exploring the potential of CpG ODN, both alone and in combination with other agents.

CpG oligonucleotides for immunotherapeutic treatment of neuroblastoma

Neuroblastoma is the most common extracranial solid tumor malignancy of childhood. Although it is generally responsive to treatment, high risk cases of neuroblastoma frequently recur. The prognosis for relapsed cases is extremely poor despite aggressive therapy. The frequency of relapse and subsequent failure of further treatment has spurred the need to develop non toxic and more effective treatments for targeting residual tumor cells during the phase of minimal residual disease. Traditional cancer therapies are non-specific, leading to the destruction of normal, healthy tissues. Failure to induce specific tumor immunity may be due to several immunosuppressive factors. Primary amongst these factors are: lack of co-stimulatory molecules on the surface of tumor cells, the ability of the tumor to modulate immunity in a suppressive manner and the presence of an immunosuppressive microenvironment at the location of the tumor. Unfortunately, tumor tolerance impedes the ability to establish immunity to tumor antigens and overcoming this tolerance is essential to developing effective tumor immunity. Vaccine strategies that target host immune effector cells with synthetic oligodeoxynucleotides (ODNs) that contain unmethylated CpG motifs (CpG-ODNs) represent a novel approach to overcoming tolerance in cancer therapy. This approach enables biasing of host immunity toward a proinflammatory Th1 and thus anti-tumor response. The addition of immunogenic tumor specific antigen to the CpG-ODN vaccine may allow for specific targeting and killing of established tumors.

Stimulatory effects of CpG oligodeoxynucleotide on dendritic cell-based immunotherapy of colon cancer in CEA/HLA-A2 transgenic mice

Immunostimulatory DNA containing unmethylated cytosine-guanine (CpG) motifs have been successfully used as adjuvants to enhance the immunity of vaccines designed to trigger antitumor T-cell responses. We examined the effect of a CpG oligodeoxynucleotide (CpG ODN) for its ability to potentiate the activity of tumor antigen-pulsed dendritic cells (DC) in a clinically relevant mouse model, which is transgenic for both carcinoembryonic antigen (CEA) and HLA-A2 for the treatment of colon carcinoma in a therapeutic setting. The systemic administration of CpG ODN 1826 alone had modest effect on tumor growth when tumors were palpable and had no effect with larger tumor burden. However, coadministration of CpG ODN 1826 with the vaccine provided significant increase in tumor-free survival compared with mice immunized with DC-based vaccines alone. The DC/CpG combined vaccination strategy resulted in increased secretion of Th1 cytokines and HLA-A2-restricted CEA-specific CTL responses were also enhanced. Both tumor regression and extended tumor-free survival resulting from DC/CpG combination therapy required the participation of T cells. Tumor-free mice were resistant to tumor rechallenge and immunity conferred by the vaccine was transferable in athymic nude mice. These results provide evidence that vaccination with antigen-pulsed DC with CpG ODN as adjuvant can lead to effective tumor regression and long-term survival in a murine model of colon carcinoma.

Rapid loss of dendritic cell and monocyte responses to TLR ligands following venipuncture

Blood samples from multiple sites are collected in multicenter trials, and frequently shipped to centralized laboratories for processing and comparable experimental evaluation. It is therefore of crucial interest to assess the preservation of immune cell functions after overnight shipment of whole blood. Here we evaluated the ability of pDCs, mDCs and monocytes to respond to TLR ligands at multiple timepoints following venipuncture as compared to immediate processing. Our results demonstrate a profound impairment of APC function, in particular of IFN-alpha production of pDCs, if whole blood was processed later than 6 h after venipuncture. Overnight shipment or extended rest of whole blood before processing therefore severely compromises the ability of APCs to respond to TLR ligands, and this has to be taken into consideration when designing multicenter trials.

CpG oligodeoxynucleotides alter lymphocyte and dendritic cell trafficking in humans

PURPOSE

CpG oligodeoxynucleotides (CpG-ODN) are being investigated as cancer vaccine adjuvants because they mature plasmacytoid dendritic cells (PDC) into potent antigen-presenting cells. CpG-ODN also induce PDC to secrete chemokines that alter lymphocyte migration. Whether CpG-ODN TLR signals enhance antigen-specific immunity and/or trafficking in humans is unknown.

EXPERIMENTAL DESIGN

We conducted a phase I study of CpG-ODN (1018 ISS) given as a vaccine adjuvant with granulocyte-macrophage colony-stimulating factor (GM-CSF) to induce T-cell immunity to a peptide vaccine from the tumor-associated antigen hTERT.

RESULTS

The adjuvant effect was limited; only 1 of 16 patients showed a high-frequency hTERT-specific tetramer CD8(+) T-cell response. However, CpG-ODN induced marked, transient peripheral blood lymphopenia. Biopsies showed dense lymphocytic infiltration at the vaccine site clustered around activated PDC. In vitro, CpG-ODN-treated PDC induced T-cell migration, showing that CpG-ODN stimulation of human PDC was sufficient to chemoattract T cells.

CONCLUSIONS

Our results show that (a) CpG-ODN with GM-CSF may not be an effective adjuvant strategy for hTERT peptide vaccines but (b) GM-CSF/CpG-ODN causes a PDC-mediated chemokine response that recruits T-cell migration to the peripheral tissues. These findings suggest a novel therapeutic role for targeted injections of CpG-ODN to direct lymphocyte migration to specific sites such as the tumor bed.

TLR agonists regulate alloresponses and uncover a critical role for donor APCs in allogeneic bone marrow rejection

Cytosine-phosphorothioate-guanine oligodeoxynucleotides (CpG ODNs) are synthetic ODNs with unmethylated DNA sequences that mimic viral and bacterial DNA and protect against infectious agents and tumor challenge. We show that CpG ODNs markedly accelerated graft-versus-host disease (GVHD) lethality by Toll-like receptor 9 (TLR9) ligation of host antigen-presenting cells (APCs), dependent upon host IFNgamma but independent of host IL-12, IL-6, or natural killer (NK) cells. Imaging studies showed significantly more green fluorescent protein-positive (GFP(+)) effector T cells in lymphoid and nonlymphoid organs. In engraftment studies, CpG ODNs promoted allogeneic donor bone marrow (BM) rejection independent of host IFNgamma, IL-12, or IL-6. During the course of these studies, we uncovered a previously unknown and critical role of donor BM APCs in modulating the rejection response. CpG ODNs promoted BM rejection by ligation of donor BM, but not host, TLR9. CpG ODNs did not impair engraftment of TLR9(-/-) BM unless wild-type myeloid (CD11b(+)) but not B-lineage (CD19(+)) BM cells were added to the donor inoculum. The importance of donor BM APCs in modulating the strength of the host antidonor rejection response was underscored by the finding that B7-1/B7-2(-/-) BM was less likely than wild-type BM to be rejected. Collectively, these data offer new insight into the mechanism of alloresponses regulating GVHD and BM rejection.

Radiation therapy and Toll-like receptor signaling: implications for the treatment of cancer

The identification of pathogen-associated molecular patterns, conserved microbial structures that act on Toll-like receptors, has led to a novel avenue of investigation aimed at developing a new generation of cancer immunotherapies. Ligation of Toll-like receptors results in the induction of robust immune responses that may be directed against tumor-associated antigens. Recent data suggest that such strategies may result in enhanced antitumor immunity. Nonetheless, as clinically effective immunotherapy for cancer remains a somewhat distant goal, attention has shifted toward multimodality approaches to cancer therapy, sometimes combining novel immune interventions and conventional treatments. The traditional view of radiation therapy as immunosuppressive has now been challenged, prompting a re-evaluation of its potential as an adjunct to immunotherapy. Radiation therapy can enhance the expression of tumor-associated antigens, induce immune-mediated targeting of tumor stroma, and diminish regulatory T cell activity. Recent evidence suggests that radiation therapy may also activate effectors of innate immunity through TLR-dependent mechanisms, thereby augmenting the adaptive immune response to cancer. In this paper, we will review evidence for enhanced tumor-directed immunity resulting from radiation exposure and early promising data suggesting synergistic effects of radiation and TLR-targeted immunotherapies.

Increased sensitivity of radiated murine cervical cancer tumors to E7 subunit vaccine-driven CTL-mediated killing induces synergistic anti-tumor activity

The development of therapeutic vaccines has important implications for the treatment of cancer patients. Here we investigate whether human papillomavirus (HPV) E7 subunit vaccines can enhance tumor radioresponse using an established cervical cancer animal model. Radiation plus E7 subunit vaccines improved complete response, cure, and recurrence rates of tumors dramatically compared with single therapy alone. In particular, both components of the E7 subunit vaccines (E7 protein and CpG-oligodeoxynucleotide) were required for the induction of antigen (Ag)-specific cytotoxic T-lymphocyte (CTL) responses and for therapeutic synergy with radiotherapy. Moreover, with combined therapy the radiation dose could be reduced by 16 Gy to achieve an equivalent anti-tumor efficacy to radiation treatment alone. This therapeutic synergy was found to be mediated by CD8(+) CTLs and was concomitant with histological changes (presence of apoptotic bodies and multinucleated giant cells; heavy infiltration of lymphocytes), as determined by in vivo T-cell depletion and histological analysis. Finally, phenotypic changes of radiated tumors and their increased sensitivity to CTL-mediated killing appeared to be responsible for therapeutic synergy. These results show that E7 subunit vaccines act as a potent enhancer of tumor radioresponse and that this is mediated by increased sensitivity of radiated tumors to CTL-mediated killing. This study further suggests that E7-targeted therapeutic vaccines have the potential to improve radiotherapy in patients with cervical cancer.

Immunostimulatory effects of CpG-ODN upon dendritic cell-based immunotherapy in a murine melanoma model

In this study, we examined the protective and therapeutic efficacy of the immunoadjuvant CpG in combination with dendritic cell (DC) immunotherapy in a murine melanoma model. We found that murine bone-marrow derived DC stimulated in vitro with CpG displayed both enhanced expression of maturation markers and secretion of IL-12p70 and IL-10. In addition, these matured DC demonstrated enhanced ability to stimulate antigen specific CD4+ and CD8+ T cell responses in vitro. In a protection model, C57BL/6 mice vaccinated with either antigen-pulsed immature or CpG matured DC were unable to reject a lethal B16 melanoma challenge. In contrast, long-term protection was achieved in mice vaccinated with both CpG and antigen-pulsed DC, which correlated with an enhanced antigen specific T cell immune response. In a therapeutic model of established subcutaneous B16 melanoma, C57BL/6 mice treated intratumorally with CpG and B16 lysate-pulsed DC demonstrated a reduced tumor burden and prolonged survival. In a similar model of established subcutaneous tumor, mice treated with CpG-matured DC pulsed with a melanoma peptide, TRP-2, alone were unable to achieve tumor regression. Conversely, mice that received the combined vaccine of CpG and peptide-pulsed DC displayed a reduced tumor burden. These experiments provide evidence that combined immunization with both antigen-pulsed DC and the immunoadjuvant, CpG, can lead to tumor regression and long-term survival in a murine B16 melanoma model.

Surgical excision combined with autologous whole tumor cell vaccination is an effective therapy for murine neuroblastoma

BACKGROUND

Although a whole tumor cell vaccine strategy based on the synergistic action of granulocyte macrophage-colony-stimulating factor (GM-CSF) transduced tumor cells and CpG oligodeoxynucleotides induces potent tumor-specific immunity, such therapy is not curative in the face of large established tumors.

PURPOSE

The primary goal of this study was to determine if combining surgical resection of the tumor with whole tumor cell vaccination is an effective therapeutic strategy for established neuroblastoma. We also wished to determine if the phenotype of the immune response generated by this vaccine strategy was altered by the presence of bulky established tumor.

METHODS

The murine neuroblastoma model was used in which syngeneic Neuro-2a was grown subcutaneously in A/J mouse. The whole tumor cell vaccine consisted of irradiated Neuro-2a as the vehicle for tumor antigens admixed with GM-CSF and CpG oligonucleotides (100 microg).

RESULTS

In the presence of large tumors, dendritic cells were effectively activated by the vaccine, but secretion of intereferon-gamma from vaccinated splenocytes in response to antigen stimulation was suppressed. The tumor's inhibitory effect on interferon-gamma production from vaccinated splenocytes was reversed after resection of the primary tumor. The use of prepared GM-CSF-secreting bystander cells simplified production of an autologous whole tumor cell vaccine that was remarkably effective in curing large tumors when combined with tumor excision.

CONCLUSIONS

These findings suggest that at least part of the immunosuppressive effects of the cancer can be reversed after surgical excision of the primary tumor. Thus, in the context of minimal residual disease, this dendritic cell-targeted immunotherapeutic approach may prove effective for the treatment of neuroblastoma.

Antitumor therapeutic effects of e7 subunit and DNA vaccines in an animal cervical cancer model: antitumor efficacy of e7 therapeutic vaccines is dependent on tumor sizes, vaccine doses, and vaccine delivery routes

We previously reported that E7 subunit and DNA vaccines are both capable of inducing antitumor protection through induction of antigen-specific CTL. In this study, we investigated their ability to control established tumors according to tumor size, vaccine doses, and vaccine delivery routes. Antitumor therapeutic efficacy of both vaccine types was dependent on tumor burden. However, E7 subunit vaccines induced a higher level of antitumor therapeutic activities at the tested dose compared to DNA vaccines. This was concomitant with induction of antibody, CTL, and IFN-gamma responses, as well as histologic changes (heavy infiltration of lymphocytes and presence of apoptotic bodies). In vaccine dose titration assays, 50 and 100 microg of DNA vaccines exhibited an equivalent antitumor efficacy to 0.5 and 1 microg of E7 subunit vaccines, respectively, i.e., a 100-fold difference in E7 dosage, suggesting the importance of vaccine doses for achieving antitumor immunity. Furthermore, tumors of a larger size were controlled by intratumoral injection with E7 subunit vaccines, underscoring the importance of vaccine delivery routes for antitumor therapeutic efficacy. Thus, these data suggest that antitumor therapeutic efficacy of E7 therapeutic vaccines is determined by vaccine doses, vaccine delivery routes, and tumor sizes, and that these vaccines could be another addition to conventional therapy modalities against cervical cancer.

Immunization with a DNA chimeric molecule encoding a hemagglutinin peptide and a scFv CD21-specific antibody fragment induces long-lasting IgM and CTL responses to influenza virus

Killed viral vaccines are known to induce primarily antibody responses. By contrast DNA vaccination using naked DNA encoding viral antigens induces both humoral and cellular immune responses. Various approaches have been used to construct DNA vaccines with build-in adjuvanticity. We hypothesized that sequences encoding a common epitope of influenza A virus hemagglutinin jointed to sequences encoding a single-chain variable fragment (scFv) antibody fragment to a costimulatory B cell surface receptor would result in the in vivo expression of a chimeric viral peptide with increased immunogenicity. Such a hybrid DNA molecule was constructed by us, encoding a T and B cell epitope-containing influenza hemagglutinin peptide and a scFv antibody fragment binding to mouse complement receptors I and II (CR1 and CR2). A single immunization with a plasmid containing the described construct induced a strong anti-influenza cytotoxic response lasting for more than six months and a weak antibody response.

Co-administration of porcine-specific CpG oligodeoxynucleotide enhances the immune responses to pseudorabies attenuated virus vaccine in newborn piglets in vivo

Oligonucleotides containing CpG motifs (CpG ODN) are strong adjuvants for humoral and cellular immune responses in mice, but data on immune responses in piglets are scarce. In this report, porcine-specific CpG ODN were used as immunoadjuvants to enhance the immune responses of the newborn piglets to Pseudorabies attenuated virus (PRV) vaccine. The titres of specific antibodies and serum IgG1/IgG2 ratio to PRV vaccine, the proliferation of peripheral blood mononuclear cells (PBMCs), IL-4 and interferon-gamma(IFN-gamma) in piglets serum were examined to identify the immune response of the newborn piglets. The results showed that piglets immunized with PRV vaccine and CpG ODN presented high titers of PRV-specific antibodies and IgG2 isotype, a Th1-dominated (IFN-gamma) cytokine profile, together with inducing higher proliferation of PBMCs. All these data indicate that CpG ODN are potential effective adjuvants for the PRV vaccine in newborn piglets.

Th2-dominated antitumor immunity induced by DNA immunization with the genes coding for a basal core peptide PDTRP and GM-CSF

Our previous study showed that DNA vaccination with a plasmid vector encoding a core peptide of mucin1 (PDTRP) provided modest protection against challenge with tumor cells that expressed mucin1 protein. We report here that a DNA vaccine comprising a modified PDTRP plasmid and GM-CSF coding sequence at the C-terminus induced better protection against tumor challenge. The increased protection was directly correlated with a stronger PDTRP-specific immune response induced by the GM-CSF fusion plasmid. The plasmid encoding GM-CSF and the target PDTRP antigen induced a greater PDTRP-specific Th proliferation, antibodies, and cytotoxicity. Interestingly, the modified plasmid vaccine predominantly enhanced the type 2 immune responses manifested by an increased IgG1 to IgG2a antibody ratio and a greater induction of GATA-3 and IL-4 mRNA than that of T-bet and IFN-gamma mRNA in spleen cells from vaccinated mice. In addition, protection against tumor challenge in vaccinated mice showed that there was no significant change in mice survival after in vivo CD8+CTL depletion, indicating that antitumor immunity augmented by plasmid encoding GM-CSF and target PDTRP gene vaccine was dominated by Th2 immune response.

Triggering TLR signaling in vaccination

Toll-like receptors (TLRs) are a family of pattern-recognition receptors that are an important link between innate and adaptive immunity. Many established, as well as experimental, vaccines incorporate ligands for TLRs, not only to protect against infectious diseases but also in therapeutic immunization against noninfectious diseases, such as cancer. We review the underlying mechanisms by which engagement of TLR signaling pathways might trigger an adaptive immune response after immunization. Although the engagement of TLR signaling pathways is a promising mechanism for boosting vaccine responses, questions of efficacy, feasibility and safety remain the subject of active investigation.

Serum alters the uptake and biologic activity of CpG oligodeoxynucleotides in B cell chronic lymphocytic leukemia

Immunostimulatory CpG-containing oligodeoxynucleotides (CpG ODN) have a number of effects on B cells, including upregulation of immunogenic molecules, and, therefore, appear attractive as potential components of immunotherapy for B cell chronic lymphocytic leukemia (B-CLL). Previous in vitro studies investigating the effect of CpG ODN on B-CLL cells used serum-low conditions and did not account for the longer-half life of CpG ODN in vitro. The present study was designed to explore how the presence of serum and exposure time affect CpG ODN-mediated changes on B-CLL cells. The optimal concentration for CpG ODN-mediated effects in the presence of 100% serum or plasma was higher (10-20 microg/ml) than for serum-low conditions. Maximal CpG ODN-mediated effects required the presence of ODN for no longer than 3 hours. The inhibition of CpG ODN-mediated effects by serum correlated with lower uptake of ODN into B-CLL cells in the presence of serum. A threshold effect on biologic response was observed, with a given amount of ODN internalized, resulting in phenotypic changes. In conclusion, systemic short-term application of CpG ODN appears to be sufficient to induce phenotypic changes, but higher doses of CpG ODN than previously thought may be necessary because of inhibition of their uptake by serum.

Effects of multiple copies of CpG on DNA vaccination

It has previously been demonstrated that a dose-dependent enhancement of immune response is derived from immunization with several copies of the CpG motif. Following that lead, we sought to incorporate a higher copy number of CpG motifs into an expression construct to evaluate the augmentation of immune responses. By multiple insertions, 30 copies of the CpG motif were cloned into the backbone of an expression construct encoding the foot-and-mouth disease virus (FMDV) capsid protein VP1. After intramuscular immunization, an augmented immune response with significantly increased levels of the specific antibody, T-cell proliferation, and IFN-gamma in Balb/c mice was observed. Compared to chemically synthesized CpG ODN, application of such a multicopy of CpG sequences within the expression backbone for DNA vaccination strategy is feasible and warranted.

CpG-independent synergistic induction of beta-chemokines and a dendritic cell phenotype by orthophosphorothioate oligodeoxynucleotides and granulocyte-macrophage colony-stimulating factor in elutriated human primary monocytes

Chemokines attract leukocytes bearing the relevant chemokine receptors and regulate innate immune responses. CpG oligodeoxynucleotides (ODN) and GM-CSF are potent vaccine adjuvants and in combination induce enhanced Th1 responses by mechanisms yet to be determined. We have examined combinations of CpG- or non-CpG-ODN and GM-CSF for effects on the production of chemokines and the differentiation of monocytes to dendritic cells. High levels of the Th1-attracting, HIV-1-inhibitory chemokines, CCL3/MIP-1alpha and CCL4/MIP-1beta, were induced in human primary monocytes when CpG- or non-CpG-ODN was combined with GM-CSF, but not with IL-4 or IFN-gamma. The synergistic induction of beta-chemokines by non-CpG-ODN was phosphorothioate (PS) chemistry dependent and inhibited by blocking endosome maturation/acidification and ERK1/2 activation. Chemokine and TLR9 mRNAs were induced by PS-ODN. Cells treated with non-CpG PS-ODN and GM-CSF expressed dendritic cell marker CD83 and high levels of HLA-DR and costimulatory molecules, and were CD14(-) or CD14(dim), consistent with monocyte differentiation into a dendritic cell phenotype. The induction of CD83 and beta-chemokines was tyrosine phosphorylation dependent. Secreted CCL3 and CCL4 were detected as a heterodimer. Our results indicate the CpG-independent synergy between PS-ODN and GM-CSF mediated through chemokine and dendritic cell induction. In addition, our observations suggest that PS-ODN plus GM-CSF may be useful as potent ex vivo dendritic cell differentiation/maturation agents for dendritic cell therapy and as vaccine adjuvants for tumor and infectious microorganisms, including HIV-1.

[Cancer immunotherapy with CpG-ODN]

Bacterial DNA and synthetic oligodeoxynucleotides containing CpG motifs (CpG-ODN) are the ligands for the Toll-like receptor 9 (TLR9), which is expressed by B-lymphocytes and a subset of dendritic cells. CpG-ODN are strong activators of both innate and specific immunity, and drive the immune response towards the Th1 phenotype. Given the promising results obtained in several experimental models of allergies or infections, CpG-ODN are now entering clinical trials for these diseases. In cancer, promising approaches combined CpG-ODN with tumor antigens, monoclonal antibodies or dendritic cells. When no relevant tumor antigen is known, CpG-ODN can be used alone to activate locally the innate immunity and trigger a tumor-specific immune response, overcoming the need for the identification of a tumoral antigen. Preclinical models have shown impressive results and several clinical trials are on-going worldwide in melanoma, lymphoma, renal carcinoma, breast cancer and glioblastoma.

Induction of autoantibody production but not autoimmune disease in HEL transgenic mice vaccinated with HEL in combination with CpG or control oligodeoxynucleotides

CpG oligodeoxynucleotides (ODN) are synthetic DNA sequences that mimic bacterial DNA, and bind to the TLR9 receptor. The cells that express TLR9, B cells and dendritic cells, are stimulated by CpG ODN and induce innate and acquired immune responses. Because CpG ODN induce antigen-independent immune activation there has been much interest in the possibility that they may break self tolerance. To test this hypothesis we used a tolerance model with hen egg lysozyme (HEL)-transgenic (Tg) mice, anti-HEL Ig-Tg mice and double (Dbl)-Tg mice injected with CpG ODN alone or together with HEL self antigen. When cultured in vitro, tolerant B cells responded to CpG ODN in a similar way as the non-tolerant Ig-Tg B cells in terms of cell proliferation, NFkappaB activation and CD69 expression. Despite these potent in vitro stimulatory effects of CpG ODN alone, HEL-Tg mice injected with CpG ODN alone, or in combination with low dose antigen (4 microg HEL), surprisingly did not produce any detectable anti-HEL Ab. However, HEL-Tg or Dbl-Tg mice immunized with CpG ODN plus higher doses of self antigen showed strong antigen-specific humoral responses. Surprisingly, control non-CpG ODN also had partial activity for breaking tolerance and inducing autoantibody production when administered in combination with self antigen, though not when used alone. Despite the production of high titers of anti-HEL Ab in the immunized HEL-Tg mice, no evidence of autoimmune disease was detected. We conclude that immunization with CpG or control ODN in the presence of a high dose of exogenous self antigen, but not treatment with ODN alone, can break tolerance to self antigen without inducing autoimmune disease in this system.

CpG DNA and cancer immunotherapy: orchestrating the antitumor immune response

PURPOSE OF REVIEW

Cancer treatment is entering an era of targeted approaches. One such approach is use of the immune system to recognize and eliminate malignant cells. Synthetic CpG oligonucleotides (CpG DNA) are a relatively new class of agents that have the ability to stimulate a potent, orchestrated tumor-specific immune response. This review provides an overview of the immunologic effects of CpG DNA and summarizes the results of preclinical investigations that have led to ongoing development of CpG DNA as a component of clinical cancer immunotherapy.

RECENT FINDINGS

New studies demonstrate that at least three classes of CpG DNA sequences exist, each with different physical characteristics and biologic effects. Preliminary studies in several animal models of cancer suggest that CpG DNA have the ability to induce tumor regression by activating innate immunity, enhancing antibody dependent cellular cytotoxicity, and serving as potent vaccine adjuvants that elicit a specific, protective immune response.

SUMMARY

Animal models suggest that CpG DNA may have many uses in cancer immunotherapy. Early clinical trials suggest that CpG DNA can be administered safely to humans, and studies are ongoing to understand how these agents may play a role in cancer immunotherapy.

Combination immunotherapy with a CpG oligonucleotide (1018 ISS) and rituximab in patients with non-Hodgkin lymphoma: increased interferon-alpha/beta-inducible gene expression, without significant toxicity

CpG oligodeoxynucleotides (CpG-ODNs) affect innate and adaptive immune responses, including antigen presentation, costimulatory molecule expression, dendritic cell maturation, and induction of cytokines enhancing antibody-dependent cell-mediated cytotoxicity (ADCC). We conducted a phase 1 study evaluating 4 dose levels of a CpG-ODN (1018 ISS) with rituximab in 20 patients with relapsed non-Hodgkin lymphoma (NHL). Patients received CpG once a week for 4 weeks beginning after the second of 4 rituximab infusions. Adverse events were minimal. Quantitative polymerase chain reaction (PCR) measurements of a panel of genes inducible by CpG-ODN and interferons were performed on blood samples collected before and 24 hours after CpG. A dose-related increase was measured in the expression of several interferon-inducible genes after CpG and correlated with serum levels of 2'-5' oligoadenylate synthetase (OAS), a validated interferon response marker. Genes induced selectively by interferon-gamma (IFN-gamma) were not significantly induced by CpG. In conclusion, we have defined a set of gene expression markers that provide a sensitive measure of biologic responses of patients to CpG therapy in a dose-related manner. Moreover, all the genes significantly induced by this CpG are regulated by type 1 interferons, providing insight into the dominant immune mechanisms in humans. CpG treatment resulted in no significant toxicity, providing rationale for further testing of this exciting combination immunotherapy approach to NHL.

Multi-subtype gp160 DNA immunization induces broadly neutralizing anti-HIV antibodies

A highly desirable feature for an human immunodeficiency virus type 1 (HIV-1) vaccine is the ability to induce broadly reactive anti-envelope antibodies that can neutralize primary HIV-1 isolates. Two immunizations with an HIV-1 envelope-encoding plasmid together with recombinant granulocyte-macrophage colony-stimulating factor (rGM-CSF) resulted in high antibody titers in mice. The antibody induction was further enhanced after immunization with genes encoding HIV-1 envelopes originating from subtypes A, B and C. The sera from these animals were able to neutralize A, B and C viral isolates, whereas the sera from animals immunized solely with subtype B DNA neutralized only subtype B virus. The combined DNA vaccine gave serum antibodies with broad recognition of HIV-1 envelope epitopes as determined by peptide mapping. Cell-mediated immunity was not compromised by the increased humoral immunity. This demonstrates the ability of multiple envelope genes to induce the desired antibody response against several subtypes. Moreover, it documents the ability of rGM-CSF to enhance the potency of such a vaccine when given simultaneously. The strategy may be useful for making an HIV vaccine more potent and broadly effective against strains of different clades.

Efficacy of cellular vaccines and genetic adjuvants against bacterial kidney disease in chinook salmon (Oncorhynchus tshawytscha)

DNA adjuvants and whole bacterial cell vaccines against bacterial kidney disease (BKD) were tested in juvenile chinook salmon. Whole cell vaccines of either a nonpathogenic Arthrobacter spp. or an attenuated Renibacterium salmoninarum strain provided limited prophylactic protection against acute intraperitoneal challenge with virulent R. salmoninarum, and the addition of either synthetic oligodeoxynucleotides or purified R. salmoninarum genomic DNA as adjuvants did not increase protection. However, a combination of both whole cell vaccines significantly increased survival among fish naturally infected with R. salmoninarum, and the surviving fish treated with the combination vaccine exhibited reduced levels of bacterial antigens in the kidney. This is the first demonstration of a potential therapeutic effect of a whole cell vaccine against BKD.

Antitumor applications of stimulating toll-like receptor 9 with CpG oligodeoxynucleotides

Tumor immunotherapy has evolved from the use of crude bacterial extracts to chemically synthesized ligands for specific immune receptors, such as Toll-like receptors (TLRs). One of the most promising targets for therapeutic immune activation is TLR9, which detects unmethylated CpG dinucleotides present in viral and prokaryotic genomes, which are generally methylated in host DNA. This review describes the immune effects of synthetic CpG oligonucleotides as TLR9 ligands and their applications in cancer immunotherapy.

CpG-containing oligodeoxynucleotide 1826 converts the weak uveitogenic rat interphotoreceptor retinoid-binding protein peptide 1181-1191 into a strong uveitogen

Aberrant activation of autoreactive T cells is one of the major causes of autoimmune disease. Autoantigens are sequestered and in many cases weak immunogens. For example, in experimental autoimmune uveitis, immunization of naive rats with autologous interphotoreceptor retinoid-binding protein (IRBP) fails to induce intraocular inflammation or a strong T cell response, whereas bovine IRBP is a strong inducer of experimental autoimmune uveitis. Such observations challenge the view that the autoantigen alone is responsible for the development of autoimmunity. Here, we demonstrate that autologous rat IRBP is converted to a strong immunogen in the presence of a small dose of CpG-containing oligodeoxynucleotides. Our results indicate that specific CpG-containing oligodeoxynucleotides may play an important role in the activation and expansion of autoreactive T cells in vivo, leading to autoimmune disease.

Immunostimulatory CpG oligodeoxynucleotides and antibody therapy of cancer

Synthetic oligodeoxynucleotides containing CG motifs (CpG ODN) have potent immunostimulatory properties, and have potential as immunotherapeutic agents in cancer. Animal models suggest CpG ODN can activate a variety of immune effector cells such as natural killer (NK) cells, and also enhance the efficacy of tumor immunization when used as immune adjuvants or to directly activate antigen-presenting cells. CpG ODN are also capable of altering the expression of a number of antigens by malignant B-cells, including those targeted by monoclonal antibodies (moAbs) and those involved in communication with T cells. The ability of CpG ODN to activate the immune effector cells that participate in antibody-dependent cellular cytotoxicity (ADCC), upregulate target antigen, and perhaps induce development of an active immune response, suggest these agents may be capable of enhancing the efficacy of antitumor moAb therapy. Such enhanced efficacy has been demonstrated in animal models and is now undergoing evaluation in clinical trials.

CpG motifs: the active ingredient in bacterial extracts?

The use of bacteria and bacterial extracts for immunotherapy has a checkered past. Recent developments in immunology reveal that these nonspecific immune activators actually work by triggering specific receptors that are expressed by subsets of immune cells. Identification of these receptors and the molecular signaling pathways that they activate has enabled a new era of specific targeted immunotherapy using chemically synthesized mimics of pathogen molecules.

Nondisposable materials, chronic inflammation, and adjuvant action

Why inflammatory responses become chronic and how adjuvants work remain unanswered. Macrophage-lineage cells are key components of chronic inflammatory reactions and in the actions of immunologic adjuvants. One explanation for the increased numbers of macrophages long term at sites of chronic inflammation could be enhanced cell survival or even local proliferation. The evidence supporting a unifying hypothesis for one way in which this macrophage survival and proliferation may be promoted is presented. Many materials, often particulate, of which macrophages have difficulty disposing, can promote monocyte/macrophage survival and even proliferation. Materials active in this regard and which can initiate chronic inflammatory reactions include oxidized low-density lipoprotein, inflammatory microcrystals (calcium phosphate, monosodium urate, talc, calcium pyrophosphate), amyloidogenic peptides (amyloid beta and prion protein), and joint implant biomaterials. Additional, similar materials, which have been shown to have adjuvant activity (alum, oil-in-water emulsions, heat-killed bacteria, CpG oligonucleotides, methylated bovine serum albumin, silica), induce similar responses. Cell proliferation can be striking, following uptake of some of the materials, when macrophage-colony stimulating factor is included at low concentrations, which normally promote mainly survival. It is proposed that if such responses were occurring in vivo, there would be a shift in the normal balance between cell survival and cell death, which maintains steady-state, macrophage-lineage numbers in tissues. Thus, there would be more cells in an inflammatory lesion or at a site of adjuvant action with the potential, following activation and/or differentiation, to perpetuate inflammatory or antigen-specific, immune responses, respectively.

Active immunotherapy in follicular lymphoma

The antigen receptors expressed by follicular lymphomas represent tumor-specific antigens ("idiotypes"). In murine models, vaccination with tumor-derived idiotype in a variety of formulations can induce protective lymphoma-specific immunity. Phase II clinical trials in follicular lymphoma have also demonstrated idiotype-specific immune responses. Clinical data from these trials indicate sustained progression-free survival, disappearance of minimal residual disease, and even frank lymphoma regression in some cases. Phase III trials to prove the beneficial effects of active immunotherapy are currently being conducted. Additional research efforts focus on the most efficacious vaccination route and on the development of convenient methods to manufacture individual idiotype vaccines.

CpG oligodeoxynucleotides activate grass carp (Ctenopharyngodon idellus) macrophages

In mice and humans, B cells, antigen-presenting cells including monocytes, macrophages and dendritic cells and natural killer cells can be stimulated directly or indirectly by the bacterial DNA and oligodeoxynucleotides (ODN) containing the CpG motifs (CpG DNA). Using head kidney macrophages of grass carp (Ctenopharyngodon idellus) as an in vitro model, we investigated the effects of several CpG-ODNs on fish immunocytes. The CpG-ODNs included the optimal motifs: the ODN-1826 (GACGTT) and -2006 (GTCGTT) for the mice and humans cells, the ODN-1670 (AACGTT) used in Atlantic salmon, the ODN-D containing two repeats motif of those in 1670 and the ODN-R with an inverted CpG. The results showed that CpG has an immunomodulatory role in grass carp, and all the ODNs except the ODN-R could activate macrophages, increasing the levels of superoxide anion (O(2)(-)), hydrogen peroxide (H(2)O(2)), acid phosphatase and bactericidal activity. New evidence was provided that CpG-ODN could induce the cell-mediated immunity in fish. Interestingly, no significant differences among the ODNs tested could be found and the ODN-D was not more efficient than 1670. It suggests that the sequence which contains the unmethylated 'CG' dinucleotides could make contribute to this immunostimulatory effect. These findings indicate that CpG-ODNs could be useful tools for understanding the important anti-bacterial defense mechanism in fish. And it may have potential application in the minimizing the impact of fish diseases and enhancing the efficacy of antigen and DNA vaccines.

DNA sequences in cationic lipid:pDNA-mediated systemic toxicities

Systemic delivery of synthetic gene transfer vectors such as cationic lipid:plasmid DNA (pDNA) complexes elicits a range of acute physiologic responses, which in the context of therapeutic gene delivery represent dose-limiting toxicities. The most prominent responses are transient leukopenia, thrombocytopenia, serum transaminase elevations, and elevations of proinflammatory cytokines such as interferon-gamma (IFN-gamma), interleukin-12 (IL-12), and tumor necrosis factor-alpha (TNF-alpha). The unmethylated CpG sequences present in plasmid DNA have been implicated as a major cause of the robust cytokine response that follows systemic administration of cationic lipid:pDNA complexes. However, the factors causing the additional significant toxicities (leukopenia, thrombocytopenia, and serum transaminase elevations) recently shown to be associated with vector administration have not been defined. We show here that DNA sequences, such as immune stimulatory CpG sequences, play a significant role in inducing the additional acute toxicities associated with cationic lipid:pDNA complex administration. Importantly, while methylating these CpG sequences results in greatly reduced cytokine levels, this modification does not eliminate their ability to generate the other systemic toxicities. Examples of non-CpG DNA sequences that induce distinct toxicity profiles when administered systemically in the form of cationic lipid:DNA complexes are also identified. Taken together, these results imply that specific DNA sequences are responsible for a significant portion of the systemic toxicities observed after administration of cationic lipid:pDNA complexes.

Peritumoral CpG DNA elicits a coordinated response of CD8 T cells and innate effectors to cure established tumors in a murine colon carcinoma model

The immune system of vertebrates is able to detect bacterial DNA based on the presence of unmethylated CpG motifs. We examined the therapeutic potential of oligodeoxynucleotides with CpG motifs (CpG ODN) in a colon carcinoma model in BALB/c mice. Tumors were induced by s.c. injection of syngeneic C26 cells or Renca kidney cancer cells as a control. Injection of CpG ODN alone or in combination with irradiated tumor cells did not protect mice against subsequent tumor challenge. In contrast, weekly injections of CpG ODN into the margin of already established tumors resulted in regression of tumors and complete cure of mice. The injection site was critical, since injection of CpG ODN at distant sites was not effective. Mice with two bilateral C26 tumors rejected both tumors upon peritumoral injection of one tumor, indicating the development of a systemic immune response. The tumor specificity of the immune response was demonstrated in mice bearing a C26 tumor and a Renca tumor at the same time. Mice that rejected a tumor upon peritumoral CpG treatment remained tumor free and were protected against rechallenge with the same tumor cells, but not with the other tumor, demonstrating long term memory. Tumor-specific CD8 T cells as well as innate effector cells contributed to the antitumor activity of treatment. In conclusion, peritumoral CpG ODN monotherapy elicits a strong CD8 T cell response and innate effector mechanisms that seem to act in concert to overcome unresponsiveness of the immune system toward a growing tumor.

Electrically mediated delivery of vector plasmid DNA elicits an antitumor effect

In vivo electroporation is an efficient means of increasing plasmid DNA delivery to normal tissues, such as skin and muscle, as well as directly to tumors. In the experiments described here, plasmid DNA was delivered by in vivo electroporation to B16 mouse melanomas using two very different pulsing protocols. Reporter expression increased 21- or 42-fold, respectively with electroporation over injection alone. The growth of experimental melanomas with an approximate diameter of 4 mm on the day of treatment was monitored after electroporation delivery of reporter plasmid DNA. Remarkably, short-term complete regressions using one of these pulsing protocols occurred in up to 100% of mice. These regressions continued long term in up to 83% of animals. 70% of these mice were resistant to challenge with B16 melanoma cells. Histological analysis revealed large numbers of apoptotic cells 24 h after treatment. This antitumor effect did not require therapeutic cDNA expression or eukaryotic sequences.

CpG motifs in bacterial DNA and their immune effects

Unmethylated CpG motifs are prevalent in bacterial but not vertebrate genomic DNAs. Oligodeoxynucleotides (ODN) containing CpG motifs activate host defense mechanisms leading to innate and acquired immune responses. The recognition of CpG motifs requires Toll-like receptor (TLR) 9, which triggers alterations in cellular redox balance and the induction of cell signaling pathways including the mitogen activated protein kinases (MAPKs) and NF kappa B. Cells that express TLR-9, which include plasmacytoid dendritic cells (PDCs) and B cells, produce Th1-like proinflammatory cytokines, interferons, and chemokines. Certain CpG motifs (CpG-A) are especially potent at activating NK cells and inducing IFN-alpha production by PDCs, while other motifs (CpG-B) are especially potent B cell activators. CpG-induced activation of innate immunity protects against lethal challenge with a wide variety of pathogens, and has therapeutic activity in murine models of cancer and allergy. CpG ODN also enhance the development of acquired immune responses for prophylactic and therapeutic vaccination.