In Ovo Vaccination with Recombinant Herpes Virus of the Turkey-Laryngotracheitis Vaccine Adjuvanted with CpG-Oligonucleotide Provides Protection against a Viral Challenge in Broiler Chickens

Infectious laryngotracheitis (ILT) is an economically important disease in chickens. We previously showed that an in ovo adjuvantation of recombinant herpesvirus of the turkey-Laryngotracheitis (rHVT-LT) vaccine with CpG-oligonucleotides (ODN) can boost vaccine-induced responses in one-day-old broiler chickens. Here, we evaluated the protective efficacy of in ovo administered rHVT-LT + CpG-ODN vaccination against a wild-type ILT virus (ILTV) challenge at 28 days of age and assessed splenic immune gene expression as well as cellular responses. A chicken-embryo-origin (CEO)-ILT vaccine administered in water at 14 days of age was also used as a comparative control for the protection assessment. The results showed that the rHVT-LT + CpG-ODN or the CEO vaccinations provided significant protection against the ILTV challenge and that the level of protection induced by both the vaccines was statistically similar. The protected birds had a significantly upregulated expression of interferon (IFN)γ or interleukin (IL)-12 cytokine genes. Furthermore, the chickens vaccinated with the rHVT-LT + CpG-ODN or CEO vaccine had a significantly higher frequency of γδ T cells and activated CD4+ or CD8+ T cells, compared to the unvaccinated-ILTV challenge control. Collectively, our findings suggest that CpG-ODN can be used as an effective adjuvant for rHVT-LT in ovo vaccination to induce protective immunity against ILT in broiler chickens.

S-540956, a CpG Oligonucleotide Annealed to a Complementary Strand With an Amphiphilic Chain Unit, Acts as a Potent Cancer Vaccine Adjuvant by Targeting Draining Lymph Nodes

Robust induction of cancer-antigen-specific CD8⁺ T cells is essential for the success of cancer peptide vaccines, which are composed of a peptide derived from a cancer-specific antigen and an immune-potentiating adjuvant, such as a Toll-like receptor (TLR) agonist. Efficient delivery of a vaccine antigen and an adjuvant to antigen-presenting cells in the draining lymph nodes (LNs) holds key to maximize vaccine efficacy. Here, we developed S-540956, a novel TLR9-agonistic adjuvant consisting of B-type CpG ODN2006 (also known as CpG7909), annealed to its complementary sequence oligodeoxynucleotide (ODN) conjugated to a lipid; it could target both a cancer peptide antigen and a CpG-adjuvant in the draining LNs. S-540956 accumulation in the draining LNs and activation of plasmacytoid dendritic cells (pDCs) were significantly higher than that of ODN2006. Mechanistic analysis revealed that S-540956 enhanced the induction of MHC class I peptide-specific CD8⁺ T cell responses via TLR9 in a CD4⁺ T cell-independent manner. In mice, the therapeutic effect of S-540956-adjuvanted with a human papillomavirus (HPV)-E7 peptide vaccine against HPV-E7-expressing TC-1 tumors was significantly better than that of an ODN2006-adjuvanted vaccine. Our findings demonstrate a novel adjuvant discovery with the complementary strand conjugated to a lipid, which enabled draining LN targeting and increased ODN2006 accumulation in draining LNs, thereby enhancing the adjuvant effect. Our findings imply that S-540956 is a promising adjuvant for cancer peptide vaccines and has a high potential for applications in various vaccines, including recombinant protein vaccines.

CpG Oligodeoxynucleotides for Anticancer Monotherapy from Preclinical Stages to Clinical Trials

CpG oligodeoxynucleotides (CpG ODNs), the artificial versions of unmethylated CpG motifs that were originally discovered in bacterial DNA, are demonstrated not only as potent immunoadjuvants but also as anticancer agents by triggering toll-like receptor 9 (TLR9) activation in immune cells. TLR9 activation triggered by CpG ODN has been shown to activate plasmacytoid dendritic cells (pDCs) and cytotoxic T lymphocytes (CTLs), enhancing T cell-mediated antitumor immunity. However, the extent of antitumor immunity carried by TLR agonists has not been optimized individually or in combinations with cancer vaccines, resulting in a decreased preference for TLR agonists as adjuvants in clinical trials. Although various combination therapies involving CpG ODNs have been applied in clinical trials, none of the CpG ODN-based drugs have been approved by the FDA, owing to the short half-life of CpG ODNs in serum that leads to low activation of natural killer cells (NK cells) and CTLs, along with increases of pro-inflammatory cytokine productions. This review summarized the current innovation on CpG ODNs that are under clinical investigation and explored the future direction for CpG ODN-based nanomedicine as an anticancer monotherapy.

Improved Functionality of Exhausted Intrahepatic CXCR5+ CD8+ T Cells Contributes to Chronic Antigen Clearance Upon Immunomodulation

Chronic hepatotropic viral infections are characterized by exhausted CD8+ T cells in the presence of cognate antigen in the liver. The impairment of T cell response limits the control of chronic hepatotropic viruses. Immune-modulatory strategies are attractive options to re-invigorate exhausted T cells. However, in hepatotropic viral infections, the knowledge about immune-modulatory effects on the in-situ regulation of exhausted intrahepatic CD8+ T cells is limited. In this study, we elucidated the functional heterogeneity in the pool of exhausted CD8+ T cells in the liver of mice expressing the model antigen Ova in a fraction of hepatocytes. We found a subpopulation of intrahepatic CXCR5+ Ova-specific CD8+ T cells, which are profoundly cytotoxic, exhibiting efficient metabolic functions as well as improved memory recall and self-maintenance. The intrahepatic Ova-specific CXCR5+ CD8+ T cells are possibly tissue resident cells, which may rely largely on OXPHOS and glycolysis to fuel their cellular processes. Importantly, host conditioning with CpG oligonucleotide reinvigorates and promotes exhausted T cell expansion, facilitating complete antigen eradication. The CpG oligonucleotide-mediated reinvigoration may support resident memory T cell formation and the maintenance of CXCR5+ Ova-specific CD8+ T cells in the liver. These findings suggest that CpG oligodinucleotide may preferentially target CXCR5+ CD8+ T cells for expansion to facilitate the revival of exhausted T cells. Thus, therapeutic strategies aiming to expand CXCR5+ CD8+ T cells might provide a novel approach against chronic liver infection.

Nanoparticle System Based on Amino-Dextran as a Drug Delivery Vehicle: Immune-Stimulatory CpG-Oligonucleotide Loading and Delivery

The aim of this study is to prepare and characterize an amino-dextran nanoparticle (aDNP) platform and investigate two loading strategies for unmethylated cytosine-phosphate-guanine (CpG) oligonucleotide. aDNP was prepared by desolvation of amino-dextran followed by the chemical crosslinking of amino groups. Size, surface charge, and surface morphology of aDNP was determined by dynamic light scattering and transmission electron microscopy. CpG was either loaded onto aDNP by adsorption (CpG-adsorbed-aDNP) or conjugated to aDNP (CpG-conjugated-aDNP). In vitro cytokine production by bone marrow-derived dendritic cells (BMDCs) was measured by flow cytometry. aDNPs size and zeta potential could be controlled to produce uniform particles in the size range of 50 to 300 nm, surface charge of −16.5 to +14 mV, and were spherical in shape. Formulation control parameters investigated included the anti-solvent, water-to-anti-solvent ratio, level of amine functionality of dextran, and the molar ratio of glutaraldehyde to amine. aDNP could be lyophilized without additional cryoprotectant. Unloaded cationic aDNP (+13 mV) showed acceptable in vitro hemolysis. Unloaded and CpG-loaded aDNPs showed no cytotoxicity on BMDCs. CpG-loaded nanoparticles stimulated cytokine production by BMDCs, the level of cytokine production was higher for CpG-conjugated-aDNP compared to CpG-absorbed-aDNP. aDNP is a promising new drug delivery platform as its offers versatility in loading and tuning of particle properties.

Short-term and longer-term protective immune responses generated by subunit vaccination with smallpox A33, B5, L1 or A27 proteins adjuvanted with aluminum hydroxide and CpG in mice challenged with vaccinia virus

Smallpox, a contagious and deadly disease caused by variola virus, was eradicated by a strategy that included vaccination with vaccinia virus, a live-virus vaccine. Because the threat of bioterrorism with smallpox persists and infections with zoonotic poxvirus infections like monkeypox continue, and there may be a time when an alternative vaccine platform is needed, recombinant-subunit vaccine strategies for poxviruses have been pursued. Our prior work focused on understanding the immune responses generated to vaccine-formulations containing the virus protein L1. In this work, we examine vaccine-formulations with additional key protein targets: A33 and B5 (components of the extracellular virus) and another protein on the mature virus (A27) adjuvanted with aluminum hydroxide (AH) with and without CpG- oligonucleotide. Each vaccine was formulated to allow either adsorption or non-adsorption of the protein (and CpG) to AH. Mice given a prime and single boost produced long-lasting antibody responses. A second boost (given ~5-months after the first) further increased antibody titers. Similar to our prior findings with L1 vaccine-formulations, the most protective A33 vaccine-formulations included CpG, resulted in the generation of IgG2a-antibody responses. Unlike the prior findings with L1 (where formulations that adsorbed both the protein and the CpG to AH resulted in 100% survival after challenge and minimal weight loss), the AH-adsorption status of A33 and CpG did not play as important a role, since both AH-adsorbed and non-adsorbed groups lost weight after challenge and had similar survival. Vaccination with B5-formulations gave different results. While CpG-containing formulations were the only ones that generated IgG2a-antibody responses, the vaccine-formulation that adsorbed B5 to AH (without CpG) was as equally effective in protecting mice after challenge. These results indicate that the mechanism of how antibodies against A33 and B5 protect differ. The data also show the complexity of designing optimized vaccine-formulations containing multiple adjuvants and recombinant protein-based antigens.

Nanotechnology-Based Vaccines for Allergen-Specific Immunotherapy: Potentials and Challenges of Conventional and Novel Adjuvants under Research

The increasing prevalence of allergic diseases demands efficient therapeutic strategies for their mitigation. Allergen-specific immunotherapy (AIT) is the only causal rather than symptomatic treatment method available for allergy. Currently, AIT is being administered using immune response modifiers or adjuvants. Adjuvants aid in the induction of a vigorous and long-lasting immune response, thereby improving the efficiency of AIT. The successful development of a novel adjuvant requires a thorough understanding of the conventional and novel adjuvants under development. Thus, this review discusses the potentials and challenges of these adjuvants and their mechanism of action. Vaccine development based on nanoparticles is a promising strategy for AIT, due to their inherent physicochemical properties, along with their ease of production and ability to stimulate innate immunity. Although nanoparticles have provided promising results as an adjuvant for AIT in in vivo studies, a deeper insight into the interaction of nanoparticle-allergen complexes with the immune system is necessary. This review focuses on the methods of harnessing the adjuvant effect of nanoparticles by detailing the molecular mechanisms underlying the immune response, which includes allergen uptake, processing, presentation, and induction of T cell differentiation.

CD93 is a cell surface lectin receptor involved in the control of the inflammatory response stimulated by exogenous DNA

Bacterial DNA contains CpG oligonucleotide (ODN) motifs to trigger innate immune responses through the endosomal receptor Toll-like receptor 9 (TLR9). One of the cell surface receptors to capture and deliver microbial DNA to intracellular TLR9 is the C-type lectin molecule DEC-205 through its N-terminal C-type lectin-like domain (CTLD). CD93 is a cell surface protein and member of the lectin group XIV with a CTLD. We hypothesized that CD93 could interact with CpG motifs, and possibly serve as a novel receptor to deliver bacterial DNA to endosomal TLR9. Using ELISA and tryptophan fluorescence binding studies we observed that the soluble histidine-tagged CD93-CTLD was specifically binding to CpG ODN and bacterial DNA. Moreover, we found that CpG ODN could bind to CD93-expressing IMR32 neuroblastoma cells and induced more robust interleukin-6 secretion when compared with mock-transfected IMR32 control cells. Our data argue for a possible contribution of CD93 to control cell responsiveness to bacterial DNA in a manner reminiscent of DEC-205. We postulate that CD93 may act as a receptor at plasma membrane for DNA or CpG ODN and to grant delivery to endosomal TLR9.

Synthetic CpG oligonucleotides as potential modulators of neutrophil survival in PAMP-associated inhibition of apoptosis

We studied the effects of a synthetic CpG oligonucleotide (CpG ODN2006) on polymorphonuclear leukocyte (PMNL, neutrophil) survival and oxidant status. CpG ODN2006 showed a dose-dependent effect on the apoptosis of resting neutrophils. Without affecting the viability of resting cells, low concentrations of CpG ODN2006 interfered with Salmonella typhimurium-mediated viability prolongation and increased neutrophil apoptosis to control levels. CpG ODN2006 stimulated neutrophil apoptosis by enhancing ROS generation. Even small doses of ODN could induce the production of intracellular superoxide anions. The high superoxide reactogenicity, including with respect to nitrogen oxide, led to increased levels of intracellular ROS and RNS, which ultimately caused apoptosis. The pro-oxidant effect of low concentrations of CpG ODN2006 was not sufficient to trigger irreversible pro-apoptotic mechanisms. However, the sensitivity of PMNLs to ODN2006, a modulator of apoptosis, increased significantly under conditions of infectious inflammation. Inactivated S. typhimurium proved to be suitable for simulating inflammatory conditions in vitro.

The In Ovo Delivery of CpG Oligonucleotides Protects against Infectious Bronchitis with the Recruitment of Immune Cells into the Respiratory Tract of Chickens

The in ovo delivery of cytosine-guanosine (CpG) oligodeoxynucleotides (ODNs) protects chickens against many bacterial and viral infections, by activating the toll-like receptor (TLR)21 signaling pathway. Although the delivery of CpG ODNs in ovo at embryo day (ED) 18 has been shown to reduce infectious bronchitis virus (IBV) loads in embryonic chicken lungs pre-hatch, whether in ovo delivered CpG ODNs are capable of protecting chickens against a post-hatch challenge is unknown. Thus, our objectives were to determine the protective effect of the in ovo delivery of CpG ODNs at ED 18 against IBV infection encountered post-hatch and, then, to investigate the mechanisms of protection. We found significantly higher survival rates and reduced IBV infection in the chickens following the pre-treatment of the ED 18 eggs with CpG ODNs. At 3 days post infection (dpi), we found an increased recruitment of macrophages, cluster of differentiation (CD)8α+ and CD4+ T lymphocytes, and an up-regulation of interferon (IFN)-γ mRNA in the respiratory tract of the chickens. Overall, it may be inferred that CpG ODNs, when delivered in ovo, provide protection against IBV infection induced morbidity and mortality with an enhanced immune response.

Synthetic CpG oligonucleotides induce a genetic profile ameliorating murine myocardial I/R injury

We previously demonstrated that pre‐conditioning with CpG oligonucleotide (ODN) 1668 induces quick up‐regulation of gene expression 3 hours post‐murine myocardial ischaemia/reperfusion (I/R) injury, terminating inflammatory processes that sustain I/R injury. Now, performing comprehensive microarray and biocomputational analyses, we sought to further enlighten the “black box” beyond these first 3 hours. C57BL/6 mice were pretreated with either CpG 1668 or with control ODN 1612, respectively. Sixteen hours later, myocardial ischaemia was induced for 1 hour in a closed‐chest model, followed by reperfusion for 24 hours. RNA was extracted from hearts, and labelled cDNA was hybridized to gene microarrays. Data analysis was performed with BRB ArrayTools and Ingenuity Pathway Analysis. Functional groups mediating restoration of cellular integrity were among the top up‐regulated categories. Genes known to influence cardiomyocyte survival were strongly induced 24 hours post‐I/R. In contrast, proinflammatory pathways were down‐regulated. Interleukin‐10, an upstream regulator, suppressed specifically selected proinflammatory target genes at 24 hours compared to 3 hours post‐I/R. The IL1 complex is supposed to be one regulator of a network increasing cardiovascular angiogenesis. The up‐regulation of numerous protective pathways and the suppression of proinflammatory activity are supposed to be the genetic correlate of the cardioprotective effects of CpG 1668 pre‐conditioning.

Structure, mechanism and therapeutic utility of immunosuppressive oligonucleotides

Synthetic oligodeoxynucleotides that can down-regulate cellular elements of the immune system have been developed and are being widely studied in preclinical models. These agents vary in sequence, mechanism of action, and cellular target(s) but share the ability to suppress a plethora of inflammatory responses. This work reviews the types of immunosuppressive oligodeoxynucleotide (Sup ODN) and compares their therapeutic activity against diseases characterized by pathologic levels of immune stimulation ranging from autoimmunity to septic shock to cancer (see graphical abstract). The mechanism(s) underlying the efficacy of Sup ODN and the influence size, sequence and nucleotide backbone on function are considered.

IRF5 and IRF8 modulate the CAL-1 human plasmacytoid dendritic cell line response following TLR9 ligation

Synthetic oligonucleotides (ODNs) containing CpG motifs stimulate human plasmacytoid dendritic cells (pDCs) to produce type-1 interferons (IFNs) and proinflammatory cytokines. Previous studies demonstrated that interferon regulatory factors (IRFs) play a central role in mediating CpG-induced pDC activation. This work explores the inverse effects of IRF5 and IRF8 (also known as IFN consensus sequence-binding protein) on CpG-dependent gene expression in the human CAL-1 pDC cell line. This cell line shares many of the phenotypic and functional properties of freshly isolated human pDCs. Results from RNA interference and microarray studies indicate that IRF5 upregulates TLR9-driven gene expression whereas IRF8 downregulates the same genes. Several findings support the conclusion that IRF8 inhibits TLR9-dependent gene expression by directly blocking the activity of IRF5. First, the inhibitory activity of IRF8 is only observed when IRF5 is present. Second, proximity ligation analysis shows that IRF8 and IRF5 colocalize within the cytoplasm of resting human pDCs and cotranslocate to the nucleus after CpG stimulation. Taken together, these findings suggest that IRF5 and IRF8, two transcription factors with opposing functions, control TLR9 signaling in human pDCs.

The stimulatory effect of different CpG oligonucleotides on the maturation of chicken bone marrow-derived dendritic cells

CpG oligonucleotide (CpG-ODN) can exert an immunostimulatory effect on different types of immune cells such as dendritic cells (DC). The immunostimulatory activity of CpG-ODN is closely related to its nucleotide sequence and structural characteristics. In this study, we aimed at evaluating the stimulatory effects of different CpG-ODN on the maturation of chicken bone marrow-derived DC (BM-DC) in vitro. First, 4 CpG-ODN were designed. Then chicken bone marrow cells were extracted from tibia and femur and cultured in the RPMI 1640 medium with recombinant chicken granulocyte-macrophage colony-stimulating factor (GM-CSF) and IL-4. After culture for 6 d, the cells were stimulated by different CpG-ODN or lipopolysaccharide for 24 h. Finally, the effects of different CpG-ODN on the maturation of chicken BM-DC were investigated by morphologic, phenotypic, and functional assays. The results showed that the cultured cells could display the typical DC morphology, and the CpG-ODN could efficiently stimulate the BM-DC to show the mature morphologic characteristics and upregulate the expression of cluster of differentiation (CD) 40 and CD86 molecules. In addition, after stimulation by CpG-ODN, the BM-DC could significantly induce T-cell proliferative response (P < 0.01). Among all the sequences, the stimulatory effect of CpG-ODN F3 with an addition of poly-guanosine strings at the 3' end was the best on the chicken BM-DC. In conclusion, this is the first report to demonstrate that different CpG-ODN have distinct stimulatory effects on the maturation of chicken BM-DC and CpG-ODN F3 with the best stimulatory effect can be a potent stimulant for the maturation of chicken BM-DC.

Modulation of antibody responses against Gnathostoma spinigerum in mice immunized with crude antigen formulated in CpG oligonucleotide and montanide ISA720

This study aimed to investigate the antibody responses in mice immunized with Gnathostoma spinigerum crude antigen (GsAg) incorporated with the combined adjuvant, a synthetic oligonucleotide containing unmethylated CpG motif (CpG ODN 1826) and a stable water in oil emulsion (Montanide ISA720). Mice immunized with GsAg and combined adjuvant produced all antibody classes and subclasses to GsAg except IgA. IgG2a/2b/3 but not IgG1 subclasses were enhanced by immunization with CpG ODN 1826 when compared with the control groups immunized with non-CpG ODN and Montanide ISA or only with Montanide ISA, suggesting a biased induction of a Th1-type response by CpG ODN. After challenge infection with live G. spinigerum larvae, the levels of IgG2a/2b/3 antibody subclasses decreased immediately and continuously, while the IgG1 subclass remained at high levels. This also corresponded to a continuous decrease of the IgG2a/IgG1 ratio after infection. Only IgM and IgG1 antibodies, but not IgG2a/2b/3, were significantly produced in adjuvant control groups after infection. These findings suggest that G. spinigerum infection potently induces a Th2-type biased response.

IRF-5 and NF-κB p50 co-regulate IFN-β and IL-6 expression in TLR9-stimulated human plasmacytoid dendritic cells

Synthetic oligonucleotides (ODN) expressing CpG motifs mimic the ability of bacterial DNA to trigger the innate immune system via TLR9. Plasmacytoid dendritic cells (pDCs) make a critical contribution to the ensuing immune response. This work examines the induction of antiviral (IFN-β) and pro-inflammatory (IL-6) cytokines by CpG-stimulated human pDCs and the human CAL-1 pDC cell line. Results show that interferon regulatory factor-5 (IRF-5) and NF-κB p50 are key co-regulators of IFN-β and IL-6 expression following TLR9-mediated activation of human pDCs. The nuclear accumulation of IRF-1 was also observed, but this was a late event that was dependant on type 1 IFN and unrelated to the initiation of gene expression. IRF-8 was identified as a novel negative regulator of gene activation in CpG-stimulated pDCs. As variants of IRF-5 and IRF-8 were recently found to correlate with susceptibility to certain autoimmune diseases, these findings are relevant to our understanding of the pharmacologic effects of "K" ODN and the role of TLR9 ligation under physiologic, pathologic, and therapeutic conditions.