Development of Nonaggregating Poly-A Tailed Immunostimulatory A/D Type CpG Oligodeoxynucleotides Applicable for Clinical Use

Exploiting bacterial-origin immunostimulants for improved vaccination and immunotherapy: current insights and future directions

Vaccination is a valid strategy to prevent and control newly emerging and reemerging infectious diseases in humans and animals. However, synthetic and recombinant antigens are poor immunogenic to stimulate efficient and protective host immune response. Immunostimulants are indispensable factors of vaccines, which can promote to trigger fast, robust, and long-lasting immune responses. Importantly, immunotherapy with immunostimulants is increasing proved to be an effective and promising treatment of cancer, which could enhance the function of the immune system against tumor cells. Pattern recognition receptors (PRRs) play vital roles in inflammation and are central to innate and adaptive immune responses. Toll-like receptors (TLRs)-targeting immunostimulants have become one of the hotspots in adjuvant research and cancer therapy. Bacterial-origin immunoreactive molecules are usually the ligands of PRRs, which could be fast recognized by PRRs and activate immune response to eliminate pathogens. Varieties of bacterial immunoreactive molecules and bacterial component-mimicking molecules have been successfully used in vaccines and clinical therapy so far. This work provides a comprehensive review of the development, current state, mechanisms, and applications of bacterial-origin immunostimulants. The exploration of bacterial immunoreactive molecules, along with their corresponding mechanisms, holds immense significance in deepening our understanding of bacterial pathogenicity and in the development of promising immunostimulants.

Control of A/D type CpG-ODN aggregates to a suitable size for induction of strong immunostimulant activity

Among several types of CpG-ODNs, A/D-type CpG-ODNs have potent adjuvant activity to induce Th-1 immune responses, but exhibit a propensity to aggregate. For the clinical application of A/D-type CpG-ODNs, it is necessary to control such aggregation and obtain a comprehensive understanding of the relationship between their structure and the immune responses. This study revealed that a representative A/D-type CpG ODN, D35, adopted a single-stranded structure in water, while it assembled into aggregates in response to Na+ ions. From polyacrylamide gel electrophoresis and circular dichroism analyses, D35 adopted a homodimeric form (duplex) via palindromic sequences in low-Na+-concentration conditions (10-50 mM NaCl). After replacement of the solution with PBS, quadruplexes began to form in a manner coordinated by Na+, resulting in large aggregates. The duplexes and small aggregates prepared in 50 mM NaCl showed not only high cellular uptake but also high affinity to Toll-like receptor 9 (TLR9) proteins, leading to the production of a large amount of interferon-α for peripheral blood mononuclear cells. The much larger aggregates prepared in 100 mM NaCl were incorporated into cells at a high level, but showed a low ability to induce cytokine production. This suggests that the large aggregates have difficulty inducing TLR9 dimerization, resulting in loss of the stimulation of the cells. We thus succeeded in inducing adequate innate immunity in vitro by controlling and adjusting the formation of D35 aggregates. Therefore, the findings in this study for D35 ODNs could be a vital research foundation for in vivo applications.

Screening of Optimal CpG-Oligodeoxynucleotide for Anti-Inflammatory Responses in the Avian Macrophage Cell Line HD11

CpG-oligodeoxynucleotides (.

CpG-ODNs

) have been shown to possess immunostimulatory features in both mammals and birds. However, compared to their proinflammatory effects, little is known about the anti-inflammatory responses triggered by CpG-ODN in avian cells. Hence, in this study, the anti-inflammatory response in the chicken macrophage cell line HD11 was characterized under stimulation with five types of CpG-ODNs: CpG-A₁₅₈₅, CpG-A_D35, CpG-B₁₅₅₅, CpG-B_K3, and CpG-C₂₃₉₅. Single-stimulus of CpG-B₁₅₅₅, CpG-B_K3, or CpG-C₂₃₉₅ induced interleukin (IL)-10 expression without causing cell injury. The effects of pretreatment with CpG-ODNs before subsequent lipopolysaccharide stimulation were also evaluated. Interestingly, pretreatment with only CpG-C₂₃₉₅ resulted in high expression levels of IL-10 mRNA in the presence of lipopolysaccharide. Finally, gene expression analysis of inflammation-related cytokines and receptors revealed that pre-treatment with CpG-C₂₃₉₅ significantly reduced the mRNA expression of tumor necrosis factor-α, IL-1β, IL-6, and Toll-like receptor 4. Overall, these results shed light on the anti-inflammatory responses triggered by CpG-C₂₃₉₅ stimulation through a comparative analysis of five types of CpG-ODNs in chicken macrophages. These results also offer insights into the use of CpG-ODNs to suppress the expression of proinflammatory cytokines, which may be valuable in the prevention of avian infectious diseases in the poultry industry.

Binding assay of human Dectin-1 variants for DNA/ β-glucan complex for active-targeting delivery of antisense DNA: Part II

A β-1,3-glucan binding receptor called Dectin-1 is mainly expressed on antigen-presenting immunocytes. Dectin-1 may be a target molecule for receptor-mediated and active-targeting delivery of drugs to regulate or interfere with the immune system. Therapeutic oligonucleotides are one such drug of interest. To this end, we have been studying the complex of schizophyllan (SPG, one of the linear (1,3)-β-ᴅ-glucan family) with oligonucleotide and its delivery mechanism to the Dectin-1 expressing cells. There are at least six types of human Dectin-1 expressed on the cell surface (designated V-1, V-2, etc.), with V-1 having a complete carbohydrate recognition domain (CRD) and stalk, V-2 having a complete CRD but no stalk, and other variants having an incomplete CRD due to exon skipping. Our previous studies have shown that SPG binds only to V-1 and V-2. By contrast, SPG/oligonucleotide complexes bind both V-1 and V-2 more strongly than SPG itself and show a certain affinity, for other variants. As a continuing work, the present paper discusses the structure and nature of all human Dectin-1 variants expressed on the cellular surface. we found that (1) a new N-linked glycosylation site is present in some variants, (2) the glycosylation of Dectin-1 plays an important role in the fate of Dectin-1 and its localization in the cells, and (3) the glycosylation is related to the amount of ingestion of the complex. The present findings suggest that, in addition to V-1 and V-2, two other variants that are highly expressed at the plasma membrane and stabilized by the glycosylation may also be targets of the complex.

Development of combination adjuvant for efficient T cell and antibody response induction against protein antigen

Most current clinical vaccines work primarily by inducing the production of neutralizing antibodies against pathogens. Vaccine adjuvants that efficiently induce T cell responses to protein antigens need to be developed. In this study, we developed a new combination adjuvant consisting of 1,2-dioleoyl-3-trimethylammonium propane (DOTAP), D35, and an aluminum salt. Among the various combinations tested, the DOTAP/D35/aluminum salt adjuvant induced strong T cell and antibody responses against the model protein antigen with a single immunization. Adjuvant component and model antigen interaction studies in vitro also revealed that the strong mutual interactions among protein antigens and other components were one of the important factors for this efficient immune induction by the novel combination adjuvant. In addition, in vivo imaging of the antigen distribution suggested that the DOTAP component in the combination adjuvant formulation elicited transient antigen accumulation at the draining lymph nodes, possibly by antigen uptake DC migration. These results indicate the potential of the new combination adjuvant as a promising vaccine adjuvant candidate to treat infectious diseases and cancers.

Comprehensive Screening of Mouse T-Cell Epitopes in Human Herpesvirus 6B Glycoprotein H/L/Q1/Q2 Tetramer Complex

Human herpesvirus 6 (HHV-6) infects over 90% of people. The HHV-6 subtype, HHV-6B in particular, is often associated with exanthem subitum in early childhood. Exanthem subitum is usually self-limiting and good prognosis disease; however, some infants primarily infected with HHV-6B develop encephalitis/encephalopathy, and half of the patients developed encephalopathy reported to have neurological sequelae. Furthermore, after primary infection, HHV-6B remains in a latent state and sometimes reactivated in immunosuppressed patients, causing life-threatening severe encephalopathy. However, effective immunotherapies or vaccines for controlling HHV-6B infection and reactivation have not yet been established. Recently, we have found that the HHV-6B tetrameric glycoprotein (g) complex, gH/gL/gQ1/gQ2 is a promising vaccine candidate, and currently under preclinical development. To confirm our vaccine candidate protein complex induce detectable T-cell responses, in this study, we comprehensively screened CD4⁺ and CD8⁺ T-cell epitopes in the gH/gL/gQ1/gQ2 tetrameric complex protein in mice immunisation model. Both BALB/c and C57BL/6 mice were immunised with the tetrameric complex protein or plasmid DNA encoding gH, gL, gQ1, and gQ2, and then restimulated with 162 20-mer peptides covering the whole gH/gL/gQ1/gQ2 sequences; multiple CD4⁺ and CD8⁺ T-cell-stimulating peptides were identified in both BALB/c and C57BL/6 mice. Our study demonstrates that gH/gL/gQ1/gQ2 tetramer-targeted vaccination has potential to induce T-cell responses in two different strains of mice and supports the future development and application of T-cell-inducing vaccine and immunotherapies against HHV-6B.

Tetrameric glycoprotein complex gH/gL/gQ1/gQ2 is a promising vaccine candidate for human herpesvirus 6B

Primary infection of human herpesvirus 6B (HHV-6B) occurs in infants after the decline of maternal immunity and causes exanthema subitum accompanied by a high fever, and it occasionally develops into encephalitis resulting in neurological sequelae. There is no effective prophylaxis for HHV-6B, and its development is urgently needed. The glycoprotein complex gH/gL/gQ1/gQ2 (called 'tetramer of HHV-6B') on the virion surface is a viral ligand for its cellular receptor human CD134, and their interaction is thus essential for virus entry into the cells. Herein we examined the potency of the tetramer as a vaccine candidate against HHV-6B. We designed a soluble form of the tetramer by replacing the transmembrane domain of gH with a cleavable tag, and the tetramer was expressed by a mammalian cell expression system. The expressed recombinant tetramer is capable of binding to hCD134. The tetramer was purified to homogeneity and then administered to mice with aluminum hydrogel adjuvant and/or CpG oligodeoxynucleotide adjuvant. After several immunizations, humoral and cellular immunity for HHV-6B was induced in the mice. These results suggest that the tetramer together with an adjuvant could be a promising candidate HHV-6B vaccine.

Human herpesvirus 6B (HHV-6B) is known as the cause of the common childhood febrile illness exanthem subitum in its primary infection, and it develops into a lifelong latent infection in almost all individuals. Severe complications such as meningitis and encephalitis can occur in both the primary infection and reactivation. There is no established treatment or vaccine. The tetrameric glycoprotein complex gH/gL/gQ1/gQ2 (tetramer) on the viral envelope is the ligand for the entry of HHV-6B, which is the critical part for its infection. Here, we established a soluble form of the tetramer and purified it to homogeneity. After several immunizations of tetramer along with different combinations of adjuvants in mice, we observed that it greatly induced defensive immunity against HHV-6B, indicating that the tetramer has the potential to become a vaccine candidate. Moreover, our results also revealed that combinations of distinct adjuvants with the tetramer would be useful as an HHV-6B vaccine strategy for different purposes.

Lipid nanoparticles of Type-A CpG D35 suppress tumor growth by changing tumor immune-microenvironment and activate CD8 T cells in mice

Type-A CpG oligodeoxynucleotides (ODNs), which have a natural phosphodiester backbone, is one of the highest IFN-α inducer from plasmacytoid dendritic cells (pDC) via Toll-like receptor 9 (TLR9)-dependent signaling. However, the in vivo application of Type-A CpG has been limited because the rapid degradation in vivo results in relatively weak biological effect compared to other Type-B, -C, and -P CpG ODNs, which have nuclease-resistant phosphorothioate backbones. To overcome this limitation, we developed lipid nanoparticles formulation containing a Type-A CpG ODN, D35 (D35LNP). When tested in a mouse tumor model, intratumoral and intravenous D35LNP administration significantly suppressed tumor growth in a CD8 T cell-dependent manner, whereas original D35 showed no efficacy. Tumor suppression was associated with Th1-related gene induction and activation of CD8 T cells in the tumor. The combination of D35LNP and an anti-PD-1 antibody increased the therapeutic efficacy. Importantly, the therapeutic schedule and dose of intravenous D35LNP did not induce apparent liver toxicity. These results suggested that D35LNP is a safe and effective immunostimulatory drug formulation for cancer immunotherapy.

Adjuvant Activity Enhanced by Cross-Linked CpG-Oligonucleotides in β-Glucan Nanogel and Its Antitumor Effect

Cancer vaccine has the ability to directly eradicate tumor cells by creating and activating cytotoxic T lymphocytes (CTLs). To achieve efficient CTL activity and to induce Th1 responses, it is essential to administer an appropriate adjuvant as well as an antigen. CpG-ODN is known as a ligand of Toll-like receptor 9 (TLR9) and strongly induces Th1 responses. In our previous study, we developed a CpG-ODN delivery system by use of the formation of complexes between ODN and a β-glucan SPG, denoted as CpG/SPG, and demonstrated that CpG/SPG induces high Th1 responses. In this study, we created a nanogel made from CpG/SPG complexes through DNA-DNA hybridization (cross-linked (CL)-CpG). Immunization with CL-CpG induced much stronger antigen-specific Th1 responses in combination with the antigenic protein ovalbumin (OVA) than that with CpG/SPG. Mice preimmunized with CL-CpG and OVA exhibited a long delay in tumor growth and an improved survival rate after tumor inoculation. These immune inductions can be attributed to the improvement of cellular uptake by the combination of increased size and the cluster effect of the β-glucan recognition site in the nanogel structure. In other words, the particle nature of CL-CpG, instead of the semiflexible rod conformation of CpG/SPG, enhanced the efficacy of a cancer vaccine. The present results indicate that CL-CpG can be used as a potent vaccine adjuvant for the treatment of cancers and infectious diseases.