Synergistic Stimulation with Different TLR7 Ligands Modulates Gene Expression Patterns in the Human Plasmacytoid Dendritic Cell Line CAL-1

Protective Efficacy of a Novel DNA Vaccine with a CL264 Molecular Adjuvant against Toxoplasma gondii in a Murine Model

Toxoplasmosis is a significant global zoonosis with devastating impacts, and an effective vaccine against toxoplasmosis for humans has not yet been developed. In this study, we designed and formulated a novel DNA vaccine encoding the inhibitor of STAT1 transcriptional activity (IST) of T. gondii utilizing the eukaryotic expression vector pEGFP-N1 for the first time, with CL264 being a molecular adjuvant. Following intramuscular injection of the vaccine into mice, the levels of antibodies and cytokines were assessed to evaluate the immune response. Additionally, mice were challenged with highly virulent RH-strain tachyzoites of T. gondii, and their survival time was observed. The results show that the levels of IgG in serum, the ratio of IgG2a/IgG1 and the levels of IFN-γ in splenocytes of mice were significantly higher in the pEGFP-TgIST group and the pEGFP-TgIST + CL264 group than in the control group. In addition, the proportion of CD4+/CD8+ T cells was higher in mice immunized with either the pEGFP-TgIST group (p < 0.001) or the pEGFP-TgIST + CL264 group (p < 0.05) compared to the three control groups. Notably, TgIST-immunized mice exhibited prolonged survival times after T. gondii RH strain infection (p < 0.05). Our findings collectively demonstrate that the TgIST DNA vaccine elicits a significant humoral and cellular immune response and offers partial protection against acute T. gondii infection in the immunized mice, which suggests that TgIST holds potential as a candidate for further development as a DNA vaccine.

TLR7 agonist loaded airway epithelial targeting nanoparticles stimulate innate immunity and suppress viral replication in human bronchial epithelial cells

Nanoparticle-based delivery is a strategy for increasing the therapeutic window of inhaled immunomodulatory drugs that have inflammatory activity. TLR7 agonists are a class of immunomodulators that have been considered for the treatment of virus-induced respiratory diseases. However, due to high immune-stimulatory activity, TLR7 agonists, delivered via direct exposure, generally have a narrow therapeutic window. To address this, we have developed lipid/polymer hybrid nanoparticles (NPs) conjugated with anti-EpCAM monoclonal antibody for targeted delivery of TLR7 agonist (CL264) to airway epithelial cells (AECs)² - the primary site of respiratory virus infection. These airway epithelial targeting nanoparticles (AEC-NPs)³ showed safety and biocompatibility, and approximately two-fold increased cellular uptake compared to non-targeting NPs. Upon cell entry, AEC-NPs were able to deliver CL264 to cytoplasm and endosomes where TLR7 is located. CL264 delivered by AEC-NPs significantly increased innate immune response through expression of IFN-β, IFN-λ 2/3 and IFN-stimulated genes and suppressed more than 92% of viral load at 48 hours post-infection compared to the drug alone and non-targeting NPs. In conclusion, AEC-NPs exhibited increased cellular uptake leading to enhanced innate immune activation and suppression of viral replication. These findings support the use of AEC-targeting approach for delivering drugs with a narrow therapeutic window.

Myeloid cell nuclear differentiation antigen controls the pathogen-stimulated type I interferon cascade in human monocytes by transcriptional regulation of IRF7

Type I interferons (IFNs) are critical for anti-viral responses, and also drive autoimmunity when dysregulated. Upon viral sensing, monocytes elicit a sequential cascade of IFNβ and IFNα production involving feedback amplification, but how exactly this cascade is regulated in human cells is incompletely understood. Here we show that the PYHIN protein myeloid cell nuclear differentiation antigen (MNDA) is required for IFNα induction in monocytes. Unlike other PYHINs, this is not due to a pathogen sensing role, but rather MNDA regulated expression of IRF7, a transcription factor essential for IFNα induction. Mechanistically, MNDA is required for recruitment of STAT2 and RNA polymerase II to the IRF7 gene promoter, and in fact MNDA is itself recruited to the IRF7 promoter after type I IFN stimulation. These data implicate MNDA as a critical regulator of the type I IFN cascade in human myeloid cells and reveal a new role for human PYHINs in innate immune gene induction.

The interferon response is a critical component of the innate immune response. Here the authors implicate MNDA in the regulation of type I interferon responses to pathogen infection.

Cytosolic d-type CpG-oligonucleotides induce a type I interferon response by activating the cGAS-STING signaling pathway

Cytosolic DNA receptor cyclic GMP-AMP (cGAMP) synthase (cGAS) has been shown to be critically involved in the detection of cytosolic, self- and non-self-DNA, initiating a type I IFN response through the adaptor protein Stimulator of Interferon Genes (STING) and interferon regulatory factor 3 (IRF3). Current studies propose that canonical binding of dsDNA by cGAS depends on DNA length, but not on base sequence. In contrast, activation of TLR9 is sequence dependent. It requires unmethylated CpG dinucleotides in microbial DNA, which is mimicked by synthetic oligodeoxynucleotides (ODN). Here, we provide evidence that d-type ODN (D-ODN), but not K-type ODN (K-ODN), bind to human cGAS and activate downstream signaling. Transfection of D-ODN into a TLR9-deficient, human monocytic cell line (THP-1) induced phosphorylation of IRF3 and secretion of IFN. This response was absent in cells with CRISPR/Cas9-mediated cGAS- or STING-deficiency. Utilizing a protein pulldown approach, we further demonstrate direct binding of D-ODN to cGAS. Induction of a type I IFN response by D-ODN was confirmed in human primary monocytes and monocyte-derived macrophages. These results are relevant to our understanding of self-nonself-discrimination by cGAS and to the pharmacologic effects of ODN, which currently are investigated in clinical studies.

Type I Interferon Production of Plasmacytoid Dendritic Cells under Control

One of the most powerful and multifaceted cytokines produced by immune cells are type I interferons (IFNs), the basal secretion of which contributes to the maintenance of immune homeostasis, while their activation-induced production is essential to effective immune responses. Although, each cell is capable of producing type I IFNs, plasmacytoid dendritic cells (pDCs) possess a unique ability to rapidly produce large amounts of them. Importantly, type I IFNs have a prominent role in the pathomechanism of various pDC-associated diseases. Deficiency in type I IFN production increases the risk of more severe viral infections and the development of certain allergic reactions, and supports tumor resistance; nevertheless, its overproduction promotes autoimmune reactions. Therefore, the tight regulation of type I IFN responses of pDCs is essential to maintain an adequate level of immune response without causing adverse effects. Here, our goal was to summarize those endogenous factors that can influence the type I IFN responses of pDCs, and thus might serve as possible therapeutic targets in pDC-associated diseases. Furthermore, we briefly discuss the current therapeutic approaches targeting the pDC-type I IFN axis in viral infections, cancer, autoimmunity, and allergy, together with their limitations defined by the Janus-faced nature of pDC-derived type I IFNs.

TLR7 and RIG-I dual-adjuvant loaded nanoparticles drive broadened and synergistic responses in dendritic cells in vitro and generate unique cellular immune responses in influenza vaccination

Although the existing flu vaccines elicit strong antigen-specific antibody responses, they fail to provide effective, long term protection - partly due to the absence of robust cellular memory immunity. We hypothesized that co-administration of combination adjuvants, mirroring the flu-virus related innate signaling pathways, could elicit strong cellular immunity. Here, we show that the small molecule adjuvant R848 and the RNA adjuvant PUUC, targeting endosomal TLR7s and cytoplasmic RLRs respectively, when delivered together in polymer nanoparticles (NP), elicits a broadened immune responses in mouse bone marrow-derived dendritic cells (mBMDCs) and a synergistic response in both mouse and human plasmacytoid dendritic cells (pDCs). In mBMDCs, NP-R848-PUUC induced both NF-κB and interferon signaling. Interferon responses to co-delivered R848 and PUUC were additive in human peripheral blood mononuclear cells (PBMCs) and synergistic in human FLT3-differentiated mBMDCs and CAL-1 pDCs. Vaccination with NPs loaded with H1N1 Flu antigen, R848, and PUUC increased percentage of CD8+ T-cells in the lungs, percentage of antigen-specific CD4-T-cells in the spleen, and enhanced overall cytokine-secreting T cell percentages upon antigen restimulation. Also, in the spleen, T lymphopenia, especially after in vitro restimulation with dual adjuvants, was observed, indicating highly antigen-reactive T cells. Our results demonstrate that simultaneous engagement of TLR7 and RIG-I pathways using particulate carriers is a potential approach to improve cellular immunity in flu vaccination.

Targeting Cellular and Tissue HIV Reservoirs With Toll-Like Receptor Agonists

The elimination of both cellular and tissue latent reservoirs is a challenge toward a successful HIV cure. "Shock and Kill" are among the therapeutic strategies that have been more extensively studied to target these reservoirs. These strategies are aimed toward the reactivation of the latent reservoir using a latency-reversal agent (LRA) with the subsequent killing of the reactivated cell either by the cytotoxic arm of the immune system, including NK and CD8 T cells, or by viral cytopathic mechanisms. Numerous LRAs are currently being investigated in vitro, ex vivo as well as in vivo for their ability to reactivate and reduce latent reservoirs. Among those, several toll-like receptor (TLR) agonists have been shown to reactivate latent HIV. In humans, there are 10 TLRs that recognize different pathogen-associated molecular patterns. TLRs are present in several cell types, including CD4 T cells, the cell compartment that harbors the majority of the latent reservoir. Besides their ability to reactivate latent HIV, TLR agonists also increase immune activation and promote an antiviral response. These combined properties make TLR agonists unique among the different LRAs characterized to date. Additionally, some of these agonists have shown promise toward finding an HIV cure in animal models. When in combination with broadly neutralizing antibodies, TLR-7 agonists have shown to impact the SIV latent reservoir and delay viral rebound. Moreover, there are FDA-approved TLR agonists that are currently being investigated for cancer therapy and other diseases. All these has prompted clinical trials using TLR agonists either alone or in combination toward HIV eradication approaches. In this review, we provide an extensive characterization of the state-of-the-art of the use of TLR agonists toward HIV eradication strategies and the mechanism behind how TLR agonists target both cellular and tissue HIV reservoirs.

Blastic Plasmacytoid Dendritic Cell Neoplasm: State of the Art and Prospects

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is an extremely rare tumour, which usually affects elderly males and presents in the skin with frequent involvement of the bone-marrow, peripheral blood and lymph nodes. It has a dismal prognosis, with most patients dying within one year when treated by conventional chemotherapies. The diagnosis is challenging, since neoplastic cells can resemble lymphoblasts or small immunoblasts, and require the use of a large panel of antibodies, including those against CD4, CD56, CD123, CD303, TCL1, and TCF4. The morphologic and in part phenotypic ambiguity explains the uncertainties as to the histogenesis of the neoplasm that led to the use of various denominations. Recently, a series of molecular studies based on karyotyping, gene expression profiling, and next generation sequencing, have largely unveiled the pathobiology of the tumour and proposed the potentially beneficial use of new drugs. The latter include SL-401, anti-CD123 immunotherapies, venetoclax, BET-inhibitors, and demethylating agents. The epidemiologic, clinical, diagnostic, molecular, and therapeutic features of BPDCN are thoroughly revised in order to contribute to an up-to-date approach to this tumour that has remained an orphan disease for too long.

SOCS1 and SOCS3 Target IRF7 Degradation To Suppress TLR7-Mediated Type I IFN Production of Human Plasmacytoid Dendritic Cells

Type I IFN production of plasmacytoid dendritic cells (pDCs) triggered by TLR-signaling is an essential part of antiviral responses and autoimmune reactions. Although it was well-documented that members of the cytokine signaling (SOCS) family regulate TLR-signaling, the mechanism of how SOCS proteins regulate TLR7-mediated type I IFN production has not been elucidated yet. In this article, we show that TLR7 activation in human pDCs induced the expression of SOCS1 and SOCS3. SOCS1 and SOCS3 strongly suppressed TLR7-mediated type I IFN production. Furthermore, we demonstrated that SOCS1- and SOCS3-bound IFN regulatory factor 7, a pivotal transcription factor of the TLR7 pathway, through the SH2 domain to promote its proteasomal degradation by lysine 48-linked polyubiquitination. Together, our results demonstrate that SOCS1/3-mediated degradation of IFN regulatory factor 7 directly regulates TLR7 signaling and type I IFN production in pDCs. This mechanism might be targeted by therapeutic approaches to either enhance type I IFN production in antiviral treatment or decrease type I IFN production in the treatment of autoimmune diseases.

Enhancement of immunomodulative effect of lactic acid bacteria on plasmacytoid dendritic cells with sucrose palmitate

Plasmacytoid dendritic cells (pDCs) play a key role in the immune response against viruses. In addition, recent research has suggested that pDCs possess direct and indirect tumoricidal activities. We previously found that a lactic acid bacteria strain, Lactococcus lactis JCM 5805 (LC-Plasma), stimulated pDCs and prevented viral infection in mouse and human studies. Meanwhile, emulsifiers have recently been highlighted as candidate adjuvants for some viral vaccines and cancer immunotherapies. In this study, we discovered some specific emulsifiers, mainly consisting of sucrose fatty acid esters, that drastically enhance the potency of LC-Plasma to activate pDCs in vitro. The emulsifiers promoted the efficient uptake of LC-Plasma by pDCs and the ratio of pDCs that took up LC-Plasma correlated with the activity of pDCs. In addition, an in vivo study showed that oral treatment with LC-Plasma mixed with an emulsifier induced a higher expression of genes related to anti-viral immunity in the lung compared to treatment with LC-Plasma alone. Both LC-Plasma and the emulsifiers used in this study have been confirmed to be safe for human use. Therefore, LC-Plasma mixed with an emulsifier might be a useful tool for certain anti-cancer and anti-viral therapies.

Resistance of human plasmacytoid dendritic CAL-1 cells to infection with lymphocytic choriomeningitis virus (LCMV) is caused by restricted virus cell entry, which is overcome by contact of CAL-1 cells with LCMV-infected cells

Plasmacytoid dendritic cells (pDCs), a main source of type I interferon in response to viral infection, are an early cell target during lymphocytic choriomeningitis virus (LCMV) infection, which has been associated with the LCMV's ability to establish chronic infections. Human blood-derived pDCs have been reported to be refractory to ex vivo LCMV infection. In the present study we show that human pDC CAL-1 cells are refractory to infection with cell-free LCMV, but highly susceptible to infection with recombinant LCMVs carrying the surface glycoprotein of VSV, indicating that LCMV infection of CAL-1 cells is restricted at the cell entry step. Co-culture of uninfected CAL-1 cells with LCMV-infected HEK293 cells enabled LCMV to infect CAL-1 cells. This cell-to-cell spread required direct cell-cell contact and did not involve exosome pathway. Our findings indicate the presence of a novel entry pathway utilized by LCMV to infect pDC.