Strategies for designing synthetic immune agonists

Risedronate-functionalized manganese-hydroxyapatite amorphous particles: A potent adjuvant for subunit vaccines and cancer immunotherapy

The cGAS-STING pathway and the Mevalonate Pathway are druggable targets for vaccine adjuvant discovery. Manganese (Mn) and bisphosphonates are known to exert adjuvant effects by targeting these two pathways, respectively. This study found the synergistic potential of the two pathways in enhancing immune response. Risedronate (Ris) significantly amplified the Mn adjuvant early antibody response by 166-fold and fortified its cellular immunity. However, direct combination of Mn2+ and Ris resulted in increased adjuvant toxicity (40% mouse mortality). By the combination of doping property of hydroxyapatite (HA) and its high affinity for Ris, we designed Ris-functionalized Mn-HA micro-nanoparticles as an organic-inorganic hybrid adjuvant, named MnHARis. MnHARis alleviated adjuvant toxicity (100% vs. 60% survival rate) and exhibited good long-term stability. When formulated with the varicella-zoster virus glycoprotein E (gE) antigen, MnHARis triggered a 274.3-fold increase in IgG titers and a 61.3-fold surge in neutralization titers while maintaining a better long-term humoral immunity compared to the aluminum adjuvant. Its efficacy spanned other antigens, including ovalbumin, HPV18 VLP, and SARS-CoV-2 spike protein. Notably, the cellular immunity elicited by the group of gE + MnHARis was comparable to the renowned Shingrix®. Moreover, intratumoral co-administration with an anti-trophoblast cell surface antigen 2 nanobody revealed synergistic antitumor capabilities. These findings underscore the potential of MnHARis as a potent adjuvant for augmenting vaccine immune responses and improving cancer immunotherapy outcomes.

Adjuvant activity of tubeimosides by mediating the local immune microenvironment

Rhizoma Bolbostemmatis, the dry tuber of Bolbostemma paniculatum, has being used for the treatment of acute mastitis and tumors in traditional Chinese medicine. In this study, tubeimoside (TBM) I, II, and III from this drug were investigated for the adjuvant activities, structure-activity relationships (SAR), and mechanisms of action. Three TBMs significantly boosted the antigen-specific humoral and cellular immune responses and elicited both Th1/Th2 and Tc1/Tc2 responses towards ovalbumin (OVA) in mice. TBM I also remarkably facilitated mRNA and protein expression of various chemokines and cytokines in the local muscle tissues. Flow cytometry revealed that TBM I promoted the recruitment and antigen uptake of immune cells in the injected muscles, and augmented the migration and antigen transport of immune cells to the draining lymph nodes. Gene expression microarray analysis manifested that TBM I modulated immune, chemotaxis, and inflammation-related genes. The integrated analysis of network pharmacology, transcriptomics, and molecular docking predicted that TBM I exerted adjuvant activity by interaction with SYK and LYN. Further investigation verified that SYK-STAT3 signaling axis was involved in the TBM I-induced inflammatory response in the C2C12 cells. Our results for the first time demonstrated that TBMs might be promising vaccine adjuvant candidates and exert the adjuvant activity through mediating the local immune microenvironment. SAR information contributes to developing the semisynthetic saponin derivatives with adjuvant activities.

Nanoparticle and virus-like particle vaccine approaches against SARS-CoV-2

The global spread of coronavirus disease 2019 caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection has provoked an urgent need for prophylactic measures. Several innovative vaccine platforms have been introduced and billions of vaccine doses have been administered worldwide. To enable the creation of safer and more effective vaccines, additional platforms are under development. These include the use of nanoparticle (NP) and virus-like particle (VLP) technology. NP vaccines utilize self-assembling scaffold structures designed to load the entire spike protein or receptor-binding domain of SARS-CoV-2 in a trimeric configuration. In contrast, VLP vaccines are genetically modified recombinant viruses that are considered safe, as they are generally replication-defective. Furthermore, VLPs have indigenous immunogenic potential due to their microbial origin. Importantly, NP and VLP vaccines have shown stronger immunogenicity with greater protection by mimicking the physicochemical characteristics of SARS-CoV-2. The study of NP- and VLP-based coronavirus vaccines will help ensure the development of rapid-response technology against SARS-CoV-2 variants and future coronavirus pandemics.

Small Molecule Calcium Channel Activator Potentiates Adjuvant Activity

There remains an unmet need for reliable fully synthetic adjuvants that increase lasting protective immune responses from vaccines. We previously reported a high-throughput screening for small molecules that extended nuclear factor kappa-light-chain enhancer of activated B cells (NF-κB) activation after a Toll-like receptor 4 (TLR4) ligand, lipopolysaccharide (LPS), stimulation using a human myeloid reporter cell line. We identified compounds with a conserved aminothiazole scaffold including 2D216 [N-(4-(2,5-dimethylphenyl)thiazol-2-yl)-4-(piperidin-1-ylsulfonyl)benzamide], which increased murine antigen-specific antibody responses when used as a co-adjuvant with LPS. Here, we examined the mechanism of action in human cells. Although 2D216 activated the major mitogen-activated protein kinases, it did not interact with common kinases and phosphatases and did not stimulate many of the pattern recognition receptors (PRRs). Instead, the mechanism of action was linked to intracellular Ca2+ elevation via Ca2+ channel(s) at the plasma membrane and nuclear translocation of the nuclear factor of activated T-cells (NFAT) as supported by RNA-seq data, analysis by reporter cells, Ca2+ flux assays, and immunoblots. Interestingly, 2D216 had minimal, if any, activity on Jurkat T cells but induced cytokine production and surface expression of costimulatory molecules on cells with antigen-presenting functions. A small series of analogs of 2D216 were tested for the ability to enhance a TLR4 ligand-stimulated autologous mixed lymphocyte reaction (MLR). In the MLR, 2E151, N-(4-(2,5-dimethylphenyl)thiazol-2-yl)-4-((4-propylpiperidin-1-yl)sulfonyl)benzamide, was more potent than 2D216. These results indicate that a small molecule that is not a direct PRR agonist can act as a co-adjuvant to an approved adjuvant to enhance human immune responses via a complementary mechanism of action.

Engineered Cell Membrane-Derived Nanoparticles in Immune Modulation

Immune modulation is one of the most effective approaches in the therapy of complex diseases, including public health emergency. However, most immune therapeutics such as drugs, vaccines, and cellular therapy suffer from the limitations of poor efficacy and adverse side effects. Fortunately, cell membrane-derived nanoparticles (CMDNs) have superior compatibility with other therapeutics and offer new opportunities to push the limits of current treatments in immune modulation. As the interface between cells and outer surroundings, cell membrane contains components which instruct intercellular communication and the plasticity of cytomembrane has significantly potentiated CMDNs to leverage our immune system. Therefore, cell membranes employed in immunomodulatory CMDNs have gradually shifted from natural to engineered. In this review, unique properties of immunomodulatory CMDNs and engineering strategies of emerging CMDNs for immune modulation, with an emphasis on the design logic are summarized. Further, this review points out some pressing problems to be solved during clinical translation and put forward some suggestions on the prospect of immunoregulatory CMDNs. It is anticipated that this review can provide new insights on the design of immunoregulatory CMDNs and expand their potentiation in the precise control of the dysregulated immune system.

The effect of concomitant use of statins, NSAIDs, low-dose aspirin, metformin and beta-blockers on outcomes in patients receiving immune checkpoint inhibitors: a systematic review and meta-analysis

Immunotherapy shows promising therapeutic efficacy against various types of cancer, but most fail to respond. Preclinical studies have suggested that concomitant medications, such as statins, non-steroidal anti-inflammatory drugs (NSAIDs), aspirin, metformin and beta-blockers, might affect clinical outcomes if used with immune checkpoint inhibitors (ICIs), but their clinical roles are conflicting. This meta-analysis investigates the effect of these concomitant medications on outcomes in patients treated with ICIs. A search was conducted for all reports published until 31 March 2021 in PubMed, Web of Science, Cochrane Library, EMBASE and conference proceedings. Studies were included if they investigated the association between the concomitant use of these medications and progression-free survival (PFS) or overall survival (OS) during ICI treatment. A total of 3331 patients from 13 eligible studies were included. Among them, five articles on statins, six studies evaluating NSAIDs, five studies employing low-dose aspirin, eight studies on metformin and four articles on beta-blockers were included. The concomitant use of statins during ICI treatment was correlated with improved OS and PFS. Low-dose aspirin was associated with better PFS instead of OS. No significant association was demonstrated between the concurrent use of NSAIDs, beta-blockers and metformin and OS or PFS. The concomitant use of statins and low-dose aspirin during ICI treatment showed a positive impact on treatment outcomes. The concurrent use of NSAIDs, beta-blockers and metformin is not significantly associated with clinical benefits. The effect of these medications in different cancer patients treated with ICI is needed to be further validated.

Evolution of Toll-like receptor 7/8 agonist therapeutics and their delivery approaches: From antiviral formulations to vaccine adjuvants

Imidazoquinoline derivatives (IMDs) and related compounds function as synthetic agonists of Toll-like receptors 7 and 8 (TLR7/8) and one is FDA approved for topical antiviral and skin cancer treatments. Nevertheless, these innate immune system-activating drugs have potentially much broader therapeutic utility; they have been pursued as antitumor immunomodulatory agents and more recently as candidate vaccine adjuvants for cancer and infectious disease. The broad expression profiles of TLR7/8, poor pharmacokinetic properties of IMDs, and toxicities associated with systemic administration, however, are formidable barriers to successful clinical translation. Herein, we review IMD formulations that have advanced to the clinic and discuss issues related to biodistribution and toxicity that have hampered the further development of these compounds. Recent strategies aimed at enhancing safety and efficacy, particularly through the use of bioconjugates and nanoparticle formulations that alter pharmacokinetics, biodistribution, and cellular targeting, are described. Finally, key aspects of the biology of TLR7 signaling, such as TLR7 tolerance, that may need to be considered in the development of new IMD therapeutics are discussed.

Immunological Mechanism and Clinical Application of PAMP Adjuvants

BACKGROUND

The host innate immune system can recognize Pathogen-Associated Molecular Patterns (PAMPs) through Pattern Recognition Receptors (PRRs), thereby initiating innate immune responses and subsequent adaptive immune responses. PAMPs can be developed as a vaccine adjuvant for modulating and optimizing antigen-specific immune responses, especially in combating viral infections and tumor therapy. Although several PAMP adjuvants have been successfully developed they are still lacking in general, and many of them are in the preclinical exploration stage.

OBJECTIVE

This review summarizes the research progress and development direction of PAMP adjuvants, focusing on their immune mechanisms and clinical applications.

METHODS

PubMed, Scopus, and Google Scholar were screened for this information. We highlight the immune mechanisms and clinical applications of PAMP adjuvants.

RESULTS

Because of the differences in receptor positions, specific immune cells targets, and signaling pathways, the detailed molecular mechanism and pharmacokinetic properties of one agonist cannot be fully generalized to another agonist, and each PAMP should be studied separately. In addition, combination therapy and effective integration of different adjuvants can increase the additional efficacy of innate and adaptive immune responses.

CONCLUSION

The mechanisms by which PAMPs exert adjuvant functions are diverse. With continuous discovery in the future, constant adjustments should be made to build new understandings. At present, the goal of therapeutic vaccination is to induce T cells that can specifically recognize and eliminate tumor cells and establish long-term immune memory. Following immune checkpoint modulation therapy, cancer treatment vaccines may be an option worthy of clinical testing.

Emerging concepts in the science of vaccine adjuvants

Adjuvants are vaccine components that enhance the magnitude, breadth and durability of the immune response. Following its introduction in the 1920s, alum remained the only adjuvant licensed for human use for the next 70 years. Since the 1990s, a further five adjuvants have been included in licensed vaccines, but the molecular mechanisms by which these adjuvants work remain only partially understood. However, a revolution in our understanding of the activation of the innate immune system through pattern recognition receptors (PRRs) is improving the mechanistic understanding of adjuvants, and recent conceptual advances highlight the notion that tissue damage, different forms of cell death, and metabolic and nutrient sensors can all modulate the innate immune system to activate adaptive immunity. Furthermore, recent advances in the use of systems biology to probe the molecular networks driving immune response to vaccines ('systems vaccinology') are revealing mechanistic insights and providing a new paradigm for the vaccine discovery and development process. Here, we review the 'known knowns' and 'known unknowns' of adjuvants, discuss these emerging concepts and highlight how our expanding knowledge about innate immunity and systems vaccinology are revitalizing the science and development of novel adjuvants for use in vaccines against COVID-19 and future pandemics.

High-intensity statins are associated with improved clinical activity of PD-1 inhibitors in malignant pleural mesothelioma and advanced non-small cell lung cancer patients

BACKGROUND

In preclinical models, statins showed vaccine adjuvant activities and synergized with PD-1 inhibitors. We analyzed the impact of statin treatment on clinical outcome in thoracic cancer patients treated with PD-1 inhibitors.

METHODS

A total of 82 malignant pleural mesothelioma (MPM) and 179 advanced non-small cell lung cancer (aNSCLC) patients treated with PD-1 inhibitors as second or further line treatment were examined. Seventy-seven MPM patients treated with standard chemotherapy were analyzed as control cohort. Objective response rate (ORR), progression-free survival (PFS), and overall survival (OS) were calculated.

RESULTS

Among 253 patients with available data, statin use was associated with increased ORR (32% versus 18%, P = .02), PFS (median 6.7 versus 2.9 months, hazard ratio [HR] 0.57, 95% CI 0.39-0.83, P < .01), and OS (median 13.1 versus 8.7 months, HR 0.67, 95% CI 0.45-1.00, P = .05). In the control MPM cohort treated with chemotherapy (n = 77), no association was found. MPM patients who used statins showed improved ORR (22% versus 6%, P = .05), PFS (median 6.7 versus 2.4 months, P < .01), and OS (median not reached versus 6.0 months, P = .01). In aNSCLC patients, statin use was associated with improved ORR (40% versus 22%, P = .04) and PFS (median 7.8 versus 3.6 months, P = .03), but no significant difference in OS was found (median 13.1 versus 10.1 months, P = .30). Multivariable analysis confirmed the correlation between statin use and better PFS and OS in MPM and better PFS in aNSCLC. In the whole cohort, high but not low/moderate-intensity statins were associated with better OS compared to no user (P = .02 and P = .59, respectively).

CONCLUSIONS

Our study showed that statins are associated with better clinical outcome in MPM and aNSCLC patients treated with PD-1 inhibitors in an intensity-dependent manner.

Development of thermosensitive resiquimod-loaded liposomes for enhanced cancer immunotherapy

Resiquimod (R848) is a toll-like receptor 7 and 8 (TLR7/8) agonist with potent antitumor and immunostimulatory activity. However, systemic delivery of R848 is poorly tolerated because of its poor solubility in water and systemic immune activation. In order to address these limitations, we developed an intravenously-injectable formulation with R848 using thermosensitive liposomes (TSLs) as a delivery vehicle. R848 was remotely loaded into TSLs composed of DPPC: DSPC: DSPE-PEG2K (85:10:5, mol%) with 100 mM FeSO₄ as the trapping agent inside. The final R848 to lipid ratio of the optimized R848-loaded TSLs (R848-TSLs) was 0.09 (w/w), 10-fold higher than the previously-reported values. R848-TSLs released 80% of R848 within 5 min at 42 °C. These TSLs were then combined with αPD-1, an immune checkpoint inhibitor, and ultrasound-mediated hyperthermia in a neu deletion (NDL) mouse mammary carcinoma model (Her2⁺, ER/PR negative). Combined with αPD-1, local injection of R848-TSLs showed superior efficacy with complete NDL tumor regression in both treated and abscopal sites achieved in 8 of 11 tumor bearing mice over 100 days. Immunohistochemistry confirmed enhanced CD8⁺ T cell infiltration and accumulation by R848-TSLs. Systemic delivery of R848-TSLs, combined with local hyperthermia and αPD-1, inhibited tumor growth and extended median survival from 28 days (non-treatment control) to 94 days. Upon re-challenge with reinjection of tumor cells, none of the previously cured mice developed tumors, as compared with 100% of age-matched control mice. The dose of R848 (10 μg for intra-tumoral injection or 6 mg/kg for intravenous injection delivered up to 4 times) was well-tolerated without weight loss or organ hypertrophy. In summary, we developed R848-TSLs that can be administered locally or systematically, resulting in tumor regression and enhanced survival when combined with αPD-1 in mouse models of breast cancer.

Nanomedicine-based tumor photothermal therapy synergized immunotherapy

The emerging anti-tumor immunotherapy has made significant progress in clinical application. However, single immunotherapy is not effective for all anti-tumor treatments, owing to the low objective response rate and the risk of immune-related side effects. Meanwhile, photothermal therapy (PTT) has attracted significant attention because of its non-invasiveness, spatiotemporal controllability and small side effects. Combining PTT with immunotherapy overcomes the issue that single photothermal therapy cannot eradicate tumors with metastasis and recurrence. However, it improves the therapeutic effect of immunotherapy, as the photothermal therapy usually promotes release of tumor-related antigens, triggers immune response by the immunogenic cell death (ICD), thereby, endowing unique synergistic mechanisms for cancer therapy. This review summarizes recent research advances in utilizing nanomedicines for PTT in combination with immunotherapy to improve the outcome of cancer treatment. The strategies include immunogenic cell death, immune agonists and cancer vaccines, immune checkpoint blockades and tumor specific monoclonal antibodies, and small-molecule immune inhibitors. The combination of synergized PTT-immunotherapy with other therapeutic strategies is also discussed.

Pharmacological modulation of nucleic acid sensors - therapeutic potential and persisting obstacles

Nucleic acid sensors, primarily TLR and RLR family members, as well as cGAS-STING signalling, play a critical role in the preservation of cellular and organismal homeostasis. Accordingly, deregulated nucleic acid sensing contributes to the origin of a diverse range of disorders, including infectious diseases, as well as cardiovascular, autoimmune and neoplastic conditions. Accumulating evidence indicates that normalizing aberrant nucleic acid sensing can mediate robust therapeutic effects. However, targeting nucleic acid sensors with pharmacological agents, such as STING agonists, presents multiple obstacles, including drug-, target-, disease- and host-related issues. Here, we discuss preclinical and clinical data supporting the potential of this therapeutic paradigm and highlight key limitations and possible strategies to overcome them.

Significance and Role of Pattern Recognition Receptors in Malignancy

Pattern recognition receptors (PRRs) are members of innate immunity, playing pivotal role in several immunological reactions. They are known to act as a bridge between innate and adaptive immunity. They are expressed on several normal cell types but have been shown with increasing frequency on/in tumor cells. Significance of this phenomenon is largely unknown, but it has been shown by several authors that they, predominantly Toll-like receptors (TLRs), act in the interest of tumor, by promotion of its growth and spreading. Preparation of artificial of TLRs ligands (agonists) paved the way to use them as a therapeutic agents for cancer, so far in a limited scale. Agonists may be combined with conventional anti-cancer modalities with apparently promising results. PRRs recognizing nucleic acids such as RIG-1 like receptors (sensing RNA) and STING (sensing DNA) constitute a novel promising approach for cancer immunotherapy.

Proximity Ligation Assays for In Situ Detection of Innate Immune Activation: Focus on In Vitro-Transcribed mRNA

The characterization of innate immune activation is crucial for vaccine and therapeutic development, including RNA-based vaccines, a promising approach. Current measurement methods quantify type I interferon and inflammatory cytokine production, but they do not allow for the isolation of individual pathways, do not provide kinetic activation or spatial information within tissues, and cannot be translated into clinical studies. Here we demonstrated the use of proximity ligation assays (PLAs) to detect pattern recognition receptor (PRR) activation in cells and in tissue samples. First, we validated PLA's sensitivity and specificity using well-characterized soluble agonists. Next, we characterized PRR activation from in vitro-transcribed (IVT) mRNAs, as well as the effect of sequence and base modifications in vitro. Finally, we established the measurement of PRR activation in tissue sections via PLA upon IVT mRNA intramuscular (i.m.) injection in mice. Overall, our results indicate that PLA is a valuable, versatile, and sensitive tool to monitor PRR activation for vaccine, adjuvant, and therapeutic screening.

Therapeutic Targeting of RIG-I and MDA5 Might Not Lead to the Same Rome

RIG-I and MDA5 receptors are key sensors of pathogen-associated molecular pattern (PAMP)-containing viral RNA and transduce downstream signals to activate an antiviral and immunomodulatory response. Fifteen years of research have put them at the center of an ongoing hunt for novel pharmacological pan-antivirals, vaccine adjuvants, and antitumor strategies. Current knowledge testifies to the redundant, but also distinct, functions mediated by RIG-I and MDA5, opening opportunities for the use of specific and potent nucleic acid agonists. We critically discuss the evidence and remaining knowledge gaps that have an impact on the choice and design of optimal RNA ligands to achieve an appropriate immunostimulatory response, with limited adverse effects, for prophylactic and therapeutic interventions against viruses and cancer in humans.

Recent advances in experimental polyphosphazene adjuvants and their mechanisms of action

Vaccination continues to be a very important public health intervention to control infectious diseases in the world. Subunit vaccines are generally poorly immunogenic and require the addition of adjuvants to induce protective immune responses. Despite their critical role in vaccines, adjuvant mechanism of action remains poorly understood, which is a barrier to the development of new, safe and effective vaccines. In the present review, we focus on recent progress in understanding the mechanisms of action of the experimental adjuvants poly[di(carboxylatophenoxy)phosphazene] (PCPP) and poly[di(sodiumcarboxylatoethyl-phenoxy)phosphazene] (PCEP) (in this review, adjuvants PCPP and PCEP are collectively referred to as PZ denoting polyphosphazenes). PZs are high molecular weight, water-soluble, synthetic polymers that have been shown to regulate innate immune response genes, induce cytokines and chemokines secretion at the site of injection and, also, induce immune cell recruitment to the site of injection to create a local immune-competent environment. There is an evidence that as well as its role as an immunoadjuvant (that activate innate immune responses), PZ can also act as a vaccine carrier. The mechanism of action that explains how PZ leads to these effects is not known and is a barrier to the development of designer vaccines.

The Mevalonate Pathway Is a Druggable Target for Vaccine Adjuvant Discovery

Motivated by the clinical observation that interruption of the mevalonate pathway stimulates immune responses, we hypothesized that this pathway may function as a druggable target for vaccine adjuvant discovery. We found that lipophilic statin drugs and rationally designed bisphosphonates that target three distinct enzymes in the mevalonate pathway have potent adjuvant activities in mice and cynomolgus monkeys. These inhibitors function independently of conventional "danger sensing." Instead, they inhibit the geranylgeranylation of small GTPases, including Rab5 in antigen-presenting cells, resulting in arrested endosomal maturation, prolonged antigen retention, enhanced antigen presentation, and T cell activation. Additionally, inhibiting the mevalonate pathway enhances antigen-specific anti-tumor immunity, inducing both Th1 and cytolytic T cell responses. As demonstrated in multiple mouse cancer models, the mevalonate pathway inhibitors are robust for cancer vaccinations and synergize with anti-PD-1 antibodies. Our research thus defines the mevalonate pathway as a druggable target for vaccine adjuvants and cancer immunotherapies.

Stable Nanoemulsions for the Delivery of Small Molecule Immune Potentiators

Adjuvants are required to enhance immune responses to typically poorly immunogenic recombinant antigens. Toll-like receptor agonists (TLRa) have been widely evaluated as adjuvants because they activate the innate immune system. Currently, licensed vaccines adjuvanted with TLRa include the TLR4 agonist monophosphoryl lipid, while additional TLRa are in clinical development. Unfortunately, naturally derived TLRa are often complex and heterogeneous entities, which brings formulation challenges. Consequently, the use of synthetic small-molecule TLRa has significant advantages because they are well-defined discrete molecules, which can be chemically modified to modulate their physicochemical properties. We previously described the discovery of a family of TLR7 agonists based on a benzonaphthyridine scaffold. In addition, we described how Alum could be used to deliver these synthetic TLRa. An alternative adjuvant approach with enhanced potency over Alum are squalene containing oil-in-water emulsions, which have been included in licensed influenza vaccines, including Fluad (MF59 adjuvanted) and Pandemrix (AS03 adjuvanted). Here, we describe how to enable the co-delivery of a TLR7 agonist in a squalene-based oil-in-water emulsion, for adjuvant evaluation.

Toll-like Receptor Agonist Conjugation: A Chemical Perspective

Toll-like receptors (TLRs) are vital elements of the mammalian immune system that function by recognizing pathogen-associated molecular patterns (PAMPs), bridging innate and adaptive immunity. They have become a prominent therapeutic target for the treatment of infectious diseases, cancer, and allergies, with many TLR agonists currently in clinical trials or approved as immunostimulants. Numerous studies have shown that conjugation of TLR agonists to other molecules can beneficially influence their potency, toxicity, pharmacokinetics, or function. The functional properties of TLR agonist conjugates, however, are highly dependent on the ligation strategy employed. Here, we review the chemical structural requirements for effective functional TLR agonist conjugation. In addition, we provide similar analysis for those that have yet to be conjugated. Moreover, we discuss applications of covalent TLR agonist conjugation and their implications for clinical use.

NAB2 is a novel immune stimulator of MDA-5 that promotes a strong type I interferon response

Novel adjuvants are needed to increase the efficacy of vaccine formulations and immune therapies for cancer and chronic infections. In particular, adjuvants that promote a strong type I IFN response are required, since this cytokine is crucial for the development of efficient anti-tumoral and anti-viral immunity. Nucleic acid band 2 (NAB2) is a double-stranded RNA molecule isolated from yeast and identified as an agonist of the pattern-recognition receptors TLR3 and MDA-5. We compared the ability of NAB2 to activate innate immunity with that of poly(I:C), a well-characterized TLR3 and MDA-5 agonist known for the induction of type I IFN. NAB2 promoted stronger IFN-α production and induced a higher activation state of both murine and human innate immune cells compared to poly(I:C). This correlated with a stronger activation of the signalling pathway downstream of MDA-5, and IFN-α induction was dependent on MDA-5. Upon injection, NAB2 induced higher levels of serum IFN-α in mice than poly(I:C). These results suggest that NAB2 has the potential to become an efficient adjuvant for the induction of type-I IFN responses in therapeutic immunization against cancer or infections.

Synthetic agonists of NOD-like, RIG-I-like, and C-type lectin receptors for probing the inflammatory immune response

Synthetic agonists of innate immune cells are of interest to immunologists due to their synthesis from well-defined materials, optimized activity, and monodisperse chemical purity. These molecules are used in both prophylactic and therapeutic contexts from vaccines to cancer immunotherapies. In this review we highlight synthetic agonists that activate innate immune cells through three classes of pattern recognition receptors: NOD-like receptors, RIG-I-like receptors, and C-type lectin receptors. We classify these agonists by the receptor they activate and present them from a chemical perspective, focusing on structural components that define agonist activity. We anticipate this review will be useful to the medicinal chemist as a guide to chemical motifs that activate each receptor, ultimately illuminating a chemical space ripe for exploration.

Impact of Early-Life Exposures to Infections, Antibiotics, and Vaccines on Perinatal and Long-term Health and Disease

Essentially, all neonates are exposed to infections, antibiotics, or vaccines early in their lives. This is especially true for those neonates born underweight or premature. In contrast to septic adults and children who are at an increased risk for subsequent infections, exposure to infection during the neonatal period is not associated with an increased risk of subsequent infection and may be paradoxically associated with reductions in late-onset sepsis (LOS) in the most premature infants. Perinatal inflammation is also associated with a decreased incidence of asthma and atopy later in life. Conversely, septic neonates are at increased risk of impaired long-term neurodevelopment. While the positive effects of antibiotics in the setting of infection are irrefutable, prolonged administration of broad-spectrum, empiric antibiotics in neonates without documented infection is associated with increased risk of LOS, necrotizing enterocolitis, or death. Vaccines provide a unique opportunity to prevent infection-associated disease; unfortunately, vaccinations have been largely unsuccessful when administered in the first month of life with the exception of vaccines against hepatitis B and tuberculosis. Future vaccines will require the use of novel adjuvants to overcome this challenge. This review describes the influence of infections, antibiotics, and vaccines during the first days of life, as well as the influence on future health and disease. We will also discuss potential immunomodulating therapies, which may serve to train the preterm immune system and reduce subsequent infectious burden without subjecting neonates to the risks accompanied by virulent pathogens.