Adjuvant-induced Human Monocyte Secretome Profiles Reveal Adjuvant- and Age-specific Protein Signatures

Vaccinology: Getting our modernization act together

Ofer Levy, Director, Precision Vaccines Program at Boston Children's Hospital, reflects on implications of the new FDA Modernization Act 2.0 on accelerating drug and vaccine discovery and development.

The BNT162b2 mRNA vaccine demonstrates reduced age-associated TH1 support in vitro and in vivo

mRNA vaccines demonstrate impaired immunogenicity and durability in vulnerable older populations. We hypothesized that human in vitro modeling and proteomics could elucidate age-specific mRNA vaccine actions. BNT162b2-stimulation changed the plasma proteome of blood samples from young (18-50Y) and older adult (≥60Y) participants, assessed by mass spectrometry, proximity extension assay, and multiplex. Young adult up-regulation (e.g., PSMC6, CPN1) contrasted reduced induction in older adults (e.g., TPM4, APOF, APOC2, CPN1, PI16). 30-85% lower TH1-polarizing cytokines and chemokines were induced in elderly blood (e.g., IFNγ, CXCL10). Analytes lower in older adult samples included human in vivo mRNA immunogenicity biomarkers (e.g., IFNγ, CXCL10, CCL4, IL-1RA). BNT162b2 also demonstrated reduced CD4+ TH1 responses in aged vs. young adult mice. Our study demonstrates the utility of human in vitro platforms modeling age-specific mRNA vaccine immunogenicity, highlights impaired support of TH1 polarization in older adults, and provides a rationale for precision mRNA vaccine adjuvantation to induce greater immunogenicity.

Immune profiling of age and adjuvant-specific activation of human blood mononuclear cells in vitro

Vaccination reduces morbidity and mortality due to infections, but efficacy may be limited due to distinct immunogenicity at the extremes of age. This raises the possibility of employing adjuvants to enhance immunogenicity and protection. Early IFNγ production is a hallmark of effective vaccine immunogenicity in adults serving as a biomarker that may predict effective adjuvanticity. We utilized mass cytometry (CyTOF) to dissect the source of adjuvant-induced cytokine production in human blood mononuclear cells (BMCs) from newborns (~39-week-gestation), adults (~18-63 years old) and elders (>65 years of age) after stimulation with pattern recognition receptors agonist (PRRa) adjuvants. Dimensionality reduction analysis of CyTOF data mapped the BMC compartment, elucidated age-specific immune responses and profiled PRR-mediated activation of monocytes and DCs upon adjuvant stimulation. Furthermore, we demonstrated PRRa adjuvants mediated innate IFNγ induction and mapped NK cells as the key source of TLR7/8 agonist (TLR7/8a) specific innate IFNγ responses. Hierarchical clustering analysis revealed age and TLR7/8a-specific accumulation of innate IFNγ producing γδ T cells. Our study demonstrates the application of mass cytometry and cutting-edge computational approaches to characterize immune responses across immunologically distinct age groups and may inform identification of the bespoke adjuvantation systems tailored to enhance immunity in distinct vulnerable populations.

Modeling human immune responses to vaccination in vitro

The human immune system is a complex network of coordinated components that are crucial for health and disease. Animal models, commonly used to study immunomodulatory agents, are limited by species-specific differences, low throughput, and ethical concerns. In contrast, in vitro modeling of human immune responses can enable species- and population-specific mechanistic studies and translational development within the same study participant. Translational accuracy of in vitro models is enhanced by accounting for genetic, epigenetic, and demographic features such as age, sex, and comorbidity. This review explores various human in vitro immune models, considers evidence that they may resemble human in vivo responses, and assesses their potential to accelerate and de-risk vaccine discovery and development.

Molecular Determinants of the Early Life Immune Response to COVID-19 Infection and Immunization

Clinical manifestations from primary COVID infection in children are generally less severe as compared to adults, and severe pediatric cases occur predominantly in children with underlying medical conditions. However, despite the lower incidence of disease severity, the burden of COVID-19 in children is not negligible. Throughout the course of the pandemic, the case incidence in children has substantially increased, with estimated cumulative rates of SARS-CoV-2 infection and COVID-19 symptomatic illness in children comparable to those in adults. Vaccination is a key approach to enhance immunogenicity and protection against SARS-CoV-2. Although the immune system of children is functionally distinct from that of other age groups, vaccine development specific for the pediatric population has mostly been limited to dose-titration of formulations that were developed primarily for adults. In this review, we summarize the literature pertaining to age-specific differences in COVID-19 pathogenesis and clinical manifestation. In addition, we review molecular distinctions in how the early life immune system responds to infection and vaccination. Finally, we discuss recent advances in development of pediatric COVID-19 vaccines and provide future directions for basic and translational research in this area.

A Precision Adjuvant Approach to Enhance Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Vaccines Optimized for Immunologically Distinct Vulnerable Populations

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic has caused significant mortality, especially among older adults whose distinct immune system reflects immunosenescence. Multiple SARS-CoV-2 vaccines have received emergency use authorization and/or licensure from the US Food and Drug Administration and throughout the world. However, their deployment has heighted significant limitations, such by age-dependent immunogenicity, requirements for multiple vaccine doses, refrigeration infrastructure that is not universally available, as well as waning immunity. Thus, there was, and continues to be a need for continued innovation during the pandemic given the desire for dose-sparing, formulations stable at more readily achievable temperatures, need for robust immunogenicity in vulnerable populations, and development of safe and effective pediatric vaccines. In this context, optimal SARS-CoV-2 vaccines may ultimately rely on inclusion of adjuvants as they can potentially enhance protection of vulnerable populations and provide dose-sparing effects enabling single shot protection.

Adjuvant Discovery via a High Throughput Screen using Human Primary Mononuclear Cells

Motivation

Vaccines are a key biomedical intervention to prevent the spread of infectious diseases, but their efficacy can be limited by insufficient immunogenicity and nonuniform reactogenic profiles. Adjuvants are molecules that potentiate vaccine responses by inducing innate immune activation. However, there are a limited number of adjuvants in approved vaccines, and current approaches for preclinical adjuvant discovery and development are inefficient. To enhance adjuvant identification, we developed a protocol based on in vitro screening of human primary leukocytes.

Summary

We describe a methodology utilizing high-throughput and high-content screening for novel adjuvant candidates that was used to screen a library of ~2,500 small molecules via a 384-well quantitative combined cytokine and flow cytometry immunoassay in primary human peripheral blood mononuclear cells (PBMCs) from 4 healthy adult study participants. Hits were identified based on their induction of soluble cytokine (TNF, IFNg and IL-10) secretion and PBMC maturation (CD 80/86, Ox40, and HLA-DR) in at least two of the four donors screened. From an initial set of 197 compounds identified using these biomarkers-an 8.6% hit rate-we downselected to five scaffolds that demonstrated robust efficacy and potency in vitro and evaluated the top hit, vinblastine sulfate, for adjuvanticity in vivo. Vinblastine sulfate significantly enhanced murine humoral responses to recombinant SARS-CoV-2 spike protein, including a four-fold enhancement of IgG titer production when compared to treatment with the spike antigen alone. Overall, we outline a methodology for discovering immunomodulators with adjuvant potential via high-throughput screening of PBMCs in vitro that yielded a lead compound with in vivo adjuvanticity.

Human Blood Plasma Shapes Distinct Neonatal TLR-Mediated Dendritic Cell Activation via Expression of the MicroRNA Let-7g

The newborn innate immune system is characterized as functionally distinct, resulting in impaired proinflammatory responses to many stimuli and a bias toward Th2 development. Although the magnitude of impairment can be partially overcome, for instance through activation of TLR7/8 in newborn dendritic cells, the newborn innate response remains distinct from that of adults. Using human in vitro modeling of newborn and adult dendritic cells, we investigated the role of extracellular and intracellular regulators in driving age-specific responses to TLR7/8 stimulation. MicroRNA expression profiling and plasma switch experiments identified Let-7g as a novel regulator of newborn innate immunity. Activation-induced expression of Let-7g in monocyte-derived dendritic cells (MoDCs) is driven by newborn plasma and reduces expression of costimulatory receptors CD86, MHC class I, and CCR7 and secretion of IFN-α and sCD40L. Conversely, an increase in secretion of the Th2-polarizing cytokine IL-12p40 is observed. Overexpression of Let-7g in adult MoDCs resulted in the same observations. Small interfering RNA-mediated ablation of Let-7g levels in newborn MoDCs resulted in an adult-like phenotype. In conclusion, this study reveals for the first time (to our knowledge) that age-specific differences in human plasma induce the microRNA Let-7g as a key mediator of the newborn innate immune phenotype. These observations shed new light on the mechanisms of immune ontogeny and may inform approaches to discover age-specific immunomodulators, such as adjuvants.

Vaccine-Induced CD8+ T Cell Responses in Children: A Review of Age-Specific Molecular Determinants Contributing to Antigen Cross-Presentation

Infections are most common and most severe at the extremes of age, the young and the elderly. Vaccination can be a key approach to enhance immunogenicity and protection against pathogens in these vulnerable populations, who have a functionally distinct immune system compared to other age groups. More than 50% of the vaccine market is for pediatric use, yet to date vaccine development is often empiric and not tailored to molecular distinctions in innate and adaptive immune activation in early life. With modern vaccine development shifting from whole-cell based vaccines to subunit vaccines also comes the need for formulations that can elicit a CD8+ T cell response when needed, for example, by promoting antigen cross-presentation. While our group and others have identified many cellular and molecular determinants of successful activation of antigen-presenting cells, B cells and CD4+ T cells in early life, much less is known about the ontogeny of CD8+ T cell induction. In this review, we summarize the literature pertaining to the frequency and phenotype of newborn and infant CD8+ T cells, and any evidence of induction of CD8+ T cells by currently licensed pediatric vaccine formulations. In addition, we review the molecular determinants of antigen cross-presentation on MHC I and successful CD8+ T cell induction and discuss potential distinctions that can be made in children. Finally, we discuss recent advances in development of novel adjuvants and provide future directions for basic and translational research in this area.

Use of human peripheral blood mononuclear cells to define immunological properties of nucleic acid nanoparticles

This protocol assesses proinflammatory properties of nucleic acid nanoparticles (NANPs) using a validated preclinical model, peripheral blood mononuclear cells (PBMCs), that is highly predictive of cytokine responses. The experimental procedure details the preparation of pyrogen-free NANPs, isolation of PBMCs from freshly collected human blood, and analysis of characteristic biomarkers (type I and III interferons) produced by PBMCs transfected with NANPs. Although representative NANPs with high and low immunostimulatory potential are used as standards throughout the procedure, this protocol can be adapted to any NANPs or therapeutic nucleic acids, irrespective of whether they are carrier based or carrier free; additional cytokine biomarkers can also be included. We test several commercial platforms and controls broadly accessible to the research community to quantify all biomarkers in either single- or multiplex format. The continuous execution of this protocol takes <48 h; when immediate analysis is not feasible, single-use aliquots of the supernatants can be frozen and stored (-20 °C; 12 months).

Toward precision adjuvants: optimizing science and safety

PURPOSE OF REVIEW

The gradual replacement of inactivated whole cell and live attenuated vaccines with subunit vaccines has generally reduced reactogenicity but in many cases also immunogenicity. Although only used when necessary, adjuvants can be key to vaccine dose/antigen-sparing, broadening immune responses to variable antigens, and enhancing immunogenicity in vulnerable populations with distinct immunity. Licensed vaccines contain an increasing variety of adjuvants, with a growing pipeline of adjuvanted vaccines under development.

RECENT FINDINGS

Most adjuvants, including Alum, Toll-like receptor agonists and oil-in-water emulsions, activate innate immunity thereby altering the quantity and quality of an adaptive immune response. Adjuvants activate leukocytes, and induce mediators (e.g., cytokines, chemokines, and prostaglandin-E2) some of which are biomarkers for reactogenicity, that is, induction of local/systemic side effects. Although there have been safety concerns regarding a hypothetical risk of adjuvants inducing auto-immunity, such associations have not been established. As immune responses vary by population (e.g., age and sex), adjuvant research now incorporates principles of precision medicine. Innovations in adjuvant research include use of human in vitro models, immuno-engineering, novel delivery systems, and systems biology to identify biomarkers of safety and adjuvanticity.

SUMMARY

Adjuvants enhance vaccine immunogenicity and can be associated with reactogenicity. Novel multidisciplinary approaches hold promise to accelerate and de-risk targeted adjuvant discovery and development. VIDEO ABSTRACT: http://links.lww.com/MOP/A53.

Activation of Human Monocytes by Colloidal Aluminum Salts

Subunit vaccines often contain colloidal aluminum salt-based adjuvants to activate the innate immune system. These aluminum salts consist of micrometer-sized aggregates. It is well-known that particle size affects the adjuvant effect of particulate adjuvants. In this study, the activation of human monocytes by hexagonal-shaped gibbsite (ø = 210 ± 40 nm) and rod-shaped boehmite (ø = 83 ± 827 nm) was compared with classical aluminum oxyhydroxide adjuvant (alum). To this end, human primary monocytes were cultured in the presence of alum, gibbsite, or boehmite. The transcriptome and proteome of the monocytes were investigated by using quantitative polymerase chain reaction and mass spectrometry. Human monocytic THP-1 cells were used to investigate the effect of the particles on cellular maturation, differentiation, activation, and cytokine secretion, as measured by flow cytometry and enzyme-linked immunosorbent assay. Each particle type resulted in a specific gene expression profile. IL-1ß and IL-6 secretion was significantly upregulated by boehmite and alum. Of the 7 surface markers investigated, only CD80 was significantly upregulated by alum and none by gibbsite or boehmite. Gibbsite hardly activated the monocytes. Boehmite activated human primary monocytes equally to alum, but induced a much milder stress-related response. Therefore, boehmite was identified as a promising adjuvant candidate.

Proteomic analysis of cholera toxin adjuvant-stimulated human monocytes identifies Thrombospondin-1 and Integrin-β1 as strongly upregulated molecules involved in adjuvant activity

Cholera Toxin (CT) as well as its related non-toxic mmCT and dmLT mutant proteins have been shown to be potent adjuvants for mucosally administered vaccines. Their adjuvant activity involves activation of cAMP/protein kinase A (PKA) signaling and inflammasome/IL-1β pathways in antigen presenting cells (APC). To get a further understanding of the signal transduction and downstream pathways activated in APCs by this group of adjuvants we have, employing quantitative proteomic analytic tools, investigated human monocytes at various time points after treatment with CT. We report the activation of three main biological pathways among upregulated proteins, peaking at 16 hours of CT treatment: cellular organization, metabolism, and immune response. Specifically, in the further analyzed immune response pathway we note a strong upregulation of thrombospondin 1 (THBS1) and integrin β1 (ITGB1) in response to CT as well as to mmCT and dmLT, mediated via cAMP/PKA and NFKB signaling. Importantly, inhibition in vitro of THSB1 and ITGB1 in monocytes or primary dendritic cells using siRNA abrogated the ability of the treated APCs to promote an adjuvant-stimulated Th17 cell response when co-cultured with peripheral blood lymphocytes indicating the involvement of these molecules in the adjuvant action on APCs by CT, mmCT and dmLT.

The Rough Guide to Monocytes in Malaria Infection

While half of the world's population is at risk of malaria, the most vulnerable are still children under five, pregnant women and returning travelers. Anopheles mosquitoes transmit malaria parasites to the human host; but how Plasmodium interact with the innate immune system remains largely unexplored. The most recent advances prove that monocytes are a key component to control parasite burden and to protect host from disease. Monocytes' protective roles include phagocytosis, cytokine production and antigen presentation. However, monocytes can be involved in pathogenesis and drive inflammation and sequestration of infected red blood cells in organs such as the brain, placenta or lungs by secreting cytokines that upregulate expression of endothelial adhesion receptors. Plasmodium DNA, hemozoin or extracellular vesicles can impair the function of monocytes. With time, reinfections with Plasmodium change the relative proportion of monocyte subsets and their physical properties. These changes relate to clinical outcomes and might constitute informative biomarkers of immunity. More importantly, at the molecular level, transcriptional, metabolic or epigenetic changes can “prime” monocytes to alter their responses in future encounters with Plasmodium. This mechanism, known as trained immunity, challenges the traditional view of monocytes as a component of the immune system that lacks memory. Overall, this rough guide serves as an update reviewing the advances made during the past 5 years on understanding the role of monocytes in innate immunity to malaria.

Increasing FIM2/3 antigen-content improves efficacy of Bordetella pertussis vaccines in mice in vivo without altering vaccine-induced human reactogenicity biomarkers in vitro

Current acellular-pertussis (aP) vaccines appear inadequate for long-term pertussis control because of short-lived efficacy and the increasing prevalence of pertactin-negative isolates which may negatively impact vaccine efficacy. In this study, we added fimbriae (FIM)2 and FIM3 protein to licensed 2-, 3- or 5-component aP vaccines (Pentavac®, Boostrix®, Adacel®, respectively) to assess whether an aP vaccine with enhanced FIM content demonstrates enhanced efficacy. Vaccine-induced protection was assessed in an intranasal mouse challenge model. In addition, potential reactogenicity was measured by biomarkers in a human whole blood assay (WBA) in vitro and benchmarked the responses against licensed whole cell pertussis (wP) and aP vaccines including Easyfive®, Pentavac® and Pentacel®. The results show that commercial vaccines demonstrated reduced efficacy against pertactin-negative versus pertactin-positive strains. However, addition of higher amounts of FIM2/3 to aP vaccines reduced lung colonization and increased vaccine efficacy against a pertactin-negative strain in a dose-dependent manner. Improvements in efficacy were similar for FIM2 and FIM3-expressing strains. Increasing the amount of FIM2/3 proteins in aP formulations did not alter vaccine-induced biomarkers of potential reactogenicity including prostaglandin E₂, cytokines and chemokines in human newborn cord and adult peripheral blood tested in vitro. These results suggest that increasing the quantity of FIM proteins in current pertussis vaccine formulations may further enhance vaccine efficacy against B. pertussis infection without increasing the reactogenicity of the vaccine.

Applications of Immunomodulatory Immune Synergies to Adjuvant Discovery and Vaccine Development

Pathogens comprise a diverse set of immunostimulatory molecules that activate the innate immune system during infection. The immune system recognizes distinct combinations of pathogenic molecules leading to multiple immune activation events that cooperate to produce enhanced immune responses, known as 'immune synergies'. Effective immune synergies are essential for the clearance of pathogens, thus inspiring novel adjuvant design to improve vaccines. We highlight current vaccine adjuvants and the importance of immune synergies to adjuvant and vaccine design. The focus is on new technologies used to study and apply immune synergies to adjuvant and vaccine development. Finally, we discuss how recent findings can be applied to the future design and characterization of synergistic adjuvants and vaccines.

Early Life HIV-1 Immunization: Providing a Window for Protection Before Sexual Debut

Limited success of current HIV-1 vaccines warrants new approaches. We discuss feasibility and potential benefits of early life HIV-1 immunization followed by vaccine boosts during childhood that may enable maturation of vaccine-induced broad anti-HIV-1 immunity over several years. By initiating this immunization approach in the very young, well before sexual debut, such a strategy may dramatically reduce the risk of HIV-1 infection.

Mass Spectrometry-based Structural Analysis and Systems Immunoproteomics Strategies for Deciphering the Host Response to Endotoxin

One cause of sepsis is systemic maladaptive immune response of the host to bacteria and specifically, to Gram-negative bacterial outer-membrane glycolipid lipopolysaccharide (LPS). On the host myeloid cell surface, proinflammatory LPS activates the innate immune system via Toll-like receptor-4/myeloid differentiation factor-2 complex. Intracellularly, LPS is also sensed by the noncanonical inflammasome through caspase-11 in mice and 4/5 in humans. The minimal functional determinant for innate immune activation is the membrane anchor of LPS called lipid A. Even subtle modifications to the lipid A scaffold can enable, diminish, or abolish immune activation. Bacteria are known to modify their LPS structure during environmental stress and infection of hosts to alter cellular immune phenotypes. In this review, we describe how mass spectrometry-based structural analysis of endotoxin helped uncover major determinations of molecular pathogenesis. Through characterization of LPS modifications, we now better understand resistance to antibiotics and cationic antimicrobial peptides, as well as how the environment impacts overall endotoxin structure. In addition, mass spectrometry-based systems immunoproteomics approaches can assist in elucidating the immune response against LPS. Many regulatory proteins have been characterized through proteomics and global/targeted analysis of protein modifications, enabling the discovery and characterization of novel endotoxin-mediated protein translational modifications.

Neonatal Immunization: Rationale, Current State, and Future Prospects

Infections take their greatest toll in early life necessitating robust approaches to protect the very young. Here, we review the rationale, current state, and future research directions for one such approach: neonatal immunization. Challenges to neonatal immunization include natural concern about safety as well as a distinct neonatal immune system that is generally polarized against Th1 responses to many stimuli such that some vaccines that are effective in adults are not in newborns. Nevertheless, neonatal immunization could result in high-population penetration as birth is a reliable point of healthcare contact, and offers an opportunity for early protection of the young, including preterm newborns who are deficient in maternal antibodies. Despite distinct immunity and reduced responses to some vaccines, several vaccines have proven safe and effective at birth. While some vaccines such as polysaccharide vaccines have little effectiveness at birth, hepatitis B vaccine can prime at birth and requires multiple doses to achieve protection, whereas the live-attenuated Bacille Calmette-Guérin (BCG), may offer single shot protection, potentially in part via heterologous ("non-specific") beneficial effects. Additional vaccines have been studied at birth including those directed against pertussis, pneumococcus, Haemophilus influenza type B and rotavirus providing important lessons. Current areas of research in neonatal vaccinology include characterization of early life immune ontogeny, heterogeneity in and heterologous effects of BCG vaccine formulations, applying systems biology and systems serology, in vitro platforms that model age-specific human immunity and discovery and development of novel age-specific adjuvantation systems. These approaches may inform, de-risk, and accelerate development of novel vaccines for use in early life. Key stakeholders, including the general public, should be engaged in assessing the opportunities and challenges inherent to neonatal immunization.

Adjuvant pretreatment with alum protects neonatal mice in sepsis through myeloid cell activation

The high mortality in neonatal sepsis has been related to both quantitative and qualitative differences in host protective immunity. Pretreatment strategies to prevent sepsis have received inadequate consideration, especially in the premature neonate, where outcomes from sepsis are so dismal. Aluminium salts-based adjuvants (alum) are used currently in many paediatric vaccines, but their use as an innate immune stimulant alone has not been well studied. We asked whether pretreatment with alum adjuvant alone could improve outcome and host innate immunity in neonatal mice given polymicrobial sepsis. Subcutaneous alum pretreatment improves survival to polymicrobial sepsis in both wild-type and T and B cell-deficient neonatal mice, but not in caspase-1/11 null mice. Moreover, alum increases peritoneal macrophage and neutrophil phagocytosis, and decreases bacterial colonization in the peritoneum. Bone marrow-derived neutrophils from alum-pretreated neonates produce more neutrophil extracellular traps (NETs) and exhibit increased expression of neutrophil elastase (NE) after in-vitro stimulation with phorbol esters. In addition, alum pretreatment increases bone marrow and splenic haematopoietic stem cell expansion following sepsis. Pretreatment of neonatal mice with an alum-based adjuvant can stimulate multiple innate immune cell functions and improve survival. These novel findings suggest a therapeutic pathway for the use of existing alum-based adjuvants for preventing sepsis in premature infants.

Protecting the Newborn and Young Infant from Infectious Diseases: Lessons from Immune Ontogeny

Infections in the first year of life are common and often severe. The newborn host demonstrates both quantitative and qualitative differences to the adult in nearly all aspects of immunity, which at least partially explain the increased susceptibility to infection. Here we discuss how differences in susceptibility to infection result not out of a state of immaturity, but rather reflect adaptation to the particular demands placed on the immune system in early life. We review the mechanisms underlying host defense in the very young, and discuss how specific developmental demands increase the risk of particular infectious diseases. In this context, we discuss how this plasticity, i.e. the capacity to adapt to demands encountered in early life, also provides the potential to leverage protection of the young against infection and disease through a number of interventions.

Human blood monocytes are able to form extracellular traps

Neutrophil extracellular traps (NETs) are extracellular DNA filaments formed during neutrophil activation. This process, called netosis, was originally associated with neutrophil antibacterial properties. However, several lines of evidence now suggest a major role for netosis in thrombosis, autoimmune diseases, and cancer. We demonstrate here that highly purified human blood monocytes are also capable of extracellular trap (ET) release in response to several stimuli. Monocyte ETs display a morphology analogous to NETs and are associated with myeloperoxidase (MPO), lactoferrin (LF), citrullinated histones, and elastase. Monocyte ET release depends on oxidative burst but not on MPO activity, in contrast to neutrophils. Moreover, we demonstrate procoagulant activity for monocyte ETs, a feature that could be relevant to monocyte thrombogenic properties. This new cellular mechanism is likely to have implications in the multiple pathologic contexts where monocytes are implicated, such as inflammatory disorders, infection, or thrombosis.

Toll-like receptor 8 agonist nanoparticles mimic immunomodulating effects of the live BCG vaccine and enhance neonatal innate and adaptive immune responses

Background

Newborns display distinct immune responses, leaving them vulnerable to infections and impairing immunization. Targeting newborn dendritic cells (DCs), which integrate vaccine signals into adaptive immune responses, might enable development of age-specific vaccine formulations to overcome suboptimal immunization.

Objective

Small-molecule imidazoquinoline Toll-like receptor (TLR) 8 agonists robustly activate newborn DCs but can result in reactogenicity when delivered in soluble form. We used rational engineering and age- and species-specific modeling to construct and characterize polymer nanocarriers encapsulating a TLR8 agonist, allowing direct intracellular release after selective uptake by DCs.

Methods

Chemically similar but morphologically distinct nanocarriers comprised of amphiphilic block copolymers were engineered for targeted uptake by murine DCs in vivo, and a range of TLR8 agonist–encapsulating polymersome formulations were then synthesized. Novel 96-well in vitro assays using neonatal human monocyte-derived DCs and humanized TLR8 mouse bone marrow–derived DCs enabled benchmarking of the TLR8 agonist–encapsulating polymersome formulations against conventional adjuvants and licensed vaccines, including live attenuated BCG vaccine. Immunogenicity of the TLR8 agonist adjuvanted antigen 85B (Ag85B)/peptide 25–loaded BCG-mimicking nanoparticle formulation was evaluated in vivo by using humanized TLR8 neonatal mice.

Results

Although alum-adjuvanted vaccines induced modest costimulatory molecule expression, limited T_H-polarizing cytokine production, and significant cell death, BCG induced a robust adult-like maturation profile of neonatal DCs. Remarkably, TLR8 agonist polymersomes induced not only newborn DC maturation profiles similar to those induced by BCG but also stronger IL-12p70 production. On subcutaneous injection to neonatal mice, the TLR8 agonist–adjuvanted Ag85B peptide 25 formulation was comparable with BCG in inducing Ag85B-specific CD4⁺ T-cell numbers.

Conclusion

TLR8 agonist–encapsulating polymersomes hold substantial potential for early-life immunization against intracellular pathogens. Overall, our study represents a novel approach for rational design of early-life vaccines.

A Meningococcal Outer Membrane Vesicle Vaccine Incorporating Genetically Attenuated Endotoxin Dissociates Inflammation from Immunogenicity

Background

Group B Neisseria meningitidis, an endotoxin-producing Gram-negative bacterium, causes the highest incidence of group B meningococcus (MenB) disease in the first year of life. The Bexsero vaccine is indicated in Europe from 8 weeks of age. Endotoxin components of outer membrane vesicles (OMVs) or soluble lipopolysaccharide (LPS) represent a potential source of inflammation and residual reactogenicity. The purpose of this study was to compare novel candidate MenB vaccine formulations with licensed vaccines, including Bexsero, using age-specific human in vitro culture systems.

Methods

OMVs from wild type- and inactivated lpxL1 gene mutant-N. meningitidis strains were characterized in human neonatal and adult in vitro whole blood assays and dendritic cell (DC) arrays. OMVs were benchmarked against licensed vaccines, including Bexsero and whole cell pertussis formulations, with respect to Th-polarizing cytokine and prostaglandin E2 production, as well as cell surface activation markers (HLA-DR, CD86, and CCR7). OMV immunogenicity was assessed in mice.

Results

ΔlpxLI native OMVs (nOMVs) demonstrated significantly less cytokine induction in human blood and DCs than Bexsero and most of the other pediatric vaccines (e.g., PedvaxHib, EasyFive, and bacillus Calmette–Guérin) tested. Despite a much lower inflammatory profile in vitro than Bexsero, ΔlpxLI nOMVs still had moderate DC maturing ability and induced robust anti-N. meningitidis antibody responses after murine immunization.

Conclusion

A meningococcal vaccine comprised of attenuated LPS-based OMVs with a limited inflammatory profile in vitro induces robust antigen-specific immunogenicity in vivo.

Harnessing the beneficial heterologous effects of vaccination

Clinical evidence strongly suggests that certain live vaccines, in particular bacille Calmette-Guérin (BCG) and measles vaccines, can reduce all-cause mortality, most probably through protection against non-targeted pathogens in addition to the targeted pathogen. The underlying mechanisms are currently unknown. We discuss how heterologous lymphocyte activation and innate immune memory could promote protection beyond the intended target pathogen and consider how vaccinologists could leverage heterologous immunity to improve outcomes in vulnerable populations, in particular the very young and the elderly.