Pediatric Vaccine Adjuvants: Components of the Modern Vaccinologist's Toolbox

Comparative immunogenicity and safety of SpikoGen®, a recombinant SARS-CoV-2 spike protein vaccine in children and young adults: An immuno-bridging clinical trial

BACKGROUND

SpikoGen® is a recombinant subunit spike protein ectodomain vaccine manufactured in insect cells and formulated with the novel polysaccharide-based Advax-CpG55.2 adjuvant. This study aimed to compare the immunogenicity and safety of SpikoGen® vaccine in children, adolescents and young adults.

METHODS

This was a non-randomized, three-arm, open-label, parallel-group, immuno-bridging, non-inferiority trial to compare the immunogenicity and safety of a primary course of two intramuscular doses of SpikoGen® vaccine in children aged 5 to < 12 years, adolescents aged 12 to < 18 years and young adults aged 18 to 40 years. Children 5-12 years received a half dose of 12.5 μg spike protein, whereas the other groups received the full vaccine dose. Vaccine immunogenicity was evaluated via assessment of serum anti-spike and neutralizing antibodies 14 days after the second dose. Solicited adverse events were recorded for 7 days after each vaccination. Safety assessments including serious adverse events were continued through six months after the second dose in children and adolescents.

RESULTS

Two weeks after the second dose, seroconversion rates for neutralizing antibody levels were not significantly different for children (59.50 %), adolescents (52.06 %) and adults (56.01 %). The 95 % confidence interval of the difference in seroconversion rates between children and adults was within the prespecified non-inferiority margin of 10 % (-12 % to 5 %). SpikoGen® vaccine was well tolerated in all age groups with the most common solicited adverse events being injection site pain and fatigue which were generally transient and mild.

CONCLUSION

SpikoGen® vaccine was shown to be safe, well tolerated and immunogenic in children as young as 5 years of age, with non-inferior responses to those seen in adults. The Iranian FDA authorisation of SpikoGen® vaccine is now extended down to 5 years of age.

Safety and immunogenicity of BK-SE36/CpG malaria vaccine in healthy Burkinabe adults and children: a phase 1b randomised, controlled, double-blinded, age de-escalation trial

Background

BK-SE36/CpG is a recombinant blood-stage malaria vaccine candidate based on the N-terminal Plasmodium falciparum serine repeat antigen5 (SE36), adsorbed to aluminium hydroxide gel and reconstituted, prior to administration, with synthetic oligodeoxynucleotides bearing CpG motifs. In healthy Japanese adult males, BK-SE36/CpG was well tolerated. This study assessed its safety and immunogenicity in healthy malaria-exposed African adults and children.

Methods

A double-blind, randomised, controlled, age de-escalating clinical trial was conducted in an urban area of Ouagadougou, Burkina Faso. Healthy participants (n=135) aged 21-45 years (Cohort 1), 5-10 years (Cohort 2) and 12-24 months (Cohort 3) were randomised to receive three vaccine doses (Day 0, 28 and 112) of BK-SE36/CpG or rabies vaccine by intramuscular injection.

Results

One hundred thirty-four of 135 (99.2%) subjects received all three scheduled vaccine doses. Vaccinations were well tolerated with no related Grade 3 (severe) adverse events (AEs). Pain/limitation of limb movement, headache in adults and fever in younger children (all mild to moderate in intensity) were the most frequently observed local and systemic AEs. Eighty-three of BK-SE36/CpG (91%) recipients and 37 of control subjects (84%) had Grade 1/2 events within 28 days post vaccination. Events considered by the investigator to be vaccine related were experienced by 38% and 14% of subjects in BK-SE36/CpG and control arms, respectively. Throughout the trial, six Grade 3 events (in 4 subjects), not related to vaccination, were recorded in the BK-SE36/CpG arm: 5 events (in 3 subjects) within 28 days of vaccination. All serious adverse events (SAEs) (n=5) were due to severe malaria (52-226 days post vaccination) and not related to vaccination. In all cohorts, BK-SE36/CpG arm had higher antibody titres after Dose 3 than after Dose 2. Younger cohorts had stronger immune responses (12-24-month-old > 5-10 years-old > 21-45 years-old). Sera predominantly reacted to peptides that lie in intrinsically unstructured regions of SE36. In the control arm, there were no marked fold changes in antibody titres and participants' sera reacted poorly to all peptides spanning SE36.

Conclusion

BK-SE36/CpG was well-tolerated and immunogenic. These results pave the way for further proof-of-concept studies to demonstrate vaccine efficacy.

Clinical trial registration

https://pactr.samrc.ac.za/TrialDisplay.aspx?TrialID=1921, PACTR201701001921166.

Precision Vaccinology Approaches for the Development of Adjuvanted Vaccines Targeted to Distinct Vulnerable Populations

Infection persists as one of the leading global causes of morbidity and mortality, with particular burden at the extremes of age and in populations who are immunocompromised or suffer chronic co-morbid diseases. By focusing discovery and innovation efforts to better understand the phenotypic and mechanistic differences in the immune systems of diverse vulnerable populations, emerging research in precision vaccine discovery and development has explored how to optimize immunizations across the lifespan. Here, we focus on two key elements of precision vaccinology, as applied to epidemic/pandemic response and preparedness, including (a) selecting robust combinations of adjuvants and antigens, and (b) coupling these platforms with appropriate formulation systems. In this context, several considerations exist, including the intended goals of immunization (e.g., achieving immunogenicity versus lessening transmission), reducing the likelihood of adverse reactogenicity, and optimizing the route of administration. Each of these considerations is accompanied by several key challenges. On-going innovation in precision vaccinology will expand and target the arsenal of vaccine components for protection of vulnerable populations.

Development of a TLR7/8 agonist adjuvant formulation to overcome early life hyporesponsiveness to DTaP vaccination

Infection is the most common cause of mortality early in life, yet the broad potential of immunization is not fully realized in this vulnerable population. Most vaccines are administered during infancy and childhood, but in some cases the full benefit of vaccination is not realized in-part. New adjuvants are cardinal to further optimize current immunization approaches for early life. However, only a few classes of adjuvants are presently incorporated in vaccines approved for human use. Recent advances in the discovery and delivery of Toll-like receptor (TLR) agonist adjuvants have provided a new toolbox for vaccinologists. Prominent among these candidate adjuvants are synthetic small molecule TLR7/8 agonists. The development of an effective infant Bordetella pertussis vaccine is urgently required because of the resurgence of pertussis in many countries, contemporaneous to the switch from whole cell to acellular vaccines. In this context, TLR7/8 adjuvant based vaccine formulation strategies may be a promising tool to enhance and accelerate early life immunity by acellular B. pertussis vaccines. In the present study, we optimized (a) the formulation delivery system, (b) structure, and (c) immunologic activity of novel small molecule imidazoquinoline TLR7/8 adjuvants towards human infant leukocytes, including dendritic cells. Upon immunization of neonatal mice, this TLR7/8 adjuvant overcame neonatal hyporesponsiveness to acellular pertussis vaccination by driving a T helper (Th)1/Th17 biased T cell- and IgG2c-skewed humoral response to a licensed acellular vaccine (DTaP). This potent immunization strategy may represent a new paradigm for effective immunization against pertussis and other pathogens in early life.

Pattern recognition receptor ligand-induced differentiation of human transitional B cells

B cells represent a critical component of the adaptive immune response whose development and differentiation are determined by antigen-dependent and antigen-independent interactions. In this study, we explored the effects of IL-4 and pattern-recognition receptor (PRR) ligands on B cell development and differentiation by investigating their capacity to drive the in vitro maturation of human transitional B cells. In the presence of IL-4, ligands for TLR7/8, TLR9, and NOD1 were effective in driving the in vitro maturation of cord blood transitional B cells into mature, naïve B cells as measured by CD23 expression, ABCB1 transporter activation and upregulation of sIgM and sIgD. In addition, several stimulation conditions, including TLR9 ligand alone, favored an expansion of CD27⁺ IgM memory B cells. Transitional B cells stimulated with TLR7/8 ligand + IL-4 or TLR9 ligand, with or without IL-4, induced a significant subpopulation of CD23⁺CD27⁺ B cells expressing high levels of sIgM and sIgD, a minor B cell subpopulation found in human peripheral blood. These studies illustrate the heterogeneity of the B cell populations induced by cytokine and PRR ligand stimulation. A comparison of transitional and mature, naïve B cells transcriptomes to identify novel genes involved in B cell maturation revealed that mature, naïve B cells were less transcriptionally active than transitional B cells. Nevertheless, a subset of differentially expressed genes in mature, naïve B cells was identified including genes associated with the IL-4 signaling pathway, PI3K signaling in B lymphocytes, the NF-κB signaling pathway, and the TNFR superfamily. When transitional B cells were stimulated in vitro with IL-4 and PRR ligands, gene expression was found to be dependent on the nature of the stimulants, suggesting that exposure to these stimulants may alter the developmental fate of transitional B cells. The influence of IL-4 and PRR signaling on transitional B cell maturation illustrates the potential synergy that may be achieved when certain PRR ligands are incorporated as adjuvants in vaccine formulations and presented to developing B cells in the context of an inflammatory cytokine environment. These studies demonstrate the potential of the PRR ligands to drive transitional B cell differentiation in the periphery during infection or vaccination independently of antigen mediated BCR signaling.

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.

A comparative study of adjuvants effects on neonatal plasma cell survival niche in bone marrow and persistence of humoral immune responses

The neonatal immune system is distinct from the immune system of older individuals rendering neonates vulnerable to infections and poor responders to vaccination. Adjuvants can be used as tools to enhance immune responses to co-administered antigens. Antibody (Ab) persistence is mediated by long-lived plasma cells that reside in specialized survival niches in the bone marrow, and transient Ab responses in early life have been associated with decreased survival of plasma cells, possibly due to lack of survival factors. Various cells can secrete these factors and which cells are the main producers is still up for debate, especially in early life where this has not been fully addressed. The receptor BCMA and its ligand APRIL have been shown to be important in the maintenance of plasma cells and Abs. Herein, we assessed age-dependent maturation of a broad range of bone marrow accessory cells and their expression of the survival factors APRIL and IL-6. Furthermore, we performed a comparative analysis of the potential of 5 different adjuvants; LT-K63, mmCT, MF59, IC31 and alum, to enhance expression of survival factors and BCMA following immunization of neonatal mice with tetanus toxoid (TT) vaccine. We found that APRIL expression was reduced in the bone marrow of young mice whereas IL-6 expression was higher. Eosinophils, macrophages, megakaryocytes, monocytes and lymphocytes were important secretors of survival factors in early life but undefined cells also constituted a large fraction of secretors. Immunization and adjuvants enhanced APRIL expression but decreased IL-6 expression in bone marrow cells early after immunization. Furthermore, neonatal immunization with adjuvants enhanced the proportion of plasmablasts and plasma cells that expressed BCMA both in spleen and bone marrow. Enhanced BCMA expression correlated with enhanced vaccine-specific humoral responses, even though the effect of alum on BCMA was less pronounced than those of the other adjuvants at later time points. We propose that low APRIL expression in bone marrow as well as low BCMA expression of plasmablasts/plasma cells in early life together cause transient Ab responses and could represent targets to be triggered by vaccine adjuvants to induce persistent humoral immune responses in this age group.

Application of Nanoparticles in Tumour Targeted Drug Delivery and Vaccine

Cancer is a major cause of death worldwide, and nearly 1 in 6 deaths each year is caused by cancer. Traditional cancer treatment strategies cannot completely solve cancer recurrence and metastasis. With the development of nanotechnology, the study of nanoparticles (NPs) has gradually become a hotspot of medical research. NPs have various advantages. NPs exploit the enhanced permeability and retention (EPR) of tumour cells to achieve targeted drug delivery and can be retained in tumours long-term. NPs can be used as a powerful design platform for vaccines as well as immunization enhancers. Liposomes, as organic nanomaterials, are widely used in the preparation of nanodrugs and vaccines. Currently, most of the anticancer drugs that have been approved and entered clinical practice are prepared from lipid materials. However, the current clinical conversion rate of NPs is still extremely low, and the transition of NPs from the laboratory to clinical practice is still a substantial challenge. In this paper, we review the in vivo targeted delivery methods, material characteristics of NPs and the application of NPs in vaccine preparation. The application of nanoliposomes is also emphasized. Furthermore, the challenges and limitations of NPs are briefly discussed.

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.

Precision Vaccine Development: Cues From Natural Immunity

Traditional vaccine development against infectious diseases has been guided by the overarching aim to generate efficacious vaccines normally indicated by an antibody and/or cellular response that correlates with protection. However, this approach has been shown to be only a partially effective measure, since vaccine- and pathogen-specific immunity may not perfectly overlap. Thus, some vaccine development strategies, normally focused on targeted generation of both antigen specific antibody and T cell responses, resulting in a long-lived heterogenous and stable pool of memory lymphocytes, may benefit from better mimicking the immune response of a natural infection. However, challenges to achieving this goal remain unattended, due to gaps in our understanding of human immunity and full elucidation of infectious pathogenesis. In this review, we describe recent advances in the development of effective vaccines, focusing on how understanding the differences in the immunizing and non-immunizing immune responses to natural infections and corresponding shifts in immune ontogeny are crucial to inform the next generation of infectious disease vaccines.

Exploration of Pattern Recognition Receptor Agonists as Candidate Adjuvants

Adjuvants are used to maximize the potency of vaccines by enhancing immune reactions. Components of adjuvants include pathogen-associated molecular patterns (PAMPs) and damage-associate molecular patterns (DAMPs) that are agonists for innate immune receptors. Innate immune responses are usually activated when pathogen recognition receptors (PRRs) recognize PAMPs derived from invading pathogens or DAMPs released by host cells upon tissue damage. Activation of innate immunity by PRR agonists in adjuvants activates acquired immune responses, which is crucial to enhance immune reactions against the targeted pathogen. For example, agonists for Toll-like receptors have yielded promising results as adjuvants, which target PRR as adjuvant candidates. However, a comprehensive understanding of the type of immunological reaction against agonists for PRRs is essential to ensure the safety and reliability of vaccine adjuvants. This review provides an overview of the current progress in development of PRR agonists as vaccine adjuvants, the molecular mechanisms that underlie activation of immune responses, and the enhancement of vaccine efficacy by these potential adjuvant candidates.

Recent trends in the development of Toll-like receptor 7/8-targeting therapeutics

Introduction: Toll-like receptor (TLR) 7 and TLR8 are functionally localized to endosomes and recognize specific RNA sequences. They play crucial roles in initiating innate and adaptive immune responses. TLR7/8 activation protects the host against invading pathogens and enhances immune responses. In contrast, sustained TLR7/8 signaling leads to immune overreaction. Therefore, agonists or antagonists targeting TLR7/8 signaling are favorable drug candidates for the treatment of immune disorders.Areas covered: Basic knowledge about TLR7 and TLR8 and their signaling pathways are briefly reviewed. Various therapeutic agents have been designed to activate or antagonize TLR7/8 signaling pathways, and their safety and efficacy for the treatment of multiple diseases have been investigated in preclinical animal models and clinical trials. TLR7/8 agonists exhibit potent antiviral activity and regulate anti-tumor immune responses. TLR7 agonists have also been used as adjuvants to improve vaccine immunogenicity and generate greater seroprotection. TLR7/8 antagonists are promising candidates for the treatment of autoimmune and inflammatory diseases.Expert opinion: TLR7/8 pathways are favorable targets for immunological therapies. Future research should concentrate on the optimization of drug safety, efficiency, and specificity. Detailed mechanistic studies will contribute to the development of TLR7/8 immunomodulators and novel therapeutic strategies.

Development of vaccine formulations: past, present, and future

The current situation, heavily influenced by the ongoing pandemic, puts vaccines back into the spotlight. However, the conventional and traditional vaccines present disadvantages, particularly related to immunogenicity, stability, and storage of the final product. Often, such products require the maintenance of a “cold chain,” impacting the costs, the availability, and the distribution of vaccines. Here, after a recall of the mode of action of vaccines and the types of vaccines currently available, we analyze the past, present, and future of vaccine formulation. The past focuses on conventional formulations, the present discusses the use of nanoparticles for vaccine delivery and as adjuvants, while the future presents microneedle patches as alternative formulation and administration route. Finally, we compare the advantages and disadvantages of injectable solutions, nanovaccines, and microneedles in terms of efficacy, stability, and patient-friendly design.

Different approaches to vaccine formulation development, the conventional vaccine formulations from the past, the current development of lipid nanoparticles as vaccines, and the near future microneedles formulations are discussed in this review. 

The sixth revolution in pediatric vaccinology: immunoengineering and delivery systems

Infection is the predominant cause of mortality in early life, and immunization is the most promising biomedical intervention to reduce this burden. However, very young infants fail to respond optimally to most vaccines currently in use, especially neonates. In 2005, Stanley Plotkin proposed that new delivery systems would spur a new revolution in pediatric vaccinology, just as attenuation, inactivation, cell culture of viruses, genetic engineering, and adjuvantation had done in preceding decades. Recent advances in the field of immunoengineering, which is evolving alongside vaccinology, have begun to increasingly influence vaccine formulation design. Historically, the particulate nature of materials used in many vaccine formulations was empiric, often because of the need to stabilize antigens or reduce endotoxin levels. However, present vaccine delivery systems are rationally engineered to mimic the size, shape, and surface chemistry of pathogens, and are therefore often referred to as "pathogen-like particles". More than a decade from his original assessment, we re-assess Plotkin's prediction. In addition, we highlight how immunoengineering and advanced delivery systems may be uniquely capable of enhancing vaccine responses in vulnerable populations, such as infants. IMPACT: Immunoengineering and advanced delivery systems are leading to new developments in pediatric vaccinology. Summarizes delivery systems currently in use and development, and prospects for the future. Broad overview of immunoengineering's impact on vaccinology, catering to Pediatric Clinicians and Immunologists.

Towards Precision Vaccines: Lessons From the Second International Precision Vaccines Conference

Other than clean drinking water, vaccines have been the most effective public health intervention in human history, yet their full potential is still untapped. To date, vaccine development has been largely limited to empirical approaches focused on infectious diseases and has targeted entire populations, potentially disregarding distinct immunity in vulnerable populations such as infants, elders, and the immunocompromised. Over the past few decades innovations in genetic engineering, adjuvant discovery, formulation science, and systems biology have fueled rapid advances in vaccine research poised to consider demographic factors (e.g., age, sex, genetics, and epigenetics) in vaccine discovery and development. Current efforts are focused on leveraging novel approaches to vaccine discovery and development to optimize vaccinal antigen and, as needed, adjuvant systems to enhance vaccine immunogenicity while maintaining safety. These approaches are ushering in an era of precision vaccinology aimed at tailoring immunization for vulnerable populations with distinct immunity. To foster collaboration among leading vaccinologists, government, policy makers, industry partners, and funders from around the world, the Precision Vaccines Program at Boston Children's Hospital hosted the 2nd International Precision Vaccines Conference (IPVC) at Harvard Medical School on the 17th-18th October 2019. The conference convened experts in vaccinology, including vaccine formulation and adjuvantation, immunology, cell signaling, systems biology, biostatistics, bioinformatics, as well as vaccines for non-infectious indications such as cancer and opioid use disorder. Herein we review highlights from the 2nd IPVC and discuss key concepts in the field of precision vaccines.

BCG as a Case Study for Precision Vaccine Development: Lessons From Vaccine Heterogeneity, Trained Immunity, and Immune Ontogeny

Vaccines have been traditionally developed with the presumption that they exert identical immunogenicity regardless of target population and that they provide protection solely against their target pathogen. However, it is increasingly appreciated that vaccines can have off-target effects and that vaccine immunogenicity can vary substantially with demographic factors such as age and sex. Bacille Calmette-Guérin (BCG), the live attenuated Mycobacterium bovis vaccine against tuberculosis (TB), represents a key example of these concepts. BCG vaccines are manufactured under different conditions across the globe generating divergent formulations. Epidemiologic studies have linked early life immunization with certain BCG formulations to an unanticipated reduction (∼50%) in all-cause mortality, especially in low birthweight males, greatly exceeding that attributable to TB prevention. This mortality benefit has been related to prevention of sepsis and respiratory infections suggesting that BCG induces "heterologous" protection against unrelated pathogens. Proposed mechanisms for heterologous protection include vaccine-induced immunometabolic shifts, epigenetic reprogramming of innate cell populations, and modulation of hematopoietic stem cell progenitors resulting in altered responses to subsequent stimuli, a phenomenon termed "trained immunity." In addition to genetic differences, licensed BCG formulations differ markedly in content of viable mycobacteria key for innate immune activation, potentially contributing to differences in the ability of these diverse formulations to induce TB-specific and heterologous protection. BCG immunomodulatory properties have also sparked interest in its potential use to prevent or alleviate autoimmune and inflammatory diseases, including type 1 diabetes mellitus and multiple sclerosis. BCG can also serve as a model: nanoparticle vaccine formulations incorporating Toll-like receptor 8 agonists can mimic some of BCG's innate immune activation, suggesting that aspects of BCG's effects can be induced with non-replicating stimuli. Overall, BCG represents a paradigm for precision vaccinology, lessons from which will help inform next generation vaccines.

The TLR5 Agonist Flagellin Shapes Phenotypical and Functional Activation of Lung Mucosal Antigen Presenting Cells in Neonatal Mice

Intranasal mucosal vaccines are an attractive approach to induce protective mucosal immune responses. Activation of lung antigen presenting cells (APCs), a phenotypically and functionally heterogeneous cell population located at distinct mucosal sites, may be key to the immunogenicity of such vaccines. Understanding responsiveness of newborn lung APCs to adjuvants may the inform design of efficacious intranasal vaccines for early life, when most infections occur. Here, we characterized and phenotyped APCs from neonatal (7 days of life) and adult (6-8 weeks of age) mice. Neonatal mice demonstrated a relatively high abundance of alveolar macrophages (AMs), with lower percentages of plasmacytoid dendritic cells (pDCs), CD103+ (cDC1), and CD11b+ (cDC2) DCs. Furthermore, neonatal CD103+ and CD11b+ DC subsets demonstrated a significantly lower expression of maturation markers (CD40, CD80, and CD86) as compared to adult mice. Upon stimulation of lung APC subsets with a panel of pattern recognition receptor (PRR) agonists, including those engaging TLRs or STING, CD11c+ enriched cells from neonatal and adult mice lungs demonstrated distinct maturation profiles. Of the agonists tested, the TLR5 ligand, flagellin, was most effective at activating neonatal lung APCs, inducing significantly higher expression of maturation markers on CD103+ (cDC1) and CD11b+ (cDC2) subsets. Intranasal administration of flagellin induced a distinct migration of CD103+ and CD11b+ DC subsets to the mediastinal lymph nodes (mLNs) of neonatal mice. Overall, these findings highlight age-specific differences in the maturation and responsiveness of lung APC subsets to different PRR agonists. The unique efficacy of flagellin in enhancing lung APC activity suggests that it may serve as an effective adjuvant for early life mucosal vaccines.

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.

Triggering of Toll-like Receptors in Old Individuals. Relevance for Vaccination

Aging is characterized by a general decline in a range of physiological functions, with a consequent increase in the risk of developing a variety of chronic diseases and geriatric syndromes. Additionally, increasing age is accompanied by a progressive decline in both innate and acquired immune system, referred to as immunosenescence. This impaired ability to mount an efficient immune response after exposure to microorganisms or vaccines represents a major challenge in acquiring protection against pathogens in aging. Therefore, there is still a great need for vaccines that are tailored to optimally stimulate the aged immune system, thus promoting more successful aging. Various strategies can be used to improve vaccine efficacy in old people. Despite this, metaanalyses have clearly shown that the magnitude of protection obtained remains lower in older adults. Recent studies show that stimulation of Toll-like receptors, using stimulatory ligands, can enhance vaccine efficacy by a number of mechanisms, including the activation of innate immune cells and the consequent production of inflammatory cytokines. Therefore, a possible strategy for more effective vaccination in the older population is the triggering of multiple TLRs, using a combined adjuvant for the synergistic activation of cellular immunity. Preliminary in vitro data suggest that in humans the presence of multiple TLR agonists can result in the greater stimulation of antigen-specific immune responses in immune cells both in the young healthy and in the immune senescent older donors. These data suggest that appropriately selected combinations of TLR agonists could enhance the efficacy of vaccination mediated immunity in older people.

First International Precision Vaccines Conference: Multidisciplinary Approaches to Next-Generation Vaccines

Vaccines represent a remarkable success in the history of medicine since they have prevented and, in some instances, eradicated a range of infectious diseases. However, for many existing vaccines, immunogenicity is limited, requiring multiple booster doses, and we are still unable to target many pathogens due to intrinsic features of the microorganism, such as genetic/antigenic variability between strains, and our limited understanding of the variables that regulate vaccine responsiveness, including age- and sex-specific differences. Moreover, the traditional approach to vaccine development is often empirical, relying on inactivation of microorganisms or purification of their components, which are usually less immunogenic than the whole microorganism from which they derive. This approach has yielded multiple important vaccines but has failed to consistently generate vaccines that are sufficiently immunogenic in populations with limited immune responsiveness such as newborns and elderly individuals. In an effort to trigger impactful collaborations, a community of scientists gathered in Boston in the United States for the first biennial International Precision Vaccines Conference, sponsored by the Boston Children's Hospital Precision Vaccines Program, to discuss innovation in vaccinology. Recent advancements in the field of systems biology that can identify vaccine immunogenicity biomarkers for target populations, in human in vitro models, and in novel adjuvant and formulation strategies offer unprecedented opportunities to dissect the human immune response to vaccines and inform dramatic improvements in vaccine efficacy. These approaches are poised to have a major scientific and translational impact in vaccinology.

TLR agonist combinations that stimulate Th type I polarizing responses from human neonates

Each year millions of neonates die due to vaccine preventable infectious diseases. Our study seeks to develop novel neonatal vaccines and improve immunogenicity of early childhood vaccines by incorporating TLR agonist-adjuvant combinations that overcome the inherent neonatal Th2 bias and stimulate Th1 polarizing response from neonatal APCs. We systematically stimulated cord blood mononuclear cells with single and multiple combinations of TLR agonists and measured levels of IL-12p70, IFN-γ, IFN-α, IL-10, IL-13, TNF-α, IL-6 and IL-1β from cell culture supernatants. APC-specific surface expression levels of costimulatory markers CD40, CD83 and PD-L1 were assessed by flow cytometry. Whole blood assays were included to account for the effect of plasma inhibitory factors and APC intracellular TNF-α and IL-12p40 secretions were measured. We found robust Th1 polarizing IL-12p70, IFN-γ and IFN-α responses when cord blood APCs were stimulated with TLR agonist combinations that contained Poly I:C, Monophosphoryl Lipid A (MPLA) or R848. Addition of class A CpG oligonucleotide (ODN) to Th1 polarizing TLR agonist combinations significantly reduced cord blood IL-12p70 and IFN-γ levels and addition of a TLR2 agonist induced significantly high Th2 polarizing IL-13. Multi-TLR agonist combinations that included R848 induced lower inhibitory PD-L1 expression on cord blood classical dendritic cells than CpG ODN-containing combinations. Incorporation of combination adjuvants containing TLR3, TLR4 and TLR7/8 agonists to neonatal vaccines may be an effective strategy to overcome neonatal Th2 bias.

Adjuvant Effect of Bacille Calmette-Guérin on Hepatitis B Vaccine Immunogenicity in the Preterm and Term Newborn

Immunization is key to protecting term and preterm infants from a heightened risk of infection. However, preterm immunity is distinct from that of the term, limiting its ability to effectively respond to vaccines routinely given at birth, such as hepatitis B vaccine (HBV). As part of the Expanded Program on Immunization, HBV is often given together with the live-attenuated vaccine Bacille Calmette-Guérin (BCG), known to activate multiple pattern-recognition receptors. Of note, some clinical studies suggest BCG can enhance efficacy of other vaccines in term newborns. However, little is known about whether BCG can shape Th-polarizing cytokine responses to HBV nor the age-dependency of such effects, including whether they may extend to the preterm. To characterize the effects of BCG on HBV immunogenicity, we studied individual and combined administration of these vaccines to cord newborn and adult human whole blood and mononuclear cells in vitro and to neonatal and adult mice in vivo. Compared to either BCG or HBV alone, (BCG + HBV) synergistically enhanced in vitro whole blood production of IL-1β, while (BCG + HBV) also promoted production of several cytokines/chemokines in all age groups, age-specific enhancement included IL-12p70 in the preterm and GM-CSF in the preterm and term. In human mononuclear cells, (BCG + HBV) enhanced mRNA expression of several genes including CSF2, which contributed to clustering of genes by vaccine treatment via principle component analysis. To assess the impact of BCG on HBV immunization, mice of three different age groups were immunized subcutaneously with, BCG, HBV, (BCG + HBV) into the same site; or BCG and HBV injected into separate sites. Whether injected into a separate site or at the same site, co-administration of BCG with HBV significantly enhanced anti-HBV IgG titers in mice immunized on day of life-0 or -7, respectively, but not in adult mice. In summary, our data demonstrate that innate and adaptive vaccine responses of preterm and term newborns are immunologically distinct. Furthermore, BCG or "BCG-like" adjuvants should be further studied as a promising adjuvantation approach to enhance immunogenicity of vaccines to protect these vulnerable populations.

Identification and Characterization of Stimulator of Interferon Genes As a Robust Adjuvant Target for Early Life Immunization

Immunization is key to preventing infectious diseases, a leading cause of death early in life. However, due to age-specific immunity, vaccines often demonstrate reduced efficacy in newborns and young infants as compared to adults. Here, we combined in vitro and in vivo approaches to identify adjuvant candidates for early life immunization. We employed newborn and adult bone marrow-derived dendritic cells (BMDCs) to perform a screening of pattern recognition receptor agonists and found that the stimulator of interferon genes ligand 2′3′-cGAMP (hereafter cGAMP) induces a comparable expression of surface maturation markers in newborn and adult BMDCs. Then, we utilized the trivalent recombinant hemagglutinin (rHA) influenza vaccine, Flublok, as a model antigen to investigate the role of cGAMP in adult and early life immunization. cGAMP adjuvantation alone could increase rHA-specific antibody titers in adult but not newborn mice. Remarkably, as compared to alum or cGAMP alone, immunization with cGAMP formulated with alum (Alhydrogel) enhanced newborn rHA-specific IgG2a/c titers ~400-fold, an antibody subclass associated with the development of IFNγ-driven type 1 immunity in vivo and endowed with higher effector functions, by 42 days of life. Highlighting the amenability for successful vaccine formulation and delivery, we next confirmed that cGAMP adsorbs onto alum in vitro. Accordingly, immunization early in life with (cGAMP+alum) promoted IFNγ production by CD4⁺ T cells and increased the proportions and absolute numbers of CD4⁺ CXCR5⁺ PD-1⁺ T follicular helper and germinal center (GC) GL-7⁺ CD138⁺ B cells, suggesting an enhancement of the GC reaction. Adjuvantation effects were apparently specific for IgG2a/c isotype switching without effect on antibody affinity maturation, as there was no effect on rHA-specific IgG avidity. Overall, our studies suggest that cGAMP when formulated with alum may represent an effective adjuvantation system to foster humoral and cellular aspects of type 1 immunity for early life immunization.

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.

TLR7/8 adjuvant overcomes newborn hyporesponsiveness to pneumococcal conjugate vaccine at birth

Infection is the most common cause of mortality in early life, and immunization is the most promising biomedical intervention to reduce this burden. However, newborns fail to respond optimally to most vaccines. Adjuvantation is a key approach to enhancing vaccine immunogenicity, but responses of human newborn leukocytes to most candidate adjuvants, including most TLR agonists, are functionally distinct. Herein, we demonstrate that 3M-052 is a locally acting lipidated imidazoquinoline TLR7/8 agonist adjuvant in mice, which, when properly formulated, can induce robust Th1 cytokine production by human newborn leukocytes in vitro, both alone and in synergy with the alum-adjuvanted pneumococcal conjugate vaccine 13 (PCV13). When admixed with PCV13 and administered i.m. on the first day of life to rhesus macaques, 3M-052 dramatically enhanced generation of Th1 CRM-197-specific neonatal CD4⁺ cells, activation of newborn and infant Streptococcus pneumoniae polysaccharide-specific (PnPS-specific) B cells as well as serotype-specific antibody titers, and opsonophagocytic killing. Remarkably, a single dose at birth of PCV13 plus 0.1 mg/kg 3M-052 induced PnPS-specific IgG responses that were approximately 10-100 times greater than a single birth dose of PCV13 alone, rapidly exceeding the serologic correlate of protection, as early as 28 days of life. This potent immunization strategy, potentially effective with one birth dose, could represent a new paradigm in early life vaccine development.

Surface Coating of Nanoparticles Reduces Background Inflammatory Activity while Increasing Particle Uptake and Delivery

In the study of host-pathogen interactions, vaccines and drug delivery, particulate delivery system are widely used to mimic pathogen size, pattern recognition receptor agonist presentation, and target cells or organs. However, some of the polymeric systems used in particulate delivery have inherent inflammatory properties that are variable and nonspecific. These properties enhance their adjuvant activity, but confound the analysis of signaling mechanisms. Here, we present a method for particle coating with minimal background immune activation via passivation of the surface with silica-silane. We show herein that a silica-silane shell passivates polymer particles rendering them inert to activation of innate immune cells. The method is broadly applicable and can be used to coat polymeric particles of many different compositions. This method of silica-silane coating also allows conjugation of amine-bearing agonists and provides for controlled variation of agonist loading. Finally, we demonstrate our particles maintain and enhance qualities of known pathogens, making this a potentially general method for improving immune agonist activity.

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.

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

Adjuvants boost vaccine responses, enhancing protective immunity against infections that are most common among the very young. Many adjuvants activate innate immunity, some via Toll-Like Receptors (TLRs), whose activities varies with age. Accordingly, characterization of age-specific adjuvant-induced immune responses may inform rational adjuvant design targeting vulnerable populations. In this study, we employed proteomics to characterize the adjuvant-induced changes of secretomes from human newborn and adult monocytes in response to Alum, the most commonly used adjuvant in licensed vaccines; Monophosphoryl Lipid A (MPLA), a TLR4-activating adjuvant component of a licensed Human Papilloma Virus vaccine; and R848 an imidazoquinoline TLR7/8 agonist that is a candidate adjuvant for early life vaccines. Monocytes were incubated in vitro for 24 h with vehicle, Alum, MPLA, or R848 and supernatants collected for proteomic analysis employing liquid chromatography-mass spectrometry (LC-MS) (data available via ProteomeXchange, ID PXD003534). 1894 non-redundant proteins were identified, of which ∼30 - 40% were common to all treatment conditions and ∼5% were treatment-specific. Adjuvant-stimulated secretome profiles, as identified by cluster analyses of over-represented proteins, varied with age and adjuvant type. Adjuvants, especially Alum, activated multiple innate immune pathways as assessed by functional enrichment analyses. Release of lactoferrin, pentraxin 3, and matrix metalloproteinase-9 was confirmed in newborn and adult whole blood and blood monocytes stimulated with adjuvants alone or adjuvanted licensed vaccines with distinct clinical reactogenicity profiles. MPLA-induced adult monocyte secretome profiles correlated in silico with transcriptome profiles induced in adults immunized with the MPLA-adjuvanted RTS,S malaria vaccine (Mosquirix™). Overall, adjuvants such as Alum, MPLA and R848 give rise to distinct and age-specific monocyte secretome profiles, paralleling responses to adjuvant-containing vaccines in vivo. Age-specific in vitro modeling coupled with proteomics may provide fresh insight into the ontogeny of adjuvant action thereby informing targeted adjuvanted vaccine development for distinct age groups.