Engineering a Next-Generation Glycoconjugate-Like Streptococcus pneumoniae Vaccine

Harnessing synthetic biology for advancing RNA therapeutics and vaccine design

Recent global events have drawn into focus the diversity of options for combatting disease across a spectrum of prophylactic and therapeutic approaches. The recent success of the mRNA-based COVID-19 vaccines has paved the way for RNA-based treatments to revolutionize the pharmaceutical industry. However, historical treatment options are continuously updated and reimagined in the context of novel technical developments, such as those facilitated through the application of synthetic biology. When it comes to the development of genetic forms of therapies and vaccines, synthetic biology offers diverse tools and approaches to influence the content, dosage, and breadth of treatment with the prospect of economic advantage provided in time and cost benefits. This can be achieved by utilizing the broad tools within this discipline to enhance the functionality and efficacy of pharmaceutical agent sequences. This review will describe how synthetic biology principles can augment RNA-based treatments through optimizing not only the vaccine antigen, therapeutic construct, therapeutic activity, and delivery vector. The enhancement of RNA vaccine technology through implementing synthetic biology has the potential to shape the next generation of vaccines and therapeutics.

Semisynthetic Pneumococcal Glycoconjugate Nanovaccine

Pneumococcal conjugate vaccines offer an excellent safety profile and high protection against the serotypes comprised in the vaccine. However, inclusion of protein antigens fromStreptococcus pneumoniaecombined with potent adjuvants and a suitable delivery system are expected to both extend protection to serotype strains not represented in the formulation and stimulate a broader immune response, thus more effective in young children, elderly, and immunocompromised populations. Along this line, nanoparticle (NP) delivery systems can enhance the immunogenicity of antigens by protecting them from degradation and increasing their uptake by antigen-presenting cells, as well as offering co-delivery with adjuvants. We report herein the encapsulation of a semisynthetic glycoconjugate (GC) composed of a synthetic tetrasaccharide mimicking theS. pneumoniae serotype 14 capsular polysaccharide (CP14) linked to the Pneumococcal surface protein A (PsaA) using chitosan NPs (CNPs). These GC-loaded chitosan nanoparticles (GC-CNPs) were not toxic to human monocyte-derived dendritic cells (MoDCs), showed enhanced uptake, and displayed better immunostimulatory properties in comparison to the naked GC. A comparative study was carried out in mice to evaluate the immune response elicited by the glycoconjugate-administered subcutaneously (SC), where the GC-CNPs displayed 100-fold higher IgG response as compared with the group treated with nonencapsulated GC. Overall, the study demonstrates the potential of this chitosan-based nanovaccine for efficient delivery of glycoconjugate antigens.

Immunobiology of Carbohydrates: Implications for Novel Vaccine and Adjuvant Design Against Infectious Diseases

Carbohydrates are ubiquitous molecules expressed on the surface of nearly all living cells, and their interaction with carbohydrate-binding proteins is critical to many immunobiological processes. Carbohydrates are utilized as antigens in many licensed vaccines against bacterial pathogens. More recently, they have also been considered as adjuvants. Interestingly, unlike other types of vaccines, adjuvants have improved immune response to carbohydrate-based vaccine in humans only in a few cases. Furthermore, despite the discovery of many new adjuvants in the last years, aluminum salts, when needed, remain the only authorized adjuvant for carbohydrate-based vaccines. In this review, we highlight historical and recent advances on the use of glycans either as vaccine antigens or adjuvants, and we review the use of currently available adjuvants to improve the efficacy of carbohydrate-based vaccines. A better understanding of the mechanism of carbohydrate interaction with innate and adaptive immune cells will benefit the design of a new generation of glycan-based vaccines and of immunomodulators to fight both longstanding and emerging diseases.

Lipid-Based Nanoparticles for Delivery of Vaccine Adjuvants and Antigens: Toward Multicomponent Vaccines

Despite the many advances that have occurred in the field of vaccine adjuvants, there are still unmet needs that may enable the development of vaccines suitable for more challenging pathogens (e.g., HIV and tuberculosis) and for cancer vaccines. Liposomes have already been shown to be highly effective as adjuvant/delivery systems due to their versatility and likely will find further uses in this space. The broad potential of lipid-based delivery systems is highlighted by the recent approval of COVID-19 vaccines comprising lipid nanoparticles with encapsulated mRNA. This review provides an overview of the different approaches that can be evaluated for the design of lipid-based vaccine adjuvant/delivery systems for protein, carbohydrate, and nucleic acid-based antigens and how these strategies might be combined to develop multicomponent vaccines.

Intranasal Vaccine Delivery Technology for Respiratory Tract Disease Application with a Special Emphasis on Pneumococcal Disease

This mini-review will cover recent trends in intranasal (IN) vaccine delivery as it relates to applications for respiratory tract diseases. The logic and rationale for IN vaccine delivery will be compared to methods and applications accompanying this particular administration route. In addition, we will focus extended discussion on the potential role of IN vaccination in the context of respiratory tract diseases, with a special emphasis on pneumococcal disease. Here, elements of this disease, including its prevalence and impact upon the elderly population, will be viewed from the standpoint of improving health outcomes through vaccine design and delivery technology and how IN administration can play a role in such efforts.

Recent advances on smart glycoconjugate vaccines in infections and cancer

Vaccination is one of the greatest achievements in biomedical research preventing death and morbidity in many infectious diseases through the induction of pathogen-specific humoral and cellular immune responses. Currently, no effective vaccines are available for pathogens with a highly variable antigenic load, such as the human immunodeficiency virus or to induce cellular T-cell immunity in the fight against cancer. The recent SARS-CoV-2 outbreak has reinforced the relevance of designing smart therapeutic vaccine modalities to ensure public health. Indeed, academic and private companies have ongoing joint efforts to develop novel vaccine prototypes for this virus. Many pathogens are covered by a dense glycan-coat, which form an attractive target for vaccine development. Moreover, many tumor types are characterized by altered glycosylation profiles that are known as "tumor-associated carbohydrate antigens". Unfortunately, glycans do not provoke a vigorous immune response and generally serve as T-cell-independent antigens, not eliciting protective immunoglobulin G responses nor inducing immunological memory. A close and continuous crosstalk between glycochemists and glycoimmunologists is essential for the successful development of efficient immune modulators. It is clear that this is a key point for the discovery of novel approaches, which could significantly improve our understanding of the immune system. In this review, we discuss the latest advancements in development of vaccines against glycan epitopes to gain selective immune responses and to provide an overview on the role of different immunogenic constructs in improving glycovaccine efficacy.

Vaccine Delivery and Immune Response Basics

In this opening chapter, we outline the basics of vaccine delivery and subsequent immune reactivity. Vaccine delivery is an augmentation to immunization more generally in that a delivery reagent is harnessed to improve administration of the key ingredient (i.e., the antigen) needed to provoke an immune response. In this chapter, we discuss the evolution of vaccine design and how such efforts evolved into targeted administration/delivery of key antigens. We then provide overview descriptions of vaccine immune responses and methods for assessment. More generally, the chapter sets the tone for the remainder of this book, which will focus upon each step of the vaccine process with a special emphasis on how vaccine delivery contributes to overall health outcomes.

Liposomal Encapsulation of Polysaccharides (LEPS) as an Effective Vaccine Strategy to Protect Aged Hosts Against S. pneumoniae Infection

Despite the availability of licensed vaccines, pneumococcal disease caused by the bacteria Streptococcus pneumoniae (pneumococcus), remains a serious infectious disease threat globally. Disease manifestations include pneumonia, bacteremia, and meningitis, resulting in over a million deaths annually. Pneumococcal disease disproportionally impacts older adults aged ≥65 years. Interventions are complicated through a combination of complex disease progression and 100 different bacterial capsular polysaccharide serotypes. This has made it challenging to develop a broad vaccine against S. pneumoniae, with current options utilizing capsular polysaccharides as the primary antigenic content. However, current vaccines are substantially less effective in protecting the elderly. We previously developed a Liposomal Encapsulation of Polysaccharides (LEPS) vaccine platform, designed around limitations of current pneumococcal vaccines, that allowed the noncovalent coupling of polysaccharide and protein antigen content and protected young hosts against pneumococcal infection in murine models. In this study, we modified the formulation to make it more economical and tested the novel LEPS vaccine in aged hosts. We found that in young mice (2-3 months), LEPS elicited comparable responses to the pneumococcal conjugate vaccine Prevnar-13. Further, LEPS immunization of old mice (18-22 months) induced comparable antibody levels and improved antibody function compared to Prevnar-13. Importantly, LEPS protected old mice against both invasive and lung localized pneumococcal infections. In summary, LEPS is an alternative and effective vaccine strategy that protects aged hosts against different manifestations of pneumococcal disease.

Liposomal Dual Delivery of Both Polysaccharide and Protein Antigens

Pneumococcal disease is caused by Streptococcus pneumoniae, a colonizing microorganism characterized by transitioning from a benign commensal to a virulent pathogen in the presence of suitable circumstances, which then poses a serious infectious disease threat afflicting millions of people. Especially affected are the young and elderly through outcomes that include pneumonia, bacteremia, meningitis, and otitis media. Current prevention vaccine options on the market contain capsular polysaccharides conjugated to the Diphtheria CRM197 protein (Pfizer) or are composed of only pneumococcal polysaccharides (Merck), and in both cases, limitations prevent the generation of comprehensive disease protection. Through the use of a liposomal carrier, we present an alternative methodology for producing a vaccine product via noncovalent colocalization of both polysaccharide and protein classes of complementary pneumococcal disease immunogens.

Extended Polysaccharide Analysis within the Liposomal Encapsulation of Polysaccharides System

The Liposomal Encapsulation of Polysaccharides (LEPS) dual antigen vaccine carrier system was assessed across two distinct polysaccharides for encapsulation efficiency, subsequent liposomal surface adornment with protein, adjuvant addition, and size and charge metrics. The polysaccharides derive from two different serotypes of Streptococcus pneumoniae and have traditionally served as the active ingredients of vaccines against pneumococcal disease. The LEPS system was designed to mimic glycoconjugate vaccines that covalently couple polysaccharides to protein carriers; however, the LEPS system uses a noncovalent co-localization mechanism through protein liposomal surface attachment. In an effort to more thoroughly characterize the LEPS system across individual vaccine components and thus support broader future utility, polysaccharides from S. pneumoniae serotypes 3 and 4 were systematically compared within the LEPS framework both pre- and post-surface protein attachment. For both polysaccharides, ≥85% encapsulation efficiency was achieved prior to protein surface attachment. Upon protein attachment with either a model protein (GFP) or a pneumococcal disease antigen (PncO), polysaccharide encapsulation was maintained at ≥61% encapsulation efficiency. Final LEPS carriers were also evaluated with and without alum as an included adjuvant, with encapsulation efficiency maintained at ≥30%, while protein surface attachment efficiency was maintained at ≥~50%. Finally, similar trends and distributions were observed across the different polysaccharides when assessed for liposomal zeta potential and size.

Enzymatic depolymerization of streptococcus pneumoniae type 8 polysaccharide

Although there have been decades of research on streptococcus pneumoniae, it is still among the leading cause of infectious disease in the world. As a type of capsular polysaccharide (CPS) of streptococcus pneumoniae, pneumococcal polysaccharides are essential components for colonization and virulence in mammalian hosts. This study aimed to characterize the CPS structure of type 8 streptococcus pneumoniae, which is one of the most fatal serotypes. In this work, heparinase I&III was used to successfully digest pneumococcal type 8 polysaccharide (Pn8P). We characterized the oligosaccharide generated from the enzymatic depolymerization of Pn8P by size exclusion chromatography, mass spectrometry and nuclear magnetic resonance. This is the first study to enzymatically depolymerize and characterize Pn8P.

Impact of Influenza on Pneumococcal Vaccine Effectiveness during Streptococcus pneumoniae Infection in Aged Murine Lung

Changes in innate and adaptive immune responses caused by viral imprinting can have a significant direct or indirect influence on secondary infections and vaccine responses. The purpose of our current study was to investigate the role of immune imprinting by influenza on pneumococcal vaccine effectiveness during Streptococcus pneumoniae infection in the aged murine lung. Aged adult (18 months) mice were vaccinated with the pneumococcal polyvalent vaccine Pneumovax (5 mg/mouse). Fourteen days post vaccination, mice were instilled with PBS or influenza A/PR8/34 virus (3.5 × 10² PFU). Control and influenza-infected mice were instilled with PBS or S. pneumoniae (1 × 10³ CFU, ATCC 6303) on day 7 of infection and antibacterial immune responses were assessed in the lung. Our results illustrate that, in response to a primary influenza infection, there was diminished bacterial clearance and heightened production of pro-inflammatory cytokines, such as IL6 and IL1β. Vaccination with Pneumovax decreased pro-inflammatory cytokine production by modulating NFҡB expression; however, these responses were significantly diminished after influenza infection. Taken together, the data in our current study illustrate that immune imprinting by influenza diminishes pneumococcal vaccine efficacy and, thereby, may contribute to increased susceptibility of older persons to a secondary infection with S. pneumoniae.

The long search for a serotype independent pneumococcal vaccine

Introduction: Serotype replacement - a consequence of polysaccharide vaccine use - will continue to drive the inclusion of new serotypes on conjugate vaccines, increasing production complexity and costs, and making an already expensive vaccine less accessible to developing countries, where prevalence is higher and resources available for health systems, scarcer. Serotype-independent formulations are a promising option, but so far they have not been successful in reducing colonization/transmission.Areas covered: Protein-based and whole-cell vaccine candidates studied in the past 30 years. Challenges for serotype-independent vaccine development and alternative approaches.Expert opinion: Clinical trials performed so far demonstrated the importance to establish more reliable animal models and better correlates of protection. Defining appropriate endpoints for clinical trials of serotype-independent vaccine candidates has been a challenge. Inhibition of colonization has been evaluated, but concern on the extent of bacterial elimination is still a matter of debate. Challenges on establishing representative sites for clinical trials, sample sizes and appropriate age groups are discussed. On a whole, although many challenges will have to be overcome, establishing protein-based antigens as serotype-independent vaccines is still the best alternative against the huge burden of pneumococcal diseases in the world.

Design Variation of a Dual-Antigen Liposomal Vaccine Carrier System

The enclosed work focuses on the construction variables associated with a dual-antigen liposomal carrier, delivering encapsulated polysaccharides and surface-localized proteins, which served as a vaccine delivery device effective against pneumococcal disease. Here, the goal was to better characterize and compare the carrier across a range of formulation steps and assessment metrics. Specifically, the vaccine carrier was subjected to new methods of liposomal formation, including alterations to the base components used for subsequent macromolecule encapsulation and surface attachment, with characterization spanning polysaccharide encapsulation, liposomal size and charge, and surface protein localization. Results demonstrate variations across the liposomal constructs comprised two means of surface-localizing proteins (either via metal or biological affinity). In general, final liposomal constructs demonstrated a size and zeta potential range of approximately 50 to 600 nm and −4 to −41 mV, respectively, while demonstrating at least 60% polysaccharide encapsulation efficiency and 60% protein surface localization for top-performing liposomal carrier constructs. The results, thus, indicate that multiple formulations could serve in support of vaccination studies, and that the selection of a suitable final delivery system would be dictated by preferences or requirements linked to target antigens and/or regulatory demands.

Glycoconjugate vaccines: current approaches towards faster vaccine design

Introduction: Over the last decades, glycoconjugate vaccines have been proven to be a successful strategy to prevent infectious diseases. Many diseases remain to be controlled, especially in developing countries, and emerging antibiotic-resistant bacteria present an alarming public-health threat. The increasing complexity of future vaccines, and the need to accelerate development processes have triggered the development of faster approaches to glycoconjugate vaccines design. Areas covered: This review provides an overview of recent progress in glycoconjugation technologies toward faster vaccine design. Expert opinion: Among the different emerging approaches, glycoengineering has the potential to combine glycan assembly and conjugation to carrier systems (such as proteins or outer membrane vesicles) in one step, resulting in a simplified manufacturing process and fewer analytical controls. Chemical and enzymatic strategies, and their automation can facilitate glycoepitope identification for vaccine design. Other approaches, such as the liposomal encapsulation of polysaccharides, potentially enable fast and easy combination of numerous antigens in the same formulation. Additional progress is envisaged in the near future, and some of these systems still need to be further validated in humans. In parallel, new strategies are needed to accelerate the vaccine development process, including the associated clinical trials, up to vaccine release onto the market.