Progress in mucosal immunization for protection against pneumococcal pneumonia

Protection against genotype VII Newcastle disease virus by a mucosal subunit vaccination based on bacterium-like particles bearing the F or HN antigen

Genotype VII Newcastle disease viruses (NDV) are still epidemic in many countries in chicken and waterfowl despite intensive vaccination with conventional live and inactivated vaccines. Here, we developed an effective mucosal subunit vaccine based on a bacterium-like particles (BLPs) delivery platform derived from Lactococcus lactis. The NDV protective antigen F or HN fused protein anchor (PA) was expressed by recombinant baculovirus and loaded on the surface of BLPs, resulting in BLPs-F and BLPs-HN, respectively. Efficient uptake of BLPs-F/HN by antigen-presenting cells activated the innate immune system depending mainly on the combination of chicken TLR2 type 1 (chTLR2t1) and chicken TLR1 type 1 (chTLR1t1) was observed. Delivered intranasally, BLPs-F, BLPs-HN, or BLPs-F/HN (a mixture containing equal amounts of BLPs-F and BLPs-HN) elicited robust local NDV-specific SIgA in the trachea as well as systemic neutralizing antibody and a mixed Th1/Th2 immune response in chickens. Notably, BLPs-F/HN provided as high as 90 % protection rate against intranasal challenge with a lethal dose of virulent genotype VII NDV NA-1 strain. These data indicate that this BLP-based subunit vaccine has the potential to be a novel mucosal vaccine against genotype VII NDV infection.

Peptide linker increased the stability of pneumococcal fusion protein vaccine candidate

Streptococcus pneumoniae is a bacterial pathogen exclusive to humans, responsible for respiratory and systemic diseases. Pneumococcal protein vaccines have been proposed as serotype-independent alternatives to currently used conjugated polysaccharide vaccines, which have presented limitations regarding their coverage. Previously in our group, pneumococcal surface protein A (PspA) and detoxified pneumolysin (PdT) were genetically fused and the hybrid protein protected mice against pneumococcal challenge, offered higher cross-protection against different strains and showed greater opsonophagocytosis rate than co-administered proteins. As juxtaposed fusion was unstable to upscale production of the protein, flexible (PspA-FL-PdT) and rigid (PspA-RL-PdT) molecular linkers were inserted between the antigens to increase stability. This work aimed to produce recombinant fusion proteins, evaluate their stability after linker insertion, both in silico and experimentally, and enable the production of two antigens in a single process. The two constructs with linkers were cloned into Escherichia coli and hybrid proteins were purified using chromatography; purity was evaluated by SDS-PAGE and stability by Western blot and high performance size exclusion chromatography. PspA-FL-PdT showed higher stability at -20°C and 4°C, without additional preservatives. In silico analyses also showed differences regarding stability of the fusion proteins, with molecule without linker presenting disallowed amino acid positions in Ramachandran plot and PspA-FL-PdT showing the best scores, in agreement with experimental results. Mice were immunized with three doses and different amounts of each protein. Both fusion proteins protected all groups of mice against intranasal lethal challenge. The results show the importance of hybrid protein structure on the stability of the products, which is essential for a successful bioprocess development.

Pneumococcal Surface Protein A-Hybrid Nanoparticles Protect Mice from Lethal Challenge after Mucosal Immunization Targeting the Lungs

Pneumococcal disease remains a global burden, with current conjugated vaccines offering protection against the common serotype strains. However, there are over 100 serotype strains, and serotype replacement is now being observed, which reduces the effectiveness of the current vaccines. Pneumococcal surface protein A (PspA) has been investigated as a candidate for new serotype-independent pneumococcal vaccines, but requires adjuvants and/or delivery systems to improve protection. Polymeric nanoparticles (NPs) are biocompatible and, besides the antigen, can incorporate mucoadhesive and adjuvant substances such as chitosans, which improve antigen presentation at mucosal surfaces. This work aimed to define the optimal NP formulation to deliver PspA into the lungs and protect mice against lethal challenge. We prepared poly(glycerol-adipate-co-ω-pentadecalactone) (PGA-co-PDL) and poly(lactic-co-glycolic acid) (PLGA) NPs using an emulsion/solvent evaporation method, incorporating chitosan hydrochloride (HCl-CS) or carboxymethyl chitosan (CM-CS) as hybrid NPs with encapsulated or adsorbed PspA. We investigated the physicochemical properties of NPs, together with the PspA integrity and biological activity. Furthermore, their ability to activate dendritic cells in vitro was evaluated, followed by mucosal immunization targeting mouse lungs. PGA-co-PDL/HCl-CS (291 nm) or CM-CS (281 nm) NPs produced smaller sizes compared to PLGA/HCl-CS (310 nm) or CM-CS (299 nm) NPs. Moreover, NPs formulated with HCl-CS possessed a positive charge (PGA-co-PDL +17 mV, PLGA + 13 mV) compared to those formulated with CM-CS (PGA-co-PDL -20 mV, PLGA -40 mV). PspA released from NPs formulated with HCl-CS preserved the integrity and biological activity, but CM-CS affected PspA binding to lactoferrin and antibody recognition. PspA adsorbed in PGA-co-PDL/HCl-CS NPs stimulated CD80+ and CD86+ cells, but this was lower compared to when PspA was encapsulated in PLGA/HCl-CS NPs, which also stimulated CD40+ and MHC II (I-A/I-E)+ cells. Despite no differences in IgG being observed between immunized animals, PGA-co-PDL/HCl-CS/adsorbed-PspA protected 83% of mice after lethal pneumococcal challenge, while 100% of mice immunized with PLGA/HCl-CS/encapsulated-PspA were protected. Therefore, this formulation is a promising vaccine strategy, which has beneficial properties for mucosal immunization and could potentially provide serotype-independent protection.

Spray-dried Pneumococcal Membrane Vesicles are Promising Candidates for Pulmonary Immunization

Pneumococcal infections represent a global health threat, which requires novel vaccine developments. Extracellular vesicles are secreted from most cells, including prokaryotes, and harbor virulence factors and antigens. Hence, bacterial membrane vesicles (MVs) may induce a protective immune response. For the first time, we formulate spray-dried gram-positive pneumococcal MVs-loaded vaccine microparticles using lactose/leucine as inert carriers to enhance their stability and delivery for pulmonary immunization. The optimized vaccine microparticles showed a mean particle size of 1-2µm, corrugated surface, and nanocrystalline nature. Their aerodynamic diameter of 2.34µm, average percentage emitted dose of 88.8%, and fine powder fraction 79.7%, demonstrated optimal flow properties for deep alveolar delivery using a next-generation impactor. Furthermore, confocal microscopy confirmed the successful encapsulation of pneumococcal MVs within the prepared microparticles. Human macrophage-like THP-1 cells displayed excellent viability, negligible cytotoxicity, and a rapid uptake around 60% of fluorescently labeled MVs after incubation with vaccine microparticles. Moreover, vaccine microparticles increased the release of pro-inflammatory cytokines tumor necrosis factor and interleukin-6 from primary human peripheral blood mononuclear cells. Vaccine microparticles exhibited excellent properties as promising vaccine candidates for pulmonary immunization and are optimal for further animal testing, scale-up and clinical translation.

Pneumococcal Vaccines: Past Findings, Present Work, and Future Strategies

The importance of Streptococcus pneumoniae has been well established. These bacteria can colonize infants and adults without symptoms, but in some cases can spread, invade other tissues and cause disease with high morbidity and mortality. The development of pneumococcal conjugate vaccines (PCV) caused an enormous impact in invasive pneumococcal disease and protected unvaccinated people by herd effect. However, serotype replacement is a well-known phenomenon that has occurred after the introduction of the 7-valent pneumococcal conjugate vaccine (PCV7) and has also been reported for other PCVs. Therefore, it is possible that serotype replacement will continue to occur even with higher valence formulations, but the development of serotype-independent vaccines might overcome this problem. Alternative vaccines are under development in order to improve cost effectiveness, either using proteins or the pneumococcal whole cell. These approaches can be used as a stand-alone strategy or together with polysaccharide vaccines. Looking ahead, the next generation of pneumococcal vaccines can be impacted by the new technologies recently approved for human use, such as mRNA vaccines and viral vectors. In this paper, we will review the advantages and disadvantages of the addition of new polysaccharides in the current PCVs, mainly for low- and middle-income countries, and we will also address future perspectives.

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.

Vaccines to Prevent Infectious Diseases in the Older Population: Immunological Challenges and Future Perspectives

Infectious diseases are a major cause for morbidity and mortality in the older population. Demographic changes will lead to increasing numbers of older persons over the next decades. Prevention of infections becomes increasingly important to ensure healthy aging for the individual, and to alleviate the socio-economic burden for societies. Undoubtedly, vaccines are the most efficient health care measure to prevent infections. Age-associated changes of the immune system are responsible for decreased immunogenicity and clinical efficacy of most currently used vaccines in older age. Efficacy of standard influenza vaccines is only 30-50% in the older population. Several approaches, such as higher antigen dose, use of MF59 as adjuvant and intradermal administration have been implemented in order to specifically target the aged immune system. The use of a 23-valent polysaccharide vaccine against Streptococcus pneumoniae has been amended by a 13-valent conjugated pneumococcal vaccine originally developed for young children several years ago to overcome at least some of the limitations of the T cell-independent polysaccharide antigens, but still is only approximately 50% protective against pneumonia. A live-attenuated vaccine against herpes zoster, which has been available for several years, demonstrated efficacy of 51% against herpes zoster and 67% against post-herpetic neuralgia. Protection was lower in the very old and decreased several years after vaccination. Recently, a recombinant vaccine containing the viral glycoprotein gE and the novel adjuvant AS01B has been licensed. Phase III studies demonstrated efficacy against herpes zoster of approx. 90% even in the oldest age groups after administration of two doses and many countries now recommend the preferential use of this vaccine. There are still many infectious diseases causing substantial morbidity in the older population, for which no vaccines are available so far. Extensive research is ongoing to develop vaccines against novel targets with several vaccine candidates already being clinically tested, which have the potential to substantially reduce health care costs and to save many lives. In addition to the development of novel and improved vaccines, which specifically target the aged immune system, it is also important to improve uptake of the existing vaccines in order to protect the vulnerable, older population.

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.