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Klebsiella pneumoniae (Kp) poses an escalating threat to public health, particularly given its association with nosocomial infections and its emergence as a leading cause of neonatal sepsis, particularly in low- and middle-income countries (LMICs). Host cell adherence and biofilm formation of Kp is mediated by type 1 and type 3 fimbriae whose major fimbrial subunits are encoded by the fimA and mrkA genes, respectively. In this study, we focus on MrkA subunit, which is a 20 KDa protein whose 3D molecular structure remains elusive. We applied solution NMR to characterize a recombinant version of MrkA in which the donor strand segment situated at the protein's N-terminus is relocated to the C-terminus, preceded by a hexaglycine linker. This construct yields a self-complemented variant of MrkA. Remarkably, the self-complemented MrkA monomer loses its capacity to interact with other monomers and to extend into fimbriae structures. Here, we report the nearly complete assignment of the 13C,15N labelled self-complemented MrkA monomer. Furthermore, an examination of its internal mobility unveiled that relaxation parameters are predominantly uniform across the polypeptide sequence, except for the glycine-rich region within loop 176–181. These data pave the way to a comprehensive structural elucidation of the MrkA monomer and to structurally map the molecular interaction regions between MrkA and antigen-induced antibodies. [ABSTRACT FROM AUTHOR]

The effect of the composition and size of polymeric particles on the immunogenicity of the fibrillogenic β2-microglobulin protein immobilized on their surface was studied. For this purpose, nanoparticles (NP) based on a copolymer of L-glutamic acid and L-phenylalanine (P(Glu-co-Phe)) and a block copolymer of poly(ethylene glycol) with poly(lactic acid) (PEG-b-PLA) as well as microparticles (MP) based on poly(lactic acid) (PLA) were selected. Materials and Methods. α-L-amino acid copolymer-based nanoparticles were prepared by gradient phase inversion, and PEG-b-PLA-based nanoparticles by nanoprecipitation. Double emulsion method was used to form polymeric microparticles based on PLA. Recombinant chimeric model protein beta-2-microglobulin-green fluorescent protein (β2M-sfGFP) was used to covalently modify all types of polymeric particles followed by immunization of four groups of laboratory animals equal in number. An enzyme immunoassay method was used to evaluate the humoral immune response. Results and discussion. In three experimental groups, mice were immunized using poly(amino acid)-based (NP-PAA) and PEG-b-PLA (NP-PLA) nanoparticles as well as PLA microparticles containing immobilized β2M-sfGFP on the surface. The control group was immunized using a physical mixture of PEG-b-PLA nanoparticles and free β2M-sfGFP. The highest level of antibodies to sfGFP in blood serum was found when mice were immunized with a mixture of protein and nanoparticles. When mice were immunized with β2M-sfGFP-modified nanoparticles, the amount of antibodies to sfGFP was statistically significantly lower (p < 0.001) compared to the control group. However, the groups immunized with nanoparticles of similar size but different composition conjugated to the model proteins did not differ significantly among themselves. It was also found that the size of the particles affects the immunogenicity of the associated protein. A similar pattern of relative antibody content in the sera of mice was maintained at all steps of immunization. [ABSTRACT FROM AUTHOR]

• A fluorescence-based DSF provides rapid assessment of adjuvant-adsorbed protein in a microplate format. • The effect of multi-factors in formulation development can be well-explored using smaller sample amount than DSC. • Good correlation of the results from well-established DSC and from high-throughput, automation amenable DSF is observed. Nano/microparticles are widely used as vaccine adjuvants to improve antigen stability and enhance immune response. Conformational stability of a given protein was normally assessed using differential scanning calorimetry (DSC) for the optimization of formulation and for ensuring antigen stability in vaccine products. Here, a higher throughput version, namely the microtiter plate-based differential scanning fluorimetry (DSF) method was developed and optimized for assessing the protein thermal stability in the particulate adjuvant-adsorbed form. Using recombinant human papillomavirus (HPV) vaccine antigens, along with several model proteins, enhanced sensitivity and correlation to the well-established differential scanning calorimetry were demonstrated. Higher throughput and much smaller sample consumption (1/10 ∼ 1/20 of the amount needed as compared to DSC) make the plate-based DSF a method of choice for formulation development, particularly during the early developmental phase of a project where the sample amount is usually quite limited. [ABSTRACT FROM AUTHOR]

In a companion paper, a two-step developability assessment is presented to rapidly evaluate low-cost formulations (multi-dose, aluminum-adjuvanted) for new subunit vaccine candidates. As a case study, a non-replicating rotavirus (NRRV) recombinant protein antigen P[4] was found to be destabilized by the vaccine preservative thimerosal, and this effect was mitigated by modification of the free cysteine (C173S). In this work, the mechanism(s) of thimerosal-P[4] protein interactions, along with subsequent effects on the P[4] protein's structural integrity, are determined. Reversible complexation of ethylmercury, a thimerosal degradation byproduct, with the single cysteine residue of P[4] protein is demonstrated by intact protein mass analysis and biophysical studies. A working mechanism involving a reversible S-Hg coordinate bond is presented based on the literature. This reaction increased the local backbone flexibility of P[4] within the helical region surrounding the cysteine residue and then caused more global destabilization, both as detected by HX-MS. These effects correlate with changes in antibody-P[4] binding parameters and alterations in P[4] conformational stability due to C173S modification. Epitope mapping by HX-MS demonstrated involvement of the same cysteine-containing helical region of P[4] in antibody-antigen binding. Future formulation challenges to develop low-cost, multi-dose formulations for new recombinant protein vaccine candidates are discussed. [ABSTRACT FROM AUTHOR]

Several vaccines targeting bacterial pathogens show reduced efficacy upon concurrent viral infection, indicating that a new vaccinology approach is required. To identify antigens for the human pathogen Streptococcus pneumoniae that are effective following influenza infection, we performed CRISPRi-seq in a murine model of superinfection and identified the conserved lafB gene as crucial for virulence. We show that LafB is a membrane-associated, intracellular protein that catalyzes the formation of galactosyl-glucosyl-diacylglycerol, a glycolipid important for cell wall homeostasis. Respiratory vaccination with recombinant LafB, in contrast to subcutaneous vaccination, was highly protective against S. pneumoniae serotypes 2, 15A, and 24F in a murine model. In contrast to standard capsule-based vaccines, protection did not require LafB-specific antibodies but was dependent on airway CD4+ T helper 17 cells. Healthy human individuals can elicit LafB-specific immune responses, indicating LafB antigenicity in humans. Collectively, these findings present a universal pneumococcal vaccine antigen that remains effective following influenza infection. [Display omitted] • CRISPRi-seq in pneumococcal superinfection identified lafB as crucial for virulence • LafB catalyzes the formation of a glycolipid important for cell wall homeostasis • Intranasal vaccination with LafB protects against pneumococcal non-vaccine serotypes • Nasal vaccine-induced protection depends on lung Th17 lymphocytes with TRM features Liu et al. identify lafB as crucial for Streptococcus pneumoniae replication in vivo using CRISPRi-seq. Intranasal vaccination with flagellin-adjuvanted LafB induces lung Th7 lymphocytes that protect against superinfections with various pneumococcal serotypes in mice. Healthy individuals can elicit LafB-specific immune responses, suggesting that LafB is a universal, capsule-independent pneumococcal antigen. [ABSTRACT FROM AUTHOR]

Pneumococcal whole cell vaccines (WCVs) could cost-effectively protect against a greater strain diversity than current capsule-based vaccines. Immunoglobulin G (IgG) responses to a WCV were characterised by applying longitudinally-sampled sera, available from 35 adult placebo-controlled phase I trial participants, to a panproteome microarray. Despite individuals maintaining distinctive antibody ‘fingerprints’, responses were consistent across vaccinated cohorts. Seventy-two functionally distinct proteins were associated with WCV-induced increases in IgG binding. These shared characteristics with naturally immunogenic proteins, being enriched for transporters and cell wall metabolism enzymes, likely unusually exposed on the unencapsulated WCV’s surface. Vaccine-induced responses were specific to variants of the diverse PclA, PspC and ZmpB proteins, whereas PspA- and ZmpA-induced antibodies recognised a broader set of alleles. Temporal variation in IgG levels suggested a mixture of anamnestic and novel responses. These reproducible increases in IgG binding to a limited, but functionally diverse, set of conserved proteins indicate WCV could provide species-wide immunity. Clinical trial registration: The trial was registered with ClinicalTrials.gov with Identifier NCT01537185; the results are available from https://clinicaltrials.gov/ct2/show/results/NCT01537185.

Oil-based emulsions are commonly used adjuvants for veterinary vaccines. After formulation, it is required to extract protein antigens from emulsified vaccines for testing their stability and antigenicity. To establish a simple method to extract the protein antigens, two emulsified vaccines, designated as Cap-206 and Cap-35, were prepared by formulating a 28-kDa capsid protein (Cap) of PCV2b with ISA 206, a water-in-oil-in-water emulsion, or ISA 35, an oil-in-water emulsion. We found that the freeze-thaw-centrifugation method with steps of freezing at −20 °C for 12 h, thawing at room temperature and centrifuging at 9000× g for 10 min could separate the aqueous phase from Cap-206, and a centrifugation method by centrifuging at 9000× g for 10 min could isolate the aqueous portion from Cap-35. The Cap proteins were recovered from the aqueous phase and could be evaluated for their stability and antigenicity by SDS-PAGE, Western blot and ELISA. The freeze-thaw-centrifugation or the centrifugation method could also be used to recover recombinant mycobacterial heat-shock protein 65, a larger protein with molecular weight of 57-kDa, from ISA 206 or ISA 35 emulsions. The methods could be used to recover protein antigens from oil-based emulsion formulated vaccines for monitoring their stability and antigenicity during vaccine manufacture and storage. [ABSTRACT FROM AUTHOR]

In the past few decades there has been a progressive understanding that epicutaneous sensitization with protein antigen is an important sensitization route in patients with atopic dermatitis. A murine protein-patch model has been established, and an abundance of data has been obtained from experiments using this model. This review discusses the characteristics of epicutaneous sensitization with protein antigen, the induced immune responses, the underlying mechanisms, and the therapeutic potential.

Most pathogens initiate their infections at the human mucosal surface. Therefore, mucosal vaccination, especially through oral or intranasal administration routes, is highly desired for infectious diseases. Meanwhile, protein-based antigens provide a safer alternative to the whole pathogen or DNA based ones in vaccine development. However, the unique biopharmaceutical hurdles that intranasally or orally delivered protein vaccines need to overcome before they reach the sites of targeting, the relatively low immunogenicity, as well as the low stability of the protein antigens, require thoughtful and fine-tuned mucosal vaccine formulations, including the selection of immunostimulants, the identification of the suitable vaccine delivery system, and the determination of the exact composition andmanufacturing conditions. This reviewaims to provide an up-to-date survey of the protein antigen-based vaccine formulation development, including the usage of immunostimulants and the optimization of vaccine delivery systems for intranasal and oral administrations. [ABSTRACT FROM AUTHOR]

Poly(lactic-co-glycolic acid) (PLGA) particles have been extensively studied as biodegradable delivery system to improve the potency and safety of protein-based vaccines. In this study we analyzed how the size of PLGA particles, and hence their ability to be engulfed by dendritic cells (DC), affects the type and magnitude of the immune response in comparison to sustained release from a local depot. PLGA microparticles (MP, volume mean diameter ≈ 112 μm) and nanoparticles (NP, Z -average diameter ≈ 350 nm) co-encapsulating ovalbumin (OVA) and poly(I:C), with comparable antigen (Ag) release characteristics, were prepared and characterized. The immunogenicity of these two distinct particulate vaccines was evaluated in vitro and in vivo . NP were efficiently taken up by DC and greatly facilitated MHC I Ag presentation in vitro , whereas DC cultured in the presence of MP failed to internalize significant amounts of Ag and hardly showed MHC I Ag presentation. Vaccination of mice with NP resulted in significantly better priming of Ag-specific CD8 + T cells compared to MP and OVA emulsified with incomplete Freund's adjuvant (IFA). Moreover, NP induced a balanced T H 1/T H 2-type antibody response, compared to vaccinations with IFA which stimulated a predominant T H 2-type response, whereas MP failed to increase antibody titers. In conclusion, we postulate that particle internalization is of crucial importance and therefore particulate vaccines should be formulated in the nano- but not micro-size range to achieve efficient uptake, significant MHC class I cross-presentation and effective T and B cell responses. [ABSTRACT FROM AUTHOR]

Linking physicochemical characterization to functional properties is crucial for defining critical quality attributes during development of subunit vaccines toward optimal safety and efficacy profiles. We investigated how the trehalose 6,6′-diester (TDX) chain length influenced the physicochemical and immunopotentiating properties of the clinically tested liposomal adjuvant composed of dimethyldioctadecylammonium (DDA) bromide and analogues of trehalose-6,6′-dibehenate (TDB). TDB analogues with symmetrically shortened acyl chains [denoted X: arachidate (A), stearate (S), palmitate (P), myristate (Myr) and laurate (L)] were incorporated into DDA liposomes and characterized with respect to size, polydispersity index, charge, thermotropic phase behavior and lipid–lipid interactions. Incorporation of 11 mol% TDX into DDA liposomes significantly decreased the polydispersity index when TDA, TDS, TDP and TDMyr were incorporated, whereas both the initial size and the charge of the liposomes were unaffected. The long-term colloidal stability was only decreased when including TDL in DDA liposomes. The fatty acid length of TDX affected the phase transition of the liposomes, and for the DDA/TDP and DDA/TDS liposomes a homogeneous distribution of the lipids in the bilayer was indicated. The membrane packing was studied further by using the Langmuir monolayer technique. Incorporation of TDS improved the packing of the lipid monolayer, as compared to the other analogues, suggesting the most favorable stability. Finally, immunization of mice with the recombinant tuberculosis fusion antigen Ag85B-ESAT-6-Rv2660c (H56) and the physicochemically most optimal formulations (DDA/TDB, DDA/TDS and DDA/TDP) induced comparable T-cell responses. In conclusion, of the investigated TDB analogues, incorporation of 11 mol% TDS or TDP into DDA liposomes resulted in an adjuvant system with the most favorable physicochemical properties and an immunological profile comparable to that of DDA/TDB. [ABSTRACT FROM AUTHOR]

Highlights: [•] Cellular immunity is a necessary component for vaccines directed to some pathogens. [•] Full-protein antigens rather than peptide epitopes ensure broad population coverage. [•] High-throughput T cell antigen identification technologies are rapidly evolving. [•] Advantages and disadvantages of T cell antigen identification methods are discussed. [ABSTRACT FROM AUTHOR]

Abstract: Oral tolerance is defined as the specific suppression of humoral and/or cellular immune responses to an antigen by administration of the same antigen through the oral route. Due to its absence of toxicity, easy administration, and antigen specificity, oral tolerance is a very attractive approach to prevent unwanted immune responses that cause a variety of diseases or that complicate treatment of a disease. Many researchers have induced oral tolerance to efficiently treat autoimmune and inflammatory diseases in different animal models. However, clinical trials yielded limited success. Thus, understanding the mechanisms of oral tolerance induction to therapeutic proteins is critical for paving the way for clinical development of oral tolerance protocols. This review will summarize progress on understanding the major underlying tolerance mechanisms and contributors, including antigen presenting cells, regulatory T cells, cytokines, and signaling pathways. Potential applications, examples for therapeutic proteins and disease targets, and recent developments in delivery methods are discussed. [Copyright &y& Elsevier]

Abstract: By screening a whole-genome λ-display library of Streptococcus pneumoniae, we have previously identified a novel surface protein, named Spr1875, that exhibited immunogenic properties and was closely related to pneumococcal virulence. In the present study, we investigated the role of the Spr1875 antigen in the interaction of S. pneumoniae with microglia, the resident brain macrophages. By using an in vitro infection model, the BV2 microglial cell line was challenged with the S. pneumoniae strain DP1004 and its isogenic spr1875-deleted mutant (Δspr1875). Both strains were phagocytosed by microglia efficiently and to a similar extent; however, the DP1004 strain was more resistant than the Δspr1875 mutant to the intracellular killing, as assessed by antibiotic protection and phagosome maturation assays. Moreover, significant differences between the two strains were also observed in terms of susceptibility to microglia-mediated killing. Taken together, these results indicate that S. pneumoniae-microglial cell interplay is influenced by the presence of Spr1875, suggesting that this protein may play a role in the pathogenesis of pneumococcal meningitis. [Copyright &y& Elsevier]