A novel technology for the production of a heterologous lipoprotein immunogen in high yield has implications for the field of vaccine design

Dengue-1 envelope protein domain III along with PELC and CpG oligodeoxynucleotides synergistically enhances immune responses

The major weaknesses of subunit vaccines are their low immunogenicity and poor efficacy. Adjuvants can help to overcome some of these inherent defects with subunit vaccines. Here, we evaluated the efficacy of the newly developed water-in-oil-in-water multiphase emulsion system, termed PELC, in potentiating the protective capacity of dengue-1 envelope protein domain III. Unlike aluminum phosphate, dengue-1 envelope protein domain III formulated with PELC plus CpG oligodeoxynucleotides induced neutralizing antibodies against dengue-1 virus and increased the splenocyte secretion of IFN-γ after in vitro re-stimulation. The induced antibodies contained both the IgG1 and IgG2a subclasses. A rapid anamnestic neutralizing antibody response against a live dengue virus challenge was elicited at week 26 after the first immunization. These results demonstrate that PELC plus CpG oligodeoxynucleotides broaden the dengue-1 envelope protein domain III-specific immune responses. PELC plus CpG oligodeoxynucleotides is a promising adjuvant for recombinant protein based vaccination against dengue virus.

Dengue is a mosquito-borne disease. Infection of dengue virus can cause clinical manifestations ranging from self-limiting dengue fever to potentially life-threatening dengue hemorrhagic fever or dengue shock syndrome. In recent years, dengue has spread to most tropical and subtropical areas, making it a global health concern. Specific approaches for dengue therapy do not exist; the development of a dengue vaccine would represent a major advance in the control of the disease. Currently, no licensed dengue vaccine is available. Subunit vaccines provide a great safety strategy for developing dengue vaccine. However, the major weaknesses of subunit vaccines are low immunogenicity and poor efficacy. Here we employed dengue-1 envelope protein domain III as a model vaccine candidate and described a newly developed water-in-oil-in water multiphase emulsion system to overcome the inherent defect of subunit vaccines. We showed that emulsification of dengue-1 envelope protein domain III and CpG oligodeoxynucleotides synergistically broadened immune responses and potentiated the protective capacity of dengue-1 envelope protein domain III. These results provide valuable information for development of recombinant protein based vaccination against dengue virus and future clinical studies.

A new cloning system based on the OprI lipoprotein for the production of recombinant bacterial cell wall-derived immunogenic formulations

The conjugation of antigens with ligands of pattern recognition receptors (PRR) is emerging as a promising strategy for the modulation of specific immunity. Here, we describe a new Escherichia coli system for the cloning and expression of heterologous antigens in fusion with the OprI lipoprotein, a TLR ligand from the Pseudomonas aeruginosa outer membrane (OM). Analysis of the OprI expressed by this system reveals a triacylated lipid moiety mainly composed by palmitic acid residues. By offering a tight regulation of expression and allowing for antigen purification by metal affinity chromatography, the new system circumvents the major drawbacks of former versions. In addition, the anchoring of OprI to the OM of the host cell is further explored for the production of novel recombinant bacterial cell wall-derived formulations (OM fragments and OM vesicles) with distinct potential for PRR activation. As an example, the African swine fever virus ORF A104R was cloned and the recombinant antigen was obtained in the three formulations. Overall, our results validate a new system suitable for the production of immunogenic formulations that can be used for the development of experimental vaccines and for studies on the modulation of acquired immunity.

Novel protein substrates of the phospho-form modification system in Neisseria gonorrhoeae and their connection to O-linked protein glycosylation

The zwitterionic phospho-form moieties phosphoethanolamine (PE) and phosphocholine (PC) are important components of bacterial membranes and cell surfaces. The major type IV pilus subunit protein of Neisseria gonorrhoeae, PilE, undergoes posttranslational modifications with these moieties via the activity of the pilin phospho-form transferase PptA. A number of observations relating to colocalization of phospho-form and O-linked glycan attachment sites in PilE suggested that these modifications might be either functionally or mechanistically linked or interact directly or indirectly. Moreover, it was unknown whether the phenomenon of phospho-form modification was solely dedicated to PilE or if other neisserial protein targets might exist. In light of these concerns, we screened for evidence of phospho-form modification on other membrane glycoproteins targeted by the broad-spectrum O-linked glycosylation system. In this way, two periplasmic lipoproteins, NGO1043 and NGO1237, were identified as substrates for PE addition. As seen previously for PilE, sites of PE modifications were clustered with those of glycan attachment. In the case of NGO1043, evidence for at least six serine phospho-form attachment sites was found, and further analyses revealed that at least two of these serines were also attachment sites for glycan. Finally, mutations altering glycosylation status led to the presence of pptA-dependent PC modifications on both proteins. Together, these results reinforce the associations established in PilE and provide evidence for dynamic interplay between phospho-form modification and O-linked glycosylation. The observations also suggest that phospho-form modifications likely contribute biologically at both intracellular and extracellular levels.

A novel single-dose dengue subunit vaccine induces memory immune responses

To protect against dengue viral infection, a novel lipidated dengue subunit vaccine was rationally designed to contain the consensus amino acid sequences derived from four serotypes of dengue viruses. We found that the lipidated consensus dengue virus envelope protein domain III (LcED III) is capable of activating antigen-presenting cells and enhancing cellular and humoral immune responses. A single-dose of LcED III immunization in mice without extra adjuvant formulation is sufficient to elicit neutralizing antibodies against all four serotypes of dengue viruses. In addition, strong memory responses were elicited in mice immunized with a single-dose of LcED III. Quick, anamnestic neutralizing antibody responses to a live dengue virus challenge were elicited at week 28 post-immunization. These results demonstrate the promising possibility of a future successful tetravalent vaccine against dengue viral infections that utilizes one-dose vaccination with LcED III.

Next generation dengue vaccines: a review of candidates in preclinical development

Dengue represents a major public health problem of growing global importance. In the absence of specific dengue therapeutics, strategies for disease control have increasingly focused on the development of dengue vaccines. While a licensed dengue vaccine is not yet available, several vaccine candidates are currently being evaluated in clinical trials and are described in detail in accompanying articles. In addition, there are a large variety of candidates in preclinical development, which are based on diverse technologies, ensuring a continued influx of innovation into the development pipeline. Potentially, some of the current preclinical candidates may become next generation dengue vaccines with superior product profiles. This review provides an overview of the various technological approaches to dengue vaccine development and specifically focuses on candidates in preclinical development.

Biochemical characterizations of Escherichia coli-expressed protective antigen Ag473 of Neisseria meningitides group B

Polysaccharide-based vaccines against Neisseria meningitidis (Nm) serogroups A, C, Y and W135 have been available since 1970, but similar vaccine candidates developed for Nm group B (NmB) have not been successful due to both poor immunogenicity and their potential immunological cross-reactivity with human neurological tissue. In previous reports, a protective antigen and vaccine candidate, Ag473, was identified using proteomics and NmB-specific bactericidal monoclonal antibody. To initiate human phase one clinical trials, antigen production and characterization, pre-clinical toxicology and animal studies are required. In the present study, we report the biochemical characterization of Escherichia coli-expressed recombinant Ag473 (rAg473). Using MALDI-TOF mass analysis, chromatographically purified rAg473 was found to have two major isoforms that have molecular masses of 11,306 and 11,544amu, respectively. The isoforms were separated using RP-HPLC and pooled into two fractions. Based on the chromatogram, the ratio of lipoproteins in fractions #1 and #2 was found to be 1-2. GC-MS analysis of lipoproteins was performed, and the acylated fatty acids were identified. The results indicated that the first lipoproteins in fraction #1 contained the lipids palmitic acid (C16:0), cyclopropaneoctanoic acid (C17:1) and, predominately, stearic acid (C18:0). A different lipid composition of cyclopropaneoctanoic acid (C17:1), oleic acid (C18:1) and, predominately, palmitic acid (C16:0) was found in the second lipoprotein fraction. Both lipoprotein isoforms were tested and found to have Toll-like receptor (TLR) agonist activity in stimulating cytokine secretion from THP-1 cells. Circular dichroism (CD) analysis showed the secondary structure of rAg473 to be dominated by α-helices (48%), and the overall protein structure was stable up to 60°C and could refold after having been exposed to a temperature cycle from 20 to 90°C. In addition, the solubility of rAg473 (5mg/mL) was not affected after several freeze-thaw cycles. These biophysical and immunological properties make rAg473 a good vaccine candidate against NmB.

A recombinant lipoprotein containing an unsaturated fatty acid activates NF-kappaB through the TLR2 signaling pathway and induces a differential gene profile from a synthetic lipopeptide

The lipid moiety of a novel recombinant lipoprotein, which contains a dengue virus envelope protein domain 3, rlipo-D1E3, has been shown to activate antigen-presenting cells (APCs) as an intrinsic adjuvant. Because the lipid moiety of rlipo-D1E3 contains an unsaturated fatty acid, it is unclear if the receptor usage by bacterially derived lipoproteins is the same as that of the synthetic lipopeptide palmitoyl-3-Cys-Ser-(Lys)(4) (Pam3). In the present study, we show that the rlipo-D1E3 lipoprotein can induce the activation of spleen cells and bone marrow-derived dendritic cells (BM-DCs) in wild-type and TLR4-deficient mice, but not in TLR2(-/-) mice. After analyzing the co-receptor usage of TLR2 using TLR1(-/-) or TLR6(-/-) mice, the TLR2 signaling triggered by rlipo-D1E3 and Pam3 could use either TLR1 or TLR6 as a co-receptor. Analysis of the MAPK signaling pathway revealed that rlipo-D1E3 could initiate the phosphorylation of p38, ERK1/2 and JNK1/2 earlier than the synthetic lipopeptide. In addition, the expression levels of IL-23, IL-27 and MIP-1 alpha in BM-DCs stimulated by rlipo-D1E3 were higher than the expression levels in BM-DCs stimulated by Pam3. Taken together, these results demonstrate that different TLR2 ligands can promote various immune responses by inducing different levels of biological cytokines and chemokines.