Development of novel O-polysaccharide based glycoconjugates for immunization against glanders

Electrochemical Immunoassay for Capturing Capsular Polysaccharide of Burkholderia pseudomallei: Early Onsite Detection of Melioidosis

This study presented the detection and quantification of capsular polysaccharide (CPS) as a biomarker for the diagnosis of melioidosis. After successfully screening four monoclonal antibodies (mAbs) previously determined to bind CPS molecules, the team developed a portable electrochemical immunosensor based on antibody-antigen interactions. The biosensor was able to detect CPS with a wide detection range from 0.1pg/mL to 1 μg/mL. The developed biosensor achieved high sensitivity for the detection of CPS spiked into both urine and serum. The developed assay platform was successfully programmed into a Windows app, and the sensor performance was evaluated with different spiked concentrations. The rapid electro-analytical device (READ) sensor showed great unprecedented sensitivity for the detection of CPS molecules in both serum and urine, and results were cross-validated with ELISA methods.

Burkholderia pseudomallei Complex Subunit and Glycoconjugate Vaccines and Their Potential to Elicit Cross-Protection to Burkholderia cepacia Complex

Burkholderia are a group of Gram-negative bacteria that can cause a variety of diseases in at-risk populations. B. pseudomallei and B. mallei, the etiological agents of melioidosis and glanders, respectively, are the two clinically relevant members of the B. pseudomallei complex (Bpc). The development of vaccines against Bpc species has been accelerated in recent years, resulting in numerous promising subunits and glycoconjugate vaccines incorporating a variety of antigens. However, a second group of pathogenic Burkholderia species exists known as the Burkholderia cepacia complex (Bcc), a group of opportunistic bacteria which tend to affect individuals with weakened immunity or cystic fibrosis. To date, there have been few attempts to develop vaccines to Bcc species. Therefore, the primary goal of this review is to provide a broad overview of the various subunit antigens that have been tested in Bpc species, their protective efficacy, study limitations, and known or suspected mechanisms of protection. Then, we assess the reviewed Bpc antigens for their amino acid sequence conservation to homologous proteins found in Bcc species. We propose that protective Bpc antigens with a high degree of Bpc-to-Bcc sequence conservation could serve as components of a pan-Burkholderia vaccine capable of protecting against both disease-causing groups.

Identification of Burkholderia cepacia strains that express a Burkholderia pseudomallei-like capsular polysaccharide

Burkholderia pseudomallei and Burkholderia cepacia are Gram-negative, soil-dwelling bacteria that are found in a wide variety of environmental niches. While B. pseudomallei is the causative agent of melioidosis in humans and animals, members of the B. cepacia complex typically only cause disease in immunocompromised hosts. In this study, we report the identification of B. cepacia strains isolated from either patients or soil in Laos and Thailand that express a B. pseudomallei-like 6-deoxyheptan capsular polysaccharide (CPS). These B. cepacia strains were initially identified based on their positive reactivity in a latex agglutination assay that uses the CPS-specific monoclonal antibody (mAb) 4B11. Mass spectrometry and recA sequencing confirmed the identity of these isolates as B. cepacia (formerly genomovar I). Total carbohydrates extracted from B. cepacia cell pellets reacted with B. pseudomallei CPS-specific mAbs MCA147, 3C5, and 4C4, but did not react with the B. pseudomallei lipopolysaccharide-specific mAb Pp-PS-W. Whole genome sequencing of the B. cepacia isolates revealed the presence of genes demonstrating significant homology to those comprising the B. pseudomallei CPS biosynthetic gene cluster. Collectively, our results provide compelling evidence that B. cepacia strains expressing the same CPS as B. pseudomallei co-exist in the environment alongside B. pseudomallei. Since CPS is a target that is often used for presumptive identification of B. pseudomallei, it is possible that the occurrence of these unique B. cepacia strains may complicate the diagnosis of melioidosis.IMPORTANCEBurkholderia pseudomallei, the etiologic agent of melioidosis, is an important cause of morbidity and mortality in tropical and subtropical regions worldwide. The 6-deoxyheptan capsular polysaccharide (CPS) expressed by this bacterial pathogen is a promising target antigen that is useful for rapidly diagnosing melioidosis. Using assays incorporating CPS-specific monoclonal antibodies, we identified both clinical and environmental isolates of Burkholderia cepacia that express the same CPS antigen as B. pseudomallei. Because of this, it is important that staff working in melioidosis-endemic areas are aware that these strains co-exist in the same niches as B. pseudomallei and do not solely rely on CPS-based assays such as latex-agglutination, AMD Plus Rapid Tests, or immunofluorescence tests for the definitive identification of B. pseudomallei isolates.

Hcp1-loaded staphylococcal membrane vesicle vaccine protects against acute melioidosis

Burkholderia pseudomallei is the causal agent of melioidosis, a deadly tropical infectious disease that lacks a vaccine. On the basis of the attenuated Staphylococcus aureus RN4220-Δagr (RN), we engineered the RN4220-Δagr/pdhB-hcp1 strain (RN-Hcp1) to generate B. pseudomallei hemolysin-coregulated protein 1 (Hcp1)-loaded membrane vesicles (^hcp1MVs). The immunization of BALB/c mice with ^hcp1MVs mixed with adjuvant by a three-dose regimen increased the serum specific IgG production. The serum levels of inflammatory factors, including TNF-α and IL-6, in ^hcp1MV-vaccinated mice were comparable with those in PBS-challenged mice. The partial adjuvant effect of staphylococcal MVs was observed with the elevation of specific antibody titer in ^hcp1MV-vaccinated mice relative to those that received the recombinant Hcp1 protein (rHcp1) or MVs derived from RN strain (^ΔagrMVs). The ^hcp1MVs/adjuvant vaccine protected 70% of mice from lethal B. pseudomallei challenge. Immunization with ^hcp1MVs only protected 60% of mice, whereas vaccination with rHcp1 or ^ΔagrMVs conferred no protection. Moreover, mice that received ^hcp1MVs/adjuvant and ^hcp1MVs immunization had low serum TNF-α and IL-6 levels and no inflammatory infiltration in comparison with other groups. In addition, all surviving mice in ^hcp1MVs/adjuvant and ^hcp1MVs groups exhibited no culturable bacteria in their lungs, livers, and spleens five days postinfection. Overall, our data highlighted a new strategy for developing B. pseudomallei vaccine and showed that Hcp1-incorporated staphylococcal MV is a promising candidate for the prevention of acute melioidosis.

Evaluation of two different vaccine platforms for immunization against melioidosis and glanders

Burkholderia pseudomallei and the closely related species, Burkholderia mallei, produce similar multifaceted diseases which range from rapidly fatal to protracted and chronic, and are a major cause of mortality in endemic regions. Besides causing natural infections, both microbes are Tier 1 potential biothreat agents. Antibiotic treatment is prolonged with variable results, hence effective vaccines are urgently needed. The purpose of our studies was to compare candidate vaccines that target both melioidosis and glanders to identify the most efficacious one(s) and define residual requirements for their transition to the non-human primate aerosol model. Studies were conducted in the C57BL/6 mouse model to evaluate the humoral and cell-mediated immune response and protective efficacy of three Burkholderia vaccine candidates against lethal aerosol challenges with B. pseudomallei K96243, B. pseudomallei MSHR5855, and B. mallei FMH. The recombinant vaccines generated significant immune responses to the vaccine antigens, and the live attenuated vaccine generated a greater immune response to OPS and the whole bacterial cells. Regardless of the candidate vaccine evaluated, the protection of mice was associated with a dampened cytokine response within the lungs after exposure to aerosolized bacteria. Despite being delivered by two different platforms and generating distinct immune responses, two experimental vaccines, a capsule conjugate + Hcp1 subunit vaccine and the live B. pseudomallei 668 ΔilvI strain, provided significant protection and were down-selected for further investigation and advanced development.

Development of Melioidosis Subunit Vaccines Using an Enzymatically Inactive Burkholderia pseudomallei AhpC

Burkholderia pseudomallei, the causative agent of melioidosis, is a facultative intracellular, Gram-negative pathogen that is highly infectious via the respiratory route and can cause severe, debilitating, and often fatal diseases in humans and animals. At present, no licensed vaccines for immunization against this CDC Tier 1 select agent exist. Studies in our lab have previously demonstrated that subunit vaccine formulations consisting of a B. pseudomallei capsular polysaccharide (CPS)-based glycoconjugate (CPS-CRM197) combined with hemolysin-coregulated protein (Hcp1) provided C57BL/6 mice with high-level protection against an acute inhalational challenge of B. pseudomallei. In this study, we evaluated the immunogenicity and protective capacity of B. pseudomallei alkyl hydroperoxide reductase subunit C (AhpC) in combination with CPS-CRM197. AhpC is a peroxiredoxin involved in oxidative stress reduction and is a potential protective antigen. To facilitate our studies and maximize safety in animals, recombinant B. pseudomallei AhpC harboring an active site mutation (AhpC^C57G) was expressed in Escherichia coli and purified using tandem nickel-cobalt affinity chromatography. Immunization of C57BL/6 mice with CPS-CRM197 combined with AhpC^C57G stimulated high-titer IgG responses against the CPS component of the glycoconjugate as well as stimulated high-titer IgG and robust interferon gamma (IFN-γ)-, interleukin-5 (IL-5)-, and IL-17-secreting T cell responses against AhpC^C57G. When challenged via an inhalational route with a high dose (~27 50% lethal doses [LD₅₀s]) of B. pseudomallei, 70% of the immunized mice survived 35 days postchallenge. Collectively, our findings demonstrate that AhpC^C57G is a potent activator of cellular and humoral immune responses and may be a promising candidate to include in future melioidosis subunit vaccines.

Multicomponent gold nano-glycoconjugate as a highly immunogenic and protective platform against Burkholderia mallei

Burkholderia mallei (Bm) is a facultative intracellular pathogen and the etiological agent of glanders, a highly infectious zoonotic disease occurring in equines and humans. The intrinsic resistance to antibiotics, lack of specific therapy, high mortality, and history as a biothreat agent, prompt the need of a safe and effective vaccine. However, the limited knowledge of protective Bm-specific antigens has hampered the development of a vaccine. Further, the use of antigen-delivery systems that enhance antigen immunogenicity and elicit robust antigen-specific immune responses has been limited and could improve vaccines against Bm. Nanovaccines, in particular gold nanoparticles (AuNPs), have been investigated as a strategy to broaden the repertoire of vaccine-mediated immunity and as a tool to produce multivalent vaccines. To synthesize a nano-glycoconjugate vaccine, six predicted highly immunogenic antigens identified by a genome-wide bio- and immuno-informatic analysis were purified and coupled to AuNPs along with lipopolysaccharide (LPS) from B. thailandensis. Mice immunized intranasally with individual AuNP-protein-LPS conjugates, showed variable degrees of protection against intranasal Bm infection, while an optimized combination formulation (containing protein antigens OmpW, OpcP, and Hemagglutinin, along with LPS) showed complete protection against lethality in a mouse model of inhalational glanders. Animals immunized with different nano-glycoconjugates showed robust antigen-specific antibody responses. Moreover, serum from animals immunized with the optimized nano-glycoconjugate formulation showed sustained antibody responses with increased serum-mediated inhibition of adherence and opsonophagocytic activity in vitro. This study provides the basis for the rational design and construction of a multicomponent vaccine platform against Bm.

Distinct classes and subclasses of antibodies to hemolysin co-regulated protein 1 and O-polysaccharide and correlation with clinical characteristics of melioidosis patients

Melioidosis is a tropical infectious disease caused by Burkholderia pseudomallei that results in high mortality. Hemolysin co-regulated protein 1 (Hcp1) and O-polysaccharide (OPS) are vaccine candidates and potential diagnostic antigens. The correlation of classes/subclasses of antibodies against these antigens with clinical characteristics of melioidosis patients is unknown. Antibodies in plasma samples from melioidosis patients and healthy donors were quantified by ELISA and compared with clinical features. In melioidosis patients, Hcp1 induced high IgG levels. OPS induced high IgG and IgA levels. The area under receiver operating characteristic curve (AUROCC) to discriminate melioidosis cases from healthy donors was highest for anti-Hcp1 IgG (0.92) compared to anti-Hcp1 IgA or IgM. In contrast, AUROCC for anti-OPS for IgG (0.91) and IgA (0.92) were comparable. Anti-Hcp1 IgG1 and anti-OPS IgG2 had the greatest AUROCCs (0.87 and 0.95, respectively) compared to other IgG subclasses for each antigen. Survivors had significantly higher anti-Hcp1 IgG3 levels than non-survivors. Male melioidosis patients with diabetes had higher anti-OPS IgA levels than males without diabetes. Thus, diverse and specific antibody responses are associated with distinct clinical characteristics in melioidosis, confirming the diagnostic utility of these responses and providing new insights into immune mechanisms.

Caprine humoral response to Burkholderia pseudomallei antigens during acute melioidosis from aerosol exposure

Burkholderia pseudomallei causes melioidosis, a common source of pneumonia and sepsis in Southeast Asia and Northern Australia that results in high mortality rates. A caprine melioidosis model of aerosol infection that leads to a systemic infection has the potential to characterize the humoral immune response. This could help identify immunogenic proteins for new diagnostics and vaccine candidates. Outbred goats may more accurately mimic human infection, in contrast to the inbred mouse models used to date. B. pseudomallei infection was delivered as an intratracheal aerosol. Antigenic protein profiling was generated from the infecting strain MSHR511. Humoral immune responses were analyzed by ELISA and western blot, and the antigenic proteins were identified by mass spectrometry. Throughout the course of the infection the assay results demonstrated a much greater humoral response with IgG antibodies, in both breadth and quantity, compared to IgM antibodies. Pre-infection sera showed multiple immunogenic proteins already reactive for IgG (7-20) and IgM (0-12) in most of the goats despite no previous exposure to B. pseudomallei. After infection, the number of IgG reactive proteins showed a marked increase as the disease progressed. Early stage infection (day 7) showed immune reaction to chaperone proteins (GroEL, EF-Tu, and DnaK). These three proteins were detected in all serum samples after infection, with GroEL immunogenically dominant. Seven common reactive antigens were selected for further analysis using ELISA. The heat shock protein GroEL1 elicited the strongest goat antibody immune response compared to the other six antigens. Most of the six antigens showed the peak IgM reactivity at day 14, whereas the IgG reactivity increased further as the disease progressed. An overall MSHR511 proteomic comparison between the goat model and human sera showed that many immune reactive proteins are common between humans and goats with melioidosis.

Development of Subunit Vaccines That Provide High-Level Protection and Sterilizing Immunity against Acute Inhalational Melioidosis

Burkholderia pseudomallei, the etiologic agent of melioidosis, causes severe disease in humans and animals. Diagnosis and treatment of melioidosis can be challenging, and no licensed vaccines currently exist. Several studies have shown that this pathogen expresses a variety of structurally conserved protective antigens that include cell surface polysaccharides and cell-associated and cell-secreted proteins. Based on those findings, such antigens have become important components of the subunit vaccine candidates that we are currently developing. In the present study, the 6-deoxyheptan capsular polysaccharide (CPS) from B. pseudomallei was purified, chemically activated, and covalently linked to recombinant CRM197 diphtheria toxin mutant (CRM197) to produce CPS-CRM197. Additionally, tandem nickel-cobalt affinity chromatography was used to prepare highly purified recombinant B. pseudomallei Hcp1 and TssM proteins. Immunization of C57BL/6 mice with CPS-CRM197 produced high-titer IgG and opsonizing antibody responses against the CPS component of the glycoconjugate, while immunization with Hcp1 and TssM produced high-titer IgG and robust gamma interferon-secreting T cell responses against the proteins. Extending upon these studies, we found that when mice were vaccinated with a combination of CPS-CRM197 and Hcp1, 100% of the mice survived a lethal inhalational challenge with B. pseudomallei. Remarkably, 70% of the survivors had no culturable bacteria in their lungs, livers, or spleens, indicating that the vaccine formulation had generated sterilizing immune responses. Collectively, these studies help to better establish surrogates of antigen-induced immunity against B. pseudomallei as well as provide valuable insights toward the development of a safe, affordable, and effective melioidosis vaccine.

Use of Reverse Vaccinology in the Design and Construction of Nanoglycoconjugate Vaccines against Burkholderia pseudomallei

Burkholderia pseudomallei is a Gram-negative, facultative intracellular pathogen that causes the disease melioidosis in humans and other mammals. Respiratory infection with B. pseudomallei leads to a fulminant and often fatal disease. It has previously been shown that glycoconjugate vaccines can provide significant protection against lethal challenge; however, the limited number of known Burkholderia antigens has slowed progress toward vaccine development. The objective of this study was to identify novel antigens and evaluate their protective capacity when incorporated into a nanoglycoconjugate vaccine platform. First, an in silico approach to identify antigens with strong predicted immunogenicity was developed. Protein candidates were screened and ranked according to predicted subcellular localization, transmembrane domains, adhesive properties, and ability to interact with major histocompatibility complex (MHC) class I and class II. From these in silico predictions, we identified seven "high priority" proteins that demonstrated seroreactivity with anti-B. pseudomallei murine sera and convalescent human melioidosis sera, providing validation of our methods. Two novel proteins, together with Hcp1, were linked to lipopolysaccharide (LPS) and incorporated with the surface of a gold nanoparticle (AuNP). Animals receiving AuNP glycoconjugate vaccines generated high protein- and polysaccharide-specific antibody titers. Importantly, immunized animals receiving the AuNP-FlgL-LPS alone or as a combination demonstrated up to 100% survival and reduced lung colonization following a lethal challenge with B. pseudomallei Together, this study provides a rational approach to vaccine design that can be adapted for other complex pathogens and provides a rationale for further preclinical testing of AuNP glycoconjugate in animal models of infection.

Deciphering minimal antigenic epitopes associated with Burkholderia pseudomallei and Burkholderia mallei lipopolysaccharide O-antigens

Burkholderia pseudomallei (Bp) and Burkholderia mallei (Bm), the etiologic agents of melioidosis and glanders, respectively, cause severe disease in both humans and animals. Studies have highlighted the importance of Bp and Bm lipopolysaccharides (LPS) as vaccine candidates. Here we describe the synthesis of seven oligosaccharides as the minimal structures featuring all of the reported acetylation/methylation patterns associated with Bp and Bm LPS O-antigens (OAgs). Our approach is based on the conversion of an l-rhamnose into a 6-deoxy-l-talose residue at a late stage of the synthetic sequence. Using biochemical and biophysical methods, we demonstrate the binding of several Bp and Bm LPS-specific monoclonal antibodies with terminal OAg residues. Mice immunized with terminal disaccharide–CRM197 constructs produced high-titer antibody responses that crossreacted with Bm-like OAgs. Collectively, these studies serve as foundation for the development of novel therapeutics, diagnostics, and vaccine candidates to combat diseases caused by Bp and Bm.

Melioidosis and glanders are multifaceted infections caused by gram-negative bacteria. Here, the authors synthesize a series of oligosaccharides that mimic the lipopolysaccharides present on the pathogens’ surface and use them to develop novel glycoconjugates for vaccine development.

Development of Immunoassays for Burkholderia pseudomallei Typical and Atypical Lipopolysaccharide Strain Typing

Burkholderia pseudomallei is the causative agent of melioidosis, a severe infection endemic to many tropical regions. Lipopolysaccharide (LPS) is recognized as an important virulence factor used by B. pseudomallei. Isolates of B. pseudomallei have been shown to express one of four different types of LPS (typical LPS, atypical LPS types B and B2, and rough LPS) and in vitro studies have demonstrated that LPS types may impact disease severity. The association between LPS types and clinical manifestations, however, is still unknown, in part because an effective method for LPS type identification is not available. Thus, we developed antigen capture immunoassays capable of distinguishing between the LPS types. Mice were injected with B or B2 LPS for atypical LPS–specific monoclonal antibody (mAb) isolation; only two mAbs (3A2 and 5B4) were isolated from mice immunized with B2 LPS. Immunoblot analysis and surface plasmon resonance demonstrated that 3A2 and 5B4 are reactive with both B2 and B LPS where 3A2 was shown to possess higher affinity. Assays were then developed using capsular polysaccharide–specific mAb 4C4 for bacterial capture and 4C7 (previously shown to bind typical LPS) or 3A2 mAbs for typical or atypical LPS strain detection, respectively. The evaluations performed with 197 strains of Burkholderia and non-Burkholderia species showed that the assays are reactive to B. pseudomallei and Burkholderia mallei strains and have an accuracy of 98.8% (zero false positives and two false negatives) for LPS typing. The results suggest that the assays are effective and applicable for B. pseudomallei LPS typing.

Burkholderia pseudomallei Capsular Polysaccharide Recognition by a Monoclonal Antibody Reveals Key Details toward a Biodefense Vaccine and Diagnostics against Melioidosis

Burkholderia pseudomallei is the bacterium responsible for melioidosis, an infectious disease with high mortality rates. Since melioidosis is a significant public health concern in endemic regions and the organism is currently classified as a potential biothreat agent, the development of effective vaccines and rapid diagnostics is a priority. The capsular polysaccharide (CPS) expressed by B. pseudomallei is a highly conserved virulence factor and a protective antigen. Because of this, CPS is considered an attractive antigen for use in the development of both vaccines and diagnostics. In the present study, we describe the interactions of CPS with the murine monoclonal antibody (mAb) 4C4 using a multidisciplinary approach including organic synthesis, molecular biology techniques, surface plasmon resonance, and nuclear magnetic spectroscopy. Using these methods, we determined the mode of binding between mAb 4C4 and native CPS or ad hoc synthesized capsular polysaccharide fragments. Interestingly, we demonstrated that the O-acetyl moiety of CPS is essential for the interaction of the CPS epitope with mAb 4C4. Collectively, our results provide important insights into the structural features of B. pseudomallei CPS that enable antibody recognition that may help the rational design of CPS-based vaccine candidates. In addition, our findings confirm that the mAb 4C4 is suitable for use in an antibody-based detection assay for diagnosis of B. pseudomallei infections.

Evaluation of Polysaccharide-Based Latex Agglutination Assays for the Rapid Detection of Antibodies to Burkholderia pseudomallei

Melioidosis is a severe disease caused by the Gram-negative bacterium Burkholderia pseudomallei. Diagnosis of melioidosis currently relies on the isolation of B. pseudomallei from clinical samples, which can take several days. An indirect hemagglutination assay (IHA) is widely used for serodiagnosis, but it has a short shelf life, is poorly standardized, and requires a viable bacteria culture performed in a biosafety level 3 (BSL-3) laboratory. To improve the diagnostic methods, we have developed two rapid latex agglutination tests based on purified B. pseudomallei O-polysaccharide (OPS) and capsular polysaccharide (CPS) antigens. The immunodiagnostic potential of these tests was evaluated using serum from culture-confirmed melioidosis patients (N = 143) and healthy donors from either endemic (N = 199) or non-endemic areas (N = 90). The sensitivity of the OPS-based latex agglutination assay (OPS-latex; 84.4%) was significantly higher than both the CPS-latex (69.5%) (P < 0.001) and IHA (69.5%) (P = 0.001). When evaluated with Thai donor serum, the OPS-latex had comparable specificity (56.9%) to the CPS-latex (63.8%) (P = 0.053), but was significantly lower than the IHA (67.6%) (P = 0.002). In contrast, all tests with U.S. donor serum were highly specific (≥ 97.8%). These results suggest that polysaccharide-based latex agglutination assays may be useful for serodiagnosis of melioidosis in non-endemic areas.

Colony morphology variation of Burkholderia pseudomallei is associated with antigenic variation and O-polysaccharide modification

Burkholderia pseudomallei is a CDC tier 1 select agent that causes melioidosis, a severe disease in humans and animals. Persistent infections are common, and there is currently no vaccine available. Lipopolysaccharide (LPS) is a potential vaccine candidate. B. pseudomallei expresses three serologically distinct LPS types. The predominant O-polysaccharide (OPS) is an unbranched heteropolymer with repeating d-glucose and 6-deoxy-l-talose residues in which the 6-deoxy-l-talose residues are variably replaced with O-acetyl and O-methyl modifications. We observed that primary clinical B. pseudomallei isolates with mucoid and nonmucoid colony morphologies from the same sample expressed different antigenic types distinguishable using an LPS-specific monoclonal antibody (MAb). MAb-reactive (nonmucoid) and nonreactive (mucoid) strains from the same patient exhibited identical LPS banding patterns by silver staining and indistinguishable genotypes. We hypothesized that LPS antigenic variation reflected modification of the OPS moieties. Mutagenesis of three genes involved in LPS synthesis was performed in B. pseudomallei K96243. Loss of MAb reactivity was observed in both wbiA (encoding a 2-O-acetyltransferase) and wbiD (putative methyl transferase) mutants. The structural characteristics of the OPS moieties from isogenic nonmucoid strain 4095a and mucoid strain 4095c were further investigated. Utilizing nuclear magnetic resonance (NMR) spectroscopy, we found that B. pseudomallei 4095a and 4095c OPS antigens exhibited substitution patterns that differed from the prototypic OPS structure. Specifically, 4095a lacked 4-O-acetylation, while 4095c lacked both 4-O-acetylation and 2-O-methylation. Our studies indicate that B. pseudomallei OPS undergoes antigenic variation and suggest that the 9D5 MAb recognizes a conformational epitope that is influenced by both O-acetyl and O-methyl substitution patterns.

Burkholderia pseudomallei capsular polysaccharide conjugates provide protection against acute melioidosis

Burkholderia pseudomallei, the etiologic agent of melioidosis, is a CDC tier 1 select agent that causes severe disease in both humans and animals. Diagnosis and treatment of melioidosis can be challenging, and in the absence of optimal chemotherapeutic intervention, acute disease is frequently fatal. Melioidosis is an emerging infectious disease for which there are currently no licensed vaccines. Due to the potential malicious use of B. pseudomallei as well as its impact on public health in regions where the disease is endemic, there is significant interest in developing vaccines for immunization against this disease. In the present study, type A O-polysaccharide (OPS) and manno-heptose capsular polysaccharide (CPS) antigens were isolated from nonpathogenic, select-agent-excluded strains of B. pseudomallei and covalently linked to carrier proteins. By using these conjugates (OPS2B1 and CPS2B1, respectively), it was shown that although high-titer IgG responses against the OPS or CPS component of the glycoconjugates could be raised in BALB/c mice, only those animals immunized with CPS2B1 were protected against intraperitoneal challenge with B. pseudomallei. Extending upon these studies, it was also demonstrated that when the mice were immunized with a combination of CPS2B1 and recombinant B. pseudomallei LolC, rather than with CPS2B1 or LolC individually, they exhibited higher survival rates when challenged with a lethal dose of B. pseudomallei. Collectively, these results suggest that CPS-based glycoconjugates are promising candidates for the development of subunit vaccines for immunization against melioidosis.