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Pulido MR, García-Quintanilla M, Pachón J, McConnell MJ. Immunization with lipopolysaccharide-free outer membrane complexes protects against Acinetobacter baumannii infection. Vaccine 2018; 36:4153-4156. [PMID: 29887323 DOI: 10.1016/j.vaccine.2018.05.113] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2018] [Revised: 05/29/2018] [Accepted: 05/31/2018] [Indexed: 12/27/2022]
Abstract
Outer membrane complex (OMC) vaccines, which contain antigens from the bacterial outer membrane, have been developed for multiple Gram-negative bacteria. However, OMC vaccines demonstrate high endotoxin activity due to the presence of lipopolysaccharide in the bacterial outer membrane, thus precluding their use in humans. We isolated OMCs from an LPS-deficient strain of A. baumannii (IB010) which completely lacks LPS due to a mutation in the lpxD gene. OMCs from IB010 demonstrated a more than 10,000-fold reduction in endotoxin activity compared to OMCs from wild type A. baumannii. Vaccination with IB010 OMCs produced similar levels of antigen-specific IgG and IgM after two administrations compared to wild type OMCs, and resulted in a similar reduction in post-infection spleen bacterial loads and serum pro-inflammatory cytokine levels. Vaccination with IB010 OMCs provided significant protection against infection compared to control mice, indicating the LPS-free OMCs could contribute to vaccine strategies for preventing infection by A. baumannii.
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Affiliation(s)
- Marina R Pulido
- Clinical Unit of Infectious Diseases, Clinical Microbiology and Preventive Medicine, Institute of Biomedicine of Seville (IBiS), University Hospital Virgen del Rocío/CSIC/University of Seville, 41013 Seville, Spain
| | - Meritxell García-Quintanilla
- Clinical Unit of Infectious Diseases, Clinical Microbiology and Preventive Medicine, Institute of Biomedicine of Seville (IBiS), University Hospital Virgen del Rocío/CSIC/University of Seville, 41013 Seville, Spain
| | - Jerónimo Pachón
- Clinical Unit of Infectious Diseases, Clinical Microbiology and Preventive Medicine, Institute of Biomedicine of Seville (IBiS), University Hospital Virgen del Rocío/CSIC/University of Seville, 41013 Seville, Spain; Department of Medicine, University of Seville, Seville, Spain.
| | - Michael J McConnell
- Clinical Unit of Infectious Diseases, Clinical Microbiology and Preventive Medicine, Institute of Biomedicine of Seville (IBiS), University Hospital Virgen del Rocío/CSIC/University of Seville, 41013 Seville, Spain.
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2
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Wang X, Teng D, Guan Q, Mao R, Hao Y, Wang X, Yao J, Wang J. Escherichia coli outer membrane protein F (OmpF): an immunogenic protein induces cross-reactive antibodies against Escherichia coli and Shigella. AMB Express 2017; 7:155. [PMID: 28728309 PMCID: PMC5517391 DOI: 10.1186/s13568-017-0452-8] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2017] [Accepted: 07/11/2017] [Indexed: 11/10/2022] Open
Abstract
Diarrhea caused by pathogenic Escherichia coli (E. coli) is one of the most serious infectious diseases in humans and animals. Due to antibiotics resistance and the lack of efficient vaccine, more attention should be paid to find potential versatile vaccine candidates to prevent diseases. In this study, the sequence homology analysis indicated that OmpF from E. coli CVCC 1515 shares a high identity (90−100%) with about half of the E. coli (46.7%) and Shigella (52.8%) strains. Then the recombinant OmpF was supposed to be developed as a versatile vaccine to prevent E. coli infection. OmpF was expressed in E. coli BL21 (DE3) using the auto-induction method. The recombinant OmpF (rOmpF) protein had an average molecular weight of 40 kDa with the purity of 90%. Immunological analysis indicated that the titers of anti-rOmpF sera against rOmpF and whole cells were 1:240,000 and 1:27,000, respectively. The opsonophagocytosis result showed that 72.21 ± 11.39 and 11.04 ± 3.90% of bacteria were killed in the rOmpF immunization and control groups, respectively. The survival ratio of mice immunized with rOmpF ranged between 40 and 60% as observed within 36 h after challenge, indicating mice were partially protected from E. coli CVCC 1515 infection. The expressed rOmpF protein induced an effective immune response, but only provide a weak protection against pathogenic E. coli CVCC 1515 and a small reduction in E. coli CICC 21530 (O157:H7) excretion in a mouse infection model. Native forms of the OmpF antigen may be studied for immunogenicity and potential protective efficacy.
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3
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Freixeiro P, Pensado A, Allen L, Humphries H, Taylor S, Seijo B, Ferreirós C, Gorringe A, Sánchez S, Sánchez A. Solid sorbitan esters nanoparticles are efficient and low-cost vehicles for subunit vaccines: Proof of concept with Neisseria meningitidis protein Mip. J Drug Deliv Sci Technol 2017. [DOI: 10.1016/j.jddst.2017.04.031] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
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4
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Matthias KA, Strader MB, Nawar HF, Gao YS, Lee J, Patel DS, Im W, Bash MC. Heterogeneity in non-epitope loop sequence and outer membrane protein complexes alters antibody binding to the major porin protein PorB in serogroup B Neisseria meningitidis. Mol Microbiol 2017; 105:934-953. [PMID: 28708335 DOI: 10.1111/mmi.13747] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/13/2017] [Indexed: 12/11/2022]
Abstract
PorB is a well-characterized outer membrane protein that is common among Neisseria species and is required for survival. A vaccine candidate, PorB induces antibody responses that are directed against six variable surface-exposed loops that differ in sequence depending on serotype. Although Neisseria meningitidis is naturally competent and porB genetic mosaicism provides evidence for strong positive selection, the sequences of PorB serotypes commonly associated with invasive disease are often conserved, calling into question the interaction of specific PorB loop sequences in immune engagement. In this report, we provide evidence that antibody binding to a PorB epitope can be altered by sequence mutations in non-epitope loops. Through the construction of hybrid PorB types and PorB molecular dynamics simulations, we demonstrate that loops both adjacent and non-adjacent to the epitope loop can enhance or diminish antibody binding, a phenotype that correlates with serum bactericidal activity. We further examine the interaction of PorB with outer membrane-associated proteins, including PorA and RmpM. Deletion of these proteins alters the composition of PorB-containing native complexes and reduces antibody binding and serum killing relative to the parental strain, suggesting that both intramolecular and intermolecular PorB interactions contribute to host adaptive immune evasion.
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Affiliation(s)
- Kathryn A Matthias
- U.S. Food and Drug Administration, Center for Biologics Evaluation and Research, Silver Spring, MD, USA
| | - Michael Brad Strader
- U.S. Food and Drug Administration, Center for Biologics Evaluation and Research, Silver Spring, MD, USA
| | - Hesham F Nawar
- U.S. Food and Drug Administration, Center for Biologics Evaluation and Research, Silver Spring, MD, USA
| | - Yamei S Gao
- U.S. Food and Drug Administration, Center for Biologics Evaluation and Research, Silver Spring, MD, USA
| | - Joonseong Lee
- Department of Biological Sciences and Bioengineering Program, Lehigh University, PA, USA
| | - Dhilon S Patel
- Department of Biological Sciences and Bioengineering Program, Lehigh University, PA, USA
| | - Wonpil Im
- Department of Biological Sciences and Bioengineering Program, Lehigh University, PA, USA
| | - Margaret C Bash
- U.S. Food and Drug Administration, Center for Biologics Evaluation and Research, Silver Spring, MD, USA
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5
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Costoya L, Marzoa J, Ferreirós C, Criado MT. Liposomes or traditional adjuvants: induction of bactericidal activity by the macrophage infectivity potentiator protein (Mip) of Neisseria meningitidis. APMIS 2017; 125:725-731. [PMID: 28543600 DOI: 10.1111/apm.12709] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2017] [Accepted: 03/20/2017] [Indexed: 01/10/2023]
Abstract
Currently, one of the main approaches to achieve a vaccine for serogroup B Neisseria meningitidis is based on outer membrane proteins with low antigenic variability among strains. Since these proteins tend to be minor components of the outer membrane, recombinant production is required to obtain them in sufficient amounts for evaluation and development of vaccines. In this study, we analysed the ability of recombinant macrophage infectivity potentiator (rMip) protein to induce protective bactericidal activity in mice. The rMip protein was cloned from N. meningitidis strain H44/76 and was used to immunise mice, and the sera obtained were tested against the homologous and several heterologous N. meningitidis strains. The sera were obtained using the rMip alone, with adjuvant Al(OH)3 , or after inclusion into liposomes. Bactericidal activity was variable depending on the strain, although high titres were seen against strains H44/76 and NmP27. Liposomes enhanced fourfold the reactivity against the homologous strain. The results presented suggest that the rMip protein should be considered a promising candidate for the improvement of future protein-based vaccines.
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Affiliation(s)
- Liliana Costoya
- Departamento de Microbioloxía e Parasitoloxía, Universidade de Santiago de Compostela, 15782, Santiago de Compostela, Spain
| | - Juan Marzoa
- Departamento de Microbioloxía e Parasitoloxía, Universidade de Santiago de Compostela, 15782, Santiago de Compostela, Spain
| | - Carlos Ferreirós
- Departamento de Microbioloxía e Parasitoloxía, Universidade de Santiago de Compostela, 15782, Santiago de Compostela, Spain
| | - Maria Teresa Criado
- Departamento de Microbioloxía e Parasitoloxía, Universidade de Santiago de Compostela, 15782, Santiago de Compostela, Spain
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6
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Wang X, Guan Q, Wang X, Teng D, Mao R, Yao J, Wang J. Paving the way to construct a new vaccine against Escherichia coli from its recombinant outer membrane protein C via a murine model. Process Biochem 2015. [DOI: 10.1016/j.procbio.2015.05.001] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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7
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Recombinant outer membrane protein A induces a protective immune response against Escherichia coli infection in mice. Appl Microbiol Biotechnol 2015; 99:5451-60. [PMID: 25567514 DOI: 10.1007/s00253-014-6339-6] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2014] [Revised: 12/12/2014] [Accepted: 12/17/2014] [Indexed: 01/19/2023]
Abstract
Pathogenic Escherichia coli (E. coli) is an important infectious Gram-negative bacterium causing millions of death every year. Outer membrane protein A (OmpA) has been suggested as a potential vaccine candidate for conferring protection against bacterial infection. In this study, a universal vaccine candidate for E. coli infection was developed and evaluated. Bioinformatics analysis revealed the OmpA protein from E. coli shares 96~100%, 90~94%, and 45% identity with Shigella, Salmonella, and Pseudomonas strains, respectively. The ompA gene was cloned from the genomic DNA of E. coli, and then the OmpA protein was expressed in BL21 (DE3) using the auto-induction method. The recombinant OmpA (rOmpA) protein had an average molecular weight of 36 kDa with the purity of 93.5%. Immunological analysis indicated that the titers of anti-rOmpA sera against rOmpA and whole cells were 1:642,000 and 1:140,000, respectively. Moreover, rOmpA not only conferred a high level of immunogenicity to protect mice against the challenge of E. coli, but also generated cross-protection against Shigella and Salmonella. The anti-rOmpA sera could enhance the phagocytic activity of neutrophils against E. coli. The survive ratios of mice immunized with rOmpA and PBS were 50% and 20% after 48 h post-challenge, indicating mice were protected from E. coli infection after immunization with rOmpA. All these results clearly indicate that rOmpA may be a promising candidate for the development of a subunit vaccine to prevent E. coli infection.
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8
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Jiang Y, Kong Q, Roland KL, Curtiss R. Membrane vesicles of Clostridium perfringens type A strains induce innate and adaptive immunity. Int J Med Microbiol 2014; 304:431-43. [PMID: 24631214 PMCID: PMC4285460 DOI: 10.1016/j.ijmm.2014.02.006] [Citation(s) in RCA: 91] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2013] [Revised: 01/21/2014] [Accepted: 02/02/2014] [Indexed: 02/07/2023] Open
Abstract
Vesicle shedding from bacteria is a universal process in most Gram-negative bacteria and a few Gram-positive bacteria. In this report, we isolate extracellular membrane vesicles (MVs) from the supernatants of Gram-positive pathogen Clostridium perfringens (C. perfringens). We demonstrated vesicle production in a variety of virulent and nonvirulent type A strains. MVs did not contain alpha-toxin and NetB toxin demonstrated by negative reaction to specific antibody and absence of specific proteins identified by LC-MS/MS. C. perfringens MVs contained DNA components such as 16S ribosomal RNA gene (16S rRNA), alpha-toxin gene (plc) and the perfringolysin O gene (pfoA) demonstrated by PCR. We also identified a total of 431 proteins in vesicles by 1-D gel separation and LC-MS/MS analysis. In vitro studies demonstrated that vesicles could be internalized into murine macrophage RAW264.7 cells without direct cytotoxicity effects, causing release of inflammation cytokines including granulocyte colony stimulating factor (G-CSF), tumor necrosis factor-alpha (TNF-α) and interleukin-1 (IL-1), which could also be detected in mice injected with MVs through intraperitoneal (i.p.) route. Mice immunized with C. perfringens MVs produced high titer IgG, especially IgG1, antibodies against C. perfringens membrane proteins. However, this kind of antibody could not provide protection in mice following challenge, though it could slightly postpone the time of death. Our results indicate that release of MVs from C. perfringens could provide a previously unknown mechanism to induce release of inflammatory cytokines, especially TNF-α, these findings may contribute to a better understanding of the pathogenesis of C. perfringens infection.
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Affiliation(s)
- Yanlong Jiang
- Center for Infectious Diseases and Vaccinology, The Biodesign Institute, Arizona State University, Tempe, AZ 85287, USA
| | - Qingke Kong
- Center for Infectious Diseases and Vaccinology, The Biodesign Institute, Arizona State University, Tempe, AZ 85287, USA
| | - Kenneth L Roland
- Center for Infectious Diseases and Vaccinology, The Biodesign Institute, Arizona State University, Tempe, AZ 85287, USA
| | - Roy Curtiss
- Center for Infectious Diseases and Vaccinology, The Biodesign Institute, Arizona State University, Tempe, AZ 85287, USA; School of Life Sciences, Arizona State University, Tempe, AZ 85287, USA.
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9
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Hey A, Li MS, Hudson MJ, Langford PR, Kroll JS. Transcriptional profiling of Neisseria meningitidis interacting with human epithelial cells in a long-term in vitro colonization model. Infect Immun 2013; 81:4149-59. [PMID: 23980104 PMCID: PMC3811814 DOI: 10.1128/iai.00397-13] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2013] [Accepted: 08/15/2013] [Indexed: 12/12/2022] Open
Abstract
Neisseria meningitidis is a commensal of humans that can colonize the nasopharyngeal epithelium for weeks to months and occasionally invades to cause life-threatening septicemia and meningitis. Comparatively little is known about meningococcal gene expression during colonization beyond those first few hours. In this study, the transcriptome of adherent serogroup B N. meningitidis strain MC58 was determined at intervals during prolonged cocultivation with confluent monolayers of the human respiratory epithelial cell line 16HBE14. At different time points up to 21 days, 7 to 14% of the meningococcal genome was found to be differentially regulated. The transcriptome of adherent meningococci obtained after 4 h of coculture was markedly different from that obtained after prolonged cocultivation (24 h, 96 h, and 21 days). Genes persistently upregulated during prolonged cocultivation included three genes (hfq, misR/phoP, and lrp) encoding global regulatory proteins. Many genes encoding known adhesins involved in epithelial adherence were upregulated, including those of a novel locus (spanning NMB0342 to NMB0348 [NMB0342-NMB0348]) encoding epithelial cell-adhesive function. Sixteen genes (including porA, porB, rmpM, and fbpA) encoding proteins previously identified by their immunoreactivity to sera from individuals colonized long term with serogroup B meningococci were also upregulated during prolonged cocultivation, indicating that our system models growth conditions in vivo during the commensal state. Surface-expressed proteins downregulated in the nasopharynx (and thus less subject to selection pressure) but upregulated in the bloodstream (and thus vulnerable to antibody-mediated bactericidal activity) should be interesting candidate vaccine antigens, and in this study, three new proteins fulfilling these criteria have been identified: NMB0497, NMB0866, and NMB1882.
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Affiliation(s)
- Ariann Hey
- Section of Paediatrics, Department of Medicine, Imperial College London, St. Mary's Campus, London, United Kingdom
| | - Ming-Shi Li
- Section of Paediatrics, Department of Medicine, Imperial College London, St. Mary's Campus, London, United Kingdom
| | - Michael J. Hudson
- Section of Paediatrics, Department of Medicine, Imperial College London, St. Mary's Campus, London, United Kingdom
- Public Health England, Porton Down, Salisbury, United Kingdom
| | - Paul R. Langford
- Section of Paediatrics, Department of Medicine, Imperial College London, St. Mary's Campus, London, United Kingdom
| | - J. Simon Kroll
- Section of Paediatrics, Department of Medicine, Imperial College London, St. Mary's Campus, London, United Kingdom
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Sanders H, Kaaijk P, van den Dobbelsteen GP. Preclinical evaluation of MenB vaccines: prerequisites for clinical development. Expert Rev Vaccines 2013; 12:31-42. [PMID: 23256737 DOI: 10.1586/erv.12.137] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Despite the widespread use of polysaccharide and conjugate vaccines against disease caused by several serogroups of Neisseria meningitidis, vaccines targeting meningococci expressing the serogroup B capsule (MenB) have focused on subcapsular antigens, due to crossreactivity of the polysaccharide with human glycoproteins. Protein vaccines composed of outer membrane vesicles have been used successfully to control epidemics of MenB disease in several countries; however, these are specific for epidemic strains. Currently, a single serogroup B vaccine, aiming to provide comprehensive coverage, has been approved for use, and several others are undergoing clinical trials. Data on potential new vaccine candidates, from discovery to initial preclinical evaluation, are regularly published. In this review, the data required to progress from preclinical to clinical development of MenB vaccines are outlined, with reference to relevant regulatory guidelines. The issues caused by a lack of reliable animal models, particularly with respect to determination of protective efficacy, are also discussed.
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Affiliation(s)
- Holly Sanders
- Bacterial Vaccines, Crucell Holland, Leiden, The Netherlands
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11
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Phillips R, Williams JN, Tan WM, Bielecka MK, Thompson H, Hung MC, Heckels JE, Christodoulides M. Immunization with recombinant Chaperonin60 (Chp60) outer membrane protein induces a bactericidal antibody response against Neisseria meningitidis. Vaccine 2013; 31:2584-90. [PMID: 23566947 DOI: 10.1016/j.vaccine.2013.03.033] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2013] [Revised: 03/18/2013] [Accepted: 03/21/2013] [Indexed: 12/30/2022]
Abstract
Sera from individuals colonized with Neisseria meningitidis and from patients with meningococcal disease contain antibodies specific for the neisserial heat-shock/chaperonin (Chp)60 protein. In this study, immunization of mice with recombinant (r)Chp60 in saline; adsorbed to aluminium hydroxide; in liposomes and detergent micelles, with and without the adjuvant MonoPhosphoryl Lipid A (MPLA), induced high and similar (p>0.05) levels of antibodies that recognized Chp60 in outer membranes (OM). FACS analysis and immuno-fluorescence experiments demonstrated that Chp60 was surface-expressed on meningococci. By western blotting, murine anti-rChp60 sera recognized a protein of Mr 60kDa in meningococcal cell lysates. However, cross-reactivity with human HSP60 protein was also observed. By comparing translated protein sequences of strains, 40 different alleles were found in meningococci in the Bacterial Isolate Genome Sequence database with an additional 5 new alleles found in our selection of 13 other strains from colonized individuals and patients. Comparison of the non-redundant translated amino acid sequences from all the strains revealed ≥97% identity between meningococcal Chp60 proteins, and in our 13 strains the protein was expressed to high and similar levels. Bactericidal antibodies (median reciprocal titres of 32-64) against the homologous strain MC58 were induced by immunization with rChp60 in liposomes, detergent micelles and on Al(OH)3. Bactericidal activity was influenced by the addition of MPLA and the delivery formulation used. Moreover, the biological activity of anti-Chp60 antisera did not extend significantly to heterologous meningococcal strains. Thus, in order to provide broad coverage, vaccines based on Chp60 would require multiple proteins and specific bactericidal epitope identification.
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Affiliation(s)
- Renee Phillips
- Neisseria Research Group, Molecular Microbiology, Clinical and Experimental Sciences, Sir Henry Wellcome Laboratories, University of Southampton Medical School, Southampton General Hospital, Southampton SO166YD, United Kingdom
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12
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Freixeiro P, Diéguez-Casal E, Costoya L, Seijo B, Ferreirós CM, Criado MT, Sánchez S. Study of the stability of proteoliposomes as vehicles for vaccines against Neisseria meningitidis based on recombinant porin complexes. Int J Pharm 2013; 443:1-8. [DOI: 10.1016/j.ijpharm.2012.12.046] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2012] [Revised: 12/21/2012] [Accepted: 12/30/2012] [Indexed: 11/29/2022]
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13
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New technologies in developing recombinant attenuated Salmonella vaccine vectors. Microb Pathog 2012; 58:17-28. [PMID: 23142647 DOI: 10.1016/j.micpath.2012.10.006] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2012] [Revised: 10/29/2012] [Accepted: 10/30/2012] [Indexed: 01/01/2023]
Abstract
Recombinant attenuated Salmonella vaccine (RASV) vectors producing recombinant gene-encoded protective antigens should have special traits. These features ensure that the vaccines survive stresses encountered in the gastrointestinal tract following oral vaccination to colonize lymphoid tissues without causing disease symptoms and to result in induction of long-lasting protective immune responses. We recently described ways to achieve these goals by using regulated delayed in vivo attenuation and regulated delayed in vivo antigen synthesis, enabling RASVs to efficiently colonize effector lymphoid tissues and to serve as factories to synthesize protective antigens that induce higher protective immune responses. We also developed some additional new strategies to increase vaccine safety and efficiency. Modification of lipid A can reduce the inflammatory responses without compromising the vaccine efficiency. Outer membrane vesicles (OMVs) from Salmonella-containing heterologous protective antigens can be used to increase vaccine efficiency. A dual-plasmid system, possessing Asd+ and DadB+ selection markers, each specifying a different protective antigen, can be used to develop multivalent live vaccines. These new technologies have been adopted to develop a novel, low-cost RASV synthesizing multiple protective pneumococcal protein antigens that could be safe for newborns/infants and induce protective immunity to diverse Streptococcus pneumoniae serotypes after oral immunization.
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