Meningococcal serogroup B infections: a search for a broadly protective vaccine

Development a multi-epitope driven subunit vaccine for immune response reinforcement against Serogroup B of Neisseria meningitidis using comprehensive immunoinformatics approaches

Serogroup B of Neisseria meningitidis is the main cause of mortality due to meningococcal meningitis. Despite of many investigations, there is still no effective vaccine to prevent this serious infection. Therefore, this study was conducted to design a multi-epitope based vaccine through immunoinformatics approaches. The T CD4⁺ and TCD8⁺ cells along with IFN-γ inducing epitopes were selected from TspA, FHbp, NspA, TbpB, PilQ and NspA antigens form serogroup B of Neisseria meningitidis. Furthermore, to induce strong helper T lymphocytes (HTLs) responses, Pan HLA DR-binding epitope (PADRE) was used. In addition, loop 5 and 7 of the PorB as a TLR2 agonist were added to the vaccine construct. Physico-chemical properties, secondary and tertiary structures of the proposed construct were assessed. Finally, homology modeling, refinement and molecular docking were carried out to evaluated the construct tertiary structure and protein-protein interaction, respectively. By fusing the CTL, HTL and IFN-γ predicted epitopes along with suitable adjuvant and linkers, a multi-epitope vaccine was constructed with a TAT sequence of HIV at the N-terminal. Immunoinformatics analyses confirmed a soluble and non-allergic protein with a molecular weight of 62.5 kDa and high antigenicity. Furthermore, the stability of the multi-epitope construct was established and showed strong potential to generate humoral and cell-mediated immune responses. In addition, through molecular docking and dynamic simulation, the microscopic interaction between the vaccine construct and TLR-2 were verified. In summary, immunoinformatics analysis demonstrated that the constructed multi-epitope vaccine had a strong potential of T and B-cell stimulation and it could possibly be used for prophylactic or therapeutic aims to protect against serogroup B of N. meningitidis.

Evaluation of truncated NhhA protein as a candidate meningococcal vaccine antigen

NhhA (Neisseria hia homologue) is an outer membrane protein from Neisseria meningitidis, the causative agent of meningococcal disease. The protein is surface exposed and its expression in a wide range of meningococcal strains suggests it is a promising vaccine candidate. In addition, immunization of mice with outer membrane vesicles of strains that overexpress NhhA in conjunction with one of TbpA, Omp85 or NspA results in synergistic bactericidal responses. We previously showed that the NhhA sequence is highly conserved between strains, with the majority of the differences localized to four distinct variable regions located in the amino-terminal region of the mature protein. In this study, N. meningitidis strains were constructed that over-express wild-type NhhA. Strains expressing truncated versions of NhhA, with deletions from the amino-terminal region that removed the most variable regions, were also made. These expression strains were also modified so that immunodominant, phase- and antigenically-variable outer membrane proteins were not expressed, truncated lipooligosaccharide (LOS) expression was genetically fixed (no phase variability), and capsular polysaccharide expression abolished. Outer membrane vesicles derived from these strains were used to immunize mice. As previously observed, a synergistic effect involving another antigen, TbpA, was required to demonstrate bactericidal activity. The highest bactericidal response against a heterologous strain was obtained with a truncated variant of NhhA. These results indicate that removal of (a) variable region(s) does not reduce bactericidal responses against NhhA, and that bactericidal targets exist in regions other than the variable N-teminus. This provides the basis for future examination of responses against truncated NhhA in protecting against heterologous NhhA strains, and further evaluation of truncated NhhA as a candidate for inclusion in a vaccine against all serogroups of N. meningitidis.

PorA VR3 Typing Database: a web-based resource for the determination of PorA VR3 alleles of Neisseria meningitidis

The variable regions (VR) of the surface-exposed PorA protein of Meningococci are used for subtyping and are considered the most abundant epitopes of outer membrane vesicle-based vaccine preparations. We have developed both a database that maintains all the known VR3 alleles and a web-based application for the rapid identification and submission of new VR3 variants based on sequence comparison.

Quest for a broad-range vaccine against Neisseria meningitidis serogroup B: implications of genetic variations of the surface-exposed proteins

Despite the development of new vaccine formulations using new biotechnology resources to combat emerging and re-emerging diseases, serogroup B meningococcal disease is still a worldwide burden, accounting for many deaths and disabilities every year. The successful approach of coupling a polysaccharide (PS) with a carrier protein in order to increase long-lasting immunity could not be exploited againstNeisseria meningitidisB because of the limitations of using the capsular PS of serogroup B meningococci. Tailor-made vaccines based on exposed proteins were shown to be a promising approach to overcome these flaws. However, the continuous adaptation of surface meningococcal structures to the external environment has led to genetic shifts of potential vaccine-target epitopes, hampering the quest for a broad-range vaccine that could be used against all serogroups, especially against serogroup B.

Towards an improved serogroup BNeisseria meningitidisvaccine

Meningococcal disease, presenting primarily as septicaemia and meningitis, continues to be a devastating problem around the world. Over the last century, vaccine development has been undertaken in earnest for the prevention of this disease. Polysaccharide vaccines have been available for almost 40 years, yet they are poorly immunogenic in young children who are at the highest risk. Since their introduction into some routine immunisation schedules in 1999, polysaccharide-protein conjugate vaccines for the prevention of serogroup C meningococcal infection have proven efficacious. A quadrivalent polysaccharide-protein conjugate vaccine against serogroups A, C, W135 and Y, which is being introduced in the US this year, is hoped to control disease caused by these serogroups. To date, however, the development of a universally safe, immunogenic and effective serogroup B Neisseria meningitidis vaccine has remained a challenge. This review details the many conventional vaccine strategies and the more recent genome-derived technological approaches being used in serogroup B vaccine development. The future prevention of serogroup B disease will rely on both outer membrane vesicle vaccines being used for serosubtype-specific outbreaks and new vaccines containing multiple other antigens. Investment by the pharmaceutical industry in preclinical research and development provides hope that an efficacious serogroup B meningococcal vaccine can be developed.

The region comprising amino acids 100 to 255 of Neisseria meningitidis lipoprotein GNA 1870 elicits bactericidal antibodies

GNA 1870 is a novel surface-exposed lipoprotein, identified by genome analysis of Neisseria meningitidis strain MC58, which induces bactericidal antibodies. Three sequence variants of the protein were shown to be sufficient to induce bactericidal antibodies against a panel of strains representative of the diversity of serogroup B meningococci. Here, we studied the antigenic and immunogenic properties of GNA 1870, which for convenience was divided into domains A, B, and C. The immune responses of mice immunized with each of the three variants were tested using overlapping peptides scanning the entire protein length and using recombinant fragments. We found that while most of the linear epitopes are located in the A domain, the bactericidal antibodies are directed against conformational epitopes located in the BC domain. This was also confirmed by the isolation of a bactericidal murine monoclonal antibody, which failed to recognize linear peptides on the A, B, and C domains separately but recognized a conformational epitope formed only by the combination of the B and C domains. Arginine in position 204 was identified as important for binding of the monoclonal antibody. The identification of the region containing bactericidal epitopes is an important step in the design of new vaccines against meningococci.