Outer membrane vesicle ofNeisseria meningitidis serogroup B as an adjuvant to induce specific antibody response against the lipopolysaccharide ofBrucella abortus S99

Evaluation of protective immunity responses against pneumococcal PhtD and its C-terminal in combination with outer-membrane vesicles as adjuvants

Introduction. Streptococcus pneumoniae is a significant bacterial pathogen in humans. Currently, there are two types of pneumococcal vaccines, but there are concerns regarding their application.

Aim. Since many pneumococcal proteins are serotype-independent, polyhistidine triad protein D (PhtD) has been selected as a vaccine candidate.

Methodology. We prepared recombinant PhtD and its C-terminal fragment (PhtD-C) using alum and outer-membrane vesicles (OMVs) as adjuvants. The combinations were injected intraperitoneally into mice, and then total immunoglobulin G (IgG) and specific IgG, IgG1 and IgG2a were measured. A serum bactericidal assay and opsonophagocytosis were also performed as complementary tests. Meningococcal OMVs were used as an adjuvant.

Results. The levels of specific IgG and IgG1 against combinations of PhtD and its C-terminal with OMVs and alum as adjuvants increased at the time of the third mouse immunization on day 35. Forty per cent and 60% of S. pneumoniae ATCC 6303 (serotype 3) as a virulent pneumococcal strain, respectively, were killed in the opsonophagocytosis test and these results could also be observed in the serum bactericidal assay. Mice mmunized iwith PhtD and its C-terminal with OMVs and alum as adjuvants survived after 10 days of pneumococcal challenge.

Conclusion. The combination of PhtD and PhtD-C with alum produced optimal results, but the combination of PhtD and PhtD-C with OMVs produced minimal results by comparison. The survival rates were also measured, and these corresponded with the results of the immunological assessments. Our findings showed that mice receiving PhtD and PhtD-C plus OMV and alum had higher survival rates than the mice in the other groups.

Preparation and Evaluation of a New Lipopolysaccharide-based Conjugate as a Vaccine Candidate for Brucellosis

OBJECTIVES

Development of an efficacious vaccine against brucellosis has been a challenge for scientists for many years. At present, there is no licensed vaccine against human brucellosis. To overcome this problem, currently, antigenic determinants of Brucella cell wall such as Lipopolysaccharide (LPS) are considered as potential candidates to develop subunit vaccines.

METHODS

In this study, Brucella abortus LPS was used for conjugation to Neisseria meningitidis serogroup B outer membrane vesicle (OMV) as carrier protein using carbodiimide and adipic acid-mediated coupling and linking, respectively. Groups of eight BALB/c mice were injected subcutaneously with 10 μg LPS alone, combined LPS + OMV and conjugated LPS-OMV on 0 days, 14 days, 28 days and 42 days. Anti-LPS IgG was measured in serum.

RESULTS

The yield of LPS to OMV in LPS-OMV conjugate was 46.55%, on the basis of carbohydrate content. The ratio for LPS to OMV was 4.07. The LPS-OMV conjugate was the most immunogenic compound that stimulated following the first injection with increased IgG titer of ∼5-fold and ∼1.3-fold higher than that produced against LPS and LPS in noncovalent complex to OMV (LPS + OMV), respectively. The highest anti-LPS IgG titer was detected 2 weeks after the third injection (Day 42) of LPS-OMV conjugate. The conjugated compound elicited higher titers of IgG than LPS + OMV, that showed a 100-120-fold rise of anti-LPS IgG in mice.

CONCLUSION

These results indicate that our conjugated LPS-OMV can be used as a brucellosis vaccine, but further investigation is required.

Outer membrane vesicle: a macromolecule with multifunctional activity

Nowadays adjuvants are extensively used as immuno-stimulatory and immuno-modulatory compounds as components of subunit and combination vaccine formulations. The adjuvants of microbial origin are more frequently used among currently used licensed or experimental adjuvants. The outer membrane vesicle (OMV) of Neisseria meningitidis is among the newly studied components of microbial origin, which could be applied as an adjuvant. Although the potency of OMV as a carrier (conjugated to a hapten) is now proven, the adjuvant properties of OMV have particular significance as a potential target for protective immunity. Since it has immune-stimulatory activity, OMV has been utilized in vaccine development. This commentary reviews the different applications of OMV as potential adjuvant in the field of vaccine development.