Measurement of opsonophagocytic activity of antibodies specific toNeisseria meningitidis serogroup A capsular polysaccharide-serogroup B outer membrane vesicle conjugate in animal model

Abstract

Neisseria meningitidis is efficiently phagocytosed by polymorphonuclear leukocytes (PMN S ) following opsonization with opsonic antibodies; opsonophagocytosis is the primary mechanism for clearance of meningococci from the host. Thus, in testing meningococcal vaccines, the level of opsonophagocytic antibodies appears to correlate with vaccine-induced protection. Our previous studies demonstrated that the conjugation of N. meningitidis serogroup A capsular polysaccharide (CPSA) to serogroup B outer membrane vesicle (OMV) could induce a high level of bactericidal antibody response against serogroup A meningococci in animals. The purpose of this study was to evaluate opsonophagocytic activity of the conjugate of CPSA to OMV (CPSA-OMV). In order to evaluate the potential efficacy of CPSA-OMV a flow cytometric opsonophagocytic assay was used. The conjugate and controls were injected intramuscularly into four groups of rabbits with boosters on days 14, 28 and 42 following primary immunization. The rabbits were bled prior to injection and two weeks after each injection. Opsonophagocytic activity of antibodies in hyperimmune sera through rabbit PMN S were measured with flow cytometer, using dihydrorhodamine-123 as a probe. The results indicated that our conjugate could induce a highly significant level of opsonophagocytic activity against serogroup A meningococci after 56 days compared to the control groups (P<0.05). We conclude that this conjugate represents a vaccine candidate against serogroups A and B meningococci after further investigation.

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

“…In addition, the potency of OMV as a carrier (conjugated to a hapten) is now proven. Overall, previous studies have shown that the predominant outer membrane proteins (PorA, PorB and RmpM) from N. meningitidis present in the Meningococci B Cuban vaccine had different capacities to prime the immune responses [1,13–16] .…”

“…OMVs were prepared as previously described [2,6,14] . N. meningitidis serogroup B strain CSBPI and G-245 cells were grown in 40 L modified Frantz medium in a fermenter for 24 hours at 36°C.…”

New insight into the application of outer membrane vesicles of Gram-negative bacteria

“…Covalent linkage of PS or LPS to carriers such as proteins produce glycol-conjugates which are T-dependent antigens and prime for long lasting immunity with either PS or LPS. On the other hand, PS or LPS-protein conjugates have been proven to be effective in several cases while well-defined glycoconjugate vaccines have also been explored with an intention to elicit discriminating immune responses [16,21,22,29]. The latest study in brucellosis vaccines have employed a conjugated B. abortus LPS with GB-OMV which could induce both humoral and cellular immune responses against Brucella spp [17].…”

Outer membrane vesicle

“…We previously synthesized a conjugate vaccine candidate with group A meningococcal capsular polysaccharide (GAMP) conjugated to OMV, which was immunogenic in rabbits, and the respective antisera showed bactericidal and opsonophagocytic activity against N. meningitidis serogroup A, [10][11][12] but the method of conjugation is very complex and needs to be controlled by multiple parameters in light of the risk of conformational changes of dominant and essential epitopes as a result of the covalent reactions between GAMP and OMV. In this respect, protective antibodies against native polysaccharide or OMV proteins would not be induced following this conformational change.…”