Biological and Immunological Characteristics of Lipooligosaccharide-Based Conjugate Vaccines for Serotype C Moraxella catarrhalis

Abstract

Moraxella catarrhalis is an important bacterial cause of otitis media in children and respiratory tract infections in the elderly. Lipooligosaccharide (LOS), a major surface antigen of this bacterium, is a potential vaccine component against the organism. There are three major LOS serotypes (serotypes A, B, and C) in clinical isolates of M. catarrhalis. Our previous studies demonstrated that serotype A and B LOS-based conjugates were immunogenic in animals and elicited bactericidal antibodies. In this study, LOS from serotype C strain 26404 was isolated, detoxified, and conjugated to tetanus toxoid (TT) or the cross-reactive mutant (CRM) of diphtheria toxin to form detoxified LOS (dLOS)-TT, dLOS-CRM-1, and dLOS-CRM-2 vaccine candidates. The molar ratios (dLOS/protein) of the resulting conjugates were 47:1, 19:1, and 32:1, respectively, while the weight ratios were 0.94, 0.84 and 1.44, respectively. All conjugates were highly immunogenic in both mouse and rabbit models. Three subcutaneous injections of each conjugate formulated with the Ribi adjuvant elicited >700-fold increases in serum anti-LOS immunoglobulin G levels in mice (5 g of dLOS) and >2,000-fold increases in rabbits (50 g of dLOS). The resulting mouse and rabbit antisera showed complement-mediated bactericidal activity against the homologous strain. In addition, a representative rabbit antiserum showed bactericidal activity against 14 of 18 testable strains, and this bactericidal activity could be 100% inhibited by the serotype C or A LOS but only 30% inhibited by the serotype B LOS. These results indicate that the serotype C LOS-based conjugates can be used as vaccine components for further investigation in humans.Moraxella catarrhalis is a gram-negative aerobic dipolococcus and is currently the third most frequent cause of bacterial otitis media (OM) and sinusitis in children (3,14,21). More than 90% of all children develop OM before the age of 7 years (35); 15 to 20% of these middle ear infections are caused by M. catarrhalis (9, 31), and it is estimated that there are 3 to 4 million cases in the United States annually (23, 26). The chronic forms of OM in these young patients may result in hearing loss and are associated with developmental and learning problems as children reach school age (2, 22). Sinusitis, however, accounts for 5 to 10% of upper respiratory tract infections in early childhood (40). In addition, M. catarrhalis often causes lower respiratory tract infections in adults with chronic obstructive pulmonary disease (3, 14, 26) and occasionally causes severe infections, including pneumonia, endocarditis, septicemia, and meningitis (3, 5, 6). Currently, treatment of the diseases has relied mainly on antimicrobial agents. However, with growing antibiotic resistance observed in clinical isolates all over the world (15, 40), attention has been focused on the possibility of vaccination against M. catarrhalis infection (4, 27).The research on vaccine antigens is presently based on the hypothesis that humoral immunity provides protection due t...

Galactose Residues on the Lipooligosaccharide ofMoraxella catarrhalis26404 Form the Epitope Recognized by the Bactericidal Antiserum from Conjugate Vaccination

“…However, the main epitope on the LOS recognized by the above-described functional anti-LOS antibodies from the conjugate vaccination remains unknown. To address this question, we generated one LOS mutant, D4, from a serotype C strain, 26404, using transposon mutagenesis followed by Western blotting with a bactericidal anti-LOS rabbit serum elicited by a serotype C dLOS-tetanus toxoid (TT) conjugate vaccine (41). The mutation was confirmed by sequence analysis to be in the lgt2 gene.…”

“…We previously synthesized LOS-based conjugate vaccines from all serotypes by detoxification of the LOSs and conjuga-tion of the detoxified LOSs (dLOSs) to protein carriers (14,40,41). The vaccines elicited high levels of anti-LOS IgG antibodies with bactericidal activity in mice or rabbits.…”

“…The vaccines elicited high levels of anti-LOS IgG antibodies with bactericidal activity in mice or rabbits. Rabbit bactericidal anti-LOS sera elicited by serotype A or C conjugates were highly cross-reactive among serotype A and C strains and moderately cross-reactive among serotype B strains (14,41), while the rabbit bactericidal anti-LOS sera elicited by serotype B conjugates were rather specific and showed cross-reactivity to only some serotype A/C strains (40). Active or passive immunization with the serotype A conjugates or their antisera generated protection against homologous and heterologous serotype A or C but not B strains in a mouse model of pulmonary clearance (19,21).…”

Importance of Antibodies to Lipopolysaccharide in Natural and Vaccine-Induced Serum Bactericidal Activity against Neisseria meningitidis Group B

“…However, T-cell-independent antigens, including LPS, when presented in the context of whole bacteria or isolated noncovalent complexes with protein also appear to exhibit T-cell-dependent properties (5,39,47). In any case, vaccines that induce anti-LPS antibodies have shown promise for inducing protection against diverse Gram-negative bacteria (5,10,11,12,21,28,39,41,58,62). While efforts to develop an LPS-based vaccine for group B N. meningitidis have been reported (10,22,41,52,56), no vaccine candidate based solely on LPS has entered clinical trials.…”

“…Since the polysaccharide or oligosaccharide epitopes on LPS behave as T-cell-independent antigens, LPS would be expected to require association with protein(s) to be effective as a vaccine for infants (17). Consequently, candidate vaccines for group B meningococcal disease and other diseases that are based on LPS or contain LPS as an important antigen have been designed to circumvent this problem by presenting the LPS as a covalent conjugate, as noncovalent complexes with proteins, or as part of an intact outer membrane (2,10,11,12,14,21,22,39,41,52,56,58,62,65).…”