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The Neisseria meningitidis factor H binding protein (FHbp) is an important virulence factor and vaccine antigen contained in both USA licensed serogroup B meningococcal vaccines. Recent studies in human factor H (hFH) transgenic mice suggest that hFH-FHbp interactions lower FHbp-elicited immunogenicity. To provide tools with which to characterize and potentially improve FHbp immunogenicity, we developed an FHbp-cholera holotoxin-like chimera vaccine expression system in Escherichia coli that utilizes cholera toxin B (CTB) as both a scaffold and adjuvant for FHbp. We developed FHbp-CTB chimeras using a wild-type (WT) FHbp and a low hFH-binding FHbp mutant R41S. Both chimeras bound to G M1 ganglioside and were recognized by the FHbp-specific monoclonal antibody JAR4. The R41S mutant had greatly reduced hFH binding compared to the WT FHbp-CTB chimera. WT and R41S FHbp-CTB chimeric antigens were compared to equimolar amounts of FHbp admixed with CTB or FHbp alone in mouse immunogenicity studies. The chimeras were significantly more immunogenic than FHbp alone or mixed with CTB, and elicited bactericidal antibodies against a panel of MenB isolates. This study demonstrates a unique and simple method for studying FHbp immunogenicity. The chimeric approach may facilitate studies of other protein-based antigens targeting pathogenic Neisseria and lay groundwork for the development of new protein based vaccines against meningococcal and gonococcal disease., (Published by Elsevier Ltd.)

Protopanaxadiol saponins (Rg3, Rd, Rc, Rb1 and Rb2) and protopanaxatriol saponins (Rg1, Re and Rg2) isolated from the root of Panax ginseng C.A. Meyer were evaluated for their adjuvant effects on the immune responses to ovalbumin (OVA) in mice. BALB/c mice were subcutaneously injected twice at a 3-week interval with 10 microg of ovalbumin or 10 microg of OVA plus 50 microg of ginsenosides Rg3, Rd, Rc, Rb1, Rb2, Rg1, Re or Rg2 or Quil A (n=5). Blood samples were collected for measuring specific total-IgG, IgG1 and IgG2a, and splenocytes were harvested for determining lymphocyte proliferation as well as IFN-gamma and IL-5 production 2 weeks after the boosting. The results indicated that OVA-specific antibody responses were significantly higher in mice immunized with OVA co-administered with Rg1, Re, Rg2, Rg3 and Rb1 but not with Rd, Rc and Rb2 when compared with the control (immunized with OVA only). Significantly enhanced splenocyte proliferative responses to Con A, LPS and OVA as well as the production of both IL-5 and IFN-gamma stimulated by OVA were also detected in mice immunized with OVA co-administered with Rg1 but not with Rb1, Re and Rg3. Of the ginsenosides studied, Rg1, Re, Rg2, Rg3 and Rb1 have more potent adjuvant properties than the others, indicating that they are the major constituents contributing to the adjuvant activities of total ginseng saponins. Varieties of ginsenosides in adjuvant activity might be attributed to the varieties of molecular conformations determined by the side sugar chains attaching to their dammarane skeleton.

Active substances from hot water extracts from 267 different Chinese and Japanese medicinal herbs were screened for mucosal adjuvant activity with influenza HA vaccine in mice. The extract from the root of Polygala tenuifolia was found to contain potent mucosal adjuvant activity. The active substances were purified and identified as onjisaponins A, E, F, and G. When each onjisaponin (10 microg) was intranasally (i.n.) inoculated with influenza vaccine (10 microg) in mice, serum hemagglutination-inhibiting (HI) antibody titers increased 3-14 times over control mice administered vaccine alone after 4 weeks. When each onjisaponin (10 microg) was i.n. inoculated with the vaccine (10 microg) followed by i.n. vaccination of the vaccine alone after 3 weeks, serum HI antibody titers increased 27-50 fold over those mice given i.n. vaccinations without onjisaponins. These same conditions also significantly increased nasal anti-influenza virus IgA antibody titers. Two inoculations with onjisaponin F (1 microg) and influenza HA vaccine (1 microg) at 3 weeks intervals, significantly increased serum HI antibody and nasal anti-influenza virus IgA and IgG antibody titers after only 1 week over mice given HA vaccine alone after the secondary vaccination. Intranasal vaccination with onjisaponin F inhibited proliferation of mouse adapted influenza virus A/PR/8/34 in bronchoalveolar lavages of infected mice. Separate intranasal vaccinations with onjisaponins A, E, F, and G (10 microg) each and diphtheria-pertussis-tetanus (DPT) vaccine (10 microg) of mice followed by i.n. vaccination with DPT vaccine alone after 4 weeks showed significant increases in serum IgG and nasal IgA antibody titers after 2 weeks following secondary vaccination over mice vaccinated with DPT vaccine alone. All onjisaponins showed little hemolytic activity at concentrations up to 100 microg/ml. The results of this study suggest that onjisaponins may provide safe and potent adjuvants for intranasal inoculation of influenza HA and DPT vaccines.

Evaluation of the efficacy of nasal influenza vaccine combined with Escherichia coli heat-labile enterotoxin B subunit (LTB) containing a trace amount of the holotoxin (LT) in inducing antibody responses among volunteers, which was conducted during the winter season of 1993-1994, is reported. A trivalent inactivated vaccine, composed of A/Yamagata/32/89 (H1N1), A/Kitakyusyu/159/93 (H3N2) and B/Bangkok/163/90 influenza virus strains, was used alone or together with the adjuvant, recombinant LTB supplemented with 0.5% recombinant LT (LTB*). The volunteers were divided into two groups: 73 volunteers (mean age 35.0 +/- 12.0 years) inoculated intranasally (i.n.) with LTB*-combined vaccine and 49 volunteers (37.9 +/- 11.3) inoculated i.n. with the vaccine alone. Vaccination was done twice 4 weeks apart. Salivary secretory IgA and serum hemagglutination-inhibiting (HI) antibodies were measured before and 8 weeks after the primary vaccination. For the sake of convenience, more than a 1.4-fold rise in IgA antibody response (units of specific IgA antibody per microgram of total IgA) and a fourfold or greater rise in HI antibody titer after vaccination were regarded as a positive antibody response. Thirty-seven (50.3%) and 36 (49.3%) of the 73 vaccinees, respectively, given the nasal LTB*-combined vaccine showed positive IgA and HI antibody responses to one or more of the three vaccine strains. In comparison, positive antibody responses in the group given vaccine alone were 32.7% for IgA and 30.6% for HI antibody. There was a significant difference between these two groups. These results suggest that the nasal LTB*-combined vaccine could enhance the production of higher levels not only of serum HI antibody but IgA antibodies in the respiratory tract than do the nasal vaccine alone.

QS-21, a purified Quillaja saponaria saponin immunologic adjuvant, contains two functional groups that we hypothesized to be involved in the adjuvant mechanism of action through charge or Schiff base interaction with a cellular target. Derivatives, prepared by modification of these sites, were prepared and tested for their ability to augment the immunogenicity of the antigen ovalbumin (OVA) in C57BL/6 mice. QS-21 derivatives that were modified at the carboxyl group on an anionic sugar, glucuronic acid, retained adjuvant activity for antibody stimulation, inducing relative increases in antibody titers similar to those induced by QS-21, although the minimum adjuvant dose required for this stimulation was increased several fold relative to the dose of unmodified QS-21. One of these derivatives also retained significant activity for induction of OVA-specific cytotoxic T-lymphocytes. In contrast, QS-21 derivatives modified at an aldehyde on the triterpene did not show adjuvant activity for antibody stimulation or for induction of cytotoxic T-lymphocytes, suggesting that this functional group may be involved in the adjuvant mechanism.

Escherichia coli heat-labile enterotoxin B subunit (LTB) (2 micrograms), supplemented with a trace amount of the holotoxin (LT) (0.02-20 ng), was examined for the adjuvant effect on antibody (Ab) responses against influenza inactivated haemagglutinin (HA) vaccine in Balb/c mice. Each mouse received a primary intranasal (i.n.) inoculation with the vaccine (1.5 micrograms), prepared from PR8 (H1N1) virus, together with LT-containing LTB and in 4 weeks a second i.n. inoculation of the vaccine alone. The inoculation of the vaccine with the LT-containing LTB induced significantly high primary and secondary anti-HA IgA and IgG Ab responses in the nasal wash and the serum, while the vaccine with LTB or less than 2 ng of LT induced little response. The synergistic adjuvant effect was maximal in the concentration of LTB supplemented with 0.2-2 ng of LT. Under these conditions, the augmented IgA and IgG Ab responses, which are cross-protective to PR8 HA molecules, provided complete cross-protection against PR8 virus challenge in mice immunized with heterologous vaccine within the same subtype. These results suggest that LTB containing a trace amount of LT can be used as a potent adjuvant for nasal vaccination of humans against influenza.