The adjuvant mechanism of cationic dimethyldioctadecylammonium liposomes.

Cationic liposomes are being used increasingly as efficient adjuvants for subunit vaccines but their precise mechanism of action is still unknown. Here, we investigated the adjuvant mechanism of cationic liposomes based on the synthetic amphiphile dimethyldioctadecylammonium (DDA). The liposomes did not have an effect on the maturation of murine bone-marrow-derived dendritic cells (BM-DCs) related to the surface expression of major histocompatibility complex (MHC) class II, CD40, CD80 and CD86. We found that ovalbumin (OVA) readily associated with the liposomes (> 90%) when mixed in equal concentrations. This efficient adsorption onto the liposomes led to an enhanced uptake of OVA by BM-DCs as assessed by flow cytometry and confocal fluorescence laser-scanning microscopy. This was an active process, which was arrested at 4 degrees and by an inhibitor of actin-dependent endocytosis, cytochalasin D. In vivo studies confirmed the observed effect because adsorption of OVA onto DDA liposomes enhanced the uptake of the antigen by peritoneal exudate cells after intraperitoneal injection. The liposomes targeted antigen preferentially to antigen-presenting cells because we only observed a minimal uptake by T cells in mixed splenocyte cultures. The adsorption of antigen onto the liposomes increased the efficiency of antigen presentation more than 100 times in a responder assay with MHC class II-restricted OVA-specific T-cell receptor transgenic DO11.10 T cells. Our data therefore suggest that the primary adjuvant mechanism of cationic DDA liposomes is to target the cell membrane of antigen-presenting cells, which subsequently leads to enhanced uptake and presentation of antigen.

The combined CTA1-DD/ISCOMs vector is an effective intranasal adjuvant for boosting prior Mycobacterium bovis BCG immunity to Mycobacterium tuberculosis.

Infection with Mycobacterium tuberculosis, the causative agent of tuberculosis (TB), remains one of the leading causes of mortality worldwide. The current "gold standard" vaccine Mycobacterium bovis BCG has a limited efficacy that wanes over time. The development of a vaccine to boost BCG-induced immunity is therefore a highly active area of research. Mucosal administration of vaccines is believed to provide better protection against pathogens, such as M. tuberculosis, that invade the host via mucosal surfaces. In this study we demonstrate that an intranasal vaccine, comprising the antigenic fusion protein Ag85B-ESAT-6 and the mucosal combined adjuvant vector CTA1-DD/ISCOMs, strongly promotes a Th1-specific immune response, dominated by gamma interferon-secreting CD4-positive T cells. Mucosal administration of Ag85B-ESAT-6 mixed with CTA1-DD/ISCOMs strongly boosted prior BCG immunity, leading to a highly increased recruitment of antigen-specific cells to the site of infection. Most importantly, we observed a significantly (P < 0.001) reduced bacterial burden in the lung compared to nonboosted control animals. Thus, the results demonstrate the effectiveness of mucosal vaccination with Ag85B-ESAT-6 mixed with CTA1-DD/ISCOMs as adjuvant for stimulating TB-specific protective immunity in the lung.

Protective immunity to tuberculosis with Ag85B-ESAT-6 in a synthetic cationic adjuvant system IC31.

In this study, we evaluated the potential of a novel synthetic adjuvant designated IC31 for the ability to augment the immune response and protective efficacy of the well-known mycobacterial vaccine antigen, Ag85B-ESAT-6. The IC31 adjuvant, consisting of a vehicle based on the cationic peptide KLKL(5)KLK and the immunostimulatory oligodeoxynucleotide ODN1a signalling through the TLR9 receptor, was found to promote highly efficient Th1 responses. The combination of Ag85B-ESAT-6 and IC31 exhibited significant levels of protection in the mouse aerosol challenge model of tuberculosis and a detailed analysis of the immune response generated revealed the induction of CD4 T cells giving rise to high levels of IFN-gamma secretion. Furthermore, the combination of Ag85B-ESAT-6/IC31 was found to confer efficient protection in the guinea pig aerosol model of tuberculosis infection and is at present moving towards clinical testing.

Cationic liposomes containing mycobacterial lipids: a new powerful Th1 adjuvant system.

The immunostimulation provided by the mycobacterial cell wall has been exploited for many decades, e.g., in Freund's complete adjuvant. Recently, the underlying mechanism behind this adjuvant activity, including Toll receptor signaling, has begun to be unraveled, confirming the potential of mycobacterial constituents to act as adjuvants. In this study, the immunostimulatory properties of a Mycobacterium bovis BCG lipid extract were tested for their adjuvant activity. Administration of the lipids in dimethyl dioctadecyl ammonium bromide-based cationic liposomes induced a powerful Th1 response characterized by markedly elevated antigen-specific immunoglobulin G2a (IgG2a) isotype antibodies and substantial production of gamma interferon. The adjuvant formulation (designated mycosomes) elicited high levels of gamma interferon both in C57BL/6 as well as in Th2-prone BALB/c mice. Furthermore, the mycosomes induced immune responses to protein antigens from several sources including Mycobacterium tuberculosis, Chlamydia muridarum, and tetanus toxoid. In a tuberculosis challenge model, the mycosomes combined with the Ag85B-ESAT-6 fusion protein were demonstrated to have a unique ability to maintain sustained immunological memory at a level superior to live BCG.